JP5674894B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker that performs cooking using electromagnetic induction.

In an induction heating cooker, how to accurately measure the cooking temperature is an important issue. Regarding the temperature measurement of induction heating cookers, non-contact infrared sensors that are durable and have a high response speed are often used.
Conventionally, as a method of detecting the temperature of an object to be heated by a non-contact type infrared sensor, the temperature is measured by directly detecting infrared rays emitted from a heating pan or pan that is an object to be heated. Therefore, it has been difficult to measure the exact temperature of the heated object itself.

  This is because when the temperature of the heated object is T and the emissivity of the infrared ray is ε, the temperature of the heated object is T × ε ^ (1/4) (^ (1 / 4) indicates the fourth power root). When adjusting the temperature error, it is only necessary to correct the fourth root of the emissivity ε. However, since the emissivity ε differs depending on the material of the object to be heated, the emissivity ε of the object to be heated of a specific material is set. If it is determined to be corrected together, an accurate temperature cannot be measured when a heated object of a different material is used.

Therefore, the following patent documents are known as induction heating cookers that accurately detect the temperature without directly detecting the infrared rays emitted from the heated object.
In the induction heating cooker presented in the following patent document, a black body layer is provided between the object to be heated and the top plate on which the object to be heated is placed, and the temperature becomes the same as that of the object to be heated due to heat conduction. Infrared rays emitted from the black body layer are detected and a temperature signal corresponding to the detected infrared rays is output. Since the emissivity of the black body layer is constant, the infrared rays emitted from the black body layer are detected by an infrared sensor through a top plate that transmits infrared rays, so that it is highly accurate regardless of the material to be measured or the object to be heated. Temperature measurement is possible.

JP2003-121261A

  However, when the black body layer is formed on the top plate, the black body layer absorbs a lot of infrared rays from an external heat source such as illumination and incident light, and re-radiates toward the infrared sensor. There has been a problem that the temperature of the object to be heated cannot be accurately determined due to the influence of infrared rays.

  An object of the present invention is to solve such problems and to provide an induction heating cooker that measures the temperature of an object to be heated quickly and accurately without being influenced by the influence of an external heat source.

Induction heating cooker of the present invention includes a top plate for placing an object to be heated on the upper surface is disposed below the top plate, an induction heating means for heating an object, it is disposed below the top plate , a temperature measuring means for detecting infrared radiation from the top plate, based on the output of the temperature measuring means, and control means for controlling the induction heating means, are formed on the upper surface of the top plate, the object to be heated An infrared radiation layer that radiates infrared rays caused by a temperature rise due to heat conduction from an object downward at a constant emissivity; and a bottom surface of the top plate excluding a region where the object to be heated is placed; and the infrared radiation it is reflected without passing through the infrared wavelength band that passes through the layer and the top plate, an optical filter layer that passes infrared than the infrared of the wavelength band, in which comprises a.

  According to the induction heating cooker of the present invention, the region on the top plate on which the object to be heated is placed is covered with the infrared attenuation layer that attenuates infrared rays. In addition, the temperature of the object to be heated can be measured quickly and accurately without being affected by the influence of the external heat source.

It is sectional drawing which shows the structure of the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a figure explaining the radiation temperature measurement in the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a figure explaining the radiation temperature measurement in the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a figure explaining the radiation temperature measurement in the induction heating cooking appliance which concerns on a prior art. It is sectional drawing which shows the structure of the induction heating cooking appliance which concerns on Embodiment 2 of this invention. It is a graph which shows the spectral radiance of the black body in the induction heating cooking appliance which concerns on Embodiment 2 of this invention. It is a graph which shows the spectral transmittance of the top plate in the induction heating cooking appliance which concerns on Embodiment 2 of this invention. It is a graph which shows the spectral radiance under a top plate in the induction heating cooking appliance which concerns on Embodiment 2 of this invention. It is a graph which expands and shows the spectral radiance under a top plate in the induction heating cooking appliance which concerns on Embodiment 2 of this invention. It is a graph which shows the characteristic of the optical filter in the induction heating cooking appliance which concerns on Embodiment 2 of this invention.

