| 摘要 |
PROBLEM TO BE SOLVED: To obtain a stable image by measuring the current value of the AC component of a developing bias and controlling an image forming condition according to the measured current value. SOLUTION: AC bias potential is impressed on the developing sleeves 13A-13D of respective developing devices by a power source 55 in addition to the DC bias potential. An AC amperemeter 14 is arranged in a bias circuit impressing a bias on the developing sleeve 13A. When the film thickness of the surface layer of a photoreceptor drum becomes thin, the surface potential of the photoreceptor drum is lowered and the AC bias current value is increased. Then, the grid voltage of the grid mesh 18 of an electrostatic charger 11 is controlled by detecting the AC bias value by the amperemeter 14. Not only controlling the grid voltage but also the power of the laser beam of a printing head part or the DC bias of the developing bias may be controlled as the image forming condition. |
