| 摘要 |
PROBLEM TO BE SOLVED: To prevent fogging of toner when a paper sheet does not pass through and to reduce the sticking of the toner to a transfer roller by switching bias supply, so as to make the absolute value of the surface potential of an image carrier when a recording material does not pass through, in a transferring nip part higher than that when the recording material passes through. SOLUTION: A bias power source part 24 is provided with a changeover switch 27 as a switching means for selecting a DC bias, constant-current AC power source 28 connected to DC power source 25 or 26 with the changeover switch 27, etc. In this device, the bias power source is switched to make the absolute value of the surface potential of the photoreceptor drum 1 when the recording material does not pass through, in the transferring nip part higher than that when the recording material passes through. In other words, the changeover switch 27 is switched to select the DC power source 25 or 26 of the bias power source part 24, so that a DC voltage power source to an electrifying roller 6 is made variable to switch the surface potential of the drum 1. |
