Printed Web Ribbon Registration Control System

Abstract

This control system maintains proper registration of several continuously advancing printed web ribbons, which are to be gathered in superimposed relationship and then perforated, cut and folded along lines located in unprinted spaces between successive printed areas. Each ribbon, while under substantially constant tension, enters an individual control nip whose velocity is corrected in accordance with the detection there of misregistration of the ribbon with respect to a reference pulse. A further correction is provided by changing the phase of this reference pulse with respect to the perforating device in accordance with ribbon misregistration at the perforating device. This latter correction is not made during every cycle of operation and it is not made unless the misregistration exceeds an acceptable minimum.

Description

This invention relates to a registration control system for printed webs.

In certain practical applications of web presses, a relatively wide printed web coming out of the press is slit longitudinally into two or more ribbons, each having a series of printed areas in succession along its length which are separated by smaller unprinted spaces. After being slit, the ribbons are advanced continuously to gathering cylinders where they are superimposed upon each other in sandwichlike fashion in a predetermined order. The gathered ribbons are then advanced to perforating and cutoff cylinders, where alternate unprinted spaces between successive printed areas are perforated and severed, respectively. The gathered ribbons are cut into lengths corresponding to half the circumference of the impression cylinder, and each cut length of the ribbon has a transverse perforated line midway along its length. The respective perforating and cutoff cylinders are driven from the press drive, as are the web ribbon drive rollers. Ideally, each revolution of the perforating cylinders and each revolution of the cutoff cylinders should correspond to movement of a predetermined length of the web ribbons so that the web ribbons will be perforated and cutoff at predetermined locations in alternate unprinted spaces between the printed areas. In practice, however, this ideal is difficult to achieve and it is an important purpose of the present invention to provide a novel and improved control system for insuring proper registration of the web ribbons with respect to a cyclically operated mechanism which acts on the gathered ribbons, such as a perforating mechanism and/or a cutoff mechanism.

It is an object of this invention to provide a novel and improved registration control system for regulating the speed of an advancing web member with respect to a cyclically operated mechanism into which the web member is fed.

Another object of this invention is to provide a novel and improved control system for regulating the velocities of two or more individual printed web ribbons to insure their proper registration with respect to each other and with respect to a cyclically operated mechanism.

Another object of this invention is to provide such a system in which each web ribbon passes through an individual control nip whose velocity may be advanced or retarded substantially in accordance with an error factor equal to the sum of twice the misregistration in the present cycle of operation of the cyclically operated mechanism plus the summation of the misregistrations in previous cycles of operation.

Another object of this invention is to provide such a system which senses the misregistration of the gathered ribbons close to the cyclically operated mechanism and, if this misregistration exceeds a tolerable minimum value, a phase correction may be applied for reducing the misregistration of the gathered ribbons with respect to the cyclically operated mechanism.

Another object of this invention is to provide such a system in which the phase corrections resulting from the detection of misregistration of the gathered ribbons near the cyclically operated mechanism do not interact with the control nip velocity corrections for the individual ribbons to produce system instability.

Further objects and advantages of this invention will be apparent from the following detailed description of a presently preferred embodiment, which is illustrated schematically in the accompanying drawings, in which:

FIG. 1A is a schematic perspective view of a printed web coming from a printing press into a slitter which slits the web longitudinally into four ribbons;

FIG. 1B is a schematic perspective view showing the four web ribbons passing through a ribbon drive system in accordance with the present invention;

FIG. 2 is a schematic diagram illustrating the complete control system of the present invention as applied to two of the web ribbons;

FIG. 3 is a schematic block diagram illustrating part of one of the control nip velocity correction computers in the present control system and pulse timing charts for this part of the control system;

FIG. 4 is a schematic block diagram illustrating the remainder of this control nip velocity correction computer;

FIG. 5 is a schematic block diagram illustrating the phase correction computer in the present system for regulating the phase of the variable phase pulse generator and hence the velocity of all control nips to tend to eliminate any misregistration detected near the perforating cylinders;

FIG. 6 is a table showing the operation of the control nip correction computer over several cycles of operation in response to an arbitrarily selected open loop error; and

FIG. 7 shows the open loop error, the correction applied and the actual error, all plotted against the number of cycles of operation, in accordance with the FIG. 6 table.

WEB RIBBON DRIVE SYSTEM -- FIGS. 1A and 1B

Referring to FIG. 1A, a printed web W coming from the chill rolls 10, 11 of a printing press is slit longitudinally by a slitter S into a series of parallel, side-by-side ribbons, here shown as the four ribbons W-1, W-2, W-3 and W-4. The modulus of elasticity of the web W may be different at different locations across its width, so that the modulus of elasticity of one ribbon, W-1 for example, may differ from that of one or more of the other ribbons W-2, W-3 and W-4.

From the slitter the four ribbons pass in separate paths into the drive system shown in FIG. 1B. Considering only the web ribbons W-1, this ribbon passes down over a fixed guide roll 15 and then in a loop extending under a constant tension device, which is shown schematically as a weighted roller 16, and then up over another fixed guide roll 17. From the latter the ribbon W-1 passes to a control nip provided by a pair of drive rollers 20 and 21, which are driven through a differential from the press drive. All of the guide rolls turn freely.

The constant tension roller 16 is floatingly supported and is loaded by means of an air cylinder (not shown), which urges roller 16 downward with a predetermined constant force. When in equilibrium, the force produced by the air cylinder is equal and opposite to the force produced by tension in the ribbon. Equilibrium can only be obtained when the control nip drive rollers 20 and 21, are driven at a specific speed: ##SPC1##where: V.sub.1 = circumferential speed of control nip drive rollers, inches per second, V.sub.o = circumferential speed of chill rolls, inches per second, T.sub.1 = ribbon tension produced by air cylinder, pounds per inch of ribbon width, E.sub.1 = modulus of elasticity of ribbon, pounds per inch of ribbon width/ in./in. of ribbon strain, E.sub.o = average modulus of elasticity of web entering the chill rolls, pounds per inch of web width/in./in. of web strain, T.sub.o = tension of web entering the chill rolls, pounds per inch of web width.

If the speed of the control nip drive rollers is temporarily increased, the constant tension roller will move in a direction to shorten the loop path of the ribbon between guide rolls 15 and 17. A temporary decrease in control nip drive roller speed will cause the loop path to lengthen.

Each of the other ribbons W-2, W-3 and W-4 advances through a similar constant tension drive arrangement to a respective control nip. Corresponding elements of the drive arrangement for each of these ribbons are given the same reference numerals as those for the first ribbon, W-1, but with a suffix added which designates the ribbon. For example, the constant tension roller for ribbon W-2 is identified by the designation 16--2. The detailed description of the ribbon drive will not be repeated for each of ribbons W-2, W-3 and W-4. It should be understood that each of these ribbon drives operates on the same principles as explained, and to be further explained hereinafter, for ribbon W-1.

