| 摘要 |
PURPOSE:To stably control toner concentration by making the number of reading times of a pattern image part different from the number of reading times of a surface part and measuring the reflected light quantity of both parts. CONSTITUTION:A measuring device 21 measures the read value VSP of the pattern image and the read value VSG of the surface part by a photosensor 9, and a memory device 22 stores the potential VSG of the surface part at the time of rotating only a photosensitive drum 1 in a state where a black developing device is not actuated. A comparison and judgement device 23 compares and judges the ratio of the potential VSP of the pattern image which is generated every time to ten copies to the potential VSG stored in the device 22 with a previously fixed reference value. The result of comparison is outputted to a toner replenishing device 24 and toner is replenished in the black developing device 7 as necessary. Thus, the effect of a noise at the time of reading the surface part of the photosensor is reduced and the toner concentration is stably controlled. |
