Color image forming apparatus

Abstract

A color image forming apparatus is provided, having a plurality of image forming units including a photosensitive drum, a charging device and a developing device; a carriage for retaining and rotating the plurality of image forming units so as to move the image forming units between an image forming position and a waiting position; an exposing device for exposing a surface of the photosensitive drum of the image forming unit located at the image forming position; an intermediate transfer belt for successive transfer and superposition of toner images of various colors from the photosensitive drum of the image forming units located at the image forming position so as to form a color toner image; a device for driving the photosensitive drum and the intermediate transfer belt; a position detector for detecting a reference position of the intermediate transfer belt when the intermediate transfer belt is driven; and outputting a reference position detection signal; a secondary transfer roller for transferring the color toner image on the intermediate transfer belt onto recording paper; and a controller for controlling the operation of the above structural elements. The controller determines an operation start time of the charging device and the developing device using a rotation command signal to the driving device as a reference, and an operation start time of the exposing device, the intermediate transfer belt and the secondary transfer roller using the reference position detection signal as a reference.