JP2011228147A - Induction heating cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain noncontact, precise, stable, responsive detection of the temperature of a pan without influence of the material quality of the pan on a top plate, the state of a bottom, or temperature elevation of a device component member such as the top plate during cooking.SOLUTION: The induction heating cooker comprises: the top plate to place the pan thereon; a heating coil under the same; a light guide tube provided to a member to fix the heating coil to guide infrared rays from the pan; and a pan temperature detection means which detects the temperature of the pan by calculating an infrared dose radiated from the top plate and the light guide tube from the temperatures of the top plate and the light guide tube and subtracting the result from the output of an infrared detection means, the infrared detection means detecting the infrared rays having passed through the light guide tube.

Description

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

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

  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. . This infrared sensor is placed near the center of the heating coil, detects the infrared radiation emitted from the bottom of the pan with the infrared sensor, and controls the output of the inverter circuit that drives the heating coil according to the output. The cooking temperature is adjusted.

  However, at the cooking temperature (100 to 300 ° C.), the radiant infrared energy is small. Further, from the optical characteristics of the top plate, the wavelength passing through the top plate is only about 2 μm with a width of 1 μm to 3 μm. Only 2%. For this reason, the sensitivity of the infrared sensor used is required to be two orders of magnitude higher than that used in thermometers.

  Furthermore, during heating, the top plate itself is also heated by heat transfer or radiation from the bottom of the pan, and this radiant infrared energy is equivalent to the radiant infrared energy of the pan. In other words, the radiant infrared energy from both the pan and the top plate is incident on the infrared sensor, and the temperature rise of the top plate itself during cooking becomes a detection disturbance of the infrared sensor that detects the pan temperature, and the detected temperature has an error. Will occur. Examples of means for solving this problem are disclosed in Patent Documents 1, 2, and 3.

  The technique of patent document 1 is provided in the top plate, the 1st measurement area which permeate | transmits the infrared rays radiated | emitted from the bottom face of a pan below a top plate, and the infrared rays provided in the top plate and radiated | emitted from the bottom face of a pan A second measurement area that cuts off the light, and an array-shaped infrared detection unit that is provided below the top plate and detects the amount of infrared rays from the first measurement area and the amount of infrared rays from the second measurement area. The amount of infrared rays from the second measurement area detected by the other array is subtracted from the amount of infrared rays from the first measurement area detected by one array (differential amplification), and the pan temperature is detected by this output. Is. That is, from the first measurement area, the infrared radiation from the pan bottom and that from the top plate are added, and from the second measurement area, only the infrared radiation radiated from the top plate itself is provided. By subtracting the second one from the one, the pan temperature detection technique is not affected by the temperature of the top plate.

  The technology of Patent Document 2 is the same idea as Patent Document 1, and the first infrared detection thermal element and the second infrared compensation element are configured with two sets of inexpensive thermal sensors (thermistors, etc.). A heat-sensitive element is provided, and each first and second heat-sensitive element has a holding body on which first and second light guide parts that guide infrared rays from the opening are formed. Then, an infrared light shielding film or a light shielding material (including a heat insulating elastic body) is disposed in the incident opening of the holding body where the second light guide is formed. The temperature at the bottom of the pan is accurately detected by differentially amplifying the first infrared detection thermal element output and the second infrared compensation thermal element output. That is, the infrared rays from the bottom of the pan that have passed through the top plate and the infrared rays that are emitted from the top plate itself are incident on the first infrared detecting thermal element under the holder where the first light guide is formed, In the second infrared thermosensitive sensing element for infrared compensation under the holder where the light guide is formed, the light shielding material is pressed against the lower surface of the top plate, so that the temperature of the upper surface of the top plate is substantially reduced. Infrared rays that are proportional to the emitted infrared rays are incident. Then, the temperature of the pan bottom is accurately detected by subtracting (differential amplification) the second infrared compensation thermal element output from the first infrared detection thermal element output.

  The technique of Patent Document 3 is the same idea as Patent Documents 1 and 2, and an infrared detection means arranged on the lower surface of the top plate (top plate), and a first temperature for detecting the pan bottom temperature from the output of the infrared detection means. Detection means, second temperature detection means (thermistor) disposed on the lower surface of the top board for detecting the temperature of the top board, and subtraction means for subtracting the output of the infrared detection means according to the output of the second temperature detection means The pan temperature detected by the output of the subtracting means is corrected to control the heating output to the heating coil. That is, the sum of the pan temperature and the top plate temperature output by the first temperature detecting means from the infrared output in which the infrared radiation from the pan bottom and that from the top plate are superimposed is added to the top temperature from the second temperature detecting means. The temperature of the pan is not affected by the temperature of the top plate by subtracting the temperature of the top plate output to the infrared detecting means by the infrared rays emitted from the plate itself.

JP 2004-111055 A Japanese Patent Laid-Open No. 2004-63451 JP 2006-40778 A

  The pan temperature detection means of Patent Document 1 must be expensive because an infrared detection unit having at least two arrays is required. The second measurement area is created by applying an expensive black body paint that blocks infrared rays on the lower surface of the top plate. The emissivity of this black body is different from that of the top plate itself. Therefore, the infrared amount of a black body at the same temperature as the top plate is different from the infrared amount of the top plate itself. Therefore, even if the output of the infrared detection means for detecting the infrared light from the second measurement area is subtracted from the output of the infrared detection means for detecting the amount of infrared light from the first measurement area, the accurate pan is not affected by the temperature of the top plate. Temperature cannot be detected.

  The pan temperature detecting means of Patent Document 2 uses a thermal element (thermistor) for infrared detection. As is well known, the resistance value of the thermistor varies nonlinearly with temperature. And since the detection temperature (pan) of the 1st infrared detection thermal element and the detection temperature (top plate) of the 2nd infrared compensation thermal element differ greatly, the resistance value of an element will differ large nonlinearly. Therefore, even if linear subtraction is performed on this resistance change output of each element, it is not possible to accurately detect the pan temperature that is not affected by the temperature of the top plate.

  The pan temperature detecting means of Patent Document 3 detects the top plate temperature by the second temperature detecting means, and estimates the value that the infrared rays emitted from the top plate itself are output to the infrared detecting means. Although it is stated that an accurate pan temperature that is not affected by the temperature of the top plate is detected by subtracting from the output of the first temperature detection means, no specific estimation means (method) is mentioned. As will be described later, in addition to the amount of infrared rays from the top plate, the output of the first temperature detection means includes the amount of infrared rays from the light guide tube that guides infrared rays to the infrared detection means or the structure around the detection means. It is. Accurate pan temperature cannot be detected unless these are eliminated or subtracted.

  Another problem in detecting temperature with an infrared sensor is that it is affected by the emissivity of the object to be measured. The infrared emissivity of the pan bottom depends greatly on the material, color and processing state of the pan bottom (painting of the pan bottom, engraving of the pan bottom, hairline processing, ring processing, driving processing, etc.). Moreover, even in the same pan, the emissivity varies depending on dirt such as cooking oil adhering to the bottom of the pan. That is, even when the pan is made of the same temperature and the same material, if the color, processing or dirt state is different, the infrared energy to be radiated is different, so the infrared energy received by the infrared sensor is also different, and a different temperature is detected. For this reason, a means for correcting the difference in temperature detection by infrared rays due to the difference in the pan bottom is required. Patent Documents 1, 2, and 3 do not mention emissivity detection necessary for accurate pan bottom temperature detection.

