Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-12-03
2001-03-06
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S216100, C347S243000
Reexamination Certificate
active
06198562
ABSTRACT:
The present invention relates to a coated web printing paper suitable for printing with cold-set offset printing ink.
Such a paper is already known from EP-A 0 785 307. As regards the need for enhanced cold-set paper qualities and the related problems, the introductory statements n this older document are referred to.
The web printing paper described in EP-A 0 785 307 is a so-called mat quality. It is explained in detail in this older document that to achieve the pressability and printability of a coated web printing paper in the cold-set offset process, special demands must be made on the paper regarding its wetting/water penetration behavior and its ink absorption speed. These are properties which at times are in turn considerably disadvantaged by a glazing on smoothnesses of 1,000 to 1,600 sec. Bekk, as is necessary for producing typical smooth papers. For this reason, it was first managed to provide a coated mat quality for the cold-set process.
Now that a high degree of advertizing effectiveness is to be achieved via newspaper supplements, only glossy paper can be considered for certain advertizing orders. In the absence of cold-set-suitable glossy LWC papers, these brochures are still printed via the conventional heat-set process as before. To enable the cold-set printer to take on such printing orders as well, the main point was to develop a glossy paper quality that closes this quality gap and can be pressed and printed without problems via the printing machine configurations that are typical in the newspaper printing domain (eight-tower and satellite printing machines). After such a quality has established itself in the domain of mass-produced printing paper, economic aspects are also to be taken into consideration.
As disclosed in Japanese Laid-Open Patent Application No. 8-304722, a conventional multi-beam scanning device utilizes a polarization beam splitter and two light sources in order to achieve the multi-beam scanning. In this conventional device, the polarization beam splitter is used to convert the multiple beams from the light sources into the converging beams incident to a rotary polygonal mirror. However, the polarization beam splitter is expensive, and it is difficult to manufacture and provide this conventional multi-beam scanning device for low cost.
Further, Japanese Laid-Open Patent Application No. 9-146024 discloses a multi-beam scanning device which is configured to perform multi-beam scanning using two light sources while eliminating the need for the expensive polarization beam splitter.
In this conventional multi-beam scanning device, the multiple beams from the light sources are converted into the converting beams, and the converging beams are directly incident to a rotary deflector. The converging beams incident to the deflector form a difference angle between them within a plane that is perpendicular to the rotation axis of the deflector. This conventional multi-beam scanning device includes a lens holder made of aluminum on which the two light sources are firmly mounted. The deviation of the relative positions of the optical axes of the multiple beams from the light sources due to heat or the use over an extended period of time can be prevented.
However, in this conventional multi-beam scanning device, different amounts of sag of the multiple beams are produced when beams are deflected on the reflection surface of the rotary deflector which is rotated about a fixed rotation axis. In order to achieve excellent optical characteristics (beam spot size, beam pitch, etc.) of the multi-beam scanning, the difference in the amounts of sag of the multiple beams must be taken into consideration. This conventional multi-beam scanning device does not take account of this problem, and thus, it is difficult to achieve excellent optical characteristics of the multi-beam scanning.
Further, in this conventional multi-beam scanning device, a cylindrical lens (or a concave cylindrical mirror) is provided to convert the multiple beams in common, and variations of the beam pitch on the image surface due to a tilt error of the cylindrical lens mounted is significant. This conventional multi-beam scanning device does not take account of this problem, and therefore, it is difficult to achieve excellent optical characteristics of the multi-beam scanning.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide an improved multi-beam scanning device which has a simple configuration that can be manufactured and provided at low cost and achieves excellent optical characteristics, such as beam spot size or beam pitch, of multi-beam scanning using a plurality of light sources, while also eliminating the need for a polarization beam splitter.
Also, preferred embodiments of the present invention provide an image forming system which includes a multi-beam scanning device which has a simple configuration that can be manufactured and provided at low cost and achieves excellent optical characteristics, such as beam spot size or beam pitch, of multi-beam scanning using a plurality of light sources, while also eliminating the need for a polarization beam splitter.
A further preferred embodiment of the present invention provides an image forming method which uses a multi-beam scanning device having a simple configuration that can be manufactured and provided at low cost and achieves excellent optical characteristics, such as beam spot size or beam pitch, of multi-beam scanning using a plurality of light sources, while also eliminating the need for a polarization beam splitter.
According to one specific preferred embodiment of the present invention, the multi-beam scanning device includes a plurality of light sources which emit multiple beams, the plurality of light sources including a first light source which emits a first beam, and a second light source which emits a second beam; a plurality of coupling lenses which couple the multiple beams from the light sources, the plurality of coupling lenses including a first coupling lens which couples the first beam, and a second coupling lens which couples the second beam; a converging lens device which converts the coupled beams from the coupling lenses into converging beams, the converging beams being elongated in a direction corresponding to a main scanning direction and converging only in a direction corresponding to a sub-scanning direction that is substantially perpendicular to the main scanning direction, the converging beams which correspond to the first and second beams forming a difference angle that is largest among difference angles formed by all of the converging beams; a rotary deflector having a reflection surface which is rotated about a fixed rotation axis, the reflection surface deflecting the converging beams from the converging lens device while the reflection surface is rotated; and a scanning lens device which scans an image surface in the main scanning direction at a substantially uniform velocity by focusing each of the deflected beams from the rotary deflector into a beam spot on the image surface, wherein the multi-beam scanning device is configured to satisfy the conditions: (1) &thgr;
2
&bgr;
2
·A/L<0.0005; and (2) &thgr;>tan
−1
[(Ø1+Ø2)/2L1], where A is a constant distance between the reflection surface and the rotation axis, &thgr; is the largest difference angle measured in terms of radians, Ø1 is an effective diameter of the first coupling lens through which the first beam passes, Ø2 is an effective diameter of the second coupling lens through which the second beam passes, &bgr; is a transverse magnification of the scanning lens device in the sub-scanning direction, L1 is the smaller one of a distance from the first coupling lens to the reflection surface and a distance from the second coupling lens to the reflection surface, and L is a distance from the reflection surface to the image surface.
According to another preferred embodiment of the present invention, a multi-beam scanning device includes a plurality of l
Hayashi Yoshinori
Kawamura Atsushi
Greenberg & Traurig, LLP
Ricoh Co. Ltd.
Schuberg Darren
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