GB696432A - Improvements in or relating to photo-copiers - Google Patents

Abstract

696,432. Photographic contact printing. MASON & SONS, Ltd., E. N., and WOODHAM E. Sept. 24, 1951 [Sept. 25, 1950; Feb. 27, 1951], Nos. 23408/50 and 4730/51. Class 98 (ii). [Also in Group XL (b)] In a photographic contact printing machine of the type in which a tracing or negative and sensitized material are passed over the surface of a glass cylinder by a conveyer band or blanket, a photo-cell senses the transparency of the tracing and sensitized material and adjusts the speed of the conveyer. As shown, the tracing and sensitized material 21 are passed over a table 23 in which are apertures 24 below which are situated photo-electric cells 25, 33, and is then fed by the conveyer 11 over the surface of the glass drum 1 finally reaching a tray 19. A longitudinal light source 3 is situated at the centre of the drum and part of the light from this source is directed through the apertures 24 by mirrors 20. A third cell receives light from the same source but which has passed only through a piece of sensitized paper which has been exposed. In operation, arrival of the tracing obscuring cell cell 25 renders cell 33 operative after a time delay, its output being combined in opposition with that of the third cell. Thus the output of the two cells, which is used to control the speed of the motor driving the conveyer, depends on the transparency of the tracing and the sensitized surface. In a modification described with reference to Figs. 3 and 4 (not shown), a separate light source is used to energize the photo-electric cell which responds to the transparency of the tracing and printing material while this separate source may also energize the third cell through the piece of sensitized paper which has been exposed. Alternatively a second separate light source may energize the third cell. Specifications 483,607 and 696,575 are referred to.