CA1089555A - Rotary cutter for successively cutting moving material to lengths - Google Patents

Abstract

ROTARY CUTTER FOR SUCCESSIVELY CUTTING
MOVING MATERIAL TO LENGTHS

Abstract of the Disclosure A system for controlling the speed of a DC motor so that the material fed to a rotary cutter is succes-sively cut to desired lengths. The speed of the rotary cutter driving DC motor is controlled in accordance with a rotary cutter speed control pattern which is deter-mined by the relation between the length of the rotary cutter circumference and the length to which the material is to be cut. This rotary cutter speed control pattern is provided in the form of speed command signals in accordance with a function output derived by setting the length of the rotary cutter circumference, the length to which the material is to be cut and the cutting distance during which the rotary cutter speed and the material travel speed synchronize with each other.
The system also accomplishes the necessary control for correcting any error caused between the speed control pattern and the actual rotary cutter speed as well as the required acceleration control of the motor in accord-ance with the speed control pattern.

Description

lV89555 Background of the Invention The present lnvention relates to rotary cutters for successively cutting a continuous moving material, such as, paper, sheeting or tube, and more particularly the invention relates to a system for controlling the speed of a rotary cutter driving DC motor in accordance with a rotary cutter speed control pattern which is dependent on the relation between the desired material-cutting length and the length of the rotary cutter circumference.
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The rotary cutters of the abo~e type now 1n use most widely are divided into those which are controlled mechanically and others which are controlled electronically.
In the case of the mechanically controlled rotary cutter, the rotary cutter i9 connected to the power source of a material feeding mechanism through a speed change gear and a crank chain 80 that the rotary cutter and the material feed mechanism are driven from the same po~er source. In other word~, a chsnge in the material-cut-ting length is effected by changing the change gear ratio.

Also during the periods of cutting operation, the cutter speed and the material travel speed must be made equal to each other, and consequently the material travel speed is made equal to the cutter speed by the ,.,,, ~ -- . . . , - ~ .

lO~ 5S

nonuniform motion of the crank chain.

A dlssdvantage of this type of mechanically con-trolled rotary cutter i8 that since the speed changing operation can be effected only gradually, when effecting a change in the material-cutting length, the materlal i~
lost during the time that the length i8 being chan~d, that during the period~ of acceleration and deceleration of the material travel speed, the material-cutting length i~ changed by the difference in mechanical de-flection between the feed mechanism and the rotary cutter, and that a cutting error i~ caused by the slip between the feed mechanism and the material.

On the other hand, while a large part of the deficiencies of the mechanical type have been overcome by the electronically controlled rotary cutter, the electronically controlled rotary cutter has the follow-ing disadvsntages.

The conventional electronically controlled rotary cutters are based on the method in which material travel detection pulses are subtractively applied to a register and also a number of pulses corresponding to the material-cutting length are also applied additively to the regi~ter each time the cutter moves past the cutting end point.
At the same time, a number of pulses corresponding to one rotation of the rotary cutter are subtractively applied to the register, and the content of the register is l(J~9S~5 converted into a DC ~oltage of the oppo~ite sign which in turn is applied in proportion to the material travel speed to the DC voltage constituting the forward runnlng speed command for the cutter. Consequently, only when the resulting 8um has the polarity which rotate~ the cutter in the ~orward direction, the sum is applied a~ a 8peed reference to a ~peed controller of the cutter driving DC motor.

With this method, slnce the pulses corresponding to the material-cutting length and thoQe corre~ponding to one rotation of the cutter are applied upon completion of cutting, excepting where the number of pulses corre~-ponding to one rotation of the cutter i8 cloBe to that corresponding to the materlal-cutting length, the rotary cutter is subjected, irrespective of the material travel speed, to rapid acceleration or deceleration which i9 dependent on the current limitation of the servomotor and con~equently the ma~imum torque is always exerted on the mechanical parts.

This tends to considerably deteriorate the dura-bility of the mechanical parts.

