JP5135386B2 - Induction heating cooker - Google Patents

Description

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

  As a method for detecting the pan temperature of the induction heating cooker, there is a method in which the temperature at the bottom of the pan is indirectly detected by a temperature sensitive element such as a thermistor brought into contact with the back of the top plate on which the pan is placed (Patent Document 1).

  As another method for detecting the pan temperature, there is a method for detecting the temperature by observing infrared rays emitted from the bottom of the pan with an infrared sensor through the top plate (Patent Document 2). Furthermore, in the pot temperature detection method using an infrared sensor, even if the bottom surface temperature of different cooking pans is the same, there is a problem that the detection temperature of the sensor is different if the emissivity of the pan is different (Patent Document) 3).

JP 2001-286449 A JP 2004-95313 A Japanese Patent Laid-Open No. 11-225881

  The pan temperature detection method of Patent Document 1 indirectly detects the pan temperature via a top plate made of glass or the like, and thus has a problem that the difference between the detected temperature and the actual pan temperature is large. In addition, if the temperature at the bottom of the pan matches the temperature at the top plate, the temperature at the bottom of the pan can be detected accurately, but the time lag until the temperature at the bottom of the pan coincides with the detected temperature is large, so the temperature at the bottom of the pan cannot be detected accurately. There was also a sex problem. Further, when the center of the pan bottom is warped and there is an air layer between the pan bottom and the top plate, the pan bottom temperature is not sufficiently transmitted to the top plate, and the pan bottom temperature cannot be accurately detected. As described above, when the pan temperature detection method of Patent Document 1 is used, the pan bottom temperature cannot be accurately detected, and thus it is difficult to perform appropriate and responsive heating control.

  In the pan temperature detection method of Patent Document 2, infrared rays emitted from the pan bottom on the top plate are received by an infrared sensor below the top plate, and the temperature is detected based on the received infrared energy. Here, the infrared energy emitted from the pan bottom at a certain temperature depends on the infrared emissivity of the pan bottom.

The amount of radiant energy (W / cm ² ) in the temperature range (about 100 ° C. to 250 ° C.) at the time of cooking is in the wavelength band of about 1 μm to 40 μm according to Planck's distribution law, and its peak is 5 μm to 8 μm. is there. On the other hand, the crystallized glass used for the top plate transmits 80% or more of light having a wavelength of 0.2 μm to 2.9 μm, transmits about 30% of light having a wavelength of 3 to 4.5 μm, and is less than 4.5 μm. Light with a long wavelength and a wavelength shorter than 0.2 μm is hardly transmitted. For this reason, the infrared energy received by the infrared sensor is limited and weak, and even when converted to an electrical signal by the infrared sensor, a circuit with a large amplification degree is required, and improvement of the stability and S / N is a problem. Moreover, as an optical filter used for the infrared sensor, an expensive filter in a narrow wavelength band is required to detect the temperature of the pan without being affected by the temperature of the top plate.

  The technique of Patent Literature 3 measures the reflectance of the pan bottom, that is, the emissivity derived therefrom using infrared light emitting and receiving elements, thereby correcting the difference in temperature detection by infrared rays due to the difference in the pan bottom. The infrared emissivity of the pan bottom depends greatly on the material, color and processing state of the pan bottom (painting of the pan bottom, engraving of the pan bottom, hairline processing, ring processing, driving processing, etc.). Moreover, even in the same pan, the emissivity varies depending on dirt such as cooking oil adhering to the bottom of the pan. In other words, even if the pan is the same temperature and the same material, the infrared energy that is radiated is different if the color, processing, or dirt state is different. To do. However, the prior art does not disclose a specific method for incorporating a means for measuring reflectivity into an induction heating cooker, and how to cope with disturbance of an induced magnetic field accompanying the incorporation. In addition, there is no specific disclosure of a method for applying correction to the reflectance measurement timing of the pan bottom in a cooking operation or temperature detection by an infrared sensor.

  An object of this invention is to provide the induction heating cooking appliance which implement | achieves making small the difference of the temperature to detect and an actual pan temperature, and improving the tracking property of the temperature of a pan bottom and detection temperature.

The above-mentioned problems include a top plate made of crystallized glass with a cooking container on the top surface, an induction heating coil provided under the top plate, a power control circuit that controls high-frequency power supplied to the induction heating coil, A thermopile that detects the amount of infrared radiation from the bottom of the cooking vessel, an electronic circuit board that mounts the thermopile and amplifies its output signal, the thermopile and the electronic circuit board are installed inside, and a case window is opened on the top surface. An infrared sensor case made of plastic material, a fan for introducing outside air, and a cooling air passage for supplying cooling air supplied from the fan to the induction heating coil through a cooling air sending hole provided on the upper surface. and, wherein the infrared sensor case, the are arranged in the cooling air delivery hole of the cooling air passage, cooling air supplied from the fan before To prevent causing per heat fluctuations directly to the electronic circuit board and the thermopile, cooling air have a windproof to prevent the directly striking the thermopile, the cooking container has passed through the casing window of said infrared sensor case This can be solved by an induction heating cooker that detects the amount of radiated infrared rays by heating the thermocouple temperature measuring contact with infrared rays from the bottom .

  According to the present invention, the difference between the temperature detected using an inexpensive infrared sensor and the actual pan temperature can be reduced. In addition, the followability of the temperature at the bottom of the pan and the detected temperature can be improved.

