US3724733A

US3724733A - Web infeed mechanism

Info

Publication number: US3724733A
Application number: US00223187A
Authority: US
Inventors: R Schaffer; J Crum
Original assignee: Harris Intertype Corp
Current assignee: Harris Graphics Corp
Priority date: 1972-02-03
Filing date: 1972-02-03
Publication date: 1973-04-03
Anticipated expiration: 1990-04-03
Also published as: FR2170775A5; DE2305249C2; JPS5712776B2; JPS4883907A; CA993000A; DE2305249A1

Abstract

An improved web infeed mechanism feeds a web of material to receiving rolls of a printing press and includes a web drive roll which is driven from the main press driveline through a chain drive assembly and harmonic drive unit. A hollow dancer roll is pivotally mounted on a pair of support arms and is pressed with a constant pressure against a bight portion of a U-shaped loop in the web by a pair of air cylinders. Upon movement of the hollow dancer roll from an initial position, a resilient member is flexed to change the resistance of a plurality of strain gauges on the resilient member. This results in a change in an output signal from a circuit containing the strain gauges and which signal is utilized to activate control apparatus to vary the peripheral speed of the web drive roll. This control apparatus includes a reversible permanent magnet control motor which is connected by a belt drive to a wave generator in the harmonic drive unit. To provide for an accurate response at different press speeds, the control apparatus also includes a tachometer which provides a signal which is directly proportional to the speed of rotation of the receiving rolls. This signal is multiplied by the signal from the strain gauges to provide an output signal which is utilized to energize the permanent magnet motor and vary the peripheral speed of the web drive roll upon movement of the dancer roll or a change in press speed.

Description

United States Patent 1 Schaffer et al. v

3,724,733 Apr. 3, 1973 [54] WEB INFEED MECHANISM [75] Inventors: Robert H. Schafier, Mystic; James N. Crum, Stonington, both of Conn.

[73] Assignee: Harris-Intertype Corporation,

Cleveland, Ohio [22] Filed: Feb. 3, 1972 [21] Appl. No.: 223,187

[52] U.S. Cl. ..226/25, 226/42, 226/44 [51] Int. Cl. ..B65h 23/18 [58] Field of Search ..226/42, 44, 30, 31, 111, 2, 226/4, 25

[56] References Cited UNITED STATES PATENTS 3,539,085 ll/l970 Anderson ..226/25 3,322,315 5/1967 Eberlin ....226/44 3,087,663 4/196-3 Anderson ....226/42 3,680,753 8/1972 Stewart ..226/25 Primary Examiner-Allen N. Knowles Assistant Examiner-Gene A. Church Attorney-J. Herman Yount, Jr. et al.

[57] ABSTRACT An improved web infeed mechanism feeds a web of material to receiving rolls of a printing press and includes a web drive roll which is driven from the main press driveline through a chain drive assembly and harmonic drive unit. A hollow dancer roll is pivotally mounted on a pair of support arms and is pressed with a constant pressure against a bight portion of a U- shaped loop in the web by a pair of air cylinders. Upon movement of the hollow dancer roll from an initial position, a resilient member is flexed to change the resistance of a plurality of strain gauges on the resilient member. This results in a change in an output signal from a circuit containing the strain gauges and which signal is utilized to activate control apparatus to vary the peripheral speed of the web drive roll. This control apparatus includes a reversible permanent magnet control motor which is connected by a belt drive to a wave generator in the harmonic drive unit. To provide for an accurate response at different press speeds, the control apparatus also includes a tachometer which provides a signal which is directly proportional to the speed of rotation of the receiving rolls. This signal is multiplied by the signal from the strain gauges to provide an output signal which is utilized to energize the permanentmagnet motor and vary the peripheral speed of the web drive roll upon movement of the dancer roll or a change in press speed.

15 Claims, 7 Drawing Figures M Lu a 7 /94 M0 TOR C/RCd/T I I .i Car/r1204 PAIENTHH-Pm 1m SHEET 4 UF 4 mWY - WEB INFEED MECHANISM This invention relates generally to a web infeed assembly, and more particularly to a web infeed assembly for maintaining a constant tension in a web advanced toward receiving rolls of a printing press.

It is desirable to maintain a constant tension in a web being advanced to a printing press, as is well known. Tension changes frequently occur due to operation of the system, web inconsistencies, etc. There are many known web infeed mechanisms which control the tension in a web fed to a printing press so as to maintain a constant tension in the web. Several of these web infeed mechanisms are shown in US. Pat. Nos. 3,539,085; 3,322,315; and 3,087,663.

