GB2031341A

GB2031341A - An adjusting device for lithographic printing plates

Info

Publication number: GB2031341A
Application number: GB7931706A
Authority: GB
Original assignee: Dainippon Screen Manufacturing Co Ltd
Current assignee: Dainippon Screen Manufacturing Co Ltd
Priority date: 1978-09-19
Filing date: 1979-09-12
Publication date: 1980-04-23
Also published as: JPS5545574U; JPS6210128Y2; FR2436679B1; DE2937880A1; FR2436679A1; GB2031341B

Abstract

A device for controlling adjustment of position of a printing plate in a lithographic cylinder printing press comprises an optical detector e.g. microscope(s) 27 mounted to a support 19 and movable sideways and lengthwise relative to the support, and fixable thereto. The support can be detachably mounted to the frame of the press in a predetermined position relative thereto so that the optical detector is inspecting the surface of a printing plate on a printing plate bed and can be fixed to the support in a particular position. Registration pins 16, cooperating with holes 17a, 17b are adjusted to accurately register subsequent plates with the first one inspected. Optionally, when the press comprises several printing plate beds, the support can be detachably mounted to the frame in several positions, one for each bed, so that points on plates positioned on the beds, which correspond to the same position in the visual field of the detector as the support is moved between its various positions, without the fixing of the detector thereto being broken, are printed to the same point on the printing paper, with the plates in these positions. <IMAGE>

Description

SPECIFICATION An adjusting device for lithographic printing plates The present invention relates to a lithographic printing press, and in particular to a device for positioning printing plates which are supported on printing beds in such a lithographic printing press, in order to ensure that the various plates in multicolor printing are correctly aligned.

The usual way for ensuring that the various plates are in register, in multicolor printing on a - lithographic press, is that register marks are included in the images on the plates, and a trial printing is made onto a piece of printing paper. If, then, the plates are not perfectly aligned together, the printed images of the register marks will not be properly superimposed, which can easily be detected by eye. Then the printing plates are repositioned.

However, this method requires a lot of time, and wastes paper during the trial printing. It would be advantageous if a method could be devised of correctly positioning the plates directly, without trial printing.

Summary of the invention Therefore, it is an object of the present invention to provide a device for controlling the adjustment of a printing plate on a printing plate bed, in a printing press, which can allowthe plate to be directly adjusted without trial printing.

According to the present invention, this, and other, objects are accomplished by, in a lithographic printing press comprising: a frame; a printing paper bed for supporting paper to be printed on, mounted to the frame; a printing plate bed mounted to the frame, for supporting a printing plate to be printed from; a carriage which can be reciprocated to and fro over the beds; and a blanket cylinder mounted rotatably to the carriage so as to cooperate 'with the printing plate bed and the printing paper bed for printing: a device for controlling the adjustment of the position of the printing plate bed, comprising: a support; a first optical detector mounted to the support in a manner to be adjustably moved in the longitudinal and the transverse directions, and to be selectively fixed relative to the support in any of a range of positions, both longitudinally and transversely; and a means for detachably mounting the support to the frame in a predetermined position relative to the frame, so that, when a printing plate is supported by the printing plate bed, the opticar detector may be fixed to the support in a position where it it inspecting the surface of the printing plate.

Brief description of the drawings The present invention will become more fully and clearly understood from the following description of several preferred embodiments thereof, which is illustrated by the accompanying drawings. However, the description of the embodiments, and the drawings, should not be taken as limitative of the scope of the present invention in any way; this scope is to be defined solely by the accompanying claims. In the drawings: Fig. 1 is a side view in somewhat scheniatic form of a two-color lithographic proof press; Fig. 2 is an elevational view of a device according to the present invention for adjusting the position of a printing plate bed in the press of Fig. 1; Fig. 3 is a side view of the device of Fig. 2, taken in the direction of the arrows Ill-Ill in Fig.

2; and Fig. 4 is a perspective view of a register pin used in the device of Figs. 2 and 3.

Description of the preferred embodiments Fig. 1 shows a typical lithographic press to which the present invention can be applied. In this figure, 1 designates the frame of the machine, and printing plate beds 2.and 3 and a printing paper bed 4 are arranged in a row, with the printing paper bed at the end of the row. A carriage 5 can reciprocate to and fro over the beds. For each printing plate bed, a blanket cylinder (two in the shown press) is mounted to the carriage, rotatably, so as to move up and down with the correct, per se well known, timing, to perform printing. Water rollers 8, and the same number of color inking roller sets 9 and 10 as printing plate beds (two, here) are provided on the carriage, and also move up and down in a well-known way.On the left hand end as seen in the figure of the frame 1 are a damper 11 for supplying water to the rollers 8, and a water distributing plate 12. On the right hand end of the frame are color inking devices 13 and 1 4 for providing color ink to the inking roller sets 9 and 10.