The perspective view which shows the structure of the induction heating cooking appliance by this invention. Sectional drawing which shows the structure of the induction heating cooking appliance by this invention. Sectional drawing which shows the detail of the induction heating coil periphery by this invention. The top view which shows arrangement | positioning of the pan temperature detection apparatus by this invention. The perspective view which shows the pan temperature detection apparatus by this invention. Sectional drawing of the pan temperature detection apparatus by this invention. Sectional drawing which shows the detail of the thermopile by this invention. The top view which shows the detail of the thermopile by this invention. The figure which shows the reflection type photointerrupter by this invention. The control block diagram of the induction heating cooking appliance by this invention. The figure which shows the spectral radiant energy by Planck's distribution law. The figure which shows the optical characteristic of crystallized glass. The figure which shows the relationship between temperature and the output of a thermopile. The figure which shows the detail of the thermopile temperature detection circuit by this invention. The figure which shows the relationship between the pan bottom temperature by this invention, and a thermopile temperature detection circuit output. The figure which shows the detail of the reflectance detection circuit by this invention. The operation | movement timing chart of the reflectance detection circuit by this invention. The output explanatory drawing by the presence or absence of a pan of the reflectance detection circuit by this invention. The figure which shows the relationship between the reflective voltage of the reflectance detection circuit by this invention, and a reflectance. The figure which shows the relationship between the pan bottom temperature of various pans by this invention, and a pan temperature detection circuit output. The figure which shows the relationship between the various pan emissivity and reflectance by this invention. The flowchart of the induction heating cooking by this invention. 5 is a flowchart of reflectance detection according to the present invention. The flowchart of the pan temperature detection by this invention. The plane and sectional drawing of the pan temperature detection apparatus by this invention. The figure which shows the relationship between the pan temperature detection voltage Vt at the time of the pan bottom temperature of various pans by this invention 250 degreeC, and the reflected voltage Vr. The flowchart of the pan temperature detection by this invention.

  A specific embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view of an induction heating cooker according to the present invention, and FIG. 2 is a longitudinal sectional view when a cooking pan 6 is placed on a portion indicated by a one-dot chain line AA ′ in FIG. In the following, an induction heating cooker having 3 pans where there are 2 pans that can be induction-heated and 1 pans that can be heated by radiant heat from a heater (heating source) such as a radiant heater or a halogen heater. However, the application target of the present invention is not limited to this, and may be, for example, an induction heating cooker provided with three pot places where induction heating is possible. The cooking pan 6 is an iron pan (magnetic body) suitable for induction heating, but may be a non-magnetic aluminum pan or copper pan.

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

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

  A cooking pan 6 is placed in each mouth (circle 4) on the upper surface of the top plate 2 and cooking is performed. As shown in FIG. 2, when a high frequency current from the inverter circuit 8 is supplied to the induction heating coil 7, the induction heating coil 7 generates a high frequency magnetic field 9 (indicated by a broken line in the figure), and this high frequency magnetic field is connected to the pan 6 and the chain. In addition, an eddy current is generated, and the cooking pan 6 itself is induction-heated by the Joule loss to generate heat. Accordingly, the food in the cooking pan 6 is cooked by the heat generated by the cooking pan 6 itself. At this time, the top plate 2 under the cooking pan 6 is also heated by heat transmitted from the cooking pan 6 that has generated heat.

  FIG. 3 shows a detailed cross section around the induction heating coil. As shown in FIG. 3, an induction heating coil 7 is disposed on the lower surface of the top plate 2 in a coiled manner in a coil base 10 made of heat-resistant plastic. Below the induction heating coil 7, rod-like ferrites 11 are radially arranged inside the coil base member. The ferrite 11 is arranged to efficiently guide the magnetic flux generated by the induction heating coil 7 to the cooking pan 6 that is a cooking container on the top plate 2. The coil base 10 is pressed by a spring 13 from a coil base receiver 12 fixed to the main body 1 and pressed against the lower surface of the top plate 2.

  The central portion of the coil base is a cylindrical cavity 14, and a coil cooling air passage 15 that guides cooling air from the cylindrical cavity 14 to the induction heating coil 7 is fixed to the main body 1 at the lower portion of the cavity. Is done. On the upper surface of the coil cooling air passage 15, a coil cooling air delivery hole 16 is formed along the circumference of the lower surface of the cylindrical cavity 14. A sealing material 17 such as glass wool is provided around the coil cooling air delivery hole 16 and connected to the cylindrical cavity 14. A pan temperature detecting device 18 is disposed in the coil cooling air delivery hole 16 in the cooling air passage 15. The pan temperature detection device 18 detects the bottom surface temperature of the cooking pan 6 heated by induction from the infrared rays transmitted through the infrared transmission window 5 of the top plate 2.

  A reflection type photo interrupter 19 is arranged beside the pan temperature detecting device 18. The reflection type photo interrupter 19 detects the reflectance of the bottom surface of the pan through the infrared transmission window 5 of the top plate 2 and corrects the temperature detected by the pan temperature detecting device 18. Detailed operations of the pan temperature detector 18 and the reflective photointerrupter 19 will be described later.

  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 cavity 14.

  Outside air is introduced into the cooling air passage 15 from a fan (not shown) built in the main body 1, and the cooling air cools the pan temperature detecting device 18 and rises up the cylindrical cavity 14 from the coil cooling air delivery hole 16. Then, it is blocked by the top plate 2 and flows from the upper part of the cavity 14 toward the induction heating coil 7 to cool the induction heating coil 7.

  FIG. 4 shows a top view of FIG. 3 excluding the top plate 2. The positional relationship on the horizontal plane of the induction heating coil 7 and the cavity 14 and the pan temperature detector 18, the reflective photointerrupter 19, and the thermistor 21 installed immediately below is shown. In the figure, the position of the infrared transmission window 5 is indicated by a thick dashed line.

