JP4089444B2 - Cooker - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a cooking device that can accurately detect the reflectance and temperature of a pan placed on a top plate.
[0002]
[Prior art]
  In a heating cooker that heats the object to be heated in the pan, as a method of detecting the temperature of the bottom surface of the pan that is approximately equivalent to the temperature of the object to be heated, a contact-type temperature sensor is installed via a top plate on which the pan is placed. A method of indirectly detecting the pan bottom temperature with a thermistor is common. Further, as a detection method with better response, a method of directly detecting the temperature of the pan bottom by detecting infrared rays emitted from the pan bottom is also known. This conventional example will be described with reference to FIG.
[0003]
  A top plate 1 is provided on the upper surface of the main body, and a pan 2 is placed thereon. A heating coil 3 that electromagnetically heats the pan 2, a high-frequency current supply means 4 that supplies a high-frequency current to the heating coil 3, an infrared sensor 5 that detects temperature, and a bottom surface temperature of the pan 2 from the output of the infrared sensor 5 And a control means 6 for controlling the power supplied to the heating coil 3 is provided. Reference numeral 21 denotes a DC power supply for supplying power to the control means 6, 22 a commercial power supply, 23 a full-wave rectifying means, and 24 an inverter comprising a power supply capacitor 25, a resonance capacitor 26, and a switching element 27.
[0004]
  In such a heating cooker, the top plate 1 is a crystallized glass (for example, “lithia ceramics” Li) in which a glass having a special composition is reheated to precipitate fine crystals in the glass in order to increase the strength.₂O-Al₂O₃-SiO₂(FIG. 22 shows a graph of an example of the transmission characteristics together with the transmission characteristics of a typical infrared window material). Infrared rays having a wavelength of 2.6 μm or less are transmitted by 80% or more, and 3 to 4 μm. Infrared light having a wavelength of approximately 30% is transmitted, and infrared light having a wavelength longer than 4 μm is hardly transmitted.
[0005]
  Therefore, it is necessary to measure the bottom temperature of the pan 2 only with a wavelength component of 4 μm or less, but generally the bottom temperature of the pan 2 during cooking is about 30 ° C. to 230 ° C., and the peak wavelength of this temperature Is a wavelength of 6 to 10 microns according to Stefan-Boltzmann law. (The higher the temperature, the faster the energy is emitted as infrared rays. The lower side of the graph of FIG. 22 shows the state at 30 ° C., 100 ° C., and 200 ° C.) The absolute temperature is T (K). Although electromagnetic waves including infrared rays are radiated from the surface of the object, the total amount of radiant energy per unit time E (W / m²) Is represented by Formula (1).
[0006]
  (1) ... E = εσT⁴
  Where ε is the emissivity, σ is the Stefan-Boltzmann constant (5.67 × 10^-8W / m²K⁴). That is, every substance emits an electromagnetic wave having an intensity proportional to the fourth power of its absolute temperature. From Equation (1), the peak of energy emitted by an object at room temperature of about 300 ° K (30 ° C.) is around about 10 μm (referred to as the thermal infrared region).
[0007]
  On the other hand, the wavelength that can be transmitted through the top plate 1 as described above is infrared light having a wavelength of 4 microns or less, and infrared light from the bottom of the pan 2 at about 570 ° K (300 ° C.) with only the wavelength component of 4 microns or less. Even if the radiant energy is transmitted only 30% or less, the infrared energy that reaches the infrared sensor 5 is weak. Therefore, the S / N ratio is poor only by converting it into an electrical signal with the detector in the infrared sensor 5, and during cooking, In order to measure temperature, accuracy is not good and another device is required.
[0008]
  As a solution, a method of integrating the infrared sensor 5 and the amplifier and a method of solving the above problem by embedding a window material in the top plate 1 (for example, see Patent Document 1) have been proposed. No mention is made of the response to various kinds of cooking methods and cooking scenes.
[0009]
  An ideal object having the best absorption and emission of infrared rays on the object surface is called a black body and has an emissivity of 1. In contrast, a general object is called a gray body, and the emissivity is a value between less than 1 and greater than 0.
[0010]
  The main methods for measuring this emissivity are the method of keying in the emissivity, the measurement method obtained by comparing with a known emissivity part, the measurement method used in combination with a contact thermometer, and the measurement method using polychromatic infrared There are a measurement method using an environmental temperature switching method, an indirect measurement method using FTIR, a method of irradiating an object with reference light (infrared rays), and measuring reflectance from reflected light. The method of measuring the reflectance from the last reflected light (see, for example, Patent Document 2 or Patent Document 3) irradiates the bottom surface of the pan 2 with reference light of a predetermined wavelength from an inexpensive light source such as an infrared LED, In this method, the reflectance of the bottom surface of the pan 2 is measured from the intensity of infrared rays of the same wavelength reflected from the bottom surface of the pan 2. This measurement method allows non-contact measurement and does not require a large-scale device or pretreatment such as black body coating on the bottom of the pan. For measuring emissivity (≈1-reflectance) in a cooking device. Is optimal.
[0011]
[Patent Document 1]
    Japanese Patent No. 2897306
[Patent Document 2]
    Japanese Patent Application Laid-Open No. 11-225881
[Patent Document 3]
    JP 2002-75624 A
[0012]
[Problems to be solved by the invention]
  The induction heating cooker having the conventional configuration shown in FIG. 18 directly detects the temperature of the bottom surface of the pan 2 by the infrared sensor 5 through the top plate 1, but most of the infrared radiation energy from the bottom surface of the pan 2. Is absorbed by the top plate 1, which results in a measurement with a poor S / N ratio, and does not support various kinds of pans having various reflectances and various cooking scenes.
[0013]
  The infrared sensor 5 is generally easily affected by the ambient temperature. The infrared sensor 5 is affected by the influence of conduction heat from the pan 2 transmitted through the heating coil 3 and the top plate 1, the radiation of the switching element 27, and the influence of convection heat. Precise radiant temperature within the main body of the heating cooker where the temperature changes greatlyDetectionIt was difficult to do.
[0014]
  An object of the present invention is to provide a cooking device capable of measuring the temperature of the bottom surface of the pan 2 with high accuracy by minimizing the influence of changes in the ambient temperature and accurately measuring the reflectance of the bottom surface of the pan 2. Is to provide.
