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US 6,184,910 B2Granted
Color image forming apparatus with polygonal mirror rotation phase control
AssigneeRicoh Company, Ltd.
InventorsEiichi Sasaki, Tsuyoshi Deki, Nobuo Iwata, Takeshi Motohashi, Takahiro Tamiya, Yutaka Shio, Tomonori Yabuta
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Abstract
A color image forming apparatus capable of superposing toner images of respective colors in accurate register by preventing an exposing position from being displaced in the subscanning direction. The rotation phase of a polygonal mirror is controlled on the basis of the mark detection timing of a mark sensor. Hence, the exposing position in the subscanning direction is prevented from being displaced without regard to irregularities in the circumferential length and feed speed of an intermediate image transfer belt.
Claims41
A color image forming apparatus comprising:
- an image carrier for causing a latent image to be electrostatically formed thereon;
- emitting means for emitting a light beam modulated by each of image signals of respective colors and representative of a document image;
- a rotatable polygonal mirror for steering said light beam to thereby electrostatically form latent images respectively associated with said image signals on said image carrier;
- drive means for causing said polygonal mirror to rotate;
- developing means for developing said latent images with developers of respective colors to thereby produce corresponding monocolor toner images;
- an intermediate transfer body formed with a plurality of marks for position detection, and for causing said monocolor toner images to be sequentially transferred thereto from said image carrier;
- sensing means located at a predetermined position for sensing said plurality of marks, and for generating an output in response to each sensed mark;
- first control means for masking said output corresponding to each sensed mark except for a selected mark which remains an unmasked mark, and for causing each of said latent images to begin to be formed based on a time when said sensing means senses said unmasked mark;
- and
- second control means for controlling a rotation phase of said polygonal mirror on the basis of the time when said sensing means senses said unmasked mark and for ensuring said monocolor toner images overlap one another without relative displacement on said intermediate transfer body.
7 more elements
A color image forming apparatus comprising:
- an image carrier configured to have electrostatically formed thereon latent images corresponding to respective colors of a document image;
- a light source configured to emit a light beam modulated by image signals;
- a rotatable polygonal mirror configured to steer said light beam in respective patterns to electrostatically form the latent images for said respective colors on said image carrier;
- a drive mechanism configured to rotate said rotatable polygonal mirror;
- a developer configured to apply respective developers to said latent images to produce corresponding monocolor toner images;
- an intermediate transfer body having a plurality of marks formed thereon for position detection of a surface position of said intermediate transfer body when said monocolor toner images are sequentially transferred to said intermediate transfer body from said image carrier;
- a sensor, positioned to oppose said plurality of marks on said intermediate transfer body so as to sense said plurality of marks when said intermediate transfer body passes said plurality of marks by said sensor and configured to generate an output in response to each sensed mark;
- a first controller configured to mask said output corresponding to each sensed mark except for a selected mark which remains an unmasked mark, and to cause each of said latent images to begin to be formed based on a time when said sensor senses said unmasked mark;
- and
- a second controller configured to control a rotation phase of said polygonal mirror in coordination with the time when said sensor senses said unmasked mark, and for ensuring said monocolor toner images overlap one another without relative displacement on said intermediate transfer body, wherein
- said second controller switches a motor synchronization signal from a first signal to a second signal during a phase matching period, and subsequently switching said motor synchronization signal back to said first signal after said phase matching period is complete.
8 more elements
Dependencies are inferred from the claim text.