JP2014011020A - Induction heating cooker and control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating cooker which can feed power with proper heating power to a heating coil even when a distance between a heated object and a top plate is unknown, by calculating the distance depending on a specified surface temperature and a specified heating time to correctly detect a surface temperature of a pot with good responsiveness.SOLUTION: A temperature estimation circuit according to the present embodiment: a) causes a memory to store a relation between a specified surface temperature (T) of a heated body when a temperature rise rate of the heated body becomes a predetermined threshold value and under, and a specified heating time (τ) until the heated body reaches the specified surface temperature (T); and b) estimates a surface temperature (T) of the heated body based on the specified surface temperature (T) at the specified heating time (τ) in the memory and a temperature (T) of a top plate when the specified heating time (τ) has elapsed and a time rate of change (ΔT/Δt) in the temperature (T) of the top plate.

Description

  The present invention relates to an induction cooking device, and more particularly to an induction heating cooking device capable of accurately estimating the surface temperature of a heated object such as a pan and heating the heated object at an appropriate temperature, and a control method thereof. Is.

  In conventional induction heating cooking equipment, there has been a strong market demand for realizing an optimum cooking method by accurately measuring the surface temperature of the pan and supplying appropriate power to the heating coil based on this measurement. Many conventional induction cooking appliances generally measure the temperature of the top plate using a thermal element (contact temperature sensor) such as a thermistor or thermocouple that is in direct contact with the lower surface of the top plate, and are in a thermal equilibrium state. The surface temperature of the pan is detected from the temperature of the top plate based on the fact that the temperature of the top plate and the surface temperature of the pan have a certain relationship.

  On the other hand, it passes through a top plate using optical sensors (optical temperature sensor), such as an infrared sensor arrange | positioned under the top plate like the induction heating cooking appliance of patent document 1, for example. Some have been proposed that detect the surface temperature of a pan by measuring radiant energy such as infrared rays.

Japanese Patent Laying-Open No. 2004-227976 (FIG. 1)

  However, the temperature of the top plate measured using a contact-type temperature sensor does not reflect the surface temperature of the pan in real time due to the large thermal resistance of the top plate made of heat-resistant glass. Immediately after that, the surface temperature of the pan detected from the temperature of the top plate rose with a delay from the actual surface temperature of the pan, so that the power supply to the heating coil could not be properly controlled.

  On the other hand, the optical temperature sensor utilizes the fact that the radiant energy from a high-temperature object is proportional to the fourth power of the surface temperature. In particular, the temperature reached by the pan surface during normal practical cooking (about 150 ° C.) At the following relatively low temperatures, the radiant energy from the surface of the pan was so small that the surface temperature of the pan could not be accurately detected. That is, when the surface temperature of the pan detected using the optical temperature sensor is lower than the practical cooking temperature (immediately after the start of heating), the temperature detection accuracy is low, and the heating coil is the same as when using the contact temperature sensor. It was not possible to accurately control the power supply to the. In addition, detecting the temperature using an optical temperature sensor is likely to impair the detection accuracy due to, for example, the surface condition of the pan (stained, glossy, etc.), and may be affected by other thermal power, contents, and the surrounding environment. It was easy to receive, making accurate detection of the surface temperature of the pan more difficult.

The present invention has been made in order to solve the above-described problems, and a top plate on which a heated object is placed, and heating for induction heating of the heated object disposed below the top plate. A coil, a drive circuit for supplying a high-frequency current to the heating coil, a temperature sensor disposed under the top plate for detecting the temperature (T _g ) of the top plate, and a temperature connected to the temperature sensor An induction heating cooker comprising an estimation circuit and a control circuit for controlling the drive circuit,
The temperature estimation circuit includes:
a) A specified surface temperature (T _sh ) of the heated body when the rate of temperature increase of the heated body is equal to or less than a predetermined threshold, and a regulation until the heated body reaches a specified surface temperature (T _sh ) Memorize the relationship of heating time (τ),
b) The specified surface temperature (T _sh ) at the specified heating time (τ) in the memory, the temperature (T _g ) of the top plate when the specified heating time (τ) has elapsed, and the rate of change with time ( Based on (ΔT _g / Δt), the surface temperature (T _p ) of the heated object is estimated,
The control circuit controls the drive circuit using the estimated temperature (T _p ) estimated by the temperature estimation circuit.

  According to the induction heating cooker according to the present invention, even if the interval between the object to be heated and the top plate is unknown, by calculating the interval from the specified surface temperature and the specified heating time, The surface temperature of a certain pan can be detected accurately and responsively (in real time), and an appropriate high frequency current can be supplied to the heating coil.

It is a perspective view showing the whole induction heating cooking appliance concerning the present invention roughly. It is the expanded sectional view seen from the II-II line of the induction heating cooking appliance of FIG. FIG. 3 is an enlarged partial sectional view in which a region indicated by a broken line in FIG. 2 is enlarged. It is a graph which shows temporal transition with the actual temperature of the pan when heating the pan which does not put water, and the estimated temperature of the pan estimated based on the actual temperature of the top plate by this invention. It is the graph which plotted the actual temperature of the top plate when the pan containing water was heated, the actual temperature of water, the actual temperature and the estimated temperature of the bottom plate of the pan. It is a circuit block diagram of the induction heating cooking appliance which concerns on this invention. It is the graph which plotted the temperature of the water and the baseplate of a pan in the case where normal boiling arises when the water in a pan is heated with a predetermined | prescribed thermal power. It is the graph which plotted the temperature of the water and the bottom plate of a pan in case a bumping phenomenon arises when the water in a pan is heated with predetermined | prescribed thermal power.

  Embodiments of an induction heating cooker according to the present invention will be described below with reference to the accompanying drawings. In the description of each embodiment, terms indicating directions (for example, “upward” and “downward”) are used as appropriate for easy understanding. It does not limit the present invention. In the accompanying drawings, the same components are referred to by the same reference numerals.

Embodiment 1 FIG.
The first embodiment of the induction heating cooker according to the present invention will be described in detail below with reference to FIGS. FIG. 1 is a perspective view schematically illustrating the entire induction heating cooker 1 according to the present invention. An induction heating cooker 1 shown in FIG. 1 schematically includes a casing 2, a top plate 3 formed of heat-resistant glass or the like covering substantially the entire upper surface thereof, and a pair of induction heating type disposed symmetrically. It has IH heating units 4a and 4b, a radiant heating type radial heating unit 5, and a grill unit 6 suitable for cooking fish and the like. Each IH heating section 4a, 4b has a heating coil 20 (FIG. 2) that is spirally wound in parallel with the top plate 3.