Also, since a large power i8 handled in the electronically controlled rotary cutter, the cutter is u~ually controlled by a DC motor and a thyristor Ward-Leonard control system~ However, it is the usual practice to increase the respon~e speed at the sacrifice ~ '. ~ ' ' ' .

of the loop gain due to the necessity to control the high speeds with the limited frequencies, and consequently the above mentioned control system i~ not able to provide the neces~ary operating speeds as well as the accelera-tion and deceleration ~peeds, thus making it impossible to compensate for the decrease in the gain by a dlgital circuit. This results in deteriorated accuracy of the ~ervomotor. On the other hand, since the content of the register i8 converted into a DC voltage of the opposite sign and combined with the material travel speed voltage 80 that the resultine sum i~ applied as an input to the rotary cutter driving servomotor only when its valus is of the polarity which rotates the cutter in the forward direction, if the sum iB within the range which does not cause the cutter to rotate in the forward direction, a zero input i~ applied as the servo input irrespective of the content of the register.

Thus, if 7 in these conditions, a zero point drift occur~ in the servomotor, despite the fact that the cutter must be at rest, the cutter i8 810wly rotated in one or the other direction.

In the case of long lengths, this has the effect of reducing the effective follow-up time and thereby deteriorating the accuracy.

Further with this system, taking one example where there i9 no need to take into consideration the 10~'3555 frictional torque of the rotary cutter and where the materia1-cutting length i~ greater than the ~ength of the cutter circumference, the DC voltage derived by converting the register content i~ 80 set that when the register content corresponds to the length of the cutter circumfere~ce, the DC voltage obtalned by converting it becomes equal to the maximum travel speed voltsge of the material which i~ permitted by the maximum acceleration/
deceleration of the rotary cutter.
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This mean3 that the feedback quantity of error cannot be set to obtain the optimum results, thue result-ing in deteriorated accuracy. With this ~ystem, the follow-up speed of the servomotor also decreases e~ponen-tially with decrease in the register content, n~mely, when the register content decrea~es to one half, the follow-up speed oi the servomotor also decreases to one half, ~nd the follow-up ~peed decrea~es to one fourth when the register content decreases to one fourth, and ~o on. Thus, as compared with the systems in which the ~ervomotor is cau~ed to follow up linearly until the error i8 decrea~ed sufficiently, far great follow-up time is requlred. ~ven if the follow-up is not sufficient, the error in the previous cutting i8 retained in the register 80 that the material can be cut to the desired length during the next cutting operation.
However, the rentention of such steady-state error tends to cause the error to be changed by a change in the speed as well as a change in the material-cutting length, thus causing the actual error.

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SUMMARY OF THE IN~ENTION
The deficiencies of the prior art are overcome by the present invention which provides a rotary cutter adapted for successively cutting a material to lengths in accordance with a rotary cutter rotational speed control pattern which is determined by the relation between a cutting length of the material and the circumferential length of the cutter, the combination comprising; coefficient generating means for com-puting an acceleration/deceleration coefficient indicative of variation of the rotational speed of the rotary cutter for every material travel speed detecting pulse in accordance with a preliminarily set material-cutting length, rotary cutter circumferential length and cutter cutting distance; function generating means for generating a rotary cutter speed control function in response to material travel speed dete~tion pulses which are counted up or counted down in accordance with the acceleration/deceleration coefficient computed by the coeffi-cient generating means and the rotary cutter rotational speed control pattern; speed computing means for multiplying together the speed control function generated by the function generator and a material travel speed obtained by converting the material travel speed detection pulses to obtain a product and then adding the material travel speed to the product to generate a rotary cutter operatins speed command signal; error computing means for adding the sum of the speed control func- .
tion generated by said function generator and the material travel speed detection pulse in response to the application of each material travel speed detection pulse to compute the amount of rotation of the cutter and for subtracting an actually detected amount of rotation of the cutter from the computed amount of cutter rotation to generate a cutter -follow-up error signal; acceleration computing means for jb/
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multiplying together the acceleration/deceleration coeffi-cient computed by the coefficient generating means and a square of the material travel speed to generate an acceler-ation signal to control the amount of current which gener-ates a DC motor driving torque necessary to accelerate or decelerate the cutter; and cutter speed controlling means including a speed amplifier and a current amplifier, the cutter speed controlling means being responsive to the operation speed command signal, the follow-up error signal and the acceleration signal for controlling a cutter driving DC motor, wherein the follow-up error signal is fed to the speed amplifier and the acceleration signal is fed to the current amplifier.
The above and other features and advantages of this invention will become apparent from the following des-cription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
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Fig. 1 is a graph showing the rotary cutter speed control pattern used with the invention when the material-cutting length is shorter than the length of the rotarycutter circumference.
Fig. 2 is a graph showing the rotary cutter speed control pattern used with the invention when the material-cutting length is longer than the length of the rotary cutter circumference.
Fig. 3 is a graph showing the rotary cutter speed control pattern used with the invention when the material-cutting length is longer than two times the length obtained jb/ - 8 -A
, i .

