CA1252205A - Method and apparatus for producing special motion effects in video recording and reproducing apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A method and apparatus for producing special motion effects such as slow and fast motion, still frame and other effects from video magnetic tape is disclosed which is par-ticularly applicable to helical wrap recording and reproducing apparatus. The apparatus employs a transducing head that is mounted on a revolving scanning drum, with the head being movable in a line generally transverse to the recorded track.
The present invention utilizes the transverse positioning of the head to accurately follow a track during reproducing or playback and, at the completion of the track, to properly position or set the head in position to either play the next adjacent successive track, replay the same track, or play yet another track so that special motion effects can be achieved without experiencing picture breakup or unwanted noise.

Description

The present invention generally relates ~o magnetic recording and reproducing and, more specifically, to tape recording and reproducing apparatus and a method for achieving signal time base reference alteration effects.
The extensive research and development effort in the field of data recording and repxoducing has resulted in many significant improvements in apparatus that record and reproduce data with respect to tape as well as other mediums~
While there have been many different formats that have been developed, the format that records video signals on magnetic tape and transports the tape in a helix around a c~lindrically shaped scanning drum has exhibited many distinct advantages in terms of relative simplicity of the tape transport drive and control mechanism, the necessary electronics involved, the number of transducing heads, and the efficient use of tape, in terms of th.e quantity of tape that is required for recording a given amount of material. By helically wrapping the tape around a rotating scanning head, a single transducing head for reproducing or playing the information that is recorded on the tape can be utilized. When a single head is used in a helical tape recording apparatus, two recognized alterna-tives are available for wrapping the scanning head, and are generally referred to as the "alpha" wrap and the "omega"
wrap apparatus.
The alpha wrap has the tape introd~ced from one side and wrapped completely around the drum so that it exits on the opposite side and is referred to as the alpha wrap for the reason that it generally conforms to the Greek symbol alpha (~ when one views the arrangement from above. The

-2-omega wrap introduces the tape by bringing it toward the d~tm in a genexally radial direction and passes it around a guide to bring it in contact with the surface of the drum, helically wraps the tape around the drum, passes it 5 around another guide so that it also exits the drum also ln a generally radial dîrectionO The tape generally conforms to the shape of the Greek symbol omega (~) when it i5 viewed from above. Both of these configurations are helical wrapped in that the tape is wrapped around the scanning drum ln a helical manner with the tape exiting the drum surface at a different axially displaced position relative to the entry thereof~ In other words, if the drum is vertically oriented, the tape leaves the drum sur~ace either higher or lower than when it first contacts the surface. The video or other data infor-mation signals are recorded on discrete parallel tracks that are positioned at an angle relative to the longitudinal direction of the tape so that a track length greatly in excess of the width of the tape can be achieved. The angular orientation of the recorded tracks are a function of both the speed of 2~ the tape being transported around the scanning drum as well as the speed of rotation of the scanning drum itself. The resultant angle therefore varies depending upon the relative ~peed~ of ~oth the rotating scanning drum and tape being transported.
2S It should therefore be appreciated that if inform-atlon signals are recorded on a tape at a predetermined angle which results from a precise rotational scanning drum ~peed and tape transport speed, the subsequent reproducing

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I.D. 2493 of the inFormation signal should be performed at the same speeds or the transducing head will not follow the track with precision. I-f the tape speed is changed during repro-duction, such as reduced or stopped, the transducing head will no longer precisely follow the recorded track and may even cross onto an adjacent track. The failure to precisely follow the track in registry during playback results in noise and cther undesirable signal effects that appear in the represented information, such as a video picture. While various prior art systems have been proposed to attempt to reduce such undesirable effects due to the lack of registry, such systems have not been entirely successul even during normal tracking at speeds that are intended to be identical to those that were used during recording.
Helical tape recorders that are adapted to create special altered time base reference effects have not been particularly successful to date because of the spurious noise that is generated during playback due to the transducing head crossing from one track to another. For example, slow motion effects in video recording necessarily require that data be repeated one or more times during playback so that the visual motion is slowed down to create such effects. If data is recorded without redundancy, a track must be repeated to accomplish this and, hence, the tape speed changed. The resultant path that must be followed by the transducing head will be substantially diferent from that which was made during the xecording process.
Extreme difference is found in stop motion or still frame operations whexe the tape transport is stopped and the videQ head rescans a pair of adjacent tracks a number of times.
While systems have been proposed to reduce or overcome the noise band that is generated by crossing rom ~ I.D. 2493 one track to anothex, the systems have not been particularly successful. One prior art system for video signals employs two video transducing heads with switching means that are adapted to select the video transducing head which has the maximum output, but this approach suffers because neither head is precisely on the video track throughout its length and the signal to noise ratio suffers because of it. Other systems for video signals have attempted to minimize the effect of the crossing by using synchronization puls~ lineup techniques and the like, and by modifying the heli~ angle by changing the tape guiding means around the scanning drum.
None of these approaches have been particularly successful and slow motion, stop motion and fast motion effects have heretofore not been successfully accomplished in helical video tape apparatus.
Accordingly, it is an object of the present inven~ion to provide an improved method and apparatus for achieving time base reference alteration effects in tape recording and reproducing apparatus.
More particularly, it is an object of the present invention to provide a method and apparatus of the foregoing type which effects time base reference alteration by precise repositioning and control of the tracking of a transducer with respect to a track along a tape of a tape recording and repro-ducing apparatus.
Furthermore, it is an object of the present invention to provide an improved method and apparatus of the foregoing type which achieves slow motion, stop motion, fast motion and other altered time base reference effects in tape recording apparatus, substantially without sacrificing the qual.ity of the reproduced signal.

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~ nother object of the present invention is to provide an improved method and apparatus of the foregoing type which permits virtually infinitely variable slow motion speeds within predetermined limits, both in forward and reverse dixections of tape transport motionO
Other objects and advantages will become apparent upon reading the following detailed descrip~ion, while referring to the attached drawings, in which:
FIGURE 1 is a perspective view of an omega wrap -5a-I.D. 2493 helical scanning drum simplified for the sake of clarity and embodying the presen~ invention;
FIG. 2 is a plan view of the scanning drum shown in FIG. 1, with portions removed;
FIG. 3 is an enlarged segment of magnetic tape having tracks A-F recorded thereon;
~IG. 4 is a further simplified plan view of an omega wrap helical recording apparatus;
FIGI Sa is a displacement pattern for a transducing head when the apparatus is operating in a skip ~ield mode;
FIG. Sb-5d are displacement patterns for a trans~
ducing head when the apparatus is operating in a slow motion mode;
FIG. 5e is a displacement pattern of a transducing head when the apparatus is operating in a still frame or stop motion mode;
FIG. 5f is a displacement pattern for a transducing head when the apparatus is operating in a surveillance mode;
FIGS. 5g and 5h are displacement patterns for a tra~sducing head when the apparatus is operating in fast motion modes;
FIGS~ 5i and 5j are displacement patterns for trans-ducing heads when the apparatus is operating in slow motion and normal speed, respectivPly, with the tape being trans-2S ported in the reverse direction;
FIG. 6 is a schematic block diagram illustrating the electrical circuitry associated with the apparatus embody-ing the present invention;

FIG. 7a is a vol.tage output wave forlll produced by the circuitry showll in FIG. 6 for producinq tlle di.s-placement pattern for the half speed slow motion operation ShOWII in FIG. 5b;
FIG. 7b is a voltage output wa~e form of the circuitr~ shown in FIG. 6 for producing the displacement pattern Lor the sl.ow motion reverse clirection operation shown in FIG. 5i; and, FIG. 3 represents electrical schematic diagrams of one form of circuitry that can be used to implement -the block diagram of FIG. 6.

- G~-FIGURE 9 is a plan view of a magnetic head drum for helical tape recording use, silowing t:he invention moun-ted thereon;
E'IGVRE 10 is an exploded perspcctive view, to an englarged scale, of a portion of the structure shown in FIGURE 9.
FIGURE 11 is an enlarged sectional view -taken on the plane of linesll-]lof FIGURE~9.
FIGURE 12 is a left-end eleva-tion view oE a portion of the structure shown in FIGURE ll.
FIGURE 13 is a right-encl elevation view oE a porkion of the structure shown in FIGURE l1.
FIGURE 14is an enlarged fragmentary perspective view illus-trating a portion of the structure shown in FIGUP~E 11.
FIGURE 15is an enlarged left-end view of a portion of the structure shown in FIGURE 11 illustrating an arrange-ment of a plurality of transducers thereon.
FIGURE 16is an elevation view of a portion of tape;
FIGURE 17is a reduced scale view of the tape of FIGURE 16enwrapped around a scanning mechanism including the structure of FIGURE 9 and FIGURE 18 is an enlarged perspective view, partly in schematic form, of arl alt~rnative embodim~nt of the invention .
FIGURES l9A and l9B are schematic bloc~ diagrams of alternative embodiments for sensing and controlling the position of supportecl transducers relative to a record surface.

_ ~b -The invention will be described in greater detail with reference to the drawings in which:
Fig.2o is a schematic illustration of a problem solved by the invention;
Fig.~l is a partlally cu~ away view of a helical head drum;
Fig~ is a schematic block diagram of a servo circuit according to the invention; and, Fig.~3 is a schematic block diagram o an improve-ment to the circuit of Fig.,3~.
Fig.~ is a detailed .electrical schematic diagram o~ one form o circuitry that can be used to implement the bloc~ diagrams of Figs.~ and æ3.
Fig.~is a perspective view o a positionable trans-ducer assem~ly.
Fig.~is a reduced scale view of the magnetic tape of Fig.~O helically wrapped around a scannin~ mechanism in-cluding the structure of Fig. ~/.
~ ig.~7 is an electrical schematic diagram of cixcuitry corresponding to the block diagram o Fig. ~.

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FIG. ~is a perspective vicw of a portion of a llelical videotape recorder simplified Eor the sake o~ clarity and particularly illustrating a rota,table scanning drum and read he~d;
FIG. ~9is a perspective vicw of a read transducer assen~ly ~or use witll the read head of FIG.~8;

FIG. ~q~is an enlarged cross-section of a portion of the transducer assembly shown in FI~9 and illustratirlg the layered construction of the assembly;
E'IG.3O is a block diayram of a feedback control system embodying various aspects of this invention for con-trolliny vibra~iolls in a billlorpll read trallsducer assembly;
F'IGS.3/a and~byrapll:ically illustrat:e ~lle l.requellcy an~ pl~ase response oE the bimorph transducer asselnbly used in tlle control systeM of FIG.~O~
FIG.~.is a schematic diagram of the control system illustrated isl FIG.3O-FIG.3~ sllows prior art mertllods of deflec-tincJ a bimorph;
~ IG.~ illustrates an improved method oE deflecting a bimorpll;
FIG.~g~ illus-trates an improvçd method of varying the direction and magnitude of deflection of a ~imorphi FIG. ~b graphically illustratesthe net voltage which is applied to one element of the bimorph shown in Ii'IG. ~
li'IG.~shows an improved method of dr,iving a himorph wl~en the bimorph deflection signal does not include very low frequency or DC components;
F'IG. ~ is a schematic diagram of a deflectable ,read ~rallsducer system em~odying the improved bimorpll de-flectioll metl)oa illustrated in li'IG. ~So), ~l~5~

Broadly stated, the present invention i.s directed to a method and apparatus for successful.ly achieving altered time base reference effects in the art of recording and reproducing information si~nals on a medium. While it is suited for use in many different kinds of sigllal recording applications, the present invention is particu].arl.y useful in creating altered or special motion ef:cccts from video signals. While a variety oE video recording formats exis-t and may be adaE)ted to the present invention the invention is particularly attractive for use witl~ helical. tape recordillg apparal,us to ach.ieve 5pecia]. mOti.OII e;~ectg ~I.lCh as slow motiorl, fast motion and stop moti.on, with the slow and fast motion being carried out in both the forward and reveLse directions. Thus, it is cont:emplated that the present invention can be used with quadrature, segmented helical and arcuate types of video tape recorders, in addition t:o the various helical tape recordins formats.
While the present invention will be specifically descrlbed in connection with an omega wrap helical video tape "

~5~ ID-2493 xecording apparatus~ it is equally applicable to an alpha wrap helical tape recording apparatus. Additionally, while the presen-t invention will be described in conjunction with a 360 omega wrap apparatus (it being understood that the tape does not contact the scanning drum a full 360 because of tape entrance and exi-t dimensional requirements), the present invention is also applicable to helical video tape recorders which utilize less than 360 wrap, e.g., a 180 wrap tape path apparatus having more than one head. It should also be understood that the present invention is applicable to arrangements where the scanning drum can move in either rotational direct:ion and the -tape can be introduced either above or below the exit path and moved around the scanning drum in either direction. The relationships of head rotation, tape transport direction and manner of tape guiding, i.e., introducing the tape above or below the path of its exit, can represent up to eight different configurational relation-ships of which only one will be specifically described hexein as shown by the direction of the arrows in FIG. 1 of the drawings.
Broadly stated, the present invention is directed to a method and apparatus for accurately positioning a trans-ducing head to follow a track and to rapidly position the transducing head, if necessary, at the beginning of the track that is desired to be followed next. The next track that is to be followed is a function of the mode of operation that is selected. In the playback of video signals, the various modes may include slow motion effects, speeded up or fast motion effects, as well as stop motion or still frame effects. Moreover, other modes of operation may include skip ~5~

field recording and compensating playback, as well as a sur-veillance mode which greatly increases the period of time that can be recorded on a given length of tape (at the expense of continuity of motion~, it eEfectively skipping a great number of fields, such as recording one of every sixty fields~
for example. The apparatus permits the tracks to be accurately followed, even though the transport speed of ~he tape can vary within wide limits. In the event fast motion effects are to be achieved, during the playback of video signals, the transport speed of the tape must be in-creased and, conversely, Eor slow mo-tion effects, the transport speed must be slowed down. Stop motion requires that the same fields be reproduced many times and in such condition the tape is not moving at all, the relative motion between the tape and the transducing head being supplied by the rotation of the scanning drum carrying the same. Since changing the tape transport speed changes the head-to-track angle as well, it is apparent that the video transducing head that is carried by the scanning drwn would not exactly follow 2d the track when the transport speed of the tape is altered, in the event the transducing head is maintained in a fixed position.
The present invention comprises means for moving the transducing head transversely relative to the longitudinal direction of the tracks of the informa~ion and thereafter selectively alters or changes the position of the head so as to correctly position the head to commence following another track, the track being a track other thc~n the next adjacent successive downstrezm track if the position of the head is in fact changed. It should be understood that during recording, one complete re~olution of the scanning drum causes the transducing head to record a track at a predetermined angular orientation relative to the length of the tape and at the end of the sweep, the movement of the tape causes the recording head to be gradually displaced a predetermined distance downstream in position to begin recording the next adjacent successive track. In this manner, the tracks are recorded parallel to another and, assuming the -transport.
speed of the tape is maintainecl constant as is the speed o~
rotation of the scanning drum carryiny the record transducing head, the tracks will have a constant spacing relative to adjacent tracks, i.e., the center to center distance between adjacent tracks will be substantially constant in the absence of geometric errors that can be introduced due to stretching, or other temperature or humidity induced dimensional changes of the tape or by faulty tensioning mechanisms in the tape transport or the like.
Turning now to the drawin~s and particularly FIGS.
1 and 2, there is shown a helical video head scanning drum, indicated generally at lO, with portions broken away in FIG~ 2. The scanning drum is shown to comprise a rotatable upper drum portion 12 and a stationary lower drum portion 14, the upper drum 12 being fixed to a shaft 16 which is rotatably journaled in a bearing 18 that is mounted on the lower drum 14~ the shaft being driven by a motor (not shown) operatively I.D. 2493 connected thereto in a conventional manner. The scanning drum lO has a video transducing head ~0 carried by the rotational ~rum portion 12 and is shown to be mounted on an elongated mova~le support element 22 that is in turn mounted at one end in a cantilever type support 24 that i5 fixed to the upper drum portion 12. The element 22 is pre-ferably of the type that flexes or bends in a direction transversely of the recorded track during playback with the amount and direction of movement being a function of elec-trical signals being applied thereto, all of which will bedescrihed in detail hereinafter.
As best shown in FIG. l, the scanning drum 10 is part of a helical omega wrap video tape recorder which has the magnetic tape 26 advancing toward the drum in the direction of the arrows as shown. More specifically, the tape is intro-duced to the drum surface from the lower ri~ht as shown in the drawing and is fed around a guide 28 which brings the tape into contact with the outer surface of the stationary lower portion 14 whereupon the tape travels substantially completely around the drum until it passes around a second guide 30 which changes direction of the tape as it exits the scanning drum after it has been either recorded or played back. ~s is best shown in FIGS. i and 4, the omega wrap video tape recorder is of a configuration such that the tape being introduced is in a noninterfering relationship with the exiting tape in the sense that they do not require being crossed over one another as in the alpha wrap format and, for this reason, the lower portion of -the exiting tape can I.D. 2493 overlap the upper portion of the tape being introduced so as to provide a small unrecorded band that can be used for audio and control signals and the like. The overlapping segment ~ is shown in the lower portion of the tape illustrated in FIG. 4O
As is best shown in FIGS. 1 and 3, the shape of the configuration is such that the tape does not contact the scan drum surface over a full 360 because of the clear-ance that is required for entrance and exit of the tape.
~Iowever, this gap preferably does not exceed a drum anyle of more than 16 which has the effect of creating a dropout o information. The dropout is preferably chosen so that the line interval that ls lost does not occur during an acti~e video line and the start of a scan of a track is field syn-chronized. As will be more fully explained hereafter, thedropout in the omega wrap configuration is used to advantage in the operation of the method and apparatus of the present invention.
As previously mentioned, the transducing head 20 is mounted upon the elongated movable, preferably flexible element 22 which may comprise an elongated two layer or bimorphous element which supports the transducer. It pre~
ferably comprises a thin leaf bimorphous or two layer element which exhibits dimensional changes in the presence of the electric or magnetic field and may be constructed of two layers of material suitably bonded together, at least one layer of which is piezoelectric, electrostrictive or mag-netostrictive, although a bimorpher or bimoxph cell comprised ~;~5~
of two piezoelectric layers with their axis of polarity oriented in such a way that application of a field causes the deflector to flex or bend is preferred, In thi5 regard9 reference is made to copending applications of Richard Allen Hathaway, Serial Nos. 274,280 and 2749284, Eiled March 18, 1977 and entitled AUTOMATIC SCAN TRACKING and POSITION~BLE
TRANSDUCER MOUNTING STRUCTURE, respectively, which are directed to a deflecting element and mounting structure of this type. Another configuration that is electromechanically 10 driven for moving the head transversely of the tracks in a manner that achieves the same result as the deflectable bimorph is also disclosed in Serial No. 274,284, both conEigurations of which are useful in practicing the present :Lnvent:ion .
The deflectable e1emellt 22 l~ effective to move the trans(lucing head 20 mounted thereto in a vertical direction as shown in FIG. 2 in accordance with the electric signals that are applied thereto through conductors 32 from circuitry schematically illustrated by block 34. The head 20 is 20 mounted so as to extend slightly beyond the outer surface of the rotating drum portion 12, the head extending through an opening 36 in the outer surface thereof. By using the thin leaf piezoelectric bending element to suspend the transducing head for controlled positioning with respect to the magnetic tape, it is cantilevered from the support 24 that is attached to the rotating drum portion 12 for controlled positioning with respect to the magnetic tape. Thus, the deflectable element 22 is adapted to sweep or bend mls/SS

and d.isplace the transducing head in response to applied electric field signals. The cantilevered deflectable element 22 is arranged with the directlon of bending motion of its free end carrying the transducing head along a path that is transverse to the direction of relative motion of the head with respect to the magnetic tape, i.e. along the direction o~ the recorded tracks. Preferab~y, the thin leaf piezoelectric deflectable element extencls from the rotating drum normal to a plane tangent to the recording surface at the point of head to-record surface interface and su~stan-tiall~ parallel to the direction of relative head-to-record surface motion. The transduci.ng head 20 is mounked on the outer free end of the pie~oelectric deflectable element 22 for operative engagement with the magnetic tape such that its transducing gap is oriented to have the gap length in a direction of width dlmension of the deflectable element and its gap width in the direction o~ the thickness dimension o the deflectable element in a direction tr.ansverse to the relative motion direction.
In order to respond rapidly to positioning commands and follow changes in the command signals, a low mass thin lea~ piezoelectric element construction is pre-ferred. More-over, the thickness of the deflectable element relative to its width should be such that virtually no deflection or movement of the transducing head can occur in a direction other than transverse relative to the track length. Thus, by applying appropriate signals to alter the position of the transducing head during operation of the apparatus, it ~s~

should be understood that the head can be moved from side to side relative to the track bein~ followed and if an appropriate error correcting signal is obtained, the head can be moved so as to accurately follow the track during playback~ In this regard, the aforemlentioned copending applications of Richard ~llen Hathaway, Serial No. 274,280 and Serial No. 274,284 describe two apparatus for generating error correcting signals for application to the drive circuitry for the deflectable element to cause it to move the transducing head into an accurate tracking position. The apparatus provided by either of these auto tracking head appl:Lcatlons e.E:Eectlvely produce error correcting sl.gnals that are appli.ed to the deflectable element 22 which moves the transduc:Lng head lnto colnclderlce w.tth the track from the start to flnlsh thereof whlch occurs during one complete revolutlon of the scannlng head 10.
If the transport speed of the magnetic tape is changed relative to the speed ln which the informatlon was recordedf then the effective angle of the helix is changed and error correcting slgnals will be produced for the purpose of havlng the transducing head follow the track at the different angle. Since the deElectable element i8 movable in either directlon~ the tape can be transported around the scanning head at either a fa9ter or slower speed relative to the record speed and the element can position the head mls/SS

