Patent ID: 8963981
Filing Date: 2015-02-24
Classification: B41J

Abstract:
1. An image forming apparatus comprising: a light source emitting a light beam; a photosensitive body; a brushless motor including a stator with a plurality of coils, and a rotor with a magnet; a rotating polygon mirror driven by the brushless motor to rotate and periodically deflect the light beam emitted by the light source so as to form scan lines successively on the photosensitive body; a current-supplying switching unit switching on and off current-supplying to the coils so as to rotate the brushless motor; a magnetic flux change detection unit outputting a detection signal in accordance with a change in a magnetic flux of the coils caused by the rotation of the rotor; an optical sensor outputting a photoreception signal in accordance with the presence or absence of reception of the light beam deflected by the rotating polygon mirror; and a control unit, wherein the control unit performs: a first rotation control process of switching on and off the current-supplying by the current-supplying switching unit in accordance with a change in a first deviation between a first rotation speed of the brushless motor based on the detection signal and a target speed regardless of a change in an integrated value of the first deviation, wherein the first rotation control process is performed using a proportional controller, and to the exclusion of the integrated value of the first deviation; a second rotation control process of calculating an integrated value of a second deviation between a second rotation speed of the brushless motor based on the photoreception signal and the target speed, and switching on and off the current-supplying by the current-supplying switching unit in accordance with a change in the second deviation and a change in the integrated value of the second deviation; a speed determination process of determining whether the first deviation is within a prescribed range; and a rotation control switching process of switching to the second rotation control process when, during the first rotation control process, it is determined by the speed determination process that the first deviation has entered the prescribed range from outside the prescribed range.