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by substracting the cutting distance of the cutter ~rom the length of the rotary cutter clrcumference.

Fig. 4 is a circuit block dlagrsm showing a pre-ferred embodiment of the in~ention.

Fig. 5 i9 a circuit block diagram showing the function generator u~ed in the embodiment of Fig. 4.

Fig. 6 is a circuit block diagram showing another form of the function generator used in the embodiment of ~ig. 4.

Fig. 7 i8 a circuit block diagram ~howing still another form of the function generator u~ed in embodiment of Fig. 4.

Detailed Description of the Preferred ~mbodiments The rotary cutter speed control patterns used with the invention can be represented by three differ- ;
ent types of speed control pattern in accordance with the relation between the cutting length Lo of a material and the circumferential length LR f one rotation of the rotary cutter edge as shown in Figs. 1 to 3.

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~ eferring to Flg. 1 in which the ordinate repre-sents the rotary cutter speed Y and thc abscissa repre-~ents the time t, there is illustrated the speed control pattern obtained when the material-cutting length Lo is shorter than the cutter circumferential length ~
or Lo ~LR with the material travel speed being at VO.
In other words, upon completion of each cutting, the rotary cutter must take up the length of the difference ~L between the circumferential length LR and the material-cutting length Lo~ and consequently the rotary cutter is accelerated to rotate faster up to a time tl at which it attains a speed alVO and then the cutter is decelerated up to a time t2 at which it attain~ the speed VO which is equal to the mateiral travel speed, thu~ completing the cutting operation at t time t~.

Fig. 2 shows the speed control pattern used when the material-cutting length Lo i~ greater than the circum-ferential Length ~, namely, when the material iB cut to longer lengths. In this case, the speed o~ the rotary cutter is decelerated by an amount corre~ponding toA L = LR ~ Lo to ~eed the material and then the cutter speed is returned to the material travel speed, thus initi-ating the cutting operation and completing it at the time t3-Fig. 3 shows the speed control pattern used incases where the material is cut to still longer lengtha Lo> 2 (LR - Ls), namely, the material-cutting length lO~S~S

~o i8 greater than two times the difference between the cutter circumferential length LR and the cutter cutting distance Ls. Here, the cutter cutting distance LS is defined as the distance travelled by the material during the time interval t2~ t~ during which the material travel ~peed is synchronized with the rotary cutter speed.
'l'hus, after the completion of each cutting, the cutter is decelerated 90 that it makes about a hal~ turn and comes to a stop at the time tl, and after the expiration of a predetermined time at rest the cutter is re~tarted 80 that it attains the material travel speed V0 at the time t2 thu~ initiating the next cutting operation.

Fig. 4 is a block diagram ehowing an embodiment of the invention. In the ~igure, numeral 1 designates a material to be cut to lengths, 2 a rotary cutter, 3 a rotary cutter driving DC motor, 4 a limit switch for detecting the completion of cutting operation of the rotary cutter 2, 5 a material travel pulse generator (PGl), 6 a pulse generator (PG2) for detecting the amount of rotation of the rotary cutter 2, 7 a tachometer generator (TG) for detecting the rotational speed of the rotary cutter 2.

In the computing unit for providing the ~peed patterns shown in Fig~. 1 to 3, numeral 8 designates an acceleration/ deceleration coefficient generating circuit, 14 a function generator, 15 a frequency-to voltage conver-ter, 16, 20 and 22 digital-to-analog converter~ (D/A), 1~''3~j~5 17, 23 and 24 multiplier~, 19 an error computing unit, 18 and 21 summing points. In a thyristor Ward-Leonard unit 25 for controlling the DC motor 3, numeral 26 desig-nates a speed controller, 27 a summing point, 28 a current controller, 29 a gate pha~e shifter, ~0 a thyris-tor.

The acceleration/deceleration coefficient generat-ing circuit 8 will now be described first.
The acceleration/deceleration coefficient generating cir-cuit 8 performs the necessary digital computation to proYide the desired acceleration/deceleration coefficient a3 .