j~2~

to follow the track being reproduced ~or either condition.
In accordance with an aspect of the present invention and referring to FIG. 3, a segment of tape 26 having a number of tracks A through F thereon is shown together with arrows 40 and 42 which illustrate the direction of tape motion around the scanning drum 10 and the direction of head scan relative to the tape itself, respectively. The orien-tation of the tracks and the arrows shown in FIG. 3 coincide with what is produced by the movements of the scanning drum 10 and tape 26 shown in FIG. 1 (see arrows 44 and 46). With a constant transport speed ancl angular velocity of the scanning drum portion 12, tracks A through F will be substantially straight and parallel to one another at angle O (of about 3,for example) relative to the longitudinal direction of the tape, with the rightward tracks shown in the drawing being subsequently produced during the recording operation. Since track B, for example, would be recorded immediately after track A was recorded during constant scanner rotation and tape transport speeds, it should also be appre-ciated that if these speeds are ma ntained during thereproducing or playback operation, the transducing head 20 would playback track B during a successive revolution immediately after having reproduced the information from track A.
If conditions were ideal and no distortion was introduced/ then the transducing head 20 would simply follOW
the successive adjacent tracks without adjustmen-t, since no error signals would be produced for transversely moving the transducing head 20 relative to the track. Stated in other words, the transducing head is automatically in posi-tion to begin reproducing the subsequent track B
a~ter completing the reproducing of the information from track A. It should also be appreciated tha-t even if the tape transport speed is varied relative to the transport ,speed during record, and the angle of the track is thereby changed relative to the transducing heacl, if it is trans-versely moved to maintain accurate tracking through playback of the track, at the end of the track being played, it i5 nevertheless in a position to begin reproducing the next adjacent downstream track, i.e., track B in the event A
was completed. This occurs even when the tape is stopped or is txaveling slower or faster than the transport record-ing speedO
To achieve special motlon and other ~ffects during reproduction of -the information signals that are recorded on a video tape or other medium, it is necessary to vary or adjust the transport speed of the tape around the scan-ning dr~m. To produce a speeded up or fast motion effect, the transport speed is increased relative to that which was used during recording. Similarly, to produce slow motion efects, it is necessary to reduce the speed of the transport tape around the scanniny drum relative to that which was used during the recording process. Stop motion requires that the tape be stopped so that the transducing head on the scanning drum can repetitively reproduce the information signal from a single track.
In accordance with the present invention, the apparatus can be placed in different modes of operation wherein either forward or reverse motion effects are achieved and the motion can be speeded up or slowed by simply adjusting the transport speed of the tape in such forward ox reverse directions to obtain the desired speed of motion during play-S back. Once the direction is chosen, the apparatus is ef-fective to automatically position the transducing head to follow a ~r~ck from ~eginning to completion and thereafter adjust the position of the transducins head (if adjustment is needed) to the beginning of the proper track.
Broadly stated, the present invention provides for resetting or transversely moving the transducing head at the end of a track to a position corresponding to the start of a track other than the next successive adjacent track under certain predetermi~ed conditions and not resetting or adjusting the transducing head under other predetermined conditions. The decision to transversely mo~e or adjust the transducing head depends upon the mode in which the apparatus is operating and whether the amount of transverse movement is within the predetermined limits that can be achieved. In other words, if the transducing head is de-flected its maximum amount in one direction it will not be moved further in that direction. The total range of movement should be within practical limits determined by the char-acteriskics of the element 22.
The manner in which the transducing head is con-trolled during the various modes of operation will now ~e described in connection with FIG. 5 with particular attention being initially given to FIG. 5e which ls ~2 ~2~ ~ ~

directed to the stlll frame or stop action mode of operation.
The stop motion or still frame mode of operation requires that the transducing head be reset at the comple-tion of the track being reproduced and be reset to the begin-ning of the track so that it can be repeat:ed as many timesas is required for the duration of the stop motion. Thus, the track is effectively replayed over and over since the tape is stationary. Since the reproducin~ head follows the track during repeating playback, it must be reset by a distance that is equal to the track to track spacing of the recorded tracks in order to be correctly positioned to replay the track. Since the angle of the track is also different when the tape is stopped from the angle that was made during recording, the head is also gradually being adjusted through the course of reproducing the information ; signal on the track. Thus, as the scanning drum moves along the track, the error correcting signals cause the trans-ducing head to be moved transversely to follow the track and it must ~e reset essentially one track transverse dis-tance d in order to be in position for beginning the replay of the same track. With the format illustrated in FIG. 1 and using the tape segment s'nown in FIG. 3, wherein the track width is about 5.6 mils (5.6/1000 of an inch) and the center-to-center spacing distance d between adjacent tracks is about 8.7 mils, The deflectable element 2~ shown in FIG. 2 is adapted to move about 8.7 mils in either direction and these design limits are shown in the dis-placement pattern versus time diagrams of FIGS. Sa through 5j. ~oreover, the scanning dr~n is rotated at a constant velocity of 60 revolutions per second so that the time for playing each of the txacks is relatively constant at about 16.7 milliseconds in duration. In all of the patterns shown in FIGS. 5a-5j, the 0 position on the ordinate is intended to be representative of the unbiased or home position of the transducing head which preferab].y occurs when no voltage is applied to the de1ectable or movable element 22.
Referring specifically to the still frame or stop motion displacement pattern for positioning the transducing head shown in FIG. 5e, it is shown that each successive play of track A, for example, has an inclined portion labeled pla~ which is followed by a reset portion that is represented by a su~stantially vertical line with the vertical distance of the reset approximating 8.7 mils, which is the center-to-center track spacing d between adjacent tracks. Thus, as the transducing head begins re-producing at the start of a track it must be positioned approximately 4.35 mils upwardly relative to the home or 0 position and through the course of the playback of the track, it gradually moves downwardly to its lowermost position indicated to be about 4.35 mils below the center line or 0 home position of the transducing head. At the end of the track, the transducing head must be reset or transversely moved to be in position to start playback of the same track again and a suitable control signal i5 applied to cause the deflectable element 22 to move the transducing head upwardly a total of 3.7 mils which will accurately position it to begin replaying the same track again. rrhe repetition occurs for as :Long as the still frame is to be maintained.
The resetting of the -transducing head is pro-duced by a pulse being gen rated which has an amplitude tha-t is proportional to and determines the 8.7 mils of deflection. The pulse will be automatically produced unless it is inhibited with the inhibiting being a function of the position of the transducing head near the end of a pl~yback i~eO at or near the lower point of the play portion of the pattern shown in FIG. 5e. If the position of the transducing head is detected to be below the home or 0 position at the end of the scan of a txack, then a reset pulse will be produced and the head will be reset in the illustrated manner. However, if the position of the transducin~ head is above the home or 0 position at the completion of scanning a track, then the reset pulse will be inhibited and the next track will be begun. In the absence of the application of any control signals that would reposition the transducing head, it would be in position to begin tracking the next ad~acent track at the completion of the foregoing track as has be~n previously described.
Thus, the absence of a reset pulse causes the transducing head to advance from track A to track B, for example, the eondition arising due to producing an inhibiting signal ; that inhibits the reset pulse. The manner in which the signals are produced and inhibited will be more fully described with respect to the description of the operation oE the circuitry show~ in the block diagram of FIG. 6.

Turning now to a general description of the dis-placement patterns that are followed during slow motion effects ref~
erence is madet FIGS- 5b~ 5c and 5d which respectively illus trake the displacement patterns for slow motion effects where the tape is transported at 1~2 (FIG. 5b~, 1/5 (FIG. 5c) and 1~10 (FIG. 5d) of the speed during recording. It should be understood that the patterns are intended to illustrate the number of repetitions or replays that occur for each track and this number is a function of the transport speed relative to the speed during the recording process. Thus, if the transport speed of the tape around the drum is reduced to 1/2 of the speed during rec,ording, it is then necessary that each track De played twice since the scanning drum continue~
to operate at the same rotational speed of 60 revolutions per second. Similarly, if the transport speed is l/lO that of record speed, then each track will be reproduced ten times before the next track is reproduced.
The present invention is adapted to adjust the number of replays to the transport speed of the tape as will be described hereinafter. Returning to the slow motion dis~
placement patterns shown in FIG. 5, and particularly FIG. Sb which illustrates the pattern o~ movement for the transducing head when the transport speed of the tape is 1/2 the speed that is used during recording, it is necessary for each of the tracks to be played two times, i.e. each track repeated once, before the next track is played. Thus, the first play o~ track A has the transducing head deflected downwardly about 4.35 mils until it reaches the completion of the track ~ 5~ 5 whereupon it is reset a total of about 8.7 mils upwardly in position to replay track A a second time. Near the completion of the second playback of track A~ the transducing head ap-proaches the home or 0 deflec~ion position which is detected and the reset is inhibited so that the track B can be scan-ned. Similarly, the transducing head is deflected down-wardly about 4.35 mils as was the case with respect to track A and the pattern is repeated from track to track as is shown.
In the event the transport speed is slowed further, such as 1/5 the record speed shown in FIG. 5c or 1/10 the record speed as is illustrated in FIG. 5d, the tracks will be replayed 5 or 10 times, respectively, as shown in the drawings. With respect to the displacement pattern in FIG. 5c, the head begins in it~ hom~ position on the first play of traok A and is deflected downwardly until it reaches the end of the track whereupon it is reset to play at the track againl requiring a~out 8.7 mils displacement. It follows the track a successive number of times, the lower displacement of each successiYe play gradually approaching the home position since the track is physically moving around the scanning drum during the suc~
cessive plays and therefore moves gradually upwardly along the helical path of the tape. During ~he last play of txack A, the position of the transducing head near the end of the play is above the 0 or home position which is detected and results in beginning the first play of the next track B. In a similar manner, the slowex movement of the tape around the scanning drum shown in FIG. 5d results in track A being replayed a total of ten times before the transducing head is at or above its home position near the completion of the ~inal play which is detected and permits the head to begin playing track s.
From the three foregoing described speeds of tape transport that results in the slow motlon play, it should be understood that a track will be replayed as many times as is required to result in the transducing head being at or above the home or 0 position at the completion of the play-back of the track being repeated, no matter how many times tnis occurs. When this condition is detected, the reset is inhibited and the transducing head starts the playback of the next adjacent successive track. The amount of movement during each reset is constant at the approximately 8.7 mils for the appara-tus descr:ibed herein, the distance being e~ual to the track to track spacing d.
In accordance with another aspect of the present invention, other special motion effects in addition to the 510w and stop motion that has been described are capable of being achieved, particularly reverse motion at normal and slower speeds. Referring to Fig. 5j, a displacement pattern is shown for the transducing head and illustrates the movement of the head during reverse direction tape transport at normal playback speed. Unlike the other pattern shown in FIG. 5, track A is shown to the right with the tracks B, C and D
belng successively leftward which is opposite the direction of the other figures. This denotes the reverse direction as is desired, it being understood that the scanning drum follows each track in the same direction as was ~ollowed with respect to slow motion and stop motion, i.e., the direction of scan ~24-~25~5 is from the top to the bottom of the angled portion of the pattern of FIG. 5j, followed by a reset mvvement to position the transducing head for playback of the next desired track.
While the scanning drum moves in the same direction relative to the tracks during playback of the tracks, the tracks must be played in reverse sequential order relative to the order during forward direction playing. The displacement pattern shown in FIG. 5j is for regular speed in the sense that the tape is transported around the scanning drum at the same velocity as was used during recording, but in the opposite direction. As is shown by the displacement pattern in FIG.
5j, tha resetting of the transducing head is greater than has been heretoore described, in effect moving kwo 8.7 mil distances for a total o 17.4 mils, with the greater movement being necessary to transverse a total of two centertO -ce~terspacings d to correctly position the tape on the upstream or prio~
track. This can be readily visualized if it is recalled that *o replay a track during slow motion or stop motion efects, it was necessary to displace the transducing head a single center-to -centerdistance of about 8.7 mils in order to reposi-tion it for repeating playback of the same track. In the event a track prior to the track being played is to be played, still another track to track distance would be required to position it at the beginning of the prior track. Thus, a total of two multiples of cenber-to-center spacing d are required to reproduce the information signal in a reverse direction at normal speed.
To achieve slow motion in the reverse direction, it is necessary to reduce the tape transport speed in the reverse direction and repeat the playback of the tracks one or more times, depending upon the reverse transport tape speed. Thus, referring to FIG. 5i, a reverse direction half speed dlsplacement pattern is illustrated wherein each of the tracks is repeated once before the next preceding track i5 played. Thus, after track C, for example, is played the first time, the transducing head is reset a distance of one centerto -centerspacing d, i.e. 8.7 mils, and track C i5 played a second time until the downward deflection of the transducing head is detected at the lower extreme of the second pla~ which causes a "double" magnitude reset signal to be produced and the transducing head i5 deflected abou-t 17.4 mils upwardly which positions it at the start o~ track B. The lower extent of the first play oE track B is at a downward deflection of about 4.35 mils which is not a suf~
ficient deflection to caùse generation of a double magnitude reset pulse so that only an 8.7 mil deflection is produced which causes the track B to be played a second time. Xn this manner, the slow motion effect in the reverse direction is achieved. When the position of the transduci~g head at the end of a track is sufficiently displaced relative to the home position, then a signal that deflects two center-t center track spacings or about 17.4 mils i5 produced.
The manner in which the circuitry associated with the present invention operates to produce the displacement patterns that have been discussed above will be described in connection with the schematic block diagram of FIG. 6. As pre~iously alluded to, an error correcting signal that is preferably a low frequency or changing D.C. level i9 produced by apparatus such as the sensing heads disclosed in the Hathaway application Ser~al No. 274,280 or the dither apparatus disclosed ln the Hathaway application Seria] No.
274,284 both of which are asslgned to the same assignee as the present invention, with the error signal being applied to an integrator 50 through input line 52. During the scanning of a track, the error signal causes the transducing head to be adjusted so as to follow the track regardless of the speed of tape transport, provided that it is within the limits of deflection of the element 22. The integrator provides a ramp signal, the slope of which i8 determined by the D.C. or low frequency error signal that is derived from the head positioner servo circuitry. Thu.s, the servo error modulates the slope of the ramp as the ~ranstluclng head posltlon error changes, and the output of the integrator appears on line 54 which extends to summation circuits that drive the transducing head movable element 22. In sddition to the low frequency or changing D.C. level error signals, a dither signal and high frequency error signals may be added ~o the composite control signal that is used to drive the posi~ioner in addition to the reset pulse which effectively produces the reset portion in the displacement patterns of FI&. 5 as previously discussed. ~ pulse generator 56 produces the reset pulse which has a magnitude that is proportional to a desired one track deflection that is to be achieved by the elernent 220 In other words, the size of the reset pulse determines the amount of deflection needed to reset mls/SS

the transducing head a distance equal ~o the center to-center distance d, i.e., the 8.7 mils in the illustrated embodiment, or a reset pulse ~hat will produce 17.4 mils of displacement which represents two multiples of the center-to-center spacing d. The pulse yenerator 56 is adapted to produce the pulses on output line 58 in both the reverse and ~orward directions and pulse generator 60 provides an output pulse on line 62 of the same magnitude as that produced by generator 56 under certain condi,ions which only occur when the tape is transported in the reverse direction. If pulses appear on both outputs, an adder 64 will provide an output pulse that is the sum of the t~o pulses and thus provide a pulse that will produce a reset of two center-to-center spacings. The rese-t pulses appear on line 66 which extends to the input of integrator 50 A forward mode tape level detector 68 monitors the indicator output and is adapted to provide an inhibit output signal on line 70 for inhibiting the pulse generator from producing a pulse on output 58 when the ran~p signal is above a set level at the end of a scan. Similarly, the reverse mode level detector 72 monitors the ramp voltage from the integrator 50 and produces an inhibit signal on line 7~ until the ramp signal reaches a predetermined level that is slightly more than one track higher than the level of detector 68. In the reverse mode, the inhibit signal inhibits an output on line 62 so that only a single track spacing reset magnitude pulse will be produced by the pulse generator 56 which is triggered in response to receiving an advanced end of scan command on line 76 derived from b~
a tachometer generator mounted for rotation with the rotatable drum 12 of the scanning drum. The tachometer may be of conventional design for providing a tachometer pulse once for each revolution of the rotatahle drum 12. For convenience, the tachometer is mounted to the rotatable drum 12 so that it occurs just before the dropout. Tachometer processing circuits conventional to helical recording devices are employed to provide from the scanner tach pulse circuit ~iming pulses to the helical recording device used to control operative functions. For the purpose of triggering pulse generator 56 to provide the reset pulse to integrator 50, the advanced end of scan command is generated from the scanner tach pulse provided just prior to the end of the scan o~ a previous track. The previous track related tach pulse is processed by a conventional counter included in the tachometer processing circuits to be present on line 76 just prior to the end of the scan of the current track.
The circuit is operable to provide a wave form at ~ 5 the output of the integrator for the vaxious modes o~ oper-ation which is generally the reciprocal or mirror image of the displacement patterns of FIG. 5 for the various modes.
As an example, the half speed slow motion in the forward direction having the displacement pattern shown in FIG. 5b results from the integrator output wave form shown in FIG.
7a. By comparing the wave forms of FIGS. 5b and 7a, it is apparent that the shape is merely inverted. Thus, in FIG.
7a, the integrator 50 provides an output wave orm that rises during the playback of a track, with the slope of the ramp portion of the wave form being a function of :the D.C. error input applied on line 52 that is derived from error detecting circuitry. With the voltage ramp rising durlng the playing of a track, the end of scan trigger pulse from the conventional trigger pulse generating circuitry (not shown but previously described) triggers the pulse generator 56 and it will provide an output pulse at the end of playing a track which will be applied through the adder 64 and line 66 to the input of the integrator 50. Since the output pulse from the pulse gener-ator 58 is a very short duration negative pulse, it has theeffect of resetting the output voltage to a level which pro-duces the desired displacement of the transducing head in position to play the track a second time. As the integrator output increases during the second playback of track A, the end of scan trigger circuitry will provide the trigger pulse to the pulse generator 56 at the appropriate time near the complet~on of the second play. However, the forward level : detector 68 continually monitors the instantaneoùs voltage at the output of the integrator 50 and provides an inhibiting signal on line 70 which inhibitx the pulse generator 56 whenever the instantaneous voltage is less than about zero.
Thus, as the second playback of track A is approaching completion and the end of scan trigger pulse is applied ~o trigger the generator, the detector will detect that the output voltage is less than 0 as shown in FIG~ 7a and the detector will generate an inhibit signal on ~ine 70. The pulse generator will thereby be inhibited which results in the integrator 50 not being reset and continues onward in effect following track B through the first playback. Since the vo:Ltage of the integrator output near the end of the first play is positive~ the forward level detector 68 does not inhibit the generator and a reset pulse is produced.
When the tape is transported in the reverse direction for the purpose of providing backward or reverse motion effects during playback, it is necessary for the transducing head to ~e reset to play a preceding in time track as previously mentioned. In the event that slow motion reverse direction playback is to be performed, at half speedl for example, the circuit of FIG. 6 will produce a voltage output wave form shown in FIG. 7b. A comparison of the wave form of FIG. 7b with the displacement pattern of FIG. 5i shows a mirror image or inverted pattern as was the case with respect to those 25 shown in FIGS. 5b and 7a. As the tape is following track A
through the first play, the instantaneous voltage near the end of the scan is above 0 as shown in FIG. 7b and pulse generator 56 will therefore produce a reset pulse which will ~;22~3t5 have the effect oE resetting the transducing head one center~
to-center spacing distance of 8.7 mils. The transducing head will then follow track A through a second scan or playback and the voltage of the ramp will approach the higher level V2, which higher voltage is detected by the reverse level detector 72. When the end of scan trigger pulse is produced, the pulse generators 56 and 60 will both he operable, because level detector 72 will not provide an inhibit on line 74.
The output pulses of the pulse generators 56 and 60 are added together by the adder circuit 64 and a pulse having a double magnitude appears on line 66 which is applied to the input of integrator 50, resetting the same so that the transducing head is moved a distance equal to two center-to-center track spacings or about 17.4 mils in the illustrated embodi-ment. In this manner the trac~ are played back in reversetime or sequence order, but are also replayed once to achieve the slow motion effect.
A specific schematic circuit diagram that can be , used to carry out the operation of the circuit shown in the block diagram in FIG. 6 is shown in FIG. 8 to comprise the integrator 50 with input line 52 receiving the low frequency or D.C. error signal from a synchronous detector circuit associated with error detecting circuitry which does not form a part of the present invention. The error signal is applied through an analog swit~h 80 which may be a CMOS device that is close circuited when a positive voltage (operater mode control command) is present on line 82 and open circuited when it is not. Its function is to disable the special effects circuitry during normal play. The S integrator 50 comprises an operational amplifier 82 having -32a ~he industry standard numbers in parenthesis and pin numbers adjacent thereto with a feedback capacitor 84 with its output connected to line 54. The forward le~el detector 68 is coupled to the output line 54 through :Line 86 and resistor 88 and comprises an operational amplifier that is set to monitor the instantaneous voltage and pr~ide a high output level on line 70 whenever the instantaneous voltage is about equal or grater than 0. Similarly, reverse level detector 72 also comprises an operational amplifier which also monitors the instantaneous output voltage through line 86 and a resistor 90 and it compares the output voltage with a voltage present on pin 1 which is adjustable controlled by a potentiometer 92 which is set at a higher level, such as about 3 volts for example. When the instantaneous output voltage approaches the preset limit, then the output voltage of the operational amplifier appearing on line 72 goes high.
The pulse generators 56 and 50 comprise-monostable multivibrators or "one shots" which are actuated or fired when both inputs A and B are high. When each of the pulse generators is fired, a negative going pulse is produced on their respective Q outputs which is applied to the input of integrator 50 through line 66, adder 64 and respective lines 58 and 62~ The Q output from each generator extends to other circuitry and is used for time base error correction. Line 76 is connected to input A of both pulse generators and is low when the advanced end of scan trigger pulse is present.
Pulse generator 56 is connected to the forward limit detector 68 by line 70 connected to the B input. Since the generator 56 will fire on a negativ~ going transition of line 76 when the input B is at a logic high level, whenever the level detector 68 detects a voltage below about 0, the pulse generator 56 will be inhibited~ Similarly, line 74 ~hich interconnects the output of reverse level detector 72 with the B input of pulse generator 60 is low whenever the voltage being monitored is less -than the preset value of about 3 volts for example. Thus, pulse generator 60 will always be inhibited except when the voltage ramp approaches the higher level which represents the limit of transducing deflection in that direction. ~hen this occurs both pulse generators fire producing the pulse of double magnitude for resetting the transducing head a total O:e 2 tracks. It shou]d he appre-ciated frorn the output wave form of FIG. 7~ that the pul~e generator 56 will be fired after every track is played and pulse generator 60 will be fired at the end of every second playback of a track.
Zener diodes 94 and 96 are provided to translate the voltage range of the outputs of the level detectors 68 and 70 to a range that is compatible with the pulse generators 56 and 60. Diodes 98 are provided to maintain a self centering feedback voltage to the lnput of the integrator to facilitate rapid lockup when a signal is resumed subse-quently of a period where no signal was applied to the input.
It should also be appreciated that the voltage of the output on line 54 extends to other summing circuits to which other signal components are added for application to the circuitry which drives the movable element 22. The output voltage is proportional to the deflection that is ultimately produced hy the elemen~, In accordance with yet another aspect of the present invention, spe~e~ up or fast motion effects can be achieved with the present invention. It should be understood that the circuitry specifically illustrated in FIGS. 6 and 8 will not accomplish fast motion operation because the ramp voltage from the integrator is inverted relative to that which is required. However~ similar circuitry with appropriate level detectors and switching circuitry for connecting the same while the apparatus is operating in the fast forward mode (while similtaneously deactivating the circuitry of FIG. 6) while not shown, is within the scope of the present invention. Fast motion eEfects would be achieved by advancing the transducing head one or more directions while the tape is bein~ transported at a speed that is faster than the txansport speed during recording. Referring to FIGS. 5g and 5h, displacement patterns for fast motion where the tape is transported two and three times, respectively, are illustrated, with repositioning of the transducing head at the completion of every track. With respect to the two times ~ast motion, it is seen that. every second track is skipped during playback with the transducing head being moved about 8.7 mils or one track to track spacing. It should be appreciated that the displacement of the txansducing head will be in the opposite direction that occurred during slow motion or still frame modes of operation. With respect to the three times fast motion shown in FIG. 5h, it is necessary to have the transducing head skip two tracks so that every third track is replayed during operation at this speed, a repositioning distance of 17.4 mils is produced.

