US Patent No. 9,285,719

IMAGE FORMING APPARATUS


Patent No. 9,285,719
Issue Date March 15, 2016
Title Image Forming Apparatus
Inventorship Shinsuke Kobayashi, Yokohama (JP)
Keisuke Ishizumi, Hiratsuka (JP)
Assignee Canon Kabushiki Kaisha, Tokyo (JP)

Claim of US Patent No. 9,285,719

1. An image forming apparatus, comprising:
an image bearing member for bearing a toner image;
an intermediate transfer member that is endless and moveable, including a primary transfer portion formed by contacting the
image bearing member, and a secondary transfer portion, wherein the toner image is primarily transferred from the image bearing
member onto the intermediate transfer member in the primary transfer portion and secondarily transferred from the intermediate
transfer member onto a transfer material in the secondary transfer portion;

a secondary transfer member to which a voltage is applied, the secondary transfer member contacting an outer peripheral surface
of the intermediate transfer member to form the secondary transfer portion;

a charging device to which a voltage is applied, the charging device contacting the outer peripheral surface of the intermediate
transfer member to charge toner remaining on the intermediate transfer member;

a first power supply capable of applying one of a positive polarity voltage and a negative polarity voltage to the secondary
transfer member;

a second power supply capable of applying one of a positive polarity voltage and a negative polarity voltage to the charging
device; and

a controller for controlling the first power supply and the second power supply,
wherein the charging device is provided on a downstream side of the secondary transfer member and an upstream side of the
primary transfer portion with respect to a moving direction of the intermediate transfer member,

wherein the intermediate transfer member is configured to determine a polarity of an electric potential formed in the primary
transfer portion by a polarity of the current supplied from the secondary transfer member independently of a polarity of a
current supplied from the charging device provided at a portion closer to the primary transfer portion, and

wherein before the intermediate transfer member starts rotating, the controller applies the positive polarity voltage to the
charging device from the second power supply while applying a negative polarity voltage to the secondary transfer member from
the first power supply.