GB1020345A - Automatic exposure control for photographic copiers - Google Patents

Abstract

1,020,345. Photo-copying apparatus. SPERRY RAND CORPORATION. Sept. 27, 1963 [Oct. 9, 1962], No. 38169/63. Heading G2A. In continuous flow copying apparatus, a photoelectric cell receives light reflected from the original at a point just before it passes into the photographing station, the cell being part of a circuit controlling the energization of the light source so as to vary its intensity inversely in proportion to the intensity of the said reflected light. In the arrangement shown, the documents to be copied are in the form of a continuous strip 14, fed at speed over a roller 16 of dark-surfaced rubber by endless belts 18, 18<SP>1</SP>. The photographing station is defined by a glass 15 under which the strip passes. In this position, light falls on the document from a source LPB, and is reflected therefrom to pass through an aperture 20 in a light shield 12. (The shield 12 divides the housing 10 into two sections.) A mirror 22 reflects the light on to the sensitive film 26, which is moving from supply reel 28 to take-up reel 30. Light from the source LPB is also reflected from the document strip at a predetermined location just before it reaches the photographing station 15, and the light reflected from this position is collected by a photoconduct cell PC. The varying resistance of this cell, as the light incident on it varies, it utilised, by means of the circuit of Fig. 2 (not shown), to control the power energizing the light source LPB, in an inverse manner. Thus if the amount of reflected light received by the photocell increases, the intensity of the light source is reduced, and vice versa. Consequently, the brightness of the document to be copied is sensed just before it reaches the photographing station, and any change therein causes a compensating change in the light source intensity by the time the document reaches the photographing station. An additional (constant) light source LP, whose reflection from the "measuring" location is picked up by the photo-cell, may be provided to afford a greater degree of linearity to the control. A reflecting disc 44, spring-loaded so as to bear against one down-bent end 40b of a trigger bar bar 40, is normally positioned as shown in full lines, so that it does not obstruct the passage of light from sources LPB and LP. The other downbent end 40a rides on the document strip. When there is no strip present, the end 40a of the spring- loaded trigger bar enters into a groove 48 in roller 16, so that its other end moves sufficiently to allow disc 44 to rotate into a position where it interrupts the light and reflects it back to the photo-cell. This prevents the overloading of the light source due to minimal reflection from the dark surface of the roller itself.