  The present invention relates to a pan temperature detecting means using a thermopile as an infrared sensor, and the temperature of a light guide tube provided in a heating coil for guiding infrared rays from the top plate and the pan bottom to the infrared sensor. Alternatively, an object of the present invention is to provide an induction heating cooker that can be detected stably and accurately without being affected by the temperature of a member disposed on the front surface of an infrared sensor, and has improved safety and usability.

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

  The above problems include a top plate made of crystallized glass with a pan serving as a cooking container on the top surface, a heating coil that is provided under the top plate and generates an induction magnetic field to heat the pan, and under the heating coil Infrared detection means comprising a thermopile for detecting infrared radiation emitted from the pan bottom and the like, and provided in a support portion of the heating coil, blocking infrared radiation emitted from the heating coil, and emitted from the pan bottom A light guide tube for guiding infrared rays to the infrared detection unit; a first temperature detection unit disposed on the lower surface of the top plate for detecting the temperature; and a second temperature disposed on the light guide tube for detecting the temperature. Detecting means; first infrared ray amount calculating means for calculating an infrared ray amount emitted from the top plate based on an output of the first temperature detecting means; and Second infrared amount calculating means for calculating the amount of infrared rays emitted from the light guide tube based on the output of the degree detecting means, and the outputs of the first and second infrared amount calculating means from the outputs of the infrared detecting means. Subtracting means for subtracting, high frequency power supply means for supplying high frequency power to the heating coil, power control means for controlling the output power of the high frequency power supply means, and the temperature of the bottom surface of the cooking container from the output of the subtraction means It can be solved by an induction heating cooker provided with a pan temperature detecting means for detecting the temperature.

  In addition to the above, a window material having the same optical characteristics as the top plate is provided on the front surface of the infrared detection means, and a third temperature detection means for detecting this temperature on the window material, and a third temperature detection means A third infrared ray amount calculating means for calculating an infrared ray amount emitted from the window material based on the output; and an output of the first, second and third infrared ray amount calculating means from the output of the infrared ray detecting means. This can be solved by an induction heating cooker provided with subtracting means.

  In addition to the above, an infrared light emitting and receiving element disposed in the vicinity of the infrared detecting means, and the infrared light emitting element projects a certain amount of infrared light on the bottom of the pan, and the reflected light is received by the infrared light receiving element. And an emissivity measuring means for measuring the emissivity of the pan bottom from the amount of the reflected light, and can be solved by an induction heating cooker comprising a correcting means for correcting the output of the subtracting means based on the output of the emissivity measuring means. .

  According to the present invention, by using a thermopile infrared sensor, the temperature at the bottom of the heating pan can be accurately and stably detected regardless of the ambient temperature during cooking, that is, the temperature of the top plate, the light guide tube, and the member disposed in front of the infrared sensor. A pan temperature detecting means can be provided. And the induction heating cooking appliance which enables safe and optimal cooking by controlling the high frequency electric power to a heating coil appropriately by the high temperature part temperature detected correctly can be provided.

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

The perspective view which shows the structure of the induction heating cooking appliance of Example 1. FIG. Sectional drawing which shows the structure of the induction heating cooking appliance of Example 1. FIG. Sectional drawing which shows the detail of the heating coil periphery of Example 1. FIG. The top view which shows arrangement | positioning of the heating coil of Example 1, and a pan temperature detection apparatus. FIG. 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. FIG. 2 is a plan view and a cross-sectional view showing details of the thermopile of Example 1. The control block diagram of the induction heating cooking appliance of Example 1. FIG. FIG. 3 is a diagram illustrating details of a thermopile temperature detection circuit according to the first embodiment. FIG. 3 is a diagram illustrating details of the reflectance detection circuit according to the first embodiment. 6 is an operation timing chart of the reflectance detection circuit according to the first embodiment. The figure which shows the spectral radiant energy by Planck's distribution law. The figure which shows the optical characteristic of glass, such as a top plate used in a present Example. The schematic diagram which shows each member of Example 1, and its radiation infrared energy. The visual field characteristic of the thermopile of Example 1. The figure which shows the relationship between each part temperature of Example 1, and the incident infrared energy to an infrared rays absorption film. The figure which shows the relationship between the black body (pan bottom) temperature of Example 1, and a thermopile temperature detection circuit output. The figure which shows the relationship between the top plate temperature of Example 1, and a thermopile temperature detection circuit output. The figure which shows the relationship between the sensor visual field cylinder of Example 1, crystallized glass optical filter temperature, and a thermopile temperature detection circuit output. Output explanatory drawing by the presence or absence of a pan of the reflectance detection circuit of Example 1. FIG. FIG. 3 is a diagram illustrating a relationship between a reflection voltage and a reflectance of the reflectance detection circuit according to the first embodiment. The figure which shows the relationship between the pot bottom temperature of the various pots of Example 1, and a pot temperature detection circuit output. The figure which shows the relationship between the various pan emissivity of Example 1, and a reflectance. 2 is a flowchart of induction heating cooking according to the first embodiment. 5 is a flowchart of reflectance detection according to the first embodiment. The flowchart of the pan temperature detection of Example 1. FIG. FIG. 6 is a plan view showing a heating coil of Example 2. The flowchart of the pot temperature detection of Example 2. FIG.

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

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

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

  On the upper surface of the top plate 2, a circle display 4 having a radius that approximately matches the outermost radius of the heating coil 7 or the radiant heater disposed thereunder is printed to indicate a place where the pan can be heated. 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 transmission 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 display 4 at the two pot places 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 6 is placed in each mouth (circle display 4) on the upper surface of the top plate 2 and cooking is performed. As shown in FIG. 2, when the high frequency current from the inverter circuit 8 (high frequency current supply means) is supplied to the heating coil 7, it is divided into a first coil 7a on the outer peripheral side and a second coil 7b on the inner peripheral side. The heating coil 7 generates a high-frequency magnetic field 9 (indicated by a broken line in the figure). This high-frequency magnetic field is linked to the cooking pan 6 to generate an eddy current, and the cooking pan 6 itself is induction-heated by the Joule heat to generate heat. To do. Accordingly, the food in the cooking pan 6 is cooked by the heat generated by the cooking pan 6 itself. At this time, the top plate 2 under the cooking pan 6 also becomes high temperature due to heat transfer or radiant heat from the cooking pan 6 that has generated heat.

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

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

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

  Under the coil cooling air passage 15, circuit cooling air passages 17a and 17b containing a circuit board such as an inverter circuit 8 are provided in two layers, and inverter circuits for the left and right heating coils 7L and 7R, etc., are built in, respectively. Has been. 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 detector 18 is arranged in the coil upper surface cooling air passage 15a below the coil upper surface cooling air delivery hole 15c. The pan temperature detection device 18 detects the bottom surface temperature of the cooking pan 6 heated by induction from the infrared rays transmitted through the infrared transmission window 5 of the top plate 2.

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

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

  The heating coil 7 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 7a on the outer peripheral side and a second coil 7b on the inner peripheral side. The The coil gap 7c has a concentric band shape with a width of about 15 mm. The winding end of the first coil 7a bridges the coil gap 7c and becomes the winding start of the second coil 7b. The first coil 7a, the bridging wire 7d, The heating coil 7 is composed of two coils 7b. The coil base 10 is provided with a cylindrical outer cavity wall 14b on the inner peripheral side of the first coil 7a, and the inside is a coil gap 7c. An inner cavity 14a is provided on the inner peripheral side of the second coil 7b. Further, a cylindrical field cylinder 19 (inner diameter of about 12 mm) is provided between two ferrites 11 arranged radially in part of the coil gap 7 c, and a pan temperature detecting device 18 is installed under the field cylinder 19. The

  A thermistor 20a (first temperature detecting means) is installed on the upper side of the field cylinder 19 so as to be in contact with the horizontal lower surface of the infrared transmitting 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 25 built in the pan temperature detector 18 described in detail later from the visual field cylinder 19.

