Drum cleaning in an electrophotographic copying machine

Claim 1

A developing-cleaning method in an electrophotographic copying machine capable of making one or multiple copies of an original sheet with a final copy representing either the only copy or the last of said multiple copies including a rotating photosensitive member, a uniform charging unit, an exposure unit for forming a latent image on said rotating photosensitive member, a combined developing-cleaning magnetic brush element for developing the latent image in one mode and for cleaning the surface of the rotating photosensitive member in another mode, a transcription unit, an erase unit for erasing the image formed on said rotating photosensitive member, and means for selectively applying at least two levels of bias voltages to said combined developing-cleaning magnetic brush element, the method comprising the steps of: applying a first bias voltage of a first polarity corresponding to the polarity of said latent image to said combined developing-cleaning magnetic brush element when said rotating photosensitive member with said latent image rotates through at least a first revolution, thereby performing the developing operation; applying a second bias voltage at ground level or at a second polarity opposite to the polarity of said first bias voltage to said combined developing-cleaning magnetic brush element as said rotating photosensitive member rotates through a first subsequent revolution after said final copy is made, thereby removing residual toner having developed the same first polarity of the first bias voltage from the surface of said rotating photosensitive member; and applying a third bias voltage to said combined developing cleaning magnetic brush element, said third bias voltage being of the same polarity as said first bias voltage, as said rotating photosensitive member rotates through a second subsequent revolution, thereby removing remaining residual toner having a polarity opposite to the polarity of said first bias voltage from the surface of said rotating photosensitive member to complete said cleaning.