The present invention also provides a web feed mechanism which readily operates to maintain a constant tension in the web. The web feed mechanism of the present invention includes a web feed mechanism of the present invention includes a web drive roll which is driven by a harmonic drive and a pivotally mounted dancer roll which is pressed against a bight portion of a variable length loop of the web with a constant pressure. A sensor means senses changes in the position of the dancer roll and activates a control means to' effect operation of the harmonic drive to vary the speed of the web drive roll in response to a sensing by the sensor means of a change in the position of the dancer roll.

The dancer roll of the present invention is hollow and is pressed against the web with a constant pressure.

FIG. 3 is an enlarged fragmentary illustration, taken along the line ,3-3 of FIG. 2, depicting the relationship between the web drive roll, harmonic drive unit, and a roll for pressing the web against the web drive roll;

FIG. 4 is a sectional view, taken generally along the line 4-4 of FIG. 3, further illustrating the construction of the harmonic drive unit;

FIG. 5 is an elevational view, taken along the line 5 5 of FIG. 2, illustrating-the relationship between a hollow dancer roll and an apparatus for sensing changes in the position of the dancer roll;

FIG. 6 is a plan view, taken generally along the line 66 of FIG. 2, illustrating a pivotal support apparatus for the hollow dancer roll; and

FIG. 7 is a schematic illustration of control circuitry for effecting operation of the harmonic drive to vary the speed of the web drive roll as a function of variations in the speed of the press rolls and the position of the dancer roll.

An improved web infeed apparatus 20 maintains a substantially constant tension in a portion 22 of a web 23. The constant tension portion 22 of the web 23 extends from the infeed apparatus 20 to receiving or intake rolls 24 and 26 of a printing press. The web infeed apparatus 20 (see FIG. 2) includes a steel drive roll 36 Due to this construction, the dancer roll tends to isolate tension changes on the input side thereof so that they are not transferred to the output side thereof. Moreover, the dancer is mounted in such a way that there is a minimum tendency thereof to skew. Specifically, the dancer is mounted on a pair of pivoted spaced arms which when they pivot operate at least one strain gauge which in turn controls circuitry for actuating a motor to operate the harmonic drive.

The signal from the strain gauge varies as a function of the extent and direction of movement of the dancer roll from an initial position upon a variation in the length of the loop and is applied to a motor control circuit. A second signal which varies as a direct function of variations in the speed of receiving rolls in the printing press is alsoapplied to the circuit. The motor control circuit provides an output signal which varies as a function of the product of the first and second signals.

This output signal (product signal) is applied to the motor for controlling the harmonic drive and the speed of the web drive roll.

These and other features of the present invention will become more apparent upon a consideration of the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic illustration depicting the relationship between a web supply roll, a web infeed ap paratus constructed in accordance with the present invention, and receiving rolls of a printing press;

' FIG. 2 is a schematic illustration of the web infeed apparatus of FIG. 1 depicting the relationship between a web drive roll, dancer roll, and control apparatus for effecting operation of a harmonic drive unit to vary the speed of the web drive roll in response to movement of i the dancer roll;

which feeds the web 23 to a U-shaped loop 38 having a bight portion 40 which is engaged by a hollow dancer roll 42. The hollow dancer roll 42 is pressed against the web 23 with a constant pressure and moves up and down about a support 44 upon a variation in the length of the loop 38.

To maintain the length of the loop 38 substantially constant, a sensor 48 is operated to provide a control signal to a motor control circuit 52 in response to movement of the dancer roll 42 from a central position. The motor control circuit 52 energizes a reversible permanent magnet control motor 56 to activate a belt drive 58 and operate a wave generator 60 (FIG. 4) in a harmonic drive unit 62 (FIG. 2). The harmonic drive unit 62 has an input member 66 (FIG. 3) which is driven by a chain drive 70 from a main press drive shaft 74 (FIG. 2). Actuation of the wave generator 60 by operation of the permanent magnet motor 56 in either a forward or reverse direction increases or decreases the rotational speed of the web drive roll 36 to maintain the length of the loop 38 substantially constant.

The web drive roll 36 (FIG. 2) is normally driven from the main press drive shaft 74 through the chain 70 and theharmonic drive unit 62 at a peripheral speed which is less than the peripheral speed of the web receiving rolls 24 and 26 of the printing press. This difference in peripheral speeds is sufficient to maintain the web in tension between the drive roll 36 and receiving rolls 24 and 26. However, due to variations in operating conditions and in the physical characteristics of the web 23, it is impossible to maintain a constant tension in the length 22 of the web 23 for an extended period of time while maintaining the peripheral speed of the web drive roll 36 constant. Therefore, the drive roll 36 is driven from the main press drive shaft 74 through the harmonic drive unit 62 which can be activated to vary the speed of rotation of the web drive roll 36 by operation of motor 56.