  In the following embodiments, the induction heating cooker 1 having a so-called side grill structure in which the grill portion 6 is arranged to be biased to the left side of the housing 2 will be described as an example, but the present invention is limited to this. In addition, the present invention can be equally applied to an induction heating cooker having a center grill structure in which the grill portion 6 is disposed at substantially the center of the housing 2 or an induction heating cooker that does not include the grill portion 6.

  The induction heating cooker 1 also includes an operation panel 7 and heating power adjustment dials 8a, 8b, and 8c used by the user to operate the IH heating units 4a and 4b, the radiant heating unit 5 and the grill unit 6, and controls thereof. A liquid crystal display unit 9 for displaying the state is provided. Furthermore, the induction heating cooker 1 has an intake hole 10 and an exhaust hole 11 provided on the top plate 3 adjacent to the rear wall of the housing 2.

FIG. 2 is an enlarged cross-sectional view of the induction heating cooker 1 of FIG. 1 as viewed from the line II-II, and a heated object P (hereinafter simply referred to as “pan”) is placed on the top plate 3. This shows the state. The induction heating cooker 1 according to the present invention has a temperature sensor 30 such as a thermistor disposed so as to abut on the lower surface of the top plate 3, and can measure the temperature (T _g ) of the top plate 3. it can.

As will be described in detail later, the induction heating cooker 1 includes a drive circuit (inverter circuit) 60 for supplying a high-frequency current to the heating coil 20 of each IH heating unit 4 and a top plate 3 measured by the temperature sensor 30. Based on the surface temperature of the pan P estimated from the temperature (T _g ) and the “heating power” (power (W) supplied to the heating coil 20) set by the user with the heating power adjustment dial 8 or the like, the heating coil 20 A control circuit 50 that controls the drive circuit 60 so as to supply an appropriate high-frequency current is provided (FIG. 6).

Next, referring to FIG. 3 and FIG. 4, a method (estimation principle) for estimating the surface temperature of the heated body P from the temperature (T _g ) of the top plate 3 measured by the temperature sensor 30 according to the present invention. explain. FIG. 3 is a partially enlarged cross-sectional view in which a region indicated by a broken line 22 in FIG. 2 is enlarged.
The control circuit 50 drives the drive circuit 60 according to a desired heating power set by the user using the operation panel 7 and the heating power adjustment dial 8 and the like, and a high frequency current is supplied to the heating coil 20 provided below the pan P. Then, an alternating magnetic field (closed magnetic path) including the bottom plate B of the pan P around the heating coil 20 is formed. At this time, an eddy current is formed near the surface of the bottom plate B of the pan P, and the bottom plate B of the pan P is heated by the Joule heat. That is, the pan P that is the object to be heated is directly induction heated.

The amount of heat generated when the bottom plate B of the pan P is heated cooks and heats the food F such as moisture contained in the pan P and is also transmitted to the top plate 3 below the bottom plate B. At this time, in particular, the bottom plate B (and the top plate 3) of the pan P cannot be formed to be completely flat (the flatness is zero) and has a minute curved shape. An air layer A having _a predetermined interval or gap (δ _a ) is formed therebetween.

Here heat is conducted from the lower surface of the bottom plate B of the pan P on the top plate 3 Q ₁ for _(i.e. the amount of heat Q ₁ to conduct air layer A is formed between the lower surface and the top plate 3 of the bottom plate B of the pan _P) Think. In this case the amount of heat _{Q 1} is, generally, as the temperature difference between the temperature _{(T a)} of the temperature _{(T p)} and the surface of the top plate 3 of the bottom plate B of the pan P _(T p -T _a) is large, both faces The larger the area (S) to be processed is, the smaller the gap (δ _a ) is. The amount of heat Q ₁ also depends on the thermal conductivity (λ _a ) of the air layer A. Therefore, the amount of heat Q ₁ conducted per unit time from the lower surface of the bottom plate B of the pan P to the top plate 3 is expressed by the following equation.

Further, the amount of heat Q ₂ conducted to the top plate 3 is transmitted from the upper surface to the lower surface of the top plate 3. At this time, when the top plate 3 formed of heat-resistant glass or the like is viewed as a sensible heat storage material, the amount of stored heat Q ₂ is the mass (M), specific heat (c _g ), and temperature (T _g ) of the top plate 3. It is expressed by the following equation using the time change rate (ΔT _g / Δt).

ここで、トッププレート３の熱伝導率（λ_ｇ）が無限大である（すなわちＴ_ａとＴ_ｇとが等しい。Ｔ_ａ＝Ｔ_ｇ）と仮定すると、［数１］および［数２］の左辺の熱量Ｑ_１，Ｑ_２（Ｑ_１＝Ｑ_２）が等しいので、これらを連立させて整理すると次式を得ることができる。

Here, assuming that the thermal conductivity (λ _g ) of the top plate 3 is infinite (that is, T _a is equal to T _g , T _a = T _g ), [Equation 1] and [Equation 2] Since the amounts of heat Q ₁ and Q ₂ (Q ₁ = Q ₂ ) on the left side are equal, the following equation can be obtained by arranging them together.

Ｔ_ｐ：鍋Ｐの推定温度
Ｔ_ｇ：温度センサで測定されたトッププレートの温度
δ_ａ：鍋Ｐとトッププレートとの間の間隔
ρ_ｇ：トッププレートの密度
ｃ_ｇ：トッププレートの比熱
δ_ｇ：トッププレートの厚み
λ_ａ：空気の熱伝導率
すなわち、上記係数Ｃはトッププレート３により一意的に決まる定数であるので、鍋Ｐの底板Ｂの温度Ｔ_ｐは、鍋Ｐの底板Ｂの下面とトッププレート３との間に形成される空気層Ａの間隔（δ_ａ）、および温度センサ３０が測定するトッププレート３の温度Ｔ_ｇとその時間変化率（ΔＴ_ｇ／Δｔ）を用いて表すことができる。

T _p : Estimated temperature of pan P T _g : Temperature of top plate measured by temperature sensor δ _a : Spacing between pan P and top plate ρ _g : Density of top plate c _g : Specific heat of top plate δ _g : Top plate thickness λ _a : Thermal conductivity of air That is, since the coefficient C is a constant uniquely determined by the top plate 3, the temperature T _p of the bottom plate B of the pan P is the lower surface of the bottom plate B of the pan P represented using intervals of the air layer a is formed between the top plate 3 ([delta] _a), and the temperature T _g and the time rate of change of the top plate 3 by the temperature sensor 30 measures the (ΔT g _/ Δt) and be able to.

As described above, even if it is assumed that the thermal conductivity (λ _g ) of the top plate 3 is infinite, the following evaluation experiment 1 is performed in order to verify that the relationship shown in [Expression 3] holds. It was.
In addition, in this evaluation experiment 1, in order to exclude the heat transfer effect by the convection of the foodstuff F etc., the foodstuff F is not accommodated in the inside of the pan P, but the pot P is heated by the heating coil 20 in the so-called “empty state”. By induction heating.

