Title: Heating apparatus that supplies power to excitation circuits based on detecting predetermined temperature
Abstract: A heating apparatus includes first and second coil members, a heat roller and an input control mechanism. The first and second coil members respectively are part of first and second excitation circuits. The heat roller generates an eddy current inside by a magnetic field generated by the first and second coil members. The input control mechanism drives the first and second excitation circuits. The input control mechanism starts driving only the first excitation circuit from a state where operations of the first and second excitation circuits are stopped. When the temperature detection mechanism detects a predetermined temperature, the input control mechanism stops supplying power to the first excitation circuit and supplies power only to the second excitation circuit, and the heat roller initiates rotating.
Patent Number: 7,016,622 Issued on 03/21/2006 to Kinouchi, et al.
| Inventors:
|
Kinouchi; Satoshi (Tokyo, JP);
Takagi; Osamu (Tokyo, JP)
|
| Assignee:
|
Kabushiki Kaisha Toshiba (Tokyo, JP);
Toshiba Tec Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
863241 |
| Filed:
|
June 9, 2004 |
| Current U.S. Class: |
399/70; 399/334; 219/619 |
| Current Intern'l Class: |
G03G 15/20 (20060101) |
| Field of Search: |
399/69,70,328.33,334
219/601,619,643,644,660,661,663,667,216,388
|
References Cited [Referenced By]
U.S. Patent Documents
| 4585325 | Apr., 1986 | Euler.
| |
| 5666627 | Sep., 1997 | Yamaguchi.
| |
| 5752150 | May., 1998 | Kato et al.
| |
| 5819134 | Oct., 1998 | Sato et al.
| |
| 6026273 | Feb., 2000 | Kinouchi et al.
| |
| 6078781 | Jun., 2000 | Takagi et al.
| |
| 6087641 | Jul., 2000 | Kinouchi et al.
| |
| 6243547 | Jun., 2001 | Mizuno et al.
| |
| 6292647 | Sep., 2001 | Ishida.
| |
| 6301454 | Oct., 2001 | Nishida et al.
| |
| 6320168 | Nov., 2001 | Kimata et al.
| |
| 6336027 | Jan., 2002 | Sakai et al.
| |
| 6337969 | Jan., 2002 | Takagi et al.
| |
| 6438335 | Aug., 2002 | Kinouchi et al.
| |
| 6449445 | Sep., 2002 | Nakamori et al.
| |
| 6463252 | Oct., 2002 | Omoto et al.
| |
| 6587654 | Jul., 2003 | Nishi.
| |
| 6643476 | Nov., 2003 | Kinouchi et al.
| |
| 6643491 | Nov., 2003 | Kinouchi et al.
| |
| 6763206 | Jul., 2004 | Kinouchi et al.
| |
| Foreign Patent Documents |
| 2-270293 | Nov., 1990 | JP.
| |
| 8-76620 | Mar., 1996 | JP.
| |
| 9-258586 | Oct., 1997 | JP.
| |
| 11288193 | Oct., 1999 | JP.
| |
| 2000/-206813 | Jul., 2000 | JP.
| |
| 2000206813 | Jul., 2000 | JP.
| |
| 2001154531 | Jun., 2001 | JP.
| |
| 2001/-185338 | Jul., 2001 | JP.
| |
| 2002063981 | Feb., 2002 | JP.
| |
| 2002-75608 | Mar., 2002 | JP.
| |
Other References
U.S. Appl. No. 09/699,472, filed Oct. 31, 2000, Kinouchi et al.
|
Primary Examiner: Beatty; Robert
Attorney, Agent or Firm: Foley & Lardner LLP
Parent Case Text
The present application is a continuation of U.S. application Ser. No. 10/143,909,
filed May 14, 2002, now U.S. Pat. No. 6,763,206, the entire contents of which are
incorporated herein by reference.
Claims
What is claimed is:
1. A heating apparatus comprising:
a first coil member which is a part of a first excitation circuit;
a second coil member which is a part of a second excitation circuit;
a heat roller which generates an eddy current inside by a magnetic field generated
from the first and second coil members; and
an input control mechanism which drives the first and second excitation circuits, wherein
the input control mechanism starts driving only the first excitation circuit
from a state where operations of the first and second excitation circuits are stopped,
the input control mechanism executes soft start in which the value of power supplied
to the first excitation circuit is gradually increased and finally power of a predetermined
value is supplied to the first excitation circuit.
2. The heating apparatus according to claim 1, further comprising:
a first temperature detecting mechanism which detects temperature of the heat
roller, wherein
when the first temperature detection mechanism detects a predetermined temperature,
the input control mechanism stops supplying power to the first excitation circuit
and supplies power only to the second excitation circuit.
3. The heating apparatus according to claim 2, further comprising:
a second temperature detection mechanism which detects temperature of a position
in the heat roller different from the position in which the first temperature detection
mechanism detects the temperature, wherein
when the second temperature detection mechanism detects a second predetermined
temperature, the input control mechanism stops supplying power to the second excitation
circuit and supplies power to the first excitation circuit.
4. The heating apparatus according to claim 3, wherein
the first temperature detection mechanism detects temperature of a region in
which the first coil of the heat roller is heated, and
the second temperature detection mechanism detects temperature of a region in
which the second coil of the heat roller is heated.