Embodiment 1 FIG.
1 is a cross-sectional view showing a configuration of an induction heating cooker according to Embodiment 1 of the present invention. As shown in the figure, the induction heating cooker according to the first embodiment is arranged on the upper portion of the main body 1, and the top plate 2 on which the cooking container 4 that is the object to be heated is placed, and the upper end of the front surface of the main body 1. An operation panel 3 provided with each operation switch (not shown), a display unit 5 arranged in the vicinity of the operation panel 3 for displaying on / off of the device and set temperature, and the inside of the main body 1 A heating coil 7 that is arranged inductively heating the object to be heated, a control means 6 that controls the magnitude of the high-frequency alternating current that is passed through the heating coil 7, and controls the magnitude of the eddy current flowing in the cooking vessel 4; The white body layer 9 made of a material having a low emissivity is formed on the top plate 2 and disposed so as to face the bottom surface of the cooking container 4 below the top plate 2. And an infrared sensor 8 for detecting by contact.
Here, the top plate 2 is made of a heat resistant material such as glass or ceramics. In addition, each operation switch provided on the operation panel 3 includes an on / off switch of the device, a switch for setting the heating temperature of the cooking container 4 placed on the top plate 2, and the like.

Next, the operation will be described. When the control means 6 detects the switch input on the operation panel 3 provided in the main body 1, the heating coil 7 starts to drive, induction heating the cooking container 4 on the top 2, and heating on the display unit 5. The status is displayed. Heat conduction occurs in the white body layer 9 from the cooking container 4 heated by induction, and the infrared rays generated in the warm white body layer reach the infrared sensor 8 through the top plate 2. The control means 6 performs drive control of the heating coil 7 according to the amount of infrared rays that has reached.
With the cooking container 4 placed at a fixed position on the top plate 2, the infrared sensor 8 is installed so that the bottom surface of the cooking container 4 faces the top plate 2 and the white body layer 9 as shown in FIG. ing. At this time, the temperature of the cooking container 4 can be measured based on the amount of infrared light received by the infrared sensor 8.

  This measurement is based on the following theory. The heat 10 generated on the bottom surface of the cooking container 4 by the heating of the heating coil 7 is radiated as infrared rays and simultaneously conducts heat toward the bottom 11 of the white body layer 9. Infrared rays emitted from the bottom surface of the cooking vessel 4 cannot pass through the white body layer 9 having a low emissivity (that is, having a high infrared reflectance) and do not reach the infrared sensor 8. On the other hand, the heat conduction toward the bottom 11 of the white body layer 9 causes the bottom 11 of the white body layer 9 to rise to substantially the same temperature as the heat 10 generated on the bottom surface of the cooking vessel 4, and from there at a constant emissivity. Infrared rays 12 are emitted. The infrared rays 12 reach the infrared sensor 8 through the top plate 2. For this reason, the amount of infrared rays per unit area of infrared rays received by the infrared sensor 8, that is, the amount of heat Q1, is expressed by the following equation (1).

ここで、容器温度Ｔｍと白体層９の温度とが等しいと仮定。
以上より、実際の赤外線センサ８の出力は（２）の式となり、

Here, it is assumed that the container temperature Tm and the temperature of the white body layer 9 are equal.
From the above, the actual output of the infrared sensor 8 is the equation (2).

よって、白体層９の温度Ｔｍは、

となる。このように、白体層９の温度を求めることができる。

Therefore, the temperature Tm of the white body layer 9 is

It becomes. Thus, the temperature of the white body layer 9 can be obtained.

