JP3907674B2 - Induction heating device - Google Patents

Description

  The present invention relates to an induction heating apparatus in which a shield body is provided between an object to be heated and an induction heating coil.

  An induction heating device that uses induction heating and uses an inverter is equipped with a temperature detection element in the vicinity of the load pan, etc., detects the pan temperature, etc., and adjusts the heating power and cooking time accordingly. By performing, it has excellent heat response and controllability. The induction heating device realizes fine cooking and has the characteristics of not polluting indoor air because it does not use a flame, high thermal efficiency, safety and cleanliness. In recent years, these characteristics have attracted attention, and the demand for induction heating devices has increased rapidly.

  The induction heating apparatus of Conventional Example 1 will be described with reference to FIG. The induction heating apparatus of Conventional Example 1 includes a high magnetic permeability (magnetic body) heated object such as iron (or a low magnetic permeability and high resistance heated object such as 18-8 stainless steel) and aluminum or copper. It is possible to heat an object to be heated with a low magnetic permeability as described above (with a non-magnetic material). FIG. 14 is a block diagram showing the configuration of the induction heating apparatus of Conventional Example 1. In FIG. 14, 110 is a heated body (a metal container such as a pan or a frying pan), 101 is an induction heating coil that generates a high-frequency magnetic field and heats the heated body 110, 127 is a commercial AC power input, and 108 is a bridge 108a. And a smoothing capacitor 108b that rectifies the commercial AC power supply, 1402 is an inverter circuit that converts the power rectified by the rectifying and smoothing unit 108 into high-frequency power and supplies high-frequency current to the induction heating coil 101, and 105 is a micro A computer, 1409 is an operation unit, and 125 is a casing. Reference numeral 118 denotes a ceramic top plate placed on the top of the casing 125 and on which the heated object 110 is placed.

The microcomputer 105 has a control unit 104. The operation unit 1409 includes a setting input unit 113 and a setting display unit 114. The setting input unit 113 includes a plurality of key switches (a key switch for inputting an output stage setting command for determining a target output of the induction heating device, a key switch for inputting an ON command for the induction heating device, and an OFF command for the induction heating device. Input key switch).
The setting display unit 114 has a plurality of visible LEDs (Light Emitting Diodes), and displays the setting state of the induction heating device.

  The control unit 104 drives the drive circuit 111 in accordance with a command input from the setting input unit 113. The drive circuit 111 controls the output of the inverter circuit 102. The control unit 104 is configured to relay a relay (with a low magnetic permeability and a low resistance heated body, and with a high magnetic permeability heated body (or a low magnetic permeability and high resistance heated body). (Not shown) is turned on / off to switch the number of turns of the induction heating coil 101 driven by the inverter circuit 102, and the voltage applied to the induction heating coil 101 is switched. The induction heating coil 101 is heated in the case of heating a heated object having a low magnetic permeability and a low resistance than in the case of heating a heated object having a high magnetic permeability (or a heated object having a low magnetic permeability and a high resistance). The number of turns is large, and the voltage applied to the induction heating coil 101 is high. When the object to be heated 110 is a pan made of aluminum, copper or the like having a low magnetic permeability and low resistance, the voltage applied to the induction heating coil 101 becomes 1 kV or more.

  A stray capacitance (equivalent capacitance) 1411 exists between the induction heating coil 101 and the heated object 110. When the user touches the object 110 to be heated, a current flows from the induction heating coil 101 to the ground through the stray capacitance (equivalent capacitance) 1411 and the internal resistance (equivalent resistance) 1412 of the user's body. It is dangerous that a predetermined current or more leaks from the high-pressure induction heating coil 101 to the human body.

  As a conventional example 2, there is an induction heating cooker that prevents current from leaking from the high-pressure induction heating coil 101 to the human body. (For example, refer to Patent Document 1). The induction heating cooker of Conventional Example 2 will be described with reference to FIGS. FIG. 15 is a block diagram showing the configuration of the induction heating cooker of Conventional Example 2. In FIG. 15, the same blocks as those in Conventional Example 1 (FIG. 14) are denoted by the same reference numerals. The induction heating cooker of Conventional Example 2 differs from Conventional Example 1 in that a conductive electrostatic shield body 1512 and an insulating layer 1513 covering the electrostatic shield body 1512 are provided on the lower surface of the top plate 118. The electrostatic shield body 1512 is connected to the low potential portion of the rectifying and smoothing circuit 108. In other respects, Conventional Example 2 is the same as Conventional Example 1.

  FIG. 16 is a diagram illustrating a pattern of the electrostatic shield body 1512 formed on the top plate 118 of the induction heating cooker according to the second conventional example. For easy understanding, FIG. 16 shows a pattern of the electrostatic shield body 1512 except for the insulating layer 1513. The electrostatic shield body 1512 is applied and baked on the lower surface of the top plate 118. The electrostatic shield body 1512 has an annular shape. A connection line from the low potential portion of the rectifying and smoothing circuit 108 is connected to the electrode 1513 of the electrostatic shield body 1512.

A stray capacitance (equivalent capacitance) 1514 exists between the induction heating coil 101 and the electrostatic shield body 1512. A current flows from the induction heating coil 101 to the ground through the stray capacitance (equivalent capacitance) 1514 and the internal resistance (equivalent resistance) 1515 of the electrostatic shield body 1512. The impedance of the internal resistance (equivalent resistance) 1515 of the conductive electrostatic shield body 1512 is sufficiently smaller than the impedance of the stray capacitance (equivalent capacity) 1514 (the frequency of the high-frequency current flowing through the induction heating coil 101 is 20 to 20). About 60 kHz). Therefore, the voltage induced in the electrostatic shield body 1512 is sufficiently low.
A stray capacitance (equivalent capacitance) 1516 exists between the electrostatic shield body 1512 and the heated object 110. When the user touches the body 110 to be heated, the leakage current flows through the stray capacitance (equivalent capacitance) 1516 and the internal resistance (equivalent resistance) 1412 of the user's body due to the voltage induced in the electrostatic shield body 1512 by the induction heating coil 101. Flows to the ground. Since the voltage induced in the electrostatic shield 1512 is sufficiently low, the leakage current flowing to the ground through the internal resistance (equivalent resistance) 1412 of the user's body is very small.

  In other words, between the electrostatic shield body 1512 and the ground, the internal resistance (equivalent resistance) 1515 of the electrostatic shield body 1512, the stray capacitance (equivalent capacity) 1516, and the internal resistance (equivalent resistance) 1412 of the user's body. And are connected in parallel. Since the impedance of the internal resistance (equivalent resistance) 1515 of the electrostatic shield body 1512 is very small compared to the impedance of the stray capacitance (equivalent capacitance) 1516 and the internal resistance (equivalent resistance) 1412 of the user's body, the induction heating coil Most of the leakage current from 101 flows to the ground through the electrostatic shield body 1512. Almost no current leaks to the user's body.

  In the configuration of Conventional Example 2, when the heated object 110 is a pan made of aluminum, copper, or the like having low magnetic permeability and low resistance, the number of turns of the induction heating coil 101 is increased. At this time, the voltage applied to the induction heating coil is 1 kV or more. In Conventional Example 2, there is an electrostatic shield body that is electrically coupled to the low potential portion, and there is almost no potential difference between the heated body 110 and the electrostatic shield body 1512 (both are at ground level). Therefore, no leakage current is induced in the heated object 110. Therefore, it is safe even if a human body touches the body 110 to be heated.

  An induction heating device is disclosed in which a thin pattern (top plate crack detection circuit) formed of a conductive paint is provided on the back surface of a top plate. (For example, refer to Patent Document 4). A direct current is passed through this pattern. The induction heating coil is stopped based on the fact that the current flowing through this pattern is interrupted by the crack of the top plate.