  FIG. 5 shows a view of FIG. 4 from the back. The coil base 10 is provided with two low voltage terminals 21a and a high voltage terminal 21b. The low voltage terminal 21a is connected to the start of winding of the first coil 7a, and the high voltage terminal 21b is connected to the second coil. End of winding is connected. The output lines 22a and 22b of the inverter circuit 8 are fixed to the terminals with screws. In a non-magnetic pot such as copper or aluminum, a high voltage output line 22b that outputs a high voltage of 4 to 5 kV is connected to a high voltage terminal 21b. A thermistor 20b (second temperature detection means) is installed on the side of the lower outer wall of the field cylinder 19 so as to be embedded inside the wall so as to detect the inner wall temperature of the field cylinder 19.

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

  FIG. 6 shows details of the pan temperature detecting device 18.

  FIG. 6A shows a plan view of the pan temperature detecting device 18. The pan temperature detection device 18 is mainly composed of an infrared detection sensor (thermopile 25) covered with a heat sink 55 and a reflective photo interrupter 26. The thermopile 25 and the reflection type photo interrupter 26 are electronic circuit boards on which a thermopile temperature detection circuit 72 (details will be described later) and a reflectance detection circuit 73 (details will be described later) for amplifying the output signal of the thermopile are mounted. 27, the thermopile 25, the reflective photo interrupter 26, and the electronic circuit board 27 are hermetically sealed in an infrared sensor case 29 (indicated by a one-dot chain line) of a plastic member. The infrared sensor case 29 has a case window 30 for transmitting infrared rays. The case window 30 has almost the same optical characteristics as the crystallized glass constituting the top plate 2 (however, 1 μm as shown by the broken line in FIG. 14). The optical characteristics on the long wavelength side are almost the same, but on the short wavelength side, there is a region with a low transmittance of about 400 nm compared to the top plate, and the visible light in this part is cut, so the eyes appear reddish. A crystallized glass cut into a thin square is fitted as a crystallized glass optical filter 31. A thermistor 20c (third temperature detecting means) for detecting the temperature is provided on the upper surface of the crystallized glass optical filter 31.

  A thermopile 25 and a reflective photointerrupter 26 with a heat sink 55 covered under the crystallized glass optical filter 31 are mounted on the electronic circuit board 27. The infrared sensor case 29 is covered with a metal case 32 (indicated by a two-dot chain line) having a permeability of approximately 1 such as aluminum. Naturally, the previous case window 30 is opened. Further, the metal case 32 made of aluminum is covered with an outer infrared sensor case 33 made of a plastic member. Of course, the previous case window 30 is opened. That is, the thermopile 25 is covered with a triple case.

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

  FIG. 6B shows a cross-sectional view along the line AA ′ in FIG. This shows the positional relationship between the thermopile 25 and the reflective photo interrupter 26 mounted on the electronic circuit board 27 installed in the infrared sensor case 29, the case window 30 of the infrared sensor case 29, and the crystallized glass optical filter 31. It is sectional drawing.

  FIG. 7 shows details of the reflective photo interrupter 26. The reflection type photo interrupter 26 is obtained by molding an infrared LED 50 as an infrared light emitting element and an infrared phototransistor 51 as an infrared light receiving element on the same plastic member. A lens is made of plastic on the light emitting surface of the infrared LED, and infrared light of around 930 nm is irradiated upward with a thin beam. A lens is made of visible light blocking plastic on the light receiving surface of the infrared phototransistor 51, and the reflected infrared light at the object (pan bottom) of the previous irradiated infrared light is received with a narrow viewing angle, and the amount of received light A current proportional to is output. This reflection type photo interrupter 26 is constituted by a pair of an infrared light emitting element and a light receiving element, and measures the reflectance of the bottom surface of the cooking pan 6 placed on the top plate 2.

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

  Infrared light emitted from the infrared LED 50 passes through the crystallized glass optical filter 31 by 85% or more, but the remaining 15% is reflected and received by the adjacent infrared phototransistor 51. This reflected light is received by the lateral infrared phototransistor 51 immediately. This light reception level is large when the distance to the reflection surface is short, and affects the reception of the reflected light at the bottom surface of the pan on the top plate 2 which is the original purpose. For this reason, in this embodiment, as shown in the figure, the distance between the crystallized glass optical filter 31 and the light emitting / receiving surface of the reflective photointerrupter 26 (infrared LED 50 and infrared phototransistor 51) is brought close to within 500 μm, The reflected light reflected by the crystallized glass optical filter 31 from the infrared LED 50 is prevented from being received by the infrared phototransistor 51. Ideally, the lower surface of the crystallized glass optical filter 31 and the upper surface of the reflective photointerrupter 26 are preferably brought into contact with each other.

  FIG. 8 shows details of the thermopile 25. FIG. 8A is a perspective view of the heat sink 55 and the thermopile 25. 8B is a cross-sectional view of the thermopile 25 taken along the line BB ′ in FIG. 8A excluding the heat sink 55, and FIG. 8C is a cross-sectional view of CC ′ in FIG. 8B. It is a top view of the cross section in the line shown by. The infrared absorption film is omitted so that the thermocouple can be seen.

  The thermopile 25 is obtained by connecting a number of thermocouples (thermocouples) in cascade (piling). The thermopile 25 is built in a metal case 37 made of a metal can 35 such as a nickel-plated steel plate and a metal stem 36. A silicon oxide film 39 is formed on the surface of the silicon substrate 38 having a thickness of about 300 μm to electrically and thermally insulate, and polysilicon and aluminum are sequentially deposited on the surface of the silicon oxide film 39 by the polysilicon deposited film 40 and the aluminum deposited film 41. Create many thermocouples and connect them in cascade. An infrared absorption film 43 such as a rubidium oxide film close to a black body is formed at the center of the silicon substrate 38 having a polysilicon / aluminum junction (temperature measuring contact). One end of the polysilicon and aluminum 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 metal stem 36 in an inert gas. A small-hole window 47 is opened on the upper surface of the metal can 35, and a glass convex lens 48 is mounted on the inside thereof. 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 glass convex 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.

  The thermocouple temperature measuring contact 42 (below the infrared absorbing film 43) in the thermopile 25 is heated by infrared rays that pass through the small hole window 47 and is condensed by the glass convex lens 48. A voltage 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 thermocouple output metal pin 46 in proportion to the infrared energy that has passed.

  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. For this reason, the heat sink 55 is mounted as a thermal buffer (increasing the heat capacity) to reduce output fluctuations due to changes in ambient temperature.

  FIG. 9 shows a control block diagram of the induction heating cooker of the present embodiment. 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 8R and 8L supply high-frequency current to the heating coils 7R and 7L. The frequency control circuits 61R and 61L and the power control circuits 62R and 62L adjust the operating frequency of the inverter circuits 8R and 8L and the power supplied to the coils. The reason for changing the operating frequency is that the induction heating efficiency changes at the frequency of the high-frequency current depending on the metal type of the pan. In general, a frequency of 20 kHz is used for iron, and a frequency of 70 kHz or more is used for copper and aluminum having a lower resistivity. This frequency switching is performed by the microcomputer 60 controlling the frequency control circuit based on the judgment of the pan type discrimination means (not shown).

