| 摘要 |
An image forming apparatus including bias application control which controls bias application to prevent unnecessary toner-adhering to a photosensitive element due to fogging at the start of operation a photosensitive drum for image forming and on completion of operation of the photosensitive drum. Bias control is implemented so that operation of the photosensitive drum starts with a positive development bias voltage applied to both a first development roller and a second development roller from a power source, and a charger for charging the drum turns on. The polarity of applied development bias voltage is then changed from the positive development bias voltage to a negative development bias voltage. Furthermore, a developer drive clutch of the developer unit turns on before a leading edge portion of an electrostatic latent image area on the photosensitive element reaches a position facing the upstream end of the first roller. On completion of the operation of the photosensitive drum, after the trailing edge portion of the electrostatic latent image area passes the position facing the upstream end of the first roller, the developer drive clutch turns off as soon as possible. On the lapse of a predetermined period, the regular negative developing bias voltage is changed to the positive development bias voltage, and the charger for charging the photosensitive turns off.
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