Electrophotography – Image formation – Fixing
Reexamination Certificate
2003-10-15
2004-11-16
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Fixing
C219S619000, C399S329000, C399S330000
Reexamination Certificate
active
06819904
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image heating device for use in image forming apparatus, such as electrophotographical apparatus, electrostatic recording apparatus or the like and suitable as a fixing device for fixing unfixed images, and to an image forming apparatus using this.
BACKGROUND ART
As this kind of image heating device, an image heating device using electromagnetic induction is disclosed in JP 10(1998)-74007 A, JP7 (1995)-295414 A, etc, and is well known.
JP 10(1998)-74007A describes an exciting coil in which a coil is wound around a core, as an exciting means applicable for electromagnetic induction.
FIG. 34
is a cross-sectional view showing an image heating device disclosed in JP 10 (1998)-74007 A.
In
FIG. 34
, reference numeral
310
denotes a coil for generating a high-frequency magnetic field, and
311
denotes a rotatable metal sleeve that generates heat by induction heating. Reference numeral
312
denotes an internal pressure member provided inside the metal sleeve
311
, and reference numeral
313
denotes an external pressure member provided outside the metal sleeve
311
. This external pressure member
313
is pressed against the internal pressure member
312
via the metal sleeve
311
so as to form a nip portion. The external pressure member
313
is rotated in the direction of the arrow a shown in FIG.
34
. The metal sleeve
311
is rotated following the rotation of the external pressure member
313
.
A recording paper
314
, as a member to be recorded, carrying an unfixed toner image thereon is fed to the nip portion in the arrow direction shown in FIG.
34
. Then, the unfixed toner image on the recording paper
314
is fixed by the heat from the metal sleeve
311
and the pressure from both pressure members
312
and
313
.
The coil
310
is provided with a plurality of separated winding portions
310
a
and
310
b
. These winding portions
310
a
and
310
b
are formed by winding a conductive wire around leg portions
315
b
and
315
d
of the core
315
via an insulating member (not shown). The core
315
has a plurality of leg portions
315
a
-
315
e
. Herein, the core
315
is made of ferrite that is a magnetic material, and forms a magnetic path for magnetic flux generated by alternating current applied to the coil
310
.
The image heating device disclosed in the above-mentioned JP 10 (1998)-74007A is thought to have the following problems.
Namely, in the configuration of the above-mentioned exciting means, since the conductive wire is wound around the leg portions of the core
315
, the position where the conductive wire is placed is limited to the position of the leg portion of the core. Therefore, the degree of freedom of design in placing a conductive wire is limited. Furthermore, it is difficult to place conductive wires in a broader range along the circumferential surface in the circumferential direction of the metal sleeve
311
.
On the other hand, JP7 (1995)-295414A describes an excitation means having a configuration in which a conductive coil is placed onto an insulating support body in a curled form.
FIG. 35
is a cross-sectional view showing an image heating device disclosed in JP7 (1995)-295414A.
FIG. 36
is a perspective view showing a heating coil used in this image heating device.
As shown in
FIG. 35
, a heating roller
201
is driven to be rotated in the arrow direction while in contact with a pressure roller
202
. The pressure roller
202
is rotated following the rotation of the heating roller
201
. Furthermore, the pressure roller
202
is pressed to the heating roller
201
and driven to be rotated. A recording paper
203
carrying an unfixed toner image thereon and fed to a place between both rollers
201
and
202
is heated and pressed between the both rollers
201
and
202
, and thereby the unfixed toner image on the recording paper
203
is fixed.
A heating coil
204
is provided in a state in which it is embedded in the insulating support body
205
. As shown in
FIGS. 35 and 36
, the heating coil
204
is formed of a narrow conductive film extending along a curved surface of a half cylinder shaped insulating support body
205
and is disposed in a curled shape along the entire width of the insulating support body
205
as a whole. Alternating current is applied to this heating coil
204
from an electric power source for induction heating. Then, due to the alternating current applied to the heating coil
204
, alternating magnetic flux is generated so as to excite the heating roller
201
. In the heating roller
201
, an eddy current is generated that flows in the opposite direction to the direction in which the alternating current flows in the heating coil
204
. When the eddy current is generated in the heating roller
201
, Joule heat is generated in the heating roller
201
, so that the heating roller
201
generates heat.
According to the configuration of the exciting means described in JP 7 (1995)-295414A, as compared with the configuration of the exciting means described in JP10 (1998)-74007A, the degree of freedom of design in placing the conductive wire is less limited, and it is possible to place the conductive wire over a broader range along the circumferential surface in the circumferential direction of the heating roller
201
.
However, the image heating device disclosed in JP 7(1995)-295414A has the following problems.
Since the heating coil
204
is formed of a conductive film arranged in a curled form, there is space in which no electric current flows between the circumferentially flowing current. Therefore, as shown by a broken line S in
FIG. 35
, the magnetic flux passes between the coils to form small loops. In this case, it is not possible to lead the magnetic flux to the heating roller
201
efficiently, thus increasing the magnetic flux that does not penetrate the heating roller
201
. Therefore, in order to obtain the electric power necessary for allowing the heating roller
201
to generate heat, a large amount of electric current is required to flow to the heating coil
204
. In order to carry a large amount of electric current to the heating coil
204
, a component having a large breakdown current is required to be used for the electric power source for induction heating, causing the electric power source for induction heating to be expensive.
Furthermore, conventionally, as image heating devices, for which fixing devices are typical example, contact-heating type devices such as heat roller type devices and belt type devices, generally have been used.
In recent years, due to the demand for shorter warm-up time and reduced energy consumption, the belt type image heating devices capable of reducing the thermal capacity are attracting great attention (see JP 6 (1994)-318001A).
FIG. 37
shows a cross-sectional view of a belt type image heating device, which is disclosed in JP 6 (1994)-318001A. As shown in
FIG. 37
, an endless rotatable fixing belt
401
is suspended between a fixing roller
402
and a heating roller
403
. By heating the heating roller
403
by the use of the heating source H
1
located inside the heating roller
403
, the fixing belt
401
is heated to a predetermined temperature.
By using the fixing belt
401
having a small thermal capacity, this image heating device is designed to achieve a fixing without offset with less oil applied.
The belt type image heating device including the above-mentioned prior art has advantages of being able to set the thermal capacity of the fixing belt small for shortening the warm-up time, which makes it possible to heat up the fixing belt itself to the predetermined temperature in a short time. However, on the other hand, as the thermal capacity is reduced, the trend for the temperature of the fixing belt to be easily reduced due to the heat removed by the recording paper, etc. when a toner image is fixed becomes larger. Therefore, in order to obtain a reliable fixing, the lowered temperature of the fixing belt should be recovered uniformly to the necessary temperature until the fixing belt arrives again to th
Asakura Kenji
Imai Masaru
Tatematsu Hideki
Terada Hiroshi
Toyoda Akinori
Merchant & Gould P.C.
Tran Hoan
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