The input element 66 (FIGS. 3 and 4) of the harmonic drive unit 62 is drivingly connected with the press drive shaft 74 by a power take-off unit 80 and a chain 82. The chain 82 drives a sprocket 84 (FIG. 3) which is integrally formed with the harmonic drive input member 66. During operation of the printing press the chain 82 drives the sprocket 84 and input member 66 at a speed which is directly proportional to the speed at which the intake rolls 24 and 26 of the printing press are driven. The input member 66 to the harmonic drive unit 62 is positively driven by the chain 82 without undue play or slippage to provide a positive drive ratio between the press drive shaft 74 and the input member 66. The input member 66 has internal gear teeth 66a which mesh with external teeth 88a on an output member 88 which is a flexible strain or spline gear. The output member 88 is fixedly attached to the roll 36 by suitable means to effect rotation of the roll 36 upon rotation of the member 88.

During operation of the web infeed apparatus 20, the web 23 will stretch or deform to an extent which depends upon the operating conditions, physical characteristics of the web and the level of tension maintained in the web. Therefore, it is necessary to make adjustments in the speed at which the web drive roll 36 is driven. These adjustments are made by rotating the flexible strain or spline gear 88 (FIGS. 3 and 4), which is fixedly connected to the web drive roll 36, relative to the input member 66 by rotation of the wave generator 60 relative to the gear 88. The wave generator 60 includes a strain inducer 94 having a generally elliptical configuration and disposed within the flexible strain or spline gear 88. Upon rotation of the strain inducer 94 in a clockwise direction (as viewed in FIG. 4), the output member 88 moves in a counterclockwise direction relative to the input member 66 to retard rotation of the web drive roll 36 relative to the press rolls 24 and 26 to thereby decrease the length of the U-shaped loop 38. Of course, rotating the strain inducer in a counterclockwise direction advances the output member 88 relative to the input member 66 to advance the web 23 relative to the press rolls 24 and 26 to thereby increase the length of the loop 38. The construction and operation of the harmonic drive unit 62 is the same as is fully described in US. Pat. No. 2,906,143 and that disclosure is incorporated herein by reference, and therefore the harmonic drive unit will not be further described herein to avoid prolixity of description.

The strain inducer 94 is rotated relative to the flexible output or strain gear 88 by operation of the reversible permanent magnet control motor 56 (FIG. 3). The control motor 56 is connected with the strain inducer 94 through the drive train 58 which includes a flexible belt 100 extending from an output pulley 104 of the motor 56. The belt 100 engages a pulley 108 which is fixedly mounted on a shaft 110 which is keyed to the strain inducer 94. Therefore, rotation of the output pulley 104 by the reversible motor 56 drives a strain inducer 94 to either advance or retard rotation of the web drive roll 36.

As noted above, the drive ratio between the press drive shaft 74 and the web drive roll 36 is such that normally the peripheral speed of the web drive roll is slightly less, in the specific preferred embodiment of the invention approximately 0.27 percent less, than the peripheral speed of the press intake rolls 24 and 26. Therefore, the web 23 is maintained in tension between the press rolls 24 and 26 and the web drive roll 36. The natural resiliency of the web 23 provides a slight stretching action so that the difference in the peripheral speed of the press rolls 24 and 26 and web drive roll 36 does not result in web breakage and such differential is common.

To prevent slippage between the web 23 and drive roll 36, the web is pressed against the peripheral surface of the steel drive roll by a rubber-covered pressure roll 116 which is continuously urged toward the web drive roll 36 by a pair of biasing cylinders 120 (only one of which is shown in FIG. 3). The biasing cylinders 120 are connected to opposite ends of a central shaft 122 which extends axially through the hollow cylindrical pressure roll 116. The pressure roll 116 is rotatably supported on the shaft 122 by bearing assemblies 124. It should be understood that although only the lefthand ends of the web drive roll 36 and pressure cylinder 120 have been shown in FIG. 3, the opposite ends of the web drive roll and pressure cylinder are mounted in the same manner as are the left-hand ends. Of course, the mounting of the opposite end of the web drive roll 36 is simplified, since a harmonic drive unit is not associated with that end of the web drive roll.

The dancer roll 42 is continuously pressed against the bight portion 40 of the U-shaped loop 38 by a pair of diaphragm type air cylinders and 132 (FIG. 5). The air cylinders 130, 132 are connected to a constant pressure source of air, such. as an accumulator tank having a pressure regulator valve. The air pressure to which the cylinders 130 and 132 are exposed is adjustable to adjust the amount of tension which is maintained in the constant tension portion 22 of the web 23.

