DE69107427T2 - Starting and stopping the printing of fed sheets. - Google Patents

Description

The invention relates to the start-up process when starting to feed sheets into a printing apparatus, in particular to a multi-section rotary printing press. The invention also relates to the stop-up process when stopping or interrupting printing.

At the start of printing on a rotary printing press, particularly a flexographic press with one or more rotary flexographic sections, the inking roller or rollers were positioned for inking as soon as the machine drive was turned on. With this method, however, the printing plate or plates were always inked whether or not sheets were fed to the machine.

In a subsequent development, the ink roller was only positioned when the feed switch for feeding sheets was turned on. But this prevented the last sheets of a print run from being printed.

A timer was then installed and set to allow the last sheet to pass through the machine based on the lowest machine speed. However, when the machine was at its maximum speed, the ink roller was still in position for thirteen or more machine revolutions.

In all these cases there was a tendency for excessive ink accumulation on the printing plate. Furthermore, sheets at the beginning and end of a print run, rendered unusable by lack of print or excess ink. When excess ink buildup occurs at the beginning of a print run, it can be particularly devastating, resulting in a large number of sheets being printed and discarded before the initial excess ink buildup is absorbed and reduced sufficiently to continue normal printing.

The present invention relates to improving the starting and/or stopping operations of print runs, in particular, passages of sheets through multi-section rotary presses.

One aspect of the present invention is based on the realization that the ink roller should be synchronized at start-up by positioning it to compensate for the difference between the ink transfer point and the sheet registration. With the first of a series of rotary flexography sections, the first section ink roller could be positioned ahead of the sheet registration and then each subsequent flexography section could be ordered depending on the center-to-center distance between the sections for ink roller positioning.

Another aspect of the present invention is based on the realization that when it is indicated to stop feeding, it is preferable to pause until the printing plates are past the ink transfer point before the ink roller has left its inking position, so as to be able to print the last sheet as it passes. Then each subsequent flexo unit could be delayed in releasing its ink roller in sequence by the relation of the center distance between successive flexo sections and their rotating equivalence.

According to one aspect of the present invention, there is provided a printing apparatus comprising a frame structure, a plurality of rotatably driven printing cylinders supported in the frame structure and rotating once per machine cycle during operation, and a plurality of associated ink rollers rotatably arranged in the frame structure for inking printing cylinders, a plurality of actuators for moving the ink rollers and the printing cylinders relative to one another and bringing them into contact with one another and moving them apart again, an input section for feeding sheets to the printing cylinders and having them printed thereby, the printing cylinders and the associated ink rollers being arranged one after the other in series to successively print each of the sheets fed through the input section, and an input switch for switching on the input station for the sheets to be fed in and for switching off the input station to interrupt the sheet feed, characterized by:

a plurality of timing devices operated synchronously with the printing cylinders and producing output pulses on each machine cycle, by a plurality of controllers activated by the output pulses when the input switch is turned on to control the actuators and cause contact of each printing cylinder with its associated ink roller, the timing devices being angularly timed to cause sequential contact of the printing cylinders and their associated ink rollers after the input switch is turned on, the sequential contact being such that after the start of the input of sheets, each printing cylinder is inked immediately before it is touched by the first sheet input, and only once to print the first sheet input. Preferably each timing device consists of a rotatable disk with a slot, a light source and a photocell.

The plurality of timing devices may be incorporated into a timer having a plurality of slotted discs, all arranged on a common rotatable shaft and the slotted discs oriented at an angle to one another around the shaft.

The input section may have a continuously driven cam disc and a cam follower actuated by the cam disc, and shutdown means for shutting off the cam follower by varying the cam follower following the cam disc, wherein switching on and off of the input section by the input switch operates the shutdown means to operate or disable the cam follower.

A sensor may be provided to sense a predetermined position of the cam, the sensors being connected to the shutdown members to delay operation of the cam follower when the input switch is turned on until the next predetermined position of the cam is sensed and the controllers are not actuated by the output pulses until the next predetermined position of the cam has been sensed.

Preferably, the sensors include an actuator on the cam disc and a proximity switch next to the cam disc.

Each ink roller can be rotatably arranged in a pivoting frame which is rotatably held in the frame, the actuating parts comprising an air cylinder which can be actuated by the pivoting frame.

Preferably, the feed section has a machine zero position for each machine cycle in relation to each sheet feed. The timer for the first printing section is angularly aligned with a first angle relative to the machine zero position at each machine cycle, and the second timer for the next printing section is angularly aligned with a predetermined angle after the first angle.

