GB854862A - Improvements in or relating to electro-mechanical means for producing printing plates - Google Patents

Abstract

854,862. Local copying by scanning. HELL, R. April 15, 1957 [April 14, 1956], No. 12294/57. Class 40(3). In apparatus for the electro-mechanical reproduction of engraved printing plates in response to electrical currents derived from the point-bypoint scanning of an original, in which the scanning light source and the engraving tool are simultaneously moved and in which the light source is focused on and moves over the original, the scale of reproduction can be varied by moving the original and the optical focusing system along the line joining the centres of the original and of the printing plate. As shown, the plate 2 to be engraved is held between adjustable supports 6 on a fixed table 1, and the engraving tool 4 is mounted in a carriage 3 carrying a light source 5 providing a light point of adjustable size and traversed across the plate 2 by a threaded shaft 8 driven by a motor 21. The movement of the carriage 3 may be reversed at the ends of the lines by engagement with limit stops which are operative to reverse the rotation of the motor 21, or the shaft 8 may have two oppositely directed threads for the forward and return movements. The shaft 8 is mounted in a carriage which is given a stepwise movement transverse to the direction of scanning at the end of each line. The original 10 to be reproduced is carried between adjustable supports 7 on the lower surface of a table 9 vertically movable in guides 12 and in the direction of the axis 11 joining the centres of the plate 2 and of the original 10. A plate 13 supported by light-proof bellows 15, 16 carries a single lens 14, or a lens system, cooperating with an annular photo-cell 17, or a ring of separate cells disposed above the plate. The output of the photo-electric device 17, which may be a photo-electric multiplier, is fed via an amplifier 19 to the circuit of the engraving tool which may also be operated to produce a screened printing plate by a screen frequency derived from a tone generator 20 driven from the shaft 8. When the supporting table 9 is adjusted in accordance with the relative sizes of the original 10 and the plate 2 to be engraved, the lens 14 of appropriate focal length is selected, and the appropriate size of the scanning light spot is employed by adjustment or substitution of the light source 5. In the arrangement shown the engraving of the plate will be spatially inverted in relation to the scanning of the original.