JP6512689B2 - Induction cooker - Google Patents

Description

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

  The conventional induction heating cooker heats the cooking container mounted in the top plate using two types of heating sources, a radiant heater and an induction heating coil (following "heating coil" abbreviation). Since the radiant heater also heats the top plate itself to a high temperature, it has been necessary to use a crystallized glass having a high heat resistance temperature as the top plate.

  As a pan temperature detection means of the induction heating cooker, there is one that detects the infrared ray radiated from the heated pan bottom with an infrared sensor through the top plate to detect the temperature (Patent Document 1). This infrared sensor is disposed under the vicinity of the heating coil center air gap, detects the infrared radiation emitted from the pan bottom with the infrared sensor over the top plate, and controls the inverter circuit output that drives the heating coil according to the output. It is to adjust the cooking temperature.

  However, in the induction heating cooker of this configuration, the magnetic flux density is largest between the concentric heating coil inner circumference and the outer circumference, ie, near the middle of the coil winding width, so the temperature distribution of the cooking vessel placed on the top plate Create a bias. That is, the portion on the middle of the heating coil is heated to the highest temperature, and the portions on the inner and outer circumferences are at a lower temperature. It becomes lower in the vicinity of the heating coil center.

  The outline of this heating coil and the temperature distribution of the pan heated by this are shown in FIG. 30 (a). This is the temperature distribution of the pan bottom when the pan center and the heating coil center are aligned. For this reason, when heating the cooking container into which only a small amount of the food to be fed is heated, the temperature of the middle portion of the coil rapidly rises, which may burn the food. In addition, when the food was a small amount of oil, it sometimes smoked. In addition, when a thin stainless pan or the like was left to dry because of poor heat conduction, this portion may be red-heated to be deformed. Although a pan temperature detection means is required to prevent these, the high temperature portion can not be detected by an infrared sensor installed under the vicinity of the coil center gap as in Patent Document 1.

  The leakage magnetic flux is weak at the bottom of the heating coil central air gap and at the neutral point of the magnetic field generated by the coil (where the magnetic fields in the opposite directions overlap) as described later. For this reason, there is little influence on the infrared sensor to be installed, and a simple magnetic shielding means such as cylindrical aluminum may be used instead of a magnetic shield to cover this, and this magnetic shielding means is inductively heated and this temperature rise is an infrared sensor There was no need to consider the impact.

  As a technique for solving the above-mentioned problems, the 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 part (Patent Document 2). The outline of this heating coil and the temperature distribution of the pan heated by this are shown in FIG. 30 (b). The high temperature part spreads and the deviation of the temperature distribution is improved, and the gap part becomes almost the same temperature as the high temperature part. Although there is a slight temperature drop, if an infrared sensor is placed under this gap, it becomes possible to accurately detect the pan temperature heated to a high temperature. However, the divided heating coils change their characteristics. When the opening area of the concentric gaps increases, the coil inductance and resistance change when the cooking vessel is placed, and it becomes necessary to adjust the inverter circuit that drives the heating coil. In particular, in the case of heating a cooking vessel made of low resistance, low permeability material such as aluminum or copper, if it is intended to have the same heating characteristics as the conventional non-divided coil, it is necessary to increase the coil drive current and voltage. That is, since the heating efficiency is lowered, it is necessary to increase the high frequency magnetic field strength. This also means that the heat generation of the coil itself is increased. Originally, this split gap is at the center of the winding width and is the place where the magnetic flux density is high. For this reason, the infrared sensor disposed under the split gap portion is affected by the leakage flux. The infrared sensor placed under the split gap strengthens protection against leakage magnetic flux, heating coil or high temperature of bottom of pan, temperature rise by radiant heat from top plate, inverter circuit driving coil which reduces heating efficiency, high frequency high voltage I have to let it go.

  In addition, it is necessary to cool the heating coil, and an air path for introducing outside air is usually disposed below the coil. When an infrared sensor is disposed in the air path, it is also 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 a part near the center of the radial winding width of the heating coil, and an infrared sensor is disposed under the opening (Patent Document 3). This is the same characteristic as the conventional non-divided heating coil by providing an opening between the windings wound adjacent to each other, and making the number of winding around the opening more (more densely) than other parts. While making it possible to detect the hot part temperature of the pan bottom heated from this opening. However, such a heating coil is difficult to mass-produce due to its structure and must be expensive. Further, the increase in the number of coil turns in the opening means that the leakage flux from this portion is further intensified. The need for enhanced protection against leakage flux, temperature rise, electromagnetic waves and high frequency high voltage of the infrared sensor is the same as the above-mentioned technology (patent document 2).

Unexamined-Japanese-Patent No. 2005-26162 JP, 2008-153046, A JP 2007-323887 A

  In the pan temperature detection means of Patent Document 1, an infrared sensor as a detection means is disposed under the vicinity of the concentric heating coil center gap, and the infrared ray emitted from the pan bottom is detected by the infrared sensor over the top plate The temperature of the pan bottom portion heated to the highest temperature on the middle of the heating coil winding width can not be detected. For this reason, the high temperature heating of the pan can not be detected by the pan temperature detecting means, and in the case of a cooking vessel into which only a small amount of the cooking material is charged, the cooking on the coil middle portion which rapidly rises in temperature may be burnt. The In addition, when the food was a small amount of oil, it sometimes smoked. In addition, when a thin stainless pan or the like was left to dry because of poor heat conduction, this part may be red-hot to be deformed.

  The pan temperature detection means of Patent Document 2 is disposed under the gap portion obtained by dividing the heating coil into a first coil on the inner circumferential side and a second coil on the outer circumferential side near the center of the radial winding width. For this reason, it becomes possible to accurately detect the pan temperature heated to a high temperature. However, since the magnetic flux density is substantially maximum at this gap portion, the leakage flux from the heating coil to the pan temperature detecting means to be disposed becomes large. During cooking, the lower surface of the top plate and the pan temperature detecting device are exposed to high temperatures by radiation from the pan bottom heated to the maximum temperature or radiation from the heat generating coil. Therefore, in order to cool the lower surface of the top plate on which the pan is placed or the coil that generates heat during cooking, the outside air is blown thereto. The pan temperature detector receives a rapid temperature change due to the air flow. In addition, it is also affected by high frequency high voltage applied to the heating coil and electromagnetic waves radiated from an inverter circuit or the like for driving the heating coil. There is no mention in the literature of the protection means of the pan temperature detection means against these disturbances.

  The pan temperature detecting means of Patent Document 3 is the same as that of Patent Document 2.

  Another problem in temperature detection with an infrared sensor is that it is affected by the emissivity of the object to be measured. The infrared emissivity of the bottom of the pot depends largely on the material, color, and processing conditions of the bottom of the pot (coating of the bottom of the pot, marking of the bottom of the pot, processing of the hairline, processing of the ring, processing of the ring, etc.). In addition, even in the same pot, the emissivity becomes different due to the contamination such as cooking oil adhering to the bottom of the pot. That is, even if the pan bottom has the same temperature and the same material, the infrared energy to be emitted is different if the color, processing or soiling state is different, and the infrared energy to be received by the infrared sensor is also different, and different temperatures are detected. Therefore, it is necessary to have a means for correcting the difference in temperature detection by infrared rays due to the difference in the pan bottom.

  In the conventional induction heating cooker, crystallized glass is used for the top plate, but if it is possible to use non-crystallized glass with high transmittance in the visible light region (high transparency) and inexpensive for the top plate, Even as an induction heating cooker, the design can be further enhanced and the price can be reduced. In order to use non-crystallized glass whose thermal shock temperature is lower than crystallized glass for the top plate of the induction heating cooker, it is solved by configuring the heating source with an induction heating coil.

  However, when, for example, borosilicate glass is used as the top plate made of non-crystallized glass, the infrared radiation generated from the cooking vessel is transmitted through the top plate as compared to the crystallized glass due to the difference in the optical characteristics of the infrared radiation. The amount of energy will be reduced.

  The infrared sensor receives infrared radiation energy which causes a thermal disturbance, in addition to the infrared radiation energy from the cooking vessel, the exhaust heat of the heating coil and the inverter substrate for controlling the heating coil. When non-crystallized glass is adopted for the top plate, the rate of thermal disturbance received by the infrared sensor is increased compared to crystallized glass, and there is a problem that the measurement accuracy for detecting the temperature of the cooking container is deteriorated.

