Image forming apparatus including multi-beam optical scanning apparatus

An image forming apparatus including a plurality of stations configured to form images of different colors on an intermediate transfer member, the apparatus comprising:

• a reading unit configured to read patterns of different colors formed on the intermediate transfer member by the plurality of stations;
• a first determination unit configured to obtain a magnitude of a color misalignment in a scanning width of a color other than a reference color with respect to the reference color based on timings at which the patterns of different colors are read, and determine a correction amount for an inter-station scanning width difference for correcting the color misalignment of the color other than the reference color;
• and
• an optical scanning apparatus provided in each of the plurality of stations and configured to scan a plurality of light beams,
• wherein
• the optical scanning apparatus includes
• a light source including a plurality of light emitting elements each configured to output, based on input image data, a light beam for irradiation of a photosensitive member driven to rotate, wherein the plurality of light emitting elements are arranged so that the photosensitive member is irradiated at different positions in a rotational direction with a plurality of the light beams output from the plurality of light emitting elements,
• a deflection unit provided in the optical scanning apparatus and configured to deflect the plurality of light beams output from the plurality of light emitting elements so that the plurality of light beams scan on the photosensitive member,
• a lens provided in the optical scanning apparatus and configured to guide the plurality of light beams deflected by the deflection unit to the photosensitive member,
• a temperature detecting unit configured to detect an internal temperature of the optical scanning apparatus, and
• a second determination unit configured to determine a correction amount for an inter-beam scanning width difference, based on a previously obtained correspondence relationship between the temperatures and correction amounts for scanning widths of scanning lines, the correction amount for an inter-beam scanning width difference corresponding to the temperature detected by the temperature detecting unit and depending on a difference in optical path length between the plurality of light beams due to a curvature factor of the photosensitive member, and
• the image forming apparatus further includes
• a correction unit configured to correct a scanning width of at least one of the plurality of light beams emitted from the plurality of light emitting elements based on the input image data, based on a result of the detection by the temperature detecting unit, so that the plurality of light beams emitted from the plurality of light emitting elements based on the input image data have the same scanning width in a scanning direction in which the plurality of light beams scan on the photosensitive member,
• wherein the correction unit corrects the scanning width of a middle one of the plurality of light beams based on the correction amount determined by the first determination unit, and for the plurality of light beams other than the middle one, corrects the scanning widths thereof based on the correction amount determined by the first determination unit and thereafter corrects the scanning widths based on the correction amount determined by the second determination unit.