Patent ID: 8331822

Claim:
An image forming apparatus, comprising: a plurality of image bearing members, each of which is configured to bear a portion of a pattern image including a plurality of reference images in a given form and each portion of the pattern image being arranged on the surface of each image bearing member in a rotation direction of each image bearing member; an endless moving member disposed facing the plurality of image bearing members and configured to receive the pattern image from each of the plurality of image bearing members; an image detecting unit configured to detect the plurality of reference images in the pattern image transferred onto the endless moving member; a rotational angle detecting unit configured to separately detect each image bearing member when each image bearing member comes to a given rotational angle; and a controller configured to detect a speed deviation pattern per one revolution of each image bearing member based on a detection timing of each of the plurality of reference images by the image detecting unit and a detection result obtained by the rotational angle detecting unit and conduct a phase adjustment control for adjusting a phase of the speed deviation pattern of the plurality of image bearing members, wherein a circumferential length of each of the plurality of image bearing members in a rotation direction of each image bearing member is equal to a dot formation pitch in the rotation direction of each image bearing member multiplied with a first integer number, and the controller is configured to control forming the reference images in the pattern image at a timing that the reference images of the pattern image are formed in a rotation direction of each image bearing member such that a pitch of the pattern image is obtained by dividing the circumferential length of each image bearing member by a second integer number.