US3787001A

US3787001A - Web roll cradle with positive drive

Info

Publication number: US3787001A
Application number: US00234494A
Authority: US
Inventors: N Henry
Original assignee: Woodman Co Inc
Current assignee: Kliklok LLC
Priority date: 1972-03-14
Filing date: 1972-03-14
Publication date: 1974-01-22
Anticipated expiration: 1991-01-22

Abstract

Apparatus and method of cyclic or intermittent feeding and unwinding of sheet material includes a pneumatic motor that drives the rotary web roll support and a brake that serves to stall out the motor when the predetermined length of material has been unwound. Draw means is provided to draw the predetermined length of film in a manufacturing process, such as packaging, with a slack loop being formed between the draw means and the web roll. The pneumatic motor is preferably a cylinder and rack combination with a drive stroke producing a capability greater than said predetermined length with the brake stalling out the motor at the end of the stroke to assure proper feed during each cycle and to maintain the tension in the web at a minimum and substantially constant during the complete operation. The slack loop is formed by a dancer assembly with linkage means comprising a cam and leaf spring applying the brake in a progressive manner only during the final moments of unwinding of the material. The dancer assembly desirably has insufficient pulling or tensioning power to pull film from the web roll so that complete reliance for feeding is put on the positive drive. The drive means and the draw means are operated at mutually exclusive times and are coordinated by first and second valves that actuate the drive means as the draw means are withdrawn to complete the drawing step.

Description

[ WEB ROLL CRADLE WITH POSITIVE DRIVE [75] Inventor:

Nelson R. Henry, Decatur, Ga.

Assignee: The Woodman Company, Inc.,

Decatur, Ga.

Filed: Mar. 14, 1972 Appl. No.: 234,494

[52] US. Cl 242/75.43, 242/55, 242/66, 242/68.7, 242/156.2 Int. Cl B65h 17/08, B65h 75/02 Field of Search.242/75.43, 68.7, 65, 66, 67.3 R,

[5 6] References Cited UNITED STATES PATENTS 9/1968 Gamberini 242/75.44 12/1963 Roberts 242/75.43

2/1971 Henry 242/55 2/1949 l-laswell.... 242/75.43 X 11/1966 Merrill 242/75.43

Primary Examiner.lohn W. l-luckert Assistant Examiner-Edward J. McCarthy [57] ABSTRACT Apparatus and method of cyclic or intermittent feed- TO PKG. MACH.

CONTROL [451 Jan. 22, 1974 the motor at the end of the stroke to assure properfeed during each cycle and to maintain the tension in the web at a minimum and substantially constant during the complete operation. The slack loop is formed by a dancer assembly with linkage means comprising a cam and leaf spring applying the brake in a progressive manner only during the final moments of unwinding of the material. The dancer assembly desirably has insufficient pulling or tensioning power to pull film from the web roll so that complete reliance for feeding is put on the positive drive. The drive means and the draw means are operated at mutually exclusive times and are coordinated by first and second valves that actuate the drive means as the draw means are withdrawn to complete the drawing step.

22 Claims, 5 Drawing Figures PHOTO CELL ONE WAY CLUTCH 3 O 7 W 58 2e 27 7 O 9 i' ASHLM 1S BRAKE n H Dl'ZkWN emcee T RoLLER'sMoVE O 4O 30 .,'5 e9 m... 43 54 IQ 81 as 79 0 l I V 86 a W 3 1 7 1 7 l 92 r U CE I H. TO PKGMACH. s CONTROL CONTROL l 93 r r l FRO M PHOTO PATENTEDJANZZIBH 3,787. 001

SHEET 2 BF 2 The present invention relates to unwinding of sheet material, such as packaging film, and relates more particularly to a system for unwinding material by positive drive of the web roll and maintenance of a constant, minimum tension in the web.

