Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1998-10-20
2001-11-06
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C347S224000, C347S261000, C359S216100
Reexamination Certificate
active
06313906
ABSTRACT:
This application is based on an application No. 9-286575 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a multibeam scanning device which is used in a multicolor image forming apparatus, such as a color copying machine and a laser printer.
(2) Related Art
A tandem-type color copying machine, as one example of a conventional multicolor image forming apparatus, has photosensitive drums corresponding to reproduction colors set along a transporting surface of a transport belt. The reproduction colors are cyan, magenta, yellow, and black, which are respectively referred to as C, M, Y, and K hereinafter, and components related to these colors are assigned numerals with a corresponding C, M, Y, or K. A multibeam scanning device has four laser beams emitted, with each laser beam scanning the surface of the corresponding photosensitive drum. As a result, electrostatic latent images corresponding to reproduction colors are respectively formed on the photosensitive drums. The electrostatic latent images are respectively developed into visible toner images using the reproduction color toner. Then, the toner images are sequentially transferred onto a recording sheet to form a color image, with the recording sheet being transported on the transport belt.
A beam scanning device used in such a color copying machine is composed of four laser diodes corresponding to four reproduction colors and an optical system which deflects laser beams emitted from the laser diodes to expose the corresponding photosensitive drums. The optical system includes optical elements, such as a polygon mirror, a scanning lens, and redirecting mirrors.
Each laser diode is driven in accordance with inputted image data and emits a laser beam. The laser beam is reflected off the surface of the polygon mirror which is rotating and deflects the laser beam. Then, the laser beam exposes the corresponding photosensitive drum via lenses, such as the scanning lens.
Here, if a polygon mirror or a scanning lens are provided for each laser beam, cost increases and the construction of the beam scanning device is increased in size.
A multibeam scanning device using one polygon mirror has been suggested. Japanese Laid-Open Patent Application No. 8-271817 teaches an example of such a multibeam scanning device.
FIG. 1
shows a front view of the schematic construction of the multibeam scanning device disclosed in the cited Japanese application.
A multibeam scanning device
100
shown in
FIG. 1
has a polygon mirror
101
. Four laser beams LK to LC are respectively emitted from four laser diodes (not shown) to one mirror face of the polygon mirror
101
as shown in FIG.
1
. The laser beams LK to LC are linearly aligned in a direction parallel to a rotational axis O of the polygon mirror
101
, that is, the laser beams LK to LC are aligned in the sub-scanning direction. The deflected laser beams LK to LC intersect with one another at a position P between a toroidal lens
102
and an f&thgr; lens
103
, with the position P being located on a plane Q which is perpendicular to the rotational axis O.
The laser beams LK to LC deflected on the mirror face of the polygon mirror
101
get closer to the plane Q as they approach the position P, and intersect with one another at the position P after passing through the toroidal lens
102
. The laser beams LK to LC separate from one another with distance from the position P and pass through the f&thgr; lens
103
. By means of redirecting mirrors
104
a
K to
104
c
K,
104
a
Y to
104
c
Y,
104
a
M to
104
c
M, and
104
C, light paths of the laser beams LK to LC are redirected so that light path lengths are made equal. Then, the laser beams LK to LC respectively exposes surfaces of photosensitive drums
201
K to
201
C to form electrostatic latent images, through dust-proof glasses
105
K to
105
C.
Accordingly, the polygon mirror
101
and the scanning lens including the toroidal lens
102
and the f&thgr; lens
103
are shared by all laser beams. This contributes to cost reduction and to the simplification of the apparatus.
Using this conventional multibeam scanning device, however, the laser beams LK to LC intersect with one another at the position P located immediately before the f&thgr; lens
103
. As a result, the laser beams LK to LC separate from one another after passing through the f
6
lens
103
in the sub-scanning direction, with only a short distance in between, thereby causing a difficulty to discriminate the laser beams LK to LC.
The laser beams LK to LC should be reliably separated from one another before reaching the photosensitive drums
201
K to
201
C. Otherwise, insufficient exposure may occur to at least one of the photosensitive drums
201
K to
201
C, or noises may be caused on a reproduced image. For efficient operation, the separation of the laser beams should be performed using the redirecting mirrors
104
a
K,
104
a
Y,
104
a
M, and
104
C. However, the laser beams are separated from one another, with a short distance in between as described above, so that there would be a problem if these mirrors are set near the position P.
To address this problem, the redirecting mirrors
104
a
K,
104
a
Y,
104
a
M, and
104
C can be set away from the position P. Yet, if doing so, a distance between the position P and these mirrors increases, making the whole distance between the mirrors and the polygon mirror
101
longer. In spite of the reduced number of the polygon mirror and the scanning lens, the apparatus is consequently increased is size.
Alternatively, a special lens, such as a toric lens, can be set at the position P for separating the laser beams LK to LC in the sub-scanning direction, so that each distance between the neighboring laser beams increases and the laser beams LK to LC are separated near the position P. In this case, although the distance between the position P and the redirecting mirrors can be shortened, the distance between the position P and the polygon mirror cannot be shortened. In addition, a price of the apparatus may be high.
This problem occurs not only to a multibeam scanning device provided in a tandem-type color copying machine having photosensitive drums, but also to that provided in an image forming apparatus having a construction for forming multicolor images using laser beams.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a multibeam scanning device that easily separates deflected laser beams within a short distance, without making the light path lengths longer or using a special lens.
The object of the present invention is achieved by A multibeam scanning device made up of: a plurality of light sources, each emitting a light beam; and a deflecting unit, provided ahead in a light beam emitting direction of each of the plurality of light sources, for deflecting all light beams respectively emitted from the plurality of light sources, wherein at least two of the plurality of light sources are arranged so that the light beams emitted from the at least two light sources intersect before reaching the deflecting unit.
With this construction, the deflected laser beams are separated from one another in the direction of the rotational axis O with distance from the mirror face. Therefore, if the redirecting mirrors are set nearer to the polygon mirror than usual, the laser beams can be reliably separated from one another.
It should be noted here that “intersect” referred to in the present specification indicates that the laser beams arm intersect with each other on a plane, and also indicates that the laser beams three-dimensionally intersect with each other.
REFERENCES:
patent: 5170181 (1992-12-01), Tamada
patent: 5251055 (1993-10-01), Koide
patent: 5450119 (1995-09-01), Hinton et al.
patent: 5463418 (1995-10-01), Tateoka
patent: 5485194 (1996-01-01), Tateoka
patent: 5691761 (1997-11-01), Fisli
patent: 5818506 (1998-10-01), Yamaguchi et al.
patent: 5850306 (1998-12-01), Fukutome et al.
patent: 5870132 (1999-
Kohsaka Jun
Nagasaka Yasushi
Takeshita Kenji
Adams Russell
Burns Doane , Swecker, Mathis LLP
Fuller Rodney
Minolta Co. , Ltd.
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