From their individual control nips the respective ribbons W-1, W-2, W-3 and W-4 advance through equal distances to a pair of gathering cylinders 22 and 23, which guide the ribbons into face-to-face, superimposed or sandwiched relationship. The superimposed ribbons then move between a pair of confronting perforating cylinders 24, 25, one of which carries two diametrically opposed, serrated blades 26 which perforates all of the superimposed ribbons twice for each revolution of the perforating cylinders.

The superimposed ribbons then move between a pair of pull rolls 12 and from there the superimposed ribbons pass between a pair of confronting cutoff cylinders 13 and 14, one of which carries two diametrically opposed blades 13a which sever all of the superimposed ribbons twice for each revolution of the cutoff cylinders.

The perforating cylinders 24, 25 and the cutoff cylinders 13, 14 are driven from the press drive.

Each ribbon has a plurality of successive identical printed impressions, each having four successive different printed areas in succession lengthwise of the ribbon. The printed areas are spaced-apart in succession along its length by much shorter unprinted spaces between the printed areas. A register mark is printed in every other unprinted space to determine the location where the ribbon is to be perforated by the perforating blade 26, as explained hereinafter. The cutoff blade 13a on cutoff cylinder 13 severs the ribbon at each of the remaining unprinted spaces between printed areas on the ribbon. The peripheral or circumferential length of each perforating cylinder and each cutoff cylinder is substantially equal to the ribbon length of a printed area plus the next adjoining unprinted space, so that one revolution of the perforating and cutoff cylinders takes place during the advance of one impression length of the ribbon (or four printed areas).

In accordance with one aspect of the present invention, the passage of one ribbon register mark per impression is sensed near the control nip and its actual instantaneous position is compared with the instantaneous position it should have with respect to the perforating cylinder blade 26 in order that the ribbon will be perforated at the desired location in the unprinted space between alternate printed areas. Any difference between the actual position of the register mark and its desired position is used to temporarily increase or decrease the velocity of the control nip for that ribbon so as to reduce or eliminate this difference, or positional error, by changing the position of the constant tension device 16. Each printed impression on the ribbon should correspond to one revolution of the perforating and cutoff cylinders.

CONTROL SYSTEM -- FIG. 2

Referring to FIG. 2, the lower control nip roller 21 for each ribbon is driven from the gear train of the press through a respective differential 27. Each differential 27 is controlled by a respective stepping motor 28 which is arranged, through circuitry to be described, to receive correction pulses so as to increase or decrease the speed at which the control nip is driven in accordance with an important aspect of the present invention, to be explained in detail hereinafter.

At each control nip a respective photoelectric sensor 29 senses the register mark on the respective ribbon as it moves past, and the sensor delivers a register mark pulse over line 30 to one input terminal of a ribbon control nip velocity correction computer 31. This computer also receives a reference pulse on a second input line 32 from a variable phase pulse generator 33 which operates in synchronism with the rotation of the perforating cylinders 24 and 25.

Ideally, the reference pulse on line 32 should coincide in time with the register mark pulse on line 30. In that case, the register mark read by the sensor 29 is correctly positioned and therefore the control nip velocity for that ribbon is correct.

However, if the pulses on lines 30 and 32 do not occur at the same time, this means that the register mark just read from the ribbon is out of registration. Such noncoincidence will be sensed by the correction computer 31, which will cause a temporary change in the number of correction pulses to be applied to the stepping motor 28 to cause the control nip velocity for that ribbon to be temporarily increased or decreased to a value which is effective to reduce or eliminate this misregistration.

It should be understood that each of the other web ribbons W-2, W-3 and W-4 has an identical control arrangement, including an individual control nip which is driven through an individual differential from the press drive and with each differential controlled by an individual stepping motor. A separate photoelectric sensor is provided at the control nip for each ribbon to sense the movement of the ribbon register mark past it. The output of this sensor is connected to one input of an individual control nip velocity correction computer, which has a second input connected to the perforator cylinder-operated pulse generator 33.

As already stated, the distances between the control nips and the gathering cylinders 22, 23 are equal, preferably.

The pull rolls 12 are driven from the press drive either through a constant torque mechanism 34, such as a constant torque clutch, or through an adjustable speed ratio device. In the former case, the gathering rolls 22, 23 produce a constant tension on the gathered ribbons.

In the latter case, the pull rolls produce a tension on the gathered ribbons as follows: ##SPC2##where: V.sub.2 = circumferential velocity of pull rolls, inches per second, E.sub.12m = modulus of elasticity of the gathered ribbons, pounds per inch of ribbon width/ in./in. of strain, E.sub.o = modulus of elasticity of the web entering the chill rolls, pounds per inch of width/ in./in. of strain, T.sub.o = tension of web entering chill rolls, pounds per inch of width, V.sub.o = circumferential velocity of chill rolls, inches per second, T.sub.12m = tension of the gathered ribbons, pounds per inch of ribbon width.

In either case, the stretch per unit length of each of the ribbons in the region between its control nip and the pull rolls 12 will be the same. Since the lengths of the ribbons between the respective control nips and the pull rolls 12 are equal, if one of the ribbons is in proper registration, both at the perforating cylinder and at the ribbon control nip, and if all the other ribbons are in correct registration at their respective control nips, then all ribbons will be in correct registration at the perforating cylinders 24 and 25.

Before proceeding with the description of the details of the control circuit for each control nip, the factors involved in correcting the ribbon speed will be explained.

For each printed impression on the ribbon, the measured instantaneous difference between the actual position of the following register mark as it passes the photoelectric sensor 29 and its desired position to provide exact registration with respect to the perforating blade 26 may be specified as the error distance, E, which is equivalent to a certain number of correction pulses into the stepping motor 28. That is, if it were possible to apply these correction pulses instantaneously to the stepping motor and thereby instantaneously change the control nip speed momentarily, the detected error would be eliminated.

However, the correction cannot be made instantaneously, and merely applying the number of correction pulses equivalent to the error distance, E, during a single cycle of operation would not necessarily bring the ribbon back into correct registration because it would not insure that the correction would catch up to the error.

In accordance with the present invention, correction pulses, C.sub.p, are applied to the stepping motor 28 in accordance with the following relationship: ##SPC3##, where E.sub.n is the misregistration error measured at the end of the present (n) cycle of operation, is the summation of the individual misregistration errors measured at the end of every preceding cycle of operation up to and including the immediately preceding (n-1) cycle, and C.sub.p is the number of correction pulses which are to be applied to the stepping motor in the next (n+1) cycle of operation.

