JP2005340130A - Induction heating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent leakage current from passing through a human body, eliminate the risk of electrification, and enhance safety. <P>SOLUTION: The apparatus comprises a heating coil 101 which generates high frequency magnetic field and heats a heated object 110, an inverter circuit 102 which drives the heating coil 101, a shielding member 112 which is prepared in between the heated object 110 and the heating coil 101 and electrically connected to a low potential part, a heating coil holding member 124 which holds the heating coil 101, an annular shielding ring 131 which is made of a conductive material, prepared around the heating coil 101 on the heating coil holding member 124 and electrically connected to the low potential part. Since most of the leakage current from the heating coil 101 flows to the ground, through the shielding member 112 and the shield ring 131, the current is mostly prevented from passing through a user's body. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an induction heating apparatus in which a shield body is provided between a heated body and a 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 device of Conventional Example 1 is 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. Such a low magnetic permeability (non-magnetic material) and a low resistance object to be heated can be heated. FIG. 5 is a block diagram showing the configuration of the induction heating apparatus of Conventional Example 1. In FIG. 5, a heating coil 101 is connected to a commercial AC power input 127 that generates a high-frequency magnetic field and heats an object to be heated (a metal container such as a pan or a frying pan) 110, and a rectifying and smoothing unit 108 is connected to a bridge 108a. An inverter circuit 1402 configured by the capacitor 108 b and rectifying the commercial AC power supply converts the power rectified by the rectifying and smoothing unit 108 into high frequency power and supplies the heating coil 101 with the high frequency current. The ceramic top plate 118 is disposed on the top of the housing 125 and carries the object 110 to be heated.

  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 ON / OFF controlled to switch the number of turns of the heating coil 101 driven by the inverter circuit 102 and switch the voltage applied to the heating coil 101. The number of turns of the heating coil 101 in the case of heating a heated object having a low magnetic permeability and a low resistance is higher than that 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 voltage applied to the heating coil 101 is high. When the object to be heated 110 is a pan made of aluminum, copper, or the like having low permeability and low resistance, the voltage applied to the heating coil 101 is 1 kV or more.

  A stray capacitance (equivalent capacitance) 1411 exists between the heating coil 101 and the heated object 110. When the user touches the object 110 to be heated, a current flows from the heating coil 101 to the ground (substantially grounded low potential portion) 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-voltage heating coil 101 to the human body.

  The induction heating apparatus of the prior art example 2 which prevents that an electric current leaks from the high voltage | pressure heating coil 101 to a human body is described (for example, refer patent document 1).

  The induction heating apparatus of Conventional Example 2 described in Patent Document 1 will be described with reference to FIGS. 6 and 7. FIG. 6 is a block diagram showing the configuration of the induction heating device of Conventional Example 2. In FIG. 6, the same blocks as those in the conventional example 1 (FIG. 5) are denoted by the same reference numerals. The induction heating apparatus of Conventional Example 2 differs from Conventional Example 1 in that a conductive shield body 1512 and an insulating layer covering the shield body 1512 are provided on the lower surface of the top plate 118. The 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. 7 is a diagram showing a pattern of the shield body 1512 formed on the top plate 118 of the induction heating device of the second conventional example. For easy understanding, the pattern of the shield body 1512 is shown in FIG. 7 except for the insulating layer. The shield body 1512 is applied and baked on the lower surface of the top plate 118. The 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 shield body 1512.

