Patent ID: 9411253
Filing Date: 2016-08-09
CPC Classification: G03G

Claim Text:
1. An image forming apparatus including: a plurality of image forming units configured to write electrostatic latent images on image carrying members by exposing portions and develop the electrostatic latent images by developing portions to form toner images of different colors; an intermediary transfer member configured to be rotatable; a primary transfer portion for transferring the toner images formed on the image carrying members to the intermediary transfer member; and a secondary transfer roller for secondarily transferring the toner images transferred to the intermediary transfer member to a transfer-destination material, the secondary transfer roller being configured to be rotatable and releasably contactable with the intermediary transfer member, the plurality of image forming units being operable to form registration patches for detection of displacements of the toner images such that, with the secondary transfer roller released from the intermediary transfer member, the registration patches are primarily transferred to the intermediary transfer member so that the registration patches on the intermediary transfer member are detected by a detecting portion and, based on results detected by the the detecting portion, calculated displacement amounts of the registration patches of the different colors in a sub scanning direction are calculated to correct positions at which the exposing portions write the electrostatic latent images, a storing portion that stores a reference rotation speed of the intermediary transfer member determined at an initial use of the intermediary transfer member, as observed when the intermediary transfer member is brand-new; and a correcting portion including a processor that performs a displacement correction procedure including the steps of: forming the registration patches on the intermediary member at the time the displacement correction procedure is performed; determining a rotation speed of the intermediary member with the secondary roller released from the intermediary transfer member using the registration patches formed at the time the displacement correction procedure is performed; correcting, based on a rotation speed difference between the rotation speed of the intermediary transfer member and the reference rotation speed stored in the storing portion, the calculated displacement amounts to form corrected displacement amounts expected when the secondary transfer roller is contacted with the intermediary transfer member, and correcting the positions at which the exposing portions write the electrostatic latent images based on the corrected displacement amounts, wherein the displacement correction procedure is performed at least twice, whereby the reference rotation speed determined once at the initial use of the intermediary transfer member is used at least twice.