~ ~ 2~ ~

It should also be appreciated that the three times fast motion shown in FIG. 5 has a total displacement of two center-to-center spacings, a displacement of about 17.4 mils, and that faster motion would require still additional deflection which must be compatible with the design and operation of the movable element 22 in terms of spePd and total range of movement.
With respect to yet another aspect of the present invention, the apparatus is adapted to operate in a surveillance mode as well as a skip frame mode of operation. Referring to FIG. Sf which illustrates the displacement pattern for the transducing head when the apparatus is operating in a surveillance mode, the inormation is recorded at a signiicantly lower transport speed than duriny normal recording. Thus, in the displacement pattern shown in FIG. 5f, the transport speed of the tape is l/60 of the normal speed and switching circuitry is adapted to record every sixtieth frame~ Thus, the video recorder scanner is triggered to record only one scan per second and disregard the next 59 scans which results in a synchronized recorded format with helix angles approx-mating a stop motion playback track. The recording of every sixtieth frame merely represents a specific example, it being understood that a greater or lesser number of frames than the 59 described could be skipped. In other words, the 2S longitudinal tape transport speed during recording does not change the static or stop motion generated helix very much.
During normal speed playback, an error in tracking occurs just as occurs in stop motion mode of operation for signals.

~52~

that were recorded at the normal transpor~. speed. The tracking pattern shown in FIG. 5f will result in the trans-ducing head accurately following the track during replay and repositioning -the transducing head at the beginning of the next track by moving it downwardly as shown. The surveillance mode of operation permits a television field o~ information to be recorded each second which provides a good record in terms of a sequence of information fields that can appro-ximate motion with an extraordinary savings in magnetic tape. Moreover, the quality of the reproduced signal is unimpaired by mistracking and crossover during playback.
With respect to the skip field mode o operation, and particularly a skip 1 field system having a displacement pattern of operation as shown in FIG. 5a, every okher field is recorded and the other field is disregarded. The record and playback tape speeds are about 1/~ the normal transport speed when no fields are skipped. Since the record and play-back speeds are identical (at the lesser speed) the angle of the tracks will be substantially identical during playback as during record so that no appreciable transverse movement of the transducing head is required during playing of a track and this is reflected by the horizontal lines during playing as shown in the drawing~ However, during playback, the continual 60 Hertz information rate is required, which necessitates repeating each track twice. Thus, track A is replayed once by moving the transducing head at the completion of the first play of track A a distance of about 4.35 mils which places it in the correct position to repeat the playback ~37-~2~ 5 of the track A. At the completion of the second play, it is necessary to advance the transducing head by moving it transversely downwardly for the irst play of track B~ It should be understood that the repositioning of the trans-S ducing head ater each track is played requires a deflectionof only 1/2 that required with respect t:o the 8~7 mils shown in the other displacement pattern for 1 center~to-center dis-tance for the reason that the tape is moving only lJ2 of the speed during recording compared to the recording speed of the tracks chat were described with respect to the other modes of operation. By utilizing the repositioning of the transducing head aEter playback of every track, the single head can achieve the same result as two heads have produced in similar skip Eie]d operakion on prior art apparatus. It lS should also be appreciated that while the skip one field system displacement pattern is shown, the invention can be used to skip more than one field (each field occupying one track).
Thus, every nth field may be recorded on a track, the inter-mediate ~ields disregarded, the tape driven at l/n the normal transport speed during recordiny and playback and the trans-ducing incrementally adjusted in a manner similar to that shown for the n equal 2 case described aboveO If every nth field is recorded, it is necessary to playback each field n times or, stated in other words, playback each track and repeat it n-l times.
Fr~m the foregoing description, it should be under-stood that the embodiment represents a closed loop system in the sense that the error correcting signals that are used to maintain the transducing head on track during playback of a track receives continuously updated information from the error detecting circuitry. Because of the closed loop oper-ation, the -transducing head will accurately follow the track -38~

regardless of the transport speed or direction khat is used.
Since the circuitry is adapted to automatically make the decision wh~n to have the transducing head advance to the next adjacent successive track during forward motion or the preceding-in-time track during revers~ transport motion of the tape, conventional "infinitely adjustable" capstan drive circuitry can be used. Since the operator may wish to vary the slow motion speed for viewing an instant replay of a sporting contest event, for e~ample, a potentiometer controller such as a "joy stick controller" may be used to control the capstan drive which transport the tape.
Furthermore, the automatic decision-making feature of the error detecting circuitry permits the operator to advance the tape at arbitrary rates, including in a field-by-field step fashion with long intervals of stop motion, by manually turning the reels. This provides the operator with a valuable tool for tape editing purposes.
While the disclosed embodiment describes the closed loop system, it should be understood that an open loop appar-atus is within the scope of the present invention and maybe used. In such an open loop system, the integrator 50 would not receive the low frequency or D.C. error signal from the error detecting circuitry, but would typically employ an adjustable ~.C. source that would be connected to the input of the integrator and adjusted to provide a voltage wave form that is related to the desired predetermined tracking or special motion effect. Such an open loop system would require that the tape ~s~
speed be very carefully controlled so that the tape ~ould run at the precise speed expected by the programming apparatus generating the voltage wave form for producing the appropriate displacement patterns similar to those shown in FIG. 5. The careful precise controlling of the transport speed may impose a limitation on such a system from a practical standpolnt.
From the foregoing description, it should be under-stood that a method and apparatus is described for achieving altered time base reference effects in the art of recording and reproducing information signals on a medium. In this regard~ the invention is particularly well suited for creating special motion and other effects in the field of video recording without detracting from the quali-ty of the signal being reproduced from the recording medium. Furthermore, the invention is especially suited for use in helical wrap video tape recorders for the reason that special motion effects, such as slow motion, still frame or stop motion and fast motion effects can be achieved without impairing the video signal that is derived from the magnetic tape. The system accurately follows the track during playback and automatically detects the position of the playback head near the completion of a track and decides whether -to move the transducing head to a track other than the next adjacent successive track or not.
Since the invention automatically makes the decision near the completion of playback of a track, the tape being trans-ported in the slow motion mode can be moved at virtually any speed, thereby permitting the infinitely adjustable slow motion playback. The fast motion effect is limited only ~:5~2~

by the range of deflection of the transducing head, with the embodiment described and shown in the drawings permitting two or three times the "normal motion speed".

., _ .... ..... .. _ .. _, ......
I

9~

~l~25;2~

Figures 9 - /9~ show the positionable element ln gr~er detail. Referring now to FIGURE Y there is shown a mag-netlc (head) transducer 3Ll, mounted for recording and sub-sequently reading an informa-tion track upon a relatively moving recording medium. The present invention relates to a novel form of mounting structure for the head311 that permits precise, continuous positioning of the head, which structure is useful in many different types of recording environments, such as, for example, magnetic drum or disc recording, longitudinal magnetic tape recording as used for computer, audio and instrumentation purposes, transverse rotating head magnetic tape recording for broad band data and/or -television signal recording, ancl helical-scan broad band data and/or television signal magnetic tape recording.
However, the structure is found to be especially suited for use in error-free positioning of heads of helical scan type magnetic tape recording/reproducing machines where large forces that act on the heads tend to promote undesirable displacements of the heads movable relative to the rotating head carrier. Therefore, the helical scan type machine as operated in a reproduce mode has been selected for illustra-tive purposes and FIGURE q shows a preferred embodiment thereof as intended for use with a single -transducer. It is not intendèd to limit the invention to helical scanning use since the advantages of the invention in such applica-tions are also useful in other applications; however, before describing the actual inven-tion, it will be useful to des-cribe the helical scanning structure shown in FIG~RES
/G and /~ and the tracking problems associated therewith, which problerns the invention overcomes.

~ $~o~ ~

l: : l , ,, ~ ID-2502 l ~ 5~
Briefly, the head3~.1 can be mounted on a separate ~- support comprising a scanning drum carrier for rotation ~ I coaxially between two stationary guide drums, most commonly cylindrical or on a support here shown as a rotatable upper guide drum313 associated with a stationary lower guide drum 315 as in EIGURE /~ ~ magnetic tape317 is helically ~rapped (i.e., substantia~ly 360~) around the drums3L3,315 for scan-. ning by the head 311. The tape317 is guided, ten~sioned and i moved (arrows319) by means not shown but well known i.n the art so that the head311 carried by drum313 rotating in ~; directlon 321 oppositc the direction of tape transport about the guide drums, scans a series of oblique transverse paths ; 323 of which only one is shown in FIGURE /G. It will be see in FIGURE /6 thak point325 of the tape moves to the positio indicated at 327 whi].e head 31.Lscans the tape hetween point 329 and point 325. Tlle resultant path on the tape (called : "track") is the ].ine323 from point329 to point325- The line 323 may also be termed the "direction of relative movement"
between the head311 and tape 3].7. In practice, the line or track 323 may be sli~htly S-shaped, for reasons which have nothing to do with the invention and, therefore, for simplicity of explanation the track 311 is illustrated as being straight.
It should be appreciated that if the head311 rotates in the same direction as that of the movement of the tape about the gulde drums313, 315, point327 of the tape moves to the position indicated at 325 while head3ll scans between point329 and point 327. Line 323' becomes the resultant track, howeverj this change in track position does not alter the implementation of : -the present invention.

~ ....... . __. ~___ __ . _ . _ . _, . . __. . , .. . . _ . .

~252~5 ID-2502 As previously mentioned, the tape is guided under tension so that recording occurs under a recommended standard value of longitudinal tension, which induces a certain degrec of stretching oE the tape. If the tape is played back at a S different tension because of faults in the tensioning mechan-ism, or because of unavoidahle variations in the mechanisms of different machines, then the length, straiglltness and inclination of track323 will be different, and the head 311 will not perfectly follow the track, leadinc~ to undesirab'e variations in the strenyth of the reproduced signal and other problems. A si.milar effect results if the correct tension is used on playback, but the tape ha~s shrunk or elongated due to changes in atmosplleric or s~.orage conditions, e.g., temperature or hun)idity. Also, irrecluklr tape edges lS and differences in ed~e-guic1in~ effects from machirle ~.o machine, can cause irregularly wandering tr~lcks or scans.
Accordingly, the invention relates -to the mounting of the head ~l on an extremely low-mass deflectable element, to enable it to be moved rapidly, substantially lateral to a desired track, such as a track of recorded informatior1 on a magnetic medium, while at the same time the head and its entire mounting is moved, or the recording surface is moved, or both are moved, in such a Wdy that there jCS relative motion between the head and the recording surface in the direction of the desirëd track. This is the condition in which the head scans or follows the desired track. In one embodiment of the present invention, the deflectable mounting is a thin leaf lying substantially in a plane that is normal to a plane tangent to the recording surface at the point of head-to-recorcl surface interface and substantially parallel to the direction of ~elative motion.

- ~ 4 -~52;~

It should be understood that the details of the means by which the amount and direction of actual deviation from the desired track for the head is sensed, in relation to the head-to-tape path that is normally followed, and the operatively associated energizing means by which the head mounting is caused to laterally deflect in response to the sensed deviations so that the head follows the desired path are not parts of the present invention, but are subject of and described în the above-mentioned co-pending applications.
Continuing now the description of the exemplary embodiment, it will be seen from FIGURE ~ that the head 311 is fitted to ; the lower portion of drum313. The view of FIGURE q is there-fore taken from the bottom of drum313, looking upward, as illustrated by the arrows ~~q of FIGUR~S/~ and // and the vi.ews of FIGURES ~O and // are also taken upside down, i.e., with the drum313 below and the drum3l5 above, for the purpose of making the description easier to follow.
Head311 is extremely small and of low mass (on the order of lO~ milligrams), and consists of two pole pieces 331 and 333 confronting one another across a non-magnetic txansducing gap 335 for recording and/or reproducing signals with respect to the tape. The gap 335 is aligned with the length thereof substantially parallel to the direction321 of drum313 movement relative to the tape 317- It will be understood that in the magnetic recording art the "length" of the gap is the dimension from pole face to pole face, in the direction of relative recording motion. Usually, the "width" of yap is ali~ned transversely to the relative motion direction and parallel to the recording surface, and the "depth" of the gap is ~L~5~2~5 normal to the recording surface. If for any reason the gap is inclined to the direction of relative motion, the length i~ still defined (at least for purposes of this invention) to be in the direction of relative motion, while the width and depth dimensions are still taken as being orthogonal to the length. Signals are carried to or from the head 311 by means of pole piece windings 337 and leads 328. Signals are coupled between the magnetic head311 and the recording surface passing the gap 335 through a coupling path that extends between the two pole pieces 331 and 333 through the recording surface in the direction of relative motion, hence the desired track on the surface.
To provide for tracking movement of the head311 transverse (arrows339) to the direction321 of the drum 313 movement, the head is mounted or bonded, as by epoxy, to one flat side of a positioning member including a thin deflectable leaf element 341 here shown by way of example as a piezoelectric ceramic bender element. In the embodiment of the invention discussed in detail hereinafter with reference to the drawings, the positionable element includes a cantilever mounted piezoelectric ceramic bender element either manufactured by Vernitron Corp~
and identified as PZT-5HN Bender Bi-Morph Poled For Parallel Operation or by Gulton Industries and identified as G 1278 Piezoceramic Bender Element Poled For Parallel Operation.
As shown in greater detail in FIGURE /~ the leaf element341 is composed of two piezoelectric ceramic members 342 and343, sandwiche~
and bonded between electrode members (nickel or silver)349, 349A, 351 or 351Aand conductively bonded as by epoxy layers344 and 345 to opposite sides of a brass vane member 347. The ceramic members 342,343 are cut and oriented with their axes of polarization vertically aligned (i.e.~ parallel to arrows339 in FIGURE/~).

~2 5Z2~3 I D - 2 s o 2 As is well-known in the bender art, the direction of polarization of the respective ceramic members:may be either the same or opposed, depending upon how the electrodes349,351 and the brass vane347, which may also be used as an electrode, are energized.
For protective purposes, the leaf341 is mounted in an open-end housing359 composed of a base shoe member 361 and a cover member363 having two side walls365 fitting on shelves~67 of the shoe361. The leaf341 is solidly mounted between twc electrically insulating spacers369 by _ ~7 _ ~5~5 ID-2502 means of a bol-t~71, which passes through the covex363, the leaf ~1, both spacers369, and is threaded into shoe361~ The bolt371 is insulated from the leaf341 by means of an electri-cally ~nsulating collar373 between the spacers369. To provide access to the head311 and leads338, the cover363 is made shorter than the shoe361 and is cut away in an upper slot375, the leads338 having terminals377 mounted on the upper inner end of cover363. Because a low mass is desired for the leaf 341, damping may be necessary or desirable. In such event, to provide damping an~ thereby lower resonant frequency for the leaf341, and to act as limit stops or restraints, the cover363 and shoe~61 may be provided with so-called dead-rubber pads379,~81, respectively, which absorb impact with-out i~nediate rebound (see also FIGURE ~ These restraints se~ve to prevent undesirable movement of the supported head 311 that could introduce errors in the recording and/or re-production of signals.
Leads353,355,357 extend respectively from elements 349,347,351 for coupling a voltage source to establish an energizing electric field in the elements and may be formed as shown in FIGURE /~, in wnich a corner of each inwardly-extending leaf end layers~49,34Z and344 is cut away to leave a soldering shelf383 for attaching the lead355 to the brass vein electrode~47, while the leads353 and357 are soldered 25 respectively to electrodes349 and351. However, this arrange-ment requires a certain extension385 (FIGURE /o! of the electrodes, and in fact of the leaf341, radially inwardly of the spacers369, away from the head311. In order to pre-vent such extension385 from responding to harmonic vibrations of the drum driving motor, and other external vibration sources,

- 4~ -~ ID-2502 ~5~
and thus upsetting the fine control o~ the movement of leaf element341, the entire extension385 is potted between the shoe361 and cover363 as illus-trated in FIGURES // and /~ in which the non-conductive potting compound (e.g.~ epoxy) is represented by reference numeral387. The cover~63 and shoe361 may be cut away to define an enlarged potting chamber~89 for this purpose.
The assembled leaf element341 and housing359 are mounted on the drum313 as shown in FIGURES 9 and //. Drum 313 is provided with a cylindrical peripheral flange391 and a central radial web393. Because the drum313 bears only one head311 as in the 360 wrap configuration, the drum web 393 and part of the flange391 are cut away to define an open-ing395 to counterbalance the mass of the head311 and its mounting means. A bracket397 ls mounted in bridging relation across the opening395, as by means of bolts399.
The shoe361 is mounted on the bridging bracket397 as by means of a boltllOl, with the shoe361 extending toward the peripheries of the drums~l3 and315 to leave nothing protruding beyond those peripheries but the tip of head311 extending through the cut away portionllO3 of the flange 391.
For optimum performance, the dimensions and pro-portions of the leaf341 are carefully selected for the particular application intended. The leaf material is available commercially and is obtainable in various stand-ard thicknesses, which can be cut to desired length and width dimensions. The selection of dimensions and propor-tions is made according to the desired leaf elemen~ dis-placement sensitivity, range and response, desired resonant ~252~
frequency, desired purity of leaf element motion, and desired structural rigidity so that the free end of the leaf element 341 (i) is permitted to move along a desired path that re-sults in the controlled displacement of the suspended mag-netic head 11 in a direct:ion relative to tape317 that moves the head's recording/reproducing gap335 transverse to the time axis of signals recorded along the tape and (ii) is restrained against movement that would result in the gap 335 of the head 11 moving in any substantial or significant manner, particularly with a component in the direction of the time axis, that would introduce undesirable timing er.ors in the recording and/or reproduction of signals. While longitudinal displacement of the free end of the leaf relative to the tape occurs in the direction of the length dimension of the leaf as it is deflected transverse to the time axis, it does not have a significant effect in coupling signals between the tape and magnetic head. For example, in the embodiment discribed below including a leaf element having a length dimension, L, of 2.4 cm., the free end of the leaf moves less than 0.0001 cm. for a typical deflection of ~0.024 cm. Such longitudinal displacements of the free end of the leaf do not have a component along the time axis of signals recorded along the rack and can be ignored for purposes of this invention. In helical scan machines, the time axis of signals recorded along the tape 317 lies along ~he path scanned by the head311 illustrated by line323 in FIGURE /~- More particularly, the leaf element341 should have a length, L, (the suspended portion measured from spacers369 to the free leaf end at head311) to width, W, aspect ratio that restrains the element341 against any ~ 52~5 ID-2502 movement in the width dimension or against any torsional movement about the length-width plane of the elemert341 that would give rise to an undesirable displacement of the suspended head311 having a component along the time axis or line323. Undesirable displacements that are to be particu-larly avoided are those that would introduce unacceptable azimuth and tim~ base errors in the recording and reproducing of signals. For signals in the color television video fre-quency range, displacement along the time axis or line323 should be limited to less than 0.13 microns in order to avoid such errors. On the other hand, it is preferred that the length-to-width aspect ratio not be so small as to unduly ~ . _ . . .. . . .. . . . _ . .. . .. . _ ~/ _ ~5~5 ID-2502 1 limit the possible head displacement range for a practical drive voltage used to control the displacement of the elemen~
341. For example, for a head displacement range of + 0.025 cm., a length-to-width aspect ratio of 2 is the most suitable.
As the aspect ra~io is increased, the leaf element341 becomes less rigid in the width dimension and, eventually, is able to move in a direction having a component along the time axis or line323 causing unacceptable azimuth and time base errors.
As the aspect ratio is decreased, the leaf element341 does !0 become more rigid in the width dimension. But, the drive voltage must be increased for a given head displacement, eventually to levels that become impractical, particularly, for the rates of displacement cycles necessary to maintain the error-free trackin~ that the present invention is intended 1.5 to provide for helical scan applicatiorls.
The thickness, t, of the leaf element341, is selected, in the preferred embodiment described herein, to provide good sensitivity, i.e., displacement per unit drive voltage, sufficiently high resonant frequency to permit the element341 ' to be displaced at desired high rates below the resonant frequency, purity of leaf element motion and a practical voltage limit for the desired maximum displacement rate and range. For example, for a displacement rate of up to about 200 displacement cycles per second over a range of '5 + 0.025 cm., a thickness on the order of 3% of the width dimension of the element341 is suitable. While leaf elements of smaller thicknesses are characterized by greater sensitivity, they also have a lowe~ resonant frequency. As the rate of leaf displacement approaches a resonant fre~uency, ~ the leaf displacement exhibits marked changes from displace-ments at frequencies either side of the resonant frequency.

