Title: Fixing apparatus and image forming apparatus
Abstract: A heat roller is configured to have a heat insulating member 4 and a metal member formed on the heat insulating member. Coils 21, 22 and 23 are provided outside the heating roller 2 to induction-heat the heating roller 2.
Patent Number: 6,871,041 Issued on 03/22/2005 to Takagi, et al.
| Inventors:
|
Takagi; Osamu (Tokyo, JP);
Kinouchi; Satoshi (Tokyo, JP);
Tsueda; Yoshinori (Fuji, JP);
Sone; Toshihiro (Fujieda, JP)
|
| Assignee:
|
Kabushiki Kaisha Toshiba (Tokyo, JP);
Toshiba Tec Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
390645 |
| Filed:
|
March 19, 2003 |
| Current U.S. Class: |
399/330; 399/335 |
| Intern'l Class: |
G03G 015//20 |
| Field of Search: |
399/92,320,328,330,333,334,335,336
|
References Cited [Referenced By]
U.S. Patent Documents
| 5713069 | Jan., 1998 | Kato | 399/330.
|
| 5822669 | Oct., 1998 | Okabayashi et al. | 399/330.
|
| 6026273 | Feb., 2000 | Kinouchi et al.
| |
| 6037576 | Mar., 2000 | Okabayashi et al. | 399/330.
|
| 6078781 | Jun., 2000 | Takagi et al.
| |
| 6087641 | Jul., 2000 | Kinouchi et al.
| |
| 6292648 | Sep., 2001 | Higaya et al. | 399/335.
|
| 6337969 | Jan., 2002 | Takagi et al.
| |
| 6377775 | Apr., 2002 | Nakayama et al. | 399/328.
|
| 6438335 | Aug., 2002 | Kinouchi et al.
| |
| 6445902 | Sep., 2002 | Hirst et al. | 399/328.
|
| 6625417 | Sep., 2003 | Terada et al. | 399/328.
|
| 6687482 | Feb., 2004 | Maeda et al. | 399/333.
|
| 2002/0051663 | May., 2002 | Kinouchi et al.
| |
| 2003/0002882 | Jan., 2003 | Takagi et al.
| |
| Foreign Patent Documents |
| 8-129313 | May., 1996 | JP.
| |
| 2001-005315 | Jan., 2001 | JP.
| |
| 2001-235964 | Aug., 2001 | JP.
| |
Other References
U.S. Appl. No. 10/378,859, filed Mar. 5, 2003, Sone et al.
U.S. Appl. No. 10/378,865, filed Mar. 5, 2003, Tsueda et al.
U.S. Appl. No. 10,382,846, filed Mar. 7, 2003, Kinouchi et al.
U.S. Appl. No. 10/387,413, filed Mar. 14, 2003, Kinouchi et al.
U.S. Appl. No. 10/143,909, filed May 14, 2002, Kinouchi et al.
U.S. Appl. No. 10/126,618, filed Apr. 22, 2002, Kikuchi et al.
|
Primary Examiner: Brase; Sandra L.
Attorney, Agent or Firm: Foley & Lardner LLP
Claims
What is claimed is:
1. A fixing apparatus comprising:
a heating roller configured to have a heat insulating member and a metal
member formed on the insulating member;
a first coil including a first core and provided outside the heating roller
to generate a high frequency magnetic field for induction-heating the
heating roller; and
a second coil including a second core and provided outside the heating
roller to generate a high frequency magnetic field for induction-heating
the heating roller,
the second core and the heating roller being spaced from each other by a
distance shorter than a distance between the first core and the heating
roller,
the first coil extending in an axial direction of the heating roller and in
parallel to the heating roller,
the second coil including a portion which is spaced from the heating roller
by a distance substantially equal to a distance between the first coil and
the heating roller, and a portion spaced from the heating roller by a
distance shorter than the distance between the first coil and the heating
roller.
2. The apparatus according to claim 1, wherein the heating roller is so
configured that the heat insulating member, the metal member and a surface
member are formed in that order on a core metal.
3. The apparatus according to claim 1, wherein the heat insulating member,
the metal member, an elastic member and a surface member are formed in
that order on a core metal.
4. The apparatus according to claim 1, further comprising an insulating
member formed between the heating roller and the first and second coils.
5. The apparatus according to claim 1, further comprising a casing which
holds the first and second coils.
6. The apparatus according to claim 1, further comprising a fan configured
to supply cooling air to the first and second coils.
7. The apparatus according to claim 1, wherein the first and second coils
are so formed that a copper wire is wound in a forward/backward repetition
fashion along an axial direction of the heating roller.
8. The apparatus according to claim 1, wherein the second coil is aligned
in the axial direction of the heating roller.
