JP2013004328A - Induction heating cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a temperature of a pan in a non-contact manner at high accuracy and stably with high responsiveness without being subject to influence of a material and a bottom state of the pan on a top plate.SOLUTION: An induction heating cooker comprises: a top plate on which a pan is placed; a heating coil arranged below the top plate; a light guide cylinder provided on a component that fixes the heating coil for guiding infrared rays from the pan; infrared detection means detecting the infrared rays; infrared projection means projecting an infrared parallel beam flux substantially perpendicular to the top plate through the light guide cylinder; light-receiving means receiving infrared rays which are projected by the infrared projection means and reflected by the pan; and pan temperature detection means detecting a pan temperature by correcting an output of the infrared detection means by an output of the light-receiving means.

Description

  The present invention relates to an induction heating cooker that detects the temperature of a pan using an infrared sensor.

  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 of an induction heating cooker, a device that detects the temperature by observing the infrared ray radiated from the bottom of the pan heated at a good response speed with an infrared sensor through the top plate is often used. This infrared sensor is placed near the center gap of the heating coil, detects the infrared radiation radiated 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.

  The problem in detecting temperature with an infrared sensor is that it is affected by the emissivity of the object to be measured (cooking pan). The infrared emissivity of the pan bottom depends greatly on the material, color, and processing state of the pan bottom (painting and engraving on the pan bottom, hairline processing, ring processing, driving processing, unevenness, etc.). Moreover, even in the same pan, the emissivity varies depending on dirt such as cooking oil adhering to the bottom of the pan. In other words, even if the pan is made of the same temperature and the same material, the infrared energy radiated differs depending on the color, processing, dirt state, or unevenness, so the infrared energy received by the infrared sensor is also different, and different temperatures are detected. Become. For this reason, a means for correcting the temperature detection by the infrared sensor due to the difference in the pan bottom is required.

  Patent Documents 1, 2, 3, and 4 include known examples for solving this problem.

  The technique of Patent Document 1 includes a light emitting unit that projects light on an object to be heated (pan) placed on a top plate and a light receiving unit that receives reflected light from the object to be heated, and is converted from the output of the light receiving unit. The temperature is detected by correcting the output of the infrared sensor with the emissivity of the heated object. This makes it an accurate pan temperature detection technique that is not affected by the emissivity of the object to be heated (pan).

  In addition to the technique of Patent Document 1, the technique of Patent Document 2 is configured such that opposing light emitting means and light receiving means are arranged with an angle a and a top plate on which a pan is placed. This angle a is an angle at which light is reflected at the bottom of the pan when the top plate and the pan are in close contact. As a result, even when the pan is warped, the emissivity can be accurately detected, and a more accurate pan temperature detection technique is realized.

  The technique of Patent Document 3 includes a plurality of light emitting means arranged around the light receiving means in addition to the technique of Patent Document 1. The reflected light from the pan of the light emitted sequentially by the plurality of light emitting means is received by the light receiving means in synchronization with the light emission, and the reflectance at a plurality of locations on the bottom of the pan is obtained by this output and converted to emissivity. The temperature is detected by correcting the output of the infrared sensor with the emissivity. This avoids local emissivity changes such as unevenness and character printing due to the engraving of the pan, so that more accurate emissivity can be detected, and this is a more accurate pan temperature detection technique. Also disclosed is a technique for detecting a more accurate emissivity by arranging a plurality of light receiving means around the light emitting means, which has the same effect.

  In addition to the technique of Patent Document 1, the technique of Patent Document 4 detects the intensity of reflected light from the bottom surface of the pan provided on the end surface facing the light emitting means and the light emitting means that enters near-infrared light from the end surface of the top plate. The emissivity of the bottom surface of the pan is obtained from the output of the reflection sensor, and the temperature is detected by correcting the output of the infrared sensor with this emissivity. This detects the emissivity over a wide range of the bottom of the pan using the inside of the top plate as a light guide, and accurately obtains the emissivity regardless of the position of the pan, the marking of the pan bottom, and the processing state. It is a hot pot temperature detection technology.

Japanese Patent Laid-Open No. 11-225881 JP 2004-241220 A JP 2006-221950 A JP 2006-260940 A

  Patent Document 1 presents a light source such as a single infrared LED or laser as a specific light emitting means, a single infrared phototransistor as a light receiving means, a wavelength used by these means, and a spectral means using an optical bandpass filter. Has been. However, as will be described later, when a single infrared LED and a single infrared phototransistor are used, it is difficult to accurately detect the reflectance or emissivity of the pan. The obtained reflectivity is that of an extremely narrow area of the pan, and is different from the reflectivity at the wide pan bottom received by the temperature detecting infrared sensor. For this reason, even if the temperature detection infrared sensor output is corrected by the detected reflectance (emissivity = 1−reflectance) and the pan temperature is detected, it is not accurate.

  In Patent Document 2, in addition to the technique of Patent Document 1, a pair of light-emitting means and light-receiving means are arranged with a top plate and an angle a, and even when the top plate and the bottom of the pan have an angle due to warpage or unevenness of the pan. This is a technique for obtaining an accurate reflectance. In addition to this pair of light-emitting means and light-receiving means, a technique for providing a plurality of pairs at an angle different from the angle a is also presented. However, when a single infrared LED and a single infrared phototransistor are used as in Patent Document 1, it is difficult to accurately detect the pan reflectance or emissivity. The obtained reflectance corresponds only to the warp of a specific angle in a very narrow area of the pan, and is different from the reflectance on the wide pan bottom received by the temperature detecting infrared sensor. For this reason, even if the temperature detection infrared sensor output is corrected by the detected reflectance (emissivity = 1−reflectance) and the pan temperature is detected, it is not accurate.

  In Patent Document 3, in addition to the technique of Patent Document 1, a plurality of light emitting means and a plurality of light receiving means are arranged around the temperature detecting infrared sensor, and reflection is performed in a narrow area of the pan detected by the pair of light emitting means and the light receiving means. A technology that calculates multiple rates, converts the reflectance information from these multiple locations to the emissivity at the field of view of the temperature detection infrared sensor, and corrects the temperature detection infrared sensor output with this emissivity to detect the correct pan temperature. is there. If the number of light emitting means or light receiving means is increased, the emissivity of a wider area can be detected accurately, but actually, for example, a large number of, for example, 10 or more light emitting means or light receiving means are provided under the heating coil. There is a problem that it is difficult and expensive even if it can be provided.

  In Patent Document 4, in addition to the technique of Patent Document 1, one light emitting means is installed on the end surface of the top plate and one light receiving means is installed on the other surface, and infrared light emitted by the light emitting means is used for a predetermined area with the top plate as a light guide path. The reflected light reflected from the bottom of the pan is received by the light receiving means using the top plate as a light guide, and the reflectance of the pan is detected. However, in order to use the top plate as a light guide, it is necessary to coat the upper and lower surfaces of the top plate with a reflective material. In particular, a heat-resistant reflective material is required on the upper surface where the pan bottom touches. Instead of the reflecting material, the light reflecting layer needs to be configured as fine irregularities by mechanical or chemical means. Further, an optical coupler for efficiently guiding the light projected by the light emitting means into the top plate and an optical coupler for separating the reflected light from the projected light and efficiently guiding only the reflected light to the light receiving means are also required. These optical parts, materials, and top plate surface treatments are complicated and expensive.

  In the pan temperature detecting means using a thermopile as an infrared sensor, the present invention stably and accurately detects the state of the pan bottom placed on the top plate, that is, unevenness, warpage and dirt, and the material, color and processing state. It is an object of the present invention to provide an induction heating cooker that can improve the safety and convenience of use.

