Patent ID: 8478167

Claim:
An image forming apparatus, comprising: an image forming station including a plurality of photoconductive drums and adapted to form toner images on surfaces of the respective photoconductive drums; and a drive control unit for rotating and driving the plurality of photoconductive drums; wherein: the image forming station includes a reference pulse output section for generating a reference pulse having a cycle which is equal to a rotation cycle of the photoconductive drums or an integral multiple of the rotation cycle of the photoconductive drums and outputting the reference pulse to the drive control unit; and the drive control unit includes: a phase peak detector for detecting phase peaks of surface speeds of the respective photoconductive drums, a phase difference detector for detecting phase differences between an edge of the reference pulse and the phase peaks, and a phase synchronization controller for synchronizing phases of the surface speeds of the respective photoconductive drums by controlling rotation speeds of the respective photoconductive drums according to the phase differences; and wherein if the phase peak of the photoconductive drum to be synchronized is ahead of the edge of the reference pulse, the phase synchronization controller controls the phase of the photoconductive drum to be synchronized by decelerating the rotation speed of the photoconductive drum at a constant deceleration rate until the phase difference is halved, then accelerating the rotation speed at a constant acceleration rate of the same magnitude as the constant deceleration rate up to an initial speed and, thereafter, setting the rotation speed at a constant speed.