9. The apparatus according to claim 1, wherein the second coil is outwardly
extended from the corresponding axial end of the heating roller.
10. The apparatus according to claim 1, further comprising a temperature
sensor configured to detect a temperature of the surface of the heating
roller, the temperature sensor being provided more at a downstream side
than the position of the first and second coils in a rotation direction of
the heating roller.
11. The apparatus according to claim 10, further comprising a pressing
roller set in contact with the surface of the heating roller; and a
temperature sensor configured to detect a temperature of the surface of
the heating roller, the temperature sensor being provided between the
heating roller and the pressing roller more at a downstream side than a
contacting site at which the heating roller and the pressing roller
contact in the rotation direction of the heating roller.
12. The apparatus according to claim 11, further comprising a high
frequency generation circuit configured to output a high frequency current
for generating a high frequency magnetic field from the first and second
coils; and a control section configured to control an output of the high
frequency generation circuit so as to set the detection temperature of the
temperature sensor to a predetermined value.
13. The apparatus according to claim 1, further comprising a pressing
roller configured to have a heat insulating member and a metal member
formed on the heat insulating member and set in contact with the surface
of the heating roller.
14. The apparatus according to claim 13, further comprising:
a pressing roller coil provided outside the pressing roller and configured
to generate a high frequency magnetic field for induction-heating the
pressing roller.
15. A fixing apparatus comprising:
a heating roller configured to have a heat insulating member and a metal
member formed on the heat insulating member;
a first coil provided outside the heating roller to generate a high
frequency magnetic field for induction-heating the heating roller; and
a second coil provided outside the heating roller to generate a high
frequency magnetic field for induction-heating the heating roller, the
second coil including portions which correspond to axial ends of the
heating roller and which are greater in area than remaining portions of
the second coil.
16. The apparatus according to claim 10, further comprising a high
frequency generation circuit configured to output a high frequency current
for generating a high frequency magnetic field from the first and second
coils; and a control section configured to control an output of the high
frequency generation circuit to allow the detection temperature of the
temperature sensor to be set to a predetermined value.
Description
BACKGROUND OF THE INVENTION
An image forming apparatus scans a document image, forms a developing agent
image corresponding to the scanned image on a sheet and fixes the
resultant image to the sheet by a fixing apparatus.
The fixing apparatus has a heating roller and pressing roller, and a
developing agent image bearing sheet is passed between the heating roller
and the pressing roller to fix the developing agent image to the sheet to
the sheet. A tungsten halogen lamp, for example, is held inside the
heating roller. The temperature of the heating roller is raised by the
heat generated by the halogen lamp heater, and the developing agent on the
sheet is melted under the heating of the heating roller.
In an induction heating type fixing apparatus, a coil for induction heating
is held inside the heating roller and, by supplying high frequency current
to the coil, a high frequency magnetic field is generated from the coil.
Under the high frequency magnetic field, an eddy current is generated from
the coil and, due to the Joule heat generated by the eddy current, heat
generation occurs in the heating roller.
A heating roller for holding a halogen lamp heater or an induction heating
coil is greater in its heat capacity. For such a heating roller of a
greater heat capacity, a longer time is taken from after a start operation
until the heating roller reaches a temperature necessary for a fixing
process.
BRIEF SUMMARY OF THE INVENTION
It is accordingly the object of the present invention to provide a fixing
apparatus and image forming apparatus which can lower a heat capacity of a
heating roller and hasten a temperature rise of the heating roller after a
start operation has been performed.
In an aspect of the present invention, there is provided a fixing apparatus
comprising a heating roller having a heat insulating layer, and a metal
layer formed on the heat insulating layer, a coil being provided outside
the heating roller and configured to generate a high frequency magnetic
field for induction-heating the heating roller.
Additional objects and advantages of the invention will be set forth in the
description which follows, and in part will be obvious from the
description, or may be learned by practice of the invention. The objects
and advantages of the invention may be realized and obtained by means of
the instrumentalities and combinations particularly pointed out
hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The accompanying drawings, which are incorporated in and constitute a part
of the specification, illustrate presently embodiments of the invention,
and together with the general description given above and the detailed
description of the embodiments given below, serve to explain the
principles of the invention.
