Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2002-01-28
2004-08-31
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S216100, C359S205100, C359S819000, C347S259000
Reexamination Certificate
active
06785030
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical element and an optical scanning device using the element and, more particularly, to a scanning optical device which records image information by reflecting/deflecting a light beam emitted from a light source means using a deflection means, and optically scanning a scanning target surface via an imaging optical system and is suitable for an apparatus using an electrophotographic process, such as a laser beam printer or digital copying machine.
2. Related Background Art
Conventionally, in an optical scanning device used for a laser printer or the like, a light beam which is optically modulated in accordance with an image signal and emitted from a light source means is periodically deflected by a deflection means formed by, for example, a polygon mirror, and the light is focused into a spot on a photosensitive recording medium surface (photosensitive drum surface) by the second imaging optical system having an f-&thgr; characteristic, thereby optically scanning the surface and recording image information.
FIG. 23
is a schematic view of the main part of a conventional optical scanning device.
Referring to
FIG. 23
, a divergent light beam emitted from a light source means
91
is converted into a substantially parallel light beam by a condenser lens (collimator lens)
82
. The light beam width is limited by an aperture stop
83
and incident on a cylindrical lens
92
. Of the substantially parallel light beam incident on the cylindrical lens
92
, the light in a main scanning cross-section emerges without any change. The light in a sub scanning cross-section converges and is substantially formed into a linear image on a deflection/reflection surface
93
a
of a deflection means
93
comprising by a polygon mirror. The light beam reflected/deflected by the deflection/reflection surface
93
a
of the polygon mirror
93
is guided onto a recording medium surface (scanning target surface)
97
via a second imaging optical system
95
constituted by f-&thgr; lenses
95
a
and
95
b
having an f-&thgr; characteristic and a return mirror
96
. By rotating the polygon mirror
93
by a driving means
94
at a substantially equiangular velocity, the recording medium surface
97
which is a photosensitive drum is optically scanned at a substantially constant speed. With this operation, a latent image based on a potential difference is formed.
The above f-&thgr; lenses
95
a
and
95
b
are accurately positioned with respect to the optical path of a light beam reflected/deflected by the polygon mirror
93
and fixed on an optical frame (not shown) by a known method, e.g., bonding or spring pressure. For example, Japanese Laid-Open Patent Application Nos. 9-73038 and 9-329755 disclose a case where an f-&thgr; lens is accurately positioned by bringing a positioning reference on the incident surface side of the f-&thgr; lens into contact with a positioning member of an optical frame.
Japanese Patent No. 3004064 discloses a case where the incident and exit surfaces of an f-&thgr; lens are simultaneously positioned by bringing the incident surface into contact with a incident-surface-side positioning member and bringing the exit surface into contact with an exit-surface-side positioning member. This prevents curvature of field on a recording medium surface or a deterioration in uniformity (f-&thgr; characteristic) of scanning speed.
Japanese Laid-Open Patent Application No. 7-113973 discloses a case where focus adjustment on a recording medium surface is performed by mounting an f-&thgr; lens on a moving means and moving it in the optical axis direction. In addition, a cylindrical lens is moved in the optical axis direction to set a spot diameter on a recording medium surface in the sub scanning direction to a desired value. At this position, the lens is fixed on an optical frame by a known method, e.g., bonding or spring pressure, thereby performing focus adjustment in the sub scanning direction.
Recently, there have been increasing demands for an increase in the resolution of an optical scanning device and a decrease in cost. With an increase in resolution, optical elements such as an f-&thgr; lens and cylindrical lens need adjustment. For this purpose, new parts are required, and the adjustment time prolongs, resulting in an increase in adjustment cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical element which can reduce an assembly cost by simplifying focus adjustment of the optical element, decreasing the number of parts required for the adjustment, and shortening the adjustment time, and an optical scanning device using the element.
In one aspect of the invention, an optical element comprises a plurality of sets of positioning references for defining a position in an optical axis direction and said plurality of sets of positioning references define different positions in the optical axis direction.
In further aspect of the foregoing optical element, said positioning references of each set are formed on opposing surfaces.
In further aspect of the foregoing optical element, said positioning reference is formed into a stepped shape.
In further aspect of the foregoing optical element, said optical element has a focusing effect in one direction.
In another aspect of the invention, an optical scanning device comprises light source means, a first imaging optical system which focuses a light beam emitted from said light source means, deflection means for causing a deflection/reflection surface to reflect/deflect a light beam passing through said first imaging optical system to deflect the light beam as a deflected light beam at an equiangular velocity, and a second imaging optical system which optically scans the deflected light beam on a scanning target surface and forms the light beam into an image as a spot on the scanning target surface, and at least one of optical elements included in said first and second imaging optical systems has a plurality of sets of positioning references for defining a position of said optical element in the optical axis direction.
In further aspect of the foregoing optical scanning device, said positioning references of said optical element are formed on front and rear surfaces in the optical axis direction.
In further aspect of the foregoing optical scanning device, said optical element has a projection portion on an outer portion formed outside an effective portion, and surfaces of the projection portion which is located on front and rear sides in the optical axis direction form the positioning references.
In further aspect of the foregoing optical scanning device, an optical frame which houses said first imaging optical system or/and said second imaging optical system has a plurality of sets of positioning portions corresponding to the positioning references of said optical element, and an interval between the positioning portions of said optical frame in the optical axis direction of said optical element is larger than an interval between the positioning references of said optical element in the optical axis direction.
In further aspect of the foregoing optical scanning device, said optical element has a recess portion in an outer portion formed outside an effective portion, and surfaces of said recess portion which are located on front and rear sides in the optical direction form the positioning references.
In further aspect of the foregoing optical scanning device, an optical frame which houses said first imaging optical system or/and said second imaging optical system has a plurality of sets of positioning portions corresponding to the positioning references of said optical element, and an interval between the positioning portions of said optical frame in the optical axis direction of said optical element is smaller than an interval between the positioning references of said optical element in the optical axis direction.
In further aspect of the foregoing optical scanning device, said optical element is positioned to a p
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