JP2016154073A - Induction heating cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating cooker which is equipped with a non-crystallized glass top plate and has high detection accuracy of temperature of a cooking pot.SOLUTION: An induction heating cooker comprises a non-crystallized glass top plate, infrared detection means provided under a heating coil, for detecting infrared radiated from a bottom of a cooking container, and pot temperature detection means for detecting pot temperature based on output of the infrared detection means. The infrared detection means includes: a first infrared sensor to which infrared radiated from the bottom of the cooking container is input and which outputs DC voltage proportional to an amount of the infrared radiation; a first DC amplifier for DC amplifying the output from the first infrared sensor; a second infrared sensor to which infrared radiated from the bottom of the cooking container does not enter by blocking of the infrared radiated from the bottom of the cooking container and which outputs DC voltage proportional to an amount of the infrared radiation; and a second DC amplifier for inverting and DC amplifying the output from the second infrared sensor. An output of the second DC amplifier is input as bias voltage of the first DC amplifier and an output of the first DC amplifier is used as an output of the infrared detection means.SELECTED DRAWING: Figure 7

Description

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

  Some conventional induction heating cookers heat a cooking vessel placed on a top plate using two types of heating sources, a radiant heater and an induction heating coil (hereinafter abbreviated as “heating coil”). Since the radiant heater also heats the top plate itself to a high temperature, it is necessary to employ crystallized glass having a high heat resistance temperature for the top plate.

  As a means for detecting the temperature of a pan in an induction heating cooker, there are many currently used devices that detect the temperature by observing the infrared rays emitted from the bottom of the pan heated at a good response speed with an infrared sensor through the top plate. . As this infrared sensor, a quantum type such as a photodiode or a thermal type sensor such as a thermopile is often used. This infrared sensor is placed near the center of the heating coil and the infrared radiation emitted from the bottom of the pan is detected by the infrared sensor through the top plate, and the output of the inverter circuit that drives the heating coil is controlled according to the output. The cooking temperature is adjusted.

  However, the radiant infrared energy is small at cooking temperature (100 to 250 ° C). Furthermore, from the optical characteristics of the crystallized glass top plate, the wavelength that passes through the top plate is only about 2 μm with a width of 1 μm to 3 μm. Only 1-2% of the total radiant infrared energy can pass through the top plate. For this reason, the sensitivity of the infrared sensor to be used is required to be one digit higher than that used in thermometers. Further, since the sensor output signal is a DC voltage, a DC amplification circuit having a high amplification factor is required. For this reason, these infrared sensors are very sensitive to fluctuations in ambient temperature, and the sensor output voltage fluctuates due to fluctuations in the temperature inside the machine during cooking, which greatly affects the accuracy of detecting the pot temperature.

As means for solving this problem, Patent Documents 1 to 4 are listed.
The technology of Patent Document 1 includes a first detection unit (thermopile) that outputs a signal according to infrared radiation from a detection target, and a second detection unit (thermopile) that outputs a signal according to infrared radiation from the surrounding environment. ) And a differential amplifier that outputs the difference between the output signals of the first and second detection units, and is a technology that accurately detects only infrared rays from the detection target.

  The technique of Patent Document 2 includes a container having an incident window through which infrared rays are incident, a first infrared detection element (thermal infrared detection element) disposed opposite to the incident window in the container, and a first infrared detection. A substrate on which an element is mounted, and a second infrared detection element (thermal infrared detection element) for temperature-compensating the detection output of the first infrared detection element disposed in the container, from the incident window In this technique, a second infrared detection element is disposed at a position where incident infrared rays are shielded by the substrate, and a reduction in detection accuracy due to a change in ambient temperature is suppressed.

  The technology of Patent Document 3 is an infrared temperature sensor that measures the temperature of a heat source in a non-contact manner, and includes a heat-sensitive element for detecting infrared rays that detects the amount of infrared radiation emitted from the heat source, and a light shielding that detects the amount of heat from the external environment. And a heat inflow / outflow region where heat flows in / out between the external environment and the infrared sensor, and heat from the heat inflow region to the detection element and the compensation element. It is a technology that makes it possible to conduct accurate temperature compensation by making the conduction substantially uniform.

  The technology of Patent Document 4 is an infrared sensor that converts infrared energy radiated from an object into an electrical signal and outputs the electrical signal, and a first infrared detection element (photodiode) that converts the infrared energy into the electrical signal. And a correction unit including a temperature characteristic compensation element including a second infrared detection element (photodiode) for correcting an output signal from the light reception unit, and the light reception unit The correction unit is formed of the same material on the same substrate and has the same structure so that the infrared rays are incident in the same manner, and an operational amplification circuit that amplifies the output signal of the light receiving unit, and the operational amplification A resistance element connected between an inverting input terminal and an output terminal of the circuit, and a reference voltage generating circuit for generating a reference voltage, wherein one terminal of the light receiving unit is a non-inverting input of the operational amplifier circuit One terminal of the temperature characteristic compensating element is connected to an inverting input terminal of the operational amplifier circuit, and the other terminal of the light receiving unit and the other terminal of the temperature characteristic compensating element are the reference voltage generating circuit. This is a technique for detecting the temperature of an object with high accuracy by using an infrared sensor commonly connected to each other.

JP 2007-85840 A JP-A-11-132857 JP 2011-75365 A WO2007-125873 Publication

In Patent Document 1, the difference between a first detection unit output to which infrared rays from a detection target and the surrounding environment (ambient temperature) are incident and a second detection unit output to which infrared rays from the surrounding environment are incident are amplified. The detection accuracy is improved by canceling output fluctuation due to infrared rays from the environment by using the high CMRR (Common-Mode Rejection Ratio) of the differential amplifier. In Patent Document 1, it is assumed that the amount of infrared rays from the surrounding environment incident on the first detection unit is equal to the amount of infrared rays incident on the second detection unit. In addition, it is assumed that the infrared detection sensitivity and temperature characteristics of each element are the same. However, in practice, it is difficult to equalize the infrared rays amount or temperature of each detection unit from the surrounding environment. In a specific circuit, a buffer amplifier is required before the differential amplifier.
This is because the internal resistance (approximately 50 to 150 kΩ) of the thermopile is large, and this output resistance is reduced in a circuit to make the next differential amplifier operate normally. Furthermore, it is known that the output (sensitivity) characteristic of an infrared sensor varies by about 30% even if it is produced by the same process. For this reason, it is difficult to realize differential amplification with two element outputs. In the case of mass-produced products such as home appliances, it is necessary to suppress this variation by finely adjusting the amplification factor of the differential amplifier. As is well known, a differential amplifier cannot maintain a high CMRR unless the resistance ratio and value connected to the inverting input and the resistance ratio and value connected to the non-inverting input are the same. For this reason, the fine adjustment of the amplification factor for suppressing the sensitivity variation of the infrared sensor needs to maintain the high CMRR by adjusting the resistance value to the same value at two locations simultaneously. This is also difficult. As described above, the configuration of Patent Document 1 has a problem that it is difficult to realize a differential amplifier and the circuit cost is high.

  In Patent Document 2, a first infrared detection element and a second infrared detection element for temperature compensation of the output are assembled in the same container, and consideration is given to placing each infrared detection element in the same temperature environment. In addition, infrared rays are incident on the first infrared detecting element from the incident window, and infrared rays are not incident on the second infrared detecting element disposed on the back surface of the first infrared detecting element. The first infrared detection element (thermistor) and the second infrared detection element (thermistor) are connected in series, and the output signal at the connection point is amplified to compensate for temperature. In the case of the thermistor, the resistance value is determined by the ambient temperature, and in the case of the same structure, the resistance value is almost the same. Therefore, when these are connected in series and a constant voltage is applied, the voltage at the connection point is determined by the resistance ratio of the series elements, and therefore does not change with respect to changes in ambient temperature. That is, temperature compensation is performed.

  However, in the configuration of Patent Document 2, there is a risk that infrared light from the incident window is reflected and stray in the container and enters the second infrared detection element. In order to prevent the incident, another countermeasure (for example, a countermeasure such as forming another light shielding wall in the container) needs to be performed on the second infrared detection element. Further, the temperature compensation that can be easily performed by connecting the elements in series is limited to a temperature sensitive resistance element such as a thermistor as described above. There is also disclosed an example in which a Wien bridge is constituted by the above-described series elements, and the output is differentially amplified to compensate for temperature with higher accuracy. Other problems are the same as in Patent Document 1.

  In Patent Document 3, as in Patent Document 2, the infrared detecting thermal element and the light-shielded temperature compensating thermal element are placed in the same container so that heat transfer from the heat inflow / outflow site to the container is substantially uniform. The temperature compensation is performed by arranging (for example, a point-symmetrical position) and differentially amplifying the connection point between each element and the resistor. In Patent Document 3, as in Patent Document 2, it is necessary that the element be a temperature-sensitive resistance element that can be compensated by this amplification configuration. Other problems are the same as in Patent Document 1.

  In Patent Document 4, a temperature characteristic compensation element composed of a first infrared detection element (multistage photodiode) and a second infrared detection element (multistage photodiode) having the same structure as that of the first is connected in series. Two terminals are connected to the inverting and non-inverting inputs of an amplifier circuit (current-voltage conversion amplifier circuit), and the temperature is compensated by connecting the connection point to a reference voltage. This type of amplifier circuit is effective for a quantum infrared sensor using a photocurrent of a PN junction, for example, a photodiode, and compensates for a forward voltage change of the PN junction due to a temperature change. For this reason, in the structure of patent document 4, this technique cannot be applied to a thermal type infrared sensor. Other problems are the same as in Patent Document 1.

  In addition, in the conventional induction heating cooker, crystallized glass is used for the top plate, but non-crystallized glass with high visible light transmittance (high transparency) and low cost is used for the top plate. If possible, the design can be further improved and the price can be reduced as an induction heating cooker. In order to employ non-crystallized glass having a thermal shock temperature lower than that of crystallized glass for the top plate of the induction heating cooker, the problem is solved by configuring the heating source with an induction heating coil.

  However, when borosilicate glass, for example, is used as the top plate made of non-crystallized glass, the infrared radiation generated from the cooking container is transmitted through the top plate compared to crystallized glass due to the difference in optical properties that transmit infrared light. The amount of energy will decrease.

  In addition to the infrared radiation energy from the cooking container, the infrared sensor receives infrared radiation energy that causes heat disturbance due to exhaust heat from the heating coil and the inverter board that controls the heating coil. When non-crystallized glass is employed for the top plate, the rate of thermal disturbance received by the infrared sensor is increased as compared with crystallized glass, and there is a problem that the measurement accuracy for detecting the temperature of the cooking container is deteriorated.

  The above-mentioned Patent Documents 1 to 4 describe a change in temperature environment at the time of steady state, that is, when the changed environmental temperature becomes constant after a long time, if the amount of infrared rays from the detected object is the same, the temperature and change before the change. The temperature compensation is performed so that the output of the infrared sensor does not change even if the later temperature is different (with respect to the difference in environmental temperature). There is no mention of temperature compensation (transient) when the ambient temperature is changing gradually. Changing the top plate from crystallized glass to non-crystallized glass increases the rate of thermal disturbance received by the infrared sensor, so the non-crystallized glass top plate compensates for temperature during transient environmental temperatures. This is important in improving the temperature detection accuracy.

  The present invention has been made in order to solve the above-described problem, and a top plate on which a cooking container is placed is provided, and an induction magnetic field is provided under the top plate to heat the cooking container. A heating coil, an infrared detecting means provided under the heating coil for detecting infrared rays emitted from the bottom of the cooking container, and a pan temperature detecting means for detecting a pan temperature from an output of the infrared detecting means, An induction heating cooker provided, wherein the infrared detection means is configured to receive a first infrared sensor that receives an infrared ray emitted from a bottom of the cooking container and outputs a direct-current voltage proportional to the amount of infrared rays; A first direct-current amplifier that amplifies the output of the infrared sensor and an infrared ray radiated from the bottom of the cooking vessel by blocking the infrared ray radiated from the bottom of the cooking vessel. , A second infrared sensor that outputs a DC voltage proportional to the amount of infrared rays, and a second DC amplifier that inverts and amplifies the second infrared sensor output, and the output of the second DC amplifier Is input as the bias voltage of the first DC amplifier, and the output of the first DC amplifier is used as the output of the infrared detecting means.

