| 摘要 |
PROBLEM TO BE SOLVED: To realize the image formation of only a black toner image at high speed and to realize color image formation where stable image exposure is performed by changing image forming speed between at the time of forming only the black toner image and at the time of forming the color image. SOLUTION: Developing device driving motors M2 and M3 are provided independently, and the respective Y, M and C developing devices 13 are directly connected to the motor M2 for a color developing device by respective driving systems. The black (K) developing device 13 arranged on the most downstream side in the rotating direction of a photoreceptor drum 10 is directly connected to the motor M3 being a driving means for the black developing device by the driving system through a developing device changing machine. Since the motor M3 for the black developing device drives only one black developing device 13, it has enough driving torque, and the rotational velocity of the developing sleeve 130 of the black developing device 13 is increased in accordance with the increase of the linear velocity of the drum 10 at the time of forming only the black toner image. |