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

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

  The thermopile 25 is connected to a thermopile temperature detection circuit 72 so that the output is amplified and input to the AD terminal of the microcomputer 60. The reflection type photo interrupter 26 is connected to the reflectance detection circuit 73, the light emission of the light emitting element is controlled by the port output of the microcomputer 60, the infrared light reflected by the cooking pan 6 is received by the light receiving element, and its output signal Is amplified and input to the AD terminal of the microcomputer 60. Details of the operations of the thermopile temperature detection circuit 72 and the reflectance detection circuit 73 will be described later. Further, the thermistors 20aR, 20bR, and 20cR are connected to a thermistor temperature detection circuit 74R that selects the input and sequentially outputs the temperature detection values to the AD terminal of the microcomputer 60. The output is input to the AD terminal of the microcomputer 60. The Similarly, the thermistors 20aL, 20bL, and 20cL are also connected to the thermistor temperature detection circuit 74L, and the output is also input to the AD terminal of the microcomputer 60.

  The infrared amount calculation means, the subtraction means, and the reflectance correction means are performed by software of the microcomputer 60. Details will be described later. The microcomputer 60 knows the temperatures of the top plate 2, the field tube 19, and the crystallized glass optical filter 31 by each thermistor, and obtains a voltage equivalent to the amount of radiant infrared rays of each member. The conversion from temperature to voltage is stored in the form of a table in advance by the method described later (operation of the infrared ray amount calculating means).

  The microcomputer 60 subtracts the previous voltages from the output of the thermopile temperature detection circuit 72 to cancel the influence of the top plate 2, the field tube 19, and the crystallized glass optical filter 31 (operation of the subtracting means).

  The microcomputer 60 knows the infrared reflectance of the cooking pot from the output of the reflectance detection circuit 73 and corrects the previous subtraction result 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 the reflectance correction means). And the heating of the cooking pan 6 is controlled via the power control circuit 62. Details of this processing method will be described later.

  FIG. 10 shows details of the thermopile temperature detection circuit 72. The thermocouple output (thermoelectromotive force) of the thermopile 25 (voltage between (+) and (−) symbols in the figure) is amplified about 2000 times by the operational amplifier 72-1, and is output to the output terminal 72-2. This output voltage is input to the AD terminal of the microcomputer 60. The amplification degree of the operational amplifier 72-1 is determined by the ratio (R2 / R1) of the resistor 72-3 (= R1) and the resistor 72-4 (= R2). The NTC thermistor 45 in the thermopile is connected in series with the resistor 72-8 to a voltage source (both ends of the resistor 72-6) obtained by dividing the circuit power supply voltage by the resistors 72-5, 72-6, and 72-7. The connection point a with the resistor 72-8 is connected to the thermocouple output terminal (-). The NTC thermistor 45 is a resistance element having negative temperature characteristics, and the resistance value decreases as the temperature rises. For this reason, when the temperature in the thermopile 25 rises, the voltage of the previous connection point a rises. The thermocouple output (the voltage between the symbols (+) and (−) in the figure) is proportional to the temperature difference between the temperature measuring contact 42 (a point heated by infrared energy) and the cold junction (thermocouple output terminal) 44. For this reason, when the atmosphere in the metal case 37 (in which the NTC thermistor is built) rises at the ambient temperature where the thermopile 25 is installed, the thermocouple output decreases. This decrease is compensated by the voltage increase at the connection point a. That is, the NTC thermistor 45 is used to prevent the output of the thermopile (thermocouple) 25, 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, cold junction temperature compensation is performed so that the output does not change unless the temperature of the measurement object, that is, the incident infrared energy changes.

  Details of the reflectance detection circuit 73 will be described with reference to FIGS. In FIG. 11, reference numeral 50 denotes an infrared LED which is a light emitting element. For example, the emission wavelength is 930 nm. Reference numeral 51 denotes an infrared phototransistor, which has a sensitivity of 80% of the peak sensitivity even when the peak sensitivity wavelength is 800 nm and the emission wavelength of the infrared LED 50 is 930 nm. An optical filter that cuts visible light is disposed on the light receiving surface. FIG. 12 shows an operation timing chart of the reflectance detection circuit 73. The infrared LED 50 which is a light emitting element of the reflective photo interrupter 26 is driven by a transistor 73-1. This drive is controlled by a signal input from the output port of the microcomputer 60 to the drive signal terminal 73-2. FIG. 12A shows this signal. When a rectangular wave signal with a duty of 50% is input to the drive signal terminal 73-2, the infrared LED 50 emits light when the signal is 5V, and turns off when the signal is 0V. This emission intensity is proportional to the current flowing through the infrared LED 50, and this current is determined by the value of the resistor 73-3. In this embodiment, the resistance value is fixed and the light emission intensity is constant. When the infrared light is reflected on the bottom surfaces of the top plate 2 and the cooking pan 6 and received by the infrared phototransistor 51 as a light receiving element, a voltage is generated in the resistor 73-4 by the photocurrent. This voltage is shown in FIG. If the reflection is large (the amount of received light is large), the voltage increases proportionally. This signal voltage has its direct current component cut by the capacitor 73-5, and is input as an alternating current signal (shown in FIG. 12C) to a normal rotation direct current amplifier composed of an operational amplifier 73-6. Here, only the positive component of the AC signal is amplified. This is shown in FIG. The amplified 50% duty signal is converted to a DC average voltage by the charge / discharge circuit 73-7 and output from the output terminal 73-8. This output is input to the AD terminal of the microcomputer 60.

  In this way, the reflectance detection circuit 73 emits carrier-modulated infrared light having a constant emission intensity to the bottom of the pan, receives the infrared light reflected by the pan, and obtains the average voltage as the reflected voltage. The value corresponding to the reflectance is detected by. When the cooking pan 6 is not placed, the reflection is only from the top plate, 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 reflectance detection of the pan. 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 infrared phototransistor 51 is also prevented.

  The operation of the first embodiment will be described below.

The cooking pan 6 placed on the top plate 2 generates heat by induction heating. By this heating, infrared rays are radiated from the bottom of the cooking pan 6. This total radiant energy E is proportional to the fourth power of the pan temperature T. (E = σT ⁴ ; Stefan-Boltzmann law) FIG. 13 shows the spectral radiant energy of the black body temperature calculated from the Planck distribution law. If this spectral radiant energy is integrated over the entire wavelength region, the total radiant energy E is obtained, which is proportional to the fourth power of the temperature (absolute temperature). This is the aforementioned Stefan-Boltzmann law, and this coefficient σ is the Stefan-Boltzmann coefficient. The peak wavelength of the spectral radiant energy is 5 μm to 8 μm at a cooking temperature of 100 to 300 ° C. based on the Vienna transition law.

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

  On the other hand, the optical characteristics of crystallized glass (top plate 2), which is a non-magnetic material, are shown by solid lines in FIG. As shown by a solid line in FIG. 14, the crystallized glass transmits 80% or more of light having a wavelength of 0.2 μm to 2.9 μm, and transmits about 30% of light having a wavelength of 3 to 4.5 μm. It hardly transmits light having a wavelength longer than 5 μm and a wavelength shorter than 0.2 μm. Due to this optical characteristic, most of the infrared radiation energy (see FIG. 13) radiated from the pan cannot pass through the top plate 2. What can pass is about 1% of the total infrared radiation energy radiated from the pan.

  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. 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 the present embodiment, since the cooking temperature range is 100 to 300 ° 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. On the other hand, the thermopile does not require such a mechanism, and in recent years, a thermocouple that uses a semiconductor process is miniaturized by technology such as MEMS, and a large number of layers are piled up (piled) to improve sensitivity. Yes.

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

  Using the thermopile with this optical filter, when trying to measure the temperature of the cooking pan (25 to 300 ° C.) through the top plate 2 in a non-contact manner, the infrared energy reaching the thermopile is attenuated to about 1/100 as described above. It is almost impossible to measure.