  According to the present invention, in an induction heating cooker provided with a non-crystallized glass top plate, an infrared ray that outputs a DC voltage proportional to an input infrared ray amount, such as a quantum type such as a photodiode or a thermal type sensor such as a thermopile. In an induction heating cooker having a pan temperature detection means composed of a detection means and a DC amplification means, the output of the infrared detection means is stabilized against a temperature change (transient temperature change) inside the casing during cooking, An induction heating cooker can be provided that accurately detects the temperature of the bottom of the cooking pan even if the temperature changes due to cooking inside the housing. And the induction heating cooking appliance which enables safe and optimal cooking by controlling the high frequency electric power to a heating coil can be provided.

  Further, since non-crystallized glass is more transparent than crystallized glass, a high-quality design can be applied by using non-crystallized glass of borosilicate glass for the top plate.

  As a result of a test in which about 500 g of steel balls were dropped on a 4 mm thick glass top plate, crystallized glass was broken by falling balls from a height of about 50 cm, and in the case of borosilicate glass, it was broken by falling balls from a height of about 130 cm. Produced. Since borosilicate glass has high outer strength compared to crystallized glass, for example, the glass thickness of the top plate can be changed from 4 mm to 3 mm, and the top plate can be thinned.

  When the top plate is thinned, the transmittance of infrared rays that pass through the glass increases, and the amount of infrared energy from the cooking pan incident on the pan temperature detecting device increases, and the effect of improving the detection accuracy of the pan temperature is obtained. In addition, by reducing the thickness of the top plate, the induction heating cooker can be reduced in weight, saving energy in transportation and distribution processes, and reducing the cost such as transportation costs.

The perspective view which shows the structure of the induction heating cooking appliance of Example 1. FIG. Sectional drawing which shows the structure of the induction heating cooking appliance of Example 1. FIG. Sectional drawing which shows the detail of the right side heating coil periphery of Example 1. FIG. Sectional drawing which shows the detail of the left side heating coil periphery of Example 1. FIG. The top view which shows arrangement | positioning of the heating coil of Example 1, and a pan temperature detection apparatus. FIG. 3 is a plan view showing the back surface of the heating coil according to the first embodiment. The top view and sectional drawing of the pan temperature detection apparatus of Example 1. FIG. FIG. 3 is a diagram illustrating a reflective photointerrupter according to the first exemplary embodiment. The top view and sectional drawing which show the detail of the thermopile 25 for pan infrared radiation detection of Example 1. FIG. FIG. 2 is a plan view and a cross-sectional view showing details of a thermopile for temperature change compensation 26 according to the first embodiment. The control block diagram of the induction heating cooking appliance of Example 1. FIG. The figure which shows the detail of the conventional infrared rays detection circuit. The figure which shows the temperature characteristic of the conventional infrared rays detection circuit output. An experimental example showing the output fluctuation when the power of the conventional infrared detection circuit output is turned on and the ambient temperature changes. FIG. 3 is a diagram illustrating details of an infrared detection circuit according to the first embodiment. FIG. 3 is a schematic diagram illustrating an infrared detection circuit operation according to the first embodiment. FIG. 3 is an experimental example showing output fluctuations when the infrared detection circuit output of Example 1 is turned on and the ambient temperature changes. FIG. FIG. 3 is a diagram illustrating details of the reflectance detection circuit according to the first embodiment. The figure which shows the spectral radiant energy by Planck's distribution law. The figure which shows the optical characteristic of glass, such as a top plate. The figure which shows the comparison of the incident energy to a thermopile. The figure which shows the relationship between each part temperature of Example 1, and the incident infrared energy to the thermopile 25. FIG. The figure which shows the relationship between the blackbody (pan bottom) temperature of Example 1, and an infrared detection circuit output. The figure which shows the relationship between the top plate temperature of Example 1, and an infrared detection circuit output. FIG. 3 is a diagram illustrating a relationship between a reflection voltage and a reflectance of the reflectance detection circuit according to the first embodiment. The figure which shows the relationship between the pot bottom temperature of the various pots of Example 1, and a pot temperature detection circuit output. The figure which shows the relationship between the various pan emissivity of Example 1, and a reflectance. 2 is a flowchart of induction heating cooking according to the first embodiment. 5 is a flowchart of reflectance detection according to the first embodiment. The flowchart of the pan temperature detection of Example 1. FIG. The top view and sectional drawing of the pan temperature detection apparatus of Example 2. FIG. Details of the infrared detection circuit of the third embodiment. The top view and sectional drawing of the pan temperature detection apparatus of Example 3. FIG. Plane and sectional view of pan temperature detector of embodiment 3 The top view and sectional drawing of the pan temperature detection apparatus of Example 3. FIG.

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

  FIG. 1 is a perspective view of a main body 1 of an induction heating cooker according to a first embodiment, and FIG. 2 is a schematic longitudinal sectional view when a cooking pan 7 is placed on a portion indicated by a one-dot chain line AA ′ in FIG. . In the following, there are 2 pans on the left and right where induction heating is possible, 1 pan on the side that can be heated by the radiant heat of a heater such as a radiant heater or halogen heater (heating source), induction cooking with a fish grill An example of a vessel will be described, but the application target of the present invention is not limited to this. In particular, when the top plate is made of non-crystallized borosilicate glass, it is desirable that the induction heating cooker is provided with three pot places where induction heating is possible. This is because the maximum temperature of the top plate 2 is lowered to 500 ° C. or lower when the cooking pan 7 is heated by induction heating as compared with the radial heater. Not limited to this. In particular, when the top plate is made of non-crystallized borosilicate glass, it is desirable that the induction heating cooker is provided with three pot places where induction heating is possible. This is because the maximum temperature of the top plate 2 is lowered to 500 ° C. or lower when the cooking pan 7 is heated by induction heating as compared with the radial heater. The cooking pan 7 may be a magnetic iron pan suitable for induction heating, or may be a non-magnetic aluminum pan or copper pan. As shown in FIGS. 1 and 2, a top plate 2 is mounted on the upper surface of the main body 1.

  The top plate 2 is based on non-crystallized glass with letters and almost the entire surface painted on the back using a heat resistant paint with a heat resistant temperature of at least 3 and several tens of degrees, and the surface is printed to prevent the pan from slipping. It is heat-resistant glass as a material. The non-crystallized glass described in this example includes quartz glass, high silicate glass, and borosilicate glass. In particular, in this example, silicon is included in about 80% and boric acid is included in about 10-15%. It means a borosilicate glass having a thermal shock temperature of 300 ° C. or more and 500 ° C. or less.

  In front of the top plate 2 is mounted an operation display unit 3 in which a switch for instructing heating start or heating course of each port and grill, and a display for displaying the heating state (temperature, etc.) of each port are arranged. ing. In the following symbols, the final characters R and L indicate structural parts below the right and left heating ports, respectively, and those without this character indicate the right and left common structural components.

  On the upper surface of the top plate 2, a circle 4 having a radius that approximately matches the outermost radius of the heating coil 8 or the radiant heater disposed thereunder is printed to indicate a place where the pan can be heated. In addition, the top plate 2 is normally transparent to visible light, so the upper surface is coated with a heat resistant and durable garment mixed with a heat resistant paint on the frit glass, and the lower surface is coated with a heat resistant surface so that the interior of the device cannot be seen. It is. An infrared transmitting window 5 that is not printed or painted for detecting the pot temperature, which will be described later, is provided at a position shifted by about 50 mm from the center of the circle 4 at the two places where the pan is placed where induction heating is possible. 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 7 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 is supplied to the heating coil 8 from the inverter circuit 9 (high frequency current supply means), the heating coil 8 is divided into a first coil 8a on the outer peripheral side and a second coil 8b on the inner peripheral side. The heating coil 8 generates a high-frequency magnetic field 10 (indicated by a broken line in the figure), and this high-frequency magnetic field is linked to the cooking pan 7 to generate an eddy current. To do. Accordingly, the food in the cooking pan 7 is cooked by the heat generated by the cooking pan 7 itself. At this time, the top plate 2 under the cooking pan 7 also becomes high temperature due to heat transfer or radiant heat from the cooking pan 7 that has generated heat.

  An inverter circuit 9 is disposed below the right heating coil 8R on the right side of the top plate, and a grill cabinet 6 is disposed on the left side and below the left heating coil 8L. In the grill cabinet 6, tube heaters 6a and 6b are arranged one above the other so that grilled fish and the like can be cooked.

  FIG. 3 shows a cross section around the right heating coil 8R in detail. As shown in FIG. 3, a heating coil 8 divided by a coil gap 8c between the first coil 8a and the second coil 8b on the lower surface of the top plate 2 is provided in a coil base 10 made of heat-resistant plastic. They are arranged concentrically (spirally). Below the heating coil 8, U-shaped ferrites 11 are radially arranged inside the coil base member with the convex portions up. The ferrite 11 is arranged to efficiently guide the magnetic flux generated by the heating coil 8 to the cooking pan 7 which is a cooking container on the top plate 2. Further, the magnetic flux is prevented from leaking to the lower part of the coil base 10. This is because the ferrite 11 has a high magnetic permeability and almost all the magnetic flux passes through the ferrite 11.

  A coil cooling air passage 15 for cooling the heating coil 8 is installed under the coil base 10. The coil cooling air passage 15 is divided into two, one is connected to the inner peripheral side of the first coil 8a, and the coil upper surface cooling air passage 15a for cooling the upper surfaces of the second coil 8b and the first coil 8a, The other one is a coil lower surface cooling air passage 15b for cooling the lower surface of the first coil 8a. On the upper surface of the coil cooling air passage 15a located under the center portion of the coil base 10, a circular coil upper surface cooling air sending hole 15c is opened.

  The central portion of the coil base 10 is a cylindrical inner cavity 14a, and an inner peripheral side of the first coil 8a is a cylindrical outer cavity wall 14b connected to a radial beam incorporating the ferrite 11. . A coil upper surface cooling air sending hole 15c of the coil cooling air passage 15a is connected to the lower portion of the outer cavity wall 14b. A sealing material 16 such as glass wool is provided around the coil upper surface cooling air sending hole 15c and connected to the outer cavity wall 14b.

  Below the cooling air passage 15 to the right heating coil 8R, circuit cooling air passages 17a and 17b containing a circuit board such as an inverter circuit 9 are provided in two layers, and the right and left heating coils 8L and 8R are respectively stacked. Built-in inverter circuit. These cooling air passages are fixed to the main body 1.

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

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

  During cooking, outside air is introduced from a fan (not shown) built in the main body 1 into the coil upper surface cooling air passage 15a, the coil lower surface cooling air passage 15b, and the circuit cooling air passages 17a, 17b. However, since the cooling air is warmed by the heat generated by the inverter circuit power element, the heat generated by the ferrite, and the heat generated by the heating coil itself, the ambient temperature of the pan temperature detecting device 18 increases with time. When cooking is finished, the ambient temperature decreases with time. The cooling air flowing in the coil upper surface cooling air passage 15a raises the coil gap 7c and the inner cavity 14a in the cylindrical outer cavity wall 14b from the coil upper surface cooling air sending hole 15c while cooling the pan temperature detecting device 18, and the coil From the gap 8c and the upper portion of the inner cavity 14a, the top plate 2 blocks the flow between the top plate 2 and the heating coil 8, and the upper surface of the heating coil 8 and the lower surface of the top plate 2 are cooled. A plurality of small holes are formed in a portion corresponding to the lower surface of the coil 8a of the coil lower surface cooling air passage 15b, and the cooling air flowing through the coil lower surface cooling air passage 15b is jetted from here toward the lower surface of the coil 8a to cool it. .