  The present invention is a pan temperature detection means employing a top plate made of non-crystallized glass using a thermopile as an infrared sensor, and means for preventing disturbances such as leakage flux from heating coils, temperature rise, electromagnetic waves, high frequency high voltage etc. An object of the present invention is to provide an induction heating cooker which enables stable and accurate detection of the pan bottom temperature which is applied and heated to the highest temperature, and improves safety and usability.

  Another object of the present invention is to provide an induction heating cooker which accurately detects the pan bottom temperature regardless of the material, color and processing state of the pan bottom.

The present invention has been made to solve the above-described problems, and a top plate for placing a cooking vessel on the top, and a first plate provided under the top plate and concentrically wound around the outer periphery. A heating coil having a coil, a second coil concentrically wound on the inner circumferential side, and a concentric coil gap between both coils, a fan for introducing the outside air, and the fan Coil cooling air path for guiding the outside air to the heating coil, 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, and the bottom of the cooking vessel A thermopile for detecting the amount of infrared radiation emitted from the bottom of the cooking vessel by transmitting an infrared ray having a wavelength of 1 to 4 .mu.m; Previous A window material made of borosilicate glass, which is disposed in the window and transmits infrared light of a wavelength of 4 .mu.m or less, and a first plastic housing incorporating the thermopile and having the window material fitted in a first case window. It is achieved by arranging the temperature detection means below the coil gap and in the coil cooling air path to detect the temperature of the bottom surface of the cooking vessel and controlling the power supplied to the heating coil based on this temperature. Be done.

  According to the present invention, in an induction heating cooker provided with a non-crystallized glass top plate, the thermopile infrared sensor is used to be resistant to ambient temperature changes during cooking, leakage flux, and disturbances of electromagnetic waves radiated from the inverter circuit. It is possible to provide pan temperature detection means for stably and accurately detecting the high temperature portion temperature of the heating pan bottom. And the induction heating cooker which enables safe and optimal cooking can be provided by controlling the high frequency electric power to a heating coil appropriately according to the high temperature part temperature detected correctly.

  Furthermore, infrared emission and light receiving element are arranged near the thermopile infrared sensor which detects the pan bottom temperature, the emissivity of the pan bottom is measured with the same field of view as temperature detection, and the output of the infrared sensor is corrected It becomes possible to accurately detect the pan bottom temperature regardless of the processing condition or the state of contamination, and since the heating can be controlled using the accurately detected pan bottom temperature, it is possible to cook well. Become.

1 is a perspective view showing the configuration of an induction heating cooker according to a first embodiment. BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows the structure of the induction heating cooker of Example 1. FIG. FIG. 2 is a cross-sectional view showing details of the vicinity of a heating coil of Example 1; FIG. 2 is a plan view showing the arrangement of a heating coil and a pan temperature detection device of Example 1; FIG. 2 is a plan view showing a heating coil of Example 1; FIG. 1 is a perspective view showing a pan temperature detection device of a first embodiment. Sectional drawing of the pan temperature detection apparatus of Example 1. FIG. 2 is a plan and sectional view showing the details of the thermopile of Example 1. FIG. FIG. 2 is a diagram showing a reflective photointerrupter of a first embodiment. The control block diagram of the induction heating cooker of Example 1. FIG. FIG. 2 is a view showing details of a thermopile temperature detection circuit of Example 1; FIG. 2 is a diagram showing details of a reflectance detection circuit of Example 1; 6 is an operation timing chart of the reflectance detection circuit of the first embodiment. The figure which shows the spectral radiation energy by the distribution rule of Plank. The figure which shows the optical characteristic of a top plate. The figure which shows the relationship between temperature and the output of a thermopile. The figure which shows the relationship of the ladle bottom temperature of Example 1, and a thermopile temperature detection circuit output. FIG. 8 is an output explanatory diagram according to the presence or absence of a pan of the reflectance detection circuit of Example 1; FIG. 6 is a graph showing the relationship between the reflection voltage and the reflectance of the reflectance detection circuit of Example 1; The figure which shows the relationship of the pot bottom temperature of 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. 3 is a flowchart of induction heating and cooking of Example 1; 6 is a flowchart of reflectance detection of the first embodiment. 5 is a flow chart of pan temperature detection according to the first embodiment. FIG. 7 is a cross-sectional view showing a thermopile of Example 2; FIG. 7 is a perspective view showing a thermopile of Example 2; FIG. 7 is a perspective view showing substrate mounting of the thermopile of Example 2; The plane and sectional view of the pan temperature detection device of Example 2. FIG. FIG. 13 is a plan view showing another example arrangement of the pan temperature detection device of the second embodiment. The figure which shows the temperature distribution of the pan mounted on the heating coil.

  Embodiments of the present invention will be described based on the drawings.

  FIG. 1 is a perspective view of the main body 1 of the induction heating cooker according to the first embodiment, and FIG. 2 is a schematic vertical sectional view when the cooking pot 6 is placed on a portion shown by a dashed dotted line AA 'in FIG. . In the following, an example of a three-pot induction heating cooker having two pans capable of induction heating and one pan position capable of heating by radiant heat of a heater (heating source) such as a radiant heater or a halogen heater However, the application of the present invention is not limited to this. When making a top plate into borosilicate glass of non-crystallizing glass especially, it is desirable that it is an induction heating cooker provided with three pans where an induction heating is possible. This is because the maximum temperature of the top plate 2 is lowered to 500 ° C. or lower at the time of heating the cooking pot 6 by induction heating, as compared with the radiant heater. The cooking pot 6 may be a magnetic iron pan suitable for induction heating, or may be a nonmagnetic aluminum pan or copper pan.

  As shown in FIGS. 1 and 2, a top plate 2 formed of a nonmagnetic material such as heat resistant glass is mounted on the top surface of the main body 1. The top plate 2 is made of non-crystallized glass printed at least with heat resistance temperature of at least three hundred and tens of degrees heat resistant paint on the back surface of the letters and almost the entire surface of the paint. It is a heat-resistant glass used as a material. The non-crystallized glass described in this embodiment includes quartz glass, high silicate glass and borosilicate glass, and in this embodiment, in particular, approximately 80% of silicon and approximately 10 to 15% of boric acid are contained. Borosilicate glass having a thermal shock temperature of 300 ° C. or more and 500 ° C. or less.

  Further, in front of the top plate 2, a switch for instructing the start of heating of each mouth or a heating course, and an operation display unit 3 in which an indicator for displaying the heating state (temperature, etc.) of each mouth is disposed .

  On the top surface of the top plate 2, a circular indication 4 of a radius approximately corresponding to the outermost radius of the heating coil 7 or the radial heater disposed therebelow is printed to indicate the pan position where it can be heated. Also, since the top plate 2 is transparent to ordinary visible light, heat resistant and durable costume printing with heat resistant paint mixed in frit glass on the upper surface, and heat resistant surface coating on the lower surface, makes the inside of the device invisible. It is An infrared transmitting window 5 which is not printed or painted as described above is provided at a position about 50 mm from the approximate center of the circle 4 of the two pot locations where induction heating is possible, which will be described later. The infrared transmission window 5 is for transmitting infrared light, and a visible light cut member (heat resistant film or glass) transparent to infrared light may be attached to the lower surface of this portion.

  The cooking pot 6 is placed in each mouth (circled 4) on the upper surface of the top plate 2 to perform heating and cooking. 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 the first coil 7a on the outer peripheral side and the 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), and the high frequency magnetic field interlinks with the pan 6 to generate an eddy current, and the Joule heat induces heating of the cooking pan 6 itself to generate heat. . Therefore, the food in the cooking pot 6 is cooked by the heat of the cooking pot 6 itself. At this time, the top plate 2 below the cooking pot 6 also becomes hot due to the heat transmitted from the cooking pot 6 that has generated heat.

  The cross section around heating coil 7 is shown in detail in FIG. As shown in FIG. 3, in the coil base 10, the heating coil 7 divided by providing a coil gap 7c between the first coil 7a and the second coil 7b on the lower surface of the top plate 2 is made of heat resistant plastic. Concentric (convoluted) wound and arranged. On the lower side of the heating coil 7, a U-shaped ferrite 11 is radially disposed inside the coil base member with the convex portion on the upper side. The ferrite 11 is disposed to efficiently guide the magnetic flux generated by the heating coil 7 to the cooking pot 6 which is a cooking vessel 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 permeability and the magnetic flux almost passes through the ferrite 11.

