JP2010251332A - Induction cooking device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a highest heating temperature without contacting and with a high precision and good response, without being affected by the material quality and a state of the bottom of a cooking pan on the top plate. <P>SOLUTION: The induction cooking device includes a thermopile which detects an emitted infrared amount from the bottom of a cooking vessel. The thermopile is structured of a metal case consisting of a metal can and a metal stem, a small-hole window through which an infrared ray passes and fitted at the metal can, an optical filter or lens arranged at the small-hole window, a silicon base material fixed to the metal stem, a silicon oxide film fitted on the surface of the silicon base material, a lot of thermocouples manufactured on the silicon oxide film and dependently connected with, an infrared absorbing film formed at a temperature measuring contact of a center part of the silicon base material, and a cold contact part fitted around the silicon base material and thermally connected with the metal case. Further, in the induction cooking device, the thermopile is provided with a heat sink thermally connected with the metal case. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an induction heating cooker provided with a thermopile as a pan temperature detecting means.

  An induction heating cooker has a concentric induction heating coil (hereinafter abbreviated as “heating coil”) installed under a top plate made of crystallized glass, etc., and a high-frequency current is passed through the top heating plate. An eddy current is induced at the bottom of the cooking vessel placed on top, and the cooking vessel is directly heated by this Joule heat.

  As a pan temperature detection means of an induction heating cooker, there is one that detects the temperature by observing infrared rays emitted from a heated pan bottom with an infrared sensor through a top plate (Patent Document 1). This infrared sensor is placed near the center of the heating coil, detects the infrared radiation emitted from the bottom of the pan with the infrared sensor, and controls the output of the inverter circuit that drives the heating coil according to the output. The cooking temperature is adjusted.

  However, in the induction heating cooker of this configuration, since the magnetic flux density is the highest between the inner circumference and the outer circumference of the concentric heating coil, that is, near the center of the coil winding width, the temperature distribution of the cooking vessel placed on the top plate Cause bias. That is, the part on the middle of the heating coil is heated to the highest temperature, and the parts on the inner and outer circumferences are at a lower temperature. It becomes even lower near the center of the heating coil.

  FIG. 30 (a) shows an outline of the heating coil and the temperature distribution of the pan heated by the heating coil. This is the temperature distribution at the bottom of the pan when the center of the pan coincides with the center of the heating coil. For this reason, when a cooking container into which only a small amount of food is put is heated, the temperature of the middle part of the coil suddenly rises, which may burn the food. In addition, when the food is a small amount of oil, smoke may be generated. In addition, when a thin stainless steel pan or the like was blown in the air due to poor heat conduction, this portion was sometimes red-hot and deformed. In order to prevent these, a pan temperature detecting means is required, but an infrared sensor installed under the vicinity of the coil center gap as in Patent Document 1 cannot detect this high temperature portion.

  In addition, the lower part of the space near the center space of the heating coil hits a neutral point of the magnetic field generated by the coil (a place where magnetic fields in opposite directions overlap) as described later, and the leakage magnetic flux is weak. For this reason, there is little influence on the installed infrared sensor, and instead of a magnetic shield that covers this, a simple magnetic shield means such as a metal such as cylindrical aluminum may be used. There was no need to consider the impact.

  As a technique for solving the above-described problem, a heating coil is divided into a first coil on the inner peripheral side and a second coil on the outer peripheral side near the center of the radial winding width, and an infrared sensor is disposed under the divided gap. Yes (Patent Document 2). FIG. 30B shows an outline of the heating coil and the temperature distribution of the pan heated by the heating coil. The high temperature part spreads and the uneven temperature distribution is improved, and the gap part has the same temperature as the high temperature part. Although there is a slight temperature drop, if an infrared sensor is placed under the gap, the temperature of the pan heated at a high temperature can be accurately detected. However, the characteristics of the divided heating coil change. When the opening area of the concentric gaps increases, the coil inductance and resistance when the cooking container is placed change, and it is necessary to adjust the inverter circuit that drives the heating coil. In particular, when heating a low-resistance, low-permeability material cooking vessel such as aluminum or copper, it is necessary to increase the coil drive current and voltage in order to provide the same heating characteristics as a conventional non-divided coil. That is, since the heating efficiency is lowered, it is necessary to increase the high-frequency magnetic field strength. This also means that the heating of the coil itself increases. Originally, this division gap is in the middle of the winding width and is a place where the magnetic flux density is high. For this reason, the infrared sensor arranged under the divided gap is affected by this leakage magnetic flux. Infrared sensor placed under the division gap enhances protection against leakage magnetic flux, heating coil or hot pot bottom, temperature rise due to radiant heat from the top plate, electromagnetic wave from inverter circuit driving coil with reduced heating efficiency, and high frequency high voltage I have to let it.

  In addition, it is necessary to cool the heating coil, and an air passage for usually introducing outside air is disposed under the coil. When the infrared sensor is disposed in the air passage, it is necessary to cope with a rapid temperature change of the ambient temperature due to the cooling air.

  As a technique for solving the above-mentioned problem, there is a technique in which an opening is provided only in the vicinity of the center of the heating coil in the radial direction and an infrared sensor is disposed below the opening (Patent Document 3). This has the same characteristics as a conventional non-divided heating coil by providing an opening between the windings that are wound next to each other and increasing the number of windings around the opening more (densely) than other parts. It is possible to detect the temperature of the hot portion of the pan bottom heated from the opening. However, such a heating coil is inevitably difficult to mass-produce due to its structure and must be expensive. An increase in the number of coil turns in the opening means that the leakage magnetic flux from this portion is further increased. The necessity of strengthening protection against leakage magnetic flux, temperature rise, electromagnetic waves, and high-frequency high voltage of the infrared sensor is the same as that of the above-described technique (Patent Document 2).

JP 2005-26162 A JP 2008-153046 A JP 2007-323887 A

  In the pan temperature detecting means using a thermopile as an infrared sensor, the present invention is provided with a means for preventing disturbance of temperature rise, making it possible to stably and accurately detect the pan bottom temperature heated at the highest temperature, An object of the present invention is to provide an induction heating cooker with improved usability.

  The above-described problems include a top plate made of crystallized glass with a cooking container on the upper surface, a heating coil provided under the top plate, high-frequency power supply means for supplying high-frequency power to the heating coil, and the high-frequency power. A power control means for controlling the output power of the supply means; and a thermopile for detecting the amount of infrared radiation emitted from the bottom surface of the cooking vessel, the thermopile comprising a metal case made of a metal can and a metal stem; and Provided on the surface of the silicon substrate, a small hole window provided in the metal can through which infrared rays pass, an optical filter or lens disposed in the small hole window, a silicon base material fixed to the metal stem, and Formed on the silicon oxide film, a number of subordinately connected thermocouples formed on the silicon oxide film, and a temperature measuring contact at the center of the silicon substrate. An infrared absorption film and a cold junction portion provided around the silicon base material and thermally connected to the metal case, and the thermopile includes a heat sink thermally connected to the metal case Can be solved by an induction heating cooker equipped with.

  ADVANTAGE OF THE INVENTION According to this invention, it is strong with respect to the disturbance of the ambient temperature change at the time of cooking using a thermopile infrared sensor, and can provide the pan temperature detection means which detects the high temperature part temperature of a heating pan bottom accurately and stably. And the induction heating cooking appliance which enables safe and optimal cooking can be provided by controlling the high frequency electric power to an overheating coil appropriately by the high temperature part temperature detected correctly.

  Furthermore, infrared light emitting and receiving elements are placed near the thermopile infrared sensor that detects the pan bottom temperature, the pan bottom emissivity is measured in the same field of view as the temperature detection, and the infrared sensor output is corrected to correct the pan bottom material, color, Regardless of the processing state or dirt state, it is possible to accurately detect the pan bottom temperature, and it is possible to control heating using the accurately detected pan bottom temperature, so it is possible to cook well Become.

The perspective view which shows the structure of the induction heating cooking appliance of Example 1. FIG. Sectional drawing which shows the structure of the induction heating cooking appliance of Example 1. FIG. Sectional drawing which shows the detail of the heating coil periphery of Example 1. FIG. The top view which shows arrangement | positioning of the heating coil of Example 1, and a pan temperature detection apparatus. FIG. 2 is a plan view showing a heating coil according to the first embodiment. The perspective view which shows the pan temperature detection apparatus of Example 1. FIG. Sectional drawing of the pan temperature detection apparatus of Example 1. FIG. FIG. 2 is a plan view and a cross-sectional view showing details of the thermopile of Example 1. FIG. 3 is a diagram illustrating a reflective photointerrupter according to the first exemplary embodiment. The control block diagram of the induction heating cooking appliance of Example 1. FIG. FIG. 3 is a diagram illustrating details of a thermopile temperature detection circuit according to the first embodiment. FIG. 3 is a diagram illustrating details of the reflectance detection circuit according to the first embodiment. 6 is an operation timing chart of the reflectance detection circuit according to the first embodiment. The figure which shows the spectral radiant energy by Planck's distribution law. The figure which shows the optical characteristic of top plate crystallized glass. The figure which shows the relationship between temperature and the output of a thermopile. The figure which shows the relationship between the pan bottom temperature of Example 1, and a thermopile temperature detection circuit output. Output explanatory drawing by the presence or absence of a pan of the reflectance detection circuit of Example 1. FIG. FIG. 3 is a diagram illustrating a relationship between a reflection voltage and a reflectance of the reflectance detection circuit according to the first embodiment. The figure which shows the relationship between the pot bottom temperature of the various pots of Example 1, and a pot temperature detection circuit output. The figure which shows the relationship between the various pan emissivity of Example 1, and a reflectance. 2 is a flowchart of induction heating cooking according to the first embodiment. 5 is a flowchart of reflectance detection according to the first embodiment. The flowchart of the pan temperature detection of Example 1. FIG. Sectional drawing which shows the thermopile of Example 2. FIG. FIG. 6 is a perspective view showing a thermopile of Example 2. The perspective view which shows the board | substrate mounting of the thermopile of Example 2. FIG. The top view and sectional drawing of the pan temperature detection apparatus of Example 2. FIG. The top view which shows other Example arrangement | positioning of the pan temperature detection apparatus of Example 2. FIG. The figure which shows the temperature distribution of the pan placed on the heating coil.

