Patent GB-237648-A (GB)
Title: Improvements in photographic printing apparatus for making offset press plates
IPC: G03B27/06
Filed: 1924-04-29
Abstract: 237,648. Koppe, A. T. April 29, 1924. Printing - apparatus for printing off-set press plates from a negative adjustable transversely on a carriage which itself is adjustable longitudinally over the press plate has pawl and rack means for advancing the carriage, rack and detent means for locking it, and cam-operated means for raising and lowering the negative frame, all of which means are controlled from a single handle. The sensitive plate is stretched between clamps 11, 16, Figs. 1, 2, and 5, over a stretched rubber blanket 4 on a fixed bed-plate 3 which is mounted between the ends 2 of the framework. The blanket 4 is fixed at one end to the bed-plate 3 and stretched by a roller 7 rotated from the shaft 10. The press plate is stretched by the adjusting screws 19 which move the block 17 carrying the clamps 16 relatively to the bed 3. The negative 20 is carried by a frame 21 which can be moved transversely by hand along bars 41 and positioned by graduated bars 44. The bars 41. 44 form part of the carriage which is longitudinally movable on guideways 31 of the framework. To provide for negative frames of different sizes the carriage comprises a centre block 33 and adjustable side blocks 34 on which the bars 41, 44 are mounted. The blocks 33, 34 are connected by plates 35 provided with a series of notches and clamping nuts 38, 40. The negative frame 21, Figs. 1, 5, and 17, carries uprights with extensions 56 overhanging the bars 41 and is attached to side blocks 48 by eyelets and pins 51 which allow a limited upward movement of the frame 21 when the bars 41 are raised. These blocks 48 are slidably supported on members 49 which themselves slide on the graduated bars 44. To register the negative frame 21 in successive positions along the bars 44, which are notched, the members 49 carry spring detents 53. To further register the pins 51 with the scale 46 the blocks 48 are adjusted on the members 49 by nuts 50. The centre blocks 33, Figs. 1, 8, and 14, carry resilient positioning detents 87a, 87<b> which are moved to engage longitudinal bars 86 by cams 88, 89 on splined shafts 82, and are so arranged that when one engages a notch the other is midway of another notch. The centre blocks 33 also carry resilient pivoted pawls 74, two on each block, which engage the teeth 69 of rack bars 67. These bars 67 slide in face grooves 66 of the track ways 31, and are moved to step the carriage longitudinally by the hand crank 57, shaft 58, pinions 73 and racks 58 on the bars 67. The inner ends of the pawls 74 are engaged by other cams 84 on the splined shafts 82. The side blocks 34 carry pins 43 which engage slots in the bars 41 and also vertically movable pillars 93 with rollers 92 engaged bv other cams 90 on the splined shafts 82. and by which the bars 41 are raised, and with them the negative frame 21. The cams 88, 89, 84 and 90 on the shafts 82 are controlled from the controlling handle 77, Figs. 2 and 4, through connected gearing between the shafts 82 and 78. When the handle 77 is in full position the cams 90 are positioned to lift the bars 41 and the negative frame 21; cams 88, 89 are out of engagement with the detents 87a, 87b which disengage from the rack bar 86; and the cams 84 disengage the pawls 74 from the teeth 69 of the rack bars 67. The carriage can then be returned to one end of the frame by endless chains 62 coanected with the blocks 33 and operated from the handle 63, Fig. 1. The negative can now be adjusted transversely along the bars 41 by hand. When the handle 77 is moved to the extreme positions 96 or 97, Fig. 4, the cams 90 release the bars 41 and the negative frame 21, the negative dropping into contact with the press plate; in one position 96 the cams 88 are moved to release the detents 87<a> which engage the bars 86, whilst in the other position 97 the cams 89 are moved to release the detents 87<b>. When the handle 77 is moved tc either intermediate position the cams 90 operate to raise the bars 41 and negative, the cams 88 89 retract the detents 87<a>, 87<b>, and the carriage feed pawls 74 are released to engage the rack bar 67 so that the carriage may be shifted to a predetermined extent from the crank handle 57 The movement of the rack bars 67 for stepping the carriage is effected by a pawl 98, Figs. 8 and 16, on the handle and a one-way ratchet wheel 99 keyed to the shaft 58, which carries the pinions 73 in gear with the bars 67. The scale disc 76 carrying a stop 95 limiting the rotation of the handle 57 is adjustable on a sleeve 103 and can be clamped by a lever 105 in set position between a flange 104 of the sleeve and a fixed bracket 108 carrying the starting stop 100. The longitudinal movement of the carriage is indicated by a pointer 102 on the block 33 and a fixed scale 101 on the carriage. The apparatus may be provided with light-excluding curtains to protect the parts of the sensitive surface not immediately below the negative, and with hinged plates forming lateral extensions o the bed-plate.