Exposure device, image forming apparatus, and method of controlling exposure device

An image forming apparatus comprising:

• a photosensitive member;
• a plurality of light emitting elements arranged in a rotational axis direction of the photosensitive member;
• a setter configured to set a basal exposure period of the plurality of light emitting elements, based on a clock count of frequency-spread clocks;
• a candidate generator configured to add, to the basal exposure period, predetermined N alteration periods (N is an integer greater than or equal to two) having different lengths from each other, thereby generating N candidate exposure periods having different lengths from each other;
• a detector configured to detect a frequency level of the clocks in a period corresponding to the basal exposure period;
• and
• a selector configured to select a longer one of the N candidate exposure periods as the frequency level detected by the detector is higher,
• wherein the plurality of light emitting elements is configured to expose the photosensitive member during the candidate exposure period.

A method of controlling an exposure device including a plurality of light emitting elements arranged in a main scanning direction, the method comprising:

• setting a basal exposure period of the plurality of light emitting elements, based on a clock count of frequency-spread clocks;
• adding, to the basal exposure period, predetermined N alteration periods (N is an integer greater than or equal to two) having different lengths from each other, thereby generating N candidate exposure periods having different lengths from each other;
• detecting a frequency level of the clocks in a period corresponding to the basal exposure period;
• and
• selecting, as an exposure period for lighting the plurality of light emitting elements, a longer one of the N candidate exposure periods as the frequency level is higher.