  Therefore, in the pan temperature detecting apparatus 18 of the present embodiment, a thermocouple (thermocouple) is a polysilicon / aluminum metal pair that can be formed relatively easily by a semiconductor process, and a thermopile 25 in which about 50 are deposited, and its output is used. Is amplified 2000 times by an amplifier circuit so that minute infrared energy 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. 8, the thermopile is formed by depositing a large number of thermocouples, and includes a large number of temperature measuring contacts heated by incident infrared rays and a large number of cold junctions on the silicon substrate 38. Since the cold junction is fixed to the metal stem 36 of the metal case 37 with a bond, the thermopile metal case 37 (metal can 35 and metal stem 36) is a cold junction. And this metal case 37 cannot be fixed to a freezing point like a normal thermocouple.

  Assuming that the thermoelectromotive force of one thermocouple is 5 μV / ° C., the number of piles is 50, and the amplification factor of the DC amplifier is 2000, if the temperature of the metal case 37 changes by 1 ° C., the output of the DC amplifier will change to a voltage of 500 mV. 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 7 is the strongest so that the hot portion of the pan bottom during cooking can be detected. The This position is between the rod-like ferrites 11 arranged radially under the heating coil 7, and the magnetic flux almost passes through the ferrite and is a place where there is little leakage magnetic flux. However, since the distance from the lower surface of the heating coil 7 is about 20 mm, the leakage magnetic flux is large, and the 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. The top plate 2 and the heating coil 7 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 7, the coil itself generates Joule heat. In order to cool the top plate and the heating coil, outside air is introduced into the coil upper surface cooling air passage 15a and the coil lower surface cooling air passage 15b, and the heating coil 7 is blown and cooled as described above.

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

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

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

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

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

  The metal case 32 is induction-heated by the ambient atmosphere temperature and the leakage magnetic flux from the heating coil 7 during cooking, and the temperature rises by 5 to 10 ° C. in the case of aluminum. When cooking is continued before the temperature rise subsides, when the outside air is rapidly introduced and applied to the metal case 32, the metal case 32 cools rapidly, and as a result, the ambient temperature of the thermopile 25 in the infrared sensor case 29 suddenly increases. Will be reduced. In the opposite case, for example, when cooking first in the winter morning, the metal case 32 in the aircraft is sufficiently cooled at night and is at about 5 ° C., and the user starts cooking in a cooking room heated to 20 ° C. The warm air is introduced into the coil upper surface cooling air passage 15a, and the warm air at 20 ° C. is applied to the metal case 32 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.

  Now, the top plate 2 is heated by absorbing infrared radiation from the induction heated cooking pan 6 and contact heat conduction. As shown by the solid line in FIG. 14, the top plate 2 transmits 80% or more of light having a wavelength of 0.2 μm to 2.9 μm and transmits about 30% of light having a wavelength of 3 to 4.5 μm. Longer wavelengths and light with wavelengths shorter than 0.2 μm are hardly transmitted.

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

  For this reason, when detecting the temperature of the cooking pan 6 on the top plate 2 using the thermopile 25, the infrared rays emitted by the heating of the top plate 2 itself become a problem. For example, if the transmission wavelength of the glass convex 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 4.5 μm radiated from the top plate 2, and The temperature at the bottom of the cooking pan cannot be detected accurately. The radiant infrared energy of the pan passing through the top plate 2 is about 2 μm band of 1 μm to 2.9 μm, whereas the infrared energy radiated by the top plate 2 itself is about 10 μm band of 4.5 μm to 15 μm. If it is temperature, five times the thermopile output due to the temperature of the cooking pan 6 will depend on the temperature of the top plate 2.

  In the present embodiment, in order to prevent the above, a case window 30 for transmitting infrared rays is opened in the infrared sensor case 29 of the pan temperature detection device 18 constituted by the thermopile 25, and the top plate 2 is configured in the case window 30. The crystallized glass to be cut into a thin square is fitted as the crystallized glass optical filter 31. Then, the amount of infrared rays radiated from the top plate 2 incident on the thermopile 25 is removed. The portion of the top plate radiating at a wavelength of 2.9 μm or more is prevented from entering the thermopile 25 by the optical characteristics of the crystallized glass optical filter 31 having the same transmission characteristics as the top plate 2.

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

  In addition, the crystallized glass optical filter 31 has an effect of making the thermopile 25 and the reflective photo interrupter 26 disposed below the crystallized glass optical filter 31 invisible from the infrared transmitting window 5 of the top plate 2. As described above (as shown by the broken line in FIG. 14), the optical characteristics on the long wavelength side of 1 μm or more are almost the same as those of the top plate 2, but there is a region having a smaller transmittance on the short wavelength side than the top plate at about 400 nm. Since the visible light in this part is cut, it looks red and black to the eyes, and the parts arranged below are invisible.

  Further, glass having a 5 μm short-pass filter that does not transmit a wavelength of 5 μm or more is used as the glass convex lens 48 of the thermopile 25 (shown by a thin line in FIG. 14). This is to prevent the infrared rays emitted from the crystallized glass optical filter 31 itself and the infrared sensor case 29 that are heated at the ambient temperature from being transmitted through the wavelength of 5 μm or more. As mentioned above, the infrared energy of 1 to 2.9 μm radiated from the pan is very small because the passage is restricted by the top plate, and the output amplification of the thermopile 25 must be increased. This is because it is sensitive to infrared radiation of 5 μm or more at ambient temperature, and it is necessary to thoroughly prevent the infrared radiation of 4.5 μm or more from other than the pan bottom from entering the infrared absorption film 43 of the thermopile.

  The glass convex lens 48 may be made of the same crystallized glass as the top plate 2 and the crystallized glass optical filter 31. This is preferable because infrared radiation due to the temperature of the crystallized glass optical filter 31 can be better blocked for the reasons described above.

  FIG. 15 schematically illustrates the present embodiment (configuration shown in FIG. 3) by radiating infrared energy of each member and each member (top plate 2, crystallized glass optical filter 31, glass convex lens 48) through which this infrared energy passes. The figure put together from a viewpoint used as the incident energy to the infrared absorption film 43 of the thermopile 25 is shown.

  The infrared radiation energy Qn0 at a certain temperature Tn with the cooking pan 6 as a black body passes through the top plate 2. At this time, Qn0 is filtered by the transmission characteristic of the top plate 2, and as a result attenuates and enters the field tube 19. Let this incident infrared energy be Qn1. This Qn1 passes through the crystallized glass optical filter 31 of the pan temperature detecting device 18. At this time, Qn1 is filtered again by the transmission characteristics of the crystallized glass optical filter 31, and as a result, further attenuates to become Qn2. Next, the light passes through the glass convex lens 48 of the thermopile 25 and is incident on the infrared absorption film 43 on the temperature measuring contact of the thermopile. At this time, it is filtered again by the transmission characteristic of the glass convex lens 48 and finally becomes Qn3 and is absorbed by the infrared absorption film 43 and becomes heat.

  The top plate 2 is heated by heat conduction and radiant heat from the cooking pan 6. Therefore, the top plate 2 also emits infrared energy. This infrared radiation energy can be calculated from the temperature Tt and emissivity of the top plate 2. The emissivity is a value obtained by subtracting the transmittance indicated by the solid line in FIG. This energy is Qt0. As described above, this is transmitted through the crystallized glass optical filter 31 and attenuated to become Qt1, and then transmitted through the glass convex lens 48 and attenuated to become Qt2, which is absorbed by the infrared absorption film 43 and becomes heat.