This kind of machine performs multi-color printing with a single motion of the carriage, and accordingly, as mentioned above, it is essential that the printing plates should be so positioned on their beds that, when printing is performed, corresponding parts on the patterns on the plates should be printed to the same point on the paper; in other words, so that the patterns should be in register.

The same problem arises in the case of a press which has only one printing plate bed. In this case, first one printing plate corresponding to one color is laid on the bed, and all the pieces of paper to be printed are printed with that color. Then the machine is washed, the color ink is changed, a plate for another color is laid on the bed, and printing is performed with that color; and so on.

Here, again, it is necessary to align each printing plate so that corresponding points on the various designs on the plates are printed to the same points on the paper; but in this case the plates must be aligned one after the other on the same bed, rather than all together on different beds. The problem is the same.

An embodiment of the present invention is shown in Fig. 2, for use with such a press. Along each side of the frame, parallel to the direction of reciprocation of the carriage, are arranged racks 18, which, in this embodiment, are helical (i.e., slanted) racks with teeth inclined symmetrically, oppositely on the two sides. As can be better seen in Fig. 3, a frame composed of two rods 21 and two saddles 19 is placed on these racks 18, and engages with them by two short helical racks 20 located under the saddles 19.Thus, because the teeth of the racks 1 8 am oppositely slanted, the frame cannot move either sideways or longitudinally to the frame, but is held by its weight on the racks 1 8. Because the racks 18 are fairly coarse in pitch, the frame can be reliably lifted off the racks, and replaced in the same position with the same teeth of the racks 20 engaging the same teeth of the racks 18. In the shown embodiment, in fact, the racks 18 are also used for driving the blanket cylinders, by means of gear wheels fitted on the ends of the axles of the blanket cylinders, which are not shown, On the rods 21 of the frame, a second frame is slidably fitted, which is formed of two rods 23 and two supports 22 sliding on the rods 21. Thus this frame can be slid to the left and to the right in the drawing.Further, its sliding can be clamped and fixed by tightening the screws 24. On the rods 23, a microscope base 25 can be slid in the up and down directions in the drawing, and this sliding can be clamped by a screw 30. Thus the microscope can be moved both in the longitudinal and the transverse directions with respect to the frame 1 of the machine, and this motion can be fixed by clamping the screws 24 and 30. The microscope points downward to inspect the surface of a printing plate 1 7 laid on a printing plate bed 2 over which this apparatus is placed.

The microscope can be moved up and down by means of a support 26, an arm 28, and a screw 29.

In the shown embodiment, two such microscope assemblies are provided, one on each side of the press; and although this is preferable, it is not essential to the present invention.

25a denotes a hole in the base 25,so that the microscope can see through it.

Adjacent to the printing plate bed 2 is located a pin bar 15, which is not part of the present invention. In the pin bar 1 5 are set three register pins, which rotate in holes in the bar. Each of these pins 16 is as shown in Fig. 4. That is, it is formed of a squat cylinder 31 which has eccentrically placed on its top a smaller squat cylinder 32 with a slot 33 formed in it. The tops of the larger cylinders 31 are flush with the top of the bar 1 5, but the smaller cylinders 32 protrude.

The printing plate 17, shown in Fig. 2, as laid on the printing plate bed 2, is formed with two transverse slots 1 7a and one longitudinal slot 17b.

These siots cooperate with the three pins 1 6, so that, by turning these pins with a screwdriver, the position of the plate can be adjusted. In more detail, by turning the center pin 1 6 the plate can be moved transversely to the press, and by turning either one of the end pins 1 6 while keeping the other fixed, that side of the plate can be moved in the longitudinal direction of the press, without moving the other side of the plate. Thus the complete position of the plate, which has three degrees of freedom, can be adjusted.

The operation of the device of the present invention will now be described.

Each of the multicolor printing plates to be printed from has register marks printed on it and, for good and accurate color printing, the register marks must all be printed to the same positions on the paper. These register marks are not shown in the drawings.

First, the operation in the case of a press which has only one printing plate bed will be described.

In this case, as outlined above, the entire printing with one plate is performed, and then the plate is changed, and another printing is performed with another color, and so on. The first color printing plate is placed on the bed 2. Then the device according to the present invention is placed over the plate, with the racks 20 engaging the racks 1 8 in a predetermined engagement. The left and the right hand microscopes 27 are then moved by sliding the base 25 aiong the rods 23 and the supports 22 along the rods 21, until the register marks appear in standard positions in the visual field of the microscopes, for instance are aligned on cross hairs therein. Then the screws 24 and 30 are clamped, so as to fix the microscopes in the horizontal and vertical directions in Fig. 2.Then the device is removed from the press, and printing with the first color is performed.

