| 摘要 |
PURPOSE:To reduce the offset quantity of a toner to a surface of fixing roller as much as possible by detecting the potential of an image supporting body before or/and after passing a pair of fixing rollers and applying a bias voltage to one of this pair of fixing rollers at least in accordance with the detected potential. CONSTITUTION:A bias electric power source 14 is controlled through a measuring circuit 13 and a control circuit 14 in accordance with the detected potential due to a potential sensor 12 to control properly the bias voltage to a fixing roller 7. Since the offset quantity is reduced if a difference DELTAV between a potential Vp of a form P passing fixing rollers 7 and 8 and a potential V7 of the fixing roller 7 is large in the positive direction, the potential Vp, which is changed in accordance with the classification of the form P, environmental conditions, etc., of the form P at the time when the form P passes a pair of fixing rollers 7 and 8 is detected by the sensor 12, and the power source 14 is controlled to hold always the bias voltage to the fixing roller 7 in a voltage (Vp+DELTAVa) or higher in accordance with the detected potential so that a potential difference DELTAVa considered as the practical level of the offset quantity or a larger potential difference is attained, and thus, the electrostatic offset of the toner on the form P side is suppressed well. |
