Light beam scanning, image forming apparatus, and method of adjusting the image forming apparatus

A light beam scanning apparatus comprising:

• a plurality of means for generating light beams;
• means for optically combining the light beams generated at said plurality of means for generating light beams and then reflecting the resulting beams to a scanning surface and making said light beams to scan said scanning surface in the main scanning direction;
• a plurality of means for shifting said light beam in a sub-scanning direction when said light beam is made to scan by said means for optically combining;
• a plurality of means for sensing passing positions in the sub-scanning direction of said light beams made by said means for optically combining to scan said scanning surface;
• means for controlling said plurality of means for shifting on the basis of the result of sensing at said means for sensing passing positions so that the passing position of each of said light beams on said scanning surface may be within a target range;
• means for, after said means for controlling has brought the passing positions of said light beams on said scanning surface into said target range, measuring the passing position of each of said light beams scamning said scanning surface a specific number of times using said means for sensing passing positions and judging whether all of said passing positions of said light beams lie in said target range;
• and
• means for making said means for controlling to execute passing position control of said light beams again when the result of measuring said light beam passing position of each of said light beams said specific number of times includes a value outside said target range.

An image forming apparatus which makes light beams to scan and expose an image retaining member and thereby forms an image on said image retaining member, said image forming apparatus comprising:

• a plurality of means for generating light beams;
• means for optically combining the light beams generated at said plurality of means for generating light beams and then reflecting the resulting beams to a scanning surface and making said light beams to scan said scanning surface in the main scanning direction;
• a plurality of means for shifting said light beam in a sub-scanning direction when said light beam is made to scan by said means for optically combining;
• a plurality of means for sensing passing positions in the sub-scanning direction of said light beams made by means for optically combining to scan said scanning surface;
• means for controlling said plurality of means for shifting on the basis of the result of sensing at said means for sensing so that the passing position of each of said light beams on said scanning surface may be within a target range;
• means for, after said means for controlling has brought the passing positions of said light beams on said scanning surface into said target range, measuring the passing position of each of said light beams scanning said scanning surface a specific number of times using said means for sensing and judging whether all of said passing positions of said light beams lie in said target range;
• means for making said means for controlling to execute passing position control of said light beams again when the result of measuring said light beam passing position of each of said light beams said specific number of times includes a value outside said target range;
• and
• means for, after said means for measuring the passing position of each of said light beams and judging has judged that all of said passing positions of said light beams are within said target range, driving said plurality of means for generating light beams and said means for optically combining on the basis of an inputted target data item and forming an image on said scanning surface.

An image forming method of making light beams to scan and expose an image retaining member and thereby forming an image on said image retaining member, said image forming method comprising the following:

• optically combining light beams generated by a light beam generator and making a polygon mirror to reflect the resulting beams to a scanning surface and then making said light beams to scan said scanning surface in the main scanning direction;
• making a plurality of light sensors sense passing positions of said light beams;
• shifting said light beams independently in the sub-scanning direction on the basis of the result of sensing in said sensing step so that the passing position of each of said light beams on said scanning surface may be within a target range;
• after the passing positions of each of said light beams have been brought into said target range, measuring the passing positions of said light beams scanning said scanning surface a specific number of times using said plurality of light sensors and judging whether all of said passing positions of said light beams lie in said target range;
• and
• bringing the passing position of each of said light beams into said target range again when the result of measuring said light beam passing position of each of said light beams said specific number of times includes a value outside said target range.