GB2167712A - Device for clamping and adjusting a print plate on the plate cylinder of a printing machine - Google Patents

Abstract

In a device for clamping and adjusting a print plate (10) on the plate cylinder (1) of a printing machine, the plate cylinder having two clamping rails (4, 5), arranged in an axially-extending channel (12) of the plate cylinder, for clamping the leading and trailing edges of the print plate, the leading edge being clamped in a front clamping rail (4) supported in the peripheral direction of the plate cylinder, by means of at least two adjusting screws (11) against one wall (12) of the channel, each adjusting screw carrying a graduated member (15) for facilitating setting of the screw, a latching device (17) is provided for each adjusting screw mounted in the front clamping rail to set the normal fixed position of the graduated member. <IMAGE>

Description

SPECIFICATION Device for clamping and adjusting a print plate on the plate cylinder of a printing machine This invention relates rio a device for clamping and possibly adjusting .i1e clamped position of a print plate on the plate cylinder of a printing machine, the cylir:ser having two clamping rails, arranged in an axially directed channel of the plate cylinder, for clamping leading and trailing edges of the print plate. A front clamping rail is used to clamp the leading end of the print plate and includes at least two adjusting screws supported in the peripheral direction of the cylinder against a wall of the channel, each adjusting screw carrying a graduated member for facilitating setting of the adjusting screw.

In clamping and adjusting a print plate on the plate cylinder of a sheet-fed rotary offset printing machine, the leading end of the print plate is clamped into the front clamping rail in a position precisely defined by means of dowel pins (see German Patent Specification 1,786,317). The trailing end of the print plate is clamped into a rear clamping rail without the aid of dowel pins. The front clamping rail is then moved into a precisely defined zero position by means of the adjusting screws, whereupon the print plate is tensioned around the plate cylinder by means of further adjusting screws provided at the rear clamping rail, which further adjusting screws are supported against a rear wall of the channel.

To facilitate locating the normal fixing position of the front clamping rail, the graduated member fixed to each adjusting screw is adjusted in the normal fixing position to a certain mark, for example zero. Typically the graduated member is a disc.

If it then turns out that the print plates of the individual inking units arranged one after the other are not exactly in register with each other when printing starts, the position of one or more of the print plates, with the aid of the adjusting screws, can be adjusted comparatively easily on the respective plate cylinder by the adjusting screws being individually turned in one direction or the other. By means of the scale located on each graduated member, which scale is calibrated, for example, in 1/10 mm steps, a positional error, which can be easily read off from a printed sheet obtained from the machine, can be corrected directly on the machine.

Now it has been shown that, during the work necessary to clamp and adjust the print plate on the plate cylinder, setting the adjusting screws to the zero position of the graduated member corresponding to the normal fixing position, is comparatively tedious, because it requires experience and further, the adjusting screws can rotate out of the zero position comparatively easily during the operation. In this way, clamping and adjusting a print plate on the plate cylinder too frequently becomes a very time-consuming operation.

One aim of the present invention is therefore to improve the known device in such a way that the normal fixing position of the adjusting screw defined after a single adjustment by means of the graduated member fixed in a defined position on the adjusting screw can be located quickly and accurately and subsequent unintentional displacements of the adjusting screws during clamping and adjusting are safely prevented.

This aim can be achieved according to the invention by providing a latching device for each adjusting screw mounted in the front clamping rail, which latching device sets the normal fixed position of the graduated member. Suitably, the latching device engages in a depression provided on a graduated disc member.

In a device according to the invention, the adjusting screws, at the start of a clamping and adjusting operation, can be turned quickly and simply, without even looking, into the zero position specifying the normal fixing position; the latching device, during the further work, keeps each adjusting screw safely in the zero position once the latter has been located. However, subsequent adjusting of the print plate on the plate cylinder is not impaired, because the adjusting screws can, when required, be turned easily out of the latched position.