  FIG. 5 shows a detailed perspective view of the pan temperature detecting device 18. The pan temperature detection device 18 is mainly configured of a thermopile 25 that is an infrared detection sensor. The thermopile 25 is mounted on an electronic circuit board 26 that amplifies the output signal of the thermopile, and a reflector 27 made of a plastic member is attached to the thermopile 25. The thermopile 25 and the electronic circuit board 26 are hermetically sealed in an infrared sensor case 28 made of a plastic member. The infrared sensor case 28 is provided with a case window 29 for transmitting infrared rays. The case window 29 has a thin square crystallized glass optical filter 30 having the same optical characteristics as the crystallized glass constituting the top plate 2. It is inserted. Further, the infrared sensor case 28 is covered with an iron plate case 31 that is a magnetic body. In addition, the part corresponding to the case window 29 of the iron plate case 31 is opened. A ground wire 32 is connected to the iron plate case 31 and is grounded to a metal part of the main body 1 to which a ground wire of a three-terminal commercial power supply line is connected.

  FIG. 6 is a cross-sectional view taken along line BB ′ in FIG. A mirror surface is formed on the inner surface 33 of the reflector 27 with an aluminum vapor deposition film, and infrared rays that have passed through the case window 29 and the crystallized glass optical filter 30 are transmitted through the optical filter of the thermopile 25 as will be described later. Condensed to

  FIG. 7 shows details of the thermopile 25. The thermopile 25 is obtained by connecting a number of thermocouples (thermocouples) in cascade (piling). The thermopile 25 is built in a metal case made of a metal can 35 such as a nickel-plated steel plate and a metal stem 36. A silicon oxide film 39 is formed on the surface of the silicon substrate 38 having a thickness of about 300 .mu.m to electrically and thermally insulate, and polysilicon and aluminum are sequentially deposited thereon to form a polysilicon vapor deposition film 40 and an aluminum vapor deposition film (not shown). At 41, a number of thermocouples are created and connected in cascade. An infrared absorption film 43 such as a rubidium oxide film close to a black body is formed at the center of the silicon substrate 38 having a polysilicon / aluminum junction (temperature measuring contact). One end of the polysilicon and aluminum vapor deposition film is a cold junction 44, which is disposed around the silicon substrate 38. The back surface of the silicon substrate 38 is etched to 299 μm leaving the periphery (cold contact portion), and the thickness of the silicon substrate having the temperature measuring contact portion is formed to 1 μm. This is to reduce the heat conduction between the temperature measuring contact portion 42 and the cold junction portion 44 by thinning silicon having good heat conduction, thereby thermally insulating the temperature measuring contact portion and the cold junction portion.

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

  The thermocouple temperature measuring contact portion 42 (below the infrared absorption film 43) in the thermopile 25 is heated by the infrared rays that have passed through the small hole window 47, and this heating temperature rise is proportional to the infrared energy that has passed. A voltage proportional to the temperature difference between the paired cold junction portion 44 and the temperature measuring contact portion 42 is output to the thermocouple output metal pin 46.

  FIG. 8 is a plan view of a cross section taken along the line CC ′ in FIG. The infrared absorption film 43 is omitted so that a thermocouple formed of the polysilicon vapor deposition film 40 and the aluminum vapor deposition film 41 can be seen.

  FIG. 9 shows details of the reflective photointerrupter 19 described in FIG. The reflection type photo interrupter 19 is formed by arranging an infrared LED 50 as an infrared light emitting element and an infrared phototransistor 51 as an infrared light receiving element on the same plastic member. A lens is made of plastic on the light emitting surface of the infrared LED, and infrared light of around 930 nm is irradiated upward with a thin beam. A lens is made of visible light blocking plastic on the light receiving surface of the infrared phototransistor 51, and the reflected infrared light at the object (pan bottom) of the previous irradiated infrared light is received with a narrow viewing angle, and the amount of received light A current proportional to is output. This reflection type photo interrupter 19 is composed of a pair of an infrared light emitting element and a light receiving element, and measures the reflectance of the bottom surface of the cooking pan 6 placed on the top plate 2.

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

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

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

  The thermopile 25 is connected to a thermopile temperature detection circuit 72 so that the output is amplified and input to the AD terminal of the microcomputer 60. The photo interrupter 19 is connected to the reflectance detection circuit 73, the light emission of the light emitting element is controlled by the port output of the microcomputer 60, the infrared light reflected by the cooking pan 6 is received by the light receiving element, and the output signal is amplified. And input to the AD terminal of the microcomputer 60. Details of the operations of the thermopile temperature detection circuit 72 and the reflectance detection circuit 73 will be described later. Further, the thermistor 21 is connected to a thermistor temperature detection circuit 74, and its output is also input to the AD terminal of the microcomputer 60.

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

  The operation of this embodiment will be described below.

The cooking pan 6 placed on the top plate 2 generates heat by induction heating. By this heating, infrared rays are emitted from the bottom of the pan 6. This total radiant energy E is proportional to the fourth power of the pan temperature T (E = σT ⁴ ; Stefan-Boltzmann law). FIG. 11 shows the spectral radiant energy of black body temperature calculated from Planck's distribution law. If this spectral radiant energy is integrated over the entire wavelength region, the total radiant energy E is obtained, which is proportional to the fourth power of the temperature (absolute temperature). This is the aforementioned Stefan-Boltzmann law, and this coefficient σ is the Stefan-Boltzmann coefficient. The peak wavelength of the spectral radiant energy is 5 μm to 8 μm at a cooking temperature of 100 to 300 ° C. based on the Vienna transition law.

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

  On the other hand, the optical characteristics of crystallized glass, which is a nonmagnetic material, are shown in FIG. As shown in FIG. 12, the crystallized glass transmits 80% or more of light having a wavelength of 0.2 μm to 2.9 μm, transmits about 30% of light having a wavelength of 3 to 4.5 μm, and from 4.5 μm. However, light having a longer wavelength and shorter than 0.2 μm is hardly transmitted. Because of this optical property, most of the infrared radiation energy emitted from the pan cannot pass through the top plate.