BACKGROUND OF THE INVENTION In form and fill packaging, as in many other environments where a web of sheet material is handled, it is necessary to withdraw predetermined lengths of material from a web roll. The length of film drawn from the roll is then used for forming a package for a commodity, or for some similar operation. Itis necessary in such operations to maintain the lengths of sheet material or film of an exact dimension and to draw the film without unduly tensioning the sheet material. The first requirement of drawing exact lengths of material has been satisfactorily met for all grades, thicknesses and types of sheet material, such as by use of photoelectric control responsive to a preprinted mark on the film at each package length. This photocell control is integrated into the overall packaging machine control and exact lengths of material or packaging film may be drawn in a continuous fashion without difficulty.

However, with regard to the latter problem related to the actual feeding and unwinding of the sheet material, some difficulty today still exists. First, there are many types of film that are used in packaging machines so that in order for a machine to be versatile it must be capable of operating on different films that vary greatly in terms of resistance to unwinding, stretchability, fracturability and general strength. In the past, unwinding systems have almost exclusively relied upon the use of the tension in the web generated by the drawing means to pull the material from the roll which is supported on a rotary support means, either on an arbor or a web roll cradle. The rotary support means is braked at the end of the drawing stroke by means of a dancer arm that is responsive to the decrease in tension of the web in a slack loop. In other words, the sheet material is pulled from the web roll by an increase in tension in the web; this increase in tension decreasing the size of the slack loop by raising a dancer arm. The connected brake means is taken out of operative engagement with the rotary support means and the spring bias of the dancer arm increases the tension in the film to, in turn, start the web roll turning for unwinding. Upon completion of the feeding, the roll will continue to turn until the dancer arm once again applies the brakes by another decrease in tension; that is, an increase in the size of the slack loop. Such a prior art system that is successful with most kinds of packaging material are shown in my previous patents Henry et al, entitled Web Roll Cradle, issued Sept. 9, 1969, U.S. Pat. No. 3,465,979 and Henry, entitled Web Roll Cradle for Loosely Wound Material, issued Feb. 9, 1971, U.S. Pat. No. 3,561,692.

One particular type of packaging film that is becoming more and more popular in the form and till environment, is polyethylene film. This film is preferred in many packaging situations, such as for frozen foods and other commodities, such as nuts and candies, because of its softness and highly pliable nature. These qualities however, make it extremely difficult to use the tension in the film itself to pull the material from a web roll in a successful manner. The successive turns of the film on the web roll tend to stick to each other under certain ambient conditions, such as in a hot and humid environment, and the web is subject to stretching when placed under tension.

Furthermore, with all kinds of packaging film in roll form, there is the problem of inadvertently dropping and/or resting a roll on its side. This forms a deleterious flat spot on the periphery of the roll. If a cradle is used, the support rollers tend to stall due to wedge-like action when the spot engages either roller. Also, the adjacent turns of the web are pressed together at the spot and thus tend to stickmore than usual during unwinding. These conditions thus prevent efficient unwinding, either on a cradle or arbor, by the previous web pull or tensioning method. Finally, the size of the web roll previously has been limited since the considerable inertia that must be overcome to start an oversized roll is greater than can be supplied by pulling on the web without damage thereto.

OBJECTIVES OF THE INVENTION And, accordingly, it is the main object of the present invention to provide a universal feeding and unwinding system for sheet material from a web roll wherein positive drive is provided directly to the web roll and the tension in the web is maintained at a minimum and substantially constant.

It is still another object of the present invention to provide an unwinding system wherein a predetermined length of material may be fed from a web roll without reliance on the tension in the material for control.

It is still another object of the present invention to provide an unwinding method and apparatus in conjunction with a drawing of a predetermined length of material for packaging film that operates on the concept of providing overdriving capacity directly to the web roll and a brake system responsive to a slack loop that overrides or stalls out the drive after a predetermined length of material has been unwound.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT My present invention is preferably embodied in a web roll cradle wherein the roll support rollers are positively driven directly in response to a'function other than the tension in the web being drawn from the roll. By tieing the control of the positive drive on another function, such as the completion of the drawing stroke of the sealing jaws of a form and fill packaging machine, the web is not subject to deleterious stretching, fracturing or tearing that has been a problem in the past especially when certain packaging films are used. The system is highly versatile because of this feature, is smoother in operation and highly reliable. This system can be used not only for any type of packaging material, but also in virtually any application other than packaging machines where intermittent unwinding is a necessity.