Then the machine is cleaned, and a second plate is placed on the bed. The device is placed again over the bed, with the microscopes inspecting the surface of the plate, so that the same teeth of the racks 20 engage the same teeth of the racks 18, i.e., in the same predetermined engagement. Thus, relative to the press, the microscopes are in the same positions as before, because their engagement to the rods 21 and saddles 19 has not been broken. Then the pins 1 6 are turned, and thereby the second plate is adjusted so that its register marks are aligned with the cross-hairs of the microscopes.This ensures that the plate is in exactly the same orientation and position on the bed as was the first plate; or, rather, that the pattern on the second plate is in exactly the same orientation and position as was the first pattern, and therefore that the second pattern will print to the same place on the paper as did the first pattern.

Then the device is removed, and printing with the second ink is performed. Subsequent printings may be done in the same way as outlined above.

Thus it is seen that the plates can be aligned without any need for any trial printing.

The same device can be used in a somewhat analogous way for aligning the plates in a multibed machine such as shown in Fig. 1. The operation in this case will now be described. In this case, it is of particular importance that the distance between each pair of blanket cylinders (i.e., between their axes) should be an exact multiple of the pitch of the helical racks 18. In practice, when as explained above in this embodiment the racks are also used for turning the cylinders, this will always be the case. By this, points on the various printing plates on the various beds which are in the same relative positions to corresponding teeth on the portions of the racks adjacent to the beds will be printed to the same point on the printing paper.

First, the plates are placed on the beds. Then, the device is placed over the first bed, engaged in a particular phase, with a particular correspondence between the teeth of the racks 1 8 and 20. As before, the microscopes are adjusted so as to view the first plate register marks on their cross-hairs, and are clamped so as not to be movable with respect to the saddles 1 9. Then the device is removed from over the first plate, and is placed over the second plate with the same teeth of the racks 20 engaging teeth of the racks 1 8 which are of course not the same teeth as before, but which are the same distance away from the previous teeth as the distance between the axes of the blanket cylinders which correspond to these plates.In other words, the position of the second device over the second plate is such that the positions on the first plate viewed by the microscopes (which were the positions of the register marks) will be printed to the same position on the printing paper as will be the positions on the second plate viewed by themicroscopes. Thus, by adjusting the second plate by its pins 16, so that its register marks are aligned with the cross-hairs of the microscopes, it is ensured that when the printing is performed the register marks on the second plate will be printed to the same positions on the paper as are the register marks on the first plate.

Similarly, the device is placed over the third plate on the third bed, if there is one, and the third plate is adjusted; and so on. Any number of plates can thus be quickly and easily adjusted precisely without the need for any trial printing.

This embodiment of the present invention may be modified. For example, although it is preferred to have two microscopes, this is not essential in principle, although it ensures perfect alignment.

Also, instead of helical racks 1 8 and 20, it would be possible to use saw-tooth racks cut with straight teeth, in which case a means would have to be provided to stop the device moving sideways on the racks, such as stops.

Or alternatively, feed screws could be used instead of the racks 18, in which case half-nuts would be used instead of the racks 20. Or alternatively, members pierced with rows of small holes could be arranged in place of the racks 18, and a rod could be arranged projecting under each of the saddles 19, to engage in the holes. Therefore, although the present invention has been shown and described in terms of several preferred embodiments, it should not be considered as limited to these, however, or mere and simple generalizations, or other detailed embodiments.

Yet further changes of features of the embodiments could be made without departing from the scope of the present invention, which it is therefore desired should be only defined by the appended claims, which follow.

Claims

1. In a lithographic printing press comprising: a frame; a printing paper bed for supporting paper to be printed on, securing to the frame; a printing plate bed for supporting a printing plate to be printed from secured to the frame; a carriage which can be reciprocated to and fro over the beds; and a blanket cylinder, mounted rotatably to the carriage so as to cooperate with the printing plate bed and the printing paper bed for printing: a device for controlling the adjustment of the position of the printing plate, comprising:: a support; a first optical detector mounted to the support in a manner to be adjustably moved in the longitudinal and the transverse directions, and to be selectively fixed relative to the support in any of a range of positions, both longitudinally and transversely; and a means for detachably mounting the support to the frame in a predetermined position relative to the frame, so that, when a printing plate is supported by the printing plate bed, the optical detector may be fixed to the support in a position where it is inspecting the surface of the printing plate.