5. The heating apparatus according to claim 2, wherein
when the input control mechanism starts supplying power to the second excitation
circuit, the input control mechanism starts supplying power of a predetermined
value to the second excitation circuit without time lag.
6. The heating apparatus according to claim 2, wherein
when the power supply is switched from supplying power to the first excitation
circuit to supplying power to the second excitation circuit, the input control
mechanism performs zero-cross control within a predetermined time from a time in
which an input voltage of power supply for commercial use becomes zero.
7. The heating apparatus according to claim 3, wherein after the input control
mechanism supplies power again to the first excitation circuit, the input control
mechanism compares the temperatures detected by the first temperature detection
mechanism and the second temperature detection mechanism and drives only the excitation
circuit corresponding to a region which has lower temperature of the two.
8. The heating apparatus according to claim 2, wherein, when the temperature
detection mechanism detects a predetermined temperature, the input control mechanism
stops supplying power to the first excitation circuit and supplies power only to
the second excitation circuit, and the heat roller initiates rotating.
9. A heating apparatus comprising:
a first coil member which is a part of a first excitation circuit;
a second coil member which is a part of a second excitation circuit;
a heat roller which generates an eddy current inside by a magnetic field generated
from the first and second coils;
an input control mechanism which drives the first and second excitation circuits;
a first temperature detection mechanism which detects temperature of a region
in which the first coil of the heat roller is heated; and
a second temperature detection mechanism which detects temperature of a region
in which the second coil of the heat roller is heated,
wherein when the input control mechanism starts driving the first and second
excitation circuits simultaneously from a state where operations of the first and
second excitation circuits are stopped, the input control mechanism executes soft
start in which the power supplied to the first and second excitation circuits is
gradually increased, and finally power of a predetermined value is supplied to
the first and second excitation circuits,
wherein when either one of the first and second temperature detection mechanisms
detects a predetermined temperature, the input control mechanism stops supplying
power to an excitation circuit corresponding to the temperature detection mechanism
which has detected the predetermined temperature, and
wherein after the input control mechanism has stopped an operation of either
one of the excitation circuits, the input control mechanism compares the temperatures
detected by the first temperature detection mechanism and the second temperature
detection mechanism, and drives only the excitation circuit corresponding to the
lower temperature of the two.
10. The heating apparatus according to claim 9, wherein
after the input control mechanism stops an operation of either one of the excitation
circuits, the heat roller initiates rotating.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a heating apparatus using induction heating.
Specifically, the present invention concerns a fixing apparatus which is used for
an electrophotographic copying apparatus, printer, etc. using toner as a visualizing
material and fixing a toner image.
A fixing apparatus installed in a copying apparatus using electrophotographic
processes
heats and melts the developer, i.e., toner formed on a fixing member to fix the
toner on the fixing member. There are widely known methods of heating toner available
for the fixing apparatus such as using radiant heat from a filament lamp, using
a flash lamp as a heat source, etc.
The fixing apparatus using a filament lamp uses light and infrared rays from
the filament lamp to heat a roller around the lamp by radiation. The thermal conversion
efficiency is 60% to 70% in consideration of the loss of heat converted from light,
the efficiency of transmitting heat to the roller by heating air in the roller,
etc. It is known that a long warm-up time is required.
Jpn. Pat. Appln. KOKAI Publication Nos. 9-258586, 8-76620, and the like propose
a fixing apparatus using an induction heating apparatus as the heat source.
Jpn. Pat. Appln. KOKAI Publication No. 9-258586 discloses a fixing apparatus
which applies an electric current to an induction coil formed around a core along
a rotating shaft of a metal roller and generates an induction current in the roller
to generate heat from the roller.
Jpn. Pat. Appln. KOKAI Publication No. 8-76620 discloses the fixing apparatus
which comprises an induction film including a magnetic field generation means and
a pressure roller adhered to the induction film. This fixing apparatus transports
a recording medium between the induction film and the pressure roller and heats
the induction film to fix toner on the recording medium.
The fixing apparatus used for copying apparatuses is subject to a specific problem
of unevenly generating temperature on the metal roller or the film due to an ununiformed
size of paper to be fixed (paper passage width). It is requested to shorten the
time to warm up the fixing apparatus.
In order to prevent uneven temperature for the paper passage width, there are
provided a plurality of induction coils in accordance with the paper passage width
along an axial direction of a fixing roller to control electric power supplied
to each coil. This example is disclosed in Jpn. Pat. Appln. KOKAI Publication No.
2000-206813. The fixing apparatus disclosed in this publication uses a plurality
of detection points to detect heating of the fixing roller and controls the electric
power supplied to the respective coils based on the temperature detected at each
detection point.
Jpn. Pat. Appln. KOKAI Publication No. 2001-185338 discloses an example of providing
a plurality of induction coils for an image forming apparatus using an induction
heating apparatus in order to eliminate uneven heating. When a plurality of coils
is powered, the example changes the high-frequency power supplied to any coil to
the parallel connection. When a plurality of coils is powered simultaneously according
to the example in this publication, each coil is connected to a common (same) high-frequency
power supply, providing the same phase to electric current supplied to respective
coils. It is possible to independently set the power supplied to each coil.
