| 摘要 |
PURPOSE:To obtain a developing device by which a supply speed to a developing sleeve of a toner is high, and a rise of a toner density is satisfactory, by applying a bias voltage which is below a collection bias voltage at the time of development and also to which an AC voltage is superposed to a toner supply/ collection roller, at the time of supplying the toner in order to switch a color of a toner. CONSTITUTION:A developing device which can switch a color of a toner by selecting one toner supply part is provided with a collection bias voltage circuit for applying a bias voltage which is below a collection bias voltage at the time of development and also to which an AC voltage is superposed to a toner supply/collection roller 12, at the time of supplying the toner in order to switch the color of the toner. At the time of switching the color of the toner, the collection bias voltage being lower than that of the time of development, therefore, the supply quantity of the toner becomes more than the collection quantity. Also, since the AC voltage is superposed to this collection bias voltage, an electrostatic holding force of the toner on the toner supply/collection roller is varied periodically by a periodical variation of the collection bias voltage, and the supply efficiently is raised. |
