Image forming apparatus

An image forming apparatus comprising:

• a light scanning device
• that includes:
• a light source including four or more light-emitting portions which are arranged at a predetermined angle with respect to a main scanning direction in a row at regular intervals;
• and a polygon mirror which deflects and scans light beams emitted from the light-emitting portions, and
• that uses the light beams to form an electrostatic latent image on an image carrying member;
• a developing portion that forms a toner image by visualizing the electrostatic latent image;
• a control portion that controls the light scanning device such that turning on and off of each of the light-emitting portions are switched to form the electrostatic latent image corresponding to image data;
• and
• a storage portion that stores a predetermined evaluation chart which is formed by dots drawn with the light beams of the light-emitting portions to determine timing at which each of the light-emitting portions starts writing,
• wherein the evaluation chart includes:
• a first evaluation pattern;
• and
• a second evaluation pattern that is arranged parallel to the first evaluation pattern in the main scanning direction or a subscanning direction perpendicular to the main scanning direction,
• the first evaluation pattern includes a first patch row that is formed by arranging a plurality of first evaluation patches at equal intervals in the subscanning direction,
• the first evaluation patch includes:
• a first dot row which is formed linearly in the main scanning direction;
• a second dot row which is formed linearly in the main scanning direction so as to be displaced with respect to the first dot row;
• and
• an auxiliary dot row which is formed linearly in the main scanning direction to be arranged on at least one of both sides, in the subscanning direction, of an aggregate including both the first dot row and the second dot row in the subscanning direction,
• a plurality of the first patch rows are arranged at predetermined equal intervals in the main scanning direction to form the first evaluation pattern,
• in at least one of the first dot row and the second dot row, a number of dots in the subscanning direction is one,
• if the number of dots in the subscanning direction in one of the first dot row and the second dot row is one and the number of dots in the subscanning direction in the other of the first dot row and the second dot row is two or more, the auxiliary dot row is arranged on the one side, but not on the other side, of the aggregate in the subscanning direction, and
• if the number of dots in the subscanning direction in both of the first dot row and the second dot row is one, the auxiliary dot row is arranged on both sides of the aggregate in the subscanning direction
• the auxiliary dot row is formed so as to be linearly continuous over an entire region between both ends of the first evaluation patch in the main scanning direction, the auxiliary dot rows in the evaluation patches adjacent in the main scanning direction overlap each other in the subscanning direction and are continuously connected to each other in the main scanning direction,
• the second evaluation pattern includes a second patch row that is formed by arranging, in the subscanning direction, a plurality of second evaluation patches at same intervals as intervals at which the first evaluation patches are arranged parallel to each other,
• the second evaluation patch is symmetrical with the first evaluation patch in a direction in which the first evaluation pattern and the second evaluation pattern are arranged parallel to each other and
• a plurality of the second patch rows are arranged at predetermined equal intervals in the main scanning direction to form the second evaluation pattern.