Due to changing operating conditions and physical characteristics of the web 23, the length of the loop 38 varies during operation of the web infeed unit 20. Therefore, the dancer roll 42 moves vertically about the support shaft 44 from the illustrated centered or initial position of FIG. 2 as the length of the loop 38 changes. The dancer roll 42 is relatively light in weight and comprises a hollow steel cylinder 138 (FIG. 5) which is rotatably mounted by bearings 142 and 144 on a shaft 146 having a central axis which is coincident with the central axis of the hollow steel cylinder. The hollow cylinder 138 is provided with an exterior layer 152 of rubber to prevent slippage between the web and the dancer roll 42. This construction of the dancer roll 42 makes it relatively light in weight so that the web infeed mechanism 20 has a relatively high natural frequency. The relatively high natural frequency of the web infeed mechanism 20 results in high frequency tension fluctuations being induced in the web 23. These high frequency tension fluctuations are attenuated to a substantial extent by spans of the web 23. In addition, the relatively light dancer roll 42 enables the cylinders 130 and 132 to provide a relatively low pressure against the support shaft 146 to tend to minimize undesirable tension fluctuations in the web 23. Moreover, due to the hollow construction of the dancer roll, it operates to substantially isolate any tension change in the input part of loop 38 from the output part of loop 38. This can be shown mathematically due to the location of the radius of gyration of the dancer relative to the periphery of the roll.

The dancer roll 42 is advantageously mounted for pivotal movement about the support shaft 44 (see FIGS. 5 and 6). Thus, when

piston rods

156 and 158 of the cylinders 130 and 132 are extended or retracted, the dancer roll 42 moves through a small portion of an arc of a circle having its center coaxial with the longitudinal axis of the support shaft 44. The dancer roll 42 is connected with the support shaft 44 by a pair of

arms

162 and 164 which are fixedly connected to the center shaft 146 and are keyed to the support shaft 44. These spaced arms minimize skewing of the dancer roll 42. The support shaft 44 is rotatably mounted in bearings 166 and 168 (FIG. 6) disposed' in side frame members 170 and 172. Therefore, the dancer roll 42 is free to pivot about the longitudinal axis of the support shaft 44 upon movement of the dancer roll from the central or initial position of FIG. 2.

As noted above, upon a tension change in the web,

the dancer roll 42 moves vertically in either the upward or downward direction, depending upon whether the tension increases or decreases. Upon such movement, the harmonic drive unit 62 is operated to vary the peripheral speed of the drive roll 36 and the rate at which the web 23 is fed into the loop 38. Thus, when the dancer roll 42 moves downwardly from the initial position of FIG. 2, the motor 56 is operated in a forward direction to drive the wave generator 60 and increase the peripheral speed of the drive roll 36. Of course, this increases the rate at which the web 23 is fed to the loop 38 and the length of the loop so that the air cylinders 130 and 132 can move the dancer roll 42 upwardly. Similarly, if the dancer roll 42 moves upwardly from the illustrated initial position of FIG. 2, the motor 56 is operated in a reverse direction to drive the wave generator 60 to decrease the peripheral speed of the drive roll 36 and the rate at which the web is fed to the loop 38. This decreases the length of the loop 38 to pull the bight portion 40 of the loop downwardly against the constant tensioning force applied against the web 23 by the cylinders 130 and 132. The present system is distinguished from one in which a motor is operated in a continuous manner at high speeds to control web infeed speed. In a system in which web speed is controlled by a motor which operates continuously, excessive wear of the parts occurs and high speeds are required of the motor in order to correct for web tension changes as compared to the present system which can correct for web tension and loop length changes with motor speeds at a lower level and which may also operate without the necessity of continuous operation of the correcting drive mechanism. I

While, as noted, the dancer roll 42 has an initial or a neutral position and moves in one direction therefrom, the motor 56 is energized in one direction and if it moves in the other direction therefrom, the motor 56 is energized in the reverse direction. The motor 56 is also a variable speed motor so that the farther the dancer moves the greater the speed of the motor. Also, if the dancer is in a given actuated position and moves therefrom, the motor speed may change without the motor reversing its direction of operation.