As described hereinafter, during any given cycle of operation (equal to one revolution of the perforating and cutoff cylinders) the correction computer 31 for each control nip will apply to the stepping motor 28, in response to the sensing of a ribbon register mark by the sensor 29 at that control nip, a number of correction pulses sufficient to provide the correction C.sub.p as stated by the foregoing equation (1). These correction pulses will cause the stepping motor to correct the control nip speed by the sum of the previous misregistration errors plus twice the present misregistration error (2E.sub.n), in accordance with the foregoing equation (1). By this correction, the control nip speed is regulated to momentarily speedup or slowdown the ribbon to compensate for the present misregistration and to establish a relatively steady state ribbon speed which will maintain a predetermined tension on the ribbon, so that the constant tension roller 16 will remain at a corresponding predetermined level and the ribbon path length through the loop at the constant tension roller will remain substantially constant.

The table of FIG. 6 and the graph of FIG. 7 show the operation of this control system under an arbitrarily assumed open loop error situation. As can best be visualized from FIG. 7, the actual error, E.sub.n, is minimized as a result of the correction pulses C.sub.p applied in accordance with equation (1) above.

CONTROL NIP VELOCITY CORRECTION COMPUTER -- FIG. 3

Referring to FIG. 3, the dashed-line enclosure 31a contains the components of the correction computer 31 (FIG. 2) for the control nip. The unprinted space (where the register mark appears) between successive printed areas on the ribbon is only a small fraction of the length of the total printed impression on the ribbon. The photoelectric sensor 29 should be disconnected from the control nip velocity correction computer while any printed area is moving past the sensor; otherwise, the computer might respond to an output signal from the sensor caused by its reading the printed area, whereas the purpose of the sensor is merely to sense the movement of a registration mark past it.

For this purpose, as shown in FIG. 3, the sensor 29 is connected by line 30 to a gate circuit 35 which is normally closed. The gate circuit 35 can be opened only during the small fraction of each revolution of the perforating and cutoff cylinders when the unprinted space between certain printed areas in the corresponding printed impression on the ribbon is moving past the sensor 29. This open period of gate circuit 35 will be referred to as the window period.

One of the perforating cylinders 25 drives an analog-to-digital encoder 36 having two different outputs, one of which produces a single output pulse on line 37 for each revolution of the perforating cylinders, and the other of which produces 240 evenly spaced pulses on line 38 for each revolution of the perforating cylinders. The timing or phase relationship of the pulses on lines 37 and 38 with respect to the rotation of cylinder 25 can be varied as explained hereinafter in the description of FIG. 5.

Referring to the pulse timing charts of FIG. 3, line a shows the register mark which occurs in the middle of each printed impression, in the unprinted space between two successive printed areas on the ribbon. The single encoder output pulse on line 37 (line b) occurs at a time, t.sub.1, somewhat ahead of this register mark. This pulse on line 37 is applied to the "open" control terminal 39 of gate circuit 35, causing this gate circuit to open. The gate circuit will remain open until a pulse appears at its "close" control terminal 40, which is connected to the 240 pulse-per-revolution encoder output line 38 through two series-connected divider circuits 41 and 42, each of which produces a single output pulse for every two input pulses it receives. With this arrangement, the fourth pulse occurring on line 38 following the single pulse on line 37 will be applied to the "close" terminal 40 of gate circuit 35, resetting the latter to its normal closed condition. This closing of the gate circuit occurs at time t.sub.2, as indicated at line c of the FIG. 3 pulse timing chart. The gate circuit 35 will remain closed until the next pulse appears on line 37, i.e., during the next revolution of the perforating cylinders 24, 25.

It will be apparent that the gate circuit 35 is open only during a small fraction (4/240) of each revolution of the perforating and cutoff cylinders.

The gate circuit 35 also has a reference pulse input terminal 43 which is connected to the output of the first divider 41. With this arrangement, the second encoder output pulse which appears on line 38 after the single encoder output pulse appears on line 37 will be applied to terminal 43. This is the reference pulse against which the register mark pulse from sensor 29 is compared. This reference pulse is shown at line d of the FIG. 3 pulse timing chart as occurring at the midway point of the window period of gate circuit 35 (between times t.sub.1 and t.sub.2).

Line e of the FIG. 3 pulse timing chart shows the error period, which is the time interval between the leading edge of the register mark pulse (line a) and the leading edge of the reference pulse (line d). The register mark pulse (line a) will occur sometime between times t.sub.1 and t.sub.2, normally, and it may occur either before or after the reference pulse, depending upon whether the misregistration is lagging or leading, or it may occur simultaneously with the reference pulse if there is no misregistration at all. The horizontal width of the error period (line e) represents the timing error of the register mark.

In practice, the press may run at speeds of from 80 to 1500 feet per minute. Therefore, the magnitude of the timing error between the register mark pulse and the reference pulse will be a function of the press speed. This timing error must be converted to terms of absolute distance, i.e., fractional inches of error of the reference mark on the web.

In the preferred embodiment of the present system this is accomplished in a simple and inexpensive manner by providing a DC tachometer 44 driven by the perforating cylinder 25 and having its output connected to a voltage-to-frequency converter 45. This converter produces a series of relatively high frequency output pulses at a frequency which is proportional to the DC voltage output of the tachometer, which in turn is proportional to the rotational speed of the perforating cylinders 24, 25 and the press speed. For example, at the assumed maximum press speed of 1500 feet per minute, the converter pulse rate is 350 kilocycles per second, so that each output pulse which converter 45 produces corresponds to approximately .000857 inch of ribbon error or misregistration.

These error pulses are applied continuously to an input terminal 46 of the gate circuit 35, but, as shown at line f of the FIG. 3 pulse timing chart, they pass through the gate circuit 35 only during the error period (line e). The number of error pulses passed by the gate circuit 35 will be a function of the time duration of this error period and of the press speed, as explained. Therefore, the number of these error pulses will be proportional to the actual misregistration or distance error of the registration mark on the ribbon.

The gate circuit 35 preferably consists of integrated circuit logic units which perform the following logic operations: 1. If, during the window period, the gate circuit receives a registration mark pulse from sensor 29 it maintains a logic 1 condition on output line 47 to indicate that the registration mark has been observed by the sensor; 2. during the error period, it passes error pulses from its inlet terminal 46 to its outlet line 48 equal in number to 2E.sub.n in equation (1) hereinbefore; 3. it delivers a signal to either its "lead" output line 49 or its "lag" outlet line 50, depending upon whether the misregistration or positional error of the register mark on the ribbon is leading or lagging.

Each ribbon nip correction computer 31 includes a pair of bidirectional counters 51 and 52 interconnected by parallel entry circuitry 53.

Counter 51 is the error summation counter for keeping the count of the term in equation (1). Counter 51 has a count input terminal 54 connected to the 2E.sub.n output line 48 of gate circuit 35 through a divider 55, which divides by two. With this arrangement, the counter input terminal 54 receives every second pulse appearing on line 48 and therefore the number of pulses applied to terminal 54 during any particular cycle of operation is equal to E.sub.n in equation (1) for that cycle. Counter 51 performs the summation of all the previous errors and it is never reset.

Counter 51 also has a pair of control terminals 56 and 57 which are connected respectively to the lead and lag output lines 49 and 50 from gate circuit 35. The lead or lag output signal from the gate circuit tells counter 51 to count up or down, as the case may be.

