Method and apparatus for image forming capable of detecting a reference signal for a lighting control

An image forming method, comprising:

• providing a light emission source to output a plurality of optical beams in accordance with image data;
• rotating a rotary polygon mirror to receive the plurality of optical beams at different mirror points with different mirror positions and to deflect the beams into a first plurality of scanning optical beams in given directions to cyclically scan on a plurality of predetermined scanning lines in a main scanning direction, said first plurality of scanning optical beams being all scanning beams used to form an image corresponding to the image data;
• driving a plurality of image carrying members to rotate in a sub-scanning direction line by line and to respectively receive the first plurality of scanning optical beams to form a plurality of primary separate color images;
• receiving the plurality of scanning optical beams reflected from oppositely positioned mirror surfaces of the rotary polygon mirror at a single synchronous detection sensor;
• and
• instructing the light emission source to light on and off at timings determined based on a plurality of detection signals from the single synchronous detection sensor.

An optical writing apparatus, comprising:

• a light emission source configured to output a plurality of optical beams in accordance with image data;
• a rotary polygon mirror configured to receive the plurality of optical beams at different mirror points with different mirror positions and to deflect the beams into a first plurality of scanning optical beams in given directions to cyclically scan along a plurality of predetermined scanning lines in a main scanning direction on a plurality of image carrying members provided to rotate in a sub-scanning direction line by line and to respectively receive the first plurality of scanning optical beams to form a plurality of primary separate color images, said plurality of scanning optical beams being all scanning beams used to form an image corresponding to the image data;
• a single synchronous detection sensor configured to detect a second plurality of scanning optical beams included in the first plurality of scanning optical beams reflected from oppositely positioned mirror surfaces of the rotary polygon mirror;
• and
• an instruction mechanism configured to instruct the light emission source to light on and off at timings determined based on a plurality of detection signals from the single synchronous detection sensor.

An image forming apparatus, comprising:

• plural light emission sources each configured to output an optical beam;
• a light reflecting unit configured to receive the optical beam from each light emission source of the plural light emission sources and to reflect the optical beam;
• plural image carrying members each configured to receive a corresponding optical beam reflected by the light reflecting unit, said corresponding optical beams reflected by the light reflecting unit being all scanning beams used to form an image;
• a single synchronous detection sensor configured to receive each optical beam of at least half of the plural light emission sources prior to arriving at the plural image carrying members, and to generate detection signals, each corresponding to one of the at least half of the plural light emission sources, wherein the optical beams received by the single synchronous detection sensor are reflected from oppositely positioned mirror surfaces of the light reflecting unit;
• and
• an instruction mechanism configured to instruct each light emission source when to light on and off, at different timings, based on the detection signals corresponding to the at least half of the plural light emission sources.