Image forming apparatus

An image forming apparatus comprising:

• a light source configured to emit a plurality of light beams;
• a rotary polygon mirror including a plurality of reflection surfaces each configured to deflect the plurality of light beams emitted by the light source so that the plurality of light beams scan a surface of a photosensitive member;
• plural count value holding units of a number that corresponds to a number of the plural reflection surfaces;
• a light receiving portion configured to output a plurality of light receiving signals by receiving the plurality of light beams reflected by each of the plurality of reflection surfaces;
• a conversion unit configured to convert the plurality of light receiving signals to a plurality of pulse signals;
• a changeover unit configured to change over between a measurement valid interval and a measurement invalid interval;
• and
• a measurement unit configured to measure a pulse width of a pulse signal in the measurement valid interval among the plurality of pulse signals corresponding to the plurality of reflection surfaces, respectively, wherein the measurement unit includes:
• a clock signal generation unit configured to generate a clock signal of a predetermined frequency;
• and a count unit configured to count the clock signal;
• and
• an identification unit configured to identify a rotation phase of the rotary polygon mirror based on a measurement result of the measurement unit and reference values to be compared with the measurement result,
• wherein the measurement unit measures pulse widths of the plurality of pulse signals by count values of the count unit, and
• wherein the count unit causes the count value holding units of the number of the reflection surfaces to sequentially hold the count values.

An image forming apparatus comprising:

• a light source configured to emit two light beams;
• a rotary polygon mirror including a plurality of reflection surfaces each configured to deflect the two light beams emitted by the light source so that the two light beams scan a surface of a photosensitive member;
• plural count value holding units of a number that corresponds to a number of the plural reflection surfaces;
• a light receiving portion configured to output two light receiving signals by receiving the two light beams reflected by each of the plurality of reflection surfaces;
• a conversion unit configured to convert the two light receiving signals to two pulse signals;
• a measurement unit configured to measure pulse widths of continuous pulse signals output from the conversion unit in every other pulse signal, wherein the measurement unit includes:
• a clock signal generation unit configured to generate a clock signal of a predetermined frequency;
• and a count unit configured to count the clock signal;
• and
• an identification unit configured to identify a rotation phase of the rotary polygon mirror based on a measurement result of the measurement unit and reference values to be compared with the measurement result,
• wherein the measurement unit measures pulse widths of the two pulse signals by count values of the count unit, and
• wherein the count unit causes the count value holding units of the number of the reflection surfaces to sequentially hold the count values.