Color image forming apparatus for preventing toner image displacement on

Abstract

A color image forming apparatus includes an image forming unit which forms a multicolor image on a second image support by sequentially transferring toner images related to a plurality of colors from a first image support to the second image support in an overlaying manner. A reference position detecting unit detects a reference mark signal every time a reference mark at a reference position on the second image support is sensed during rotation of the second image support. A laser scan start timing control unit controls a laser scan start timing for the image forming unit to start scanning the first image support by a laser beam, based on the reference mark signal. A phase error measurement unit measures a phase error between a line sync signal and the reference mark signal by counting system clocks before the laser scan start timing. A drive speed control unit adjusts a rotating speed of the second image support to a controlled speed by outputting a drive pulse to a motor which rotates the second image support, the drive speed control unit determining an ON-state period of the drive pulse depending on the phase error measurement such that a timing of detection of the reference mark signal matches the laser scan start timing.