If the operating conditions and physical characteristics of the web 23 happen to be such that when the tension in the web is at the desired level and the web stretches to such an extent that the speed differential between the web drive roll 36 and press drive rolls 24 and 26 maintains the desired tension, the reversible permanent magnet control motor is not energized and the drive rolls 36 would be driven under the influence of forces transmitted only from the press drive shaft 74. However, it is contemplated that under many operating conditions when the desired tension is applied to certain webs, they will stretch to such an extent that it will be necessary to reduce the peripheral speed of the main drive roll 36 relative to the press rolls 24 and 26. Under these operating conditions, the reversible motor 56 will be continuously operated in the reverse direction to continuously activate the wave generator 60 in the harmonic drive unit 62 to retard rotation of the drive roll 36. It is also contemplated that certain webs will be relatively inelastic and the peripheral speed of the web drive roll 36 will have to be increased relative to the peripheral speed .of the press drive rolls 24 and 26. Under these operating conditions, the reversible motor 56 will be continuously operated in the forward direction to drive the wave generator 60 and increase the peripheral speed of the web drive roll 36. It should be noted that the differential in speed between the web drive roll 36 and press rolls 24 and 26 enables the various webs to be maintained in tension without operating the wave generator 60 at excessive speeds. In addition, the web drive roll 36 enables different values of tension to be maintained depending upon the conditions of press operation.

The harmonic drive unit 62, as noted, is operated from the sensor assembly 48 which senses the positionto which the dancer roll 42 moves under the influence of a predetermined constant force applied to the dancer roll by the air cylinders and 132. If the dancer roll 42 moves upwardly under the influence of the biasing force applied by the cylinders 130 and 132, the sensor assembly 48 will transmit an error signal to the motor control circuit 52 to effect continuous energization of the permanent magnet motor 56 in the reverse direction to reduce the peripheral speed of the web drive cylinder 36. Similarly, the web pulls the dancer roll 42 downwardly. The sensor assembly 48 will transmit a signal to the motor control circuit 52 to effect energization of the motor in the forward direction to increase the peripheral speed of the web drive roll 36.

The sensor assembly 48 detects the extent of movement of the dancer roll 42 from the illustrated center or neutral position of FIG. 2. Thus, as the length of the loop 38 is increased, the;dancer roll 42 moves upwardly and the sensor assembly 48 provides a signal to the motor control circuit 52 which is of a magnitude proportional to the extent of upward movement of the dancer roll. Similarly, if the length of the loop 38 is decreased, the sensor assembly 48 provides a signal of a magnitude which is proportional to the extent of downward movement of the dancer roll 42. The signal which'is indicative of upward movement of the dancer roll 42 causes the motor control circuit to provide a signal of a sign which is opposite from the sign of the signal which is indicative of downward movement of the dancer roll. Of course, the sign of the signal provided by the motor control circuit 52 determines the direction in which the motor 56 is operated. For example, upward movement of the dancer roll causes the sensor assembly 48'to provide a negative voltage signal to effect operation of the motor 56 in the reverse direction. In this example, downward movement of the dancer roll would cause the sensor assembly 48 to provide a positive voltage signal to effect operation of the motor 56 in the forward direction.

The sensor assembly 48 senses the position of the dancer roll 42 by sensing the extent to which a flexible sensor or spring element 180 (see FIGS. 2 and 4) is deflected by rotation of the shaft 44 as the dancer roll 42 moves from the initial position, illustrated in FIG. 2. Thus, when the dancer roll 42 is in the initial position, the spring member 180 is pressed against a stop 182 mounted on side frame 172 and is flexed to a predetermined extent. Upon downward movement of the dancer roll 42, the spring element 180 is flexed even further, since the support shaft 44 is rotated in a counterclockwise direction, as viewed in FIG. 2. Similarly, upon upward movement of the dancer roll 42, the support shaft 44 is rotated in a clockwise direction to decrease the extent to which the spring element 180 is flexed.

A plurality of strain gauges 184 are mounted on the spring element 180 and change in resistance upon a change in flexure of the member 180 to thereby vary an electrical signal transmitted to the motor control circuit 52. The strain gauges 184 are connected in a known bridge circuit 190 (see FIG. 7) which is balanced when the spring member 180 is flexed to an extent corresponding to the initial position of the dancer roll 42 (FIG. 2). Upon movement of the dancer roll 42 from the initial position, the resistance of the strain gauges 184 changes to a proportional extent. This enables the bridge circuit to provide an output signal which varies in magnitude to an extent which is proportional to movement of the dancer roll 42 from the initial position.

