Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-06-12
2002-10-08
Beatty, Robert (Department: 2852)
Electrophotography
Image formation
Transfer
Reexamination Certificate
active
06463247
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image formation apparatus capable of forming a synthetic image by superimposing image informations, using electrophotography or the like.
2. Description of the Related Art
In a conventional image formation apparatus using electrophotography, an electrophotographic photosensitive member, serving as an image-carrying member, is charged by a static charger, and light is applied to this photosensitive member in accordance with image information to form a latent image, and this latent image is developed by a developing device to form a toner image, and the formed toner image is transferred to a sheet or the like, thus forming the image.
On the other hand, with the advent of color images, there has been proposed an image formation apparatus of the tandem type in which a plurality of image-carrying members are provided, each of which is for effecting such an image-forming process, and color images, that is, a cyan image, a magenta image, a yellow image and preferably a black image, are formed on the respective image-carrying members, and these color images are transferred at respective transfer positions of the image-carrying members to a sheet in a superimposed manner, thereby forming a full-color image.
Such an image formation apparatus of the tandem type, because of the plurality of image-forming portions for forming the color images, is advantageous for a high-speed operation. What is important is to satisfactorily effect the registration in position of the color images formed by the different image-forming portions.
The reason is that a misregistration of the four color images, transferred to the sheet, results in a color drift or a variation in color tone.
FIG. 8
shows a conventional image formation apparatus using four photosensitive drums.
As shown in
FIG. 8
, the image formation apparatus comprises the photosensitive drums (photosensitive members)
51
for respectively forming toner images of four colors, for example, black (K), yellow (Y), magenta (M) and cyan (C), which drums serve as image-carrying members, and toner image-forming members
3
for forming the toner images on the surfaces of the photosensitive drums
51
, respectively.
The toner image-forming member
3
comprises a charger
11
for charging the surface of the photosensitive drum
51
with electricity, an exposure device
12
for forming an electrostatic latent image, corresponding to specified color image data, on the charged photosensitive drum
51
, a developing device
13
for developing the electrostatic latent image, a first transfer roller
21
, which has an elastic material, e.g. an electrically-conductive urethane sponge, formed on a surface thereof, and urges an intermediate transfer belt
52
toward the photosensitive drum
51
so as to transfer the toner image, developed on the surface of the photosensitive drum
51
, to the intermediate transfer belt
52
, and a cleaner
14
for removing the residual toner remaining on the photosensitive drum
51
after the transfer of the toner image to the intermediate transfer belt
52
.
The intermediate transfer belt
52
, arranged along the plurality of photosensitive drums
51
, are supported by a drive roller
20
, a driven roller
22
and a tension roller
28
, and is revolved in a direction of arrow A. An intermediate transfer belt cleaner
27
for removing the residual toner, remaining on the surface of the intermediate transfer belt
52
, is provided adjacent to this belt
52
. A color drift sensor
29
for detecting the amount of a color misregistration or drift of the toner images on the intermediate transfer belt
52
is provided adjacent to the intermediate transfer belt
52
.
A paper cassette
15
, storing printing paper
7
, is provided at a lower portion of the apparatus, and the printing paper sheets
7
are fed one by one into a path of feed of the paper by a feed roller
16
.
Resist rollers
17
for controlling the transfer timing for the printing paper
7
, a second transfer roller
10
for transferring the color image, formed on the intermediate transfer belt
52
, to the printing paper
7
, and a fixing device
40
for fixing the transferred color image to the printing paper
7
by a fixing roller
18
and a pressure roller
19
are provided in the paper feed path.
In the image formation apparatus of this construction, for example, a latent image of a black color component of image information is first formed on the photosensitive drum
51
corresponding to the black color. This latent image is formed into a visible image, serving as a black toner image, by the developing device
13
, and this black toner image is transferred onto the intermediate transfer belt
52
by the first transfer roller
21
.
During this operation, a latent image of a cyan color component of the image information is formed on the photosensitive drum
51
corresponding to the cyan color, and this latent image is developed as a cyan toner image by the developing device
13
, using a cyan toner. Then, the cyan toner image is transferred by the first transfer roller
21
onto the intermediate transfer belt
52
, to which the black toner image has already been transferred, in superimposed relation to this black toner image.
Subsequently, a magenta toner image and a yellow toner image are formed in the same manner as described above, and thus the toner images of the four colors are superimposed together on the intermediate transfer belt
52
.
On the other hand, the printing paper
7
is fed from the paper cassette
15
by the feed roller
16
, and the toner images of the four colors are transferred at a time onto the printing paper
7
, controlled in transfer timing by the resist rollers
17
, by the second transfer roller
10
. The thus transferred toner images are heated and fixed to the printing paper
7
by the fixing roller
18
and the pressure roller
19
, so that a full-color image is formed on this printing paper
7
.
The residual toner is removed from each of the photosensitive drums
51
by the cleaner
14
after the transfer of the toner image therefrom is finished.
In the above conventional construction, each transfer roller
21
is rotatably supported beneath the corresponding photosensitive drum
51
, with the intermediate transfer belt
52
held therebetween. The outer diameter of the transfer roller
21
, defined by the outer peripheral surface thereof, changes with the lapse of time, so that the force of pressing of the intermediate transfer belt
52
against the transfer roller
21
gradually decreases. Therefore, taking this into consideration, the force of pressing of the transfer roller
21
against the intermediate transfer belt
52
has beforehand been set to a little higher value.
And besides, the toner image is transferred from each photosensitive drum
51
to the intermediate transfer belt
52
, and therefore the intermediate transfer belt
52
and the photosensitive drum
51
stand in contact with each other while maintaining the surface potential of the photosensitive drum
51
.
Furthermore, the intermediate transfer belt
52
is pressed into the surface of each photosensitive drum
51
by the elastic force of the elastic material formed on the surface of the first transfer roller
21
.
Furthermore, because of manufacturing errors such as a variation in the outer diameter and the eccentricity of the rotation axis, the peripheral speed of the photosensitive drum
51
deviates from the predetermined speed, so that the speed difference develops between the photosensitive drum
51
and the intermediate transfer belt
52
.
Because of these factors, a dip or sag due to an electrical attracting force develops in the intermediate transfer belt
52
between any two adjacent photosensitive drums
51
, and the belt distances between the adjacent photosensitive drums
51
, that is, the belt distance between K and Y, the belt distance between Y and M and the belt distance between M and C, are varied, and this causes a deviation in the timing of transfer from each photos
Kawano Yuzo
Shimada Masaya
Suyama Kohei
Beatty Robert
Stevens Davis Miller & Mosher LLP
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