[0015]
[Means for Solving the Problems]
  The present invention comprises a heating coil for heating the pan,SaidA heating means for supplying electric power to the heating coil; a top plate on which the pan is placed above the heating coil; and a lower surface of the top plateSo as not to contact the lower surfaceAn infrared sensor that detects infrared rays emitted from the bottom of the pan, a band-pass filter that is attached to the light-receiving surface of the infrared sensor and transmits light having a wavelength in a predetermined band, and an amplifier that amplifies the output of the infrared sensor Temperature calculating means for calculating the bottom temperature of the pan from the output of the amplifier, and the bottom surface of the top plateSo as not to contact the lower surfaceIrradiate the pan with infrared rays for reference of a predetermined wavelength.LEDLight emitting means, pulse driving means for driving the light emitting means in pulses, andThe light emitted by the light emitting means is obtained through the top plate.Reflected light measuring means for measuring reflected light from the pan, and the pan from the output of the reflected light measuring meansbottomofInfraredReflectance calculating means for calculating the reflectance, and control means for controlling the power supplied to the heating coil according to the outputs of the temperature calculating means and the reflectance calculating means.When, The light emitting meansForward current If intermittently with a predetermined dutyFlowOf the light emitting meansPerform pulse drivePulse drive means,The reflected light measurement means is a Vpp detection type circuit that measures Vpp, which is a difference in output voltage of the reflected light measurement means when there is reflected light from the pan and when there is no reference light, and the Vpp detection type By calculating the infrared reflectance of the pan bottom from the output of the circuit,Infrared illuminance for reference to transmit through the top plateEnlarge,Eliminates the effects of ambient light with a wavelength close to that of the reference light and fluctuations in photocurrent due to changes in element temperatureIt is a cooking device that measures accurate reflectivity and can accurately measure the temperature of the pan bottom without contact.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
  Claim1The described invention includes a heating coil for heating the pan,SaidA heating means for supplying electric power to the heating coil; a top plate on which the pan is placed above the heating coil; and a lower surface of the top plateSo as not to contact the lower surfaceArrangedSaidAn infrared sensor for detecting infrared radiation radiated from the bottom of the pan, a bandpass filter that transmits light of a predetermined wavelength band attached to a light receiving surface of the infrared sensor, an amplifier that amplifies the output of the infrared sensor, Temperature calculating means for calculating the bottom surface temperature of the pan from the output of the amplifier, and the bottom surface of the top plateSo as not to contact the lower surfaceIrradiate the pan with infrared rays for referenceLEDLight emitting means, pulse driving means for driving the light emitting means in pulses, andThe light emitted by the light emitting means is obtained through the top plate.Reflected light measuring means for measuring reflected light from the pan, and the pan from the output of the reflected light measuring meansbottomofInfraredReflectance calculating means for calculating the reflectance, and control means for controlling the power supplied to the heating coil according to the outputs of the temperature calculating means and the reflectance calculating means.When, The light emitting meansForward current If intermittently with a predetermined dutyFlowAnd a pulse driving means for performing pulse driving of the light emitting means, and a forward currentIncrease the If and increase the reference infrared illuminance that passes through the top plate.bigBy doing so, the cooking device is capable of measuring the temperature of the pan with high accuracy without being affected by the ambient temperature.
[0017]
  Also, Reflected light measuring meansMeasures Vpp which is the difference in the output voltage of the reflected light measuring means when there is reflected light from the pan and when there is no reference lightVpp detection circuitAnd calculating the infrared reflectance of the pan bottom from the output of the Vpp detection circuit.,Eliminates the effects of ambient light with a wavelength close to that of the reference light and fluctuations in photocurrent due to changes in element temperatureIt is possible to detect reflected light with higher accuracy.
[0018]
  Claim2The invention described inVfIf stabilizing means is provided, and the VfIf stabilizing means keeps the product of the forward voltage Vf and the forward current If of the light emitting means constant, so that stable reflected light can be obtained. Furthermore, the radiant flux irradiated from the light emitting means also has a very flat characteristic that does not depend on the ambient temperature, and an accurate reflectance measurement is possible.
[0019]
  Claim3The invention described inThe top plate is made of crystallized glass, and the bandpass filter sets the upper limit wavelength of the transmission wavelength range to the transmission wavelength range of the top plate, thereby cutting off the infrared radiation emitted from the top plate itself that causes measurement errors. be able to.
[0020]
【Example】
  Embodiments of the present invention will be described below with reference to the drawings.
[0021]
  Example 1
  FIG. 1 is a block diagram showing the configuration of the cooking device in the present embodiment. The cooking device of the present embodiment is placed on the top plate 1, a pan 2 for cooking the food, a heating coil 3 for heating the pan 2, and a high frequency current is supplied to the heating coil 3 to heat the pan 2. Heating means 4, an infrared sensor 5 arranged on the lower surface of the top plate 1 for detecting infrared rays radiated from the bottom surface of the pan 2, and a band pass for transmitting light of a predetermined band wavelength attached to the light receiving surface of the infrared sensor 5. A filter 28, an amplifier 29 integrated with the infrared sensor 5 and amplifying the output thereof, a temperature calculation means 30 for calculating the bottom surface temperature of the pan 2 from the output of the amplifier 29, and a pan 2 disposed on the lower surface of the top plate 1. A light emitting means 31 for irradiating a reference infrared ray having a predetermined wavelength to the light source, a pulse driving means 32 for pulse-driving a light emitting element in the light emitting means 31, and a reference infrared reflected light from the bottom of the pan 2 are measured. The reflectance of the bottom surface of the pan 2 is calculated from the reflected light measuring means 33, the bandpass filter 34 that transmits light of a predetermined wavelength band mounted on the light receiving surface of the reflected light measuring means 33, and the output of the reflected light measuring means 33. And a control means 36 for controlling the power supplied to the heating coil 3 according to the outputs of the temperature calculation means 30 and the reflectance calculation means 35, and through the top plate 1, The output of the temperature calculating means 30 is corrected by calculating the infrared reflectance. 37 is a cooling means and 38 is the temperature control means.
[0022]
  Next, the operation of the first embodiment will be described. When a power switch (not shown) is turned on and a predetermined temperature is set with the operation switch, the control unit 36 controls the heating unit 4 to supply predetermined power to the heating coil 3. When a high frequency current is supplied to the heating coil 3, an induction magnetic field is generated from the heating coil 3, and the bottom of the pan 2 placed on the top plate 1 is induction heated. The temperature of the pot 2 rises due to this heat, and the food in the pot 2 is cooked. The infrared sensor 5 outputs a voltage proportional to the energy of the received infrared light. The bolometer, which is a heat-responsive detector, the thermopile that collects thermocouples at one point, the pyroelectric element, or silicon such as quantum type HgTdTe or IgAs. An element detector is used.
[0023]
  Therefore, when the temperature of the pan 2 rises, the infrared radiation intensity from the bottom surface of the pan 2 also increases, the amount of infrared energy received by the infrared sensor 5 increases, and the output signal voltage of the infrared sensor 5 increases.
[0024]
  As described above, the top plate 1 transmits only infrared light having a wavelength of 4 μm or less, and the infrared energy reaching the infrared sensor 5 is weak. However, the amplifier 29 integrated with the infrared sensor 5 as a module is 500 to 5000 times larger. By outputting after amplification to a certain extent, the S / N ratio is ensured, and practical temperature measurement is possible.
