Patent ID: 7590372

Claim:
A multi-pass type color image forming apparatus including a photosensitive drum, a laser scanning unit, a driving motor, a plurality of developing devices, a cam device which has a camshaft to rotate by the driving motor and a plurality of cams provided at the camshaft corresponding to the developing devices, and a power transmission device provided between the developing devices and the cam device and selectively transmits a rotational force from the driving motor to the developing devices according to a rotational phase of the driving motor, comprising: an indicating member which is provided at the camshaft and has a plurality of indicating portions; a sensing part which detects the plurality of indicating portions; and a control unit which receives a signal from the sensing part when the indicating member passes by the sensing part by the rotation of the camshaft, and determines a home position by a rotational position of the camshaft when a signal pattern from a sequence of signals from the sensing part corresponds with a preset reference pattern.