Electric heating – Inductive heating – With heat exchange
Reexamination Certificate
2001-05-08
2003-04-08
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
With heat exchange
C219S667000, C399S330000, C399S336000
Reexamination Certificate
active
06545255
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heating apparatus of induction heating type for heating an image formed on a recording material.
2. Related Background Art
In an image forming apparatus such as a printer, a copying apparatus or a facsimile apparatus, there is widely employed a heating apparatus of contact heating type such as heat roller type, film heating type or magnetic induction heating type, as an image heating apparatus represented by a heat fixing apparatus for fixing, to a recording material to be heated such as a transfer sheet, a printing sheet, a photosensitive (electrofax) sheet or an electrostatic recording sheet, an unfixed visible image (unfixed toner image), formed by an appropriate image forming process such as an electrophotographic process, an electrostatic recording process or a magnetic recording process on such recording material to be heated and borne thereon by a transfer (indirect) method or a direct method.
The heating apparatus of heat roller type is basically composed of a pair of rollers consisting of a heat roller (fixing roller) heated and regulated to a predetermined temperature by a heat source such as a halogen lamp and a pressure roller maintained in pressure contact therewith, and the material to be heated is introduced into and conveyed in the contact nip (fixing nip) of the rollers whereby the unfixed visible image on the material to be heated is fixed thereto by the heat of the heat roller.
Also the heating apparatus of the film heating type is disclosed for example in the Japanese Patent Applications Laid-open Nos. 63-313182, 1-263679, 2-157878, 4-44075, 4-44075 to 4-44083; and 4-20498 to 4-204984 and is commercially used.
In such heating apparatus, the material to be heated is maintained in contact with a heating body fixedly supported by a support member across a thin heat-resistant film material (fixing film) and the film material is made to slide over the heating body thereby giving the heat of the heating body to the material to be heated across the film material. The heating body can be composed of so-called ceramic heater, basically composed of a ceramic substrate (hereinafter simply called substrate) of sufficient heat resistance, electrical insulation and heat conductivity such as alumina (Al
2
O
3
) or aluminum nitride (AlN) and a resistance layer formed on the surface of the substrate and capable of generating heat by electric current supply. Also the film material can be composed of a thin film of a low heat capacity. Therefore, in comparison with the heating apparatus of heat roller type, the heating apparatus of film heating type has a higher heat transmitting efficiency and a faster start-up, thereby enabling reduction of the waiting time (quick starting property or on-demand operability) and electric power saving.
Also in the image heating apparatus of magnetic induction heating type, as disclosed in the Japanese Patent Application Laid-open No. 7-319312, it is proposed to generate an eddy current in a metal core of the fixing roller by an alternating magnetic field, thereby generating Joule's heat by magnetic induction in such metal core namely in the fixing roller.
As shown in
FIG. 8
, there are shown a cylindrical heating roller
1
provided rotatably in a direction a by an unrepresented driving source. and a pressure roller
2
maintained in pressure contact with the heating roller
1
and rotated by the rotation thereof. Inside the heating roller
1
, there is provided a coil assembly
3
for generating an induction magnetic field. The pressure roller
2
is provided with a silicone rubber layer
6
around a shaft core
4
. There are shown a thermistor
6
serving as a temperature sensor for detecting the surface temperature of the heating roller
1
, and a separating claw
7
for separating sheet from the heating roller
1
.
In the coil assembly
3
, a square-shaped bobbin
8
with an aperture in the center is wound with a copper wire by plural turns in a single direction to constitute an excitation coil
9
, and a core
10
is inserted into the central aperture
8
a
of the bobbin
8
in a direction perpendicular to the copper wire of the excitation coil
9
. The coil assembly
3
is so positioned that the copper wire wound on the bobbin
8
extends along a plane parallel to the rotary axis of the heating roller
1
, namely that the core
10
is perpendicular to the rotary axis, thereby generating magnetic flux in a direction perpendicular to the rotary axis of the heating roller
1
.
Plural coil assemblies
3
are arranged along the axial direction of the heating roller
1
by means of a holder
11
in such a manner that the core is parallel to the conveying direction of the sheet and an end of the excitation coil
9
is opposed to the pressure roller
2
while the other end of the coil
9
is opposed to the thermistor
6
. The holder
11
is composed of a heat-resistant plastic material, and has a diameter somewhat smaller than the internal diameter of the heating roller
1
in order to form a gap to the internal wall of the heating roller
1
.
FIG. 9
is a block diagram of a circuit for supplying the induction heating coil
9
with a high frequency current thereby controlling the temperature of the heating roller
1
. The AC current of a commercial power source
13
is rectified by a rectifying circuit
14
and is converted by an inverter circuit
20
into the high frequency current. The current to the inverter circuit
20
is supplied through a thermostat
15
constituting a temperature fuse maintained in contact with the surface of the heating roller
1
.
The thermostat
15
serves to cut off the current supplied to the circuit when the surface temperature of the heating roller
1
reaches a predetermined abnormal temperature, and is provided, like the thermistor
6
, in a position opposed to the excitation coil
9
wound on the core
10
. A control circuit
16
is composed of a microprocessor, a memory etc., and provides a drive circuit
21
in the inverter circuit
20
with an on/off signal while monitoring the temperature of the heating roller
1
based on a potential corresponding to the temperature detected by the thermistor
6
, thereby executing temperature control.
In the inverter circuit
20
, when the control signal from the control circuit
16
is turned on, the drive circuit
21
turns on a switching element
22
consisting for example of a transistor, an FET or an IGBT thereby providing the excitation coil
9
with a current.
On the other hand, a current detecting circuit
22
, upon detecting that the current reaches a predetermined current value IP, sends a signal to the drive circuit
21
so as to turn off the switching element
22
. When the switching element
22
is turned off, a resonance current is generated between the excitation coil
9
and a resonance capacitor
24
. Then, upon detecting that the voltage V of the switching element
22
at the side of the excitation coil
9
is lowered to about 0 V by the resonance, a voltage detecting circuit
25
sends a signal to the drive circuit
21
so as to turn on again the switching element
22
.
In the heating apparatus of magnetic induction heating type of the above-described configuration, the temperature control at the heating position (nip portion) for the material to be heated is executed by employing a thermistor as the temperature detecting element, detecting the temperature by positioning such thermistor in contact with the surface or internal surface of the roller body or the film member constituting the heating body for the material to be heated (contact type temperature detection) and controlling the electric power supply from the driving power source to the excitation coil
9
by the control circuit
16
based on the information of such temperature detection, thereby maintaining the temperature of the heating portion of the material to be heated at a predetermined value.
In such configuration, however, the exact temperature detection is hindered since the temperature dete
Mano Hiroshi
Sato Takashi
Sekiguchi Hajime
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Leung Philip H.
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