FIG. 1 is a view showing a structure of a fixing apparatus according to a
first embodiment of the present invention;
FIG. 2 is a view showing a structure of a heating roller and respective
coils in the first embodiment of the present invention;
FIG. 3 is a view showing a heating roller, respective coils and respective
cores in the first embodiment;
FIG. 4 is a block diagram showing a control circuit in an image forming
apparatus of respective embodiments;
FIG. 5 is a block diagram showing an electric circuit for a fixing
apparatus in the first to eighth embodiments;
FIG. 6 is a view showing a structure of the fixing apparatus of the second
embodiment of the present invention;
FIG. 7 is a view showing a structure of the third embodiment of the present
invention;
FIG. 8 is a view showing a structure of the fixing structure of the fourth
embodiment of the present invention;
FIG. 9 is a view showing a structure of the fifth embodiment of the present
invention;
FIG. 10 is a view showing a structure of a heating roller, respective coils
and respective cores in the sixth embodiment of the present invention;
FIG. 11 is a view showing a structure of a heating roller, respective coils
and respective cores in the seventh embodiment of the present invention;
FIG. 12 is a view showing a structure of a heating roller, respective coils
and respective cores of the eighth embodiment of the present invention;
FIG. 13 is a view showing a structure of a heating roller, pressing roller
and coils in a ninth embodiment of the present invention;
FIG. 14 is a block diagram of an electric circuit of a fixing apparatus of
the ninth embodiment of the present invention;
FIG. 15 is a view showing a heating roller, pressing roller and respective
coils in a tenth embodiment of the present invention;
FIG. 16 is a block diagram showing an electric circuit of a fixing
apparatus in the tenth embodiment;
FIG. 17 is a view showing a structure showing a heating roller, pressing
roller and respective coils in the eleventh embodiment of the present
invention;
FIG. 18 is a block diagram of an electric circuit of a fixing apparatus
shown in the eleventh embodiment of the present invention;
FIG. 19 is a view showing a structure of a fixing apparatus of a twelfth
embodiment; and
FIG. 20 is a view showing a structure of a fixing apparatus of a thirteenth
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[1] With reference to the accompanying drawings, an explanation will be
made below about a first embodiment of the present invention.
An image forming apparatus according to the present invention comprises a
scanning unit (later-described scanning unit 33) for optically reading out
a document image, a process unit (later-described process unit 45) for
allowing a developing agent image which corresponds to the read-out
document image to be formed on an image formation sheet, a fixing
apparatus (later-described fixing apparatus 1) for allowing the developing
agent image which is formed on the sheet to be fixed to the sheet under
heating, and so on. The detailed arrangement of the image forming
apparatus is described in earlier application Ser. No. 09/955,089. The
explanation of its structure is omitted here.
The structure of the fixing apparatus above is shown in FIGS. 1, 2 and 3.
The fixing apparatus 1 has a heating roller 2. The heating roller 2 and
pressing roller 8 are so arranged as to allow a sheet passing path to be
formed between the heating roller 2 and the pressing roller 8. The
pressing roller 8 is pressed, by a pressure applying mechanism not shown,
against a surface (outer peripheral surface) of the heating roller 2. A
given nip width is provided at a contacting site between the heating
roller 2 and the pressing roller 8.
The heating roller 2 is so configured as to have a heat insulating member 4
of, for example, 5 mm thick, a metal member 5 of, for example, 40 .mu.m
thick, an elastic member 6 of, for example, 0.3 mm thick, and a surface
member 7 of, for example, 20 .mu.m, formed in that order on a core metal
3. The heating roller 2 is rotationally driven in a clockwise (as
indicated) direction. The heat insulating member 4, if being over 0.5 mm
thick, exhibits an adequate heat insulating property.
The pressing roller 8 is rotated in a counter-clockwise (as indicated)
direction upon receipt of a rotation force of the heating roller 2. The
sheet P is conveyed between the heating roller 2 and the pressing roller 8
in an up/down sandwiched fashion and, by transmitting heat of the heating
roller 2 to the sheet P, a developing agent image T on the sheet P is
melted to allow the melted developing agent image T to be fixed to the
sheet P.
Around the heating roller 2, a claw 9 for separating the sheet P from the
heating roller 2, a cleaning member 10 for removing a residual developing
agent, sheet dust, etc., on the heating roller 2, an oil coating roller 11
for coating an oil on the surface of the heating roller 2, induction
heating coils 21, 22 and 23, temperature sensors 12 and 13 for detecting a
temperature on a surface (surface member 7) of the heating roller 2 and a
thermostat 14 configured to be opened, when a surface temperature of the
heating roller 2 abnormally rises, are provided in that order.
The coil 21 is provided at a position corresponding to a middle portion of
an axial direction of the heating roller 2. The coil 22 is provided at a
position corresponding to one axial end portion of the heating roller 2.
The coil 23 is provided at a position corresponding to the other axial end
portion of the heating roller 2. These coils 21, 22 and 23 are provided on
the coils 24, 25 and 26, respectively, and generate a high frequency
magnetic field for induction heating. By applying the high frequency
magnetic field to the heating roller 2, an eddy current is generated in
the metal member 5 of the heating roller 2 and the metal member 5 is
self-heat generated due to the Joule heat generated by the eddy current.