According to another aspect of the invention, there is provided a method for starting a printing run of sheets with a rotating printing press with a plurality of printing sections arranged in series, each having an inking roller and a printing cylinder which are brought into contact with one another for inking and separated again, with the printing press running idle, without the sheets to be fed in and without ink transfer from the individual inking rollers to the associated printing cylinders, characterized by the following steps:

Movement of the ink roller and the printing cylinder of each printing section into an ink transfer contact in chronological order by starting the sheet input with a first sheet of a sheet run,

successive printing of the first sheet by each of the printing sections and

Start of the printing process after the first sheet has reached the printing section and the printing cylinder of the corresponding printing section has been inked for the first time for the printing run.

By interrupting the feeding of the sheets to be fed one after the other, the ink roller and the printing cylinder of each printing section can preferably cancel the ink application contact with each other and one after the other in the same time ratio with which they previously touched each other.

In a particularly preferred embodiment of the present invention, applied to a printing press with several Flexographic printing sections receiving sheets from an input unit, each printing section is arranged to have a synchronized position setting determined as a function of the rotational position of that section in relation to the linear position of the sheet passing through the printing press. At the beginning of a print run, controls adjust the ink roller of each section when the sheet registration point meets the ink transfer point, with each printing section sequentially ordered in position. At the end of each run, each ink roller drops out of its inking relation in the same order at the same point in the machine cycle. In this way, each stamper or plate is inked only once, and the first and last sheets of a run are all of saleable print quality.

Other objects, features and advantages of the present invention will be more fully disclosed by the following detailed description of the preferred embodiment of the claims and the accompanying drawings.

In the accompanying drawings, in which like reference characters indicate like parts in the same or different figures:

Figure 1 is a schematic side view of a flexographic printing press, with some parts omitted and others simplified for ease of understanding,

Figure 2 shows a view of part of the mechanism, but including more details,

Figure 3 is a simplified perspective view of several electronic rotary cam switches used in the embodiment of Figures 1 and 2 to control the movement of the inking rollers to bring them into inking contact with the corresponding printing cylinders and to remove them from them again.

Figure 4 is an axial view of one of the switching cams of the arrangement according to Figure 3 after adjustment to provide impulses according to Figure 6,

Figure 5 is an electrical diagram of the control circuits for controlling sequential contact and removal according to the invention of the ink rollers of Figure 1 when starting and stopping the printing process for the sheets and

Figure 6 is a logic diagram for the operation according to the invention of the flexographic printing press according to Figure 1 in the case of the presence of four flexographic printing sections, taking into account the situation of a single sheet passing through, furthermore the stopping of the press and then the passage of a continuous series of sheets shown.

The preferred embodiment of the invention will first be described in relation to the simplified schematic views of Figures 1 to 5, and then the sequencing of the operations for starting and stopping or interrupting, with the printing of the individually fed sheets being described in relation to the logic diagram of Figure 6.

Figure 1 shows schematically a flexographic printing press with a sheet feeding section 10, a first flexographic printing section 12 and a second flexographic printing section 13, further flexographic printing sections can be added if desired, e.g. when three or more colours are printed, while Figure 5 shows the electrical control scheme for the press according to Figure 1 when equipped with four flexographic printing sections.

Each pressure section 12, 13 etc. has its own frame structure 14 which is removable from adjacent sections for maintenance, carrying out set-up work etc., as generally known. In each section there are arranged an aniline or ink roller 16, a printing cylinder 18, a pressure roller 20 and a pair of feed rollers 22, 24. Each of these rollers is rotatably driven in the direction of the associated arrows during printing. A flexible printing plate 26 is arranged on and encompassing each printing cylinder 18, maintaining a small arcuate gap 28 between the leading and trailing edges of the printing plate 26. Each ink roller 16 is rotatably mounted in a fork 30 which in turn is pivotally mounted at 32 in the associated frame structure 14. An air cylinder 34 supports and pivots the fork 30 for adjustment about its pivot point 32 to move the ink roller into inking contact with the corresponding printing cylinder 18, or more precisely to move the printing plate 26 mounted thereon for printing and away from the printing cylinder when not printing. The pressure cylinder 34 is mounted on a platform 36 of the frame structure 14. It is connected to one end of the fork 30 at the end remote from the pivot point 32. Each fork 30 is thus supported and moved by two cylinders, one of which is arranged on each side of the adjoining frame structure 14.