However, since it is actually affected by an external heat source, the exact temperature cannot be obtained from equation (3). Therefore, how to obtain the temperature of the cooking vessel 4 and the theory in consideration of the influence from the external heat source will be described with reference to FIG.
When the infrared ray 14 having the heat quantity Qe1 radiated from the external heat source 13 is incident on the incident portion 15 on the surface of the white body layer 9, the infrared ray 14 having the heat quantity Qe1 is absorbed by the white body layer 9, and the heat of the heat quantity Qe2 is obtained. 16 is converted. Since the emissivity at the time of thermal equilibrium is equal to the absorption rate, the heat quantity Qe2 is expressed by the following equation (4).
Qe2 = εw · Qe1 (4)

  In the white body layer 9 having a low emissivity ε (usually 0.2 or less), the rate of absorption from the amount of heat Qe1 to the amount of heat Qe2 is small, and the rate of reflection is large. That is, since the value of the emissivity εw is small, the infrared rays 14 from the external heat source 13 are hardly absorbed. The slight infrared ray 14 absorbed is thermally conducted from the incident part 15 to the bottom part 17 of the white body layer 9. Due to this heat conduction, the temperature of the bottom 11 of the white body layer 9 rises, and infrared rays 12 are radiated therefrom at a constant emissivity. The infrared rays 12 reach the infrared sensor 8 through the top plate 2. Therefore, the heat quantity Qew per unit area of the infrared ray 18 radiated from the bottom portion 17 of the white body layer 9 is expressed by the following equation (5).

（６）式から、実際の赤外線センサ８の出力は、

となることから、白体層９の温度Ｔｍは、（８）式のように求めることができる。

That is, the total amount of radiant heat Q ′ reaching the infrared sensor 8 is the sum of the above formulas (1) and (5), resulting in the following formula (6).

From the equation (6), the actual output of the infrared sensor 8 is

Therefore, the temperature Tm of the white body layer 9 can be obtained as shown in Equation (8).

  From the above formula, it can be seen that the temperature Tm of the white body layer 9 is affected by the temperature Tew of the bottom 17 of the white body layer 9. However, since the induction heating cooker of this Embodiment has provided the white body layer 9 on the top plate 2, it is hard to receive the influence of the infrared rays 14 from the external heat source 13 conventionally. This will be described in comparison with the conventional black body layer.

放射率εの高い（通常０．９５以上）黒体層１９は、黒体層１９の放射率εｂの値が大きいため、外部熱源１３からの赤外線の多くを吸収する。 The conventional black body layer is also affected by the infrared rays 14 from the external heat source 13 in addition to the heat from the bottom surface of the cooking vessel 4. The amount of infrared rays from the external heat source 13 will be described with reference to FIG. Infrared rays 14 radiated from the external heat source 13 enter the incident portion 22 of the black body layer 19. Since the incident infrared ray 14 cannot pass through the black body layer 19 having a high emissivity (that is, a high infrared absorption factor), it is absorbed by the black body layer 19 and converted into heat 23. The converted heat 23 is thermally conducted to the bottom 24 of the black body layer 19, and the bottom 24 of the black body layer 19 rises to substantially the same temperature as the incident portion 22 of the black body layer 19. Due to this temperature rise, infrared rays 25 are emitted from the bottom 24 of the black body layer 19 at a constant emissivity. The infrared rays 25 reach the infrared sensor 8 through the top plate 2. Therefore, the amount of heat Qeb per unit area of the infrared rays 25 radiated from the bottom 24 of the black body layer 19 is expressed by the following equation (9).

The black body layer 19 having a high emissivity ε (usually 0.95 or more) absorbs most of infrared rays from the external heat source 13 because the emissivity εb of the black body layer 19 is large.

天板２上に白体層９を形成した方が、天板２上に黒体層１９を形成した場合に比べ、放射率比分、赤外線センサ８に到達する赤外線の熱量が少ないことがわかる。つまり、天板２上に白体層９を形成した方が、外部熱源１３からの赤外線１４の多くを反射させるので、外部熱源１３からの赤外線１４がほとんど吸収されず、外部熱源１３に基づく赤外線１８は赤外線センサ８ではほとんど受光されない。このように、赤外線センサ８で検出できる赤外線のほとんどは、調理容器４の底面で発生した熱１０に基づく赤外線１２であるため、外部熱源１３からの影響に左右されずに、調理容器４の温度を正確に測定することができる。 Therefore, when the influence of the infrared ray 14 from the external heat source 13 is compared between the case of the white body layer 9 and the case of the black body layer 19, the following expression (10) is obtained from the expressions (5) and (9).

