Image forming apparatus that prints image by electrophotography

An image forming apparatus comprising:

• an image forming device including an optical scanning device that forms, using a light source having a plurality of light emitters, aligned at regular intervals at a predetermined angle with respect to a main scanning direction, and a polygon mirror that deflectively scans a light beam emitted from each of the light emitters, an electrostatic latent image on an image carrier with the light beam, and prints an image on a sheet, by transferring a toner image obtained by developing the electrostatic latent image, onto the sheet;
• a density detection device that detects image density of the image printed on the sheet;
• a storage device that stores therein a predetermined plurality of types of dot patterns, for calculating a beam pitch shift amount, which is a shift amount of a pitch between the light beams in the main scanning direction, and formed on the image carrier by the light beam emitted from an adjacent light emitter;
• and
• a control device that includes a processor, and acts, when the processor executes a control program, as a controller that:
• causes the image forming device to form detection patches, each including a plurality of the dot patterns of a same shape, arranged in the main scanning direction and a sub scanning direction at predetermined intervals, with respect to each of the dot patterns, and to print the detection patches on the sheet, acquires density of the detection patches, among which the dot pattern is different, from the density detection device, calculates the beam pitch shift amount using the density of each of the detection patches, and controls the optical scanning device to adjust light emission timing of the light beam emitted from the light emitter, using the beam pitch shift amount calculated;
• and
• sets, when the image forming device forms the detection patch, a light amount of the light beam emitted from the light emitter to a predetermined light amount for adjustment, smaller than a predetermined normal light amount of the light beam, emitted to form a normal electrostatic latent image, and which secures detection accuracy of the beam pitch shift amount, equal to or higher than a predetermined threshold.