| 摘要 |
PURPOSE:To compensate the degradation of image quality based on the deterioration of a developer with a toner concentration by using a magnetic roller and a doctor, as counter electrodes, measuring a current flowing between the electrodes via the developer, and detecting a change in the resistance of the developer. CONSTITUTION:A developing tank 1 is provided with the magnetic roller 2, the doctor 3 regulating the napping of the developer on the magnetic roller 2, and a toner concentration detector 4 detecting the toner concentration of the developer, inside. A power source circuit 5 applying a bias voltage, a circuit 6 measuring the resistance of the developer by the current flowing via the developer, by using the doctor 3 as the counter electrode, and a control part 7 changing the reference value of the toner concentration, based on the signal of the detection from the circuit 6, are provided on the magnetic roller 2. At this time, a control part 7 executes control so as to set a toner concentration reference value high with the increase of the resistance of the developer. Therefore, the existing magnetic roller and doctor, and a developing bias voltage can be used, and the stable image quality can be obtained without increasing the number of parts. |