  A stray capacitance (equivalent capacitance) 1514 exists between the heating coil 101 and the shield body 1512. A current flows from the heating coil 101 to the ground (signal ground) through the stray capacitance (equivalent capacitance) 1514 and the internal resistance (equivalent resistance) 1515 of the shield body 1512. The impedance of the internal resistance (equivalent resistance) 1515 of the conductive shield 1512 is sufficiently smaller than the impedance of the stray capacitance (equivalent capacity) 1514 (the frequency of the high-frequency current flowing through the heating coil 101 is about 20-60 kHz. is there). Therefore, the voltage induced in the shield body 1512 is sufficiently low. A stray capacitance (equivalent capacitance) 1516 exists between the shield body 1512 and the heated object 110. When the user touches the body 110 to be heated, the leakage current is grounded 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 shield body 1512 by the heating coil 101. Flows to the earth). Since the voltage induced in the shield body 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, an internal resistance (equivalent resistance) 1515 of the shield body 1512, a stray capacitance (equivalent capacity) 1516, and an internal resistance of the user's body (between the shield body 1512 and the ground (signal ground or substantially earth ground)). Equivalent resistance) 1412 is connected in parallel (when the signal ground and the substantially earth ground can be regarded as the same potential, particularly when the direction pole is connected to the earth ground through a predetermined resistance in a 100V commercial AC power source). . The impedance of the internal resistance (equivalent resistance) 1515 of the 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. Most of the leakage current flows to the ground (signal ground) through the 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 a low magnetic permeability and a low resistance, the number of turns of the heating coil 101 is increased. At this time, the voltage applied to the heating coil is 1 kV or more. In Conventional Example 2, there is a shield body that is electrically coupled to the low potential portion, and there is almost no potential difference between the heated object 110 and the shield body 1512 (both of them are close to the 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.

  Patent Document 4 discloses an induction heating device 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. A direct current is passed through this pattern. The heating coil is stopped based on the fact that the current flowing through this pattern is interrupted by the crack of the top plate.

Patent Document 2 and Patent Document 3 disclose an induction heating device in which a thin conductive pattern is provided on a top plate. When the heating coil is driven, a leakage current flows through this pattern. When the leakage current becomes smaller than a reference value proportional to the output of the heating coil, the heating coil is stopped.
Japanese Patent Publication No. 4-75634 Japanese Patent Laid-Open No. 62-278785 Japanese Patent Laid-Open No. 62-278786 Japanese Patent Publication No.55-869

  However, when trying to achieve higher performance (higher output, higher frequency) such as improved thermal feeling, especially when the heated object is a pan made of aluminum, copper, etc. with low magnetic permeability and low resistance. Since the voltage applied to the heating coil is further increased, a leakage current is easily induced in the heated object. Therefore, there is a problem that safety is not always sufficiently ensured (when the user touches the object to be heated, a leakage current of a predetermined level or more may flow through the human body).

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a highly safe induction heating apparatus that prevents leakage current from flowing through the human body and does not cause electric shock.

  In order to solve the above-mentioned conventional problems, the induction heating device of the present invention is provided with an annular shield ring made of a conductive material disposed around a heating coil and electrically connected to a low potential portion. .

  As a result, the internal resistance (equivalent resistance) of the shield body and the shield ring, the stray capacitance (equivalent capacitance), and the internal resistance (equivalent resistance) of the user's body between the shield body and the shield ring and the ground. Connected in parallel. Since the impedance of the internal resistance (equivalent resistance) of the shield body and the shield ring is very small compared to the impedance of the stray capacitance (equivalent capacitance) and the internal resistance (equivalent resistance) of the user's body, the leakage current from the heating coil Almost flows to the ground through the shield body and the shield ring (compared to the internal resistance of the shield body only, the internal resistance of the shield body and the shield ring is smaller, and the leakage current prevention effect is greater).

  In other words, the shield ring connected to the low potential part around the heating coil against the stray capacitance (equivalent capacity) that passes through the outer periphery of the shield body and is about to occur between the heated body and the heating coil. As a result, the stray capacitance (equivalent capacity) that is about to occur between the heated body and the heating coil can be reduced by positioning the shield body and the shield ring between the heated body and the heating coil. it can.

  Therefore, almost no current leaks to the user's body.

  The induction heating apparatus of the present invention can further reduce the leakage current in addition to the shield body provided between the body to be heated and the heating coil.

  A first invention is provided between a heating coil that generates a high-frequency magnetic field and heats a heated body, an inverter circuit that drives the heating coil, and the heated body and the heating coil. An electrically connected conductive shield body, a heating coil holding member that supports the heating coil, and arranged around the heating coil and provided on the heating coil holding member, and electrically connected to a low potential portion By having the annular shield ring made of the conductive material formed, the internal resistance (equivalent resistance) of the shield body and the shield ring is between the shield body and the shield ring and the ground (signal ground or substantially earth ground). The stray capacitance (equivalent capacitance) and the internal resistance (equivalent resistance) of the user's body are connected in parallel. Since the impedance of the internal resistance (equivalent resistance) of the shield body and the shield ring is very small compared to the impedance of the stray capacitance (equivalent capacitance) and the internal resistance (equivalent resistance) of the user's body, the leakage current from the heating coil Almost flows to the ground (signal ground) through the shield body and the shield ring (compared to the internal resistance of only the shield body, the internal resistance of the shield body and the shield ring is smaller, and the leakage current prevention effect is greater).