The sheet feed section 10 may be any suitable feeding device for feeding sheets in the downstream direction 38 from a stack 40 or sheet feeder. Preferably, the feed section is a leading edge feeder as disclosed in Ward Sr. et al United States Patent 4,494,745. The bottom sheet 42, shown in Figure 1 being fed from the stack 40, is normally supported by a central support surface 44. This sheet is fed in the direction 38 by a leading edge feed mechanism 46 which includes an endstop belt which can be raised above the support surface 44 and is intermittently driven to guide the bottom sheet 42 through the gate 48 until the leading edge of this sheet 42 passes through a nip 50 of a feed roller pair 52, 54. is gripped and half-way through. The upper runs of these endless belts are raised and lowered by a mechanism driven by a rotating cam disc in conjunction with cam roller 58 mounted on the lower end of a pivot arm 60. The continuous rotary drive of the cam disc 56 and the intermittent drive for the sheet feed belts are accomplished through gear assemblies (two gear boxes, one for each drive, are sufficient) shown schematically as box 62. The sheet feed belts, the arrangement for raising and lowering their upper runs, and vacuum boxes for drawing the lowermost sheet 42 into stationary frictional contact with these belt upper runs are shown schematically by mechanism 64. The intermittent drive between the gear assembly 62 and the sheet feed belts of mechanism 64 is illustrated by the dashed line 66. The mechanism 64 and drive 66 are shown in greater detail in Figures 1, 2 and 3 of the above-referenced Ward Sr. et al patent. The timing of their use therein is shown in Figure 4.

Wells et al United States Patent 4,867,433 discloses an advantageous modified form of the feed section 10, particularly the belt lifting mechanism shown therein in Figure 3.

In normal operation, the lowermost sheet 42 is brought into the position shown in Figure 1 by the mechanism 64. The feeding of this sheet is then taken over by the feed rollers 52, 54 and the sheet is guided into and through the gap between the printing cylinder 18 and the pressure roller 20 of the first printing section 12. With the ink roller 16 held against the printing plate 26 by the cylinder 34, and thus inked, the printing plate 26 of the first printing section prints the sheet 42. This printed sheet is grasped by the feed rollers 22, 24 of this section and fed to the second printing section 13, in which it is similarly printed in the same way by the printing plate 26 located therein.

In order to maintain a register for each sheet fed with the printed material printed thereon by successive printing sections 12, 13, etc., the various sections 50 are constructed such that when the center of the cam roller 58 is at the end of the concentric portion 68 of the cam disc 56 and in the radial position 70 (that is the end of the sheet feeding by the feed belts), the leading edges of the printing plates of the printing sections 12, 13 are in corresponding radial positions 72, 74. The various sections of the printing press are interconnected to operate at the same machine throughput speed. In this way, the cam disc 56 and all of the printing cylinders 18 rotate at the same speed. The registration accuracy between the sections is such that when the leading edge of the fed sheet 42 reaches the gap between the impression cylinder 18 and the pressure roller 20 of the first printing section 12 and is in the middle, the radial position 72 will have reached the radial position 76 which passes through the central line of the rollers 18, 20, that is, through the centre or roller attack of the gap between them. Similarly, when the leading edge of this sheet 43 reaches the centre of the gap between the impression cylinder and the pressure roller 20 of the next printing section 13, the radial position 74 will have reached the radial position 78 which passes through the centre of this gap.

In a printing press having a standard circle of 66 inches (168 cm) corresponding to the circumference of each printing cylinder 18, the distance between the centers of the printing cylinders 18 is 27 inches (69 cm). The angle A between the radial positions 72 and 76 in the first printing section 12 is 73.6º, and the angle B between the radial positions 74, 78 in the next printing section 13 is 220.9º. Thus, the second printing section 13 is set back 147.3º from the first printing section 12. If additional printing sections are present, each is set back 147.3º from the previous printing section.

It is known for an electrically controlled stop 80, e.g., a lifting air cylinder controlled by an air valve 79 operated by a relay, to advance the swing arm 60 from rotating clockwise and thus prevent the follower roller 58 from entering the lower concentric portion 68 of the cam disk 56. This, in turn, prevents the feed belts of the feed mechanism 64 from being raised to feed sheets. The stop 80 thus expands when the feeding of sheets from the stack 40 is to be interrupted. This expansion can be caused, when the air valve 79 is energized, by interrupting the power supply to the air valve relay. Energization of the air valve relay occurs during normal sheet feeding to cause the cylinder 80 to retract.

A stationary proximity switch 81, close to one side of the cam 56, is actuated by an actuator 83 on the cam at each revolution immediately after the cam passes through the machine zero position 70 of Figure 1. Preferably, this occurs when the cam has rotated 16º past the position in Figure 1. When this sheet feed is to be restarted after the feed switch is turned on by the actuator, the cam 56 is to rotate until the next actuation of the proximity switch 81 before the valve 79 is actuated to release the stop 80 and allow the cam follower 58 to follow the cam 56. As is known, this prevents incomplete feeding of a sheet when the feed is restarted.

