Image forming apparatus and controlling method therefor

A control method for an image forming apparatus for forming a multi-color image by superposing in succession color component images formed according to the image information of respective color components, the method comprising:

• a first detection step of detecting, at formation of a first color image, the phase difference between a sub scanning start signal generated in synchronization with the rotation of an image bearing member and a main scanning start signal generated by detecting a light beam put into scanning motion by a rotary polygonal mirror;
• a retaining step of retaining said detected phase difference;
• a second detecting step of detecting the phase difference between said sub scanning start signal and said main scanning start signal at formation of the n-th color image;
• a comparison step of comparing the phase difference detected at formation of a first color image and retained in said retaining step with the phase difference detected at the formation of the n-th color image in said second detection step;
• and
• an image formation step of effecting image formation by counting the main scanning start signal of a number based on the result of said comparison, after the generation of said sub scanning start signal.

An image forming apparatus for forming a multi-color image by superposing in succession color component images formed according to the image information of respective color components, comprising:

• a rotary polygonal mirror for deflecting a light beam based on the image information of each of said color components thereby scanning a rotated image bearing member;
• main scanning start signal generation means for generating a main scanning start signal by detecting the light beam put in a scanning motion by said rotary polygonal mirror;
• sub scanning start signal generation means for generating a sub scanning start signal in synchronization with the rotation of said image bearing member;
• control means for controlling an output start of the image information of each of said color components in accordance with counting of the main scanning start signals to a predetermined number, after generation of the sub scanning start signal;
• first discrimination means for detecting and retaining the phase difference between the sub scanning start signal and the main scanning start signal at formation of a first color image, and discriminating whether the phase difference detected is within a first range;
• and
• second discrimination means for detecting the phase difference between the sub scanning start signal and the main scanning start signal at formation of an n-th color image, and discriminating whether the phase difference detected at each formation of the color component image is within a second range,
• wherein said control means changes the count number of the main scanning start signals until the output start of the image information, on the basis of the discriminated results of said first discrimination means and said second discrimination means.

A control method for an image forming apparatus for forming a multi-color image by superposing in succession color component images formed according to the image information of respective color components, the method comprising:

• a first detection step of detecting, at formation of a first color image, the phase difference between a sub scanning start signal generated in synchronization with the rotation of an image bearing member and a main scanning start signal generated by detecting a light beam put into scanning motion by a rotary polygonal mirror;
• a retaining step of retaining said detected phase difference;
• a first discrimination step of discriminating whether said retained phase difference detected at formation of the first color image is within a first range;
• a second detection step of detecting the phase difference between said sub scanning start signal and said main scanning start signal at formation of the n-th color image;
• a second discrimination step of discriminating whether the phase difference detected at each formation of the color component image is within a second range;
• and
• an image formation step of effecting image formation by counting, after the generation of said sub scanning start signal, the main scanning start signal of a number based on the results of discrimination by said first and second discrimination steps.