Patent ID: 8170430

Claim:
A color image forming apparatus comprising: a color image forming unit that forms a toner image of a corresponding one of a plurality of colors on a corresponding one of a plurality of photoconductors and sequentially transfers the toner images from the photoconductors onto a transfer medium; an out-of-color-registration amount detector that detects an amount of out-of-color registration for each color by measuring an out-of-color registration detection pattern formed on the transfer medium; a write-position correction-amount setting unit that sets a write-position correction amount with respect to one or more of the photoconductors based on the amount of out-of-color registration detected by the out-of-color-registration amount detector; a machine state detector that detects a machine state indicative of a state of a body of the color image forming apparatus at a time point when the out-of-color-registration amount detector detects an amount of out-of-color registration; an out-of-color-registration table constructing unit that constructs an out-of-color registration table containing a correspondence of the amount of out-of-color registration detected by the out-of-color-registration amount detector and the machine state detected by the machine state detector; a replacement detector configured to detect replacement of the color image forming unit; and an out-of-color-registration amount determining unit that determines, based on the out-of-color registration table, a current amount of out-of-color registration corresponding to a current machine state detected by the machine state detector, wherein the out-of-color-registration table constructing unit deletes whole or a part of the out-of-color registration table when the replacement detector detects replacement of the color image forming unit, when the out-of-color-registration amount determining unit can determine the current amount of out-of-color registration based on the out-of-color registration table, the write-position correction-amount setting unit sets the write-position correction amount based on the current amount of out-of-color registration, and when the out-of-color-registration amount determining unit cannot determine the current amount of out-of-color registration based on the out-of-color registration table, (i) the out-of-color-registration amount detector detects an amount of out-of-color registration, (ii) the write-position correction-amount setting unit sets the write-position correction amount based on the amount detected by the out-of-color-registration amount detector in (i), and (iii) the out-of-color-registration table constructing unit updates the out-of-color registration table with the amount of out-of-color registration detected by the out-of-color-registration amount detector.