The lower counter 52 has a pair of control terminals 58 and 59, which are connected respectively to the lead and lag lines 49 and 50, so that the lead or lag output signal from gate circuit 35 tells the counter 52 to count up or countdown.

The lower counter 52 has two different count inputs: 1. it receives the count stored in the error summation counter 51 for all of the previous cycles of operation through the parallel entry circuit 53 at the beginning of the window period; 2. during the error period portion of the window period (line e of the FIG. 3 pulse timing chart) it receives the 2E.sub.n error pulses for the present cycle of operation from the gate circuit output line 48 by way of its serial entry input terminal 60. Therefore, at the end (t.sub.2) of the window period the counter 52 has received the previous error summation count, from counter 51, and it has received the count, 2E.sub.n, of twice the error for the present cycle of revolution of the cutoff cylinders. These two counts are added by counter 52 to provide the count, according to equation (1), for determining the number of correction pulses to be applied to the corresponding stepping motor 28 during the next cycle of operation or revolution of the perforating and cutoff cylinders. This count is transferred out of counter 52 during the interval between window periods, as will be explained later.

At the beginning of the next window period, counter 52 is reset to the new count which is now stored in the error summation counter 51, which is different from the previous error summation count by the amount of the error count, E.sub.n, in the cycle just ended. Added to this new count in counter 52 is the 2E.sub.n which will occur in the error period portion of the window period just begun.

CONTROL NIP VELOCITY CORRECTION COMPUTER -- FIG. 4

The correction pulses which are applied to the stepping motor 28 for the control nip for ribbon W-1 are derived from the 240 pulse per impression output of the encoder 36 during the major portion of each cycle outside the window period shown at line c of the FIG. 3 pulse timing chart. Referring to FIG. 4, the 240 pulse per impression encoder output line 38 is connected to a divider 70, which divides by four, so that for every four pulses on its input line 38 the divider passes a single pulse to its output line 71. Line 71 is connected to the input of a normally closed gate 72 having an output line 73 connected to the inputs of a pair of gates 74 and 75 for clockwise and counterclockwise rotation of the stepping motor 28 for ribbon W-1, respectively. The outputs from these gates are both connected to the input of a translator 76 of known design which produces a rotation of the stepping motor 28 proportional to the number of input pulses it receives from either gate 74 or gate 75 and in a direction determined by whether these pulses are received from the clockwise gate 74 or the counterclockwise gate 75.

The output line 73 of gate 72 is also connected to the serial entry input terminal 60 of the counter 52. This connection is made through a divider 77, which divides by two the number of pulses coming from the gate 72. The reason for this is to match the resolution of the count stored in counter 52 to the correction provided by each stepping motor pulse. The correction pulses from gate 72 which are applied through the divider 77 cause the counter 52 to count down toward zero from the count stored therein.

Since the operation of the system is intended to minimize the position error of the register mark on the ribbon, it is also intended to minimize the count stored in counter 52.

If this count ever reaches zero, which means that the register mark on the ribbon is in perfect registration, this occurrence would be detected by a zero coincidence portion of a coincidence circuit 78 associated with counter 52, which would then apply a pulse to its outlet line 79 to close the gate 72. The closing of gate 72 would prevent any more correction pulses from being applied to the stepping motor 28 (through the translator 76) or to the counter 52.

As long as the count C.sub.n stored in counter 52 is positive (i.e., greater than zero), then the coincidence circuit 78 applies a pulse to its output line 80 to open the clockwise gate 74 and also to energize the "count down" control terminal 59 of counter 52.

Conversely, as long as the count stored in counter 52 is negative, then the coincidence circuit 78 applies a pulse to its output line 81 to open the counterclockwise gate 75 and also to energize the "count up" control terminal 58 of counter 52.

In FIG. 4 the register mark detection circuit 82 is part of the gate circuitry 35 in FIG. 3. This detection circuit receives an input pulse from the photoelectric sensor 29 for ribbon W-1 via input line 30 in response to the sensor's detection of a registration mark on this ribbon. This happens once during each revolution of the perforating cylinders, i.e., once for each printed impression on the web. This input pulse causes the register mark detection circuit 82 to maintain a logic 1 condition via its output line 47 to open the gate 72. If no registration mark on the ribbon W-1 is detected during a given cycle of operation, line 47 will go to logic 0 and the gate 72 will remain closed, thereby preventing any correction pulses from being applied to the stepping motor 28 for ribbon W-1 until after the next registration mark is detected. In addition, if no registration mark is detected, this circuit causes transfer of a relay contact which is used to lock up the constant tension roller 16 for ribbon W-1.

Once during each cycle of operation the gate circuit 35 forms a window pulse as was described earlier. During this window period, gate circuit 35 produces a signal on its output line 47 which causes gate 72 to close.

There is a practical upper limit on the number of correction pulses which can be applied to the stepping motor 28 during a single revolution of the perforating and cutoff cylinders; otherwise, the web tension might be high enough to cause the web to break. In one practical embodiment of this invention, the maximum advance or retardation of the ribbon which the stepping motor will be permitted to provide is 0.05 inch per impression. In this embodiment, for the particular gearing ratios used with the stepping motor, this maximum advance or retardation would require 59 correction pulses per impression to the stepping motor.

These correction pulses are applied to the stepping motor 28 for ribbon W-1 only during the major portion of each cycle outside the window period shown at line c of the FIG. 3 pulse timing chart. Since this window period occupies no more than 4/240 of each cycle, only one of each 60 pulses per cycle appearing on line 71 in FIG. 4 will be blocked by gate 72 during the window period. Assuming that gate 72 is reopened by the detection of a register mark and by a large misregister error, the remaining 59 pulses for this cycle will pass through gate 72 to line 73. Consequently, the translator 76 for the stepping motor 28 can receive as many as 59 pulses per printed impression if the misregistration exceeds a certain value. The misregistration can be corrected during a given cycle of operation only to the extent of these 59 correction pulses.

Since there is a physical limit on the rate at which the web can be retarded or speeded up, which limits the number of correction pulses per cycle for the stepping motor, the maximum count of each bidirectional counter 51 and 52 is similarly limited, preferably. For example, each counter may be limited to a maximum count of plus or minus 62. If the counter is instructed to count beyond this, it simply stops counting and holds the maximum count which it is capable of accepting. Consequently, if there is a very large misregistration, the stepping motor 28 will run at its maximum rate of 59 correction pulses per second for enough impressions until the error is reduced enough to bring the count in counter 52 below the maximum number. This feature minimizes the overshoot which would otherwise occur if the counter capacity were not limited to approximately match the maximum correction per impression.

The control nip for each of the other ribbons W-2, W-3 and W-4 is provided with an individual stepping motor 28-2, 28-3 and 28-4. Each of these stepping motors is controlled individually by a control nip velocity correction computer identical to that just described in detail with reference to FIG. 4.

