JP2004227976A - Induction heating cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the temperature of a pan put on a top plate with high accuracy. <P>SOLUTION: An induction heating cooker comprises: a heating coil 6 which heats the pan; a top plate 7 which the pan is put on the top of the heating coil 6; a photodiode 2 which is placed on the back surface of the top plate 7 and detects infrared radiation in short wave length radiated from the bottom of the pan; a temperature calculating means 4 which calculates the temperature of the bottom of the pan from an output of the photodiode 2; and a control means 5 which controls a power supplied to the heating coil 6 depending on an output from the temperature calculating means 4. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an induction heating cooker that can accurately detect the temperature of a pan on a top plate.
[0002]
[Prior art]
In a conventional induction heating cooker, the temperature of the bottom of the pot is detected by a thermosensitive element such as a thermistor brought into contact with a top plate on which the pot is placed. In addition, there is an apparatus that detects infrared rays emitted from the bottom of the pan with an infrared sensor through a top plate to detect the temperature of the bottom of the pan (for example, see Patent Document 1).
[0003]
Further, there is also a method in which a temperature of a pot bottom and a temperature change gradient are detected by using both a thermosensitive element in contact with a top plate and an infrared sensor (for example, see Patent Document 2).
[0004]
FIG. 3 is a configuration diagram of a conventional infrared sensor induction heating cooker. The main body 21 is provided with a heating coil 6 for heating the pan 8 and an infrared sensor 22 for detecting a temperature. The top plate 7 provided on the upper surface of the main body 21 transmits infrared rays having a wavelength of 2.5 μm or less well, transmits infrared rays having a wavelength of 2.5 to 4 μm by about several tens%, and has a wavelength longer than 4 μm. Infrared rays hardly pass. Therefore, the wavelength component of the infrared rays radiated from the pan 8 of 4 μm or less passes through the top plate 7 and the infrared sensor 22 measures the temperature at the bottom of the pan.
[0005]
[Patent Document 1]
JP 03-184295 A [Patent Document 2]
Japanese Patent Application Laid-Open No. 03-208288
[Problems to be solved by the invention]
The induction heating cooker having the conventional configuration shown in FIG. 3 detects infrared rays emitted from the pan 8 through the top plate 7. Generally, the temperature of the pot 8 during cooking is about 30 ° C. to 230 ° C., and the peak wavelength of this temperature is 6 μm to 10 μm according to Stefan-Boltzmann's law. The wavelength that the top plate 7 can transmit is infrared light having a wavelength of 4 μm or less, and only the wavelength component of 4 μm or less makes up only about 10% of the infrared radiation energy from the bottom of the pan, and most of the infrared radiation energy from the bottom of the pan Is absorbed by the top plate 7. For this reason, the infrared energy reaching the infrared sensor 22 is weak, and even if converted into an electric signal by the infrared sensor 22, the S / N ratio is poor, and the accuracy of measuring the temperature during cooking is not good.
[0007]
The inventors have repeatedly used thermopiles as infrared sensors and incorporated them in induction heating cookers. Since the thermopile is a thermal infrared sensor, when the temperature of the light receiving surface rises due to the effect of increasing the temperature of the received infrared light, a voltage is generated from multiple thermocouples arranged on the minute light receiving surface, which is amplified and amplified. Is to detect the temperature. Therefore, in order to use the thermopile effectively, it is necessary to irradiate infrared rays having a wavelength region (5 μm or more) excellent in temperature raising effect.
[0008]
However, as described above, the infrared ray that best passes through the top plate has a wavelength of 2.5 μm or less, and only the infrared ray whose temperature change on the light receiving surface of the thermopile hardly appears is passed. For this reason, it was necessary to connect an amplifier having a large amplification factor of 100,000 or more to the output of the thermopile.
[0009]
Further, since the thermopile is a thermal sensor, the temperature of the object is calculated from the voltage obtained from the light receiving surface based on the temperature of the sensor itself. Therefore, if the temperature of the sensor itself is not stable, the temperature of the target object cannot be accurately calculated. Particularly, in the induction heating cooker, the temperature around the sensor starts to rise as soon as cooking starts, so that it is extremely difficult to measure the pot bottom temperature stably. For this reason, the thermopile is placed downward to separate it from the top plate 7, or the thermopile is inserted into the cylindrical aluminum or zinc cavity so that sufficient thermal coupling can be obtained. Care was needed to make it less likely to occur.