[Evaluation Experiment 1]
FIG. 4 shows that when the power supplied to the heating coil 20 is 1000 W,
i) Measured temperature (T _g ) of the top plate 3 measured by the temperature sensor 30
ii) the measured temperature (T _b ) of the bottom plate B of the pan P measured by another temperature sensor (not shown), and
iii) Estimated temperature (T _p ) of the pan P determined in [Equation 3] above,
It is the graph obtained by plotting the time transition of. At this time, a spacer (thickness: 1.5 mm, not shown) is arranged between the pan P and the top plate 3 so that the interval (δ _a ) of the air layer A is defined as 1.5 mm, and the heating coil 20 After heating the pan P by supplying a high frequency current for 250 seconds, power supply to the heating coil 20 was stopped.

As is apparent from the graph of FIG. 4, when 250 seconds have elapsed since the start of heating, the actual temperature (T _b ) of the pan P has reached 200 ° C. or more, whereas the actual measurement of the top plate 3 measured by the temperature sensor 30. The temperature (T _g ) is about 70 ° C., there is a temperature difference of about 130 ° C. or more between the two, and the responsiveness is very poor.
On the other hand, the estimated temperature (T _p ) of the pan P obtained by the above [Equation 3] generally approximates (estimates) the measured temperature (T _b ) of the pan P immediately after the start of heating with good followability. Therefore, according to the method for estimating the temperature of the heated object according to the present invention defined by the above [Equation 3], the surface temperature (T _b ) of the pan P is extremely precisely determined from the measured temperature (T _g ) of the top plate 3. It was confirmed from the graph of FIG. 4 that it can be estimated with good followability.

As described above, the actual thermal conductivity (λ _g ) of the glass that is the constituent material of the top plate 3 is about 1 W / (m · K), but is assumed to be infinite. [Equation 3] is derived, but the estimated temperature (T _p ) of the pan P obtained based on the above [Equation 3] is an approximation of the measured temperature (T _b ) of the pan P accurately. confirmed.
In other words, the density, specific heat, and thickness of the glass constituting the top plate 3 are design matters and are known (the coefficient C is uniquely determined), so that the distance between the pan P and the top plate 3 ( Based on δ _a ), the measured temperature (T _g ) of the top plate 3 and the rate of change over time (ΔT _g / Δt), the temperature of the pan P is accurately tracked (in real time) using the above [Equation 3]. Can be estimated.

By the way, in the said evaluation experiment 1, by arrange | positioning the spacer which has fixed thickness between the pan P and the top plate 3, so that the space | interval ((delta) _a ) between the pan P and the top plate 3 may become fixed. Set. However, there are many actual induction heating cookers 1 in which no spacer is provided on the top plate 3, and the bottom plate B of the pan P (or the top surface of the top plate 3) is uneven, or the pan P and the top. When a foreign substance (small piece of food material F) is present between the plate 3 and the plate 3, the interval (δ _a ) is not necessarily constant, but may vary from use to use.

Therefore, the induction heating cooker 1 according to the present invention, as will be described in detail below, before estimating the bottom plate temperature of the pan P using the above equation [Equation 3], between the pan P and the top plate 3. The interval (δ _a ) is defined by a specified surface temperature (T _sh ) and a specified heating time (τ), which will be described later, the temperature (T _g ) of the top plate 3 at a predetermined time after the specified heating time has elapsed, and the rate of change over time. The distance (δ _a ) between the pan P and the top plate 3 is to be estimated from (ΔT _g / Δt). In order to confirm that the interval (δ _a ) can be estimated in this way, the following evaluation experiment 2 was performed.

[Evaluation Experiment 2]
Unlike the evaluation experiment 1, in the evaluation experiment 2, 0.75 liter of water was put in the pan P, and a relatively large electric power (3000 W) was supplied to the heating coil 20 from the drive circuit 60. At this time,
i) Measured temperature (T _g ) of the top plate 3 measured by the temperature sensor 30
ii) the measured temperature (T _b ) of the bottom plate B of the pan P measured by another temperature sensor (not shown), and
iii) Measured temperature (T _f ) of water in the pan P measured by another temperature sensor (not shown),
5 was plotted to obtain the graph of FIG.

As in the above [Equation 1], the heat transfer amount Q between the bottom plate B of the pan P and the food F (water) generally has a heat transfer coefficient h, a superheat degree ΔT _bf (temperature difference between the bottom plate B and water ( T _b −T _f )), and the transmission area A,

すなわち熱伝達量Ｑは、熱伝達係数ｈおよび過熱度ΔＴ_ｂｆに依存して変動する。

That is, the heat transfer amount Q varies depending on the heat transfer coefficient h and the degree of superheat ΔT _bf .

In the graph of FIG. 5, attention is paid to the actually measured temperature (T _b ) of the bottom plate B of the pan P. Immediately after feeding the heating coil 20 (starting cooking), the temperature difference between the temperature (T _r ) of the bottom plate B of the pan P and the food F (water) is not so large. Until almost a certain period of time (τ ₁ , for example, about 20 seconds) elapses because there is almost no heat exchange with water contained in the water (because there is little natural convection and the heat transfer coefficient h is small) The actually measured temperature (T _b ) of the bottom plate B of the pan P rises rapidly.

However, if the heating coil 20 continues to be fed for a certain period of time (τ ₂ , for example, up to about 50 seconds), the actually measured temperature (T _b ) of the bottom plate B of the pan P increases, that is, the degree of superheat ΔT _bf The larger the is, the more natural convection of the food F (water) in the pan P is promoted, and the heat transfer coefficient between the pan P and water increases, that is, the heat from the bottom plate B of the pan P to the food F (water). Since it becomes easy to be transmitted, the temperature (T _b ) of the bottom plate B of the pan P temporarily rises gently and changes substantially constant. That is, the temperature increase rate ΔT _b / Δt of the measured temperature (T _b ) of the bottom plate B of the pan P is equal to or less than a predetermined threshold value.

Furthermore, when the heating coil 20 is fed for a certain period of time (τ ₃ , for example, up to about 80 seconds), subcooled boiling begins to occur in the bottom plate B of the pan P, and bubbles adhere to the bottom plate B. Therefore, the transmission area A is reduced, it is difficult to transfer heat from the bottom plate B to the water, and the rate of increase in the temperature (T _b ) of the bottom plate B of the pan P increases.