  An induction heating cooker in which a thin conductive pattern is provided on a top plate is disclosed. (For example, refer to Patent Document 2 and Patent Document 3). When the induction heating coil is driven, a leakage current flows in this pattern. When the leakage current becomes smaller than a reference value proportional to the output of the induction heating coil, the induction heating coil is stopped.

Japanese Patent Publication No. 4-75634 JP 62-278785 A Japanese Patent Laid-Open No. 62-278786 Japanese Patent Publication No.55-869 Japanese Patent Laid-Open No. 54-149954 Japanese Utility Model Publication No. 56-49089

  In the configuration of Conventional Example 2, as long as the electrostatic shield body sufficiently fulfills its function, it is safe even if the human body touches the body to be heated. However, when the electrostatic shield body does not function sufficiently due to aging, for example, due to aging, the safety is not always sufficiently ensured (when the user touches the object to be heated, it exceeds a predetermined level). There is a problem that leakage current may flow through the human body).

  The present invention solves the above-described conventional problems, prevents leakage current from flowing into the human body, and ensures safety even when the electrostatic shield body does not fully perform its function. It aims at providing a high induction heating device.

In order to solve the above-mentioned conventional problems, the induction heating device of the present invention is provided with a fixed plate made of a heat-resistant insulating material and placed on an induction heating coil, and on or in the fixed plate, A conductive shield body that is provided under the fixed plate and whose surface is covered with an insulating layer and is electrically connected to the low potential portion, and a voltage different from the voltage generated by the induction heating coil is applied to the shield body. In addition, a detection unit that detects the energization state (conduction state) of the shield body is provided at least when the induction heating coil is not energized , and induction is performed based on the detection output of the detection unit when the induction heating coil is not energized. It was set as the structure which controls the drive part (inverter circuit) which drives a heating coil. With this configuration, when the shield body cannot exhibit its function for some reason, the detection unit can detect that the conduction state of the shield body has deteriorated and reduce or stop the output of the induction heating coil. Even when the electrostatic shield body does not sufficiently perform its function, it is possible to realize a highly safe induction heating device that does not cause an electric shock.

According to the present invention, even when the electrostatic shield body does not sufficiently perform its function, it can be made highly safe without fear of electric shock, and can be made of a heat-resistant insulating material. Luke provided a shielding member to its on or in, by placing the provided and heating coil creates a fixed plate covering the surface with an insulating layer thereunder, with reliably insulate the induction heating coil and shield The development effort and time can be reduced.

An induction heating apparatus according to one aspect of the present invention includes a top plate disposed on an upper portion of a housing and on which a heated body is placed, and an induction that is provided below the top plate and generates a high-frequency magnetic field to heat the heated body. a heating coil, an inverter circuit for driving the induction heating coil, a fixed plate mounted on the fabricated and the induction heating coil of a heat insulating material, is provided on or in the fixed plate Luke, A conductive shield provided under the fixed plate and covered with an insulating layer and electrically connected to a low potential portion; and a voltage different from a voltage generated by the induction heating coil. is applied to the body, it said in a state not energized and detecting unit for detecting the conduction state of the shield body in a state not energized at least the induction heating coil, the induction heating coil test When the conducting state based on the component of the detection result detects that the deteriorated and a control unit for output of the induction heating coil to control the inverter circuit so as to be or stopped reduced.

The fixed plate is placed on the induction heating coil. By mounting a versatile fixing plate having a shield body on the induction heating coil according to the model, it is not necessary to design an individual shield body for each model.
“The shield body is provided in the fixed plate” means that, for example, the fixed plate is formed of laminated glass, and the shield body is provided between the glasses of the laminated glass. When the shield body is provided under the fixed plate (on the induction heating coil side), preferably an insulating layer is provided to cover the surface of the shield body, and the insulating layer reliably insulates the shield body from the induction heating coil. .

  The induction heating cooker described in Patent Document 1 prevents a leakage current from flowing from the induction heating coil to the human body through the object to be heated by providing a shield body. However, when the shield body can no longer perform its function, a leakage current may flow from the induction heating coil to the human body through the object to be heated.

  The induction heating devices described in Patent Literature 2, Patent Literature 3 and Patent Literature 4 detect cracks in the top plate and stop the induction heating device. However, the pattern provided on the top plate is thin, exclusively for detecting cracks in the top plate, and has little shielding effect to prevent leakage current from the induction heating coil to the object to be heated. These inventions of the prior art did not have the idea of preventing leakage current. For example, when an induction heating coil outputs a high voltage to heat an object to be heated having a low magnetic permeability such as aluminum, a thin conductive pattern is insufficient to prevent leakage current. It has been difficult to detect that the shield body can no longer perform its function only by changing the conductive pattern provided on the top plate to a shield body (having a size sufficient to provide a shielding effect). To provide a shield body between the induction heating coil and the body to be heated and detect that the shield body can no longer perform its function, as described in the embodiment, a new idea for the signal detection method It was necessary to include.

The present invention provides a shield body between the induction heating coil and the body to be heated to prevent leakage current, and when the shield body cannot perform its function for some reason, the detector is in a conductive state of the shield body. By detecting the deterioration, the control unit realized a highly safe induction heating apparatus that reduces or stops the output of the induction heating coil. Even when the shield body cannot exhibit its function, when a person touches the object to be heated, there is no possibility that the leakage current flows through the human body and the user gets an electric shock.
The “low potential portion” may be any potential as long as the leakage current flowing from the heated body to the human body can be sufficiently lowered by the induction heating coil. Preferably, the low potential portion is a ground line or a portion having a potential close to the ground line.
The shield body and the low potential portion may be connected by a connection line (so that a DC component and an AC component flow), or may be connected by a capacitor in an AC manner.
Further, at least in a state where the induction heating coil is not energized, the detection unit detects the conduction state of the shield body.
Thereby, even when the induction heating is not used, the energization state (conduction state) of the shield body can be confirmed, and high safety of the induction heating device can be ensured. There is a case where the leakage current is very large and is disturbed by the leakage current, so that the detection unit cannot correctly detect the conduction state of the shield body. Even in such a case, according to the present invention, when the induction heating coil is not operating, the conduction state of the shield body is detected, and the detection unit outputs a correct detection result.
In such a case, the detection unit preferably detects a conduction state of the shield body by applying a voltage different from the voltage generated by the induction heating coil to the shield body when the induction heating coil is not operating. When is operated, the conduction state of the shield body is not detected using a voltage different from the voltage generated by the induction heating coil. More preferably, when the induction heating coil operates, the conduction state of the shield body is detected by another method.

In the induction heating apparatus according to another aspect of the present invention, the detection unit determines whether the impedance of the shield body is equal to or lower than a predetermined threshold value, and the voltage between the predetermined terminals of the shield body is a predetermined threshold value. It is determined whether or not the current flowing through the shield body is equal to or greater than a predetermined threshold value, and the degree of deterioration of the conduction state is detected. When the impedance is larger than a predetermined threshold, the voltage between the predetermined terminals of the shield body is higher than the predetermined threshold, or the current flowing through the shield body is smaller than the predetermined threshold, the output of the induction heating coil is reduced. Or stop it.

  With this configuration, when the function of the shield body has deteriorated for some reason (when the conduction state of the shield body has deteriorated), the detection unit detects the degree of function deterioration by energizing the shield body, and is determined in advance. When the reference value (threshold value) is exceeded, the induction heating device can reduce or stop the output of the induction heating coil. Even when the shield body cannot exhibit its function, when a person touches the object to be heated, there is no possibility that the leakage current flows through the human body and the user gets an electric shock.