The computational procedures for obtalning the acceleration/deceleration coefficient a3 will now be described. In the computational procedure~ described hereunder, the following symbols represent aq follows.
VO = material travel speed V = cutter rotational speed ~R = cutter circumferential length ~S = cutter cutting distance = distance travelled by material during period of corrective operation in which cutter i8 subjected to acceleration/deceleration cont-rol (correction travel distance) tl - time of turning point in speed patterns of Fig~. 1 to 3.
t2 = time at which cutter speed becomes equal to ~o~9s~s material travel speed t3 = time of one cutting cycle K = straight line slope of speed patt~rn al, a2 = constants a3 = acceleration/deceleration coef~iclent ~R = cutter rotational distance QO = material travel distance Referring to Fig. 1, a~suming that the cutter speed V attains the speed alVO during the period O~tl, the resulting straight line slope ~ iB given by K = alVO/t~
In this case, the cutter speed VO~ tl i~ given by VO tl Vo+ Kt = VO + (alvo/tl)t (2) On the other hand, the correction tra~el distance Lf is given by Lf = Vot2 = Vo 2tl, and sub~tituting this in the equation (2), we obtain VO ~ tl = VO + (2alvo2/Lf)t (3) A~suming here that al/Lf = a2, then we obtain VO~ t = VO + 2a2Vo2t (4) In the like manner, the cutter speed Vt ~ t during the time period tl~ t2 is given by Vtl~ t2 = VO + 2a2VO tl - 2a2Vo2(t - tl) (53 Also, the cutter speed Vt2~ t3 during the time period t2~ t3 is given by t2~ t3 = VO (6) In this way, the necessary equation ~or computing the desired speed pattern is obtained.

.;
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95~5 Thus, ~ince the cutter rotational distance LR iB
given a~ the ~um of th~ time lntegrals of the cutter eed~ VO~ tl~ Vtl~ t2 and V.t ~ t ~ we obt in LR ~0 VO~ tldt + ~t Vtl~ t2dt + It Vt2- t~dt = Vot3 + 4a2VO tlt2 - a2VO t2 Since 2tl = t2, we obtain LR = Vot3 + a2V02~22 (10) Further, ~ince Vot2 = ~f (correction travel di~tance) and Vot3 = Lo (material-cutting length), we obtain ~ = ~0 + a2Lf2 (11) Here it i8 assumed that a2 = a3/2. This i~ ~ con~tant given to simplify as 2a2 = a3 in the equatione (4) and (5). Consequently, the equation (11) i8 written as ; LR + Lo + a3Lf /2 Thus, a3 is given by a3 = 2 (LR - Lo)/Lf Since Lf = Lo - L~, it is finally given by 3 (~R Lo) / (Lo - L~) (12) A~ will be ~een from the above equation (12), the accele-ration/decelerstion coefficient can be computed by giving the cutter circumferential length LR, the ~aterial-cutting length Lo and the cutting distance L8.

By substituting a2 = a3/2 in the above equations (4) and (5), the speed pattern of Fig. 1 is given by ~ ~ .

, . - -~0~S 5 5 Vo~t V0 + 83Vo t (1~) tl~ t2 = V0 + ~3Vo tl - a~V0 (t- tl) (14) Vt2~ t3 = V0 (15) Thus, the rotational speed of the rotary cutter can be given a~ a function of the acceleration/deceleration coefficient a3, material travel speed V0, turning point time tl and time t.

As regards the ~eaning of the acceleration/deceler-ation coefficient a3, it represents the rotational speed di~placement which the rotary cutter 2 mu~t make for every pulse from the material travel pulse generator 5 of Fig. 4. As a result, by adding or subtracting the acceleration/deceleration coefficient a3 for every material travel pulse, the speed pattern for the straight line slope segment9 (during tl~ t2 and t2~ t3) in Figs. 1 to 3 can be functionally output.

To execute the computation of the acceleration~
deceleration coefficient given by the equation (12), the acceleration/deceleration coefficient generating cir-cuit 8 shown in Fig. 4 includes setting means 9, 10 and 11 for respectively setting the material-cutting length Lo~ cutter circumferential length LR and cutting distance Ls, 8c that the setting means apply the values of Lo~
LR and ~ in the form of digital binary codes to a coeffi-cient generator 12, and the coefficient generator 12 generates an acceleration/deceleration coefficient a3 lO~i9S~5 by the computation of the equation (12). Setting mean~
13 has preset therein, a~ a con~tant, the required acceleration/deceleration coefficient a3 for cutting the material to the longer lengths shown in Fig. ~, and these coefficient outputs are selectively delivered by a switch Sl.