When the heating coil 20 is further fed for a certain period of time (τ ₄ , for example, up to about 130 seconds), the food F (water) in the pan P is in a stable saturated boiling state (boiling is activated), and the pan P The temperature (T _b ) of the bottom plate B of the pan P is maintained at a constant temperature by balancing the Joule heat generated in the bottom plate B of the plate and the heat taken away as the heat of vaporization of water. When in the saturated boiling state, the degree of superheat ΔT _bf and the heat transfer coefficient h mainly depend on the surface properties of the bottom plate B of the pan P, the physical properties of the food F, and the heating power (W) to the heating coil 20. In FIG. 5 (when the supplied power is 3000 W), the temperature (T _b ) of the bottom plate B is maintained at about 140 ° C., and the degree of superheat ΔT _bf is about 40 ° C.

As described above, in the period from time (τ ₁ ) to time (τ ₂ ), the actually measured temperature (T _b ) of the bottom plate B of the pan P temporarily changes to be substantially constant, and the rate of temperature increase is a predetermined value. In the present invention, this temperature is defined as “specified surface temperature (T _sh )”, and the time required to reach the specified surface temperature (T _sh ) is defined as “specified heating time (τ) (τ ₁ ). <Τ <τ ₂ ) ”. In the series of boiling processes, the inventor of the present application mainly determines the specified surface temperature (T _sh ) and the specified heating time (τ) between the bottom plate B of the pan P and the top plate 3 (δ _a ) and It was confirmed that the structure as the induction heating cooker 1 was slightly affected depending on the power (W) supplied to the heating coil 20. That is, the inventor of the present application assumes that the interval (δ _a ) is constant if the specific induction heating cooker 1 is limited in the evaluation experiment 2, and the supply power (W) supplied to the heating coil 20 is assumed to be constant. Accordingly, it was confirmed that the specified surface temperature (T _sh ) and the specified heating time (τ) can be specified. In other words, after specifying the specified surface temperature (T _sh ) and the specified heating time (τ), the interval (δ _a ) in the specific induction heating cooker 1 is set to the heating coil 20 as described later. It can be estimated depending on the supply power (W) supplied.

Specifically, in the induction heating cooker 1 used in the evaluation experiment 2, when the power supplied (W) to the heating coil 20 is 3000 W, the specified surface temperature (T _sh ) is as shown in FIG. The temperature is about 120 ° C., and the specified heating time (τ) is, for example, about 40 seconds (about 20 seconds to about 50 seconds). Although not specifically shown using a graph or the like, when a similar evaluation experiment is performed using another induction heating cooker, the specified surface temperature (T _sh ) and the specified heating time (τ) are caused by the structure. ) May differ slightly from the above. However, in the induction heating cooker 1 according to the present invention, the specified surface temperature (T _sh ) and the specified heating time (τ) corresponding to the power (W) supplied to the heating coil 20 are set in advance by an experiment before shipping. The temperature is estimated to be stored in a memory (not shown) in the temperature estimation circuit 40. Further, if the specified surface temperature (T _sh ) and the specified heating time (τ) can be expressed by a function of a predetermined supply power (W), the temperature estimation circuit 40 stores the function formula in a memory and supplies the supply power (W ), The specified surface temperature (T _sh ) and the specified heating time (τ) may be obtained. In any case, the temperature estimation circuit 40 according to the present invention can specify the specified surface temperature (T _sh ) and the specified heating time (τ) according to the power (W) supplied to the heating coil 20.

Therefore, in the temperature estimation circuit 40 according to the present invention, the specified surface temperature (T _sh ) specified as described above and the specified heating time (τ) have elapsed using the following equation obtained by modifying the above [Equation 3]. Sometimes, the distance (δ _a ) between the bottom plate B of the pan P and the top plate 3 can be calculated from the temperature (T _g ) of the top plate measured by the temperature sensor 30 and the rate of change with time.

ここで、Ｔ_{ｇ，ｔ＝τ}は、加熱コイル２０への給電開始後、規定加熱時間（τ）経過した時における温度センサ３０で測定されたトッププレートの温度（Ｔ_ｇ）であり、（ΔＴ_ｇ／Δｔ）_ｔ＝τはその時の時間変化率を示すものである。また、各係数λ_ａ，ρ_ｇ，ｃ_ｇ，δ_ｇは上記と同様で、λ_ａは空気の熱伝導率、ρ_ｇはトッププレート３の密度、ｃ_ｇはトッププレート３の比熱、δ_ｇはトッププレート３の厚みであり、既知の設計値である。

Here, T _{g, t = τ} is the temperature (T _g ) of the top plate measured by the temperature sensor 30 when the specified heating time (τ) has elapsed after the start of power supply to the heating coil 20, and (ΔT _g / Δt) _{t = τ} indicates the time change rate at that time. The coefficients λ _a , ρ _g , c _g , and δ _g are the same as described above, λ _a is the thermal conductivity of air, ρ _g is the density of the top plate 3, c _g is the specific heat of the top plate 3, δ _g Is the thickness of the top plate 3, which is a known design value.

The temperature estimation circuit 40 according to the present invention is configured so that the bottom plate B of the pan P has a specified surface temperature (T _sh ) when, for example, about 40 seconds of the specified heating time (τ) has elapsed after the start of power supply to the heating coil 20. Assuming that the temperature reaches about 120 ° C., the temperature (T _g ) of the top plate and its rate of change over time are specified, and the interval (δ _a ) between the bottom plate B of the pan P and the top plate 3 is set as described above [Equation 5 ] Is obtained from the above.

The specified surface temperature (T _sh ) and the specified heating time (τ) are the same as the specified surface temperature (T _sh ) and the specified heating time (τ) corresponding to the power (W) supplied to the heating coil 20 before shipping. It may be set in advance by an experiment or the like, and may be stored in a memory (not shown) in the temperature estimation circuit 40. The specified surface temperature (T _sh ) and the specified heating time (τ) are set to a predetermined supply power. If it can be expressed by the function of (W), the function expression may be stored in a memory, and the specified surface temperature (T _sh ) and the specified heating time (τ) may be obtained according to the supplied power (W).

The temperature estimation circuit 40 of the induction heating cooker 1 according to the present invention specifies or stores the specified surface temperature (T _sh ) and the specified heating time (τ) according to the supplied power (W), and then specifies the specified surface temperature ( T _sh ), the temperature (T _g ) of the top plate 3 measured by the temperature sensor 30 after the lapse of the specified heating time (τ), and the time change rate (ΔT _g / Δt) _{t = τ} By substituting into Equation 5], the distance (δ _a ) between the wall bottom of the pan P and the top plate 3 can be calculated.

