| 摘要 |
PURPOSE:To recover stable toner concentration by detecting the toner concentration of two- component developer, changing the duty of a toner supply time according to the level of a toner requirement signal corresponding to the degree of lack and repeatedly supplying toner. CONSTITUTION:One part of the two-component developer 4 in a developer container 3 obtained by mixing magnetic carrier and the toner is guided to a sensor 7 and the toner concentration thereof is detected. The electric coil of the sensor 7 is used as an factor for deciding the oscillation frequency of an oscillation circuit 15a and a toner concentration detection signal is outputted by a frequency-voltage converter 15b. Then, the level of the toner concentration detection signal and the reference voltages of three stages V1 - V3 from a reference voltage generator 17 are compared by comparators 16a - 16c and the toner requirement signals S1 - S3 having the levels corresponding to the degree of the lack of the toner concentration of the developer 4 are generated. By a main controller 18, the existence of the toner require ment signal is regularly decided and a motor 19 is driven by the duty according to the level. Then, a toner supply motor driving circuit 20 is controlled so as to supply the toner by rotating a roller 14. Besides, a toner exhaustion display circuit 22 is controlled by the control ler 18 so as to turn on a lamp 21 in the case that the toner concentration is not recovered even when the toner is repeatedly supplied in prescribed times. |
