| 主权项 |
1. An image forming apparatus comprising:
a rotatable photosensitive member; a first charging roller for charging the photosensitive member; a second charging roller for charging the photosensitive member on the downstream side of the first charging roller in a rotation direction of the photosensitive member; a toner image forming unit disposed on the downstream side of the second charging roller in the rotation direction of the photosensitive member, the toner image forming unit forming a latent image on a surface of the photosensitive member which has been charged by using the first charging roller and the second charging roller, and developing the latent image by using toner so as to form a toner image; a first power supply that applies a changing voltage to the first charging roller, a voltage value of the changing voltage being made to change; a second power supply that applies a voltage obtained by superimposing an alternating voltage on a direct voltage, to the second charging roller; and control means for changing the changing voltage applied from the first power supply to the first charging roller in such a manner that a magnitude relationship between a potential of the photosensitive member which has been charged by using the first charging roller and which has reached a position at which the photosensitive member is charged by using the second charging roller, and the direct voltage applied to the second charging roller is alternately switched, when the photosensitive member is to be charged by using the first charging roller and the second charging roller to form a toner image, wherein, when the photosensitive member is to be charged by using the first charging roller and the second charging roller to form a toner image, the following relations are satisfied,
X>(W/PS),Y>(W/PS), where X (s) represents a time period for which the potential of the surface of the photosensitive member which has been charged by using the first charging roller and which has reached a position at which the photosensitive member is charged by using the second charging roller is less than the direct voltage applied to the second charging roller, Y (s) represents a time period for which the potential is more than the direct voltage, PS (mm/s) represents a peripheral velocity of the photosensitive member, and W (mm) represents a width of a contact portion between the second charging roller and the photosensitive member in the rotation direction of the photosensitive member, and wherein a sum of X and Y is larger than a period of the alternating voltage applied to the second charging roller. |
