Image forming apparatus featuring a transfer bias having a polarity opposite to a polarity of a charged toner

摘要

An image forming apparatus includes a rotatable latent image bearing member; a charging device contacting with the latent image bearing member and being provided with a voltage applied thereto for charging the latent image bearing member; a cleaning device contacting with the latent image bearing member for cleaning the latent image bearing member; and a transfer device contacting with the latent image bearing member and being provided with a transfer voltage for transferring, to a transfer medium, an image developed with a developer in an image forming area. The charging device, when in contact with an area constituting an image forming area of the latent image bearing member, is provided with an AC voltage for charging a non-image forming area having a peak-to-peak voltage larger than a peak-to-peak voltage of a charging AC voltage applied to the charging device for charging an area constituting the image forming area. When an area of the latent image bearing member, charged by the AC voltage for charging the non-image forming area applied to the charging device, comes into contact with the transfer device, a DC voltage of a polarity opposite to a normal charging polarity of the latent image bearing member is applied to the transfer device. More specifically, the transfer voltage is determined based on the DC voltage. The transfer voltage is determined, based on a current flowing between the latent image bearing member and the transfer means when the DC voltage is applied to the transfer means.