Image forming apparatus with multiple medium-dependent measurements for relative emission timings

An image forming apparatus including a light source that includes a plurality of light emitting elements that each emit a light beam, and a deflection unit configured to deflect a plurality of light beams emitted from the plurality of light emitting elements such that the plurality of light beams scan a photosensitive member, the image forming apparatus being configured to:

• use toner to develop an electrostatic latent image formed on the photosensitive member by scanning the photosensitive member with the plurality of light beams;
• to transfer a developed toner image onto a recording medium;
• and to fix the transferred toner image to the recording medium by heating the transferred toner image, the image forming apparatus being further configured to change, depending on a type of a recording medium onto which a toner image is to be transferred, a length of a non-image-forming period, wherein the non-image-forming period is a period from when formation of an electrostatic latent image for forming a toner image to be transferred onto one recording medium ends to when formation of an electrostatic latent image for forming a toner image to be transferred onto a next recording medium starts, the image forming apparatus comprising:
• an optical sensor provided on a scanning path of a light beam deflected by the deflection unit, configured to, in response to the deflected light beam being incident on the optical sensor, output a detection signal indicating that the light beam has been detected;
• a measurement unit configured to, in the non-image-forming period, control the light source such that light beams from first and second light emitting elements among the plurality of light emitting elements are incident on the optical sensor in sequence, and further configured to measure a time interval between two detection signals output in sequence from the optical sensor;
• a determination unit configured to determine a number of times of measurement of the time interval to be executed by the measurement unit in the non-image-forming period, based on a type of a recording medium onto which a toner image is to be transferred;
• and
• a control unit configured to, based on an average value of measurement values obtained by the measurement unit, control relative emission timings according to which the plurality of light emitting elements emit light beams based on image data, when image formation on a recording medium is to be performed.