US3575411A

US3575411A - Sheet feeding mechanism

Info

Publication number: US3575411A
Application number: US767167A
Authority: US
Inventors: Frank L Kastelic
Original assignee: Harris Intertype Corp
Current assignee: Harris Graphics Corp
Priority date: 1968-10-14
Filing date: 1968-10-14
Publication date: 1971-04-20
Anticipated expiration: 1988-04-20

Abstract

Sheet-sensing means senses when the lead edge of sheets moving in a stream to a register position from which they are fed to a sheet-processing machine pass a sensing location. If the sheets are late or early, the timing of mechanisms for separating sheets from the top of a pile and for forming and forwarding the stream is changed or the speed of the stream is adjusted in a direction to correct the out-of-time arrival of sheets.

Description

United States Patent Frank L. Kastelic Cleveland, Ohio Oct. 14, 1968 Apr. 20, 197 l llarris-lntertype Corporation Cleveland, Ohio Inventor Appl. No. Filed Patented Assignee snEET FEEDING MECHANISM 11 Claims, 4 Drawing Figs.

US. Cl Int. Cl

Field of Search .11. 271/50, 47, 46, 57, 60, 3s, 12, 3

[56 l References Cited UNITED STATES PATENTS 1,478,464 12/1923 Waters 27l/38UX 1,535,217 4/1925 Ehlig 271/38 Primary Examiner-Even C. Blunk Assistant Examiner-Joseph Wegbreit AttorneyYount, Flynn & Tarolli ABSTRACT: Sheet-sensing means senses when the lead edge of sheets moving in a stream to a register position from which they are fed to a sheet-processing machine pass a sensing location. if the sheets are late or. early, the timing of mechanisms for separating sheets from the top of a pile and for forming and forwarding the stream is changed or the speed of the stream is adjusted in a direction to correct the out-oftime arrival of sheets. I

Patented April 20, 1971 2 Sheets-Sheet 1 INVENTOR.

SHEE9T FAST FIG. I

F RANK L. KASTEL/C BY v W M ATTORNEYS Patented April 20, 1971 I 3,575,411

2 Sheets-Sheet 2 MANUAL PRESET IBIDIRECTIONAL E4 Y UN E Y /246 9 T R INVENTOR H64 FRANK L. KASTEL/C The present invention relates to a sheet-fed printing press or other sheet-processing machine in which a separating mechanism separates sheets from the top of the pile and forwards them one at a time to form a sheet stream with the sheets moving in succession to a register position where the sheets are registered and from which they are advanced to a sheet-processing machine such as a printing press.

in the operation of such a machine, it is preferable that the sheets arrive at the register position during an ontime portion of the cycle of operation of the machine. While some deviation from the ontime portion is permissible, if the sheet arrives sufficiently late or sufficiently early in the cycle it will not properly feed and conventionally the printing press will be tripped off and the feeding of sheets stopped until the condition leading to the late or early arrival of the sheet is corrected.

it is an object of the present invention to provide a new and improved sheet-feeding apparatus in which the movement of a sheet which is part of a sheet stream to a register position is sensed to determine whether the sheet is late or early in the cycle and if the sheet is not on time to advance or retard the sheet stream.

it is a further object of the present invention to provide a new and improved sheet-feeding apparatus in which the movement of a sheet to the registering position from which it is fed to the printing press is sensed to determine whether the sheet is arriving late or early with respect to the ontime portion of the cycle of the printing press and to change the timing of the mechanism for separating the sheet from the top of a pile and forwarding it to the register position if the sheet is behind or ahead of the ontime portion.

it is a further object of the present invention to provide a new and improved printing press and mechanism for feeding sheets thereto in which sheets are moved on a feedboard to a register position from which they are fed to the printing press by a variable feed mechanism whose rate of operation is controlled by sensing the movement of a sheet toward the register position and adjusting the variable speed mechanism to cause the mechanism to increase or decrease its speed depending upon whether the sheet is late or early.

