Patent ID: 8055145

Claim:
An image forming apparatus comprising: a transfer belt for receiving a toner image from a photoreceptor; a secondary transfer unit for transferring the toner image on the transfer belt to a recording medium; an optical sensor for detecting a reference toner image on the transfer belt; a shutter for protecting a detecting surface of the optical sensor; an opening/closing portion for opening and closing the shutter; and, a controller for detecting the opening and closing of the shutter from an output from the optical sensor and controlling an opening and closing operation of the shutter based on the detected result, wherein the controller determines whether the optical sensor has erroneously detected the shutter being open or closed, and when occurrence of mis-detection is determined, repeating an opening and closing operation over again to perform detection, and further comprising: a separation/contact mechanism for the transfer belt and the secondary transfer unit; and, a linkage mechanism for linking the opening and closing of the shutter with a separation and contact of the secondary transfer unit.