In a preferred embodiment, the graduated member is a disc and the latching device consists of a pin which is flexibly movable parallel to the axis of the adjusting screw and has a free end formed as a hemisphere, a latching depression being provided on the side of the graduated disc, which faces towards the clamping rail.

The normal fixing position of each adjusting screw can be established in such a way that it is signalled when each adjusting screw is screwed in and the first noticeable latching of the latching pin into the depression is detected. When there is adequate spring travel of the latching pin, one or more further latching positions will be attained when the adjusting screws are turned, one, two or more complete turns, so that, in each case these further latched positions differ from the normal fixing position by an integral number of multiples of the pitch of the screw. The integral multiple of the pitch of the adjusting screw can be marked in both directions of rotation of the adjusting screw so that instead of selecting the first latching point, a subsequent latching point, for example the second or third, can be selected as the normal fixing position of the adjusting screw.

In a further preferred embodiment, the latching device consists of a ball which is flexibly mounted to move perpendicular to the axis of the adjusting screw and the latching depression is arranged on the periphery of a graduated disc member.

With this arrangement, only one fixing position is obtained over the entire screw-in length of the adjusting screws. This represents a further simplification, because normally only a few tenths of a millimetre need to be compensated for, by means of the adjusting screw, from this fixing position.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 shows a schematic partial section of a plate cylinder with a channel and clamping rails arranged therein, and Figures 2 and 3 show partial views, in the direction of the arrow A of Figure 1, of respective first and second embodiments of latching device.

Figure 1 shows a partial section through a plate cylinder 1 of a printing machine, which section extends transversely to the axis of the plate cylinder 1. A channel 2 is formed in the cylinder 1 which extends parallel to the axis of the cylinder. A plurality of guide strips 3, extending in the peripheral direction of the plate cylinder 1, are fixed in the base of the channel 2, each guide strip 3 being in engagement, via a dovetail channel connection, with respective front and rear clamping rails 4 and 5. The clamping rails 4 and 5 each comprise a clamping strip 6 and a cover strip 7, the strip 7 being fixed to the strip 6 by means of a number of cover screws 8. The front edge of a print plate 10 consists of flexible material and is held in place at the start of a printing operation by means of two dowel pins 9 arranged along the front clamping rail 4.The dowel pins 9 engage into both the strips 6 and 7. (Only those details of the clamping rail arrangement in the channel which are necessary for an understanding of how it operates are shown in Figure 1.) At least two adjusting screws 11 are threaded into the front clamping rail 4, the head of each adjusting screw 11 lying towards the centre of the channel, and the opposite end of each adjusting screw 11 bearing against the front wall 12 of the channel 2. In a similar manner, further clamping screws 13 are threaded into the rear clamping rail 5, these further clamping screws 13 bearing against the rear channel wall 14 of the channel 2.

Additional adjusting screws 11 can be arranged between the adjusting screws 11 of the front clamping rail 4, should it be found that the front clamping rail 4 deflects too severely when only two adjusting screws 11 are used. Likewise, additional screws 8 and 13 can be used if required.

Each adjusting screw 11 is provided with an unthreaded shoulder region adjacent to its head, in which shoulder region an axially directed groove (not shown) is formed. A graduated disc 15 is located on this shoulder region and is fixed to the adjusting screw 11 by means of a grub screw 16 engaging in the groove.

In the embodiment shown in Figure 2, a pin 17, which is movable parallel to the axis of the adjusting screw 11 and has a free end radiused hemispherically, is fixed in the front clamping rail 4 and engages into a latching depression 18 formed on that side of the graduated disc 15 which confronts the front clamping rail 4.

