ELECTROSTATIC CHARGE IMAGE DEVELOPING DEVICE

摘要

PURPOSE:To obtain a developing device with which an image concentration can be maintained at a constant even if the amount of charge of toner is varied by environmental conditions and aging, and also a fogging cannot be produced. CONSTITUTION:A concentration of an image printed on a sheet 7 is measured by an image concentration sensor 8 and processed in a control circuit 9 to obtain an image concentration and a fogging concentration. By calculating a difference between these concentrations and the set values, a pulse width and a pulse frequency of a pulse-form developing bias are obtained and the signals of the pulse width and the pulse frequency are generated by a pulse width modulator 10. Then the bias power supply 11 is controlled by the signals.