  FIG. 4 shows a detailed cross section around the left heating coil 8L. The heating coil, coil base, cooling air passage, and coil base support structure are the same as in FIG. An upper pipe heater 6a and a lower pipe heater 6b are arranged inside the grill cabinet 6, and a net plate 6c is fixed therebetween, and a cooked food (fish or the like) is placed here to cook the grilled food. When grilled food is cooked in the grill cabinet 6, the upper surface of the grill 6 and the lower surface of the coil upper surface cooling air passage 15a of the heating coil 8L are in a high temperature state. This temperature heats the lower surface of the pan temperature detector 18L.

  FIG. 5 shows details of the top view of FIG. 3 excluding the top plate 2. It is a detailed block diagram of the heating coil 8, the coil base 10, and the coil cooling air path 15a. The positional relationship in the horizontal surface of the heating coil 8, the inner cavity 14a, and the pan temperature detection apparatus 18 is shown.

  The heating coil 8 is concentrically wound in the same direction with a litz wire that is insulated with Teflon (registered trademark) or the like, and is divided into a first coil 8a on the outer peripheral side and a second coil 8b on the inner peripheral side. The The gap 8c has a concentric band shape with a width of about 15 mm, and the winding end of the first coil 8a bridges the gap 8c and becomes the winding start of the second coil 8b. The first coil 8a, the bridging wire 8d, and the second winding The heating coil 8 is constituted by the coil 8b. The coil base 10 is provided with a cylindrical outer cavity wall 14b on the inner peripheral side of the first coil 8a, and the inside thereof is a coil gap portion 8c. An inner cavity 14a is provided on the inner peripheral side of the second coil 8b. Further, a sensor field cylinder 19 having an elliptical cylindrical shape (a short diameter of about 12 mm in the coil radial direction and a long diameter of 25 mm in the coil circumferential direction) is provided between a portion of the coil gap portion 8c and the two ferrites 11 arranged radially. A pan temperature detecting device 18 is installed under the sensor visual field cylinder 19.

  In the heating coil 8 wound concentrically in the embodiment, the induction magnetic field in the vicinity of the center of the winding width is the strongest, and when the pan is induction-heated, the temperature at the center portion of the winding width becomes the highest. The reason why the heating coil 8 is divided into two is that a pan temperature detection device 18 is provided under the division gap to detect the pan temperature of this high temperature portion.

  A thermistor 20 is installed on the upper side of the sensor visual field cylinder 19 so as to be in contact with the lateral lower surface of the infrared transmission window 5 of the top plate 2.

  Infrared rays from the bottom of the pan heated by induction pass through the infrared transmission window 5 of the top plate 2 and enter the thermopile (thermocouple) 25 built in the pan temperature detecting device 18 described in detail later from the sensor field tube 19. To do.

  FIG. 6 shows a view of FIG. 5 (the preceding heating coil 8) seen from the back. The coil base 10 is provided with two coil terminals 21a and 21b, the low voltage terminal 21a is connected to the start of winding of the first coil 8a, and the high voltage terminal 21b is connected to the end of winding of the second coil. Is done. The output lines 22a and 22b of the inverter circuit 9 are fixed to the terminals with screws. In a non-magnetic pot such as copper or aluminum, a high voltage output line 22b that outputs a high voltage of 4 to 5 kV is connected to a high voltage terminal 21b.

  As described with reference to FIGS. 5 and 6, the pan temperature detecting device 18 avoids the vicinity of the bridge line 8d and is disposed in the coil gap portion 8c located at a position away from the high voltage terminal 21b to which the high voltage output line 22b is connected. The case window 30 is installed under the sensor field cylinder 19 provided. The reason for avoiding the installation in the vicinity of the bridge line 8d is to prevent the magnetic field here from being disturbed and the magnetic field further leaking to the lower part, and heating the metal case 32 for electromagnetic shielding of the sensor case described later.

  The structure described in FIGS. 5 and 6 is the same for the left and right heating coils. In order to distinguish left and right, the last character of the code is indicated by R and L. For example, 8R indicates a right side heating coil, and 8L indicates a left side heating coil. A part of the right cooling air flows through the left cooling air passage. However, it is obvious that an independent intake fan may be provided on the left side to separate the air flowing in the left and right cooling air passages.

  FIG. 7 shows details of the pan temperature detecting device 18.

  FIG. 7A shows a plan view of the pan temperature detecting device 18. The pan temperature detection device 18 is not shielded from the infrared rays emitted from the bottom of the cooking container because the pan temperature detection device 18 is shielded from the infrared sensor (thermopile 25) for detecting infrared rays emitted from the bottom of the cooking vessel. A temperature change compensating infrared sensor (thermopile 26) and a reflective photo interrupter 27 are mainly configured. The thermopile 25, 26 and the reflection type photo interrupter 27 are disposed on the electronic circuit board 28 on which the infrared detection circuit 72 and the reflectance detection circuit 73 for amplifying the thermopile output signal are mounted. The change compensation thermopile 26, the reflective photo interrupter 27, and the electronic circuit board 28 are hermetically sealed in an infrared sensor case 29 (indicated by a one-dot chain line) made of a plastic member. The infrared sensor case 29 is provided with a case window 30 for transmitting infrared rays. The case window 30 is formed by thinly cutting non-crystallized glass having almost the same optical characteristics as the non-crystallized glass constituting the top plate 2. The optical filter 31 is fitted. In addition, although the optical filter 31 of a present Example demonstrates by non-crystallized glass, if it is a material which permeate | transmits infrared rays, it will not be restricted to this, For example, you may use crystallized glass. Further, the optical filter 31 may be any optical characteristic that has a low visible light transmittance at a wavelength of 1 μm or less from the top plate 2, and the optical filter 31 blocks visible light incident on the thermopile 25. The temperature detection error can be reduced.

  Thermopiles 25 and 26 and a reflective photo interrupter 27 are mounted on the electronic circuit board 28 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 previous case window 30 is opened. Further, the aluminum metal case 32 is covered with an outer infrared sensor case 33 made of a plastic member. Of course, the previous case window 30 is opened. That is, the thermopile 25, 26 is covered with a triple case.

  The reason why the thermopile 25 and the thermopile 26 are built in the same case is to match the ambient temperature conditions of these two elements as much as possible. The thermopile 25 and the reflective photo interrupter 27 are installed on the substrate 28 so as to look inside the sensor visual field cylinder 19.

  The pan temperature detecting device 18 configured as described above is installed in the coil upper surface cooling air passage 15a so that the case window 30 looks inside the sensor visual field cylinder 19 of the coil base 10.

  FIG. 7B shows a cross-sectional view along the line AA ′ in FIG. This is a cross section showing the positional relationship between the thermopiles 25 and 26 and the reflection type photo interrupter 27 mounted on the electronic circuit board 28 installed in the infrared sensor case 29 and the case window 30 and the optical filter 31 of the infrared sensor case 29. FIG.

  FIG. 8 shows details of the reflective photointerrupter 27. The reflective photo interrupter 27 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 near 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 27 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 7 placed on the top plate 2.

  The light emitting and light receiving portions on the front surface of the reflective photointerrupter 27 are arranged immediately below the lower surface of the optical filter 31. This is to prevent infrared light from being reflected and received by the optical filter 31 directly above.

FIG. 9 shows the details of the thermopile 25 for detecting pan radiant infrared rays.
FIG. 9A shows a perspective view of the thermopile 25. 9B is a cross-sectional view of the thermopile 25 taken along the line BB ′ in FIG. 9A, and FIG. 9C is a line taken along the line CC ′ in FIG. 9B. It is a top view of a cross section. The infrared absorption film is omitted so that the thermocouple can be seen.

  The thermopile 25 is obtained by connecting a number of thermocouples (thermocouples) in cascade (piling). The thermopile 25 is built in a metal case 37 made of a metal can 35 such as a nickel-plated steel plate and a metal stem 36. A silicon oxide film 39 is formed on the surface of the silicon substrate 38 having a thickness of about 300 μm to electrically and thermally insulate. Polysilicon and aluminum are sequentially deposited on the silicon oxide film 39 to form a polysilicon deposited film 40 and an aluminum deposited film 41. Create many thermocouples and connect them in cascade. An infrared absorption film 43 such as a rubidium oxide film or a polyimide film close to a black body is formed as a protective film at the center of the silicon substrate 38 having polysilicon and aluminum junctions (temperature measuring contacts). 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 290 μm leaving the periphery (cold contact portion), and the thickness of the silicon substrate having the temperature measuring contact portion is formed to 10 μm. This is to reduce the heat conduction between the temperature measuring contact portion 42 and the cold junction portion 44 by thinning the silicon having good thermal conductivity, thereby thermally insulating the temperature measuring contact portion and the cold junction portion.

  The silicon substrate 38 is fixed to the metal stem 36 of the metal case 37 with a bond or the like. At the same time, the NTC thermistor 45 formed on the ceramic is similarly disposed on the metal stem 36. This is for detecting the ambient temperature of the thermocouple in the metal case 37 and correcting the thermoelectromotive force of the thermocouple. Details will be described later. Four metal pins 46 that are insulated and sealed pass through the metal stem 36, and the output of the previous thermocouple and the NTC thermistor 45 are wire-connected to the metal pins 36. A cylindrical metal can 35 is covered and welded to the stem 36 in an inert gas such as nitrogen. A small-hole window 47 is opened on the upper surface of the metal can 35, and a glass lens 48 is mounted on the inside thereof. The optical characteristic of the lens 48 (solid line in FIG. 20) blocks visible light because it has a transmittance of 1 μm or less compared to the non-crystallized glass of the top plate 2. 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 lens 48 is designed so that the field of view of the infrared transmission window 5 forms an image on the infrared absorption film 43. This is to narrow the visual field characteristics of the thermopile 25 and increase the light collection efficiency.

  The thermocouple temperature measuring contact portion 42 (below the infrared absorption film 43) in the thermopile 25 is heated by the infrared light that passes through the small hole window 46 and is condensed by the lens 48, and this heating temperature rise has passed. A voltage proportional to the infrared energy and proportional to the temperature difference between the cold junction portion 44 and the temperature measuring contact portion 42 of the thermocouple is output to the metal pin 46 of the thermocouple output.

  As described above, in the thermopile 25, the metal case 37 is thermally the same as the cold junction of the thermocouple, and this temperature fluctuation directly becomes the output fluctuation of the thermopile 25.

  FIG. 10 shows details of the thermopile 26 for temperature change compensation used as a temperature compensation element. In the figure, the same reference numerals as those in FIG.

The thermopile 26 of the temperature compensation element includes a window 46 on the upper surface of the metal case 37 and the lens 4.
8 and NTC thermistor 45 are not provided, but the other structure is the same as that of thermopile 25. The upper surface of the infrared absorption film 43 is shielded by a metal case 37 and is built in a metal case 37 including a metal can 35 and a metal stem 36 so that infrared rays do not enter the infrared absorption film 43. The composition, shape, dimensions, and enclosed inert gas of the thermocouple (including logarithm and pattern), silicon substrate 38, silicon oxide film 39, metal case 37, and metal stem 36 are the same as the above-described identical structure. say. In other words, the heat transfer characteristics of the ambient temperature to the cold junction part 44 and the temperature measurement contact part 42 are the same as the heat transfer characteristics from the cold junction part 44 to the temperature measurement contact part 42.

  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. In the following, symbol R represents a block relating to the induction heating port located on the right side in FIG. 1, and symbol L represents a block relating to the induction heating port located on the left side in FIG. The two inverter circuits 9R and 9L supply high-frequency current to the heating coils 8R and 8L. The frequency control circuits 61R and 61L and the power control circuits 62R and 62L adjust the operating frequency of the inverter circuits 9R and 9L 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. Generally, 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 9R and 9L. 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. A commercial power supply 65 of 3 terminals 200V is connected to the upper and lower grill heaters 6a and 6b via a grill heater circuit 68. The grill heater circuit 68 controls the power supplied to the grill heaters 6a and 6b.

  The microcomputer 60 is connected with an operation switch 69 and a display circuit 70 of a display / operation unit, and accepts a user's operation instruction and displays an operation state of the device. Further, a buzzer 71 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, the radiant heater circuit 67, and the grill heater circuit 68 according to the instructions of the user, and the cooking pan 7 or the grill box 6 on the top plate 2 is controlled. Heat the inside.

