Patent GB-834017-A (GB)
Title: Improvements in or relating to apparatus for the electro-mechanical production of screened printing plates
IPC: H04N1/393
Filed: 1956-07-05
Abstract: 834,017. Copying telegraphy. HELL, R. July 5, 1956 [July 5, 1955], No. 20890/56. Class 40 (3). In an apparatus for the electro-mechanical reproduction of printing plates in which the scanned original and the plate to be engraved are carried on opposite sides of a reciprocated table, the scale of reproduction is varied by applying to the scanning device or to the engraving head an additional movement in the direction of the scanning or engraving motion, and effecting corresponding adjustments of the movements at right angles to the scanning direction to accord with the modified scale of reproduction and the desired screen arrangement. The original to be reproduced is mounted on the lower side of a table 1 which carries the plate 3 to be engraved by the tool 17 of the engraving head 14 and which is secured to a head 13 reciprocated by a threaded shaft 12 driven from a motor 5 via belts 6, 10 and gearbox 8. The scanning beam 49 from a source 48 is reflected to the lower side of the table 1 by a mirror 55 carried by a support 52, normally fixed, but slidable on a rod 50 secured at the ends to a frame 47 and to a carriage 51 which can roll on a support 100. The support 52 has projections 53, 54 engaging a bar 38 carried by a frame member 36 carrying a slidable head 34 with a nut 33 engaging a screwthreaded shaft 35 and carrying a pin 32 engaging a slot 31 in a member 28 embracing a shaft 29 and connected at its upper end to a crosshead 20 which can slide on a fixed bar 21. The head 20 is connected to a shaft 24 which by means of operating levers 22, 23 can be coupled to the support 13 or to a nut 25 mounted on a threaded shaft 26, which is rotated in the direction oppositely to shaft 12 when gears 56, 57, 59, 60 are brought into engagement by the movement of the control lever 58 to the position shown. The position of the pin 32 in the slot 31 can be set by a motor 41 rotating the shaft 35 via gear-box 42 and gear train 43, 44. Normally the lever 58 is in its right-hand position so that shaft 26 is not driven and the lever 22 is in the position such that the head 20 is not coupled to the support 13. The link 28 remains stationary and the support 52 is not moved so that the scanning beam is fixed and 1 : 1 reproduction is effected. If the lever 22 is operated so that the head 20 moves with the support 13 the rod 28 via the pin 32 and support 34 traverses the rod 38 so that the support 52 and scanning beam 49 have a velocity in the scanning direction of the table, resulting in an enlarged reproduction. If the levers 22, 23 are operated so that the head 20 is connected to the nut 25 and the control lever 58 moved to the position shown, the support 52 is given a movement opposite that of the table so that the reproduced image is reduced in relation to the original. The transverse movement of the engraving head 14 is effected by the stepped rotation of a threaded shaft 67 at the end of each scanned line and three different amounts of displacement are provided under control of magnets 82, 83, 84 with associated pawls 72, 73, 74 engaging corresponding ratchet wheels 69, 70, 71 driven through a friction clutch from gearing elements 62... 66, the two assemblies not required being locked in the inoperative positions. The frame 68 attached to the head 14 and engaging the shaft 67 is attached by a pin 87 to a slotted bar 85 engaging a pin 91 carried by a nut 92 adjustable on a threaded shaft 93 on an arm of a U-shaped member 94 having its screwed arm secured to the support 47 which carries the light source 48 and is slidable on a rod 98. The position of the pin 91 in the slot is adjusted by the nut 92 which is moved by a motor 95 and gears 96, 97 so that an independent adjustment of the transverse movement of the scanning beam can be effected to produce screens of the desired line density.