Next, the function generator 14 shown in Fig. 4 will be described.

The function generator 14 perform~ the following three operations in response to the acceleration/decele-ration coefficient a3 applied from the acceleration/
deceleration coefficient generating circuit 8, the material travel pulses Pl applied from the material tr,avel pulse generator 5 and the reset pulse P2 applied from the limit switch 4 for detecting the end of each cutting operation:
(a) The computation of the time of turning point of the speed pattern (time tl).
(b) The computation of the rotational speed displace-ment which must be made by the rotary cutter for every travel pul6e Pl (during O ~tl and tl~ t2).
(c) The stopping of the function output (the time t2) .

Embodiments of the function generator 14 are 6hown in Figs. 5 and 6.

lO~!~S~5 In Fig. 5, the circuit construction of the function generator 14 comprise~ an up-down counter 31, a turning point generator 32, a zero point generator 33, a compars-tor 34 and a multiplier 35.

The operation for pro~iding the function output corresponding to the speed pattern shown in Fig. 1 i~ as follow~. Upon completion of each cutting, a reset pul~e P2 i8 applied to the up-down counter 31 80 that the up-down counter 31 i8 reset to its initial state and the next cutting cycle i8 started. The up-down counter 31 count~ up the travel pulses Pl up to the time tl and the resulting count N is successively applied to the multiplier 35 which in turn multiplies together the applied count N and the acceleration/deceleration coef~i-cient a3 to generate a function output indicative of the speed displacement which must be made by the rotary cutter in response to the movement of the material. This count N is also applied to the comparator 34 which in turn compares it with the count indicative of the turning point or ~(Lo ~ LS)/2 ~, 80 that when the count N attains ~( 0 ~S)/2) , a di~crimination output iq generated to switch the up-down counter 31 to perform subtraction or countdown operation. In respon~e to the comparison value from the zero point generator 33, the comparator 34 discriminates that the content of the up-down counter 31 is decreased to zero, so that when the counter content ~s reduced to zero, the operation of the up-down counter 31 is stopped and the generation of the l~9~tjs function is terminated.

Fig. 6 show~ another embodiment of the ~unction generator 14.

While, in the function generator shown in Fig.
5, the count N o~ travel pulses Pl i8 obtained and multiplied by the acceleration/deceleration coefficient a~, this ic equivalent to addition or subtraction of the acceleration/deceleration coefficient a3 in response to every travel pulse Pl- Thus, in accordance with the embodiment shown in Fig. ~, the circuit construction of the function generator comprises an adding and sub-tracting unit 36, a comparator 37, a turning point generator 38 and a zero point generator 39, whereby the adding and subtracting unit 36 adds or subtracts the accelerstion/dece1eration coefficient a3 in response to every travel pul3e Pl- In other words, the addition is performed up to the turning point after which the subtraction iB performed, and the computation is completed when the output of the adding and subtracting unit 36 i~ reduced to zero. In this case, the reference dis-crimination output of the turning point generator 38 iB
given by [(LR -~0)a3/2~ .

In the case of the speed pattern of Fig. 2 for cutting the material to the.longer lengths, there is a relation LR <Lo 80 that the acceleration/deceleration coefficient given by the equation (12) assumes a negative - ~8 -: .- .
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value snd a function i8 generated in a m~nner rever~e to th~t used in the case of Fig. 1. Thu8, in re~pon~e to the re8etting by the re~et pul~e P2 indicative o~ the completion of the cutting cycle, a deceleration function i8 computed and the computation of an acceleration fun-ction i~ started at the turning point. The g~neration of the function i~ 8topped when the rotary cutter Bpeed becomes equal to the materlal travel speed.

In the case of the speed pattern of Fig. 3 for cutting the material to still longer lengths such as given by ¦LO> 2 ( ~ ~ ~S)~ ~ the desired cutting operation ca.~not be accomplished by the generation of such fun-ction. As a result, the desired accleration/deceleration coefficient a3 is computed from the equation (12) on the basis of[L0 = 2 (LR ~ L8)~ and the resulting value is preset in the coefficient setting means 13 of the coeffi-cient generating circuit 8 shown in Fig. 4, whereby the switch Sl is operated to apply this value to the function generator 14. Where thi~ coefficient a3 is used, the function output is reduced to zero at the point of [(LR ~ LS)/2~ or the time tl is reached, and consequently the generation of function i8 stopped to stop the operation of the cutter during the time corresponding to a material travel distance(L0 - 2 (LR - Ls)] which cannot be ab80rbed by the acceleration/deceleration coefficient a3.
After the lapse of the time corre~ponding to[L0 - 2 (LR -LS)~ or at a time tl , the generation of the functionoutput iB resumed in accordance with the coefficient a3.