Further objects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiment thereof made with reference to the accompanying drawings in which:

FlG. l is a diagrammatic view illustrating a preferred embodiment of the present invention as embodied in a printing press;

FIG. 2 is a cross-sectional view of a differential used in the system of lFlG. ll;

H6. 3 is a fragmentary view of a timing and pulse generating wheel used in the system of FIG. ll; and

lFlG. 41 is a diagrammatic view illustrating a different form of the present invention.

Referring to the drawings, H6. 1 schematically illustrates a printing press including a printing unit A and sheet-feeding mechanism embodying the preferred embodiment of the present invention. Sheets to be printed are separated one at a time from the top of a pile by conventional sheetseparating and forwarding mechanism llll comprising sheetseparating suckers 112 and sheet-forwarding suckers M. The separating mechanism may also include forwarding and separating air nozzles, one of which has been shown and designated with the reference numeral R5.

The top sheet is separated from the top of the pile by the sheet-separating suclters which transfer the sheet to the forwarding suckers M. The sheet-forwarding suckers 14 move the separated sheet to feed rolls to which receive the sheet from the forwarding suckers and forward it to a feedboard 18. The sheets form a stream and are moved down the feedboard ltd by conventional sheet-forwarding feed tape mechanism comprising a feed tape to a sheet register position at the forward end of die feedboard. The sheets are registered at the register position and are fed from the register position to a feed cylinder 21 by conventional feed rolls 22. The feed cylinder 21 conveys the sheet to an advance cylinder 24 which in turn conveys the sheet to an impression cylinder 26 of the printing unit A. The printing unit A is illustrated as comprising the impression cylinder 26 and aprinting cylinder 28 which may be a blanket cylinder or a plate cylinder. It will be understood that the present invention may be used with other sheet-processing machines, e.g. cutters and creasers.

The pile of sheets 10 is supported in a conventional pile elevator which operates to maintain the top of the pile at a level where the sheet-separating sucker 12 of the sheetseparating and forwarding mechanism may grip and separate the top sheet of the pile. The sheet-separating and forwarding mechanism for separating the top sheet of the pile and moving it to the feedboard llb is of conventional construction as well as the feed tapes 20 for moving the sheets down the feedboard. The sheets are registered at the forward end of the feedboard by conventional sheet-registering mechanism including front stops 30 for engaging and registering the leading edges of the sheets.

Preferably the sheets are fed from the top of the pile to the feedboard 1h so that they move down the feedboard in a conventional underlapped relationship. As the sheet moves down the feedboard, it is to arrive at the front stops 30 during an ontime interval in the machine cycle so that it will be registered and in position at the time in the cycle for the feed rolls 22 to forward it to the feed cylinder 21. If the sheet arrives at the front stops too early, the front stops which are reciprocated below the top of the feedboard when a sheet is fed from the register position to the feed cylinder may not be in proper position to stop and register the lead edge of the sheet. if the sheet arrives too late, it will not be properly fed to the feed cylinder 20 or it may not be fed at all. There is a portion of the cycle of the machine during which the sheet preferably arrives at the front stop 30 for proper feeding. If the sheet arrives during this portion of the machine cycle the sheet is said to be on time and no adjustment is necessary. If the sheet arrives ahead of this portion it is said to be early and if behind this portion it is said to be late. Nonnally sheets may arrive some late or early and still be properly registered and fed but it is desirable to make an adjustment to bring the arrival of sheets at the front stop into the ontime interval.

In accordance with the embodiment of the invention illustrated in H6. 1 the movement of sheets to the sheetregistering position on the feedboard w is sensed so that if the sheets are late or early in moving down the feedboard the sheet separating and forwarding mechanism may be adjusted.

