Sheet-fed printing press

Abstract

Sheet-fed printing press with two cylinders (27; 08) defining a printing gap (26), at least one cylinder (27) of which is adjustable in a radial direction by a first actuator (43) to vary the width of the printing gap (26), wherein a second actuator (39) acts on one of the cylinders (27) to adjust the width of the printing gap (26) at a higher speed than the first actuator (43), characterized in that it further comprises a sheet delivery (04) and a control unit (32) is provided to widen the printing gap (26) by means of the second actuator (39) during a stack change at the sheet delivery (04), and in that the second actuator (39) is coupled to a sheet feeder (01) to interrupt the feeding of a sheet (11) by the sheet feeder (01) to the printing gap (26) while the printing gap (26) is being adjusted by the second actuator (39). has widened.

Description

The invention relates to a sheet-fed printing press according to the preamble of claim 1. A sheet-fed printing press of this type typically has a sheet feeder, which picks up individual sheets from a stack and feeds them into the machine, and a delivery unit that lays the printed sheets onto a support, such as a pallet. When the resulting delivery stack reaches a certain height, it must be removed to make room for new sheets. During the time required for removal, printed sheets cannot be added to the delivery stack. Therefore, according to a known technique, before the removal of the completed delivery stack begins, a temporary tray, called a roller blind, is inserted between the delivery unit and the top of the delivery stack. Sheets printed during the removal of the completed stack are then placed on this tray.As soon as a new pallet is placed on the boom, the roller blind is retracted, the sheets accumulated on it fall onto the pallet and form the beginning of the next stack. If, when the roller shutter is being inserted, the sheet that was printed immediately beforehand is not yet lying flat on the stack, it can happen that the sheet is caught by the extending shutter and compressed. Depending on where the compressed sheet is located, it will obstruct the removal of the stack or the placement of new sheets on the shutter. Therefore, the printing process must be interrupted to remove the compressed sheet manually. EP 0 591 792 B1 discloses a printing machine in which, to adapt to the thickness of a substrate, the width of a printing gap between a printing cylinder and a printing blanket cylinder can be changed by means of an actuator which shifts the position of the axis of the printing blanket cylinder via an eccentric. In principle, a design based on the type known from EP 0 591 792 B1 would make it possible to increase the distance between the two cylinders to such an extent that contact between them—and thus contamination of the printing cylinder by ink from the blanket cylinder—is reliably prevented when no substrate is present in the printing gap. This would allow printing to be temporarily interrupted during a stack change at the delivery head by suspending the sheet feed, without having to stop the cylinders. The problem of sheet compression during the stack change would then be solved, as no sheets would need to be printed or laid out during this time.However, a problem arises because while adjusting the gap width to the thickness of the substrate is achieved with the printing press stationary in a movement that, although slow, should be precise, a temporary interruption of printing during a stack change requires a rapid movement of the cylinder in at least one direction, even if the precision requirements are low. If the actuator is even capable of moving at the necessary speed, its abrupt acceleration and deceleration cause vibrations in the machine frame, which can result in duplication in the printed product. EP 0 736 384 B1 discloses a sheet-fed printing machine with two cylinders defining a printing gap, at least one of which is adjustable in a radial direction by a first actuator to vary the width of the printing gap, wherein a second actuator acts on one of the cylinders to adjust the width of the printing gap at a higher speed than the first actuator. DE 40 13 075 C1, DE 10 2005 014 256 A1 and DE 100 21 540 A1 disclose devices for adjusting a pressure gap. The invention is based on the objective of creating a sheet-fed printing machine. The problem is solved according to the invention by the features of claim 1. The advantages achievable with the invention consist in particular of the fact that the sheet of a substrate can be conveyed individually and without connection to each other through a printing gap and printed in the process, and that a trouble-free stack change is possible. Of the two actuators, the first can be designed to adjust the width of the printing gap to the substrate with high accuracy. This actuator can have high inertia because, if it does not need to be actuated during printing, it cannot induce any vibrations that would cause duplication. The second actuator, on the other hand, can be built lighter due to lower positioning accuracy requirements; its lower weight enables low-vibration operation without duplication. Typically, the actuators are hydraulic or pneumatic cylinders. A hydraulic cylinder has the advantage that it only needs to be locked by blocking the inlet and outlet. Preferably, the first and second actuators act on the same cylinder, so that a simply constructed bearing with a frame-fixed axis of rotation can be provided on the other cylinder. To keep the design simple, the two actuators are preferably kinematically connected in series between a frame of the printing press, in particular a sheet-fed printing press, and the cylinder, i.e., one of the actuators has a frame-fixed first point of application and an adjustable second point of application, and of the two mutually movable points of application of the other actuator, one is connected to the cylinder and the other to the second point of application of the first actuator. The two actuators can be connected via a lever. Regardless of any design differences between the two actuators, the second actuator can then adjust the cylinder at a higher speed than the first, because its point of application on the lever has a shorter lever arm than the point of application of the first