Jpn. Pat. Appln. KOKAI Publication No. 2-270293 discloses an induction heating
apparatus having two induction coils. There is provided a zero-voltage detection
circuit to detect a zero point of the alternating-current (input) power supply.
The publication discloses changeover of electric current supplied to a targeted
coil by passing the zero point (0 volt) of the alternating-current (input) power
supply. During the changeover of electric current supplied to a targeted coil,
an impulse sound (interference sound) occurs between the coil and the roller. To
prevent this sound, there is disclosed provision of a specified time interval at
the changeover time.
According to the method of driving coils disclosed in the above-mentioned
Jpn. Pat. Appln. KOKAI Publication No. 2000-206813, the power supplied to a plurality
of coils changes simultaneously. Because of this, a frequency difference occurs
between high-frequency currents supplied to respective coils, causing an interference
sound (buzzing). Further, there must be independently provided an apparatus to
detect the magnitude of power supplied to each coil. In addition, the warm-up time
is prolonged when every possible effort is made to uniform the axial temperature
of the metal roller.
Jpn. Pat. Appln. KOKAI Publication No. 2001-185338 discloses the common high-frequency
power supply apparatus to which respective coils are connected in order to prevent
an inverter's interference. However, there are not disclosed actual control timings,
control methods, etc. in detail. Nothing is disclosed about a method of shortening
the warm-up time.
The method of driving coils disclosed in Jpn. Pat. Appln. KOKAI Publication No.
2-270293 uses the soft start feature to prevent occurrence of an excess rush current
or to prevent application of a power larger than the controlled one. Soft start
is a method of driving coils for preventing an excess rush current from occurring.
When a coil is powered, the method feeds back the power by gradually applying an
output smaller than the specified output value until this specified value is reached.
When the soft start is performed each time each coil is powered, the heating
efficiency degrades and the warm-up time increases. There also arises a problem
of increasing the amount of the varying power supplied to each coil. The power
supplied to each coil is switched by passing the zero point of the alternating-current
power (input) voltage and providing a specified time interval. This causes a flicker
etc. caused by the power fluctuation when the coils are changed.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image forming apparatus
using an induction heating fixing apparatus capable of shortening the warm-up time.
The present invention provides a heating apparatus comprising:
a first coil member and a second coil member, wherein each coil member heats
an object;
a first temperature detection mechanism and a second temperature detection mechanism,
wherein the first temperature detection mechanism detects a temperature as a result
of heating the object by supplying the first coil member with a first specified
output and the second temperature detection mechanism detects a temperature as
a result of heating the object by supplying the second coil member with a second
specified output; and
an output control mechanism which can respectively supply the first and second
coil members with the first and second specified outputs,
wherein the output control mechanism continuously supplies the first coil
member with the first specified output until the first temperature detection mechanism
detects that the first coil member heats the object and consequently the temperature
of an area heated by the first coil member reaches a specified temperature, and
the second coil member is not supplied with the second specified output while the
first coil member is supplied with the first specified output.
Further, the present invention provides a heating apparatus comprising:
a first coil member and a second coil member, wherein each coil member heats
an object;
a first temperature detection mechanism and a second temperature detection mechanism,
wherein the first temperature detection mechanism detects a temperature as a result
of heating the object by supplying the first coil member with a first specified
output and the second temperature detection mechanism detects a temperature as
a result of heating the object by supplying the second coil member with a second
specified output; and
an output control mechanism which can respectively supply the first and second
coil members with the first and second specified outputs,
wherein the output control mechanism can select either a first control method
of simultaneously driving the first and second coil members or a second control
method of not driving the other coil member when the first coil member or the second
coil member is driven.
Moreover, the present invention provides a heating apparatus comprising:
a first coil member and a second coil member, wherein each coil member heats
an object;
a first temperature detection mechanism configured to detect a temperature as
a
result of heating the object by supplying the first coil member with a first specified
output and a second temperature detection mechanism configured to detect a temperature
as a result of heating the object by supplying the second coil member with a second
specified output; and
an output control mechanism which can respectively supply the first and second
coil members with the first and second specified outputs,
wherein when the first and second coil members are supplied with the first
and second specified outputs, from a state of all coil members turned off, at least
either coil member is supplied with either of the first and second specified outputs
and wherein, until the heating intensity generated from the coil member supplied
with the output reaches a specified magnitude, the output control mechanism gradually
increases the first and second specified outputs at a given interval.