  In the induction heating apparatus according to another aspect of the present invention, the detection unit applies a direct current to the shield body to detect the conduction state. Thereby, the detection part can detect the conduction | electrical_connection state (energization state) of a shield body easily and reliably.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1
The induction heating apparatus according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram illustrating a schematic configuration of the induction heating device according to the first embodiment, and FIG. 3 is a diagram illustrating a circuit configuration of the induction heating device according to the first embodiment. The induction heating apparatus according to Embodiment 1 includes a high magnetic permeability (magnetic material) heated object such as iron (or a low magnetic permeability and high resistance heated object such as 18-8 stainless steel), aluminum, or It is possible to heat an object to be heated with a low magnetic permeability such as copper (with a nonmagnetic material) and a low resistance.
1 and 3, reference numeral 110 denotes a heated object (a load that is a metal container such as a pan or a frying pan), 125 a casing, and 118 a top plate that is provided on the upper surface of the casing and on which the heated body 110 is placed. , 112 is an electrostatic shield provided on the top plate, 117 is an insulating layer covering the electrostatic shield 112, 101 is an induction heating coil that generates a high-frequency magnetic field and heats the object 110 to be heated, and 124 is induction heating. An induction heating coil holding member for placing the coil 101 on the upper surface, 127 is a commercial AC power supply, 121 is a plug for inputting commercial AC power, 126 is a control board, and 109 is an operation unit.

The control board 126 rectifies the commercial AC power supply, the rectifying / smoothing unit 108, the inverter circuit 102 that converts the power rectified by the rectifying / smoothing unit 108 into high-frequency power and supplies the induction heating coil 101 with high-frequency current, and the drive of the inverter circuit 102 A circuit 111, a detection unit 103, a microcomputer 105, an LED drive circuit 106, a piezoelectric buzzer drive circuit (warning buzzer drive circuit) 107, and a setting display unit drive circuit 108 are included. Each block on the control board 126 has a common ground line (ground pattern).
Reference numerals 119 and 120 denote two connection lines that connect the inverter circuit 102 and the induction heating coil 101. Reference numerals 122 and 123 denote two connection lines for connecting the electrostatic shield body 112 and the control board 126.

The connection line 119 connects the outer peripheral end of the induction heating coil 101 and one end of the resonant capacitor 102g, and the connection line 120 connects the inner peripheral end of the induction heating coil 101, the emitter of the switching element 102c, and the collector of the switching element 102d. Connecting. The electric potential at the outer end of the induction heating coil 101 wound in a spiral is lower than the electric potential at the inner peripheral end.
The microcomputer 105 has a control unit 104. The function of the control unit 104 is processed by software.
The operation unit 109 includes a setting input unit 113, a setting display unit 114, a red warning LED 116, and a piezoelectric buzzer (warning buzzer) 115.
The setting input unit 113 includes a plurality of input key switches operated by the user to input a heating output setting command or a heating start or stop command. The command input by the setting input unit 113 is input to the control unit 104.

  The control unit 104 drives the drive circuit 111, the LED drive circuit 106, the piezoelectric buzzer drive circuit 107, and the setting display unit drive circuit 108. The drive circuit 111 drives the switching elements 102c and 102d of the inverter circuit 102. The setting display unit driving circuit 108 drives the setting display unit 114 (having a plurality of visible LEDs). The setting display unit 114 displays the heating output setting contents set through the setting input unit 113 to the user.

  The control unit 104 responds to various commands input from the setting input unit 113, an output signal of an output detection unit (not shown) (a signal corresponding to the power supply current of the inverter circuit 102), and an output signal of the detection unit 103. The output of the inverter circuit 102 is controlled through the drive circuit 111. The variation of the heating output is performed by controlling the driving frequency of the switching element. When the heated object 110 is made of a material having a low magnetic permeability (non-magnetic material) such as aluminum or copper, it is made of a material having a high magnetic permeability (magnetic material) such as iron. Compared to the case (or the case made of a material having low permeability and high resistance such as 18-8 stainless steel), the induction heating coil 101 is driven at a high frequency and a high voltage. When the heated object 110 is made of a material having low permeability and low resistance, the number of turns of the induction heating coil may be increased by switching the contact of a relay (not shown).

The commercial power supply 127 is input to the rectifying / smoothing unit 108. The rectifying / smoothing unit 108 includes a full-wave rectifier 108a formed of a bridge diode, and a first smoothing capacitor 108b connected between the DC output terminals.
The input terminal of the inverter circuit 102 is connected to both ends of the first smoothing capacitor 108b (the output terminal of the rectifying / smoothing unit 108). An induction heating coil 101 is connected to the output terminal of the inverter circuit 102. The inverter circuit 102 and the induction heating coil 101 constitute a high frequency inverter. The inverter circuit 102 includes a series connection body (“series connection”) of a first switching element 102c (in this embodiment, an IGBT (Insulated Gate Bipolar Transistor)) and a second switching element 102d (in this embodiment, an IGBT). Body 102c and 102d ") are provided. The first diode 102e is connected to the first switching element 102c in the reverse direction and in parallel, and the second diode 102f is connected to the second switching element 102d in the reverse direction and in parallel. A second smoothing capacitor 102b is connected to both ends of the series connection bodies 102c and 102d.

A choke coil 102a is connected between the connection point of the first switching element 102c and the second switching element 102d (referred to as “the midpoint of the series connection bodies 102c and 102d”) and the positive terminal of the full-wave rectifier 108a. Is done. The low potential terminals of the series connectors 102c and 102d are connected to the negative terminal (ground terminal in the embodiment) of the full-wave rectifier 108a. A series connection body of the induction heating coil 101 and the resonance capacitor 102g is connected between the midpoint of the series connection bodies 102c and 102d and the negative terminal of the full-wave rectifier 108a.
The control unit 104 drives the first switching element 102 c and the second switching element 102 d through the drive circuit 111.

The operation of the induction cooking device configured as described above will be described. The full wave rectifier 108 a rectifies the commercial AC power supply 127. The first smoothing capacitor 108 b supplies power to the high-frequency inverter having the inverter circuit 102 and the induction heating coil 101.
When the second switching element 102d is on, a resonance current flows through a closed circuit including the second switching element 102d (or the second diode 102f), the induction heating coil 101, and the resonance capacitor 102g. At the same time, energy is stored in the choke coil 102a. When the second switching element 102d is turned off, the stored energy is discharged to the second smoothing capacitor 102b through the first diode 102e.

  After the second switching element 102d is turned off, the first switching element 102c is turned on, and a current flows through the first switching element 102c and the first diode 102e. A resonance current flows through a closed circuit including the first switching element 102c (or the first diode 102e), the induction heating coil 101, the resonance capacitor 102g, and the second smoothing capacitor 102b.

  The driving frequency of the first switching element 102c and the second switching element 102d is variable in the vicinity of about 20 kHz. When heating an object to be heated (typically an iron cooking vessel), a high frequency current of about 20 kHz flows through the induction heating coil 101. The drive time ratios of the first switching element 102c and the second switching element 102d are each varied in the vicinity of about ½. The impedance of the induction heating coil 101 and the resonant capacitor 102g is a specified material (for example, a high-conductivity nonmagnetic material such as aluminum) and has a standard size (for example, a diameter equal to or greater than the diameter of the induction heating coil) When the cooking pan 110 is placed in a designated place (for example, a place shown as a heated portion) of the top plate, the resonance frequency is set to be about three times the driving frequency. Therefore, in this case, the resonance frequency is set to be about 60 kHz.

If the object to be heated 110 is made of aluminum, a high frequency current of about 60 kHz, which is a higher frequency than normal, flows through the induction heating coil 101, so that the cooking pot 110 can be heated efficiently. The high-frequency inverter of this embodiment has high heating efficiency because the regenerative current flowing through the first diode 102e and the second diode 102f does not flow into the first smoothing capacitor 108b but is supplied to the second smoothing capacitor 102b. .
The second smoothing capacitor 102b smoothes the envelope (envelope) of the high-frequency current supplied to the induction heating coil 101 from the conventional induction heating device. Thereby, the commercial frequency component of the current IL flowing through the induction heating coil 101 that causes vibration noise from the pan 110 or the like during heating is reduced.