PHASE CORRECTION CONTROL -- FIG. 5

In accordance with another aspect of the present invention, the phase of the reference signal, which is produced by the pulse generator 33 (FIG. 2) once during each cycle of operation, may be advanced or retarded in accordance with the sensing of the registration mark on one of the ribbons just before the gathered ribbons pass between the perforating cylinders 24, 25. As already explained, the pulse generator 33 produces a single reference pulse (line d of the FIG. 3 pulse timing chart) which is applied to the input of each ribbon nip correction computer 31 during each window period. The time difference between the leading edge of this reference pulse and the leading edge of the register mark pulse is the error period for that ribbon nip.

The variable phase reference pulse generator 33 is controlled by the perforating cylinder 25 such that at a predetermined rotational position of the perforating cylinder 25 it causes the variable phase pulse generator 33 to deliver an output pulse via line 32 to the respective control nip correction computers for the individual ribbons. The phase relationship of the variable phase reference pulse generator 33 with respect to the position of the perforating cylinder may be modified by a stepping motor 128 (FIG. 2). The stepping motor 128 can either advance or retard the timing of the reference pulse produced by variable phase pulse generator 33, as explained hereinafter.

The operation of the stepping motor 128 is under the control of a phase correction computer 131 which is similar in many respects to the already-described ribbon nip correction computer 31. Corresponding elements of the phase correction computer 131 are given the same reference numerals plus 100 as the elements of the ribbon nip correction computer 31, and the complete description of these elements will not be repeated.

Before proceeding with the description of the phase correction computer 131, shown in the dashed-line enclosure in FIG. 5, it will be recalled that the purpose of each of the individual ribbon nip correction computers 31 is to regulate the individual ribbon nip velocity so that the registration mark on each ribbon will appear at the nip at the correct time with respect to the rotational position of the perforating blade 26. This should bring the corresponding registration marks on the several ribbons into synchronism with each other at the individual ribbon nips, and they should be in precise registration with each other when they reach the perforating cylinders.

However, because of the physical spacing between the individual ribbon control nips and the perforating cylinders 24, 25, modulus changes in the paper can cause the ribbons as a group to be out of registration with respect to the rotational position of the perforating blade 26 by the time the grouped ribbons reach the perforating cylinders. Normally, any misregistration error of this sort will occur gradually, rather than abruptly.

In accordance with the preferred embodiment of the present invention, the phase correction of the reference pulse generator 33 will be performed: 1. only if the misregistration error at the perforating cylinders exceeds a predetermined acceptable minimum (e.g., 0.005 inch); and 2. only during one out of several cycles (e.g., one out of 10). The purpose of these limitations is to minimize the possibility of system instability which might occur if every misregistration detected at the perforating cylinders were to cause a correction of the variable phase reference pulse generator 33 which in turn would cause a correction of control nip velocities for the individual ribbons.

The phase correction computer 131 is controlled by a photoelectric sensor 129 which senses the registration mark on the ribbon W-4 as the gathered ribbons pass from the gathering cylinders 22, 23 toward the perforating cylinders 24, 25. Preferably, the sensor 129 is located as close as possible to the perforating cylinders.

Referring to FIG. 5, the phase correction computer 131 includes a gate circuit 135 similar to the already-described gate circuit 35 in the ribbon nip correction computer 31. Gate circuit 135 is connected to the registration mark sensor 129 through line 130.

This portion of the system includes a fixed phase pulse generator which provides one reference pulse per revolution of the perforating cylinders 24, 25. To this end, the encoder 36 delivers to its output line 142 a single pulse whose timing is dependent entirely upon the rotational position of the perforating cylinder 25, such that this fixed phase reference pulse will always occur at the same instant during each revolution of the perforating cylinders. This fixed phase reference pulse is applied to the reference terminal 143 of gate circuit 135. Coincidence of the fixed phase reference pulse with the register mark pulse observed by the perforating cylinder sensor 129 indicates correct registration of the register mark with the perforating blade 26.

The already-mentioned analog-to-digital converter 36 is driven by the perforating cylinder 25 to produce a single pulse per each revolution on line 137 and 240 pulses per revolution on line 138. In contrast to the fixed phase pulse on line 142, the timing of the pulses on lines 137 and 138 can be adjusted with respect to the rotational position of the cutoff cylinder 25. Consequently, the pulses on lines 137 and 138 will be referred to as variable phase pulses. Line 137 is connected to a control terminal 139 of gate circuit 135 to begin the window period of gate 135 at a predetermined time during each cycle of operation, while the unprinted space between the printed areas on each ribbon is passing the perforating cylinder sensor 129. Line 138 is connected to the input terminal 200 of a counter 201 which delivers a "window close" pulse to the control terminal 140 of gate circuit 135 in response to the fourth pulse on line 138 following the "window open" pulse on line 137.

The already-mentioned DC tachometer 44 and the voltage-to-frequency converter 45 cause high frequency output pulses to be applied to the input terminal 146 of gate circuit 135. The pulse frequency is proportional to the speed of the perforating cylinders which, as already explained, is proportional to the press speed.

With this arrangement (similar to the operation of the gate circuit 35 in the correction computer 31 for each individual ribbon nip), once during each revolution of the perforating cylinders the normally closed gate circuit 135 is opened when a pulse appears on the output line 137 of encoder 36. Gate circuit 135 remains open until the fourth following pulse appears on line 138, which will happen at not more than 4/240 of a revolution later. The time interval between the opening and closing of gate circuit 135 is referred to as the window period. The fixed phase reference pulse on line 142 will occur during this window period.

During this window period, the time difference between the occurrence of the fixed phase reference pulse at terminal 143 of gate circuit 135 and the occurrence of the registration mark pulse on line 130 produces the error period during which the gate circuit 135 passes the error signal pulses coming from the voltage-to-frequency converter 45. The number of error pulses passed by the gate circuit 135 depends upon the time difference between the fixed phase reference pulse on line 142 and the registration mark pulse on line 130, as well as upon the press speed. Consequently, the number of error pulses passed by the gate circuit 135 is a measure of the distance error or misregistration of the registration mark on ribbon W-4 as the gathered ribbons pass between the perforating cylinders.

These error signals produce a control signal on either the "lead" output line 149 leading to gate 174 or the "lag" output line 150 leading to gate 175. Gates 174 and 175 are connected to a translator 176 to provide clockwise and counterclockwise rotation, respectively, of the stepping motor 128. Both gates 174 and 175 are normally closed, and neither opens until it receives a control signal on line 173 from gate 172. Consequently, the error signals coming from the gate circuit 135 (whether leading or lagging) cannot be applied to the translator 176 for the stepping motor 128 unless gate 172 is open.

