Patent ID: 7962067

Claim:
An image forming apparatus comprising: a black photoconductor being used for forming a black image; a plurality of color photoconductors being used with the black photoconductor for forming color components to compose a full-color image; a first drive section for rotating the black photoconductor; a second drive section for rotating the color photoconductors; a first drive control section for controlling the first drive section to rotate the black photoconductor; a second drive control section for controlling the second drive section to rotate the color photoconductors; a phase detecting section for detecting rotational phases of the black photoconductor and the color photoconductors; and a rotational phase correcting section for correcting the rotational phases of the black photoconductor and the color photoconductors, wherein the first and the second drive control sections respectively control the first and the second drive sections so that the black photoconductor and the color photoconductors are driven simultaneously with a same target speed while a full-color image is composed; the target speed starts with an initial drive speed and changes to a predetermined speed for image-formation, which is higher than the initial drive speed, after speeds of the black photoconductor and the color photoconductors reach the initial drive speed, the black photoconductor and the color photoconductors are engaged to the corresponding drive sections with the rotational phases being matched with one another; the rotational phases of the black photoconductor and the color photoconductors are adjusted to be matched with one another; and the rotational phase correcting section determines based on detection by the phase detecting section whether the rotational phases of the black photoconductor and the color photoconductors are matched and maintained, and in the case where the rotational phases are not matched, the rotational phase correcting section corrects the rotational phases to be matched by controlling the first or the second drive control section, or both, when the black photoconductor and the color photoconductors stop.