Patent ID: 7376363

Claim:
An image forming apparatus comprising: a plurality of detachable image forming devices, each configured to form a color image; an image carrying device configured to carry the color images sequentially overlaid into a single color image; an exchange detecting device configured to detect an exchange of the plurality of detachable image forming devices; a test pattern reading device configured to read a predetermined test pattern formed by the plurality of detachable image forming devices on the image carrying device; and a controller configured to instruct the plurality of detachable image forming devices to form the predetermined test pattern on the image carrying device when one of events occurs, the events including a first event that the exchange detecting device detects the exchange, a second event that a fixing temperature is lower than a predetermined temperature, a third event that a color print adjustment command is provided, and a fourth event that the total number of color prints is greater than that at the last color print adjustment by a predetermined number of prints, and to perform color image position adjustment based on readings of the predetermined test pattern by the test pattern reading device.