| 摘要 |
PURPOSE:To provide a copying machine not causing fog even if there is fatigue of continuous copying and changes of atmospheric temp. etc., not requiring a sensor for detecting potential of a photoreceptor surface, and capable of forming a stable sharp image. CONSTITUTION:A white preceding projection part 6 giving the same projection intensity to a photoreceptor 3 as the background part of an original 5 is provided on the position to be projected prior to the original 5 in contact with the original placing position of a platen 4. When an electrostatic latent image formed by projection of the part 6 passes through a developing device 1, a bias voltage controller 7 applies bias voltage to a sleeve 2 so as to control developing current iD flowing to the sleeve 2 to almost zero, and this bias voltage is held until an electrostatic latent image formed by projection of the following original 5 has passed, thus permitting a developer not to be attached to the background part of the electrostatic latent image of the original 5 obtaining the same potential as that of the latent image of the part 6, and fog to be perfectly prevented. |
