| 摘要 |
PURPOSE:To control toner concentration accurately by detecting the toner concentration in a developer on the basis of a reference developed image formed at a reference developed image formation part of low or high density when black or color toner is used for development. CONSTITUTION:When the black toner is used, the reference developed image to be detected is formed on the formation part of low density as its background. Therefore, when no black toner sticks on the formation part 3a, the quantity of reflected light is maximum and the output of a photodetecting element 26b is minimum. Then when the quantity of sticking black toner T1 increases, the quantity of reflected light decreases and the output of the element 26b rises. For the purpose,the output value of the element 26b is compared by a control circuit with the output of the density of the reference developed image when the toner concentration in the developer in a developing device is a set value and when the output of the element 26b is low, a deficiency in toner density is judged, thereby supplying toner. Then when the color toner is used, the reference developed image to be detected has a color part 3b of high density as its background and the output of the photodetecting element 26b is compared with a reference value by the control circuit; when the output of the element 26b is higher, a deficiency of toner is judged and toner is supplied. |