Gate 172 is under the control of a counter 202 which receives, via line 148, the error signal pulse output from gate circuit 135. The pulse output from counter 202 goes into a latch device 203 having its output connected via line 204 to the gate 172. If during any cycle of operation the error pulse input to the counter is less than 6, the latch 203 will maintain gate 172 closed. However, if the error pulse count is 6 or more, the latch 203 will apply a gate-opening signal to line 204. This insures that gate 172 will open only if the misregistration is in excess of a predetermined tolerable minimum value, corresponding to 6 error pulses.

The counter 202 is reset to zero and the latch 203 is reset to its normal gate-closing condition once during each cycle of operation, when the single encoder pulse appears on line 137, which is connected to a reset control terminal 205 of counter 202 and to a reset control terminal 206 of latch 203.

The opening of gate 172 is also under the control of line 147, which receives a gate-opening signal during each cycle of operation only if the registration mark on the ribbon has been detected by sensor 129.

It will be understood that gate 172 will be opened only if a gate-opening signal appears on line 147 and a gate-opening signal appears on line 204. If either gate-opening signal does not occur, then gate 172 will not open during that revolution of the cutoff cylinders.

In addition, gate 172 is controlled by a decade counter 207 having its input connected to the single pulse per cycle output line 137 from encoder 36. The decade counter 207 delivers a gate-opening signal via its output line 208 to gate 172 once for every 10 input pulses which it receives from line 137--that is, only for one out of 10 cycles of operation (or revolutions) of the perforating cylinders 24, 25. Consequently, gate 172 can be opened only once in every 10 cycles, and even then it will be opened only if a registration mark has been detected (producing a gate-opening signal on line 147) and the error signal pulse count exceeds a predetermined minimum value (producing a gate-opening signal on line 204).

After the end of the window period, the input pulse for the motor 128 is delivered to gate 172 from counter 201. As already stated, the signal input to counter 201 is the variable phase 240 pulse per cycle signal on line 138. The output of counter 201 is connected to a latch device 209, which passes this stepping motor pulse to the gate 172 after the sixth count on line 138 in each cycle of operation, which will be shortly after the end of the window period. Counter 201 and latch 209 are both reset once each cycle by the single pulse appearing on line 137.

The single correction pulse passed by gate 172 is applied to the translator 176 for stepping motor 128 either through gate 174 or through gate 175, depending upon whether the misregistration is leading or lagging. This correction pulse causes the stepping motor 128 to either advance or retard the timing of the variable phase reference pulse produced by the pulse generator 33, in the following manner:

The shaft of the encoder 36 carries a disc 211 having alternate opaque and transparent regions. This disc is positioned between one or more light sources 212 and photoelectric sensors 213 carried by a drum 214 which is attached to the shaft 229 of the stepping motor 128. The sensors 213 are connected to lines 137 and 138 to deliver, respectively, 1 pulse per cycle of the perforating cylinders 24, 25 and 240 pulses per cycle.

Normally (i.e., in the absence of an input pulse to the stepping motor 128), the drum 214 is stationary, so that the light source or sources 212 and the photoelectric sensors 213 have fixed positions and the 1 pulse per cycle on line 137 and the 240 pulses per cycle on line 138 will occur at fixed times during the revolution of the perforating cylinder 25.

However, a pulse input to the stepping motor 128 will turn the drum 214 so as to change the positions of the light source 212 and sensors 213, thereby changing the timing, or phase relationship, of the pulses on lines 137 and 138 with respect to the cyclic operations of the perforating cylinders.

Consequently, the beginning and the end of the window period for gate circuit 135 in the phase correction computer 31a can be varied in time, with respect to the rotation of the perforating cylinders.

The pulse output lines 37 and 38 for the individual control nip correction computers 31 are also connected to the photoelectric sensors 213, so that the timing or phase relationship of the pulses on these lines can be varied with respect to the cyclic operation of the perforating cylinders 24, 25. Therefore, the timing of the beginning and the end of the window period for the gate circuit 35 (FIG. 2) in the correction computer for each ribbon control nip will be changed in accordance with the correction provided by the stepping motor 128 in response to the detection of a positional error of the gathered ribbons just before they pass between the perforating cylinders. Also, the adjustment of the timing of the pulses appearing on line 38 varies the timing of the reference pulse (line d of the FIG. 3 pulse timing charts) whose leading edge occurs midway during the window period. Since the time difference between this reference pulse and the register mark pulse determines the error period for the ribbon control nip in that cycle of operation, it will be evident that the phase (or timing) adjustment provided by the stepping motor 128 provides a correction for the velocity of each ribbon control nip in response to the detected misregistration of the gathered ribbons just before they pass between the perforating cylinders.

While a presently preferred embodiment of this invention has been described in detail with reference to the accompanying drawings, it is to be understood that various modifications, omissions and adaptations which depart from the disclosed embodiment may be adopted without departing from the scope of the invention, as defined in the appended claims.

Claims

1. A registration control system for a web member passing through a control nip and from there into a cyclically operated mechanism, said system comprising: variable speed drive means operatively associated with the control nip to control its velocity; sensing means operatively associated with the web member for sensing any positional error of the advancing web member with respect to the cyclic operation of said mechanism; and correction means operatively associated with said variable speed drive means to vary the speed of the control nip substantially in accordance with an error factor equal to ##SPC4##, where E.sub.n is the detected positional error of the web member in the present cycle of operation of said mechanism; and is the summation of the positional errors of the web member in previous cycles of

2. A registration control system according to claim 1, wherein said correction means comprises a first counter for maintaining a count of a second counter for receiving a count of 2E.sub.n during each cycle of operation of said cyclically operated mechanism and for receiving the count stored in said first counter, and means for resetting said second counter after each cycle of operation of said cyclically operated

3. A registration control system for a plurality of printed web ribbons passing through respective individual control nips and from there into superimposed relationship and thereafter into a cyclically operated mechanism, said system comprising: variable speed drive means operatively associated individually with the respective control nips to control individually the velocity of each control nip; sensing means operatively associated individually with each web ribbon for sensing any positional error of the advancing ribbon with respect to the cyclic operation of said mechanism; and correction means operatively associated with each variable speed drive means individually to vary the speed of the respective control nip substantially in accordance with an error factor equal to ##SPC5## where E.sub.n is the detected positional error of the respective ribbon in the present cycle of operation of said mechanism, and is the summation of the positional errors of the respective ribbon in previous

4. A registration control system according to claim 3, wherein said variable speed drive means for each control nip comprises a differential and a stepping motor for varying the output speed of the differential in

5. A registration control system according to claim 3, wherein said correction means comprises a first counter for maintaining a count of a second counter for receiving a count of 2E.sub.n during each cycle of operation of said cyclically operated mechanism and for receiving the count stored in said first counter, and means for resetting said second counter after each cycle of operation of said cyclically operated

