| 摘要 |
PURPOSE:To measure toner concentration always at proper timing by making a timing singal generate by the leading edge of a detecting signal for a toner concentration measuring pattern on a photosensitive element in a conpying machine. CONSTITUTION:A monostable multivibrator MM1 is triggered by the leading edge of an output from a comparator A4 and a monostable multivibrator MM2 is also triggered by the leading edge of an output from the MM1. The output of the MM2 is generated only the period when a sensor 16 detects a toner concentration detecting pattern on a drum 1 and inputted to a gate circuit G1. A comparator A3 sends its output through the gate circuit G1 and, when the input of the comparator A3 falls less that the standard voltage, the output is turned to high level. consequently when the toner concentration is reduced less than a set point, the output of the circuit G1 is turned to high level and triggers the monostable multivibrator and the output of the monostable multivibrator actuates a toner feeding circuit, so that toner is supplied to a developer in a developing device and the toner concentration is controlled to be set to the set point. Thus, the toner concentration can be measured at proper timing. |
