Patent ID: 9450526
Filing Date: 2016-09-20
CPC Classification: B41J,H02P

Claim Text:
1. An image forming apparatus comprising: a light source configured to emit a light beam; a polygon mirror configured to reflect the light beam emitted from the light source; a brushless motor including a plurality of coils, the brushless motor being configured to rotate the polygon mirror; a light receiver configured to receive the light beam reflected by the polygon mirror; and a controller configured to: perform driving control on the brushless motor by switching between supply and interruption of power to each of the plurality of coils; detect a value related to an induced voltage which is generated in at least one of the plurality of coils in a period of the interruption of the power during the brushless motor is rotated; perform a first control of referring to the detected value and performing phase switching based on a timing when the detected value reaches a reference value; and in a start-up period when the brushless motor is started up from a stop state, perform a second control of performing switching from first rotation speed control based on the induced voltage according to the first control to second rotation speed control based on the light receiving timing of the light beam by the light receiver in a specific range in which a length from a start timing of an interruption period of the power to a timing when the detected value reaches the reference value does not become shorter than a length of a reference-disabled period in which the induced voltage cannot be detected due to a regeneration current attributable to the phase switching in the first control, the second rotation speed control operable without regard to the induced voltage; after the second control performs switching from the first rotation speed control to the second rotation speed control, perform the second rotation speed control and not the first rotation speed control to increase a rotation speed of the polygon mirror to reach a target rotation speed; and when the rotation speed of the polygon mirror reaches the target rotation speed, perform a constant speed control based on the light receiving timing of the light beam by the light receiver, and wherein the specific range is a range of a rotation speed slower than the target rotation speed.