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 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 schematically shows an example of an image forming apparatus which installs
an induction heating fixing apparatus according to the present invention;
FIG. 2 is a sectional view schematically showing an example of an induction
heating fixing apparatus usable for the image forming apparatus as shown in FIG. 1;
FIG. 3 is a plan view schematically showing the fixing apparatus in FIG. 2 with
a cover etc. removed;
FIG. 4 is a block diagram illustrating an example of an excitation unit (fixing
apparatus drive circuit) for driving the fixing apparatus in FIGS. 2 and 3;
FIG. 5 is a graph for explaining temperature rise characteristics at startup
(power-on sequence initiation) of a fixing roller heated through the use of the
fixing apparatus drive circuit as shown in FIG. 4;
FIG. 6 is a flowchart for explaining an example of control at startup (power-on
sequence initiation) for raising the roller temperature through the use of the
fixing apparatus drive circuit as shown in FIG. 4;
FIG. 7 is a flowchart for explaining another example of warm-up control different
from an embodiment shown in FIGS. 4 to 6;
FIG. 8 is a graph for explaining the relationship between the time and the fixing
roller's temperature rise based on the warm-up control shown in FIG. 7;
FIG. 9 is a flowchart for explaining another example of warm-up control different
from the embodiment shown in FIGS. 4 to 8;
FIG. 10 schematically shows another example of the excitation unit different
from the one shown in FIG. 4;
FIG. 11 is a flowchart for explaining an example of temperature control applicable
to the excitation unit shown in FIG. 10;
FIG. 12 is a graph for explaining the relationship between the time and the
fixing roller's temperature rise based on the excitation unit shown in FIG. 10
and the warm-up control shown in FIG. 11;
FIG. 13 schematically shows an example of an embodiment by modifying the excitation
unit in FIG. 10;
FIGS. 14A, 14B, and 14C are timing charts for chronologically
showing specified outputs according to another example of drive control applicable
to the heating apparatus using a coil as a heat-up mechanism;
FIG. 15 is a graph showing an output change of the coil with the use of a soft
start in FIG. 14B;
FIG. 16 is a graph showing an output change of the coil in FIG. 14C by directly
supplying a specified output to the coil without the use of a soft start in FIG.
14C; and
FIGS. 17A, 17B, and 17C are timing charts for explaining an example
of timing for changing coils to be driven in the heating apparatus containing a
plurality of coils.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the accompanying drawings, the following describes a digital
copying apparatus as an example of the image forming apparatus to which embodiments
of the present invention are applied.
As shown in FIG. 1, a digital copying apparatus (image forming apparatus)
101
includes an image reading apparatus (scanner)
102 and an image forming section
103. The scanner
102 photoelectrically converts an object image as
brightness and darkness of the light to generate an image signal. The image forming
section
103 forms an image corresponding to the image signal supplied from
the scanner
102 or from the outside and fixes the formed image on paper
P as a fixing member (copy material).
The image forming section
103 contains a cylindrical photosensitive drum
105. A photo conductor is formed on the drum's external surface. When the
light is irradiated with a specified electric potential supplied, the electric
potential changes at the area where the light is irradiated. The photo conductor
can maintain the electric potential change as an electrostatic image for a specified
time period.
An exposing apparatus
106 exposes image information onto the photosensitive
drum
105. The exposing apparatus
106 can generate a laser beam with
variable light intensity in accordance with the image information supplied from
the scanner
102 or an external apparatus. In this manner, an electrostatic
image is formed on the photosensitive drum
105. A developing apparatus
107
selectively supplies toner (developer) to visualize the image formed on the photosensitive
drum
105.
Supplying toner from the developing apparatus
107 develops a toner
image, i.e., an aggregate of toner, on the photosensitive drum
105. When
a transfer apparatus (not detailed) supplies a voltage for transfer, the toner
image is transferred to a transfer material P supplied from a paper feed section
to be described.
The fixing apparatus
1 applies heat and pressure to melt the toner image
transferred to the transfer material P. The image is fixed to the transfer material
P due to the pressure from the fixing apparatus.
The image forming apparatus is supplied with an image signal from the scanner
102 or an external apparatus. The exposing apparatus
106 irradiates
a laser beam (not detailed) to a specified position of the photosensitive drum
105 which is already charged to a specified electric potential. Thus, the
photo-sensitive drum
105 forms an electrostatic latent image corresponding
to the image to be copied (output).
When the developing apparatus
107 selectively supplies toner, the electrostatic
latent image formed on the photosensitive drum
105 is developed and is converted
to a toner image (not shown).
The toner image on the photosensitive drum
105 is transferred to a transfer
material, i.e., paper P at a transfer position opposite the transfer apparatus
assigned with no reference numeral. The paper P is transferred to the transfer
position. Though not detailed, a pickup roller
109 takes out the paper P
sheet by sheet from a paper cassette
108. The paper P is then transported
to an aligning roller
111. The paper P is fed to the transfer position with
the adjusted paper feed timing.
When the transfer apparatus transfers the toner onto the paper P, it is transported
to the fixing apparatus
1. The fixing apparatus
1 melts the toner
on the paper P and applies pressure to fix the toner on the paper P.
FIGS. 2 and 3 schematically show an example of the fixing apparatus used for
the image forming apparatus as shown in FIG. 1. FIG. 2 is a cross sectional view
taken along a longer direction of the fixing apparatus
1 at the approximate
center. FIG. 3 is a plan view schematically showing the fixing apparatus
1
with a cover etc. (not detailed) removed.
The fixing apparatus
1 comprises a heating (fixing) roller
2 approximately
50 mm in diameter and a pressure roller
3 approximately 50 mm in diameter.
The fixing roller
2 is made of metal approximately 1.5 mm thick. In this
example, the fixing roller
2 is made of iron and is cylindrical. On the
surface of the fixing roller
2, there is formed a release layer (not shown)
by depositing fluorocarbon resin such as polytetrafluoroethylene (Teflon as a brand
name) for a specified thickness.