The electrostatic shield body 112 shields between the induction heating coil 101 and the body 110 to be heated, and prevents leakage current induced by the induction heating coil 101 from flowing through the user's body.
FIG. 2 is a diagram showing a pattern of the electrostatic shield body 118 formed on the top plate 118 of the induction heating apparatus of the first embodiment. For ease of understanding, FIG. 2 shows the pattern of the electrostatic shield body 112 except for the insulating layer 117. The electrostatic shield body 112 is formed by applying and baking a conductive carbon paint on the top surface of the top plate 118. The electrostatic shield body 112 is formed of any conductive material. For example, aluminum may be deposited on the top surface of the top plate 118. The electrostatic shield body 112 has an outer diameter substantially the same as that of the induction heating coil 101, is divided by the slit 201, and has a substantially arc shape that is coaxial with the induction heating coil 101 and substantially covers the induction heating coil 101. The electrostatic shield body 112 has a shape in which a closed loop including the central axis of the induction heating coil 101 does not exist thereon. The electrostatic shield body 112 has two connection portions 202 at both ends of the pattern. Connection lines 122 and 123 are connected to the connection unit 202, respectively. The other end of the connection line 122 is connected to the ground of the detection unit 103. The other end of the connection line 123 is connected to the input terminal of the detection unit 103 (one end of the resistor 103c).

The detection unit 103 detects a conduction state between the electrostatic shield body 112 and the control board 126. The detection unit 103 includes a transistor 103a and resistors 103b, 103c, and 103d. The detection unit 103 applies a direct current (voltage different from the voltage generated by the induction heating coil 101) to the electrostatic shield body 112 through the connection lines 122 and 123, and detects the conduction state.
The detection unit 103 causes a current to flow through the electrostatic shield 112 to the low potential unit (ground in the embodiment).

  Usually, the conduction state between the electrostatic shield body 112 and the control board 126 is good. In this case, a DC current flows from the + 5V DC power supply voltage to the ground line through the resistor 103b, the transistor 103a, the resistor 103c, the connection line 123, the electrostatic shield body 112, and the connection line 123. When the base current of the PNP transistor 103a flows, the transistor 103a becomes conductive. When a current flows between the emitter and collector of the transistor 103a, the collector potential of the transistor 103a (the voltage across the resistor 103d) becomes approximately + 5V.

  For example, if one end of the connection line 122 is disconnected (if the continuity between the electrostatic shield body 112 and the control board 126 is deteriorated), the resistor 103b, the transistor 103a, the resistor 103c, A direct current does not flow to the ground line through the connection line 123, the electrostatic shield body 112, and the connection line 123. When the base current of the PNP transistor 103a stops flowing, the transistor 103a is cut off. When no current flows between the emitter and collector of the transistor 103a, the collector potential of the transistor 103a (the voltage across the resistor 103d) becomes 0V.

The control unit 104 (microcomputer 105) inputs the collector potential of the transistor 103a. When the conduction state between the electrostatic shield body 112 and the control board 126 deteriorates, the control unit 104 stops the induction heating coil 101, lights up the red warning LED 116 through the LED drive circuit 106, and the piezoelectric buzzer drive circuit 107. The piezoelectric buzzer 115 is sounded through. The user can easily recognize that the electrostatic shield body 112 is abnormal.
Instead of the warning LED 116, a liquid crystal display may be used. Instead of the piezoelectric buzzer 115, a speaker for voice guidance may be used.

FIG. 4 is a flowchart illustrating a method for controlling the induction heating apparatus according to the first embodiment. FIG. 4 includes steps 401 to 409. First, the control unit 104 checks whether or not the conductive state of the electrostatic shield body 112 is good (whether the collector potential of the transistor 103a is + 5V or 0V) (step 401). If the conduction state is good, the process proceeds to step 402, and if the conduction state is bad, the process proceeds to step 407.
In step 402, the control unit 104 checks whether or not a command to turn on the induction heating coil 101 is issued. If a command to turn on the induction heating coil 101 is issued, the process proceeds to step 404. If the command to turn on the induction heating coil 101 is not issued, the process proceeds to step 403, where the inverter circuit 102 is controlled to stop the induction heating coil 101. Proceed to step 405.

In step 404 (a command to turn on the induction heating coil is issued), the control unit 104 controls the inverter circuit 102 to apply the commanded power to the induction heating coil 101. In step 405, the warning LED 116 is turned off. Next, the warning buzzer (piezoelectric buzzer) 115 is turned off (step 406). Returning to step 401, the above processing is repeated.
In step 407 (the conduction state is bad), the control unit 104 controls the inverter circuit 102 to stop the induction heating coil 101. Next, in step 408, the warning LED 116 is turned on. Next, the warning buzzer (piezoelectric buzzer) 115 is turned on (step 409). Returning to step 401, the above processing is repeated.

  In the first embodiment, if the stray capacitance (equivalent capacitance) 1514 between the electrostatic shield body 112 and the induction heating coil 101 is large, when the induction heating coil 101 is energized, the input voltage of the detection unit 103 is There is a case where a large noise is applied and the detection unit 103 cannot correctly detect the conduction state of the electrostatic shield body 112. In such a case, the detection unit 103 detects the conduction state of the electrostatic shield body 112 only when the induction heating coil 101 is not energized. That is, if the conduction state of the electrostatic shield body 112 is poor when a command for changing the induction heating coil 101 from OFF to ON is input, the control unit 104 does not cause the induction heating coil 101 to conduct. Thereby, the detection unit 103 can correctly detect the conduction state of the electrostatic shield body 112. Once the induction heating coil 101 is in the operating state (energized state), the detection unit 103 does not check the conduction state of the electrostatic shield body 112.

  When the inverter circuit 102 (drive unit) is driven and a high-frequency current is passed through the induction heating coil 101, an eddy current is generated in the heated object 110 such as a pan by the generated high-frequency magnetic field. The heated object 110 generates heat, and cooking is thereby performed. If the heated object 110 is a high permeability pan such as iron, the heated object 110 can be heated by applying a low voltage to the induction heating coil 101 at a relatively low frequency. However, in order to heat a low permeability pan such as aluminum or copper, it is necessary to apply a high voltage to the induction heating coil 101 at a high frequency. Therefore, for example, the number of turns of the induction heating coil 101 must be increased.

  In FIG. 1, the induction heating coil 101 is described as a single-layer coil having about 12 turns. The induction heating coil 101 may be a multilayer, for example, a multilayer having a total number of turns of about 30 to 60 turns. The voltage across the induction heating coil 101 having such a number of turns becomes a high voltage exceeding 1 kV. In the induction heating apparatus of Conventional Example 1, when the user touches the object to be heated 110, a leakage current may flow to the human body through the object to be heated 110 due to the equivalent capacitance 1411 between the induction heating coil 101 and the object to be heated 110. There is. Therefore, in the present embodiment, the electrostatic shield body 112 is provided and connected to the low potential portion, thereby lowering the potential of the heated body 110 so that the leakage current is not induced.

  An insulating layer 117 is provided on the electrostatic shield body 112. This prevents leakage current induced in the electrostatic shield body 112 from leaking to the heated body 110 and prevents damage to the electrostatic shield body 112 due to movement of the heated body 110 or the like.