[0010]
In addition, the thermopile has a wide range of infrared wavelengths to be detected, and the wavelength of infrared rays radiated from the top plate to the lower surface is broad, including infrared rays of 5 microns or more, which have the highest energy, and penetrates the top plate from the bottom of the pot. The energy of the infrared radiation emitted from the top plate toward the lower surface is much stronger than the infrared radiation coming. To suppress this problem, the inventors have tried placing a filter on the thermopile that cuts infrared rays having a wavelength longer than 5 microns of infrared rays emitted from the top plate toward the lower surface. However, since the long-wavelength infrared rays are radiated from the long-wavelength cut filter due to its own temperature, the cause of the measurement error is eventually increased.
[0011]
On the other hand, the inventors have attempted to make a hole in the top plate and embed an infrared transmitting material that transmits infrared light having a long wavelength well in the hole. Artificial sapphire or the like is suitable for this infrared transmitting material. Since this artificial sapphire is expensive, it has been avoided to make a large hole so that the artificial sapphire can be used in a small amount. Since the viewing angle of the thermopile is wide and the light receiving sensitivity is almost all over 180 °, when the diameter of the hole formed in the top plate is reduced, as shown in FIG. It was necessary to narrow the field of view of the thermopile using a pinhole 24 or the like so that infrared rays transmitted through the artificial sapphire 23 did not enter the thermopile. However, narrowing the field of view using a pinhole reduced the sensitivity of the thermopile, and eventually required an amplifier with a large amplification factor.
[0012]
[Means for Solving the Problems]
The present invention provides a heating coil that heats a pan, a top plate on which the pan is placed above the heating coil, a photodiode that is placed on the lower surface of the top plate and detects the intensity of infrared radiation emitted from the bottom of the pan, Temperature calculating means for calculating the temperature of the bottom of the pot from the output of the photodiode, and control means for controlling the power supplied to the heating coil according to the output of the temperature calculating means, transmitted through the top plate by the photodiode It reacts only to short-wave infrared rays from the bottom of the pot, does not react to long-wave infrared rays with a large amount of energy radiated from the top plate.Furthermore, since the principle of infrared detection is quantum type, thermal type There is no need to measure the temperature of the infrared sensor itself, such as a thermopile, as compared to an infrared sensor such as a thermopile, which operates on the principle of Since hardly affected changes in ambient temperature, but that the induction heating cooker capable of performing temperature detection with high accuracy.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the first aspect of the present invention, a heating coil for heating the pan, a top plate on which the pan is placed above the heating coil, and an infrared intensity radiated from the bottom of the pan placed on the lower surface of the top plate are detected. A photodiode, temperature calculating means for calculating the temperature of the bottom surface of the pot from the output of the photodiode, control means for controlling the power supplied to the heating coil according to the output of the temperature calculating means, and blocking transmission of light. A lens barrel formed of a material and formed in a substantially cylindrical shape, wherein the lens barrel is arranged to limit light incident on the photodiode, and the photodiode is transmitted through the top plate. Responds to infrared rays coming from the bottom of the pot, but does not respond to long-wavelength infrared rays with a large amount of energy radiated from the top plate. In order to detect well, quantum type infrared detection is used, and the photodiode reacts only to infrared light from the bottom of the pot that penetrates the top plate with the photodiode. Is to detect only infrared rays from the bottom of the pot by not reacting.In addition, since the principle of infrared detection is a quantum type, infrared rays such as thermopiles operate in comparison with infrared sensors such as thermopiles that operate on the principle of heat type. It is not necessary to correct the calculated temperature by measuring the temperature of the sensor itself, and it is hardly affected by changes in the ambient temperature, so it is an induction heating cooker that can measure the pot temperature with high accuracy. .
[0014]
According to the second aspect of the present invention, it is possible to dispose the photodiode away from the top plate or the heating coil which becomes high temperature by disposing the lens barrel for limiting the field of view of the photodiode in the first aspect of the invention. The induction heating cooker described above.
[0015]
According to the third aspect of the present invention, an induction heating cooker having a structure provided with a means for reducing heat conduction from a lens barrel to a photodiode is provided, so that temperature can be measured more thermally. Is what it is.
[0016]
According to a fourth aspect of the present invention, in the third aspect, the inner diameter of the lens barrel is larger than the outer diameter of the photodiode, so that the lens barrel does not contact the photodiode and is not thermally coupled. The induction heating cooker is capable of performing temperature measurement while being thermally stable.