  Infrared sensors include 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 type sensor is characterized by high sensitivity in a narrow wavelength band because it detects infrared rays by the quantum effect, and the thermal type has low sensitivity in a wide wavelength band. For the quantum type, the sensitivity wavelength is determined by the type of semiconductor, and those that can be purchased at a low cost, such as silicon, have a practical sensitivity wavelength of 1 μm or less from outside visible light (0.8 μm), so the detection temperature range is 300 ° C. or more. Become. On the other hand, the thermal type has a uniform low sensitivity in a wide wavelength band of 20 μm or less from visible light as compared with the quantum type. (In principle, it does not have wavelength dependence.) For this reason, an optical filter is provided in front of the infrared light receiving surface of the sensor to prevent the disturbance by narrowing the detection temperature range wavelength.

  In this embodiment, since the cooking temperature range is 100 to 250 ° C., a thermopile thermopile is used as the infrared sensor. Since the pyroelectric element of the same thermal type is a differential type sensor, it is necessary to interrupt infrared incidence, and a normal mechanical chopper mechanism is used. For this reason, it is unsuitable to use for household appliances like a heating cooker in terms of reliability. On the other hand, the thermopile does not require such a mechanism, and in recent years, a thermocouple configured by using a semiconductor process by using a technique such as a MEMS is miniaturized and a large number of the thermocouples are deposited to improve sensitivity.

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

  If the temperature (25-300 degreeC) of a cooking pan is measured non-contactingly using the thermopile which has this optical filter, the output shown with a dashed-dotted line in FIG. 13 will be obtained as an output of a thermopile. As described above, the bottom surface of the cooking pan is regarded as a black body, and the infrared energy (according to Planck's distribution law) radiated from the cooking pan is converted into a voltage by the sensitivity of the thermopile and obtained as a result of a predetermined amplification. At this time, it is assumed that the sensitivity of the thermopile is a constant value having a wavelength of 1 to 15 μm, and infrared light having a wavelength of 1 to 15 μm is uniformly transmitted through the optical filter by 90% and enters the thermopile.

  Now, when this thermopile is used for detecting the pan temperature in the configuration of FIG. 3, the infrared rays from the bottom of the pan pass through the top plate 2 and enter the thermopile 25. Therefore, the infrared rays of each wavelength that are transmitted are limited by the optical characteristics of the top plate 2 (FIG. 12). As described above, infrared rays of about 5 μm or more hardly pass through and do not enter the thermopile 25. When the output in this case is calculated in the same manner as described above, it is shown by a solid line in FIG. It can be seen that the output drops by an order of magnitude. For this reason, it is necessary to amplify the output of the thermopile 25 with a gain (about 10,000 times) that is one digit higher than the gain (about 1000 times) of a DC amplifier used in a conventional thermometer or the like. For this reason, the pan temperature detecting device 18 of the present embodiment is provided with a thermopile 25 and a circuit board (a thermopile temperature detecting circuit 72 described later) for amplifying this output in an infrared sensor case 28 which is the same windproof case. Then, after the output of the thermopile 25 is DC amplified, it is output to the AD terminal of the microcomputer 60 described later as a signal voltage having a low output impedance. Further, the case is shielded against the strong magnetic field of the induction heating coil 7 by covering the case with an iron plate case 31 made of a magnetic material, and the iron plate case 31 is grounded against pulse noise from other circuits, particularly an inverter circuit. An electrostatic shield is also provided by grounding to the metal part of the main body 1 at 32.

  FIG. 14 shows details of the thermopile temperature detection circuit 72. Thermocouple output (thermoelectromotive force) of thermopile 25 (voltage between symbols (+) and (−) in the figure) is amplified about 10,000 times by operational amplifiers 72-1 and 72-2 and output to output terminal 72-3. The This voltage is input to the AD terminal of the microcomputer 60. The NTC thermistor 45 in the thermopile is connected in series with the resistor 72-7 to a voltage source (both ends of the resistor 72-5) obtained by dividing the circuit power supply voltage by the resistors 72-4, 72-5, and 72-6. The connection point a with the resistor 72-7 is connected to the thermocouple output terminal (-). As is well known, the NTC thermistor 45 is a resistance element having a negative temperature characteristic, and its resistance value decreases as the temperature rises. For this reason, when the temperature in the thermopile 25 rises, the voltage of the previous connection point a rises. The thermocouple output (voltage between (+) and (-) symbols in the figure) is proportional to the temperature difference between the temperature measuring contact portion 42 (a point heated by infrared energy) and the cold junction portion (thermocouple output terminal) 44. . For this reason, when the atmosphere in the metal case 37 (in which the NTC thermistor is incorporated) rises at the ambient temperature where the thermopile 25 is installed, the thermocouple output decreases. This decrease is compensated by the voltage increase at the connection point a. That is, the NTC thermistor 45 is used to prevent the output of the thermopile (thermocouple) 25 from changing at the ambient temperature.

