| 摘要 |
PURPOSE:To prevent an unnecessary toner consumption and a deterioration in a picture image quality by starting an electrostatic charge to a photosensitive body after the end of scanning and before exposure, and also controlling its potential. CONSTITUTION:In case of a scan before an exposure, a part of a reflected light from an original by an exposing operation is made incident on a photodetector 12, and its output current is brought to a voltage conversion by a variable resistance VR1, and compared with reference voltages V1, V2 by comparators 23, 24. A scan pulse P1 before an exposure is veried to a low level from a high level, when a scan before an exposure is started, outputs of invertors 25, 27 are changed to a high level, and outputs of the comparators 23, 24 are sent to RS- FFs 29, 30 through invertors 26, 28. In accordance with a variable density of the original, output levels of the comparators 23, 24 are varied, and in accordance with it, output levels of outputs Q1, Q2 of the RS-FFs 29, 30 are also varied, and the surface potential of a photosensitive body is controlled. On the other hand, the pulse P1 passes through invertors 31, 32 and a diffentiation circuit and executes a control so that electrostatic charge to the photosensitive body is not executed at the time of a scan before an exposure. |
