Electrophotography – Image formation – Development
Reexamination Certificate
2003-02-26
2004-10-19
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Development
C399S088000, C399S090000
Reexamination Certificate
active
06807394
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the priority of Korean Patent Application No. 2002-32525, filed Jun. 11, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for connecting and disconnecting a developing bias power supply and, more particularly, to an apparatus for connecting and disconnecting a developing bias power supply in an image forming system in which a developing unit is spaced apart from a photosensitive body by a predetermined distance.
2. Description of the Related Art
In general, an electrophotographic printer such as a color laser printer, has an image forming apparatus, which forms an electrostatic latent image on a photosensitive body, develops the electrostatic latent image with toner using a developing unit, transfers the developed image onto paper via a transfer body, heats and pressurizes the paper, and completely fixes the transferred image on the paper.
FIG. 1
shows an example of an image forming system for such an electrophotographic printer.
The image forming system includes a photosensitive drum
10
as a photosensitive body; a charger
11
which charges the surface of the photosensitive drum
10
at a predetermined potential; a laser scanning unit (LSU)
12
as an exposing unit, which radiates light onto the charged photosensitive drum
10
and forms an electrostatic latent image; a developing unit
13
which develops the electrostatic latent image with toner having four colors such as yellow (Y), magenta (M), cyan (C), and black (K) into a predetermined toner image; a transfer belt
14
which sequentially overlaps the toner image having four colors developed on the photosensitive drum
10
; a first transfer roller
14
a
which transfers the image developed on the photosensitive drum
10
onto the transfer belt
14
; a second transfer roller
14
b
which transfers the image having four colors overlapped on the transfer belt
14
onto a piece of paper; and a fusing unit
15
which heats the paper at a predetermined temperature, pressurizes the paper and fixes the transferred image on the paper. Four developers
13
-Y,
13
-M,
13
-C, and
13
-K are provided in the developing unit
13
. The four developers
13
-Y,
13
-M,
13
-C, and
13
-K are elastically biased in a direction that is spaced apart from the photosensitive drum
10
by a predetermined gap, selectively move toward the photosensitive drum
10
by rotation of cams
13
b
-Y,
13
b
-M,
13
b
-C and
13
b
-K, respectively, and allow developing rollers
13
a
-Y,
13
a
-M,
13
a
-C, and
13
a
-K, respectively, provided at a front end of the developer to contact the photosensitive drum
10
. Reference numerals
16
,
17
,
18
, and
19
denote a paper cassette, a photosensitive drum cleaning blade, an eraser, and a paper ejecting route, respectively.
In the above structure, an image forming process will be performed as described below.
If the photosensitive drum
10
is charged by the charger
11
, the LSU
12
radiates light onto the photosensitive drum
10
, thereby forming an electrostatic latent image of an image to be developed as a first color. For example, if an image of yellow color is first developed, the developer
13
-Y of yellow color accesses the photosensitive drum
10
through being driven by a corresponding cam
13
b
-Y, thereby developing the electrostatic latent image formed on the photosensitive drum
10
with toner of yellow color, as shown in FIG.
2
. Toner T on the outer surface of a developing roller
13
a
-Y is transferred to a portion of the electrostatic latent image of the photosensitive drum
10
that contacts the developing roller
13
a
-Y. A yellow image developed in the above manner is transferred onto the transfer belt
14
via a first transfer nip N
1
(FIG.
1
). Subsequently, a second color electrostatic latent image is formed by charging and exposing the photosensitive drum
10
. If a second color is magenta, the developer
13
-M of magenta color accesses the photosensitive drum
10
, thereby developing an electrostatic latent image. A magenta image developed in this way is superimposed onto the photosensitive drum
10
and transferred onto the transfer belt
14
onto which the yellow image has been transferred. Similarly, a third image of cyan color and a fourth image of black color are developed and transferred, thereby a desired color image is finally formed on the transfer belt
14
. Subsequently, the completed color image is transferred onto the paper fed to a second transfer nip N
2
between the transfer belt
14
and the second transfer roller
14
b
, is heated and pressured by the fusing unit
15
, and is completely fixed on the paper.
However, in the above structure, the four-color developers
13
-Y,
13
-M,
13
-C, and
13
-K of the developing unit
13
alternately contact with and separate from the photosensitive drum
10
to develop images. Thus, whenever the developing rollers
13
a
-Y,
13
a
-M,
13
a
-C and
13
a
-K of the developers
13
-Y,
13
-M,
13
-C, and
13
-K, respectively, collide with the photosensitive drum
10
, the collision may shock the photosensitive drum
10
, causing a jitter error in which an image jitters.
Accordingly, to fundamentally solve problems of the development method, it is preferable to employ a developing unit for performing a development step, in which the developers
13
-Y,
13
-M,
13
-C, and
13
-Y are secured to be spaced apart from the photosensitive drum
10
by a predetermined gap. An example thereof is shown in FIG.
3
. In the description of
FIG. 3
, reference numerals which are the same as reference numerals used in
FIG. 1
refer to the same elements as those in
FIG. 1
, and further descriptions thereof will be omitted.
Referring to
FIG. 3
, an image forming system does not include a cam which mechanically contacts each of developers
20
-Y,
20
-M,
20
-C, and
20
-K to the photosensitive drum
10
, and the developers
20
-Y,
20
-M,
20
-C, and
20
-K are spaced apart from the photosensitive drum
10
by a predetermined gap. A respective toner-supplying roller, a respective seal blade, a respective doctor blade and a respective developing roller (
21
a
-Y,
21
a
-M,
21
a
-C and
21
a
-K) are provided in each of the developers
20
-Y,
20
-M,
20
-C, and
20
-K. A plurality of switches (not shown) and a connection circuit are used in each of the developers
20
-Y,
20
-M,
20
-C, and
20
-K to connect a high voltage power supply to the respective developing rollers
21
a
-Y,
21
a
-M,
21
a
-C and
21
a
-K, the corresponding toner-supplying roller, and the corresponding doctor blade when the developers
20
-Y,
20
-M,
20
-C, and
20
-K are used, and to disconnect the high voltage power supply from the developing rollers
21
a
-Y,
21
a
-M,
21
a
-C and
21
a
-K, the toner-supplying rollers, and the doctor blades when the developers
20
-Y,
20
-M,
20
-C, and
20
-K are not used. Hence, the structure of each developer becomes complicated.
SUMMARY OF THE INVENTION
The present invention provides an apparatus for connecting and disconnecting a developing bias power supply that supplies a high voltage to each developer of an image forming system in which the developers are secured to be spaced apart from a photosensitive drum by a predetermined gap.
According to one aspect of the present invention, there is provided an apparatus for connecting and disconnecting a developing bias power supply in an image forming system, which operates a plurality of developers in sequence and develops an electrostatic latent image formed on a photosensitive body in a predetermined color. The apparatus comprises a plurality of electro-magnetic clutches, each clutch being provided to correspond to a respective developer to connect and disconnect driving of the respective developer. A deceleration gear assembly, which is rotated according to the rotation of a gear of the respective developer connected to the respective electro-magne
Chen Sophia S.
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
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