Patent ID: 7791628

Claim:
A deviation amount detecting device which computes an amount of deviation for toner images of different colors in an electrophotographic color image forming device wherein a color image is formed on a transporting member by superimposing the toner images of different colors, the deviation amount detecting device comprising; a first computing unit configured to compute a first deviation amount repeatedly at cycles of a predetermined time based on a result of reading of deviation detection patterns formed on the transporting member of the image forming device; a second computing unit configured to compute a second deviation amount based on a result of measurement of a scanning time between a start and an end of one main scan of a light beam on an image support of the image forming device; and a third computing unit configured to correct, during an inter-cycle period in which the computation of the first deviation amount by the first computing unit is held in a waiting state, the second deviation amount computed by the second computing unit, based on the first deviation amount computed by the first computing unit at a latest cycle, so that a corrected amount of deviation of a main scanning direction and a corrected amount of deviation of a sub-scanning direction are computed, wherein the first computing unit is configured to compute a main deviation amount of the main scanning direction and a sub-deviation amount of the sub-scanning direction respectively based on the result of reading of the deviation detection patterns, and wherein the third computing unit is configured to compute a corrected amount of deviation of the main scanning direction and a corrected amount of deviation of the sub-scanning direction respectively by using both a ratio of the sub-deviation amount computed by the first computing unit to a sum of the main deviation amount and the sub-deviation amount both computed by the first computing unit, and a ratio of the second deviation amount computed by the second computing unit to the sum of the main deviation amount and the sub-deviation amount both computed by the first computing unit.