| 摘要 |
PURPOSE:To always obtain a copied image having excellent image quality by changing the voltage value of a developing bias according to a toner concentration detected by a toner concentration detecting means. CONSTITUTION:The toner concentration detecting means 9 detecting the toner concentration in a developer and a developing bias applying means for applying the developing bias on a developing electrode 21 are provided, and the voltage value of the developing bias applied according to the detected toner concentration is changed. For instance, when development is carried out with toner electrostatically charged to the polarity reverse to the potential of the surface of a photosensitive body, the potential having the polarity reverse to the electrifying polarity of the toner is applied as the developing bias. When the toner concentration is reduced, the developing bias voltage is tentatively decreased and the quantity of the toner sticking to an image part is added. On the other hand, when the toner concentration is increased, the developing bias voltage is increased, and the toner sticking quantity is reduced. Thus, even if the toner concentration is fluctuated, the excellent copied image can be always obtained. |