These coils 21, 22 and 23 are so formed that a copper wire is wound in a
forward/backward repeated fashion along an axial direction of the heating
roller 2. The copper wire is coated with a heat resistant enamel.
The coil 22 is outwardly extended by a distance A from the axial end edge
of the heating roller 2. The coil 23 is outwardly extended by a distance A
from the axial end edge of the heating roller 2.
The temperature sensor 12 is provided at a position corresponding to a
middle area in the axial direction of the heating roller 2. The
temperature sensor 13 is provided at a position corresponding to the other
axial end portion of the heating roller 2. Further, the thermostat 14 is
provided near the temperature sensor 12.
These temperature sensors 12 and 13 and thermostat 14 maybe of either a
contact type, for contacting the surface of the heating roller, or a
non-contact type, set away from the heating roller 2.
A plate-like insulating member 27 is provided between the heating roller 2
and the coils 21, 22 and 23. The insulating member 27 is made of a heat
resistant resin, such as heat resistant phenol, polyimide, or liquid
crystal polymer.
A control section of the image forming apparatus is shown in FIG. 4.
A control panel controller 31, scanning controller 32 and print controller
40 are connected to a main controller 30.
The main controller 30 controls the control panel controller 31, scanning
controller 32 and print controller 40. The scanning controller 32 controls
the scanning unit 33 for optically reading out a document image.
A ROM 41 for control program storage, a RAM 42 for data storage, a print
engine 43, a sheet conveying unit 44, a process unit 45, and a fixing
apparatus 1 are connected to the print controller 40. The print engine 43
generates laser light for forming an image which is canned by the scanning
unit 33 onto a photosensitive drum of the process unit 45. The sheet
conveying unit 44 comprises a sheet (P) conveying mechanism, a drive
circuit, and so on. The process unit 45 allows an electrostatic latent
image corresponding to a scanned image to be formed on the surface of the
photosensitive drum by the laser light emitted from the print engine 43,
the thus formed electrostatic latent image to be developed by a developing
agent on the photosensitive drum and the thus formed developing agent
image to be transferred to the sheet P.
FIG. 5 shows an electric circuit of the fixing apparatus 1.
Rectifier circuits 60 and 70 are connected to a commercial AC current
source 50 through an input detection section 51 and thermostat 14. High
frequency generation circuits (also called switching circuits or
half-bridge type inverters) 61 and 71 are connected to the output
terminals of the rectifier circuits 60 and 70.
The high frequency generation circuit 61 comprises a resonant capacitor 62
which, together with the coil 21, forms a resonance circuit, a switching
element such as transistor 63 configured to excite the resonance circuit
and a damper diode 64 connected in parallel with the transistor 63 and, by
allowing the transistor 63 to be driven by the drive circuit 52 in an
ON/OFF fashion, generates a high frequency current.
The high frequency generation circuit 71 comprises a resonant capacitor 72
which, together with the coils 22 and 23, forms a resonance circuit, a
switching element such as a transistor 73 configured to excite the
resonance circuit and a damper diode 74 connected in parallel with the
transistor 73 and, by allowing the transistor 73 to be driven by the drive
circuit 52 in an ON/OFF fashion, generates a high frequency current.
By supplying the high frequency currents from the high frequency generation
circuits 61 and 71 to the coils 21, 22, and 23, high frequency magnetic
fields are generated from the coils 21, 22, and 23. The metal members of
the heating roller 2 generates an eddy current under the high frequency
magnetic field and is self-heated due to Joule heat generated by the eddy
current.
In order to allow the energy of the high frequency magnetic field, which is
generated from the coils 21, 22, and 23, to be efficiently absorbed in the
metal member 5 of the heating roller 2, the metal member 5 may be made
thicker or a higher frequency may be used as the frequency of the high
frequency magnetic field generated from the coils 21, 22, and 23. For this
reason, the frequency of the high frequency magnetic field generated from
the coils 21, 22, and 23 is set to over 20 KHz, for example, 1 MHz to 4
MHz.
The input detection section 51 detects a voltage and current of the
commercial AC current source 50 and, based on a result of detection,
detects input power to the fixing apparatus 1. The result of the input
detection section 51 is supplied to a CPU 53. The temperature sensors 12
and 13, print controller 40 and drive circuit 52 are connected to the CPU
53.
The CPU 53 has control sections 54 and 55. The control section 54 controls
the output (the drive of the drive circuit 52) of the high frequency
generation circuit 61 so as to set the detection temperature of the
temperature sensor 12 to a predetermined value. The controller 55 controls
the output (the drive of the drive circuit 52) of the high frequency
generation circuit 71 so as to set the detection temperature of the
temperature sensor 13 to a predetermined value.
