GB2244676A - Apparatus for adjusting the distance between the axes of a blanket cylinder and a plate cylinder of a sheet-fed offset press - Google Patents

Abstract

To be able to adjust centrally from the delivery side (1) of a sheet-fed offset press having a number of printing units, more particularly of the series type, the distance between the axes of the blanket cylinder (G) and impression cylinder (D) actuating or adjusting means which are present in the various printing units and which provide adjustment of the distance between the axes of the blanket cylinder (G) and the impression cylinder (D) in the respective printing unit are pivotally connected to an adjusting rod (4) disposed at one end of the machine (control side). The rod (4) can take the form of a longitudinally adjustable rod or of an adjusting spindle. The rod (4) can be so adjusted by way of a control element (5) at the delivery end (1) that the distances between the axes of the blanket cylinder (G) and the impression cylinder (D) alter in the same sense in all the printing units. <IMAGE>

Description

APPARATUS FOR ADJUSTING THE DISTANCE BETWEEN THE AXES OF A BLANKET CYLINDER AND A PLATE CYLINDER OF A SHEET-FED OFFSET PRESS The invention relates to apparatus for adjusting the distance between the axes of a blanket cylinder and a plate cylinder of a sheet-fed offset press having more than one printing unit, more particularly of the series kind wherein, in each printing unit, the blanket cylinder which is mounted at both its ends in pivotable eccentric bushes, is adapted to have its distance from the impression cylinder (contact pressure) varied by adjusting means.

It is known from Swiss Patent Specification 441 382 to adjust the blanket cylinder of the printing unit of an offset press to the required distance from the axis of the impression cylinder (contact pressure adjustment) by pivoting the eccentric bushes in which the blanket cylinder is mounted at both its ends. This eccentric mounting also enables the blanket cylinder to be thrown on and off the impression cylinder and the plate cylinder. To this end, a toggle mechanism embodied by two links is provided which acts on the eccentric bushes and which has as its abutment actuating or adjusting means for altering the contact pressure - i.e., the between-axes distance. When the toggle mechanism is in its extended (throw-on) position, it acts just as an ordinary rod and the contact pressure can be varied by the adjusting means.Modern adjusting means have a dial and a scale on which the distance between the axes of the blanket cylinder and plate cylinder and the variation of such distance - i.e., the contact pressure adjustment can be read. When zero is indicated on the scale, the blanket cylinder is just making contact with the impression cylinder surface without appreciable pressure (kissing contact).

A disadvantage of this system is that contact pressure adjustment must be altered individually for each printing unit, an operation which, when printing units are numerous and presses are correspondingly long, is complex and time-consuming because of the distances involved. It is precisely when adjusting the press for running-on that the printer assesses contact pressure by the quality of printed sheets - i.e. he concludes from the print results whether there is any need to alter the contact pressure of the printing units. When contact pressure is required to be increased or reduced in the same sense in every printing unit, the distances which have to be covered to the printing units cause much waste of time and, therefore, spoilage.

The present invention provides apparatus enabling the contact pressure to be varied in a simple and time-saving manner.

The contact pressure adjustment effected using the apparatus according to the invention can be operated centrally from the delivery end for all printing units.

The printer can take printed specimen sheets from the delivery, assess them for any necessary changes in contact pressure and then immediately alter the same correspondingly. This is very advantageous more particularly when the grade or thickness of paper is changed during printing. The contact pressure must then be readjusted rapidly to suit the new paper thickness.

Similar considerations apply when a predetermined number of dummy sheets, more particularly of a different paper thickness, pass through the press before the sheets which are actually to be printed and the printer has to change the contact pressure immediately after the change of paper yet wants to assess the quality of the first sheets printed on the actual paper thickness.

An embodiment of the invention will be described by way of example in greater detail hereinafter and with reference to the accompanying drawings in which: Figure 1 shows diagrammatically a series type offset press, and Figure 2 shows a detail concerning contact pressure.

