| 摘要 |
PURPOSE:To prevent a carrier from sticking to a no-image part and toner from sticking to an image ground part by switching a developing roll bias voltage for the no-image part between images on a photosensitive body so that the voltage is lower than that for image parts on the photosensitive body. CONSTITUTION:The developing roll bias circuit 13 consisting of a boosting and rectifying circuit 10, oscillation control circuit 11, and reference signal circuit 12 is provided so as to prevent a carrier from sticking to the no-image part. The bias voltage V of a developing roll 7 is switched between the image part and no- image part. Namely, the bias voltage V is so controlled that V=VB>VD+VL when the image part faces the developing roll and VB>V>VD when the no- image part faces the developing roll. In this case, VL is the potential of the image background part and VB is the potential for density. Thus, the developing roll bias voltage is controlled to prevent completely the toner from sticking to the image background part and the carrier from sticking to the no-image part between images. |