  Embodiments of the present invention will be described with reference to the drawings.

  1 is a perspective view of a main body 1 of an induction heating cooker according to a first embodiment, and FIG. 2 is a schematic longitudinal sectional view when a cooking pan 6 is placed on a portion indicated by a one-dot chain line AA ′ in FIG. . In the following, an induction heating cooker having three units with two pan storage locations where induction heating is possible and one pan storage location capable of being heated by radiant heat from a heater (heating source) such as a radiant heater or a halogen heater will be described. However, the application target of the present invention is not limited to this, and may be, for example, an induction heating cooker provided with three pot places where induction heating is possible. The cooking pan 6 is an iron pan (magnetic body) suitable for induction heating, but the induction heating cooker may be a non-magnetic aluminum pan or copper pan.

  As shown in FIGS. 1 and 2, a top plate 2 formed of a nonmagnetic material (crystallized glass or the like) is attached to the upper surface of the main body 1. In front of the top plate 2, an operation display unit 3 in which a switch for instructing heating start or heating course of each port and a display for displaying the heating state (temperature, etc.) of each port is mounted.

On the upper surface of the top plate 2, a circle display 4 having a radius that approximately matches the outermost radius of the heating coil 7 or the radiant heater disposed thereunder is printed to indicate a place where the pan can be heated. Since the top plate 2 is normally transparent to visible light, the upper surface is coated with heat-resistant and durable clothes with heat-resistant paint mixed in the frit glass, and the lower surface is coated with a heat-resistant surface so that the inside of the device cannot be seen. It is. An infrared transmission window 5 that has not been printed or painted is provided at a position approximately 50 mm from the center of the circle display 4 at the two pot places where induction heating is possible to detect the pot temperature described later. This infrared transmission window 5 is for transmitting infrared light, and a visible light cut member (heat-resistant film or glass) that is transparent to infrared light only on this portion may be attached to the lower surface.

  A cooking pan 6 is placed in each mouth (circle display 4) on the upper surface of the top plate 2 and cooking is performed. As shown in FIG. 2, when the high frequency current from the inverter circuit 8 (high frequency current supply means) is supplied to the heating coil 7, it is divided into a first coil 7a on the outer peripheral side and a second coil 7b on the inner peripheral side. The heating coil 7 generates a high-frequency magnetic field 9 (indicated by a broken line in the figure). This high-frequency magnetic field is linked to the pan 6 to generate an eddy current, and the cooking pan 6 itself is induction-heated by the Joule heat to generate heat. . Accordingly, the food in the cooking pan 6 is cooked by the heat generated by the cooking pan 6 itself. At this time, the top plate 2 under the cooking pan 6 is also heated by heat transmitted from the cooking pan 6 that has generated heat.

  FIG. 3 shows a cross section around the heating coil 7 in detail. As shown in FIG. 3, a heating coil 7 divided with a coil gap 7c between the first coil 7a and the second coil 7b on the lower surface of the top plate 2 is placed in a coil base 10 made of heat-resistant plastic. They are arranged concentrically (spirally). Below the heating coil 7, U-shaped ferrites 11 are radially arranged inside the coil base member with the convex portions up. The ferrite 11 is arranged to efficiently guide the magnetic flux generated by the heating coil 7 to the cooking pan 6 that is a cooking container on the top plate 2. Further, the magnetic flux is prevented from leaking to the lower part of the coil base 10. This is because the ferrite 11 has a high magnetic permeability and almost all the magnetic flux passes through the ferrite 11.

  A coil cooling air passage 15 for cooling the heating coil 7 is installed under the coil base 10. The coil cooling air passage 15 is divided into two, one is connected to the inner peripheral side of the first coil 7a, and the coil upper surface cooling air passage 15a for cooling the upper surfaces of the second coil 7b and the first coil 7a, The other one is a coil lower surface cooling air feed hole 15b for cooling the lower surface of the first coil 7a. On the upper surface of the coil upper surface cooling air passage 15a located under the center portion of the coil base 10, a circular coil upper surface cooling air sending hole 15c is opened.

  The central portion of the coil base 10 is a cylindrical inner cavity 14a, and a cylindrical outer cavity wall 14b connected to the radial beam containing the ferrite 11 is formed on the inner peripheral side of the first coil 7a. . A coil upper surface cooling air sending hole 15c of the coil upper surface cooling air passage 15a is connected to the lower portion of the outer cavity wall 14b. A sealing material 16 such as glass wool is provided around the coil upper surface cooling air sending hole 15c and connected to the outer cavity wall 14b.

  Under the cooling air passage 15, circuit cooling air passages 17a and 17b containing a circuit board such as an inverter circuit 8 are provided in two layers, and inverter circuits for the left and right heating coils 7L and 7R are provided respectively. ing. These cooling air passages are fixed to the main body 1.

  The coil base 10 is pressed by the spring 13 from the three coil base receivers 12 fixed to the coil lower surface cooling air sending hole 15b or the circuit cooling air passage 17a, and is pressed against the lower surface of the top plate 2.

  A pan temperature detector 18 is arranged in the coil upper surface cooling air passage 15a below the coil upper surface cooling air delivery hole 15c. The pan temperature detection device 18 detects the bottom surface temperature of the cooking pan 6 heated by induction from the infrared rays transmitted through the infrared transmission window 5 of the top plate 2.

  Further, a thermistor 21 is disposed in the ceramic case 20 in contact with the lower surface of the top plate 2 at the center of the upper surface of the inner cavity 14a.

  During cooking, outside air is introduced into the coil upper surface cooling air passage 15a, the coil lower surface cooling air sending hole 15b, and the circuit cooling air passages 17a and 17b from a fan (not shown) built in the main body 1. The cooling air flowing in the coil upper surface cooling air passage 15a raises the coil gap 7c and the inner cavity 14a in the cylindrical outer cavity wall 14b from the coil upper surface cooling air sending hole 15c while cooling the pan temperature detecting device 18, and the coil From the upper part of the gap 7c and the inner cavity 14a, it is blocked by the top plate 2 and flows between the top plate 2 and the heating coil 7 outward in the coil radial direction, and the upper surface of the heating coil 7 and the lower surface of the top plate 2 are cooled. A plurality of small holes are formed in a portion corresponding to the lower surface of the first coil 7a of the coil lower surface cooling air sending hole 15b, and the cooling air flowing in the coil lower surface cooling air sending hole 15b is directed from here to the lower surface of the first coil 7a. To cool it.

  FIG. 4 shows details of the top view of FIG. 3 excluding the top plate 2. It is a detailed block diagram of the heating coil 7, the coil base 10, and the coil upper surface cooling air path 15a. The positional relationship in the horizontal surface of the heating coil 7 and the inner cavity 14a, the pan temperature detection apparatus 18, and the thermistor 21 is shown.

  The heating coil 7 is concentrically wound in the same direction with a litz wire that is insulated with a fluororesin or the like typified by polytetrafluoroethylene, and has a first coil 7a on the outer peripheral side and a second coil on the inner peripheral side. Divided into coils 7b. The coil gap 7c has a concentric band shape with a width of about 15 mm. The winding end of the first coil 7a bridges the coil gap 7c and becomes the winding start of the second coil 7b. The first coil 7a, the bridging wire 7d, The heating coil 7 is composed of two coils 7b. The coil base 10 is provided with a cylindrical outer cavity wall 14b on the inner peripheral side of the first coil 7a, and the inside is a coil gap 7c. Further, an inner cavity 14a is provided on the inner peripheral side of the second coil 7b, and a thermistor 21 built in the ceramic case 20 is disposed therein. Furthermore, a cylindrical sensor field cylinder 19 (inner diameter of about 12 mm) is provided between a portion of the coil gap 7c and two radially disposed ferrites 11, and a pan temperature detecting device 18 is installed below the sensor field cylinder 19. Is done.

  Infrared rays from the bottom of the pan heated by induction pass through the infrared transmission window 5 of the top plate 2 and enter the thermopile 25 built in the pan temperature detector 18 described in detail later from the sensor visual field cylinder 19.

