Patent ID: 8558858

Claim:
An image forming apparatus comprising: a light source configured to emit a light beam; a photosensitive member; a brushless motor comprising a stator where a plurality of coils are placed and a rotor where a plurality of magnets are placed; a rotary polygon mirror, which is configured to be rotated by the brushless motor, and which is configured to periodically deflect the light beam emitted from the light source to sequentially form scanning lines on the photosensitive member; an energization switching unit configured to turn on and off energizations of the coils; a voltage detecting unit configured to output a detection signal based on induced voltages that are generated in the coils by rotation of the rotor; a control unit configured to: control the energization switching unit to turn on and off the energizations of the coils based on the detection signal; and perform a chopping control on the energization switching unit during an energization-on time for the plurality of coils; and a sensor configured to receive the light beam deflected by the rotary polygon mirror and to output a light receiving signal, wherein the plurality of coils are connected via a star connection, wherein the voltage detecting unit is connected to a neutral point of the star connection and an end point of each coil of the plurality of coils different from the neutral point and is configured to output a signal, which is based on a difference in potential between the neutral point of the star connection and the end point of each coil of the plurality of coils different from the neutral point, as the detection signal, wherein, in a start-up process of the brushless motor, the control unit is configured to execute a rotation speed control of the brushless motor based on the detection signal, and wherein, in a stabilized time period during which a rotation speed of the brushless motor is within a target speed range, the control unit is configured to execute a rotation speed control of the brushless motor based on the light receiving signal and to increase a frequency of the chopping control to a frequency greater than a frequency in the rotation speed control of the brushless motor based on the detection signal.