In the embodiment shown in Figure 3, an Lshaped holder 19 is fixed to the front clamping rail 4. A through bore is provided in one leg of the holder 19, which bore accommodates a ball 21 which is acted upon by a compression spring 20 to move perpendicularly to the axis of the adjusting screw 11. In its latched position, the ball 21 locates in a latching depression 22 provided on the periphery of the graduated disc 15.The normal fixing position of the front clamping rail 4 is set by the manufacturer, or when setting up the printing machine, by the adjusting screws 11 being screwed into the clamping rails 4 until a so-called register position is reached and the front end of the screws 11 project by a certain reproducible distance out of the clamping rails 4, which corresponds to the requisite distance between the front channel wall 12 and the adjacent edge of the clamping rail 4. The graduated discs 15 are thereupon fixed in their zero positions by means of the grub screws 16.

Since the graduated discs 15 are adjustably attached to the adjusting screws 11, small changes arising from time to time, for example, as a result of wear, can be compensated for.

Before a print plate 10 is clamped in place on the plate cylinder 1, the clamping rails 4 and 5 are first of all moved on the guide strips 3 in the peripheral direction of the plate cylinder 1 towards the respective adjacent channel wall 12, 14.

When the cover strip 7 is released, stamped dowel holes, spaced apart along the front edge of the print plate 10, can be located one over each dowel pin, whereupon the cover strip 7 can be refastened by means of the cover screws 8. Thus the front edge of the print plate 10 is clamped in a precisely defined position relative to the front clamping rail 4. The print plate 10, which is flexible in the peripheral direction of the plate cylinder 1, is then drawn onto the generated surface of the latter, normally over the top of an underlay (not shown), which can slide relative to the cylinder 1 and the plate 10. The rear edge of the print plate 10 is then fastened in a similar manner in the rear clamping rail 5.After that, or immediately after the clamping of the front ede of the print plate 10 into the front clamping rail 4, the adjusting screws 11 are turned manually into the required latching position, so that the front edge of the print plate 10 is located, via the front clamping rail 4, in a precisely defined normal fixing position relative to the plate cylinder 1. The clamping screws 13 of the rear clamping rail 5 are then tightened to the degree required to correctly tension the plate 10 on the cylinder 1. Thus the entire print plate 10 is located in a precisely defined position which in most cases will not need further adjustment.

However, if it is apparent during a printing operation, that there are registration errors between the respective printing machine print plates used one after the other in a multicolour printing operation, the registration errors can be gauged with a graduated magnifying glass, the clamping screws 13 can be slackened slightly and the noted registration errors compensated by turning the adjusting screws 11. After retightening the clamping screws 13, the printing machine can resume operation. To reset the machine for a new commission, the zero start position for the screws 11 can be easily found by means of the latch arrangement 17,18; 21, 22.

Claims (6)

1. A device for clamping and adjusting a print plate on the plate cylinder of a printing machine, the plate cylinder having two clamping rails, arranged in an axially-extending channel of the plate cylinder, for clamping the leading and trailing edges of the print plate, the leading edge being clamped in a front clamping rail supported in the peripheral direction of the plate cylinder, by means of at least two adjusting screws against one wall of the channel, each adjusting screw carrying a graduated member for facilitating setting of the screw, wherein a latching device is provided for each adjusting screw mounted in the front clamping rail, which latching device sets the normal fixed position of the graduated member.

2. A device according to claim 1, in which each latching device comprises a pin, which is resiliently movable parallel to the axis of the respective adjusting screw and has a radiused free end, and a latching depression provided in the graduated member to receive the radiused end of the said pin.

3. A device according to claim 2, in which the graduated member is a disc, the side thereof which faces the front clamping rail containing the latching depression.

4. A device according to claim 1, in which each latching device comprises a ball which is resiliently movable perpendicular to the axis of the respective adjusting screw and a latching depression provided in the periphery of the graduated member.

5. A device for clamping and adjusting a printing plate on the plate cylinder of a printing machine substan-tially as hereinbefore described with reference to, and as illustrated in, Figures 1 and 2 or Figure 3 of the accompanying drawings.

6. A printing machine incorporating at least one device as claimed in any preceding claim.