GB2272403A

GB2272403A - Printing press plate tensioning device

Info

Publication number: GB2272403A
Application number: GB9323354A
Authority: GB
Inventors: Roland Hoell; Manfred Herold; Josef Mathes
Original assignee: MAN Roland Druckmaschinen AG
Current assignee: Manroland AG
Priority date: 1992-11-12
Filing date: 1993-11-12
Publication date: 1994-05-18
Anticipated expiration: 2013-11-12
Also published as: GB9323354D0; DE4238121A1; JP2635921B2; GB2272403B; FR2697775B1; FR2697775A1; JPH06198849A; DE4238121C2

Abstract

A device for tensioning a printing plate on the plate cylinder of a printing press, e.g. an offset sheet printing press, is of compact construction and uses fluid motors which apply a tensioning force to one or more bars (3.1, 3.2) which extend across the width of the printing plate and clamp one end of the plate. The bar (3.1) is supported along its length by several adjustment screws (4) bearing on individual edge cams (5). The cams are disposed in a longitudinal recess in the plate cylinder surface. Each cam (5) is rotated, to displace the bar and the end of the printing plate, by means of a fluid motor (10), which may be a double-acting hydraulic cylinder with a toothed rod (13) engaging a pinion (9) rotatable with the cam. <IMAGE>

Description

2272403 PRINTING PRESSES The invention relates to printing presses, and

particularly to a device for tensioning printing plates on the plate cylinder of a printing press.

The plate cylinders of known offset sheet printing presses have, in a channel running parallel to the cylinder axis, tensioning bars arranged for the lead and the trail ends of a printing plate. A printing plate to be tensioned is inserted with its lead edge towards its tensioning bar, fixed therein (clamped), and then laid around the exterior periphery of the plate cylinder until the trail edge can be fixed to its tensioning bar. After this, the printing plate is tensioned by moving the respective tensioning bar, by manually-actuatable (e.g. tensioning bolts) or remotely- actuatable devices, away from the respective wall of the channel towards the centre of the channel. Particularly with large format printing plates, it is important for satisfactory printing results that the tensioning force exerted on the trail end of the printing plate is exerted uniformly across its width.

A rapid tensioning unit for flexible printing plates as disclosed in DE-2 200 187 C3 has a series switching of a rapid tension eccentric (several eccentrics seated on a central tensioning shaft) and individual tensioning bolts extending through the respective tensioning bar. In order that the tensioning force to be transferred from the eccentrics on to the tensioning bolts for the print end of the printing plate is not exceeded, in the force transfer path between the eccentrics and the tensioning bolts springs are arranged which prevent any overextension of the printing plate. Disadvantageous in this known unit is that the rapid tensioning takes place via a central tensioning shaft and accordingly, with a remotely-operable set-up of the plate cylinder, a motor of really large dimensions has to be provided.

EP-0 425 936 A2 discloses a device for tensioning printing plates in which an adjusting drive, becoming active on being subjected to a pressure medium, drives a rapid tensioning mechanism. The rapid tensioning mechanism according to this specification consists of a format-width pressure bar which is supported via inclined planes on corresponding counterpieces fixed to the cylinder of the print end wall of the cylinder channel and accordingly moves the rear tensioning bar via individual tensioning bolts in the direction of the centre of the cylinder channel. In order that also here the tensioning force exerted by the rapid tensioning device on the print end of the printing plate does not over-extend the plate, springs and support levers are arranged relative to the individual tensioning bolts as force control means. Also here it is to be seen as disadvantageous that additional force limiting means are to be provided, and furthermore the rapid tensioning lc k 3 - mechanism only emerges from a drive which has to be dimensioned correspondingly large.

DE 3 604 071 C2 discloses a printing plate tensioning unit in which the rear tensioning bar is pressed away via several hydraulic pistons set axially spaced apart from the corresponding wall of the cylinder channel. In order that the tensioning force exerted on the printing plate can continue to be maintained without maintenance of the hydraulic pressure, additional locking mechanisms are provided. This additional constructional outlay should be seen as disadvantageous and, furthermore, this sort of tensioning bar because of the hydraulic piston integrated therein, is constructed overall quite otherwise than the is manually-actuatable tensioning bars. Also, no manuallyactuatable adjustment means are provided by which the rear tensioning bar for example before tensioning can be aligned exactly parallel to the nominal print end of the plate cylinder.

DE-3 936 446 C2 discloses a plate cylinder of a printing press in which the front and rear tensioning bars are mounted swivellably in the cylinder channel for corrections (oblique register). Both tensioning bars are pressed away from the respective wall of the cylinder channel by means of springs, and are returned by means of roller levers of eccentrics against these spring forces into the desired positions. The roller levers or eccentrics lie in the plane in which the swivelling or displacement of the tensioning bars takes place, though these adjusting means are also located in the cylinder channel in such a way that the swivelling of the tensioning bars takes place against the spring forces between cylinder channel wall and tensioning bar. The tensioning of the printing plate via the rear tensioning bar in this unit thus takes place by means of force stored in the springs. By means of stored spring forces, however, large differences in printing plate length cannot however be compensated on tensioning the printing plate.

