Electrophotography – Image formation – Development
Reexamination Certificate
2002-10-16
2004-07-13
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Development
Reexamination Certificate
active
06763213
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Patent Application No. 2002-6752, filed Feb. 6, 2002, in the Korean Industrial 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 forming a color image, and more particularly, to an apparatus for forming a color image using electrophotograpy, reducing a shock occurring when a developing roller contacts a photosensitive drum, and having a developing unit capable of reducing a pressure difference between the developing roller and the photosensitive drum.
2. Description of the Related Art
In an apparatus for forming a color image using electrophotography, such as a digital copying machine, a color laser printer or the like, a predetermined electrostatic latent image is formed on a photosensitive body. Then, the electrostatic latent image is developed with toner, and the developed image is transferred onto paper via a predetermined transfer medium. Thereafter, the transferred image is heated and pressed, thereby being permanently fused on the paper.
Referring to
FIG. 1
, the apparatus for forming the color image using electrophotography includes a photosensitive drum
10
as a photosensitive body, a charger
11
charging the photosensitive drum
10
, a laser scanning unit (LSU)
12
radiating light onto the charged photosensitive drum
10
and forming a predetermined electrostatic latent image, developing units
13
developing the electrostatic latent image with the toner having four colors, such as yellow (Y), magenta (M), cyan (C), and black (K), a transfer belt
14
on which each developed image having one of the four colors is sequentially overlapped, a first transfer roller
14
a
transferring the developed image from the photosensitive drum
10
onto the transfer belt
14
, a second transfer roller
14
b
transferring the transfer image having four colors overlapped on the transfer belt
14
onto paper, and a fusing unit
15
heating and pressing the paper and permanently fusing the transferred image on the paper.
Four developing units
13
-Y,
13
-M,
13
-C, and
13
-K are elastically biased by corresponding springs (not shown) to be apart from the photosensitive drum
10
and selectively move toward the photosensitive drum
10
according to a rotation of cams
13
b
. A developing roller
13
a
is disposed on a front end of the developing units to contact the photosensitive drum
10
. The apparatus includes a paper cassette
16
, a blade
17
cleaning the photosensitive drum
10
, an eraser
18
, and a transfer path
19
in which paper is exhausted.
In the apparatus for forming the color image using electrophotography shown in
FIG. 1
, the color image is formed as follows. First, the photosensitive drum
10
is charged by the charger
11
, light is radiated on the photosensitive drum
10
by the LSU
12
, and then, an electrostatic latent image of the color image to be developed with a first color is formed in a predetermined region of the photosensitive drum
10
. For example, if a yellow image having a yellow color is developed first, as shown in
FIG. 2
, a developing unit
13
-Y having the yellow color accesses the photosensitive drum
10
by the rotation of a corresponding cam
13
b
-Y, and thus the electrostatic latent image formed on the photosensitive drum
10
is developed with a yellow toner.
FIG. 3
is an enlarged view of the photosensitive drum
10
and a developing roller
13
a
-Y of the developing unit
13
-Y in a development operation. Referring to
FIG. 3
, when a predetermined force is applied to a leaf spring
13
c
placed at a rear side of the developing unit
13
-Y by a rotation of the cams
13
b
, the leaf spring
13
c
is displaced by a predetermined distance ▾X, a force is transferred to the developing unit
13
-Y, and thus the developing roller
13
a
-Y contacts the photosensitive drum
10
. Toner T stained on an outer circumference of the developing roller
13
a
-Y is transferred by this contact to the electrostatic latent image of the photosensitive drum
10
contacting the developing roller
13
a
-Y In this case, in order to increase an amount of a toner per area stained on the photosensitive drum
10
, the developing roller
13
a
-Y rotates at an angular velocity larger than that of the photosensitive drum
10
. The developed yellow image is transferred onto the transfer belt
14
through a first transfer nib N
1
as shown in FIG.
1
.
Subsequently, another electrostatic latent image for a second color is formed by charging and exposing the photosensitive drum
10
. If a second color is magenta, as shown in
FIG. 4
, a developing unit
13
-M having a magenta color accesses the photosensitive drum
10
, thereby forming the electrostatic latent image. The developed magenta image is overlapped with the developed yellow image and transferred on the transfer belt
14
on which the yellow image was transferred. In the same way, another image having a cyan color as a third color, and another image having a black color as a fourth color are developed and transferred, thereby forming the color image having a desired color on the transfer belt
14
. After that, the color image is transferred onto the paper supplied to a second transfer nib N
2
between the transfer belt
14
and the second transfer roller
14
b
and is heated and pressed through the fusing unit
15
and is permanently fused on the paper.
Likewise, since the electrostatic latent image formed on the photosensitive drum
10
is developed while the four developing units
13
-Y,
13
-M,
13
-C, and
13
-K sequentially or selectively contact and/or separate from the photosensitive drum
10
, shock may be applied to the photosensitive drum
10
whenever the developing rollers
13
a
of the developing units
13
-Y,
13
-M,
13
-C, and
13
-K collide with the photosensitive drum
10
. In this case, jitter of the developed image may occur at the time of collision of the developing units
13
-Y,
13
-M,
13
-C, and
13
-K and the photosensitive drum
10
.
An angular velocity of the developing rollers
13
a
of the four developing units
13
-Y,
13
-M,
13
-C, and
13
-K is larger than that of the photosensitive drum
10
. Due to this angular velocity difference, a shock applied to the photosensitive drum
10
increases when the developing roller
13
a
contacts the photosensitive drum
10
to develop the electrostatic latent image. In general, a photosensitive layer is coated on an aluminum material to form the photosensitive drum
10
, and the developing roller
13
a
formed of a rubber material has a predetermined hardness. Thus, if a hardness of the rubber material is reduced, the shock due to the contact may be slightly reduced.
However, an angular velocity difference is set such that toner T is supplied from the developing roller
13
a
to the photosensitive drum
10
. When the developing roller
13
a
contacts the photosensitive drum
10
, the developing units
13
-Y,
13
-M,
13
-C, and
13
-K are instantaneously pushed against the photosensitive drum
10
, registration defects where overlapped layers of developed images of the colors are dislocated, and the jitter occurs. As a result, a resolution of the color image deteriorates. In addition, due to the contact shock, the toner T is scattered in the apparatus, and thus peripheral devices of the apparatus may be contaminated. Problems caused by the angular velocity difference may occur whenever the developing roller
13
a
contacts the photosensitive drum
10
and is separated from the photosensitive drum
10
. These problems can be slightly reduced by limiting the angular velocity of the developing roller
13
a
. However, if the angular velocity of the developing roller
13
a
is too small, the toner T is not sufficiently supplied to the photosensitive drum
10
to develop the latent electrostatic image, and thus a quality of the color image deteriorates.
As mentioned above, since the photosensitive drum
10
is a rigid
Chen Sophia S.
Staas & Halsey , LLP
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