Patent ID: 6347200
Filing Date: 2002-02-12
Classification: G03G

Abstract:
A duplex image forming apparatus, comprising:an image bearing member; a toner image forming section to form a toner image on said image bearing member; an intermediate transfer element, shaped like a belt and having a first surface onto which said toner image is transferred from said image bearing member and a second surface located opposite said first surface, to bear said toner image transferred from said image bearing member and to convey a transfer sheet while holding it on said first surface; a transfer sheet charging device, disposed opposite a charging position and facing said first surface of said intermediate transfer element, to apply a bias voltage onto said transfer sheet at said charging position, so that said transfer sheet adheres onto said first surface of said intermediate transfer element; a first transfer device, disposed opposite a first transferring position and facing said second surface of said intermediate transfer element, to transfer said toner image, formed on said image bearing member, onto said transfer sheet or said intermediate transfer element at said first transferring position; a second transfer device, disposed opposite a second transferring position and facing said first surface of said intermediate transfer element, to transfer said toner image, borne on said first surface of said intermediate transfer element, onto said transfer sheet at said second transferring position; and a control section to control a transfer current or a transfer voltage applied to said first transfer device, wherein, under a condition that a length of said transfer sheet in its conveyance direction is longer than a length of a conveyance path ranging from said charging position to said second transferring position, said control section changes said transfer current or said transfer voltage, corresponding to each of three states, including a first state in which a leading edge of said transfer sheet has not arrived at said second transferring position, a second state in which said leading edge of said transfer sheet has passed through said second transferring position while a trailing edge of said transfer sheet has not arrived at said charging position and a third state in which said trailing edge of said transfer sheet has passed through said charging position.