Available materials for the fixing roller
2 include stainless steel,
aluminum, alloys of stainless steel and aluminum, etc. In this example, the fixing
roller
2 is approximately 340 mm long.
Instead of the fixing roller
2, it is possible to use a metallic film
formed in an endless belt by depositing metal for a specified thickness on the
surface of a highly heat-resistant resin film.
The pressure roller
3 is an elastic roller coated with silicon rubber,
fluoro rubber, etc. having a specified thickness around a shaft having a specified
diameter. The pressure roller
3 is approximately 320 mm long.
The pressure roller
3 is placed approximately parallel to an axis line
of the fixing roller
2. A pressurization mechanism
4 presses the
pressure roller
3 with a specified pressure against the axis line of the
fixing roller
2. This elastically deforms part of the outer peripheral surface
of the fixing roller
3, defining a given nip between both rollers. When
a metallic film is used instead of the fixing roller
2, a nip may be formed
on the film.
The fixing roller
2 rotates in the direction of an arrow at an approximately
constant speed by means of a driving force supplied from a fixing motor
123
or a drum motor
121 which rotates the photosensitive drum
105. The
pressure roller
3 is supplied with a given pressure from the pressurization
mechanism
4 to touch the fixing roller
2. Accordingly, rotating the
fixing roller
2 rotates the pressure roller
3 in the reverse direction
of the fixing roller
2.
The pressure roller
3 touches the outer peripheral surface of the fixing
roller
2 at a specified position called a nip. A release claw
5 is
provided to release the paper P passing the nip from the fixing roller
2.
The release claw
5 is positioned as specified near the nip at the downstream
of the rotating direction of the fixing roller
2.
Around the fixing roller
2, there are provided at least two temperature
detection elements
6a and
6b, a cleaner
7, and
a heating error detection element
8 in order clockwise from the release
claw
5.
The temperature detection elements
6a and
6b detect
temperature on the outer peripheral surface of the fixing roller
2.
The temperature detection elements
6a and
6b are
thermistors, for example. At least one thermistor is approximately centered on
the roller
2 in a longitudinal direction.
The other of the temperature detection elements
6a and
6b
is positioned at one end of the roller
2 in a longitudinal direction.
Each of the thermistors
6a and
6b is provided anywhere
on the outer periphery of the roller
2, i.e., at a position where the phase
viewed from the sectional direction is not subject to a specific condition. Obviously,
it is possible to provide three or more thermistors.
The cleaner
7 removes toner or paper dust generated from the paper. The
toner or paper dust may adhere to the fluorocarbon resin which has a specified
thickness and is provided on the outer periphery of the fixing roller
2.
The cleaner
7 also removes dirt or the like which floats in the apparatus
and adheres to the fixing roller
2. The cleaner
7 includes a cleaning
member and a support member which supports the cleaning member. The cleaning member
is made of, e.g., a felt, a fur brush, or any other material whose contact with
the fixing roller
2, if any, hardly damages the fluorocarbon resin layer.
The cleaning member may rotate in contact with the surface of the fixing roller
2 or may be pressed against the outer peripheral surface of the fixing roller
2.
For example, a thermostat is used for the heating error detection element
8
to detect a heating error which causes the surface temperature of the fixing roller
2 to rise abnormally. When a heating error occurs, the heating error detection
element
8 is used to prevent power supply to a heating coil (to be described).
The order and positions for arranging the temperature detection elements
6a
and
6b, the cleaner
7, and the heating error detection
element
8 are not limited to those indicated in FIG. 2.
On the periphery of the pressure roller
3, there are provided a release
claw
9 to release the paper P from the pressure roller
3 and a cleaning
roller
10 to remove toner applied to the outer peripheral surface of the
pressure roller
3.
The inside of the fixing roller
2 is provided with an excitation coil
11 for generating an eddy current in the material of the roller
2.
According to the example in FIG. 3, the excitation coil
11 includes a first
coil
11a and a second coil
11b. The first coil
11a
is positioned approximately at the center of the fixing roller
2 along
its longer direction. The second coil
11b is provided near each end
of the roller
2.
The second coil
11b is made of a wire having approximately the
same resistivity and approximately the same sectional area (the number of strands)
as those of the first coil
11a. The second coil
11b is
formed by winding such wire for approximately the same number of turns as for the
first coil
11a. The second coil
11b is arranged along
the longer direction of the roller
2 and is positioned at each end of the
roller
2 in the axial direction to sandwich the first coil
11a.
The second coil
11b can produce an output equivalent to that of
the first coil
11a at two locations, i.e., both ends of the first
coil
11a. In the description to follow, each part of the second coil
11b is referred to as a coil
11-
1 or
11-
2
when each part needs to be identified independently.
While the first coil
11a can heat near the center of the fixing
roller
2 in the longitudinal direction, the second coil
11b is
useful for heating near both ends of the fixing roller
2.
When, for example, an A4-size sheet of paper is transported so that its shorter
side parallels the axial line of the fixing roller
2, the first coil
11a
is formed to have enough length to heat the width of paper in contact with
the outer peripheral surface of the roller
2.