Figure 1 shows a series type offset press having a plate cylinder P, a blanket cylinder G, an impression cylinder D and a transfer cylinder T. The sheets printed in the final printing unit are stacked at a delivery 1. As the drawing shows, each blanket cylinder G is mounted in two eccentric bushes 2 jointly pivotable by adjusting means 3 in each printing unit for contact pressure adjustment.

The illustration given in Figure 1 should be understood purely diagrammatically and a fuller description will be given with reference to Figure 2. Each printing unit has actuating or adjusting means 3 which pivot the two bushes 2 to the same extent. This is achieved, in a manner which is not shown, by the adjusting means 3 acting on a shaft which extends over the press width and has at both ends levers and pivotally connected links, the same producing the pivoting of the bushes 2. The adjusting means 3 can take the form of a spindle drive or the like operable manually (knurled screw) or by means of a tool.

According to the invention, a central actuating or adjusting rod 4 is provided and the adjusting means 3 of the various printing units bear on the rod 4. The rod 4 can be so operated from the delivery 1 that the distance between the axes of the blanket cylinder G and the impression cylinder D is varied in the same sense in all the printing units. The rod 4 can extend on the inside of the press frame wall and be mounted correspondingly.

As indicated in Figure 1, the adjusting means are disposed between the printing units and at a place accessible for their operation. The rod 4 extends more particularly at the control end of the offset press.

In one embodiment of the invention, the rod 4 is mounted for longitudinal movement and can be displaced by way of an adjustment dial with a scale (screwthreaded drive having a reduced pitch), as a rule by means of a control element 5 disposed at the delivery 1. This displacement of the rod 4 acts by way of the adjusting means 3 (series arrangement) disposed after it to vary the contact pressure in all the printing units.

By means of the adjusting means 3 which are present at the individual printing units and which bear on the rod 4, the contact pressures of individual printing units can also be adjusted relatively to one another. For example, after a change of blankets in the printing units, the scale of the control element 5 (dial) of the rod 4 can be set to zero at the delivery 1, whereafter the blanket cylinder G of the individual printing units can, by means of the individual adjusting means 3, be brought into "kiss-print" contact with the surface of the impression cylinder D. All the printing units are then in kissprint contact without pressure. Operation of the control element 5 then produces the same variation of contact pressure in all the printing units, more particularly in accordance with paper thickness.

Instead of an extending mounted rod 4, an adjusting spindle having the same effect can be provided, the various adjusting means 3 bearing, by way of spindle nuts on the spindle, the nuts being secured against co-rotation on the spindle.

Figure 2 is a detailed view of an embodiment of the invention. Advantageously, the device for varying contact pressure is incorporated in the throw-on/throwoff mechanism.

Figure 2 shows a blanket cylinder G having its journal at each end mounted in eccentric bushes 2. Links 6 are connected to the two bushes 2 and are each pivoted at their end to a lever 7 disposed on a throw-off shaft 8.

The same extends over the press width and at the two frame walls extends therethrough. The elements hereinbefore described and to be described hereinafter are disposed on the outside of the frame. By means of a further lever 9 of the shaft 8, the lever 9 being disposed more particularly at the control end of the press, the shaft 8 can be rotated to pivot the two bushes 2.

A link 10 of a toggle mechanism embodied by links 10, 11 is pivotally connected to the lever 9 and bears on a lever 12 of a contact pressure adjustment shaft 13. A throw-off rod 14 is pivotally connected to the link 11 and operates the toggle mechanism 10, 11 for throw-on and throw-off. The rod 14 is driven, for example, by way of cam follower levers which run on cams and which have pawls. The position in which the toggle mechanism is shown in Figure 2 corresponds to the throw-on position.

The shaft 13 has a second lever 15 to which the adjusting means 3 are pivotally connected. As shown, the end of lever 15 is in the form of a fork in which a pin 16 of the adjusting means 3 engages.

