Patent ID: 8744325

Claim:
A color image forming apparatus comprising: an image bearing member to be rotationally driven; a first image forming unit configured to form a chromatic color toner image on the image bearing member; a second image forming unit configured to form an achromatic color toner image on the image bearing member; a control unit configured to cause the first and the second image forming units to form a first detection toner pattern having the achromatic toner image superposed upon the chromatic color toner image and to cause the first image forming unit to form a second detection toner pattern having the chromatic color toner image, wherein the first detection toner pattern is a detection toner pattern of the achromatic color toner image being superimposed upon the chromatic color toner image with an interval in a rotation direction of the image bearing member; an emission unit configured to emit light on the first detection toner pattern, the second detection toner pattern, or the image bearing member; a light-receiving unit configured to receive a light reflected from the first detection toner pattern, the second detection toner pattern, or the image bearing member, and generate a signal according to an amount of the received light; and a detection unit configured to identify a relative position of the chromatic color toner image and the achromatic color toner image on the image bearing member by detecting, based on the signal generated by the light-receiving unit, the relative position of the chromatic color toner image included in each of the first and the second detection toner patterns, wherein the second image forming unit forms the achromatic color toner image included in the first detection toner pattern so that the achromatic color toner image that is superimposed on an upstream side of the chromatic color toner image included in the first detection toner pattern is longer than the achromatic color toner image that is superimposed on a downstream side of the chromatic color toner image included in the first detection toner pattern in the rotation direction of the image bearing member.