| 摘要 |
PURPOSE:To control toner density stably without any influence of the outside environment by providing a density detector with plural magnetic circuits and comparing their output signals. CONSTITUTION:When the colored toner in a developer decreases in amount and the toner density decreases, the developer increases in apparent transmissivity and the coupling degree of the magnetic circuit of a transformer 19a becomes larger than that of a transformer 19b to generate a differential output. Then, the differential output is detected by a phase detector 21, which outputs a phase detection output corresponding to the phase and amplitude. This signal is compared by a potential comparator 22 with a reference voltage corresponding to preset toner density and a supplement valve driving circuit 23 is driven by the comparison output to operate a toner supplement valve 12, supplementing colored toner 13. |