6. A registration control system for a plurality of printed web ribbons, each having printed areas in succession along its length which are separated by spaces having a register mark therein, said control system comprising: A plurality of pairs of confronting rollers providing control nips for the respective web ribbons; A variable speed drive means operatively associated individually with each control nip to control the latter's velocity; Means operatively associated individually with each web ribbon ahead of the respective control nip therefor for maintaining a substantially constant tension on said web ribbon; sensing means positioned near each control nip for sensing the movement past it of each register mark on the respective web ribbon and for producing a register mark pulse in response to said sensing of a register mark; gathering cylinders located after said control nips and operatively associated with the web ribbons to urge the latter into superimposed relationship; a cyclically operated mechanism located after said gathering cylinders and operatively associated with the superimposed web ribbons to act on the latter at said spaces between the printed impressions; means operated in timed relationship with the cyclic operation of said mechanism for producing a reference pulse at a predetermined point in each cycle of operation of said mechanism; means for comparing the timing of said register mark pulse and said reference pulse to determine any positional error of the respective register mark on the web ribbon with respect to the cyclic operation of said mechanism; and correction means operated by said last-mentioned means and operatively associated with each control nip drive means individually to vary the speed of the respective control nip substantially in accordance with an error factor equal to ##SPC6##, where E.sub.n is the detected positional error of the register mark on the respective ribbon in the present cycle of operation of said mechanism, and is the summation of the positional errors of the register marks

7. A registration control system according to claim 6, and further comprising a first counter connected to receive E.sub.n error pulses during each cycle of operation and operative to maintain a count of the summation of all the error pulses for previous cycles of operation, a second counter for receiving during each cycle of operation both the count stored in the first counter at the end of the preceding cycle of operation and 2E.sub.n error pulses for the present cycle of operation, and means for resetting said second counter at the end of each cycle of operation.

8. A registration control system according to claim 7, and further comprising means for passing a series of correction pulses to said correction means, and means for subtracting said correction pulses from

9. A registration control system according to claim 8, and further comprising means for blocking said correction pulses from said correction

10. A registration control system according to claim 8, wherein said first and second counters receive their respective counts during the interval in each cycle of operation while said space between successive printed areas on the respective ribbon is moving past said means for sensing the

11. A registration control system according to claim 10, wherein the correction pulses reduce the count stored in said second counter while a printed area on the respective ribbon is moving past said means for

12. A registration control system for a plurality of printed web ribbons passing through respective individual control nips and from there into superimposed relationship and thereafter into a cyclically operated mechanism, said system comprising: variable speed drive means operatively associated individually with the respective control nips to control individually the velocity of each control nip; sensing means operatively associated individually with each web ribbon near the respective control nip for sensing any positional error of the advancing ribbon thereat with respect to the cyclic operation of said cyclically operated mechanism; correction means controlling each variable speed drive means individually and operable in response to said sensing means to vary the speed of the respective control nip; additional sensing means operatively associated with one of the web ribbons near said cyclically operated mechanism for sensing a positional error of the superimposed ribbons with respect to the cyclic operation of said mechanism; and means operated by said additional sensing means for varying the operation of said correction means for each variable speed drive means in accordance

13. A registration control system according to claim 12, wherein said correction means varies the speed of the respective control nip substantially in accordance with an error factor equal to ##SPC7##, where E.sub.n is the detected positional error of the respective ribbon in the present cycle of operation of said cutoff mechanism, and is the summation of the positional errors of the respective ribbon in

14. A registration control system according to claim 12, and further comprising means for preventing said last-mentioned means from varying the operation of said correction means except during certain cycles of

15. A registration control system according to claim 14, and further comprising means for preventing said means operated by said additional sensing means from varying the operation of said correction means except when said positional error of the superimposed web ribbons exceed a

16. A registration control system for a plurality of printed ribbons passing into superimposed relationship and thereafter into a cyclically operated mechanism, said system comprising: means operatively associated individually with the respective ribbons to control individually the velocity of each of the ribbons; sensing means operatively associated individually with each ribbon for sensing any positional error of the advancing ribbon with respect to the cyclic operation of said mechanism; means for determining for each of the ribbons an error factor which includes a summation of the positional errors of the respective ribbon in previous cycles of operation of the mechanism; and correction means operatively associated with each ribbon individually for varying the speed of the respective ribbon in accordance with said error factor which includes a summation of the positional errors of the

17. A registration control system according to claim 16, wherein each ribbon has a plurality of successive printed areas with spaces therebetween having a registration mark therein, and said sensing means for each ribbon comprises: means for sensing the passing of a register mark on the respective ribbon and for producing a register mark pulse in response thereto; means operated in response to the cyclic operation of said mechanism for producing a reference pulse at a predetermined point in the latter's cycle of operation; and and means for determining the magnitude of the detected positional error of each ribbon for each cycle of operation said mechanism in accordance with the time difference between said register mark pulse and said reference

18. A registration control system according to claim 17, wherein said last-mentioned means comprises a normally closed gate circuit, means for opening said gate circuit in response to either said register mark pulse or said reference pulse and for closing the gate circuit in response to the other of said pulses, and means for producing a series of pulses whose frequency is proportional to the speed of said cyclically operated mechanism and for applying said last-mentioned pulses to said gate circuit

19. A registration control system according to claim 18, wherein said means for producing a series of pulses comprises a tachometer driven by said cyclically operated mechanism for producing a voltage proportional to the speed of the cyclic operation of said mechanism, and a voltage-to-frequency converter operated by said tachometer to generate said series of pulses at a frequency proportional to the voltage produced

20. A registration control system according to claim 16, wherein said error factor further includes at least the detected positional error of the respective ribbon in the present cycle of said mechanism, and said correction means includes a first counter for maintaining a count of the summation of the positional errors of the respective ribbon in previous cycles of operation of said mechanism, a second counter for receiving a count of at least the detected positional error of the respective ribbon in the present cycle of said mechanism during each cycle of operation of said cyclically operated mechanism, and means for resetting said second counter after each cycle of operation of said cyclically operated

21. A registration control system for a plurality of printed ribbons, each having printed areas in succession along its length which are separated by spaces having a register mark therein, said control system comprising: a plurality of rollers operatively associated with each ribbon to control the velocity of the associated ribbon; sensing means positioned near each of the respective ribbons for sensing the movement past it of each register mark on the respective ribbon and for producing a register mark pulse in response to said sensing of a register mark; gathering cylinders located after said rollers and operatively associated with the ribbons to urge the latter into superimposed relationship; a cyclically operated mechanism located after said gathering cylinders and operatively associated with the superimposed ribbons to act on the latter at said spaces between the printed impressions; means operated in timed relationship with the cyclic operation of said mechanism for producing a reference pulse at a predetermined point in each cycle of operation of said mechanism; means for determining for each of the ribbons an error factor which includes at least the detected positional error of the register mark on the respective ribbon in the present cycle of operation of said mechanism and the summation of the positional errors of the register marks on the respective ribbon in previous cycles of operation; and correction means operated by said last-mentioned means and operatively associated with said plurality of rollers and each ribbon individually to vary the speed of the respective ribbons substantially in accordance with said error factor which includes the detected positional error of the register mark in the present cycle of operation of said mechanism and the summation of the positional errors of the register marks on the respective