  Under the coil base 10, a coil cooling air passage 15 for cooling the heating coil 7 is installed. The coil cooling air passage 15 is divided into two, and one is connected to the inner peripheral side of the first coil 7a, and the coil upper surface cooling air passage 15a, which cools the upper surface of the second coil 7b and the first coil 7a, The other is a coil lower surface cooling air delivery hole 15b for cooling the lower surface of the first coil 7a. A circular coil upper surface cooling air delivery hole 15 c is opened at the upper surface of the coil upper surface cooling air passage 15 a located below the central portion of the coil base 10.

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

  Below the cooling air passage 15, circuit cooling air passages 17a and 17b incorporating a circuit board such as an inverter circuit 8 are provided in two stages, and inverter circuits of the left and right heating coils 7L and 7R are incorporated respectively. ing. These cooling air paths are fixed to the main body 1.

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

  A pan temperature detection device 18 is disposed in the coil top surface cooling air passage 15a below the coil top surface cooling air delivery hole 15c. The pan temperature detection device 18 detects the bottom temperature of the induction pan 6 which has been induction heated, 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 substantially at the center of the upper surface of the inner cavity 14a.

  During the heating and cooking, outside air is introduced from a fan (not shown) incorporated in the main body 1 into the coil upper surface cooling air passage 15a, the coil lower surface cooling air delivery hole 15b, and the circuit cooling air passages 17a and 17b. The cooling air flowing in the coil upper surface cooling air path 15a cools the pan temperature detecting device 18 and ascends the coil gap 7c and the inner cavity 14a in the cylindrical outer cavity wall 14b from the coil upper surface cooling air delivery hole 15c. The top plate 2 is interrupted from the top of the gap 7c and the inner cavity 14a, and flows outward between the top plate 2 and the heating coil 7 in the radial direction of the coil to cool the upper surface of the heating coil 7 and the lower surface of the top plate 2. A plurality of small holes are opened in a portion of the coil lower surface cooling air delivery hole 15b corresponding to the lower surface of the first coil 7a, and the cooling air flowing in the coil lower surface cooling air delivery hole 15b is directed to the lower surface of the first coil 7a from here. It jets and cools it.

  FIG. 4 shows details of the top view of FIG. 3 excluding the top plate 2. It is a detailed block diagram of heating coil 7, coil base 10, and coil upper surface cooling air course 15a. The positional relationship in the horizontal surface of the heating coil 7 and the internal 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 concentrically by a litz wire insulating coated with a fluorine resin represented by polytetrafluoroethylene, etc., and the first coil 7a on the outer circumferential side and the second on the inner circumferential side It is divided into coils 7b. The coil gap 7c is in the form of a concentric band having a width of about 15 mm, and the end of winding of the first coil 7a bridges the coil gap 7c and the winding of the second coil 7b starts, and the first coil 7a, the bridge wire 7d, and The heating coil 7 is composed of the 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 inner side thereof 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 in the inner cavity 14a. Furthermore, a cylindrical sensor field tube 19 is provided between a part of the coil gap 7c and two ferrites 11 arranged radially, and a pan temperature detecting device 18 is installed under the sensor field tube 19.

  The infrared ray from the bottom of the induction-heated pan is transmitted through the infrared transmission window 5 of the top plate 2 and enters the thermopile 25 built in the pan temperature detection device 18 which will be described in detail later from the sensor field tube 19.

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

  As described with reference to FIGS. 4 and 5, the pan temperature detecting device 18 is provided in the coil gap 7c at a position distant from the high voltage terminal 21b connected to the high voltage output line 22b. The case window 30 is installed under the sensor field tube 19 that has been set.

  A detailed perspective view of the pan temperature detection device 18 is shown in FIG. The pan temperature detection device 18 is configured around a thermopile 25 which is an infrared detection sensor and a reflection type photo interrupter 26. The thermopile 25 and the reflective photointerrupter 26 are electronic circuit boards on which a thermopile temperature detection circuit 72 (to be described later in detail) for amplifying the output signal of the thermopile and a reflectance detection circuit 73 (to be described later in detail) are mounted. The thermopile 25 is provided with a reflector 28 formed of a plastic member. The thermopile 25 and the reflective photointerrupter 26 and the electronic circuit board 27 are entirely sealed in an infrared sensor case 29 (shown by an alternate long and short dash line) of a plastic member. A case window 30 is opened in the infrared sensor case 29 in order to transmit infrared light, and the case window 30 has almost the same optical characteristics as the top plate 2 (however, as shown in FIG. A thin glass having a characteristic substantially the same as that of the case window 30 is fitted as an optical filter 31. In the present embodiment, the glass of the case window 30 is described using non-crystallized glass, but the invention is not limited to this and crystallized glass may be used. In addition, it is desirable for the case window 30 to use an optical characteristic that has a lower visible light transmittance than the top plate 2 in order to cut visible light as well.

  A thermopile 25 and a reflective photointerrupter 26 are mounted on the electronic circuit board 27. The thermopile 25 has a reflector 28 mounted under the optical filter 31. 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 former case window 30 is open. Furthermore, the aluminum metal case 32 is covered with an outer infrared sensor case 33 of a plastic member. Naturally, the former case window 30 is open. That is, the thermopile 25 is covered with a triple case.

  Then, the pan temperature detection device 18 is installed in the coil top surface cooling air path 15 a so that the case window 30 views the inside of the sensor field tube 19 of the coil base 10.

  FIG. 7A shows a cross-sectional view along the line A-A '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 mounted thereon, and the electronic circuit board 27 of the thermopile 25. On the inner surface of the reflector 28 mounted on the thermopile 25, a part of an elliptical curved surface 28a connecting one focal point is formed on the infrared absorbing film in the thermopile 25. The elliptical curved surface 28a is a mirror surface of the aluminum vapor deposition film 28b. Therefore, as shown by the alternate long and short dash line in the drawing, the infrared light transmitted through the optical filter 31 disposed in the case window 30 is reflected by the elliptical curved surface which is this mirror surface, and condensed on the infrared absorbing film through the optical filter 48 of the thermopile 25 described later. Do. The metal pins (connection terminals) 46 of the thermopile 25 are soldered to the pattern of the electronic circuit board 27.

  FIG. 7 (b) also shows a cross-sectional view taken along the line B-B 'in FIG. This is a cross-sectional view showing the positional relationship between the thermopile 25 and reflective photointerrupter 26 mounted on the electronic circuit board 27 installed in the infrared sensor case 29, and the case window 30 of the infrared sensor case 29, and the optical filter 31. is there.

  The details of the thermopile 25 are shown in FIG. FIG. 8 (a) is a cross-sectional view of the thermopile 25, and FIG. 8 (b) is a plan view of a cross-section taken along line CC 'in FIG. 8 (a). The infrared absorbing film is shown omitted so that the thermocouple can be seen.

  The thermopile 25 is obtained by connecting a large number of thermocouples (thermocouples) in tandem (piling), and is incorporated in a metal case 37 composed 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 a silicon substrate 38 about 300 μm thick to electrically and thermally insulate, polysilicon and aluminum are sequentially pattern-deposited thereon, and a polysilicon deposition film 40 and an aluminum deposition film 41 are formed. Create many thermocouples and connect them in cascade. An infrared absorbing film 43 such as a rubidium oxide film close to a black body is formed in the central portion of the silicon base 38 having polysilicon, aluminum junctions (temperature measurement contacts). One end of the polysilicon and aluminum deposited film is a cold contact 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 silicon substrate having the temperature measurement contact portion is formed to a thickness of 10 μm. This is to reduce the thermal conduction between the temperature measurement contact portion 42 and the cold contact portion 44 and to thermally insulate the temperature measurement contact portion from the cold contact portion by thinning silicon having good thermal conductivity.

  The silicon base 38 is fixed to the metal stem 36 of the metal case 37 by bonding or the like. At the same time, an NTC thermistor 45 film-formed on the ceramic is similarly disposed on the metal stem 36. This is to detect the ambient temperature of the thermocouple in the metal case 37 and correct the thermoelectromotive force of the thermocouple. Details will be described later. In the metal stem 36, four metal pins 46 which are insulated and sealed are penetrated, and the output of the previous thermocouple and the NTC thermistor 45 are wire connected to the metal pins. A cylindrical metal can 35 is covered and welded to the stem 36 in an inert gas. A small hole window 47 is opened on the top surface of the metal can 35, and an optical filter 48 (a member transmitting a light beam in a certain wavelength range) is attached thereto from the inside. The silicon substrate 38 is fixed so that the above-mentioned temperature measurement contact portion 42 (under the infrared absorption film 43) is positioned vertically below the small hole.