  The thermopile 25, 26 is connected to the infrared detection circuit 72, and the output of the thermopile 25 is amplified and input to the AD terminal of the microcomputer 60. The photo interrupter 27 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 7 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 operations of the infrared detection circuit 72 and the reflectance detection circuit 73 will be described later. Further, the thermistor 20R is connected to the thermistor temperature detection circuit 74R, and its output is input to the AD terminal of the microcomputer 60. Similarly, the thermistor 20L is also connected to the thermistor temperature detection circuit 74L, and its output is also input to the AD terminal of the microcomputer 60. These detect the temperature of the top plate 2.

  Further, the microcomputer 60 knows the infrared reflectance of the cooking pot from the output of the reflectance detection circuit 73 and corrects it with the reflectance to detect the temperature of the cooking pot. This process is also performed by the software of the microcomputer 60. (Operation of reflectance correction means) Then, the temperature is converted into a pan temperature using a temperature conversion table (relationship between the output voltage of the infrared detection circuit 72 and the pan temperature) prepared in advance.

  The microcomputer 60 controls heating of the cooking pan 7 via the power control circuit 62 based on the pan temperature. Details of this processing method will be described later.

  FIG. 12 shows details of a conventional infrared detection circuit 72. Thermopile output (thermoelectromotive force) of thermopile 25 (voltage between symbols (+) and (-) in the figure) is amplified about 3000 times by an operational amplifier (hereinafter abbreviated as OP amplifier) 72-1, and output terminal 7-2 and input to the AD terminal of the microcomputer 60. The amplification factor G of the OP amplifier 72-1 is determined by the resistors R1 and R2 (amplification factor G = (R2 / R1 + 1)).

  The NTC thermistor 45 in the thermopile 25 is connected in series with a resistor R8 to a voltage source (both ends of the resistor R6) obtained by dividing the circuit power supply voltage Vcc (= 5V) by resistors R5, R6, and R7. . A connection point (shown by a in the figure) with the resistor R8 is connected to an input of a buffer amplifier (voltage follower) constituted by an OP amplifier 72-3, and the voltage at the connection point a is directly output from the OP amplifier 72-3. Appear in The voltage at the point indicated by b in this figure (the output of the OP amplifier 72-3) is applied to the connection point of the resistor R1 and the thermocouple output terminal (-) as the bias voltage Vbias of the OP amplifier 72-1. The output impedance of the buffer amplifier constituted by the OP amplifier 72-3 is almost zero, and the bias voltage Vbias (same as the voltage at the connection point a) that is the output of the OP amplifier 72-3 is used as an ideal voltage source. To -1. The OP amplifier 72-1 uses the Vbias value as an operation reference voltage (value when the output voltage of the thermopile 25 is zero), and the thermocouple output of the thermopile 25 (DC voltage between (+) and (−) symbols in the figure). Is multiplied by G = (R2 / R1 + 1) and added to the Vbais value for output. This Vbias value is designed to be 0.5V as the resistance value of the NTC thermistor 45 at a temperature of 25 ° C. The bias voltage Vbais value offset by 0.5V from this zero voltage is used for detecting the failure of the infrared detection circuit 72. If the operational amplifier 72-1 is broken, the output terminal 72-2 is opened, or the output terminal 72-2 is short-circuited to the power supply VCC or circuit ground, the voltage read by the microcomputer 60 is different from 0.5V. .

In the circuit diagram shown in FIG. 12, an electronic circuit board in which both ends of R6 are short-circuited so that the temperature resistance value change of the NTC thermistor 45 does not affect the Vbias value and the amplification factor G of the OP amplifier 72-1 is set to 2700 is used. The conventional infrared detection circuit 72 shown in FIG. 12 was mounted on the pan temperature detection device 18 of FIG. 8, and the output of the OP amplifier 72-1 was measured while varying the temperature in the thermostatic bath. FIG. 13 shows an example of the results at a bath temperature of 25 ° C. to 60 ° C. This is measured by multiplying the thermocouple 25 thermocouple output (voltage between (+) and (−) symbols in the figure) by 2700 times. Here, the infrared rays from the upper wall of the thermostat are incident on the thermopile 25, but the wall of the thermostat is made of stainless steel (emissivity 0.3 or less) and low temperature (60 ° C. or less), as will be described later (FIG. 21). , See Fig. 26) The radiant infrared energy is 10% of that from the pan bottom (100 ° C)
Can be ignored below. Moreover, since the observation at each temperature point is performed after a sufficient time has elapsed, there is no temperature difference between the temperature measuring junction 42 (a point heated by infrared energy) and the cold junction 44, and the thermocouple has an electromotive force of zero. is there. That is, this measurement is a measurement of the temperature characteristics of the thermopile 25 in a state where no infrared light is incident. The input offset voltage of the OP amplifier 72-1 itself is 0.1 μV, and this temperature coefficient is 0.05 nV / ° C. The input offset voltage of the OP amplifier itself is constant and can be ignored in the above observation.

  From FIG. 13, the output of the thermopile 25 without infrared incidence has a negative temperature characteristic. The temperature coefficient is substantially the same for the five thermopiles, and is 0.22 μV / ° C. as an input conversion value (a value obtained by halving the value in the figure). Because of this temperature coefficient, even if the temperature of the pan (radiated energy) is constant, if the ambient temperature of the thermopile 25 rises, the output of the thermopile 25 will decrease, and the pan temperature cannot be accurately detected.

  This negative temperature characteristic depends on the temperature characteristic of the polysilicon wire resistance value of the aluminum-polysilicon thermocouple constituting the thermopile. As is well known, a metal wire has a positive resistance temperature characteristic. When the temperature rises, the resistance value rises and a voltage drop occurs with the input current (pA) of the OP amplifier. The fluctuation in the voltage drop becomes the negative temperature characteristic of the output.

  The NTC thermistor 45 is a resistance element having negative temperature characteristics, and the resistance value decreases as the temperature rises. For this reason, when the temperature in the thermopile 25 increases, the voltage at the previous connection point a (the connection point between the thermistor 45 and the resistor R8) increases. If the increase coefficient is designed to be 0.22 μV / ° C., the thermopile output decrease can be canceled. That is, the decrease in the thermopile 25 output is compensated by the increase in the voltage at the connection point a, that is, the bias voltage Vbias value of the OP amplifier 72-1. That is, the NTC thermistor 45 is used to prevent the output of the thermopile 25, that is, the output due to the radiant infrared energy of the measurement object from changing at the ambient temperature. That is, even if the ambient temperature of the thermopile 25 changes, the temperature of the measurement object, that is, the incident infrared energy, changes in a steady state (a state where the ambient temperature is constant and the temperature of the cold junction and the temperature measuring junction are the same). Otherwise, temperature compensation is performed so that no change in output occurs. The output after temperature compensation of the thermopile E-1 is shown by a broken line in FIG. It can be seen that the output is constant in the steady state even if the ambient (thermopile) temperature changes.

  In the conventional circuit of FIG. 12 in which temperature compensation is performed in a steady state (the ambient temperature is constant and the temperature measuring contact and the cold contact are the same temperature) in the thermistor 45, infrared rays are not incident on the thermopile 25. FIG. 14 shows sensor output fluctuation when the ambient temperature is gradually increased from 25 ° C. to 40 ° C. with time after the power is turned on. In the induction cooking device, the ambient temperature gradually rises to the pan temperature detecting device 18 in which the infrared detection circuit 72 is built in due to the heat of the inverter circuit power element, the heat of ferrite, and the heat of the heating coil itself as the pan is heated. This is because the cooling air is warmed. Moreover, in the state which is heating with the grill cabinet 6, in addition to the above-mentioned, the bottom face of the pan temperature detection apparatus 18 is heated greatly. This is a result of simulating this gradually warming in a thermostatic bath.

  From FIG. 14, it can be seen that immediately after the power is turned on, the sensor output overshoots and takes about 2 minutes to stabilize to the designed bias voltage (Vbias voltage value) of 0.5V. The circuit of FIG. 12 does not have such a time constant. Further, when the ambient temperature is changing, the sensor output dip greatly (about 50 mV output decreases), and after reaching a temperature of 40 ° C. and a sufficient time has elapsed, the designed bias voltage Vbias = 0.5V is reached. That is, it can be seen that the output voltage is the same when the ambient temperature is 25 ° C. and 40 ° C., and that the temperature compensation in the steady state is performed by the thermistor 45 described above. However, it can be seen that the sensor output changes greatly immediately after power-on and in a transient state where the temperature changes. When cooking with an induction heating cooker, as described above, the ambient temperature of the pan temperature detecting device 18 changes every moment. When the pan temperature is detected in this state, the fluctuation becomes a pan temperature detection error in the process of converting the output voltage of the infrared sensor described above into the pan temperature. Details will be described later.

  The cause of the output fluctuation is due to the structure of the sensor element (see FIG. 9). First, the cause of fluctuation at power-on will be described. The thermocouple 25 thermocouple is patterned on a 10 μm thick silicon oxide film. When voltage is applied to this pattern. A capacitor of silicon oxide film between the patterns is charged. For example, if the capacitor capacity and parallel resistance value are calculated from the silicon oxide film thickness 10 μm, resistivity, and dielectric constant, it will be about 10 pF and 1000 MΩ, and this time constant will be about 2 minutes. It almost coincides with the time to reach 0.5V.

  The output fluctuation at the time of temperature change is explained by the heat transfer delay from the cold junction part 44 to the temperature measuring junction part 42. The cold junction 44 is on bulk silicon, and the temperature measuring junction 42 is on a 10 μm silicon film and a 10 μm silicon oxide film. For this reason, the cold junction portion 44 becomes the same as the ambient temperature of the metal stem 36 and thus the metal can 35 in a relatively short time, but the temperature measuring contact portion 42 is delayed for a long time to reach the ambient temperature of the metal can 35 due to the heat transfer delay. . Assuming that there is no incidence of infrared rays, the temperature of the cold junction 44 is T1, and the temperature of the temperature measuring junction 42 is T2, T2 is a heat transfer coefficient proportional to the temperature difference (T1-T2) and is delayed from T1. As the temperature rises, the same temperature T1 = T2 is obtained after a long time. In the thermopile used in the experiment, as shown in FIG. In such a transient state where the ambient temperature is changing, the temperatures of the cold junction portion 44 and the temperature measuring contact portion 42 are different, and a voltage is generated at both ends of the thermocouple, that is, the thermopile 25 terminal. This is amplified by the amplification circuit and output to the output terminal 72-2 of the infrared detection circuit 72. While the ambient temperature rises, T1 reaches the ambient temperature relatively quickly, but T2 delays to the ambient temperature as described above. Therefore, during the rise, T1> T2 and a negative voltage is output. Conversely, if the ambient temperature is decreasing, the temperature decrease of T2 is delayed and T2> T1 is generated, and a positive voltage is generated (thermopile 25 is a voltage proportional to (T2-T1) at (+) terminal with respect to (-) terminal). Is output.)

  In such a state, when the pan temperature on the top plate 2 is detected, the voltage fluctuation becomes an error in detecting the infrared radiation from the pan, and the pan temperature detection accuracy is deteriorated.

  FIG. 15 shows an infrared detection circuit of this embodiment. The same reference numerals as those in FIG. 11 denote the same items. The OP amplifier 72-4 is a forward amplifier circuit with an amplification factor G = (R10 / R9 + 1) with R9 and R10, and the thermocouple output of the thermopile 26 shielded from this input (indicated by (+) and (-) in the figure). ) Is connected. The negative output of the thermopile (indicated by (−)) is connected to the normal input of the OP amplifier 72-4, and the positive output (indicated by (+)) is connected to R10. As a result, the thermocouple output having the opposite phase to that of the thermopile 25 is amplified by the OP amplifier 72-4 having an amplification factor G = (R10 / R9 + 1), and this output voltage is used as the bias voltage Vbias. Applied to the bias point indicated by middle b.