[0017]
According to a fifth aspect of the present invention, there is provided a packing structure for preventing air from flowing into the inside of the lens barrel according to the second to fourth aspects of the present invention, which is disposed between the lower surface of the top plate and the upper end of the lens barrel. Is an induction heating cooker in which the light-receiving window of the photodiode does not fog into the inside of the lens barrel.
[0018]
The invention described in claim 6 is simple in that the lens barrel in the invention described in claim 4 is formed of a resin cylinder, and the inner surface is mirror-plated or a tape with a high glossiness is attached to the inner surface. The induction heating cooker has a simple configuration.
[0019]
According to a seventh aspect of the present invention, in the second to sixth aspects of the present invention, a metal cylinder is arranged on the outer periphery of the lens barrel to shield the magnetic field induced from the heating coil from affecting the inside of the lens barrel. It is an induction heating cooker.
[0020]
According to an eighth aspect of the present invention, there is provided the temperature detecting element for detecting the temperature of the photodiode in the first to seventh aspects of the present invention, and the temperature change of the dark current of the photodiode when the received infrared ray energy is small is compensated. It is an induction heating cooker.
[0021]
According to a ninth aspect of the present invention, in the invention according to the seventh or eighth aspect, a heat insulating layer is provided between the lens barrel and the outer metal cylinder to thermally stabilize the photodiode, thereby achieving more accurate temperature control. It is an induction heating cooker that can measure.
[0022]
According to a tenth aspect of the present invention, in the inventions of the second to ninth aspects, the inside diameter of the upper end portion of the lens barrel is made smaller than the inside diameter of the lower portion of the lens barrel, so that oil smoke and the like hardly enter the inside of the lens barrel. It is an induction heating cooker.
[0023]
【Example】
(Example 1)
Hereinafter, Embodiment 1 of the present invention will be described. FIG. 1 is a block diagram showing the configuration of the present embodiment. In FIG. 1, reference numeral 1 denotes a main body of the induction heating cooker according to the present embodiment. 6 is a heating coil, 7 is a top plate, and 8 is a pot.
[0024]
Reference numeral 2 denotes a photodiode for detecting the intensity of infrared light emitted from the bottom of the pot 8, which is highly sensitive to infrared light having a wavelength of about 1 to 2.5 microns, and sensitive to infrared light of other wavelengths. Is designed not to feel. Of course, this photodiode may be a PIN photodiode. Reference numeral 2a denotes a printed board that supports the photodiode 2. Reference numeral 3 denotes a cylindrical lens barrel made of a resin having low thermal conductivity, and an inner surface 3a of the cylinder is aluminum-plated so as to reflect infrared rays well.
[0025]
The inner diameter of the lens barrel 3 is larger than that of the photodiode 2. Since the upper end of the lens barrel 3 is close to the top plate 7, the temperature of the lens barrel 3 becomes high during cooking. By making the inner diameter of the lens barrel 3 larger than that of the photodiode 2, the photodiode 2 is less affected by the temperature of the lens barrel 3.
[0026]
Reference numeral 9 denotes a cylinder made of aluminum, which shields a high-frequency magnetic field emitted from the heating coil 6 so as not to adversely affect the inside of the lens barrel 3. Reference numeral 10 denotes a ring-shaped packing sandwiched between the upper end of the lens barrel 3 and the lower surface of the top plate 7 to prevent oily smoke and dust from entering the inside of the lens barrel 3 and sticking to the light receiving window of the photodiode 2. ing. Reducing the inner diameter of only the upper end portion of the lens barrel 3 is also effective in preventing oil smoke and the like from entering. FIG. 2 is a configuration diagram showing an embodiment in which only the inner diameter of the upper end portion of the lens barrel 3 is reduced. 2, the same components as those in FIG. 1 are denoted by the same reference numerals.
[0027]
Further, in FIG. 1, reference numeral 4 denotes a temperature calculating means, which calculates the temperature of the pan 8 from the output signal of the photodiode 2. The control means 5 controls the power supplied to the heating coil 6 according to the output of the temperature calculation means 4.
[0028]
Reference numeral 11 denotes a temperature detecting element such as a thermistor for measuring the temperature of the photodiode 2. In general, a slight current called a dark current flows even when a photodiode does not receive light. The dark current has a property of increasing as the temperature increases. A dark current is also generated in the photodiode 2 when the temperature of the pot is low and the received infrared ray energy is small, but the magnitude of the dark current differs depending on the temperature of the photodiode 2 at that time. The thermistor 11 is not absolutely necessary, but is used for detecting the temperature of the photodiode 2 and compensating for a temperature-dependent change in dark current that occurs when the temperature of the pan is low.