The coils
11a and
11b of the excitation coil
11
are formed of a plurality of 0.5 mm diameter copper wires each insulated by heat-resistant
polyamide-imide. In this example, each coil is formed of a Litz wire comprising
a bundle of 16 such wires. The use of the Litz wire to form the excitation coil
11 enables the diameter of each wire to be smaller than the penetration
depth of a skin effect occurring when a high-frequency alternating current is applied
to the wire. Thus, it is possible to effectively apply a high-frequency current.
According to the example in FIG. 2, the coils
11a and
11b
are fixed to a support member
12 via a coil supporter
13 formed
of highly heat-resistant and insulative engineering plastics or ceramics. For the
coil supporter
13, it is possible to use a PEEK (poly ether ether ketone)
material, a phenol material, unsaturated polyester, etc., for example.
There is available any method of winding a wire to form the coils. By modifying
the shape of the coil supporter
13, the flat excitation coil
11 may
be formed to a shape that matches the inner circular periphery of the fixing roller
2.
In this embodiment, a ferrite core
14 is provided inside the coil to strengthen
the magnetic flux. It may be preferable to use an air-core coil without using a
core material such as ferrite, etc.
FIG. 4 schematically shows an example of an excitation unit (excitation circuit)
for driving the coils
11a and
11b of the excitation
coil
11 as shown in FIGS. 2 and 3.
As shown in FIG. 4, the first coil
11a at the center is connected
to a first switching circuit (inverter circuit)
32a of the excitation
unit
31. The second coil
11b (including the coil
11-
1
at one end and the coil
11-
2 at the other end) is connected to a
second switching circuit (inverter circuit)
32b.
In response to a control output from a drive circuit
33, the respective
switching circuits
32a and
32b change the commercial
power (AC power) frequency supplied from the outside to a specified frequency and
supply the frequency to the respectively connected coils
11a and
11b. Accordingly, a specified electric power is independently or
simultaneously supplied to the first and second coils
11a and
11b
respectively connected to the switching circuits
32a and
32b.
Obviously, the current applied to each coil changes at any time in accordance with
a change of the time for enabling a switching element (transistor etc.)
Under control of a control CPU
34, the drive circuit
33 generates
control output to the first and second switching circuits
32a and
32b so that the switching circuits
32a and
32b
can generate the requested high-frequency output, i.e., inverter output with
a specified frequency. The magnitude of high-frequency current supplied to coils
varies with a change of the time for enabling the switching element to drive each
coil. Accordingly, it is possible to set any magnitude of power supplied to each coil.
The first and second thermistors
6a and
6b detect
the temperature near the center of the outer peripheral surface on the fixing roller
2 and temperature at both ends. A temperature detection circuit
35
converts the detected temperatures to temperature data (A/D converts). Based on
the temperature data, the control CPU
34 sets high-frequency outputs to
be generated from the first and second switching circuits
32a and
32b and supplies the outputs to the drive circuit
33.
Memory
36 capable of rewriting data previously stores the correspondence
between temperature data and high-frequency output, the timing to drive the switching
circuits
32a and
32b, etc. Data stored in the memory
36 can be freely rewritten according to power supply requirements for a
country or a district where the copying apparatus
101 is installed or an
allowable maximum value of power that can be supplied.
The following describes an example of first control for heating the outer peripheral
surface of the fixing roller
2 to a specified temperature.
In the case of almost uniformly heating the entire area of the fixing roller
2
in the longitudinal direction (normal heating), for example, the first and second
switching circuits
32a and
32b shown in FIG. 4 supply
the respective coils
11a and
11b with output having
a specified frequency (high-frequency output).
When the inverter circuits (first and second switching circuits
32a
and
32b) are used, the power supplied to the coils
11a
and
11b installed in the circuits depends on the magnitude of
high-frequency current supplied to the coils. The magnitude of the high-frequency
current is set based on the time for turning on the switching element, i.e., the
ON time of the switching element. The magnitude of the current supplied to each
coil is set based on the ON time of the switching element to be supplied to the
inverter circuit. Namely, the magnitude of power supplied to each coil varies with
the frequency determined by the ON time of the switching element and the time for
turning off the switching element, i.e., the OFF time issued to the drive circuit
33 from the CPU
34. The power will be described as power to be output
to the coils hereinafter.
Each of the coils
11a and
11b generates a magnetic
flux having a specified direction according to the coil shapes and the magnitude
of power supplied to the coils.
A change of the magnetic field generated by this magnetic flux is prevented by
a magnetic flux and an eddy current occurring at a metallic part of the fixing
roller
2. Accordingly, the metallic part of the fixing roller
2 generates
Joule heat due to the eddy current and the resistance of the metallic part itself.
The Joule heat heats the fixing roller
2, thus heating the paper P passing
between the fixing roller
2 and the pressure roller
3 (see FIG. 2).
For example, the drive unit shown in FIG. 4 is used to supply the center excitation
coil
11a with an output that produces 900 W power at the frequency
of 25 through to 30 kHz. In this case, eddy currents are generated to heat the
center of the fixing roller
2 in the longitudinal direction, increasing
the temperature of the center or vicinity of the fixing roller
2 in the
longitudinal direction to a specified temperature.
When the center coil
11a is not powered, the coil
11b
at the end is also supplied with an output that produces 900 W power at the
frequency of 25 through to 30 kHz, increasing the temperature at both ends of the
roller
2 to a specified temperature.
Of course, when either coil is powered, the other coil is not powered.