  FIG. 5 shows a view of FIG. 4 from the back. The coil base 10 is provided with a low voltage terminal 21a and a high voltage terminal 21b of two coils, the start of winding of the first coil 7a is connected to the low voltage terminal 21a, and a second voltage is connected to the high voltage terminal 21b. The end of winding of the coil is connected. The output lines 22a and 22b of the inverter circuit 8 are fixed to the terminals with screws. In a non-magnetic pot such as copper or aluminum, a high voltage output line 22b that outputs a high voltage of 4 to 5 kV is connected to a high voltage terminal 21b.

  As described in FIGS. 4 and 5, the pan temperature detecting device 18 is provided in the coil gap 7c at a position away from the high-voltage terminal 21b to which the high-voltage output line 22b is connected while avoiding the vicinity of the bridge line 7d. The case window 30 is placed under the sensor field cylinder 19 thus placed.

  FIG. 6 shows a detailed perspective view of the pan temperature detecting device 18. The pan temperature detecting device 18 is mainly composed of a thermopile 25 which is an infrared detection sensor and a reflective photo interrupter 26. The thermopile 25 and the reflection type photo interrupter 26 are electronic circuit boards on which a thermopile temperature detection circuit 72 (details will be described later) and a reflectance detection circuit 73 (details will be described later) for amplifying the output signal of the thermopile are mounted. The thermopile 25 is provided with a reflector 28 made of a plastic member. The thermopile 25, the reflective photo interrupter 26, and the electronic circuit board 27 are hermetically sealed in an infrared sensor case 29 (indicated by a one-dot chain line) made of a plastic member. The infrared sensor case 29 has a case window 30 for transmitting infrared rays. The case window 30 has almost the same optical characteristics as the crystallized glass constituting the top plate 2 (however, 1 μm as shown by the broken line in FIG. 15). The optical characteristics on the long wavelength side are almost the same, but on the short wavelength side, there is a region with a low transmittance of about 400 nm compared to the top plate, and the visible light in this part is cut, so the eyes appear reddish. A crystallized glass cut into a thin square is fitted as a crystallized glass optical filter 31. A thermopile 25 in which a reflector 28 is mounted under a crystallized glass optical filter 31 and a reflective photo interrupter 26 are mounted on an electronic circuit board 27. The infrared sensor case 29 is covered with a metal case 32 (indicated by a two-dot chain line) having a permeability of approximately 1 such as aluminum. Naturally, the previous case window 30 is opened. Further, the aluminum metal case 32 is covered with an outer infrared sensor case 33 made of a plastic member. Of course, the previous case window 30 is opened. That is, the thermopile 25 is covered with a triple case.

  And the pan temperature detection apparatus 18 is installed in the coil upper surface cooling air path 15a so that the case window 30 may desire the inside of the sensor visual field cylinder 19 of the coil base 10. FIG.

  FIG. 7A shows a cross-sectional view taken along the line AA ′ in FIG. This is a cross-sectional view of the thermopile 25 installed in the infrared sensor case 29, the cross section of the reflector 28 attached thereto, and the thermopile 25 including the electronic circuit board 27. On the inner surface of the reflector 28 attached to the thermopile 25, a part of an elliptical curved surface 28a that focuses on the infrared absorbing film in the thermopile 25 is formed, and this elliptical curved surface 28a is a mirror surface with an aluminum vapor deposition film 28b. For this reason, as shown by the alternate long and short dash line in the figure, the infrared light transmitted through the crystallized glass optical filter 31 disposed in the case window 30 is reflected by the elliptical curved surface which is the mirror surface, and passes through the optical filter 48 described later of the thermopile 25 to absorb the infrared rays. Condensed to The metal pins (connection terminals) 46 of the thermopile 25 are soldered to the pattern of the electronic circuit board 27.

  FIG. 7B similarly shows a cross-sectional view along the line BB ′ in FIG. This shows the positional relationship between the thermopile 25 and the reflective photo interrupter 26 mounted on the electronic circuit board 27 installed in the infrared sensor case 29, the case window 30 of the infrared sensor case 29, and the crystallized glass optical filter 31. It is sectional drawing.

  FIG. 8 shows details of the thermopile 25. 8A is a cross-sectional view of the thermopile 25, and FIG. 8B is a plan view of a cross section taken along the line CC ′ in FIG. 8A. The infrared absorption film is omitted so that the thermocouple can be seen.

  The thermopile 25 is obtained by connecting a number of thermocouples (thermocouples) in cascade (piling). The thermopile 25 is built in a metal case 37 made of a metal can 35 such as a nickel-plated steel plate and a metal stem 36. A silicon oxide film 39 is formed on the surface of the silicon substrate 38 having a thickness of about 300 μm to electrically and thermally insulate, and polysilicon and aluminum are sequentially deposited on the surface of the silicon oxide film 39 by the polysilicon deposited film 40 and the aluminum deposited film 41. Create a number of thermocouples and connect them in cascade. An infrared absorption film 43 such as a rubidium oxide film close to a black body is formed at the center of the silicon substrate 38 having a polysilicon / aluminum junction (temperature measuring contact). One end of the polysilicon and aluminum deposition film is a cold junction 44, which is disposed around the silicon substrate 38. The back surface of the silicon substrate 38 is etched to 290 μm leaving the periphery (cold contact portion), and the thickness of the silicon substrate having the temperature measuring contact portion is formed to 10 μm. This is to reduce the thermal conductivity of the temperature measuring contact portion 42 and the cold junction portion 44 by thinning the silicon having good thermal conductivity so as to thermally insulate the temperature measuring contact portion and the cold junction portion.

  The silicon substrate 38 is fixed to the metal stem 36 of the metal case 37 with a bond or the like. At the same time, the NTC thermistor 45 formed on the ceramic is similarly disposed on the metal stem 36. This is for detecting the ambient temperature of the thermocouple in the metal case 37 and correcting the thermoelectromotive force of the thermocouple. Details will be described later. Four metal pins 46 that are insulated and sealed pass through the metal stem 36, and the output of the previous thermocouple and the NTC thermistor 45 are wire-connected to the metal pins 36. A cylindrical metal can 35 is placed on the stem 36 in an inert gas and welded. A small-hole window 47 is opened on the upper surface of the metal can 35, and an optical filter 48 (a member that transmits light in a certain wavelength region) is attached thereto from the inside. The silicon substrate 38 is fixed so that the temperature measuring contact portion 42 (below the infrared absorption film 43) is positioned below the small hole.

  The thermocouple temperature measuring contact portion 42 (below the infrared absorbing film 43) in the thermopile 25 is heated by the infrared light that has passed through the small hole window 46, and this heating temperature rise is proportional to the infrared energy that has passed, A voltage proportional to the temperature difference between the paired cold junction portion 44 and the temperature measuring contact portion 42 is output to the thermocouple output metal pin 46.

  FIG. 9 shows details of the reflection type photo interrupter 26. The reflection type photo interrupter 26 is obtained by molding an infrared LED 50 as an infrared light emitting element and an infrared phototransistor 51 as an infrared light receiving element on the same plastic member. A lens is made of plastic on the light emitting surface of the infrared LED, and infrared light of around 930 nm is irradiated upward with a thin beam. A lens is made of visible light blocking plastic on the light receiving surface of the infrared phototransistor 51, and the reflected infrared light at the object (pan bottom) of the previous irradiated infrared light is received with a narrow viewing angle, and the amount of received light A current proportional to is output. This reflection type photo interrupter 26 is constituted by a pair of an infrared light emitting element and a light receiving element, and measures the reflectance of the bottom surface of the cooking pan 6 placed on the top plate 2.

  The control block diagram of the induction heating cooking appliance of a present Example is shown in FIG. The microcomputer 60 controls the operation of the induction heating cooker. Hereinafter, symbol R represents a block related to the induction heating port on the right side in FIG. 1, and symbol L represents a block related to the induction heating port on the left side in FIG. The two inverter circuits 8R and 8L supply high-frequency current to the heating coils 7R and 7L. The frequency control circuits 61R and 61L and the power control circuits 62R and 62L adjust the operating frequency of the inverter circuits 8R and 8L and the power supplied to the coils. The reason for changing the operating frequency is that the induction heating efficiency changes at the frequency of the high-frequency current depending on the metal type of the pan. In general, a frequency of 20 kHz is used for iron, and a frequency of 70 kHz or more is used for copper and aluminum having a lower resistivity. This frequency switching is performed by the microcomputer 60 controlling the frequency control circuit based on the judgment of the pan type discrimination means (not shown).

A DC voltage is supplied from the rectifier circuit 63 to each of the inverter circuits 8R and 8L. The rectifier circuit 63 is connected to a commercial power supply 65 having three terminals 200V via a power switch 64.
The ground terminal of the commercial power supply is connected to the metal part of the main body 1 with a ground wire. A commercial power supply 65 is connected to the radiant heater 66 through a radiant heater circuit 67, and the radiant heater circuit 67 controls the power supplied to the radiant heater 66.

  The microcomputer 60 is connected with an operation switch 68 and a display circuit 69 of the operation display unit 3 to receive a user's operation instruction and display an operation state of the device. Further, a buzzer 70 is connected to notify a user of an operation button press or a warning such as an error. The microcomputer 60 controls the frequency control circuits 61R and 61L, the power control circuits 62R and 62L, and the radiant heater circuit 67 in accordance with a user instruction to heat the cooking pan 6 on the top plate 2.