  The thermocouple measuring temperature contact portion 42 (under the infrared absorbing film 43) in the thermopile 25 is heated by the infrared ray passing through the window 46 of this small hole, and the heating temperature rise is proportional to the infrared energy passing through. A voltage proportional to the temperature difference between the pair of cold junctions 44 and the temperature measurement junction 42 is output to the metal pin 46 of the thermocouple output.

  The details of the reflective photointerrupter 26 are shown in FIG. The reflection type photointerrupter 26 is formed by arranging and molding the infrared LED 50 as an infrared light emitting element and the infrared phototransistor 51 as an infrared light receiving element on the same plastic member. A lens made of plastic is formed on the light emitting surface of the infrared LED, and a thin beam emits infrared light near 930 nm upward. A lens is made of a visible light blocking plastic on the light receiving surface of the infrared phototransistor 51, and the reflected infrared light of the object (the bottom of the pan) of the previous irradiation infrared light is received at a narrow viewing angle, and the amount of light received Output a current proportional to The reflection type photo interrupter 26 is composed of a pair of infrared light emitting element and light receiving element, and measures the reflectance of the bottom surface of the cooking pot 6 placed on the top plate 2.

  The control block diagram of the induction heating cooker of a present Example is shown in FIG. A microcomputer 60 controls the operation of the induction heating cooker. In the following, the symbol R represents the block relating to the induction heating port in the front right of FIG. 1 and the symbol L represents the block relating to the induction heating port in the front left of 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 operating frequency is changed because 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 than this. The frequency switching is performed by the microcomputer 60 controlling the frequency control circuit based on the judgment of the pan type judging means (not shown).

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

  The operation switch 68 of the operation display unit 3 and the display circuit 69 are connected to the microcomputer 60, and the operation instruction of the user is received to display the operation state of the device. In addition, the buzzer 70 is connected to notify the user of a push on the operation button or a warning such as an error. The microcomputer 60 controls the frequency control circuits 61R, 61L, the power control circuits 62R, 62L and the radiant heater circuit 67 to heat the cooking pot 6 on the top plate 2 according to the instruction of the user.

  The thermopile 25 is connected to the thermopile temperature detection circuit 72, the output is amplified, and is 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 pot 6 is received by the light receiving element, and the output signal Is amplified and input to the AD terminal of the microcomputer 60. The details of the operation of the thermopile temperature detection circuit 72 and the reflectance detection circuit 73 will be described later. Further, the thermistor 21 is connected to the thermistor temperature detection circuit 74, and the output is also input to the AD terminal of the microcomputer 60.

  The microcomputer 60 obtains the infrared reflectance of the cooking pot from the output of the reflectance detection circuit 73, corrects the output of the thermopile temperature detection circuit 72 with the reflectance, and detects the temperature of the cooking pot. Then, heating of the cooking pot 6 is controlled via the power control circuit 62.

  The details of the thermopile temperature detection circuit 72 are shown in FIG. The thermocouple output (thermoelectromotive force) (voltage between (+) and (-) symbols in the figure) of the thermopile 25 is amplified by about 2000 times by the operational amplifier 72-1 and 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) to 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) in which the circuit power supply voltage is divided by the resistors 72-5, 72-2, 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 resistive element having a negative temperature characteristic, and its resistance value decreases with an increase in temperature. Therefore, when the temperature in the thermopile 25 rises, the voltage at the connection point a increases. The thermocouple output (voltage between (+) and (-) symbols in the figure) is proportional to the temperature difference between the temperature measurement contact 42 (point heated by infrared energy) and the cold junction (thermocouple output terminal) 44. Therefore, when the temperature in the metal case 37 (in which the NTC thermistor is incorporated) rises at the ambient temperature at which the thermopile 25 is installed, the thermocouple output decreases. This decrease is compensated by the voltage rise at node a. That is, the NTC thermistor 45 is used to prevent the output of the thermopile (thermocouple) 25 from changing at ambient temperature. A resistor 72-9 (= R3) and three diodes 72-10 connected in series are connected in parallel to the resistor 72-4 (= R2) which determines the amplification degree. This is to reduce the amplification degree when the output voltage of the operational amplifier exceeds the forward voltage (about 0.6 V) of the diode by three of 1.8 V. Although the amplification degree is R2 / R1 up to 1.8 V, the amplification degree becomes (R2 // R3) / R1 beyond this. This expands the pan temperature detection range of the thermopile as described later. Without this, the thermopile output is proportional to the 4th power of the pan bottom temperature, and the output increases rapidly at high temperature, and the pan bottom temperature saturates at 300 ° C and the circuit output voltage saturates at 5 V, but in some cases up to 400 ° C You can try not to saturate.

  The detail of the reflectance detection circuit 73 is shown using FIG. 12 and FIG. In FIG. 12, reference numeral 50 denotes an infrared LED which is a light emitting element, and its emission wavelength is, for example, 930 nm. An infrared phototransistor 51 has, for example, a peak sensitivity wavelength of 800 nm and an emission wavelength of 930 nm of the infrared LED 50 and has sensitivity of 80% of the peak sensitivity. 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 reflection type photo interrupter 26 is driven by the 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. 13 (a) 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 5 V and turns off when the signal is 0 V. The 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 of the cooking pot and received by the infrared phototransistor 51 which is a light receiving element, a voltage is generated in the resistor 73-4 by the photocurrent. This voltage is shown in FIG. 13 (b). If the reflection is large (the amount of received light is large), the voltage increases in proportion. This signal voltage is cut off by the capacitor 73-5 as a direct current component, and is input as an alternating current signal (shown in FIG. 13C) to a non-inverted direct current amplifier including an operational amplifier 73-6. Here, only the positive side component of the AC signal is amplified. This is shown in FIG. The amplified 50% duty signal is converted to a DC average value 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.

  Thus, the reflectance detection circuit 73 emits carrier-modulated infrared light with constant emission intensity to the bottom of the pan, receives the infrared light reflected by the pan, and obtains the average voltage as a reflected voltage. Detects the value corresponding to the reflectance. Carrier modulation of infrared light emission and cutting of DC component in the light receiving path prevent infrared light contained in lighting equipment such as natural light or incandescent light and fluorescent light from affecting the reflectance detection of the pan In order to Further, the influence of the dark current of the infrared phototransistor 51 is also prevented.

  The operation of the first embodiment will be described below.

The cooking pot 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 ; Stephan-Boltzmann's Law) FIG. 14 shows the spectral radiation energy of black body temperature calculated from Planck's distribution law. If this spectral radiation energy is integrated over the entire wavelength range, the total radiation energy E is obtained, which is proportional to the fourth power of the temperature (absolute temperature). This is the aforementioned Stefan-Boltzmann's law, and this coefficient σ is the Stefan-Boltzmann coefficient. The peak wavelength of the spectral radiation energy is 5 μm to 8 μm at a cooking temperature of 100 to 300 ° C. according to the Vienna transition law.

The induction-heated pan bottom releases total radiant energy according to the temperature, which is the total radiant energy E at black body temperature multiplied by the pan bottom emissivity ε. 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 the nonmagnetic glass (top plate 2) which is a nonmagnetic material are shown by a solid line in FIG. As shown by the solid line in FIG. 15, the non-crystallized glass transmits 80% or more of light with a wavelength of 0.4 μm to 2.5 μm, transmits about 25% of light with a wavelength of 3 to 4 μm, and is more than 4 μm It hardly transmits light of long wavelength and wavelength shorter than 0.4 μm. Most of the infrared radiation energy (see FIG. 14) emitted from the pan (mostly having a wavelength of 4 μm or more) can not pass through the top plate 2 because of this optical property. What can pass through is about 1% of the total infrared radiation energy emitted from the pan.