The specified heating time (τ) has a large temperature difference between the measured temperature (T _b ) of the bottom plate B of the pan P and the food F (water), and the heat exchange coefficient h is large. Although it has been described as a period (τ ₁ <τ <τ ₂ ) in which the temperature (T _b ) of B rises gradually and gently, it is not strictly limited to this, and subcooled boiling occurs in the bottom plate B Even during the period (τ ₃ , τ ₂ <τ <τ ₃ ), the natural convection of water is remarkable (the heat exchange coefficient h is large), and the temperature (T _b ) of the bottom plate B of the pan P and the interval (δ _a ), a specified heating time (τ) for obtaining a specified surface temperature (T _sh ) is set, for example, from about 20 seconds to about 80 seconds (τ ₁ <τ <τ ₃ ). Also good. However, the period in which the temperature (T _b ) of the bottom plate B of the pan P is maintained at a constant temperature, for example, about 140 ° C. (τ ₄ , for example, after about 130 seconds) when the food F (water) is in a saturated boiling state. In this case, since it does not depend on the interval (δ _a ), it is not appropriate to set this period as the specified heating time (τ).

In other words, the specified heating time (τ) for reaching the specified surface temperature (T _sh ) may be from time (τ ₁ , for example, about 20 seconds) to time (τ ₃ , for example, about 80 seconds). Since the temperature of the top plate 3 is usually measured by the temperature sensor 30 with a delay of about 10 seconds, the specified heating time (τ) may be about 30 seconds to about 90 seconds. However, it is preferable to estimate the interval (δ _a ) at an early stage after the start of heating from the viewpoint that it is calculated earlier and used for the estimation of the temperature (T _p ) of the subsequent pan P. (Τ) is preferably about 30 seconds to about 60 seconds.

As described above, after calculating the distance (δ _a ) between the bottom plate B and the top plate 3 of the pan P, the temperature estimation circuit 40 of the present invention is calculated using the above [Equation 3]. The temperature of the pan P is estimated from the interval (δ _a ), the temperature (T _g ) of the top plate 3 measured by the temperature sensor 30 and the rate of change with time (ΔT _g / Δt) after the specified heating time (τ) has elapsed. be able to. The estimated temperature (T _p ) of the pan P thus estimated is similarly plotted in FIG. 5, and follows a measured temperature of the pan P after a certain time (τ ₂ , especially 80 seconds) has elapsed. It is a good approximation (estimation). In FIG. 5, the actually measured estimated temperature (T _b ) of the bottom plate B of the pan P stably changes at about 140 ° C., which is higher than the boiling point of water by 100 ° C. by the degree of superheat (about 40 ° C.).

In the specific example described in FIG. 5 (Evaluation Experiment 2), the food F (water) accommodated in the pan P is described as being initially in the room temperature state, but when different foods F are continuously cooked. When the same food material F is reheated, the actually measured temperature (T _g ) of the top plate 3 detected by the temperature sensor 30 may exceed the specified surface temperature (T _sh ). At this time, if the bottom plate temperature of the pan P when the predetermined specified heating time (τ) has elapsed after the start of heating is set as the specified surface temperature (T _sh ), the interval (δ _a ) is accurately set as described above. Cannot be estimated.

Therefore, the measured temperature (T _g ) of the top plate 3 immediately after the start of heating is compared with the specified surface temperature (T _sh ).
a) When the measured temperature (T _g ) of the top plate 3 immediately after the start of heating is higher than the specified surface temperature (T _sh ) (T _g −T _sh > 0), and when the measured temperature (T _g of the top plate 3 immediately after the start of heating) _When the difference between _g ) and the specified surface temperature (T _sh ) is smaller than a predetermined temperature difference (T _X ) (T _sh −T _g > T _X > 0: T _X is a predetermined temperature, for example, 10 ° C. ), The temperature estimation process according to the present invention of calculating the temperature (T _b ) of the pan P after calculating the interval (δ _a ) and the like is stopped,
b) When the measured temperature (T _g ) of the top plate 3 immediately after the start of heating is larger than the specified surface temperature (T _sh ) and the temperature difference is equal to or higher than a predetermined temperature (T _sh −T _g > T _X > 0). For example, it is preferable to perform the temperature estimation processing according to the present invention. Thereby, the accuracy (temperature estimation accuracy) when estimating the temperature (T _b ) of the pan P after calculating the interval (δ _a ) and the like can be improved.

The distance (δ _a ) between the bottom plate B of the pan P and the top plate 3 can usually vary in the range of 0.1 mm (0 mm is also conceivable) to 3 mm, and the maximum with respect to the minimum value of the distance (δ _a ) The value is 30 times, and the error that can occur when the interval (δ _a ) itself is estimated directly becomes considerably large. On the other hand, when the supplied power (W) is 3000 W, for example, when the specified surface temperature (T _sh ) is 120 ° C., the measured temperature (T _g ) of the top plate 3 immediately after the start of heating is 30 ° C., which is room temperature. The variation of the term (T _sh −T _{g, t = τ} ) on the right side of the above [Equation 5] is 70 ° C. (when T _sh is 120 ° C. and T _{g, t = 50} is 50 ° C.), The range is 110 ° C. (when T _sh is 140 ° C. and T _{g, t = 20} is 30 ° C.), and the maximum value 110 ° C. with respect to the minimum variation 70 ° C. is about 1.57 times, and the interval (δ _a ) It can be substantially reduced from variations that may occur in itself, and the temperature estimation accuracy can be considerably improved.
When the heated body is oil, the specified surface temperature (T _sh ) is preferably about 140 ° C. to 200 ° C.

The temperature estimation circuit according to the present invention is assigned by substituting [Equation 5] for obtaining the interval (δ _a ) into the above [Equation 3] for obtaining the estimated temperature (T _p ) of the bottom plate B of the pan P. 40 represents the following equation from the specified surface temperature (T _sh ), the temperature (T _{g, t = τ} ) of the top plate 3 after the lapse of the specified heating time ( _τ ), and the time change rate (ΔT _g / Δt) _{t = τ.} Can be used to directly calculate the bottom plate temperature (T _p ) of the pan P.

なお、上式の右辺にあるトッププレート３の温度（Ｔ_ｇ）およびその時間変化率（ΔＴ_ｇ／Δｔ）は、鍋Ｐの底板Ｂの温度推定精度をいっそう向上させるために、規定加熱時間（τ）経過後の複数の時点において測定および算出した温度（Ｔ_ｇ）およびその時間変化率（ΔＴ_ｇ／Δｔ）の平均値を用いることが好ましい。

Note that the temperature (T _g ) of the top plate 3 on the right side of the above equation and the rate of change over time (ΔT _g / Δt) are set to the specified heating time (in order to further improve the temperature estimation accuracy of the bottom plate B of the pan P ( It is preferable to use the average value of the temperature (T _g ) measured and calculated at a plurality of time points after τ) and the rate of change over time (ΔT _g / Δt).

Similarly, the induction heating cooker 1 preferably measures the temperature (T _g ) of the top plate 3 using a larger number of temperature sensors 30 (not shown in detail) in order to further improve the temperature estimation accuracy. . By using a larger number of temperature sensors 30, when a locally high temperature portion is detected, it is possible to achieve an appropriate temperature estimation by not using the measured value for the temperature estimation of the pan P. it can.