  The thermopile 25 is connected to a thermopile temperature detection circuit 72 so that the output is amplified and input to the AD terminal of the microcomputer 60. The reflection type photo interrupter 26 is connected to the reflectance detection circuit 73, the light emission of the light emitting element is controlled by the port output of the microcomputer 60, the infrared light reflected by the cooking pan 6 is received by the light receiving element, and its output signal Is amplified and input to the AD terminal of the microcomputer 60. Details of the operations of the thermopile temperature detection circuit 72 and the reflectance detection circuit 73 will be described later. Further, the thermistor 21 is connected to a thermistor temperature detection circuit 74, and its output is also input to the AD terminal of the microcomputer 60.

The microcomputer 60 knows the infrared reflectance of the cooking pan from the output of the reflectance detection circuit 73 and corrects the output of the thermopile temperature detection circuit 72 with the reflectance to detect the temperature of the cooking pan.
And the heating of the cooking pan 6 is controlled via the power control circuit 62.

  FIG. 11 shows details of the thermopile temperature detection circuit 72. The thermocouple output (thermoelectromotive force) of the thermopile 25 (voltage between (+) and (−) symbols in the figure) is amplified about 2000 times by the operational amplifier 72-1, and is output to the output terminal 72-2. This output voltage is input to the AD terminal of the microcomputer 60. The amplification degree of the operational amplifier 72-1 is determined by the ratio (R2 / R1) of the resistor 72-3 (= R1) and the resistor 72-4 (= R2). The NTC thermistor 45 in the thermopile is connected in series with the resistor 72-8 to a voltage source (both ends of the resistor 72-6) obtained by dividing the circuit power supply voltage by the resistors 72-5, 72-6, and 72-7. The connection point a with the resistor 72-8 is connected to the thermocouple output terminal (-). The NTC thermistor 45 is a resistance element having negative temperature characteristics, and the resistance value decreases as the temperature rises. For this reason, when the temperature in the thermopile 25 rises, the voltage of the previous connection point a rises. The thermocouple output (the voltage between the symbols (+) and (−) in the figure) is proportional to the temperature difference between the temperature measuring junction 42 (a point heated by infrared energy) and the cold junction (thermocouple output terminal) 44. For this reason, when the atmosphere in the metal case 37 (in which the NTC thermistor is incorporated) rises at the ambient temperature where the thermopile 25 is installed, the thermocouple output decreases. This decrease is compensated by the voltage increase at the connection point a. That is, the NTC thermistor 45 is used to prevent the output of the thermopile (thermocouple) 25 from changing at the ambient temperature. A resistor 72-9 (= R3) and three diodes 72-10 connected in series are connected in parallel to a resistor 72-4 (= R2) that determines the degree of amplification. This reduces the amplification factor when the output voltage of the operational amplifier exceeds 1.8 V of three diode forward voltages (about 0.6 V). Up to 1.8V, the amplification factor = R2 / R1, but beyond this, the amplification factor = (R2 // R3) / R1. This expands the pan temperature detection range of the thermopile as will be described later. Without this, the thermopile output is proportional to the 4th power of the pan bottom temperature, so the output increases rapidly at high temperature, and the pan bottom temperature is 300 ° C and the circuit output voltage is saturated at 5V. Do not saturate.

  Details of the reflectance detection circuit 73 will be described with reference to FIGS. In FIG. 12, 50 is an infrared LED which is a light emitting element, for example, the emission wavelength is 930 nm. Reference numeral 51 denotes an infrared phototransistor, which has a sensitivity of 80% of the peak sensitivity even when the peak sensitivity wavelength is 800 nm and the emission wavelength of the infrared LED 50 is 930 nm. FIG. 13 shows an operation timing chart of the reflectance detection circuit 73. The infrared LED 50 which is a light emitting element of the reflective photo interrupter 26 is driven by a transistor 73-1. This drive is controlled by a signal input from the output port of the microcomputer 60 to the drive signal terminal 73-2. FIG. 13A shows this signal. When a rectangular wave signal with a duty of 50% is input to the drive signal terminal 73-2, the infrared LED 50 emits light when the signal is 5V, and turns off when the signal is 0V. This emission intensity is proportional to the current flowing through the infrared LED 50, and this current is determined by the value of the resistor 73-3. In this embodiment, the resistance value is fixed and the light emission intensity is constant. When the infrared light is reflected by the bottom surface of the cooking pan and received by the infrared phototransistor 51 as a light receiving element, a voltage is generated in the resistor 73-4 by the photocurrent. This voltage is shown in FIG. If the reflection is large (the amount of received light is large), the voltage increases proportionally. This signal voltage has its direct current component cut by the capacitor 73-5 and is input as an alternating current signal (shown in FIG. 13C) to a normal rotation direct current amplifier composed of an operational amplifier 73-6. Here, only the positive component of the AC signal is amplified. This is shown in FIG. The amplified 50% duty signal is converted to a DC average voltage by the charge / discharge circuit 73-7 and output from the output terminal 73-8. This output is input to the AD terminal of the microcomputer 60.

  In this way, the reflectance detection circuit 73 emits carrier-modulated infrared light having a constant emission intensity to the bottom of the pan, receives the infrared light reflected by the pan, and obtains the average voltage as the reflected voltage. The value corresponding to the reflectance is detected by. Infrared emission is carrier-modulated and the direct current component is cut off in the light-receiving path to prevent natural light or infrared light contained in lighting equipment such as incandescent lamps and fluorescent lamps from affecting the detection of pan reflectivity. It is to do. Moreover, the influence of the dark current of the infrared phototransistor 51 is also prevented.

  The operation of this embodiment will be described below.

The cooking pan 6 placed on the top plate 2 generates heat by induction heating. By this heating, infrared rays are emitted from the bottom of the pan 6. This total radiant energy E is proportional to the fourth power of the pan temperature T. (E = σT ⁴ ; Stefan-Boltzmann law) FIG. 14 shows the spectral radiant energy of the black body temperature calculated from the Planck distribution law. If this spectral radiant energy is integrated over the entire wavelength region, the total radiant energy E is obtained, which is proportional to the fourth power of the temperature (absolute temperature). This is the aforementioned Stefan-Boltzmann law, and this coefficient σ is the Stefan-Boltzmann coefficient. The peak wavelength of the spectral radiant energy is 5 μm to 8 μm at a cooking temperature of 100 to 300 ° C. based on the Vienna transition law.

The induction-heated pan bottom emits the total radiant energy obtained by multiplying the total radiant energy E of the black body temperature by the emissivity ε of the pan bottom according to the temperature. That is, the ratio of the total radiant energy E of the black body temperature to that of the pan bottom temperature (E ′ = εσT ⁴ ) is the emissivity ε.

  On the other hand, the optical characteristics of crystallized glass (top plate 2), which is a non-magnetic material, are shown by a solid line in FIG. As shown by the solid line in FIG. 15, the crystallized glass transmits 80% or more of light having a wavelength of 0.2 μm to 2.9 μm, and transmits about 30% of light having a wavelength of 3 to 4.5 μm. It hardly transmits light having a wavelength longer than 5 μm and a wavelength shorter than 0.2 μm. Because of this optical property, most of the infrared radiation energy radiated from the pan (see FIG. 14) cannot pass through the top plate.

  As is well known, infrared sensors include quantum types such as infrared photodiodes and infrared phototransistors, and thermal types such as thermopiles and pyroelectric elements. The quantum type sensor is characterized by high sensitivity in a narrow wavelength band because it detects infrared rays by the quantum effect, and the thermal type has low sensitivity in a wide wavelength band. For the quantum type, the sensitivity wavelength is determined by the type of semiconductor, and those that can be purchased at a low cost, such as silicon, have a practical sensitivity wavelength of 1 μm or less from outside visible light (0.8 μm), so the detection temperature range is 300 ° C. or more. Become. On the other hand, the thermal type has a uniform and low sensitivity in a wide wavelength band of 20 μm or less from visible light as compared with the quantum type (in principle, it has no wavelength dependence). For this reason, an optical filter is provided in front of the infrared light receiving surface to the sensor to prevent disturbance by narrowing the detection temperature range wavelength.

  In this embodiment, since the cooking temperature range is 100 to 250 ° C., a thermopile thermopile is used as the infrared sensor. Since the pyroelectric element of the same thermal type is a differential type sensor, it is necessary to interrupt infrared incidence, and a normal mechanical chopper mechanism is used. For this reason, it is unsuitable to use for household appliances like an induction heating cooker from the point of reliability. On the other hand, the thermopile does not require such a mechanism, and in recent years, a thermocouple that uses a semiconductor process is miniaturized by technology such as MEMS, and a large number of layers are piled up (piled) to improve sensitivity. .

  In recent years, a thermopile optical filter used in many thermometers has a transmission wavelength of 1 to 15 μm. This is because the peak wavelength of the infrared radiation energy of the human body is about 10 μm (body temperature 36 ° C.), and it is optimal to use the above optical filter, based on the Vienna transition rule.

