Patent ID: 9229355
Filing Date: 2016-01-05
CPC Classification: G03G

Claim Text:
1. An image forming apparatus comprising: a light source configured to emit a light beam for exposing a photosensitive member; a rotating polygonal mirror configured to deflect the light beam with a plurality of reflection surfaces so the light beam scans the photosensitive member; a driving motor that includes a rotor to which the rotating polygonal mirror is fixed, a stator including a coil to which a driving current for rotating the rotor is supplied, and a magnet that is attached to the rotor and in which a plurality of N poles and a plurality of S poles are alternately magnetized along a rotation direction of the rotor; a detection element configured to detect a magnetic pattern of the magnet; a storage unit configured to store period data for performing pattern matching with a period of a detection waveform output by the detection element detecting the magnetic pattern of the magnet which is attached to the rotor rotated by the driving current being supplied to the coil, the period data being associated with the plurality of reflection surfaces; and an identification unit configured to calculate period ratios of respective periods of the detection waveform included in one rotation of the rotor with respect to a period of one rotation of the rotor based on a detection result of the detection element while the driving motor is accelerating and identify a reflection surface on which the light beam is incident among the plurality of reflection surfaces while the driving motor is rotating, based on a result of the pattern matching between the period ratios and the period data.