FIG. 6 is a circuit block diagram of the induction heating cooker 1 according to the first embodiment of the present invention. As described above, the induction heating cooker 1 includes a drive circuit (inverter circuit) 60 for supplying a high-frequency current to the heating coil 20 and a temperature sensor 30 such as a thermistor for measuring the temperature (T _g ) of the top plate 3. Then, a temperature estimation circuit 40 that obtains the interval (δ _a ) from the specified surface temperature (T _sh ), the specified heating time (τ), and the like, and estimates the surface temperature of the pan P from the measured temperature (T _g ) of the top plate 3 and the like. And have. Further, the induction heating cooker 1 is configured so that an appropriate high-frequency current is supplied to the heating coil 20 based on the “heating power” (supplied power (W)) set by the user with the setting device 70 such as the heating power adjustment dial 8. A control circuit 50 that controls the drive circuit 60 is included. The control circuit 50 according to the present invention receives information about the temperature (T _p ) of the pan P, which is precisely estimated with good followability as described above, from the temperature estimation circuit 40 so that a more accurate high-frequency current is supplied. The drive circuit 60 is controlled.

  The induction heating cooker 1 is preferably described in detail later, but when it is detected that the estimated temperature of the pan P is abnormally high, such as when the estimated temperature of the pan P reaches an abnormally high temperature, A warning device 80 such as a liquid crystal display unit 9 that displays a warning signal or a beeper that receives a warning signal from 80 and emits a warning sound for giving a warning to the user is provided.

  The operation of the induction heating cooker 1 according to the present invention will be described with reference to FIG. When the user places a heated object P such as a pan or a frying pan on the top plate 3 and the heating power is set by the setting device 70 such as the operation panel 7 and the heating power adjustment dial 8, the control circuit 50 responds accordingly. The drive circuit 60 is controlled to supply a high frequency current to the heating coil 20. When a high frequency current is supplied to the heating coil 20, a high frequency magnetic field is generated around the heating coil 20, an eddy current is generated in the bottom plate B of the pan P, and the pan P is heated by the Joule heat. The heat generated in the bottom plate B of the pan P by induction heating is transmitted from the pan P to the food F, and the food F is cooked.

On the other hand, the heat generated in the bottom plate B of the pan P is transmitted to the top plate 3 through the air layer A formed therebelow to raise the temperature of the top plate 3. The temperature sensor 30 provided below the top plate 3 continuously measures the temperature (T _g ) of the top plate 3 and transmits the measurement signal to the temperature estimation circuit 40.

Then, the temperature estimation circuit 40 calculates the time change rate (ΔT _g / Δt) of the temperature (T _g ) based on the measurement signal from the temperature sensor 30 as described above, and between the pan P and the top plate 3. The bottom plate temperature (T _p ) of the pan P is estimated using the calculated interval (δ _a ), and the signal is transmitted to the control circuit 50.

  The control circuit 50 calls a drive program (default value) stored in a memory (not shown) built in the control circuit 50 in accordance with the input signal set by the setting device 70, and based on this drive program A driving signal is transmitted to the driving circuit 60 and, if necessary, a warning signal is supplied to the warning device 80 to give a warning to the user.

  The drive circuit 60 drives a semiconductor switching element such as an IGBT by a drive signal from the control circuit 50, supplies an appropriate high-frequency current to the heating coil 20, and according to an input signal set by the setting device 70. Adjust the heating power to the pan P. The warning device 80 gives a warning to the user based on a warning signal from the control circuit 50.

  As described above, the control circuit 50 according to the present invention repeatedly monitors the setting signal from the setting device 70 and the measurement signal from the temperature sensor 30 in the above-described series of operations, so that the cooking state desired by the user is obtained. The drive circuit 60 can be controlled to maintain the above.

According to the prior art, as shown in the graph of FIG. 4, since the measured temperature (T _g ) of the top plate does not change responsively to the measured temperature of the pan P, the accurate temperature of the pan P can be detected in real time. The cooking state desired by the user cannot always be realized. For example, although the actual temperature of the pan P is sufficiently high and the food F is boiling, the pan P may be heated excessively to cause spillage.

However, according to the present invention, by using the time change rate (ΔT _g / Δt) of the actually measured temperature (T _g ) of the top plate as a new parameter, the responsiveness of the estimated temperature of the pan P is increased, and the actual pan Since it can be approximated and estimated by the temperature of P, the user can grasp the desired cooking state with good followability.

Further, as described in the evaluation experiment 2, the interval (δ _a ) is not always constant. However, according to the present invention, by introducing the concept of the specified surface temperature (T _sh ) and the specified heating time (τ), the top It is possible to calculate the interval (δ _a ) from the measured temperature (T _g ) of the plate 3 and its time change rate (ΔT _g / Δt), and the induction heating cooker 1 that can have an arbitrary interval (δ _a ) In, the actual temperature (T _b ) of the pan P can be accurately estimated.

  The top plate 3 is generally a translucent glass plate. However, when a contact temperature sensor such as a thermistor is used in the present invention, a non-translucent glass plate may be used. In addition, the temperature of the pan P can be accurately detected with good responsiveness. Therefore, according to the present invention, it is possible to improve the design by forming a non-translucent film (paint) on the surface of the top plate 3, and the top plate 3 can be colored glass material, resin material, ceramic. It is also possible to improve heat resistance and impact resistance by using a material or the like.

  In particular, resin materials and ceramic materials have excellent impact resistance and moldability, can suppress cracking (crushing) of the top plate 3, and have various shapes (concave shapes, convex shapes, curved shapes at corners). Etc.) and can be formed integrally with a frame member provided on the peripheral edge (not shown) of the top plate 3, or the frame member may be omitted. Therefore, the number of parts can be reduced, and the manufacturing cost can be reduced.

  Further, by producing the top plate 3 using a material having excellent moldability, moisture is generated when the food F is blown out on the surface of the top plate 3 to guide the proper placement position of the pan P or the food F. Concavities and convexities that constitute guides or flow paths for guiding the above can be easily formed. Furthermore, by forming Braille on the top plate 3, it is possible to provide the induction heating cooker 1 that is easy to use even for visually impaired persons.

  The foodstuff accommodated in to-be-heated bodies P, such as a pot here, means foodstuffs, such as water, soup stock, oil, vegetables, meat, and fish. Moreover, the to-be-heated body P means what accommodates the said foodstuffs, such as a pan, a frying pan, a kettle which can be heated by induction heating.

  The setting device 70 refers to the operation state of the induction heating cooker 1 such as an ON / OFF switch of a power source, a cooking mode, a thermal power mode, or a pan temperature selection switch in addition to the operation panel 7 and the thermal power adjustment dial 8 described above. This means that a signal for setting is input to the control circuit 50.