During operation of the infeed assembly 20, it is contemplated that the speed of operation of the associated printing press and the press rolls 24 and 26 will be varied by changing the rate of rotation of the main press drive shaft 74. Of course, this results in a change in the speed at which the web drive roll 36 is driven by the chain drive assembly 70 and harmonic drive unit 62. If the speed change signal provided by the motor control circuit 52 is a function only of the position of the dancer roll 42, the same speed change signal would be provided during both high and low speed movement of the web 23. Therefore, the time required for the motor 56 to retard or advance the peripheral speed of the web drive roll 36 would be the same for both high and low speed operation of the printing press. However, due to the relatively high speed of movement of the web 23, it is desirable during high speed press operation to increase the responsiveness of the motor 56 to a change in the position of the dancer roll 42.

To provide for increased responsiveness during high speed press operation, the motor control circuit 52 multiplies the signal from the sensor assembly 48 by a factor which varies as a direct function of changes in the speed of the press. This is effected by impressing a voltage across the bridge 190 (FIG. 7) which is proportional to the speed of rotation of the press drive shaft 74. To this end, a tachometer 194 is driven directlyrby the press drive shaft 74 so that the output voltage from the tachometer varies as a direct function or variations in the speed rotation of the drive shaft. Operation of the tachometer 194 results in the presence of a positive voltage level at the node 196 and a negative voltage level at the node 198. Therefore, the voltage at an output node 202 of the bridge circuit 190 varies in both magnitude and sign as a direct product of a signal indicating the press drive speed and another signal indicating dancer roll position. Since the resistance of the strain gauges 184 varies as a direct function of variations in the position of the dancer roll 42, the output voltage at the node 202 is function of both press speed and dancer roll position.

From the foregoing, it can be seen that when the press drive speed is being maintained constant and the dancer roll 42 is moved, the extent to which the spring member is flexed and the resistance of the strain gauges 184 varies in direct proportion to the extent of movement of the dancer roll. This results in an increase or a decrease in voltage at the output node 202 by an extent which is directly proportional to and of a sign which is determined by the extent and direction of movement of the dancer roll 42. Similarly, if the speed of the press is changed, the output voltage from the tachometer 194 will be changed by a corresponding extent to thereby vary the output voltage at the node 202 to the same extent. Since the voltage from the tachometer 194 is impressed across the bridge formed by the strain gauges 184, the voltage at the output node 202 will vary in both sign and magnitude as a function of the product of press speed and dancer roll position.

The output voltage at the node 202 can be expressed by the following equation:

e EkS Where:

e= the output voltage at the node 202 E the voltage provided by the press tachometer 194 across the nodes 196 and 198 k a gauge factor determined by the physical characteristics of the strain gauges 184 S deflection per inch of the spring member 180 Thus, the output voltage at the node 202 is the product of two factors. One of these factors varies as a function of variations in press speed. The other factor varies as a function of variations in the position of the dancer roll 42. A constant gain voltage amplifier 208 applies a voltage to the armature of the permanent magnet motor which is a function of the voltage at the node 202.

Due to the torque operating characteristics of the permanent magnet motor 56, a negative feedback is provided to obtain the desired torque from the motor. The torque as seen by the permanent magnet motor 56 can be expected to vary over a considerable range. Under certain operating conditions, the motor may actually be operating as a brake. The motor must thus be able to operate in all four quadrents of its speed torque characteristics. In order to insure that the motor delivers a speed proportional to the output voltage at the node 202, negative feedback is used. To provide this negative feedback, the output from a tachometer 212 driven by the permanent magnet 56 is transmitted through a resistor 214 to the summing junction of the Amplifier 208.

in view of the foregoing description, it can be seen that the web infeed assembly 20 includes a web drive roll 36 for feeding a web 23 to press or receiving rolls 24 and 26. The web drive roll 36 is driven by a harmonic drive unit 62 which has an input member 66 which is driven by a chain drive assembly 70 from the press drive shaft 74 at a speed proportional to the speed of rotation of the press rolls 24 and 26. A wave generator 60 has a strain inducer 94 which is operable to effect relative movement between an output member 88 of the harmonic drive unit 62 and the input member 66 to thereby vary the speed of output member 88 and web drive roll 36 relative to the speed of the press rolls 24 and 26.

To effect operation of the wave generator 60, a permanent magnet control motor 56 is energizable in either a forward or reverse direction to drive a belt 100 which is connected with the strain inducer 94 of the wave generator. The reversible motor 56 is energizable by motor control circuit 52 in response to movement of the hollow dancer roll 42 from the neutral position illustrated' in FIG. 2. Upon movement of the dancer roll 42 and a change in the length of the loop 38, the sensor assembly 48 detects the extent to which the dancer roll 42 is rotated about the support shaft 44 to provide a signal which is directly proportional to the extent of this movement. This signal is multiplied by a factor which is directly proportional to the speed of rotation of the press drive shaft 74 to provide an output voltage to the motor 56. This output voltage is the product of factors determined by the position of the dancer roll 42 and the speed of the press cyliners 24 and 26. Therefore, the output voltages causes the permanent magnet motor 56 to drive the wave generator 60 at a speed which is proportional to the product of press speed and dancer position to either advance or retard the peripheral speed of the web drive roll 36.