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lO~,g5~5 This stopping operation may be accompliahed by inhiblting the function eenerator from opersting in reeponse to the applied travel pulses Pl or by preventing the application of travel pulses Pl to the function generator until the time that the travel distance [Lo - 2 (LR - Ls)] haa been ab~orbed. In other words, by establishing the desired function generator stopping interval after the point [(Lo - LS)/2~ in accordance with [~0 - 2 (LR ~ ~S)~
it i~ possible to generate the desired function for cutting the material to the de~ired length~ having the relatin [~0> 2 (LR LS) ]

Fig. 7 shows still another embodiment of the function generator which further comprises a function stopping controller 40, whereby when the function out-put is reduced to zero at the time tl in Fig. 3, the counting operation of the up-down counter 31 is ~topped during the time that the material travels the distance [Lo - 2 (L~ - Ls) ]. The function stopping controller 40 i~ connected to the comparator 34 through switch means S2 which is operatively a~sociated with the switch mean6 Sl provided in the coefficient generator 8 of Fig. 4. As a result, when the ewitch S2 is moved to the position shown in the Figure, the function output corres-ponding to the speed pattern of Fig. 3 is generated.

Referring again to Fig. 4, the function output of the function generator 14 is applied to the D/A con-verter 1~ who~e output is applied to the multiplier 17 lO~ 5 ir. which it ie multiplied by the material travel speed VO applied from the frequency/voltage converter 15, snd the resulting multiplication output is combined with the material travel ~peed at the ~umming point 18, thus generating a cutter speed signal ~1 for the rotary cutter

2.

Again the cutter speed is given from the equation~
(4), (5) and (6) in accordance with the acceleration/
deceleration coefficient a3, as follows:
VO ~tl = VO + a3VO t (13) l~ t2 = VO + a3VO tl- a3Vo2(t-tl) (14) Vt2~ t3 = VO (15) Limitting the de~cription of the operation to the time interval o~tl in Fig. 1 for purposes of simplicity, since the second term VO t in the right member of the equation (13) is equal to the material travel distance , it i9 given by VO~ t = VO + a3~oVo (16) The second term a3~0 in the right member of the equation (16) corresponds to the function output of the function generator 14. In other words, the function output a3~b i~ the result obtained by adding the acceleration/
deceleration coefficient a3 for every travel pulse Pl.
Since each of the travel pul~es Pl from the material travel ~ ~;
pulse generator 5 corresponds to 1 mm or 0.1 mm travelled by the material, the material travel distance ~0 may be rewritten in terms of the count N of travel pulses Pl, .
, 10~'~5S5 and consequently the value obtained by subjecting the function output a3N of the function generator 14 to D/A
conversion in the D/A converter 16 repre~ents the value f 3 o This a3~0 is applied to the multiplier 17 in which it i8 multiplied by the material travel speed VO obtained by converting the frequency of travel pulses Pl to the corresponding voltage, and the resulting value a3~0VO
is combined with the material travel speed VO at the summing point 18, thus producing the cutter speed signal ~1 for the time interval o~ tl which iB given by the equation (16). This cutter speed ~ignal El i8 applied, as a speed setting value, to the ~peed controller 26 of the thyristor Ward-Leonard unit 25 through the summing point 21, thus controlling the DC motor 3 to accelerQte it.

It will thus be seen that it is only neces~ary to perform the computation in response to the material travel detecting pulses Pl, although the computation i~ subject to variations in accordance with the distance travelled by the material.

In the like manner, the cutter speed signal El given by the equation (14) is computed for the time inter-val tl~ t2, and the output of the function generator 14 is stopped during the time interval t2~ t3.
Consequently, the output of the multiplier 17 is reduced to zero and only the material travel speed VO is delivered ~ ' ~ . :
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iOl~S5 through the summing point l~ a~ the cutter ~peed eignal El .