  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 for detecting infrared radiation radiated from the bottom of the pan and the like, provided on the support portion of the heating coil, blocking infrared radiation radiated from the heating coil, and infrared radiation radiated from the pan bottom A light guide tube that leads to the infrared detection means, a parabolic reflector, and infrared light emission means that is disposed at the focal point thereof, is disposed beside the infrared detection means below the light guide tube and passes through the light guide tube. Infrared light projecting means for projecting an infrared light beam vertically onto the top plate, and the infrared light beam reflected in the pan installed in the infrared light beam projected by the infrared light projecting means Infrared reflected light receiving means for emitting light, high frequency power supplying means for supplying high frequency power to the heating coil, power control means for controlling output power of the high frequency power supplying means, and the infrared detecting means from the output of the infrared reflected light receiving means And a pan temperature detecting means for detecting the temperature of the bottom surface of the cooking container from the output of the reflectance correcting means, and the power control means is controlled by the output of the pan temperature detecting means. It can be solved by induction heating cooker.

  According to the present invention, the infrared light projecting means projects infrared parallel rays onto a wide area of the pan bottom, and most of the reflected light is received by the infrared reflection light receiving means. The rate (= 1-emissivity) can be detected. For this reason, the detected reflectance is not easily affected by local stains on the bottom of the pan, unevenness, engraving, printing painting, and the like. Also, since the infrared light projecting means, the infrared reflection light receiving means and the infrared detection means are arranged side by side, the infrared detection range (field of view of the infrared detection means) radiated by the pan, the infrared light projection means and the infrared reflection light reception means The reflectance detection range of the pan to be detected (light projection surface and field of view of the reflection light receiving means) can be overlapped. For this reason, an infrared detection output proportional to the reflectance detected by the reflectance detection, that is, the emissivity can be obtained on substantially the same surface of the pan bottom, and an accurate radiation temperature can be detected by correcting the reflectance.

  By performing this correction, it becomes possible to accurately detect the pan bottom temperature regardless of the material, color, processing state or dirt state of the pan bottom, and heating can be controlled using the accurately detected pan bottom temperature. Because you can, you can cook well. In other words, it is possible to provide a pan temperature detecting means for stably detecting the temperature of the bottom of the heating pan accurately with any pan. And the induction heating cooking appliance which enables safe and optimal cooking can be provided by controlling the high frequency electric power to a heating coil appropriately by the pan temperature detected correctly.

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. The figure which shows the detail of the infrared rays light projection means and infrared rays reflection light-receiving means of Example 1. FIG. FIG. 5 is a diagram showing optical characteristics of glass such as a top plate used in Example 1; FIG. 3 shows optical characteristics of the infrared LED and phototransistor of Example 1. FIG. 2 is a plan view and a cross-sectional view showing details of the thermopile of the first embodiment. FIG. 3 is a view showing visual field characteristics of the thermopile of Example 1. The figure which shows the relationship between the reflectance detection range of Example 1, and a thermopile detection range. 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 output by the presence or absence of a pan of the reflectance detection circuit of Example 1. FIG. The figure which shows the spectral radiant energy distribution of black body temperature. 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. 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 emissivity and reflectance of the various pans of Example 1. FIG. The figure which shows the relationship between the reflective correction coefficient K and the reflective voltage Vr of the various pans of Example 1. FIG. The figure which shows typically the difference of the reflection detection by a single element, and the reflection detection of Example 1. FIG. The figure which shows the detection variation of the reflection detection by a single element, and the reflection detection of Example 1. FIG. 2 is a flowchart of induction heating cooking according to the first embodiment. 5 is a flowchart of reflectance detection according to the first embodiment. The flowchart of the pan temperature detection of Example 1. FIG. The flowchart of the pan temperature detection of Example 1. FIG. The figure which shows the infrared rays light projection means and infrared rays reflection light-receiving means of Example 2. FIG. 5 is a diagram showing a schematic configuration of a reflective infrared LED of Example 2. FIG. 6 is a diagram illustrating an infrared light projecting unit and an infrared reflection light receiving unit according to a third embodiment. The figure which shows the infrared rays light projection means and infrared rays reflection light-receiving means of Example 4. FIG. 6 is a diagram illustrating an infrared light projecting unit and an infrared reflection light receiving unit according to a fifth embodiment. The control block diagram of the induction heating cooking appliance of Example 6. FIG. FIG. 10 is a diagram illustrating details of an illuminance detection circuit according to a sixth embodiment. The figure which shows the relationship between the output voltage of the illumination intensity detection circuit of Example 6, and illumination intensity. 10 is a flowchart of induction heating cooking according to the sixth embodiment.

  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 3 pans where there are 2 pans that can be induction-heated and 1 pans that can be heated by radiant heat from a heater (heating source) such as a radiant heater or a halogen heater. However, the application target of the present invention is not limited to this, and may be, for example, an induction heating cooker provided with three pot places where induction heating is possible. The cooking pan 6 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 4 having a radius that approximately matches the outermost radius of the heating coil 7 or the radiant heater disposed below the top plate 2 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 subjected to the above-described printing or coating is provided for detecting the pot temperature, which will be described later, at a position shifted by about 50 mm from the center of the circle 4 at the two pot-holding 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 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 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 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 detecting device 18 is disposed in the coil upper surface cooling air passage 15a below the coil cooling air delivery hole 15c. The pan temperature detection device 18 detects the bottom surface temperature of the cooking pan 6 heated by induction from the infrared rays transmitted through the infrared transmission window 5 of the top plate 2. Moreover, the infrared projector 35 and the infrared reflective light receiver 36 are also incorporated, and the reflectance of the bottom face of the cooking pan 6 heated is detected.

  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 is a detailed configuration diagram in which the top plate 2 is removed from FIG. 3 and the heating coil 7, the coil base 10, and the coil cooling air passage 15a are viewed from above. Here, in particular, the positional relationship of the heating coil 7 and the inner cavity 14a and the pan temperature detecting device 18 on the horizontal plane 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 gap 7c has a concentric band shape with a width of about 15 mm, and the winding end of the first coil 7a bridges the gap 7c and becomes the winding start of the second coil 7b. The first coil 7a, the bridging wire 7d, and the second winding The heating coil 7 is composed of the coil 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 thereof is a coil gap portion 7c. An inner cavity 14a is provided on the inner peripheral side of the second coil 7b. Further, an elliptical sensor field cylinder 19 (approximately 12 mm long and 24 mm wide ellipse) is provided between a portion of the coil gap 7 c and the two radially arranged ferrites 11. A pan temperature detecting device 18 is installed.

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

  Infrared rays from the bottom of the pan heated by induction pass through the infrared transmission window 5 of the top plate 2 and enter the thermopile 25 built in the pan temperature detector 18 described in detail later from the sensor visual field cylinder 19. Further, the infrared light projected by the infrared projector 35 passes through the sensor visual field cylinder 19 and the infrared transmission window 5 and is reflected at the bottom of the cooking pan 6, and the reflected light is received by the infrared reflection receiver 36.

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

  As described with reference to FIGS. 4 and 5, the pan temperature detecting device 18 avoids the vicinity of the bridging wire 7 d and the coil gap portion 7 c located at a position away from the high voltage terminal 21 b to which the high voltage output wire 22 b is connected. The case window 30 is installed under the sensor field cylinder 19 provided.

  The heating coil 7 is divided into two parts, the sensor viewing tube 19 is provided in the gap 7c, and the pan temperature detecting device 18 is provided below the sensor viewing tube 19, and the magnetic flux at the intermediate portion in the radial width of the heating coil 7 is the strongest. This is because the top of the pan is heated to the highest temperature, and accurately detecting the temperature of that portion helps to prevent abnormal overheating.

