Patent ID: 8442419

Claim:
A color image forming apparatus comprising: a first rotary member configured to form a color toner image; a second rotary member configured to form a black toner image; wherein in black mono-color printing an image is formed using the second rotary member without use of the first rotary member, in full-color printing an image is formed using the first and second rotary members, and a phase difference between the first and second rotary members is adjusted to reduce color shift, a deactivation controller configured to stop the second rotary member after a current black mono-color printing is performed such that the phase difference, when the second rotary member is activated for the current black mono-color printing, is different from the phase difference based on a stop position of the second rotary member stopped by the deactivation controller and a stop position of the first rotary member; and an activation controller configured to, in full-color printing, activate one of the first and second rotary members with a time lag after the other of the first and second rotary members is activated such that the phase difference between the first and second rotary members is an adjusted phase difference, wherein the activation controller is configured to change the time lag in response to the phase difference between the first and second rotary members generated by performing the black mono-color printing being changed by control on stopping of the second rotary member performed by the deactivation controller.