[0029]
Next, the operation will be described. When a power supply (not shown) is turned on and a predetermined temperature is set by an operation switch, the control means 5 supplies a high-frequency power of about 20 kHz to the heating coil 6. When high-frequency power is supplied to the heating coil 6, an induction magnetic field is generated from the heating coil 6, an induction current flows through the pan 8 on the top plate 7, and the bottom of the pan is heated by Joule heat.
[0030]
Generally, there is Stefan-Boltzmann's law that the infrared energy emitted by an object is proportional to the fourth power of the absolute temperature of the object, and the higher the temperature, the more energy is radiated as infrared rays at an accelerated rate. The photodiode 2 outputs a current proportional to the energy of the received infrared light, and is manufactured using a compound semiconductor such as indium, gallium, and arsenic. Therefore, when the temperature of the pan 8 rises, the intensity of infrared radiation from the bottom of the pan also increases, the amount of infrared energy received by the photodiode 2 increases, and the output current of the photodiode 2 also increases. The temperature calculation means 4 also incorporates a current-voltage conversion circuit for converting the signal current of the photodiode 2 into a voltage.
[0031]
Further, the temperature calculating means 4 calculates the temperature of the pot 8 from the output signal of the photodiode 2 and sends it to the control means 5. The control means 5 controls the high-frequency power supplied to the heating coil 6 according to the temperature signal so as to control the temperature to a predetermined pan temperature.
[0032]
The top plate 7 is made of crystallized glass, and does not transmit infrared rays having a wavelength of 5 μm or more, which is the strongest among infrared rays emitted from the pot. However, the infrared ray having a wavelength of 2.5 microns or less, which can be detected by the photodiode 2, is very well transmitted.
[0033]
On the other hand, the top plate 7 does not transmit infrared light having a long wavelength of 5 microns or more, but emits infrared light of this wavelength at an intensity corresponding to its own temperature. However, since the photodiode 2 is sensitive to only infrared rays of 2.5 microns or less, it is not hindered by the long-wavelength infrared radiation from the top plate 7 and accurately emits short-wavelength infrared rays of 2.5 microns or less from the bottom of the pot. Can be detected.
[0034]
Further, it is necessary to keep the photodiode 2 away from the top plate 7 where the temperature becomes high. However, if the photodiode 2 is disposed below the heating coil 6, the photodiode 2 receives infrared rays from the heating coil 6 this time. By using the lens barrel 3, the bottom of the pot 8 can be seen from the upper end of the lens barrel 3 at a viewing angle indicated by dotted lines B and B ′, and the infrared rays from the heating coil 6 are not received. Can be.
[0035]
In addition, the cylinder 9 made of aluminum for magnetic shielding does not prevent the intrusion of magnetism into the inside of the cylinder, but generates a high-frequency current under the influence of the high-frequency magnetic field from the heating coil 6 and generates heat by Joule heat. However, by arranging a gap between the aluminum cylinder 9 and the lens barrel 3 so that an air layer is formed, air insulation can be performed, and the temperature of the cylinder 9 can be reduced by the lens barrel 3 and the photodiode 2 inside the cylinder. Can be prevented from affecting.
[0036]
As described above, the temperature at the bottom of the pot is measured via the top plate 7, but by using a photodiode capable of detecting infrared light of 2.5 microns or less, the top plate is not affected by infrared radiation from the top plate. The transmitted infrared rays from the bottom of the pot can be detected, and the bottom temperature can be accurately calculated.
[0037]
In addition, by using the lens barrel, the bottom of the pot can be seen from the upper end of the lens barrel, so that infrared rays from the heating coil can be prevented.
[0038]
Further, by disposing the barrel and the photodiode so as not to be in contact with each other and insulating the photodiode with air, the photodiode can be hardly affected by the temperature of the barrel.
[0039]
Further, if the inner diameter of the lens barrel is made larger than that of the photodiode, it is easy to make the photodiode less affected by the temperature of the lens barrel.
[0040]
Further, by sandwiching the ring-shaped packing between the upper end of the lens barrel and the lower surface of the top plate, it is possible to prevent oil smoke and dust from entering the inside of the lens barrel and fogging the light receiving window of the photodiode.
