Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-03-01
2001-08-21
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Transfer
C318S085000, C347S116000
Reexamination Certificate
active
06278857
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a color image forming apparatus for controlling registration in sub-scanning direction of an image formed on each photosensitive drum by scanning a plurality of photosensitive drums individually by a plurality of laser scanning units.
BACKGROUND OF THE INVENTION
In a conventional image forming apparatus of electrophotographic type, a uniform electric charge of about 1 millicoulomb per square centimeter is applied on the surface of a photosensitive drum. This photosensitive drum is exposed depending on the image information, and the electric charge of the irradiated portion is released to the photosensitive drum substrate, and an image (electrostatic latent image) is formed as a result of distribution of electric charge. This electrostatic latent image is developed by coloring charged particles (toner particles), and a powder image is formed (toner development). The powder image is transferred onto a sheet material or the like. The transferred powder image is fused and fixed by heat or other energy, and formed as an image.
Recently, on the other hand, the image by the image forming apparatus of electrophotographic type is becoming colorful. As the color image forming apparatus, a color image forming apparatus of tandem engine type is proposed. This color image forming apparatus includes a plurality of image forming stations having photosensitive drums. The plurality of image forming stations are image forming stations for forming cyan image, magenta image, yellow image, and, preferably, black image on each photosensitive drum. The powder image formed on each photosensitive drum is overlaid on an intermediate transfer material at transfer position of each color powder image, and transferred and synthesized. In the color image forming apparatus of tandem engine type, the image can be formed at high speed because each image is formed parallel in each color.
In the case of such color image forming apparatus, each powder image formed in a different image forming station may be deviated in position due to positioning error between image forming stations, resulting in color deviation. To develop a color image forming apparatus of high quality, such color deviation is a serious problem, and the technique for correcting color deviation (registration) is required.
In the first place, a reference pattern for detecting color deviation (hereinafter called registration pattern) is drawn. The registration pattern is detected by a plurality of sensors (color deviation detection), and the deviation amount is detected from this result. On the basis of the calculated deviation amount, each image is positioned (color deviation correction).
The operation and color deviation detection of the conventional color image forming apparatus are described below.
FIG. 10
is a structural diagram showing a general color image forming apparatus,
FIG. 11
is a structural diagram showing a color deviation detector,
FIG. 12
is a layout diagram showing configuration of registration pattern and color deviation detector on an intermediate transfer material, and
FIG. 13
is a block diagram showing a conventional drive unit.
First, the configuration in
FIG. 10
is explained. The image forming apparatus has four image stations
21
k
,
21
y
,
21
m
,
21
c
. The image stations
21
k
,
21
y
,
21
m
,
21
c
have photosensitive drums
22
k
,
22
y
,
22
m
,
22
c
, respectively.
Around the circumference of the photosensitive drums
22
k
,
22
y
,
22
m
,
22
c
, the following components are disposed:
a) chargers
23
k
,
23
y
,
23
m
,
23
c,
b) exposure units
26
k
,
26
y
,
26
m
,
26
c
of scanning optical system for irradiating the photosensitive drums
22
k
,
22
y
,
22
m
,
22
c
with laser beams
29
k
,
29
y
,
29
m
,
29
c
depending on the image information,
c) developing units
24
k
,
24
y
,
24
m
,
24
c
,
d) transfer units
28
k
,
28
y
,
28
m
,
28
c
in a transfer section
27
, and
e) cleaning units
25
k
,
25
y
,
25
m
,
25
c.
Herein, the image stations
21
k
,
21
y
,
21
m
, and
21
c
are the units for forming black image, yellow image, magenta image, and cyan image, respectively. On the other hand, so as to pass through the image stations
21
k
,
21
y
,
21
m
, and
21
c
, an intermediate transfer belt
32
is disposed beneath the photosensitive drums
22
k
,
22
y
,
22
m
,
22
c
, and moves in the direction of arrow A.
In the conventional color image forming apparatus having such constitution, the image forming operation is as follows.
First, at the image forming station
21
k
, the surface of the photosensitive drum
22
k
is uniformly charged with an electrostatic charge by the charger
23
k.
Then, an electrostatic latent image corresponding to image information of black component is formed on the photosensitive drum
22
k
by means of the exposure unit
26
k.
This electrostatic latent image is developed on the photosensitive drum
22
k
as a powder image by black toner particles by the developing unit
24
k.
This powder image is transferred on the intermediate transfer belt
32
as a black toner image by the transfer unit
28
k.
The surface of the photosensitive drum
22
k
after transfer process is cleaned by the cleaning unit
25
k
, and residual toner particles are removed to be ready for next image formation.
On the other hand, parallel to the timing of formation of the black toner image, at the image forming station
21
y
, the surface of the photosensitive drum
22
y
is uniformly charged with an electrostatic charge by the charger
23
y
, and an electrostatic latent image corresponding to the image information of yellow component is formed on the photosensitive drum
22
y
by the exposure unit
26
y.
This electrostatic latent image is developed on the photosensitive drum
22
y
as a powder image by yellow toner particles by the developing unit
24
y
, and it is laid over the black toner image formed on the intermediate transfer belt
32
, and formed as a synthetic toner image.
Similarly, thereafter, a magenta toner image is overlaid by the image forming station
21
m
, and a cyan toner image by the image forming station
21
c
sequentially on the intermediate transfer belt
32
. In this way, the synthetic toner image is formed by overlaying four color toner images on the intermediate transfer belt
32
.
After the transfer process, the photosensitive drums
22
k
,
22
y
,
22
m
,
22
c
are cleaned by the cleaning units
25
k
,
25
y
,
25
m
,
25
c
, and residual toner particles are removed to be ready for next image formation, and the printing operation is finished.
After completion of formation of the synthetic toner image, a sheet material
35
of paper or the like is supplied in between the intermediate transfer belt
32
and a transfer roller
37
from a paper feed cassette
34
through a paper feed roller
36
. The transfer roller
37
is disposed at a position contacting with the intermediate transfer belt
32
for inserting the sheet material
35
between it and the intermediate transfer belt
32
. When the sheet material
35
is supplied, the synthetic toner image is transferred on the sheet material
35
. Then, after being heated and fixed by a fixing unit
38
, a color image is formed on the sheet material
35
.
As shown in
FIG. 13
, the drive unit is controlled depending on a control signal from a control unit
50
such as CPU for controlling the operation of the entire apparatus, and a motor rotation controller
51
starts a drive motor
52
, and controls its rotating speed. A drive transmission unit
53
transmits the drive force to a rotation moving unit
54
by gear or the like from a rotary shaft of the drive motor
52
. By this driving force, the rotation moving unit
54
including the photosensitive drums
22
k
,
22
y
,
22
m
,
22
c
, intermediate transfer belt
32
, heating roller
38
a
in the fixing unit
38
, and others is rotated and driven.
As the drive motor
52
, when a known stepping motor (not shown) is used, the motor rotation controller
51
controls the rotating speed by issuing
Kajiwara Tadayuki
Maeda Takami
Monji Yosuke
Nakamura Kazunori
Matsushita Electric - Industrial Co., Ltd.
Pendegrass Joan
Ratner & Prestia
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