The object of the present invention is accordingly to improve a tensioning device in such a way that, in a small volume, it provides even generation of a tensioning force for the printing plate ends across the format width, wherein the drive means to be used, which becomes active on subjecting it to a pressure medium, should makepossible a maintenance of the tensioning force during printing without additional locking means.

In accordance with the invention, it is provided that each tensioning bolt of the rear tensioning bar is arranged relative to a cam disc provided, for example, with a spiral cam surface against which the ends of the respective tensioning bolts bears, and furthermore the cam discs lie parallel to that plane in which the movement of the tensioning bar takes place, with each cam disc being rotatable by means of a drive which becomes active on being subjected to pressure medium arranged thereto in each case.

In the case of the drives, in advantageous fashion these can be hydraulic drives. The preferred embodiment of the invention provides for this in such a way that each drive is constructed as a double-acting hydraulic cylinder, on the piston rod of which a toothed rod is fixed. This toothed rod meshes with a pinion which is connected with the respective cam disc. With such an embodiment of the X invention, the individual drives for the cam discs lie in very space-saving fashion directly below the rear tensioning bar. The orientation of the individual hydraulic linear drives (double-acting cylinders) is thereby parallel to the tensioning bar.

In a further embodiment of the invention, it can be provided that each individual cam disc can be driven via a rotary vane motor, in particular hydraulically actuatable. arranged thereto.

is By the use of cam discs provided in accordance with the invention having an end face exterior contour formed spiral shaped, there emerges in contrast to known eccentrics or other cam disc with even or continuous cam surface the advantage that the complete stroke provided by the cam disc is available for use with substantially one revolution of the cam disc. In the case of an eccentric, the maximum stroke is achieved only with half a revolution. One thus achieves an optimal usage in the conversion of a rotational movement into a travel movement for tensioning the printing plate.

Because each tensioning bolt is supported directly with its free end on the cam surface, there arises a backlashfree generation of the tensioning force on the tensioning bar. In this way the tensioning force exerted on the printing plate is maintained even when the hydraulic rams are not pressurised. With appropriate determination on the one hand of the coefficient of sliding friction between each bolt and the cam surface and on the other hand the stroke of the cam, a device is produced which is self-clamping and which maintains the tension in the printing plate. Also adjustment of the tensioning bolts 6 - generates no backlash forces.

Since each of the several tensioning bolts distributed across the format width of the tensioning bar has a cam disc with a separate drive arranged relative to it,, by each drive only a part of the overall tensioning force has to be applied. These several drives require in each case for themselves less space than a correspondingly dimensioned individual drive, and are accordingly easier to accommodate underneath the rear tensioning bar.

Since several hydraulic drives are provided, yet a further advantage is, however, evident. If all hydraulic drives are simultaneously subjected to the same pressure, is then a divided rear tensioning bar pulls the print end region of the printing plate with a force which is nearly uniform across the format width. By controlling one or several, but not all, of the drives also a one-sided or a desired distortion of the printing plate on the plate cylinder is possible. This can be advantageous in particular when correcting register errors, which are generated by subject dependent paper pulling. The individual drives for the cam discs are, in this connection, advantageously controlled with the slowly turning plate cylinder corresponding to the desired correction.

The feed of the pressure medium (hydraulic oil) to supply the individual drives takes place via one or two rotary connections installed on the trunnion(s) of the plate cylinder.

Since the rear tensioning bar is supported on the several cam discs, in each case respectively via a tensioning 1 - 7 bolt and as well as the corrections which can be achieved by corresponding control of the individual drives naturally also subsequent manual corrections are possible for example with the printing plate already tensioned. In particular, the rear tensioning bar can be oriented by the tensioning bolts in the starting position before the tensioning of a printing plate exactly parallel to the nominal print end of the plate cylinder.

An advantage likewise to be promoted of the present invention is that the tensioning bar itself, as well as its mounting relative to the movability in the channel of the plate cylinder, is the same as those tensioning bars which are to be actuated with a customary hand-operated rapid tensioning mechanism.

An exemplary embodiment of the present invention will mow be described with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a tensioning bar in a channel of a plate cylinder; Figure 2 shows the drives for the individual cam discs in the plane below the tensioning bar, and Figure 3 is a section through the tensioning bar showing the location of its drive.

Figure 1 shows a part of a plate cylinder 1 with a channel 2 in its outer surface parallel to the cylinder axis. At the wall turned towards the print end DE of the channel 2, a rear tensioning bar 3 is arranged which is of divided construction. As is evident in Figure 3, this tensioning bar 3 consists of a lower clamping bar 3.1 and an upper clamping bar 3.2. In Figure 3, likewise the actuation mechanism is indicated by means of which the upper movable clamping rail 3.2 can be clamped (by motor hydraulically) relative to the lower clamping rail 3.1 to receive the end of a printing plate.