In the illustrated embodiment, a drive motor 33 drives the printing unit A, the feed rolls 22 and the sheet-registering mechanism 30 including the front stops in timed relationship to each other. The feed and advance cylinders are intergeared with the impression, printing cylinder of the printing unit A. The drive motor 33 also drives a shaft 34 which in turn is connected through a differential 36 to drive the sheetseparating and forwarding mechanism and the feed tapes 20. The shaft M drives the ring gear of the differential mechanism 36 which has an output shaft 10 connected to drive the sheetforvvarding feed tapes 20 and to operate the sheet-separating and forwarding mechanism and the feed rolls 16 in timed relationship to each other through conventional drive mechanism. The differential mechanism 36 is shown in FIG. 2 and as shown therein the shaft 10 is aligned with a shaft d1 and the shafts have respective bevel gears Ml on their adjacent ends. The bevel gears mate with idler pinions 46 freely rotatable on a shaft db which is mounted along a diameter of a cage member 50. The cage member 50 has a ring gear 52 thereon which meshes with a pinion drive gear 51 on the shaft M. it can be seen that if the bevel gear M on the shaft 41 is held against rotation and the ring gear 52 and cage 50 rotated, the output shaft 4W will be driven in timed relationship to the ring gear $2. if the bevel gear Ml on the shaft 41 is also rotated the shaft 40 will be rotated at a faster or slower speed than it is with the gear stationary, depending on the direction of rotation of the shaft 41. The shaft 41 can be, therefore, rotated to advance or retard the shaft 34 in phase relative to the cycle of the printing unit A.

If the lead edge of the sheet moving to sheet register position at the forward end of the feedboard arrives at a sensing station S along the feed portion at a portion of the cycle that indicates that the sheet is early or late in its movement to the register position, the shaft 41 will be operated to advance or retard the sheet-separating and forwarding mechanism including the feed tapes to correct the timing of the sheet stream. 1f the sheet is late, the timing will be advanced and the feed tapes 20, when advanced, will advance the sheet and cause it to arrive earlier in the cycle then would have normally been the case. The advancing of the shaft 40 also causes the sheet-separating and forwarding suckers 12, 14 to operate in an earlier time in the cycle of the machine so that the subsequent sheets will be moved to the feedboard at an earlier adjusted time in the cycle.

The sheet-sensing station S may comprise a sensing device 54 as shown in US. Pat. No. 3,182,301 issued May 4, 1965 to Edwin R. Kolb. This patent discloses a sheet detector which may be used to detect the lead edge of a sheet as it moves by a position on the feedboard even though the sheet is covered by other sheets. The output from the sensing device 54 is applied to circuitry 53 fully disclosed in the patent for providing a pulse signal suitable for use in circuitry for determining the time of sheet arrival.

As illustrated in P16. 1, this pulse signal from the circuitry 53 is compared with a timing signal from a timing pulse generator 60. The timing pulse generator comprises a wheel 62 which is rotated once for every machine revolution i.e. for each revolution of the feed cylinder 21 and of the impression cylinder 26. The wheel 62 has a transparent portion therein for transmitting light from a light source 64 on one side of the wheel to a light-responsive sensor e.g. photocell, 66 on the opposite side of the wheel once during each revolution of the wheel. This light produces a pulse from the sensor 66 on a line 67 and the wheel is timed so that the pulse is produced during that portion of the machine cycle during which the leading edge of the machine will arrive at the sensing station S if the sheet is proceeding to the register position on time. The width 'of the pulse corresponds to the width of the on time cycle portion for which no adjustment is to be made. A pulse stretcher may be utilized to provide a pulse of appropriate width.

1f the pulse from the sensing device 54 occurs before the reference pulse from the timing generator 60, the shaft 41 of the differential 36 will be turned by a motor 68 to rotate the shaft 41 to retard the shaft 40 so that the sheet proceeding to the register station will be retarded as well as the timing of the sheet-separating and forwarding mechanism relative to the printing press. The motor is connected to drive the shaft 41 by a locking worm 69 and worm wheel 70.