  In other words, the shield ring connected to the low potential part around the heating coil against the stray capacitance (equivalent capacity) that passes through the outer periphery of the shield body and is about to occur between the heated body and the heating coil. As a result, the stray capacitance (equivalent capacity) that is about to occur between the heated body and the heating coil can be reduced by positioning the shield body and the shield ring between the heated body and the heating coil. it can.

  Therefore, almost no current leaks to the user's body.

  In particular, the second invention includes at least one connection portion with the low potential portion in the shield body and the shield ring of the first invention, and electrically connects the connection portion of the shield body and the connection portion of the shield ring. By using the common low potential portion, the connection is minimized and the structure is simplified, so that the cost is reduced and the reliability is improved.

  In particular, the third invention includes at least one connection portion with the low potential portion in the shield body and the shield ring of the first or second invention, and each of the connection portions is viewed from the same direction as viewed from the heating coil holding member. With this connection, all the connection work is performed from the same direction, and assemblability is improved.

  In the fourth aspect of the invention, in particular, by mutually screwing the connection line connecting the low potential portion of any one of the first to third aspects of the invention and the shield ring to the shield ring, mutual contact is ensured, The electrical reliability of the connecting portion is improved.

  According to a fifth aspect of the invention, in particular, a tab terminal and a receptacle terminal are formed by connecting a connection line connecting the low potential portion of any one of the first to third aspects and the shield ring to the shield ring with a flat connection terminal. Therefore, the workability of the connecting portion is improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(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 showing a schematic configuration of the induction heating device according to the first embodiment, FIG. 2A is a diagram showing a pattern of a shield body of the induction heating device according to the first embodiment, and FIG. FIG. 3 is a diagram showing a circuit configuration of the induction heating apparatus according to the first embodiment.

  The induction heating device of the embodiment 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 copper. It is possible to heat an object to be heated with a low magnetic permeability (non-magnetic material) and a low resistance.

  1 to 3, the top plate 118 is provided on the upper surface of the casing 125 and places a heated object (a load which is a metal container such as a pan or a frying pan) 110. A shield body 112 is provided below the top plate. The insulating layer 117 covers the shield 112, the heating coil 101 generates a high-frequency magnetic field and heats the heated object 110, and the heating coil holding member 124 is heated. The coil 101 is placed on the upper surface. Plug 121 receives commercial AC power supply 127. The control board 126 rectifies and smoothes the commercial AC power supply 127, the inverter circuit 102 that converts the power rectified by the rectifying and smoothing section 108 into high-frequency power and supplies high-frequency current to the heating coil 101, and 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, signal ground). Two connection lines 119 and 120 connect the inverter circuit 102 and the heating coil 101. The two connection lines 122 and 123 connect the shield body 112 and the control board 126.

  The shield body 112 has an outer diameter substantially the same as that of the heating coil 101, is divided by a slit 128, and has a substantially arc shape that is coaxial with the heating coil 101 and substantially covers the heating coil 101. The shield body 112 has a shape in which a closed loop including the central axis of the heating coil 101 does not exist thereon.

  The shield body 112 is provided with two connection portions 129. The connecting portion 129 is an L-shaped tab terminal 130, and one end thereof is electrically connected to the conductive carbon paint. The other end protrudes below the coil holding member 124 and is connected by faston terminals (receptacle terminals) of the connecting wires 122 and 123. The other end protrudes below the coil holding member 124 because the wiring (not shown) connected to various temperature detection thermistors and the like is arranged below the coil holding member 124 so that it is easy to assemble and perform. This is because there are few above problems, and when the connection lines 122 and 123 are included as a unit in a part of the wiring, it is preferable that all wiring processing is completed below the coil holding member 124. The other end of the connection line 122 is connected to the ground of the detection unit 103, and the other end of the connection line 123 is connected to an input terminal of the detection unit 103 (one end of the resistor 103c).