[0041]
In addition, it is difficult to transmit the temperature of the top plate to the vicinity of the photodiode by forming the lens barrel with a resin with low thermal conductivity and plating the inner surface of the cylinder with aluminum or attaching aluminum foil tape to the inner surface of the cylinder. A lens barrel can be configured.
[0042]
In addition, a metal cylinder is placed around the outer periphery of the lens barrel to shield the induced magnetic field from the heating coil from affecting the inside of the lens barrel. That can be prevented.
[0043]
Further, by disposing the temperature detecting element for detecting the temperature of the photodiode near the photodiode, it is possible to compensate for the temperature change of the dark current of the photodiode when the received infrared energy is small due to the low pot temperature.
[0044]
Further, by providing a heat insulating layer between the metal cylinder for magnetic shielding disposed outside the lens barrel and the lens barrel, the photodiode is thermally stabilized, and more accurate temperature measurement can be performed.
[0045]
In addition, by making the inner diameter of the upper end of the lens barrel smaller than the inner diameter of the lower part of the lens barrel, the lens barrel does not come into contact with the photodiode and is not thermally coupled. A configuration that is difficult to enter can be realized.
[0046]
【The invention's effect】
As described above, according to the present invention, the photodiode detects only short-wavelength infrared rays from the bottom of the pot that pass through the top plate, and has an effect on long-wavelength infrared rays with a large amount of energy emitted from the top plate. No, and because the principle of infrared detection is of the quantum type, there is no need to measure the temperature of the infrared sensor itself, unlike a thermopile or the like, which operates based on the principle of thermal type. Since it is hardly affected by a change in temperature, it is possible to realize an induction heating cooker that can perform temperature detection with high accuracy.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an induction heating cooker according to a first embodiment of the present invention. FIG. 2 is a block diagram illustrating an induction heating cooker according to a first embodiment of the present invention in the case of a lens barrel having a small tip inside diameter. 3 is a block diagram showing a conventional first induction heating cooker. FIG. 4 is a block diagram showing a conventional second induction heating cooker.
DESCRIPTION OF SYMBOLS 1 Main body 2 Infrared sensor 2a Printed circuit board 3 Lens barrel 3a Aluminum plating 4 Temperature calculating means 5 Control means 6 Heating coil 7 Top plate 8 Pot 9 Cylinder 10 Packing 11 Temperature detecting element

Claims (10)

A heating coil that heats the pan, a top plate on which the pan is placed above the heating coil, a photodiode that is placed below the top plate and detects the intensity of infrared radiation emitted from the bottom of the pan, and an output of the photodiode A temperature calculating means for calculating a temperature of the bottom of the pan from a controller, a control means for controlling electric power supplied to the heating coil according to the output of the temperature calculating means, and a substantially cylindrical shape containing a material for blocking light transmission. A lens barrel, wherein the lens barrel is arranged to limit light incident on the photodiode, and the photodiode is responsive to infrared rays from the bottom of the pot that passes through the top plate, In order to detect infrared rays from the bottom of the pot accurately by not reacting to long wavelength infrared rays with a large amount of energy emitted from the top plate, quantum Induction heating cooker as infrared detection. The induction heating cooker according to claim 1, wherein the lens barrel is arranged to limit a field of view of the photodiode. 3. The induction heating cooker according to claim 2, further comprising means for reducing heat conduction from the lens barrel to the photodiode. 4. The induction heating cooker according to claim 3, wherein the inner diameter of the lens barrel is larger than the outer diameter of the photodiode. The induction heating cooker according to any one of claims 2 to 4, wherein a packing structure for preventing air from flowing into the lens barrel is disposed between the lower surface of the top plate and the upper end of the lens barrel. 5. The induction heating cooker according to claim 4, wherein the lens barrel has a structure in which mirror plating or a tape having a high glossiness is attached to an inner surface of a resin cylinder. The induction heating cooker according to any one of claims 2 to 6, wherein a metal cylinder is arranged around the outer periphery of the lens barrel to shield an induction magnetic field from the heating coil from entering the inside of the lens barrel. The induction heating cooker according to any one of claims 1 to 7, further comprising a temperature detecting element for detecting a temperature of the photodiode. 9. The induction heating cooker according to claim 7, wherein a heat insulating layer is provided between the lens barrel and the outer metal cylinder. The induction heating cooker according to any one of claims 2 to 9, wherein an inner diameter of an upper end of the lens barrel is smaller than an inner diameter of a lower part of the lens barrel.

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