If the temperature (25-300 degreeC) of a cooking pot is measured non-contactingly using the thermopile which has this optical filter, the output shown with a dashed-dotted line in FIG. 16 will be obtained as an output of a thermopile.
As described above, the bottom surface of the cooking pan is regarded as a black body, and the infrared energy (according to Planck's distribution law) radiated from the cooking pan is converted into a voltage by the sensitivity of the thermopile and obtained as a result of a predetermined amplification. At this time, it is assumed that the sensitivity of the thermopile is a constant value having a wavelength of 1 to 15 μm, and infrared light having a wavelength of 1 to 15 μm is uniformly transmitted through the optical filter by 90% and enters the thermopile.

  Now, when this thermopile is used for detecting the pan temperature in the configuration of FIG. 3, the infrared rays from the bottom of the pan pass through the top plate 2 and enter the thermopile 25. Therefore, the infrared rays of each wavelength transmitted through the optical characteristics of the top plate 2 (solid line in FIG. 15) are limited. As described above, infrared rays of about 5 μm or more hardly pass through and do not enter the thermopile 25. When the output in this case is calculated in the same manner as described above, it is shown by a solid line in FIG. It can be seen that the output drops by an order of magnitude. For this reason, it is necessary to amplify the output of the thermopile 25 with a gain that is about one digit higher than the gain of a DC amplifier used in a conventional thermometer or the like.

As described above, a thermopile is a stack of thermocouples (thermocouples) stacked (connected in series) (piled). If the thermoelectromotive force of one thermocouple is Ei volts / ° C. and N are connected, the thermoelectromotive force V of the thermopile is N · Ei volts / ° C.
In other words, the thermocouple output of N piles is N · Ei volts / ° C. If a thermopile that is practically used with an amplification factor of about 1000 times as in the thermometer described above is used in an induction heating cooker, the amplification factor of 10,000 times is required due to the influence of the top plate. In general, in a DC amplifier, an amplification degree of about 1000 times is said to be a limit due to a temperature drift of an offset voltage. Therefore, in the thermopile used for the induction heating cooker, the number of piles increased from several tens to several hundreds is used. In other words, sensitivity is increased by increasing the number of piles compared to general thermopile.

  A thermocouple metal pair often used in a thermopile is polysilicon aluminum which can be made relatively easily by a semiconductor process as described with reference to FIG. 8, and its thermoelectromotive force is about 10 μV / ° C. As the thermopile used in the electromagnetic cooker, a stack of about 50 piles is used.

  When measuring the temperature of an object with a thermocouple, the cold junction is fixed at the freezing point (0 ° C.) and the temperature measuring contact is brought into contact with the object. As described with reference to FIG. 8, the thermopile is formed by depositing a large number of thermocouples, and includes a large number of temperature measuring contacts heated by incident infrared rays and a large number of cold junctions on the silicon substrate 38. Since the cold junction is fixed to the metal stem 36 of the metal case 37 with a bond, the thermopile metal case 37 (metal can 35 and metal stem 36) is a cold junction. And this metal case 37 cannot be fixed to a freezing point like a normal thermocouple.

  Assuming that the thermoelectromotive force of the thermocouple is 10 μV / ° C., the number of piles is 50, and the amplification factor of the DC amplifier is 1000, if the temperature of the metal case 37 changes by 1 ° C., the voltage fluctuation of 500 mV occurs at the output of the DC amplifier. That is, it is necessary to suppress the temperature fluctuation around the thermopile 25.

  The pan temperature detecting device 18 of the present embodiment is disposed immediately below the coil gap 7c where the magnetic flux density of the high-frequency magnetic field generated by the divided heating coil 7 is the strongest so that the hot portion of the pan bottom during cooking can be detected. The This position is between the rod-shaped ferrites 11 arranged radially under the heating coil 7, and since the magnetic flux almost passes through the ferrite, it is a place where there is little leakage magnetic flux. However, since the distance from the lower surface of the heating coil 7 is about 20 mm, the leakage magnetic flux is large, and the metal located here is induction-heated to raise its temperature. For example, when high frequency power of 3 kW is input to the heating coil and a pot serving as a cooking vessel placed on the top plate 2 is induction heated, the temperature of the magnetic steel plate at this location rises by about 30 ° C. . Even with non-magnetic aluminum, the temperature rises by about 5 ° C.

  During cooking, the pan bottom heated by induction becomes a high temperature of 100 to 300 ° C. The top plate 2 and the heating coil 7 on the lower surface are also heated by heat conduction and heat radiation from the pan bottom.

  Furthermore, since a high frequency current of several tens of amperes flows through the heating coil 7, the coil itself also generates heat. In order to cool the top plate and the heating coil, outside air is introduced into the coil upper surface cooling air passage 15a and the coil lower surface cooling air sending hole 15b, and the heating coil 7 is blown and cooled as described above.

  In addition, an inverter circuit 8 that supplies high-frequency power to the heating coil is disposed in the cooling air passages 17a and 17b under the pan temperature detector 18. This inverter circuit is composed of a circuit that switches a current of 20 to 90 kHz and several tens of amperes. For this reason, a large electromagnetic wave is radiated.

  As described above, the pan temperature detecting device 18, particularly the thermopile 25 incorporated therein, includes (1) leakage magnetic flux from the heating coil 7, (2) temperature change due to cooling air for cooling the coil, and (3) radiation from the inverter circuit. Will be exposed to electromagnetic noise. In response to these disturbances, the pan temperature detecting device 18 must detect the hot portion of the pan bottom during cooking.

  As described for the operation of the thermopile temperature detection circuit 72 described above, temperature compensation is performed in a circuit using the built-in NTC thermistor 45 so that the output of the thermopile 25 does not change with the ambient temperature. However, since the NTC thermistor 45 is formed as a thin film on the ceramic chip and is fixed to the metal stem 36 with a bond or the like, the temperature of the metal stem 36, that is, the metal case 37, which is thermally equivalent to the cold junction, is used. It is difficult to follow the change and a time delay occurs. In addition, it is difficult to accurately compensate the temperature over a wide temperature range due to the nonlinearity of the temperature resistance characteristic. In these respects, it is difficult to perform sufficient temperature compensation with the above-described circuit in response to a change in the ambient temperature of the thermopile 25. Specifically, it can cope with a temperature change of about 1 ° C./10 minutes, but it is difficult to follow the temperature change of about 1 ° C./1 minute. As described above, outside air is introduced to cool the heating coil 7 simultaneously with the start of induction heating cooking. If the ambient temperature of the pan temperature detecting device 18 and the surroundings has risen to some extent in the previous cooking, the pan temperature detecting device 18 is rapidly cooled (at 1 ° C./1 minute or more) at this time. .

  It is desirable that the pan temperature detection device 18 in which the thermopile 25 is built is placed in a constant temperature atmosphere as much as possible. For this reason, in this embodiment, the pan temperature detecting device 18 is installed in the coil upper surface cooling air passage 15a into which the outside air is introduced, and during cooking, the thermopile 25 and the thermopile temperature detecting circuit 72 are cooled by the outside air, and these temperatures rise. Is preventing. Further, in order to prevent the airflow in the coil upper surface cooling air passage 15a from directly hitting the metal case 37 of the thermopile 25 and the semiconductor, resistance, etc. of the thermopile temperature detection circuit 72, the infrared sensor case 29 which is a windproof case is used. It covers this. Further, the thermopile 25 and the thermopile temperature detection circuit 72 are thermally insulated by the air in the infrared sensor case 29. The output of the thermopile 25 is dc-amplified in a stable manner with respect to the temperature change, and then output as a signal voltage with a low output impedance to the AD terminal of the microcomputer 60 described later.

  Further, the infrared sensor case 29 is covered with a metal case 32 such as aluminum having a permeability of approximately 1, and the AC magnetic field generated by the heating coil is shielded, so that the metal case 37 of the thermopile 25 generates a high frequency generated by the heating coil 7. Induction heating with an alternating magnetic field prevents the temperature from rising. The metal case 32 also serves as an electromagnetic shield against pulse noise (radiated electromagnetic waves) from an inverter circuit disposed below the pan temperature detection device 18.

  The metal case 32 is induction-heated by the ambient atmosphere temperature and the leakage magnetic flux from the heating coil 7 during cooking, and the temperature rises by 5 to 10 ° C. in the case of aluminum. When cooking is continued before the temperature rise subsides, when the outside air is rapidly introduced and applied to the metal case 32, the metal case 32 cools rapidly, and as a result, the ambient temperature of the thermopile 25 in the infrared sensor case 29 suddenly increases. Will be reduced. In the opposite case, for example, when cooking first in the winter morning, the metal case 32 in the aircraft is sufficiently cooled at night and is at about 5 ° C., and the user starts cooking in a cooking room heated to 20 ° C. The warm air is introduced into the coil upper surface cooling air passage 15a, and the warm air of 20 ° C. is applied to the metal case 37 of 5 ° C. In this embodiment, in order to prevent such a sudden temperature change of the metal case 32 due to the outside air, the metal case 32 is further covered with a plastic outer infrared sensor case 33. Thus, the cooling air is not directly applied to the metal case 32, thereby preventing a sudden temperature change due to the wind.