According to the invention, the timing of the ink rollers 16 contacting and disengaging from the printing cylinders 18 of the printing sections 12, 13, etc. is carried out sequentially. The preferred way of doing this is to use a timing device in the form of a rotary switch box 82 driven by a drive 84 of a suitable element of the printing press, e.g. by a part of the gear assembly 62. The control box 82 contains a plurality of switches which rotate separately in coordination and operate relays which control air valves for operating the air cylinders 34.

The figure shows in detail how the rotary switch box 82 is driven by the gear assembly 62. This gear assembly includes a gear box for driving the cam disc 56 (Figure 1) and a separate transmission gear box 86 for intermittently driving the feed belts. This gear box 86 is mounted in the frame structure 88 of the feed section 10. An input shaft is continuously rotated via a pulley 92 and belt 94 by a pulley 96 driven by the main drive of the printing press. Below the gear box 86, the switch box 82 is mounted to a cross member 98 of the frame structure 88. A small pulley 100 is secured to the outer end of the input shaft 90 and drives via a timing belt 102 an input pulley 104 secured to a drive shaft 106 of the switch box 82. The shaft 106 is rotated at the same speed as the transmission input shaft 90 and also as the pressure cylinders 18 (Figure 1).

Figure 3 is a simplified perspective view of the main element of the rotary switch box 82. The drive shaft 106 is rotated within the switch box 82 and extends the length thereof. The ends of the shaft 106 project through the housing of the switch box 82. The input pulley 104 (Figure 2) is keyed to one of these projecting shaft ends. Two electronic rotary cam switches 108 are shown, one for each of the pressure sections 12, 13, but more such cam switches 108 can be positioned along the shaft, which can extend as indicated by the dashed line. For four pressure sections there would be four switches 108, for six pressure sections six switches would be used. Each cam switch 108 has a cam disc 110 consisting of two semi-circular segments 112, 114 connected in position between a pair of hexagonal nuts 116. By loosening and then tightening these nuts 116 the arc gap or slot through the composite cam disc 110 can be adjusted in arc size and rotational position relative to the shaft 106. The arc gap is fully adjustable from 1 to 180º. For the preferred embodiment this arc gap 118 is set at about 7º as shown in Figure 4. Each compound cam 110 passes through an electronic photocoupler 120 as it rotates. Each photocoupler 120 is U-shaped with two upright legs 122, 124. A light source 126 is located in leg 122 and produces a beam of light onto a photocell 128 located in the opposite leg 124. When the compound cam allows light to pass, the electronic circuit of cam switch 108 produces an output voltage. When this light is blocked, no output is produced. Thus, with the narrow slot 118 of Figure 4, an output pulse is produced for each revolution of each of these cams 110. The angular positions of all of these compound cams are set on shaft 106 so that the bank of cam switches 108 produces output pulses in a controlled and timed sequence, one for each printing section, as will be explained later.

The shaft 106 carries at one end a timing wheel 130 which is marked in 0-360º increments. A timing pointer 132 is secured to the housing of the switch box 82 by a bracket 134 and extends across the scale on the wheel 130 parallel to the axis of the shaft 106. After the angular position of the wheel 130 on the shaft 106 has been calibrated (using a lock nut) so that 0º aligns with the Machine position zero (which is the relative position of cam 56 and impression cylinder 18 as shown in Figure 1), the angular positions of the compound cam disks 110 can be set accordingly to enable the correctly timed output pulse to be sent to each printing section 12, 13, etc. The first disk slot 118 for the first printing section 12 is angularly calibrated or timed 125.2º ahead of machine zero for a 66-inch (168 cm) rotary press, that is, 198.8º less 73.6º (angle at inking position 154 minus angle A). Each subsequent disk slot 118 for each subsequent printing section 13, etc. is then angularly offset 147.3º after the disk slot 118 of the preceding printing section.

A suitable rotary switch housing with electronic rotary cam switches 108 is marketed by Electro Cam Corp., 13647 Metric Road, Roscoe, Illinois 61073, U.S.

Figure 5 is an electrical diagram showing the connection of rotary cam switches 108 (referenced 108(1), 108(2), 108(3), 108(4) for four printing sections) to operate relays 136(1), 136(2), 136(3), 136(4) for controlling operations of air valves which operate air cylinders 34 of Figure 1, which air cylinders 34 move ink rollers 16 into and out of ink contact with printing cylinders 18 of the two printing sections 12, 13 of Figure 1, now expanded to four printing sections.

