Patent ID: 8369724

Claim:
An image forming apparatus comprising: a carrier configured to convey a recording medium; a plurality of forming devices configured to form respective images at respective image forming positions on the recording medium, wherein the plurality of forming devices form a pattern on the carrier; a measuring device configured to measure the pattern formed on the carrier; and a correcting device configured to execute a steady-deviation detection with respect to at least one of the plurality of forming devices and, based on a result of the steady-deviation detection, correct the image forming position of the at least of one of the plurality of forming devices, wherein: in execution of the steady-deviation detection, the correcting device controls the plurality of forming devices to form a first pattern including a plurality of marks formed by the plurality of forming devices, controls the measuring device to measure the first pattern, and detects a steady deviation amount of the image forming position based on a measurement result of the first pattern by the measuring device, wherein the measurement result of the first pattern includes a first relationship between marks formed by different ones of the plurality of forming devices and a second relationship between marks formed by identical ones of the plurality of forming devices; the correcting device is further configured to execute a varying-deviation detection, in which the correcting device controls at least one of the plurality of forming devices to form a second pattern, controls the measuring device to measure the second pattern, and detects a varying deviation amount of the image forming position based on a measurement result of the second pattern by the measuring device, the varying deviation amount of the image forming position having a cycle; the correcting device executes the steady-deviation detection by calculating the steady deviation amount of the image forming position based on the first relationship, and determines a necessity of executing the varying-deviation detection by calculating a cyclic deviation amount of the image forming position based on the second relationship; and the correcting device further determines the necessity of executing the varying-deviation detection based on the measurement result of the first pattern obtained in the steady-deviation detection, and, upon determination that execution of the varying-deviation detection is necessary, executes the varying-deviation detection.