[0025]
  Moreover, in order to cut the infrared rays radiated from the top plate 1 itself, which becomes a measurement error, light having a wavelength in a predetermined band (for example, 0.8 to 6.5 μm, the upper limit wavelength is the transmission wavelength region of the top plate 1). A transmitting band-pass filter 28 is mounted on the light receiving surface of the infrared sensor 5. The temperature calculating means 30 calculates the bottom surface temperature of the pan 2 from the output signal voltage of the amplifier 29 by using an indefinite integral expression based on the above Stefan-Boltzmann expression or a power-approximation approximate expression, and sends it to the control means 36.
[0026]
  Next, the light emitting means 31 disposed on the lower surface of the top plate 1 and driven at a predetermined duty by the pulse driving means 32 intermittently irradiates the pan 2 with infrared rays having a reference wavelength of 0.5 to 1.5 μm. The reflected light measuring means 33 measures the reflected infrared light for reference from the bottom surface of. And the reflectance calculation means 35 calculates the reflectance of the bottom face of the pan 2 from the output of the reflected light measurement means 33. By inputting this calculated reflectance (≈1-emissivity) signal, the control means 36 corrects the detected temperature of the pot 2 obtained from the output of the temperature calculating means 30 so that the temperature of the pot bottom is contactless and highly accurate. Is possible.
[0027]
  FIG. 2 is a graph showing the relationship between the reflectance of the object (pot 2) and the detection output of the reflected light measuring means 33 by the reflected light. The reflectance of the object and the detection output are in a good proportional relationship, and the detection output at the light receiving element in the reflected light measuring means 33 increases as the drive current If of the light emitting element in the light emitting means 31 increases. As can be seen from the graph 2, since the reflectance can be detected from less than 1 to a value exceeding 0, it is possible to deal with all types of pots and cooking scenes.
[0028]
  As described above, in particular, according to the first embodiment, the light emitting element in the light emitting means 31 is intermittently driven by the pulse driving means 32, thereby solving the problem of deterioration due to the temperature rise of the light emitting element, and the DC driving. Since it can be driven with a larger driving current If than the time, a larger detection output can be obtained, and the reflectance calculation means 35 can measure the reflectance accurately. The control means 36 corrects the temperature signal output from the temperature calculation means 30 with the reflectance signal output from the reflectance calculation means 35 to obtain an accurate and responsive detection temperature by calculation, and based on this detection temperature, the heating coil 3 is controlled. Therefore, the bottom surface temperature of the pan 2 becomes a set temperature, and it is possible to realize the subtle fire adjustment necessary for cooking.
[0029]
  Although basic temperature measurement is possible with the above-described configuration, as described above, since the infrared sensor 5 and the light receiving / emitting element are easily affected by the ambient temperature, the cooling means 37 cools the sensor from the surroundings. The temperature control means 38 controls the cooling temperature to a predetermined value so that the temperature can be measured more accurately and stably.
[0030]
  Note that light outside the wavelength range of the reference light that causes an error in reflectance measurement is cut by the band-pass filter 34 mounted on the light receiving surface of the reflected light measuring means 33. Generally, the band-pass filter 34 is supplied in a state where it is mounted on the surface of the light receiving element.
[0031]
  In addition, in the wavelength of reference light of 0.5 to 1.5 μm, the reflectance: ρ of the top plate 1 is substantially close to 0 and shows a low value.Impact ofThere are few.
[0032]
  In addition, infrared light having a wavelength of 0.5 to 1.5 μm is hardly attenuated by the top plate 1 and transmits an amount exceeding 80%, so that the reflectance can be measured with high accuracy. In addition, the measured reflectance is the same as the reflectance in the infrared of the wavelength band received by the infrared sensor 5 through the bandpass filter 28 in a generally used pan type.
[0033]
  The mounting angle between the light emitting element in the light emitting means 31 and the light receiving element in the reflected light measuring means 33 (FIG. 3 shows a cross-sectional view of the main part of the light transmitting / receiving section.₁, Θ₁'Is the mounting angle. ) Is determined in consideration of a change in the distance to the pan 2 so that the maximum reflected light can be obtained uniformly in any case.
[0034]
  Although a method in which the infrared sensor 5 and the amplifier 29 are not integrated is conceivable, it is possible to improve the S / N ratio and noise resistance by integrating and immediately amplifying the detection output of the infrared sensor 5 and then outputting the wiring. I can plan.
[0035]
  A product that measures the reflectivity of the side of the pan and corrects the temperature measured by the infrared sensor has also been put into practical use and is in use, but there are various obstacles for measuring the side, such as water vapor generated from the pan. Or cooking oil placed for cooking, cooking utensils such as balls. Therefore, there are many cases where the pan and the light emitting / receiving section are blocked, making measurement impossible or errors in the measured value, so the method of the present invention for measuring the reflectance of the bottom of the pan is superior. Obviously, this is another technique in terms of configuration.
[0036]
  (referenceExample1)
  BookreferenceIn the example, the basic configuration as a cooking device is the same as that of the first embodiment, and the description of the basic configuration is omitted. thisreferenceExample1Is different from the first embodiment in that the pulse driving duty of the light emitting means 31 is 50% or the duty is set such that the If of the light emitting element in the light emitting means 31 becomes the maximum value. Yes, this point will be mainly described. FIG. 4 is a circuit diagram showing an example in which a digital IC inverter is used for the pulse driving means 32. In FIG. 4, 40 is a DC power source, 41 to 44 are CMOS inverters, 45 is a transistor, 46 is a resistor for extracting positive carriers of the light emitting means 31, and may be connected in parallel with the light emitting means 31. Reference numerals 47 to 49 denote current limiting resistors, reference numeral 50 denotes a capacitor, and reference numeral 51 denotes a resistor that together with the capacitor 50 determines a charge / discharge time constant.
[0037]
  Next, the operation will be described. When the output of the inverter 43 is High, when the capacitor 50 starts to be charged through the resistor 51, the input of the inverter 41 gradually increases. The upper limit threshold voltage V of the inverter 41_THWhen the value exceeds, each inverter is inverted, the output of the inverter 43 becomes Low, and the capacitor 50 starts discharging through the resistor 51.
[0038]
  Next, the lower limit threshold voltage V of the inverter 41_TLIf it falls below, each inverter inverts again. By repeating the above operation, the circuit of FIG. 4 oscillates with a duty of 50%, and the light emitting means 31 is intermittently driven. Here, a low V in parallel with the resistor 51_FIf the Schottky barrier or the series circuit (not shown) of the germanium diode 52 and the resistor 53 is connected in parallel, the ON time of the transistor 45 is the same and the OFF time can be lengthened. That is, an arbitrary duty ratio can be set.
