Fixing and image forming devices comprising thin heated sheets

Details Fixing and image forming devices comprising thin heated sheets Fixing and image forming devices comprising thin heated sheets

2002-08-02

2004-05-04

Royer, William J. (Department: 2852)

Electrophotography

Image formation

Fixing

C219S216000

Reexamination Certificate

active

06731900

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Japanese application serial no. 2001-235852, filed on Aug. 3, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to a fixing device and an image forming device, which can be used in a facsimile device, a printer, a copier, or a multi-function machine with the above functions.
2. Description of Related Art
FIG. 7
is a side view showing an internal structure of a conventional fixing device. The item
100
is a fixing roller. A pressing roller
101
is pressed to be in contact with the fixing roller
100
. A fixing heater
102
is arranged inside the fixing roller
100
for heating the fixing roller
100
. A temperature detecting device
103
is used for detecting the temperature of the fixing roller
100
. A separation claw
104
is used for separating the recording paper wound on the fixing roller
100
from the fixing roller
100
. A cleaning pad
105
is in contact with the fixing roller
100
for cleaning the fixing roller
100
. A cleaning pad holder
106
is used for supporting the cleaning pad
105
. A cleaning pad invasion-regulating unit
107
is installed at a downstream side of the rotational direction of the fixing roller
100
with respect to the cleaning pad
105
. An entrance guiding plate
108
is installed at a recording paper entrance of the fixing device
100
. A paper-ejecting roller is installed at a recording paper exit of the fixing device
100
.
The recording paper which the toner image has been transcribed thereon enters a nip portion between the fixing roller
100
and the pressing roller
101
through the entrance guiding plate
108
. By pressing and heating at the nip portion, the toner image is fixed on the recording paper, and then the recording paper is ejected through a paper-ejecting roller
109
. When the recording paper passes the nip portion, the toner attached on the fixing roller
100
is removed by the cleaning pad
105
.
The surface temperature of the fixing roller
100
is detected by the temperature detecting device
103
. According to a detected result of the temperature detecting device
103
, a heating control of the fixing heater
102
is performed by a controlling device (not shown).
Conventionally, an infrared heater or a halogen heater is used as the fixing heater
102
in the fixing device, and a structure constituted of the fixing roller
100
and the pressing roller
101
pair is most common. The pressing roller
101
is a structure that is made by forming silicon rubber on a core bar and then a mold-releasing layer (such as Teflon, registered Trademark) is formed on the silicon rubber, so that the heat capacity of the pressing roller
101
becomes larger. At the beginning of heating, the pressing roller
101
does not get warm easily, causing incomplete fixing problems. Furthermore, there is also a demerit that parts have high cost. In addition, in order to assure a suitable nip width of the nip portion between the fixing roller
100
and the pressing roller
101
, a large pressing force (pressure) is required. Because of the pressure, stress will act on the recording paper, causing fixing wrinkle problems.
Instead of the pressing roller
101
, a nip portion is formed by pressing a sheet to be in contact with the fixing roller
100
. For example, a fixing device, where a non-fixed image is fixed on the recording paper by making the recording paper pass the nip portion, is well studied and researched. By the above structure, the sheet can be easily warmed up, and the nip width can be also assured.
However, regarding the fixing device using the sheet material, the heat capacity of the nip portion is small. Therefore, when the recording paper enters the nip portion, the heat will dissipate suddenly. At this time, the temperature detected by a thermistor might cause the temperature at the nip portion to be lowered and incomplete fixing might occur at the rear end of the recording paper because the position of the thermistor is located outside the nip portion and the response time of the detection is slow.
SUMMARY OF THE INVENTION
According to the foregoing description, an object of this invention is to provide a fixing device and an image forming device. The fixing device is composed of a heat conducting unit and a sheet. When a recording paper enters a nip portion, the heat from the sheet being suddenly dissipated can be prevented.
According to the objects mentioned above, the invention provides a fixing device, comprising a heat conducting unit, having a heating source, and being heated by the heating source; and a sheet that is in contact with and presses the heat conducting unit. One end of the sheet is mounted on a fixing frame that is located at an upstream side of a transporting direction of a recording paper, and the other end of the sheet is in contact with the heat conducting unit under a pressing status. When the recording paper onto which a toner image has been transcribed is passed through a nip portion between the sheet and the heat conducting unit, by pressing and heating, the toner image is fixed on the recording paper. Furthermore, a heating unit of line shape is laid on a back surface of the sheet at a region in the vicinity of the nip portion. According to the above structure, because the sheet is heated by the heating unit, the fixing device can be in a fixable status quickly. Additionally, when the recording paper passes the nip portion between the heat conducting unit and the sheet, the temperature of the nip portion can be prevented from being suddenly reduced.
In the above fixing device, the heating unit can be laid parallel to a transporting direction of the recording paper. According to this structure, the strength of the sheet becomes robust and the pressure against the heat conducting unit can become more stable. Furthermore, because the central portion of the sheet can be bent in the up-and-down direction, the sheet can be changed to a suitable shape to meet the shape of the heat conducting unit.
Alternatively, the heating unit can be laid in a grid shape. According to this structure, the strength of the entire sheet becomes more robust and the pressure against the heat conducting unit can become more stable.
The invention further provides an image forming device, comprising a fixing device that has the aforementioned structure and features. According to the above structure, the fixing property can be improved


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patent: 5058877 (1991-10-01), Fujiwara et al.
patent: 5298952 (1994-03-01), Kamijo et al.
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patent: 5809389 (1998-09-01), Tamura et al.
patent: 6151466 (2000-11-01), Fujiwara
patent: 6542712 (2003-04-01), Kimijo et al.
patent: 7-45357 (1995-02-01), None
patent: 11-296011 (1999-10-01), None
patent: 2001-29331 (2000-01-01), None

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