The motor 68 is a stepping motor which is operated by pulses derived from the pulse generator 60. The pulse generator wheel 62 has a pulse zone track comprised of a plurality of circularly arranged alternate transparent and opaque sections which, upon rotation of the wheel 62 alternately block and transmit light from the light source 64 to a light-responsive element, eg a photocell, 72 to provide a train of pulses on an output line 74. The output 74 is connected through a gating system including

control gates

79 and 80 to the motor 68.

1f the pulse from the sensing station S occurs before the reference pulse from the timing generator 60, the pulse will operate a fast sheet bistable circuit 82 to an ON condition. The pulse from the sensing means S is applied to one input 84b of an AND gate 84 having its output connected to actuate the bistable circuit 82 to its on condition. The AND gate 84 has two other inputs 84a and 840 which are normally conditioned to pass the pulse from the sensing station S when the pulse occurs before the reference pulse from the timing generator. The input 844 is connected to the reference pulse sensor 66 through an inverter 85 so that the input 84a has a logic 1 applied thereto except during the period that the reference pulse exists. The input 840 is normally conditioned to a logic 1 by a slow sheet bistable circuit 86 which is normally in its off condition but actuated to its on condition when the sheet arrives at the sheet-sensing station after the reference pulse. When the fast sheet bistable circuit 82 is turned on it conditions the gate 79 to pass pulses from the pulse generator 60 to the motor 68 to step the motor in a direction to retard the feed tapes 20 and the timing of the sheet-separating and forwarding mechanism of the feeder. The pulses are applied to the motor 68 until the bistable circuit 82 is returned to its off condition. The bistable circuit 82 is returned to its off condition by the occurrence of the reference pulse from the light-responsive element 66 which is applied to the off terminal of the bistable circuit 82. Therefore, the number of pulses which are applied to the motor 68 will be directly proportional to the time period between the arrival of the sheet at the sheet-sensing station S and the later reference pulse and to the speed of the printing unit since the pulsegenerating wheel is driven therewith.

If the pulse from the sensing station S occurs after the reference pulse, the reference pulse, when it occurs, will turn on the sheet slow bistable circuit 86. The reference pulse from the light-responsive element 66 is applied to the on terminal of the sheet slow bistable circuit 86 through a differentiating circuit 90 and an AND gate 92 having three

inputs

92a, 92b and 92c. The leading edge of the reference pulse is differentiated by the circuit 90 and applied to the input 92a. The input 92b is connected to the fast sheet bistable circuit 82 and is conditioned to pass the pulse if the bistable circuit 82 is in an off condition. It will be in an off condition when the reference pulse occurs before the sheet pulse. The third input 920 is connected to the sensing device through an inverter 94 so that the input 92c is normally conditioned by a logic 1 and so that the reference pulse will be passed by the gate 92, assuming bistable circuit 82 is off, unless the pulse from the sensing station 8 occurs simultaneously therewith indicating an ontime condition.

When the bistable circuit 86 is turned on it conditions a gate 80 to pass pulses from the light-responsive element 72 to the motor 68 to operate the motor 68 in a direction to advance the timing of the shaft 40 relative to the shaft 34 and the press and to advance the feed tapes 20 and the timing of the sheet of the sheet-separating and forwarding suckers. The advancement of the feed tapes 20 advances the sheets on the feedboard moving to the sheet register position and the advancement of the timing of the sheet-separating and forwarding suckers adjusts for subsequent sheets. Pulses will be applied to the motor 68 through the AND gate 80 until the bistable circuit 86 is turned off. The bistable circuit 86 is turned off when the sheet arrives at the sensing station S. The sensing means at the station is connected directly to the off terminal of the bistable circuit 86. Consequently when the sheet, arrives the bistable circuit 86 will be turned off and the number of pulses which have been applied to the motor 68 is a direct function of the lateness of the sheet in arriving at the sheet-sensing station S.