~1 ~5~5 Such marked displacement changes make control of the position r hence tracking of the leaf element341, exceedinyly difficult.
The opposite is the case for leaf elements of grea-ter thick-ness, i.e., decreased sensitivity and higher resonant fre quency. Further, thicker leaf elements require higher drive voltages for a desired displacement range and rate. Torsional displacements giving rise to unacceptable time base and azimuth errors are further restrained by constructing the leaf element 341 to experience a pure bending motion type displacement when subjected to an energizing electric field. Such displacement is achieved by constructing the leaf element341 to have a uniform thickness over its length. A thickness uniformity along the leaf's length of + 10% of khe thickness design value provides excellent res-traint against unacceptable torsional displacements.
The positionable head mounting structure of the present invention is further characterized as being capable of a very lo~ mass (1.5 grams is a typical example) construc tion. The low mass construction is possible because the structure utilizes a single thin leaf positionable element 341, from which is suspended a magnetic head311 of relatively negligible mass. The low mass characteristic of the struc-ture facilitates the rapid displacement of the head311 under carefully controlled conditions whereby lt can be precisely positioned to follow a desired path along the magnetic tape317. Furthermore, it enables the positionable head mounting structure to be used in rotary scan record/
S reproduce machines, such as helical scan machines of the kind in current commercial use.
In one embodiment of the positionable head mounting structure used in a helical scan machine, the leaf element was constructed to have a thickness, t, of 0.05 cm., and an extension (or length, L,) dimension of 2.4 cm. ln order to provide ~ resonant frequency of about 400 deflection cycles per second. The width of the leaf element341 was selected to be 1.27 cm., a value that provided adequate stiffness or ~ rigidity in the direction of the scan of the head311 over the tape317 (or time axis of the signal recorded along the tape), considering the frictional drag created by the tape, and the repeated extremely large impulse change in the frictional forces acting on the head311 as it enters and leaves each scan of the tape317. Particularly to be avoided is an effect of twisting of the leaf about its longitudinal axis, which would cause a skewing effect of the head with respect to the tape. The dimensions selected were found satisfactory to avoid skew.
For some applications, it may be desirable to mount a plurality of magnetic transducers on the positionable element. For example, FIGURE /~ illustrates an applica~ion in which a pair of left-offset and right-offset t~ack sensing magnetic heads1105 and1107 are employed to monitor _ 5~_ ~ 5 ~Q 5 continuously the posltion of a sin~,le record/reproduce magnetic head lla relative to a recorded track and provide information that i5 used to control the position of the record/
reproduce head. The implementation of ~hi.s embodinent for controlling the position of a single record/
reproduce head is described more ~ully in my above-referenced co-pending Canadian Application Serial No . 274,284 filed March 18r--1977. The single record/reproduce head lla is mounted just as is head311, while track sensing headsllO5!1107 are mounted on either side of head311a, but are oppositely staggered transversely to the direction of motion321a, so as to sweep, respectively, left-offset and right-offset zonesllll and1113 that overlap the middle zone1115, which corresponds to the expected range of track displacement of head311a. As shown in FIGU~E ~ record/reproduce head lla is mounted directly on the surfa~e of ~he leaf341a for sweeping a range o~ displacemer.ts represented by middle zone1115.
Left-offset track sensing headll~5 is mounted on a spacer element1109 fastened to the surface cf the l~af341a, the thickness of the spacer ~09 being less than the width of the head311a so that the sersing head1105 is spaced above the head311a by an amount less than the width of the head311a.
Right-offset track sensing headllO7 is mounted on a recessed mounting shelf1117 provided by cutting away leaf341a at the corner, somewhat as in FIGURE ~. Moun~ing shelflll7 is recessed below the surface of leaf341a a distan~e equal to the thickness of the spacerllO9 so that the sensing headllO7 is space~ below the head311a by an amount less than thP width of the head311a. With the track sensing heads~105,110 - sr -mounted in the aforcdescribed manner relative to the record/
reproduce head311a, the paths scanned by the sensing heads always overlap the edges of the path scanned by head311a as it is displaced through the expected range1115 of track displacement. In the event the path scanned by the head311a is a recorded track of information, the sensing headsllO5, 1107 reproduce information from the overlapped edges of the recorded -tracks as they follow the record/reproduce head311a~
Alternatively, the sensing headsllO5,1107 may be made narrower in width (i.e., transverse to direction of motion321a) than head311a, so as to have less overlap upon the path scanned by head311a, or even zero overlap. However, the headsllO5,1107 preferably do not extend laterally beyond the dimension of the guard bands flanking the recorded track, when the head 311a is correctly following the track, and thus heads llO5,1107 do not ordinarily read parts of adjacent tracks. With regard to other structural features of the transducer mourltiny structure of FIGURE /S~ such as, or example, a housing, head windings, electrical leads, and restrains, they may be con-structed similarly as described with reference to the embodiment of FIGURES q~ through /~.
FIGURES /~ and 1/B illustrate, in schematic block diagram form, embodiments of means for sensing the position of the record/reproduce head relative to a desired path along a record surface, such as a recorded track of information, and generating a suitable signal for actuating the positioning element by, for example, energizing the piezoelectric member s, ~42 and343 for displacement to control the position of the head so that it follows the path or recorded track. The embodiment of F~;URE /q~ is for use with the magnetic transducer mounting structure embodiment illustrated by FIGURES ~ through ~and -~G ~

utilizes a dithering technique to sense and control the posltion of the record/reproduced head 3110 The embodiment of FIGURE l9B is for use with the magnetic ~ransducer mounting structure embodiment illustrated by FIGURE 15 and utilizes a track following technique described in detail in my above-referenced co-pending application, Serial No.
274,280 to sense and control the position of the record/reproduce head 31la. Considering first the position sense and control embodiment of FIGURE 19A as employed with the mounting structure embodiment of FIGU~ES 9 through 14 an oscillator 1151 is operated to provide at its output a fixed frequency alternating dither signal~ which is coupled to the leaf element 341 causing it to vibrate within a displacement range. Before coupling to the leaf element 341, the dither signal is coupled to one input of a voltage summing circuit 1152 to be algebraically summed wlth n voltage control sLgnal provided by an adjustable blas voltage source 1153 and coupled to a second input of the summing circuit. The resulting summed dither and control signal provided at the output of the summing circuit 1152 is coupled by line 154 to be applied between the two leads 353 and 357 so that the summed signal is impressed across the entire leaf elemen~
struct~lre. If the summed signal ls to be applied to leaf element 341 with reference to the brass vein electrode 347, the other electrode 355 is required. One of the electrodes, for example, 351 connected to the lead 357, serves as a reference for the applied summed signal.
The dither signal component of the applied summed signal causes the leaf element 341 to vibrate over the _ 57 -mls/SS

, .

~25~2~5 ID-2502 selected range as the suspended head 11 is operated to reproduce signals recorded along the track, such as repre-sented by line~23. This vibration causes an amplitude modulation of the envelope of the reproduced signal. When head~ll is located in the proper track position at the center of the track323, the amplitude modulation of the reproduced signal at the dither frequency is at a minimum and increases to a maximum as the head 311 is displaced to one side or the other of the track center. Thus, minimum peak-to-peak values of the signal envelope at the dither frequency occur when the head311 passes through track center and greater peak-to~peak signal envelope values at the dither frequency occur when the head311 is displaced to one side or the other of the track center. With the head311 in the proper track position, the frequency of the envelope variation is twice the frequency of the dither signal component. However, with the head311 to either side of the proper track position, the maximum-to-minimum envelope amplitude variation occurs once for each cycle of the dither signal ~omponent, or at the dither signal frequency, with the order of occurrence of the maximum and m nimum points depending upon the side of track center to which the head311 is offset. Detection of the order of occurrence of the maximum and minimum points provides infor-' mation definitive of the direction the head311 is offset from the center of track323 and detection of the envelope ampli-tude variation provides information definitive of the amount of offset.
To obtain this track offset inormation, leads338 of the head311 are coupled to the input of an envelope detector 1156. The detector provides a signal representative of the amplitude modulated envelope component of reproduced signal at the frequency of the dither signal.
This signal is coupled to a control input of syn-chronous detector1157 for phase and amplitude comparisonwith the dither signal provided by the oscillator1151 and coupled to a reference input of the detectorll57. The detector1157 is responsive to the input signals to generate an output signal having an amplitude proportional to the amount head311 is offse-t from track center and a polarity representing the direction of the offset. This output signal is provided to the input of the adjustable bias voltage sourcell53 to adjust the voltage level of the control signal in accordance with the amplitude and sense oE the output signal. Source 1153 is responsive to the output signal to generate a control signal whose voltage level follows the amplitude and sense variations of the output signal so that the positioning leaf element341 is energized to compensate for detected track ofsets of the head~ll upon application of the summed control signal and dither signal.
With reference to the track following embodiment of FIGURE l9~ as employed with the transducer molmting structure embodiment of FIGURE /~ it includes an adjustable bias voltage 80urcell61 that provides a control signal at its output, which is coupled by linell62 to leads353a and357a to be applied, as in the embodiment of FI~7URE /9~ across the entire leaf element structure341a. Two inputs of a difference detector 1163 are respectively coupled to receive the signals repro-duced by the sensing heads1105,1107. The difference detector - S~

5 ~ ~ 5 1163 compares the average amplitudes of the reproduced signal envelopes and provides an output difference signal whose amplitude is proportional to the difference in the average amplitudes and whose sense is representative of which of the average amplitudes is the largest. ~Then head311a is located in the proper trac~ position at the center of the trac~23, the average amplitudes of the signals reproduced bv the sensing heads1105,lL07 are equal. Thus, the output signal of the difference detector will be zero, or correspond to the desired track position for head311a. However, as the head311a is displaced ~ro~ traclc center in the direction of the lef~-offset track sensing headllO5 tsee FIGU~E ~5~, the average amplitude of the signal envelope reproduced by the sensing headlln5 proportionately decreases while that reproduced by tlle right-offset trac~; sensing headllO7 proportionately increases. The contrary occurs as the record/reproduce head311a is displaced from tracl; center in the direction of the ri~,ht-offset track sensing headllO7, i.e., the average amplitude of the signal envelope reproduced by the sensing headllO7 proportionately decreases while that reproduced by the sensingl].O5 proportionately increases. The di~ference detectorll63 is responsive to such proportionately changing signals to generate a difference signal whose amplitude follows the amplitude diference OL
the signal envelopes reproduced by the sensing headsllO5, 1107 and whose sense is dependent upon which of the signal envelopes has the greatest average amplitude. This difference signal is provided to an input of the adjustable bias voltage sourcell61, which is responsive to adJust the voltage level of the control signal in accordance with the amplltude and sense of the difference signals so that, upon its application ~-~s~
to the positioning lea~ element341a, the element is energized to compensate for detected track offsets of the head311~.
An alternative arrangement for mounting the trans-ducer is shown in FIGURE /8 In this example, the leaf S elementll21 is not piezoelectric but is made of magnetically-permeable material, and is arranged to pivot from a sta~lc support, rather than bend, provided by means of a pair of widely-spaced knife-edge type hingesll23 formed between the leaf ~21 and a base memberll~5 with ~he leafll21 loaded a~ainst a basell25 by means of a compression spring element 1127 extending between the leaf and the ~ase. Xead llb is mounted at the end of the leafll21. The basell25 also includes a pair of electromagnetsll29 positioned" by suitable retainin~
means (not shown), on opposi~e sides of the leaf for p~oducing a magnetic fleld thrcugh the leafl~21 in a directionll31 (orll33) that is normal to the plane of the leaf. r!rive means 1135 for energizing the electromagnetics to position the leaf 1121 are sche~.atically shown.
The embodiment illustrated by FIG~E /~ utilizes a dithering technique like that described with reference to FIGU~E /q~ for controlling the position of the leafll21 at its head end. ~Iore specifically, the leaf1121, and its pivoted support structure, is made of magnetically permeable material.
The drive means1135 includes a current sourcell37 that delivers over lines1134,1141 a su~med dither and control current signal to the exciting coils of the electromagnetsll2g. For con-venience, the windings of the coils are wound abou~ the cores of the electromagnets in opposite phase senses so that opposite magnetic poles are established at the facing surfaces of the cores. This permits the same phased current signal to be used -G~-ID-~.502 ~ 5 for excit.ing both coils to control and vary the position of the leaE1121.
As in the embodiment of FIGURE /~ an oscillatorll~3, detector and bias sourcell45 and summing circuitll47 are operatively associated together and coupled to receive the signal reproduced by the head311b and generate a summed dither and bias control signal for application to the control input of the current source~l37. The oscillatorll43 generates the fixed frequency alternating dither signal for exciting -the electromagnet coils to vi~ra-te the leaf1121 within a determined displacement range. The bias control signal determines the current level about which the current signal provided by source1137 is made to vary at the dither signal frequency and has an amplitude determlned by the amplitude variation at the dither frecluency of the signal envelope repxoduced by the head 311b and by the order of occurrence of maximum and minimum envelope amplitude points.
While the transducer mounting of the present invention has been descri~ed particularly in relation to magnetic helical sean applications, it will be apparent that the positionable transducer mounting is equally well adapted for use with other signal recording systems employing transducers other than magnetic heads. ~lso, other types of reeord medium scanning apparatus may be used, such as transverse scan apparatus, magnetic discs and magnetie drums, and logitudinally recorded tapes. For transverse sean, the head, or an appropriate number of them, may ~e mounted in a similar manner on the scanning drum. In the magnetic drum and disc art, the mounting is well adapted to enable the head to follow apparent track irregularities that may be caused by wobble or run-out, such as may, in turn, be caused by eccentric or axially misaligned drums/discs or mis~alignment of the head moving mechanism. In longitudinal recording, the head mount of the invention permits the head to follow apparent track irregularities such as may be caused by m~s-alignment of the tape guides or head mounting base, or simply by ~avy tape edges engaging well-aligned guides when the tape has shrunk or expanded after having been recorded.
For parallel channel recording applications, more than one r~cord/reproduce head can be supported from a single positioning element.
What has been described is the adaptation of a magnetic transducer to automatic tracking use in association wlth a relatively moving magnetic recording surface such as a magnetic tape, drum or disc, the transducer being supported from a positioning element for displacement lateral to lS the time axis of signals recorded along the record surface, commonly, the direction of relative motion with respect to ~he record surface, while restrained against deleterious displacement along the time axis. For applications in which the transducer is to follow a previously recorded track, the transducer is displaced with a predeter-ined range corresponding to the expected range of trac~
deviation on the record surface.

G~-.

Figures 20 - 27 ~show greater ~etail relatin~
to tlle use of ditl~er signals for position error correction. In helical scan video tape recorders, the path followed by a magnetic video head transducer during reproduction often does not coincide with the track of a previously recorded video data. Referring to Fig.~O, a section of magnetic video tape ~/Ois schematically shown with one track ~ of data (depicted in a dashed line) previously recorded by a helical scan video tape recorder. As previously mentioned, during data recording and reproducing operations, the tape is guided under tension so that recording occurs under a recommended standard value of longitudinal tension, which induces a certain degree of stretching of the tape. If the tape is played back at a different tension because of faults in the tensioniny mech~nism, or because oE unavoidable variations in the meehanisms of different maehlnes, then the len~th, straightness and inelination of the data relative to the video head track will be different. ~nder sùch eircumstances, the head will not perfect]y follow the data track, leading to undesirable variations in the strength of the reproduced signal, such as variations in the amplitude of the RF envelope ~. A similar effect results if the correct tension is used on playback, but the tape has shrunk or elongated due to changes in atmospheric or storage conditions, e.g. temperature or humidity.
Also, irregular tape edges and differences in edge-guiding effects from machine to machine, can cause irregularly wandering tracks or scans. Consequently, the path ~ taken by the video head during reproduction as it scans the tape ~/O often fails to exactly coincide with the recorded track ~. In actual practice it has been found that a deviation of 0.0025 cm between the recorded track ~ and the path ~/~taken by the reproduce head ean result in significant deterioration in the quality of the reproduced video signal, One solution to precise tracking of paths by signal transducers along a record medium is offered by the present invention. Briefly, a magnetic video head signal transducer 4~can be mounted on a separate support comprising a scanning drum carrier for rotation coaxially between two stationary guide drums, most commonly cylindrical. Alter-natively, the video head ~Y~can be carried on a support here shown as a rotatable upper guide drum 4~ associated with a stationary lower guide drum ~as in Figs.~/and ~ the co~xially disposed drums forming a scanning assembly providing a surface ~Y for guiding the tape 4/O. The upper drum ~ is fixed to a driven shaft ~ which is fi-tted for rotation in a bearing ~ mounted on the lower drum ~ ~ and driven by a motor (not shown) in a known manner. The mag-netic tape ~D iS helically wrapped (i.e., substantially 360) around the drums ~ ~ for scanning by the head ~O. The tape ~/O is guided, tensioned and moved (arrows~25) by means not shown but well known in the art so that the head 4 ~O
carxied by drum 4~,rotating in direction ~opposite the direction of tape transport about the guide drums, ~ . ....

scans a series of oblique transverse paths ~of which only one is shown in Fig.~O. It should be appreciated that the head ~ can rotate in the same direction as that of the move-ment of the tape 4/o about the guide drums ~o, ~. However, this change in head rotation does not alter the implementation of the present invention.
Head ~ois extremely small and of ].ow mass (on the order of 100 milligrams), and consists of two pole pieces and ~ff4c confronting one another across a non-magnetic trans-ducing gap ~Q for recordlng and/or reproducing signals withrespect to the tape ~D (see Fig.~6~. The gap ~o~ is aligned with the ler.gth thereof substantially parallel to the direction of drum ~ movement relative to the tape ~~ It will be understood that in the magnetic recording art the "length" of the gap is the dimension from pole face to pole face, in the direction of relative recording motion. Usually, the "width"
o~ gap is aligned transversely to the relative motion clirection and parallel to the recordlng surface, and the "depth" of the gap is normal to the recording surface. If for any reason the gap is inclined to the direction of relative motion, the length is still defined (at least for purposes of this invention) to be in the direction of relative motion, while the width and depth dimensions are still taken as being orthogonal to the length. Signals are carried to or from the head ~4~by means of pole piece windings ~/ and lead ~(see Fig.2~/. Signals are coupled between the magnetic head ~oand the recording surface _~G -I D -- 2 '1 ~3 1 passing the ga~ 4~0~through a coupling path that extends between the two pole pieces 4~o6and ~c through the record~
ing surface in the direction of relative motion, hence the desired track on the surface.
I'o provide for tracking movernent of the head~
transverse to the direction 4~ of the drum ~2 movemen-t, the head is mounted or bonded, as by epoxy to one flat side of a positionable element ~D,here shown by way of example as a piezoelectric ceramic bender element. It will be seen from Fig.~/ that -the head ~'~is fitted to the upper rotating drum ~. The piezoelectric bender element ~30is elongated and is mounted at one end in a cantilever support element ~3~'fixed to upper drum ~'~- As will be more particularly described later, the bender element bends in response to lS an applied voltage in directions transverse to track ~/~ to deflect the video head ~olateral to the recorded track ~/~
Support ~'may be constructed in any suitable manner such as from machined aluminum and may be attached to drum 4~2 by screws, or other means. The support must be electrically insulated from deflector ~30when a pie20electric ceramic bender is used as the deflector.
The details of the particular construction of the positionable element ~Oare the subject of and are described in the aforementioned commonly assigned and co-pending application of Richard Allen Hathaway ~V-- ' . .... .

a7~, a~J
Serial No~ 668,G5' ~T~ for Positionable Transducer Mounting Structure. A brief description will be included herein to facilitate understanding the present invention.
The piezoelectric ceramic bender element ~30is constructed of two layers ~0~ and 43~of piezoelectric ceramic material sandwiched between electrode members and bonded to~ether in a known manner to an intervening brass vane 4~. The element is elongated and significantly wider than thick.
For cantilevered positionable elements, a length-to--G~-~_ . . .. . . . . . _ ~s~

width aspect ratio of 2:1 and a thickness on the order of 3.0~ of the width provides the desired deflection character-istics. The axes of polarization of the two piezoelectric layers are oriented with respect to one another so that, when a voltage is applied across the bonded layers, one layer is caused to expand and the other to con-tract in a known manner. The device is thereby caused to flex or bend. The amo~lnt of movement depends on the voltage applied across the layers of piezoelectric material. The piezo-electric element ~ois fixed to the cantilever support by two electrically insulating spacers~3~located on both flat sides of the element ~0 proximate one of its ends~
An open-ended protective housing lnot shown) surrounds the bender element 4~0, with the lea~ disposed therein to extend from the spacers ~33 with __ . . . . ..... . _ _ .. _ _ _ __ _ _ _ . ... . . .... . .

i.ts free end outside the open end of the unshown housing whereby the head ~4~is supported so that it slightly pro-jects beyond the outside surface ~ of the tape guide drums y~ in transducing relationship with respect to the tape ~/~
Leads ~ ~ ~3~ are soldered to the electrodes of the piezoelectric ele~ent ~for coupling a driving voltage to the element. A servo drive circuit ~0 is connected to control the drive applied to the element ~30 in a manner to be described below so that the head ~Y~is maintained in a desired transducing relationship with respect to the tape ~

2~5 Referring to Figs. 22-24 and 27, a servo circuit for maintaining a video reproduce head 440 in the optimum transducing relationship with respect to a track 412 extending obliquely across the tape 410 is shown. ~ dither oscillator 2101 generates a sinusoidally varying signal at a fixed frequency fD. To avoid harmful signal interferences with the recorded ~ideo signal reproduced by the head 440, the dither oscillator 2101 is operated to provide a pure sinusoidally varying signal at the fundamental frequency fD
preferably having less than 1% higher order harmonic content.
The output of dither oscillator 2101 is applied to an adjustable attenuator 2102 which may be manually ad~justed to calibrate the oscillator output to an appropriate amplitude.
The output oE attenuator 2102 i9 fed to one input 2104 of a s~lmming circult 2103 where it is added to a low rate or DC
error correction signal, to be described later, Qlld present at input 2106 and, if high rate error correction is desired9 a high rate or AC error correction signal at input 2107 (see Fig. 23). The output o~ summing circuit 2103 is amplified by a drive amplifier 2108 and the amplified signal i9 coupled to drive the bender element 430 by way of leads 434, 435, 436.
Circultry for developing the drive signal i9 described in my co-pending application Serial No. 274,424 for Drive Circuitry For Controlling Movable Video Head, filed on March 219 19770 The oscillator drive signal ,,~ /

mls/SS ~~

excites the bender element ~3~to impart a small peak-to-peak (preferably 10% to lS~ of the width of track 4~) oscillatory motion (dither) to the head ~4~to cause the head to move laterally to the track ~/~ alternately between limits as it scans the track to reproduce the recorded signal. Limiting the oscillatory motion of the head 4 to the small amount insures that the head is kept well within the boundaries of the track 4~ and its flanking guard bands, thereby avoiding detrimental cross talk.
In the helical scan video tape recorder environment in which this embodiment of the invention is constructed to operate, the recorded tracks of video are 0.145 mm wide separated by guard bands of 0.076 mm. Thus, the drive amplifier ~/o8 is arranged to provide an oscillatory drive signal that causes the he~d ~oto oscillate or dither laterally to each track ~~ .010 mm about the head's home position as it follows the track ~/~ (The head's home position is determined by the servo drive circuit ! S
negative feedback loop to be described hereinbelow.) The oscillatory motion imparted to the head ~4 causes an amplitude modulation of the reproduced signal, which, when recording video or other such high frequency signals, as in the form of an RF envelope of frequency modulated carrier. Because the magnitude of amplitude deviations in the modulation of the RF envelope are used to maintain the head in the desired transducing position with respect to tlle track ~ the precision with which such pOSitiOIl iS maintained - 702 ' __ ID-2481 ~2~ 5 is dependent upon the sensltivity of the servo drive cir-cuit and how free the reproduced RF envelope is from spurious modulations.
As described hereinbefore, periodic reproduced signal interruptions or dropouts common to track segmented recoraer and/or reproduce machines act on the reproduced RF envelope as a spurious pulse modulation, which have harmonically related components distributed at frequency intervals of the dropout rate. For a single head and field per track helical scan recording format used to record signals of a 60 Hz television signal standard, the dropout rate is 60 ~Iz. In 50 Hz television standards, the dropout rate would be 50 Hz. If any of the harmonically related components of the spurious dropout i.nduced pulse lS modulation components coincide or fall close to that of the dither frequency, fD, harmful interference results.
Minimum interferences will result if the dither frequency, fD, is an odd multiple of one-half the dropout rate.
In addition, the dither frequency, fD, should be selected to avoid regions about anti-resonance points found to be present in the response characteristic of piezoelectric ~ ,7~ ~

.. ..