Having a specific preferred embodiment of the invention, the following is claimed:

1. An apparatus for feeding a web of material from a source to receiving rollers driven at a predetermined speed by a main drive mechanism, said apparatus comprising a web drive roll, a harmonic drive unit drivingly connected with said web drive roll, said harmonic drive unit including an input member driven by the main drive mechanism at a speed which is a direct function of the speed of the receiving rolls, an output member connected with said web drive roll and driven at a speed which is a function of the speed of said input member, and wave generator means drivingly connected with said output member and operable to vary the speed of said output member and web drive roll relative to said input member and receiving rolls, said apparatus further including motor means energizable in either a forward or a reverse direction to effect operation of said wave generator means to either increase or decrease the speed of said web drive roll relative to said receiving rolls to adjust the length of a variable length loop in the web, drive means for transmitting drive forces from said motor means to said wave generator means upon energization of said motor means in either the forward or reverse directions, dancer roll means disposed in engagement with a bight portion of the variable length loop at a location downstream of said drive roll and upsteam of the receiving rolls, arm means connected with said dancer roll means and extending transversely to a longitudinal axis of the variable length loop for supporting said dancer roll means for pivotal movement relative to said drive roll upon a change in the length of the loop, means for pressing said dancer roll means against the bight portion of the loop with a constant pressure to maintain a substantially constant tension in the web with variations in the length of the loop, sensor means connected with said arm means and said motor means for sensing changes in the position of said dancer roll means with variations in the length of the loop, and control means for effecting operation of said motor means to operate said wave generator means and vary the speed of said web drive roll relative to said receiving rolls in response to a sensing by said sensor means of a change in the position of said dancer roll means.

2. An apparatus as set forth in claim 1 wherein said dancer roll means includes a hollow cylinder and axially extending support means connected with said cylinder and said arm means for supporting said cylinder for rotation relative to said arm means.

3. An apparatus as set forth in claim 2 wherein said support means includes a shaft extending axially through said cylinder and bearing means for supporting said cylinder for rotation relative to said shaft, said arm means including first and second pivotally mounted arm members connected to opposite end portions of said shaft to support said cylinder for pivotal movement upon a change in the length of the loop, said means for pressing said dancer roll means against the bight portion of the loop including a first air cylinder connected with said first arm and a second air cylinder connected with said second arm and means for equalizing forces applied by said first and second air cylinders against said first and second arms to maintain said hollow cylinder in a predetermined orientation relative to the web as the length of the loop varies.

4. An apparatus as set forth in claim ll wherein said control means includes first signal generator means for supplying a first signal which varies as a function of variations in the speed of the receiving rolls, said sensor means including second signal generator means for supplying a second signal which varies as a function of variations in the length of the loop, said control means being connected with said first and second signal generator means and said motor means for effecting operation of said motor means at a speed which varies as a function of variations in a multiple of said first and second signals.

5. An apparatus as set forth in claim 1 wherein said sensor means includes a resiliently yieldable member, means for flexing said yieldable member to an extent which varies with pivotal movement of said dancer roll means, and strain gauge means connected with said yieldable member for providing an output signal which varies as a function of the extent to which said yieldable member is flexed in response to pivotal movement of said dancer roll means.

6. An apparatus as set forth in claim 1 further including chain drive means operatively connected with said main drive mechanism and said input member for driving said input member at the same speed as said receiving rollers.

7. An apparatus as set forth in claim 1 wherein said drive means includes first pulley means connected to said motor means, second pulley means connected to said wave generator means, and belt means for transmitting drive forces between said first and second pulley means.

8. An apparatus as set forth in claim 1 wherein said motor means includes a permanent magnet field winding and armature coil means for receiving a signal which varies as a function of variations in the length of the loop.

