Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-03-23
2001-11-20
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S204200, C359S216100, C359S207110
Reexamination Certificate
active
06320690
ABSTRACT:
This application is based on application No. H11-084348 filed in Japan on Mar. 26, 1999, the entire content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a laser beam scanning apparatus for use in a laser printer or the like.
BACKGROUND OF THE INVENTION
Conventionally, in the field of laser beam scanning apparatuses of this type, for example as disclosed in U. S. Pat. Nos. 5,801,869 and 5,408,095, a technique has been proposed whereby two mirrors are combined together to form a scanning optical system so as to realize a laser beam scanning apparatus that offers stable image-formation performance against wavelength fluctuations in the light emitted from a light source.
In this construction, however, the mirrors are each so designed to have a reflecting surface that is rotation-symmetric about an axis. This makes it impossible to achieve satisfactory correction of aberrations. For example, in the construction disclosed in U.S. Pat. No. 5,408,095, the two mirrors constituting the scanning optical system have their reflecting surfaces formed as an axisymmetric aspherical surface and a cylindrical surface, respectively. This makes it difficult to achieve proper correction of f&thgr; characteristics and curvature of field.
On the other hand, in the construction disclosed in U.S. Pat. No. 5,801,869, the two mirrors constituting the scanning optical system have their reflecting surfaces formed as a barrel-shaped toric surface and a toric surface, respectively, or alternatively an axisymmetric aspherical surface and a barrel-shaped toric surface, respectively. This allows proper correction of f&thgr; characteristics and curvature of field, but makes it difficult to achieve proper correction of unevenness of the magnification in the sub-scanning-direction and groove-shaped aberration.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a laser beam scanning apparatus that offers table image-formation performance which is not significantly affected by wavelength fluctuations in the light emitted from a light source and that offers excellent optical performance in terms of f&thgr; characteristics, curvature of field, evenness of the sub-scanning-direction magnification, and groove-shaped aberration.
To achieve the above object, according to one aspect of the present invention, a scanning optical apparatus is provided with a light source for emitting a light beam, a deflector, and at least two reflecting surfaces. The deflector deflects the light beam emitted from the light source so that the light beam scans the scanned surface. Each of the two reflecting surfaces has an optical power both in the main-scanning direction and the sub-scanning direction and is not rotation-symmetric about an axis.
According to another aspect of the present invention, a laser scanning apparatus is provided with a light source for emitting a laser beam, a polygonal mirror, and at least two scanning mirrors. The polygonal mirror reflects and thereby deflects the laser beam emitted from the light source and is rotatable about a predetermined axis of rotation. The two scanning mirrors reflect the laser beam deflected by the polygonal mirror so that the laser beam is focused onto the scanned surface. The scanning mirrors each has a reflecting surface that has an optical power both in the main-scanning direction and the sub-scanning direction and that is not rotation-symmetric about an axis.
According to still another aspect of the present invention, a laser scanning apparatus is provided with a light source for emitting a laser beam, a polygonal mirror, and an imaging optical system. The polygonal mirror reflects and thereby deflects the laser beam emitted from the light source and is rotatable about a predetermined axis of rotation. The imaging optical system focuses the laser beam deflected by the polygonal mirror on the scanned surface while moving the laser beam at a substantially uniform speed across the scanned surface. The imaging optical system includes two scanning mirrors each having a reflecting surface that has an optical power both in the main-scanning direction and the sub-scanning direction and that is not rotation-symmetric about an axis.
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Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
Phan James
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