Image forming apparatus and image correction method

A printing device, comprising:

• a laser scanning unit comprising:
• a housing;
• a polygonal mirror inside the housing;
• a motor inside the housing and configured to rotate the polygonal mirror;
• a first laser unit configured to emit a laser beam to form an electrostatic image on a first electrostatic drum;
• a second laser unit configured to emit a laser beam to form an electrostatic image on a second electrostatic drum;
• a first temperature sensor spaced from the motor at a first distance;
• and
• a second temperature sensor spaced from the motor at a second distance greater than the first distance;
• a first developing unit configured to develop the electrostatic image on the first electrostatic drum using a first type of toner;
• a second developing unit configured to develop the electrostatic image on the second electrostatic drum using a second type of toner;
• an intermediate transfer belt to which toner images developed on the first and second electrostatic drums are transferred in a positionally aligned manner;
• and
• a controller configured to correct positional alignment of the toner images transferred to the intermediate transfer belt when either a detected temperature change of the first portion is greater than or equal to a first threshold value or a detected temperature change of the second portion is greater than or equal to a second threshold value.

A color positional shift correction method for an image forming apparatus, the method comprising:

• receiving a first temperature detection signal from a first temperature sensor positioned to detect a temperature of a first portion of an optical scanning device of a printer unit, the first portion being proximate to a heat generating element;
• receiving a second temperature detection signal from a second temperature sensor positioned to detect a temperature of a second portion of the optical scanning device, the second portion being farther from the heat generating element than the first portion;
• and
• performing an alignment control for correcting a color shift of the printer unit when either a detected temperature change of the first portion is greater than or equal to a first threshold value or a detected temperature change of the second portion is greater than or equal to a second threshold value.