The AND gate 80 includes an input 95 which is connected through an inverter 96 to the light-responsive element 67 so that the AND gate 80 is not conditioned to pass pulses during the reference pulse time of the cycle. The reference pulse has a length which corresponds to the ontime portion of the cycle for which no adjustment is to be made if the sheet arrives during that cycle portion. Consequently if the pulse from the sensing station S occurs simultaneously with the reference pulse but after the leading edge thereof so that the bistable circuit 86 is first turned on by the leading edge of the reference pulse and it is turned off by the pulse from the sensing station S before the reference pulse terminates, there will be no pulses applied to the motor 68 since the input 95 will not be conditioned during the ontime period represented by the reference pulse. It will also be noted that the slow sheet bistable circuit 86 controls the input file of the gate 81. The pulse from the sensing station S cannot, therefore, turn on the fast sheet bistable circuit 82 if it occurs after the reference pulse since the reference pulse will have turned on bistable circuit 86. For the situation where the pulse from the sensing station S occurs simultaneously with the leading edge of the reference pulse, the bistable circuit 36 will not be turned on to prevent the AND gate 84 from operating. The sensing station pulse, however, will not be effective to turn on the sheet fast bistable circuit 82 because the AND gate 84 will have lost its input Ma from the inverter 85 which loses its output on the occurrence of the reference pulse.

From the foregoing it can be seen that the timing of the separating and feeding mechanism will be advanced or retarded automatically depending upon whether or not the sheets are arriving late or early at the sheet-sensing station S with reference to the ontime portion of the cycle and the advancement or retarding of the sheet tapes simultaneously with the advancement and retarding timing of the sheetseparating and forwarding mechanism will also adjust the arrival of the sheet moving to the sheet register position.

Under certain circumstances it may be desirable not to adjust the timing of the sheet-separating and feeding mechanism and in this situation the differential 36 would be incorporated only in the drive to the feed tapes 20. This adjustment would advance or retard only the sheets on the feedboard.

A further embodiment of the present invention is schematically shown in H6. 4. In FIG. 41, the feed tapes 20 and the feed rolls 116 are driven by a variable-speed motor 120 separate from the press drive which also operates the sheetseparating and forwarding mechanism including the separating and forwarding suckers 12, 113. The sensing station S controls the speed of the motor 20 to control the arrival sheets moving down the feedboard at the register position. In this embodiment the sheet-sensing station S does not change the timing of the sheet-separating and forwarding apparatus.

The speed of the motor 120 is controlled by a digital-toanalogue converter 1122 which converts the count in a bidirectional counter lZd to an analogue signal having a magnitude which is dependent upon the count in the counter. The predetermined count may be set in the counter 124 in a conventional manner either manually or automatically as described hereinafter and is such that the feed tapes 20 normally operate at the speed required to bring the sheets to the sheet register position at the proper time. If however, the sheet is slow, pulses are applied from an AND gate 126 corresponding to the slow sheet gate 80 to an add terminal 112441 of the counter RM to increase the count of the counter and to speed the tapes 20. Similarly if the sheet is fast, pulses are applied from an AND gate 1127 corresponding to the fast sheet AND gate 79 to the substract terminal 12% of the counter to reduce the count in the tapes. The control of the gates 1126, B27 by the sensing station S may be the same as in the first-described embodiment for the control of the gates 78, 79.

it will be recognized that in the embodiment of FIG. 4, the timing of the sheet-separating and feeding mechanism is less critical since the tapes may be speeded up or slowed down to correct for the out of time operation of the feeder.

In operation the tapes 20 may be driven from the main press drive until the press is at run speed and the drive from motor 120 then clutched in. Alternatively a tachometer 130 may generate an analogue voltage signal which is converted to digital form by a converter 1131 and utilized to set the counter in accordance with press speed during starting. The presetting circuit would be broken after running speed is reached and the predetermined count established in the counter.

