Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-08-31
2003-09-23
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Fixing
C399S329000, C219S216000
Reexamination Certificate
active
06625417
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
extended in the direction of the rotation axis of the heat-generating member and circumferentially wound along the circumferential direction of the heat-generating member, and the bundled wires extending in the direction of the rotation axis of the heat-generating member are arranged in close contact with each other in at least one place.
Furthermore, an image heating device according to a tenth configuration of the present invention includes: a heat-generating member comprising a rotatable body having conductivity, and an exciting coil arranged in opposition to the outer peripheral surface of the heat-generating member and adapted for allowing the heat-generating member to generate heat with electromagnetic induction; wherein the exciting coil composed of a bundle of wires having an insulated surface, which are extended in the direction of the rotation axis of the heat-generating member and circumferentially wound along the circumferential direction of the heat-generating member, and a larger number of bundled wires are superimposed at both ends than at the central portion in the direction of the rotation axis of the heat-generating member.
Furthermore, an image heating device according to an eleventh configuration of the present invention includes: a heat-generating member comprising a rotatable body having conductivity, and an exciting coil arranged in opposition to the outer peripheral surface of the heat-generating member and adapted for allowing the heat-generating member to generate heat with electromagnetic induction; further comprising a core made of magnetic material arranged outside the exciting coil, and the length of the core along the direction of the rotation axis of the heat-generating member is not shorter than the width of a recording material having the maximum width of all the recording materials to be used.”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)-295414 A, as compared with the configuration of the exciting means described in JP10 (1998)-74007 A, 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)-295414 A 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)-318001 A).
FIG. 37
shows a cross-sectional view of a belt type image heating device, which is disclosed in JP 6 (1994)-318001 A. 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 the fixing portion.
Furthermore, there is another problem in that how the temperature of the fixing belt decreases when the fixing belt passes though the fixing portion varies dependent greatly upon the temperature conditions of the recording paper, the members to be used for pressure means, or the like. Therefore, in order to obtain the stable fixing, regardless of the temperature conditions of the recording paper, the member to be used for pressure means, or the like, that is, even if the manner in which the temperature of the fixing belt decreases changes greatly after the fixing belt passes through the fixing portion, it is necessary to restore the temperature of the fixing belt to the optimum constant temperature when the fixing belt comes again to the fixing portion.
In order to restore the fixing belt to a predetermined temperature stably and uniformly, a
Asakura Kenji
Imai Masaru
Tatematsu Hideki
Terada Hiroshi
Toyoda Akinori
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Tran Hoan
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