The positive drive is preferably provided by a pneumatic cylinder having a drive rack connected to the piston and operating through a gear train and one-way clutch to drive the support rollers of the cradle. The actuation of the cylinder is controlled to feed a new length of film from the web roll by the packaging machine control including the photocell detector that interrupts the drawing of the film by the sealing jaws. In

this manner, the initiation of the drive cycle is independent of the tension, and yet is invariably in step with the needs of the machine. On each cycle of the machine, the pneumatic cylinder has sufficient capacity to unwind more than a single, predetermined length of material in order to assure that a shortage does not exist. The exact length of film is obtained in a novel manner by employing a dancer assembly control brake that serves to stall out or override the pneumatic motor when the proper length has been unwound. A slack loop formed between the web roll and the draw means controls the dancer with the maximum slack loop being provided at the start of the drawing step and the minimum slack loop being provided at the start of the driving step.

Further in accordance with the present invention, a linkage means in the form of a cam and leaf spring is provided between the dancer assembly and the brake in order to progressively apply the braking pressure in the last moments of each tin-winding step and to assure a rapid and positive stop without virtually any increase in tension in the web. Although a conventional arbor can be used in accordance with the broader aspects of the present invention, a roll cradle is preferred so that the drive stroke is the same regardless of the diameter of the web roll. The system automatically adapts to drawing different lengths of film over a limited range through the extra driving capacity since the brake means or disabling means would merely override the driving motor at an earlier or later point, as required.

Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein I have shown and described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by me of carrying out my invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modification in various obvious respects, all Without departing from the invention. Accordingiy, the drawings and description are to be regarded as illustrative in nature, and not as restrictrve.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a schematic view of the feeding and unwinding system of the present invention showing the web roll cradle in a standby position and the draw means ready to draw a new predetermined length of packaging film;

FIG. la is a schematic view of the feeding and unwinding system of HG. 1 showing the web roll cradle being driven after the completion of the drawing step;

FIG. 2 is a side view of the system of HG. i but showing the components in the sequence at the end of the cradle driving stroke and prior to the next cycle;

FIG. 3 is a rear view of the web roll cradle taken in the direction shown by the line 33 of FIG. 2; and

FIG. 4 is a perspective view, enlarged to show detail, of the brake shoe and the operating linkage means on the dancer arm assembly.

DETAlLED DESCRlPTlON OF THE PREFERRED EMBODIMENT schematic form and the salient features may be more fully described. The figure essentially shows the feeding system for the packaging film of a form, fill and packaging machine, which comprises generally a package forming device it) and a web roll cradle H with a web W being in readiness for unwinding and feeding from a web roll R. As mentioned above, it will be readily understood by those skilled in the art that the broadest as pects of the invention are concerned with the novel manner of handling the web W and unwinding the same in an intermittent fashion from the roll R and that therefore the concepts could be used in environments other than packaging where intermittent draw-out of film or other sheet material is necessary.

The packaging forming device it) may be of any conventional structure suitable to draw a predetermined length of material in an intermittent or cyclic fashion. In the embodiment shown, the predetermined length of film or web W to be drawn during each cycle is represented by the length of package P formed by successive heat seals transversely positioned across a tube T formed of the web W. These heat seals are formed by cooperating sealing jaws l5, 16 that are operated toward and away from the tube T by a pair of air cylinders l7, 18. The cylinders 17', T8 are carried on a reciprocating carriage 19 that is moved through any suitable power means, such as a crank 20 and arm 21 driven from the main drive of the packaging machine. Of course, if desired, the relative movement between the tube T and the carriage l9 alternatively may be obtained by reciprocating a component in engagement with the tube T while holding the carriage 19 in a fixed position, as is well known.