For example, when the cooking mode is selected and input from a number of menus stored in advance in the memory of the control circuit 50 using the cooking mode selection switch, the pan P estimated by the temperature estimation circuit 40 according to the present invention is used. On the basis of the temperature (T _p ), the heating power may be adjusted according to the cooking program of the rice cooking mode stored in the memory. Also, select the fried food cooking mode with the cooking mode selection switch, set the pan temperature to “180” ° C. using the pan temperature selection switch, and adjust the heating power so that the oil temperature is kept constant. You can also.

  The induction heating cooker 1 also has a communication device (communication cable, infrared sensor, etc.) that enables communication with a slot that accepts an electronic storage medium (SD card, USB) or an external PC or mobile phone as the setting device 70. ) May be included.

  The warning device 80 is a warning when the safety standard is deviated by using sounds such as synthetic voice, beep sound, melody, etc. in addition to the liquid crystal display unit 9 or using light such as lighting / flashing of light. Or something that informs the user of the cooking status. Moreover, you may make it display the temperature of the actual pan P in the liquid crystal display part 9 in real time so that it can compare with the temperature of the pan P set with the setting apparatus 70 by the user. Further, the progress of cooking may be displayed on the liquid crystal display unit 9.

  As the temperature sensor 30 according to the present invention, in addition to the thermistor (which estimates the temperature by utilizing the characteristic that the electrical resistance of the semiconductor changes depending on the temperature), any sensor can be used as long as it can measure the temperature of the top plate 3 ( Contact temperature sensors and optical temperature sensors) can be used. A contact-type temperature sensor uses, for example, a thermocouple (a weak thermoelectromotive force generated according to the temperature difference between the two ends when a temperature is applied to the joint with a temperature sensor in which one end of two types of metal wires having different properties is joined. Temperature sensor), resistance thermometer (if the material is metal, the temperature is estimated using the property that the electrical resistance increases in proportion to the temperature), radiation thermometer (the object radiates) Infrared energy is received by an infrared sensor, and the temperature is estimated by performing reference temperature correction, emissivity correction, and the like. When the temperature of the pan P is measured using a radiation thermometer of an optical temperature sensor, a film (painting or the like) that suppresses transmission of infrared light may be formed on the lower surface of the top plate 3.

Embodiment 2. FIG.
In addition to FIG. 5, Embodiment 2 of the induction heating cooking appliance which concerns on this invention is demonstrated in detail below, referring FIG. 6 and FIG. In the first embodiment, the specified surface temperature (T _sh ) and the specified heating time (τ) depend on the electric power (W) supplied to the heating coil 20, and therefore can be set in advance for each induction heating cooker. Although described, in the second embodiment, a method for determining the specified surface temperature (T _sh ) according to the supplied power (W) will be described below.

In the induction heating cooker 1 according to the first embodiment, the estimated temperature (T _p ) of the pan P is approximately constant at about 140 ° C. after about 130 seconds from the start of heating, and similarly The measured temperature (T _f ) of the food F (water) in the pan P is also maintained at the boiling point (about 100 ° C.). This is because the food F (water) in the pan P is in a saturated boiling state, and the power supplied from the heating coil 20 (heat amount) and the amount of heat (including heat of vaporization) released by the food F (water) are balanced, This means that the heat transfer coefficient h and the degree of superheat (ΔT _bf ) on the right side are constant with respect to the specified heating amount Q ₀ (constant) on the left side of the above equation [Equation 4].

On the other hand, as described above, the temperature (T _p ) of the pan P in the boiling state is generally determined by the surface properties of the bottom plate B of the pan P, the physical properties of the food F, and the power supplied to the heating coil 20 ( Mainly depends on W). On the other hand, commercially available pans P are formed using a magnetic material (or a cocoon material coated thereon), and the thickness of these magnetic materials and cocoon materials varies, and further, laminated materials, adhesive materials, etc. A number of additional coatings are provided, and the surface texture of the bottom plate B varies greatly depending on the bottom plate B of the pan P. However, most pans P are designed so that the surface properties of the bottom plate B in contact with the food F (water) optimize the heat transfer coefficient h. In the present invention, the temperature (T _p ) of the pan P can be estimated only when cooking the food F containing water or oil in the pan P.

In order to simplify the explanation, when considering the case where the food material F is water, the boiling point of water is about 100 ° C., although the boiling point of water may slightly increase due to seasonings, salt, or the like. At this time, in the evaluation experiment 2 shown in FIG. 5, the power supplied (W) to the heating coil 20 was 3000 W, and the degree of superheat (ΔT _bf ) was about 40 ° C.

The degree of superheat (ΔT _bf ) when the amount of heat Q is added to the pan P in order to boil the water is the amount of heat Q ₀ (specified heating amount Q ₀ ) required to bring the water to saturation boiling. It is known that it can be estimated by the following equation using the degree of superheat (ΔT _bf0 ).

ここで指数（ｎ）は０．５〜０．９であり、好適には０．６〜０．８である。すなわち、各誘導加熱調理器１において、加熱コイル２０への供給電力（Ｗ）を変化させて、過熱度（ΔＴ_ｂｆ）を事前に測定し、温度推定回路４０のメモリ内に記憶しておいてもよい。たとえば飽和沸騰させるために必要な熱量Ｑ_０（規定加熱量Ｑ_０）が３０００Ｗで、上記指数（ｎ）が０．７で、過熱度（ΔＴ_ｂｆ０）が４０℃および３０℃である誘導加熱調理器について、鍋Ｐに加えた熱量Ｑに対する過熱度（ΔＴ_ｂｆ）は、上式［数７］に基づき、下表のように算出される。

Here, the index (n) is 0.5 to 0.9, preferably 0.6 to 0.8. That is, in each induction heating cooker 1, the power (W) supplied to the heating coil 20 is changed, and the degree of superheat (ΔT _bf ) is measured in advance and stored in the memory of the temperature estimation circuit 40. Also good. For example, induction heating cooking in which the amount of heat Q ₀ (stipulated heating amount Q ₀ ) required for saturation boiling is 3000 W, the index (n) is 0.7, and the degree of superheat (ΔT _bf0 ) is 40 ° C. and 30 ° C. The degree of superheat (ΔT _bf ) with respect to the amount of heat Q applied to the pan P is calculated as shown in the table below based on the above equation [Equation 7].

Therefore, in the evaluation experiment 2, the specified surface temperature (T _sh ) when the power supplied to the heating coil 20 (W = heating amount Q) is 3000 W and the degree of superheat (ΔT _bf0 ) is 40 ° C. is 120 ° C. Set. However, since the superheat degree (ΔT _bf ) when the power supplied (W) to the heating coil 20 is 1000 W is 18.5 ° C., the bottom plate temperature of the pan P is 118.5 ° C. even in the saturated boiling state. However, it is not appropriate to estimate the bottom plate temperature (T _p ) of the pan P as described above while maintaining the specified surface temperature (T _sh ) at 120 ° C. That is, the “specified surface temperature (T _sh )” needs to be corrected to a different value depending on the power supplied to the heating coil 20 (W = heating amount Q).

