ELECTROPHOTOGRAPHIC COPYING MACHINE

摘要

PURPOSE:To obtain a good copy image by providing a means for comparing the detected output of original image density with a reference voltage and means for controlling automatically a developing bias and detecting the min. density value of an image as the ground texture density of a original. CONSTITUTION:The reflected light from a toner image is converted to a voltage by a phototransistor 17 and a variable resistor VR1 and is conducted to comparators 23 and 24. The voltage is compared with reference voltages V1, V2 preset by the variable resistor VR1 and VR2. The outputs Q1, Q2 of two RS-FF29, 30 rise both to a high level when the original image density is low and the voltage V proportional to the quantity of the refelected light from the toner image is V>V1. Q1 is the low level and Q2 is the high level at such density at which the voltages are V1>V>V2. Both Q1 and Q2 are the low level when the original image density is high and V