| 摘要 |
PURPOSE:To prevent a drop in picture density at the time of consecutive image formation by comparing a signal indicating the concentration of toner included in a developer with plural reference values and controlling toner supply or an image forming action. CONSTITUTION:A sensor 11 detects the concentration of the toner included in the developer in a developing tank, amplifies 12 the detecting signal and then sends it to comparators CMPs 13 and 17. The CMP 13 compares the signal with the reference value Vo. If the toner concentration lowers than a desired value, the output of the CMP 13 becomes 'L' and is sent to a driver 14, a restart circuit 15 and a timer 16, whereby the toner is supplied to the two- component developer in the tank. On the other hand, the CMP 17 compares the signal with the reference value V1. If the toner concentration lowers below the lower limit of the desired value, the output of the CMP 17 becomes 'L', and the image forming action is stopped. The timer 16 is triggered, a toner run-out signal is sent to a display. |
