Printing machine with block-cleaning device

#The invention relates to a printing machine with a printing cylinder, the rotation of which can be driven, and a cleaning device for the local cleaning of blocks, clamped on the printing cylinder, for which the cleaning device is constructed as a rotatable cleaning roller, which can be placed in contact with the peripheral surface of the printing cylinder and is equipped with cleaning organs, so that the angular positions of the cleaning organs vary in the axial direction of the cleaning roller.

#For a printing machine, especially for a flexographic printing machine, there is increasing contamination of the blocks during the printing operation due to dust on the material being printed, due to the dust in the surrounding air and due to drying residues of ink. The dirt is deposited especially on the edges of the raised, printing parts of the blocks. Especially when a finely structured pattern, such as letters in a very small font or halftone images with a fine grid of points, is being printed, the lower lying, not printing parts of the blocks can easily become blocked as the dirt builds up, so that the quality of the printed image is affected.

#From the EP-A-0 461 898 there is a printing machine with a cleaning device of the type named above, for which the cleaning roller is a brush roller, which is equipped with helically disposed bristles. The bristles are disposed in several turns on the periphery of the cleaning roller. The cleaning roller is caused to rotate by fictional contact with the rotating printing cylinder, so that the whole surface of the printing cylinder is cleaned uniformly. In one embodiment, the cleaning roller is divided into several axial segments, which can be placed, independently of one another, in contact with the printing cylinder, so that a concerted cleaning of particularly contaminated places on the printing cylinder becomes possible. However, a complicated mechanism is required in order to make or break contact between the individual segments of the cleaning roller and the printing cylinder. In addition, small gaps, in which the surface of the printing cylinder cannot be cleaned, remain between the individuals segments of the cleaning roller.

#In the following, an example of the invention is explained by means of the drawings, in which

#FIG. 1 shows a front view of a printing cylinder and an associated cleaning roller and

#FIG. 2 shows a diagrammatic sketch of a printing machine with the cleaning device of FIG. 1.

#FIG. 1 shows a printing cylinder 10 of a printing machine, such as a flexographic printing machine, on the peripheral surface of which several blocks 12 are clamped. A cleaning roller 14, which is equipped with a helically extending row of bristles 16, runs parallel to the printing cylinder 10. The row of bristles 16 extends over the whole of the axial length of the cleaning roller 14 and runs in an almost complete turn about the periphery of the cleaning roller 14.

#The cleaning roller 14 can be rotated about its longitudinal axis and locked sensitively in different angular positions with the help of a stepper motor 18. The stepper motor 18 and a bearing 20 at the opposite end of the cleaning roller 14 are held by pneumatic operating cylinders 22, with which the cleaning roller 14 can be placed radially against the printing cylinder 10. The extension length of the operating cylinders 22 can be adjusted, so that the contacting force of the brushes of row 16 against the surface of the blocks 12 can be set as required.

#In each angular position of the cleaning roller 14, the row of bristles 16 lies in only a relatively narrow axial section 24 against the surface of one of the blocks 12, so that only this section 24 is cleaned selectively. The boundaries of section 24 are not defined sharply, since the row of bristles 16, because of the curvature of the cleaning roller 14, constantly moves away from the surface of the block 12. If a different axial section of one of the blocks 12 is to be cleaned, the angular position of the cleaning roller 14 is changed with the help of the stepper motor 18, so that the row of bristles 16 comes into contact with one of the blocks 12 in a new position.