Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-01-27
2001-11-06
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S299000, C399S308000
Reexamination Certificate
active
06314264
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to, for example, an image forming apparatus such as a copy device, a printer or a facsimile, and more particularly to such an image forming apparatus that transfers an image on an image bearing member onto an intermediate transfer member and then transfers the image on the intermediate transfer member onto a transfer material.
2. Description of the Related Art
Heretofore, there is known such an image forming apparatus that transfers a toner image formed on an image bearing member using an electrophotographic technique onto a recording material and then fixes that unfixed toner image in order to obtain a permanent image on the recording material. Such apparatus is more widely used as a color-image forming apparatus as society has become more information oriented in recent years.
FIG. 5
shows an outline configuration of one example of a conventional electrophotographic full-color image forming apparatus. To accelerate a speed of outputting color images, this image forming apparatus has in itself a plurality of photosensitive members (i.e., image bearing members), each of which is used to form toner images sequentially, which are once multi-transferred on an intermediate transfer member and then transferred onto a recording material collectively.
As shown in
FIG. 5
, the present image forming apparatus has four image forming sections (image forming stations) of
10
Y,
10
M,
10
C, and
10
K for four colors of yellow, magenta, cyan, and black respectively and also an intermediate transfer belt
80
as transfer means and a fixing device
40
as fixing means.
The image forming sections
10
Y,
10
M,
10
C, and
10
K are each provided as a unit, together with photosensitive drums as image bearing members
70
Y,
70
M,
70
C, and
70
K respectively, around which are respectively arranged primary charging rollers
12
Y,
12
M,
12
C, and
12
K; laser exposure devices
13
Y,
13
M,
13
C, and
13
K; developing devices
14
Y,
14
M,
14
C, and
14
K; primary transfer rollers
54
Y,
54
M,
54
C, and
54
K; and cleaners
16
Y,
16
M,
16
C, and
16
K. The intermediate transfer belt
80
is disposed in contact with each of the photosensitive drums
70
Y through
70
K and stretched over three rollers of a drive roller
51
, a tension roller
52
, and a secondary transfer opposed roller
53
, thus being driven in rotation in the direction indicated by an arrow b in the figure.
The photosensitive drums
70
(
70
Y-
70
K) are each uniformly charged on their surface by the primary charging rollers
12
(
12
Y-
12
K), to subsequently expose a color-separated image to light using the laser exposure devices
13
(
13
Y-
13
K), in order to form on the surface of the photosensitive drums
70
an electrostatic latent image which corresponds to an original. This latent image is developed by the developing devices
14
(
14
Y-
14
K) using minus toner, to form a toner image on the surface of the photosensitive drums
70
.
The above-mentioned image forming operations are performed on each of the image forming sections
10
Y through
10
K at their respective predetermined timing points, thereby forming various colors of toner images on the photosensitive drums
70
. These various colors of toner images are sequentially transferred onto the intermediate transfer belt
80
at each of the primary transfer sections opposed to the primary transfer rollers
54
(
54
Y-
54
K) (primary transfer), to once form on the intermediate transfer belt
80
a full-color image in which those four colors (yellow, magenta, cyan, and black) of toner images are superposed on top of each other.
Then, these four colors of toner images are collectively transferred using a secondary transfer roller
55
onto a recording material P fed at predetermined timing by a feed roller
20
(secondary transfer). The recording material P as finished by this transfer process is conveyed to the fixing device
40
, where it is heated and pressured to fix the toner images.
As mentioned above, the full-color image forming apparatus with an intermediate transfer member collectively transfers four colors of toner images on the intermediate transfer member onto a recording material, thus being excellent in that it produces less misregister in color (color registration). Also, in contrast to a system that absorbs a recording material on a recording material bearing member such as for example a transfer belt or transfer drum and then conveys the material, to directly transfer onto the material each color of toner images formed on a photosensitive drum and superpose these toner images on the recording material, this system of using an intermediate transfer member need not absorb or convey the recording material but only needs to collectively transfer onto the recording material full-color toner images formed by rotating the intermediate transfer member such as for example an intermediate transfer belt, thus forming images regardless of the kind of recording material, such as an envelope, cardboard, etc., with no variations in color registration due to the thickness of the recording material employed.
For this reason, therefore, particularly such an image forming apparatus using an intermediate transfer member is widely used for the electrophotographic-type full-color image forming apparatuses.
The above-mentioned primary transfer system, however, usually needs complicated transfer bias control. To achieve good transferability in all of the image forming sections
10
Y through
10
K, larger constant-voltage biases must be set at more downstream side image forming sections to give a sufficient transfer current to all the image forming sections, thus making it necessary to apply transfer biases from a total of four high-tension power supplies each independently for each of the image forming sections.
This is because the intermediate transfer belt is gradually charged up as it sequentially passes the image forming sections so that various colors of toner images may be superposed and transferred thereon, thus causing effective impedance in the width direction of the intermediate transfer belt passing the transfer nip sections to be increased as the belt passes more downstream side image forming sections.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image forming apparatus capable of preferably forming an image on an intermediate transfer member without the intermediate transfer member being charged up.
The other objects of the present invention will be better understood upon reading of the following detailed description.
REFERENCES:
patent: 5585905 (1996-12-01), Mammino et al.
patent: 6042917 (2000-03-01), Schlueter et al.
patent: 6088565 (2000-07-01), Jia et al.
Iida Kenichi
Nakai Tomoaki
Yoda Yasuo
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Royer William J.
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