With reference to FIGS. l3, the main components of the web roll cradle 11 may be more fully understood. The web roll R is supported between a pair of

support rollers

25, 26 which are coupled for mutual rotation by a suitable chain and sprocket coupling 27. Positioned outboard of the chain sprocket on support shaft 28 of the rear roller 26 is a power gear 29 (see FIG. 3), which gear forms a part of a gear train also including a driving step-up gear 3@ mounted on a stub shaft 31 supported on the side frame F of the cradle i l. Formed as an integral part of the power gear 29 is a one-way clutch 33 that permits rotation of the driving gear in a direction to unwind the web W from the roll R but slips when the gear is driven in the reverse direction.

The step-up gear 30 is driven from a drive rack 40 that is urged into engagement with the smaller of the two gears by a guide roller 41, as shown in FIG. 2. The rack is attached to piston rod 42 of the pneumatic cylinder 43. Thus, as is apparent and as will be further explained, the actuation of the cylinder 43 operates to drive the web

roll support rollers

25, 26 in a forward direction to feed the web W with the one-way clutch 33 permitting the return stroke in readiness for the next feeding cycle.

The web W passes around suitable stationary guide rollers 50 where multiple slack loops 5, and S are formed in the web W by cooperating movable guide rollers 51 (see FIG. 2). The movable rollers 51 are mounted on a dancer arm assembly including spaced arms 52, 53 (see MG. 3), which are mounted on pivot cross bar 54 supported by the side frames F, F; at the rear of the cradle assembly 11.

The rear end of the

arms

52, 53 carry

cam rollers

55, 56 that serve as a part of an operating linkage means to brake shoes 57, 5% operating against circumferential friction surfaces 59, 6d at the ends of the rear roller 26. As best shown in FIG. 4, the brake shoe 58 is mounted on a shaft 65 extending outwardly from the side frame F, and includes a suitable frictional padding 66 that engages the brake surface till to bring about the braking effect. A leaf spring 67 is fixed to the back of the brake shoe 58 at the upper portion of a curved base 68. The spring 57 provides resiliency in the operation of the brake shoe 58 toward the braking surface bit since the operating cam roller 56 engages the shoe 58 only through the spring 67.

When the dancer arm assembly is in the raised position (see FIG. la), the brake shoe 58 is spaced from the cooperating surface 60 and thus there is no braking force applied to the support roller 26. However, when the dance arm assembly is in the lowered position of FIG. I (see also FIG. 2) the brake shoe 58 is applied with maximum force due to the camming action of the roller 56 against the spring 67. With the dancer arm assembly in its lowermost position, the leaf spring 67 is bent under maximum conditions and the inside face thereof has been brought into engagement with the curved surface 68 (see FIG. 2) to a point 69 (FIG. ll) below the initial or attachment point (FIG. 2). This means that the leverage against the brake shoe 57 is progressively increased and thus the braking force is progressively increased to a maximum during, and only during, the final moments of downward movement of the dancer arm assembly. This gives a positive braking action that assures positive stalling out of the motor or cylinder 33 with a desirably rapid and progressive but smooth deceleration motion. It will be understood that the operation of the brake shoe 57 at the far side of the cradle ll is identical and complementary to that just described.

The interconnected control between the package forming device It and the web roll cradle II forms an important aspect of the present invention and will now be discussed. The pneumatic cylinders 17, III that operate the sealing jaws I5, I6 are provided with pressurized fluid and exhausted through feed lines 74), 7i, re spectively. A first valve 72 distributes the pressurized air from a feed conduit 73 to the line 74 when the sealing jaws T5, In are to be moved toward the tube T that is being sealed to form the package P. Simultaneously, the first valve 72 exhausts through the line 71, the opposite side of the cylinders 17, I8 through the exhaust ports 74- or 75.

The pneumatic cylinder 43 is connected to a second control valve 76 (preferably, identical to the first valve 72) that is operative to feed and exhaust said cylinder 43 through the transfer lines 77, 78. In other words, in the position shown in FIG. ll, spool element 7? connects feed conduit 73a to the transfer line 77 to cause piston 80 of the cylinder 43 to be shifted to the right for the return stroke. At the same time, the spool element 79 exhausts the line 78 through exhaust port 81. When the spool 79 of the second valve 76 is in the opposite position, as shown in FIG. la, the piston 8t) is moved toward the fully extended position with the line 7% supplying the pressurized fluid and the line 77 exhausting the fluid from the soft side by releasing the same through exhaust port $2. The feed conduits 73a and 73 are provided with pressurized air from pressure source 85, and a separate air pressure regulator 86 is or may be provided along the conduit 73a in order to adjust the air pressure acting against the piston 80 to control force and speed of the driving of the

rollers

25, 26.