The cam switches 108(1), 108(2), 108(3) and 108(4) are all attached to the control shaft 106 as shown in Figures 3 and 4. Each of the four pressure sections 12, 13 etc. has its corresponding relays 136(1), 136(2), 136(3), 136(4) for operating the air valves for extending and contracting the air cylinders 34. The relay 136(1) is for the first pressure section 12, the relay 136(2) is for the second pressure section 13 and the relays 136(3) and 136(4) are for the third and fourth printing section in the feed direction 38 according to Figure 1. Each printing section has its own sub-control panel with a programmable logic controller (PLC) 138(1), 138(2), 138(3), 138(4) respectively for the first to fourth printing sections. The four PLCs are connected by lines 140 to a common power supply line 142. Each of the cam switches 108 is connected to the common supply line 142 and the associated PLC.

The outputs of the four PLCs 138(1), 138(2), 138(3), 138(4) are respectively fed to the air valve relays 136(1), 136(2), 136(3), 136(4) which are located between and connected to their PLCs and a common neutral line 144. The PLC of the first pressure section 12 has two additional inputs, one through line 146 from the feed switch which controls the operation of the feed section 10 (Figure 1) and the other through line 149 which energizes the feed relay 150, also controlled by the feed switch 148 via a time delay circuit. The feed relay 150 controls and is part of the air valve 79 (Figure 1). This relay is energized when the feed switch 148 is on. Thus, when the feeding of sheets through the feed section 40 is to be interrupted, manually opening the feed switch 148 will consequently cause the relay 150 to drop to cause the air cylinder stop 80 in Figure 1 to extend and disable the swing arm 60 to keep the cam follower roller 58 from the cam 56. Upon closing the feed switch 148 to begin feeding of sheets, there is a time delay until the cam actuator 83 next actuates the proximity switch 81 (Figure 1) before the line 149 and thus the feed relay 150 are energized to allow the cam follower 58 to follow the cam switch 56 and feed the sheets. This time delay allows the first print section switch 108(1) to have a "negative" timing, thus forcing the ink roller 16 to come into pressure contact with the first Sectional pressure cylinder 18 for a portion of a revolution of cam 56 before the arm begins to pivot to insert first sheet 42. The second, third and fourth PLCs also receive sequentially timed inputs from the immediately preceding PLC via lines 152(2), 152(3), 152(4).

During operation, even if the shaft 106 is driven through the transmission gear box 86 (Figure 2), there is no input to the PLC 138(1) on the feed relay input line 149 when the feed switch 148 is in the off position, and there are no outputs to the PLC interconnect lines 152(2), 152(3), 152(4). In this situation, no voltage is applied to the air valve relays 136(1), 136(2), 136(3), 136(4) so that the air cylinders 34 are in their contracted positions with the ink rollers 16 out of contact with their corresponding impression cylinders 18. Thus, no sheets are fed and the impression plates 26 are not inked.

When the feed switch 148 is closed, there is a delay before a first cycle for feeding the expected bottom sheet 42 begins. As previously explained, the proximity switch 81 is actuated immediately after the cam 56 passes through the radial position 70 corresponding to the machine zero position for synchronizing the fed sheets. Since the leading edge of the sheet 42 only has to travel the distance of the gap 50 of the feed rollers 52, 54 to the gap between the first section impression cylinder 18 and the pinch roller 20 after the cam 56 passes through the zero position 70, the first section impression cylinder 18 must be inked before the machine zero position. The first section air cylinder 34 must cause its ink roller 16 to contact the first impression cylinder 18 at the gap 28 between the ends of the printing plate 26 before the stop 80 allows the arm 60 to activate to 42. The first printing section rotary cam 110 is angularly adjusted ahead of the machine zero so that the first section air cylinder is actuated via relay 136(1) to bring the first section ink roller 16 into an inking position for printing when the platen nip 28 is at the ink transfer point 154. This occurs during the last revolution of the cam before the cam 56 reaches the machine zero position 70 with the first sheet being fed by the feed mechanism 64, during the last part of that revolution. The remaining cam switches 108(2), 108(3), 108(4) are each relatively angularly aligned so that sequentially the platen nip 28 of the next printing section reaches the ink transfer position 158 etc., moving the corresponding ink roller 16 to its inking position. In this way, as the leading edge of the first fed sheet 42 is fed along and through the printing press, it is aligned with the leading edge of a printing plate 26 that has just been inked for the first time since the printing operation was previously stopped or interrupted.

