Information
-
Patent Grant
-
6477349
-
Patent Number
6,477,349
-
Date Filed
Friday, May 11, 200123 years ago
-
Date Issued
Tuesday, November 5, 200221 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 399 298
- 399 299
- 399 301
- 399 302
- 399 307
- 399 308
- 399 310
- 399 313
- 399 314
-
International Classifications
-
Abstract
Utilizing an action of a transfer roller transferring a toner image formed on an intermediate transfer belt onto a sheet of paper can provide the belt with tension, and allows the belt and an urging roller to nip the sheet of paper. Thanks to this structure, a compact and inexpensive color image forming apparatus is obtainable.
Description
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.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a cross section illustrating an essential part of a color image forming apparatus in accordance with an exemplary embodiment of the present invention.
FIG. 2
is a schematic perspective view illustrating a shift mechanism of a second-transfer-roller of the apparatus shown in FIG.
1
.
FIG. 3A
is a lateral view illustrating a positional relation between the second-transfer-roller held by a holder and an urging roller of the apparatus shown in FIG.
1
.
FIG. 3B
is a lateral view showing the second-transfer-roller shifted to the urging roller of the apparatus shown in FIG.
1
.
FIG. 4A
is a lateral view showing a positional relation between the urging roller and a the intermediate-transfer-belt during a non-printing period in the apparatus shown in FIG.
1
.
FIG. 4B
is a lateral view showing a positional relation between the urging roller and the intermediate-transfer-belt during a printing period in the apparatus shown in FIG.
1
.
FIG. 5
is a schematic diagram illustrating displacement of a nip portion (first nip section) between the transfer roller and the urging roller due to extension and contraction of the intermediate-transfer-belt in the apparatus shown in FIG.
1
.
FIG.
6
A and
FIG. 6B
are schematic diagrams illustrating a sheet of paper entering a nip portion (second nip section) between a heating roller and a pressure roller due to displacement of the transfer roller in the apparatus shown in FIG.
1
.
FIG. 7
is a cross section showing an essential part of a conventional color image forming apparatus.
DETAILED DESCRIPTION OF EXAMPLARY EMBODIMENT
An exemplary embodiment of the present invention is demonstrated hereinafter with reference to the accompanying drawings.
In
FIG. 1
, in apparatus
1
, image-forming-units
2
,
3
,
4
and
5
are disposed in this order for forming toner images of yellow, magenta, cyan and black. Exposure devices
61
,
62
,
63
, and
64
are disposed corresponding to units
2
-
5
respectively. Units
2
-
5
include photosensitive drums
21
,
31
,
41
and
51
, and developing rollers
22
,
32
,
42
and
52
. Each photosensitive drum deposits an electrostatic latent image on its surface by laser beam radiated from each exposure device, i.e., functioning as an image carrying body. Each developing roller attaches toner supplied from a toner tank to each photosensitive drum, thereby revealing an electrostatic latent image as a visible toner image.
Under units
2
-
5
arrayed, loop type intermediate-transfer-belt
7
circulates in an arrow marked direction passing by four first-transfer-rollers
91
,
92
,
93
and
94
, driving roller
8
, and second-transfer-roller
10
. The first-transfer-rollers correspond to respective photosensitive drums
21
,
31
,
41
and
51
, and the second-transfer-roller transfers an image to a recording sheet such as a sheet of paper. The four first-transfer-rollers, second-transfer-roller and the driving roller are placed in the loop of belt
7
, and second-transfer-roller
10
and driving roller
8
confront each other at opposite ends of belt
7
.
Under belt
7
a paper tray
20
is disposed. Paper P supplied from tray
20
is nipped between belt
7
around roller
10
and urging roller
60
confronting second-transfer-roller
10
. Toner images formed on belt
7
are transferred onto-paper P. Then paper P is fed to fixing device
80
thereby fixing the toner image. Finally, paper P is discharged.
On the surface of belt
7
, toner images in yellow, magenta, cyan and black are attach ed by drums
21
,
31
,
41
and
51
, thereby forming a color image. This toner color image is transferred onto paper P by nipping force yielded between rollers
10
and
60
.
Belt
7
is wound on first-transfer-rollers
91
,
92
,
93
and
94
, driving roller
8
, and second-transfer-roller
10
. In other words, the present invention saves tension roller
550
of the conventional case shown in
FIG. 7
, and changes the position of second-transfer-roller
10
, thereby providing belt
7
with tension and removing/contacting roller
10
from/to urging roller
60
. Driving roller
8
, first transfer-rollers
91
-
94
, second-transfer-roller
10
and belt
7
form one unit, and the unit can be detached from a chassis (not shown) built in the apparatus
1
.
