Patent ID: 9588456
Date: 2017-03-07
CPC Classifications: G02B,G03G

Claim:
1. A scanning optical device comprising: a laser light source that emits a laser light beam; a laser control section that controls a light amount of the laser light beam emitted from the laser light source; a rotary polygon mirror having a plurality of surfaces that reflect the laser light beam and scan an image bearing member surface; a photodetector that converts the laser light beam reflected by the rotary polygon mirror into an electric signal; a signal-width detecting section that detects a signal width using an output waveform of the photodetector as a detection signal on the basis of a threshold set in advance; and a control section that cause the laser light source emit laser light beams at light amounts in a plurality of stages controlled by the laser control section, causes the signal-width detecting section to detect the signal width from output waveforms of the photodetector of the respective laser light beams, acquires, from information concerning the light amounts and the detected signal width, an increase ratio of the signal width increasing according to an increase in the light amounts, and determines, as the light amount affected by stray light, the light amount at which the increase ratio of the signal width of at least one reflection surface of the rotary polygon mirror is equal to or larger than an increase ratio set in advance, wherein when the light amount used in image formation is equal to or larger than the light amount affected by the stray light, the control section acquires a corrected signal width corresponding to the light amount used in the image formation from the increase ratio of the signal width of the detection signal acquired in a region having a light amount smaller than the light amount affected by the stray light.