When the first section cam switch 108(1) generates a pulse when its slot 118 passes through its light source 126 and the feed switch 148 is closed, this short pulse causes the first PLC 138(1) to provide a sustained output to latch relay 136(1). This relay remains latched until the feed switch 148 is opened again. Once relay 136(1) is latched to the "ON" position, the first PLC 138(1) generates an output on line 152(2) which allows the next pulse from the second section cam switch 108(2) to latch the second section relay 136(2) to the "ON" position via the PLC 138(2). This in turn, in chronological order, forces relay 136(3) to latch into the "ON" position and finally the fourth section relay 136(4) to latch into the "ON" position. As long as the feed switch 148 remains closed, the PLCs then hold all relays 136(1), 136(2), 136(3), 136(4) continuously in the latched position, and the inking of all printing sections is effected continuously, as in a normal printing run.

However, once the feed switch 148 is opened, the feed relay 150 is energized after completion of feeding the lower stack sheet to the nip 50, whereupon the feed section 10 stops feeding sheets. In this case, the cam actuator 83 has to pass the proximity switch 81 after the feed switch 148 is opened and before the sheet feeding stops. This lower sheet 42 entering the nip 50 is then still fed to and through the first printing section by the feed rollers 52, 54 which continue to rotate. With the feed relay 150 now de-energized, the first PLC 138(1) opens relay 136(1) on the next pulse from the first section cam switch 108(1) and the first ink roller 16 of the first section disengages from the first section impression cylinder 18. This occurs when the plate gap 28 reaches the ink transfer point 154 so that after the first section impression plate 26 completes printing on the last fed plate 42, no more ink is transferred to that plate. Once relay 136(1) is switched, the first PLC 138(1) changes the signal over line 152(2) to the second PLC 138(2). This in turn causes the second section relay 136(1) to de-energize on the next pulse from the second section cam switch 108(2). This in turn moves the ink roller 16 away from the impression cylinder 18 of the second section 13 when the impression plate gap 28 reaches the ink transfer point 158. Thus, when the last fed sheet 52 passes in contact with the second section impression cylinder, this sheet 42 is printed by the inked second impression plate 26, but thereafter the inking of this second impression plate 26 is stopped. The relays 136(3) and 136(4) are similarly turned off one after the other when the signals in the lines 152(3) and 152(4) change so that the printing of the last sheet 42 is completed in the third and fourth impression sections. can be done, but any further inking of the printing plates of these sections is then stopped sequentially.

It is believed that, therefore, in accordance with the invention, upon commencement of sheet feeding, each printing plate is inked only immediately before it is contacted by the first sheet. Thus, over-inking of the first and subsequent sheets is avoided, while correct multi-stage printing of the first and subsequent sheets is assured in any case. Furthermore, in accordance with the preferred arrangement of the invention, upon interruption of sheet feeding, the last sheet fed is correctly printed in each printing station, but no printing plate is further inked after it has printed the last sheet. In this way, over-inking of each of the first fed sheets is avoided, and incomplete printing of the last fed sheets at the end of a run is also avoided.

To avoid inking the printing plates 26 if the sheet stack 40 runs out unnoticed, a sheet sensor 160 can be placed under the position of the stack 40, as shown in Figure 1. This sensor 160 can be a photoelectric sensor unit or a pressure (or contact) sensor. If the sensor 160 detects at least one sheet, printing is carried out as described above. However, as soon as the sensor does not detect a sheet, it generates a signal to the first section PLC 138(1). This is the same as when the feed relay 150 drops out. It initiates the sequential movement of the ink rollers 16 described above, so that the last sheet fed is completely printed, but the printing plates are no longer inked.

Figure 6 illustrates the timed sequence of operation of the feed switch 148, the feed cam 56, the rotary switches 108 and the air cylinders 34 through the relays 138 to activate or stop the ink rollers 16 as a single sheet is fed to and through the printing press and also as a new set of sheets is fed through. The vertical axis is marked with eleven items and the timing of the action of each item extends horizontally.

The feed switch indicated on the top line shows the turning on of the feed switch 148 (Figure 5) for a short period of time and then turning it off to allow only the feeding of a single sheet. Thereafter, the turning on of the feed switch is again shown and it remains on for a new set of sheets to be fed through the press and printed.

The second line, labeled Zero Tuning, shows the times at which the actuator 83 on the cam 56 passes the machine zero position 70, these zero tuning positions also being designated by the reference numerals 70. Just after each zero tuning position 70, a pulse 162 is seen, each time coming from the stationary proximity switch 81, this is passed by the actuator 83. The feed circuit connected to the proximity switch 81 also determines whether the feed switch 148 is in the on or off position when the pulses 162 appear - this scanning is indicated schematically by the dashed line 164.

