| 摘要 |
PURPOSE:To prevent a background from being stained by providing a square wave voltage generating means which generates voltages which are higher and lower than a mean potential alternately. CONSTITUTION:The voltage of a developing electrode 13 is a square wave consisting of the high voltages E3 with time width t1 and the low voltage E1 with time width t2 which alternate at a frequency (f) according to the frequency and duty factor of output pulses of a pulse generator 20, and its mean voltage E2 is set according to the surface potential of the photosensitive body 14 corresponding to the background density of an original. Further, the (f), t1, and t2 are varied according to the linear speed of the photosensitive body 14 and the flowing speed of toner by varying the frequency and duty factor of the output of the pulse generator 20. Consequently, only an image part having a surface potential higher than the background potential is developed and the background is never stained. |