  If the thermopiles 25 and 26 have the same structure, they have the same phase and the same output with respect to infrared input, ambient temperature, or temperature change. The output of the thermopile 25 is amplified in the positive phase by the OP amplifier 72-1 having the amplification factor G = (R2 / R1 + 1), and the output of the thermopile 26 is the OP amplifier having the amplification factor G = (R10 / R9 + 1) in the opposite phase to the thermopile 25. The bias point voltage (indicated by b in the figure) of the OP amplifier 72-1 is amplified by 72-4 and is changed. This fluctuation becomes the output fluctuation of the OP amplifier 72-1. If there is no infrared incident on the thermopile 25 and the amplification factors G of the respective OP amplifiers are the same (R2 / R1 + 1 = R10 / R9 + 1), the fluctuation output due to the temperature change of the output terminal 72-2 has the same amplified signal and It is canceled out by the fluctuation output of the bias voltage Vbias which is the output of the OP amplifier 72-4 having the opposite phase. This is schematically shown in FIG.

  FIG. 16 shows the voltage of each part of the infrared detection circuit 72 when the ambient temperature is changed from 25 ° C. to 40 ° C. after the power is turned on. Note that there is no infrared incident on the thermopile 25. As indicated by a two-dot chain line in the figure, when there is no steady temperature compensation by the thermistor 45, the output of the OP amplifier 72-1 decreases at 40 ° C compared to 25 ° C. In order to prevent this, the voltage (bias voltage Vbais) at point 11a in FIG. 11a is raised as the temperature rises (b) as indicated by a one-dot chain line using the negative resistance temperature characteristic of the thermistor 45. As a result, as shown in the solid line (c), the conventional infrared detection circuit of FIG. 11 performs temperature compensation in the steady state (the output at 25 ° C. is the same as the output at 40 ° C.), but the temperature is changing. As described above, a dip occurs. The bias voltage (Vbais) indicated by the point b in FIG. 15 of the present application is a voltage obtained by adding the inverted (inverse phase) voltage of the voltage shown in (c) to the voltage shown in (b) as shown by the broken line (d). In this bias voltage Vbais, the two-dot chain line (there is no compensation for temperature change during steady state and transient state) voltage is canceled out, and as a result (e), the temperature changes even during steady state as shown by a thick solid line. The voltage is constant even during the transition. That is, the terminal 72-2 output of the infrared detection circuit 72 is compensated for steady and transient temperature fluctuations.

  Thus, the dip at the time of the temperature change shown in FIG. 14 output by the conventional circuit is the same and is canceled by the bias voltage Vbias of the antiphase signal, and the output terminal 72-2 has a mismatch between the dip and the steady state. Disappear.

  Note that, as described above, the steady-state temperature compensation by the thermistor 45 performed in the conventional circuit (FIG. 12) is the OP amplifier 72-4 that is the amplifier of the temperature compensation thermopile 26 in FIG. The bias voltage is applied to the connection point between the (−) terminal of the thermopile 26 and the resistor R9. In this way, temperature compensation during steady state is also possible. In the patent document, it is difficult to perform temperature compensation at the time of steady and transient at the same time, and it is not mentioned.

  When the power is turned on, the output fluctuation at the time of turning on is canceled by applying the reverse phase and the same output fluctuation to the bias voltage (Vbias) indicated by b, and no fluctuation is output to the output terminal 72-2. Here, since the thermopile 26 is shielded from light, there is no output due to infrared light reception, but the output fluctuation due to power-on or transient temperature fluctuation is the same as the thermopile 25. On the other hand, the thermopile 25 also outputs a voltage proportional to the incident infrared ray. As a result, the infrared detection circuit 72 eliminates output fluctuations due to power-on or transient temperature fluctuations, and outputs an output signal from the terminal 72-2 that is proportional only to the amount of infrared rays received by the thermopile 25.

  FIG. 17 shows the output of the circuit of this embodiment of FIG. 15 in comparison with the output of the conventional circuit of FIG. The fluctuation at the time of turning on the power is reduced to ¼, and the dip at the time of temperature change can be almost eliminated. Some variation remains due to variations in the sensitivity and heat transfer characteristics of the thermopiles 25 and 26, and deviations in temperature environment changes in each element. The deviation of the heat transfer characteristics is caused by the difference between the thermopile 25 which is a lens on the thermocouple and the thermopile 26 which is a light shielding metal can, or the positional relationship of each element, for example, the height from the substrate 28 and the mutual distance. Some variation due to this deviation can be corrected by finely adjusting the amplification factor G of the OP amplifier 72-4. Of course, the variation in the infrared detection sensitivity adjusts the amplification factor of the OP amplifier 72-1. In the present application, variation in infrared detection sensitivity, variation in heat transfer characteristics, and deviation in temperature environment change in each element can be adjusted independently. In the prior art disclosed in Patent Document 1, it is difficult to independently correct variations in the infrared detecting thermopile 25 and the temperature compensating thermopile 26.

  FIG. 18 shows details of the reflectance detection circuit 73. The infrared LED 50 which is a light emitting element of the photo interrupter 27 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. When a rectangular wave signal with a duty of 50% is input to the drive signal terminal 73-2, the infrared LED 50 emits light when the signal is 5V, and turns off when the signal is 0V. This emission intensity is proportional to the current passed through the infrared LED 50, and this current is determined by the value of the resistor R11. In this embodiment, the resistance value is fixed and the light emission intensity is constant. When the infrared light is reflected by the top plate 2 and the bottom surface of the cooking pan 7 and received by the phototransistor 51 as a light receiving element, a voltage is generated in the resistor R12 by the photocurrent. If the reflection is large (the amount of received light is large), the voltage increases proportionally. This signal voltage is cut in DC by the capacitor C1 and input as an AC signal to a normal DC amplifier constituted by an OP amplifier 73-3. Here, only the positive component of the AC signal is amplified. The amplified 50% duty signal is converted into a DC average voltage by a charge / discharge circuit (comprising R13 and C2) 73-4 and output from an 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. When the cooking pan 7 is not placed, the reflection is only from the top plate 2, which shows a constant value. The future increase is the reflection from the pan, and this amount corresponds to the reflectivity of the pan.

  Infrared emission is carrier-modulated and the direct current component is cut off in the light receiving path because natural light or certain infrared light contained in lighting equipment such as incandescent lamps and fluorescent lamps affects the detection of pan reflectivity. It is for preventing. (Visible light is cut by the optical filter of the light receiving element.) Further, the influence of the dark current of the phototransistor 51 is also prevented.

Hereinafter, the pan temperature detection operation of the first embodiment will be described.
The cooking pan 7 placed on the top plate 2 generates heat by induction heating. By this heating, infrared rays are emitted from the bottom of the cooking pan 7. This total radiant energy E is proportional to the fourth power of the pan temperature T. (E = σT ⁴ ; Stefan-Boltzmann law) FIG. 19 shows the spectral radiant energy of the black body temperature calculated from the Planck distribution law. If this spectral radiant energy is integrated over the entire wavelength region, the total radiant energy E is obtained, which is proportional to the fourth power of the temperature (absolute temperature). This is the aforementioned Stefan-Boltzmann law, and this coefficient σ is the Stefan-Boltzmann coefficient. The peak wavelength of the spectral radiant energy is 5 μm to 8 μm at a cooking temperature of 100 to 300 ° C. based on the Vienna transition law.

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

  On the other hand, the optical characteristics of non-crystallized glass (top plate 2), which is a non-magnetic material, are shown by solid lines (thin lines) in FIG. As shown by a solid line (thin line) in FIG. 20, the borosilicate glass used as the non-crystallized glass transmits light having a wavelength of 0.4 μm to 2.5 μm by 80% or more, and 25 light having a wavelength of 3 to 4 μm. %, And transmits almost no light having a wavelength longer than 4 μm and a wavelength shorter than 0.4 μm. Due to this optical characteristic, most of the infrared radiation energy (see FIG. 19) radiated from the pan cannot pass through the top plate 2. Only about 1% of the total infrared radiation energy radiated from the pan can pass. Moreover, the optical characteristic of the crystallized glass employ | adopted with the top plate of the conventional induction heating cooking appliance is shown with a broken line in FIG. Crystallized glass transmits 80% or more of light having a wavelength of 0.5 μm to 2.5 μm, transmits about 50% of light having a wavelength of 3 to 4.5 μm, has a wavelength longer than 4.5 μm, and 0 It hardly transmits light having a wavelength shorter than .5 μm.

  FIG. 21 shows a case where only the air is between the black body and the thermopile, and a case where the non-crystallized glass borosilicate glass top plate 2 and the optical filter 31 are inserted between the black body and the thermopile as shown in FIG. The relationship between the incident energy incident on the thermopile and the black body temperature radiating infrared rays is shown in comparison. Moreover, the incident energy which injects into a thermopile at the time of combining a crystallized glass top plate and an optical filter as a comparison with the conventional induction heating cooker is shown. This is obtained by multiplying the spectral radiant energy of FIG. 19 by the optical characteristic (transmittance) of FIG. In the case of only air, the calculation is performed assuming that the transmittance is 1 in all wavelength regions. From the figure, since the non-crystallized glass top plate 2 and the optical filter 31 of the present embodiment (induction heating cooker) are interposed, about 2 digits or more at around 100 ° C., compared to the case without air (only air), 300 Even at ℃, the energy incident on the thermopile has decreased by an order of magnitude. Compared with the incident energy of the combination of the conventional crystallized glass top plate and the optical filter, the ratio of the incident energy is reduced to about 10% near 100 ° C. and to about 35% near 300 ° C.

  The reason for the large decrease in incident energy on the low temperature side is that more of the low temperature radiation spectral energy is removed (filtered) by the top plate. For this reason, high sensitivity is required for the infrared sensor, and the sensor output must be amplified with a high amplification factor G.

  As is well known, infrared sensors include quantum types such as infrared photodiodes and infrared phototransistors, and thermal types such as thermopile and pyroelectric elements. The quantum type sensor is characterized by high sensitivity in a narrow wavelength band because it detects infrared rays by the quantum effect, and the thermal type has low sensitivity in a wide wavelength band. For the quantum type, the sensitivity wavelength is determined by the type of semiconductor, and those that can be purchased at a low cost, such as silicon, have a practical sensitivity wavelength of 1 μm or less from outside visible light (0.8 μm), so the detection temperature range is 300 ° C. or more. Become. Further, an infrared phototransistor having a detection sensitivity (wavelength 2 μm) on the low temperature side is a compound semiconductor (for example, InGaAs), and therefore is about 1 to 2 digits more expensive than silicon. On the other hand, the thermal type has a uniform and low sensitivity in a wide wavelength band of 20 μm or less from visible light compared to the quantum type (in principle, it has no wavelength dependence). For this reason, an optical filter is provided in front of the infrared light receiving surface to the sensor to prevent disturbance by narrowing the detection temperature range wavelength.

  In this embodiment, since the detected temperature range is from around 100 to 380 ° C., a thermal type thermopile is used as the infrared sensor. Since the pyroelectric element of the same thermal type is a differential type sensor, it is necessary to interrupt infrared incidence, and a normal mechanical chopper mechanism is used. For this reason, it is unsuitable to use for household appliances like an induction heating cooker from the point of reliability. In the same thermal type thermistor element, there is nonlinearity between the incident infrared energy and the output (resistance value), and it is necessary to correct this. Further, in order to increase the sensitivity, it must be thinned to have a folded long line, which increases the resistance value of the element. On the other hand, thermopile does not require such a mechanism and correction, and in recent years, a thermocouple that uses a semiconductor process is miniaturized by a technique such as MEMS, and a large number of layers are piled up (piled) to improve sensitivity. Has been.

  The incident energy to the thermopile used in conventional thermometers and microwave ovens is large, the sensitivity of the thermopile itself does not matter so much, and the amplification factor G of the amplification circuit that amplifies the thermopile output may be 100 times or less. However, in the pan temperature detection device 18 of this embodiment, which is an induction heating cooker, a thermocouple (thermocouple) is a polysilicon / aluminum metal pair that can be formed relatively easily by a semiconductor process, and a thermopile 25 having about 50 deposited thermocouples is formed. In addition, the sensitivity is increased by about 10 times compared with a general lens focusing light. The output is amplified 3000 times by an amplifier circuit so that the minute incident infrared energy described above can be detected.