~5~:2~5 ceramic bender devi.ces commonly employed as the positionable element ~3cin transducer mounting structures of the kind described in the aforementioned Hathaway application Serial ~,2~
~ No. G~,G51 (ID~-2.~2). Furthermore, the dither frequency, fD, should be set so that the piezoelectric element ~30is operated in a region of high sensitivity.
Piezoelec-tric ceramic bender devices have been found to have a family of anti-resonant frequencies, fA, within their response characteristic. Furthermore, the lower-most anti-resonant frequency f l~ of -the same type piezoelectrlc device has been :Eound to vary from device to device over a range of h~ndreds of hertz. Ii'or example, devices of the aforementioned types constructed in accordance with the aforementioned dimension specifications are found to have a lower-most anti-resonant frequency, fAll anywhere within the range of about 750 to llO0 Hz. Furthermore, such devices ordinarily have fundamental and higher order resonances with a lower-most resonant frequency, fR, of about 400 Hz, but it can vary between typical values of 350 Hz to 450 Hz from device to device.
For maximum sensitivity and immunity against anti-resonance effects, the dither frequency, fD, should be set at a frequency situated within a resonance region and outside any anti-resonance region. Because of the wide variations from device to device of the anti-resonant frequency characteristic and the fixed lower-most resonant frequency of devices of the same kind, it is convenient to place the di-ther frequency within the aforementioned range of the lower-most resonance. A dither frequency, fD, of 450 Hz satisfies this convenience cri~eria and also is an odd multiple of one-half the 60 Hz dropout rate (i.e., 15 x

6 ), thereby satisfying the minimum interference criteria.

- 7~~

. ~. ... _ _ . __ _ _ __ _ .. _. _ __ _ ~_ _ . _. _. _ _ .. _.. _ .. _ . . . . . _ _~,_, . , Dithering of the head 440 causes an amplitude modulation of the reproduced RF envelope. If the head 440 is located at the center of the track 412, only even harmonic components of the dither signal are produced by the action of the positionable element 430, because the average head position is at track center and the envelope variation caused by dithering appears as a symmetrical function. The amplitude of the RF envelope reproduced from the tape 410 is maximum at track center. As the head 440 moves to either side of track center, the amplitude of the reproduced RF
envelope decreases by the same amount. The fundamental of the dither signal is, thereby, balanced out and does not appear as RF envelope modulation. Therefore, dithering the head 440 laterally to the traclc 412 introduces amplitude deviations in the RF envelope only at twlce the dLtller Ere(luency, f~, On the other hand, if the head 440 is located slightly off the center of the track 412 to either side, the reproduced RF envelope amplitude variation will no longer be symmetrical because head 440 excursions to one side of the track 412 will produce a different RF envelope amplitude decrease then produced by an excursion towards the opposite side. Hence, a maximum-to minimum envelope amplitude variation occurs once for each cycle of the dlther signal, or at the dither frequency, fD, with the order of occurrence of the maximum and minimum points dependlng upon the side of track center to which the head 440 is offset. I'he i 76 mls/SS

$

fundamental of the dither frequency is no longer balanced out and the reproduced RF envelope variations will exhibit a fundamental component of the dither frequency, with the phase of the fundamental component for an offset to one side of the center of the track 412 180 out of phase with respect to that for an offset to the other side of track center, Detection of the order of occurrence of the maximum and minimum points, hence phase of the envelope amplitude variations, provides informat~on definitive of the direction 10 the head 440 i3 offset from the center of track 412, and detection of the envelope amplitude variation provides information definitive of the amount of offset, or a track error signal.
To obtain this head position information, the modulated RF envelope sLgnfll reproduced by the head 440 i9 coupled to detection circu:Ltry through a video reproduce preamplifier 2111 commonly found in video tape record and/or reproduce systems. To an extent, the tracking error signal which varies the amplitude of the reproduced RF envelope i9 exhibited as a double-sideband, suppressed carrier (DSB/SC) modulation of the detector fundamental frequency. Therefore, to recover the tracking error signal, the reproduced signal output by the preamplifier 2111 i8 coupled for processing by two arnplitude modulation detectors 2112 and 2113. The first detector 2112 i8 a simple amplitude modulation RF envelope detector, which is constructed to recover the dither signal fundamental and its sidebands. The output signal from mls/SS

~25~

envelope detector 2112 is merely a rectified version of the reproduced signal, contalning the fundamental and sideband components of the dither frequency, D. This output signal is applied to a 450 Hz AC coupled amplifier 2114 and then after passed through a 175 Hz high pass filter 2116, the bandwidthof which is sufficient to include the dither fundamental and its sidebands, and, thereby~ to pass the significant error signal - 77a -`:
mls/SS

spectrum. The purpose of the filter is to attenuate undesirable low frequency spurious signals ancl noise which may be present in the error signal spectrum. The output of the hiyh pass filter æ"~ is connected via terminal ~J8 of an electronically actuated switch ~ to the signal input of a second detector æJ/3, which is a synchronous amplitude modulation detector.
As will be described hereinbelow in greater de-tail, switch ~//7 serves to by-pass the filter ~i~ during start-up times to facilitate rapid synchronization of head tracking.

- 7~

~:5;~
Sync detec~or ~J3 is of conventional design oE the kind which operates on the principle of coherently detecting the amplitude and polarity of an unknown input signal with reference to the phase of a reference signal of the same frequency. Such detectors provide a rectified output having the amplitude of the unknown input signal and being positive when the two signals are in phase and negative when the two signals are 180 degrees out of phase. To ensure that the correct reference signal phase is applied to the sync detector ~ , a phase adjuster ~//9 is coupled between the output of the oscillator æ/~/ and the reference input ~ of the detector ~3. The phase ad~uster ~9 adjusts the reference dither frequency provided by osclllator,~/~/ to be at the proper 0 or laO with respect to the fundamental dither frequency component pre9ent in the input to the sync detector æ~3. Since the signal present at the input of sync detector ~/3 will have a component at the fundamental dither frequency, fD, whenever an error occurs in head track position, Syllc detector ~3 will provide at its output ~ , a track error signal representative of the head track position error. The amplitude of the error signal is proportional to the amount that the bias position of head ~ois displaced from track center. The polarity of the track error signal is indicative of the direction of head displacemen-t from track center.

-79~

t35 The output ~/~3 of the sync detector ~/3 is coupled to the input of a loop gain DC amplifier~ which introduces sorne gain in the servo circuit to provide a suitable signal level for driving the drive amplifier for the positionable element4~0. The output from the loop gain amplifier ~/æ~is fed to a low pass filter ~ which compensates the servo loop response for optimum loop stability. This low pass filter~ provides the dominant time constant of this loop of the servo circuit ~ro-This compensated track error signal corresponds to the low rate or DC error in the position of the head ~4 relative to the track ~. The low rate error signal is applied to the summing circuit ~o3 where it is summed with the dither frequency output from the oscillator ~~. The composite signal resulting therefrom is fed from the outputof the sul~ing circuit~3 to the drive amplifier ~0~
which applies the composite signal to the piezoelectric bender positionable element ~30 The low rate or DC component of the composite signal adjusts the bias position of the head ~ in accordance with the track error signal detected by the synchronous detector æ"~, thereby, laterally dis-placing the head ~oto maintain an optimum transducing position with respect to the track 4~.

~ ~0~

~ .

~s~

Since the recorded tracks are parallel to o~le another and adjacent tracks tend to produce similar track errors in a helical scan format, the track error signal can be considered during a short interval as being repetitive from track to track. ~he conten-t of the error signal includes a DC component plus components related to the rate of head rotation. The exact harmonic content will vary with changes in the instantaneous head position error. Improved circuitry to take advantage of the repetitive nature of the track error signal is shown in Figure ~, A band selective or comb filter~/ is placed in parallel with the loop gain amplifier ~/~and low pass eomposite filter ~/~ three stage form of comb fllte:r is employed in the embodiment herein described; whose f:irst stage ~/J~/~ is centered at 60 ilz (the fundamental of head rotation), whose second state ~ is centered at 120 Hz, and whose third stage ~/3/e is centered at 180 Hz. Each of the stages of the comb filter ~/ has a Q equal to 100.
The outputs of the two stages ~J~ and ~C centered at the second and third harmonie of the head rotation rate are coupled through switches to be described below for comparing in a summing circuit ~32. The output of the first comb Eilter stage ~3/a is directly coupled to the summing circuit ~3~ .
The combined outputs of the three stages of the comb filter ~/ are coupled to the input ~O~ of the summing circuit æ~

~, . __ . .. , .__ . . . __ . .. .... _. ... . _.__. . . _ ~522~

for combining with the low rate error signal and dither signal and subsequent application to the positionable element ~o. This provides an AC error signal component to the composite track error signal and has an effect of enhancing the signal-to~noise ratio of the servo circuit ~O by eliminating noise contributions from frequencies away from the error component. The comb filter ~ effectively provides an electrical inertia which resists any sudden changes in the error waveform once a proper error signal has been generated. Consequently, the servo circuit ~Ohas a response bandwidth capable of responding to errors up to, in this embodiment, the third harmonic head rotation rate with a relative bandwidth with respect to noise or other perturbations at frequencies away from the error components. Because of tile high rate of gain change with frequencies exhibited by the comb filter and the fact that the net phase shift passes through 0 at each pass band of a comb filter stage or tooth, the servo is capable of providing much more correction gain at multiple track scan rate frequencies when compared to a simple R-C open loop roll-off filter means. Therefore, the correction waveform of the composite track error signal which is applied to the positionable element ~3O more accurately represents the original head position error.

~V' .

~;~5;~ 5 'i'he commonly employed process of frequellcy modu-lating a carrier with a video signal for recording gives rise to spurious amplitude modulated components in the envelopes of the reproduce signal output by the preamplifier ~ . These spurious envelope modulations are in addition to those arising out of the dithering of the positionable element ~3O. The spurious components primarily result from the non-uniform frequency response in the record/reproduce system. Such spurious components may have a significant effect on the envelope produced in the reproduced signal.
False track error indications could result.
To avoid such false track error indications, the input of the envelope detector ~ is coupled to the video reproduce system at a circuit point ~/~o between the input lS of the straight line equalizer ~/~/ and the output of a flat equalizer ~/~3 which receives the output of an RF auto-matic gain control circuit æ/~commonly found in video record/reproduce systems for color television signals.
This arrangement is shown in Fig.~. The straight line equalizer ~/ usually is of the kind described in U.S.
Pat. No. 3,340,767. The flat equalizeræ~43 is preferably in the form of a filter whose frequency response complements the response of the sys-tem up to the input of the equalizer ~43 so as to compensate for undesired amplitude variations in the RF signal due to the non-uniform frequency response of that part of the system ~hich precedes the equalizer ~4. The automatic gain control circuit maintains the average level of the RF signal at a predetermined level so as to maintain the loop gain o~ the system of a desired level.
In single head helical scan tape recorders of the kind described hereinabove, the head ~ois actually

-8~ ~

off -the tape during an interval between the end of the scan of one track and the beginning of a scan of another track.
The absence of a reproduced signal at this time would appear as a false high rate track error signal. To obviate the apparent false error thus generated, the AC
coupled amplifier ~J~ has an electronic switch ~J~ in parallel with its gain controlling resistor ~ which is closed to cause the AC amplifier to have zero gain during the dropout interval. The electronic switch is responsive to a dropout signal commonly provided by the control signal processing system of helical scan recorders of the type described herein. In addition, the second and third harmonically related teeth of the comb filter ~/~/ are disconnected from the summing circuit ~ by the opening of the electronic switches ~/~3 and 7~S~ in response to a start signal initiated by the operator. In this manner an apparent false track error signal is prevented from affecting the operation of the servo circuit ~during start-up times and dropout intervals.

The circuitry of FIG. ~2 is a bloc~ diagram of merely one arrangement of components that may be used in I accordance with the present invention. The electrical ! schematic diagram of specific circuitry used to construct the embodiment of FIG.2~ is shown in FIG.~7. Reference numbers have been added to FIG.~ relating to specific circuitry to the block diagram of FIG.~. In addition to the features of the present invention discussed with refer-ence to FIGS.~ the servo drive ~5 also includes provisions for enhancing the operations during start-up time. In this regard, the operator initiates the generation of an enable command which is coupled to the electronic switches ~8~ and æ/~ The switch ~/8oopens in response to the enable command to free the DC amplifier ~for normal operation. The lS s~itch is normally closed wllell the servo circuit ~Sois in a standl~y condi~ion to keep the output provided by the DC amplifier ~ at zero DC, thereby, maintaining the DC
amplifier in a condition for immediate operation. The switch ~r couples the dither frequency signal to the summing circuit ~3 for application to the positionable element ~~
After a suitable delay to permit all servo conditions to be established, a delay command, timed to the enable command, is coupled to allow switch2117 to remove the shorted path .

between t-he AC coupled ampliEier ~ and sync detector æ~3 and connect the high pass filter ~ to the input of the sync detector ~/3, This delay command is also coupled to an electronic switch ~/~ to return the amplitude of -the dither frequency signal to its normal level after having been increased to two times the normal level during the interval between the enable command and delay command.
An electronic switch ~rin the path between line ~/~7 and summing circuit ~o3 also is opened by the delay command to return the amplitude of the high rate error component to its normal level after the start-up interval. The increased amplitude signals facilitate rapid synchroni-zation of the heads to the proper track position.

-8~ -, . . . _ Th~ circuit components used in constructing the specific circuitry embodiment of Fig. 27 are identified as follows:
MC1330P manufactured by Motorola 4136 manufactured by Raytheon 4066 manufactured by RCA
The automatic scan tracking system o~ this invention is particularly suited for use with the inventions subject of the above-identified applications. With respect to the special motion effects system previously described such system is coupled to receive the low rate track error component from servo circuit 450 at terminal 2171. The special motion effects invention returns a positioning command to terminal 2170 coupled to the summing circuit 2103 and thereby is added ko the drive signal provided to the piezoelectric bendiny positionable elemenk 430.

MLS/lcm ~S2~2~,S

The deflectable element will now be described in greater detail. Referring to the drawings, and particularly FIG. 28, a scanning drum 520 of a helical videotape recorder is shown and has a rotatable portion which carries a reproducing or "read'l head which contacts and scans successive tracks on a magnetic videotape.
The scanning drum 520 has a pair of drum portions 522 and 524 around which a videotape 526 is wrapped. The tape 526 is mls/SS

caused to move by tape transport means (llOt shown) in the di-rection of the arrows ~ and wraps around the drum portions 522 and524 in a helical path. The tapeS26 is kept in tight contact and alignment with the drums by guide rollers528 and~30 and by 5 tension exerted on the tape by the tape transport.
In a helical videotape recorder the lnformation tracks run diagonally with respect to the lengthwise dimension of the tape, and a portion of one such track~32 whose size is exaggerated for clarity is shown in FIG.,~8. In order to sense the information recorded on track~32 a read transducing head53~1 is mounted on drum portion~22 which rotates in the direction of the arrow B.
The movement of the tape~26 and the rotation oE the transclucel-~34 causes transducer~34 to contact the tape along -the track~32 and to generate an electrical signal repre~senta-tive of the information lS previously recorded on the track. This electrical signal is fed to signal processing circuitry for processing in a manner well known in the art.
It is apparent that the extent to which the transducer ~3~ can faithfully reproduce the information originally recorded 20 on the track532 depends on the transducerS34 accurately following or tracking the track 532. Trackiny problems arise, for example, when videotapes or the tracks become distorted, as by temperature or humidity induced dimensional changes in the tape, or by faulty tensioning mechanisms in the tape transport, for e~ample.
Because of such trac]cing problems, it i5 desirable to sense the instantaneous position of transducer 534 with respect to track ~32. Apparatus for sensing the position of a read trans-ducer with respect to a track is disclosed and claimed in - ~q-the aforementioned llathaway application, Serial No. 274,280.
Briefly, when perfect tracklng between the read transducer and the track is not occurring, an electrical correction signal is applied to a deflec-table support arm such as a bimorph on which the read transducing head is mounted. The correction signal causes the support arm to deElect the transducer toward track center and ~hus reduces tracking errors.
Deflection of the read transducer is also desirable in helical videotape recorders such as previously described, wherein slow motion and other effects in a reproduced video scene are generated, the approximately half speed 910w motion effect, for example, being produced by reducing the tape transport speed to one-half its normal speed and by causing the read transducer to read each track twice. In order to read a track twice, the read transducer must be physically repositioned or reset to the beginning of the track which is to be repeated. This reset of the read transducer is accomplished in one embodiment of the recorder disclosed in the above noted application by applying an e]ectrical reset signal to the deflectable support arm upon which the read transducer is mounted and thereby deflecting the ~upport arm and the transducer 90 as to reset mls/SS

~5;2~

the transducer to the beginning of the desired track. The reset signal is in the form of an electrical impulse which may tend to cause the support arm to vibrate or oscillate, and such vibrations must be damped to assure correct alignment between the transducer and the tape.
Vibrations in the deflectable transducex support arm are also induced when the transducer makes and loses contact _ ql -"

~522~i with the tape. E'or example, in the scanning drum arrangement of FIG. 2~ read transducer534 experiences a dropQut because it loses contact with tape526 in the gap between guide rollers528 andS30 during each rotation of the drum520. Contact between the transducer534 and the tapeS26 is re-established as transducer 534 passes rollerS28 as it rotates in the direction of arrow B.
The vibrations set up in a deflectable transducer support arm are, of course, undesirable since they can produce a loss of tracking. This loss of tracking due to vibrations can be minimized or eliminated by sensing the vibrations in the deflectable support arm and applying a damping signal to the support arm to counteract the vibrations.
Thus, in helical videotape recorders :in which it is desirable to include a deElectabl~ support arm Eor reducincJ
tracking errors, it is also desirable to include means for damp-ing electrically and mechanically induced vibrations in the deflectable support arm. Preferably, damping the vibrations can be done electronically, in which case some means for sensing the amplitude of the vibrations and for generating an electrical - ' signal indicative therebf, is required.
A deflectable read transducer assembly which includes means for sensing vibrations induced therein is shown in FIGo and is indicated generally by reference numeralS36.
At one end of assembly~36 is the read transducer534 itself. Its output is coupled via wires~38 to a pair of trans-ducer output terminals540 from which the transducer output is fed via lines82 to a conventional video processing circl~it584 A support arm, indicated generally atS~2, for holding and deflecting transducer53~ is a piezoelectric bimorph which _ 9;2,-deflects or bends when a deflection potential is applied to it. The bimorph is formed from a number of lay~rs bonded together to act as a piezoelectric motor ~43 and includes a top piezo-ceramic element or layer~44 and a bottom piezo-ceramic element or layer546. The various layers of transducer assembly ~36 are shown more clearly in FIG. ~,q~. Piezo-ceramic elements544 and~46 are both bonded to a common, electrically conductive substrate ~48. Substrate ~48 limits the movement of the bimorph to a bending motion in response to an applied 10 electrical potential.
In order to impress an electrical potential to piezo~ceramic elements 544 andS46, conductive layers~50 ancl552 cover the outer surfaces of elements 544 and546. Terminals 554 and556 (FIG.~q) are electrically connected to layers~50 and~52, 15 respectively, for receiving an electrical deflection potential.
Substrate j48 also has an input terminal~58 to serve as electrical common for the appliecl deflection potential. The electrical potential for deflecting support arm~42 is applied across piezo-ceramic element544 between terminalsS54 and558 and across piezo-20 ceramic element~46 between terminals556 and558.
In order to force support arm~42 to deflect at its free end560 where transducer 534 is mounted, arm~42 is canti-levered between insulating spacers 564 which may be held in place by a bolt (not shown) passing through hole566.
In operation, appropriate deflection potentials are applied across piezo-ceramic elemen-ts~4'1 and546 via input ~ q3~

terminals554,556 and~58. Support arm542 then bends at its free end~60 and deflects transducer~34 in a clirection and to an ex-tent which is depelldent on the magnitude and polarity of the potentials applied to terminals~54,~56 andS58.
In some applications, a piezoe]ectric motor need include only one piezo-ceramic element bonded to a substrate.
For e~ample, a single piezo-ceramic elenlent could have a top surface covered by a conductive layer and a bottom surface bonded to a conductive substrate which forces the element to 1~ bend when an electric potential is applied b~tweell the substra~e and conductive layer. ~lowever, where lar~ amoullts of de-flection are re~3uired, such as in videotar)e tratlsclllcers~ a motor element cornpriSinCJ two plezo-(e3-lmic e]ement!3544 and~46, as shown in ~;IG..~ is preEerable.
In addition to having a piezoelectric motor~43 for deflectiny transducer~34, the assembly~36 also includes a deflectlon or vibration sensor in the form of a piezoelectric generator568. The generator~68 includes, in the illustrated embodiment, an edge portion~70 of the piezo-ceramic element~44 whose bottom surface is bonded to substrate548 as previously described. It should be appreciate(3, however, the generator~68 could be ~ormed by a portion located in the center of the element 544. The generator has a separate conductive layer572 overlying the element portions5/0. The conduct:ive layerS72 is isol~ted from conductive layer~50 by a dielectric gap~7~ to electrically isolate the output of generator568 from potential applied to the conductive layer~50.
The ~eneratol-568 is cantilevered a-t576 and has an ~,~i . , 9~,_ ~5~

opposi.te, free deflectable end578. Thus, whenever vibrations or de.flections occur in the motorS43 due to electrica]. or mechanical impulses, a corresponding deflecti.on or vibration of the free end578 of generator element~6~ occurs and produces, 5 between the common substrate~4B and the conductive layer572, an electrical signal indicative of the installtaneous degree of deflection of the motor543 and of the transducerS34.
In the description of tlle piezoelectric motor and generator above, generator568 was said to include a piezo-10 ceramic element port:~.onS70 o the element~4~ anc3 th~: motor~l3 lncludes the bulk o~ -the piezo-c~ramic eleme~llt5~ s shown in FI(.S. 29 an(l ~qa~ piezo-ceralllic ~lem~nt l~or~:i.oll57CI i s ~re~el--ably part oE the unitary pie~.o-ceramic l~yer or e~me~ 54~.
;: However, it is not necessary that thè po.rtlon ~70 be part o:~
~ 15 a larger unitary piece. For example, gap574 could be extended :~ downwardly to cu-t -through layer 544 and form a separate element 570. It has been found, however, that evell witll large amplitude deflection signals applied to the elements~94 and5~6, these de~lection si~nals are not substantia l~ycoupled to yenerator 20 s6a when the element portion~70 is.part of the larger unitary element 54~ lowever, cutting the element down to the ground plane results in an i.ncr~ased isolati~n o-E the motor-to-cJener~tor and increases the element'.s tolerance to surace cc~ntamination.
Any vibration sensor which develops an electrical 25 output indicative of vibrations in arm542 should be responsive to vibrations over a frequency range exten(linc~ from approxi-mately 10 llertz up to at least 400 llertz, at which the illustra-ted bimorph support arm has a reson~llt frequenc~.