  During cooking, a high frequency current of ten and several amperes flows through the induction heating coil 7 so that the coil itself generates heat. A high-temperature cooking pot heated by induction is placed on the top plate 2 on the induction heating coil 7, and the lower part of the induction heating coil in the main body 1 becomes a high temperature of 70 ° C. during cooking. Since the pan temperature detection device 18 including the thermopile 25 and the thermopile temperature detection circuit 72 is installed at the lower center of the induction heating coil 7, it is placed in this high temperature atmosphere. As described above, temperature compensation is performed using the built-in NTC thermistor 45 so that the output of the thermopile 25 does not change depending on the ambient temperature, but sufficient temperature compensation is performed over a wide temperature range due to the non-linearity of the thermistor. Therefore, it is desirable to place the pan temperature detecting device 18 in a constant temperature atmosphere as low as possible. Therefore, in this embodiment, the pan temperature detecting device 18 is installed in the coil cooling air passage 15 into which the outside air is introduced, and the thermopile 25 and the thermopile temperature detecting circuit 72 are cooled by the outside air to prevent the temperature from rising. Yes. Further, in order to prevent the airflow in the coil cooling air passage from directly hitting the metal case of the thermopile 25 and the semiconductor of the circuit, resistance, etc., and causing thermal fluctuation, the infrared sensor case 28 which is a windproof case is covered. Further, the thermopile 25 and the thermopile temperature detection circuit 72 are thermally insulated by the air in the infrared sensor case 28. That is, the infrared sensor case 28 also has a function as a heat insulating case. Further, the infrared sensor case 28 is covered with an iron plate case 31 made of a magnetic material and magnetically shielded so that the metal case of the thermopile 25 is induction-heated by a high magnetic field generated by the induction heating coil 7 so that the temperature does not rise. As a result, the temperature at the bottom of the pan can be detected stably even in a high temperature and high magnetic field.

  Now, the top plate 2 is heated by absorbing infrared radiation from the induction-heated cooking pan 6 and by contact heat conduction. From the optical characteristics of the top plate 2 shown in FIG. 12, 80% or more of light having a wavelength of 0.2 μm to 2.9 μm is transmitted, and approximately 30% of light having a wavelength of 3 to 4.5 μm is transmitted. However, light having a longer wavelength and shorter than 0.2 μm is hardly transmitted.

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

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

  In the present embodiment, in order to prevent the above, a case window 29 for transmitting infrared rays is opened in the infrared sensor case 28 of the pan temperature detecting device 18 constituted by the thermopile 25, and the top plate 2 is configured in the case window 29. The crystallized glass to be cut into a thin square is fitted as a crystallized glass optical filter 30. Then, the amount of infrared rays radiated from the top plate 2 incident on the thermopile 25 is removed. The wavelength of the portion indicated by hatching in FIG. 12 emitted from the top plate is prevented from entering the thermopile 25 due to the optical characteristics of the crystallized glass optical filter 30 (the wavelength indicated by the hatching in FIG. 12 is not transmitted).

  Although the crystallized glass optical filter 30 may be made of a material other than the top plate, it is very difficult and expensive to make an optical filter having steep characteristics as shown in FIG.

  Further, a 5 μm short pass filter that does not transmit a wavelength of 5 μm or more is used as the optical filter 48 of the thermopile 25. This is to prevent the infrared rays radiated from the crystallized glass optical filter 30 itself and the infrared sensor case 28 that are warmed at the ambient temperature from passing through the wavelength of 5 μm or more. As mentioned above, the infrared energy of 1 to 2.9 μm radiated from the pan is very small because the passage is restricted by the top plate, and the output amplification of the thermopile 25 must be increased. This is because it is sensitive to infrared radiation of 5 μm or more at ambient temperature, and it is necessary to thoroughly prevent the infrared radiation of 4.5 μm or more from other than the pan bottom from entering the infrared absorption film 43 of the thermopile.

  Assuming that the crystallized glass optical filter 30 itself and the infrared sensor case 28 have a temperature of 70 ° C., the voltage output from the thermopile 25 by the infrared rays radiated from the filter is calculated as A in FIG. Here, the optical filter 48 of the thermopile 25 is assumed to transmit 90% of a wavelength of 1 to 15 μm. This voltage is substantially the same as the voltage output from the thermopile 25 when the pan bottom on the top plate 2 shown by the solid line in FIG. That is, unless the pass band of the optical filter 48 is limited to 5 μm or less, the pan temperature detection device 18 cannot detect the pan temperature on the top plate 2 in an atmosphere of 70 ° C. or higher.

  For the above reason, the pan temperature detecting device 18 is installed in the coil cooling air passage 15 in this embodiment.

  FIG. 15A shows the pan bottom temperature T and the output voltage V of the thermopile temperature detection circuit 72 output terminal 72-3 when the tempura pan having the pan bottom in a state close to a black body is induction-heated in the embodiment of FIG. The relationship is shown. The voltage from room temperature to 100 ° C. is approximately 0.5 V, and when it exceeds 100 ° C., a voltage proportional to the fourth power of the temperature is output. 0.5V is a voltage obtained by dividing the power supply voltage (5V) of the thermopile temperature detection circuit 72 by resistors 72-4, 72-5, and 72-6 (shown by a point in FIG. 14), and 0.5V is an operational amplifier 72-1. , 72-2 is given as a bias voltage. When the temperature exceeds 100 ° C., the output voltage of the thermopile 25 becomes large, is amplified about 10,000 times by the operational amplifiers 72-1 and 72-2, and is observed as a voltage of 0.5 V or more. This bias voltage is provided for detecting a failure of the thermopile temperature detection circuit 72. A value obtained by subtracting 0.5 V from the output voltage value of the output terminal 72-3 (voltage increase value from 0.5 V) is proportional to the detected pan bottom temperature. This is shown in FIG. The microcomputer 60 AD-converts and reads the output voltage of the thermopile temperature detection circuit 72 output terminal 72-3. The pan temperature detection voltage Vt (= V−0.5), which is a value obtained by subtracting 0.5V from this voltage. Get the pot temperature based on The relationship shown in FIG. 15B is stored in advance in the ROM of the microcomputer 60 as table data.

