| 摘要 |
PURPOSE:To obtain a clear and colorful picture having sufficient high density by changing the characteristics of a light emitting means in accordance with the divided light reflection factor of toner to be used. CONSTITUTION:An LED18d functioning as a photodetecting element is arranged in an optical path 18b formed on the body 18a of a density sensor 18 and a phototransistor 18e to be a photodetecting element is arranged in an optical path 18c. In a detecting circuit, the phototransistor 18e of the density sensor 18 is connected between a power supply voltage Vcc and the earth through a resistor R7 and the common connection point between the resistor R7 and the phototransistor 18e is connected to the non-inversion input terminal of an operational amplifier 22. If an output from the operational amplifier 22 to an inversion input terminal is raised higher than a reference voltage, the output voltage is turned to the low level to indicate that the density of the detected toner image is lower than the prescribed value. A signal indicating the density is sent to a solenoid valve of a developing device and toner feeding from a hopper is started or stopped to control the tone concentration. |
