Feedback system for controlling image light energy in electrostatic photocopiers

Claim 1

In an electrostatic photocopier having a projection lamp for illuminating a document at an illuminating station and a motor coupled to feed photoconductive copy paper through an imaging station where the copy paper is exposed to a light image reflected from the document and projected by projection optics, a system for regulating the total image light energy incident on the copy paper comprising, in combination: A. lamp control means operative to maintain lamp current at a predetermined constant value despite fluctuations in line voltage, B. sensing means for monitoring the light intensity of a reference beam reflected from a target illuminated by the lamp and transmitted through the projection optics, C. feedback motor control means for varying motor speed and thus the copy paper feed rate through the imaging station, and D. means coupling a feedback signal from said sensing means to said motor control means proportional to the light intensity of said reference beam, 1. said feedback signal serving to actuate said motor control means to control motor speed in accordance with reference beam light intensity.