  The inner wall of the visual field cylinder 19 is also heated by the radiant heat of the cooking pan 6 and the heat conduction from the heating coil 7. For this reason, the inner wall of the viewing tube 19 also emits infrared energy. A part of the infrared radiant energy is incident on the thermopile 25 depending on the visual field characteristics of the thermopile 25 and the dimensions (inner diameter, length) of the visual field cylinder 19. FIG. 16 shows the visual field characteristics of the thermopile 25 used in the example. If the field characteristic is very narrow, infrared radiation from the sensor field tube does not enter the thermopile 25. However, it is generally difficult to produce a narrow field characteristic with a small and inexpensive thermopile. When the distance of the field cylinder is short, infrared radiation from the field cylinder is incident on the thermopile. The infrared radiation energy Qb0 incident on the thermopile can be calculated from the temperature Tb and emissivity (about 0.7) of the field tube 19 and the field characteristics of the thermopile. As described above, this is transmitted through the crystallized glass optical filter 31 and attenuated to Qb1, and then transmitted through the glass convex lens 48 and attenuated to Qb2, which is absorbed by the infrared absorption film 43 and becomes heat.

  The crystallized glass optical filter 31 is also heated by the radiant heat from the cooking pan 6 and the ambient temperature of the coil upper surface cooling air passage 15a where the pan temperature detecting device 18 is installed. For this reason, the crystallized glass optical filter 31 also emits infrared energy. The radiant energy Qg0 can be calculated from the temperature Tg and the emissivity in the same manner as the top plate 2. The emissivity is a value obtained by subtracting the transmittance indicated by the broken line in FIG. As described above, this is transmitted through the glass convex lens 48 and attenuates to become Qg1, which is absorbed by the infrared absorption film 43 and becomes heat.

  As described above, the infrared energy detected by the thermopile 25 during cooking includes 1) Qn3 from the cooking pan, 2) Qt2 from the top plate 2, 3) Qb2 from the inner wall of the viewing tube 19 and 4) Qg1 from the crystallized glass optical filter 31 is superimposed, and the thermopile 25 generates a voltage proportional to the infrared energy. And in order to detect a pan temperature correctly, it is necessary to subtract the voltage by the infrared energy of 2), 3), 4).

  FIG. 17 summarizes the relationship between the temperature of each part and the infrared energy (Qn3, Qt2, Qb2, Qg1 shown in FIG. 15) (calculation results) that is radiated from each part and incident on the infrared absorption film 43 of the thermopile 25 in this embodiment. Show. This is calculated using the spectral radiant energy of FIG. 13 and the transmission characteristics of each member (shown in FIG. 14). The temperature of each part is shown only in the temperature range reached during cooking.

  When the typical temperature of each member during cooking, for example, the incident energy from a 300 ° C. pan (black body) is 1, it is 1/6 from the 200 ° C. top plate and 1 from the 80 ° C. sensor field tube. / 60, that from the crystallized glass optical filter 31 at 40 ° C. is 1/60. If the emissivity of the pan becomes, for example, 0.25, the incident energy 1 from the pan becomes ¼, which is not much different from the incident energy from other members. In other words, it can be understood that it cannot be ignored as a disturbance to the pot temperature detection.

  FIG. 18 shows the relationship between the black body temperature Tn and the output voltage V of the output terminal 72-2 of the thermopile temperature detection circuit 72 when a black body is placed on the infrared transmission window 5 of the embodiment of FIG. The black body is a case where the top plate is placed for a short time so that the top plate is not heated, and the temperature of the field tube 19 and the crystallized glass optical filter 31 is not increased. That is, this is obtained by converting Qn3 in FIG. 15 into a voltage.

  The voltage from room temperature to 100 ° C. is almost 0.5 V, and when the temperature exceeds 100 ° C., a voltage proportional to the temperature is output. 0.5V is a voltage obtained by dividing the power supply voltage (5V) of the thermopile temperature detection circuit 72 by resistors 72-5, 72-6, and 72-7 (indicated by a point in FIG. 10), and 0.5V is an operational amplifier 72-1. This is because it is given as a bias voltage. When the temperature exceeds 100 ° C., the output voltage of the thermopile 25 increases, and is amplified about 2000 times by the operational amplifier 72-1, and is observed as a voltage of 0.5V or more. This bias voltage is provided for detecting a failure of the thermopile temperature detection circuit 72. A value obtained by subtracting 0.5 V from the output voltage value of the output terminal 72-2 (a voltage increase value from 0.5 V) is proportional to the detected pan bottom temperature. The microcomputer 60 AD-converts and reads the output voltage of the output terminal 72-2 of the thermopile temperature 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. The relationship shown in FIG. 18 is stored in advance in the ROM of the microcomputer 60 as table data TBLn.

  FIG. 19 shows the relationship between the top plate temperature Tt when only the top plate 2 is heated and the output voltage V of the output terminal 72-2 of the thermopile temperature detection circuit 72. However, it is shown by a value obtained by subtracting 0.5 V described above. The relationship between the top plate temperature Tt and the output voltage of the thermopile temperature detection circuit 72 output terminal 72-2 when the vicinity of the infrared transmission window 5 of the top plate 2 where the pan is not placed is heated with hot air is shown. At this time, the field cylinder 19 and the crystallized glass optical filter 31 are prevented from being heated. That is, this is obtained by converting Qt2 in FIG. 15 into a voltage. 19 is stored in advance in the ROM of the microcomputer 60 as table data TBLt.

  FIG. 20 shows the relationship between the sensor field tube temperature Tb and the output voltage V of the thermopile temperature detection circuit 72 output terminal 72-2 when the top plate 2 of the embodiment is removed and a heater is wound around the field tube 19 and heated independently. Indicates. (The figure shows a value obtained by subtracting 0.5 V described above.) At this time, the crystallized glass optical filter 31 is prevented from being heated. That is, this is obtained by converting Qb2 in FIG. 15 into a voltage.

  Similarly, the pan temperature detecting device 18 is taken out, and the crystallized glass optical filter 31 is heated for a short time with a drier or the like so that the thermopile 25 or the like is not heated or the temperature of the thermopile 25 does not fluctuate. The relationship between temperature Tg and the output voltage V of the output terminal 72-2 of the thermopile temperature detection circuit 72 is shown. (The figure shows a value obtained by subtracting the above-mentioned 0.5 V.) That is, this is a result of converting Qg1 in FIG. 15 into a voltage. The two relationships shown in FIG. 20 are also stored in advance in the ROM of the microcomputer 60 as table data TBLb and TBLg.

  When the reflection type photo interrupter 26 built in the pan temperature detection device 18 is arranged as shown in FIG. 6, 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 large. It passes through the crystallized glass optical filter 31 and the top plate 2 and does not return to the infrared phototransistor 51. However, a part is reflected by the crystallized glass optical filter 31 and the top plate 2. This is because the transmittance of the crystallized glass optical filter 31 and the top plate 2 is 85% and 90% at a wavelength of 930 nm, and the remaining 15% and 10% of infrared light is reflected. In particular, since the amount reflected by the crystallized glass optical filter 31 returns directly to the infrared phototransistor 51 located immediately beside it, in this embodiment, as shown in FIG. It arrange | positions so that a lower surface may be touched, and it prevents that this reflected light injects into the infrared phototransistor 51. FIG. In addition, because of the radiation angle of the infrared LED, there is also infrared light reflected by an object (inner surface of the viewing tube 19) that does not reach the bottom surface of the top plate and is in the middle of the path.

  Therefore, as shown in FIG. 21, the output of the reflectance detection circuit 73 is (a) V1 when there is a pan on the top plate, and (b) V2 when there is no pan. The reflected voltage Vr at the net pan is Vr = V2−V1.