The third line, labelled Feed Eject, shows when the tappet roller 58 is free to follow the cam detent 68 to start the feed mechanism to feed sheets (by lifting the feed sheets the tappet 58 is always in the detent 68). When a pulse 162 appears and the When the feed switch 168 is closed (i.e., "ON" position), the relay 150 of the air valve 79 is in the "ON" position to permit sheet feeding, but when a pulse 162 appears and the feed switch is open (i.e., "OFF" position), the latching force is released and the relay 150 acts on the air cylinder 80 to interrupt sheet feeding by preventing the feed belts from raising. It will be seen that as soon as a timed pulse 162 (see second line) senses that the feed switch is in the "ON" position (see first line), the latching force to feed sheets occurs, but as soon as a subsequent timed pulse 162 senses the feed switch is in the "OFF" position, the latching force disappears and sheet feeding does not continue.

The fourth line shows the pulse output of the rotary switch 108(1) for the first printing section 12. The first section PLC 138(1) determines whether the feed power (see third line) is locked or not, with a pulse 166 being output from the first section switch 108(1) at any time. This sampling is indicated by the dashed lines 168.

The fifth line shows when the ink roller 16 of the first section 12 is in operation, i.e. in inking contact with the printing cylinder 18 of the first section. It can be seen that as soon as a switching pulse 166 finds the feed output engaged (by sensing 168), the first ink roller 16 touches the printing cylinder of the first section and begins inking it. Conversely, the sensing process 168 immediately determines that the feed output has decreased, i.e. has been turned off, and the first ink roller 16 has moved away from the associated printing cylinder 18 and the inking process has stopped.

The sixth line shows the pulses 170 of the second rotary switch 108(2) and the sensing 172 via the second section PLC 138(2) as to whether the ink roller 16 of the first printing section is inking or not.

The seventh line shows when the ink roller of the second printing section is inking or not inking. Such inking immediately causes the sensing 172 to detect that the ink roller of the first section is inking, and the cessation of inking immediately causes the sensing 172 to detect that the ink roller of the first section is out of contact.

In the next two lines, the pulses 174 of the third section switch 108(3) and show the operating or inoperative position of the ink roller 16 of the third printing section. The dashed lines 176 show the sampling of the position of the second section ink roller at every third section timing pulse 174.

Similarly, the second to last lines show the pulses 178 of the fourth section switch 108(4) and the position of the fourth section ink roller with the dashed lines 180 showing the scanning of the third section ink roller at each pulse 178 to control the position of the fourth section ink roller.

The left part of Figure 6 starts with the feed switch with the feeder turned off. The feed switch is then turned on and off to allow a single sheet to be fed.

It can be clearly seen how the ink rollers of the successive printing sections move into the inking position one after the other in timed relation to the printing of that sheet. It can also be seen that they then return one after the other to their home position when the sheet has been printed in the corresponding section. The passage of the single sheet 181 through the four printing sections, being printed in the corresponding sections, is illustrated by the dashed line 182. In this respect, it should be noted that the ink roller is disengaged while the printing plate just inked is still in the printing process for the sheet.

The right hand part of Figure 6 shows the feed switch turned on again, which then remains on to continue printing a new run of sheets through the printing press. The passage of the first sheet 183 of this new run through the four printing sections is illustrated by the dashed line 184.

It is therefore welcomed that, whether a single sheet or a continuous run of sheets is fed through the printing press, the printing plate of each printing section is inked immediately before the first sheet passes through that section for printing, thereby avoiding over-inking of a printing plate and also avoiding incomplete printing of the sheet by the first (or only) printing section.

It is also appreciated that when the printing process or the sheet feed is interrupted, each printing plate continues to be inked until it has printed the last sheet, but that after the last sheet has been printed, inking is not continued. Thus, no unprinted sheets appear at the end of a run. In multi-stage printing, the last sheets of the run are thus included, the last sheet is cleanly and completely printed by each printing station.

This avoids wasted sheets at the beginning and end of each print run, even if the print run is temporarily or accidentally interrupted. Furthermore, and this is very important, it avoids excessive inking in each individual plate at the beginning of the print run.

With regard to Figure 5, it should be noted that if one or more print sections are removed - even in the case of the middle sections - then the intermediate section signal line 152(2, 3 or 4) from the previous section PLC to the next section PLC is always connected as the top input therefor. In this way, correct sequencing of the start and end of inking is achieved, regardless of the printing sections present. Each printing plate is inked once before printing and is no longer inked after the last sheet is printed. Furthermore, once the rotary switches 108 are angularly aligned relative to one another, regardless of their number, correct sequential alignment for multiple printing sections is achieved by simply plugging the correctly numbered rotary switch into the printing section having that number position. If there are fewer printing sections than rotary switches, the excess rotary switches are left unconnected. The embodiments described above do not, of course, limit the breadth of the present invention. Modifications and other alternative constructions are conceivable within the scope of the invention as defined by the claims.

