Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2002-03-08
2004-03-02
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Photoconductive member
Reexamination Certificate
active
06701109
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus using the electrophotographic technology such as a printer, a copy machine, a facsimile machine, or the like. More particularly, the invention relates to a color image forming apparatus in which a plurality of toner images respectively formed by a plurality of single-color toner image formers are sequentially transferred on a transferring member or a recording medium held by the transferring member.
In general, an image forming apparatus and in particular, a tandem image forming apparatus using electrophotography has a photoconductor as an image supporting member having a photosensitive layer on the outer peripheral surface thereof, a charger for uniformly charging the outer peripheral surface of the photoconductor, an exposer for selectively exposing the charged outer peripheral surface to light for forming an electrostatic latent image thereon, and a developer for giving toner to the electrostatic latent image for providing a visible image (toner image).
FIG. 7
shows an example of the tandem-type color image forming apparatus disclosed in Japanese Patent Publication No. 11-231754A. In this example, a plurality of (four) toner image formers
10
a
-
10
d
each including a image supporting member
2
a
-
2
d
are brought into contact with an intermediate transfer belt
1
serving as a transferring member, for sequentially transferring multiple-color toner images (for example, yellow, cyan, magenta and black) supported by the respective image supporting members
2
a
-
2
d
onto the intermediate transfer belt
1
. A full-color image thus formed on the intermediate transfer belt
1
is then secondarily transferred onto a recording medium P such as paper by a transfer roller
6
.
There is another type of the tandem-type color image forming apparatus in which a recording medium such as paper is held and transported by a belt member serving as a transferring member so that toner image formed on the above image supporting members are sequentially transferred onto the recording medium.
In
FIG. 7
, the intermediate transfer belt
1
is circulated by a drive roller
3
and a driven roller
5
. Therefore, the image supporting members
2
a
-
2
d
are brought into contact with a slack side of the transfer belt
1
.
In such a configuration, a tension roller
4
for giving a relatively large tension to the intermediate transfer belt
1
by a relatively large force F has been provided to stabilize the contact between the transfer belt
1
and the image supporting members
2
a
-
2
d
. Thus, the stretching structure of the transfer belt becomes complicated so that it is difficult to reduce the size of the image forming apparatus.
Since a relatively large tension is given to the transfer belt
1
when the image forming apparatus is not activated (the transfer belt is not circulated) for a long time period, creep deformation would occur in the transfer belt, adversely affecting the later image formation.
By the way, to provide a good transfer condition of toner images (therefore providing a fine image) in the image formation apparatus as described above, it is desirable that the circumferential velocity of the image supporting member and that of the transferring member should be completely matched with each other. More practically, however, manufacturing errors and varying tolerances are usually introduced into the image supporting member, the transferring member, or the parts making up their driver units at the manufacturing stage. Thus, it is practically impossible to completely match the circumferential velocity of the image supporting member and that of the transferring member.
If the difference between the circumferential velocity of the image supporting member and that of the transferring member varies, for example, if the circumferential velocity of the image supporting member is higher than that of the transferring member at one point in time and the former becomes lower than the latter at another point in time, the transfer condition becomes remarkably unstable and a fine image cannot be obtained. Particularly, to superpose multiple-color toner images on each other for forming a full-color image as described above, a color-to-color shift occurs and the image quality is remarkably degraded.
To solve this problem, as shown in
FIG. 8
, Japanese Patent Publication No. 4-324881A discloses a color image forming apparatus wherein the velocity of each image supporting member is always higher than that of transferring member.
Four photoconductive drums
11
(Y, M, C, and K), each associated with a single color are brought into contact with an intermediate transfer drum
12
. A yellow toner image provided by the photoconductive drum
11
Y, a magenta toner image provided by the photoconductive drum
11
M, a cyan toner image provided by the photoconductive drum
11
C, and a black toner image provided by the photoconductive drum
11
K are sequentially transferred to the intermediate transfer drum
12
to form a full-color toner image thereon, which is then transferred from the intermediate transfer drum
12
to a recording medium P.
The intermediate transfer drum
12
is driven by a driving system
14
and the photoconductive drums
11
(Y, M, C, and K) are driven by driving systems
13
(Y, M, C, and K). The driving systems
13
(Y, M, C, and K) comprise velocity converter
15
(Y, M, C, and K), respectively.
In this apparatus, to set the circumferential velocity V (Y, M, C and K) of each photoconductive drum
1
(Y, M, C and K) higher than the circumferential velocity V
1
of the intermediate transfer drum
2
, separate drive sources are provided. Accordingly, the driving mechanism becomes very complicated and the apparatus size is also increased.
Further, this publication is silent about fluctuation in the difference between the circumferential velocity of the image supporting members and that of the transferring member. Therefore, the transfer condition would become remarkably unstable as described above, so that a fine image cannot be provided. Particularly, when multiple-color toner images are superposed on each other for forming a full-color image as described above, a color-to-color shift would occur and the image quality is remarkably degraded.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a color image forming apparatus that can solve the problems as described above, can be miniaturized, and does not promote creep in a transfer belt.
It is another object of the invention to provide a color image formation apparatus which stabilizes the transfer condition from an image supporting member to a transferring member with a simple driving system.
In order to achieve the above objects, according to one embodiment of the present invention, there is provided a color image forming apparatus, comprising:
a drive roller and a driven roller;
a looped belt member stretched and circulated by at least the drive roller and the driven roller so as to have a slack side and a tensed side; and
a plurality of image supporting members, each supporting a single color toner image thereon, and abutting onto the slack side of the belt member to define a transferring position at which the toner image is transferred onto either the belt member or a recording medium held by the belt member, while being rotated, wherein:
a circumferential velocity of each image supporting member is determined so as to be higher than a circulation velocity of the belt member.
In this configuration, slack in the transfer belt originally occurred in the winding release point of the drive roller, is taken up so that the transfer belt is placed in a tensed state between the respective transferring positions. Accordingly, the running condition of the transfer belt becomes stable without wrinkles or slack, and the transfer position is fixed uniquely to a predetermined position.
Further, because of this configuration, an additional tension roller as employed in the related art is not needed so that the stretching structu
Abe Nobumasa
Nomura Yujiro
Yoda Kaneo
Seiko Epson Corporation
Tran Hoan
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