The power supplied to coils has different upper bounds depending on countries
and districts where the copying apparatus
101 is used. By changing frequencies
up to an upper bound, the power can be changed within a range from 700 to 1300 W.
There is a warm-up period after the copying apparatus
101 is turned
on until the surface temperature of the fixing roller
2 in the fixing apparatus
1 reaches a temperature capable of fixing. During the warm-up period, the
control CPU
34 in the excitation unit
31 directs the drive circuit
33 to supply a specified power. This drives the first switching circuit
32a to supply the specified power to the center coil
11a.
The coils b at the ends are not powered until a specified temperature is reached
on the surface of the fixing roller
2 heated by the magnetic flux from the
center coil
11a. Namely, the second switching circuit
32b
remains OFF because of no drive output from the drive circuit
33 under
control of the CPU
34.
The first and second thermistors
6a and
6b always
monitor the surface temperature of the fixing roller
2. The monitor output
is converted (A/D converted) in the temperature detection circuit
35 and
is input to the CPU
34.
When the thermistor
6a detects that the temperature at the center
of the roller
2 reaches the specified temperature, this state is notified
to the CPU
34 via the temperature detection circuit
35. According
to a control pattern already stored in the memory
36, control is provided
to stop power supply to the center coil
11a, i.e., a drive output
to the first switching circuit
32a from the drive circuit
33
as shown in FIG. 5. At a specified timing, the drive circuit
33 then generates
a specified drive output to the second switching circuit
32a.
Consequently, the specified power is supplied to the coil
11b
provided at both ends of the roller
2. In many cases, the electrical
energy supplied to the coil
11b is the same as that so far supplied
to the center coil
11a. The description to follow covers timing for
switching the power between the coils
11a and
11b and
special control for the power switching.
The specified power is applied to the coil b at both ends of the coil
2
to heat both ends of the fixing roller
2 to a specified temperature. Since
no power is supplied to the coil
11a at this time, the temperature
at the center of the fixing roller
2 gradually decreases. The time needed
to heat both ends of the fixing roller
2 to a specified temperature is shorter
than the time needed to heat the center of the roller
2 to the same specified temperature.
While the temperature increases at both ends of the fixing roller
2,
heat conduction (diffusion) occurs from the center (of the roller
2) already
heated to the specified temperature to both ends. Even when the same power is supplied
to the respective coils, the time needed to heat both ends of the roller
2 shortens.
The temperature at both ends of the roller
2 increases because the coil
11b at the end is powered. The temperature at the heated center of
the roller
2 decreases because the power supplied to the coil is cut. These
temperatures reach approximately the same temperature as shown in FIG. 5. At this
point, a specified power is then alternately applied to the coil
11a
used to heat the center of the roller
2 and the coil
11b used
to heat both ends thereof.
Thereafter, the specified power is alternately applied to the coils
11a
and
11b (for alternately driving the coils
11a and
11b) until each of the first and second thermistors
6a
and
6b detects the temperature that has reached 200° C.,
for example.
All coils may be driven simultaneously during the warm-up period and the normal
operation. When driving all coils simultaneously, however, it is necessary to provide
a power detection mechanism capable of detecting the power supplied to the coils
11a and
11b independently. This is the cause of increasing
costs of the fixing apparatus (image forming apparatus). Accordingly, during the
warm-up period and the normal operation, it is preferable to supply the power to
only either coil, not to power all coils simultaneously. Namely, it is preferable
to alternately drive one of the coils, not to drive all coils simultaneously.
When the coils
11a and
11b are alternately supplied
with specified outputs (powers), a large difference between magnitudes of the outputs
(powers) supplied to the coils
11a and
11b causes different
frequencies for turning on or off the switching element.
Namely, a large difference between magnitudes of the outputs (powers) supplied
to the coils
11a and
11b causes different high-frequency
current frequencies.
For this reason, as mentioned above, an impulsive sound (interference sound)
may occur between the coil and the roller. When there is a case of alternately
driving the coils supplied with outputs having different magnitudes, the voltage
greatly fluctuates each time the coils are switched. This may cause a flicker etc.
Accordingly, it is preferable to provide approximately the same power to the center
coil
11a and the coil
11b at the end.
However, a difference may occur between the power supplied to the center
coil and that supplied to the coil at the end making it impossible to approximately
equalize the two power magnitudes. When a maximum suppliable power is 1,500 W,
for example, it is preferable to keep a difference between two powers up to 200
W. It is allowed to increase a difference between powers supplied to respective
coils unless flickering light is irradiated from the lighting equipment, especially
a fluorescent lamp etc. placed near a position where the copying apparatus is installed
or a switching noise is generated from a stabilizer used for the fluorescent lighting equipment.
FIG. 6 is a flowchart for explaining in more detail an example of controlling
the excitation unit which enables heating of the fixing roller shown in FIG. 5.
During the warm-up for heating the surface of the fixing roller
2 of
the fixing apparatus
1 to a temperature capable of fixing, a specified power
is first applied to the coil
11a for heating the center of the roller
2 (S
1).
Thereafter, turning on electricity for (supplying power to) the center
coil
11a continues (S
2, S
2-Yes) until the temperature
at the center of the roller
2 becomes higher than 180° C., for example.
