| 摘要 |
PURPOSE:To directly and accurately detect concentration of developing toner and to miniaturize a developing device by providing a sensor electrode in which a concentration sensor faces the surface of a conductive developing sleeve to which developing bias voltage is applied and placed keeping a specified space from the surface of the developing sleeve. CONSTITUTION:With consumption of developing toner in a mixed developer 9, the developer 9 that adheres on the surface of a developing sleeve increases and becomes thick gradually. When the space H between a sensor electrode 17 and the developing sleeve 13 is set a specific value, sensor current that flows in the sensor electrode 17 varies according to the thickness of the layer of developer 9. That is, sensor current changes abruptly when the layer of developer 9 came into contact with the sensor electrode 17. A concentration sensor 16 outputs a detection signal regarding it to correspond to the lower limit value of the set range of toner concentration, and opens and closes a rotary valve 22 for replenishing developing toner to adjust the quantity of replenishing toner. Thus, concentration of the developing toner is controlled within the set range. |