  The present embodiment is characterized in that the energized state of the electrostatic shield body 112 is detected. The detection unit 103 detects whether the electrostatic shield body 112 is in a normal state by detecting the energization state of the electrostatic shield body 112. For example, the electrostatic shield body 112 or the connection lines 122 and 123 may not be allowed to flow due to thermal stimulation such as a cold cycle or deterioration over time such as corrosion, or may not flow due to disconnection. When an abnormal state occurs, this is detected and transmitted to the control unit 104 (a part of the drive unit). The control unit 104 reduces or stops the output of the inverter circuit 102 (another part of the driving unit). Thus, even when the current leakage prevention function is lost due to the abnormality of the electrostatic shield body 112, the leakage current can be prevented from flowing to the person through the heated body 110, and safety can be ensured.

  When the abnormal state is clear, such as disconnection, it is easy to determine whether the energized state is good. There may be a case where the energized state gradually deteriorates, such as thermal stimulation or deterioration over time. In this case, the relationship between the energized state and the leakage current to the heated object 110 is preferably obtained in advance by experiments or the like, and a reference value that can ensure safety of the energized state is determined. When the value falls below the reference value, the output of the inverter circuit 102 is reduced or stopped.

  The size of the pattern of the electrostatic shield body 112 is substantially the same as that of the induction heating coil 101, and the shape is a substantially arc shape divided by the slits 201. Lead wires 122 and 123 are connected to connection portions 202 at both ends of the pattern, respectively. Thereby, the electrostatic shield can be uniformly applied to the substantially circular induction heating coil 101, and a stable shielding effect can be produced against the electric field generated from the induction heating coil 101. Since the detection part 103 detects the energization state between the connection parts 202, even if the electrostatic shield body itself is disconnected due to damage or the like, an abnormal state can be accurately detected.

  When the power supply switch (not shown) of the main body is turned on, the detection unit 103 constantly detects the conduction state by flowing a current through the electrostatic shield body 112 even when the induction heating coil 101 is not energized. Yes. When the detection unit 17 detects an abnormal state when the induction heating coil 101 is not energized, the output of the inverter circuit 102 can be stopped before the user operates the heating, and higher safety is maintained. it can. If the detection unit 103 can detect the conduction state of the electrostatic shield body 112 even when there is a leakage current from the induction heating coil 101, the detection unit 103 operates even when the induction heating coil 101 is energized.

  As described above, in this embodiment, the electrostatic shield body is provided, and the conduction state (energization state) of the electrostatic shield body is always checked (even when the induction heating coil is stopped), and the conduction state is the reference value. When it becomes below, a control part controls an inverter circuit, and reduces or stops the output. As a result, the leakage current does not flow to the human body through the body to be heated and is safe.

  The induction heating apparatus of the first embodiment includes a display unit (warning LED 116) that displays that the continuity of the electrostatic shield body 112 has deteriorated, and a notification unit (piezoelectric buzzer (warning buzzer) 115) that informs of this. Had. You may have only one of a display part and an alerting | reporting part.

  The induction heating device has a configuration in which the potential at the outer end of the induction heating coil 101 wound in a spiral shape is lower than the potential at the inner peripheral end. When heating the heated object 110 having a large bottom surface (for example, a pan having a large diameter), the stray capacitance (equivalent capacity) connecting the induction heating coil 101 and the heated object 110 via the outer peripheral side of the shield body 112 is increased. appear. In this configuration, since the potential at the outer end of the induction heating coil 101 is low, the voltage applied to the stray capacitance (equivalent capacitance) connecting the induction heating coil 101 and the heated object 110 is very low. Leakage current hardly flows from the induction heating coil 101 to the user through the heated object 110.

<< Reference Form 1 >>
The induction heating apparatus according to the first embodiment of the present invention will be described with reference to FIGS. The schematic configuration of the induction heating apparatus of Reference Embodiment 1 is the same as that of Embodiment 1 (FIG. 1). FIG. 5 is a diagram illustrating a circuit configuration of the induction heating apparatus according to the first embodiment. The induction heating apparatus of Reference Form 1 includes a high magnetic permeability (magnetic material) heated object such as iron (or a low magnetic permeability and high resistance heated object such as 18-8 stainless steel), aluminum or It is possible to heat an object to be heated with a low magnetic permeability such as copper (with a nonmagnetic material) and a low resistance. The induction heating device of Reference Embodiment 1 is different from that of Embodiment 1 in the circuit configuration of the detection unit 503 and the control method related to detection of the conduction state of the electrostatic shield body 112. One end of induction heating coil 101 is directly connected to the ground line of inverter circuit 102 (resonance capacitor 102g is disposed between the emitter of switching element 102c and the collector of switching element 102d and induction heating coil 101. Yes.) In other respects, Reference Embodiment 1 is the same as Embodiment 1. Since the basic configuration of the present embodiment is the same as that of the first embodiment, different points will be mainly described. The same functions as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The detection unit 503 includes comparators 503a and 503b, resistors 503c, 503d, 503e, 503f, 503g, 503h, 503j, 503k and 503n, and transistors 503i and 503m. The transistors 503i and 503m and the resistors 503j, 503k, and 503n constitute a power switch circuit that supplies power to the detection unit 503. The control unit 104 controls ON / OFF of the power switch circuit (+ 5V is input to the base of the transistor 503 through the resistor 503n to turn on the power switch circuit, and 0V is input to turn off the power switch circuit. 104, the power switch circuit is turned on once every time T0 (for example, T0 = 10 seconds) When the power switch circuit is in the OFF state, the detection unit 503 consumes little power. Only when the switch circuit is turned on, the conduction state of the electrostatic shield body 112 is detected.

  The operation of the detection unit 503 when the power switch circuit is turned on will be described. A DC voltage + 5V (a power supply voltage separate from the voltage generated by the induction heating coil 101) is applied to the electrostatic shield body 112 through the resistors 503f and 503e. A direct current flows through the electrostatic shield body 112. The potential at the connection point between the resistors 503f and 503e is input to the non-inverting input terminal of the comparator 503a and the inverting input terminal of the comparator 503b. The first reference voltage Vref1 is input to the inverting input terminal of the comparator 503a, and the second reference voltage Vref2 is input to the non-inverting input terminal of the comparator 503b. In the reference form 1, the first reference voltage Vref1 <the second reference voltage Vref2. The control unit 104 inputs output signals from the comparators 503a and 503b.

  When the induction heating coil 101 is stopped, the control unit 104 inputs and checks the output signal of the comparator 503b, and does not check the output signal of the comparator 503a. The impedance of the electrostatic shield body 112 having a good conduction state is low, and the potential of the inverting input terminal of the comparator 503b is lower than the threshold value (second reference voltage Vref2). The impedance of the electrostatic shield body 112 whose conductive state has deteriorated becomes high, and the potential of the inverting input terminal of the comparator 503b becomes higher than the threshold (second reference voltage Vref2). When the induction heating coil 101 is stopped, the control unit 104 determines that the energized state of the electrostatic shield body 112 is good if the output signal of the comparator 503b is at a high level (+5 V), and induction heating is performed. The energization of the coil 101 is permitted. If the output signal of the comparator 503b is low level (0 V), the control unit 104 determines that the energization state of the electrostatic shield body 112 has deteriorated, and keeps the induction heating coil 101 in a stopped state (allow energization). do not do).

  When the induction heating coil 101 is operating (when energized), the control unit 104 inputs and checks the output signal of the comparator 503a and does not check the output signal of the comparator 503b. In the energized state, a leakage current (operation frequency component) flows from the induction heating coil 101 to the electrostatic shield body 112 as a large noise. In the reference form 1, when the induction heating coil 101 is operated, the comparator 503b is low level even when the energization state of the electrostatic shield body 112 is good due to the large noise of the leakage current (operation frequency component). Is output. Therefore, during the operation of the induction heating coil 101, the output signal of the comparator 503b is not useful as data for determining the energization state of the electrostatic shield body 112.