  A shield ring 131 for magnetic shielding is attached to the coil holding member 124 around the heating coil 101. The shield ring 131 is made of a conductive material such as aluminum or copper which is not easily heated by induction, and has an annular shape. In production, aluminum die-casting or aluminum plate press parts are common. A connecting portion 132 is formed to protrude from the shield ring 131 through the coil holding member 124. In the case of thick aluminum die casting, the connecting portion 132 is provided with a pilot hole 133 capable of self-tapping. Further, in the case of a thin aluminum press, the connecting portion 132 is provided with a tab 134 that allows a faston terminal to be connected.

  The connection part 132 is connected to one side of the connection part 129 by a connection line 135. In the case of this embodiment, the connection line 122 or the connection line 123 and the connection line 135 are double caulked to the faston terminal 136 of the connection portion 129, and the round terminal 137 provided at the other end of the connection line 135 is connected. The shield body 112 and the shield ring 131 are electrically connected to each other by self-tapping to the connection portion 132, and also connected to the low potential portion (signal ground).

  The connection line 119 connects the outer peripheral end of the heating coil 101 and one end of the resonant capacitor 102g, and the connection line 120 connects the inner peripheral end of the heating coil 101 to the emitter of the switching element 102c and the collector of the switching element 102d. . The potential at the outer end of the heating coil 101 wound in a spiral is lower than the 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. Thus, 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 heated body 110 is made of a material having a low magnetic permeability (non-magnetic material) such as aluminum or copper and a material having a high magnetic permeability (magnetic material) such as iron. The heating coil 101 is driven at a high frequency and a high voltage as compared to (or when it is made of a material having low magnetic permeability and high resistance such as 18-8 stainless steel). When the heated object 110 is made of a material having low permeability and low resistance, the number of turns of the heating coil may be increased by switching contacts 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). The heating coil 101 is connected to the output terminal of the inverter circuit 102. The inverter circuit 102 and the heating coil 101 constitute a high frequency inverter. The inverter circuit 102 includes a series connection body (“series connection bodies 102c and 102d”) of a first switching element 102c (IGBT (Insulated Gate Bipolar Transistor)) and a second switching element 102d (IGBT in this embodiment). Is 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 (the ground terminal in the embodiment) of the full-wave rectifier 108a. A series connection body of the 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 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 heating coil 101, and the resonance capacitor 102g. The 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 in a closed circuit including the first switching element 102c (or the first diode 102e), the 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 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 heating coil 101 and the resonant capacitor 102g is an object to be heated (cooking pot) of a specified material (for example, a high-conductivity nonmagnetic material such as aluminum) and having a standard size (for example, a diameter equal to or greater than the diameter of the heating coil). ) 110 is placed at a designated place on the top plate (for example, a place shown as a heated portion), the resonance frequency is set to be about three times the drive 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 heating coil 101, so that the cooking pot 110 can be efficiently heated. 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 envelope of the high frequency current supplied to the heating coil 101 is smoothed by the second smoothing capacitor 102b by the induction heating device. This reduces the commercial frequency component of the current IL flowing through the heating coil 101 that causes vibration noise from the pan 110 or the like during heating.

  The shield body 112 and the shield ring 131 shield between the heating coil 101 and the body 110 to be heated, and effectively prevent the leakage current induced by the heating coil 101 from flowing through the user's body. That is, compared to the shield power of only the shield body 112, the shield power obtained by combining the shield body 112 and the shield ring 131 is large as a shield area, and is smaller as an internal resistance, and the leakage current prevention effect is also large. come.

  In other words, the low potential portion (signal) around the heating coil 101 is compared with the stray capacitance (equivalent capacitance) that passes through the outer periphery of the shield body 112 and is generated between the heated body 110 and the heating coil 101. And the shield body 112 and the shield ring 131 are positioned between the heated body 110 and the heating coil 101, so that there is a gap between the heated body 110 and the heating coil 101. The stray capacitance (equivalent capacitance) to be generated can be reduced.