The valves 76 may include suitable electrical actuators, such as solenoids 9d, 91, and in accordance with this invention, the solenoids are controlled in synchronization by the central or master packaging machine control 92. Feeding information to this control is a conventional photocell @3 that is operative to sense control marks on the web W to designate the length of film to form the package F by opening of the sealing jaws 15, In at the proper instant. The signal from the photocell 93 is fed to the packaging machine control 92, and this signal in turn, operates solenoid 94) to open the sealing jaws I5, I16, as shown in FIG. 2, which is the end of the drawing stroke in the operation.

The cutting loose of the package P and the opening of the sealing jaws I5, 16 preferably occurs before bottom dead center of the crank Zll for built-in overtravel to assure full length drawing on each cycle (FIG. 2). Similarly, the start of drawing film of FIG. I may be below top dead center to permit stripping (settling) of product into the package P,'if desired.

OPERATION The basic overall operation of the above-described apparatus and the related method for unwinding the web roll R should now be evident to one skilled in the art, but it will be now reviewed to further bring out and emphasize the novel aspects of the invention. The carriage 119 of the device I0, which is in the preferred embodiment the package forming mechanism, is shown in FIG. l at the start of the drawing stroke where the sealing jaws I5, I6 have finally closed and have formed a transverse seal across the tube T. The crank 20 operating from the main drive of the machine on a definite recurring cycle, starts the downward motion of the carriage I9 to carry out this drawing step.

At this time, the rollers SI of the dancer arm assembly are in their lowermost position shown by the full lines of FIG. I with the brake shoe 58 (and the brake shoe 57) in the fully applied condition. The piston of the cylinder 43 has moved the rack 40 into the fully retracted position in standby for the forward drive of the rolls 25, 2b. In this position, the web W is tensioned; however, since a portion of the weight of the dancer arm assembly is supported by the camming engagement at the cam roller 56 (and roller 55), the tension is reduced even below the operating minimum so that the web is not deleteriously stretched or deformed even during shut-down periods that can be experienced with a machine between work shifts, for example.

As soon as the carriage I9 has moved a finite or predetermined distance downwardly from the position shown in FIG. I, the guide rollers fill are raised, as shown by the arrows in FIG. I. During this time, the brake is released so that the

rolls

25, 26 are ready to be freely driven; however, the cylinder 43 is still retained in the standby or retracted position.

As the guide rollers 51 are lifted from their lowermost position, the tension in the web is now determined solely by the weight of the dancer arm assembly pivoted about the pivot shaft 54. It is a desiratum of the invention that this operating tension be maintained at a minimum and not vary by a significant amount. This is accomplished by making the components of a light material and/or providing counterbalancing weight at the rear of the dancer arm assembly; the tension thus being only that necessary to promote a wrinkle-free and non-sag condition. Also, there is no spring urging the assembly to the lowermost position, as is common on prior art devices.

With the drawing step reachingconclusion, the sealing jaws l5, 16 approach their lowermost position and the photocell 93 senses the package length mark. At this moment, the sealing

jaws

15, 16 are withdrawn from their dotted line position to the full line position (FIG. la) to release the tube T and to cause the package P that has been previously cut to drop away in tinished form. The photocell 93 has caused this action through the master packaging machine control 92, the valve 72 and its actuator 90. Concurrently, because of the direct interconnection of the actuator 91 with the actuator 90, the spool element 79 of the valve 76 is switched to the position shown in FIG. 1a and the piston 80 thus begins the drive motion. This is continued until at the moment that the step of driving the roll R is finished, the dancer guide rollers 51 are at their lowermost position.

