Patent ID: 7528853

Claim:
A color image forming apparatus that forms a color image by superposing a plurality of toner images formed by a plurality of printer engines corresponding to respective colors, the color image forming apparatus comprising: a plurality of light sources each of which emits light as image data to optically write an electrostatic latent image of a respective color on a photosensitive element provided in each of the printer engines; a rotating polygon mirror that reflects the light from each of the light sources while rotating to expose and scan the photosensitive element; a plurality of light receiving elements that receives the light reflected by the rotating polygon mirror and outputs a synchronization detection signal that becomes a reference for a start position of an optical writing in a main scanning direction with respect to the photosensitive element; a plurality of write controllers that makes a transfer request for the image data from each of the light sources to control the optical writing performed by each of the light sources, wherein each of the write controllers performs the transfer request for the image data based on a time, as a reference time, at which the synchronization detection signals for whole colors in same main-scanning lines are included in either of a forward direction and a backward direction of the main-scanning lines, when an operation start signal that is asynchronous with the synchronization detection signal and becomes a start point of an imaging operation is input; and a counter that counts a delay time from the reference time to a time when the transfer request for the image data is made, wherein a plurality of counters are provided for each of the colors, a number of counters being the same as a number of printer engines of the plurality of printer engines, and the counters are switched for each printing medium of a plurality of printing medium, and wherein when the image is formed continuously on each of the plurality of printing medium, one of the counters for each of the colors is selected to count a delay time for a current printing medium, and wherein for a subsequent printing medium, the counter used for each of the colors is a different one of said counters which corresponds to the color other than a most recently used counter for the color.