[0039]
  FIG. 5 shows the If of the light emitting element in the light emitting means 31._DCAnd ambient temperature, and duty ratio and If_pulseIt is a graph which shows the relationship. Since the derating ratio of the light emitting element is −0.8 mA / ° C. from FIG. 5A, when the ambient temperature rise is 75 ° C., 50% duty (Duty ratio = 0.5) from FIG. If_peak50= If at 42mA, 10% duty (Duty ratio = 0.1)_peak10= If at 180 mA, 1% duty (Duty ratio = 0.01)_peak1It can be seen that a current of 960 mA can flow. Since DC driving can only flow up to 20 mA, if pulse driving is performed, it is possible to flow If from twice to 48 times, increasing the intensity of irradiation light and making it possible to perform accurate reflected light measurement. As a result of experiments, duty ratio = 0.1 to 0.5 stabilizes the intensity of reflected light, and even if the duty ratio varies due to circuit factors, it is possible to prevent deterioration of the element. It is good to use. Therefore, in this circuit form, If_max.Is practically 180 mA / Duty ratio = 0.1.
[0040]
  Note that the voltage of the DC power supply 40 is set to about 12 V when a 4000 series CMOS-IC is used for the inverters 41 to 44, and about 5.5 V when an HC or AHC family is used.
[0041]
  The resistor 49 is applied for input protection because a voltage exceeding the rating is applied to the input of the inverter 41 due to the circuit configuration, and an appropriate value is about 10 kΩ to 500 kΩ. If it becomes too large, noise will be applied to the resistor 49, and chattering may occur when the output is inverted. On the other hand, if the resistance 49 is too small, an excessive current flows through the input terminal of the inverter 41, and the IC is damaged or the oscillation frequency changes when the type of IC is changed.
[0042]
  The oscillation frequency is f_osc≒ 1 / (2.2C₄₉R₅₀) Can be used as a guide.
[0043]
  (referenceExample2)
  BookreferenceIn the example, the basic configuration as a cooking device is the same as that of the first embodiment, and the description of the basic configuration is omitted. The pulse driving duty of the light emitting means 31 is that the temperature of the light emitting element is detected and varied, as described in the first embodiment.Reference example 1This is different from the above, and this point will be mainly described.
[0044]
  FIG. 6 is a circuit diagram showing an example in which a digital IC inverter and a PTC (positive characteristic) thermistor are used for the pulse driving means 32. In FIG. 6, 54 is a PTC thermistor disposed in the vicinity of the light emitting means 31, 55 and 56 are resistors for linearizing the characteristics of the PTC thermistor 54, and 57 is a Schottky barrier or a germanium diode. The capacitor 50 is discharged through the resistor 51 and the diode 57, and is charged through the resistor 51, a parallel circuit of the PTC thermistor 54 and the resistor 55, and the resistor 56. The values of the PTC thermistor 54 and the resistors 55 and 56 for linearization are, for example, If_peakIn order to flow = 220 mA, the duty ratio is set to 0.1 when the temperature of the light emitting means 31 is 25 ° C., and the duty ratio is set to approximately 0.07 when the temperature is 75 ° C. The ON time of the transistor 45 is determined by the time constant of the capacitor 50 and the resistor 51, but is set to about 100 μS (from FIG. 5). Since the resistance value of the PTC thermistor increases as the temperature rises, the charging time of the capacitor 50 increases, the OFF time of the transistor 45 increases, and the duty ratio decreases.
[0045]
  As described above, a large current of, for example, 220 mA (Duty ratio = 0.1 to 0.07) is applied in an environment of −25 ° C. to + 75 ° C. by changing the duty ratio according to the element temperature of the light emitting element. The intensity of the irradiated light is increased, and the reflected light can be measured with high accuracy.
[0046]
  BookreferenceIn the example, the pulse driving means 32 is configured with a simple circuit configuration of one inverter IC (including four elements), several resistors, and a capacitor, but other means such as Colpitts can be used if the circuit configuration is inexpensive. An oscillation circuit and a Schmitt trigger inverter may be used.
[0047]
  (Example2)
  In this embodiment, the basic configuration as a cooking device is the same as that of the first embodiment, and the description of the basic configuration is omitted. By the VfIf stabilizing means, V of the light emitting element in the light emitting means 31 is obtained._FExample 1 is that the product, sum, difference, or ratio of A and If is kept constant, and the light emitting element is pulse driven by the pulse driving means.Reference example 1~2This is different from the above, and this point will be mainly described.
[0048]
  FIG. 7 is a circuit diagram showing an example in which an OP amplifier and a multiplier are used for the VfIf stabilizing means 60 and a digital IC inverter is used for the pulse driving means 32. In FIG. 7, 61 and 62 are current limiting resistors, 63 is a resistor for detecting the current If of the light emitting means 31, 64 is an OP amplifier, 65 to 68 are resistors, and form an OP amplifier 64 and a differential amplifier circuit 69. A Vf measuring means for measuring the Vf of the light emitting element in 31 is used. 70 is a multiplier for calculating the product of the output of the Vf measuring means 69 and the voltage across the If detection resistor 63, 71 is a reference power supply, 72 is a reference voltage value of the reference power supply 71 and the output of the multiplier 70 are compared. The comparator 73 is a MOS-FET, and 74 is a transistor. Comparator 72 compares the reference voltage value and controls the output of MOS-FET 73 so that the product of Vf and If is constant. The transistor 74 is turned on / off at a predetermined duty ratio (Duty ratio = 0.1 to 0.07) by the output of the pulse driving means 32, and the light emitting means 31 is in a state where the product of Vf and If is always kept constant. Since it is intermittently driven, it can be driven with a large current If.
[0049]
  The transistor OFF time (light emission time of the light emitting means 31) is the threshold voltage of the capacitor 50, the resistor 56, the inverter 41, and the Vf of the diode 57.₂(V_TH→ V_TL+ Vf₂The ON time (the extinction time of the light emitting means 31) is determined by the threshold voltage of the capacitor 50, the resistor 56, the resistor 75, and the inverter 41 (V_TL+ Vf₂→ V_TH).
[0050]
  By intermittent driving by the pulse driving means 32, driving can be performed with a large current If. That is, a large reflected light detection output can be obtained, and a stable reflected light can be obtained even if the duty ratio is about 0.07 by constantly maintaining the product of Vf and If of the light emitting means 31 by the VfIf stabilizing means 60. Further, as shown in the graph of FIG. 8, the radiant flux emitted from the light emitting means 31 has a very flat characteristic that does not depend on the ambient temperature, and enables accurate reflectance measurement.
[0051]
  In the above circuit, since the current for driving the switching element also flows through the If detection resistor 63, when a MOS-FET having the lowest driving power compared to a bipolar transistor or the like is used, the product of Vf and If. The accuracy of making the or sum or difference or ratio constant is the best.
