Patent ID: 8295736

Claim:
An image forming apparatus comprising: a rotatable image carrier corresponding to each of a plurality of colors and configured to carry a visible image of a corresponding one of the colors on a surface thereof; a plurality of image-carrier drive sources configured to drive one or more of the image carriers; a belt member that is stretched and supported by a plurality of stretching and supporting members in the vicinity of the image carriers; a drive rotating body configured to support the belt member and when driven causes the belt member to endlessly move over the stretching and supporting members; a belt drive source configured to drive the drive rotating body, wherein one of the image-carrier drive sources functions as the belt drive source as a shared drive source; a velocity detector configured to detect velocity of the belt member when driven by the belt drive source; a drive control unit configured to control a drive speed of the belt drive source based on a result of detection by the velocity detector; a transfer unit configured to transfer the visible images from the surfaces of the image carriers onto a surface of the belt member or to a recording member held on the surface thereof; and a rotation detector configured to detect a parameter indicative of at least one among an angular velocity and an angular displacement of the shared drive source and an angular velocity and an angular displacement of the image carrier driven by the shared drive source, wherein the drive control unit executes a process for controlling a drive speed of the image-carrier drive sources other than the shared drive source based on the parameter detected by the rotation detector.