As set out above, by adopting the heating roller 2 with the metal member 5
formed on the heat insulating member 4 and providing the induction heating
coils 21, 22, and 23 outside the heating roller 2, it is possible to
largely lower the heat capacity of the heating roller 2. Since the heat
capacity of the heating roller 2 can be largely lowered, a rapid
temperature rise of the heating roller 2 is obtained after a start
operation.
The coils 21, 22, and 23 are provided outside the heating roller 2 and,
therefore, a core metal 3 can be provided as a center member of the
heating roller 2. By providing the core metal 3 it is possible to increase
the strength of the heating roller 2.
It is to be noted that the core member 3 may be omitted if, in this case,
an adequate strength of the heating roller 2 can be secured. In this case,
the heating roller 2 becomes an air core structure. If an adequate
strength of the heating roller 2 can be maintained, it is possible to use
a resin member, such as plastic, in place of the core member 3.
The heat capacity of the heating roller 2 differs according to the axial
position of the heating roller 2. That is, the heat capacity on both the
axial end portions of the heating roller 2 is greater than that on the
axial middle portion of the heating roller 2. Therefore, a temperature
rise at each axial end portion of the heating roller 2 becomes slower than
that at the axial middle portion of the heating roller 2.
In order to deal with such a different heat capacity problem, the coil 22
is outwardly extended by a distance A from the axial end edge of the
heating roller 2 and the coil 23 is outwardly extended by a distance A
from the axial end edge of the heating roller 2. By this structure, a high
frequency magnetic field from the coils 22 and 23 can be efficiently
applied to both the axial end portions of the heating roller 2. By doing
so, a heating level is increased at both the axial end portions of the
heating roller 2, so that the temperature distribution becomes uniform
over the axial direction of the heating roller 2.
In the case where the sheet (P) passing area is displaced toward the axial
end of the heating roller 2, the above-mentioned outwardly extending
(distance A) coil structure may be adopted only on one side of either of
the coils 22 and 23. That is, in the case where a passing area of the
sheet P is displaced toward one axial end of the heating roller 2, at
least the coil 22 is outwardly extended from one axial end edge of the
heating roller 2. In the case where a passing area of the sheet P is
displaced toward the other axial end of the heating roller 2, on the other
hand, at least the coil 23 is outwardly extended from the other axial end
edge of the heating roller 2.
Further, since the insulating member 27 is provided between the heating
roller 2 and the coils 21, 22, and 23, there is no possibility that the
coils 21, 22, and 23 will contact the surface of the heating roller 2. As
a result, no damage is caused to the surface of the heating roller 2 and
there is no short-circuiting between the metal member 5 of the heating
roller 2 and the coils 21, 22, and 23.
Since the temperature sensors 12 and 13 are provided more on a downstream
side than at the positions of the coils 21, 22, and 23 in the rotation
direction of the heating roller 2, it is possible to accurately detect the
temperature of the heating roller 2 under the induction heating.
The thermostat 14 is provided more on a downstream side than at the
positions of the coils 21, 22, and 23 in the rotation direction of the
heating roller 2 and it is possible to accurately detect any abnormal
temperature rise of the heating roller 2 under the induction heating. In
this case, the thermostat 14 is opened, thereby interrupting a conduction
current from the commercial AC current source 50 to the fixing apparatus
1.
It may be considered that, in place of the heating roller 2, use is made of
a heating belt comprised of a metal member stacked on an upper surface of
an elastic belt. This heating belt, like the heating roller 2, has a
smaller heat capacity and is entrained around a pair of rollers. In this
connection it is to be noted that the heating belt is likely to be
displaced in a direction perpendicular to the rotation direction. If
therefore, the heating belt is used, it is necessary to adjust the
position of the heating belt in the direction perpendicular to the
rotation direction. It is also necessary to adjust the tension of the
heating belt since the heating belt is entrained between the pair of
rollers.
Such positional adjustment and tension adjustment is unnecessary by
adopting the heating roller.
[2] An explanation will be made below about a second embodiment of the
present invention.
As shown in FIG. 6, a heating roller 2 is so configured as to form a heat
insulating member 4 of, for example, 5 mm thick, metal member 5 of, for
example, 40 .mu.m thick and surface member 7 of, for example, 20 .mu.m, in
that order, on a core metal 3. That is, the elastic member 6 of the first
embodiment is not used in the second embodiment and the remaining
structure, function and effects of the second embodiment are the same as
those of the first embodiment.
[3] A third embodiment of the present invention will be explained below.