[0052]
  (Example3)
  In this embodiment, the basic configuration as a cooking device is the same as that of the first embodiment, and the description of the basic configuration is omitted. This example3The reflected light measuring means 33 is either a double integration type detection circuit, a synchronous detection type circuit, or a Vpp detection type circuit.~ 2, Reference Example 1~2This is different from the above, and this point will be mainly described.
[0053]
  FIG. 9 is a circuit diagram showing the configuration of the double integration type detection circuit of this embodiment. In FIG. 9, 79 is a phototransistor which is a light receiving element in the reflected light measuring means 33, 80 is an IV conversion circuit, and 81 is a peak detection circuit. The current output ic of the phototransistor 79 due to the intermittently received reflected light is converted into a large voltage output by the IV conversion circuit 80, and the peak value is detected and output by the peak detection circuit 81. 82 is a noise bypass capacitor, 83 and 84 are resistors for determining an IV conversion ratio (conversion ratio = 100 in this embodiment), 85 is an OP amplifier, 86 and 87 are bias dividing resistors, 88 Is a resistor, 89 is a capacitor, and the resistor 88 and the capacitor 89 constitute a low-pass filter 90. Reference numerals 91 and 92 are resistors for determining the amplification degree (in this embodiment, the amplification degree is 1), 93 is an OP amplifier, 94 is a diode, 95 is an output protection resistor, 96 is a capacitor for holding a peak value, and 97 is a reset. Switch.
[0054]
  Next, the operation will be described with reference to the timing chart of FIG. Since the light emitting means 31 is intermittently driven by the pulse driving means 32, the reflected light received by the reflected light measuring means 33 is also intermittently received, and the current output ic due to the incident reflected light is converted into an IV conversion circuit. When amplified at 80, FIG.0A rectangular wave as shown in FIG. The bias voltage of the OP amplifier 85 is the output voltage V_C89When the light emitting means 31 is OFF and there is no reference light, the value is 0 or more. When the light emitting means 31 is ON and the reference light is present, and when there is a pan, the resistance 86 and the resistance 87 are negative. It is set.
[0055]
  Here, after the reset switch 97 is turned on and the charge of the capacitor 96 for holding the peak value is sufficiently discharged, the reset switch 97 is set to t₀The voltage of the capacitor 96 remains zero while the output of the IV conversion circuit 80 is positive, and charging starts when the voltage becomes negative (t in FIG. 11).₁) After reaching the peak value (t in FIG. 11)₂) And hold that value. Therefore, the reflectance calculation means 35 inputs a stable signal corresponding to the reflectance of the pan if the output of the peak detection circuit 81 is input after a predetermined time has elapsed since the reset switch 97 is turned OFF. I can do it.
[0056]
  The capacitor 82 and the low-pass filter 90 remove high frequency noise. A sufficient S / N ratio can be obtained with a pulse drive frequency of 5 kHz and an IV conversion ratio of about 100. Also, time t₀May be at any timing from the principle of operation.
[0057]
  Next, a synchronous detection circuit diagram of this embodiment is shown in FIG. In FIG. 11, 79 is a phototransistor which is a light receiving element in the reflected light measuring means 33, 101 is a C-MOSIC analog switch, 102 is a current detection resistor, 103 is a peak detection circuit, 104 is a pulse delay circuit, 105 is It is a reset switch. 106 is an OP amplifier, 107 is a diode, 108 is an output protection resistor, 109 is a capacitor for holding a peak value, 110 is a resistor, and 111 is a delay capacitor.
[0058]
  Next, the operation will be described based on the timing chart of FIG. The analog switch 101 is an output V of the pulse driving means 32 using the inverter of the digital IC of FIG._OSCSignal V obtained by delaying the inverted signal of_SWG101Turn ON / OFF with. (Fig. 12 (b), V_CNT101When is high, the analog switch 101 is ON, V_CNT101The analog switch 101 is OFF when is low) Time t₃When the reset switch 105 is turned OFF at time t₄Then, the current output ic (FIG. 12A) of the phototransistor 79 proportional to the reflected light starts to flow, but since the analog switch 101 is ON, Vo remains zero.
[0059]
  The analog switch 101 delayed by the pulse delay circuit 104 is switched to the time t₅When the current is turned off by the current, the currents Ic and R of the phototransistor 79 due to reflected light₁₀₂Voltage Vo = Ic × R₁₀₂Is charged in the capacitor 109 of the peak detection circuit 103, and t₆Thereafter, it is held (FIG. 12C). The reflectivity calculating means 35 turns on the switch 105 and discharges the capacitor 109, and then turns off the switch 105. After a predetermined time, the output V of the pulse driving means 32 is output._OSCBy inputting a voltage Vo that is proportional to the reflected light that is peak-holded in synchronization with, the reflectance of the bottom surface of the pan 2 can be calculated. Note that the timing for turning off the reset switch 105 is preferably within a period during which the analog switch 101 is on.
[0060]
  Next, a Vpp detection type circuit diagram of the present embodiment is shown in FIG. In FIG. 13, 79 is a phototransistor which is a light receiving element in the reflected light measuring means 33, 120 is a resistor for detecting photocurrent, 121 and 122 are capacitors, 123 and 124 are diodes, 125 and 128 are OP amplifiers, 126, Reference numerals 127, 129, and 130 denote resistors that determine the amplification degree of the OP amplifiers 125 and 128, 131 and 132 denote resistors that apply a bias voltage to the OP amplifier 128, and 133 and 134 denote reset analog switches.
[0061]
  Next, the operation will be described based on the timing chart of FIG. The light emitting means 31 is intermittently driven by the pulse driving means 32, and the current output Ic of the phototransistor 79 by the reflected light is converted into a voltage by the resistor 120 (FIG. 14 (a)). The bias voltage of the OP amplifier 128 is the output voltage V₁Is set to a value exceeding 0 when the light emitting means 31 is OFF and there is no reference light, and is set to a negative value when the light emitting means 31 is ON and the reference light is present and there is a pan. (FIG. 14B).
[0062]
  First, after the analog switches 133 and 134 are turned on to discharge the capacitors 121 and 122, the time t₇In FIG. 14, the analog switches 133 and 134 are turned off.
[0063]
  Output voltage V₁In the positive peak, the diode 123 connected to the output of the OP amplifier 128 functions as an ideal diode, and the right terminal side of the capacitor 121 is kept at the ground potential, so that the capacitor 121 has a positive peak value of the voltage across the resistor 120. Will be charged properly.
[0064]
  On the other hand, when the voltage at both ends of the resistor 120 falls below that, the diode 123 is turned OFF, and in the negative peak value of the voltage at both ends of the resistor 120, the positive peak value charged earlier is displayed on the right terminal side of the capacitor 121. A summed voltage results. Since the OP amplifier 125, the diode 124, and the resistors 126 and 127 operate as a peak detector, the capacitor 122 is correctly charged to a value Vpp obtained by adding positive and negative peak values (FIG. 14C). Since the reflectance calculating means 35 inputs this Vpp value as the output Vo of the reflected light measuring means 33, a stable reflected light signal can be input and the reflectance of the bottom surface of the pan 2 can be calculated.
