Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2001-03-19
2003-09-23
Robinson, MMark A. (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S217200, C347S263000
Reexamination Certificate
active
06624920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical scanning device, a scanning optical system, a scanning imaging optical component, an optical scanning method, a ghost image preventing method and an image forming apparatus.
2. Description of the Related Art
An optical scanning device which deflects a beam from a light source by a light deflector, condenses the deflected beam toward a surface to be scanned by a scanning imaging optical system, forms a beam spot on the surface to be scanned and performs optical scanning of the surface to be scanned, is widely well-known in connection with a digital copier, an optical printer, a facsimile machine, and so fourth.
In such an optical scanning device, ideally, the surface to be scanned is scanned only by a proper scanning light. However, various optical components disposed from the light source to the surface to be scanned reflect light in some degree, and light thus reflected by these optical components and reaching the surface to be scanned acts as stray light against the proper scanning light.
Some stray light which generates a ghost image causing degradation in image quality of an image formed through the proper scanning light and is harmful is called ‘ghost light’. Generally, a ghost image generated due to ghost light has a form in which a black stripe overlaps a proper image.
Respective optical components disposed on a light path extending from the light source to the surface to be scanned may generate ghost light.
In a first part of the light path extending from the light source to the light deflector, the light path of the beam is fixed. Accordingly, it is relatively easy to prevent ghost light from being generated, by adjusting the dispositions of the optical components properly.
However, in the second part of the light path extending from the light deflector to the surface to be scanned, the light path dynamically changes as a result the beam being deflected. Accordingly, ghost light may be easily generated from unexpected parts.
As the light deflector, one which reflects the beam from the light source by a deflection reflective surface which is rotated or swung is generally used. Such a light deflector is contained in a housing in order to avoid adherence of dust to a driving part or the deflection reflective surface of the light deflector, or to avoid leakage of machine noise or air flow noise therefrom, and, via a transparent parallel plate which covers a window formed in the housing, the beam is incident on the light deflector and exits from the housing, in many cases.
In such a case, light reflected by the transparent parallel plate covering the window of the housing may become ghost light. In order to prevent the ghost light in this case from adversely affecting proper image formation, the parallel plate is inclined so that the reflected light strays in a sub-scanning direction. However, thus-straying light may become secondary ghost light as a result of being reflected by a part of the scanning imaging optical system.
SUMMARY OF THE INVENTION
An object of the present invention is mainly to effectively reduce or prevent generation of ghost image due to reflection by a non-effective surface of the scanning imaging optical component such as a lens disposed between the light deflector and surface to be scanned in the optical scanning device.
A scanning imaging optical component used in an optical scanning device which deflects a beam from a light source by a light deflector, condenses the deflected beam toward a surface to be scanned by a scanning imaging optical system, forms a beam spot on the surface to be scanned, and performs optical scanning of the surface to be scanned,
the optical component forming at least a part of the scanning imaging optical system; and
at least a part of a surface of said optical component other than an effective optical surface is made to be a roughened surface, and roughness thereof is such that:
Rmax>0.5 (&mgr;m)
The scanning imaging optical component may comprise a lens, may comprise an imaging mirror having an imaging function, or may comprise a mirror having no imaging function.
The effective optical surface is lens surfaces or parts of the lens surfaces which participate formation of a beam spot, when the scanning imaging optical component is a lens. The effective optical surface is a mirror surface or a part of the mirror surface which participates formation of a beam spot, when the scanning imaging optical component is a mirror.
As mentioned above, the scanning imaging optical component is an optical system which forms at least a part of the scanning imaging optical system. Accordingly, the scanning imaging optical system may include only the scanning imaging optical component, for example. When the scanning imaging optical system includes only a single f&thgr; lens, this f&thgr; lens is the scanning imaging optical component, and at least a partial surface of the effective optical surfaces thereof is made to be the roughened surface.
Alternatively, when the scanning imaging optical system includes a plurality of lenses, each lens may be the scanning imaging optical component which has the roughened surface other than the effective optical surfaces thereof; or only one or some of the plurality of lenses may be the scanning imaging optical component which has the roughened surface other than the effective optical surfaces thereof and the other lenses may have no roughened surface.
The scanning imaging optical system may include a mirror having no imaging function (plane mirror for bending a light path) as the scanning imaging optical component. In this case, at least a part of the mirror surface thereof other than the effective optical surface may be made to be the roughened surface.
When a stray light other than a proper scanning beam is incident on the roughened surface of the scanning imaging optical component, the stray light reflected thereby is dispersed by the roughened surface. Accordingly, even it reaches the surface to be scanned, concentration of light intensity thereof is low. Therefore, even if it forms a latent image, the density thereof is low, and, when the latent image is visualized, no black stripe which problematically degrades a proper image results therefrom.
When the roughness Rmax of the roughened surface is not larger than 0.5 &mgr;m, dispersion of the stray light reflected thereby is not sufficient, and, thereby, this reflected light may still act as ghost light when reaching the surface to be scanned, and form a ghost image as a somewhat wide gray stripe.
The roughness of the roughened surface is preferably large in the view point of preventing generation of ghost image. However, when the scanning imaging optical component is formed through molding of plastic material, too large surface roughness Rmax thereof may result in difficulty of sliding of the product when it is separated from the mold. Therefore, in such a case, the roughness Rmax of the roughened surface of the scanning imaging optical component may be preferably such that Rmax<10 (&mgr;m).
When the scanning imaging optical component is formed of a glass, there is no such a problem for removing the product from a mold. Accordingly, the roughness Rmax may be on the order of 100 &mgr;m.
The light deflector of the optical scanning device according to the present invention may be a rotary mono-surface mirror, a rotary bi-surface mirror, a rotary polygon mirror, a galvano mirror, or the like, for example.
In a scanning optical system according to the present invention,
the light deflector is contained in a housing;
a window is provided in said housing for causing the beam from the light source to be incident on the deflection reflective surface, and, also, causing the deflected beam reflected by the deflection reflective surface to exit from the housing;
a transparent parallel plate is provided for covering the window therewith; and
the transparent parallel plate is inclined with respect to a direction perpendicular to a deflection scanning plane.
A
Ricoh & Company, Ltd.
Robinson MMark A.
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