actuator. Preferably, the second actuator is held in a stop position during printing and arranged so that the printing gap widens when it leaves this stop position. If printing is to be interrupted, the movement of the second actuator does not need to be precisely controlled, as it is only important that the printing gap widens sufficiently, not that a specific width is set. Conversely, if printing is to be resumed and a precisely specified gap width must be set, this is achieved by moving the second actuator back to its stop position with minimal control effort. A control unit of the sheet-fed printing press is set up to widen the printing gap during a stack change at the sheet delivery using the second actuator. Such a control unit can further be coupled to an inking unit to interrupt the ink transport via the inking unit to the printing nip while the printing nip is widened by the second actuator. Such an interruption can be achieved at least by moving ink application rollers of the inking unit away from a plate cylinder of the printing unit; preferably, an interruption also occurs within the inking unit by moving rollers of the inking unit away from each other. The control unit is also coupled to a sheet feeder to interrupt the feeding of sheets through the sheet feeder to the printing gap while the printing gap is widened by the second actuator. An embodiment of the invention is shown in the drawings and is described in more detail below. Fig. 1 shows a schematic section through a sheet-fed printing press; Fig. 2 shows a printing unit of the sheet-fed printing press in operating position; Fig. 3 shows the printing unit in interrupted position. The printing press shown in Fig. 1, in particular a sheet-fed printing press, comprises a sheet feeder 01, a belt table 02, a sheet feeder 03, and a sheet delivery 04. Between the sheet feeder 03 and the sheet delivery 04, so-called units 05 and 06 are arranged, which are configured, for example, as a printing unit 05, a coating unit 06, a calibration unit, or in another suitable manner. Fig. 1 shows, by way of example, two printing units 05 and one coating unit 06, each with a cylinder 07, e.g., a plate cylinder 07, and a cylinder 08, e.g., a transport and impression cylinder 08. Further printing and coating units, not shown in the figure, can be provided between the printing units 05 and the coating unit 06. The printing units 05 shown in the figure each print different colors, in particular printing inks, on the same side of the sheets passing through them, and the coating unit 06 applies a coating layer to the same side.The printing or coating units not shown can print on the same side of the sheets, but a sheet turner may also be present to allow double-sided printing of the sheets, or a stack of 09 sheets can be turned over after single-sided printing and reloaded into the sheet feeder 01 to print the second side as well. The stack 09 of sheets, hereinafter also referred to as stack 09, rests on a stacking plate 10. The stacking plate 10 is height-adjustable in order to keep the uppermost sheet 11 of the stack 09 at a constant height accessible to a sheet separator 12 during processing. The sheet separator 12 comprises separating suction cups 13, which are vertically movable above the stack of sheets 09 to lift the uppermost sheet 11 from the stack of sheets 09, and transport suction cups 14, which take over the lifted sheet 11 from the separating suction cups 13 to pull it in a substantially horizontal direction onto the conveyor table 02. The conveyor table 02 comprises, in a manner customary in the industry, a flat table top 15, deflection rollers 16 arranged at the front or rear edge of the table top 15 in the transport direction T of the arc 11, and one or more conveyor belts 18 which are looped around the deflection rollers 16, so that an upper run of the conveyor belt 18 rests on the table top 15, while a lower run is taut below the table top 15 by rollers 19. A feed table 21 of the sheet feeder 03 is flush with the table top 15. On the downstream edge of this feed table 21 are retractable front marks 23 and a gripper beam 24 pivoting about an axis. By having the front edges of the sheets 11 touch the front marks 23 at at least two points, the sheets 11 are stopped and their edges are aligned perpendicular or parallel to the transport direction T of the sheets 11. The gripper bar 24 transfers the leading edge of a gripped sheet 11 to a cylinder 25, e.g., gripper cylinder 25, which in turn passes the sheet 11 to the transport and impression cylinder 08 of the first printing unit 05. After passing through a printing gap 26 between the transport and impression cylinder 08 and a cylinder 27, e.g., blanket cylinder 27, the sheet 11 reaches a second gripper cylinder 25 and via this to the next printing unit 05. The boom 04 connects to a transport and counter-pressure cylinder 08 of a final unit 05; 06, here the coating unit 06. The boom 04 comprises chains 28, which are placed over and driven by sprockets and guided in laterally arranged guide rails (not shown). Gripper carriages 29 are arranged on these chains for transporting the sheets 11. From the gripper carriages 29, the sheets are conveyed along a lower run of the chains 28 to a delivery stack 31, which is stored, for example, on a pallet 30 or another type of transportable stacking plate 30. For the safe transport of the sheets 11 held by the gripper carriages 29, a sheet guiding device is provided in the sheet boom 04. The sheet guiding device has sheet guide plates facing the gripper carriages 29, which are equipped with air nozzles and extend across the width of the machine. Air boxes are arranged below the sheet guide plates, through which the air nozzles are supplied with compressed air, so that a cushion of air is formed between the sheet guide plates and the sheets 11 transported by the gripper carriages 29. In front of the delivery stack 31, an unspecified braking device is arranged to decelerate the sheets 11 released by the gripper carriages 29. The braking device may include rotating suction rings and / or circulating suction belts or be designed as a secondary gripper system. The sheets 11, decelerated by the braking device, rest against front stops and are thus aligned and deposited onto the delivery stack 31. The delivery stack 31 is preferably lowered by a