  As an infrared sensor, as well known, there are a quantum type such as an infrared photodiode and an infrared phototransistor, and a thermal type such as a thermopile and a pyroelectric element. The quantum sensor has high sensitivity in a narrow wavelength band because it detects infrared light by quantum effect, and the thermal sensor is characterized by having low sensitivity in a wide wavelength band. For quantum type, the sensitivity wavelength is determined by the type of semiconductor, and for silicon that can be purchased inexpensively, the practical sensitivity wavelength is outside the visible light (0.8 μm) to 1 μm or less, so the detection temperature range is 300 ° C or more Become. On the other hand, the thermal type has uniform 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 dependency). Therefore, an optical filter is provided in front of the infrared light receiving surface to the sensor to narrow the wavelength of the detected temperature range and prevent disturbance.

  In the present embodiment, since the cooking temperature range is 100 to 250 ° C., a thermopile which is a thermal type 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 light incidence, and a mechanical chopper mechanism is usually used. For this reason, it is unsuitable to use for household appliances, such as an induction heating cooker, in terms of reliability. Thermopile, on the other hand, does not require such a mechanism, and in recent years, it has been inexpensively supplied that its sensitivity has been improved by miniaturizing and piling many thermocouples configured using semiconductor processes by techniques such as MEMS etc. .

  As an optical filter of a thermopile used for many thermometers in recent years, a thing with a transmission wavelength of 1-15 micrometers is used. This is because the peak wavelength of infrared radiation energy of the human body is about 10 μm (body temperature 36 ° C.) according to the Vienna transition law, and it is optimal to use the above optical filter.

  When the temperature (25 to 300 ° C.) of the cooking pot is measured in a noncontact manner using the thermopile having the optical filter, an output indicated by an alternate long and short dash line in FIG. 16 is obtained as an output of the thermopile. This is obtained by assuming that the bottom surface of the cooking pan is a black body as described above, and the infrared energy (according to Planck's distribution law) emitted by this is converted to a voltage by the sensitivity of the thermopile and amplified as predetermined. At this time, it is assumed that the sensitivity of the thermopile is a constant value of 1 to 15 .mu.m, and infrared rays of 1 to 15 .mu.m uniformly pass through the optical filter by 90% and enter the thermopile.

  When this thermopile is used for pan temperature detection in the configuration of FIG. 3, infrared rays from the pan bottom penetrate the top plate 2 and enter the thermopile 25. Therefore, the infrared rays of each wavelength transmitted by the optical characteristics of the top plate 2 (solid line in FIG. 15) are limited. As described above, infrared rays of about 4 μm or more hardly transmit and do not enter the thermopile 25. If the output in this case is calculated in the same manner as described above, it becomes as shown by a solid line in FIG. It can be seen that the output drops by about one digit. For this reason, it is necessary to DC amplify the output of the thermopile 25 at an amplification degree which is about one digit higher than the amplification degree of a DC amplifier used in a conventional thermometer or the like.

  As described above, the thermopile is a stack of many thermocouples (thermocouples) (connected in series) (piled). If the thermoelectromotive force of one thermocouple is set to Ei volt / ° C. and N pieces are connected, the thermopile V of the thermopile becomes N · Ei volt / ° C. That is, the thermocouple output of the pile number N is N · Ei volt / ° C. If a thermopile practically used with an amplification degree of about 1000 times as in the thermometer described above is used for an induction heating cooker, the amplification degree of 10000 times is required due to the influence of the top plate described above. In general, in a DC amplifier, an amplification degree of about 1000 is said to be a limit due to temperature drift of the offset voltage. Therefore, in the thermopile used for the induction heating cooker, the number of piles is increased from several tens to several hundreds. In other words, sensitivity is increased by increasing the number of piles compared to general thermopiles.

  A thermocouple metal pair commonly used in thermopiles is polysilicon aluminum which can be relatively easily fabricated in a semiconductor process as described in FIG. 8, and its thermoelectromotive force is about 10 μV / ° C. As the thermopile used in the electromagnetic cooker, one in which this is deposited to 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 measurement contact is brought into contact with the object for measurement. The thermopile, as described in FIG. 8, has a large number of thermocouples deposited, and is composed of a large number of temperature measuring contacts heated by incident infrared rays and a large number of cold contacts on a silicon substrate 38. Since the cold junction is fixed to the metal stem 36 of the metal case 37 by bonding, the metal case 37 (the metal can 35 and the metal stem 36) of the thermopile thermally serves as a cold junction. And this metal case 37 can not be fixed to the 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 degree of the DC amplifier is 1000, when the temperature of the metal case 37 changes by 1 ° C., the output of the DC amplifier fluctuates by 500 mV. That is, it is necessary to suppress temperature fluctuations around the thermopile 25.

  The pan temperature detection device 18 of this 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 strongest in order to detect the pan bottom high temperature portion during cooking. Ru. This position is between the rod-like ferrites 11 radially disposed under the heating coil 7 and is a place where little magnetic flux leaks because magnetic flux mostly passes through the ferrite. However, since the distance from the lower surface of the heating coil 7 is about 20 mm, the leakage flux is large, and the temperature of the metal located there is increased by induction heating. For example, when induction heating is performed on a pan, which is a cooking vessel placed on the top plate 2 by inputting a high frequency power of 3 kW into the heating coil, the temperature of the magnetic steel plate at this place also rises by about 30 ° C. . Even non-magnetic aluminum raises the temperature by about 5 ° C.

  During cooking, the pan bottom which is inductively heated reaches a high temperature of 100 to 300 ° C. And the heating coil 7 of the top plate 2 and the lower surface also becomes high temperature by heat conduction and heat radiation from the pan bottom.

  Further, since a high frequency current of a few tens of amperes flows in 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 delivery hole 15b, and the heating coil 7 is cooled by blowing air as described above.

  Further, an inverter circuit 8 for supplying high frequency power to the heating coil is disposed in the cooling air paths 17a and 17b under the position where the pan temperature detection device 18 is disposed. This inverter circuit is composed of a circuit that switches a current of 20 to 90 kHz and a few tens of amperes. For this reason, it radiates a large electromagnetic wave.

  Thus, the pan temperature detection device 18, particularly the built-in thermopile 25, (1) leakage flux from the heating coil 7, (2) temperature change due to cooling air for coil cooling, (3) radiation from the inverter circuit Be exposed to electromagnetic noise. In response to these disturbances, the pan temperature detection device 18 must detect the pan bottom high temperature portion during cooking.

  As described above for the operation of the thermopile temperature detection circuit 72, temperature compensation is performed on the circuit using the built-in NTC thermistor 45 so that the output of the thermopile 25 does not change due to the ambient temperature. However, since the NTC thermistor 45 is formed of a thin film on a ceramic chip and is fixed to the metal stem 36 by bonding or the like, the temperature of the metal stem 36 or metal case 37 which is thermally equivalent to a cold junction It is difficult to keep up with changes and time delays occur. In addition, it is difficult to accurately compensate the temperature over a wide temperature range because of the non-linearity of the temperature resistance characteristic. In these points, it is difficult to perform sufficient temperature compensation in the above-mentioned circuit immediately in response to changes in the ambient temperature of the thermopile 25. Specifically, although a temperature change of about 1 ° C./10 minutes can be coped with, it is difficult to follow a 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 cooking. If the pan temperature detection device 18 and the surrounding ambient temperature rise to some extent at the previous cooking, then the pan temperature detection device 18 will be cooled rapidly (at 1 ° C./1 min or more) at this time .

  It is desirable that the pan temperature detection device 18 in which the thermopile 25 is built be kept at a constant temperature atmosphere as much as possible. Therefore, in the present embodiment, the pan temperature detection device 18 is installed in the coil upper surface cooling air path 15a into which the outside air is introduced, and the thermopile 25 and the thermopile temperature detection circuit 72 are cooled by the outside air during cooking. To prevent. In addition, the infrared sensor case 29, which is a windproof case, is used to prevent air flow in the coil upper surface cooling air path 15a from directly hitting the semiconductors and resistance of the metal case 37 of the thermopile 25 and the thermopile temperature detection circuit 72 and resistance. I'm covering this. Further, the thermopile 25 and the thermopile temperature detection circuit 72 are also thermally insulated by the air in the infrared sensor case 29. After the output of the thermopile 25 is DC amplified stably with respect to temperature change, it is output to the AD terminal of the microcomputer 60 described later as a signal voltage of low output impedance.

