Electrophotography – Having particular structure – Modular or displaceable
Reexamination Certificate
1999-04-09
2001-04-03
Grainger, Quana M. (Department: 2852)
Electrophotography
Having particular structure
Modular or displaceable
C399S113000
Reexamination Certificate
active
06212344
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image forming apparatus in which a plurality of image forming means are juxtaposed along the convey direction of a transfer medium and, more particularly, to an image forming apparatus such as an electrophotographic color copying machine, color printer, or the like, in which four image forming units for respectively outputting four color images are juxtaposed.
BACKGROUND ART
FIG. 27
schematically shows the arrangement of a color copying machine as a conventional image forming apparatus, in which image forming units Ya to Yd (image forming means) for four colors are juxtaposed along the convey direction of a paper sheet P (transfer medium).
The image forming units Ya to Yd respectively comprise photosensitive drums
1
a
to
1
d
serving as image carriers. A conveyor belt T nearly horizontally extends below the photosensitive drums
1
a
to
1
d
. Charging devices
2
a
to
2
d
, exposure devices
3
a
to
3
d
, developing devices
4
a
to
4
d
, transfer devices
5
a
to
5
d
, cleaning devices
6
a
to
6
d
, and charge removing devices
7
a
to
7
d
are disposed around the corresponding photosensitive drums along the rotation direction of the drum. Note that the transfer devices
5
a
to
5
d
are disposed on the back surface side of the conveyor belt T.
The image forming unit Ya which is located on the most upstream side along the convey direction of the paper sheet P outputs a yellow image, the second image forming unit Yb a magenta image, the third image forming unit Yc a cyan image, and the last image forming unit Yd a black image.
When a color image is formed on a paper sheet P by the color copying machine with the above-mentioned arrangement, the paper sheet P is conveyed by the conveyor belt T, and image forming processes are done in the order of charging, exposure, development, transfer, cleaning, and charge removal for the surfaces of the photosensitive drums
1
a
to
1
d
in the image forming units Ya to Yd. Color developing agent images formed by the individual image forming units Ya to Yd are transferred onto the paper sheet P to overlap each other. The paper sheet P on which the color developing agent images are transferred to overlap each other passes through a fixing device (not shown) which neighbors the fourth image forming unit Yd on its downstream side, and the color developing agent images are melted and fixed on the paper sheet P there, thus forming a color image on the paper sheet P.
However, the conventional color copying machine is constructed by serially disposing four image forming units, each of which constructs a so-called monochrome copying machine for forming a monochrome image, along the convey direction of the paper sheet P.
More specifically, the cleaning devices
6
a
to
6
c
except for the cleaning device
6
d
of the fourth image forming unit Yd, and developing devices
4
b
to
4
d
except for the developing device
4
a
of the first image forming unit Ya are interposed between the neighboring photosensitive drums
1
a
to
1
d
. Since the cleaning devices
6
a
to
6
c
and developing devices
4
b
to
4
d
have predetermined volumes, minimum required spaces must be assured between the neighboring photosensitive drums to attach the devices
4
and
6
between the neighboring photosensitive drums
1
a
to
1
d
and to adjust the attachment positions of the devices
4
and
6
.
Hence, in the aforementioned conventional color copying machine, given spaces are required between the neighboring photosensitive drums
1
a
to
1
d
, and the size of the entire apparatus along the line-up direction of the photosensitive drums
1
a
to
1
d
(longitudinal direction), i.e., the convey direction of the paper sheet P, becomes large.
In addition, in the color copying machine, since the individual color image forming units Ya to Yd are used nonuniformly, they must independently undergo exchange, adjustment, and maintenance. For this purpose, a structure that can insert/remove each unit into/from the copying machine independently is required, thus disturbing a size reduction of the apparatus.
In order to attain a size reduction of the apparatus, the photosensitive performance of the photosensitive drums
1
a
to
1
d
must be improved. When the process speed is increased to process a large number of paper sheets P within a short period of time in consideration of the photosensitive performance, the exposure-development distance becomes insufficient, and a size reduction is limited in consideration of the sheet convey portion. For example, the exposure-development processing time normally requires 0.15 sec, and it is impossible to reduce the diameter of the photosensitive drum to be smaller than the current diameter.
As a consequence, in order to shorten the size of a color copying machine of this type along the longitudinal direction, it is effective to reduce the pitch between the neighboring photosensitive drums
1
a
to
1
d.
For this purpose, size reductions of the developing devices
4
b
to
4
d
and cleaning devices
6
a
to
6
c
interposed between the neighboring photosensitive drums
1
a
to
1
d
need only be promoted.
In the conventional color copying machine, each of the image forming units Ya to Yd has many constituent devices (the photosensitive drum
1
, charging device
2
, exposure device
3
, developing device
4
, transfer device
5
, cleaning device, and charge removing device
7
will be generally referred to as constituent devices hereinafter), and four sets of these constituent devices must be equipped. For this reason, it is troublesome to manufacture and manage the devices that make up each unit, thus adversely influencing the manufacturing cost. In the image forming units Ya to Yd, since the constituent devices arranged around their photosensitive drums
1
a
to
1
d
must be independently and accurately aligned with respect to the photosensitive drums, many manufacturing processes are required, and assembly of the copying machine requires much labor.
DISCLOSURE OF INVENTION
The present invention has been made in consideration of the above situation, and has as its object to provide an image forming apparatus in which a plurality of image forming means are juxtaposed along the convey direction of a transfer medium, and which can reduce the size of the apparatus along the line-up direction of the image forming means.
It is another object of the present invention to provide an image forming apparatus which can reduce the number of manufacturing processes required for assembling the apparatus, and labor that pertains to the manufacture and management of constituent devices, and can reduce the manufacturing cost of the apparatus.
In order to achieve the above objects, an image forming apparatus of claim
1
in the present invention comprises:
convey means for conveying a transfer medium in a predetermined direction;
a first image carrier which is free to rotate along a convey direction of the transfer medium;
a second image carrier which is free to rotate along the convey direction and is spaced from the first image carrier on the downstream side in the convey direction;
first and second latent image forming means for respectively forming latent images on the first and second image carriers;
first and second developing means for developing the latent images respectively formed on the first and second image carriers by the first and second latent image forming means by supplying developing agents;
first and second transfer means for sequentially transferring the developing agent images developed by the first and second developing means onto the transfer medium conveyed by the convey means;
first and second removing means for respectively removing residual developing agents which remain on the first and second image carriers without being transferred onto the transfer medium by the first and second transfer means; and
holding means for integrally holding the first removing means for removing the residual developing agent on the first image carrier, and the second developing me
Hashimoto Yoshiya
Kimura Kazuhisa
Murata Hiroshi
Takagi Osamu
Foley & Lardner
Grainger Quana M.
Kabushiki Kaisha Toshiba
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