  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 detector 18 includes an infrared detection sensor (thermopile 25) covered with a heat sink 59, an infrared projector 35 (infrared projector) including a parabolic reflector 51 and an infrared LED 50, an infrared phototransistor 54, and the like. The infrared reflection light receiver 36 (infrared reflection light receiving means) is mainly configured. The thermopile 25, the infrared projector 35, and the infrared reflection receiver 36 are mounted with 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 25. The thermopile 25, the infrared projector 35, the infrared reflection receiver 36, and the electronic circuit board 27 are hermetically sealed in a plastic member infrared sensor case 29 (shown by a one-dot chain line). . 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, as shown by the thin line in FIG. 8). The optical characteristics on the long wavelength side of 1 μm or more are almost the same, but there is a region with a low transmittance on the short wavelength side of 400 nm compared to the top plate, and the visible light in this part is cut, so the eyes appear reddish. A crystallized glass obtained by cutting the crystallized glass into a thin square is fitted as a crystallized glass optical filter 31.

  Then, a thermopile 25 covered with a heat sink 26 under the crystallized glass optical filter 31, an infrared projector 35, and an infrared reflection receiver 36 are mounted on an electronic circuit board 27. The infrared sensor case 29 is covered with a metal case 32 (indicated by a two-dot chain line) having a permeability of approximately 1 such as aluminum. Naturally, the previous case window 30 is opened. Further, the aluminum metal case 32 is covered with an outer infrared sensor case 33 made of a plastic member. Of course, the previous case window 30 is opened. That is, the thermopile 25 is covered with a triple case. And the pan temperature detection apparatus 18 is installed in the coil upper surface cooling air path 15a so that the case window 30 may desire the inside of the sensor visual field cylinder 19 of the coil base 10. FIG.

  FIG. 6B shows a cross-sectional view along the line AA ′ in FIG. This is because the thermopile 25 and the infrared projector 35, the infrared reflection receiver 36, the case window 30 of the infrared sensor case 29, and the crystallized glass optical filter 31 are mounted on the electronic circuit board 27 installed in the infrared sensor case 29. It is sectional drawing which shows a positional relationship.

FIG. 7A shows the detailed configuration of the infrared projector 35 and the infrared reflection receiver 36. The infrared projector 35 includes a surface-mount type infrared LED 50 as an infrared light emitting element, a parabolic reflector 51 in which a high reflectivity metal such as aluminum or chromium is plated or deposited on a parabolic surface, and a projector light shielding wall 52. The paraboloid is a surface formed by rotating a parabola Y = X ² / 4F ((0, F): focal position). This surface is formed as a concave on the upper surface of the plastic member, and aluminum or chromium is formed on the surface. A parabolic reflector 51 is formed by plating or vapor deposition. The parabolic reflecting mirror 51 may be formed by molding high-brightness aluminum. The infrared LED 50 is arranged at the focal point of the parabolic reflector so that the emitted light is irradiated to the parabolic reflector.

  The infrared reflection light receiver 36 is composed of an infrared phototransistor 54 having a bullet-shaped plastic lens, and is mounted on the focal axis of the parabolic reflector with the light receiving surface facing upward on the opposite side of the infrared LED 50.

  As shown in the figure, the parabolic reflecting mirror 51 is surrounded by a projector light-shielding wall 52. The reason why the parabolic reflecting mirror 51 is surrounded by the projector light shielding wall 52 is to prevent the projected infrared rays from affecting other electronic components mounted on the electronic circuit board 27. The light emitted from the infrared LED 50 is not point light emission (point light source), so even if the light emission point is arranged at the focal point of the parabolic reflector, the light beam reflected by the parabolic reflector 51 does not become a completely parallel light beam. This is because if there is no projector light-shielding wall 52, light rays that are not parallel are reflected by the crystallized glass optical filter 31 and reach other electronic components. In addition, the infrared phototransistor 54 surrounds the periphery and the lower surface except the upper surface with a light-shielding wall 55 so that the projected infrared light does not directly enter the infrared phototransistor 54.

  FIG. 7B shows the lower surface of the small substrate 53 on which the infrared LED 50 and the infrared phototransistor 54 are mounted. A surface mount type infrared LED 50 is soldered to the lower surface of the small substrate 53. A pin of a bullet-type infrared phototransistor 54 is soldered on the upper surface. The infrared phototransistor 54 is covered with a plastic cylindrical tube as a light-receiving light shielding wall 55. And this small board | substrate is engage | inserted by the projector light-shielding wall 52 so that the light emission position of infrared LED50 may be located in the focus of the parabolic reflector 51. FIG. The terminals of the infrared LED 50 and the infrared phototransistor 54 are connected to the reflectance detection circuit 73 on the electronic circuit board 27 from the pattern outside the projector light shielding wall 52 of the small board 53.

  FIG. 8 shows the optical characteristics (transmittance at each wavelength) of the top plate 2 and the crystallized glass optical filter 31. FIG. 9A shows the spectral intensity characteristic of the infrared LED 50 and the spectral sensitivity characteristic of the infrared phototransistor 54. FIG. 9B shows the light emission intensity directivity characteristic of the infrared LED 50 and the light reception sensitivity directivity characteristic of the infrared phototransistor 54.

  The infrared LED 50 emits near-infrared light in the vicinity of 930 nm, has a wide viewing angle (half-value angle of about 120 °), and the light beam is reflected by the parabolic reflecting mirror 51 to be almost parallel and projected upward. . The reason for having a wide viewing angle is to make the intensity distribution of parallel rays reflected by the paraboloid uniform. On the light receiving surface of the infrared phototransistor 54, a bullet-shaped lens is formed of visible light plastic, and the reflected infrared light from the previously projected infrared light object (the bottom of the pan) is viewed at a relatively narrow viewing angle (half-value angle 20). The photocurrent proportional to the amount of light received is output. However, the light reception is defined by the opening of the light-shielding light-shielding wall 55 rather than the viewing angle. Although a phototransistor without a bullet-type lens may be used, it is desirable to have a lens in terms of light collection efficiency and light receiving sensitivity. Note that the emission wavelength of the infrared LED 50 is not limited to 930 nm, and may be in the near infrared region of 700 nm to 900 nm. The infrared phototransistor 54 only needs to have spectral sensitivity characteristics in the near-infrared region with a wavelength of 700 nm to 900 nm. These wavelengths are defined from the optical characteristics of the top plate 2 and the crystallized glass optical filter 31 shown in FIG. 8 and the infrared wavelength region emitted from the cooking pan. In other words, the wavelength of the infrared rays to be used is only required to be transmitted through the top plate 2 and the crystallized glass optical filter 31, and is required to be an inexpensive element. Further, it is desirable to remove the infrared region (wavelength range of 1 μm or more from the cooking temperature of the pan, see FIG. 18 described later) received by the thermopile 25 that is an infrared sensor for temperature detection. For this reason, in this embodiment, the infrared LED 50 and the infrared phototransistor 54 having the optical characteristics shown in FIG. 9 are used.

  The infrared projector 35 and the infrared reflection receiver 36 are configured by a pair of an infrared LED 50 and an infrared phototransistor 54 and detect the reflectance of the bottom surface of the cooking pan 6 placed on the top plate 2 as described above.

  The upper surfaces of the infrared projector 35, the projector light shielding wall 52 of the infrared reflection receiver 36, and the light receiver shielding wall 55 are located directly below the lower surface of the crystallized glass optical filter 31. This is to prevent the projected infrared emission from being reflected by the crystallized glass optical filter 31 directly above and received by the infrared phototransistor 54 of the infrared reflection receiver 36.

  As shown in FIG. 8, 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 this reflected light is immediately arranged on the same axis as the infrared phototransistor 54. There is a risk of receiving light. This light receiving level is large when the distance from the lower surface of the crystallized glass optical filter 31 that is a reflecting surface is short, and affects the reception of reflected light at the bottom surface of the pan on the top plate 2 that is originally intended. For this reason, in this embodiment, as shown in the figure, the distance between the crystallized glass optical filter 31 and the upper ends of the projector light-shielding wall 52 and the light-receiving light-shielding wall 55 is brought close to within 500 μm, and the crystal of the emitted infrared rays of the infrared LED 50 is obtained. The reflected part reflected by the vitrified glass optical filter 31 is prevented from being received by the infrared phototransistor 54. Ideally, it is desirable to bring the lower surface of the crystallized glass optical filter 31 into contact with the upper surfaces of the light projector light shielding wall 52 and the light receiver light shielding wall 55.