22. A registration control system according to claim 21 wherein said correction means includes means for providing during each cycle of operation of said cyclically operated mechanism a series of correction pulses proportional to the speed of the cyclic operation of said mechanism and the timing difference between said registration mark pulse and said reference pulse, and means for changing the speed of the respective ribbon

23. A registration control system according to claim 22, wherein said means for providing the correction pulses includes a normally closed gate circuit, means for opening said gate circuit in response to either said register mark pulse or said reference pulse and for closing the gate circuit in response to the other of said pulses, and means for generating a series of pulses whose frequency is proportional to the speed of said cyclically operated mechanism and for applying said last-mentioned pulses to said gate circuit to pass through the gate circuit while the latter is

24. A registration control system according to claim 23, wherein said last-mentioned means comprises a tachometer driven by said cyclically operated mechanism for producing a voltage proportional to the speed of the cyclic operation of said mechanism, and a voltage-to-frequency converter operated by said tachometer to generate said series of pulses at

25. A registration control system according to claim 21, and further comprising means for varying the timing of said reference pulse with respect to the cyclic operation of said mechanism in accordance with a

26. A registration control system according to claim 21, and wherein said last-mentioned means is operative during only certain of the operating

27. A registration control system according to claim 21, and further comprising: additional sensing means between said gathering cylinders and said cyclically operated mechanism for sensing the movement past it of a register mark on one of the superimposed ribbons and for producing a register mark pulse in response to said sensing of said register mark; and means for comparing the timing of said last-mentioned register mark pulse and a fixed phase reference pulse produced in the corresponding cycle of operation of said mechanism to indicate the positional error of the

28. A registration control system according to claim 21, and further comprising means for providing error pulses during each cycle of operation of said cyclically operated mechanism, said means for determining an error factor including a first counter connected to receive error pulses corresponding to the detected positional error of the register mark on the respective ribbon during the present cycle of operation of said mechanism during each cycle of operation and operative to maintain a count of the summation of all the error pulses for previous cycles of operation, a second counter for receiving during each cycle of operation both the count stored in the first counter at the end of the preceding cycle of operation and error pulses corresponding to at least the detected positional error of the register mark on the respective ribbon for the present cycle of operation, and means for resetting said second counter at the end of each

29. A registration control system according to claim 21, 21 and further comprising means operative in accordance with said positional error of the gathered ribbons for varying the timing of the reference pulses which are compared with the register mark pulses to control the individual speeds of

30. A registration control system for a plurality of printed ribbons, each having printed areas in succession along its length which are separated by spaces having a register mark therein, said control system comprising: a plurality of pairs of confronting rollers providing control nips for the respective web ribbons; a variable speed drive means operatively associated individually with each control nip to control the latter's velocity; means operatively associated individually with each web ribbon ahead of the respective control nip therefor for maintaining a substantially constant tension on said web ribbon; sensing means positioned near each control nip for sensing the movement past it of each register mark on the respective web ribbon and for producing a register mark pulse in response to said sensing of a register mark; gathering cylinders located after said control nips and operatively associated with the web ribbons to urge the latter into superimposed relationship; a cyclically operated mechanism located after said gathering cylinders and operatively associated with the superimposed web ribbons to act on the latter at said spaces between the printed impressions; means operated in timed relationship with the cyclic operation of said mechanism for producing a reference pulse at a predetermined point in each cycle of operation of said mechanism; means for comparing the timing of said register mark pulse and said reference pulse to determine any positional error of the respective register mark on the web ribbon with respect to the cyclic operation of said mechanism; correction means operated by said last-mentioned means and operatively associated with each control nip drive means individually to vary the speed of the respective control nip as a function of the detected positional error of the register mark on the respective ribbon, additional sensing means between said gathering cylinders and said cyclically operated mechanism for sensing the movement past it of a register mark on one of the superimposed web ribbons and for producing a register mark pulse in response to said sensing of said register mark; and means for comparing the timing of said last-mentioned register mark pulse and a fixed phase reference pulse produced in the corresponding cycle of operation of said mechanism to indicate the positional error of the

31. A registration control system according to claim 30, and further comprising means operative in accordance with said positional error of the gathered ribbons for varying the timing of the reference pulses which are compared with the register mark pulses to control the individual speeds of

32. A registration control system according to claim 31, and further comprising means for preventing said last-mentioned means from changing the timing of said last-mentioned reference pulses with respect to the cyclic operation of said mechanism except when said positional error of

33. A registration control system according to claim 31, and further comprising means for preventing said last-mentioned means from varying the timing of said reference pulses except during certain cycles of operation

34. A registration control system according to claim 3, and further comprising means for preventing the variation of the timing of said reference pulses with respect to the cyclic operation of said mechanism except when said positional error of the gathered ribbons exceeds a

35. A registration control system for registering a plurality of ribbons relative to a cyclically operated mechanism, said system comprising means for providing a first reference signal having a predetermined relationship with a cycle of operation of the mechanism, sensor means for providing a plurality of registration signals each of which is associated with one of the ribbons when the associated ribbons is in a predetermined position relative to the mechanism, first control means for detecting an error in the position of any one of the ribbons relative to the mechanism in response to a relationship between said first reference signal and a registration signal associated with said one of the ribbons and for effecting a change in the position of said one of the ribbons relative to the mechanism in response to the detecting of an error in the position of said one of the ribbons relative to the mechanism, means for providing a second reference signal having a predetermined relationship with the cycle of operation of the mechanism, second control means for detecting an error in the position of at least one of the ribbons relative to the mechanism in response to a relationship between a registration signal associated with that ribbon and said second reference signal, and means for varying the predetermined relationship between said first reference signal and the cycle of operation of the mechanism in response to the detection by said second control means of an error of a predetermined magnitude in the position of at least one of the ribbons relative to the mechanism to thereby vary the relationship between said first reference signal and said

36. A registration control system as set forth in claim 35 wherein said first control means includes a plurality control nips each of which is for operating on an associated one of the ribbons, said sensor means including first sensor elements each of which is associated with one of the ribbons and is operable provide a registration signal which said first control means relates to said first reference signal to detect error in the position of the associated ribbon relative to the mechanism and a second sensor element which is associated with one of the ribbons at a location along the ribbon which is closer to the mechanism than said control nips, said second sensor element being operable to provide a registration signal which said second control means relates to said second reference signal to detect error in the position of the ribbon which said second sensor element is associated after this ribbon has passed through an associated

37. A registration system as set forth in claim 36 wherein said first control means further includes variable speed drive means operatively associated with said control nips for individually controlling the velocity of the associated ribbons at each of said control nips and correction means operatively associated with said variable speed drive means to individually vary the speed of said control nips substantially in accordance with an error factor equal to where E.sub.n is the detected error in the position a ribbon in the present cycle of operation of the mechanism, and is the summation of the positional errors of a ribbon in previous cycles of operation of the mechanism.