Apparatus for Adjusting a Tensioning Device in Plate Cylinders of Rotary Printing Machines

The invention relates to rotary printing machines in general, to one or more printing plates thereof and more particularly to a method of and apparatus for adjusting the leading, tensioning rail of tensioning devices in the printing plate support cylinder of a rotary printing machine.

In rotary printing machines, thin, flexible printing plates are used. Usually, one or more plates are mounted under tension on a plate support cylinder. The ends of each of the printing plates are bent away in an accurately registering manner and the ends are inserted into tensioning devices formed in the plate cylinder. Tensioning rails are formed as part of the tensioning device. These rails have a generally beak shaped portion, and the printing plate ends are secured over these beak-like portions. There are a leading tensioning device and its tensioning rail at the leading or forward end of the printing plate (as the cylinder rotates) and a trailing tensioning device and trailing tensioning rail at the trailing end of the printing plate. The tensioning of the plate is usually effected by means of the trailing tensioning rail. The leading tensioning rail determines the position of the printing plate on the printing cylinder. The leading rail must be adjusted in a perfectly registering manner, particularly in multiple color printing.

The adjustment in an accurately registering manner of the leading tensioning rail may be disturbed by initial manufacturing tolerances and by division faults that become noticeable in the tensioning device, as well as in the receiving grooves for the tensioning device in the plate cylinders.

It is an object of the invention to provide a method for adjusting the position of the tensioning rail of a tensioning device of a printing plate cylinder from the desired position.

It is another object of the invention to provide an apparatus for performing that purpose.

It is a further object of the invention to accomplish the foregoing objects using an optical adjusting technique.

The present invention concerns a method of and an apparatus for adjusting in an accurately registering manner the leading tensioning rail of a tensioning device in the plate cylinder of a rotary printing machine. According to the invention, at least two control marks (although one could be used) for the tensioning device are formed on the cylinder, preferably by being accurately machined into the surface of the cylinder. Any arrangement of these marks is acceptable, but it is preferable that they be arrayed parallel to the axis of and on the surface of the plate cylinder and at a predetermined control spacing and spaced at a predetermined angle around the cylinder from the receiving grooves for the tensioning devices. Using these marks as a guide, the base position of the tensioning rail can be optically determined and then accurately adjusted for printing purposes.

The present invention also concerns an apparatus for adjusting the leading tensioning rail of a tensioning device in the plate cylinder of a rotary printing machine. Such apparatus includes a base member. It includes at least one optical control device mounted on the base member, with one such device being provided for each control mark on the cuylinder. A plurality of guides are formed in the base member. A plurality of abutment members are diplaceable with respect to and received in the respective guides so as to be adjustable with respect to the base member to previously calculated positions. The abutment members are provided for engaging the tensioning rail that is to be adjusted. A plurality of base member supports are provided on the base member for engaging the plate cylinder at locations that are angularly spaced around the cylinder from the tensioning device. The supports are arranged so that each optical control device is itself oriented substantially radially but more particularly such that its field of view is oriented substantially radially to the plate cylinder when the apparatus is in use with the abutment members abutting against the front or leading edge of the leading tensioning rail. The tensioning rail is adjusted in position until the field of view off each optical device takes in its control mark.

A preferred embodiment of the invention will be described with reference to the accompanying drawings, in which:

FIG. 1 is an end elevational view of an apparatus according to the invention for performing the method according to the invention; and

FIG. 2 is a side view of the apparatus of FIG. 1 in position on a plate cylinder having a tensioning device.

Referring to the drawings, a conventional cylindrically shaped printing plate support cylinder 4 is shown. It includes a conventional tensioning device 2, which is mounted in a receiving groove 3 of the plate cylinder 4. The tensioning device includes a conventional break-line tensioning rail 1.

Control marks 5, e.g. control circles, are machined with extreme accuracy into the surface of the plate cylinder 4 to serve as a base for measurement. Although any number of control marks 5 may be used, two control marks 5 are preferable for each tensioning device 2 and for each direction of rotation of the control cylinder 4, i.e. some cylinders are intended to rotate clockwise or counterclockwise in FIG. 2 for different printing operations. These marks 5 are in previously calculated positions relative to each other and are preferably arranged axially along the plate cylinder.

There are two optical control devices 7, or a number of such devices corresponding to the number of marks 5, provided for a particular tensioning rail adjustment. Devices 7 are disposed on top of a base plate 6 and they are spaced apart a distance corresponding to the distance axially of the cylinder 4 between the control marks 5.

At the side of the base plate 6, there are provided guides 8, 9 and 10 into which are inserted abutments 11 and 12 and a forked abutment 13, respectively. The abutments are fixable at desired positions, moving sideways with respect to the base plate 6 and transverse to the fields of view of the optical control devices, in their guides to be at predetermined distances from optical control devices 7, by means of adjusting screws 14, 15 and 16. The abutments 11 and 12 are adjusted and fixed, left and right in FIG. 2, by means of limit members 20 to a previously calculated measure which is related to any individual plate cylinder 4.

Two fixed supports 17 and 18 near groove 3 and an adjustable support 19 remote from groove 3 and all connected beneath base plate 6 are provided for supporting the entire apparatus on the surface of plate cylinder 4. The adjustable support 19 is correctly positioned on cylinder 4 by means of a spacer member 21. The thickness of spacer member 21 depends upon the diameter of the plate cylinder 4. Spacer member 21 is selected so that in use, each optical control device 7 is oriented to extend exactly radially to the plate cylinder 4 and, more important, to take in a field off view radially to that cylinder.

Then the apparatus is seated on the plate cylinder 4 with the abutments 11 and 12 resting against the front or leading side (or the side away from devices 7) of the tensioning rail 1 and with the forked abutment 13 embracing a bolt 22 that serves to center the printing plate.

The position of the tensioning rail 1 is changed, by means of a previously known, conventional adjusting device (not shown) built into each tensioning device 2, until the centers of the optical control devices 7 coincide exactly with the control marks 5. With the adjustments completed, the entire apparatus is then removed.

When the leading tensioning rails 1 are adjusted in the foregoing manner, using the above described apparatus, the printing plates (not shown), when bent over the tensioning rails in an accurately registering manner, are located under tension on the plate cylinder 4 in their correct printing positions. At any later time, a control check of the position of the leading tensioning rail, which may be necessary under certain circumstances, can be effected with the apparatus according to the invention within a very short time.

Although the present invention has been described in connection with a preferred embodiment thereof, many variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.