Patent ID: 7469109

Claim:
An image forming apparatus, comprising: a photosensitive member; a charging member configured to electrically charge said photosensitive member at a charging position to form an electrostatic image on said photosensitive member; a charging bias applier configured to apply an AC voltage superposed with a DC voltage to said charging member to charge said photosensitive member; a developing device configured to develop the electrostatic image on said photosensitive member with toner to form a toner image; a developing bias applier configured to apply a developing bias to said developing device to develop the electrostatic image; a toner charging member configured to electrically charge a residual toner on said photosensitive member, after the toner image on said photosensitive member is transferred and before said photosensitive member is charged by said charging member, to collect the residual toner on said developing device; a toner charging bias applier configured to apply a DC voltage having a same polarity as a regular charge polarity of the toner to charge the residual toner; a detector configured to detect an AC current flowing through said charging member by applying an AC voltage to said charging member when an area of which said photosensitive member is charged by said toner charging member passes through the charging position; and a setting device configured to set the AC voltage applied to said charging member by said charging bias applier during an image formation based on an output of said detector, wherein said charging bias applier applies a DC voltage within ± 100V of a potential of the area of said photosensitive member, when the area of said photosensitive member passes through the charging position.