  FIG. 16 shows details of the reflectance detection circuit 73. In FIG. 16, 50 is an infrared LED which is a light emitting element, for example, the emission wavelength is 930 nm. Reference numeral 51 denotes a phototransistor having, for example, a peak sensitivity wavelength of 800 nm and an infrared LED 50 emission wavelength of 930 nm having a sensitivity of 80% of the peak sensitivity. FIG. 17 shows an operation timing chart of the reflectance detection circuit 73. The infrared LED 50 which is a light emitting element of the photo interrupter 19 is driven by a transistor 73-1. This drive is controlled by a signal input from the output port of the microcomputer 60 to the drive signal terminal 73-2. FIG. 17A shows this signal. When a rectangular wave signal having a duty of 50% is input to the drive signal terminal 73-2, the infrared LED 50 emits light when the signal is 5V, and performs intermittent light emission that is turned off when the signal is 0V. This emission intensity is proportional to the current flowing through the infrared LED 50, and this current is determined by the value of the resistor 73-3. In this embodiment, the resistance value is fixed and the light emission intensity is constant. When the infrared light is reflected by the bottom surface of the cooking pan and received by the 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. If the reflection is large (the amount of received light is large), the voltage increases proportionally. This signal voltage has its direct current component cut by the capacitor 73-5, and is input as an alternating current signal (shown in (c) in FIG. 17) to a normal rotation direct current amplifier composed of an operational amplifier 73-6. Here, only the positive component of the AC signal is amplified. This is shown in FIG. The amplified 50% duty signal is converted to a DC average voltage by the charge / discharge circuit 73-7 and output from the output terminal 73-8. This output is input to the AD terminal of the microcomputer 60.

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

  When the photo interrupter 19 is arranged as shown in FIG. 3, when there is no cooking pan on the top plate 2, most of the infrared light emitted from the infrared LED 50 is transmitted through the top plate 2, but a part is the top plate 2. Reflected. This is because the transmittance of the top plate 2 is 90% at a wavelength of 930 nm, and the remaining 10% of infrared light is reflected. In addition, because of the radiation angle of the infrared LED, there is also infrared light that does not reach the bottom surface of the top plate and is reflected by an object in the middle of the path. Therefore, as shown in FIG. 18, the output of the reflectance detection circuit 73 is (a) V1 when there is a pan on the top plate, and (b) V2 when there is no pan. The reflected voltage Vr at the net pan is Vr = V2−V1.

  In FIG. 19, the reflectance detection circuit 73 is arranged as shown in FIG. 3, and the reflected voltage Vr obtained from the output of the reflectance detection circuit 73 when a metal plate with a known reflectance is arranged on the top plate. And the reflectance. An approximate line is also shown in the figure. If this relationship is used, the reflectance can be obtained from the output voltage of the reflectance detection circuit 73. This relationship is stored in the table data or the approximate coefficient value in the ROM of the microcomputer 60 in advance.

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

For several types of pans placed on the top plate 2 in FIG. 20, a value Vt (pot) obtained by subtracting the above-described 0.5 V offset voltage Vo from the output of the pan temperature detection device 18 (output V of the thermopile temperature detection circuit 72). The relationship between (temperature detection voltage) and pan bottom temperature T is shown. The emissivity at the bottom of each pan in the figure is 0.9, which is close to a black body, (b) is 0.57, (c) is 0.43, and (d) is 0.24. As shown in the upper diagram of FIG. 20, it can be seen that the relationship between the output of the pan temperature detecting device 18 and the pan bottom temperature differs depending on the emissivity. When the voltage values of (a) to (d) are divided by the emissivity, it is shown by a broken line in the lower diagram of FIG. Each output Vt is proportional to the total radiation energy of each pot (E '= εσT ^4), which to divide by emissivity is converted into the total radiant energy of a black body as described above (E = σT ⁴⁾ Means that. And if the emissivity of each pan is known, it means that the pan temperature of each pan can be reduced to the radiation temperature of a black body. For example, in FIG. 3 embodiment, a black body is arranged on the top plate, and a pan temperature detection voltage Vt that is a value obtained by subtracting 0.5 from the black body temperature T and the output V of the pan temperature detection device 18 is obtained. And Vt (FIG. 15B) are recorded and stored in advance in the ROM of the microcomputer 60 as table data or as an approximate coefficient value. Then, when the pan is being induction-heated, the output V of the pan temperature detection device 18 is AD-converted and read at regular intervals, and the pan temperature detection voltage Vt = V−0.5 is calculated. The reflectance is obtained by the detection circuit 73 as described above, the emissivity ε is obtained from Kirchhoff's law (ρ + ε = 1) based on the reflectance ρ, and the pan temperature detection voltage Vt is divided by this. By checking the table data with values or substituting it into the approximate expression, the temperature T is obtained from the pan temperature detection voltage Vt, and this is used as the detection pan temperature. The pan temperature correction of this embodiment is performed based on the above.

  FIG. 21 shows the relationship between the emissivity measured using a radiation thermometer in each pan and the reflectance obtained by using the reflectance detection circuit 73 in the embodiment of FIG. 3 (applying the approximate expression of the relationship of FIG. 19). . Some pans deviate from Kirchhoff's law, but there is a strong correlation between emissivity and reflectivity. The reason for deviating from Kirchhoff's law is that in the detection of reflectance, not all of the reflected infrared rays are received due to scattering on the pan surface. When obtaining the reflectance, it is desirable that the emitted light of the infrared LED 50 is incident as vertically as possible on the top plate 2 and the reflected light from the pan is guided to the phototransistor 51 as vertically as possible. For this reason, it is preferable to arrange a light guide tube on the light receiving and emitting surface of the photo interrupter 19. Further, it is desirable that the visual field surface of the pan temperature detection device 18 on the top plate 2 and the reflection surface on the top plate 2 of the reflectance detection light emission are the same surface. For this reason, as shown in FIG. 4, it is good to arrange | position the pan temperature detection apparatus 18 and the reflection type photo interrupter 19 side by side.

