Patent ID: 8768200

Claim:
A transfer unit comprising: a belt member extended in a loop around a plurality of rollers and having a movable surface on which a toner image is transferred from an image carrier; a bending roller externally contacting the surface of the belt member to bend the belt member toward an interior of the loop and rotating in conjunction with movement of the surface of the belt member; a transfer section including one roller of the plurality of rollers and a surface moving member, the one roller located upstream from the bending roller and downstream from a transfer point at which the toner image is transferred from the image carrier onto the surface of the belt member in a surface moving direction of the belt member, the surface moving member facing the one roller of the plurality of rollers via the belt member, the transfer section transferring the toner image from the belt member onto a transfer material at a transfer nip formed as the surface moving member presses against the one roller via the belt member; and an electrical bias application unit to simultaneously apply an electrical bias to both the transfer section and the bending roller to form an electric field to transfer toner adhered to a surface of the surface moving member from the surface moving member onto the belt member and an electric field to transfer toner adhering to a surface of the bending roller from the bending roller onto the belt member, the surface moving member rotating at least one full turn while cleaning is performed on the surface moving member and the bending roller by transferring the toner adhering to the surface of the surface moving member and the surface of the bending roller onto the belt member using the electrical bias applied from the electrical bias application unit to the transfer section and the bending roller, a surface moving speed of the bending roller equal to or greater than a surface moving speed of the surface moving member, a circumferential length L 1 of the surface moving member and a circumferential length L 2 of the bending roller satisfying the relation L 1 ≧L 2 , and the surface moving speed of the bending roller is equal to the surface moving speed of the surface moving member, a surface moving distance D 1 of the surface moving member in applying the electrical bias from the electrical bias application unit to the transfer section and the bending roller is set to satisfy the relation D 1 =L 1 ×n, where n is an integer equal to or greater than 2, and the bending roller is located at a position at which a distance L 3 from a contact position between the surface moving member and the belt member to a contact position between the bending roller and the belt member toward a downstream side in the surface moving direction of the belt member satisfies one of the relations L 3 ≦(n−1)×L 1 and L 3 ≦D 1 ×(n−1)/n, where n is an integer equal to or greater than 2.