Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2003-10-17
2004-09-21
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S196100, C347S257000, C347S259000
Reexamination Certificate
active
06795224
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical scanning apparatus and an image forming apparatus using the same, and is particularly suitable for a laser beam printer, a digital copier, a multifunction printer or the like having, for example, the electrophotographic process designed such that a light beam emitted from light source means is deflected by deflecting means, and a surface to be scanned is optically scanned through scanning optical means to thereby record image information.
2. Related Background Art
In the optical scanning apparatus of a laser beam printer, a digital copier or the like, a beam optically modulated and emitted from light source means in conformity with an image signal is periodically deflected by deflecting means comprising, for example, a polygon mirror, and is condensed into a spot-like shape on the surface of a photosensitive recording medium by scanning optical means having an f&thgr; characteristic, and is optically scanned to thereby record image information.
FIG. 9
of the accompanying drawings is a schematic view of the essential portions of a conventional optical scanning apparatus. In
FIG. 9
, a divergent beam emitted from a light source unit
91
is converted into a substantially parallel beam by a collimator lens (not shown), and has its width limited by an aperture (not shown) and enters a cylindrical lens
92
having predetermined power only in a sub-scanning direction. The substantially parallel beam having entered the cylindrical lens
92
, in a main scanning cross-section, emerges while keeping the state of the substantially parallel beam. Also, in a sub-scanning cross-section, it converges and is imaged as a substantially linear image on the deflecting surface (reflecting surface)
93
a
of a light deflector
93
comprising a polygon mirror. The beam reflected and deflected by the deflecting surface
93
a
of the light deflector
93
is directed to the surface
97
of a photosensitive drum as a surface to be scanned through scanning optical means (an f&thgr; lens system) having first and second scanning lenses (f&thgr; lenses)
95
a
and
95
b
having the f&thgr; characteristic, and scans on the surface
97
of a photosensitive drum at a substantially constant speed by the light deflector
93
being rotated at a substantially equal angular speed by a polygon motor
94
, to thereby effect the recording of image information.
The first and second scanning lenses
95
a
and
95
b
in
FIG. 9
are strictly positioned relative to the optical path of the beam deflected by the light deflector
93
, and thereafter are fixed to an optical box (housing), not shown, by a known method such as adhesive securing or spring hold-down.
The first and second scanning lenses
95
a
and
95
b
are generally inexpensive plastic lenses, and positioning reference surfaces
99
a
1
,
99
a
2
,
99
b
11
,
99
b
12
,
99
b
21
and
99
b
22
for positioning in the direction of an optical axis are provided on configurational portions
90
a
1
,
90
a
2
,
90
b
1
and
90
b
2
, respectively, outside the effective lens areas thereof. That is, on the first scanning lens
95
a
, the positioning reference surfaces
99
a
1
and
99
a
2
are provided on the same plane as the configurational portions
90
a
1
and
90
a
2
, respectively, and on the second scanning lens
95
b
, the two positioning reference surfaces
99
b
11
,
99
b
12
and
99
b
21
,
99
b
22
are protrudedly provided separately in the sub-scanning direction from the configurational portions
90
b
1
and
90
b
2
, respectively.
These positioning reference surfaces
99
a
1
,
99
a
2
,
99
b
11
,
99
b
12
,
99
b
21
and
99
b
22
are brought into contact with the positioning pins of the optical box, not shown to thereby effect the positioning in the direction of the optical axis, whereby the deterioration of the curvature of image field on the surface
97
to be scanned and the deterioration of the uniformity of the scanning speed (f&thgr; characteristic) is prevented.
Japanese Patent Application Laid-Open No. 09-329755 discloses an optical scanning apparatus in which a scanning lens is provided with a pair of positioning reference surfaces differing in height by a predetermined amount and these are brought into contact with the positioning portion of an optical box, whereby an optical box of the same specification can be applied over a wide range.
Incidentally, recently, with the demand for the compactness of the entire apparatus, the compactness of a scanning optical system as scanning optical means has been contrived and for example, as a method therefor, mention may be made of making the angle of field of the scanning optical system wider or disposing the scanning optical system near a light deflector.
On the other hand, when in an optical scanning apparatus of this type, a beam emitted from a light source is made to be incident on the deflecting surface of a light deflector from a oblique direction thereto in the main scanning cross-section, the position of the beam reflected and deflected by the deflecting surface becomes asymmetrical with respect to the optical axis of the scanning optical system. This asymmetry becomes greater as the angle of field becomes wider, and recently the effective diameter of a scanning lens constituting the scanning optical system and the shape thereof in the main scanning cross-section have also become great in the asymmetry thereof. Along therewith, the configurational portion outside the effective lens area of the scanning lens also becomes great in asymmetry and for example, in
FIG. 9
, to make a straight line linking the points on two positioning reference surfaces together or a plane formed by the points on three or more positioning reference surfaces orthogonal to the optical axis of the scanning optical system, the amount of protrusion (height) of at least one positioning reference surface must be made great.
The scanning lens, however, is generally a plastic lens, as described above, and when the amount of protrusion becomes great, there arises the problem that the moldability of the lens is aggravated and desired surface accuracy is not obtained.
Also, near the light deflector, there are disposed many members such as a driving motor, a motor substrate, not shown, and a cylindrical lens, and when the scanning lens is disposed near the light deflector, there also arises the problem that a positioning member on the optical box side cannot be disposed due to the physical interference with other member.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide an optical scanning apparatus in which a scanning lens can be positioned highly accurately without aggravating the surface accuracy of the positioning reference surface of the scanning lens, and an image forming apparatus using the same.
It is a second object of the present invention to provide an optical scanning apparatus in which a positioning reference surface is freely disposed such as contriving energy saving, whereby the degree of freedom of the disposition of a scanning lens can be enhanced, and an image forming apparatus using the same.
In one aspect of the invention, an optical scanning apparatus comprises deflecting means for deflecting a beam emitted from light source means, and scanning optical means having at least one scanning lens for causing the beam deflected by the deflecting means to be imaged on a surface to be scanned, wherein the at least one scanning lens constituting the scanning optical means has a plurality of positioning reference surfaces for effecting the positioning of the scanning lens in the direction of the optical axis thereof, and is disposed so that a straight line linking the points on two positioning reference surfaces together or a plane formed by the points on three or more positioning reference surfaces may be non-orthogonal to the optical axis, and in a main scanning cross-section, the shape of the effective portion of the scanning lens is asymmetrical with respect to the optical axis.
In further aspe
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