Color image forming apparatus

Abstract

A color image forming machine includes a plurality of exposure units for irradiating an image carrier movable in a secondary scanning direction of the exposure units by primary scanning beams, at a plurality of irradiation positions to form latent images, a plurality of charging units for charging the image carrier corresponding to the irradiation positions of the exposure units and a plurality of developing units to form toner images corresponding the latent images. The plurality of toner images are superimposed on the image carrier to obtain a multi-color or full-color images trough transferring and fixing. A light-reflective registration mark is provided to a non-image area on one side of the image carrier. Employing at least two exposure units, irradiation by each primary scanning beam is conducted to the light-reflective registration mark moving in the secondary scanning direction. Each reflected beam from the registration mark is received by a plurality of photoreceptor sensors and then detection signals of a registration mark position are generated. Timing of writing by the primary scanning beam and a distance between bright lines formed on the image carrier by primary scanning beams of at least two exposure units are detected. The detected result is fed back to control the start timing of image writing and the driving of the image carrier.