US Patent 7193639 Image forming apparatus

The present invention provides a tandem-style image forming apparatus that has multiple image forming units and a controller that controls the rotation of the polygon mirrors of the image forming units, wherein during image formation, the controller performs steady rotation control for the polygon mirrors of the image forming units used for image formation, and where a color image forming session is performed after a monochrome image formation session is completed, the controller performs steady rotation control for polygon mirrors of the image forming units used for color image formation but not for monochrome image formation a prescribed period of time prior to the commencement of image formation by such image forming units, thereby extending the useful lives of the motors that drive the polygon mirrors and producing high-quality color images.