At the time of energization, the control unit 104 uses the output signal of the comparator 503a. When the energization state of the electrostatic shield body 112 is good, a large leakage current flows from the induction heating coil 101 to the electrostatic shield body as noise. Therefore, the potential of the non-inverting input terminal of the comparator 503a is higher than the threshold value (first reference voltage Vref1). For example, when the electrostatic shield body 112 is damaged, the leakage current (noise) flowing from the induction heating coil 101 to the electrostatic shield body is reduced. Therefore, the potential of the non-inverting input terminal of the comparator 503a is lower than the threshold value (first reference voltage Vref1). The comparator 503a outputs a high level when the energization state of the electrostatic shield body 112 is good. When the induction heating coil 101 is operating (when energized), the control unit 104 determines that the energized state of the electrostatic shield body 112 is good if the output signal of the comparator 503a is at a high level (+5 V). Then, energization of the induction heating coil 101 is continued. If the output signal of the comparator 503a is low level (0 V), the control unit 104 determines that the energization state of the electrostatic shield body 112 has deteriorated and stops the induction heating coil 101. The leakage current flowing through the electrostatic shield body 112 having a large area is large and the level is not stable (like noise). In such a case, the detection unit 503 compares the detection voltage based on the leakage current with a certain threshold rather than comparing it with a reference voltage proportional to the output level of the induction heating coil (for example, Japanese Patent Application Laid-Open No. Sho 62-278785). Works stably.
With the above configuration, the induction heating coil can be appropriately controlled by detecting the conduction state of the electrostatic shield body by an appropriate method both when the induction heating coil is stopped and during operation. A safe induction heating device can be realized.

  The microcomputer 105 executes the function of the control unit 104 by software processing. In software processing, a delay of a processing cycle period occurs at a maximum from when a signal is input until the processing result is output. If, for example, the top plate is cracked when the induction heating coil 101 is energized (in this case, the energization state of the electrostatic shield 112 deteriorates), it is preferable to stop the induction heating coil 101 as soon as possible. In the reference form 1, when the induction heating coil 101 is energized, the microcomputer 105 inputs the output signal of the comparator 503a (detection output during the operation of the induction heating coil 101) to the external interrupt terminal. When the output signal of the comparator 503a changes from the high level to the low level, the microcomputer 105 immediately executes an interrupt process and stops the induction heating coil 101. Thereby, high safety is realized. The microcomputer 105 inputs the output signal of the comparator 503b (detection output when the induction heating coil 101 is stopped) to a normal input terminal, and processes it every processing cycle period.

  FIG. 6 is a flowchart illustrating a method for controlling the induction heating apparatus according to the first embodiment. FIG. 6 includes steps 601 to 616. First, time t = T0 (T0 = 10 seconds in the reference form 1) is set (step 601). Next, the control unit 104 determines whether or not the conduction state of the electrostatic shield body 112 is good (when the induction heating coil 101 is stopped, the output of the comparator 503b is +5 V or 0 V, or the induction heating coil 101 is in an operating state). In step 602, it is checked whether the output of the comparator 503a is + 5V or 0V. Only in step 602, the detection unit 503 consumes power. If the conduction state is good, the process proceeds to step 606 and the shield flag is set to zero. If the conduction state is bad, the process proceeds to step 603 and the shield flag is set to 1. Proceed to step 607.

  In step 607, the control unit 104 checks whether an ON command for the induction heating coil 101 is input. If the ON command for the induction heating coil 101 has not been input (if the OFF command has been input), the induction heating coil 101 is stopped (step 613). Proceed to step 610. If the ON command of the induction heating coil 101 is input (step 607), it is checked whether or not the shield flag is 1 (step 608). If the shield flag is 1 (if the conduction state is bad), the voltage applied to the induction heating coil 101 is lowered below a predetermined level (step 614). In the reference form 1, the induction heating coil 101 is stopped. Small electric power may be applied to the induction heating coil 101. If the shield flag is 0 (if the conduction state is good), the control unit 104 controls the inverter circuit 102 to apply the commanded power to the induction heating coil 101 (step 609). Proceed to step 610.

  In step 610, it is checked whether or not the shield flag is 1. If the shield flag is 1 (if the conduction state is bad), the warning LED 116 is turned on (step 615), and the warning buzzer 115 is turned on (step 616). Proceed to step 604. If the shield flag is 0 (if the conduction state is good), the warning LED 116 is turned off (step 611), and the warning buzzer 115 is turned off (step 612). Proceed to step 604.

  In step 604, it is checked whether or not t = 0 (actually, steps 604 and 605 are executed at predetermined time intervals). If t = 0, the process proceeds to step 601 and the above processing is repeated. If t is not 0, the value of t is decremented (step 605). Proceeding to step 607, the above processing is repeated.

The detection unit 503 checks the conduction state of the electrostatic shield body 112 every predetermined time, and stops the power supply to the detection unit 503 at times other than the check time, thereby reducing the average power consumption of the induction heating device. be able to.
The detection unit may switch between detecting the conduction state of the electrostatic shield body in real time and detecting it intermittently according to load detection. This makes it less susceptible to noise and can output a stable and accurate detection result.
When the dielectric heating coil 101 is energized, the detection unit 503 may preferably detect the conduction state of the electrostatic shield body 112 quickly. When the dielectric heating coil 101 is energized, the detection unit 503 checks the conduction state of the electrostatic shield body 112 in real time (for example, by an interrupt process), and detects when the dielectric heating coil 101 is not energized. The unit 503 may check the conduction state of the electrostatic shield body 112 every predetermined time.
In the reference form 1, the detection unit 503 detects the conduction state of the electrostatic shield body 112 at every predetermined time T0 when the induction heating coil 101 is energized and stopped. The detection unit 503 may detect the conduction state of the electrostatic shield body 112 when the induction heating coil 101 is turned on from OFF and every predetermined time T0 during which the induction heating coil 101 is energized.

The comparator 503b determines whether or not the impedance of the electrostatic shield body 112 is equal to or lower than a predetermined threshold value, and the control unit 104 determines that the impedance of the electrostatic shield body 112 is greater than the predetermined threshold value. The output of 101 may be reduced or stopped.
The comparator 503b determines whether or not the voltage across the electrostatic shield body 112 is less than or equal to a predetermined threshold, and the control unit 104 induces when the voltage across the electrostatic shield body 112 is greater than the predetermined threshold. The output of the heating coil 101 may be reduced or stopped.
The comparator 503b determines whether or not the current flowing through the electrostatic shield body 112 is equal to or greater than a predetermined threshold, and the control unit 104 performs induction when the current flowing through the electrostatic shield body 112 is smaller than the predetermined threshold. The output of the heating coil 101 may be reduced or stopped.

  In this reference embodiment, one end of the induction heating coil 101 is directly connected to the ground line of the inverter circuit 102. Leakage current does not flow to the user through the heated object 110 from the side directly connected to the ground wire of the induction heating coil 101. What is necessary is just to shield so that a leakage current may not flow into the heated object 110 from the other end side of the induction heating coil 101. In this configuration, the induction heating coil 101 and the heated object 110 can be easily shielded, and a higher shielding effect can be obtained.

<< Reference form 2 >>
The induction heating apparatus according to the second embodiment of the present invention will be described with reference to FIG. The schematic configuration (FIG. 1) and circuit configuration (FIG. 3) of the induction heating apparatus of Reference Embodiment 2 are the same as those of Embodiment 1. The induction heating device of Reference Form 2 includes a high magnetic permeability (magnetic material) heated object such as iron (or a low magnetic permeability and high resistance heated object such as 18-8 stainless steel) and aluminum or It is possible to heat an object to be heated with a low magnetic permeability such as copper (with a nonmagnetic material) and a low resistance. The induction heating device of Reference Embodiment 2 differs from Embodiment 1 only in the control method related to detection of the conduction state of the electrostatic shield body 112. In other respects, Reference Embodiment 2 is the same as Embodiment 1. Since the basic configuration of the present embodiment is the same as that of the first embodiment, different points will be mainly described. The same functions as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 7 is a flowchart showing a method for controlling the induction heating apparatus according to the second embodiment. FIG. 7 includes steps 701 to 709. First, the control unit 104 checks whether or not the conductive state of the electrostatic shield body 112 is good (whether the collector potential of the transistor 103a is + 5V or 0V) (step 701). If the conduction state is good, the warning LED 116 is turned off (step 703). If the conduction state is bad, the warning LED 116 is turned on (step 702). Proceed to step 704.