It can be seen that when the white body layer 9 is formed on the top plate 2, the amount of heat of infrared rays reaching the infrared sensor 8 is smaller than when the black body layer 19 is formed on the top plate 2. That is, when the white body layer 9 is formed on the top plate 2, most of the infrared rays 14 from the external heat source 13 are reflected, so that the infrared rays 14 from the external heat source 13 are hardly absorbed and the infrared rays based on the external heat source 13 are used. 18 is hardly received by the infrared sensor 8. Thus, most of the infrared rays that can be detected by the infrared sensor 8 are infrared rays 12 based on the heat 10 generated on the bottom surface of the cooking vessel 4, so that the temperature of the cooking vessel 4 is not affected by the influence from the external heat source 13. Can be measured accurately.

Embodiment 2. FIG.
Next, an induction heating cooker according to Embodiment 2 will be described. FIG. 5 is a cross-sectional view showing the configuration of the induction heating cooker according to the second embodiment. The second embodiment is different from the first embodiment shown in FIG. 1 except that the black body layer 19 is formed on the top plate 2 instead of the white body layer 9, and the region where the cooking container 4 is placed is excluded. The bottom surface of the top plate 2 is covered with an optical filter layer 26 that reflects a specific wavelength band of infrared rays. Other configurations are the same as or equivalent to those of the first embodiment. In addition, the same code | symbol is attached | subjected about the component which is the same as that of Embodiment 1, or equivalent, and the description is abbreviate | omitted.

  Next, the operation will be described. When the control means 6 detects a switch input on the operation panel 3 provided in the main body 1, the heating coil 7 starts to drive, induction heating the cooking container 4 on the top 2, and the display unit 5 is in a heating-on state. Is displayed. The heat 10 generated on the bottom surface of the cooking container 4 by induction heating is conducted to the bottom of the black body layer 19, and the bottom of the black body layer 19 rises to substantially the same temperature as the cooking container 4, from which a constant emissivity is obtained. Infrared rays are emitted downward. The infrared rays reach the infrared sensor 8 through the top plate 2. The control means 6 performs drive control of the heating coil 7 according to the amount of infrared rays that has reached. Here, since the optical filter layer 26 is not provided in the region where the cooking container 4 is placed, infrared rays radiated from the bottom of the black body layer 19 through the top plate 2 are affected by the optical filter layer 26. There is no.

  On the other hand, when infrared rays emitted from an external heat source enter the black body layer 19, the infrared rays are absorbed by the black body layer 19 and converted into heat. This heat is conducted to the bottom of the black body layer 19, and infrared rays are emitted from the bottom of the black body layer 19 with a constant emissivity. Due to the characteristics of the top plate 2 described later, infrared rays in a specific wavelength band among the infrared rays radiated from the bottom of the black body layer 19 pass through the top plate 2. However, since the optical filter layer 26 that reflects the specific wavelength band of infrared rays is provided on the bottom surface of the top plate 2, all infrared rays in the specific wavelength band that reach the bottom surface of the top plate 2 are all on the bottom surface of the top plate 2. It is reflected and does not pass through the top plate 2. As a result, it is possible to effectively prevent infrared rays caused by the external heat source from reaching the infrared sensor 8 through the top 2.

The specific wavelength band of infrared light reflected by the optical filter layer 26 is the wavelength band of infrared light that reaches the infrared sensor 8 through the black body layer 19 and the top plate 2. The infrared wavelength band that passes through the black body layer 19 and the top plate 2 will be described with reference to FIGS.
FIG. 6 shows the spectral radiance of the black body layer 19 for each infrared wavelength. FIG. 7 shows an example of transmittance characteristics of the top 2. The spectral radiance obtained by multiplying the spectral radiance of FIG. 6 by the transmittance of FIG. 7 is the spectral radiance after passing through the black body layer 19 and the top plate 2. A graph of spectral radiance after passing through the black body layer 19 and the top plate 2 is shown in FIG. 8, and a graph in which the horizontal axis is enlarged is shown in FIG. From FIG. 9, the radiance after passing through the black body layer 19 and the top plate 2 is distributed in the range of 1.75 to 4.25 μm. This is an infrared wavelength band that passes through the black body layer 19 and the top plate 2.

