Electrophotography – Image formation – Fixing
Reexamination Certificate
2002-05-24
2004-10-26
Braun, Fred (Department: 2852)
Electrophotography
Image formation
Fixing
C219S619000
Reexamination Certificate
active
06810230
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image heating device that is used in an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording apparatus and includes a heat generating source for thermally fixing an unfixed image, which employs an electromagnetic induction heating method, and an image forming apparatus using the same.
BACKGROUND ART
Image heating devices employing electromagnetic induction are disclosed in JP2000-181258 A and JP2000-206813 A
FIG. 27
is a cross-sectional view of the image heating device disclosed in JP2000-181258 A.
FIG. 28
is a front view showing a moving mechanism of a fixing device used in the image heating device. In
FIG. 27
, reference numerals
101
and
102
denote a heating roller that generates heat by induction heating and is rotated and a pressurizing roller that makes contact under pressure with the heating roller
101
, respectively. A recording material (sheet)
105
is passed through a pressure-contacting portion between both the rollers
101
and
102
, so that an unfixed image on the recording material
105
is fixed. Further, reference numerals
103
and
104
denote an excitation coil that is arranged on an outer periphery of the heating roller
101
and generates a high-frequency magnetic field, and a magnetic field shielding material that regulates an amount of heat to be generated, respectively.
The recording material
105
carrying the unfixed toner image is conveyed to a nip portion defined by the heating roller
101
and the pressurizing roller. Then, the toner image on the recording material
105
is fixed by heat of the heating roller
101
and pressure of the pressurizing roller
102
.
The magnetic field shielding material
104
is, as shown in
FIG. 28
, divided into a plurality of portions in a width direction of the recording material
105
. The magnetic field shielding materials
104
as the portions of the divided magnetic field shielding material
104
are housed in three separate cases, i.e. a case
104
a
arranged in a center portion so as to correspond to a passing area P
A4L
through which a JIS size A4 paper sheet is passed in a longitudinal direction, and cases
104
b
and
104
c
arranged on both outer sides of the case
104
a
. A distance between the respective outer side ends of the cases
104
b
and
104
c
corresponds to a passing area P
A4T
(P
A4T
>P
A4L
) through which a JIS size A4 paper sheet is passed in a lateral direction. The cases
104
b
and
104
c
on both outer sides can be raised or lowered by a case moving mechanism
108
that is composed of a shaft
106
with a thread groove formed on an outer periphery and a sliding portion
107
provided with an internal thread that is threaded in the thread groove. When passing A4-sized paper sheets continuously in the longitudinal direction, the cases
104
b
and
104
c
on both the outer sides are retracted upward so that the magnetic field shielding materials
104
housed therein are moved away from the excitation coil
103
. Thus, in portions opposed to the cases
104
b
and
104
c
, a magnetic flux reaching the heating roller
101
is weakened, thereby allowing a temperature rise of the heating roller
101
in the portions to be suppressed. When passing an A4-sized paper sheet in the lateral direction, the cases
104
b
and
104
c
on both the outer sides are lowered. Thus, an amount of heat generated by the heating roller
101
can be made substantially uniform over the full width.
FIG. 29
shows a configuration of an induction heating circuit of an image heating device of an image forming apparatus disclosed in JP2000-206813 A. In the figure, three sets of induction heating portions, each composed of a magnetic core
201
and an induction heating coil
202
, are arranged so as to be opposed to a fixing roller
203
. The induction heating portion in the center is supplied with power from a center portion induction heating power supply
205
, and the induction heating portions at both ends are supplied with power from an end portion induction heating power supply
207
. In a center portion and an end portion, temperature detecting portions TH
1
and TH
2
are provided, respectively. According to a detected temperature, the power supply to each of the induction heating portions is controlled. In this configuration, when heat is radiated to a greater degree in both the end portions than in the center portion of the fixing roller
203
, a larger amount of power is injected into the induction heating coils opposed to the end portions. When a larger amount of heat is lost in the center portion of the fixing roller
203
as in the case where a paper sheet of a small width is passed, a reduced amount of power is supplied to the induction heating coils opposed to the end portions. In this manner, a temperature of the fixing roller
203
in an axial direction is kept uniform.
However, the image heating device
FIGS. 27 and 28
) disclosed in JP2000-181258 A has presented the following problems.
First of all, in this configuration, a core of a magnetic material is not present in an inner peripheral portion of the excitation coil
103
, and thus magnetic coupling between the excitation coil
103
and the heating roller
101
does not work well. Therefore, in order for the heating roller
101
to be heated to a desired temperature by induction heating, a large electric current is required, thereby making an excitation circuit costly. Furthermore, because of a configuration in which the magnetic field shielding materials
104
are moved according to a width of a paper sheet to be passed, passing various types of paper sheets results in many combinations of the magnetic field shielding material to be moved and the magnetic field shielding material not to be moved. This requires a plurality of moving mechanisms, thereby making the configuration complicated and costly. Moreover, a space for moving the magnetic field shielding materials
104
and a space for the moving mechanism are required. Thus, the fixing device is made bulky, thereby making a whole image forming apparatus bulky, which has been disadvantageous.
The image heating device (
FIG. 29
) disclosed in JP2000-206813 A has presented the following problems.
First of all, a plurality of the induction heating portions, each composed of the magnetic core
201
and the induction heating coil
202
, and a plurality of the induction heating power supplies are required, thereby making the device costly. Further, because of a configuration in which the induction heating portions and the induction heating power supplies are provided according to the sizes of paper sheets to be passed, when passing various types of paper sheets, a cost increase becomes considerable. For example, in order to achieve the passing of paper sheets varying in size between a maximum of JIS size A3 and a minimum of a post card size, and further to achieve the feeding of A4-sized and B5-sized paper sheets in longitudinal and lateral directions, it is necessary to provide five to seven induction heating portions, thereby making the device more costly. Furthermore, spaces for housing the plurality of the induction heating power supplies are required. Thus, the device is increased in size, which has been disadvantageous.
DISCLOSURE OF THE INVENTION
In order to solve these problems of the conventional image heating devices, it is an object of the present invention to provide an image heating device that can heat a heat generating roller uniformly in a width direction of a paper sheet to be passed. Further, it is another object of the present invention to provide an image heating device that is reduced in size and weight, in which an amount of heat generated by a heat generating roller can be controlled easily at low cost according to a width of a paper sheet to be passed. Moreover, it is still another object of the present invention to provide an image forming apparatus that includes the image heating device as a thermal fixing device.
In order to achieve the aforementioned objects, the pr
Asakura Kenji
Imai Masaru
Tatematsu Hideki
Watanabe Shuichi
Braun Fred
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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