| 摘要 |
A bias applied to a transfer roller is subjected to the constant-current control when the resistances of the transfer roller and a sheet are high. Thereby, a sufficient amount of current is supplied to the sheet and the toner on a photosensitive drum is reliably transferred to the sheet. If the constant-current control is continuously performed after the resistances of the transfer roller and the sheet decrease, the amount of current flowing through the sheet decreases and the toner on the photosensitive drum is not transferred to the sheet. Instead, by controlling the bias applied to the transfer roller such that the transfer current increases when the resistances of the transferring element and the sheet are low, the amount of current flowing through the sheet increases enough to allow the toner transfer from the photosensitive drum to the sheet. By switching the method of controlling the current of the bias applied to the transfer roller depending on whether the resistances of the transfer roller and the sheet are high or low, the toner on the photosensitive drum is reliably transferred to the sheet at all times.
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