  When measuring the temperature of an object with a thermocouple, the cold junction is fixed at the freezing point (0 ° C.) and the temperature measuring contact is brought into contact with the object. As described with reference to FIG. 9, the thermopile is formed by depositing a large number of thermocouples, and is composed of a large number of temperature measuring contacts heated by incident infrared rays and a large number of cold contacts on the silicon substrate 38. Since the cold junction is fixed to the metal stem 36 of the metal case 37 with a bond, the thermopile metal case 37 (metal can 36 and metal stem 37) is a cold junction. And this metal case 37 cannot be fixed to a freezing point like a normal thermocouple.

  Assuming that the thermoelectromotive force of one thermocouple is 5 μV / ° C., the number of piles is 50, and the amplification factor of the DC amplifier is 2000, when the temperature of the metal case 37 changes by 1 ° C., the voltage fluctuation of 500 mV occurs at the output of the DC amplifier. Become. That is, it is necessary to suppress the temperature fluctuation around the thermopile 25.

  The pan temperature detecting device 18 of the present embodiment is disposed immediately below the coil gap 7c where the magnetic flux density of the high frequency magnetic field generated by the divided heating coil 8 is the strongest so that the hot portion of the pan bottom during cooking can be detected. The This position is between the rod-shaped ferrites 11 arranged radially under the heating coil 8, and since the magnetic flux almost passes through the ferrite, it is a place where there is little leakage magnetic flux. However, since the distance from the lower surface of the heating coil 8 is about 20 mm, the magnetic flux leakage is large, and the temperature of the metal located here is increased by induction heating. For example, when high frequency power of 3 kW is input to the heating coil and a pot serving as a cooking vessel placed on the top plate 2 is induction heated, the temperature of the magnetic steel plate at this location rises by about 30 ° C. . Even with non-magnetic aluminum, the temperature rises by about 5 ° C.

  During cooking, the pan bottom heated by induction becomes a high temperature of 100 to 300 ° C. And the top plate 2 and the heating coil 8 on the lower surface also become high temperature due to heat conduction and heat radiation from the pan bottom.

  Furthermore, since a high frequency current of more than ten amperes flows through the heating coil 8, the coil itself generates Joule heat. In order to cool the top plate and the heating coil, outside air is introduced into the coil cooling air passages 15a and 15b, and the heating coil 8 is blown and cooled as described above.

  In addition, an inverter circuit 9 that supplies high-frequency power to the heating coil is disposed in the cooling air passages 17a and 17b below the pan temperature detector 18. This inverter circuit is composed of a circuit that switches a current of 20 to 90 kHz and several tens of amperes. For this reason, a large electromagnetic wave is radiated.

  As described above, the pan temperature detecting device 18, particularly the thermopiles 25 and 26 incorporated therein, are (1) leakage magnetic flux from the heating coil 8, (2) temperature change due to cooling air for cooling the coil, and (3) inverter circuit. It will be exposed to electromagnetic noise radiated from. In response to these disturbances, the pan temperature detection device 18 must detect the pan bottom temperature during cooking.

  It is desirable that the pan temperature detecting device 18 in which the thermopile 25, 26 is built is placed in a constant temperature atmosphere as much as possible. For this reason, in this embodiment, the pan temperature detection device 18 is installed in the coil cooling air passage 15a into which the outside air is introduced, and the thermopile 25, 26 and the infrared detection circuit 72 are cooled with the outside air during cooking, and these temperatures rise. Is preventing. In addition, in order to prevent the airflow in the coil cooling air passage 15a from directly hitting the metal case 37 of the thermopile 25, 26 and the semiconductor, resistance, etc. of the infrared detection circuit 72, the thermal sensor 25 is a windproof case. It covers this. Further, the thermopiles 25 and 26 and the infrared detection circuit 72 are also thermally insulated by the air in the infrared case 29. The output of the thermopile 25 is dc-amplified in a stable manner with respect to the temperature change, and then output as a signal voltage with a low output impedance to the AD terminal of the microcomputer 60 described later.

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

  The metal case 32 is induction-heated by the ambient atmosphere temperature and the leakage magnetic flux from the heating coil 7 during cooking, and the temperature rises by 5 to 10 ° C. in the case of aluminum. When cooking is continued before the temperature rise subsides, when the outside air is rapidly introduced and applied to the metal case 32, the metal case 32 cools rapidly, and as a result, the ambient temperature of the thermopile 25 in the infrared sensor case 29 suddenly increases. Will be reduced. In the opposite case, for example, when cooking first in the winter morning, the metal case 32 in the aircraft is sufficiently cooled at night and is at about 5 ° C., and the user starts cooking in a cooking room heated to 20 ° C. The warm air is introduced into the cooling air passage 15a, and the warm air at 20 ° C. is applied to the metal case 31 at 5 ° C. In this embodiment, in order to prevent such a sudden temperature change of the metal case 32 due to the outside air, the metal case 32 is further covered with a plastic outer infrared sensor case 33. Thus, the cooling air is not directly applied to the metal case 32, thereby preventing a sudden temperature change due to the wind.

  Even when taking measures against such environmental temperature fluctuations, as shown in FIG. 14, the sensor output fluctuates when the power is turned on and when the environmental temperature changes. By performing the new temperature compensation shown in FIG. 15, the sensor output fluctuation can be greatly reduced as shown in FIG.

  Now, the top plate 2 is heated by absorbing infrared radiation from the induction-heated cooking pan 7 and by contact heat conduction. As shown by a solid line (thin line) in FIG. 20, the top plate 2 transmits light having a wavelength of 0.4 μm to 2.5 μm by 80% or more, transmits light having a wavelength of 3 μm to 4 μm by about 25%, and more than 4 μm. Light with a long wavelength and a wavelength shorter than 0.4 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 7 is placed on the top plate 2, the reflection of the infrared radiation energy of the cooking pan 7 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 has an absorption rate α = emissivity ε, the top plate 2 transmits 80% or more of infrared radiation energy from the cooking pan 7 at a wavelength of 0.4 μm to 2.5 μm, and the remaining 20%. Absorb and radiate it. Further, at a wavelength of 3 μm to 4 μm, about 25% is transmitted, and the remaining 75% is absorbed and emitted. At a wavelength longer than 4 μm and at a wavelength shorter than 0.4 μm, the light is hardly transmitted and is absorbed and emitted. The same applies to the portion heated by heat conduction. When the wavelength is 4 μm or more, most of the infrared energy for heat conduction is emitted from the surface of the top plate 2.

  For this reason, when the temperature of the cooking pan 7 on the top plate 2 is detected using the thermopile 25, the infrared rays emitted by the heating of the top plate 2 itself become a problem. For example, if the transmission wavelength of the lens 48 attached to the thermopile 25 is 1 to 15 μm, the output of the thermopile 25 is greatly affected by infrared rays having a wavelength longer than 4 μm emitted from the top plate 2, and the bottom of the cooking pan on the top plate 2 It is impossible to accurately detect the temperature. The radiant infrared energy of the pan passing through the top plate 2 is about 2 μm band of 1 μm to 2.5 μm, whereas the infrared energy radiated by the top plate 2 itself is about 10 μm band of 4 μm to 15 μm at the same temperature. If there is any thermopile output, five times the temperature depending on the temperature of the cooking pan 7 depends on the temperature of the top plate 2.

  In the present embodiment, in order to prevent the above, a case window 30 for transmitting infrared rays is opened in the infrared sensor case 29 of the pan temperature detection device 18 constituted by the thermopile 25, and the top plate 2 is configured in the case window 30. A non-crystallized glass to be cut is thinly fitted as an optical filter 31. Then, the amount of infrared rays radiated from the top plate 2 incident on the thermopile 25 is removed. The portion with a wavelength of 4 μm or more emitted from the top plate is blocked from entering the thermopile 25 by the optical characteristics of the optical filter 31 having the same transmission characteristics as the top plate 2.

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

  In addition, when crystallized glass is used for the optical filter, infrared light having a wavelength of 4 to 5 μm emitted from the top plate is incident on the infrared sensor as thermal disturbance in the crystallized glass, which causes a detection error of the pan temperature. Therefore, it is desirable that the optical filter and the top plate are made of the same material.

  As the lens 48 of the thermopile 25, glass having a transmittance of 1 μm or less in wavelength and lower optical characteristics than the top plate (shown by a solid line (thick line) broken line in FIG. 20) is used. Since visible light has a wavelength characteristic of 0.38 to 0.8 μm, a light shielding effect of visible light such as illumination and the sun can be obtained by optical characteristics of the lens. When visible light is incident on the thermopile, the thermopile output increases regardless of the temperature rise of the cooking pan 7, so the pan temperature cannot be detected correctly. In detecting the pan temperature in the induction heating cooker, a pan temperature detecting means for providing a visible light shielding effect is required.

  Infrared energy detected by the thermopile 25 during cooking is (2) Infrared energy from the top plate 2 in addition to (1) Infrared energy from the cooking pan, (3) From the inner wall of the sensor visual field cylinder 19 Infrared energy, (4) infrared energy from the optical filter 31, and (5) infrared energy from other members are superimposed, and the thermopile 25 generates a voltage proportional to the infrared energy. In order to accurately detect the pan temperature, (2) it is necessary to subtract the voltage due to the infrared energy from the top plate.

  The item (3) narrows the field of view of the thermopile 25 to a half-value angle of 10 degrees, the temperature of the inner wall is kept at 60 ° C. or lower during operation with cooling air, and the item (4) is for placing the pan temperature detector 18 in the cooling air passage. Since it is disposed, its temperature is suppressed to 40 ° C. or lower, and infrared energy that becomes a thermal disturbance incident on the thermopile is reduced. The item (5) is the same as the item (4).

  However, as shown in FIG. 21, in contrast to the conventional combination of the crystallized glass top plate and the optical filter, the combination of the non-crystallized glass top plate 2 and the optical filter 31 of the present embodiment is a thermopile. Since the infrared energy from the incident cooking pan 7 falls to about 10 to 35%, the proportion of infrared energy that becomes a thermal disturbance due to (3) to (5) increases.

  In this regard, by providing the thermopile 26 with the same light receiving structure as the thermopile 25, fluctuations in the thermopile output due to thermal disturbance in which the ambient temperature of the pan temperature detecting device 18 changes due to temperature changes of (3) to (5). Can be prevented.

  FIG. 22 collectively shows the relationship between the temperature of each part and the infrared energy (calculation result) that is emitted from each part and incident on the infrared absorption film 43 of the thermopile 25 in this embodiment. This is calculated using the spectral radiant energy of FIG. 19 and the transmission characteristics of each member (shown in FIG. 20). The temperature of each part is shown only in the temperature range reached during cooking.

  Assuming that the typical energy of each member during cooking, for example, the incident energy from a 300 ° C. pan (black body) is 1, the heat transfer rate of the top plate 2 (glass) is 200 It is only 1/6 from the top plate of the sensor plate at 80 ° C, 1/120 from the sensor field tube at 80 ° C, and 1 from the optical filter 31 at 40 ° C. / 60. If the emissivity of the pan becomes, for example, 0.25, the incident energy 1 from the pan becomes 1/4, and the incident energy from other members, particularly the top plate 2, is not so much different. That is, it can be understood that the disturbance to the pan temperature detection at a low temperature cannot be ignored.

  FIG. 23 shows the black body temperature T and the output voltage V of the infrared detection circuit 72 output terminal 72-2 when the black body is placed on the infrared transmission window 5 of the embodiment of FIG. The relationship is shown. The black body is a case where the top plate is placed for such a short time that the top plate is not heated, and the temperature of the sensor field tube 19 and the optical filter 31 is not increased. That is, this is obtained by converting only the incident infrared energy from the cooking pan described in the item (1) into a voltage by the thermopile 25 and amplifying and outputting the voltage by the infrared detection circuit 72.

  The output voltage V is approximately 0.5 V from room temperature to 100 ° C., and when it exceeds 100 ° C., a voltage proportional to the power of temperature (absolute temperature) is output.