  FIG. 10 shows details of the thermopile 25. FIG. 10A is a perspective view of the heat sink 26 and the thermopile 25. 10B is a cross-sectional view of the thermopile 25 taken along the line BB ′ in FIG. 10A excluding the heat sink 26, and FIG. 10C is a cross-sectional view of CC ′ in FIG. 10B. It is a top view of the cross section in the line shown by. The infrared absorption film 25-9 is omitted so that the thermocouple can be seen.

  The thermopile 25 has a large number of thermocouples (thermocouples) connected in cascade (piling). The thermopile 25 is built in a metal case 25-3 composed of a metal can 25-1 such as a nickel-plated steel plate and a metal stem 25-2. Yes. A silicon oxide film 25-5 is formed on the surface of the silicon substrate 25-4 having a thickness of about 300 μm to electrically and thermally insulate, and polysilicon and aluminum are sequentially deposited on the silicon oxide film 25-5 to form a polysilicon deposited film 25-6. , A large number of thermocouples are formed with the aluminum vapor deposition film 25-7, and these are connected in cascade. An infrared absorption film 25-9 such as a rubidium oxide film close to a black body is formed at the center of the silicon base material 25-4 having a polysilicon / aluminum junction (temperature measuring contact). One end of the polysilicon and aluminum vapor deposition film is a cold junction 25-10, which is disposed on the silicon oxide film 25-5 around the silicon substrate 25-4. The back surface of the silicon base material 25-4 is etched to 290 μm leaving the periphery (cold contact portion), and the thickness of the silicon base material having the temperature measuring contact portion is formed to 10 μm. This is because by reducing the thickness of the silicon with good thermal conductivity, the thermal contact between the temperature measuring contact portion 26-8 and the cold junction portion 25-10 is reduced, and the temperature measuring contact portion and the cold junction portion are thermally insulated. is there.

  This silicon substrate 25-4 is fixed to the metal stem 25-2 of the metal case 25-3 with an adhesive such as a bond. At the same time, an NTC thermistor 25-11 formed on a ceramic is similarly arranged on the metal stem 25-2. This is for detecting the ambient temperature of the thermocouple in the metal case 25-3 and correcting the thermoelectromotive force of the thermocouple. Details will be described later. Four metal pins 25-12, which are insulated and sealed, pass through the metal stem 25-2, and the output of the previous thermocouple and the NTC thermistor 25-11 are wire-connected to the metal pins 25-12. A cylindrical metal can 25-1 is placed on and welded to the metal stem 25-2 in an inert gas such as nitrogen. A small hole window 25-13 is formed on the upper surface of the metal can 25-1, and a glass convex lens 25-14 is attached thereto from the inside. The silicon base material 25-4 is fixed so that the temperature measuring contact portion 25-8 (below the infrared absorption film 25-9) is positioned below the small hole. The glass convex lens 25-14 is designed so that the visual field range of the infrared transmission window 5 forms an image on the infrared absorption film 25-9.

  The thermocouple temperature measuring contact 25-25 (below the infrared absorbing film 25-9) in the thermopile 25 is heated by infrared light that passes through the small hole window 25-13 and is condensed by the glass convex lens 25-14. This heating temperature rise is proportional to the infrared energy that has passed, and a voltage proportional to the temperature difference between the cold junction portion 25-10 of the thermocouple and the temperature measuring contact portion 25-8 is applied to the metal pin 25-12 of the thermocouple output. Is output. FIG. 11 shows the visual field characteristics of this thermopile. Because of the glass convex lens 25-14, the viewing angle is narrow, and in this embodiment, a circle having a diameter of about 10 mm is within the half-value angle at the upper end of the sensor light guide tube 19.

  As described above, in the thermopile 25, the metal case 25-3 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 26 is mounted as a thermal buffer (increasing the heat capacity) to reduce output fluctuations due to changes in ambient temperature.

  FIG. 12 shows a state in which the infrared projector 35 projects infrared rays toward the pan bottom to detect reflectance, and the infrared reflection receiver 36 receives the reflected light from the pan. In addition, a schematic relationship between the light projecting range of the infrared projector 35, that is, the infrared range projected by the infrared projector 35 to the bottom of the pan and the light receiving range of the thermopile 25 is shown. Infrared light emitted from the infrared LED 50 is reflected by the parabolic reflecting mirror 51 to become parallel rays, and is projected substantially vertically onto the top plate 2, that is, the pan bottom. The infrared ray reflected here is received by the infrared reflection receiver 36. In the figure, the scattering component of the reflected light is shown. Further, in this embodiment, the infrared projector 35 is disposed immediately next to the thermopile so that the left half of the thermopile light receiving field overlaps the light projection range for reflectance detection. The left side of the portion wider than the half-value angle overlaps the light projection range for reflectance detection. Although the infrared phototransistor 54 is arranged coaxially with the focal point of the parabolic reflector 51, it is obvious that the infrared phototransistor 54 may slightly deviate from the coaxiality.

  The control block diagram of the induction heating cooking appliance of a present Example is shown in FIG. The microcomputer 60 controls the operation of the induction heating cooker. In the following, symbol R represents a block relating to the induction heating port located on the right side in FIG. 1, and symbol L represents a block relating to the induction heating port located on the left side in FIG. The two inverter circuits 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 a display / operation unit, accepts a user's operation instruction, and displays an operation state of the device. Further, a buzzer 70 is connected to notify a user of an operation button press or a warning such as an error. The microcomputer 60 controls the frequency control circuits 61R and 61L, the power control circuits 62R and 62L, and the radiant heater circuit 67 in accordance with a user instruction to heat the cooking pan 6 on the top plate 2.

  The thermopile 25 is connected to a thermopile temperature detection circuit 72 so that the output is amplified and input to the AD terminal of the microcomputer 60. The infrared LED 50 of the infrared projector and the infrared phototransistor 54 of the infrared reflection receiver are connected to the reflectance detection circuit 73, the emission of the infrared LED 50 is controlled by the port output of the microcomputer 60, and the infrared light reflected by the cooking pan 6. Is received by the infrared phototransistor 54 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.

  The reflectance correction means is performed by software of the microcomputer 60. Details will be described later.

  Further, the microcomputer 60 knows the infrared reflectance of the cooking pot from the output of the reflectance detection circuit 73 and corrects it with the reflectance to detect the temperature of the cooking pot. This process is also performed by the software of the microcomputer 60. (Operation of Reflectance Correction Unit) Then, heating of the cooking pan 6 is controlled via the power control circuit 62. Details of this processing method will be described later.

  FIG. 14 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 25-11 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, 72-7. The connection point “a” with the resistor 72-8 is connected to the thermocouple output terminal (−). The NTC thermistor 25-11 is a resistance element having a negative temperature characteristic, 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. Thermocouple output (voltage between (+) and (-) symbols in the figure) is the temperature difference between temperature measuring junction 25-8 (point heated by infrared energy) and cold junction (thermocouple output terminal) 25-10. Proportional. For this reason, when the atmosphere in the metal case 25-3 (in which the NTC thermistor 25-11 is incorporated) rises at the ambient temperature where the thermopile 25 is installed, the thermocouple output decreases. This decrease is compensated by the voltage increase at the connection point a. That is, the NTC thermistor 25-11 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.

