Patent GB-554465-A (GB)
Title: Improvements in photographic printing apparatus
IPC: G03B27/02
Filed: 1941-09-26
Abstract: 554,465. Photographic contact printing-apparatus. PHILLIPS & POWIS, AIRCRAFT, Ltd., and ROBERTS, G. Sept. 26, 1941, No. 12537. [Class 98 (ii)] In apparatus for negative or reflex copying including a platen accommodating negative or original and copy material of varying thickness, said platen consisting in a fixed base and a relatively movable clamping plate between which the negative &c. are compressed on closing the platen, a single movement of an operating lever first lowers the clamping plate until it rests upon the work on the fixed base, then through ratchet mechanism grips said plate, and finally draws the plate down to apply to the work a predetermined pressure which is independent of the thickness of the work. In the form shown, a stand 4 supports a casing 3 into the top of which is let a box 5 provided with a fixed glass panel 6, above which is a glass clamping-plate 7 supported on members 8, 9 having depending runners 10 engaging rollers 11 on the casing 3, and crossconnected below by a bar 12 pivotally supporting a rod 13 engaging at its lower end, to an extent limited by a stop 19 on the rod, a perforated plate 20 carried by a foot-lever 14. A resilient pad comprising a plate 17 faced on each side with rubber rests on the panel 6 and supports the original and copy material for reflex copying; it is transferred to the underside of the plate 7 for negative copying, the negative and copy material in this case resting directly on the panel 6. On depressing the lever 14, the structure supporting the plate 7 descends under-gravity until the plate rests upon the sensitive material on the pad 17 or panel 6. In order to cause the plate to apply automatically the predetermined pressure upon the pad 17, the lever 14 is pivotally connected by a link 21 to a crossbar 22 to each end of which is pivoted a plunger 23 having a head 24 slidable within a casing 25 pivotally connected to the lower end of a ratchet bar 28 which in turn is pivotally connected at its upper end to a spring anchorage 32 on the casing 3. Tension springs 31 anchored to the casing 3 normally bend the linkage 25, 28 to hold the ratchet bars away from co-operating teeth 30 carried by the runners 10; and springs 26 are housed in the lower ends of the casings 25. During the initial pressure on the foot lever 14 to lower the plate 7, the link 21 causes the cross-bar 22 to descend, but no effect is produced on the ratchet lock because of the gap between the plunger heads 24 and springs 26. When, however, continued pressure is applied to the foot-lever, its further movement is permitted, notwithstanding the arrest of the plate 7, because of the sliding engagement between the rod 13 and the perforated plate 20 ; this further movement, through the link 21 and crossbar 22, pulls down the plunger heads 24 so that they engage the springs 26, whereafter the linkage 25, 28 is straightened, thereby moving the rack bars 28 into locking engagement with the teeth 30. The remaining movement of the lever, until it is engaged by a catch 14a, applies the predetermined pressure to the platen through the ratchet mechanism. On releasing the catch, the lever is raised by an elastic cord 15 to unlock the ratchet mechanism through the link 21, and lift the plate 7, through the rod 13, back to its initial position. For reflex copying, an external lamp source 44 is provided having provision in its casing for the insertion of colour filters ; while for negative copying, lamps 33 are provided in the box 5 ; there may be a selectively-operable switch to permit either method of lighting to be adopted. The foot lever 14 may carry a switch contact for the lamps, preferably associated with a time-switch. A cam-operated linkage, carried by the pad plate 17, is also described, whereby the pad may be transferred from the panel 6 to the underside of the plate 7 and clamped thereto by first lowering the plate 7 by operating the foot lever, and then manually actuating the cam. The casing 3 may include a storage cupboard for negatives &c.