It will also be understood that the pulse-generating wheel 62 could be utilized to generate a gating signal during the period in a cycle when the sheet is sufficiently late or early that the machine should be tripped off. This gating signal would be used to gate the pulse from the sheet sensor to a machine trip control.

lclaim:

1. In a sheet-processing apparatus comprising a sheetprocessing unit, sheet-advancing means for feeding sheets from a register position to the sheet-processing unit, sheet-forwarding means for moving a stream of sheets to said register position with the successive sheets being timed to arrive in successive machine cycles at said register position during a predetermined portion of the cycles, registering mechanism for registering a sheet at said position, and drive means for driving said sheet-forwarding means in a predetermined relationship to said sheet-processing unit and said sheetadvancing means to effect the arrival of successive sheets of said stream at said register position during successive cycles and at a predetermined portion of the cycle, the improvement comprising a sheet-sensing station adjacent said stream including sheet-sensing means for sensing the time of arrival of a sheet in said stream at said station, reference means providing a signal for indicating the predetermined time in each cycle at which a sheet is to arrive at said sheet-sensing station and adjusting means responsive to said sheet-sensing means and to said reference means for adjusting said drive means to change the time of arrival of sheets at said register position when a sheet arrives at said sheet-sensing station at a time in a cycle different from said predetermined time.

2. In a sheet-processing apparatus as defined in claim 1, wherein said sheet-forwarding means comprises sheetconveying means for moving sheets toward said register position and said drive means comprises a drive mechanism for driving said sheet-conveying means in timed relationship to the sheet-processing unit including differential means having an element operable to advance or retard selectively the timing of said sheet-conveying means relative to said processing unit and said adjusting means comprises means for operating said element.

3. lo a sheet-processing unit as defined in claim 1, wherein said drive means for driving said sheet-forwarding means comprises drive mechanism having an input shaft and an output shaft and means for driving said output shaft in timed relationship with said input shaft including an element actuatable to add or subtract a component of rotation to the rotation imparted to said output shaft from said input shaft and said adjusting means comprises means for operating said element.

4. In a sheet-processing apparatus as defined in claim 1, wherein said reference means comprises a pulse generator for generating a reference signal rotated in timed relation to said drive means, and said adjusting means comprises second pulse-generating means for generating a train of pulses, and means responsive to the sheet signal from said sensing station and said reference signal to gate said train of pulses during the time interval between the signals when said sheet pulse occurs at a time different from said reference pulse and means responsive to said pulses when gated to advance or retard said sheet stream to adjust the out of time relationship.

5. In a sheet-processing apparatus, a sheet-processing unit, first means for advancing a sheet to said unit from a register position during each cycle of said unit, sheet-feeding means for forming and moving a stream of sheets to said register position, a sheet-sensing station adjacent said stream including a sensing device for sensing and signaling the arrival of each sheet at the station as it moves to said register position, and control means responsive to said sensing device for adjusting said sheet-feeding means to change the time of arrival of sheets at said sensing station to effect the arrival of the sheets at said register position during predetermined parts of said machine cycles.

6. In a sheet-processing unit as defined in claim 5 wherein said control means'comprises means providing a periodic reference signal timed with said processing unit and means for comparing the signal from said sensing means and said reference signal and adjusting the operation of said sheetfeeding means when said signals differ in phase in a predetermined manner.

7. ln a sheet-processing unit as defined in claim wherein said sheet-feeding means comprises a sheet-separating and forwarding mechanism driven in timed relationship to said processing unit including means for separating the top sheet of a pile at a predetermined cycle time and forming a sheet stream and said control means comprises means for changing the timing of said sheet-separating and forwarding means relative to said processing unit and said first means.

8. In a sheet-processing unit as defined in claim 7 wherein said control means comprises means providing a periodic reference signal timed with said processing unit and means for comparing the signal from said sensing means and said reference signal and adjusting the operation of said sheetseparating and forwarding mechanism when said signals differ in phase in a predetermined manner.

