Electrophotography – Control of electrophotography process – Responsive to copy media characteristic
Reexamination Certificate
2000-01-31
2001-04-17
Pendegrass, Joan (Department: 2852)
Electrophotography
Control of electrophotography process
Responsive to copy media characteristic
C399S069000, C399S389000
Reexamination Certificate
active
06219498
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine and a laser printer, and particularly to an image forming apparatus which transfers a color toner image formed on a photoreceptor at once onto a recording medium such as paper via an intermediate transfer medium.
BACKGROUND OF THE INVENTION
Conventionally, a variety of image forming apparatuses such as a copying machine have been proposed. Such image forming apparatuses are roughly divided into two types by a difference in transfer system of a color toner image onto a recording medium. One is an image forming apparatus adopting a so-called direct transfer system in which a recording medium is held by being wrapped around a transfer medium, and a toner image on a photoreceptor is directly transferred onto the recording medium color by color. The other is an image forming apparatus in which a color toner image formed on a photoreceptor is transferred at once onto an intermediate transfer medium, and thereafter transferred onto a recording medium from the intermediate transfer medium.
However, in the former image forming apparatus, there is a case where a desired color image cannot be obtained depending on the type of a recording medium used. This is because of the fact that the transfer characteristics of the toner image are different for different colors depending on the type (especially thickness) of the recording medium used. As a result, in a color toner image composed of overlapping toner images of different colors, the coloring differs among recording media. Thus, in order to obtain a desired color image in this image forming apparatus, it is required to limit the range of thickness, etc., of the recording medium used.
However, in recent years, a demand for color copying for a recording medium of various thicknesses and various paper types has come to a level which cannot be met by the described image forming apparatus. Further, in the above image forming apparatus, because the toner image is transferred to the recording medium color by color, the overlapping accuracy of the toner images is always a problem. However, it has come to a level where the overlapping accuracy cannot be improved any further.
Therefore, it now has been a focus of ongoing research to develop an image forming apparatus provided with an intermediate transfer medium, which is capable of color copying regardless of the type of a recording medium used. As an example of such an image forming apparatus, the image forming apparatus as disclosed in Japanese Unexamined Patent Publication No. 251864/1991 (Tokukaihei 3-251864) is described below. In this image forming apparatus, a copying process is carried out for each of a high density portion and a low density portion of a single document image. As a result, a color toner image obtained by a single copying process is overlapped with another color toner image on the intermediate transfer medium, thus forming a single color toner image.
The above image forming apparatus as a copying machine as disclosed in the above publication is provided with, as shown in
FIG. 27
, a transparent document plate
101
on an upper surface. Below the document plate
101
is provided an exposure optical system
103
for exposing and scanning a document
102
and exposing a photoreceptor
104
(mentioned later).
The exposure optical system
103
is provided with a light source lamp
103
a
for projecting light onto the document
102
placed on the document plate
101
, a plurality of reflecting mirrors
103
b
through
103
f
for guiding, as shown by the alternate short and long line in
FIG. 27
, the reflected light off the document
102
onto the photoreceptor
104
, a focus lens
103
g
provided in the path of the reflected light, and a color separating filter composed of color filters of three primary colors of red, green, and blue.
Underneath the exposure optical system
103
is provided the photoreceptor
104
having a belt shape. The photoreceptor
104
is suspended between two rollers
105
and
106
, which are placed with a certain gap therebetween, and the photoreceptor
104
is rotatably driven by a motor (not shown).
Around the photoreceptor
104
on the roller
106
side are provided, along with other members, a static charger
107
for charging the photoreceptor
104
, a cleaning device
108
for removing toner remaining on the photoreceptor
104
, and a screen filter
109
for splitting the reflected light off the document
102
into rays.
On the upper side of the photoreceptor
104
is provided a developing device
113
having three developer tanks
110
through
112
without contacting the photoreceptor
104
. The developer tanks
110
through
112
store color developers of yellow, magenta, and cyan, respectively, which are complementary colors of the three primary colors of the color filters of the color separating filter
103
h
. The developer tanks
110
through
112
are provided with magnet rollers
110
a
through
112
a
, respectively, which give the respective color developers to the photoreceptor
104
.
Below the photoreceptor
104
are provided sheet feeding cassettes
114
and
115
on top of the other having different sizes for feeding a recording sheet
130
as a recording medium. On the discharge sides of the sheet feeding cassettes
114
and
115
, sheet feeding rollers
116
and
117
are provided, respectively. In front of the sheet feeding cassettes
114
and
115
are provided timing rollers
118
for temporarily stopping the recording sheet
130
so that the recording sheet
130
is supplied at a predetermined timing.
On the roller
105
side of the photoreceptor
104
is provided an intermediate transfer device
119
. The intermediate transfer device
119
is composed of, along with other members, the intermediate transfer medium
120
having a belt shape, three rollers
121
through
123
for rotatably driving the intermediate transfer medium
120
, a transfer charger
124
for transferring a toner image of each color component on the photoreceptor
104
onto the intermediate transfer medium
120
, a transfer charger
125
for transferring a color toner image formed on the intermediate transfer medium
120
onto the recording sheet
130
, a separating charger
126
for separating the recording sheet
130
from the intermediate transfer medium
120
, and the cleaning device
127
for removing toner remaining on the intermediate transfer medium
120
.
In the discharge direction of the intermediate transfer medium
120
are provided a transport belt
128
for transporting the recording sheet
130
and a fixing device
129
for fixing the color toner image onto the recording sheet
130
.
When carrying out full-color copying in the described arrangement, first, the screen filter
109
is set aside from the exposure path and the exposure is started with respect to a high density portion.
Specifically, the light source lamp
103
a
projects light onto the document
102
placed on the document plate
101
so as to carry out optical-scan three times. The reflected light off the document
102
is incident on the color separating filter
103
h
via the reflecting mirrors
103
b
through
103
d
and the focus lens
103
g
, and is separated into color components by the color separating filter
103
h
. The reflected light separated into color components is then successively projected, via the reflecting mirrors
103
e
and
103
f
, onto the photoreceptor
104
, which has been uniformly charged by the static charger
107
, so as to expose the photoreceptor
104
. As a result, an electrostatic latent image of each color component, corresponding to the document image is formed on the photoreceptor
104
.
The electrostatic latent image of each color is made visible by being developed by the corresponding developers of yellow, magenta, and cyan of the developing device
113
, which are complementary colors of the three primary colors of the color filters of the color separating filter
103
h
, and the electrostatic latent image becomes a toner image.
Katoh Atsuyuki
Kinoshita Yoshiya
Sugimura Kenji
Tachiki Hiroshi
Tsuji Masaru
Pendegrass Joan
Sharp Kabushiki Kaisha
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