To further explain and to note the important braking operation, as the rack 40 continues to drive the

rollers

25, 26, the dancer guide rollers 51 continue their downward movement toward the dotted line position of FIG. la. Just before the rollers reach the rest position, the cam roller 56 is brought into engagement with the leaf spring 67 (see FIG. 4) and the application of brakin g force is begun. At this point, the rack 40 has almost, but not completely, reached the end of its stroke. The braking force is rapidly, but smoothly applied until the point of maximum leverage engagement 69 (FIG. 1) is obtained between the leaf spring 67 and the curved base 68. At this point, the

support rollers

25, 26 have been locked in position by the braking action and the pneumatic motor or cylinder 43 has had its piston 80 stalled out. The pressure provided through the regulator 86 is such that the compressible fluid on the right of the piston 80 is not sufficient to overdrive the application of the brake 58 (and the brake 57 on the other side). Accordingly the feed of the web W stops at just the desired point, or in other words, when the guide rollers 51 are in their dotted line position (FIG. la) at the lowermost point of travel.

When the carriage 19 has returned to its uppermost position by moving relative to the tube T (see FIG. 1), the master packaging machine control 92 through a suitable timing device, such as a cam, trips the

actuator solenoids

90, 91 to bring the sealing

jaws

15, 16 together for the start of the next drawing stroke, and concurrently, quick returns the piston 80 and the drive rack 40 to the standby position in readiness for the next cycle.

In summary, it can be seen that one. of the salient features of the intermittent unwind method and apparatus of the present invention is that the tension in the web is held at an operating minimum throughout the cycle. This is accomplished by initiating and performing the driving operation in response to an independent machine function, such as the completion of the drawing stroke, rather than in response to a design increase in the tension, and stalling out the driving motor or cylinder 43 of the web cradle 11 by a braking operation when the proper length has been unwound from the roll R. For simplicity of control, the actuating means for the sealing

jaws

15, 16 of the packaging device are directly interconnected with the actuating cylinder 43 of the roll cradle 11 causing the operations to be at mutually exclusive times; or in other words, each is operative during the rest period of the other. Exact feeding of the web W is performed with case since the drive rack 40 has a builtin overrun that allows for at least some stalling period by the brakes during each cycle.

In this disclosure, there is shown and described only the preferred embodiment of the invention, but, as aforementioned, it is to be understood that the invention is capable of use in various'other combinations and environment and is capable of changes or modifications within the scope of the inventive concept as expressed herein.

I claim:

1. Apparatus for cyclic or intermittent feeding and unwinding of sheet material from a web roll comprising rotary support means for said web roll, means to positively drive said support means to unwind a predetermined length of said material from said roll, means to intermittently draw said predetermined length of said material, slack take-up means for tensioning said material in a slack loop between said web roll and said draw means, control means for said drive means interconnected with said draw means to activate said drive means independently of the tension in said web, disabling means for said drive means responsive to said slack take-up means, whereby the tension in said web may be maintained at a minimum and substantially constant as determined by the action of said slack takeup means.

2. The apparatus of claim 1 wherein said drive means has sufficient capacity to unwind more than one predetermined length of material on each cycle, said disabling means being operative to limit the actual unwind of material to said predetermined length.

3. The apparatus of claim 2 wherein said drive means comprises a pneumatic motor, an air pressure source for supplying pressurized air to said motor, said control means comprises valve means for operating said motor, and said disabling means includes brake means associated with said rotary support means and responsive to said slack take-up means, said brake means being applied when the slack loop formed by the slack take-up means is at a maximum, said brake means providing sufficient force to stall out said pneumatic motor when said slack loop is at a maximum, said brake means being released for drive of said roll by said pneumatic motor when said slack loop is reduced from a maximum.

4. The apparatus of claim 3 wherein said pneumatic motor comprises an air cylinder to provide drive strokes, a drive rack mounted on the piston of said cylinder, transfer means connected between said rack and said support means, and one-way clutch means in said transfer means to allow free reverse motion of said rack to provide an additional drive stroke.