2. A device as in claim 1, whereof the lithographic printing press comprises a plurality of such printing plate beds arranged in a row with the printing paper bed, which is at the end of the row, and also comprises a plurality of such blanket cylinders, the same number as the number of printing plate beds; wherein the mounting means can detachably mount the support to the frame in any of a plurality of predetermined positions relative to the frame, one corresponding to each printing plate bed; the optical detector, when the support is mounted to the frame in any one of said predetermined positions relative thereto, being able to be fixed to the support in a position wherein it is inspecting the surface of a printing plate supported by the printing plate bed to which that position corresponds; said predetermined positions relative to the frame being such that:: points on printing plates which are positioned on the various printing plate beds, which correspond to the same position in the visual field of the detector as the support is moved between the various said predetermined positions relative to the frame without the fixing of the detector to the support being broken, are printed to the same point on a printing paper supported on the printing paper bed when printing is done with the printing plates not being moved from their positions on the printing plate beds.

3. In a lithographic printing press comprising: a frame; a printing paper bed for supporting paper to be printed on, secured to the frame; a plurality of printing plate beds arranged in a row with the printing paper bed, which is at the end of the row, secured to the frame, for supporting printing plates to be printed from; a carriage which can be reciprocated to and fro over the beds; and a plurality of blanket cylinders, the same number as the number of printing plate beds, mounted rotatably to the carriage so as to cooperate with the printing plate beds and the printing paper bed for printing: a device for controlling the adjustment of the positions of the printing plates, comprising:: a suport; a first optical detector mounted to the support in a manner to be adjustaby moved in the longitudinal and the transverse directions, and to be selectively fixed relative to the support in any of a range of positions, both longitudinally and transversely; and a means for detachably mounting the support to the frame in any of a plurality of predetermined positions relative to the frame, one corresponding to each printing plate bed; the optical detector, when the support is mounted to the frame in any one of said predetermined positions relative thereto, being able to be fixed to the support in a position wherein it is inspecting the surface of a printing plate supported by the printing plate bed to which that position corresponds; said predetermined positions relative to the frame being such that:: points on printing plates which are positioned on the various printing plate beds, which correspond to the same position in the visual field of the detector as the support is moved between the various said predetermined positions relative to the frame without the fixing of the detector to the support being broken, are printed to the same point on a printing paper supported on the printing paper bed when printing is done with the printing plates not being moved from their positions on the printing plate beds.

4. A device as in any of claims 1-3, further comprising a second optical detector, mounted to the support in a manner to be adjustably moved in the longitudinal and the transverse directions, and to be selectively fixed to the support in any of a range of positions, both longitudinally and transversely, and able, when the support is mounted in any such predetermined position relative to the frame, to inspect the surface of a printing plate which corresponds to that predetermined position, the first and the second optical detectors lying generally on opposite sides of the frame, when the support is mounted to the frame in any such predetermined position.

5. A device as in claim 1, 2, or 3, wherein the mounting means for mounting the support to the frame comprises two racks, each mounted to one side of the frame, and two latching devices, each mounted to one side of the support, and adapted to index into the racks so as to hold the support fixed in the longitudinal direction and the transverse direction of the frame.

6. A device as in claim 4, wherein the mounting means for mounting the support to the frame comprises two racks, each mounted to one side of the frame, and two latching devices each mounted to one side of the support, and adapted to index into the racks so as to hold the support fixed in the longitudinal direction and the transverse direction of the frame.

7. A device as in claim 5, wherein the racks are saw-tooth racks, and the latching devices index into the gaps between the teeth, and further comprise stop means which prevent movement of the support in the horizontal direction perpendicular to the racks.

8. A device as in claim 6, wherein the racks are saw-tooth racks, and the latching devices index into the gaps between the teeth, and further comprise stop means which prevent movement of the support in the horizontal direction perpendicular to the racks.

9. A device as in claim 5, wherein the racks are helical racks, and the latching devices are also helical racks.

10. A device as in claim 6, wherein the racks are helical racks, and the latching devices are also helical racks.

11. A device as in claim 5, wherein the racks are screws, and the latching devices are half-nuts.

12. A device as in claim 6, wherein the racks are screws, and the latching devices are half-nuts.

13. A device as in claim 1,2, or 3, wherein the mounting means for mounting the support to the frame comprises two members, each formed with a row of holes parallel to the longitudinal direction of the frame, and two rods which engage one into one of each of the rows of holes.

14. A device as in claim 4, wherein the mounting means for mounting the support to the frame comprises two members, each formed with a row of holes parallel to the longitudinal direction of the frame, and two rods which engage one into one of each of the rows of holes.

1 5 A device for controlling the adjustment of the points of a printing' press, substantially as hereinbefore described with reference to the accompanying drawings.

1 6. A lithographic printing press which includes a device as claimed in any preceding claim.

1 7. The features as hereinbefore disclosed or their equivalents in any novel selection.