  Below, the operation | movement of a present Example demonstrates the case where the cooking pan 6 is set | placed in the front right front opening, and cooking is performed by heating a cooking pan for a predetermined time at predetermined temperature. FIG. 22 shows a flowchart of this operation. When a power source (not shown) is turned on, a predetermined temperature and cooking time are set with the operation switch of the induction heating port on which the cooking pan 6 is placed (step S1), and the start of cooking is instructed (step S2), the microcomputer 60 first starts. Reflection data (corresponding to the reflectance) of the pan placed by controlling the reflectance detection circuit 73 is taken in to detect the reflectance (step S3).

  FIG. 23 shows a detailed flowchart of the reflectance detection (step S3). The microcomputer 60 outputs the infrared LED drive signal of FIG. 16A from the port to the terminal 73-2 of the reflectance detection circuit 73 (step S3-1). After outputting 200 ms for a predetermined time (step S3-2), the voltage V2 output to the terminal 73-8 is read from the AD terminal (step S3-3). Then, the infrared LED drive signal is stopped (step S3-4). Next, the reflected voltage Vr is calculated from the previously read voltage V2 with respect to the voltage V1 when no pre-stored pan is placed (step S3-5). Then, the reflectance ρ is obtained from the relationship between the reflection voltage and the reflectance stored in advance (step S3-6).

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

  FIG. 24 shows a detailed flowchart of the pan temperature detection (step S5). The microcomputer 60 reads the output voltage of the pan temperature detection device 18 (pan temperature detection circuit 72) (step S5A-1), subtracts 0.5V from this value, and sets this as the pan temperature detection voltage Vt (step S5A-2). ). And emissivity (= 1-reflectance) is obtained from the reflectance detected just before induction heating (step S5A-3), and this pan temperature detection voltage Vt is divided (step S5A-4). Subtracting the data table which is the relationship between Vt and T shown in FIG. 15 (b) stored in advance using Vt after division (step S5A-5), converts it to temperature T, and outputs pan temperature T (step S5A-5). S5A-6).

  Instead of the process of calculating the emissivity (step S5A-3) and the process of dividing the pan temperature detection voltage Vt by the emissivity (step S5A-4), the magnification a = 1 / emissivity (a = 1 / ε). ) (Which becomes a value of 1 or more) and the reflectance (or reflection voltage Vr) are stored as a table, the magnification a is obtained from the reflectance (or reflection voltage Vr) using the table, and the pan temperature detection voltage is obtained. After multiplying Vt by a magnification, the pan temperature T may be output by drawing a data table that is a relationship between Vt and T. In this way, it is possible to speed up the processing without using a division requiring a processing time of the microcomputer.

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

  In the above description, the example in which the reflectance detection is performed only once just before induction heating is shown, but the present invention is not limited to this. In ordinary pans, the reflectance does not change during induction heating (even when the temperature rises). In addition, the infrared light emitting LED has a problem of life in continuous light emission for a long time. Further, the reflectance detection circuit 73 is disturbed by a high magnetic field during induction heating. In this description, in consideration of these points, one cooking is limited to one reflectance detection immediately before induction heating. Naturally, the reflectance may be detected at regular intervals during cooking by reducing the emission current. Especially in thin pans, the reflectivity may change due to pan deformation due to high temperature. Furthermore, in pans with color coating on the bottom, the coating may be denatured at high temperatures and the reflectivity may change. In this case, it is desirable to periodically detect the reflectance even during heating. In this case, of course, in order to avoid the influence of the magnetic field, it is desirable to surround the reflection type photo interrupter 19 and the reflectance detection circuit 73 with a magnetic material as in the embodiment shown in FIG. Or you may stop the electric power supply to the induction heating coil 7 for a short time at the timing which performs reflectance detection.

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

  Another embodiment of the pan temperature detector 18 is shown in FIG. The same reference numerals as those in FIGS. 5, 6, and 9 denote the same components. In this embodiment, a thermopile 25 and a reflective photo interrupter 19 are incorporated in an infrared sensor case 28 of a pan temperature detecting device 18. A portion of the crystallized glass optical filter 30 fitted in the case window 29 of the infrared sensor case 28 is a convex lens, and the thermopile 25 is disposed under the lens, and the reflector 27 is omitted. Further, the light emitting and light receiving portions of the reflective photointerrupter 19 are arranged immediately below the lower surface of the crystallized glass optical filter 30. This is to prevent infrared light from being reflected and received by the crystallized glass optical filter 30 immediately above.

  Infrared light emitted from the infrared LED 50 passes through the crystallized glass optical filter 30 by 90% or more, but the remaining 10% is reflected and received by the phototransistor 51 next to it. When the distance to the reflecting surface is short, this level is large and affects the reception of reflected light on the bottom surface of the pan on the top plate 2 which is the original purpose. For this reason, in this embodiment, as shown in the figure, the distance between the crystallized glass optical filter 30 and the light emitting / receiving surface of the reflective photointerrupter 19 (infrared LED 50 and phototransistor 51) is reduced to about 500 μm or less. Is prevented from being received by the phototransistor 51. Ideally, it is desirable that the lower surface of the crystallized glass optical filter 30 and the upper surface of the reflective photointerrupter 19 are in contact with each other, but this is difficult in terms of assembly tolerances.

