Patent ID: 7574154

Claim:
An image forming apparatus comprising: (a) an image carrier having a movable surface thereon; (b) a charging unit which electrically charges the surface of the image carrier; (c) an exposure unit which imagewise exposes the surface of the image carrier charged by the charging unit to form an electrostatic latent image; (d) a developing unit having a developer bearing member to hold a toner thereon, which develops the electrostatic latent image by moving a surface of the developer bearing member relative to a surface of the image carrier; (e) a fog toner detection section which detects a value corresponding to an amount of fog toner adhered from the developer bearing member; (f) a controller which determines a fog control parameter based on the result of detection by the fog toner detection section; (g) a moving speed ratio change section which changes a circumferential speed ratio between the surface of the developer bearing member and the surface of the image carrier; and (h) a memory section which stores a target value of fog toner, wherein after the circumferential speed ratio has been changed by the moving speed ratio change section, the controller determines the fog control parameter based on comparing the value detected by the fog toner detection section with the target value stored in the memory section, and controls the moving speed ratio change section to return the circumferential speed ratio to the circumferential speed ratio prior to the change.