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 the voltage of an exposing lamp according to the result of the comparison and determining the min. density value of the image as the ground texture density of the 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 min. density value of the document image density is determined as the ground texture density of the document. The outputs Q1, Q2 of 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 reflected light from the toner image is V>V1. Q1 is the low level and Q2 is the high level at such original 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