  Further, the infrared sensor case 29 is covered with a metal case 32 having a permeability of approximately 1 such as aluminum, and the AC case generated by the heating coil is shielded to thereby cause the metal case 37 of the thermopile 25 to generate a high frequency generated by the heating coil 7. The induction heating is performed by an alternating magnetic field so that the temperature does not rise. 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 inductively heated during cooking by the ambient atmosphere temperature and the leakage flux from the heating coil 7, and in the case of aluminum, the temperature rises by 5 to 10 ° C. If cooking is continued before this temperature rise stops, external air is introduced rapidly and applied to the metal case 32. As a result, the metal case 32 cools rapidly, and as a result, the ambient temperature of the thermopile 25 in the infrared sensor case 29 suddenly It will decline. In the opposite case, for example, when cooking is performed first in the winter morning, the metal case 32 in the machine is sufficiently cooled at night and at approximately 5 ° C., and the user starts cooking in the cooking chamber heated to 20 ° C. In this case, the warm air is introduced into the coil top surface cooling air path 15a, and the warm air of 20.degree. C. is applied to the metal case 37 of 5.degree. In the present embodiment, in order to prevent such a rapid temperature change of the metal case 32 due to the outside air, the metal case 32 is further covered with an infrared sensor case 33 at the outside of plastic. As a result, the temperature change due to the wind is prevented without directly applying the cooling air to the metal case 32.

  Now, the top plate 2 is heated by absorbing infrared radiation from the induction heated cooking pot 6 and by contact heat conduction. As shown by the solid line in FIG. 15, the top plate 2 transmits 80% or more of light with a wavelength of 0.4 μm to 2.5 μm, transmits about 25% of light with a wavelength of 3 to 4 μm, and has a wavelength longer than 4 μm , And hardly transmit light of wavelengths shorter than 0.4 μm.

  When radiant energy is incident on the surface of the material, a portion は is reflected, a portion α is absorbed, and the remaining τ is transmitted. Among these quantities, ρ + α + τ = 1 holds from the energy conservation law. In the state where the cooking pot 6 is placed on the top plate 2, the reflection of the infrared radiation energy of the cooking pot 6 on the top plate 2 can be regarded as almost zero, so the absorption coefficient α + transmittance τ = 1 is established in the top plate 2 It is good to see that you are doing. According to Kirchhoff's law, since the absorptivity α = emissivity ε, the top plate 2 transmits 80% or more of the infrared radiation energy from the cooking pot 6 at a wavelength of 0.4 μm to 2.5 μm, and the remaining 20% Absorb and radiate it. Also, at a wavelength of 3 to 4 μm, it transmits about 25%, absorbs the remaining 75% and emits it. It hardly transmits at wavelengths longer than 4 μm and wavelengths shorter than 0.4 μm, and absorbs and emits all. The same applies to the portion heated by heat conduction. When the wavelength is 4 μm or more, almost all infrared energy of heat conduction heating is emitted from the top plate 2 surface.

  For this reason, when detecting the temperature of the cooking pot 6 on the top plate 2 using the thermopile 25, an infrared ray with a wavelength of 4 μm or more emitted by the heating of the top plate 2 itself becomes a problem. 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 the infrared radiation of a wavelength longer than 4 μm emitted by the top plate 2. The temperature at the bottom of the pot can not be detected accurately. The radiant infrared energy of the pan transmitted through the top plate 2 is about 1.5 μm in the range of 1 μm to 2.5 μm, whereas the infrared energy emitted by the top plate 2 itself is about 11 μm in the range of 4 μm to 15 μm. Of the thermopile output, if the temperature is five times the temperature of the cooking pot 6, the temperature depends on the temperature of the top plate 2.

  In the present embodiment, a case window 30 for transmitting infrared rays is opened in the infrared sensor case 29 of the pan temperature detection device 18 configured of the thermopile 25 to prevent the above, and the top plate 2 is configured in the case window 30. The thin film of the non-crystallized glass is fitted as an optical filter 31. And the part which the top plate 2 of the infrared rays which injects into the thermopile 25 radiates is removed. The portion of the top plate that emits at a wavelength of 2.5 μm or more is prevented from entering the thermopile 25 by the optical characteristics of the optical filter 31 having the same transmission characteristics as the top plate 2.

  The optical filter 31 may be made of a material other than the top plate, or may be one that imparts the visible light cut effect with an optical characteristic having a transmittance of 700 nm or less lower than that of the top plate 2.

  Furthermore, the optical filter 48 of the thermopile 25 transmits infrared light from the pan that has been transmitted through the top plate 2 and the optical filter 31, and the transmittance of 1 μm or less in wavelength is an optical characteristic having a lower transmittance than the top plate 2. This is because it is necessary to prevent infrared rays from the pan that has been transmitted through the top plate 2 from entering the infrared absorbing film 43 of the thermopile and from causing visible light to enter the infrared absorbing film 43. Thereby, the output change of the thermopile by visible light can be reduced, and the detection error of the pan temperature can be reduced.

Assuming that the optical filter 31 itself and the infrared sensor case 29 have a temperature of 70 ° C., the voltage output from the thermopile 25 by the infrared rays emitted by this is calculated as shown by A in FIG. Here, the optical filter 48 of the thermopile 25 transmits 90% of a wavelength of 1 to 15 μm. This voltage is substantially the same as the voltage output by 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 4 μm or less, the pan temperature on the top plate 2 can not be detected in the atmosphere where the pan temperature detection device 18 is 70 ° C. or higher.

  Also for the above reason, the pan temperature detection device 18 is installed in the coil top surface cooling air passage 15a in the present embodiment.

  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 induction heating is performed in the templar pan having the pan bottom near black body 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 rises, and the circuit output is saturated to the power supply voltage 5V. It is the circuit of the diode 72-10 and the resistor 72-9 that prevents this. The circuit can expand the temperature range that can be detected by decreasing the amplification degree of the operational amplifier 72-1 from the vicinity where the output exceeds 1.8 V and preventing the output from saturating to 400 ° C as shown by the solid line in the figure. There is.

  The voltage is approximately 0.5 V from normal temperature to 100 ° C. When the temperature exceeds 100 ° C., a voltage proportional to the temperature is output. 0.5 V is a voltage obtained by dividing the power supply voltage (5 V) of the thermopile temperature detection circuit 72 by resistors 72-5, 72-2, and 72-7 (indicated by a point in FIG. 11) 0.5 V is the operational amplifier 72-1. It is because it is given as a bias voltage of When the temperature exceeds 100 ° C., the output voltage of the thermopile 25 becomes large and is amplified about 2000 times by the operational amplifier 72-1 and observed as a voltage of 0.5 V or more. This bias voltage is provided for detecting a fault in the thermopile temperature detection circuit 72. A value (voltage increase value from 0.5 V) obtained by subtracting 0.5 V from the output voltage value of the output terminal 72-2 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, but a pan temperature detection voltage Vt (= V-0.5) which is a value obtained by subtracting 0.5 V from this voltage Based on the pot temperature. The relationship in FIG. 17 is stored in advance as table data in the ROM of the microcomputer 60.

  When the reflection type photo interrupter 26 built in the pan temperature detection device 18 is arranged as shown in FIG. 3, when there is no cooking pan on the top plate 2, most of the infrared light (wavelength 930 nm) emitted by the infrared LED 50 is The light passes through the optical filter 31 and the top plate 2 and does not return to the infrared phototransistor 51. However, a part is reflected by the optical filter 31 and the top plate 2. This is because the transmittance of the 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, in the present embodiment, as shown in FIG. 3, the front surface of the reflective photointerrupter 26 is disposed so that the front surface of the reflective photointerrupter 26 is in contact with the lower surface of the optical filter 31 since The reflected light is prevented from entering the infrared phototransistor 51. Further, because of the radiation angle of the infrared LED, there is also infrared light reflected by an object (inside of the sensor field tube 19) which does not reach the lower surface of the top plate and is on the way.

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

  The reflectance detection circuit 73 is arranged as shown in FIG. 3, and the reflection voltage Vr and the 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 of is shown in FIG. An approximate line is also shown in the figure. Using this relationship, the reflectance can be obtained from the output voltage of the reflectance detection circuit 73. Then, the relationship is stored in table data or the coefficient value of the approximate expression is stored in advance in the ROM of the microcomputer 60.