In the case of the speed patterns ~hown ln Flgs.
2 and 3, the desired cutter ~peed ~ignal El iB computed in accordance with the function output o~ the function generator 14.

Next, the follow-up error signal E2 applied to the summing point 21 will be described.

The computation of follow-up error is effected in the error computing unit l9 in response to the function output of the function generator 14 and the pulee output P3 of the pulse generator 6 which detects the rotational po~ition information of the rotary cutter 2.

Here, the relation between the material travel distance ~0 (instantaneous value) and the cutter travel distance ~ ~ derived by differentiating with ~t the equation ~l6) repre~enting the cutter speed Vo~t during the time interval o ~t1, iB given as ~o1lows tl = ~ t = ~o/~t + a3~0-~ ~ t ~ 0+ a3~'o-~o (17) Thus, the cutter trave1 distance ~ can be obtained in terms of the material travel pulses Pl indicative of~
and consequent1y the cutter rotational distance ~R corre8-ponding to the material travel d1stance ~0 can be obtained ':. . ' ~ . :
',`,, ' ~ ' 10~55~

by integrating the travel distance~ ~

'l'o obtsin the cutter rotational di~tance~R
correRponding to the material travel distance, the error computin~ unit 19 obtains the cutter rotational distance ~ in terms of a rotational poqition by an integration operation in which the function output a3~0 applied from the function generator 14 for each material travel pulse Pl i~ combined with the material travel pul~e Pl, and then the resulting sum i~ added for every material travel pulse Pl The error computing unit 19 also receives the pulse signals P3 from the pulse generator 6 adapted to measure the actual amount of rotation of the cutter 2. Coneequently, the error computing unit 19 subtracts the actually measured cutter rotational distance fro~
the cutter rotational distance ~R obtained in term~
of an integrated value to finally generate a rotary cutter follow-up error.

The follow-up error generated from the error computing unit 19 i8 converted into a voltage signal E2 by the D/A converter 20 and it i8 then fed back to the summing point 21, thus effecting an error follow-up control which alway~ reduces the content of the error computing unit 19 to zero. By virtue of this error follow-up control, the cutter follow~ up the integrated value porduced in the error computing unit 19, thus 10~95S5 accomplishing the desired cutting o~ the material with a high degree of accuracy.

Also fed back to the summing point 21 i8 a rota-tional ~peed signal E4 detected by the tachometer gene-rator 7 and corre~ponding to the cutter speed signal E
applied from the ~umming point 18.

Next, the computation of the acceleration eignal E3 applied to the summing point 27 of the thyrietor Ward-Leonard unit 25 will be described. The purpoee of this computation of the acceleration signal ~3 i8 to generate a voltage signal corresponding to a current which appliec the required driving torque to the DC
motor 3 to sccelerate or decelerste the rotational speed of the cutter.

By differentiating the cutter rotational speed V0~ t given by the equation (16), the acceleration rate during the time interval o~tl i9 given by dVo~tl/dt = a3V0 (17) In other words, the acceleration rate is the one obtained by multiplying the acceleration/deceleration coefficient a3 by the square of the material travel speed V0.
This computation of acceleration is effected by the D/A converter 22 and the multipliers 23 and 24. In other words, the acceleration signal ~3 of a3V02 i~ obtained by subjecting the acceleration/deceleration coefficient a3 to D/A conversion in the D/A converter 22, squaring ~ ~ . . . .
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in the multiplier 23 the material travel speed applied from the F/V converter 15 and then mult$plying the D/A
converted value a3 by the squared value Vo2 in the multiplier 24.

The acceleration signal ~3 become~ -a3V02 during the time interval tl~ t2, and it i~ reduced to zero during the time interval t2~ t3.

It will thus be seen from the foregoing descrip-tion that by virtue of the fact that a function output corresponding to the detection of material travel pulse~
is generated in accordance with an acceleration/decelera-tion coefficient for providing a predetermined cutter rotational speed pattern which is dependent on the relation between a materiai-cutting length Lo and an inherent cutter circumferential length LR, and the computation of three control function~, i.e., a desired rotary cutter speed, follow-up error and acceleration are computed according to the function output, the rotary cutter according to the present invention i8 ~:
capable of accomplishing the desired continuous auto-matic cutting of a material to desired lengths with a high degree of accuracy and al~o overcoming the deficien-cie~ of the prior art rotary cutter.

~ ~ .

