GB2259052A

GB2259052A - Compensating for lack of roundness in printing cylinders.

Info

Publication number: GB2259052A
Application number: GB9212232A
Authority: GB
Inventors: Carl Langemeyer
Original assignee: Windmoeller and Hoelscher KG
Current assignee: Windmoeller and Hoelscher KG
Priority date: 1991-07-01
Filing date: 1992-06-09
Publication date: 1993-03-03
Also published as: DE4121749A1; JPH05185577A; ITBZ920025A1; IT1260318B; GB9212232D0; ITBZ920025A0

Description

2 2 -, g-i s -) - 1 Method of controlling the pressure of the printing

cylinders of printing units on a printing press The invention concerns a method of controlling the pressure of the printing cylinders of printing units on a printing press, preferably a flexographic printer, against a common counter-pressure cylinder against which the printing cylinders are pressed and from which they are released, said printing cylinders being mounted on carriages, and driving mechanisms being provided to slidably move said carriages within guide units fixed relative to the frame.

A flexographic printer of this kind, having six printing cylinders that can be pressed against its single c ounter-pres sure cylinder, is known, for example, from DE-OS 34 37 216. For printing operations, said printing cylinders, which are mounted on guide units fixed relative to the machine frame and disposed tangentially to radially to the counter-pressure cylinder, can be pressed against said counter-pres sure cylinder and released therefrom. With a printing press of this kind, clean printing can only be ensured if the counter-pressure cylinder is perfectly cylindrical in shape and runs concentrically to its axis, so that its outer casing does not perform any radial movements which might lead to a variation in pressure between the printing cylinders and the counter-pres sure cylinder. Because of the 1 - 2 large diameter of the counter-pres sure cylinder, it is extremely difficult and requires considerable effort to manufacture it in the form of such a perfect cylinder that no circularity error occurs and such that all the printing cylinders can be pressed against it with the same force as it revolves.

The object of the present invention is therefore to produce a printing press of the type described above with which clean printing can be achieved even if the counter-pressure cylinder is not perfectly cylindrical.

This problem is solved according to the invention by means of a method of controlling the pressure of the printing cylinders in which the circularity errors of the counter-pressure cylinder are measured about its circumference as a function of its angle of rotation, proceeding from a zero position, and, depending on the position of the counter-pre ssure cylinder's angle of rotation, the printing cylinders are moved in their guide units, according to the circularity error values measured and stored, in such a way that the f orce with which they are pressed against the counter-pressure cylinder remains substantially constant. According to the invention, in order to achieve a substantially constant force with which the printing cylinders are pressed against the counter-pres sure cylinder, the circularity errors of the counter-pressure cylinder, which could only be avoided at the expense of undue effort and cost, are compensated for in that the printing cylinders are moved within their guide units in accordance with the circularity errors of the counterpressure cylinder measured. The ef f ort and cost involved in controlling the movements of the printing cylinders are less than what would be necessary to produce a perfectly cylindrical counter-pressure cylinder.

P- -L It is appropriate f or the pressure of the printing cylinders to be controlled by servo motors which drive the spindles that move the printing cylinder carriages. It is standard today f or f lexographic printers to be computer-controlled. All that is needed, therefore, is to provide a program that takes the counter-pres sure cylinder's circularity errors into account and which can then be used to control the servo motors, especially stepping motors, moving the printing cylinders. At each revolution of the counter-pres sure cylinder, the servo motors then perf orm, drive movements in both directions of rotation, which compensate the measured circularity errors of the c ounter-pres sure cylinder. Servo motors capable of being controlled in the necessary way are available.

In a further embodiment of the invention, it is provided that to measure the counter-pressure cylinder's circularity errors, said counter-pressure cylinder is mounted in a bearing, and a straight-edge is placed along a line of the outer casing of said counterpressure cylinder, in a radial plane. In the course of one revolution of the counter-pressure cylinder, the radial movements of the straight-edge are measured and stored as a function of the angle. The movements of the straight-edge during the measuring process are detected by displacement transducers. The deviations measured.are stored and are then used to control the corresponding compensation movements of the printing cylinders by means of a computer. In the process, the printing cylinders of all the printing units are controlled in accordance with the circularity errors measured. The circularity errors of the counter-pres sure cylinder can alsb be caused by the lines of the outer casing running at an angle to its axis. In such cases, the two servo motors moving a printing cylinder carriage must accordingly be controlled differently.

4 - A device according to the invention f or measuring the circularity errors of the counter-pres sure cylinder is characterized by the facts that two bearings f ixed relative to the frame are provided for the counterpressure cylinder and guide units f ixed relative to the frame are provided for a straight-edge, said guide units guiding said straight-edge in a radial plane; the straight-edge is mounted in its central portion, in such a way that it can rock, on the piston rod of a pressing cylinder; on both sides of the pressing cylinder and at equal distances therefrom, there are provided pressing rollers applying pressure to the straightedge; and the movements of the piston rod and/or the pressing rollers are measured and stored. It is appropriate for the pressing rollers to be mounted on the ends of piston rods of pressing cylinders f ixed relative to the frame, the movements of the pressing rollers being measured and stored. If it is to be expected that the lines of the outer casing of the counter-pressure cylinder are likely to be crooked, the movements of the lateral pressing rollers must be measured so that the servo motors on both sides of a printing cylinder carriage can be controlled appropriately, according to the values measured.

one embodiment of the invention will be described in greater detail below, with reference to the drawing. In said drawing, Fig. 1 is a schematic side view of a flexographic printer, Fig. 2 is a schematic presentation of a view of a device for measuring the circularity etrors of a counter-pressure cylinder, and Fig. 3 is a view in perspective of the radial guide unit of the measuring straight-edge on one side of the counter-pressure cylinder.