As shown in FIG. 7, coils 21, 22, and 23 and cores 24, 25, and 26 are held
in a casing made of an insulating material. The casing 28 is such that its
surface at least opposite a heating roller 2 is formed of a heat resistant
resin, such as a heat resistant phenol, polyimide, or liquid crystal
polymer.
The third embodiment adopts the casing 28 and does not use the insulating
member 27 of the first embodiment.
In this way, the coils 21, 22, and 23 and cores 24, 25 and 26 are held as
one unit in the casing 28 and, by doing so, it is easier to exchange the
coils 21, 22, and 23 and cores 24, 25, and 26. The remaining structure,
function and effects of this third embodiment are the same as those of the
first embodiment.
[4] A fourth embodiment of the present invention will be explained below.
As shown in FIG. 8, a cooling fan 29 is provided near a casing 28 to allow
cooling air to be supplied through an opening of the casing 28 onto coils
21, 22, and 23. The air of the cooling fan is supplied into the casing 28
alone and not onto a heating roller 2.
The other structure, function and effects of the fourth embodiment are the
same as those of the third embodiment.
[5] A fifth embodiment of the present invention will be explained below.
As shown in FIG. 9, coils 21, 22, and 23 and cores 24, 25 and 26 are
covered with an insulating member 90. The insulating member 90 is formed
of a heat resistant resin, such as heat resistant phenol, polyimide or
liquid crystal polymer.
The fifth embodiment adopts the insulating member 90 and does not use the
insulating member 27 of the first embodiment. The other structure,
function and effects are the same as those of the first embodiment.
[6] A sixth embodiment of the present invention will be explained below.
As set out above, a heat capacity of both axial end portions of a heating
roller 2 is greater than that of an axial middle portion of the heating
roller 2. In order to deal with such a problem, as shown in FIG. 10, cores
25 and 26, holding coils 22 and 23 in place are arranged near the surface
of the heating roller 2. That is, a distance B is set between a coil 21
and the surface of the heating roller 2 and a distance C (<B) is set
between coils 22 and 23 and the surface of the heating roller 2.
By this structure, a high frequency magnetic field generated from the coils
22 and 23 can be applied efficiently to both axial ends of the heating
roller 2. A heating level at both axial end portions of the heating roller
is increased and a temperature distribution is made uniform over the axial
direction of the heating roller 2.
If a sheet passing area is displaced toward one of the axial ends of the
heating roller 2, either one of the cores 25 and 26 may be set close to
the surface of the heat roller 2. That is, if the sheet passing area is
displaced toward one axial end of the heating roller 2, at least a core 24
is set close to the surface of the heating roller 2. If, on the other
hand, the sheet passing area is displaced toward the other axial end side
of the heating roller 2, at least the core 25 is set close to the surface
of the heating roller.
The other structure, function and effects are the same as those of the
first embodiment.
[7] An explanation will be made below about a seventh embodiment of the
present invention.
As shown in FIG. 11, coils 21, 22 and 23 are retained on retaining members
91, 92 and 93. A portion of the coil 22 (an area corresponding to one
axial end edge portion of a heating roller 2) is set near the surface of
the heating roller 2. A portion of the coil 23 (an area corresponding to
the other axial end edge portion of the heating roller 2) is set near the
surface of the heating roller 2. That is, a distance B is set between the
coil 21 and the surface of the heating roller 2 and a distance C (<B)
is set between these portions of the coils 22 and 23 and the surface of
the heating roller 2.
By this structure, a high frequency magnetic field generated from the coils
22 and 23 can be applied efficiently to both axial ends of the heating
roller 2. A heating level at both axial end portions of the heating roller
is increased and a temperature distribution is made uniform over the axial
direction of the heating roller 2.
If a passing area of a sheet P is displaced toward one of the axial ends of
the heating roller 2, only one of coils 22 and 23 is set near the surface
of the heating roller 2. That is, in the case where a passing area of the
sheet P is displaced toward one axial end of the heating roller 2, at
least a portion of the coil 22 is set near the surface of the heating
roller 2. In the case where, on the other hand, the passing area of the
sheet P is displaced toward the other end of the heating roller 2, at
least a portion of the core 25 is set near the surface of the heating
roller 2.
The other structure, function and effects of this embodiment are the same
as in the first embodiment.
[8] An eighth embodiment of the present invention will be described below.
As shown in FIG. 12, coils 21, 22 and 23 are mounted on retaining members
91, 92 and 93. The diameter of a portion of the coil 22 (an area
corresponding to one axial end edge portion of a heating roller 2) is
enlarged in a direction substantially orthogonal to the axial direction of
the heating roller 2. A diameter of a portion of the coil 23 (an area
corresponding to the other axial end edge portion of the heating roller 2)
is enlarged in a direction substantially orthogonal to the axial direction
of the heating roller 2. That is, the diameter of the coil 21 is set to D
and the diameters of the coils 22 and 23 are set to E (<D).
