| 摘要 |
PURPOSE:To approximately maintain image quality even when the states of a photosensitive drum and a primary electrostatic charging means are changed by exposing the surface of the photosensitive drum in the midst of the prerotation of the photosensitive drum and deciding DC voltage impressed in accordance with a DC current flowing in the primary electrostatic charging means at such a time. CONSTITUTION:Fixed primary bias is impressed on an electrostatic charging roller 2, the photosensitive drum 1 is rotated twice, for example, and the surface potential of the photosensitive drum 1 is set as dark potential VD. The surface of the drum 1 is exposed by an exposure device 3 in the case of 3rd rotation, and the surface potential of the drum 1 is set as light potential VL. When an electrostatic latent image on the drum 1 passes the part of the roller 2, the DC component of current flowing from the roller 2 to the drum 1 is measured by an amperemeter 25. At the time of forming the image, the DC bias of the roller 2 is decided in accordance with the measured DC current by a controller 24. Then, contrast potential 1VD-VL1 is controlled to be constant by a power source 20. |