[0065]
  In this embodiment, in particular, V_PPBy measuring the value, the influence of disturbance light having a wavelength close to that of the reference light and the fluctuation of the photocurrent due to the change in the element temperature can be eliminated, and the reflectance can be measured with high accuracy.
[0066]
  It should be noted that the time t for turning off the analog switches 133 and 134 for resetting₇Is V₁Output voltage is all V_PPSince the value is lower than the value, any time can be used. The ON resistance of the analog switch also serves as the output protection resistance of the OP amplifiers 125 and 128.
[0067]
  In the double integration type detection circuit and the synchronous detection type circuit, the influence of disturbance light having a wavelength close to that of the reference light and the fluctuation of the photocurrent due to the change of the element temperature are eliminated as much as possible when there is no reference light. The detection voltage is configured to be close to the ground potential.
[0068]
  (referenceExample3)
  BookreferenceIn the example, the basic configuration as a cooking device is the same as that of the first embodiment, and the description of the basic configuration is omitted. thisreferenceExample3The reflected light measuring means is a weak light pulse detection circuit in the above-described first to first embodiments.3. Reference examples 1-2This is different from the above, and this point will be mainly described. Figure 15 shows the bookreferenceIt is a weak light pulse detection circuit diagram which shows the structure of an example. In FIG. 15, 139 is a photo diode which is a light receiving element in the reflected light measuring means 33, 140 and 141 are resistors for applying a reverse bias to the photo diode 33, 142 and 143 are capacitors, 144 is a charge amplification circuit, and 145 is a waveform. A shaping circuit, 146 is a peak detection circuit, 147 to 150 are operational amplifiers, 152 to 157 are capacitors, 158 to 164 are resistors, 165 is a variable resistor, 166 is a diode, and 167 is a reset switch.
[0069]
  Next, the operation will be described based on the timing chart of FIG. The light emitting means 31 is intermittently driven by the pulse driving means 32. BookreferenceIn the example, in order to save the average value of the drive current, that is, the current consumption, the light emission time is set to less than 100 microseconds, for example, 50 microseconds. The current output id of the photodiode 139 by the reflected light of the infrared ray of a predetermined wavelength irradiated by the light emitting means 31 is converted into a voltage by the charge amplification circuit 144 (FIG. 16A). Time constant T with capacitor 153 and resistor 159₁Is a time constant T with a capacitor 154 and a resistor 160.₂With a time constant T by a capacitor 156 and a resistor 163.₃Is generated.
[0070]
  BookreferenceIn the example T₁= T₃Therefore, the rise time To of the output pulse of the waveform shaping circuit 145 is To = T₁+ T₂It becomes. First, the reset switch 167 is turned on to discharge the capacitor 157, and then the time t₁₀In FIG. 16, the reset switch 167 is turned off. Output voltage V₂Accordingly, the capacitor 157 is charged and reaches a peak value t₁₂Thereafter, the peak detector 146 holds the peak value. (FIG. 16 (c)). Since the reflectance calculation means 35 inputs this peak value as the output Vo of the reflected light measurement means 33, a stable reflected light signal can be input.
[0071]
  BookreferenceParticularly in the example, a stable reflection is obtained by amplifying a light amount of a weak light pulse having a duration of less than 100 microseconds with a charge amplifier and converting a voltage proportional to the light amount into an amplitude of a predetermined pulse by a waveform shaping circuit. It can measure light, and enables low power consumption reflectivity measurement.
[0072]
  Since the weak light pulse detection circuit has high sensitivity and easily picks up external electric noise, it is necessary to completely perform electrical shielding. Further, in order to prevent microphonic noise due to mechanical vibration around the sensor, it is also necessary to perform vibration isolation processing.
[0073]
  (referenceExample4)
  BookreferenceIn the example, the basic configuration as a cooking device is the same as that of the first embodiment, and the description of the basic configuration is omitted. thisreferenceExample4Is that the PLL circuit synchronizes with the received light pulse in the above-described first to first embodiments.3, Reference Examples 1-3This is different from the above, and this point will be mainly described.
[0074]
  Figure 17 shows a bookreferenceIt is a circuit diagram which shows the structure of the reflected light detection part by the PLL circuit in an example. In FIG. 17, 170 is a variable resistor, 171 and 172 are Schmitt trigger inverters, 173 is a D type flip-flop, 174 is a commercially available PLL circuit, 175 and 176 are retriggerable monostable multivibrators, 177 Reference numeral 178 denotes an analog switch, 179 denotes a capacitor that holds a voltage value proportional to the reflected photocurrent, 180 denotes an OP amplifier, and 181 denotes an integrating circuit.
[0075]
  BookreferenceIn the example, the PLL circuit 174 includes a phase comparator 182, a loop filter 183, a gain amplifier 184, and a voltage control oscillator 185, and the integration circuit 181 includes resistors 186 and 187, a capacitor 188, and a diode 189. is doing. A resistor 190 and a capacitor 191, and a resistor 192 and a capacitor 193 are external resistors and capacitors that determine the output pulse width of the multivibrators 175 and 176, respectively.
[0076]
  Next, the operation will be described based on the timing chart of FIG. When the pan 2 is not placed, there is no reflected light, the voltage across the resistor 102 is almost zero, the output of the inverter 171 is continuously High, and the capacitor of the integrating circuit 181 is charged to Vdd ( FIG. 17B).
[0077]
  Accordingly, the analog switch 178 is turned on, and the output Vo as reflected light measuring means is also zero (FIG. 1).8(F)). A pot 2 is placed and the voltage V across the resistor 102 is detected by the detected current ic from the reflected light._R102When a high pulse is generated (FIG. 1)8(A), time t₁₃) When a low pulse is generated at the output of the inverter 171, the voltage of the capacitor 188 of the integrating circuit 181 in which the discharging time is set longer than the charging time is the threshold voltage V of the analog switch 178._IHTherefore, the analog switch 178 is turned off.
[0078]
  On the other hand, since the PLL circuit 174 is synchronized with the rectangular wave signal obtained by dividing the pulse of the inverter 172 ((c) of FIG. 17) by the D-type flip-flop 173, the voltage-controlled oscillator 185 in the PLL circuit 174 The output rectangular wave signal ((d) in FIG. 17) is exactly the voltage V_R102A rectangular wave signal obtained by dividing the high pulse by 1/2 and in synchronization with the high pulse. The rectangular wave signal is delayed by the rising multivibrator 175 (time t in FIG. 17).₁₃~ Time t₁₄), And the multivibrator 176 outputs a control signal pulse ((e) of FIG. 17) for turning on the analog switch 177.