9. In a sheet-processing apparatus as defined in claim 6 wherein said control means includes means for providing first and second trains of pulses when the sheet-sensing signal leads and lags the reference signal respectively and means responsive to said pulse trains to respectively retard and advance the arrival of sheets in said stream at said register position.

10. In a sheet-processing apparatus as defined in claim 9 wherein said apparatus includes a differential having an input shaft driven in timed relationship to said unit, an output shaft for driving said sheet-forwarding and separating means and said control means includes motor means connected to said differential and responsive to said first and second pulse trains to advance or retard said output shaft relative to said input shaft on operation of said motor.

11. In a sheet-processing apparatus, a cyclically operating sheet-processing unit, first means for advancing a sheet to said unit from a register position, sheet feeding means for forming a stream of moving sheets with each sheet displaced from the adjacent sheets and for moving the lead sheet of said stream to said register position during a predetermined time interval in the cycle of the processing unit, said sheet-feeding means including control means for advancing or retarding the time in the cycle at which the lead sheet arrives at said register position, a sheet-sensing station adjacent said stream including a sensing device for sensing and signaling the arrival of each sheet of the stream at said station as it moves to said register position, and means responsive to said sensing device and interconnecting said sensing device and said control means to actuate said control means to advance or retard the time in the cycle that the sheets of the stream arrive at said station to effect arrival during said interval.

Claims

1. In a sheet-processing apparatus comprising a sheet-processing unit, sheet-advancing means for feeding sheets from a register position to the sheet-processing unit, sheet-forwarding means for moving a stream of sheets to said register position with the successive sheets being timed to arrive in successive machine cycles at said register position during a predetermined portion of the cycles, registering mechanism for registering a sheet at said position, and drive means for driving said sheet-forwarding means in a predetermined relationship to said sheet-processing unit and said sheet-advancing means to effect the arrival of successive sheets of said stream at said register position during successive cycles and at a predetermined portion of the cycle, the improvement comprising a sheet-sensing station adjacent said stream including sheet-sensing means for sensing the time of arrival of a sheet in said stream at said station, reference means providing a signal for indicating the predetermined time in each cycle at which a sheet is to arrive at said sheet-sensing station and adjusting means responsive to said sheet-sensing means and to said reference means for adjusting said drive means to change the time of arrival of sheets at said register position when a sheet arrives at said sheet-sensing station at a time in a cycle different from said predetermined time.

2. In a sheet-processing apparatus as defined in claim 1, wherein said sheet-forwarding means comprises sheet-conveying means for moving sheets toward said register position and said drive means comprises a drive mechanism for driving said sheet-conveying means in timed relationship to the sheet-processing unit including differential means having an element operable to advance or retard selectively the timing of said sheet-conveying means relative to said processing unit and said adjusting means comprises means for operating said element.

3. In a sheet-processing unit as defined in claim 1, wherein said drive means for driving said sheet-forwarding means comprises drive mechanism having an input shaft and an output shaft and means for driving said output shaft in timed relationship with said input shaft including an element actuatable to add or subtract a component of rotation to the rotation imparted to said output shaft from said input shaft and said adjusting means comprises means for operating said element.

6. In a sheet-processing unit as defined in claim 5 wherein said control means comprises means providing a periodic reference signal timed with said processing unit and means for comparing the signal from said sensing means and said reference signal and adjusting the operation of said sheet-feeding means when said signals differ in phase in a predetermined manner.

7. In a sheet-processing unit as defined in claim 5 wherein said sheet-feeding means comprises a sheet-separating and forwarding mechanism driven in timed relationship to said processing unit including means for separating the top sheet of a pile at a predetermined cycle time and forming a sheet stream and said control means comprises means for changing the timing of said sheet-separating and forwarding means relative to said processing unit and said first means.

8. In a sheet-processing unit as defined in claim 7 wherein said control means comprises means providing a periodic reference signal timed with said processing unit and means for comparing the signal from said sensing means and said reference signal and adjusting the operation of said sheet-separating and forwarding mechanism when said signals differ in phase in a predetermined manner.