| 摘要 |
PURPOSE:To prevent excessive density control in case of partial trouble of a control system or the like by not performing density control if the deviation of the density of a trial stuck toner from a reference value is larger than the deviation of an abnormal density signal. CONSTITUTION:The density of the toner stuck to a photosensitive drum 2 on trial before copying is detected by a density reading sensor 13, and the detection signal and a reference signal are compared with each other by an arithmetic amplifier 14, and a toner supply motor driving circuit 17 and a developing bias voltage generator 18 are controlled through a control circuit 16 to control automatically the copy density. Meanwhile, the detection signal of the sensor 13 is compared with the abnormal density signal by a comparator 31. If the deviation of the detection signal from the reference signal is larger than that of the abnormal density signal from the reference signal, the circuit 16 is operated in accordance with the output of the comparator 31, and density control due to the circuit 17 and the generator 18 is not performed. Consequently, excessive control is prevented when a part of the control system such as the density reading sensor or the lie is faulty. |