  FIG. 15 shows details of the reflectance detection circuit 73. In FIG. 15, 50 is an infrared LED which is a light emitting element, and its emission wavelength is 930 nm. An infrared phototransistor 54 has, for example, a peak sensitivity wavelength of 880 nm and an infrared LED 50 emission wavelength of 930 nm, which has a sensitivity of 95% of the peak sensitivity. FIG. 16 shows an operation timing chart of the reflectance detection circuit 73. The infrared LED 50 is driven by the transistor 73-1. This drive is controlled by a signal input from the output port of the microcomputer 60 to the drive signal terminal 73-8. FIG. 16A shows this signal. When a rectangular wave signal with a duty of 50% (frequency about 2 kHz) is input to the drive signal terminal 73-8, 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 73-2. In this embodiment, the resistance value is fixed and the light emission intensity is constant. The infrared light is reflected by the parabolic reflecting mirror 51 to become parallel light, passes through the crystallized glass optical filter 31, is reflected by the bottom surfaces of the top plate 2 and the cooking pan 6, and is an infrared phototransistor 54 which is a light receiving element. When the light is received, a voltage is generated in the resistor 73-3 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 is cut in direct current by a capacitor 73-5, doubled by voltage rectification by diodes 73-5 and 73-6, and input as a direct current signal to a direct current amplifier composed of an operational amplifier 73-7, where it is amplified. The This is shown in FIGS. 16 (c) and 16 (d). This amplified DC voltage is output from the output terminal 73-9. This output is input to the AD terminal of the microcomputer 60.

  As described above, the reflectance detection circuit 73 projects near-infrared light, which has a constant light emission intensity and is carrier-modulated, as parallel light on the bottom of the pan, receives the infrared light reflected by the pan, and reflects the DC voltage. By obtaining the voltage, a value corresponding to the reflectance is detected. FIG. 17 shows the output of the reflectance detection circuit when the cooking pan 6 is placed on the top plate and when it is not placed. When the cooking pan 6 is not placed, the reflection is only from the top plate 2, which shows a constant value. The transmittance of the top plate at an infrared wavelength of 930 nm is 90%, and the rest is reflected. The future increase is the reflection from the pan, and this amount corresponds to the reflectivity of the pan.

  Infrared light emission is carrier-modulated at about 2 kHz, and the direct current component is cut by the capacitor 73-4 in the light receiving circuit. The direct current component of natural light or low frequency components (such as incandescent lamps and fluorescent lamps) This is to prevent the commercial power frequency) from affecting the reflectance detection of the pan. The visible light is cut to some extent by the crystallized glass optical filter 31. Further, the influence of the dark current of the infrared phototransistor 54 is also prevented.

  Hereinafter, the operation of the first embodiment, particularly the reflectance detection, the pan temperature detection, and the cooking operation will be described.

The cooking pan 6 placed on the top plate 2 generates heat by induction heating. By this heating, infrared rays are emitted from the bottom of the pan 6. This total radiant energy E is proportional to the fourth power of the pan temperature T (E = σT ⁴ ), and is known as Stefan-Boltzmann law. FIG. 18 shows the spectral radiant energy of the black body temperature calculated from Planck's distribution law. If this spectral radiant energy is integrated over the entire wavelength region, the total radiant energy E is obtained, which is proportional to the fourth power of the temperature (absolute temperature). This is the aforementioned Stefan-Boltzmann law, and this coefficient σ is the Stefan-Boltzmann coefficient. The peak wavelength of the spectral radiant energy is 5 μm to 8 μm at a cooking temperature of 100 to 300 ° C. based on the Vienna transition law.

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

  On the other hand, the optical characteristics of crystallized glass (top plate 2), which is a non-magnetic material, transmit light having a wavelength of 0.2 μm to 2.9 μm for 80% or more as shown by the solid line in FIG. It transmits about 30% of light having a wavelength of 0.5 μm and hardly transmits light having a wavelength longer than 4.5 μm and shorter than 0.2 μm. Due to this optical characteristic, most of the infrared radiation energy (see FIG. 18) 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.

  As a thermopile optical filter used in many thermometers in recent years, one having a transmission wavelength of 1 to 15 μm is used. 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. 10, the thermopile 25 is formed by depositing a large number of thermocouples, and is composed of a large number of temperature measuring contacts heated by incident infrared rays and a large number of cold contacts on the silicon substrate 38. Since the cold junction is fixed to the metal stem 25-2 of the metal case 25-3 with a bond, the metal case 25-3 (metal can 25-1 and metal stem 25-2) of the thermopile 25 is thermally provided. It is a cold junction. And this metal case 25-3 cannot be fixed to a freezing point like a normal thermocouple.

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

  The pan temperature detecting device 18 of the present embodiment is disposed immediately below the coil gap 7c where the magnetic flux density of the high-frequency magnetic field generated by the divided heating coil 7 is the strongest so that the hot portion of the pan bottom during cooking can be detected. The This position is between the rod-shaped ferrites 11 arranged radially under the heating coil 7, and since the magnetic flux almost passes through the ferrite, it is a place where there is little leakage magnetic flux. However, since the distance from the lower surface of the heating coil 7 is about 20 mm, the leakage magnetic flux is large, and the temperature of the metal located here is increased by induction heating. For example, when induction heating is performed on a pan, which is a cooking vessel placed on the top plate 2, by inputting high frequency power of 3 kW to the heating coil, the temperature of the magnetic steel plate at this location rises by about 30 ° C. To do. 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 2 and the heating coil 7, outside air is introduced into the coil cooling air passages 15a and 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.

  Thus, the pan temperature detecting device 18, particularly the built-in thermopile 25, includes (1) leakage magnetic flux from the heating coil 7, (2) temperature change due to cooling air for cooling the coil, and (3) from the inverter circuit. You will be exposed to radiated 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 above for the operation of the thermopile temperature detection circuit 72, temperature compensation is performed in a circuit using the built-in NTC thermistor 25-11 so that the output of the thermopile 25 does not change with the ambient temperature. However, since the NTC thermistor 25-11 is formed as a thin film on the ceramic chip and is fixed to the metal stem 25-2 with a bond or the like, the metal stem 25-2 that is thermally equivalent to a cold junction is used. That is, it is difficult to follow the temperature change of the metal case 25-3 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 the present embodiment, the pan temperature detecting device 18 is installed in the coil 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 the temperature rises. It is preventing. In addition, in order to prevent the airflow in the coil cooling air passage 15a from directly hitting the metal case 25-2 of the thermopile 25 and the semiconductor, resistance, etc. of the thermopile temperature detecting circuit 72, the infrared sensor case 29 which is a windproof case is prevented. Cover 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. In this case, this warm air is introduced into the 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 a solid line in FIG. 8, 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 25-14 attached to the thermopile 25 is 1 to 15 μm, the output of the thermopile 25 is greatly affected by the infrared light having a wavelength longer than 4.5 μm radiated from the top plate 2. The temperature of the bottom of the cooking pan on the plate 2 cannot be accurately detected. 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, the infrared projector 35, the infrared reflection receiver 36, and the like disposed under the crystallized glass optical filter 31 invisible from the infrared transmission window 5 of the top plate 2. As described above (as shown by the broken line in FIG. 8), 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 with a transmittance of about 400 nm on the short wavelength side compared to the top plate. Since the visible light in this part is cut, it looks red and black to the eyes, and the parts arranged below are invisible.

  As described above, the light emission wavelength of the infrared LED 50 constituting the infrared projector 35 and the spectral sensitivity wavelength of the infrared phototransistor 54 constituting the infrared reflection receiver 36 are set in the near infrared region of 700 nm to 1 μm. The radiant infrared energy is determined from the wavelength region where the top plate and the crystallized glass optical filter 31 transmit, while removing the band of about 2 μm from 1 μm to 2.9 μm.

  Further, a glass (shown by a thin line in FIG. 8) 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 25-14 of the thermopile 25. This is to prevent the infrared rays emitted from the crystallized glass optical filter 31 itself and the infrared sensor case 29 that are heated at the ambient temperature from being transmitted through the wavelength of 5 μm or more. As mentioned above, the infrared energy of 1 to 2.9 μm radiated from the pan is very small because the passage is restricted by the top plate, and the output amplification of the thermopile 25 must be increased. This is because it is sensitive to infrared radiation of 5 μm or more at ambient temperature, and it is necessary to thoroughly prevent infrared rays of 4.5 μm or more from other than the pan bottom from entering the infrared absorption film 25-9 of the thermopile. is there.