  Now, the top plate 2 is heated by absorbing infrared radiation from the induction heated cooking pan 6 and contact heat conduction. As shown by the solid line in FIG. 15, the top plate 2 transmits 80% or more of light having a wavelength of 0.2 μm to 2.9 μm, and transmits about 30% of light having a wavelength of 3 to 4.5 μm. Longer wavelengths and light with wavelengths shorter than 0.2 μm are hardly transmitted.

  When the radiant energy is incident on the surface of the material, a part ρ is reflected, a part α is absorbed, and the remaining τ is transmitted. Between these quantities, ρ + α + τ = 1 holds from the law of conservation of energy. In the state where the cooking pan 6 is placed on the top plate 2, the reflection of the infrared radiation energy of the cooking pan 6 on the top plate 2 can be regarded as almost zero, so that the absorption rate α + transmittance τ = 1 is established in the top plate 2. You can see it. Since Kirchhoff's law is the absorption rate α = emissivity ε, the top plate 2 transmits 80% or more of the infrared radiation energy from the cooking pan 6 at a wavelength of 0.2 μm to 2.9 μm, and the remaining 20%. Absorb and radiate it. Further, it transmits about 30% at a wavelength of 3 to 4.5 μm, and absorbs and radiates the remaining 70%. At wavelengths longer than 4.5 μm and wavelengths shorter than 0.2 μm, almost no transmission occurs, and all is absorbed and emitted. The same applies to the portion heated by heat conduction. When the wavelength is 4.5 μm or more, most of the infrared energy for heat conduction heating is radiated from the surface of the top plate 2.

  For this reason, when detecting the temperature of the cooking pan 6 on the top plate 2 using the thermopile 25, the infrared rays emitted by the heating of the top plate 2 itself become a problem. In particular, infrared rays having a wavelength indicated by hatching in FIG. For example, if the transmission wavelength of the optical filter 48 attached to the thermopile 25 is 1 to 15 μm, the output of the thermopile 25 is greatly affected by infrared light having a wavelength longer than 4.5 μm radiated from the top plate 2. The temperature at the bottom of the cooking pan cannot be detected accurately. The radiant infrared energy of the pan passing through the top plate 2 is about 2 μm band of 1 μm to 2.9 μm, whereas the infrared energy radiated by the top plate 2 itself is about 10 μm band of 4.5 μm to 15 μm. If it is temperature, five times the thermopile output due to the temperature of the cooking pan 6 will depend on the temperature of the top plate 2.

  In the present embodiment, in order to prevent the above, a case window 30 for transmitting infrared rays is opened in the infrared sensor case 29 of the pan temperature detection device 18 constituted by the thermopile 25, and the top plate 2 is configured in the case window 30. The crystallized glass to be cut into a thin square is fitted as the crystallized glass optical filter 31. Then, the amount of infrared rays radiated from the top plate 2 incident on the thermopile 25 is removed. The wavelength of the portion indicated by hatching in FIG. 15 emitted from the top plate is prevented from entering the thermopile 25 due to the optical characteristics of the crystallized glass optical filter 31 (the wavelength indicated by hatching in FIG. 15 is not transmitted).

  Although the crystallized glass optical filter 31 may be made of a material other than the top plate, it is very difficult and expensive to produce an optical filter having a steep characteristic as shown by a solid line in FIG.

  Further, the crystallized glass optical filter 31 has an effect of making the aluminum vapor deposition reflecting mirror surface 28 b of the reflector 28 disposed below it invisible from the infrared transmission window 5 of the top plate 2. As described above (as shown by the broken line in FIG. 15), the optical characteristics on the long wavelength side of 1 μm or more are almost the same as those of the top plate 2, but there is a region having a smaller transmittance on the short wavelength side than the top plate at about 400 nm. Because the visible light in this part is cut, it looks red and black to the eyes, making the aluminum mirror surface invisible.

  Further, a 5 μm short-pass filter (shown by a thin line in FIG. 15) that does not transmit a wavelength of 5 μm or more is used as the optical filter 48 of the thermopile 25. This is to prevent the infrared rays emitted from the crystallized glass optical filter 31 itself and the infrared sensor case 29 that are heated at the ambient temperature from being transmitted through the wavelength of 5 μm or more. As mentioned above, the infrared energy of 1 to 2.9 μm radiated from the pan is very small because the passage is restricted by the top plate, and the output amplification of the thermopile 25 must be increased. This is because it is sensitive to infrared radiation of 5 μm or more at ambient temperature, and it is necessary to thoroughly prevent the infrared radiation of 4.5 μm or more from other than the pan bottom from entering the infrared absorption film 43 of the thermopile.

  Assuming that the crystallized glass optical filter 31 itself and the infrared sensor case 29 are at 70 ° C., the voltage output from the thermopile 25 by the infrared rays emitted from the filter is calculated as shown by A in FIG. Here, the optical filter 48 of the thermopile 25 is assumed to transmit 90% of a wavelength of 1 to 15 μm. This voltage is substantially the same as the voltage output from the thermopile 25 when the pan bottom on the top plate 2 shown by the solid line in FIG. That is, unless the pass band of the optical filter 48 is limited to 5 μm or less, the pan temperature detection device 18 cannot detect the pan temperature on the top plate 2 in an atmosphere of 70 ° C. or higher.

  Also from the above reason, in this embodiment, the pan temperature detecting device 18 is installed in the coil upper surface cooling air passage 15a.

  FIG. 17 shows the relationship between the pan bottom temperature T and the output voltage V of the thermopile temperature detection circuit 72 output terminal 72-2 when the tempura pan having the pan bottom in a state close to a black body is induction-heated in the embodiment of FIG. Show. The broken line in the figure shows the case where the thermopile temperature detection circuit 72 does not have the resistor 72-9 and the diode 72-10. In this case, since the thermopile output is proportional to the fourth power of the temperature as described above, when the pan bottom temperature T exceeds 200 ° C., the output rapidly increases and the circuit output is saturated to the power supply voltage 5V. This is prevented by the circuit of the diode 72-10 and the resistor 72-9. By reducing the amplification factor of the operational amplifier 72-1 from the vicinity where the output exceeds 1.8 V and preventing the output from being saturated up to 400 ° C. as shown by the solid line in the figure, the detectable temperature range is expanded by the circuit. Yes.

  The voltage from room temperature to 100 ° C. is almost 0.5 V, and when the temperature exceeds 100 ° C., a voltage proportional to the temperature is output. 0.5V is a voltage obtained by dividing the power supply voltage (5V) of the thermopile temperature detection circuit 72 by resistors 72-5, 72-6, and 72-7 (indicated by a point in FIG. 11), and 0.5V is an operational amplifier 72-1. This is because it is given as a bias voltage. When the temperature exceeds 100 ° C., the output voltage of the thermopile 25 increases, and is amplified about 2000 times by the operational amplifier 72-1, and is observed as a voltage of 0.5V or more. This bias voltage is provided for detecting a failure of the thermopile temperature detection circuit 72. A value obtained by subtracting 0.5 V from the output voltage value of the output terminal 72-2 (a voltage increase value from 0.5 V) is proportional to the detected pan bottom temperature. The microcomputer 60 AD-converts and reads the output voltage of the thermopile temperature detection circuit 72 output terminal 72-2, and the pan temperature detection voltage Vt (= V−0.5), which is a value obtained by subtracting 0.5V from this voltage. Get the pot temperature based on The relationship shown in FIG. 17 is stored in advance in the ROM of the microcomputer 60 as table data.

  When the reflection type photo interrupter 26 built in the pan temperature detector 18 is arranged as shown in FIG. 3, when there is no cooking pan on the top plate 2, most of infrared light (wavelength 930 nm) emitted from the infrared LED 50 is large. It passes through the crystallized glass optical filter 31 and the top plate 2 and does not return to the infrared phototransistor 51. However, a part is reflected by the crystallized glass optical filter 31 and the top plate 2. This is because the transmittance of the crystallized glass optical filter 31 and the top plate 2 is 85% and 90% at a wavelength of 930 nm, and the remaining 15% and 10% of infrared light is reflected. In particular, since the amount reflected by the crystallized glass optical filter 31 returns directly to the infrared phototransistor 51 located immediately beside it, in this embodiment, the front surface of the reflective photointerrupter 26 is placed on the crystallized glass optical filter 31 as shown in FIG. It arrange | positions so that a lower surface may be touched, and it prevents that this reflected light injects into the infrared phototransistor 51. FIG. Further, because of the radiation angle of the infrared LED, there is also infrared light that is reflected by an object (inner surface of the sensor visual field cylinder 19) that does not reach the lower surface of the top plate and is in the middle of the path.

  Therefore, as shown in FIG. 18, the output of the reflectance detection circuit 73 is (a) V1 when there is a pan on the top plate, and (b) V2 when there is no pan. The reflected voltage Vr at the net pan is Vr = V2−V1.

  The reflectance detection circuit 73 is arranged as shown in FIG. 3, and the previous reflection voltage Vr and reflectance obtained from the output of the reflectance detection circuit 73 when a metal plate with a known reflectance is arranged on the top plate. The relationship is shown in FIG. An approximate line is also shown in the figure. If this relationship is used, the reflectance can be obtained from the output voltage of the reflectance detection circuit 73. This relationship is stored in the table data or the approximate coefficient value in the ROM of the microcomputer 60 in advance.