In metallic materials such as cooking pots, the relationship of ε + = 1 = 1 is established between the emissivity ε of infrared energy (E = εσT ⁴ ) radiated from the surface of the material at temperature T by the Kirchhoff law and the reflectance ρ of the surface. Do. In the cooking pot (transmittance α = 0), the infrared energy to be radiated is different while maintaining the same pot bottom temperature due to the difference in the emissivity. For this reason, the problem that the thermopile output, ie, the output of the pan temperature detection apparatus 18 differs may arise. Therefore, it is necessary to detect the reflectance of the bottom of the cooking pan to obtain the emissivity and correct the output of the pan temperature detection device 18 before converting it into temperature. In order to do this, it is the reflectance detection circuit 73 that obtains the reflection voltage Vr, which is an amount corresponding to the reflectance described above, and obtains the reflectance therefrom. This reflectance is subtracted from 1 to obtain the emissivity.

In FIG. 20, for several kinds of pots placed on the top plate 2, a value Vt obtained by subtracting the offset voltage Vo of 0.5 V described above from the output of the pot temperature detection device 18 (output V of the thermopile temperature detection circuit 72) An example of the relationship between a temperature detection voltage) and the pan bottom temperature T is shown. The emissivity of each pan bottom 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 detection device 18 and the pan bottom temperature differs depending on the emissivity. The pan shown in (a) of FIG. 20 has an emissivity of 0.9, which is close to a black body. In (b), the emissivity is 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 understood 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⁾ It means that. And if the emissivity of each pot is known, it means that the pot temperature of each pot can be reduced to the radiation temperature of the black body. For example, a black body is disposed on the top plate in the embodiment of FIG. 3, and a pan temperature detection voltage Vt which 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 determined. The relationship between V.sub.t and V.sub.t is recorded, and this is stored in advance in the ROM of the microcomputer 60 as table data or as a coefficient value of an approximate expression. Then, when induction heating is performed on the pan, the output V of the pan temperature detection device 18 is AD converted and read every certain time, and the pan temperature detection voltage Vt = V−0.5 is calculated, and then the reflectance is measured. The reflectance is obtained by the detection circuit 73 as described above, and based on this reflectance ρ, the emissivity ε is obtained from Kirchhoff's law (ρ + ε = 1), and the pan temperature detection voltage Vt is divided by this, The table data is checked by the value or substituted into an approximate expression to obtain the temperature T from the pan temperature detection voltage Vt, which is defined as a 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 using the reflectance detection circuit 73 in FIG. 3 (approximating the approximate expression of the relationship in FIG. 19). Although some pots deviate from Kirchhoff's law, there is a strong correlation between emissivity and reflectance. The reason for deviation from the Kirchhoff's law is that in the detection of the reflectance, not all the reflected infrared light is received due to the scattering on the pan surface. When the reflectance is to be determined, it is desirable that the emitted light of the infrared LED 50 be incident as vertically as possible on the top plate 2 and the reflected light from the pan be guided to the infrared phototransistor 51 as vertically as possible. In the present embodiment, the visual field surface of the thermopile 25 on the top plate 2 in the pan temperature detection device 18 and the reflection surface on the top plate 2 of this reflectance detection light emission are the same surface. For this reason, as shown in FIG. 3, the thermopile 25 and the reflection type photo interrupter 26 are arranged side by side in the pan temperature detection device 18.

  Hereinafter, the operation of the present embodiment will be described as a case where the cooking pot 6 is placed on the circle display 4 on the front right side and the cooking pot is heated at a predetermined temperature for a predetermined time to perform cooking. FIG. 22 shows a flowchart of this operation. The power supply (not shown) is turned on, and a predetermined temperature and cooking time are set by the operation switch of the induction heating port on which the cooking pot 6 is placed (step S1). When start of cooking is instructed (step S2), the microcomputer 60 first The reflectance detection circuit 73 is controlled to take in the reflection data (corresponding to the reflectance) of the placed pan and detect the reflectance (step S3). At the same time, in order to cool the heating coil 7 and the inverter circuit 8 etc., 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 delivery hole 15b.

  Step S3 of detecting the reflectance will be described in detail using the flowchart shown in FIG. The microcomputer 60 outputs the infrared LED drive signal of FIG. 13A from the port to the terminal 73-2 of the reflectance detection circuit 73 (step S3-1). After outputting for a predetermined time, for example, 200 ms (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 voltage V1 when the pot stored in advance is not placed is calculated from the voltage V2 read in advance (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).

  Following 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 generated from the heating coil 7, and the cooking pot 6 on the top plate 2 is inductively heated. The induction heating causes the temperature of the cooking pot 6 to rise, and the cooking of the heating target in the cooking pot 6 is started. When the induction heating is started, the microcomputer 60 reads the output of the pan temperature detecting device 18 every predetermined time to detect the pan temperature (step S5).

  Here, the pan temperature detection operation (step S5) will be described in detail. FIG. 24 shows a flow chart of 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 0.5 V from this value, and sets this as the pan temperature detection voltage Vt (step S5). 2). Then, an emissivity (= 1−reflectance) is obtained from the reflectance detected immediately before induction heating (step S5-3), and the pan temperature detection voltage Vt is divided (step S5-4). A data table, which is a relationship between Tt and Vt stored in advance, is drawn using Vt after division (step S5-5), converted to temperature T, and pan temperature T is output (step S5-6).

  Instead of calculating the emissivity (step S5-3) and dividing the pan temperature detection voltage Vt by the emissivity (step S5-4), the magnification a = 1 / the emissivity (a = 1/1) in advance. 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, and the magnification a is obtained from the table from the reflectance (or reflection voltage Vr), pan temperature detection 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. By doing this, it is possible to speed up the processing without using division which requires 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 reduce the current supplied to the heating coil 7 by a predetermined amount (step S7). Then, the cooking time timer is started (step S8). The electric current supplied to the heating coil 7 is increased or decreased by a predetermined amount (steps S11 and S12) while the pan temperature detection (step S9) for each constant time is continued (step S10), and the pan temperature is kept constant (Tc). Then, when a predetermined cooking time has elapsed (step S13), the user is notified of the completion of cooking by a buzzer and power supply to the heating coil 7 is stopped (step S14). Thus, the material to be cooked in the cooking pot 6 is cooked at the set temperature and time.

  In the above description, an example is shown in which the reflectance detection is performed only once immediately before induction heating, but the present invention is not limited to this. In a conventional pot, the reflectance does not change during induction heating (even when the temperature becomes high). In addition, the infrared light emitting LED has a lifetime problem in continuous light emission for a long time. In this description, in consideration of these points, the present invention is limited to one reflectance detection immediately before induction heating per cooking. Naturally, the light emission current may be reduced and reflectance detection may be performed at a constant cycle during cooking. Especially in a thin pot, the reflectance may change due to the pot bottom deformation due to high temperature. Furthermore, in a pot with color coating applied to the bottom, the coating may be denatured at high temperature and the reflectance may change. In this case, it is desirable to perform reflectance detection periodically even during heating. In this case, of course, in order to avoid the influence of the magnetic field, it is desirable to surround the reflective photointerrupter 26 and the reflectance detection circuit 73 with a nonmagnetic metal body as in the embodiment.

  Also, during cooking, the pot may be replaced with another pot. At this time, the reflectance naturally changes. In this case, the voltage detected by the pan temperature detector 18 drops sharply when the existing pan is withdrawn. And when another temperature pot is placed, the voltage detected by the pot temperature detection device 18 returns to the value corresponding to the bottom surface temperature of the pot. It is desirable to detect this change and detect the reflectance again.

    Then, Example 2 is demonstrated using FIGS. 25-29. Descriptions of parts in common with the configuration of the first embodiment will be omitted.

  In the thermopile 25 described with reference to FIG. 8, the optical filter 48 is disposed in the window 47 of the small hole through which the infrared rays pass, and the optical filter itself does not have a condensing action. Was. In the induction heating cooker of the second embodiment, a thermopile 25 shown in FIG. 25 is used in place of the thermopile 25 described in FIG. In FIG. 25, the same reference numerals as in FIG. 8 denote the same components. In the thermopile 25 shown in FIG. 25, a convex lens 49 is disposed in a window 47 of a small hole, instead of the optical filter 48 described in FIG. The convex lens 49 of the thermopile 25 transmits infrared light from the pan that has been transmitted through the top plate 2 and the optical filter 31, and the transmittance at a wavelength of 1 μm or less is an optical characteristic whose transmittance is lower than that of the top plate 2.

