Patent ID: 7567264
Filing Date: 2009-07-28
Classification: G03G,H04N

Abstract:
1. An image forming apparatus for forming color images comprising at least two or more colors, having a function of magnification correction of image size by one page unit, the image forming apparatus comprising: an image carrier; a polygonal mirror rotator independently provided for each color, wherein a latent image is formed by an exposure beam scanned by the polygonal mirror rotator and the latent image is developed to be a color image; and a controller which conducts first control for changing rotation speed of the polygonal mirror rotator in order for changing image size in a sub-scanning direction perpendicular to a main scanning direction, and second control for correcting a correction amount for color registration error depending on magnification correction of image size, and for adjusting a rotating phase of the polygonal mirror rotator depending on the corrected correction amount for color registration error; where the main scanning direction is a direction in which the image carrier is scanned with an exposure beam coming from the polygonal mirror rotator wherein the controller conducts the second control simultaneously with the first control, not by waiting until the rotation speed of the polygonal mirror rotator stabilizes after an execution of the first control; wherein the controller comprises: wherein the controller executes polygonal mirror rotator drive control in a case of magnification correction for image sizes by the drive clock signal, which is generated based on the calculated drive clock signal cycle and the calculated counter values corresponding to the rising edge and the falling edge of the drive clock signal.