As already intimated with reference to Figure 1, the adjusting means 3 bear on the rod 4. In the case shown in Figure 2, the rod 4 is in the form of an extending rod. As can be gathered from Figure 2, the adjusting means 3 take the form of a first screwthreaded block 17 secured to the rod 4, a second screwthreaded block 18 engaging by way of pin 16 in the fork of lever 15 and a screwthreaded spindle 19 for varying the distance between the two blocks 17 and 18. The spindle 19 can be operated by way of a hexagon. Other forms of adjusting means 3 providing an equivalent effect can, of course, be used.

When, by way of the spindle 19, the distance between the blocks 17 and 18 is altered without any change in the position of the rod 4 - the same bears on the control or operating element 5 (spindle with dial) at the delivery 1 - the pin 16 actuates the lever 15 and so, in known manner in the thrown-on position of the bushes 2, the toggle mechanism 10, 11 and the lever 12 of the shaft 13 are pivoted by way of the shaft 8 and lever 9, leading to an alteration in the distance between the axes of the blanket cylinder G and the impression cylinder D.

Similarly, a displacement of the rod 4 produced by the control element 5 acts by way of the adjusting means 3 to pivot the bushes 2 but, in this case, in all the printing units.

As shown in Figure 2, the block 17 is mounted by guide rollers R so as to be displaceable parallel to the rod 4.

The same can be mounted similarly if embodied as a displaceable rod.

In conclusion, a device for varying the distance between the axes of a blanket cylinder G and an impression cylinder D according to the invention not only provides the advantages of convenience of control which have already been mentioned, but entails only a reduced constructional outlay and, as explained, can readily be incorporated in the throw-on/throw-off mechanism.

Claims (9)

1. Apparatus for adjusting the distance between the axes of the blanket cylinder and impression cylinder of a sheet-fed offset press having more than one printing unit, more particularly of the series kind wherein, in each printing unit, the blanket cylinder which is mounted at both its ends in pivotable eccentric bushes, is adapted too have its distance from the impression cylinder (contact pressure) varied by adjusting means, wherein the adjusting means of all the printing units are pivotally connected to a common adjusting rod which is so adjustable by a control element at the delivery that the distance between the axes of the blanket cylinder and the impression cylinder can be varied in the same sense in all the printing units.

2. Apparatus according to Claim 1 wherein the adjusting rod extends at the control end of the offset press and on the inside of the press frame wall.

3. Apparatus according to Claim 1 or 2 wherein the adjusting rod is a rod mounted for longitudinal displacement and can be controlled from the control element by a spindle drive which bears non-displaceably on the press.

4. Apparatus according to Claim 1 or 2 wherein the adjusting rod is a screwthreaded spindle having spindle nuts which are secured against co-rotating with the spindle and to which the adjusting means are connected in a pivoting and bearing relationship.

5. Apparatus according to any one of the preceding claims wherein the control element is a dial having a scale on which the variation of the between-axes distances can be read.

6. Apparatus according to any one of the preceding claims wherein the adjusting means take the form of a spindle drive which is disposed at an externally accessible place between the printing units and which can be operated manually or by means of a tool.

7. Apparatus according to any one of the preceding claims wherein the adjusting means for varying the distance between the axes of a blanket cylinder and an impression cylinder so act on a first lever that a second lever effective as abutment for a toggle mechanism embodied by two links is pivotable by way of a contact pressure adjustment shaft, the one link is pivotally connected to a lever of a throw-off shaft extending over the press width, the throw-off shaft has, at both its ends, levers pivotally connected by way of links too the two eccentric bushes disposed at both ends of the blanket cylinder and a throw-off rod is pivotally connected to the other link of the toggle mechanism for throwing the blanket cylinder on and off the impression cylinder and the plate cylinder.

8. Apparatus for adjusting the distance between axes of blanket and impression cylinders in a sheet-fed offset press substantially as hereinbefore described with reference to the accompanying drawings.

9. A sheet-fed offset press having more than one printing unit and including apparatus according to any one of the preceding claims.