;
~95-~ ~ 2~ ~

The generator 568 of Figure 29, by extending lengthwise along the support arm 542, does e~hibit a good frequency response over the range desired. This response appears much better, particularly at low frequencies, than the frequency response of a generator which may extend transverse to the lengthwise dimension of the support arm 542.
The preferred dimensions ;for support arm 542 include a length L extending from free end 560 to the cantilevered point 576 of approximately 0.9 inch and a width W of approximately 0.5 inch. Each of the layers 544, 546 and 548 are preferably approximately 0.006 inch thlck while conductive layers 550, 552, and 572 have thickness in the range of a few microns. The width of the conductive layer 572, as measured between the gap 574 and the nearest edge oE
the support arm 536, is preferably about 50 mils. The substrate 548 is preferably mflde of brass and the conductive layers 550, 552 and 572 are nickel depositions. The piezo-ceramic layers 544 and 546 are bonded to substrate 548 by an epoxy adhesive or the like.
2~ The read transducer assembly 536 may be closed in a housing (not shown) having top and bottom portions which hold assembly 536 between them. The entire housed assembly may be held together by a bolt passing through appropriate holes in a top portion of the housing, through hole 566 (FIG. 29), and through another hole in a bottom portion of the housing.
more detailed description of a housing whlch may be used for assembly 536 is given in the aforementioned Richard Allen ~athaway application, Serial No. 274,284.

mls/SS

~52~

The piezoelectric motor-generator combination des-cribed above is a low cost, reliable dev:ice capable of bein~
controllably deflected and for simultaneously generating an output signal representative of the controlled deflection or of vibration-induced deflection. It is particularly useful as part of a read transducer assembly for a videotape recorder and is illustrated schematically in connection with the video-tape recorder systems described below.
The piezoelectric motor-generator combination des~
cribed above which simul.taneously deflects a read transducer and senses vibrations therein is used in an electronic feedback control system for damping vibrations in a videotApe read trans-ducer.
There have been transducer damping sche~es.which have used so-called dead rubber pads to absorb vi~rations in a transducer but the pads also limit the effective deflection range of the transducer. If the pads are mounted on the read head adjacent the transducer in a rotatable scannlng drive, they are subjected to high G forces as the drum rotates. Under these conditions, it can be difficult to keep the pads properly situated on the dr-lm. An improved damping system in whlch thc above-described motor-generator combination can be used is shown schematically in FIG. 3~. ~efore describing the improved damping systcm, how~ver, a brief description of associated transducer circuitry will be given in order to clearly indicate how t~e damping system cooperates with the associa-ted circuitry.
Referring now to FIG. 3~a read transducer~3~ operates as described above to ~ense or read previously recorded informa-tion in videotape tracks. The transducc.~r534 is part of the

- 9 7 ~

read transducer assembly 536 such as that shown in FIGURE 2 q and has a deflectable support arm~42 for deflecting transducer ~34 in response to deflection signals to correct the alignment of transducer334 with a track or to reset transducer534 to 5 the beginning of a track, as in the slow motion mode of operation described above. The support arm~2 is cantilevered at point~76 and its opposite end portion which suppor-ts transducer534 is free to deflect.
The electrical signal output of transducerS34 appears

10 on conductor~82 which conducts this signal to conventional video processing circuitry5û4 for generating, for example, a composite television signal for RF transmission.
The OlltpUt ot~ transducer~3~ is also fed to a trans-ducer position control circuil:~û6. The Eunction of control 15 circuit~36 is described in the aforementioned co-pending ~'~Y~
,~ ~ V. S. Application by ~lathaway, Serial No.~668,~I-~, and is not a part of the present invention. Briefly, however, it describes a position control circuit~86 which generates a "dither" signal of fixed frequency for application to the 20 deElectable support arm~42 for deflecting or "dithering"

transducer534 back-and-forth across a track at a fixed rate~
Since dithering causes the transducer 534 to move trans-versely relative to the track, the signal output of transducer~34 wil] be ampli-tude modula-ted at the dither 25 frequency. The amplitude modulated signal envelope contains information concerning the alignment between trans-ducer534 and the track being read and is detected to produce a correction signal for moving the transclucer~3~1 toward the center of the track. This correction signal and the dither _ 9~ -~ o ~

signal appear on conductor 588 and are ultimately applied tothe deflectable support arm 542.
A transducer reset signal generator 590 develops an electrical signal for application to the deflectable support arm 542 for selectively resetting the transducer 534 to the beginning of a track when such i9 required. Circuitry for developing such reset signals has been previously described.
The reset signal from slgnal generator 590 and the dither correction signal from circuit 586 are both fed to a frequency compensator 592 which comprises an amplifier whose frequency response complements the undesired residual response variations of support arm 5~2 when electronic feedback control damping ls applied to it as shown schematically in FIG. 30. Frequency compensator 592 augments the action of the electronlc damping circuit in order to provlde the desired uniEorm Erequency resposlse Eor the overall system. The aren of augmentation is in the 300 to 400 ~Iz region where the electronic damping action does not completely remove the rise in frequency response of arm 542 at its Eirst order mechanical resonant frequency.
The frequency compensated deflection signals from compensator 592 are fed via conductor 594 to a summing amplifier 596 which sums the deflection signals with a transducer damping signal generated ,by the Eee~back loop described below. The output of the summing amplifier 596 i:
fed via conductor 598 to a drive amplifier 3100 which amplifies its input and applies it to deflectable support arm 542 for controllably deflecting transducer 534 to the center of the track and maintaining proper transducer to track alignment.
.~ _ 9 9 mls/SS ~-~

5;2~3t5 The various deflection signals which are applied to the support arm~42, particularly signals genera-ted by the reset generator~90, may set up unwanted vibrations in the arm 542. This is particularly true wher~ the arm~42 is a bimorph since bimorphs exhibit resonance characteristics which tend to drive the bimorph into da~ed oscillation.
To damp such oscillakions, a negative feedback loop is included in the system shown in FIG. 30for developing an electrical damping signal and for applying the damping signal to support arm~42 to dampen i-ts vibrations or oscillations.
The required damping signal is derived, in general, ~rom a signal generator which cJenerates a de1cction velocity signal represclltative of,the instantaneous deElection velocity o~ the read transducer53~. In the en~odiment illustrated in FIG. 3~ said sigllal gerlerator includes a sensor~102 integral to the support arrn542 for genera~ing a signal repr~sentative of the instantaneous dcflected position of the transducer~34 and a di~ferentiator3104 for converting the transducer position signal to a transducer velocity si.gnal. The sensor 3102 is preferahly a piezoelectric generator of th~ type shown in Figure 29which is integrally formed wi-th the bimorph support arm. "
The output of sensor3102 is fed to a hic3h input impedance amplifier310G which presents a very small load to the sensor3102. Since the sensor3102 is typically equivalent to a voltage source in series with a capacitance, any electrical load on sensor3102 rnust be small in order to effectively couple low frequency signal~s from the s~nsor3102.

_1~ 0 ~

~s~

The output of amplifier3106 is coupl.ed through a summer3108, whose other inpu~ wi].l be c1escriL)ed below, and to the differentiator~109 which differentiates the transducer position signal from the sensor~102 and converts it to a signal repres~ntative of instantaneous transducer velocity.
The differentiator3104 is illnstrated as having an amplitude versus frequerlcy characteristi.c similar to that of a high pass filter and thereEore introduces a phase lead to the signals .it passes. The significance of the phase shift experienced by a signal traversing the feedback loop is explained immediately below in order to bett:er appreeiate the .funet:ion o:~ t:he re1nr~ incl ul-ldescrll)ed c~ ?mt~nts o:~ the feedback loop.
secause the support arm542 is preferably a piezo-electric bimorph, it exhibits the well known first order resonanc and anti-resonance characteristi.cs of pi.ezoelectric crystals, as well as higher order resonance characteristics. FIG. 3/R~
illustrates tlle combined frequency response of a bimorph motor-generator comblnation of the type shown ln FIG. 2q. This response is generated ~y applyi.llg a varyiny frequency, constant ampli.tude sine wave to the piezoelectric motor and measuring the resultant output of the piezoelectric generator. The results of such a measurement are shown ln FIG. 3~ WlliCIl inclicates a resonance point near 400 llertz ancl an anti-resonallce point, which has been found to vary from aroulld 700 Hertz to abou-t 1000 llertz, dependin on the particular bimorpll beiny used. 'I'he maximum output o.f the motor-generator combination occurs at resonance and the minimum output oceurs at very low fre(luencic!s allc3 at anti-resonarlce.
Iliyh order resc~nance c~n.lr,lcterist;.cs are not sh(~wn in l;'It;. 3Ic~,.

_1~) / , ~2~

Since the output of the motor-generator combination is maximum at resonance, vibrations or oscillations will tend to occur at its resonant frequency whcen the bimorph is excited by an electrical or mechanical im~ulse. 'rhcrefore, to eliminate the possibility of such oscillations, thc ~cedback loop is tailored to eed back to the bimorph damping signals which are 180 degrees out of Ijhase with respect to the sicJnals which initially excited the bimorph into oscillation, thereby eounteracting the tendency of the bimorph to oscillate.
To insure tha-t the damping signals are of the correct phase, the phase response oE the bimolE~Il motor-genera-tor eombination must be taken into accourlt. ~s indieatecl in FIG.3l~
on the eurve labeled "bimorph", signa],s near resonanee (about 400 llertz) experience a phase shif-t oE about 90 degrees in passing through the motor-generator combination, and high frequency signals experience a phase shift of 180 degrees.
In order to ensure that signals near resonance experience a net phase shift of 180 degrees around -the fceclback loop, and since all slgnals i,n the loop will be pha.sc sllite(l L~0 (Icc]r?es by an invertlng feec-lback amp]ifier prior to being applied to support arm542, -the signals near resonance must be phase compensated by 90 degrees so that their net phase shift is zero at the input to the inverting feedback amplifier. This insures that the loop will not oscilla-tc at thc resonant frec~uency due to instability in the feedback system. Since signals having a frequcncy far from resonance have a very low amplitude, -the loop gain of -the feedback loop will always bc less than unity for them so that the phase shift which they experience wi],l not cause i,nstability in tlle loop.

-/o2 ~522;~

Returning to the feedback loop of FIG. 30,the transducer velocity signal. deve].oped ]~y differentiator3104 is fea to a low pass filter3].10 whose upper cutoff frequency is chosen to substantially attenuatc signals attributable to secon( order and higller order resonance characteri.stics of the bimorpll.
Such signals generally have a frequellcy of over 2000 Ilertz and are atten~ated at least 20 dccibels by the filter3110.
The filter3110 contributes some phase lag to signals which it passes in addition to the initial phase lag of 90 degrees due to the bimorph itself (as shown i.n FIG. 3Ib~.
To compensate for the~ total phasc l.ag experienced by sicJna.l.s ncar rcsonallce, a pllase leacllletwork3112 fo].lows iltcr3110 and slliCts tllc pll.lsc o~ s.lgnals .rccc.i.ve(:l ~rom tllc fi.l-ter3110 so that those signals having a frequency near resonance have net phase shift of zero degrees upon leaving the lead network3112. The curve labeled "with lead network"
of FIG.31b illustrates the effect of lead network3112. Tn : : practiGe, the differenti.ator3104 also aclds some phase lead and thereby assists -the lead network3112 in properly adjusting the phase of the signals near resonance.
The signals near resonance from lead network3112 have a phase oE zero degrees with respect to the signals initially e~citing the bimorph and are in condi-tion to be applied to a negative feedback amplifier31l.4 wllich inverts tlie signals received from the lead network3112. The output of negative feedback amplifier3114 is the damping signal which is combined in the summer596 with the tr~nsducer deflcction signals :Erom thc conductor~94, ampliflec1 by tllc drive ampliEier3100, alld applicd -to the b:i.morph support arm _/o3-~42 to damp vibrations tllerein. Llle Ecedback arnplifier3114 has a variable amount of negative feedback for adju~sting the gain of the feedback loop to accommodate differences among bimorphs.
The feedback loop illustrated in I;IG. 30also includes means for compensating for the different anti-resonance responses among bimorphs. ~ frequency response curve is shown by the solid line in FIG. 3lo~ and a dashed line indicates the variable nature of the anti-resonance characteristic among various bimorphs. For cxample a-t 700 llertz the frecluency response of one bimorpll may be considerably less than thclt of another bimor~)h as indicated by the difference ~et~c~n the solid line and the dashe~l line at tlle frequency oE 700 ller-tz. Referring to FIG.3~b the phase response of -tlle feedhack system with the lead network is such that signals near 700 I-lertz undergo a 180 degree phase snift. If sic3nals havin~ a 180 degree phase shift are applied to inverting feedback amplifier3114 they will ultimately be applied to a deflectable support arm542 in pllase with the original excitillg deflection si~nals and may lead to oscil]ations a-t that frequency if their amplitude is large enough at frequencies correspondin~ to positive feedback conditions for the feedback loop. Bimorphs havin~ a frequency response illus-trated by the solid curve of FIG.3l~
have a very small outpu-t at 700 l~er-tz so that the overall loop ~ain of tlle system for such signals wlll be low enough to avoid oscillations irrespective of their phase response. Ilowever ~imorphs exhibiting greater gain at 700 llertz as il]ustrat(d by thc clasi~ed linc may induce instability intO tl~e systcm if not otllcrwisc compellsated for. Thc feedbaclc systelll illustratcd in Pl~. 30conlæellsatcs _Ja~--~5~

for such differences between bimorphs by adding a por-tion of the e~citing deflection signals to the output of the sensing device~102 so tha-t signals normally experiencing a~l80 degree phase shift between their application to bimorph 542 and their output at sensor3102 will be effectively nulled.
Signals experiencing such a~l80 degree phase shiLt are shown by FIG. 31b to be in the vicinity of anti-resonance. Therefore, signals near anti-resonance can be effectively nulled by coupling across the transducer assembly~36 a portion of the signal normally fed thereto.
Referring to FIG. 30~a means ~or E~edirly throucJh a portion o~ the de~l~ction signal and combinincJ it wikh the position signal developed by the sensor~102 includes the potentiometer3116 and the summer3108.~ Deflection signals appearing at the output of the summer596 are fed to both the drive amplifier3100 and the potentiometer3116, whereupon a portion of the deflection signals are fed via conductor3118 to summer~108. Summer3108 also receives, from amplifier ~106, deflection position signals developed by sensor3102.
Deflection signals which undergo a 180 degree phase shift in passing through the input to support arm542 to the output of sensor~102 ~i.e. frequencies near an-ti-resonance) are nulled in summer~108 so that the loop is stabilized for frequencies near anti-resonance~ This oyeration cffect:ively creatcs an artificial null near 700 Elertz so that, regardless of the bimorph bcing used in transducer assembly~36, it will appear to have an effective null near 700 Hertz so that the loop gain for signals near 700 I-lertz will always be less than unity and the feedbac~ loop will be stabilized for signals at those 30 freqllencies.

~5~5 Circuitry for effec-ting the functions of the various blocks in FIG. 30is illustrated in FIG. 3~
Transducer deflection signals, including the dither signal and reset signals referred to above, are applied at terminal 3120 to fxequency compensator592 which includes a pair of eonventional amplifiers~l22 and3124. The frequency response of compensator592 is shaped conventionally by the RC couplin~
around amplifier3122 and between amplifiers~l22 and~l24 to have an overall amplification which decreases with frequency in the 300 to 400 H~ region in order to eompensate for the residual frequency-dependent variations in defleetion sensitivity of support arm~2 after electronic dampi.ncJ has been applied.
The output of amplifier~l~4 is fed via co~ductor594 to summing amplifier~96 which also receives, at its non-inverting input, an input rom the feedback control loop.
The output of summing amplifier~96 is applied to drive amplifier~100 via conductorS98.
The negative feedback loop begins at terminal3126 at which the output from sensor3102 appears. The signal from sensor~102 is applied to amplifier3106 which is a conventional, frequency compensa-ted, feedback amplifier3128. The output of ampliier3128 is fed to the inverting terminal of summing amplifier3108 which also receives, at the same input, a portion of the transducer deflection signals for creating the artifieal null at an-ti-resonanee as described above. Diodes 3131 protect amplifier3128 from damaging hi~h voltage transients due to accidental short~circuits between sensor3102 and the input to support arm ~2.
The output of summing amplifier3108 is then conducted to differentiator3104, comprising serially conneetecl capacitor 3129 and resistor3130. /~G~

The low pass filter3110 WhiCIl receives the output of differentiator3104 is an active elli.ptical filter comprised of amplifiers~132 and3134 and indicated generally at3136.
The lead network3112 receives the output of the filter3110 and comprises a capacitor3136 serially coupled to resis-tor3138. ~he output of the lead network3112 is applied to the inverting input of a conventional fecdback amplifier ~114 whose feedbaclc and therefore forward gain is varied by adjus-ting the varlable resistor~l40. The output of amplifier 3114 is coup.led to tlle non-invertillcJ input Oe sumllling ampliEier ~96 ancl tllell appliecl to the drive amE~liEier3.l.0() wllicll, .in turll, drives the def:l.ectable support arm~42 for clefle(;tinc3 the transducer~34 in the manner previously described.
The damping system described above provides improved damping for deflectable videotape transducers without restricting their dynamie range. The feedback eontrol loop, in eombina-tion with the motor-generator transducer assem~ly, provicles a r.el.iab:l.e and low cost vibration damE~er for vicleotape recorders ancl otller applicati.olls wllerc vibratlons in a defleetable bimorph transducer assemb.l.y require damplng.
From the foregoing it should be understood how~a videotape read transducer can be controllably deflected and damped to maintain alignment between itself and a tape track.
~n improved bimorph transducer system, including a method of applying deflection signal.s to a deflectable bimorph to achieve maximum de:Election sensitivity will now be described.
Such an improved system is use:Eul in the tape recorder apparatus already described and wil.l be illustrated in that environment.
!

It is understood, however, that the improved method of driving a d~flectable bimorph disclosed below is also useful in other applications where it is desirable to achieve a large amount of bimorph deflection.
A bimorph which is used for bi-directional deflection consists generally of two layers of piezo-ceramic material bonded to opposite sides of a conductive substrate. One end of the bimorph is cantilevered and the opposite end is left free to deflect in response to a voltage applied to the bimorph.
The direction in which a bimorph deflects depends on the polarity of the voltage applied to it and the poling direction of the pair of piezo-ceramic elements. The poling direction of a piezo-ceramic element is established by being lS initially subjected to a unidirectional electric field which polarizes the element according to the direction of the field.
The polarized piezo-ceramic element is then said to have a "poling direction" and thereafter exhibits unic~ue mechanical properties wllen subiected -to subsequently applied voltages.
A known meLhod of causing a bimorph to deflect or bend is illustrated in FIG.33 wherein a bimorph3142 includes piezo-ceramic elements~144 and3146 bonded to opposite sides of conductive substrate3148. Bimorph3192 is cantilevered at 3150 while its opposite end3152 is free to deflect.
Piezo-ceramic elements3144 and3146 are each shown with an arrow to indicate their respective poling directions.
~hen they are aliyned as shown in FIG.33 with their arrows pointing in the same direction, they are referred to herein as having a commoll polinc3 direction.

/~~

r~

The polin~ directions shown are obtained by applying a voltage across a piezo-ceramic element such that the more positive potential is at the tail of the arrow and the more negative potential is at the head of the arrow.
For example, in FIG.~3~ bimorph3142 is shown being deflected upwardly by a voltage source~154 connected between elements 3144,3146 and substrate3148. The polarity of source3154 is such that it is applying a voltage to element3144 in the same directlon as its original polarizing voltage, whereas source3154 is applying a voltage to element3146 of a polarity opposed to i.ts original polarizing voltac~e. When the polarity of ~ de~lectiorl voltagc ~pplied to a pi~%o-ce~amic ~lement is identical to the polarity of that element's original polar~
; izing voltage, the applied deflection~voltage is refe,rred to herein as being applied in the poling direction. Thus, source3154 is applied to element3144 in its poling direction and is applied to element~l46 in a polarity opposed to its poling direction.
When pairs of piezo-ceramic elements are aligned and cantilevered as indicated in FIG. 33, th~ bimorph will bend in the direction of the element which is being driven in its poling direction. Thus, bimorph3142 bends upwardly toward element3144 when driven by source3154 with the indicated polarity. When no voltage is applied to the bimorph, there is no deflection. When a source~156 is con-; nected between substrate314g and elements3144 ~nd~146 as shown in FIG. 33, elemcnt~l46 is driven in its poliny direction and bimorph3142 deflects downwardly as indicated.