9. An apparatus for feeding a web of material from a source to receiving rollers driven at a predetermined speed by a main drive mechanism, said apparatus comprising a web drive roll, a harmonic drive unit drivingly connected with said web drive roll, said harmonic drive unit including an input member driven by the main drive mechanism at a speed which is a direct function of the speed of the receiving rolls, an output member connected with said web drive roll and driven at a speed which is a function of the speed of said input member, and wave generator means drivingly connected with said output member and operable to vary the speed of said output member and web drive roll relative to said input member and receiving rolls, said apparatus further including motor means for effecting operation of said wave generator means to either increase or decrease the speed of said web drive roll relative to said receiving rolls to adjust the length of a variable length loop in the web, drive means for transmitting drive forces from said motor means to said wave generator means, dancer roll means disposed in engagement with a bight portion of the variable length loop at a location downstream of said drive roll and upstream of the receiving rolls, said dancer roll means including a hollow cylinder disposed in engagement with the bight portion of the loop, a shaft extending axially through said hollow cylinder, and bearing means for rotatably supporting said hollow cylinder on said shaft, said apparatus further including means for pressing said hollow cylinder against the bight portion of the loop with a constant pressure to maintain a substantially constant tension in the web with variations in the length of the loop, sensor means for sensing changes in the position of said hollow cylinder with variations in the length of the loop, and control means for effecting operation of said motor means to operate said wave generator means and vary the speed of said web drive roll relative to said receiving rolls in response to a sensing by said sensor means of a change in position of said hollow cylinder.

10. An apparatus as set forth in claim 9 wherein said sensor means includes means for providing a signal which varies as a function of the direction of movement of said hollow cylinder from a predetermined position, said control means including means for effecting operation of said motor means in a forward direction in response to movement of said hollow cylinder in a first direction from the predetermined position and for effecting operation of said motor means in a reverse direction in response to movement of said hollow cylinder in a second direction from the predetermined position.

11. An apparatus as set forth in claim 9 wherein said sensor means includes a flexible member, means for flexing said member to an extent corresponding to the extent of movement of said hollow cylinder, and strain gauge means for providing an output signal which varies as a function of the extent to which said flexible member is flexed.

12. An apparatus as set forth in claim 9 further including first and second arm members fixedly connected with opposite end portions of said shaft and means supporting said arm members and hollow cylinder for rotation about a common axis extending parallel to and spaced apart from the longitudinal axis of said hollow cylinder.

13. An apparatus for feeding a web of material from a source to receiving rollers driven at a predetermined speed by a main drive mechanism, said apparatus comprising a web drive roll, a variable speed drive unit drivingly connected with said web drive roll, motor means energizable in either a forward or a reverse direction to effect operation of said variable speed drive unit to either increase or decrease the speed of said web drive roll relative to said receiving rolls to adjust the length of a variable length loop in the web, drive means for transmitting drive forces from said motor means to said variable speed drive unit upon energization of said motor means in either the forward or reverse directions, dancer roll means disposed in engagement with a bight portion of the variable length loop at a location downstream of said drive roll and upstream of the receiving rolls, means for pressing said dancer roll means against the bight portion of the loop with a constant pressure to maintain a substantially constant tension in the web with variations in the length of the loop, sensor means operatively connected with said dancer roll means for sensing changes in the position of said dancer roll means with variations in the length of the loop, said sensor means including first signal generator means for providing a first signal which varies as a function of the extent and direction of movement of said dancer roll means from an initial position upon a variation in the length of the loop, and control means connected with said sensor means and said motor means for effecting operation of said motor means to operate said variable speed drive unit to vary the speed of said web drive roll relatife to said receiving rolls, said control means including means for providing a second signal which varies as a function of variations in the speed of the receiving rolls, multiplier means for providing a third signal which is a direct function of the product of said first and second signals, and means for effecting operation of said motor means in response to said third signal.

14. An apparatus as set forth in claim 13 wherein said sigial generator means includes a flexible member, means for flexing said flexible member to an extent which is directly proportional to the extent of movement of said dancer roll means from the initial position, and strain gauge means for providing a resistance which varies as a function of the extent to which said flexible member is flexed.

15. An apparatus as set forth in claim 14 wherein said strain gauge means includes a plurality of strain gauges, and said multiplier means includes means for connecting said strain gauges in a bridge circuit and for imposing on said bridge circuit a voltage which varies as a function of variations in the speed of said receiving rolls.

Claims

4. An apparatus as set forth in claim 1 wherein said control means includes first signal generator means for supplying a first signal which varies as a function of variations in the speed of the receiving rolls, said sensor means including second signal generator means for supplying a second signal which varies as a function of variations in the length of the loop, said control means being connected with said first and second signal generator means and said motor means for effecting operation of said motor means at a speed which varies as a function of variations in a multiple of said first and second signals.

14. An apparatus as set forth in claim 13 wherein said signal generator means includes a flexible member, means for flexing said flexible member to an extent which is directly proportional to the extent of movement of said dancer roll means from the initial position, and strain gauge means for providing a resistance which varies as a function of the extent to which said flexible member is flexed.