5. The apparatus of claim 1 wherein said drive means comprises a pneumatic motor, an air pressure source for operating said motor, air pressure regulating means for controlling the pressure of the air from said source to said motor, and said disabling means comprises brake means for said rotary support means having sufficient power to override said pneumatic motor.

6. The apparatus of claim 5 wherein is included linkage means operated by said slack take-up means, said linkage means serving to progressively apply said brakes to said support means, whereby the braking of said support means remains isolated from said web means to prevent an increase in tension in said web.

7. The apparatus of claim 6 wherein said slack takeup means includes a dancer arm and roller assembly, pivot means for mounting said dancer arm assembly, said linkage means including cam means mounted on the end of said arm, and said brake means comprises a brake shoe engaging said rotary support means and operated by said cam means] 8. The apparatus of claim 7 wherein said linkage means further includes a leaf spring mounted on said brake shoe on a curved surface to engage said cam means, the length of said spring progressively decreasing to increase the leverage of said cam means as the braking effect is increased.

9. The apparatus of claim 1 wherein said draw means comprises a pair of reciprocating jaws for toward and away movement with respect to said web, and carriage means for supporting said reciprocating jaws to move the jaws in the longitudinal direction of said web when said jaws are in the gripping position across said web.

10. The aparatus of claim 9 wherein air cylinder means is provided to operate said reciprocating jaws, valve means for operating said air cylinder means and said control means includes a first valve for supplying pressurized air to said air cylinder means and a second valve for supplying pressurized air to said pneumatic motor and means for operating said valves simultaneously so that said web roll is being driven only during the time when said gripping jaws are not drawing film, whereby the maintenance of constant tension in said web as determined bysaid slack take-up means is assured.

1 1. The apparatus of claim 1 wherein said slack takeup means includes a dancer roller extending transversely across said web within the slack loop, arm means mounting said roller at opposite ends to form a dancer assembly, pivot means for mounting said dancer assembly and wherein said disabling means comprises brake means for retarding and stopping the rotation of said rotary support means, said brake means being operative in response to the positioning of said dancer roller.

12. The combination of claim ll wherein said drive means comprises a pneumatic motor and said brake means is sufficient to stall said motor upon formation of a maximum slack loop by said slack take-up means.

13. The apparatus of claim ll wherein said rotary support means includes an arborless roll cradle having a pair of spaced support rollers with parallel and horizontally disposed axes, said rollers being spaced to allow said roll to rest between the same for unwinding, the surface of said support rollers moving a distance equal to said predetermined length during each cycle, and said drive means connected to said support rollers, whereby movement of said drive means during each cycle regardless of the diameter of said web-roll is the same.

14. The apparatus of claim 13 wherein said drive means comprises an air cylinder, rack means mounted on the piston of said cylinder, gear train means positioned between one of said support rollers and said rack to transfer the driving relationship and one-way clutch means in said drive train to allow a return stroke of said rack in readiness for the next cycle.

15. The apparatus of claim 1 wherein said control means being operative to allow driving of said support means by said drive means only during a period of inoperativeness of said draw means, whereby the web be tween said web roll and said draw means is moving in response to said drive means and said draw means in succession forming in turn maximum and minimum slack loops.

16. The method of cyclic or intermittent feeding and unwinding of sheet material from a web roll comprising the steps of intermittently drawing a predetermined length of sheet material of said web roll, intermittently directly driving said web roll to unwind a predetermined length of material substantially equal to that drawn and concurrently forming a slack loop between said web roll and said draw means varying from a minimum to a maximum slack loop, said direct driving step being initiated and performed substantially independently of the tension in said web, whereby the tension in said web remains at a minimum and substantially constant as determined by the formation of said slack loop.

17. The method of feeding and unwinding of claim 21 wherein the driving step is commenced concurrently with the completion of the drawing step.

18. The method of feeding and unwinding of claim 16 wherein said driving step lasts longer than necessary to produce the predetermined length of material and braking is applied with respect to said roll to override said driving to produce said predetermined length.

19. The method of feeding and unwinding of claim 16 wherein tension is placed on said web in said slack loop that is limited to a value insufficient to unwind said material by itself.