  The glass convex lens 25-14 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. 19 shows the relationship between the black body temperature Tn and the output voltage V of the thermopile temperature detection circuit 72 output terminal 72-2 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 sensor field tube 19 and the crystallized glass optical filter 31 is not increased.

  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. 13), and 0.5V is an operational amplifier 72-1. This is because it is given as a bias voltage. When the temperature exceeds 100 ° C., the output voltage of the thermopile 25 increases, and is amplified about 2000 times by the operational amplifier 72-1, and is observed as a voltage of 0.5V or more. This bias voltage is provided for detecting a failure of the thermopile temperature detection circuit 72. A value obtained by subtracting 0.5 V from the output voltage value of the output terminal 72-2 (a voltage increase value from 0.5 V) is proportional to the detected pan bottom temperature. The microcomputer 60 AD-converts and reads the output voltage of the thermopile temperature detection circuit 72 output terminal 72-2, and the pan temperature detection voltage Vt (= V−0.5), which is a value obtained by subtracting 0.5V from this voltage. Based on the above, the following process is performed to obtain the pan temperature. 19 is stored in advance in the ROM of the microcomputer 60 as table data (pan temperature conversion TBL).

  FIG. 20 shows the relationship between the top plate temperature Tt when only the top plate 2 is heated and the output voltage V of the thermopile temperature detection circuit 72 output terminal 72-2. However, it is shown by a value obtained by subtracting 0.5 V described above. The relationship between the top plate temperature Tt and the output voltage of the thermopile temperature detection circuit 72 output terminal 72-2 when the vicinity of the sensor window 5 of the top plate 2 where the pan is not placed is heated with hot air is shown. At this time, the sensor field tube 19 and the crystallized glass optical filter 31 are prevented from being heated. The relationship shown in FIG. 20 is stored in advance in the ROM of the microcomputer 60 as table data (top plate TBL).

  When the pan is induction-heated in actual cooking, in addition to the infrared radiation from the induction-heated pan, the infrared radiation from the top plate 2 itself is also incident on the thermopile. This is because the top plate itself is heated for heat radiation and heat conduction from the pan and emits infrared light at this temperature. Therefore, it is necessary to provide the data table of FIG. 20, detect the temperature of the top plate 2 with the thermistor 20, and subtract this radiation. As described above, it has been described that the effect of infrared radiation due to the temperature of the top plate 2 is removed and reduced by the crystallized glass optical filter 31 in the pan temperature detection. In the wavelength range of 2.9 to 4.9 μm, the top plate temperature This is because the radiation component cannot be removed by the crystallized glass optical filter 31.

  When the infrared projector 35 and the infrared reflection receiver 36 incorporated in the pan temperature detector 18 are arranged as shown in FIG. 12, when there is no cooking pan on the top plate 2, infrared light emitted from the infrared LED 50 (wavelength 930 nm). Mostly passes through the crystallized glass optical filter 31 and the top plate 2 and does not return to the infrared phototransistor 54. 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 directly returns to the infrared phototransistor 54 on the same axis as the infrared LED 50, in this embodiment, as shown in FIG. The upper surface 55 is disposed so as to be in contact with the lower surface of the crystallized glass optical filter 31 to prevent the reflected light from entering the infrared phototransistor 54.

  Therefore, as shown in FIG. 19, 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 detection device 18 is arranged as shown in FIG. 3, and the output of the reflectance detection circuit 73 when a metal plate with a known reflectance is arranged on the top plate 2 using the built-in reflectance detection circuit 73. FIG. 21 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. To do. In a cooking pan (transmittance α = 0), the infrared energy radiated differs due to the difference in emissivity, while the same pan bottom temperature. For this reason, the problem that a thermopile output, ie, the output of the pan temperature detection apparatus 18, differs arises. Therefore, it is necessary to detect the reflectance of the bottom of the cooking pan to obtain the emissivity, correct the output of the pan temperature detection device 18 and then convert it to a temperature. In order to do this, the reflectance detection circuit 73 obtains the reflectance from the reflected voltage Vr, which is an amount corresponding to the reflectance described above. This reflectance is subtracted from 1 to obtain the emissivity.

FIG. 22 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. 22, 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. 22A 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 the values are summarized into 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.

  In FIG. 23, the emissivity measured using a radiation thermometer in various pans and the reflectivity (FIG. 12) obtained by using the reflectivity detection circuit 73 by placing the various pans on the top plate 2 in FIG. The relationship between the reflection voltage 21 and the reflectance 21) is shown. Some pans deviate from Kirchhoff's law (emissivity + reflectivity = 1), but there is a strong correlation between emissivity and reflectivity. The reason for deviating from Kirchhoff's law is that not all the reflected infrared rays of the projected infrared rays are received in the reflectance detection. To obtain physical accuracy, irradiate the object to be measured with spot light such as a laser beam directly, receive the total reflected light with an integrating sphere, and calculate the reflectivity from the ratio of irradiated infrared energy and total reflected infrared energy. Need to ask. However, when the infrared LED 50 and the infrared phototransistor 54 are used as in the present embodiment and are performed through the top plate 2, it is not possible to receive all the reflected infrared light. For this reason, as shown in the figure, it deviates from the linear relationship (Kirchhoff's law) and varies.

  In the example of FIG. 12 (FIG. 3), the reflected voltage Vr of various pans and the output voltage Vt of the thermopile temperature detection circuit 72 when the pan temperature reached 200 ° C. by induction heating were observed. And this data is reconstructed from the viewpoint of how many times the output voltage of each pan can be adjusted to the output of the standard pan, with the pan close to the black body (emissivity = 0.95) as the reference. did. This magnification corresponds to 1 / (1 / ε) of the emissivity described in FIG. FIG. 24 shows this magnification as the reflection correction coefficient K in relation to the reflection voltage Vr. The reflection correction coefficient K and the reflection voltage Vr have a strong correlation and can be approximated by a straight line as shown (originally, it should be a straight line as described in the explanation of FIG. 23). This approximate straight line is stored in the ROM of the microcomputer 60 as a reflection correction coefficient table (TBL).

  Here, the difference between the reflectance detection by the conventional single element and the reflectance detection by the parallel light projection and the reflection light reception of this embodiment will be described. FIG. 25 schematically shows this outline. The single light emitting element and the light receiving element are provided with a 3 mm diameter cannonball type lens, the opening surface is also 3 mm in diameter, the parabolic reflector is 10 mm square, and the distance between the single light receiving and emitting elements is 1 mm. In the figure, the top plate 2 and the crystallized glass optical filter 31 are omitted as merely transmitting infrared light. To be precise, the refraction of light (refractive index = 1.45) due to these needs to be taken into consideration, but the thickness of the top plate is 4 mm, and considering the distance to the light emitting and receiving elements of about 35 mm, the incident angle is It can be considered that the light goes straight through the glass and reflects off the pan surface because it is several degrees. The crystallized glass optical filter 31 is close to the light receiving element, and the light projector light shielding wall 52 and the light receiver light shielding wall 55 are provided so that the emitted light does not enter the light receiving element.