A shift mechanism of the second-transfer-roller is detailed hereinafter.
FIG. 2
is a schematic perspective view illustrating the shift mechanism of the second-transfer-roller of the apparatus shown in FIG.
1
.
FIG. 3A
is a lateral view illustrating a positional relation between the second-transfer-roller held by a holder and the urging roller of the same apparatus.
FIG. 3B
is a lateral view showing the second-transfer-roller shifted to the urging roller.
In
FIG. 2
, a pair of holders
11
are rigidly disposed in the chassis (not shown). Both, ends of second-transfer-roller
10
are journaled by a pair of holding blocks.
111
disposed in a sliding manner with respect to holders
11
. As shown in
FIG. 3A
, springs
112
are disposed between respective holding blocks
111
and stoppers
70
. The pair of holders
11
journal both ends of driving shaft
121
, which is driven by motor
12
shown in
FIG. 2
, and shaft
121
has a pair of cams
122
for moving holders
11
to both sides as shown in FIG.
3
A and FIG.
3
B.
FIG.
2
and
FIG. 3A
show a status of non-printing period, and second-transfer-roller
10
is away from urging roller
60
held on the chassis side in apparatus
1
. Both ends of urging roller
60
are journaled by a pair of blocks
211
, and coupled to the chassis via a pair of springs
212
linked with blocks
211
. On the other hand,
FIG. 3B
shows a status of printing period. When motor
12
is driven to spin cams
122
, holders
11
move in an arrow marked direction as shown in FIG.
3
B. This movement urges second-transfer-roller
10
aganist urging roller
60
. At this time, as shown in
FIG. 1
, paper P is nipped between urging roller
60
and intermediate-transfer-belt
7
around the second-transfer-roller
10
. Intermediate-transfer-belt
7
has been urged against urging roller
60
by second-transfer-roller
10
. At the nipping portion, a toner image formed on belt
7
is transferred onto paper P.
Next, the tension provided to the intermediate-transfer-belt is described.
FIG. 4A
shows a lateral view illustrating a positional relation between the urging roller and the intermediate-transfer-belt during the non-printing period of the apparatus shown in FIG.
1
.
FIG. 4B
shows a lateral view illustrating a positional relation between the urging roller and the intermediate-transfer-belt during a printing period in the same apparatus.
During the non-printing period, a position of cam
122
is set as shown in FIG.
3
A. Since second-transfer-roller
10
is away from urging roller
60
as shown in FIG. A, tension is not provided to intermediate-transfer-belt
7
.
A print instruction drives motor
12
, and cam
122
is rotated until it takes a position shown in
FIG. 3B
, so that holder
11
moves toward urging roller
60
. Spring
112
biases second-transfer-roller
10
to urging roller
60
. This movement of roller
10
forms a nipping portion between belt
7
around roller
10
and urging roller
60
as shown in
FIG. 4B
, and belt
7
is pulled so that tension is provided to belt
7
. The nipping portion, in general, nips paper P, and urging roller
60
presses second-transfer-roller
10
via paper P and belt
7
during the printing period. In other words, urging roller
60
nips paper P with belt
7
around the second-transfer-roller
10
.
In this embodiment, as discussed above, second-transfer-roller
10
is held by holders
11
, and urged against urging roller
60
by cams
122
, so that a nipping portion is formed between belt
7
around roller
10
and urging roller
60
. At the same time, tension is provided to belt
7
. Therefore, a tension roller, which the conventional apparatus employs, is not needed, and a driving mechanism for urging the urging roller against the second-transfer-roller is also unnecessary. As a result, the apparatus can be downsized.
FIG. 5
is a schematic diagram illustrating displacement of a nip portion between the transfer roller and the urging roller due to extension and contraction of the intermediate-transfer-belt in the apparatus shown in FIG.
1
.
In
FIG. 1
, paper P, on which a toner image has been transferred, travels to fixing device
80
through between belt
7
around roller
10
and urging roller
60
. Fixing device
80
comprises heating roller
221
and pressure roller
222
. Paper P travels along an arrow mark in a solid line drawn in FIG.
5
.
