| 摘要 |
PURPOSE:To make a copying machine compact by arranging plural developing devices storing different color developers respectively and setting a developing bias voltage of a developing sleeve in each developing device at the time of non-operation to a value higher than that at the time of developing operation. CONSTITUTION:In the copying machine provided with two developing devices for color and black/white, developing is executed as follows. In case of executing color developing by a 1st developing device 10a, the bias of the developing sleeve 20 is set to -150V and a developer is supplied to a photosensitive drum 1 through a backet roller 22 and the sleeve 20 to form a toner image. At that time, a developing device 10b stops the supply of the developer by the action of a guide plate 27 and sets the developing bias to 0V. In case of black-to-white developing by a 2nd developing device 10b, the guide plate 27 is set so as to be supplied, -150V developing bias is impressed and then the developer is supplied. At that time, the developing device 10a holds the developing bias at -300V. Thus, the developing device can be simply charged only by switching the bias.
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