As shown in FIG. 25, the emitted light beam (thick line) is reflected at the bottom of the pan, and the reflected light beam (thin line) is received by the light receiving element. The reflected light from the pan includes direct reflected light that is specularly reflected at an incident angle = reflecting angle and scattered light having an incident angle ≠ reflecting angle. In an actual pan, scattered light becomes dominant. In the figure, the hatched area on the pan surface indicates the distribution of light rays reflected and received by the pan surface. Conventionally, in the case of a single element, what can receive light is limited to a narrow range on the left side of light reception. In the case of the present embodiment, a single element emits a light beam perpendicular to the bottom of the pan as a plurality of light beams on the entire surface of the parabolic reflector, and is projected vertically onto the pan, and much of this scattered reflection is received. Is done. Directly reflected light is not received if it is a completely parallel light beam, but there are many non-parallel light beams because light emission is not a point light source as described above. For this reason, direct reflected light is also received around the light receiving area. According to experiments, when LEDs having the same light emission intensity and light receiving elements with the same sensitivity are used, conventionally, only a reflected light having an area of 1 mm ² or less is received in the case of a single element, whereas in this embodiment, 16 mm ^{2 is received.} We could receive the reflected light of the area.

  Thus, when calculating | requiring a reflectance, the projection light beam of infrared LED50 enters as perpendicularly as possible to the top plate 2, and all the reflected light (mainly scattered light) in the pan put here is an infrared phototransistor. 54 is desirable. That is, as in the present embodiment, the infrared LED 50 is disposed at the focal point of the parabolic reflecting mirror 51, and parallel light (vertical light with respect to the top plate 2) may be projected. By doing this, it is possible to detect the average reflectance over a wider area.

  FIG. 26 shows an example in which the relationship between the reflection voltage Vr and the reflection correction coefficient K (1 / emissivity) is observed for two types of pans with 8 pan bottom positions as in FIG. An example reflectance detection circuit will be described. In the case of a single element, the reflected voltage Vr varies greatly depending on the location even in the same pan. On the other hand, in the case of the present embodiment, the reflected voltage is almost the same even if the detection location is changed. In the case of a single element, the reflection is in a narrow range, and is greatly influenced by the state of the pan bottom in that range. If there happens to be dirt, the reflected voltage will be large and different from other places. In this embodiment, since the average reflectance is detected in a wide range, the detected reflectance is hardly affected by partial dirt, scratches, patterns, and the like.

  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 is substantially the same as the reflecting surface on the top plate 2 for the reflectance detection light emission. For this reason, as shown in FIG. 12, the thermopile 25, the infrared projector 35, and the infrared reflection light receiver 36 are arranged side by side in the pan temperature detection device 18. For this reason, there is little deviation (variation) between the reflection correction coefficient and the reflectance.

  In the analysis, if the reflection correction coefficient K is different by 0.1, an error of 4 ° C. occurs in temperature detection. In the case of a single element, the B correction pan of FIG.

  As described above, in this embodiment, it is possible to detect the average and accurate reflectance regardless of the material of the pan, the shape of the pan bottom, and the strength of the dirt, and this enables accurate pan temperature detection in any pan by correcting the thermopile output. Is possible.

  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. 27 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 cooling air passages 15a, 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 for a predetermined time (for example, 200 ms) (step S3-2), the voltage V2 output to the terminal 73-8 is read from the AD terminal (step S3-3). Then, the infrared LED drive signal is stopped (step S3-4). Next, the 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. 29 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 temperature of the top plate 2 is read from the thermistor 20 and the thermistor temperature detection circuit 75 (step S5-3). An 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 a top plate table (the table is abbreviated as TBL) and the output of the thermopile temperature detection circuit 72. (Step S5-4). Subsequently, the Va is subtracted from the previous pan temperature detection voltage Vt (step S5-5). By this processing, the amount of infrared rays from the top plate 2 as the disturbance described above 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 the data table which is the relationship between Vn and Tn stored in advance as the temperature conversion TBL is drawn (step S5-8), and converted into the pan temperature to convert the pan temperature Tn is 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 value of ε) (becomes a value of 1 or more) is used as the reflection correction coefficient K, and the relationship between the reflection correction coefficient K and the reflection voltage Vr (relation shown by a straight line in FIG. 24) is stored as a table. The reflection correction coefficient value K is obtained from the reflection correction table (step S-10), Vt is multiplied by K (step S-11), and then the data table (pot temperature conversion TBL) that is the relationship between Vn and Tn is subtracted. The pan temperature may be output. In this way, it is possible to speed up the processing without using a division requiring a processing time of the microcomputer. FIG. 30 shows a flowchart in this case.

  Subsequently, when the pan temperature Tn detected in step S5 reaches a predetermined temperature (step S6), the power control circuit 62 is controlled to reduce the current supplied to the heating coil 7 by a predetermined amount (step S7). Then, the cooking time timer is started (step S8). 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. In particular, in thin pans, the reflectivity may change due to pan deformation due to high temperatures. 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 infrared projector 35, the infrared reflection receiver 36 and the reflectance detection circuit 73 with a non-magnetic metal material as in the embodiment.

  Also, the pan may be moved (floated) during cooking. At this time, since the position of the pan bottom on the infrared transmission window 5 changes, the reflectance (emissivity) also changes. In this case, the voltage detected by the thermopile temperature detection circuit 72 changes abruptly when the pan is moved (floated). When the pan is placed again, the voltage detected by the thermopile temperature detection circuit 72 returns to a value corresponding to the pan bottom temperature at this point. It is desirable to detect this change and detect the reflectance again.

  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 thermopile temperature detection circuit 72 rapidly decreases when the existing pan is retracted. And the voltage which the thermopile temperature detection circuit 72 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.

  FIG. 31 shows an infrared projector 35 and an infrared reflection light receiver 36 according to the second embodiment. Components and operations equivalent to those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In this embodiment, the infrared projector 35 composed of the infrared LED 50 and the parabolic reflector 51 is changed to a commercially available reflective infrared LED 57. As the reflective infrared LED, for example, there is one used for a long distance projector for an infrared camera. FIG. 32 shows this schematic configuration. The infrared light emitting LED chip 57-4 mounted on the lead frame 57-1 is sealed in an epoxy resin 57-2 having a parabolic reflecting mirror 57-5 on the lower surface where it is located at the focal point. -4 light is reflected by a parabolic reflector 57-5, and substantially parallel rays of infrared light are projected from the radiation surface 57-3. As in the first embodiment, the infrared reflection light receiving device 36 is provided with an infrared phototransistor 54 having a light receiving light shielding wall 55 on a small substrate 53 and is fitted into the light projecting light shielding wall 52.

  In the present embodiment, since a commercially available reflective infrared LED can be used, the cost can be reduced as compared with the configuration of the first embodiment.

FIG. 33 shows an infrared projector 35 and an infrared reflection receiver 36 according to the third embodiment. Components and operations equivalent to those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In FIG. 7 of the first embodiment, the pattern portion of the small substrate 53 disposed on the parabolic reflecting mirror 51 blocks the projected infrared light. For example, if the parabolic reflecting mirror 51 is a square having a side of 10 mm and the small substrate 53 is mounted with an infrared phototransistor 54 having a bullet-type lens having a diameter of 3 mm, a rectangular substrate of 4 mm × 10 mm is assumed to be 100 mm ² . In fact, 40% (40 mm ² ) of the light area is shielded from light. In order to reduce the light shielding portion, in this embodiment, the small substrate 53 is reduced to a size that fixes the infrared phototransistor 54 and the infrared LED 50 (16 mm light shielding as a square of 4 mm × 4 mm). From 53, four infrared LED lead frames 50-1 having a cross section of 0.5 mm × 0.5 mm square for the infrared LED 50 and two similar lead frames 54-1 for the infrared phototransistor 54 are set up in total. Is connected to the electronic circuit board 27 through the through hole 51-1 of the parabolic reflecting mirror 51.

  In this embodiment, since light shielding can be reduced, a larger amount of received light can be obtained than in the configuration of Embodiment 1, and the pan temperature can be detected more accurately.

  FIG. 34 shows an infrared projector 35 and an infrared reflection light receiver 36 according to the fourth embodiment. Components and operations equivalent to those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In the first embodiment, the infrared LED 50 and the infrared phototransistor 54 are mounted on the small board 53, but in the present embodiment, these are mounted on both surfaces of the electronic circuit board 27. The parabolic reflector 51 also has one half of the parabolic reflector 51 fixed to the electronic circuit board 27 so that the focal point thereof is the infrared LED 50. This infrared LED 50 is a so-called side view type, and emits infrared rays laterally as shown in the figure.