For example, the timing switches or devices may suitably include a resolver or encoder having a rotatably driven input member and producing a series of counts, pulses or signals for each 360° revolution. To produce the appropriate outputs to control all of the relays 136, selected signals may be arranged for each 360° cycle, preferably via a computer. In this way, one resolver or encoder could contain all of the timing switches 108 for all of the printing sections 12, 13, etc.

Claims (10)

1. Printing apparatus with a frame (14), with a plurality of rotatably driven printing cylinders (18) which are held in the frame and rotate once per machine cycle during operation, with a plurality of associated ink rollers (16) which are rotatably arranged in the frame for inking the printing cylinders (18), with a plurality of adjusting parts (30, 32, 34) for moving the ink rollers and the printing cylinders (18) relative to one another and bringing them into contact with one another and moving them apart again, with an input section (10) for feeding sheets to the printing cylinders (18) and having them printed by them, the printing cylinders and the associated ink rollers (16) being arranged one after the other in a row in order to successively print each of the sheets fed through the input section (10) and with an input switch (148) for switching on the input station for the sheets to be fed in and for switching off the input station to interrupt the sheet feed, characterized by a plurality of Timing devices (108) operated synchronously with the printing cylinders (18) and generating output pulses (166, 170, 174, 178) at each machine cycle, by a plurality of controllers (PLC) activated by the output pulses when the input switch (148) is switched on, to control the actuators (30, 32, 34) and to cause contact of each printing cylinder (18) with its associated ink roller (16), the timing devices (108) being angularly timed to cause sequential contact of the printing cylinders (18) and their associated ink rollers (16) after the input switch (148) is switched on, the sequential contact being such that after the start of the input of sheets, each printing cylinder (18), immediately before it is first entered sheet (42) is touched, is provided with ink and only once for printing the first entered sheet. 2. Printing apparatus according to claim 1, characterized in that each time measuring device (108) consists of a rotatable disk (110) with a slot (118), a light source (126) and a photocell (128). 3. Printing apparatus according to claim 1 or 2, characterized in that the time measuring devices (108) are incorporated in a time switch (82) with a plurality of slotted disks (110), all arranged on a common rotatable shaft (106) and the slotted disks (110) are oriented at an angle to one another around the shaft. 4. Printing apparatus according to claim 1, 2 or 3, characterized in that the input section (10) has a continuously driven cam disk (56) and a cam follower (58) operable by the cam disk, and shut-off members (80) for shutting off the cam follower (58) by preventing the cam follower from following the cam disk, the switching on and off of the input section (10) by the input switch (148) actuating the shut-off members (80) to put the cam follower into operation or out of operation. 5. Printing apparatus according to claim 4, characterized in that it contains sensors (81) to sense a predetermined position of the cam disk (56), that the sensors are connected to the shutdown parts (80) to delay the operation of the cam follower (58) when the input switch (148) is switched on until the next predetermined position of the cam disk (56) is sensed and the controllers (PLC) are not activated by the output pulses (166, 170, 174, 178) until the next predetermined position of the cam disk has been sensed. 6. Printing apparatus according to claim 5, characterized in that the sensors (81) comprise an actuator (83) on the cam disk and a proximity switch (81) next to the cam disk. 7. Printing apparatus according to one of claims 1 to 6, characterized in that each ink roller (16) is rotatably arranged in a pivoting frame (30) which is rotatably held in the frame (14), and in that the actuating parts (30, 32, 34) have an air cylinder (34) which can be actuated by the pivoting frame (30). 8. Method for starting a printing run of sheets with a rotating printing press with several printing sections (12, 13) arranged in series one after the other, each having an inking roller (16) and a printing cylinder (18), which are brought into contact with one another for inking and separated from one another again, with an idle run of the printing press without the sheets to be fed in and no ink transfer from the individual inking rollers (16) to the associated printing cylinders (18), characterized by the following steps: Movement of the ink roller and the printing cylinder of each printing section into an ink transfer contact in chronological succession by starting the sheet input with a first sheet (42) of a sheet run, successive printing of the first sheet by each printing section (12, 13) and Start of the printing process after the first sheet (42) has reached the printing section and the printing cylinder (18) of the corresponding printing section has been inked for the first time for the printing run. 9. Method according to claim 8, characterized in that after the first sheet (42) the sheets are successively guided through the printing press. 10. Method according to claim 9, characterized in that when the feed of the sheets to be fed one after the other is interrupted, the ink roller (16) and the printing cylinder (18) of each printing section (12, 13) adjust the ink application contact with one another and one after the other in the same time ratio with which they previously touched one another.