Image forming apparatus

An image forming apparatus comprising:

• a light source for emitting a plurality of beams that are aligned at uniform intervals in a direction not parallel to a main-scanning direction;
• a deflector for deflecting the beams;
• a light receiving element for receiving the beams and generating a detection signal;
• a cover for covering a light receiving surface of the light receiving element, the cover having a first slit and a second slit, the first slit having a width smaller than diameters of spots of the beams on the cover and extending in a direction perpendicular to the main-scanning direction, and the second slit having a width smaller than diameters of spots of the beams on the cover and extending in a direction not parallel to the first slit;
• a converter for converting electric potentials of the detection signal into data values and generating time data associated with the data values;
• and
• a first calculator for calculating positions of centers of the beams, based on the data values and the time data;
• wherein:
• the plurality of beams include a first beam and a second beam;
• a distance in the main-scanning direction between the first beam and the second beam is greater than a maximum distance in the main-scanning direction between the first slit and the second slit such that the second beam passes across the first slit and the second slit after the first beam passes across the first slit and the second slit;
• and
• the image forming apparatus further comprises:
• a second calculator for calculating a distance in the sub-scanning direction between the first beam and the second beam from a distance between a position of center of the first beam passing across the first slit and a position of center of the first beam passing across the second slit, a distance between a position of center of the second beam passing across the first slit and a position of center of the second beam passing across the second slit, and an angle of the first slit and the second slit to each other;
• and
• the second calculator for further calculating a distance in the main-scanning direction between the first beam and the second beam from a distance between a position of center of the first beam passing across the first slit and a position of center of the first beam passing across the second slit, and a distance between a position of center of the second beam passing across the first slit and a position of center of the second beam passing across the second slit,
• wherein the first calculator calculates the positions of centers xg of the beams by using the following expression, wherein d1 to dn denote the data values, t1 to denote the time data associated with the data values d1 to dn, and v denotes travelling speed of the beams,
• xg
• =
• ∑
• i
• =
• 1
• n
• ⁢
• (
• di
• ·
• xi
• )
• ∑
• i
• =
• 1
• n
• ⁢
• di
• ·
• v
• .