  By electrically connecting the connecting portion 129 of the shield body 112 and the connecting portion 132 of the shield ring 131, the use of a common low potential portion minimizes the connection and simplifies the structure. Costs are reduced and reliability is improved.

  By connecting the connecting portions 129 and 132 of the shield body 112 and the shield ring 131 from the same direction as viewed from the heating coil holding member 124, the connection work is all performed from the same direction, and the assemblability is improved.

  When the shield ring 131 is made of aluminum die-casting or the like, the connection wire 135 is connected to the shield ring 131 by screwing the round terminal 137 provided in the connection wire 135 into the pilot hole 133 of the shield ring 131 with the connection portion 132 by self-tapping. By fastening the screws directly by fastening, mutual contact is ensured, and the electrical reliability of the connecting portion 132 is improved.

  When the shield ring 131 is made of an aluminum thin plate, the connection line 135 is connected to the shield ring by connecting to the shield ring 131 with a flat connection terminal (faston terminal), that is, the shield ring 131 of the connection portion 132. Since the faston terminal (tab terminal) 134 (not shown) provided in the connector and the faston terminal (receptacle terminal) (not shown) connected to the connection line 135 may be connected, Workability can be improved.

  The detection unit 103 detects a conduction state between the 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 detects a conduction state by passing a direct current (a voltage different from the voltage generated by the heating coil 101) through the shield body 112 through the connection lines 122 and 123. The detection unit 103 causes a current to flow through the shield body 112 to the low potential unit (signal ground in the first embodiment).

  Normally, the conduction state between the 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 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 conduction state between the shield body 112 and the control board 126 is deteriorated), the resistor 103b, the transistor 103a, the resistor 103c, and the connection line are connected from the + 5V DC power supply voltage. 123, the direct current does not flow to the ground line through the 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 shield body 112 and the control board 126 deteriorates, the control unit 104 stops the heating coil 101, turns on the red warning LED 116 through the LED drive circuit 106, and turns on the piezoelectric buzzer through the piezoelectric buzzer drive circuit 107. Sound 115. The user can easily recognize that the 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 conduction state of the 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 heating coil 101 is issued. If a command to turn on the heating coil 101 is issued, the process proceeds to step 404. If the command to turn on the heating coil 101 is not issued, the process proceeds to step 403 to control the inverter circuit 102 to stop the heating coil 101. Proceed to step 405.

  In step 404 (a command to turn on the heating coil is issued), the control unit 104 controls the inverter circuit 102 to apply electric power according to the command to the 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 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 shield body 112 and the heating coil 101 is large, a large noise is applied to the input voltage of the detection unit 103 when the heating coil 101 is energized. In some cases, the detection unit 103 cannot correctly detect the conduction state of the shield body 112. In such a case, the detection unit 103 detects the conduction state of the shield body 112 only when the heating coil 101 is not energized. That is, if the conduction state of the shield body 112 is poor when a command to change the heating coil 101 from OFF to ON is input, the control unit 104 does not cause the heating coil 101 to conduct. Thereby, the detection part 103 can detect correctly the conduction | electrical_connection state of the shield body 112. FIG. Once the heating coil 101 is in the operating state (energized state), the detection unit 103 does not check the conduction state of the shield body 112.

  When the inverter circuit 102 (drive unit) is driven and a high-frequency current is passed through the 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 pan with high permeability such as iron, the heated object 110 can be heated by applying a low voltage to the 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 heating coil 101 at a high frequency. Therefore, for example, the number of turns of the heating coil 101 must be increased.

  In FIG. 1, the heating coil 101 is described as a single-layer coil having about 12 turns. The 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 heating coil 101 having such a number of turns becomes a high voltage exceeding 1 kV. In the induction heating apparatus of the first embodiment, when the user touches the object 110 to be heated, a leakage current may flow to the human body through the object 110 due to the equivalent capacitance 1411 between the heating coil 101 and the object 110 to be heated. There is. Therefore, in this embodiment, the shield body 112 is provided and connected to the low potential portion, thereby lowering the potential of the heated body 110 and preventing leakage current from being induced.