- /q For some applications, the method of driving a bimorpll illustrated i.n FIG. 339 wherein a deflection voltage is applied in the poling direction of one piezo-ceramic element and opposite to the poling direction of a second piezo-ceramic element is satisfactory. Ilowever, where a large amount of deflcction is rcquired, large dcflection vol.tagcs are also required. It has been found that applying large vol-tayes in a dircction opposed to the poling direction of a piezo-ceramic element tends to depolarize that elenlent ancl reduce ;its abi.lity to ~end ox deElect.
A mcthod o.~ driving a bimorpl~ witll large amplltude deflection voltages without depolarizing e:itller piezo-ceramic element is illustratcd in FlG. 3~ In thc imL)roved method, a : bimorph3158 has a pair of clectrically poled piezo-ceramic j 1 elemcnts~l60 and3162 which are also aligned in a common poling direction and bonded to a common substrate3164 between them.
lle bimorph3158 is can-tilevered at one end3166 and is free to deflect at opposed end~l68. In -this irnproved method of deflecting a bimorph, de:Election voltages are applied to the piezo-ceramic elements SUC]l that the polarity of the applied ~ voltage is ~lways in the poling direction of the element to :~ whicll it i.s applied so that a large degree of deflection of ; the bimorph can bc effecteci without depolarizing elther of the piezo-ceramic elements.
~s shown in FI~. 3Y, when bimorph3158 is to be deflectcd upwardly, a voltage source3170 is connected between the piezo-ceramic element3160 and the substrate3164 such that the polarity of t]lc applied vol.tage is in the poling direction of elelnent31~0. No opposcd polarity voltagc is ~pL>licc~ to /D
i ~5~5 the element3162 since most of the bendinc3 of a bimorph is effected by the element which is driven in its poling direction.
When the bimorph~l58 is to be deflected downwardly, S a voltage source3172 is connected between the element3162 and the substrate~l64 such that the polarity of the applied voltage is in the poling direction of the element3162. No opposed polarity voltage is applied to the element3160.
When bimorph3158 is to remain undeflected, sources 3170 and~l72 of equal magnitud~s are applied be~ween the el~ments3160 and~162 and the substr~te~16~l so that both piezo-ceramic elements~l60 and3162 are driven in their poling directions. The net result of driving both elements equally is that no deflection takes place.
Although the sources3170 and~l72 are depicted as being constant amplitude voltage sources, they need not be.
If the bimorph3158 is to be deflected upwardly and downwardly with variable amounts of de~lectlon, sources3170 and3172 could be made variable to accomplisll such nlovelllent. ~owever, the polarity of the voltages applied to elemen-ts3160 and3162 shouId always be in the poling direction of the elern~nt to which the voltage is applied.
A method of varying the magnitude and frequency of the deflection of bimorph3158 is illustrated schematically in PIG. 3~. As shown therein, a DC voltage from a source3174 is appli~d to the element3160 in its poling direction. The element3162 receives a l)C voltage from source3176 which is in its poling direction. ~referabl~r, sources317~ and3176 gcnerate I I I

~2~

positive and negative DC voltages respectively, of maynitudes equal to 1/2 Vmax, wllcre VmaX is the peak to peak amplitude of -the largest deflection signal which will be applied to the elements~l60 ancl3162. ~lenlell~s31fi() and~l62 arc th~ls oppositely "biased" to 1/2 VmaX and, in the absence of any other deflection voltages, no deflection of bimorph3158 will occur.
For effecting alternatin~ deflec-tion of bimorph 3158, an ~C deflection source3178 is coupled between elements 3160,3162 and substrate~l64 through a pair of amplifiers3180 and~l82 and l)C sources~l74 and3176. ~rhe peak-to-peak magnitude of thc AC cleflect:ion signal appl.i.cd in pllase to e1.elllents3160 and ~162 may now be as largc as V wi~hout evcr applying to e~ithe.r element a nct volta(Je wllich :is opposecl to .i.ts poling direction.
When tlle deflection signal from the source3178 varies generally sinusoidalIy, the net voltage which appears across element3160 is indlcated in FIG . 356. With the elements 3160 and3162 oppositely biased at 1/2 VmaX and the superimposecl AC deflecti.on signal applied in phase -to the elements, the nct voltage cross each of thc? elements3160 and 3162 always has a polarity which is in -the poling direction of elements. l'lle curves labeled "deflec-tion" in FIG. ~5~
indicate that bimorph3158 de~lects in accordançe with tlle two times the instantaneous amplitude of the ~C deflection voltage provided by source3l78.
When the net voltage on element3160 becomes more (or less) positive about 1/2 Vmax, the net amplitude of the voltage on element3162 becomes less (or more) negative correspondingly.
Ilowever, because of the hias provided by source3176, the net 3n voltage on the elelllent3162 will al~ays be in its poling direction as long as the magnitude of the AC cleflection voltage does not exceed Vn)ax The system shown in FIG.35~ for driving the bimorph3158 is completely DC coupled so that bimorph3158 can be driven at very low frequencies by the source3178.
In applications where low frequency bimorph deflection is not required, a system such as that shown in FIG.~6 may be used. Irl the system of FIG.36, only one amplifier3184 is needed for amplifying the AC deflection voltage from source3186. The amplified deflecti~n voltage is applied to elements3160 and~l62 via coupling capacitors~l86 and3188, respectively. Separate DC bias voltage sources3190 and3192, each having an ampli-tude of 1/2 Vmax, bias the elements3160 and3]62 so that the net voltage on either element will be in its poling dir~ction.
~eferring again to FIG. ~a~ the DC source3174 and amplifier3180 are enclosed in a dashed triangle to indicate that, in practice, they may be embodied together in one composite amplifier which amplifies the deflection signal and also provides the proper bias. Similarly, sources3176 and3182 may also be combined in a single composite amplifier.
An example of a pair of composite amplifiers ~or driving a bimorph is shown in FIG. 3~. The bimorph which is being driven in FIG.~ is part of a read transducer assembly3194 for use with the videotape apparatus shown in FIG. 33-Transducer assembly3194 is shown schematically and in simplified form in FIG. 3~ but is preferably similar to transducer assembly~36 shown in FIG. 2q, (The piezo-ceramic generator~68 is not shown as part of transducer assembly 3194 only in order to simplify the drawing.) ~5~

The transduccr assembly3194 has a top pie~o-ceramic layer3196 and a '~ottom piezo-ceramic ]ayer3198 bonded to a common substrate3200 ~hich is ~rouode~. I)eflectio signals are applied to the -transducer assembly~l94 at uppcr and lower conductive layers3202 and~204. Pie~o-ceramic elements~l96 and3198 are poled in a common direction as indicated by the arrows.
~ read transducer3199 is mounted on assembly3194 and is to be deflected in accordance Witll the prineiples and apparatus hereinbefore descrlbed. 'l'he piezo-ceramic layer3196 is driven by composite amplifier320fi ancl pieio-cercllllie layer 31~8 is ~Irivcll t~y tlle COIIIpO.Si~C! amL)IiFier3208. 'I`hc? anlpllfi.ers 3206 and3208 recc:ive low level ~(1 dcf;lectiorl .si~na:ls at input terminal~210, ampliEy the cleflection siynals, and apply them superimposed on a DC bias volta~e, to conductive layers3202 and3204. Generally, amplifier3206 includes a first stage of amplification provided by differential transis-tor pair 3212 ancl3214 and a seconcl stagc oE amplif:icatioll providccl by differential transistor pair3216 and3218. The output of transistor3218 is takcn across constclllt cllrrellt source transistor3220. The amplified signal at the collector of transistor3218 is applied to the bases of emitter followers 3224 and3226 and throucJh cmitter resistors3228 and3230 to an output terminal3232. The siynal a-t terminal3232 is fed back to the base of transistor3214 via a feedback resistor3234 so that amplifier3206 operates as a conventional operational amplifier with negative feedbaek.

~ rhe DC bias appearing at output terminal~232 is typically ~100 volts and is determ.inecl by resistors~236, 3238, the feedback resistor3234 and the t200 volt power supply.
An ~C def].ection signal of 200 volts peak to peak can appear at the output terminal3232 without opposing ttle polarization polarity of piezo-cerami.c layer3196. The transistors3240 and 32~2 provide sllort circuit protection For emitter followers 3229 ancl3226, respectively, .in order to limit their output current in the event -that terminal3232 becolnes inaclvertently grounded. ~m~lifier3208 is similar to ampl.ifier3206 and provides an ampl.ified cleflec-tion sic]nal at its output terminal ~2~4 superimposed on a D~ bias o~ -1()0 volts. Amplifiers3206 and3208 can bc usecl togetller to plovicle tlle arnp:lifica~ion performed l~y drive amplif.Ler3100 in FI~. 3~, I5 Ttle composite amplifiers3206 and3208 provide large amplitude ~C deflec-tion signals superimposed on a DC
bias voltage for clriving the de:Electable bimorpll Wit]lOUt depolarizing it and thereby ensure that the driven bimorph does not l.ose its deflc~ction sensitlvi.ty. Ttlc~ transducer system shown in FIG. 3~r and the methods i.llalstratecl in l~l~;S.
35~ and3~ and described herein provicle improved performance for deflectable bimorphs.
From the foregoing, it should be appreciated that vari.ous improved bimorph devi.ces and me-thods have been described WlliCIl, wh:ile represcllting different inventions, have been disclosed together in the environment of an improved videotape read system. The bimorph motor-generator combination, for example, provides a compact, reliable device : ' ~5~ 5 for sensing the instantaneous deflected position of a deflectable piezo-ceramic support arm. The illustrated embodiment of this device shows it as part of an improved videotape read assembly for generating an output signal indicative of the deflected position of a read transducer.
This novel assembly overcomes problems associated with deflectable read assemblies which vibrate when they receive an eleetrical or mechanieal impulse by generating an output signal whieh ean be eonVerted to a damping signal for damping the transducer vibrations.
The darnpiny Oe tr~nsdueer vihrations is achi~ved by the described ~eedb~ck con~rol systelll WhiCIl CJ~nerates a siqrlal indicative of t~le velocity of a cleflected or vibrating trans-dUcer~converts the velocity signal to a damping signal, and applies the damping signal to the transdueer support arm to dampen vibrations therein. The improved bimorph motor-generator eombination is preferably used in this damping system to genera~e a signal indieative of installtaneous transdueer position, tlle transdueer veloeity signal being derived by differentiating the transclueer position signal.
Various means are included in the damping system for stabilizing the feedback control system at frequencies near the resonant and anti-resonant points of the bimorph-motor-generator. This feedbaek eontrol system, in eom~ina-tion ~ith the novel bimorph motor-generator transducer assembly, provides effeetive dampincJ of a defleetable videotape read transdueer withGut restricting the dynamic range of the transdueer. Moreover, this electronic damping system is not adversely affected by t}~e hic~h G accelerations normally encounte~
in vicleotap~ reacl sy.stenls.

~5;2~5 I~Do 2519 The damping signals and transducer deflection signals are preferably applied to the bimorph transducer support arm by -the method and appara-tus described herein which overcomes the depolarizing effects associated ~ith prior methods by ensuring that the applied deflection signals are always in the polin~ direction of the piezo-ceram.ic element to which they are applied. A composite ampli.fier embodying th.is improved metllod receives large amplitude transducer deflection signals and applies them to the bimorph so as to achieve large bidirectional bimorph deflection without depolarizing the bimorph, thereby maintaining high bimorph deflection sensitivity.
The above-described improvements have been combined in a new improved videotape read systom for use with video-tape recorders, and particularly for use with helical video-tape recorders~ However, the improvements may be used independently of one another and in applications other than videotape read systems. Moreover, many alternatives, modifications and variations in the specific embodimen-ts described herein will be apparent to those skilled in the art. ~ccordingly, the p.resent invention is intended to include all such alternatives, modifications and variations which fall within the spirit and scope of the invention as defined by the appended claims and equivalents thereof.

Various features of the invention are set forth in the following claims.

Claims (75)

1. Claim 1. A method for providing variable motion playback of previously recorded information on magnetic tape, said previous recording having been accomplished at a first tape transport speed, said method being adapted for use in a helical magnetic tape recording-playback apparatus of the type which has transducing means operably supported by rotation means for scanning a magnetic tape along a plur-ality of adjacent discrete tracks oriented at an acute angle relative to the lengthwise direction of the tape, the rotation means including elongated movable means carrying said trans-ducing means and effecting movement of said transducing means in opposite directions from a home position along a path generally transverse to the direction of said tracks and including means for transversely moving said transducing means relative to said home position to accurately follow the track during playback, comprising the steps of:
   maintaining the angular velocity of said rotation means generally constant;
   adjusting the transport speed of the tape traveling around said rotation means to a desired speed within the range between a forward direction upper limit and a reverse direction limit, said range including zero speed;
   monitoring the position of the transducing means relative to said home position near the completion of playback of one of said tracks; and controlling the position of the transducing means to begin playback of the next desired track, the next desired track being determined by the movement of the tape being trans-ported and the monitored position of said transducing means.
2. Claim 2. A method as defined in Claim 1 wherein said next track is the next adjacent later recorded track when the position of said transducing means is approximately at the home position at the completion of playback of a track and said tape is being transported in the forward direction.
3. Claim 3. A method as defined in Claim 1 wherein the next track is the same track that was played back, the position of the transducing means being transversely moved a distance approximately equal to the center-to-center spacing between adjacent tracks so that the transducing means is posi-tioned to begin playing the same track again, when the posi-tion of said transducing means is not at the home position at the completion of playback of the track when the tape is at zero speed or is being transported in the forward direction.
4. Claim 4. A method as defined in Claim 1 wherein said next track is the preceding-in-time adjacent track that was recorded before the track undergoing playback, the posi-tion of the transducing means being transversely moved a dis-tance approximately equal to two center-to-center spacings between adjacent tracks to position the transducing means to begin playing the next preceding-in-time adjacent track when the tape is being transported in the reverse direction at said first speed.
5. Claim 5. A method as defined in Claim 1 wherein said next desired track is the next nonadjacent track that was recorded later than the track undergoing playback and said tape is being transported in the forward direction at twice said first tape transport speed to produce faster than normal motion effects.
6. Claim 6. A method as defined in Claim 1 wherein said next desired track is the second nonadjacent track that was recorded later than the track undergoing playback and said tape is being transported in the forward direction at three times said first speed.
7. Claim 7. A method as defined in Claim 1 wherein said tape is being transported in the reverse direction at a speed less than said first speed and said next desired track is either the same track that is undergoing playback whereupon said transducing means is transversely moved a distance appro-ximately equal to the center-to-center spacing between adjacent tracks or said next desired track is the preceding-in-time adjacent track that was recorded before the track undergoing playback whereupon said transducing means is moved a distance approximately equal to two center-to-center spacings, the two center-to-center spacing distance being moved in the event said transducing head reaches a distance away from said home position that closely approaches said center-to-center spacing distance near the completion of playback of a track.
8. Claim 8. A method as defined in Claim 1 wherein said reverse direction speed limit is about one third the forward direction speed limit.
9. Claim 9. A method as defined in Claim 1 wherein said transducing means is movable through a transverse path having a length approximately equal to two center-to-center distances between adjacent tracks.
10. Claim 10. A method as defined in Claim 9 wherein said home position is generally midway between the outer extremes of said path.
11. Claim 11. A method as defined in Claim 9 wherein said forward upper speed limit is approximately three times said first speed.
    
    Claim 12. In a helical magnetic tape recording-playback apparatus of the type which has a transducing head operably supported by a rotatable drum for scanning a magnetic tape along a plurality of adjacent discrete parallel tracks oriented at an acute angle relative to the lengthwise direction of tape, the drum including an elongated movable means carrying said head and effecting movement of said head in opposite directions from a center position along a path generally trans-verse to the direction of said tracks, and including means for transversely moving said head relative to said center position to accurately follow the track during playback, a method of providing playback or previously recorded information on said tracks at various speeds and in opposite directions, said
12. Claim 12 continued previous recording having been accomplished at a first tape transport speed, comprising the steps of:
    maintaining the speed of the rotation of said drum substantially constant and at the rotational speed maintained during recording;
    adjusting the speed and direction of said tape being transported around said drum, said speed being within predeter-mined maximum limits;
    detecting the position of the head relative to its home portion near the completion of playback of a track; and, controlling the position of the head to begin play-back of the next desired track, said next desired track being determined by the detected position of the head near the com-pletion of the track undergoing playback and the direction of the tape being transported if it is being moved, the next desired track being the same track undergoing playback in the event the tape is stopped.
    
    Claim 13. In a helical magnetic tape recording-playback apparatus of the type which has a transducing head operably supported by a rotatable drum for scanning a magnetic tape along a plurality of adjacent discrete parallel tracks oriented at an acute angle relative to the lengthwise direction of tape, each of said tracks having a capacity of one field, the drum including an elongated movable means carrying said head and effecting movement of said head in opposite directions from a center position along a path generally transverse to the direction of said tracks, and including means for trans-versely moving said head relative to said center position to
13. Claim 13 continued accurately follow the track during playback, a method of performing skip field recording and playback, comprising the steps of:
    recording every nth field of information on said tape while transporting the tape around said rotatable drum at 1/n the normal tape transport speed, while disregarding the intermediate fields of information between every nth field;
    maintaining the speed of rotation of said drum substantially constant and substantially at the same rotational speed during playback and recording;
    transporting the tape around said rotation drum at substantially the recording transport speed to playback information from the tracks thereon;
    transversely moving said transducing head at the completion of playback of each track so as to playback each track n times, and to move the transducing head to the next track after repeating playback of each track n-1 times.
14. Claim 14. A method as defined in Claim 13 wherein alternate fields are recorded and the intermediate fields disregarded and each of said tracks is repeated once when n equals 2.
15. Claim 15. An information reproducing system comprising:
    transducing means for reproducing information recorded on a plurality of generally straight tracks located adjacent one another on a recording medium;
    means for mounting said transducing means so that said transducing means is capable of moving only along a path substantially transversely of the tracks, said mounting means being carried by a rotatable element that is rotated to provide substantially all of the relative movement between said transducing means and said medium to reproduce said information from said medium;
    means for selectively moving said mounting means so that said transducing means is moved along said path in either direction from a home position in response to a control signal being applied to said moving means, wherein the value of the applied control signal is indicative of the position of the transducing means relative to said home position; and means for producing said control signal and applying the same to said moving means, said signal producing means being operable to produce a control signal having a value to effect positioning of said transducing means to accurately follow a track during reproducing, said producing means detecting the value of the applied control signal at a predetermined time during the rotation of said rotatable element, said producing means producing a control signal for application to the moving means to selectively effect the positioning of said transducing means to begin following a track subsequently to be reproduced, the track subsequently to be reproduced being determined by the detected value of the applied control signal.
16. Claim 16. A system as defined in Claim 15 wherein said rotatable element comprises a rotatable cylindrical drum carrying said mounting means and said transducing means and said recording medium is magnetic tape, said tape being helically wrapped therearound.
17. Claim 17. A system as defined in Claim 16 wherein said desired track is the same track that was completed, in the event said mode is forward slow motion playback and the transducing means is not in its home position at the conclusion of playback of the prior track, said signal producing means producing signals adapted to transversely move said transducing means a distance approximately equal to one center-to-center spacing between adjacent tracks.
18. Claim 18. A system as defined in Claim 16 wherein said desired track is the same track and is repeated in said system for operating in a still frame mode wherein said medium is stopped, said signal producing means generating signals for application to said moving means to move said transducing means a distance approximately equal to one center-to-center distance between adjacent tracks.
19. Claim 19. A system as defined in Claim 16 wherein said desired track is a preceding-in-time adjacent track that was recorded before the track completing playback when said medium is being transported in reverse direction at substan-tially the transport speed of the medium during information recording, said signal producing means producing signals for application to said moving means to transversely move said transducing means a distance approximately equal to two center-to-center spacings between adjacent tracks.
20. Claim 20. A system as defined in Claim 16 wherein said signal producing means detects the position of said trans-ducing means near the completion of playback of a track and refrains from generating transverse movement producing signals when the position of said transducing means is approximately at said home position near the completion of said track play-back when said medium is being transported in the forward direction.
    
