Electrophotography – Image formation – Development
Reexamination Certificate
2002-12-16
2004-02-17
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Development
Reexamination Certificate
active
06694118
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Patent Application No. 2002-1381, filed Jan. 10, 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 a developing apparatus of an electrophotographic printer, and more particularly, to a developing apparatus having a structure of attaching/detaching a developing roller to/from a photoreceptive drum.
2. Description of the Related Art
In general, an electrophotographic printer, such as a color laser printer, includes an image forming apparatus which forms an electrostatic latent image on a photoreceptor and develops the electrostatic latent image using toner. The developed image is transferred to a predetermined transfer medium and retransferred to a sheet of paper therefrom. The transferred image of the paper is heated and pressed to be completely fixed on the paper.
FIG. 1
shows a conventional electrophotographic printer. Referring to
FIG. 1
, the conventional electrophotographic printer includes a photoreceptive drum
100
which is a photoreceptor, a charger
111
charging the photoreceptive drum
100
, an LSU (laser scanning unit)
112
, as an exposure unit, scanning a light beam onto the charged photoreceptive drum
100
to form an electrostatic latent image, a developing unit
113
developing the electrostatic latent image by using toner of four colors: yellow (Y), magenta (M), cyan (C), and black (K), a transfer belt
114
sequentially receiving the four colored images developed on the photoreceptive drum
100
to overlap one another, a first transfer roller
114
a
transferring the developed images formed on the photoreceptive drum
100
to the transfer belt
114
, a second transfer roller
114
b
transferring the image of four overlapping colors on the transfer belt
114
to a sheet of paper, and a fusing unit
115
fusing the transferred image by heating and pressing the paper. The conventional electrophotographic printer further includes a paper cassette
116
containing sheets of paper, a cleaning unit
117
cleaning a surface of the photoreceptive drum
100
, a discharger
118
, and a transfer path
119
along which the paper is exhausted.
In the above structure, the image of four overlapping colors is formed as follows. First, when the photoreceptive drum
100
is charged by the charger
111
to a predetermined electric potential, the LSU
112
scans the light beam to form an electrostatic latent image of a first color to be developed with first color toner. A developing unit of the first color first accesses toward the surface of the photoreceptive drum
100
to develop the electrostatic latent image of the first color. For example, if a yellow color is to be developed first as shown in
FIG. 2A
, a yellow color developing unit
113
-Y accesses the photoreceptive drum
100
to develop the electrostatic latent image formed on the photoreceptive drum
100
using yellow color toner. Here, remaining developing units of other colors maintain a particular gap with the photoreceptive drum
100
to be separated from the surface of the photoreceptive drum
100
. The developed yellow image is transferred to the transfer belt
114
. When the development of the yellow color is complete, the yellow color developing unit
113
-Y retreats from the photoreceptive drum
100
.
Next, the electric potential supplied to the photoreceptive drum
100
is removed from the photoreceptive drum
100
by the discharger
118
. Then, another electrostatic latent image of a second color is formed on the photoreceptive drum
100
by charging and exposing of the photoreceptive drum
100
. For example, if the second color to be developed is magenta as shown in
FIG. 2B
, a magenta color developing unit
113
-M accesses the photoreceptive drum
100
to develop the electrostatic latent image using magenta color toner. The developed magenta image is transferred to the transfer belt
114
to which the yellow image has been previously transferred, and thus overlaps the yellow image. Third and fourth colors, for example, cyan and black, are developed in the same manner while each developing unit repeats access and retreat movements with respect to the photoreceptive drum
100
.
FIG. 3
shows a structure of a conventional developing apparatus of the electrophotographic printer. Here, although a description is limited to the yellow color developing unit
113
-Y, it can be equally applied to the other color developing units. The yellow color developing unit
113
-Y includes a housing
121
containing toner
120
, a developing roller
122
having the toner
120
adhering to the surface thereof and developing an electrostatic latent image of the yellow color formed on the photoreceptive drum
100
with the toner
120
, and a supply roller
124
cleaning a surface of the developing roller
122
and supplying the toner
120
to the developing roller
122
. A cam
125
and a shock prevention plate
127
are disposed on a rear side of the housing
121
to control the housing
121
to access toward the photoreceptive drum
100
. The developing apparatus includes a doctor blade
128
to allow the toner
120
to adhere to the surface of the developing roller
122
with a uniform thickness.
The yellow color developing unit
113
-Y accesses or retreats with respect to the photoreceptive drum
100
by an operation of the cam
125
. In doing so, during one turn of the photoreceptive drum
100
, a developing roller of a color to be developed contacts the surface of the photoreceptive drum
100
while developing rollers of the other colors are maintained to be separated therefrom. The yellow color developing unit
113
-Y retreats from the photoreceptive drum
100
by a rotation of the cam
125
after the development of the yellow color is completed. Then, another color developing unit of a subsequent color accesses the photoreceptive drum
100
.
Consequently, all colors are completely developed through the above development processes, and a desired color image is finally formed on the transfer belt
114
. Here, in order to transfer the respective color images onto the transfer belt
114
to overlap one another, the photoreceptive drum
100
and the transfer belt
114
need to be matched in rotation period, and the photoreceptive drum
100
and the transfer belt
114
rotate one time for each color. Then, the desired color image completely formed through the above development processes is transferred to the sheet of paper supplied between the transfer belt
114
and the second transfer roller
114
b
. While passing through the fusing unit
115
, the paper is heated and pressed so that the color image is completely fixed to the paper. The paper is exhausted along the transfer path
119
.
However, since the photoreceptive drum
100
is cylindrical, when the developing units
113
-Y,
113
-M,
113
-C, and
113
-K for yellow, magenta, cyan, and black colors, respectively contact the photoreceptive drum
100
in the development processes, contact angles between the photoreceptive drum
100
and the respective developing rollers
122
are different. Thus, since a direction of a force received from a contact portion of each developing unit against the photoreceptive drum
100
is different from that of other developing units, a constant pressure and position is not maintained during performing the development processes. Also, the developing roller
122
cannot stably contact the photoreceptive drum
100
in response to a linear movement of the developing unit
113
by the cam
125
. Further, apparatuses for driving the cam
125
are additionally installed in the conventional developing apparatus. In a case of the printer shown in
FIG. 1
, since the paper transfer path
119
is complicatedly located in a rear side of the developing unit
113
, it is difficult to secure a space for the additional apparatuses in the conventional electrophotographic printer.
SUMMARY OF THE INVENTION
To solve the above
Gleitz Ryan
Grimley Arthur T.
Samsung Electronics Co,. Ltd.
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