Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2001-11-08
2003-06-17
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S118000, C347S232000, C359S204200
Reexamination Certificate
active
06580443
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to color image forming devices such as color laser printers and, more particularly, to a color image forming device of which optical unit has a simplified structure.
2. Description of the Related Art
The tandem type color laser printer requires as many photoconductive drums as the colors needed for transferring, and each of the photosensitive drums must be exposed by laser. Thus the conventional color laser printer is equipped with as many scanning optical units as the photosensitive drums for exposing the respective photosensitive drums. This scanning optical unit includes components such as a polygon mirror that reflects laser light to provide a laser scanning plane, a rotation motor that rotates the polygon mirror and a reflection mirror that reflects the laser light reflected by the polygon mirror toward the photosensitive drum.
Such configuration, however, makes the resulting color laser printer expensive because it needs the installation of two or more polygon mirrors and rotation motors. Besides, since the device includes two or more scanning optical units that are similar to each other in its housing, the dimensions of the whole device grow, making it difficult to provide a compact device and easy maintenance. To solve these problems, a number of proposals have been made as follows.
FIG. 1
is a schematic diagram showing the configuration of the color image forming device disclosed in Japanese Patent Laid-Open Publication No. Hei. 10-207171. Referring now to
FIG. 1
, in order to make maintenance of the color image forming device easy, the exposure units
102
including polygon mirrors are collected in a specific site
104
in the housing, instead of the respective sites over the image forming units
103
including photosensitive drums. Inside the housing, a plurality of reflection mirrors
105
are provided for reflecting the laser light
101
provided by each exposure unit
102
and then directing the laser to each image formation unit
103
. The image formation unit
103
, which forms an image on a recording medium
106
, is provided so that the recording medium
106
runs under the respective image formation units
103
one after another. In the downstream of the transfer path of the recording medium
106
beyond the image formation units
103
, a fixing unit
107
is provided to fix the image created on the recording medium
106
. In the device shown in
FIG. 1
, two or more exposure units
102
provide laser beams
101
and then two or more reflection mirrors
105
reflect the provided laser beams
101
toward the respective image formation units
103
. Each image formation unit
103
forms an image on the recording medium
106
, and then the fixing unit
107
fixes the formed image on the recording medium
106
.
FIG. 2
is a schematic diagram showing the configuration of the color image forming device disclosed in Japanese Patent Laid-Open Publication No. Hei. 7-76137. Referring to
FIG. 2
, in order to reduce the quantity of polygon mirrors
108
and simplify the structure of the color image forming device, a single exposure unit
102
is provided over a position close to the center of a series of image formation units
103
a
-
103
d
. The exposure unit
102
has a single rotation motor (not shown) that rotates a pair of polygon mirrors
108
, and these polygon mirrors
108
expose the respective photosensitive drums. Namely, the pair of polygon mirrors
108
provide four laser beams
101
and two or more reflection mirrors
105
reflect these laser beams
101
toward the image formation units
103
a
-
103
d
for image formation.
FIG. 3
is a schematic diagram showing the configuration of the color image forming device disclosed in Japanese Patent Laid-Open Publication No. Hei. 6-5409. Referring now to
FIG. 3
, in order to reduce the quantity of polygon mirrors
108
to one in the color image forming device of this type, a single polygon mirror
108
is provided on either side of a series of photosensitive drums
109
. And, a number of reflection mirrors
105
direct the respective laser beams
101
to each photosensitive drum
109
to expose each photosensitive drum
109
are provided. The color image forming device described in Japanese Patent No. 2659360 has a configuration similar to this device.
FIG. 4
is a schematic diagram showing the configuration of the color image forming device disclosed in Japanese Patent Laid-Open Publication No. 2000-162523. Referring now to
FIG. 4
, the color image forming device of this type employs a single polygon mirror
108
, and a plurality of reflection mirrors
105
reflect the laser beams
101
to guide them to photosensitive drums
109
.
FIG. 5
is a schematic diagram showing the configuration of the color image forming device disclosed in Japanese Patent Laid-Open Publication No. Hei. 8-305115. Referring now to
FIG. 5
, in order to reduce the quantity of polygon mirrors to one and eliminate reflection mirrors in the color image forming device, two or more photosensitive drums
109
are arranged around the polygon mirror
108
, and the laser beams
101
provided by the polygon mirror
108
are directly guided to the respective photosensitive drums
109
without using any reflection mirrors for exposure of the photosensitive drums
109
.
Such conventional devices, however, have the following problems. In the color image forming device of
FIG. 1
disclosed in Japanese Patent Laid-Open Publication No. Hei. 10-207171, the resulting improvement is limited to that the exposure units
102
are collected in a specific position in the housing. It still needs a number of reflection mirrors
105
and therefore its device cost may become even higher. Even if the quantities of exposure units
102
and polygon mirrors
108
are each reduced to one, there is no change in the quantity of reflection mirrors
105
, and the problem in terms of cost is left unsolved.
In the color image forming device of
FIG. 2
disclosed in Japanese Patent Laid-Open Publication No. Hei. 7-76137, the laser beams
101
reflected by the polygon mirrors
108
conduct laser scanning in different directions between the image formation units
103
a
-
103
b
and those
103
c
-
103
d
. Then it poses a problem that the registration accuracy in the horizontal direction, which is an important factor in creating color images of high quality, becomes low. Also in this prior art device, the necessity of assembly and adjustment of such a multitude of reflection mirrors
105
leads to high costs and poor maintenance.
The color image forming devices of
FIG. 3
disclosed in Japanese Patent Publication No. Hei. 6-5409 and Japanese Patent No. 2659360 use a multitude of reflection mirrors
105
, as is the case with the color image forming device disclosed in Japanese Patent Laid-Open Publication No. Hei. 7-76137. Thus the device cost is raised and maintenance becomes hard to perform.
Also a multitude of reflection mirrors
105
are used in the color image forming device of
FIG. 4
disclosed in Japanese Patent Laid-Open Publication No. 2000-162523, as is the case with the color image forming devices disclosed in Japanese Patent Laid-Open Publication No. Hei. 7-76137 and Japanese Patent Publication No. Hei. 6-5409. As a result, the device cost is raised, and it becomes difficult to make the device compact and maintenance easy.
Also in the color image forming device of
FIG. 5
disclosed in Japanese Patent Laid-Open Publication No. Hei. 8-305115, the device becomes too large for practical use because its optical unit occupies a large installation space.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a color image forming device equipped with a simple scanning optical unit that makes the device cost low, device size compact and maintenance easy.
A color image forming device according to the present invention forms a color image of a plurality of colors onto a recording medium. This color image forming device has a laser source for emitting a plurality of laser beams b
Iwamura Takuya
Kusayanagi Toshiya
Watanabe Takaaki
Yamaguchi Chiseki
Yoshii Tomoyuki
Fuji 'Xerox Co., Ltd.
Pendegrass Joan
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