Patent ID: 7164877

Claim:
An image forming apparatus having a full-color mode, a monochrome mode and a standby mode, said image forming apparatus comprising: a removable image transfer unit which includes: an endless belt forming a loop-shaped moving path; a plurality of full-color image transfer rollers located inside the endless belt; a monochrome image transfer roller located inside the endless belt; a full-color image transfer part moving mechanism including a sliding member which moves back and forth generally parallel to a fixed turning direction of the endless belt to raise and lower the full-color image transfer rollers; and a monochrome image transfer part moving mechanism including a sliding member which moves back and forth generally parallel to the turning direction of the endless belt to raise and lower the monochrome image transfer roller; a full-color image forming sensor for detecting the current position of the sliding member of the full-color image transfer part moving mechanism; and a monochrome image forming sensor for detecting the current position of the sliding member of the monochrome image transfer part moving mechanism; wherein the moving path of the endless belt is selectively switched to one of three locations for the full-color mode, the monochrome mode and the standby mode as a result of ascending and descending motions of the full-color image transfer rollers and the monochrome image transfer roller; and wherein said image forming apparatus judges based on results of detection by the full-color image forming sensor and the monochrome image forming sensor whether said image forming apparatus is currently in the full-color mode for producing a full-color image, the monochrome mode for producing a monochrome image or the standby mode for performing standby processing operation and whether the image transfer unit is installed in said image forming apparatus.