Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-07-08
2002-10-01
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S212100, C359S216100, C347S243000, C250S234000
Reexamination Certificate
active
06459520
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical scanning apparatus and an image forming apparatus using it, and, more particularly, to the apparatus constructed in such structure that in formation of an image with a plurality of light beams, a detecting means comprised of a single sensor detects environmental variation of the optical scanning apparatus, particularly, deviation of scanning positions and variation of magnification occurring with temperature changes, and that drawing positions of the light beams on a scanned surface are corrected based thereon, thereby obtaining a good image.
2. Related Background Art
FIG. 1
is a schematic diagram of a major part of a conventional optical scanning apparatus using a multi-laser light source.
In the same figure a plurality of (two in the same figure) light beams (nearly parallel beams) emitted from laser unit
131
are incident into a cylindrical lens
132
having a predetermined refracting power in the sub-scanning direction. The nearly parallel beams incident into the cylindrical lens
132
emerge as nearly parallel beams in the principal scanning section. In the sub-scanning section they converge to be focused as almost line images on a deflecting face (reflecting surface)
133
a
of optical defector
133
. The plurality of light beams deflected and reflected by the deflecting face
133
a
are condensed through imaging means (f&thgr; lens system)
140
having spherical lens
134
and toric lens
135
, onto the surface of a photosensitive drum
136
. With rotating the optical deflector
133
in the direction of arrow A, the plurality of light beams scan the area on the surface of the photosensitive drum
136
at constant speed in the direction of arrow
8
(in the main scanning direction). This effects recording of an image on the surface of photosensitive drum
136
being a recording medium. Although the laser unit
131
emits the two light beams, only one of them is illustrated in FIG.
1
.
A color image forming apparatus such as a full color printer or the like for multi-color development by use of a plurality of such optical scanning devices described above is suggested, for example, in Japanese Laid-open Patent Application No. 1-281468. The application describes the apparatus for forming a color image by multiply transferring images obtained by the respective optical scanning devices onto a recording medium. In the apparatus of the application, in order to prevent chromatic deviation occurring upon superposition of the images on the recording medium, a detecting means detects positions of detected images drawn on a transfer medium conveyed on a transfer belt in each of the optical scanning devices and the chromatic deviation is prevented by controlling image forming portions according to output signals from the detecting means.
The apparatus of the above application, however, had such tendencies that the structure of the detecting means became complicated and could not easily effect the detection in real time. Further, the application disclosed nothing about a method for detecting the environmental variation of each optical scanning device, particularly, about a method for detecting deviation of the scanning positions, variation of magnification of the optical system, etc. occurring with temperature change.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical scanning apparatus having a multi-laser light source, capable of obtaining a good image by such structure that simple detecting means, including a single sensor, detects the deviation of the scanning positions and the variation of magnification, and that correcting means corrects image deviation based on the result of the detection, and also provides an image forming apparatus using it.
Another object of the present invention is to provide an optical scanning apparatus having a multi-laser light source, capable of obtaining a good image by such structure that simple detecting means, including a single sensor, detects the deviation of the scanning positions and the variation of magnification occurring with temperature changes of the apparatus and that correcting means corrects image deviation based on the result of the detection, and also provides an image forming apparatus using it.
An optical scanning apparatus of the present invention is an optical scanning apparatus arranged to guide a plurality of light beams, emitted from light source means having a plurality of light-emitting portions arranged as inclined with respect to a main scanning direction, to a deflecting means, guide the plurality of light beams deflected and reflected by the deflecting means onto a scanned surface by imaging means, and optically scan an area on the scanned surface simultaneously with the plurality of light beams.
The detecting means are arranged on a surface substantially at the same position as the scanned surface and in a normal direction to the main scanning. The plurality of light beams from the light source means via the deflecting means are focused by the imaging means, wherein the detecting means detects scanning positions of the plurality of light beams and differences between pass times of the plurality of light beams, thereby detecting deviation of the scanning positions and variation of magnification occurring with temperature changes of the optical scanning apparatus. Correcting means correct drawing positions of the plurality of light beams on the scanned surface, based on the result of the detection.
Another optical scanning apparatus of the present invention is an optical scanning apparatus arranged to guide a plurality of light beams, emitted from light source means having a plurality of light-emitting portions arranged in a normal direction to a main scanning direction, to a deflecting means, guide the plurality of light beams deflected and reflected by the deflecting means onto a scanned surface by imaging means, and optically scan an area on the scanned surface simultaneously with the plurality of light beams.
The detecting means are arranged on a surface substantially at the same position as the scanned surface and as inclined with respect to the main scanning direction. The plurality of light beams from the light source means via the deflecting means are focused by the imaging means, wherein the detecting means detects scanning positions of the plurality of light beams and differences between pass times of the plurality of light beams, thereby detecting deviation of the scanning positions and variation of magnification occurring with temperature changes of the optical scanning apparatus, and wherein correcting means corrects drawing positions of the plurality of light beams on the scanned surface, based on the result of the detection.
Another optical scanning apparatus of the present invention is an optical scanning apparatus arranged to guide a plurality of light beams emitted from a light source means having a plurality of light-emitting portions, arranged as inclined with respect to a main scanning direction, to a deflecting means, guide the plurality of light beams deflected and reflected by the deflecting means onto a scanned surface by imaging means, and optically scan an area on the scanned surface simultaneously with the plurality of light beams.
A slit is disposed in front of a detecting means arranged substantially at the same position as the scanned surface and in a normal direction to the main scanning direction. The plurality of light beams from the light source means via the deflecting means are focused on a surface of the detecting means through the slit by the imaging means, and the detecting means detects scanning positions of the plurality of light beams and intensity variation of output signals, thereby detecting deviation of the scanning positions and variation of magnification occurring with temperature changes of the optical scanning apparatus. Correcting means corrects drawing positions of the plurality of light beams on the scanned surface, based on the result
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