Patent ID: 7929891

Claim:
An image forming apparatus comprising: a plurality of photosensitive drums; a latent image forming unit for forming an electrostatic latent image on each photosensitive drum; a developing unit for developing each electrostatic latent image; a transferring unit for superimposing and transferring the developed images onto a moving record medium; a measurement unit for measuring positions of the transferred images on the record medium; and a control unit for controlling the photosensitive drums, the latent image forming unit, the developing unit and the transferring unit; wherein the control unit includes: a calculating unit for calculating a value related to alignment errors in the positions measured by said measurement unit in accordance with a sine-curve fitting method, the alignment error including at least one of a phase shift of each photosensitive drum with respect to a reference position and an alignment error in a sub scanning direction; and a correcting unit for correcting the alignment errors based on the calculated value.