  The convex lens 49 is designed such that the visual field range of the infrared transmitting window 5 is focused on the infrared absorbing film 43. Therefore, the metal can 35 is taller than that of FIG. FIG. 26 shows how the heat sink 55 is attached to the thermopile 25. As shown in FIG. 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. Therefore, the heat sink 55 is mounted as a thermal buffer (increases the thermal capacity) to reduce the output fluctuation with respect to the ambient temperature change. FIG. 27 shows the thermopile 25 mounted on the electronic circuit board 27 together with the reflective photointerrupter 26. As shown in FIG.

The pan temperature detection apparatus 18 of Example 2 is shown in FIG. The same reference numerals as in FIGS. 6, 7 and 9 denote the same components. In the second embodiment, the heat sink 5 is mounted in the infrared sensor case 29 of the pan temperature detection device 18.
The thermopile 25 and the reflection type photointerrupter 26 shown in FIG. As shown in FIG. 28A, the thermopile 25 and the reflection type photointerrupter 26 mounted upward on the electronic circuit board 27 are disposed with the front surface (infrared receiving surface) directly below the optical filter 31 and in the infrared sensor case 29. Sealed. The infrared sensor case 29 is covered with an aluminum metal case 32 that shields the AC magnetic flux from the heating coil 7 and the electromagnetic wave from the inverter circuit 8, and heat insulation is provided internally to prevent a rapid temperature change due to the cooling air of the aluminum metal case 32. It is covered by an outer side infrared sensor case 33 including the material 34. The difference from the triple-layer structure of the first embodiment is that the heat insulating material 34 is incorporated inside the outer side infrared sensor case 33. This is for the purpose of reducing the temperature change around the thermopile 25 more firmly than in the first embodiment and stabilizing the temperature detection of the pan bottom.

  FIG. 28 (b) shows a cross-sectional view along the line B-B 'in (a). This shows how the thermopile 25 installed in the infrared sensor case 29, the heat sink 55 attached thereto, and the reflective photointerrupter 26 are mounted on the electronic circuit board 27.

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

  The infrared emission of the infrared LED 50 passes through the optical filter 31 by 85% or more, but the remaining 15% is reflected and is received by the infrared phototransistor 51 immediately next to it. When the distance to the reflecting surface is short, this level is large, and affects the reception of the reflected light at the bottom of the pan on the top plate 2 which is the purpose. For this reason, in the present embodiment, as shown in the figure, the distance between the optical filter 31 and the light emitting / receiving surface of the reflective photointerrupter 26 (infrared LED 50 and infrared phototransistor 51) is made as close as 500 .mu.m or less, Is not received by the infrared phototransistor 51. Ideally, it is desirable to bring the lower surface of the optical filter 31 into contact with the upper surface of the reflective photointerrupter 26, but this is difficult in terms of assembly tolerance.

  The pan temperature detection and its correction operation in the second embodiment are the same as those in the first embodiment described above, and thus the description thereof is omitted.

  FIG. 29 (b) shows another embodiment of the pan temperature detection device 18 under the heating coil 7. In the embodiments shown in FIGS. 3 and 4, the pan temperature detecting device 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. In the second embodiment, the pan temperature detection device 18 is disposed outside the coil top surface cooling air passage 15a. A part of the outer cavity wall 14b of the coil base 10 is expanded inward below the coil gap 7c to be along the sensor field cylinder 19, and the wall of the coil upper surface cooling air passage 15a and the coil upper surface cooling air delivery hole 15c are matched accordingly It is possible to deform and arrange the pan temperature detection device 18 outside the coil top surface cooling air path 15a. Then, the coil cooling air does not hit the pan temperature detecting device 18 without obstructing the flow of the coil cooling air. By doing this, it is possible to prevent a rapid temperature change due to cooling air (outside air) at the time of cooking of the pan temperature detection device 18 and to enable efficient cooling of the heating coil 7.

  According to the induction heating cooker of the non-crystallized glass top plate described above, the maximum heating temperature of the cooking pot 6 regardless of the material of the pan, the shape of the pan bottom, and the strength of the stain over a wide temperature range of 150 to 300 ° C. Temperature can be detected accurately and stably, and optimum cooking can be achieved by appropriately controlling the high frequency power to the heating coil.

  Also, since there is no delay in temperature detection like a thermistor, it is possible to follow a rapid rise in pan bottom maximum temperature such as open air, and it is possible to detect this and immediately stop induction heating when there is a risk of oil firing etc. Become. The thermal shock temperature of borosilicate glass which is the non-crystallized glass of the top plate is about 350 ° C. (the thermal shock temperature of crystallized glass is about 800 ° C.), which is lower than that of crystallized glass. Since the pan bottom maximum temperature rise can be suppressed at around 300 ° C. by the pan temperature detection means of the above, damage to the borosilicate glass can be prevented, and a safe induction heating cooker can be provided.

DESCRIPTION OF SYMBOLS 1 Main body 2 of induction heating cooker 2 Top plate 3 Operation part 4 Circle display 5 which shows the position to put a cooking pot 5 Infrared transmission window 6 Cooking pot 7 Heating coil 7a 1st coil 7b 2nd coil 7c Coil gap 7d Crosslinking wire 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 detection device 19 Sensor 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 Optical filter 32 Metal case 33 Outer infrared sensor case 34 Heat insulator 35 Metal can 36 Metal Stem 38 Siriko 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 convex lens 50 Infrared LED
DESCRIPTION OF SYMBOLS 51 Infrared phototransistor 55 Heat sink 60 Microcomputer 61 Frequency control circuit 62 Power control circuit 63 Rectification circuit 64 Power switch 68 Operation switch 69 Display circuit 70 Buzzer 72 Thermopile temperature detection circuit 72-1, 73-6 Op amp 72-9 Resistance 72- 10 diode 73 reflectance detection circuit 73-5 capacitor 73-7 charge and discharge circuit

Claims (7)

A top plate made of borosilicate glass with the cooking vessel on top,
A first coil provided under the top plate and concentrically wound on the outer peripheral side, a second coil concentrically wound on the inner peripheral side, and a concentric shape between both the coils A heating coil having a coil gap;
With fans to introduce outside air,
A coil cooling air passage that guides the outside air supplied from the fan to the heating coil;
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;
Temperature detection means for detecting the temperature of the bottom surface of the cooking vessel;
The temperature detection means
A thermopile that transmits infrared light having a wavelength of 1 to 4 μm and detects the amount of infrared light emitted from the bottom surface of the cooking vessel;
A window material made of borosilicate glass disposed on the light receiving front surface of the thermopile and transmitting an infrared ray having a wavelength of 4 μm or less;
A first plastic housing incorporating the thermopile and having the window member fitted in a first case window;
Equipped with
The induction heating is characterized in that the temperature detection means is disposed below the coil gap and in the coil cooling air path to detect the temperature of the bottom surface of the cooking vessel and control the power supplied to the heating coil based on this temperature. Cooking device. In the induction heating cooker according to claim 1,
An induction heating cooker characterized by disposing the temperature detecting means below the coil gap avoiding a lower part of a winding which bridges the first coil and the second coil. In the induction heating cooker according to claim 1,
The high frequency power supply means supplies high frequency power to the heating coil with a low voltage line connected to the winding start of the first coil and a high voltage line connected to the winding end of the second coil,
An induction heating cooker characterized by disposing the temperature detection means below the coil gap avoiding the vicinity of the high voltage line and below. In the induction heating cooker according to claim 1,
The temperature detection means
A nonmagnetic metal housing covering the first plastic housing and having a second case window corresponding to the window material open;
A second plastic casing covering the metal casing and having a third case window corresponding to the window member open;
What is claimed is: 1. An induction heating cooker characterized in that it is a temperature detection means in a triple case configured of the above. In the induction heating cooker according to claim 4,
An induction heating cooker characterized in that an air layer or a heat insulating material is inserted between the second plastic casing and the metal casing. In the induction heating cooker according to claim 1,
The temperature detection means comprises a DC amplifier for amplifying the output of the thermopile,
An induction heating cooker characterized in that the direct current amplifier decreases its amplification degree above a predetermined output voltage to expand a temperature detection range.   The induction heating cooker according to any one of claims 1 to 6, wherein the top plate is borosilicate glass containing 10 to 15% of boric acid.