Method and apparatus for developing and for the image traeger - cleaning in electrophotographic copying differential straight

摘要

PURPOSE:To prevent filming of remaining toner by switching a bias voltage in a cleaning device. CONSTITUTION:A cleaning operation is performed in the third rotation in an electrostatic copying machine of a twice rotating-copying type. In the start, the surface of a photosensitive drum is charged negatively with a charger 7 and is developed with positively charged toner using a magnetic brush 3 with a negative bias (VD) applied to transfer an image onto a copying paper 9 via a transfer device 4. In the second rotation, without operating the charger 7 and the device 4, the new positive toner adheres onto the surface of the drum when a bias (VC1) having positive or 0 voltage is applied to the magnetic brush 3 by a bias switch. Thus, in the second rotation, all the positive toner adheres onto the surface. A negative bias VC2 is applied onto the brush 3 in the third rotation to remove all the positive toner on the drum by electrostatic attraction acting between the toner and the brush 3.