In step 704, the control unit 104 checks whether or not a command to turn on the induction heating coil 101 is issued. If a command to turn on the induction heating coil 101 is issued, the process proceeds to step 705. If the command to turn on the induction heating coil 101 is not issued, the process proceeds to step 708.
In step 708, the induction heating coil 101 is stopped. Returning to step 701, the above processing is repeated.

  In step 705, the control unit 104 checks whether or not the load of the induction heating coil 101 (the heated object 110) is a magnetic substance (or a low-permeability and high-resistance heated object). If the load (heated object 110) is a magnetic material (or a low magnetic permeability and high resistance heated object), the process proceeds to step 709, and the load (heated object 110) is a magnetic material (or low magnetic permeability and high resistance). If it is not the object to be heated (if it is a to-be-heated object having a low magnetic permeability (non-magnetic substance) and a low resistance), the process proceeds to step 706.

In step 706, the control unit 104 checks whether or not the conduction of the electrostatic shield body 112 is good based on the output of the detection unit 103. If the continuity of the electrostatic shield body 112 is good, the process proceeds to step 709 and the commanded power is applied to the induction heating coil 101. Returning to step 701, the above processing is repeated.
In step 706, if the continuity of the electrostatic shield body 112 has deteriorated, the process proceeds to step 707, where the induction heating coil 101 is stopped or its applied power is lowered. Returning to step 701, the above processing is repeated.

  When the object to be heated is a non-magnetic material and has a low resistance, a leakage current flows from the induction heating coil 101 to the user through the object 110 to be heated. In this configuration, for example, the output of the induction heating coil 101 is reduced or stopped only when the heated object 110 is a non-magnetic material and has low resistance and the conduction of the electrostatic shield body 112 deteriorates. When the electrostatic shield body 112 has a good conduction state, it is difficult for the detection unit 103 to erroneously detect and trouble the user. An induction heating device that appropriately operates the safety function is realized.

  In the reference form 2, the operations of the warning LED 116 and the warning buzzer 115 are the same as those in the first embodiment. Instead, the warning LED 116 is lit to indicate that the induction heating device cannot be used only when the conduction state of the electrostatic shield body 112 deteriorates and the heated object 110 is a non-magnetic material and has a low resistance. , And / or the warning buzzer 115 may be turned on for notification. Only when the object to be heated is a non-magnetic material and has a low resistance, the user can be accurately informed that the induction heating device cannot be used. The user can properly use and repair the induction heating device.

<< Reference form 3 >>
An induction heating apparatus according to Reference Embodiment 3 of the present invention will be described with reference to FIG. The induction heating apparatus of Reference Embodiment 3 differs from Embodiment 1 only in the method for attaching the electrostatic shield body 112. In other respects, Reference Embodiment 3 is the same as Embodiment 1. Since the basic configuration of the present embodiment is the same as that of the first embodiment, different points will be mainly described. The same functions as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 8 is a cross-sectional view of the main part of the induction heating device of Reference Embodiment 3 (only the vicinity of the place where the electrostatic shield body 112 is attached is shown). In FIG. 8, the electrostatic shield body 112 is provided on the lower surface of the top plate 118. If there is sufficient space between the electrostatic shield body 112 and the induction heating coil 101, the insulating layer 117 covering the electrostatic shield body 112 is not necessarily provided.
The shield body can be stably provided near the heated body, and the space between the induction heating coil and the heated body can be reliably shielded.
The electrostatic shield body 112 may be provided on the upper and lower surfaces of the top plate 118.

<< Reference form 4 >>
The induction heating apparatus according to the fourth embodiment of the present invention will be described with reference to FIG. The induction heating apparatus of the reference form 4 has a top plate 918 formed of laminated glass instead of the top plate 118, and the attachment method of the electrostatic shield body 112 is different from that of the first embodiment. In other respects, Reference Embodiment 4 is the same as Embodiment 1. Since the basic configuration of the present embodiment is the same as that of the first embodiment, different points will be mainly described. The same functions as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 9 is a cross-sectional view of an essential part of the induction heating device of Reference Embodiment 4 (only the vicinity of the place where the electrostatic shield body 112 is attached is shown). In FIG. 9, the electrostatic shield body 112 is provided between the glass of the top plate 918 of laminated glass. The electrostatic shield 112 is securely held by the laminated glass. Since the thickness of the electrostatic shield body 112 is very thin, there is substantially no gap between the two glasses. The shield body can be stably provided near the heated body. The shield body is reliably insulated from the heated body and the induction heating coil without providing an insulating layer.

<< Embodiment 2 >>
The induction heating apparatus according to the second embodiment of the present invention will be described with reference to FIG. The induction heating apparatus according to the second embodiment includes a fixed plate 1001 between the induction heating coil 101 and the body 110 to be heated, and an electrostatic shield body 112 is provided on the upper surface of the fixed plate 1001. In other points, the second embodiment is the same as the first embodiment. Since the basic configuration of the present embodiment is the same as that of the first embodiment, differences will be mainly described. The same functions as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 10 is a cross-sectional view of a main part of the induction heating apparatus according to the second embodiment (only the vicinity of the mounting location of the fixed plate 1001 and the electrostatic shield body 112 is shown). In FIG. 10, a fixing plate 1001 is made of heat-resistant and insulation-resistant glass, porcelain, mica, heat-resistant resin, or the like, and an electrostatic shield body 112 is provided on the upper surface. The fixed plate 1001 is placed on the induction heating coil 101. Since the fixing plate 1001 is made of a heat-resistant and insulation-resistant material, there is no possibility of deterioration due to heat due to long-term use.

A space is provided between the fixed plate 1001 and the top plate 118. The wind generated by the cooling fan 1002 passes through this space, either directly or guided by an air guide. Thereby, the induction heating coil 101 can be cooled.
A standard fixing plate 1001 having an electrostatic shield body 112 provided on the upper surface is made, and a standard fixing plate can be freely provided at any appropriate position for each model of the induction heating apparatus. It is only necessary to determine the mounting position of the fixing plate for each model, and standardization of product design can be achieved. Reduce development effort and time.

<< Embodiment 3 >>
The induction heating apparatus of Embodiment 3 of this invention is demonstrated using FIG. In the induction heating device of the third embodiment, a space is provided between the fixed plate 1001 and the induction heating coil 101. In other respects, the third embodiment is the same as the second embodiment.
FIG. 11 is a cross-sectional view of an essential part of the induction heating apparatus according to the third embodiment (only the vicinity of the mounting location of the fixed plate 1001 and the electrostatic shield body 112 is shown). In FIG. 11, since a space is provided between the fixed plate 1001 and the induction heating coil 101, the fixed plate 1001 may have a lower insulating performance than that in the second embodiment. The fixing plate 1001 can be formed of an inexpensive insulating material.

  Compared to the second embodiment, the heat dissipation of the surface of the induction heating coil 101 of the third embodiment is high. The wind generated by the cooling fan 1002 is guided directly or by an air guide and passes through the space between the fixed plate 1001 and the induction heating coil 101. Thereby, the induction heating coil 101 can be further cooled.

