Electrophotography – Image formation – Transfer
Reexamination Certificate
2001-05-11
2002-11-05
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S313000
Reexamination Certificate
active
06477349
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a color image forming apparatus which transfers a color image onto a sheet of paper via an intermediate transfer belt. More particularly, it relates to the color image forming apparatus including a new mechanism which provides an intermediate transfer belt with tension, so that a number of components can be reduced and the apparatus can be downsized.
BACKGROUND OF THE INVENTION
A conventional image forming apparatus employing electro-photographic technique forms an image through the following steps: First, charge a photosensitive body—an image carrying body—with a charger, second, photo-radiate the photosensitive body responsive to image information for depositing a latent image. Then develop the latent image with a developing device for forming a toner image. Finally, transfer the toner image onto a recording sheet such as a sheet of paper to form a visible image.
Recently, color images have become popular in the market, and a number of images forming apparatuses employing a tandem style have been proposed. One of these apparatuses includes a plurality of image-carrying-bodies on which a series of image forming processes are carried out. Images of respective colors including cyan, magenta, yellow and preferably black are formed on each image-carrying-body, and images of respective colors are overlaid for transferring so that a full color image can be formed. This kind of image forming apparatus includes an image forming unit for each color, and this structure is advantageous to an operation at higher speed.
FIG. 7
is a cross section illustrating an essential part of a conventional color image forming apparatus. In
FIG. 7
, image forming units
502
,
503
,
504
and
505
are disposed in this order within apparatus
501
. These units
502
-
505
form toner images of yellow, magenta, cyan and black respectively. Apparatus
501
includes exposure devices
561
,
562
,
563
and
564
corresponding to units
502
-
505
. These units
502
-
505
include photosensitive drums
521
,
531
,
541
and
551
, as well as developing rollers
522
,
532
,
542
and
552
. These photosensitive drums function as image-carrying-bodies for depositing electrostatic latent images on their surfaces by laser-beam-radiation from exposure devices
561
-
564
. Developing rollers
522
,
532
,
542
and
552
attach toner supplied from toner tanks to those photosensitive drums thereby revealing the electrostatic latent images to visible toner images.
Under units
502
-
505
arrayed, intermediate-transfer-belt
507
circulates in an arrow marked direction passing by four first-transfer-rollers
591
,
592
,
593
and
594
, driving roller
508
, tension roller
550
and second-transfer-roller
510
. The first-transfer-rollers correspond to respective photosensitive drums, and the second-transfer-roller transfers an image to a sheet of paper.
Under belt
507
, paper tray
520
is disposed. Paper P supplied from tray
520
is nipped between belt
507
around second-transfer-roller
510
and urging roller
560
confronting second-transfer-roller
510
. On the surface of belt
507
, toner images in yellow, magenta, cyan and black are attached by drums
521
,
531
,
541
and
551
, thereby forming a color image. This toner color image is transferred on paper P by nipping force yielded between rollers
510
and
560
. Then paper P is fed to fixing device
580
thereby fixing the toner image. Finally, paper P is discharged.
Driving roller
508
and second-transfer-roller
510
are both rigidly disposed, and tension roller
550
is specifically disposed in order to provide belt
507
with tension. In
FIG. 7
, during a printing period, tension roller
550
is biased by a spring (not shown) and moves down right, thereby providing belt
507
with tension. During a non-printing period, on the other hand, the tension provided by roller
550
to belt
507
is released in order to avoid curling of belt
507
due to long time rolling around respective rollers.
As discussed above, a given tension is provided to belt
507
, so that drums
521
,
531
,
541
and
551
transfer a toner image onto belt
507
, and second-transfer-roller
510
transfers the toner image onto paper P.
However, tension roller
550
is prepared only for providing belt
507
with the tension, and this not only increases a number of components, but also blocks downsizing the apparatus. The cost of the apparatus tends to increase. A tension providing/releasing mechanism to/from belt
507
is additionally required, which further makes it difficult to downsize the apparatus.
Urging roller
560
is away from second-transfer-roller
510
during the non-printing period, and it moves rightward to nip paper P together with roller
510
during the printing period. During the non-printing period, urging roller
560
is kept away from belt
507
so that it will not contact with belt
507
for extending a service life of belt
507
by avoiding a local stress.
This removal mechanism of urging roller
560
from second-transfer-roller
510
is additionally required, which increases the cost and also blocks downsizing the apparatus.
The conventional color image forming apparatus not only requires tension roller
550
, but also needs a driving mechanism for providing/releasing the tension to/from belt
507
as well as the removal mechanism for removing urging roller
560
from second-transfer-roller
510
. These components boost the cost and blocks downsizing the apparatus.
SUMMARY OF THE INVENTION
The present invention addresses the problems discussed above and aims to provide a compact and inexpensive color image forming apparatus which utilizes movement of a transfer roller, thereby allowing to provide an intermediate-transfer-belt with tension.
The color image forming apparatus of the present invention comprises the following elements:
(a) a, plurality of image forming units which have respective photosensitive bodies carrying toner images and form images of different colored toners;
(b) a loop type intermediate-transfer-belt, disposed allowable to contact with a photosensitive body, and on which a toner image is transferred;
(c) a transfer roller, disposed in the loop of the intermediate-transfer-belt, for transferring the toner image formed on the intermediate-transfer-belt to a recording sheet;
(d) a driving roller, disposed in the loop and facing the transfer roller, for rotating the intermediate-transfer-belt.
The transfer roller provides the intermediate-transfer-belt with tension.
Another color image forming apparatus of the present invention comprises the following elements:
(a) a plurality of image forming units which have respective photosensitive bodies carrying toner images and form images of different colored toners;
(b) a loop type intermediate-transfer-belt, disposed allowable to contact with a photosensitive body, and on which a toner image is transferred;
(c) a plurality of first-transfer-rollers, disposed in the loop of the intermediate-transfer-belt, for biasing the intermediate-transfer-belt to the photosensitive body;
(d) a second-transfer-roller, disposed in the loop, for transferring a toner image on the intermediate-transfer-belt; and
(e) a driving roller, disposed in the loop and facing the second-transfer-roller, for rotating the intermediate-transfer-belt.
The intermediate-transfer-belt is rotatably held only by the second-transfer-roller and the driving roller, and only the second-transfer-roller provides the belt with tension.
These structures can provide the belt with tension by shifting the transfer-roller (the first case discussed above) or shifting the second-transfer-roller (the second case discussed above), and save a tension roller included in the conventional apparatus and reduces a number of components as well as achieves easy assembly. These structures also contribute to downsizing and reducing the cost of the apparatus.
REFERENCES:
patent: 5794111 (1998-08-01), Tombs et al.
patent: 5930556 (1999-07-01), Imamiya
patent: 5966561 (1999-10-01), Yamaguchi et al.
Kanekura Kazunori
Yamaguchi Naoki
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
Royer William J.
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