  The pan temperature detector 18 is arranged as shown in FIG. 3, and the output of the reflectivity detection circuit 73 when a metal plate with a known reflectivity is arranged on the top plate using the reflectivity detection circuit 73 built in the pan temperature detection device 18. FIG. 22 shows the relationship between the reflection voltage Vr obtained from the above and the reflectance. An approximate line is also shown in the figure. If this relationship is used, the reflectance can be obtained from the output voltage of the reflectance detection circuit 73. 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.

In a metal material such as a cooking pot, a relationship of ε + ρ = 1 holds between the emissivity ε of infrared energy (E = εσT ⁴ ) radiated from the surface of the material at temperature T and the reflectance ρ of the surface according to Kirchhoff's law. (Transmittance α = 0). In a cooking pan, the infrared energy radiated differs due to the difference in emissivity, while the same pan bottom temperature. For this reason, the problem that a thermopile output, ie, the output of the pan temperature detection apparatus 18, differs arises. Therefore, it is necessary to detect the reflectance of the 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. 23 shows a value Vt (pot) obtained by subtracting the above-described offset voltage Vo of 0.5 V from the output of the pot temperature detection device 18 (output V of the thermopile temperature detection circuit 72) for several kinds of pots placed on the top plate 2. An example of the relationship between (temperature detection voltage) and pan bottom temperature T is shown. The emissivity at the bottom of each pan is also shown in the figure. As shown in FIG. 23, 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. 23A has an emissivity of 0.9, which is close to a black body. (B) has an emissivity of 0.57, (c) is 0.43, and (d) is 0.24. When the voltage values of (b), (c), and (d) are divided by the emissivity, it is shown by a broken line in the figure, and it can be seen that it can be summarized into almost one curve. Each output Vt is proportional to the total radiation energy of each pot (E '= εσT ^4), which to divide by emissivity is converted into the total radiant energy of a black body as described above (E = σT ⁴⁾ Means that. And if the emissivity of each pan is known, it means that the pan temperature of each pan can be reduced to the radiation temperature of a black body.

  FIG. 24 shows the relationship between the emissivity measured using a radiation thermometer in each pan and the reflectance obtained by using the reflectance detection circuit 73 in FIG. 3 (applying the approximate expression of the relationship of FIG. 22). Some pans deviate from Kirchhoff's law, but there is a strong correlation between emissivity and reflectivity. The reason for deviating from Kirchhoff's law is that in the detection of reflectance, not all of the reflected infrared rays are received due to scattering on the pan surface. When obtaining the reflectance, it is desirable that the emitted light of the infrared LED 50 is incident as vertically as possible on the top plate 2 and the reflected light from the pan is guided to the infrared phototransistor 51 as vertically as possible. In the present embodiment, the visual field surface of the thermopile 25 in the pan temperature detecting device 18 at the position on the top plate 2 and the reflective surface on the top plate 2 for the reflectance detection light emission are the same surface. For this reason, as shown in FIG. 6, the thermopile 25 and the reflective photointerrupter 26 are arranged side by side in the pan temperature detection device 18.

  Below, operation | movement of a present Example demonstrates the case where the cooking pan 6 is set | placed on the circle display 4 of the near right side, and cooking is performed by heating a cooking pan for a predetermined time at predetermined temperature. FIG. 25 shows a flowchart of this operation. When a power source (not shown) is turned on, a predetermined temperature and cooking time are set with the operation switch of the induction heating port on which the cooking pan 6 is placed (step S1), and the start of cooking is instructed (step S2), the microcomputer 60 first starts. Reflection data (corresponding to the reflectance) of the pan placed by controlling the reflectance detection circuit 73 is taken in to detect the reflectance (step S3). At the same time, in order to cool the heating coil 7, the inverter circuit 8, and the like, a fan (not shown) is driven to introduce outside air into the coil upper surface cooling air passage 15a and the coil lower surface cooling air passages 15b and 16a, 16b.

  Step S3 for detecting the reflectance will be described in detail with reference to the flowchart shown in FIG. The microcomputer 60 outputs the infrared LED drive signal of FIG. 12A from the port to the terminal 73-2 of the reflectance detection circuit 73 (step S3-1). After outputting 200 ms for a predetermined time (step S3-2), the voltage V2 output to the terminal 73-8 is read from the AD terminal (step S3-3). Then, the infrared LED drive signal is stopped (step S3-4). Next, the pulling reflection voltage Vr is calculated from the voltage V2 obtained by reading the voltage V1 when the pan stored in advance is not placed (step S3-5). Then, the reflectance ρ is obtained from the relationship between the reflection voltage and the reflectance stored in advance (step S3-6).

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

  Here, the pan temperature detection operation (step S5) will be described in detail. FIG. 27 shows a flowchart of the pan temperature detection. The microcomputer 60 reads the output voltage V of the pan temperature detection device 18 (thermopile temperature detection circuit 72) (step S5-1), subtracts 0.5V from this value, and sets this as the pan temperature detection voltage Vt (step S5-). 2).

  At the same time, the temperatures T1a, T1b, T1c of the top plate 2, the field tube 19, and the crystallized glass optical filter 31 are read from the thermistors 20a, 20b, 20c and the thermistor temperature calculation circuit 74 (step S5-3). Then, the infrared amount voltage Va at the temperature T1a of the top plate 2 is obtained from the relationship between the top plate temperature Tt stored in advance as the table TBLt and the output of the thermopile temperature detection circuit 72. Similarly, the infrared amount voltage Vb at the temperature T1b of the viewing tube 19 is obtained from the table TBLb, and the infrared amount voltage Vc at the temperature T1c of the crystallized glass optical filter 31 is obtained from the table TBLg (step S5-4). (Operation of Infrared Amount Calculation Means) Subsequently, Va, Vb and Vc are subtracted from the previous pan temperature detection voltage Vt (step S5-5). (Operation of the subtracting means) By this processing, the amount of infrared rays from the top plate 2, the field tube 19, and the crystallized glass optical filter 31 as disturbances is removed. The voltage after this subtraction is Vt.

  And the emissivity (= 1-reflectance) is obtained from the reflectance detected immediately before induction heating (step S5-6), and the pan temperature detection voltage Vt after this subtraction is divided (step S5-7) ( Reflectance correction operation). The above-mentioned V0 = 0.5V is added to Vt after the division, and a data table which is a relationship between Vn and Tn stored in advance as TBLn is drawn (step S5-8), converted into a pan temperature, and the pan temperature Tn is calculated. Output (step S5-9).

  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 that is the relationship between Vn and Tn may be subtracted to output the pot temperature. In this way, it is possible to speed up the processing without using a division requiring a processing time of the microcomputer.

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

  In the above description, 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 regular intervals during cooking by reducing the emission current. Especially in thin pans, the reflectivity may change due to pan deformation due to high temperature. Furthermore, in 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.

  As shown in FIG. 20, when the temperature of the crystallized glass optical filter 31 is lower than 30 ° C., the amount of infrared rays it gives to the thermopile 25 is one digit less than that of the pan. For this reason, if the pan temperature detection device 18 can sufficiently cool during cooking (if the ambient temperature of the pan temperature detection device 18 can be maintained at 30 ° C. or less with cooling air), the above-described omission of TBLg and steps S5-4 and S5-5 are performed. It is clear that the calculation and subtraction of Vc can be omitted. Of course, in this case, the thermistor 20c can also be omitted.