  In the configuration of this embodiment, the small substrate 53 can be eliminated, and the infrared projector 35 and the infrared reflection receiver 36 can be provided at lower costs.

  In the first embodiment as well, it is obvious that the infrared LED 50 and the infrared phototransistor 54 may be mounted on the electronic circuit board 27 and the parabolic reflecting mirror 51 may be fitted under the electronic circuit board 27 in this way.

  FIG. 35 shows the infrared projector 35 and the infrared reflection receiver 36 of the fifth embodiment. Components and operations equivalent to those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. It is created by a projector convex lens 56 in which infrared parallel light is fitted into the projector light shielding wall 52 and an infrared LED 50 arranged at the focal point thereof. As is well known, if a point light source is arranged at the focal point of a convex lens, the light transmitted through the lens becomes parallel light. Apply this to create infrared parallel light.

  In this embodiment, it is not necessary to mount the infrared LED 50 and the infrared phototransistor 54 on both surfaces of the same substrate, and the mounting is performed on separate substrates, so that the working efficiency can be improved.

  FIG. 36 shows control blocks of the sixth embodiment. Example 6 is an induction heating cooker that uses the infrared phototransistor 54 of the infrared reflection light receiver 36 for illuminance detection and has a function of detecting whether or not a pan is placed on the top plate 2. is there. FIG. 37 shows details of the reflectance detection circuit 73 and the illuminance detection circuit 74 of the sixth embodiment. These functions are as follows: (1) the cooking pan 6 is correctly placed on the circle 4 by detecting visible light such as illumination or sunlight passing through the infrared transmission window 5 on the top plate 2; It is possible to heat and (3) to confirm that the pan bottom temperature can be detected by the thermopile 25 of the pan temperature detecting device 18 and that the cooking temperature can be controlled safely and accurately, thereby ensuring the convenience and safety of the user.

  From the optical characteristics of FIG. 8, visible light (light having a wavelength of 500 to 700 nm) passes through the top plate 2 and the crystallized glass optical filter 31 and is received by the infrared phototransistor 54. From the sensitivity characteristics of the infrared phototransistor 54 in FIG. 9, since the infrared phototransistor 54 has sensitivity to this visible light, a photocurrent flows, and a DC voltage is generated in the resistor 73-3 in the reflectance detection circuit 73. The illuminance detection circuit 74 extracts, amplifies, and outputs this voltage. This voltage is input to the OP amplifier 74-1, amplified with high gain (ratio of resistors 74-2 and 74-3), and output to the terminal 74-6. Then, it is read by the AD terminal of the microcomputer 60. When the output voltage exceeds the forward voltage of the two diodes 74-5, the gain is reduced to the ratio of the parallel resistance values of the resistor 74-2 and the resistors 74-3 and 74-4. This is to prevent the output from saturating to 5 V in the case of high illuminance. FIG. 38 shows the output characteristics of the illuminance detection circuit 74. The horizontal illuminance is the illuminance at the side of the infrared transmission window 5. The figure also shows the output when the infrared transmission window 5 is closed with a pan. Using the difference of whether or not this pan is blocking the infrared transmission window 5, (1) the cooking pan 6 is correctly placed on the circle 4 (whether there is a pan on the infrared transmission window 5), (2) Induction heating can be performed, and (3) Whether the pan bottom temperature can be detected by the thermopile 25 of the pan temperature detecting device 18 can be determined. However, at the timing of reflectance detection, that is, at the timing when the infrared LED 50 is caused to emit light, the illuminance detection is disturbed because the emission intensity of this LED is stronger than that of illumination and sunlight. For this reason, reflectance detection and illuminance detection are used exclusively.

  FIG. 39 shows a control flow in the case where it is determined whether or not there is a pan on the infrared transmission window 5 using the illuminance detection circuit 74 and the cooking pan is induction-heated. This is obtained by putting the pan presence / absence judgment into the flow of FIG.

  At the start of cooking, the output of the illuminance detection circuit 74 is read (step SS-1), and the presence or absence of a pan is judged whether this value is larger than a predetermined threshold (step SS-2). A warning such as “The heating is stopped because the pan is not properly placed” is given by voice (step SS-3), and the process returns to the detection of pressing the start key (step S-2). If the pan is correctly placed, the process proceeds to reflectance detection which is the next step. Subsequent operation processing is the same as that of the first embodiment, and thus description thereof is omitted. In addition, since illuminance detection is possible except at the time of reflectance detection, it is clear that the presence / absence detection of the pan on the infrared transmission window 5 may be always performed during cooking.

  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 5 Infrared transmission window 6 Cooking pan 7 Heating coil 8 Inverter circuit 10 Coil base 15 Coil cooling air path 18 Pan temperature detection apparatus 19 Sensor visual field cylinder 20 Thermistor 25 Thermopile 25-14 Glass convex lens 26 Heat sink 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 Infrared projector 36 Infrared reflective receiver 50 Infrared LED
50-1 Infrared LED lead frame 51 Parabolic reflector 51-1 Parabolic reflector through hole 52 Projector light-shielding wall 53 Small substrate 54 Infrared phototransistor 54-1 Infrared phototransistor lead frame 55 Receiver light-shielding wall 56 Projector convex lens 57 reflective infrared LED
60 microcomputer 61 frequency control circuit 62 power control circuit 70 buzzer 72 thermopile temperature detection circuit 73 reflectance detection circuit 74 illuminance detection circuit 75 thermistor temperature detection circuit

Claims (10)

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 light projecting means provided under the heating coil and projecting an infrared parallel light beam substantially perpendicular to the top plate;
An induction heating cooker provided under the heating coil and provided with a light receiving means for receiving the infrared ray reflected by the cooking container and projected by the infrared light projecting means. The induction heating cooker according to claim 1,
An induction heating cooker including the light receiving means in the infrared parallel light bundle. The induction heating cooker according to claim 1,
An induction heating cooker in which the infrared light projecting means comprises a parabolic mirror and an infrared light emitting means disposed at the focal point thereof.   2. The induction heating cooker according to claim 1, further comprising an infrared detecting unit that detects infrared rays radiated from the cooking container beside the light projecting unit.   The induction heating cooker according to claim 1, wherein the heating coil includes a light guide tube that guides the infrared rays and the infrared parallel light bundle radiated from the cooking container.   The induction heating cooker of Claim 4 provided with the infrared output correction | amendment means which correct | amends the output of the said infrared detection means by the output of the said light-receiving means. 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;
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;
An infrared detecting means provided under the heating coil for detecting infrared rays emitted from the cooking container;
Infrared light projecting means that is provided next to the infrared detection means and projects an infrared parallel light bundle that is substantially perpendicular to the top plate through the light guide tube,
An induction heating cooker comprising light receiving means for receiving the infrared ray reflected by the cooking container and projected by the infrared light projecting means. In the induction heating cooker according to claim 7,
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;
Infrared output correcting means for correcting the output of the infrared detecting means by the output of the light receiving means;
Cooking container temperature detection means for detecting the temperature of the bottom surface of the cooking container by the output of the infrared output correction 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. 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;
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;
An infrared detecting means provided under the heating coil for detecting infrared rays emitted from the cooking container;
Infrared light projecting means that is provided next to the infrared detection means and projects an infrared parallel light bundle that is substantially perpendicular to the top plate through the light guide tube,
A light receiving means for projecting the infrared light projecting means and receiving an infrared ray reflected by the cooking container;
An induction heating cooker comprising: visible light detecting means for detecting visible light passing through the light guide tube by the output of the light receiving means. The induction heating cooker according to claim 9,
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,
An induction heating cooker characterized in that the power supplied to the heating coil is controlled based on the output of the visible light detection means.