Optical scanning device and image forming apparatus including same

An optical scanning device for exposing a surface of an image carrier so as to form an electrostatic latent image whose charge is decreased, the optical scanning device comprising:

• a scanning optical system that scans the image carrier with a light beam;
• a housing that holds optical elements constituting the scanning optical system;
• a skew adjustment mechanism that corrects scanning inclination by changing position of the optical element from a reference position;
• and
• a control unit that controls drive of the skew adjustment mechanism, wherein
• the skew adjustment mechanism includes a skew adjustment motor for adjusting an angle of the optical element, and rotates the skew adjustment motor in a fixed direction so that the position of the optical element changes periodically, and that when rotating the skew adjustment motor by a rotation amount corresponding to a half period of position change of the optical element from an arbitrary position of the optical element, average value of the position change of the optical element before and after rotating the skew adjustment motor is substantially the same as average value of the position change of the optical element per one period,
• when returning the optical element to the reference position, the control unit forms a reference image on the image carrier at three points obtained by equally dividing the position change of the optical element per half period into two, so as to measure skew amounts of the optical element, and calculates rotation amount of the skew adjustment motor necessary for returning the optical element to the reference position, on the basis of rotation amounts of the skew adjustment motor when moving the optical element to the three points, and skew amounts measured at the three points,
• the skew amounts at a first point, a second point, and a third point, in which the rotation amount of the skew adjustment motor increases in order of the first, second, and third points, obtained by equally dividing the position change of the plane mirror per a half period into two, are represented by SkewA, SkewB, and SkewC, respectively,
• the control unit checks a large or small relationship between SkewB and average value SkewA_C of SkewA and SkewC,
• in a first reference position adjustment for returning the optical element to the reference position in an interval in which the skew amount decreases with respect to rotation direction of the skew adjustment motor,
• if SkewB<SkewA_C holds, the control unit rotates the skew adjustment motor by rotation amount obtained by adding a second rotation amount, which corresponds to a half period of the position change of the optical element, to a first rotation amount corresponding to (SkewA−SkewC)/2, while
• if SkewB≥SkewA_C holds, the control unit rotates the skew adjustment motor by a third rotation amount corresponding to (SkewC−SkewA)/2, and
• in a second reference position adjustment for returning the optical element to the reference position in an interval in which the skew amount increases with reference to the rotation direction of the skew adjustment motor,
• if SkewB<SkewA_C holds, the control unit rotates the skew adjustment motor by the first rotation amount, while
• if SkewB≥SkewA_C holds, the control unit rotates the skew adjustment motor by rotation amount obtained by adding the second rotation amount to the third rotation amount.