    Claim 21. In a helical recording and reproducing system in which an information signal is recorded on a plur-ality of discrete tracks located adjacent one another on a medium, each of said tracks being of sufficient length to contain a predetermined quantity of information:
    transducing means for reproducing said information signal in response to relative movement between said trans-ducing means and said medium in a direction along one of said tracks;
    means for mounting said transducing means for move-ment substantially transversely and the direction of said tracks, said means being movable by an amount and along a transverse path relative to a home position and determined by control signals being applied thereto;
    said control signals being effective to control the position of said transducing means during relative movement between said transducing means and said medium;
21. Claim 21 continued means for generating said control signals and apply-ing the same to said movable mounting means to cause said transducing means to follow said discrete tracks during re-producing thereof, the value of said control signals varying in proportion to the transducing means position relative to said home position, said control signal generating means monitoring the value of said control signals and being adapted to generate signals for moving or refraining from transversely moving said transducing means at the completion of reproducing of said track, so that said transducing means is positioned to begin reproducing the proper track determined by the mode of operation of said system and the speed and direction of movement of the medium.
22. Claim 22. A system as defined in Claim 21 wherein said predetermined quantity of information comprises the information content of one television field.
23. Claim 23. A system as defined in Claim 21 wherein said amount and direction of movement of said mounting means is proportional to the magnitude and sign of the voltage of said control signals.
24. Claim 24. A system as defined in Claim 21 wherein said mounting means comprises an elongated deflectable element supported at one end position and adapted to bend in one of two opposite directions upon application of voltage thereto, the amount of bending movement being proportional to the magnitude of the voltage applied, said transducing means being located on the nonsupported free end portion thereof.
25. Claim 25. A system as defined in Claim 24 wherein the sign of said voltage applied to said element determines the direction of bending movement from a home position.
26. Claim 26. A system as defined in Claim 21 wherein said mounting means comprises an elongated pivotable element that is electromechanically movable in either transverse direction upon selective application of positive or negative voltage.
27. Claim 27. A system as defined in Claim 21 wherein said transverse movement of said mounting means is gradual to have the transducing means follow the track during repro-ducing and is abrupt at the completion of reproducing of a track in the event a track other than the next successive adjacent track is to be reproduced.
28. Claim 28. A system as defined in Claim 27 wherein the range of maximum transverse movement is about two center-to-center distances between adjacent tracks.
29. Claim 29. A system as defined in Claim 21 wherein said transducing means at the completion of reproducing of one track is positioned for beginning reproducing of the next successive adjacent track in the absence of transverse move-ment of said transducing means, transverse movement appro-ximately equal to the center-to-center spacing between adjacent tracks of said transducing means in a first direction being effective to repeat the reproducing of the track having being immediately reproduced, an equal amount of movement in the opposite direction being effective to skip one track,
30. Claim 30. A system as defined in Claim 21 wherein the information signal represents television video signals or the like and said signal is reproduced whereby the inform-ation content appears to be slower than normal motion when the path of said transducing means is such that said tracks are repeated a number of times, the greater number of repetitions being proportional to the greater slowness of the motion, the medium speed being inversely proportional to the number of repetitions.
31. Claim 31. A system as defined in Claim 30 wherein said medium is magnetic tape.
32. Claim 32. A system as defined in Claim 23 wherein said control signal generating means comprises:
    means for integrating the voltage of an error correcting signal that is used to drive said mounting means to position said transducing means to keep the same on a track during play-back, the voltage being indicative of the position of said transducing means relative to its home position;
    first means for generating a positioning signal for driving said mounting means to produce a transverse movement approximately equal to the center-to-center spacing between adjacent tracks in response to receiving a trigger signal indicating playback of the track in nearing completion when said medium is moving in either direction;
    second means operably associated with said voltage integrating means for generating a signal for inhibiting said first means when said integrated voltage is below a first predetermined level.
33. Claim 33. A system as defined in Claim 32 wherein said first predetermined level is approximately zero,
34. Claim 34. A system as defined in Claim 33 wherein said control signal generating means further comprises:
    third means for generating a positioning signal for driving said mounting means to produce a predetermined transverse movement approximately equal to the center-to-center spacing between adjacent tracks in response to receiving said trigger signal; and, fourth means operably associated with said voltage integrating means for generating a signal for inhibiting said third means when said integrated voltage is above a second predetermined level.
35. Claim 35. A system as defined in Claim 34 wherein said second predetermined level is higher than said first predetermined level.
36. Claim 36. A system as defined in Claim 35 wherein said integrating means comprises a voltage integrator having an output voltage proportional to the position of said trans-ducing head relative to its home position.
37. Claim 37. A system as defined in Claim 36 wherein said first means is connected to the input of said integrator and said positioning signal comprises an opposite going short duration pulse for resetting the voltage level of said inte-grator.
38. Claim 38. A system as defined in Claim 36 wherein said second means is connected to the input of said integrator and said positioning signal comprises an opposite going short duration pulse for resetting the voltage level of said inte-grator.
39. Claim 39. A signal transduction apparatus in which there is relative motion between at least one transducer and a record medium for transferring signals with respect to a track as the transducer follows a corresponding path and in which each of the transducers is carried by movable means for effecting movement of each transducer in opposite directions from a home position along a path generally transverse to the direction of said relative motion, comprising:
    first means coupled to each movable means to effect transverse movement of the transducer in one of said transverse directions to follow a track for an interval during the transduction of signals by the transducer carried by said movable means;
    second means coupled to each movable means for effecting movement in the opposite transverse direction prior to a further interval during which said transducer carried by said movable means again transduces signals; and third means for detecting a signal indicative of the position of said transducer relative to said home position and for inhibiting said second means responsive to the detected signal reaching a predetermined value at a predetermined time during each interval.
40. Claim 40. A system for reproducing video information from a recording medium, the video information recorded on said recording medium along a plurality of generally straight tracks located adjacent one another on said recording medium while said recording medium is transported at a first velocity, comprising:
    transducing means for reproducing the video information, said transducing means being carried by a rotatable means that is rotated to provide substantially all of the relative movement between said transducing means and the recording medium to reproduce video information from said recording medium;
    means for mounting the transducing means relative to the rotatable means so that said transducing means is capable of moving relative to said rotatable means along a path substantially transverse of the tracks;
    means for selectively moving the mounting means so that said transducing means is moved along said path in either direction relative to a home position in response to a control signal being applied to said moving means; and means for generating said control signal and applying the same to the moving means, said control signal generating means being operable to generate a control signal having a value that varies in accordance with the difference between the recording medium transport velocity during reproducing a track and the recording medium transport velocity during the recording of said track to move said moving means to effect positioning of said transducing means to accurately follow said track during reproducing.
41. 41. Apparatus for reproducing a video signal recorded on a recording medium in successive parallel track sections which are skewed relative to a direction of movement of said medium, and apparatus comprising:
    signal transuducer means repeatedly scanning said recording medium in a direction generally along said track sections for reproducing the video signal from said successive track sections upon said movement of the latter;
    controllable support means movably supporting said signal transducer means and being responsive to variations in a tracking control signal for displacing said transducer means from a neutral position in first and second opposed directions respectively extending transversely with respect to the track sections, said support means having predetermined limits of its displacement of said transducer means in said first and second directions from said neutral position; and control signal generating means for providing said tracking control signal and being normally operative, upon mistracking of said transducer means relative to a track section, to vary said tracking control signal in the sense for causing said support means to displace said transducer means in a respective one of said directions for restoring correct tracking of said track section by said transducer means, said control signal generating means including means operative upon displacement of said transducer means to said limit thereof in one of said directions for varying said tracking control signal in the sense causing said support means to displace said transducer means in the other of said directions substantially to the respective limit thereof.
42. 42. In an information reproducing system:
    transducing means for reproducing information recorded on a plurality of generally straight tracks located adjacent one another on a recording medium;
    means for mounting said transducing means so that said transducing means is capable of moving only along a path substantially transversely of the tracks, said mounting means being carried by a rotatable element that is rotated to provide substantially all of the relative movement between said transducing means and said medium to reproduce information from said medium;
    
    means for selectively moving said mounting means so that said transducing means is moved along said path in either direction and in predetermined amounts from a neutral position in response to selective electrical signals being applied to said mounting means;
    means for producing said electric signals and applying the same to said moving means, said signal producing means being operable to produce signals for positioning said transducing means to accurately follow a subject track during playback and to begin playback of a desired track subsequently of the completion of playback of said subject track, said desired track being determined by the mode of operation of said system and the speed of transport of said recording medium.
43. 43. A system as defined in Claim 41, wherein said rotatable element comprises a rotatable cylindrical drum carrying said mounting means and said transducing means and said recording medium is magnetic tape, said tape being helically wrapped therearound.
44. 44. A system as defined in Claim 42, wherein said signal producing means detects the position of said transducing means near the completion of playback of a track and refrains from generating transverse movement producing signals when the position of said transducing means is approximately at said home position near the completion of said track playback when said medium is being transported in the forward direction.
45. 45. In a helical recording and reproducing system in which an information signal is recorded on a plurality of discrete tracks located adjacent one another on a medium, each of said tracks being of sufficient length to contain a predetermined quantity of information:
    transducing means for reproducing said information signal in response to relative movement between said transducing means and said medium in a direction along one of said tracks;
    
    means for mounting said transducing means for movement substantially transversely to the direction of said tracks, said means being movable by an amount and along a transverse path relative to a neutral position and determined by control signals being applied thereto;
    said control means being effective to control the position of said transducing means during relative movement between said transducing means and said medium;
    means for generating said control signals and applying the same to said movable mounting means to cause said transducing means to follow said discrete tracks during reproducing thereof, the value of said control signals is varied in proportion to the shift between the movement of said medium and the rotary phase of said transducing means, which shift corresponds to said transducing means position relative to said home position, said control signal generating means monitoring the value of said control signals and being adapted to generate signals for moving or refraining from transversely moving said transducing means at the completion of reproducing of said track, so that said transducing means is positioned to begin reproducing the proper track determined by the mode of operation of said system and the speed and direction of movement of the medium.
46. 46. A system as defined in Claim 45, wherein said predetermined quantity of information comprises the information content of one television field.
47. 47. A system as defined in Claim 45, wherein said amount and direction of movement of said mounting means is proportional to the magnitude and sign of the voltage of said control signals.
48. 48. A system as defined in Claim 45, wherein said mounting means comprises an elongated deflectable element supported at one end position and adapted to bend in one of two opposite directions from application of voltage thereto, the amount of bending movement being proportional to the magnitude of the voltage applied, said transducing means being located on the nonsupported free end portion thereof.
49. 49. A system as defined in Claim 45, wherein said transducing means at the completion of reproducing of one track is positioned for beginning reproducing of the next successive adjacent track in the absence of transverse movement of said transducing means, transverse movement approximately equal to the center-to-center spacing between adjacent tracks of said transducing means in a first direction being effective to repeat the reproducing of the track having been immediately reproduced, an equal amount of movement in the opposite direction being effective to skip one track.
50. 50. Apparatus for reproducing video signals recorded in successive parallel tracks on a moving recording medium, said tracks being skewed relative to the direction of movement of said medium, said apparatus comprising:
    signal transducer means repeatedly scanning said recording medium in a direction generally along said tracks for reproducing the video signals from successive tracks on the recording medium upon said movement of the latter;
    controllable support means movably supporting said signal transducer means and being responsive to values of a tracking control signal above and below a predetermined level to displace said transducer means from a neutral position in first and second opposed directions respectively extending transversely with respect to the tracks for maintaining substantial alignment between the transducer means and the successive tracks; and control signal generating means including means for providing first and second position indicating signals which respectively indicate the position of said recording medium in said direction of movement and the position of said transducer means in said direction of scanning, and means responsive to the relative timing of said first and second position indicating signals to provide said tracking control signal at said predetermined level when said relative timing corresponds to alignment of said transducer means with a track and to provide said values of the tracking control signal selectively above and below said predetermined level in response to said relative timing corresponding to displacement of said transducer means to one side and the other, respectively, of a track.
51. 51. The apparatus according to Claim 50, wherein said means for providing the first position indicating signals includes a position sensor reproducing a position control signal recorded on said medium and by which the position of said medium in said direction of movement is detected; said means for providing a second position indicating signal includes a pulse generator generating a pulse signal in response to the scanning position of said transducer means; and said means responsive to the relative timing of the position indicating signals includes a phase comparator for phase-comparing the outputs from said position sensor and said pulse generator, the output of said comparator being connected to control said support means to move the transducer means in a direction substantially perpendicular to said tracks, each of said tracks having an integral multiple of a television field recorded thereon, whereby when said transducer means is displaced in said transverse direction from a field in one of said tracks to another track, it is displaced to a corresponding location on another field.
52. 52. The apparatus according to Claim 51, wherein said support means supplied or given predetermined limits of its displacement of said transducer means in said first and second directions from said neutral position, and said means responsive to the relative timing of said first and second position indicating signals is operative, upon said relative timing corresponding to the limit of the displacement in one of said directions, to provide said tracking control signal at a value corresponding to displacement of said transducer means substantially to said limit thereof in the other of said directions.
53. 53. Apparatus for reproducing a video signal recorded in successive parallel track sections on a moving recording medium, said track sections being skewed relative to the direction of movement of said medium, said apparatus comprising:
    signal transducer means repeatedly scanning said recording medium in a direction generally along said track sections for reproducing the video signal from said successive track sections on the recording medium upon said movement of the latter;
    
    controllable support means movably supporting said signal transducer means and being responsive to values of a tracking control signal above and below a predetermined level to displace said transducer means from a neutral position in first and second opposed directions respectively extending transversely with respect to the track sections for maintaining substantial alignment between the transducer means and the successive track sections; and control signal generating means including means for providing first and second position indicating signals which respectively indicate the position of said recording medium in said direction of movement and the position of said transducer means in said direction of scanning, and means responsive to the relative timing of said first and second position indicating signals to provide said tracking control signal at said predetermined level when said relative timing corresponds to alignment of said transducer means with a track section and to provide said values of the tracking control signal increasingly above and then below said predetermined level in response to changes in said relative timing corresponding to increasing deviation of said transducer means from a track section.
54. 54. The apparatus according to Claim 53, wherein said signal transducer means is a magnetic head with an air gap, and said support means flexes in response to said tracking control signals to move said head in a direction along the length of said gap and substantially perpendicularly with respect to the longitudinal direction of said parallel track sections.
55. 55. The apparatus according to Claim 54, wherein said support means for supporting said magnetic head comprises piezoceramic material.
56. 56. The apparatus according to Claim 55, wherein said piezoceramic material is a bi-morph leaf assembly which moves said magnetic head in either direction along the gap length from a predetermined recording position.
57. 57. The apparatus according to Claim 55, wherein said recording medium is a magnetic tape and said magnetic head is rotated to scan the said magnetic tape at a predetermined skew angle relative to the tape length and said track sections are at nearly the same skew angle.
58. 58. The apparatus according to Claim 57, wherein said means for providing the first position indicating signals includes:
    a position sensor reproducing a position control signal recorded on said magnetic tape and by which the longitudinal position of said tape is detected;
    said means for providing the second position indicating signals includes a pulse generator generating a pulse signal in response to the rotational position of said magnetic head; and said means responsive to the relative timing of the position indicating signals includes a phase comparator for phase-comparing the outputs from said position sensor and said pulse generator, the output of said comparator being connected to control said piezoceramic material to move the magnetic head in a direction substantially perpendicular to said tracks, each of said tracks having an integral multiple of a television field recorded thereon, whereby when said transducer means is displaced in the opposite transverse direction, it is displaced to a corresponding location on another field.
59. 59. Apparatus for reproducing video signals recorded on a magnetic tape in successive parallel tracks which are skewed relative to the longitudinal direction of transport of the tape, said apparatus comprising:
    rotary mounting means;
    signal transducer means rotatably movable with said rotary mounting means for reproducing video signals recorded in said tracks;
    
    controllable support means movably supporting said signal transducer means in respect to said rotary mounting means and being responsive to variations in a tricking control signal for displacing said transducer means in a direction substantially transverse to the direction along said tracks; and control signal generating means for providing said tracking control signal with stepwise level changes occurring periodically in synchronism with the rotational cycle of said rotary mounting means, with the amount of each of said level changes corresponding to mistracking of said transducer means relative to a predetermined one of said tracks.
60. 60. Apparatus for reproducing video signals recorded on a recording medium in successive parallel tracks which are skewed relative to a direction of movement of the medium, said apparatus comprising:
    siganl transducer means repeatedly scanning said recording medium in a path directed generally along said trucks for reproducing the video signals from the successive tracks upon said movement of the medium;
    controllable support means movably supporting said signal transducer means and being responsive to variations in a tracking control signal for displacing said transducer means in directions substantially transverse to the direction along said tracks; and control signal generating means for providing said tracking control signal and being normally operative, upon mis-tracking of said transducer means relative to one of said tracks, to vary said tracking control signal in the sense for causing said support means to retore said transducer means substantially to correct tracking of said one track, said control signal generating means including means operative, upon said mis-tracking of said transducer means relative to said one track exceeding a predetermined amount, to vary said tracking control signal in the sense for causing said transducer means to effect correct tracking of another of said tracks which is relatively adjacent to said path of scanning.
61. 61. Apparatus for reproducing video signals recorded on a recording medium in successive parallel tracks which are skewed relative to a direction of movement of the medium, said apparatus comprising:
    
    (Claim 61 cont'd....) signal transducer means repeatedly scanning said recording medium in a path directed generally along said tracks for reproducing the video signals recorded therein;
    controllable support means movably supporting said signal transducer means and being responsive to variations in a tracking control signal for displacing said transducer means in directions substantially transverse to the direction along said tracks; and control signal generating means for providing said tracking control signal including means for detecting a voltage which is proportional to the tracking error of said transducer means relative to one of said tracks at the commencement of the scanning of said one track by said transducer means, and means for determining the value of said tracking control signal, at least at the commencement of the scanning of said one track, in dependence on said detected voltage.
62. Claim 62. Apparatus for transferring information sig-nals with respect to discrete tracks on and at an angle relative to the longitudinal direction of a tape while the tape is caused to be transported at a velocity different from a first velocity that produces a path of travel of at least one transducer that is at a predetermined angle relative to the longitudinal direc-tion of the tape, the transducer being carried by a rotatable means for scanning said transducer relative to the tape, and the transducer being mounted to the rotatable means by means for moving said transducer in a direction substantially trans-verse of the path of travel in response to applied control signals, comprising:
    means for detecting the velocity at which the tape is transported;
    means responsive to the detected velocity for generat-ing a first control signal and applying the same to said moving means, said first control signal varying in accordance with the difference between the detected velocity and the first velocity to cause said moving means to move the transducer in the trans-verse direction to follow a track during an interval of transfer of information signals with respect thereto; and means for generating a second control signal according to the difference between the detected velocity and the first velocity and applying the same to said moving means to cause the transducer to be positioned following said interval to begin following a track with respect to which information signals are to be transferred subsequent to said interval.
63. Claim 63. Apparatus for transferring information sig-nals with respect to discrete tracks on and at an angle relative to the longitudinal direction of a tape while the tape is caused to be transported at a velocity different from a first velocity that produces a path of travel of at least one transducer that is at a predetermined angle relative to the longitudinal direc-tion of the tape, the transducer being carried by a rotatable means for scanning said transducer relative to the tape, and the transducer being mounted to the rotatable means by means for moving said transducer in a direction substantially transverse of the path of travel in response to applied control signals, comprising:
    means for detecting the position of the transducer relative to the path of travel;
    means for generating a first control signal and apply-ing the same to said moving means, said first control signal varying in accordance with the difference between the velocity at which the tape is caused to be transported and the first velocity to cause said moving means to move the transducer in the transverse direction to follow a track during an interval of transfer of information signals with respect thereto; and means responsive to the detected position of the trans-ducer for generating a second control signal according to said detected position and applying the same to said moving means to cause the transducer to be positioned following said interval to begin following a track with respect to which information signals are to be transferred subsequent to said interval.
64. Claim 64 Apparatus as defined in Claim 63 further comprising:
    
    means for detecting the velocity at which the tape is transported; and wherein the means for generating a first control signal is responsive to the detected velocity to generate said first con-trol signal varying in accordance with the difference between the detected velocity and the first velocity.
65. Claim 65. Apparatus for transferring information signals with respect to discrete tracks on and at an angle relative to the longitudinal direction of a tape while the tape is caused to be transported at a velocity different from a first velocity that produces a path of travel of at least one transducing means that is at a predetermined angle relative to the longitudinal direction of the tape, comprising:
    at least one transducing means carried by a rotatable means so as to rotate said transducing means to scan said tape;
    means mounting said transducing means to said rotatable means for moving said transducing means substantially transverse of the direction of the path of travel in response to an applied control signal to enable said transducing means to follow tracks on the tape; and means for generating said control signal as a composite signal having first and second components and applying the same to said moving means, said first component being a ramp signal having a slope in accordance with the difference between the velocity at which the tape is caused to be transported and said first velocity to cause said moving means to move the transduc-ing means in the transverse direction to follow a track during an interval of transfer of information signals with respect to the tape, said second component varying subsequent to said interval according to the difference between the velocity at which the tape is caused to be transported and said first velocity to cause said moving means to position the transducing means to begin following a track with respect to which informa-tion signals are to be transferred subsequent to said interval, said first component having an amplitude that is different from the amplitude of the second component whereby said transducing means follows a track as the tape is transported at said velocity different from said first velocity.
66. Claim 66. Apparatus according to Claim 65 wherein the first component causes the moving means to move the transducing means in a first direction transverse to the path of travel of the transducing means, and the second component causes the moving means to move the transducing means in a second direction transverse to the path of travel of the transducing means opposite said first direction.
67. Claim 67. Apparatus according to Claim 65 wherein the second component is generated upon completion of each interval of transfer of information signals with respect to the tape.
68. Claim 68. Apparatus as in any one of Claims 62, 63 or 64 in which the first control signal causes the moving means to move the transducer in a first direction transverse to the path of travel of the transducer, and the second control signal causes the moving means to move the transducer selectively in a second direction transverse to the path of travel of the trans-ducer and opposite said first direction.
69. Claim 69. Apparatus as in Claim 62 in which said first control signal is a ramp signal having a slope dependent upon the difference between the velocity at which the tape is caused to be transported and said first velocity.
70. Claim 70. Apparatus as in Claim 69 in which means are provided which is responsive to the trans-verse position of said transducer relative to the path of travel for generating an error signal indicative of a tracking position error of said transducer in following said path of travel; and said error signal being applied to the input of the ramp generator to thereby vary the slope of the ramp signal in accordance with the error signal.
71. Claim 71. Apparatus as in Claim 70 in which said second control signal generating means includes means for detecting the level of the ramp signal at a predeter-mined time during the rotation of the rotatable means, and means responsive to the level detecting means for generating the second control signal following said interval to move the transducer in the second direction when the detected level of the ramp signal corresponds to the transducer being at least to a predetermined position.
72. Claim 72. Apparatus as in Claim 69 in which said second control signal generating means includes means for detecting the level of the ramp signal at a predeter-mined time during the rotation of the rotatable means, and means responsive to the level detecting means for generating the second control signal following said interval to move the transducer in the second direction when the detected level of the ramp signal corresponds to the transducer being at least to a predetermined position.
73. Claim 73. Apparatus as in Claim 65 in which means are provided which is responsive to the trans-verse position of said transducing means relative to the path of travel for generating an error signal indicative of a track-ing position error of said transducing means in following said path of travel; and said control signal generating means includes a ramp generator for generating the first component, said error signal being applied to the input of the ramp generator to thereby vary the slope of the ramp signal in accordance with the error signal.
74. Claim 74. Apparatus as in Claim 65, 66 or 67 in which said second component is generated by means for detect-ing the level of the ramp signal at a predetermined time during the rotation of the rotatable means, and means responsive to the level detecting means for generating the second component subsequent to said interval to position the transducing means to begin following a track with respect to which information signals are to be transferred subsequent to said interval.
75. Claim 75. Apparatus as in Claim 73 in which said second component is generated by means for detecting the level of the ramp signal at a predetermined time during the rotation of the rotatable means, and means responsive to the level detecting means for generating the second component subsequent to said interval to position the transducing means to begin following a track with respect to which information signals are to be transferred subsequent to said interval.