<< Embodiment 4 >>
The induction heating apparatus of Embodiment 4 of this invention is demonstrated using FIG. The induction heating device of the fourth embodiment is different from the third embodiment in that it has a fixed plate 1201 instead of the fixed plate 1001 and the method of attaching the electrostatic shield body 112. In other respects, the fourth embodiment is the same as the third embodiment.
FIG. 12 is a cross-sectional view of a main part of the induction heating apparatus according to the fourth embodiment (only the vicinity of the mounting location of the fixed plate 1201 and the electrostatic shield body 112 is shown). In FIG. 12, the fixing plate 1201 is formed by laminating two thin plates made of heat and insulation resistant glass, porcelain, mica, heat resistant resin, or the like. An electrostatic shield body 112 is provided between the two thin plates.

<< Embodiment 5 >>
The induction heating apparatus of Embodiment 5 of this invention is demonstrated using FIG. The induction heating apparatus according to the fifth embodiment has an electrostatic shield body 112 and an insulating layer 117 covering the electrostatic shield body 112 on the lower surface of the fixed plate 1001. In other respects, the fifth embodiment is the same as the third embodiment. Although the insulating layer 117 is provided in the fifth embodiment, the insulating layer 117 covering the electrostatic shield body 112 may be deleted when a sufficient spatial distance between the fixed plate 1001 and the induction heating coil 101 can be obtained.

  In the above-described embodiment, the induction heating apparatus that places the object to be heated on the top plate has been described. However, the present invention is not limited to this. For example, an induction heating device that holds the object to be heated in the air, a virtues or a cover made of an insulating heat-resistant material such as synthetic resin, porcelain, or glass is provided on the induction heating coil. The present invention can also be applied to an induction heating apparatus on which a heated body is placed or an induction heating apparatus in which a hole is provided in an insulating heat-resistant material and the heated body is fitted into the hole. In the induction heating apparatus having these configurations, the distance between the induction heating coil and the object to be heated can be shortened to increase the heating efficiency.

  The pattern of the electrostatic shield body 112 according to the present embodiment has a size substantially the same as that of the induction heating coil 101 and a substantially arc shape divided by the slits 201. Such a shape is preferable, but the shape is not limited to this, and any shape having a size covering the high voltage portion of the electrostatic shield body and the induction heating coil 101 may be used. For example, the shape may be rectangular or donut shape.

  The electrostatic shield body 112 of the present embodiment has connection portions 202 at both ends of the pattern. Each connection unit 202 is connected to the detection unit 103 via lead wires 122 and 123. Any other configuration may be adopted as long as two or more connection portions are provided, and the conduction portion of the electrostatic shield body is detected by energizing the connection portions from the detection portion. By providing two or more connection parts, it is easy for the detection part to detect the conduction state of the electrostatic shield body, and also when the conduction of one line deteriorates, the electrostatic shield The body can have a shielding effect.

The electrostatic shield body and the low potential portion may be connected by a connection line as in the embodiment (so that a DC component and an AC component flow), or may be connected by a capacitor in an AC manner. When the electrostatic shield body and the low potential portion are connected by a capacitor, the detection unit, for example, when the induction heating coil is stopped, for example, an alternating voltage (inductive heating coil is output from an oscillation circuit built in the detection unit). A voltage different from the generated voltage) is applied to the electrostatic shield body, and the conduction state of the electrostatic shield body is detected.
Although the invention has been described in its preferred form with a certain degree of detail, the present disclosure of this preferred form should vary in the details of construction, and combinations of elements and changes in order may vary in the claimed invention. It can be realized without departing from the scope and spirit.

  As described above, since the induction heating device according to the present invention can be made highly safe without fear of electric shock even when the electrostatic shield body does not sufficiently perform its function, It can also be used for cooking appliances.

FIG. 1 is a schematic configuration diagram of an induction heating apparatus according to Embodiment 1 of the present invention. FIG. 2 is a diagram illustrating an example of a pattern of an electrostatic shield body of the induction heating device according to the first embodiment of the present invention. FIG. 3 is a block diagram showing the configuration of the induction heating apparatus according to Embodiment 1 of the present invention. FIG. 4 is a flowchart showing a method for controlling the induction heating apparatus according to the first embodiment of the present invention. FIG. 5 is a block diagram showing the configuration of the induction heating apparatus according to the first embodiment of the present invention. FIG. 6 is a flowchart showing a method for controlling the induction heating apparatus according to the first embodiment of the present invention. FIG. 7 is a flowchart showing a control method of the induction heating apparatus according to the second embodiment of the present invention. FIG. 8 is a cross-sectional view of the main part of the induction heating apparatus according to Reference Embodiment 3 of the present invention. FIG. 9 is a cross-sectional view of the main part of the induction heating apparatus according to the fourth embodiment of the present invention. FIG. 10 is a cross-sectional view of the main part of the induction heating apparatus according to the second embodiment of the present invention. FIG. 11 is a cross-sectional view of main parts of the induction heating device according to the third embodiment of the present invention. FIG. 12 is a cross-sectional view of main parts of the induction heating device according to the fourth embodiment of the present invention. FIG. 13 is a cross-sectional view of the main part of the induction heating apparatus according to the fifth embodiment of the present invention. FIG. 14 is a block diagram showing the configuration of the induction heating device of Conventional Example 1 FIG. 15 is a block diagram showing the configuration of the induction heating device of Conventional Example 2 FIG. 16 is a diagram showing a pattern of an electrostatic shield formed on the top plate of the induction heating device of Conventional Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Induction heating coil 102 Inverter circuit 103,503 Detection part 104 Control part 105 Microcomputer 106 LED drive circuit 107 Piezoelectric buzzer drive circuit 108 Setting display part drive circuit 109 Operation part 110 Heated body 111 Drive circuit 112 Electrostatic shield body 113 Setting Input section 114 Setting display section 115 Warning buzzer 116 Warning LED
117 Insulating layer 118, 918 Top plate 119, 120, 122, 123 Connection line 121 Plug 124 Induction heating coil holding member 125 Case 126 Control board 127 Commercial AC power supply 201 Slit 202 Connection part 1001, 1201 Fixing plate 1002 Cooling fan

Claims (4)

A top plate placed on the top of the housing and on which the object to be heated is placed;
An induction heating coil that is provided below the top plate and generates a high-frequency magnetic field to heat the object to be heated;
An inverter circuit for driving the induction heating coil;
A fixed plate made of a heat-resistant insulating material and placed on the induction heating coil;
Wherein provided on or in the fixed plate Luke, the provided under the fixing plate and becomes covered the surface with the insulating layer, and the shield of electrically connected conductive to the low potential portion,
A detection unit that applies a voltage different from the voltage generated by the induction heating coil to the shield body, and detects a conduction state of the shield body in a state where at least the induction heating coil is not energized ;
When detecting that the conduction state has deteriorated based on the detection result of the detection unit when the induction heating coil is not energized, the inverter circuit is controlled so that the output of the induction heating coil is reduced or stopped. And an induction heating device. The detection unit determines whether the impedance of the shield body is a predetermined threshold value or less, whether the voltage between the predetermined terminals of the shield body is a predetermined threshold value or less, or a current flowing through the shield body. It is determined whether or not a predetermined threshold or more, and the degree of deterioration of the conduction state is detected,
When the impedance of the shield body is larger than a predetermined threshold, the voltage between the predetermined terminals of the shield body is higher than a predetermined threshold, or the current flowing through the shield body is smaller than a predetermined threshold. The induction heating apparatus according to claim 1, wherein the output of the induction heating coil is reduced or stopped. The induction heating apparatus according to claim 2, wherein the detection unit applies a direct current to the shield body to detect a conduction state thereof . A display unit and / or a notification unit;
  The induction heating apparatus according to claim 1, wherein if the conduction state of the shield body deteriorates, the display unit displays an abnormal state and / or the notification unit notifies the abnormal state.

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