[0079]
  With this control signal pulse, the voltage V due to the reflected photocurrent_R102Is sampled by the analog switch 177 and held by the capacitor 179 and the OP amplifier 180 ((f) in FIG. 17). The reflectance calculating means 35 can calculate the reflectance of the bottom surface of the pan 2 by inputting a voltage Vo proportional to the reflected light.
[0080]
  Especially booksreferenceIn the example, the voltage V generated across the resistor 102 due to the detection current ic by reflected light in the PLL circuit._R102In order to generate a rectangular wave signal synchronized with the high pulse of the signal and to sample in synchronization with the rising edge of the rectangular wave signal, the voltage V_R102Even if noise or the like due to the heating means is superimposed on the high pulse or the instantaneous deformation, the voltage V_R102Thus, it is possible to stably input a voltage portion proportional to the reflected light.
[0081]
  Note that the CLR and PR terminals of the D-type flip-flop 173 are connected to Vdd. The diode 189 has V_FA small Schottky barrier diode is used. Further, since the DC power source 40 uses 4000 series CMOS-ICs for the inverters 171, 172, the flip-flops 173, the PLL 174, the multivibrators 175, 176, and the analog switches 177, 178, it is set to about 12V and reflected light. The current detection range is wide.
[0082]
  (referenceExample5)
  BookreferenceFor example, the basic configuration as a cooking device is the first embodiment.-3, Reference Examples 1-4The description of the basic configuration is omitted. thisreferenceExample5In the above embodiment, the dark current is canceled by setting the reverse bias of the photodiode to zero.Reference examplesThis is different from the above, and this point will be mainly described.
[0083]
  19 is a bookreferenceIt is a circuit diagram of the zero bias type reflected light measuring means in the example. In FIG. 19, 195 and 196 are OP amplifiers, 197 to 200 are resistors, 201 is a diode, 202 is a capacitor, and 203 is a reset switch. The resistors 198 to 200, the diode 201, the capacitor 202, and the OP amplifier 196 constitute a peak detection circuit 204. Reference numeral 205 denotes a low-pass filter or a band-pass filter as a detection output of the reflected light measuring means as a noise countermeasure. The current Id flowing from the photodiode 139 to the load is Id = I_L+ I_s(1-e^{Vd / Vr}) And the photocurrent I proportional to the incident light_LAnd the output current I when the incident light is zero_s(1-e^{Vd / Vr}), And the latter is called dark current. Since the dark current becomes a measurement error, the smaller the better, the better. The dark current increases as the reverse voltage applied to the photodiode 139 increases.referenceIn the example, as shown in FIG. 19, a photodiode 139 is connected to the virtual ground point of the OP amplifier 195 as a current source. Therefore, since the bias to the photodiode 139 is zero, the dark current is very small.
[0084]
  Next, the operation will be described with reference to the timing chart of FIG. Since the light emitting means 31 is intermittently driven by the pulse driving means 32, the reflected light received by the reflected light measuring means 33 is also intermittently incident, and the current output id due to this reflected reflected light is zero balance type circuit. When it is amplified by the above, a waveform as shown in FIG. When the light emitting means 31 is OFF and there is no reference light, it becomes 0. When the light emitting means 31 is ON and there is a reference light, and there is a pan, it becomes a negative value corresponding to the reflectance (the higher the reflectance, the larger the reflectance). , The degree of negative is large).
[0085]
  Here, after the reset switch 203 is turned ON and the electric charge of the capacitor 202 for holding the peak value is sufficiently discharged, the reset switch 203 is set to t₁₆When the output of the capacitor 202 is turned OFF, the voltage of the capacitor 202 remains zero when the output of the zero balance type amplifier circuit is zero, and charging starts when it becomes negative (t in FIG. 20).₁₇) After reaching the peak value (t in FIG. 20)₁₈) And hold that value. Therefore, the reflectance calculating means 35 inputs a stable signal corresponding to the reflectance of the pan if the output Vo of the reflected light measuring means is input after a predetermined time has elapsed since the reset switch 203 is turned OFF. I can do it.
[0086]
  Since the input current of the OP amplifier 190 becomes an error, an FET input type OP amplifier having a small input bias current is used. In addition, because of the zero bias, the junction capacitance of the photodiode 139 increases, and a fast operation cannot be performed. Therefore, the drive pulse of the light emitting means has a duty ratio of ½ or less and a long OFF period.
[0087]
  The photodiode is connected to the light emitting means 31 through light, so that the direct current power source of the reflected light measuring means is completely insulated if the power source is different from the direct current power source of the light emitting means. Switching noise and the like superimposed from the means can be cut off, and reflected light measurement with low noise can be performed. Further, the DC power source of the reflected light measuring means uses a low noise type power source using a transformer and a three-terminal regulator.
[0088]
  For noise countermeasures, a low-pass filter or a band-pass filter is inserted into the detection output of the reflected light measuring means, and large noise superimposed from the heating means, thermal noise generated in the reflected light measuring means 33, shot noise, or the like. In addition, flicker noise was reduced and more stable reflectance measurement was performed.
[0089]
  For example, the cutoff frequency of the low-pass filter is set to 33 Hz or the like that is not synchronized with the noise and the 1 / N component of the commercial power supply frequency. Therefore, the above various noises are blocked by a low-pass filter or a band-pass filter, and only a signal corresponding to the reflectance is input to the reflectance calculation means, more accurate reflectance measurement is performed, and the temperature of the pan is more accurately measured. This is an induction heating cooker that can measure.
[0090]
  (referenceExample6)
  BookreferenceIn the example, the basic configuration as a cooking device is the same as that of the first embodiment, and the description of the basic configuration is omitted. thisreferenceExample6In order to cut out disturbance light, the point that the light guide part which receives only infrared rays directly reflected from the pan and the vicinity of the irradiation point is provided is the above embodiment.Reference examplesThis is different from the above, and this point will be mainly described. Figure 21 shows a bookreferenceIt is principal part sectional drawing of the light guide part periphery in an example. In FIG. 21, 205 is a support member made of a material having high thermal conductivity, and 206 is a light guide. The inner surface of the light guide unit 206 is mirror-finished and is uniformly coated with a material that reflects infrared rays well.
[0091]
  Further, in order to block the conduction heat from the top plate 1, a gap is provided between the support member 205 and the light guide unit 206 and the top plate 1, and the cooling fan (not shown) is uniformly cooled from both the left and right sides or the lower part. is doing.
[0092]
  With the above configuration, the reference infrared rays emitted from the light emitting means 31 are almost all guided to the bottom surface of the pan 2, and most of the reflected light reflected from the bottom surface of the pan 2 is guided to the light receiving means 33. An induction heating cooker that can block ambient light entering from the side of the top plate 1, the surroundings of the pan 2, the light emitting means 31, and the light receiving means 33, and can measure the temperature of the pan with higher accuracy. It is what you are trying.
