Patent ID: 7865119

Claim:
A color registration method to be executed by a computer, in a color image forming apparatus including a plurality of drum-type photoconductors, each photoconductor having a peripheral surface on which images in a predetermined color are formed, the predetermined color being different in each photoconductor, in which some or all of the photoconductors having the same diameter are driven to match pitch fluctuations which are contained in the images formed on the respective photoconductors and which correspond to a rotational cycle of the photoconductors, the method comprising: a first measurement step for forming a first registration image for each color and measuring formation positions of a plurality of predetermined portions in each registration image; a second measurement step for forming a second registration image for each color and measuring formation positions of a plurality of predetermined portions in each registration image; wherein said first and second measurement steps further include forming each of the first and second registration images on the peripheral surface of the same photoconductor so that the first and second registration images are formed at a predetermined interval with respect to corresponding portions of each of the first and second registration images, the predetermined interval being an interval in a rotating direction of the photoconductor; a calculation step for obtaining deviations of the formation positions of each of the predetermined portions measured in the first and second measurement steps, from a reference position, and for calculating the deviations of each portion for every photoconductor; wherein the predetermined interval is established so that for disturbance components occurring when the first and second registration images are being formed, in which a cycle is assumed beforehand, such disturbance components are canceled with each other during said calculating the deviations of each portion step; a step for calculating a periodic fluctuation component corresponding to the rotational cycle of the photoconductor on which the registration images are formed on the basis of the calculated deviation for each registration image, so as to obtain phases thereof; a step for adjusting a rotational phase of each photoconductor in order for the obtained phases matching to each other; wherein the color image forming apparatus includes a first photoconductor having a first diameter, a second photoconductor having a second diameter and a drive roller; and wherein the predetermined interval is substantially equal to the integral multiple of the peripheral length of the first photoconductor, to the sum of the integral multiple of the peripheral length of the second photoconductor and its half rotation, and to the sum of the integral multiple of the peripheral length of the drive roller and its half rotation.