In a metal material such as a cooking pot, a relationship of ε + ρ = 1 holds between the emissivity ε of infrared energy (E = εσT ⁴ ) radiated from the surface of the material at temperature T and the reflectance ρ of the surface according to Kirchhoff's law. To do. In a cooking pan (transmittance α = 0), the infrared energy radiated differs due to the difference in emissivity, while the same pan bottom temperature. For this reason, the problem that a thermopile output, ie, the output of the pan temperature detection apparatus 18, differs arises. Therefore, it is necessary to detect the reflectance of the bottom of the cooking pan to obtain the emissivity, correct the output of the pan temperature detection device 18 and then convert it to a temperature. In order to do this, the reflectance detection circuit 73 obtains the reflectance from the reflected voltage Vr, which is an amount corresponding to the reflectance described above. This reflectance is subtracted from 1 to obtain the emissivity.

For several types of pans placed on the top plate 2 in FIG. 20, a value Vt (pot) obtained by subtracting the above-described 0.5 V offset voltage Vo from the output of the pan temperature detection device 18 (output V of the thermopile temperature detection circuit 72). An example of the relationship between (temperature detection voltage) and pan bottom temperature T is shown. The emissivity at the bottom of each pan is also shown in the figure. As shown in FIG. 20, it can be seen that the relationship between the output of the pan temperature detector 18 and the pan bottom temperature varies depending on the emissivity. The pan shown in FIG. 20A has an emissivity of 0.9, which is close to a black body. (B) has an emissivity of 0.57, (c) is 0.43, and (d) is 0.24. When the voltage values of (b), (c), and (d) are divided by the emissivity, it is shown by a broken line in the figure, and it can be seen that it can be summarized into almost one curve. Each output Vt is proportional to the total radiation energy of each pot (E '= εσT ^4), which to divide by emissivity is converted into the total radiant energy of a black body as described above (E = σT ⁴⁾ Means that. And if the emissivity of each pan is known, it means that the pan temperature of each pan can be reduced to the radiation temperature of a black body. For example, in FIG. 3 embodiment, a black body is arranged on the top plate, and a pan temperature detection voltage Vt that is a value obtained by subtracting 0.5 from the black body temperature T and the output V of the pan temperature detection device 18 is obtained. And Vt are recorded and stored in advance in the ROM of the microcomputer 60 as table data or as a coefficient value of an approximate expression. Then, when the pan is being induction-heated, the output V of the pan temperature detection device 18 is AD-converted and read at regular intervals, and the pan temperature detection voltage Vt = V−0.5 is calculated. The reflectance is obtained by the detection circuit 73 as described above, the emissivity ε is obtained from Kirchhoff's law (ρ + ε = 1) based on the reflectance ρ, and the pan temperature detection voltage Vt is divided by this. By checking the table data with values or substituting it into the approximate expression, the temperature T is obtained from the pan temperature detection voltage Vt, and this is used as the detection pan temperature. The pan temperature correction of this embodiment is performed based on the above.

  FIG. 21 shows the relationship between the emissivity measured using a radiation thermometer in each pan and the reflectance obtained by using the reflectance detection circuit 73 in FIG. 3 (applying the approximate expression of the relationship of FIG. 19). Some pans deviate from Kirchhoff's law, but there is a strong correlation between emissivity and reflectivity. The reason for deviating from Kirchhoff's law is that in the detection of reflectance, not all of the reflected infrared rays are received due to scattering on the pan surface. When obtaining the reflectance, it is desirable that the emitted light of the infrared LED 50 is incident as vertically as possible on the top plate 2 and the reflected light from the pan is guided to the infrared phototransistor 51 as vertically as possible. In the present embodiment, the visual field surface of the thermopile 25 in the pan temperature detecting device 18 at the position on the top plate 2 and the reflective surface on the top plate 2 for the reflectance detection light emission are the same surface. For this reason, as shown in FIG. 3, the thermopile 25 and the reflective photointerrupter 26 are arranged side by side in the pan temperature detection device 18.

  Below, operation | movement of a present Example demonstrates the case where the cooking pan 6 is set | placed on the circle display 4 of the near right side, and cooking is performed by heating a cooking pan for a predetermined time at predetermined temperature. FIG. 22 shows a flowchart of this operation. When a power source (not shown) is turned on, a predetermined temperature and cooking time are set with the operation switch of the induction heating port on which the cooking pan 6 is placed (step S1), and the start of cooking is instructed (step S2), the microcomputer 60 first starts. Reflection data (corresponding to the reflectance) of the pan placed by controlling the reflectance detection circuit 73 is taken in and the reflectance is detected (step S3). At the same time, in order to cool the heating coil 7, the inverter circuit 8 and the like, a fan (not shown) is driven to introduce outside air into the coil upper surface cooling air passage 15a and the coil lower surface cooling air sending hole 15b.

  Step S3 for detecting the reflectance will be described in detail with reference to the flowchart shown in FIG. The microcomputer 60 outputs the infrared LED drive signal of FIG. 16A from the port to the terminal 73-2 of the reflectance detection circuit 73 (step S3-1). After outputting 200 ms for a predetermined time (step S3-2), the voltage V2 output to the terminal 73-8 is read from the AD terminal (step S3-3). Then, the infrared LED drive signal is stopped (step S3-4). Next, the pulling reflection voltage Vr is calculated from the voltage V2 obtained by reading the voltage V1 when the pan stored in advance is not placed (step S3-5). Then, the reflectance ρ is obtained from the relationship between the reflection voltage and the reflectance stored in advance (step S3-6).

  Subsequent to step S3, the power control circuit 62, the frequency control circuit 61, and the inverter circuit 8 are controlled to supply power to the heating coil 7 to start induction heating (step S4). When electric power is supplied to the heating coil 7, an induction magnetic field is emitted from the heating coil 7, and the cooking pan 6 on the top plate 2 is induction-heated. Due to this induction heating, the temperature of the cooking pan 6 rises, and cooking of the object to be heated in the cooking pan 6 is started. When the induction heating is started, the microcomputer 60 reads the output of the pan temperature detecting device 18 at regular intervals and detects the pan temperature (step S5).

  Here, the pan temperature detection operation (step S5) will be described in detail. FIG. 24 shows a flowchart of the pan temperature detection. The microcomputer 60 reads the output voltage V of the pan temperature detection device 18 (pan temperature detection circuit 72) (step S5-1), subtracts 0.5V from this value, and sets this as the pan temperature detection voltage Vt (step S5-). 2). And emissivity (= 1-reflectance) is obtained from the reflectance detected just before induction heating (step S5-3), and this pan temperature detection voltage Vt is divided (step S5-4). A data table having a relationship between Vt and T stored in advance using Vt after division is drawn (step S5-5), converted to temperature T, and pan temperature T is output (step S5-6).

  Instead of the process of calculating the emissivity (step S5-3) and the process of dividing the pan temperature detection voltage Vt by the emissivity (step S5-4), the magnification a = 1 / emissivity (a = 1/1 / The relationship between the value of ε) (becomes a value of 1 or more) and the reflectance (or reflection voltage Vr) is stored as a table, the magnification a is obtained from the reflectance (or reflection voltage Vr) with the table, and the pan temperature is detected. After multiplying the voltage Vt by the magnification, the pan temperature T may be output by drawing a data table that is a relationship between Vt and T. In this way, it is possible to speed up the processing without using a division requiring a processing time of the microcomputer.

  When the temperature detected in step S5 reaches a predetermined temperature (step S6), the power control circuit 62 is controlled to decrease the current supplied to the heating coil 7 by a predetermined amount (step S7). Then, the cooking time timer is started (step S8). While continuing to detect the pan temperature at regular intervals (step S9) (step S10), the current supplied to the heating coil 7 is increased or decreased by a predetermined amount (steps S11 and S12), and the pan temperature is kept constant (Tc). When a predetermined cooking time has elapsed (step S13), the user is notified of the end of cooking with a buzzer, and the power supply to the heating coil 7 is stopped (step S14). Thus, the food to be cooked in the cooking pan 6 is cooked at the set temperature and time.

  In the above description, the example in which the reflectance detection is performed only immediately before the induction heating is shown, but the present invention is not limited to this. In ordinary pans, the reflectance does not change during induction heating (even when the temperature rises). In addition, the infrared light emitting LED has a problem of life in continuous light emission for a long time. In this description, in consideration of these points, one cooking is limited to one reflectance detection immediately before induction heating. Naturally, the reflectance may be detected at regular intervals during cooking by reducing the emission current. Especially in thin pans, the reflectivity may change due to pan deformation due to high temperature. Furthermore, in pans with color coating on the bottom, the coating may be denatured at high temperatures and the reflectivity may change. In this case, it is desirable to periodically detect the reflectance even during heating. In this case, of course, in order to avoid the influence of the magnetic field, it is desirable to surround the reflection type photointerrupter 26 and the reflectance detection circuit 73 with a nonmagnetic metal material as in the embodiment.