Therefore, as shown in FIG. 10, the object to be heated is placed on the optical filter layer 26 that reflects infrared light in the wavelength band of 1.75 to 4.25 μm and transmits infrared light in the other wavelength bands. By forming on the bottom surface of the top plate 2 excluding the region, infrared light in a wavelength band that can pass through the top plate 2 out of infrared rays from the external heat source is reflected by the optical filter layer 26. For this reason, almost no infrared rays from the external heat source can pass through the top plate 2, and infrared rays based on the external heat source are hardly received by the infrared sensor 8.
Thus, most of the infrared rays that can be detected by the infrared sensor 8 are infrared rays based on the heat generated on the bottom surface of the cooking vessel 4, so that the temperature of the cooking vessel 4 can be accurately determined without being influenced by the influence of the external heat source. Can be measured.

  As shown in FIGS. 6, 8, and 9, the spectral radiance increases as the temperature of the black body layer 19 increases, but the wavelength of infrared rays reflected by the optical filter layer 26 at any temperature. It is within the range. Therefore, the temperature of the cooking container 4 can be accurately measured without being affected by the external heat source 13 regardless of the temperature of the black body layer.

  Moreover, in this Embodiment, although the case of the induction heating cooking appliance with which the black body layer 19 and the top plate 2 are arrange | positioned is shown as an example, it is not limited to this, The to-be-heated object of a different material is shown. If it is an induction heating cooker in which a layer that emits infrared rays with a constant emissivity and a top plate on which an object to be heated is placed, the infrared sensor 8 passes through these layers and reaches the infrared sensor 8. By setting the transmittance of the optical filter layer so as not to transmit the infrared wavelength band, the temperature of the cooking container 4 can be accurately measured as in the present embodiment.

In addition, it is possible to prevent reflection of infrared rays by using a paint or shielding layer instead of an optical filter layer, but in order to absorb infrared rays, it is converted into heat and emitted as infrared rays, which interfere with infrared sensors. Therefore, an effect like an optical filter layer cannot be obtained. Furthermore, in the case of a coating or shielding layer, it is not clear how much infrared reflection / transmission / absorption occurs, so it is difficult to correct it. Therefore, like an optical filter layer, it is affected by the influence from an external heat source. Otherwise, the temperature of the cooking container cannot be measured accurately.
On the other hand, the optical filter layer does not absorb infrared rays, and furthermore, by setting the transmittance, it can be corrected to reflect almost no unnecessary infrared rays. The temperature can be measured accurately.

  As an application example of the present invention, application to temperature detection of various apparatuses that perform induction heating is possible.

1 main body, 2 top plate, 3 operation panel, 4 cooking container, 5 display section, 6 control means, 7
Heating coil, 8 Infrared sensor, 9 White body layer, 10, 16, 23 Heat, 11, 17, 2
0, 24 Bottom, 12, 14, 18, 21, 25 Infrared, 13 External heat source, 15, 22
Incident part, 19 black body layer, 26 optical filter layer.

Claims (2)

A top plate for placing an object to be heated on the top surface;
An induction heating means disposed below the top plate for heating an object to be heated;
A temperature measuring means disposed below the top plate and detecting infrared rays radiated from the top plate;
Control means for controlling the induction heating means based on the output of the temperature measuring means;
An infrared radiation layer that is formed on the top surface of the top plate, and radiates infrared rays at a constant emissivity downward due to temperature rise due to heat conduction from the object to be heated;
Covers the bottom surface of the top plate excluding the region where the object to be heated is placed , reflects the infrared radiation layer and the infrared light in the wavelength band passing through the top plate without passing through, and other than the infrared light in the wavelength band An optical filter layer that transmits infrared rays ;
An induction heating cooker comprising: The induction heating cooker according to claim 1, wherein the wavelength band of infrared rays reflected without passing through the optical filter layer is 1.75 to 4.25 µm.

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