  0.5V is a voltage obtained by dividing the power supply voltage (5V) of the infrared detection circuit 72 by resistors R5, R6, and R7 (indicated by points a / b in FIG. 11 / FIG. 15). This is because it is given as the bias voltage Vbias. A value obtained by subtracting 0.5 V from the output voltage value of the output terminal 72-2 (a voltage increase value from 0.5 V) is proportional to the pan bottom temperature. The microcomputer 60 AD-converts and reads the output voltage V of the output terminal 72-2 of the infrared detection circuit 72. The pan temperature detection voltage Vt (= V−0.5), which is a value obtained by subtracting 0.5V from this voltage. ) To obtain the pan temperature. 23 is stored in advance in the ROM of the microcomputer 60 as table data TBLn. This is a data table for obtaining the pan temperature from the thermopile 25 output, that is, the pan temperature detection circuit 72 output voltage.

  FIG. 24 shows the relationship between the top plate temperature Tt when only the top plate 2 is heated and the output voltage V of the infrared detection circuit 72 output terminal 72-2. However, it is shown by a value obtained by subtracting 0.5 V described above. The relationship between the top plate temperature Tt when the vicinity of the sensor window 5 of the top plate 2 where the pan is not placed is heated with hot air and the output voltage V of the infrared detection circuit 72 output terminal 72-2 is shown. At this time, the sensor visual field cylinder 19 and the optical filter 31 are prevented from being heated. That is, this is obtained by converting the radiant infrared energy from the top plate 2 into a voltage. 24 is stored in advance in the ROM of the microcomputer 60 as table data TBLt.

  When the photo interrupter 27 built in the pan temperature detecting device 18 is arranged as shown in FIG. 8, when there is no cooking pan on the top plate 2, most of the infrared light (wavelength 930 nm) emitted from the infrared LED 50 is an optical filter. 31 does not pass through the top plate 2 and 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, since the amount reflected by the optical filter 31 is directly returned to the infrared phototransistor 51 immediately beside it, as shown in FIG. 8, in this embodiment, the front surface of the photo interrupter 26 is disposed so as to be in contact with the lower surface of the optical filter 31. This 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 that is reflected by an object (inner surface of the sensor visual field cylinder 19) that does not reach the lower surface of the top plate and is in the middle of the path.

  For this reason, the output of the reflectance detection circuit 73 is (a) Vr1 when there is a pan on the top plate, and (b) Vr2 when there is no pan. The reflected voltage Vr at the net pan is Vr = Vr1-Vr2.

  FIG. 25 shows the relationship between 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 disposed on the top plate. 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. Then, this relationship is stored in the table data or the coefficient value of the approximate expression 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. To do. In a cooking pan (transmittance α = 0), the infrared energy radiated differs due to the difference in emissivity, while the same pan bottom temperature. For this reason, the problem that a thermopile output, ie, the output of the pan temperature detection apparatus 18, differs arises. Therefore, it is necessary to detect the reflectance of the bottom of the cooking pan to obtain the emissivity, correct the output of the pan temperature detection device 18 and then convert it to a temperature. In order to do this, the reflectance detection circuit 73 obtains the reflectance from the reflected voltage Vr, which is an amount corresponding to the reflectance described above. This reflectance is subtracted from 1 to obtain the emissivity.

FIG. 26 shows values obtained by subtracting the aforementioned 0.5 V bias voltage Vbias from the output of the pan temperature detection device 18 (output V of the infrared detection circuit 72) for several types of pans placed on the top plate 2 and having different emissivities. An example of the relationship between Vt (pan temperature detection voltage) and pan bottom temperature T is shown. The emissivity at the bottom of each pan is also shown in the figure. 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. The pan shown in FIG. 26 (a) has an emissivity of 0.9, which is close to a black body. (B) has an emissivity of 0.57, (c) is 0.43, and (d) is 0.24. When the voltage values of (b), (c), and (d) are divided by the emissivity, it is shown by a broken line in the figure, and it can be seen that it can be summarized into almost one curve. Each output Vt1 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.

  FIG. 27 shows the relationship between the emissivity measured using a radiation thermometer in each pan and the reflectivity obtained using the reflectivity detection circuit 73 in FIG. 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 due to scattering on the pan surface are received.

  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. In the present embodiment, the visual field surface of the thermopile 25 in the pan temperature detecting device 18 at the position on the top plate 2 and the reflective surface on the top plate 2 for the reflectance detection light emission are the same surface. For this reason, as shown in FIG. 7, the thermopile 25 and the reflective photointerrupter 26 are arranged side by side in the pan temperature detection device 18.

  Below, operation | movement of a present Example is demonstrated as the case where the cooking pan 7 is set | placed on the circle display 4 of the front right side, and cooking is performed by heating a cooking pan for a predetermined time at predetermined temperature. FIG. 28 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 where the cooking pan 7 is placed (step S1), and the start of cooking is instructed (step S2), the microcomputer 60 first starts. The reflection data (corresponding to the reflectance) of the pan placed by controlling the reflectance detection circuit 73 is taken in, and the reflectance (emissivity) is detected (step S3). At the same time, in order to cool the heating coil 7, the inverter circuit 8, and the like, a fan (not shown) is driven to introduce outside air into the cooling air passages 15a, 15b and 16a, 16b.

  Here, step S3 for detecting the reflectance will be described in detail with reference to the flowchart shown in FIG. The microcomputer 60 outputs an infrared LED drive signal 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 Vr2 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 drawing reflection voltage Vr is calculated from the voltage Vr2 previously read in when the voltage Vr1 stored in advance is not placed (step S3-5). Then, an emissivity ε (= 1-reflectance) is obtained from the reflectance ρ from the relationship between the reflection voltage and the reflectance stored in advance (shown in FIG. 25) (step S3-6).

  Subsequent to the reflectance detection step S3, the power control circuit 62, the frequency control circuit 61, and the inverter circuit 9 are controlled to supply power to the heating coil 8 to start induction heating (step S4). When electric power is supplied to the heating coil 8, an induction magnetic field is emitted from the heating coil 8, and the cooking pan 7 on the top plate 2 is induction-heated. Due to this induction heating, the temperature of the cooking pan 7 rises, and cooking of the object to be heated in the cooking pan 7 is started. When the induction heating is started, the microcomputer 60 reads the output of the pan temperature detecting device 18 at regular intervals and detects the pan temperature (step S5).

  Here, the pan temperature detection operation (step S5) will be described in detail. FIG. 30 shows a flowchart of the pan temperature detection. The microcomputer 60 reads the output voltage V of the output terminal 72-2 of the pan temperature detector 18 (infrared detector circuit 72) (step S5-1), and design Vbias = 0.5V (designed at a steady room temperature of 25 ° C.) from this value. The obtained value is subtracted and used as the pan temperature detection voltage Vt (step S5-2).

  At the same time, the temperature Ta of the top plate 2 is read from the thermistor 20 and the thermistor temperature calculation circuit 73 (step S5-3). Then, the output voltage Va at the temperature Ta is obtained from the relationship between the top plate temperature Tt previously stored as the table TBLt and the output V (terminal 72-2) of the thermopile temperature detection circuit 72 (step S5-4, top Operation of obtaining plate temperature compensation voltage).

  Subsequently, Va is subtracted from the previous pan temperature detection voltage Vt (step S5-5). By this processing, the amount of infrared rays from the top plate 2 as a disturbance is removed. The voltage after this subtraction is defined as Vt (top plate temperature compensation operation by subtraction).

  Then, the pan temperature detection voltage Vt after this subtraction is divided by the emissivity ε (= 1−reflectance) obtained immediately before induction heating (step S5-6) (reflectance correction operation). Vbias = 0.5 V is added to Vt after division (step S5-7), and a data table that is a relationship between Vt and pan temperature T stored in advance as temperature conversion table TBLn is subtracted (step S5-8). ) To convert to pan temperature to obtain pan temperature T.

  Here, it is assumed that cooking is being performed in the oven cabinet 6 and the ambient temperature of the pan temperature detection device 18L is increasing. At this time, as shown in FIG. 14, in the conventional infrared detection circuit (FIG. 11), the output value is decreased (a voltage proportional to the incident infrared light is applied to the bias voltage which is decreased by temperature change and decreased). The above-described Vt (= the read output value−the bias voltage 0.5V at the steady state of design 25 ° C.) is lower than usual. As a result, the detection pan temperature is detected lower than that at normal temperature. On the contrary, when the ambient temperature is decreasing, the detected pan temperature is detected higher than that at the normal temperature. In the circuit of the present embodiment shown in FIG. 15, the infrared detection output does not fluctuate even when the ambient temperature changes, so the above-described pan temperature error does not occur.

  If the pan temperature T detected in the pan temperature detection operation (step S5) has not reached the predetermined temperature, the induction heating is continued while performing the pan temperature detection operation (step S5) (step S6). Subsequently, when the pan temperature T reaches a predetermined temperature, abnormal heating is checked (step S7). This is because it is dangerous if the pan temperature rises rapidly due to emptying or the like and reaches the ignition temperature of the oil. If the pan temperature exceeds 330 ° C., induction heating is stopped (step S12).

  When the pan temperature T reaches a predetermined temperature, the induction heating current is reduced (step S8), and the cooking time timer is set (step 9).

  Subsequently, the pan temperature is detected at regular intervals (step S5), the pan temperature is checked (step S6), the abnormal heating is also checked (step S7), and the current supplied to the heating coil 7 is decreased or increased by a predetermined amount. (Steps S8 and S10), and the pan temperature is kept constant (Tc). When a predetermined cooking time has elapsed (step S11), the user is notified of the end of cooking with a buzzer, and the power supply to the heating coil 8 is stopped (step S12). Thus, the food to be cooked in the cooking pan 7 is cooked at the set temperature and time. Again, when cooking, it becomes empty (no water), the pan temperature rises rapidly, and if it reaches the ignition temperature of the oil, it is dangerous. If this happens, induction heating is stopped (step S12).

  Instead of the process of calculating the emissivity (step S5-6) and the process of dividing the pan temperature detection voltage Vt by the emissivity (step S5-7), the magnification a = 1 / emissivity (a = 1/1 / The relationship between the value of ε) (becoming a value of 1 or more) and the reflectance (or reflection voltage Vr) is stored as a table, the magnification a is obtained from the reflectance (or reflection voltage Vr) with the table, and the magnification is expressed as Vt. , The data table TBLn may be subtracted to output the pan temperature. In this way, it is possible to speed up the processing without using a division requiring a processing time of the microcomputer.

  In the above description, an example in which 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. 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 a constant period, for example, every 2 seconds, while reducing the emission current. For temperature detection, correction processing (step S5-5) is performed using the immediately preceding reflectance (emissivity). Especially in thin pans, the reflectivity may change due to pan deformation due to high temperature. Furthermore, in a pan with color coating on the bottom, the coating may be denatured at high temperatures and the reflectance may change. In this case, it is desirable to periodically detect the reflectance even during heating. In this case, of course, in order to avoid the influence of the magnetic field, it is desirable to surround the reflection type photointerrupter 26 and the reflectance detection circuit 73 with a nonmagnetic metal material as in the embodiment.

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

  Although the NTC thermistor 45 built in the thermopile 25 is used as the temperature detecting element in the steady state, the present invention is not limited to this. Obviously, an NTC thermistor provided on the substrate may be used. Further, the temperature detection element is not limited to the NTC thermistor but may be a semiconductor element such as a temperature detection element using a change in the forward voltage of a diode.

  From the above, even if non-crystallized glass is used for the top plate 2, the infrared radiation sensor for detecting the infrared radiation from the pan (thermopile 25) can be used under conditions that cause a temperature fluctuation at the time when the ambient temperature of the pan temperature detector 18 changes suddenly. The temperature of the cooking pan 7 can be detected with high accuracy by the pan temperature detecting device 18 configured to be combined with the temperature change compensating infrared sensor (thermopile 26).

  FIG. 31 shows a pan temperature detecting device 18 in which the thermopiles 25 and 26 are installed in the same infrared sensor case 29 and are further thermally coupled by a thermal coupling means composed of a plastic member 75. In Example 1 (FIG. 7), the thermopile 25 and 26 are arranged side by side on the board | substrate 28, and it is an air layer with low heat transfer between them. In the present embodiment, the metal cans 35 of the thermopiles 25 and 26 are connected to each other by a plastic member 75 having better heat transfer than the air layer, and the temperatures (environments) of the thermopiles 25 and 26 are the same between the metal cans 35. I am doing so. As a result, the temperature change compensation accuracy is further increased. Obviously, member 75 may be a metal with good heat transfer.