  In some cases, the pan may be replaced with another pan during cooking. At this time, the reflectivity naturally changes. In this case, the voltage detected by the pan temperature detecting device 18 rapidly decreases when the existing pan is retracted. And when the pan of another temperature is placed, the voltage detected by the pan temperature detector 18 returns to a value corresponding to the pan bottom temperature. It is desirable to detect this change and detect the reflectance again.

  Then, Example 2 is demonstrated using FIGS. 25-29. A description of portions common to the configuration of the first embodiment will be omitted.

  The thermopile 25 described with reference to FIG. 8 has an optical filter 48 disposed in a small hole window 47 through which infrared rays pass, and the optical filter itself has no light collecting action. Was. In the induction heating cooker of the second embodiment, a thermopile 25 shown in FIG. 25 is used instead of the thermopile 25 described in FIG. In FIG. 25, the same reference numerals as those in FIG. A thermopile 25 shown in FIG. 25 is obtained by forming a convex lens 49 of the same crystallized glass as that of the top plate 2 in place of the optical filter 48 described in FIG. The crystallized glass convex lens 49 is designed so that the visual field range of the infrared transmission window 5 is focused on the infrared absorption film 43. For this reason, the metal can 35 is taller than that of FIG. FIG. 26 shows a state where a heat sink 55 is attached to the thermopile 25. As described above, in the thermopile, the metal case 37 is thermally the same as the cold junction of the thermocouple, and this temperature fluctuation directly becomes the thermopile output fluctuation. For this reason, the heat sink 55 is mounted as a thermal buffer (increasing the heat capacity) to reduce output fluctuations due to changes in ambient temperature. FIG. 27 shows a state where the thermopile 25 is mounted on the electronic circuit board 27 together with the reflective photo interrupter 26.

  FIG. 28 shows a pan temperature detecting device 18 according to the second embodiment. 6, 7, and 9 indicate the same items. In the second embodiment, the thermopile 25 and the reflection type photo interrupter 26 shown in FIG. 25 in which the heat sink 55 is mounted in the infrared sensor case 29 of the pan temperature detecting device 18 are incorporated. As shown in FIG. 28A, the thermopile 25 and the reflective photointerrupter 26 mounted upward on the electronic circuit board 27 are arranged so that the front surface (infrared light receiving surface) is directly below the crystallized glass optical filter 31 and the infrared sensor. Sealed in case 29. The infrared sensor case 29 is covered with an aluminum metal case 32 that shields AC magnetic flux from the heating coil 7 and electromagnetic waves from the inverter circuit 8, and further heat-insulated on the inside to prevent abrupt temperature change due to cooling air of the aluminum metal case 32. The outer infrared sensor case 33 including the material 34 is covered. The difference from the triple structure of the first embodiment is that a heat insulating material 34 is built inside the outer infrared sensor case 33. This is because the temperature change around the thermopile 25 is reduced more firmly than in the first embodiment and the temperature detection of the pan bottom is stabilized.

  FIG. 28B is a sectional view taken along line BB ′ in FIG. This shows a state in which the thermopile 25 installed in the infrared sensor case 29, the heat sink 55 mounted on the thermopile 25, and the reflective photo interrupter 26 are mounted on the electronic circuit board 27.

  In addition, the light emitting and receiving portions on the front surface of the reflective photointerrupter 26 are disposed immediately below the lower surface of the crystallized glass optical filter 31. This is to prevent infrared light from being reflected and received by the crystallized glass optical filter 31 directly above.

  Infrared light emitted from the infrared LED 50 passes through the crystallized glass optical filter 31 by 85% or more, but the remaining 15% is reflected and received by the adjacent infrared phototransistor 51. When the distance to the reflecting surface is short, this level is large and affects the reception of reflected light on the bottom surface of the pan on the top plate 2 which is the original purpose. For this reason, in this embodiment, as shown in the figure, the distance between the crystallized glass optical filter 31 and the light emitting / receiving surface of the reflective photointerrupter 26 (infrared LED 50 and infrared phototransistor 51) is reduced to within 500 μm to emit light. Infrared reflection is prevented from being received by the infrared phototransistor 51. Ideally, it is desirable that the lower surface of the crystallized glass optical filter 31 and the upper surface of the reflective photointerrupter 26 are in contact with each other, but this is difficult in terms of assembly tolerances.

  Since the pan temperature detection and its correction operation in the second embodiment are the same as those in the first embodiment, the description thereof will be omitted.

  FIG. 29B shows another installation example of the pan temperature detecting device 18 below the heating coil 7. 3 and 4 described above, the pan temperature detector 18 is disposed in the coil upper surface cooling air passage 15a at a position immediately below the coil gap 7c of the heating coil 7 as shown in FIG. 29 (a). In the second embodiment, the pan temperature detecting device 18 is disposed outside the coil upper surface cooling air passage 15a. A part of the outer cavity wall 14b of the coil base 10 is inflated below the coil gap 7c and along the sensor visual field cylinder 19, and the wall of the coil upper surface cooling air passage 15a and the coil upper surface cooling air sending hole 15c are formed accordingly. The pan temperature detecting device 18 can be arranged outside the coil upper surface cooling air passage 15a. The coil cooling air is not obstructed and the coil cooling air is prevented from hitting the pan temperature detecting device 18. By doing so, a rapid temperature change due to cooling air (outside air) during cooking of the pan temperature detection device 18 is prevented, and the heating coil 7 can be efficiently cooled.

  According to the induction heating cooker described above, the maximum heating temperature of the cooking pan 6 can be accurately and stably detected in a wide temperature range from 150 to 300 ° C., regardless of the material of the pan, the shape of the pan bottom, and the level of dirt. It is possible to optimally cook by appropriately controlling the high frequency power to the overheating coil.

  In addition, unlike the thermistor, there is no temperature detection delay, so it is possible to follow a sudden rise in the maximum temperature at the bottom of the pan such as emptying, and if there is a risk of oil ignition, induction heating can be stopped immediately. Therefore, a safe induction heating cooker can be provided.

DESCRIPTION OF SYMBOLS 1 Main body of induction heating cooker 2 Top plate 3 Operation part 4 Circle display which shows the position which puts a cooking pan 5 Infrared transmission window 6 Cooking pan 7 Heating coil 7a 1st coil 7b 2nd coil 7c Coil gap | interval 7d Bridge line 8 Inverter circuit 10 Coil base 11 Ferrite 14a Inner cavity 14b Outer cavity wall 15 Coil cooling air passage 15a Coil upper surface cooling air passage 15b Coil lower surface cooling air delivery hole 15c Coil upper surface cooling air delivery hole 16 Seal material 18 Pan temperature detector 19 Sensor field of view Tube 21 Thermistor 21a Low voltage terminal 21b High voltage terminal 25 Thermopile 26 Reflective photo interrupter 27 Electronic circuit board 28 Reflector 29 Infrared sensor case 30 Case window 31 Crystallized glass optical filter 32 Metal case 33 Outside infrared sensor case 34 Insulating material 35 Metal Can 36 Metal 38 silicon substrate 39 a silicon oxide film 40 a polysilicon deposited film 41 aluminum deposited film 42 measuring junction portion 43 infrared absorbing film 44 cold junction 45 NTC thermistor 46 metal pin 47 window 48 optical filter 49 crystallized glass lens 50 Infrared LED
51 Infrared Phototransistor 55 Heat Sink 60 Microcomputer 61 Frequency Control Circuit 62 Power Control Circuit 63 Rectifier Circuit 64 Power Switch 68 Operation Switch 69 Display Circuit 70 Buzzer 72 Thermopile Temperature Detection Circuits 72-1, 73-6 Operational Amplifier 72-9 Resistance 72- 10 Diode 73 Reflectance Detection Circuit 73-5 Capacitor 73-7 Charge / Discharge Circuit

Claims (3)

A top plate made of crystallized glass with a cooking vessel on top;
A heating coil provided under the top plate;
High-frequency power supply means for supplying high-frequency power to the heating coil;
Power control means for controlling the output power of the high-frequency power supply means;
A thermopile for detecting the amount of infrared radiation emitted from the bottom surface of the cooking container,
The thermopile is
A metal case consisting of a metal can and a metal stem;
Provided in the metal can, a small hole window through which infrared rays pass;
An optical filter or lens disposed in the small hole window;
A silicon substrate fixed to the metal stem;
A silicon oxide film provided on the surface of the silicon substrate;
Many thermocouples created and cascade-connected on the silicon oxide film;
An infrared absorption film formed at a temperature measuring contact at the center of the silicon substrate;
A cold junction portion provided around the silicon base material and thermally connected to the metal case; and
An induction heating cooker, wherein the thermopile is equipped with a heat sink thermally connected to the metal case. The induction heating cooker according to claim 1,
The induction heat cooker, wherein the heat sink functions as a heat buffer for the metal case and reduces output fluctuation of the thermopile with respect to a change in ambient temperature. The induction heating cooker according to claim 1,
The thermopile is housed in an infrared sensor case together with a thermopile temperature detection circuit that amplifies the output signal of the thermopile, a reflectance detection circuit that detects the infrared reflectance of the cooking pan, and an electronic circuit board on which these are mounted. An induction heating cooker characterized by

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