Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2002-01-17
2002-09-03
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S197100, C359S212100, C359S207110, C359S820000
Reexamination Certificate
active
06445482
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical scanning apparatus, and more particularly to an optical scanning apparatus which is constructed to correct a change in the curvature of field of a lens caused by an operating temperature change so as to form a small-diameter optical beam spot on a surface to be scanned regardless of changes in the operating temperature.
2. Description of Related Art
An optical scanning apparatus is often provided in laser printers, digital copying machines or facsimile machines. It is also well known to use plastic material for manufacturing a lens to reduce the cost of the lens or to form a surface of the lens so as to have a specific shape. For a scanning image forming lens used for forming a deflected light flux into an image on a scanning surface, there are proposed various lens shapes for correcting the curvature of field and the constant velocity characteristics, and plastic material is known to be suitable for forming such lens shapes to achieve such correction of curvature of field.
The curvature of field and the refractive index of the surface of a plastic lens both change in accordance with a change in the volume of the lens due to an operating temperature change. As a result, the lens performance and especially the curvature of field changes in accordance with changes in the operating temperature. A change of the curvature of field causes an increase in the diameter of an optical beam spot formed on a scanning surface, and consequently, lowers the resolution of optical scanning and images formed by such scanning.
A change of the curvature of field of a plastic lens caused by a temperature change occurs in an opposite manner in positive and negative lenses. Accordingly, a change of the curvature of field of a plastic scanning image forming lens caused by a temperature change can be corrected by arranging another plastic lens having a power opposite to that of the scanning image forming lens along an optical path between a light source and an optical deflector. Such an arrangement offsets the change in the curvature of field of the plastic scanning image forming lens by having a suitable change in the curvature of field of another plastic lens, as disclosed in Japanese Patent Laid-open Publication Nos. 8-160330 and 8-292388.
In the optical scanning apparatus described in JP 8-160330 and 8-292388, the plastic lens arranged between the light source and the optical deflector does not have a power relative to a direction corresponding to a main scanning direction. Therefore, the plastic lens arranged between the light source and the optical deflector does not correct a change of the curvature of field in the direction corresponding to the main scanning direction which is caused by the changes in operation temperature. As a result, an increase in the diameter of the optical beam spot in the main scanning direction cannot be prevented. The direction corresponding to a main scanning direction herein refers to the direction corresponding a scanning direction of an optical scanning apparatus along an optical path from a light source to a scanning surface and the direction corresponding to a sub scanning direction refers to a direction corresponding to a sub scanning direction of the optical scanning apparatus along the same light path, which is substantially perpendicular to the main scanning direction.
Further, for preventing an increase of an optical beam spot diameter in the sub scanning direction, it is known that wave-front aberration must be considered not only for paraxial light fluxes but also for the entire light fluxes.
SUMMARY OF THE INVENTION
Preferred embodiments of the present invention overcome the problems described above by providing an optical scanning apparatus, which is constructed and arranged to include a plastic lens for a scanning image forming lens for forming a deflected light flux into an image on a scanning surface such that the plastic lens corrects any change in the curvature of field in both the main scanning direction and the sub scanning direction, which change in curvature of field is caused by a change in operating temperature, and to consequently form an optical beam spot having a very small diameter on the scanning surface regardless of changes in the operating temperature.
The preferred embodiments of the present invention also provide an optical scanning apparatus which is constructed to correct an effect of the change in the curvature of field relative to the paraxial light fluxes in the sub scanning direction and also to correct the wave-front aberration relative to the entire light fluxes in the sub scanning direction.
According to a specific preferred embodiment of the present invention, an optical scanning apparatus includes a light source, a first optical lens system, a second optical lens system, an optical deflector and a third optical lens system. A semiconductor laser or a light emitting diode (LED) may be used as the light source. The first optical lens system couples a divergent light flux emitted from the light source to a subsequent optical lens system, which is the second optical lens system. The first optical lens system converts the light flux emitted from the light source either to a parallel light flux or to a weak converging or weak diverging light flux. The second optical lens system forms the light flux emerged from the first optical lens system into a line image extending in a direction corresponding to the main scanning direction. The optical deflector has a deflecting reflective surface located near where the line image is formed and deflects the light flux reflected by the deflecting reflective surface. A rotating polygonal mirror, a rotating single-surface mirror or a rotating double-surface mirror may be used for the optical deflector. The third optical lens system condenses the deflected light flux on a surface to be scanned as an optical beam spot so as to scan the surface to be scanned. The third optical lens system preferably includes at least one plastic lens. The third optical lens system may include two or more lenses, or may be constructed by a combination of one or more lenses and a concave-shaped mirror having an image forming function. A flat-surface mirror may be arranged to bend a light path for the deflected light flux, in addition to the third optical lens system, between the optical deflector and the surface to be scanned, depending upon the arrangement of the optical scanning apparatus. The second optical lens system preferably includes at least one plastic lens and one glass lens.
According to one feature of preferred embodiments of the present invention, the surface of the plastic lens in the second optical lens system is formed such that a change in the curvature of field in the main scanning direction and in the sub scanning direction caused by a change in the volume of the plastic lens in the third optical lens system, which is caused by a change in the operating temperature, is accurately and completely corrected. Accordingly, the change in the curvature of field in the main scanning direction and the sub scanning direction, which is caused by changes in the operating temperature, is substantially prevented and thereby the diameter of the optical beam spot is kept very small.
In the above described optical scanning apparatus, the plastic lens of the third optical lens system may be configured to have a positive power in both directions corresponding to the main scanning direction and the sub scanning direction, respectively, and the plastic lens of the second optical lens system may be configured so as to be an anamorphic lens having a negative power in both directions corresponding to the main scanning direction and the sub scanning direction and the glass lens of the second optical lens system may be configured to have a positive power at least in the sub scanning direction. By constructing the second optical lens system as described above to achieve a synergistic effect of the glass and plastic lenses, th
Assai Fayez
Greenberg & Traurig
Ricoh Technology Research Inc.
Rzucidlo Eugene C.
Spyrou Cassandra
LandOfFree
Optical scanning apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical scanning apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical scanning apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2879253