20. The method of claim 16 wherein is provided a progressive braking of said web roll only during the final moments of unwinding, whereby free rotation at other times allows minimum tension, and progressively reducing said tension further during braking to avoid stretching of said material during down time.

21. The method of cyclic or intermittent feeding and unwinding of sheet material from a web roll comprising the steps of intermittently drawing a predetermined length of sheet material of said web roll, intermittently driving said web roll to unwind a predetermined length of material substantially equal to that drawn and concurrently forming a slack loop between said web roll and said draw means varying from a minimum to a maximum slack loop, said driving step being initiated and performed substantially independently of the tension in said web, the drawing step and the driving step being at different times and the driving step being terminated prior to said drawing step, whereby the tension in said web remains at a minimum and substantially constant as determined by the formation of said slack loop.

22. The method of cyclic or intermittent feeding and unwinding of sheet material from a web roll comprising the steps of intermittently drawing a predetermined length of sheet material of said web roll, intermittently driving said web roll to unwind a predetermined length of material substantially equal to that drawn and concurrently forming a slack loop between said web roll and said draw means varying from a minimum to a maximum slack loop, said driving step being initiated and performed substantially independently of the tension in said web, said maximum slack loop being provided at the start of the drawing step and the minimum slack loop being provided at the start of said driving step, whereby the tension in said web remains at a minimum and sub-stantially constant as determined by the formation of said slack loop.

Claims

1. Apparatus for cyclic or intermittent feeding and unwinding of sheet material from a web roll comprising rotary support means for said web roll, means to positively drive said support means to unwind a predetermined length of said material from said roll, means to intermittently draw said predetermined length of said material, slack take-up means for tensioning said material in a slack loop between said web roll and said draw means, control means for said drive means interconnected with said draw means to activate said drive means independently of the tension in said web, disabling means for said drive means responsive to said slack take-up means, whereby the tension in said web may be maintained at a minimum and substantially constant as determined by the action of said slack take-up means.

7. The apparatus of claim 6 wherein said slack take-up means includes a dancer arm and roller assembly, pivot means for mounting said dancer arm assembly, said linkage means including cam means mounted on the end of said arm, and said brake means comprises a brake shoe engaging said rotary support means and operated by said cam means.

8. The apparatus of claim 7 wherein said linkage means further includes a leaf spring mounted on said brake shoe on a curved surface to engage said cam means, the length of said spring progressively decreasing to increase the leverage of said cam means as the braking effect is increased.

10. The aparatus of claim 9 wherein air cylinder means is provided to operate said reciprocating jaws, valve means for operating said air cylinder means and said control means includes a first valve for supplying pressurized air to said air cylinder means and a second valve for supplying pressurized air to said pneumatic motor and means for operating said valves simultaneously so that said web roll is being driven only during the time when said gripping jaws are not drawing film, whereby the maintenance of constant tension in said web as determined by said slack take-up means is assured.

11. The apparatus of claim 1 wherein said slack take-up means includes a dancer roller extending transversely across said web within the slack loop, arm means mounting said roller at opposite ends to form a dancer assembly, pivot means for mounting said dancer assembly and wherein said disabling means comprises brake means for retarding and stopping the rotation of said rotary support means, said brake means being operative in response to the positioning of said dancer roller.

12. The combination of claim 11 wherein said drive means comprises a pneumatic motor and said brake means is sufficient to stall said motor upon formation of a maximum slack loop by said slack take-up means.

13. The apparatus of claim 1 wherein said rotary support means includes an arborless roll cradle Having a pair of spaced support rollers with parallel and horizontally disposed axes, said rollers being spaced to allow said roll to rest between the same for unwinding, the surface of said support rollers moving a distance equal to said predetermined length during each cycle, and said drive means connected to said support rollers, whereby movement of said drive means during each cycle regardless of the diameter of said web roll is the same.

15. The apparatus of claim 1 wherein said control means being operative to allow driving of said support means by said drive means only during a period of inoperativeness of said draw means, whereby the web between said web roll and said draw means is moving in response to said drive means and said draw means in succession forming in turn maximum and minimum slack loops.