stack lift drive by the thickness of each sheet deposited, so that the stack surface maintains a nearly constant level. A control unit 32 monitors the level of the pallet 30, which serves as the base for the delivery stack 31. When the pallet is lowered to a limit level, the delivery stack 31 is complete and must be removed. When this occurs, the control unit 32 stops the movement of the sheet separator 12 and the conveyor belts 18 in the sheet feeder 03, preventing new sheets 11 from the feeder stack 09 onto the feed table 21. The leading marks 23 remain stationary, projecting above the feed table 21. The gripper bar 24 continues its pendulum motion unchanged, but can no longer grasp a sheet 11 on the feed table 21 because its path is blocked by the leading marks 23. The gripper cylinders 25 and the transport and counter-pressure cylinders 08 also continue to rotate without interruption. Fig. 2 and Fig. 3 show one of the printing units 05 in operating position, while sheets 11 are conveyed through the printing gap 26 of the printing unit 05, or when printing is interrupted due to the removal of the delivery stack 31. The blanket cylinder 27 is movably mounted about the axis of the plate cylinder 07, illustrated here by a link 33 that connects the frame-fixed axis 34 of the plate cylinder 07 with a movable axis 35 of the blanket cylinder 27. The link 33 is acted upon counterclockwise by means not shown, such as a spring, so that a surface of the blanket cylinder 27 not involved in the transmission of the printed image is pressed against an eccentric 36. The eccentric 36 comprises a toothed ring that engages with a rack 37. The rack 37 is rigidly connected to a first point of application 38, here on a piston, of a hydraulic or pneumatic actuator 39, from which a second point of application 40, here located on a cylinder of the actuator 39, is articulated to a lever 41. The actuator 39 is in a stop position, here with the piston fully extended.The lever 41 is pivotable about a frame-fixed axis 42. A first actuating element 43 has a frame-fixed point of application 44 and a point of application 45 on the lever 41. The point of application 45 is further away from the axis 42 than the point of application 40. The actuator 43 is expandable and contractable in the position shown. Contraction of the actuator 43 causes the lever 41 to rotate clockwise, the rack 37 to move downwards, and the eccentric 36 to rotate clockwise. This pushes the rubber blanket cylinder 27 in Fig. 2 to the left, thus narrowing the printing gap 26. Similarly, expansion of the actuator 43 widens the printing gap 26. Therefore, by adjusting the actuator 43, the width of the printing gap 26 can be adapted to the thickness of the sheets 11 to be printed. The actuator 39 is only contractible in the position shown in Fig. 2. Its contraction causes the pressure gap 26 to widen. Due to the different lever arm lengths, a contraction of the actuator 39 by a given amount ΔI causes a greater widening of the pressure gap 26 than an expansion of the actuator 43 by the same amount ΔI. Therefore, the actuator 39 can open the pressure gap 26 faster than the actuator 43, even if both have the same cross-section and the same flow rate of pressurized fluid. Furthermore, to enable rapid adjustment, the actuator 39 can have a smaller cross-section than the actuator 43, or its inlets and outlets for pressurized fluid can have a larger cross-section than those of the actuator 43. An inking unit 46 arranged above the plate cylinder 07 is in operation in the position of Fig. 2; an uninterrupted chain of rollers touching each other in pairs extends from a first inking unit roller 48 cooperating with an ink lifter 47 via friction rollers 49 and ink application rollers 50 to the plate cylinder 07. In Fig. 3, the actuator 39 is contracted, and thereby the eccentric 36 is rotated into a position in which the width of the printing gap 26 is large enough to reliably prevent contact between the cylinders 08 and 27 when no sheet 11 is located in the printing gap 26. The transport and impression cylinder 08 thus remains free of ink, and a printed image on the blanket cylinder 27 therefore remains unchanged as it passes through the printing gap 26. Since the starting position of the rubber blanket cylinder 27 can vary depending on the sheet thickness set on the actuator 43, the control unit 32 is expediently coupled to the actuators in order to detect the position of the actuator 43 during printing and, based on this, to control the adjustment of the actuator 39 necessary to interrupt the printing operation. The inking rollers 50 are pivoted about the axes of the friction rollers 49 contacting them in the position shown in Fig. 3, and are thus moved away from the surface of the plate cylinder 07, so that no fresh ink is transferred to the plate cylinder 07. At the same time, the ink lifter 47 is deactivated, and individual rollers 51 within the inking unit 46 may also be adjusted to prevent ink transport within the inking unit 46 and thus counteract any change in the ink layer thickness on the rollers of the inking unit 46 during the printing interruption. After removing the delivery stack 31 and placing an empty stacking plate 30 on the sheet delivery arm 04, it is sufficient to resume the sheet feed from the feed stack 09 and, immediately before the arrival of the first new sheet 11 in each printing unit 05, to return the actuating element 39 to the stop position in order to restore the previously set width of the printing gap 26. Reference symbol list 01 Sheet feeder 02 Belt table 03 Sheet feeder 04 Sheet delivery 05 Printing unit 06 Coating unit 07 Plate cylinder 08 Transport and impression cylinder 09 Stack 10 Stacking plate 11 Sheet 12 Sheet separator 13 Separator suction cup 14 Transport suction cup 15 Table top 16 Deflection roller 17-18 Conveyor belt 19 Roller 20-21 Feeding table 22-23 Front mark 24 Gripper beam 25 Gripper cylinder 26 Printing gap 27 Transport and blanket cylinder 28 Chain 29 Gripper carriage 30 Pallet 31 Delivery stack 32 Control unit 33 Link 34 Axle 35 Axle 36 Eccentric 37 Rack 38 Point of contact 39 Actuator 40 Point of contact 41 Lever 42 Axle 43 Actuator 44 Point of attack 45 Point of attack 46 Inking unit 47 Ink lifter 48 Inking unit roller 49 Rubbing roller 50 Ink application roller 51 Roller T Transport direction