  FIG. 32 shows an infrared detection circuit 72 using a thermopile 76 having a structure having a lens 48 for condensing incident infrared rays and a window 47 for attaching the same as the infrared detection thermopile 25 as a temperature change compensating thermopile. The same reference numerals as those in FIG. 15 denote the same items. A thermocouple output (indicated by (+) and (-) in the figure), which is the output of the thermopile 76, is connected to the OP amplifier 72-4 for temperature change compensation. The negative output (indicated by (−)) of the thermopile 76 is connected to the normal rotation input of the OP amplifier 72-4, and the positive output (indicated by (+)) is connected to R10. As a result, the thermocouple output having the opposite phase to that of the thermopile 25 is amplified by the OP amplifier 72-4 having an amplification factor G = (R10 / R9 + 1), and this output voltage is used as the bias voltage Vbias. Applied to the bias point indicated by middle b. As in FIG. 15, however, the thermopile 76 requires a change in the structure of the built-in infrared sensor case 29 so that infrared rays from the pan bottom do not enter.

  FIG. 33 shows a plan view and a cross-sectional view of the pan temperature detecting device 18. The same reference numerals as those in FIG. The upper surface of the infrared sensor case 29 is extended so as to block the front visual field of the thermopile 76 so that the infrared rays from the pan do not enter the thermopile 76, and the infrared rays incident on the thermopile 25 between the thermopile 25 and the thermopile 76 stray to cause thermopile. A light-shielding partition wall 77 is provided so as not to be incident on 76. By doing so, the thermopile 6 does not receive the infrared rays from the pan 7 but receives the infrared rays from the inner wall of the infrared sensor case 29. Since the thermopile 25 receives infrared rays from the pan and infrared rays from the inner wall of the infrared sensor case, the pan temperature detecting device 18 uses the infrared rays from the inner wall of the infrared sensor case, that is, disturbance due to the temperature of the inner wall of the infrared sensor case (sensor output fluctuation). ) Can be prevented. Similarly to the description in FIG. 7, if the amplification factors of the OP amplifiers 72-1 and 72-4 are substantially the same, the output of the OP amplifier 72-1 due to the temperature of the inner wall is the bias voltage that is the output of the same OP amplifier 72-4. Will be canceled. As a result, it is possible to detect a stable pan temperature. Since other operations are the same as those in the first embodiment, description thereof is omitted.

  FIG. 34 shows a cross-sectional view of the pan temperature detecting device 18 having a configuration in which the light shielding partition wall 77 is removed from the pan temperature detecting device 18 shown in FIG. The front field of view of the thermopile 76 is extended so as to be blocked by the upper surface of the infrared case 29, so that the infrared rays from the cooking pan 7 do not enter the thermopile 76. Also in this configuration, the pan temperature detection similar to that in FIG. 33 is possible.

  FIG. 35 shows a plan view and a cross-sectional view of the pan temperature detection apparatus 18 including the infrared detection circuit of FIG. The same reference numerals as those in FIG. 33 denote the same items. In the pan temperature detection device 18, the thermopile 76 is covered with a light-shielding cylinder 78 whose front surface reaches the lower surface of the optical filter 31 so that the thermopile 76 can only have the optical filter 31 in the front visual field. Further, the arrangement positions of the sensor visual field cylinder 19 and the pan temperature detecting device 18 are arranged so that infrared rays from the pan 7 do not enter the thermopile 76 as shown in the figure. Obviously, if the viewing angle of the thermopile 76 is narrow, it is possible for the thermopile 76 to include only the optical filter 31 in the front field of view even without the light blocking cylinder 78.

  As a result, as described with reference to FIG. 33, the output fluctuation due to the infrared light from the optical filter 31, that is, the temperature of the optical filter, is similar to the thermopile 25 and the thermopile 76 if the amplification factors of the OP amplifiers 72-1 and 72-4 are approximately the same. In the same manner, the phase is canceled due to the opposite phase, and does not appear at the output (terminal 72-2) of the pan temperature detecting device 18. That is, the thermal disturbance of the optical filter 31 can be prevented.

  In the above description, the infrared detection element is limited to the thermopile, but is not limited thereto. It may be a thermistor or a quantum type infrared detecting element. The present invention, which amplifies the infrared detection element output of the same structure in the opposite phase and uses this as the bias voltage of the amplifier circuit for detecting infrared radiation, is not limited to a thermopile, but can be applied to a thermistor or a photodiode. It is clear.

  In addition, unlike the thermistor, there is no temperature detection delay, so it is possible to follow a sudden rise in the maximum temperature at the bottom of the pan such as emptying, and if there is a risk of oil ignition, induction heating can be stopped immediately. Become. The thermal shock temperature of the borosilicate glass that is the non-crystallized glass of the top plate is about 350 ° C. (the thermal shock temperature of the crystallized glass is about 800 ° C.), which is lower than that of the crystallized glass. Since the pot temperature detection means can suppress the pot bottom maximum temperature rise at around 300 ° C., damage to the borosilicate glass can be prevented, and a safe induction heating cooker can be provided.

  Further, since non-crystallized glass is more transparent than crystallized glass, a high-quality design can be applied by using non-crystallized glass of borosilicate glass for the top plate.

  The strength of the top plate that forms the outer shell of the induction heating cooker is 250 g in mass and Rockwell hardness R100, as described in Appendix 8 (2) of the Electrical Appliance and Material Safety Law (called the Electrical Safety Act). It is necessary to drop a weight (steel ball) having a spherical surface with a radius of 10 mm and a surface of which is polyamide processed from a height of 20 cm to confirm that there are no cracks or cracks.

  The non-crystallized glass of borosilicate glass satisfies the outer strength standard of the electric safety method. Furthermore, as a result of a test in which about 500 g of steel balls were dropped on a 4 mm thick top plate, crystallized glass was broken by falling balls from a height of about 50 cm. In the case of borosilicate glass, falling balls from a height of about 130 cm Cracking occurred. Since borosilicate glass has high outer strength compared to crystallized glass, for example, the glass thickness of the top plate can be changed from 4 mm to 3 mm, and the top plate can be thinned.

  When the top plate is thinned, the transmittance of infrared rays that pass through the glass increases, and the amount of infrared energy from the cooking pan incident on the pan temperature detecting device increases, and the effect of improving the detection accuracy of the pan temperature is obtained.

  In addition, by reducing the thickness of the top plate, the induction heating cooker can be reduced in weight, saving energy in transportation and distribution processes, and reducing the cost such as transportation costs.

DESCRIPTION OF SYMBOLS 1 Main body of induction heating cooker 2 Top plate 3 Operation part 4 Circle display which shows the position which puts a cooking pan 5 Infrared transmission window 6 Grill box 6a Upper grill heater 6b Lower grill heater 6c Net shelf 7 Cooking pan 8 Heating coil 8a 1st Coil 8b Second coil 8c Coil gap 8d Bridge wire 9 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 Sealing material 18 Pan temperature detector 19 Sensor viewing tube 20 Thermistor 21a Low voltage terminal 21b High voltage terminal 25 Thermopile 26 for detecting pan temperature Shading thermopile 27 for compensating temperature change Reflective photo interrupter 28 Electronic circuit board 29 Infrared sensor case 30 Case window 31 Optical filter 32 Metal case 33 Outside infrared sensor case 35 Metal can 36 Metal stem 38 Silicon substrate 39 Silicon oxide film 40 Polysilicon vapor deposition film 41 Aluminum vapor deposition film 42 Temperature measuring contact portion 43 Infrared absorption film 44 Cold junction portion 45 NTC thermistor 46 Metal pin 47 Window 48 Glass convex lens 50 Infrared LED
51 Infrared phototransistor 60 Microcomputer 61 Frequency control circuit 62 Power control circuit 63 Rectifier circuit 64 Power switch 68 Grill heater control circuit 69 Operation switch 70 Display circuit 71 Buzzer 72 Infrared detection circuits 72-1, 72-3, 72-4, 73-3 Operational Amplifier 73 Reflectance Detection Circuit 73-1 Transistor 73-4 Charge / Discharge Circuit 75 Plastic Member 76 Pan Peel Temperature Detection Thermopile 77 Light-shielding Partition 78 Light-shielding Tube

Claims (13)

A top plate with a cooking container on top,
A heating coil that is provided under the top plate and generates an induction magnetic field to heat the cooking vessel, and an infrared detection that is provided under the heating coil and detects infrared rays emitted from the bottom of the cooking vessel Means, pan temperature detecting means for detecting the pan temperature from the output of the infrared detection means,
An infrared heating means, wherein the infrared detecting means receives an infrared ray radiated from the bottom of the cooking container, and outputs a direct-current voltage proportional to the amount of infrared rays;
A first DC amplifier that DC amplifies the output of the first infrared sensor;
A second infrared sensor that outputs a direct-current voltage proportional to the amount of infrared rays, by blocking infrared rays emitted from the bottom of the cooking vessel so that infrared rays emitted from the bottom of the cooking vessel are not incident;
A second DC amplifier for inverting DC amplification of the second infrared sensor output,
An induction heating cooker, wherein the output of the second DC amplifier is input as a bias voltage of the first DC amplifier, and the output of the first DC amplifier is used as the output of the infrared detecting means. The induction heating cooker according to claim 1,
The first infrared sensor is covered with a metal can provided with a lens that transmits infrared rays emitted from the bottom of the cooking container,
The induction heating cooker, wherein the second infrared sensor is covered with a metal can that shields infrared rays emitted from the bottom of the cooking vessel. The induction heating cooker according to claim 1,
The first infrared sensor is covered with a metal can provided with a lens that transmits infrared rays emitted from the bottom of the cooking container,
The induction heating cooker, wherein the second infrared sensor includes a lens that transmits infrared rays that shield infrared rays emitted from the bottom of the cooking container. In the induction heating cooker according to claims 1 to 3,
An induction heating cooker characterized in that the first and second infrared sensors are coupled to each other by a thermal coupling means. In the induction heating cooker according to claims 1 to 4,
An induction heating cooker characterized in that an amplification factor of the first DC amplifier and an amplification factor of the second DC amplifier are substantially equal. In the induction heating cooker according to claim 1 to 5,
The induction heating cooker, wherein the first infrared sensor and the second infrared sensor are thermopile. The induction heating cooker according to claim 1 to 6,
A temperature detecting element is disposed in or near the first infrared sensor;
An induction heating cooker, wherein a bias voltage output from the second DC amplifier is controlled by a temperature detected by the temperature detecting element. In the induction heating cooker according to claim 1 to 7,
Further, a light guide tube that blocks infrared rays emitted from the heating coil and guides infrared rays emitted from the bottom of the cooking container to the infrared detection means, and a window that is disposed under the light guide tube and transmits infrared rays. An induction heating cooker characterized in that a windproof case having a material on the front surface of the first infrared sensor is provided, and the first infrared sensor and the second infrared sensor are built in the windproof case. In the induction heating cooker according to claim 1 to 7,
Further, a light guide tube that blocks infrared rays emitted from the heating coil and guides infrared rays emitted from the bottom of the cooking container to the infrared detection means, and a window that is disposed under the light guide tube and transmits infrared rays. A windproof case having a material in front of the first infrared sensor and the second infrared sensor is provided, and the first infrared sensor and the second infrared sensor are built in the windproof case. Cooking cooker. The induction heating cooker according to claim 1 to 9,
The induction heating cooker, wherein the top plate is non-crystallized glass. The induction heating cooker according to claim 1 to 10,
The induction heating cooker, wherein the window material is non-crystallized glass.   12. The induction heating cooker according to claim 1, wherein the top plate is borosilicate glass containing 10 to 15% boric acid.   13. The induction heating cooker according to claim 1, wherein the infrared ray transmitting lens provided in the infrared sensor has an optical characteristic having a visible light transmittance lower than that of the top plate. Cooking cooker.