By this structure, a high frequency magnetic field generated from the coils
22 and 23 can be efficiently applied to both the axial ends of the heating
roller. As a result, a heating level is increased relative to both the
axial end portions of the heating roller 2 to allow a temperature
distribution to be set uniform relative to the axial direction of the
heating roller 2.
In the case where a passing area of a sheet P is displaced toward one of
the axial ends of the heating roller 2, a diameter enlarging structure may
be adopted to either one of the coils 22 and 23. That is, in the case
where the sheet passing area is displaced toward one axial end of the
heating roller 2, the diameter of at least a portion of the coil 22 is
enlarged in a direction substantially orthogonal to the axial direction of
the heating roller 2. In the case where the sheet passing area is
displaced toward the other axial end of the heating roller 2, the diameter
of at least a portion of the coil 25 is enlarged in a direction
substantially orthogonal to the axial direction of the heating roller 2.
The other structure, function and effects of this embodiment are the same
as in the first embodiment.
[9] An explanation will be made below about a ninth embodiment of the
present invention.
As shown in FIG. 13, a pressing roller 8, like a heating roller 2, is so
configured that a heat insulating member 4, metal member 5, elastic member
6 and surface member 7 are formed, in that order, on a core metal 3.
One coil 100 for induction heating is provided at a position corresponding
to both the pressing roller 8 and heating roller 2. Though not shown in
the Figure, the coil 100 is mounted on a core and generates a high
frequency magnetic field for induction heating. The metal member 5 of the
heating roller 2 and metal member 5 of the pressing roller 8 are heat
generated by applying the high frequency magnetic field to the heating
roller 2 and pressing roller 8.
Further, the coil 100 is so configured that a copper wire is wound, in a
forward/backward repetition fashion, along an axial direction of the
heating roller 2.
FIG. 14 shows an electric circuit for the fixing device 1.
A rectifier circuit 60 is connected to a commercial AC current source 50
through an input detection section 51 and thermostat 14. A high frequency
generation circuit 61 is connected to an output terminal of the rectifier
circuit 60.
The high frequency generation circuit 61 comprises a resonant capacitor 62
constituting, together with the coil 100, a resonance capacitance, a
switching element, such as a transistor 63, configured to excite the
resonance circuit, and a damper diode 64 connected in parallel with the
transistor 63 and generates a high frequency current by allowing the
transistor to be driven by a drive circuit 52 in an ON/OFF fashion. The
high frequency current is supplied to the coil 100.
A temperature sensor 12, print controller 40 and drive circuit 52 are
connected to a CPU 53. The CPU 53 has a control section 56. The control
section 56 controls an output (a drive of the drive circuit 52) of the
high frequency generation circuit 61 to allow the detection temperature of
the temperature sensor 12 to be set to a predetermined value.
By thus induction-heating the heating roller 2 and pressing roller 8 it is
possible to secure a necessary and sufficient heating level for a sheet P
even if the heat capacity of the heating roller 2 is smaller. That is, a
heat energy rather less likely to be produced due to less heat capacity of
the heating roller 2 is compensated by the heat generation of the pressing
roller 8.
The other structure, function and effects are the same as in the first
embodiment.
[10] An explanation will be made below about a tenth embodiment of the
present invention.
As shown in FIG. 15, a pressing roller 8, like a heating roller 2, is so
configured that a heat insulating member 4, metal member 5, elastic member
6, and surface member 7 are formed, in that order, on a core metal 3.
One coil 101 for the heating roller for induction heating is provided at a
position corresponding to the heating roller 2. The coil 101 is mounted on
the core, though not shown, and generates a high frequency magnetic field
for induction heating. The metal member 5 of the heating roller 2 is
heat-generated by applying the high frequency magnetic field to the
heating roller 2.
One coil 102 for the pressing roller 8 for induction heating is provided at
a position corresponding to the pressing roller 8. The coil 102 is mounted
on the core, though not shown, and generates a high frequency magnetic
field for induction heating. The metal member 5 of the pressing roller 8
is heat-generated by applying the high frequency magnetic field to the
pressing roller 8.
FIG. 16 shows an electric circuit of a fixing apparatus 1.
Rectifier circuits 60 and 80 are connected to a commercial AC current
source 50 through an input detection section 51 and thermostat 14. High
frequency generation circuits 61 and 81 are connected to the output
terminals of the rectifier circuits 60 and 80, respectively.