Claims

Sheet-fed printing press with two cylinders (27; 08) defining a printing gap (26), at least one cylinder (27) of which is adjustable in a radial direction by a first actuator (43) to vary the width of the printing gap (26), wherein a second actuator (39) acts on one of the cylinders (27) to adjust the width of the printing gap (26) at a higher speed than the first actuator (43), characterized in that it further comprises a sheet delivery (04) and a control unit (32) is provided to widen the printing gap (26) by means of the second actuator (39) during a stack change at the sheet delivery (04), and in that the second actuator (39) is coupled to a sheet feeder (01) to interrupt the feeding of a sheet (11) by the sheet feeder (01) to the printing gap (26) while the printing gap (26) is being adjusted by the second actuator (39). has widened. Sheet-fed printing press according to claim 1, characterized in that the first and the second actuating element (39; 43) act on the same cylinder (27). Sheet-fed printing press according to claim 2, characterized in that one of the actuators (43; 39) has a frame-fixed first point of application (44) and an adjustable second point of application (45), and that of two mutually movable points of application (38; 40) of the other actuator (39; 43) one point of application (38) is connected to the cylinder (27) and the other point of application (40) is connected to the second point of application (45) of the one actuator (43; 39). Sheet-fed printing press according to claim 3, characterized in that the actuating elements (39; 43) are connected via a lever (41) and the point of application (40) of the second actuating element (39) on the lever (41) has a shorter lever arm than the point of application (45) of the first actuating element (43). Sheet-fed printing press according to one of the preceding claims, characterized in that the second actuating element (39) is held in a stop position during the printing process and is arranged to widen the printing gap (26) when leaving the stop position. Sheet-fed printing press according to claim 1, characterized in that the second actuating element (39) is functionally coupled to an inking unit (46) in order to interrupt the ink transport via the inking unit (46) to the printing gap (26) while the printing gap (26) is widened by the second actuating element (39).

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