In this case, when a first nipping section between belt
7
wound on second-transfer-roller
10
and urging roller
60
is almost aligned with a second nipping section between heating roller
221
and pressure roller
222
, paper P is fed between rollers
221
and
222
smoothly. However, belt
7
extends or contracts due to temperature or the like, and the first nipping section between rollers
10
and
60
sometimes deviates from the aligned position as shown in a broken line. In such a case, paper P hits against outer rim of heating roller
221
and results in jamming.
A countermeasure against this jamming is described hereinafter. FIG.
6
A and
FIG. 6B
are schematic diagrams illustrating a sheet of paper entering a nipping portion between the heating roller and the pressure roller due to displacement of the transfer roller in the apparatus shown in FIG.
1
.
In
FIGS. 6A and 6B
, slanted long hole
231
is provided to bearing
23
which journals urging roller
60
, and a shaft of roller
60
is movable in this long hole
231
. As shown in
FIG. 6A
, when second-transfer-roller
10
is deviated to the right side with respect to the nipping portion (the second nipping section) between heating roller
221
and pressure roller
222
, another nipping portion (the first nipping section) between second-transfer-roller
10
and urging roller
60
deviates to the right side. Then paper P can enter slantingly into the second nipping section. As shown in
FIG. 6B
, when second-transfer-roller
10
deviates to the left side with respect to the second nipping section, the first nipping section deviates to the left, and paper P can enter slantingly into the second nipping section. As such, even if the second-transfer-roller
10
moves, long hole
231
allows paper P to enter smoothly into the nipping portion between heating roller
221
and pressure roller
222
. As a result, the jamming of paper P can be prevented.
As discussed above, according to the present invention, shifting of the transfer roller can provide the intermediate-transfer-belt with tension, thus a conventional tension roller is not required. As a result, a number of components is reduced, which makes assembly easier. The transfer roller can be shifted to the place where the intermediate-transfer-belt wound thereon contacts to the urging roller, a conventional driving mechanism, which removes the urging roller from the belt, is not required. Thus the construction of the apparatus is further simplified.
Claims
- 1. A color image forming apparatus comprising:(a) a plurality of image forming units arrayed, each unit having a photosensitive body carrying a toner image, and each unit forming an image of a different colored toner from each other; (b) a loop type intermediate transfer belt, disposed allowable to contact to the photosensitive body, and on which the toner image is transferred; (c) a transfer roller, disposed in the loop of said intermediate transfer belt, for transferring a toner image formed on said belt onto a recording sheet, said transfer roller provides said belt with tension; (d) a driving roller, disposed in the loop of said intermediate transfer belt and confronting said transfer roller, for rotating said belt, said belt is rotatably held by said transfer roller and said driving roller; and an urging roller, disposed outside the loop of said intermediate transfer belt and confronting said transfer roller, for nipping the recording sheet with said belt, wherein when said transfer roller provides said belt with the tension, said transfer roller and said urging roller urge against each other, and when the tension is released, said urging roller is removed from said transfer roller.
- 2. A color image forming apparatus comprising:(a) a plurality of image forming units arrayed, each unit having a photosensitive body carrying a toner image, and each unit forming an image of a different colored toner from each other; (b) a loop type intermediate transfer belt, disposed allowable to contact to the photosensitive body, and on which the toner image is transferred; (c) a first transfer roller, disposed in the loop of said belt, for biasing said belt to the photosensitive body; (d) a second transfer roller, disposed in the loop of said belt, for transferring a toner image formed on said belt onto a recording sheet; (e) a driving roller, disposed in the loop of said belt and confronting said second transfer roller, for rotating said belt, said belt is rotatably held by said second transfer roller and said driving roller, and said second transfer roller provides said belt with tension; (f) an urging roller, disposed outside the loop of said belt and confronting said second transfer roller, for nipping the recording sheet at a first nipping section between said belt and said urging roller; (g) a fixing device, disposed downstream of flow of the recording sheet viewed from the first nipping section, including a heating roller and a pressure roller, wherein said urging roller can change a position thereof responsive to a movement of said second transfer roller for leading the recording sheet into a second nipping section between said heating roller and said pressure roller.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2000-138659 |
May 2000 |
JP |
|
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Number |
Name |
Date |
Kind |
5794111 |
Tombs et al. |
Aug 1998 |
A |
5930556 |
Imamiya |
Jul 1999 |
A |
5966561 |
Yamaguchi et al. |
Oct 1999 |
A |
Foreign Referenced Citations (1)
Number |
Date |
Country |
11-59947 |
Mar 1999 |
JP |