The rear divided tensioning bar 3 has four tensioning bolts 4 wherei n as illustrated in Figure 3, the tensioning bolts 4 in each case being screw-threaded into the lower clamping rail 3.1. Each end of the tensioning bolt 4 which has been threaded through the clamping rail 3 bears against a cam disc 5 arranged in each case rotatably in the region of the trail end DE of the printing plate intended to be wrapped around plate cylinder 1. The cam discs 5 seen end-on have an exterior one-turn spiral cam surface. In the transition between the minimum and maximum radius of the cam surface 5 accordingly a step 5.1 arises.

The cam discs 5 arranged relative to the tensioning bolts 4 lie parallel to the plane of extension of the tensioning bar 3 or in the plane of the tensioning bolts 4 (Figure 3). The tensioning bar 3 is arranged by guides or mountings (not shown) in such a way in the channel 2 of the plate cylinder 1 that for tensioning a printing plate, it can carry out the necessary movement and in particular also an axial justification of the printing plate end is possible.

In Figure 1, the cam discs 5 are reproduced in a position in which the tensioning rail 3 is located in a wholly detensioned position and accordingly takes up the smallest distance relative to nominal trail end DE of the plate v A 911 cylinder 1. Correspondingly, the tensioning screws 4 support themselves on the region of the cam surface with the smallest radius. The step 5.1 of the cam discs 5 accordingly lies substantially next to the shafts of the tensioning bolts 4. The tensioning bolts 4 are screwed into the tensioning bar 3 so that the maximum stroke of the cam disc 5 does not come into contact with the tensioning bar 3 or the lower clamping rail 3. 1.

The rotational axes of the cams 5, as well as the axes of the tensioning bolts 4, lie in two planes perpendicular to one another, wherein here such an offset of the axes relative to one another can be provided so that, as far as possible, the ends of the bolts 4 sit squarely on the cam surface. Between the cam surfaces and the tensioning bolts 4 there arises friction inhibiting rotation of the tensioning bolts 4 and the cams.

As shown in Figure 3, each cam disc 5 is arranged in a correspondingly-shaped recess 6 in the region below the print end DE of the plate cylinder 1, and is located there fast on one end of shaft 7. Shaft 7 is rotatably mounted in a post 8 fixed relative to the cylinder and has on its other end in each case a pinion 9 with external teeth. This pinion 9 in turn is located in a recess towards the cylinder. Below the tensioning bar 3 in the channel 2 of plate cylinder 1 are arranged the drives 10 which are arranged relative to each cam disc 5 which become active on being subjected to fluid pressure.

As illustrated in Figures 1 and 2 with a divided tensioning rail 3, the orientation of cam discs 5 as well as the drives 10 is arranged in mirrorimage fashion relative to the centre of the plate cylinder 1.

Each drive 10 consists in accordance with the present exemplary embodiment of a hydraulic double-acting cylinder 11 which on its piston rod 12 has in each case a toothed rod 13. Each toothed rod 13 meshes with a pinion 9 of the cam disc 5 correspondingly arranged thereto and is mounted on the floor of the channel 2 of plate cylinder 1 movable linearly. The mounting of the toothed rod 13 with respect to the pinion 9 is structured in this connection in such a way that the necessary pressing on force with respect to the pinion 9 is provided. The hydraulic ram exemplified is only one example of fluid motor which is used to rotate each cam, of which another example is a rotary vane motor.

is On subjecting the working cylinder 11 to pressure, pinion 9 is turned via the toothed rod 13, together with cam 5. There thus arises the displacement of the tensioning bar 3 away from the trail end DE. The hydraulic feed lines for the working cylinders 11 or the drives 10 are not 20 illustrated in the drawings.

1

Claims

1. Device for tensioning printing plates on plate cylinders of printing presses, particularly offset sheet printing presses in which, in a longitudinal recess in the surface of the plate cylinder, there is arranged at least one displaceable tensioning bar to which one end of a printing plate may be secured and which has at least 10 two adjustment screws projecting from it, in which the projecting end of each screw bears on a rotary edge cam, with the cams lying in the plane of the screws and being able to be rotated, either singly or in unison, by means of individual fluid motors.

is

2. Device according to Claim 1, in which the fluid motors for the individual cams are disposed in the recess below the tensioning bar.

3. Device according to Claim 1 or 2, in which each fluid motor is a double-acting hydraulic cylinder to the piston rod of which a toothed rod is applied which meshes with a pinion fast with a cam.

4. Device according to Claim 1 or 2, in which the fluid motor for each cam is a hydraulically-actuatable rotary vane motor.