The high frequency generation circuit 61 comprises a resonant capacitor 62
constituting, together with the coil 101, a resonance circuit, a switching
element, such as a transistor 63, configured to excite the resonance
circuit, and a damper diode 64 connected in parallel with the transistor
63 and generates a high frequency current by allowing the transistor 63 to
be driven by a drive circuit 52 in an ON/OFF fashion. The high frequency
current is supplied to the coil 101.
The high frequency generation circuit 81 comprises a resonant capacitor 82
constituting, together with the coil 102, a resonance circuit, a switching
element such as a transistor 83 configured to excite the resonance
circuit, and a damper diode 84 connected in parallel with the transistor
83 and, by allowing the transistor 83 to be driven by the drive circuit 52
in an ON/OFF fashion, generates a high frequency current. The high
frequency current is supplied to the coil 102.
A temperature sensor 12, print controller 40 and drive circuit 52 are
connected to a CPU 53.
The CPU 53 has control sections 56 and 57. The control section 56 controls
an output (drive of the drive circuit) of the high frequency generation
circuit 61 so as to set a detection temperature of the temperature sensor
12 to a predetermined value. In the case where the detection temperature
of the temperature sensor 12 is lowered to below that set value, the
control section 57 operates the high frequency generation circuit 81.
If, in this way, the heat capacity of the heating roller 2 is smaller by
induction-heating both the heating roller 2 and pressing roller 8, it is
possible to secure a necessary and sufficient heating level for a sheet P.
It is to be noted that the electric circuit is not restricted to the one
alone as shown in FIG. 16 and it is possible to adopt a circuit by which
either one of the coils 101 and 102 is selectively operated by a mutually
different resonance frequency.
The other structure, function and effects are the same as in the first
embodiment.
[11] An explanation will be made below about an eleventh embodiment of the
present invention.
As shown in FIG. 17, a pressing roller 8, like a heating roller 2, is so
configured that a heat insulating member 4, metal member 5, elastic member
6 and heating member 7 are formed, in that order, on a core member 3.
As in the first embodiment, three coils 21, 22 and 23 for induction heating
are provided at those positions corresponding to the heating roller 2. The
coils 21, 22 and 23 are mounted on the cores 24, 25 and 26, not shown in
FIG. 17, as in the first embodiment of the present invention.
As in the tenth embodiment, one coil 102 for induction heating is provided,
as in the tenth embodiment, at a position corresponding to the pressing
roller 8.
FIG. 18 shows an electric circuit of a fixing apparatus 1. This electric
circuit corresponds to a combination of the electric circuit shown in the
first embodiment and electric circuit shown in the tenth embodiment.
By thus induction-heating both the heating roller 2 and pressing roller 8
it is possible to secure a necessary and sufficient heating level for a
sheet P even if, for example, the heat capacity of the heating roller 2 is
smaller.
The other structure, function and effects are the same as in the first
embodiment.
[12] An explanation will be made below about a twelfth embodiment of the
present invention.
As shown in FIG. 19, temperature sensors 12 and 13 and thermostat 14 are
provided more on a downstream side in a rotation direction of a heating
roller 2 than a contacting site (nip) between the heating roller 2 and a
pressing roller 8.
The temperature sensors 12 and 13 detect, of a surface temperature of the
heating roller 2, a surface temperature just after a nip between the
heating roller 2 and the pressing roller 8. The thermostat 14 is set in an
opened state in the case where, of the surface temperature of the heating
temperature, the temperature just after the nip between the heating roller
2 and the pressing roller 8 is raised to an abnormal level.
The other structure, function and effects are the same as in the first
embodiment of the present invention.
[13] An explanation will be made below about a thirteenth embodiment of the
present invention.
As shown in FIG. 20, a heating roller 2 is such that a nonmetal member 112
of, for example 2 mm thick, heat insulating member 4 of, for example, 0.5
mm thick, metal member 5 of, for example, 50 .mu.m and surface member 7
of, for example, 20 .mu.m are formed are formed in that order as a
drum-like configuration. A coil 110 for induction heating is held within
an inner space of the heating roller 2.
The coil 110 is mounted on a retaining member 111 and generates a high
frequency magnetic field for induction heating, and the metal member 5 is
heat-generated by applying the high frequency magnetic field to the metal
member 5.
It is to be noted that an elastic member 6 may be provided between the
metal member 5 and the surface member 7 as in the first embodiment of the
present invention.
The other structure, function and effects are the same as in the tenth
embodiment of the present invention.
Additional advantages and modifications will readily occur to those skilled
in the art. Therefore, the invention in its broader aspects is not limited
to the specific details and representative embodiments shown and described
herein. Accordingly various modifications may be made without departing
from the spirit or scope of the general inventive concept as defined by
the appended claims and their equivalents.
*
