Patent ID: 11960226
Assignee: CANON KABUSHIKI KAISHA
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 0:
1. An image forming apparatus comprising:
a rotatable photosensitive member;
a charging roller configured to perform a charging process of a surface of the photosensitive member;
a charging voltage power source configured to apply a charging voltage for the charging process to the charging roller;
an exposure portion configured to expose the charging processed surface of the photosensitive member and to form an electrostatic image on the photosensitive member;
a developing member configured to supply toner to the electrostatic image on the photosensitive member at a developing portion and to form a toner image on the photosensitive member;
a developing voltage power source configured to apply a developing voltage for the developing to the developing member;
a transfer member configured to form a transfer portion by contacting the photosensitive member and to transfer the toner image to a recording material passing through the transfer portion from the photosensitive member;
a transfer voltage power source configured to apply a transfer voltage for the transfer to the transfer member; and
a control portion configured to control at least one of the charging voltage power source, the developing voltage power source and the exposure portion,
wherein an absolute value of a difference between a potential of a non-image portion of the surface of the photosensitive member at the developing portion and a potential of the developing voltage is defined as a back contrast, and
wherein, in a case which the transfer is performed to a first recording material of which width in a direction substantially perpendicular to a feeding direction of the recording material is a first width, and thereafter, the transfer is successively performed to a second recording material of which width is a second width longer than the first width,
the control portion controls a first back contrast which is the back contrast to be formed when an area of the surface of the photosensitive member corresponding to the transfer portion through which the first recording material is passing reaches the developing portion, and a second back contrast which is the back contrast to be formed when an area of the surface of the photosensitive member corresponding to the transfer portion through which the second recording material is passing reaches the developing portion so that the second back contrast is higher than the first back contrast.