W 1 -1 The flexographic printer 1 which can be seen in Fig. 1 consists of a stand 2 with six consoles 3 for the printing units 5. Each bracket 3, consisting of one console, is provided with a guide unit on which a carriage is slidably mounted, a printing cylinder being mounted to the front end of said carriage. An inking unit carriage is slidably mounted to the printing cylinder carriage in the customary manner, so that the inking unit rollers can be pressed against the printing cylinders and released therefrom.

The printing cylinder carriages can be moved in their guide units by spindle drives the spindles of which can be driven by servo motors.

All the printing cylinders can be pressed against the common counterpressure cylinder 4, which is mounted in the usual way in the stand 2.

Fig. 2 shows a device for measuring the circularity errors of a counterpres sure cylinder 4. In Fig. 2, the counter-pres sure cylinder 4 is depicted to a reduced scale and is held rotatably in retainers 6 of the measuring device, which form bearings. Via a pneumatic piston-cylinder unit 7, the cylinder of which is held fixed relative to the frame, a straight-edge 8 is pressed against the counter-pressure cylinder to be measured, the straight-edge 8 being held in guide units at its two end portions, said guide units guiding said straightedge 8 in a radial plane. Fig. 3 is a view in perspective of the schematic design of these radial guide units.

If the cylinder 4 is now slowly rotated in the retainers 6 in a manner not described in detail, the straight-edge 8 will remain in contact with the surface of the cylinder 4 because of the pressure applied by the pneumatic piston-cylinder unit 7. The position of the straight-edge 8 is detected in the process by tracer 1 - 6 rollers 10 mounted in housings 12 via brackets 11, said tracer rollers being resiliently capable of axial movement. The deviation of the rollers 10, whether negative or positive, from a predetermined fundamental position is detected and transmitted to a transducer 13, which stores the values in an appropriate manner, such as on a cassette, for example. The counter-pres sure cylinder 4, having been measured in this way, is then inserted in a printing press according to Fig. 1, which is computercontrolled in a manner known per se. The tape recorded by the transducer 13 is played into said computer, so that a signal is sent via the computer (not shown) to the servo motors 14 or stepping motors in such a way that the circularity errors can be compensated for accordingly. This means, on the one hand, that the servo motors 14 located on each side of a single printing unit 5 can be driven jointly, so that the printing unit 5 can be pressed down steadily. On the other hand, the two servomotors 14 allocated to one printer 9 can also be driven separately, so that a printing unit 5 can if necessary be pressed down at an angle in order to be able to compensate, for example, for the sloping position of the outer casing 15 shown in Figure 2.

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Claims

C L A I M S

Method of controlling the pressure of the printing cylinders of printing units on a printing press, preferably a flexographic printer, against a common counter-pressure cylinder against which the printing cylinders are pressed and from which they are released, said printing cylinders being mounted on carriages, and driving mechanisms being provided to slidably move said carriages within guide units fixed relative to the frame.

characterized in that the circularity errors of the counter-pres sure cylinder are measured about its circumference as a function of its angle of rotation, proceeding from a zero position, and, depending on the position of the counter-pres sure cylinder's angle of rotation, 1Che printing cylinders are moved in their guide units according to the circularity error values measured and stored, in such a way that the f orce with which they are pressed against the counter-pressure cylinder remains substantially constant.

1 Method as claimed in claim 1, characterized in that the pressure of the printing cylinders against the counter-pressure cylinder is controlled by servo motors, preferably stepping motors, which drive the spindles that move the printing cylinder carriages.

Method as claimed in Claim 1, characterized in that, to measure the counter-pressure cylinder's circularity errors, said counter-pressure cylinder is mounted in a bearing, and a straight-edge is placed along a line of the outer casing of said counter-pres sure cylinder, in a radial plane, and that in the course of one revolution of the counter-pres sure cylinder, the radial movements of the straight-edge are measured and stored as a function of the angle.

Device for carrying out the method of Claim 2, characterized in that two bearings fixed relative to the frame are provided for the counterpressure cylinder and guide units are provided for a straight-edge, said guide units guiding said straight-edge in a plane radial to said counterpressure cylinder, further characterized in that the straight-edge is mounted in its central portion, in such a way that it can rock, on the piston rod of a pressing cylinder, and that on both sides of the pressing cylinder and at equal distances therefrom there are provided pressing rollers applying pressure to the straightedge, and further characterized in that the movements of the piston rod and/or the pressing rollers are measured and stored.

Device as claimed in Claim 4, characterized in that the pressing rollers are mounted on the ends of the piston rods of pressing cylinders fixed relative to the frame and the movements of the pressing rollers are measured and stored.

1 Z - 9 6. A method of controlling the pressure of printing cylinders of printing units on a printing press, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

7. A device for controlling the pressure of the printing cylinders of printing units on a printing press, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.