The first thermistor
6a always monitors the temperature of the roller
2 and notifies the CPU
34 of the temperature via the temperature
detection circuit
35.
When an output from the first thermistor
6a shows that the temperature
of the roller
2 reaches 180° C. or more at step S
2 (S
2-No),
the power supply to the coil
11a stops temporarily (S
3). In
order to heat both ends of the roller
2, the end coil
11b is
supplied with the power having approximately the same magnitude of the power so
far supplied to the coil
11a (S
4).
Thereafter, the power supply to the coil
11b continues
until the temperature at both ends of the roller
2 becomes the temperature
at the center of the roller
2 (S
5, S
5-Yes). The second thermistor
6b always monitors the temperature of the roller
2 and notifies
the CPU
34 of the temperature via the temperature detection circuit
35.
As mentioned above, the time needed to heat both ends of the fixing roller
2
becomes shorter than the time for heating the center even if the power supplied
to the coil
11b is the same as that supplied to the coil
11a.
Namely, heat conduction (diffusion) occurs from the center to the both ends
to slightly heat the both ends. This heat can be also used for heating the both ends.
When the temperature at both ends of the roller
2 becomes higher than
the temperature at the center of the roller
2 at step S
5 (S
5-No),
the process stops supplying the coil
11b with the electricity (power)
for heating the both ends of the coil (S
6).
When the process stops supplying the coil
11b with the electricity
for heating the both ends of the coil at step S
6, it is determined whether
the temperature detected by the thermistor
6a at the center of the
roller
2 reaches a standby temperature, e.g., 180° C. (S
7).
As will be described later, the warm-up terminates when the temperature at the
both ends reaches the standby temperature and the center maintains the standby temperature.
If the temperature detected by the thermistor
6a at the center
of
the roller
2 does not reach 180° C. at step S
7 (S
7-Yes),
the temperature at the both ends of the roller
2 is compared to the temperature
at the center of the roller
2 (S
8).
At step S
8, it is determined whether the temperature at the center of
the
roller
2 is lower than the temperature at the both ends of the roller
2
(S
8-No) or the temperature at the center of the roller
2 is higher
than the temperature at the both ends of the roller
2 (S
8-Yes).
Subsequently, the specified drive current is supplied to the coil capable
of heating the lower-temperature side (S
9, S
10), i.e., the center
or the both sides of the roller
2.
The routine in FIG. 6 has explained the example of detecting that the temperature
at the center reaches the standby temperature, then increasing the temperature
at the both ends. It is possible to use any other method of equalizing temperatures
at the center and the both ends.
Namely, the routines at steps S
7 through S
10 are combined to
alternately drive the coil for heating the both ends and the coil for heating the center.
In this manner, the warm-up continues until the temperature at the center finally
reaches the standby temperature, i.e., 180° C. while the temperature along
the longitudinal direction of the fixing roller
2 is heated to a specified
uniform temperature. This can evenly increase the temperature in the longitudinal
direction of the fixing roller
2 to a specified standby temperature across
the entire area of the roller
2.
As mentioned above, when the coil
11a heats the center of the roller
2, the generated heat diffuses to the end of the roller
2 due to
the heat conduction of the roller itself. The heat diffusing from the center to
the end of the roller
2 is approximately settled within an area of the roller
2 heated by the coil
11b.
The above-mentioned examples simultaneously heat the full length of the fixing
roller
2 (by simultaneously applying high-frequency output with a specified
frequency to all coils) or equally apply a drive current to the coils
11a
and
11b. Compared to these examples, first heating the center
of the roller
2 can heat the full length of the roller
2 to a specified
temperature with small power consumption in a short time.
The example of the embodiment as shown in FIGS. 4 to 6 first heats the center
of the fixing roller
2 to the temperature as high as 180° C. It is
possible to set an optimal temperature according to the metallic material, thickness,
thermal conductivity, etc. of the roller
2, the magnetic flux generated
from the coils
11a and
11b, etc. For example, the temperature
may be 200° C. or 170° C.
As mentioned above, the inside of the fixing roller
2 is provided with
a plurality of excitation coils along the longer direction of the roller
2
such as the coil
11b at one end, the coil
11a at the
center, and the coil
11b at the other end. In this case, the conventional
heating (control) method generally supplies a specified power to the coil capable
of heating a low-temperature part of the roller. The temperature, if increased,
easily decreases at the roller's end because it touches a bearing rotatably supporting
the roller
2, a metallic member supporting the bearing, etc. When the respective
coils evenly heat the roller along the longer direction, much heat is diffused
somewhere other than the roller.
According to the embodiment of the present invention, by contrast, the
center coil
11a is supplied with a specified power to first heat
the center of the roller
2. In this case, the heat increased at the center
of the roller
2 is partially diffused to both ends of the roller due to
heat conduction. While this naturally decreases the temperature at the center of
the roller
2, the temperature at both ends of the roller increases.
The heat conduction transfers the heat to the end of the roller
2. This
heat is useful for shortening the time for heating the roller's ends.
When the coil
11b at the end heats both ends of the roller
2,
the heat is diffused somewhere other than the roller. However, this method shortens
the time needed to heat the entire area of the roller
2 along the longer
direction. Accordingly, the total amount of heat lost due to the diff
