Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2002-06-25
2004-08-10
Cherry, Euncha (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S204200
Reexamination Certificate
active
06775042
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light scanner, a multibeam scanner, and an image forming apparatus using the same. More particularly, the present invention relates to an image forming apparatus which is suitable for use as a laser beam printer or a digital copying machine, making use of an electrophotographic process or the like, and which is used to record image information by deflecting (reflecting) light which has been emitted from a light source using a polygon mirror, serving as deflecting means, and by scanning a scan surface with the light through scanning optical means (that is, an image-forming scanning optical system). Even more particularly, the present invention relates to a multibeam scanner which achieves higher speed and higher definition by performing optical scanning operations using a plurality of light beams at the same time, and which provides a good image by reducing jitters and pitch errors.
2. Description of the Related Art
FIG. 18
is a sectional view (main scanning sectional view) of the main portion of a related multibeam scanning optical system in a main scanning direction thereof.
In
FIG. 18
, reference numeral
91
denotes light source means, which is, for example, a semiconductor laser array including two light-emitting points (light sources). The two light-emitting points are disposed apart from each other in the main scanning direction and a subscanning direction. Reference numeral
92
denotes a condenser lens system which includes one collimator lens and which converts two light beams that have been emitted by the light source means
91
into substantially parallel light beams or convergent light beams. Reference numeral
93
denotes a cylindrical lens which has a predetermined refractive power only in the subscanning direction. Reference numeral
94
denotes an aperture diaphragm which shapes the two light beams that have passed through the cylindrical lens
93
so that they have desired optimal shapes. Reference numeral
95
denotes deflecting means (light deflector), which is, for example, a rotating polygon mirror, and which rotates at a constant speed in the direction of arrow A by driving means
98
such as a motor. Reference numeral
96
denotes a scanning lens system (image-forming scanning optical system), serving as scanning optical means, having an f&thgr; characteristic. The scanning lens system
96
includes two f&thgr; lenses, a first f&thgr; lens
96
a
and a second f&thgr; lens
96
b
. The scanning lens system
96
has a tilt correcting function as a result of putting a location near a deflecting surface
95
a
of the light deflector
95
and a location near a photosensitive drum surface
97
, serving as a scan surface, in a conjugate relationship within a subscanning cross-sectional plane.
In
FIG. 18
, the two light beams that have been emitted by the light source means
91
after being modulated in accordance with image information are converted into substantially parallel light beams or convergent light beams by the condenser lens system
92
, and the converted light beams are incident upon the cylindrical lens
93
. Of the light beams portions incident upon the cylindrical lens
93
, those within a main scanning cross-sectional plane exit from the cylindrical lens
93
unchanged, while those within the subscanning cross-sectional plane are focused in order to form a substantially linear image (a longitudinal linear image in the main scanning direction) on the deflecting surface
95
a
of the light deflector
95
through the aperture diaphragm
94
. Here, by the aperture diaphragm
94
, the cross-sectional sizes of the light beams are limited. The trio light beams that have been deflected (reflected) at the deflecting surface
95
a
of the light deflector
95
are focused in the form of a spot on the photosensitive drum surface
97
bat the scanning lens system
96
. By rotating the light deflector
95
in the direction of arrow A, the photosensitive drum surface
97
is optically scanned at a constant velocity in the direction of arrow B (main scanning direction). By this, two scanning lines are formed on the photosensitive drum surface
97
, which is a recording medium, in order to record an image.
In order to record image information with high precision using this type of multibeam scanner, it is important to properly correct jitters (displacements in printing positions) and non-uniform pitches over the entire scan surface by properly focusing a plurality of light beams on the entire scan surface.
In general, when forming an image by scanning the photosensitive drum surface with light beams that have been emitted by the light source, in order to obtain a good image with high resolution, it is necessary to reduce the diameter of a light beam spot on the photosensitive drum surface and to reduce the pitch in the subscanning direction.
In order to reduce the pitch in the subscanning direction in the multibeam scanner, light source means (or a semiconductor laser array) disposed by being tilted obliquely from the main scanning direction is often used.
FIG. 19
is a sectional view (main scanning sectional view) of another related multibeam scanner of this type in a main scanning direction thereof. In
FIG. 19
, component parts corresponding to those shown in
FIG. 18
are given the same reference numerals.
In
FIG. 19
, since a plurality of light-emitting points
91
a
and
91
b
of light source means
91
are disposed apart from each other by a certain distance in the main scanning direction, light beams that have exited from a condenser lens system
92
are not parallel to each other, so that they are at a certain angle from each other. Each light beam that has exited from the condenser lens system
92
is incident upon a polygon mirror
95
, which is a light deflector, through a cylindrical lens
93
.
At this time, the light beams cross each other at the location of an aperture diaphragm
94
disposed between the condenser lens system
92
and the polygon mirror
95
, so that, by the angle of each light beam and by a distance L from a reference position of a deflecting surface
95
a
of the polygon mirror
95
to the aperture diaphragm
94
, the interval between the light beams on the deflecting surface
95
a
of the polygon mirror
95
is determined (restricted). By reducing the interval between the light beams on the deflecting surface
95
a
of the polygon mirror
95
, the light beams are properly focused on a photosensitive drum surface
97
.
A multibeam scanner which satisfies such optical characteristics is disclosed in, for example, Japanese Patent Laid-Open No. 5-34613. According to this document, in the structure of the multibeam scanner, a plurality of light beams are converted into substantially parallel light beams at a condenser lens system, and the substantially parallel light beams are caused to impinge upon a polygon mirror through an aperture diaphragm. Then, by a scanning lens system, the substantially parallel light beams are led onto a scan surface. When scanning the scan surface with the plurality of light beams at the same time, the relationship among the number of light-emitting points of the light source means, the pitch in a main scanning direction, the distance from the polygon mirror to the aperture diaphragm, and the focal length of the condenser lens system is specified in order to properly focus the plurality of light beams on the scan surface.
When a multibeam scanner is used, it is necessary to properly correct jitters and pitch errors. Jitter refers to a relative displacement in positions for printing using a plurality of light beams in a main scanning direction. Pitch error refers to a deviation from a specified value (for example, 42.3 &mgr;m when printing resolution is 600 dpi) of the interval between scanning lines that are formed when a plurality of light beams are used at the same time for light scanning.
In order to reduce jitters, it is necessary to cause the light beams to reach the same location of the scanning lens system
Canon Kabushiki Kaisha
Cherry Euncha
Fitzpatrick ,Cella, Harper & Scinto
LandOfFree
Light scanner, multibeam scanner, and image forming... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light scanner, multibeam scanner, and image forming..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light scanner, multibeam scanner, and image forming... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3316572