Claims (8)

What is claimed is:

1. In a rotary cutter adapted for successively cutting a material to lengths in accordance with a rotary cutter rotational speed control pattern which is deter-mined by the relation between a cutting length of said material and the circumferential length of said cutter, the combination comprising:

Coefficient generating means for computing an acceleration/deceleration coefficient indicative of variation of the rotational speed of said rotary cutter for every material travel speed detecting pulse in accor-dance with a preliminarily set material-cutting length, rotary cutter circumferential length and cutter cutting distance;
function generating means for generating a rotary cutter speed control function in response to material travel speed detection pulses which are counted up or counted down in accordance with the acceleration/decele-ration coefficient computed by said coefficient generating means and said rotary cutter rotational speed control pattern;
speed computing means for multiplying together the speed control function generated by said function generator and a material travel speed obtained by conver-ting said material travel speed detection pulses to obtain a product and then adding said material travel speed to said product to generate a rotary cutter operating speed command signal;

error computing means for adding the sum of the speed control function generated by said function generator and said material travel speed detection pulse in response to the application of each said material travel speed detection pulse to compute the amount of rotation of said cutter and for subtracting an actually detected amount of rotation of said cutter from said computed amount of cutter rotation to generate a cutter follow-up error signal;
acceleration computing means for multiplying together the acceleration/deceleration coefficient computed by said coefficient generating means and a square of said material travel speed to generate an acceleration signal to control the amount of current which generates a DC motor driving torque necessary to accelerate or decelerate said cutter; and cutter speed controlling means including a speed amplifier and a current amplifier, said cutter speed controlling means being responsive to said operation speed command signal, said follow-up error signal and said acceleration signal for con-trolling a cutter driving DC motor, wherein said follow-up error signal is fed to said speed amplifier and said acceler-ation signal is fed to said current amplifier.

2. A rotary cutter according to claim 1, wherein said coefficient generating means comprises a plurality of setting means for respectively setting said rotary cutter circumferen-tial length, said material-cutting length and said cutter cutting distance, and a coefficient generator responsive to the set values of said setting means to compute said acceler-ation/deceleration coefficient according to the following equation:

where a3 = acceleration/deceleration coefficient LR = rotary cutter circumferential length LO = material-cutting length LS = cutter cutting distance

3. A rotary cutter according to claim 2, wherein said coefficient generating means further comprises another setting means for setting a preliminarily computed acceleration/deceleration coefficient, and switching means for selectively supplying the outputs of said plurality of setting means and said another setting means.

4. A rotary cutter according to claim 1, wherein said function generating means comprises:
an up-down counter for counting up or counting down said material travel speed detecting pulses to generate a count output;
a turning point generator for setting a transition point at which said up-down counter is switched from the forward counting operation to the backward counting operation;
a zero point generator for setting a stop point for said up-down counter;
a comparator for comparing the forward count output of said up-down counter with the set value of said turning point generator to switch said up-down counter from the forward counting operation to the backward coun-ting operation when the equality is found between said count value and said set value, and for comparing the backward count value of said up-down counter with the set value of said zero point generator to stop said up-down counter when the equality is found therebetween;
and a multiplier for multiplying together the count value of said up-down counter and the acceleration/
deceleration coefficient from said coefficient generating means to compute said speed control function.

5. A rotary cutter according to claim 4, wherein said turning point generator sets said transition point in terms of (LO - LS)/2.

6. A rotary cutter according to claim 1, wherein said function generating means comprises:
an adder/subtractor for adding or subtracting the acceleration/deceleration coefficient applied from said coefficient generating means for every material travel speed detection pulse to generate said speed control function;
a turning point generator for setting a transition point at which said adder/subtractor with the set value of said turning point generator to switch said adder/
subtractor from the adding operation to the subtraction operation when the equality is found between said addi-tion output and said set value, and for comparing the subtraction output of said adder/subtractor with the set value of said zero point generator to stop said adder/
subtractor when the equality is found therebetween.

7. A rotary cutter according to claim 6, wherein said turning point generator sets said transition point in terms of (LO - LS)a3/2.

8. A rotary cutter according to claim 4, wherein said function generating means further comprises circuit means, whereby when the acceleration/deceleration coeffici-ent from said coefficient generator is applied as a set value, said circuit means responds to the turning point discrimination output of said comparator to stop said up-down counter for a period of time which allows said material to travel a length of LO - 2(LR - LS).