In FIG. 5 of Example 1, the temperature of the field cylinder 19 was detected by the thermistor 20b provided in the light guide cylinder. FIG. 28 shows the back surface of the coil base 10. In the second embodiment, the temperature of the field cylinder 19 is detected by the thermistor 20d provided on the back surface of the heating coil 7 and the thermistor 20a provided on the lower surface of the top plate 2. As described above, the visual field cylinder 19 is heated by the heat transfer of the radiant heat from the induction heated pan and the Joule heat generated by the heating coil 7. For this reason, the radiant heat is estimated from the temperature of the top plate 2, and the heat transfer is estimated from the temperature of the heating coil 7. Then, the temperature of the visual field cylinder 19 is calculated as a load linear sum of the thermistor 20d and the thermistor 20a. For example, if the temperature detected by the thermistor 20a is T1a and the temperature detected by the thermistor 20d is T1c, the temperature T1b of the sensor field tube is
T1b = k1 × T1a + k2 × T1c (k1 and k2 are constants) (Equation 1)
It is represented by

  28, the same reference numerals as those in FIG. 5 denote the same items. The control block diagram of this embodiment is omitted because the thermistor 20b in the control block of FIG. 9 is replaced with the thermistor 20d.

  The pan temperature detection process in this case is shown in the flowchart of FIG. 29, the same reference numerals as those in FIG. 27 denote the same processes.

  Since other operations in the second embodiment are the same as those in the first embodiment, description thereof will be omitted.

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

DESCRIPTION OF SYMBOLS 1 Main body of induction heating cooker 2 Top plate 3 Operation display part 4 Circle display which shows the position which puts a cooking pan 5 Infrared transmission window 6 Cooking pan 7 Heating coil 7a 1st coil 7b 2nd coil 7c Coil gap | interval 7d Bridge line 8 Inverter circuit 10 Coil base 11 Ferrite 14a Inner cavity 14b Outer cavity wall 15 Coil cooling air passage 15a Coil upper surface cooling air passage 15b Coil lower surface cooling air passage 15c Coil upper surface cooling air delivery hole 16 Seal material 18 Pan temperature detection device 19 Field cylinder 20a thermistor (first temperature detecting means)
20b thermistor (second temperature detection means)
20c thermistor (third temperature detecting means)
21a Low voltage terminal 21b High voltage terminal 25 Thermopile 26 Reflective photo interrupter 27 Electronic circuit board 29 Infrared sensor case 30 Case window 31 Crystallized glass optical filter 32 Metal case 33 Outer 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 part 43 Infrared absorption film 44 Cold junction part 45 NTC thermistor 46 Metal pin 47 Window 48 Glass convex lens 49 Crystallized glass convex lens 50 Infrared LED
51 Infrared Phototransistor 55 Heat Sink 60 Microcomputer 61 Frequency Control Circuit 62 Power Control Circuit 63 Rectifier Circuit 64 Power Switch 68 Operation Switch 69 Display Circuit 70 Buzzer 72 Thermopile Temperature Detection Circuit 72-1, 73-6 Operational Amplifier 72-9 Resistance 73 Reflection Rate detection circuit 73-5 Capacitor 73-7 Charge / discharge circuit

Claims (6)

A top plate made of crystallized glass with a cooking vessel on top;
A heating coil provided under the top plate for generating an induction magnetic field to heat the cooking vessel;
An infrared detecting means provided under the heating coil for detecting infrared rays emitted from the cooking container;
A light guide tube that is provided at a support portion of the heating coil, blocks infrared rays emitted from the heating coil, and guides infrared rays emitted from the cooking container to the infrared detection means;
First temperature detecting means disposed on the lower surface of the top plate for detecting this temperature;
Second temperature detecting means arranged in the light guide tube for detecting the temperature;
First infrared light amount calculating means for calculating the amount of infrared light emitted from the top plate from the output of the first temperature detecting means;
Second infrared ray amount calculating means for calculating an infrared ray amount radiated from the light guide tube from the output of the second temperature detecting means;
Subtracting means for subtracting the outputs of the first and second infrared light amount calculating means from the output of the infrared detecting means;
High-frequency power supply means for supplying high-frequency power to the heating coil;
Power control means for controlling the output power of the high-frequency power supply means;
Cooking container temperature detecting means for detecting the temperature of the bottom surface of the cooking container from the output of the subtracting means,
An induction heating cooker characterized in that the power supplied to the heating coil is controlled based on the output of the cooking vessel temperature detection means. The induction heating cooker according to claim 1,
An induction heating cooker characterized in that the first temperature detection means is provided on the lower surface of the top plate near the outside of the upper opening of the light guide tube. The induction heating cooker according to claim 1,
An induction heating cooker characterized in that the second temperature detecting means is inserted from the outer wall to the inner wall side so as to detect the outer wall or inner wall temperature of the light guide tube and is arranged in the immediate vicinity of the inner wall. A top plate made of crystallized glass with a cooking vessel on top;
A heating coil provided under the top plate for generating an induction magnetic field to heat the cooking vessel;
An infrared detecting means provided under the heating coil for detecting infrared rays emitted from the cooking container;
A light guide tube that is provided at a support portion of the heating coil, blocks infrared rays emitted from the heating coil, and guides infrared rays emitted from the cooking container to the infrared detection means;
First temperature detecting means disposed on the lower surface of the top plate for detecting this temperature;
Second temperature detecting means disposed on the heating coil for detecting the temperature;
First infrared light amount calculating means for calculating the amount of infrared light emitted from the top plate from the output of the first temperature detecting means;
Second infrared light amount calculating means for calculating the amount of infrared light emitted from the light guide tube from the output of the first temperature detecting means and the output of the second temperature detecting means;
Subtracting means for subtracting the outputs of the first and second infrared light amount calculating means from the output of the infrared detecting means;
High-frequency power supply means for supplying high-frequency power to the heating coil;
Power control means for controlling the output power of the high-frequency power supply means;
Cooking container temperature detecting means for detecting the temperature of the bottom surface of the cooking container from the output of the subtracting means,
An induction heating cooker characterized in that the power supplied to the heating coil is controlled based on the output of the cooking vessel temperature detection means. The induction heating cooker according to claim 4,
The first temperature detection means is provided on the lower surface of the top plate near the outside of the upper opening of the light guide tube, and the second temperature detection means is provided on a heating coil located near the outside of the light guide tube. Induction heating cooker characterized by. A top plate made of crystallized glass with a cooking vessel on top;
A heating coil provided under the top plate for generating an induction magnetic field to heat the cooking vessel;
Infrared detection means provided under the heating coil, detecting infrared radiation emitted from the cooking container, etc., and having a window member having the same optical characteristics as the top plate on the infrared receiving front surface;
A light guide tube that is provided at a support portion of the heating coil, blocks infrared rays emitted from the heating coil, and guides infrared rays emitted from the cooking container to the infrared detection means;
First temperature detecting means disposed on the lower surface of the top plate for detecting this temperature;
Second temperature detecting means arranged in the light guide tube for detecting the temperature;
A third temperature detecting means arranged on the window member for detecting the temperature;
First infrared light amount calculating means for calculating the amount of infrared light emitted from the top plate from the output of the first temperature detecting means;
Second infrared ray amount calculating means for calculating an infrared ray amount radiated from the light guide tube from the output of the second temperature detecting means;
Third infrared light amount calculating means for calculating the amount of infrared light emitted from the window material from the output of the third temperature detecting means;
Subtracting means for subtracting the outputs of the first, second and third infrared light amount calculating means from the output of the infrared detecting means;
High-frequency power supply means for supplying high-frequency power to the heating coil;
Power control means for controlling the output power of the high-frequency power supply means;
Cooking container temperature detecting means for detecting the temperature of the bottom surface of the cooking container from the output of the subtracting means,
An induction heating cooker characterized in that the power supplied to the heating coil is controlled based on the output of the cooking vessel temperature detection means.

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