[0093]
  A light collecting unit such as a lens may be attached to the tip of the light guide unit to collect reflected light from a predetermined angle to increase the amount of light.
[0094]
【The invention's effect】
  As described above, the invention of the present invention comprises a heating coil for heating a pan,SaidA heating means for supplying electric power to the heating coil; a top plate on which the pan is placed above the heating coil; and a lower surface of the top plateSo as not to contact the lower surfaceArrangedSaidAn infrared sensor for detecting infrared radiation radiated from the bottom of the pan, a bandpass filter that transmits light of a predetermined wavelength band attached to a light receiving surface of the infrared sensor, an amplifier that amplifies the output of the infrared sensor, Temperature calculating means for calculating the bottom surface temperature of the pan from the output of the amplifier, and the bottom surface of the top plateSo as not to contact the lower surfaceIrradiate the pan with infrared rays for referenceLEDLight emitting means, pulse driving means for driving the light emitting means in pulses, andThe light emitted by the light emitting means is obtained through the top plate.Reflected light measuring means for measuring reflected light from the pan, and the pan from the output of the reflected light measuring meansbottomofInfraredReflectance calculating means for calculating the reflectance, and control means for controlling the power supplied to the heating coil according to the outputs of the temperature calculating means and the reflectance calculating means.When, The light emitting meansForward current If intermittently with a predetermined dutyFlowAnd a pulse driving means for performing pulse driving of the light emitting means, and a forward currentIncrease the If and increase the reference infrared illuminance that passes through the top plate.bigBy doing so, the cooking device is capable of measuring the temperature of the pan with high accuracy without being affected by the ambient temperature.
[0095]
  Also, Reflected light measuring meansMeasures Vpp which is the difference in the output voltage of the reflected light measuring means when there is reflected light from the pan and when there is no reference lightVpp detection circuitAnd calculating the infrared reflectance of the pan bottom from the output of the Vpp detection circuit.,Eliminates the effects of ambient light with a wavelength close to that of the reference light and fluctuations in photocurrent due to changes in element temperatureIt is possible to detect reflected light with higher accuracy.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a cooking device according to a first embodiment of the present invention.
FIG. 2 is a graph showing the relationship between the reflectance of an object (pot 2) and the detection output of reflected light measurement means 33 based on the reflected light.
FIG. 3 is a cross-sectional view of an essential part showing the mounting angle of a light emitting element and a light receiving element in an embodiment of the present invention.
FIG. 4 of the present inventionreferenceExample1Circuit diagram of light emitting means and pulse driving means
FIG. 5 (a) If of the light emitting element in the light emitting means 31_DCShowing the relationship between the ambient temperature and the ambient temperature
  (B) The duty ratio of the light emitting element in the light emitting means 31 and If_pulseGraph showing the relationship between
FIG. 6 of the present inventionreferenceExample2Circuit diagram of light emitting means and pulse driving means
FIG. 7 shows an embodiment of the present invention.2Circuit diagram of light emitting means and pulse driving means
FIG. 8 (a) V of a light emitting device in an example of the present invention._FThe graph which shows the amount of change with the ambient temperature of If
  (B) The graph which shows the stability with respect to ambient temperature of the radiant flux of the light emitting element in the Example of this invention.
FIG. 9 shows an embodiment of the present invention.3Of reflected light measuring means
FIG. 10 shows an embodiment of the present invention.3Of timing in
FIG. 11 shows an embodiment of the present invention.3Of reflected light measuring means
FIG. 12 shows an example of the present invention.3Of timing in
FIG. 13 shows an example of the present invention.3Of reflected light measuring means
FIG. 14 shows an example of the present invention.3Of timing in
FIG. 15 shows the present invention.referenceExample3Of reflected light measuring means
FIG. 16 shows the present invention.referenceExample3Of timing in
FIG. 17 shows the present invention.referenceExample4Of reflected light measuring means
FIG. 18 shows the present invention.referenceExample4Of timing in
FIG. 19 shows the present invention.referenceExample5~6Of reflected light measuring means
FIG. 20 shows the present invention.referenceExample5~6Of timing in
FIG. 21 shows the present invention.referenceMain part sectional view which shows the attachment angle of the light emitting element in the example, a light receiving element, and a light guide part
FIG. 22 is a graph of infrared transmission characteristics of top plate and window material.
FIG. 23 is a block diagram showing a conventional induction heating cooker
[Explanation of symbols]
  1 Top plate
  2 hot pot
  3 Heating coil
  5 Infrared sensor
  28, 34 Band pass filter
  29 amplifiers
  30 Temperature calculation means
  31 Light emitting means
  32 Pulse drive means
  33 Reflected light measuring means
  35 Reflectance calculation means
  36 Control means
  37 Cooling means
  55 PTC thermistor
  70 Multiplier
  81 Peak detection circuit
  80 IV conversion circuit
106 op amp

Claims (3)

A heating coil for heating a pan, the heating means for supplying electric power to the heating coil, a top plate for placing the pan on top of the heating coil, distribution so as not to contact with the lower surface under the top plate lower surface an infrared sensor to detect infrared rays radiated from the pan bottom, a band-pass filter that transmits light having a predetermined wavelength band which is mounted on the light receiving surface of the infrared sensor, and an amplifier for amplifying an output of the infrared sensor A temperature calculating means for calculating the temperature at the bottom of the pan from the output of the amplifier, and an LED for irradiating the pan with a reference infrared ray having a predetermined wavelength, arranged below the lower surface of the top plate so as not to contact the lower surface. light emitting means, and pulse driving means for driving the light emitting elements in said light emitting means, said light emitting means is irradiated is obtained by passing through the top plate wherein A reflected light measuring means for measuring the light reflected from the reflectance calculating means for calculating an infrared reflectance of the pot bottom from the output of the reflected light measuring means, depending on the output of the reflectance calculating means and said temperature calculation means and control means for controlling the power supplied to the heating coil Te, with the forward current If and pulse driving means for performing a pulse driving of the light emitting means as the flow intermittently with a predetermined duty to the light emitting means, said The reflected light measuring means is a Vpp detection type circuit for measuring Vpp which is a difference in output voltage of the reflected light measurement means when there is reflected light from the pan and when there is no reference light, and the Vpp detection type circuit Cooking device that calculates the infrared reflectance of the bottom of the pan from the output of . Comprising a VfIf constant means, VfIf constant means is heating cooker according to claim 1 which is a so as to keep the product of the forward voltage Vf and forward direction current If of the light emitting means to be constant. The top plate is formed of crystallized glass, and the bandpass filter sets an upper limit wavelength of a transmission wavelength region to the transmission wavelength region of the top plate and cuts infrared rays emitted from the top plate itself. Cooking device.

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