  Obviously, the optical filter 48 of the thermopile 25 may have the optical characteristics of the top plate 2 in order to avoid the temperature effect of the top plate 2. That is, the optical filter 48 of FIG. 7 is replaced with the crystallized glass optical filter 30 in the embodiment of FIG. In this case, the crystallized glass optical filter 30 fitted in the case window 29 of the infrared sensor case 28 may be replaced with simple quartz glass or the like. Quartz glass transmits 90% of infrared rays up to a wavelength of 5 μm. Further, if the crystallized glass used as the optical filter of the thermopile 25 is a convex lens, the light can be condensed by this, and the reflector 27 can be omitted.

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

  Another embodiment of the above-described pan temperature correction will be described. This is not a method of calculating the reflectance and converting it into emissivity as described above, but correcting the detected pan temperature only by grouping and table lookup based on the reflected voltage Vr.

  FIG. 26 shows the pan temperature detection voltage Vt (value obtained by subtracting 0.5 V from the output of the pan temperature detection device 18) and the reflected voltage Vr when the pan bottom temperature T in the embodiment of FIG. Show the relationship. Thus, there is a strong correlation between the reflected voltage Vr and the pan temperature detection voltage Vt. Therefore, for example, the pans are classified into four groups (a, b, c, d) as shown by the reflected voltage Vr. A representative pan is selected from the group, and the relationship between the pan temperature detection voltage Vt and the pan bottom temperature T is stored in advance as a table. For example, the relationship between the pan temperature detection voltage Vt and the pan bottom temperature T is stored in advance as a table with (a), (b), (c), and (d) of FIG. In this case, four tables are created corresponding to the four groups. Then, while obtaining the pan temperature detection voltage Vt, it is grouped by the reflected voltage Vr, the table of the pan temperature detection voltage Vt and the temperature T of that group is switched, and the temperature T is output.

  FIG. 27 shows a pan temperature detection flowchart according to the above method. The output of the pan temperature detector 18 is read (step S5B-1), and the offset 0.5V is pulled from this to obtain the pan temperature detection voltage Vt (step S5B-2). Then, it is determined where the reflected voltage Vr enters the group (step S5B-3), and a relation table between the pan temperature detection voltage Vt and the pan bottom temperature T, which is representative of the group, is drawn (step S5B-4), and the temperature T is output (step S5B-5). If the table includes the offset voltage 0.5V, that is, the output voltage V of the pan temperature detector 18 and the pan bottom temperature T as shown in FIG. Processing can be eliminated. According to this embodiment, the temperature T can be corrected and output more easily.

  According to the heating cooker of the present invention described above, the cooking pan 6 is not affected by the material of the pan, the shape of the pan bottom, the strength of the dirt, and the top plate temperature in a wide temperature range from 150 to 300 ° C. The temperature is accurately captured. For this reason, the power control for the induction heating coil 7 of the microcomputer 60 can also be adapted to the temperature change of the cooking pan 6, resulting in skillful cooking. In addition, because there is no temperature detection delay like a thermistor, it can follow a sudden pan temperature rise such as emptying, and if there is a risk of oil ignition, induction heating can be stopped immediately. A safe induction heating cooker can be provided.

DESCRIPTION OF SYMBOLS 1 Induction heating cooker body 2 Top plate 3 Operation display part 4 Circle display which shows the position which puts a cooking pan 5 Infrared transmission window 6 Cooking pan 7 Induction heating coil 8 Inverter circuit 10 Coil base 14 Cylindrical cavity 15 Coil cooling air path 16 Coil cooling air delivery hole 18 Pan temperature detection device 19 Reflection type photo interrupter 25 Thermopile 26 Electronic circuit board 27 Reflector 28 Infrared sensor case 29 Case window 30 Crystallized glass optical filter 31 Iron plate case 32 Ground wire 37 Metal case 38 Silicon substrate 39 Silicon oxide film 40 Polysilicon vapor deposition film 41 Aluminum vapor deposition film 42 Temperature measuring contact part 43 Infrared absorption film 44 Cold junction part 45 NTC thermistor 46 Metal pin 47 Window 48 Optical filter 50 Infrared LED
51 Infrared phototransistor 60 Microcomputer 61 Frequency control circuit 62 Power control circuit 63 Rectifier circuit 64 Power switch 68 Operation switch 69 Display circuit 70 Buzzer 72 Thermopile temperature detection circuit 72-1, 72-2, 73-6 Operational amplifier 73 Reflectance detection Circuit 73-5 Capacitor 73-7 Charge / Discharge circuit

Claims (2)

A top plate made of crystallized glass with a cooking vessel on top;
An induction heating coil provided under the top plate;
A power control circuit for controlling the high-frequency supply power to the induction heating coil;
A thermopile for detecting the amount of infrared radiation emitted from the bottom of the cooking container;
An electronic circuit board for mounting the thermopile and amplifying the output signal;
An infrared sensor case of a plastic member in which the thermopile and the electronic circuit board are installed inside, and a case window is opened on the upper surface;
With fans that introduce outside air,
A cooling air path for supplying cooling air supplied from the fan to the induction heating coil through a cooling air delivery hole provided on the upper surface ,
The infrared sensor case is disposed in the cooling air delivery hole of the cooling air path , and prevents the cooling air supplied from the fan from directly hitting the thermopile and the electronic circuit board and causing thermal fluctuations. cooling air have a windproof function to prevent the hit directly,
The thermopile detects the amount of radiated infrared rays by detecting the amount of radiated infrared rays by heating a thermocouple temperature measuring contact portion with infrared rays from the bottom surface of the cooking container that has passed through the case window of the infrared sensor case. vessel. The induction heating cooker according to claim 1,
The infrared sensor case, the induction heating cooker which comprises said thermopile and the electronic circuit substrate from the cooling air in the air staying before Symbol the infrared sensor case a heat insulating function of insulating air.

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