  The first embodiment is also characterized in that the energization state of the shield body 112 is detected. The detection unit 103 detects whether the shield body 112 is in a normal state by detecting the energization state of the shield body 112. For example, the shield body 112 or the connection wires 122 and 123 is abnormal due to thermal stimulation such as a thermal cycle, or deterioration over time such as corrosion, or current is difficult to flow or is not flown due to disconnection. 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 shield body 112, the leakage current is 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 with which the energized state can guarantee safety 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 shield body 112 is substantially the same as that of the 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. As a result, the substantially circular heating coil 101 can be shielded evenly, and a stable shielding effect can be produced against the electric field generated from the heating coil 101. Since the detection part 103 detects the energization state between the connection parts 202, even if a shield body itself is disconnected by damage etc., an abnormal state can be detected accurately.

  When the power switch (not shown) of the main body is turned on, the detection unit 103 constantly detects the conduction state by passing a current through the shield body 112 even when the heating coil 101 is not energized. When the detection unit 17 detects an abnormal state when the 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 can be maintained. . If the detection unit 103 can detect the conduction state of the shield body 112 even when there is a leakage current from the heating coil 101, the detection unit 103 operates even while the heating coil 101 is energized.

  In the present embodiment, a shield body is provided, and the conduction state (energization state) of the shield body is always checked (even when the heating coil is stopped). To reduce or stop its 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 device of the first embodiment has a display unit (warning LED 116) that displays that the continuity of the shield body 112 has deteriorated, and a notification unit (piezoelectric buzzer (warning buzzer) 115) that informs of this. . You may have only one of a display part and an alerting | reporting part.

  The induction heating apparatus has a configuration in which the potential at the outer end of the 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), a stray capacitance (equivalent capacity) connecting the heating coil 101 and the heated object 110 is generated via the outer peripheral side of the shield body 112. To do. In this configuration, since the potential at the outer end of the heating coil 101 is low, the voltage applied to the stray capacitance (equivalent capacitance) connecting the heating coil 101 and the heated object 110 is very low. Leakage current hardly flows from the heating coil 101 to the user through the heated object 110.

  As described above, since the induction heating device according to the present invention can reduce the leakage current when touching the object to be heated, the object may be heated by induction heating and the user touching the object to be heated. It can also be applied to uses such as a heating device.

1 is a schematic configuration diagram of an induction heating apparatus according to Embodiment 1 of the present invention. (A) The figure which shows the pattern of the shield body of the induction heating apparatus of Embodiment 1 of this invention (b) Main part sectional drawing of the induction heating apparatus of Embodiment 1 of this invention The block diagram which shows the structure of the induction heating apparatus of Embodiment 1 of this invention. The flowchart which shows the control method of the induction heating apparatus of Embodiment 1 of this invention. The block diagram which shows the structure of the induction heating apparatus of the prior art example 1. The block diagram which shows the structure of the induction heating apparatus of the prior art example 2. The figure which shows the pattern of the electrostatic shield body formed in the top plate of the induction heating apparatus of the prior art example 2

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Heating coil 102 Inverter circuit 110 To-be-heated body 112 Shield body 122, 123, 135 Connection line 124 Heating coil holding member 129, 132 Connection part 131 Shield ring

Claims (5)

A heating coil that generates a high-frequency magnetic field and heats the object to be heated, an inverter circuit that drives the heating coil, and is provided between the object to be heated and the heating coil, and is electrically connected to a low potential portion A conductive shield body, a heating coil holding member that supports the heating coil, and a conductive material disposed around the heating coil and provided on the heating coil holding member and electrically connected to the low potential portion An induction heating device having an annular shield ring. The induction heating apparatus according to claim 1, wherein the shield body and the shield ring are provided with one or more connection portions with a low potential portion, and the connection portion of the shield body and the connection portion of the shield ring are electrically connected. The induction heating apparatus according to claim 1 or 2, wherein the shield body and the shield ring are provided with one or more connection portions with a low potential portion, and each connection portion is connected from the same direction as viewed from the heating coil holding member. The induction heating apparatus according to any one of claims 1 to 3, wherein a connection line connecting the low potential portion and the shield ring is directly screwed to the shield ring. The induction heating apparatus according to any one of claims 1 to 3, wherein a connection line connecting the low potential portion and the shield ring is connected to the shield ring by a flat connection terminal.

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