Therefore, for example, the ratio between the degree of superheat (ΔT _bf0 ) where the supplied power (W ₀ = heating amount Q ₀ ) is 3000 W and the degree of superheat (ΔT _bf ) when arbitrary power (W = heating amount Q) is supplied is The specified surface so that the ratio of the specified surface temperature (T _sh ) when supplied power (W ₀ ) is supplied and the specified surface temperature (T _sh ′) when supplied with arbitrary power (W) is the same. The temperature (T _sh ') may be calculated.

すなわち本願発明に係る温度推定回路４０は、加熱コイルに供給される加熱電力（Ｗ）に応じて、上式［数８］および［数９］を用いて、規定表面温度（Ｔ_ｓｈ）を補正することができる。 Alternatively, in order to simplify the complicated calculation process as described above in the temperature estimation circuit 40, the specified surface temperature (T _sh ') with respect to the power supplied to the heating coil 20 (W = heating amount Q) is set. The specified surface temperature (T _sh ′) may be calculated using the following equation based on the specified surface temperature (T _sh ) with the supplied power (W) set to 3000 W. The following equation is an approximate equation obtained empirically, but agrees with the result obtained by the above equation [Equation 8].

That is, the temperature estimation circuit 40 according to the present invention corrects the specified surface temperature (T _sh ) using the above equations [Equation 8] and [Equation 9] according to the heating power (W) supplied to the heating coil. can do.

As described above, the accuracy of estimating the temperature (T _p ) of the bottom plate B of the pan P can be improved by setting the specified surface temperature (T _sh ′) so as to depend on the supplied power (W). That is, according to the induction heating cooker 1 according to the present invention, based on the surface temperature of the pan P accurately and accurately estimated by the temperature estimation circuit 40, the control circuit 50 has various abnormal modes (ignition, smoke, (Sudden boiling, spilling, scorching, scorching, etc.) can be detected, and the drive circuit 60 can be brought to an emergency stop or reduced in thermal power (including stepwise reduction), so that safety during cooking can be improved. Further, the control circuit 50 according to the present invention controls the drive circuit 60 so as to adjust the temperature of the pan P to a temperature desired by the user based on the “thermal power” set by the user using the setting device 70 such as the thermal power adjustment dial 8. Can be controlled.

Of the above abnormal modes, with regard to the ignition of oil, for example, when fried food is cooked, if the temperature of the pan P rises to an arbitrary temperature or higher, the oil will ignite, but particularly when the amount of oil is small, the temperature is likely to rise and easily ignite. . Accordingly, when the temperature change rate (ΔT _g / Δt) of the temperature (T _g ) of the top plate 3 or the temperature (T _g ) of the top plate 3 obtained by the temperature estimation circuit 40 at this time exceeds a predetermined threshold value, The control circuit 50 determines that there is a possibility that the oil will ignite, and causes the drive circuit 60 to perform an emergency stop.

Regarding the occurrence of scorching, which is another abnormal mode, when scorching occurs, a film made of carbide of food F is formed on the bottom plate B of the pan P, heat is not easily transmitted to the food F, and the temperature of the pan P gradually rises. To do. When the estimated temperature of the pan P becomes higher than a predetermined temperature, or when the temperature continues to rise, the control circuit 50 stops or suppresses power feeding to the heating coil 20. For example, when the food F containing moisture reaches 100 ° C. or higher, the moisture in the food F boils and flows out of the food F, so that scorching is likely to occur. Therefore, the induction heating cooker 1 according to the present invention estimates the temperature (T _p ) of the bottom plate B of the pan P, supplies power to the heating coil 20 (W = heating amount Q), and superheat degree (ΔT _bf). ) And the like, it is preferable that the temperature of the food material F is controlled to be kept at 100 ° C. or lower so as to suppress scorching. That is, the control circuit 50 according to the present invention includes a heating coil so as to maintain the temperature of the food F at 100 ° C. or less according to the estimated temperature (T _p ) of the bottom plate B of the pan P and the degree of superheat (ΔT _bf ). By adjusting the heating power (W) to be supplied to the heater, it is prevented from being burnt.

  As another abnormal mode, a bumping phenomenon may occur, although rarely. The bumping phenomenon is, for example, when boiling water, even if the water exceeds the boiling point (100 ° C.), it does not boil, is overheated above the boiling point, and explosively boils due to some external impact, and the food F moves from the pan P It is a phenomenon in which the temperature of the food material F (water) is suddenly released and suddenly drops. This is a very dangerous phenomenon because the hot food F suddenly blows up from the pan P.

  FIGS. 7 and 8 show the temperature of water and the bottom plate B of the pan P when water in the pan P is heated with a supply power (thermal power) of 1500 W, when normal boiling occurs and when a bumping phenomenon occurs. It is the graph which plotted the time transition of. When normal boiling occurs (FIG. 7), the temperature of the bottom plate B of the pan P rises until it reaches about 120 ° C., and is maintained almost constant, and the water in the pan P is continuously evaporated and vaporized. Since the heat is taken away, the temperature does not exceed the boiling point. In contrast, when the temperature of the bottom plate B of the pan P exceeds 120 ° C. and reaches 140 ° C., the water in the pan P exceeds the boiling point, a bumping phenomenon occurs, and the temperature of the water and the bottom plate B of the pan P suddenly increases. (FIG. 8).

  Thus, before the bumping phenomenon occurs, as apparent from FIG. 8, the temperature of the bottom plate B of the pan P exceeds the temperature that should be maintained during normal boiling. If this state continues for a predetermined time (for example, 100 seconds) or more, the control circuit 50 determines that a bumping phenomenon may occur, and the power (W) supplied to the heating coil 20 It is possible to prevent the occurrence of bumping by controlling the drive circuit 60 so as to reduce or stop the above.

  Moreover, according to the induction heating cooker 1 which concerns on this invention, when the said abnormal mode is detected, a warning can be given to a user using the said warning device 80. FIG. This is particularly useful when the user leaves the induction heating cooker 1.

  For example, when the above abnormal mode is detected, the control circuit 50 controls various warning devices 80, emits a beep, outputs a synthesized voice, lights or flashes a warning lamp, or displays a warning on the liquid crystal display unit 9. Can be made. Thereby, when the abnormal mode is detected, the control circuit 50 promptly notifies the user to call attention and stop or suppress the power supply to the heating coil 20 to realize higher safety. Can do.

  Furthermore, according to the induction heating cooker 1 according to the present invention, the control circuit 50 controls the temperature of the pan P set by the heating power adjustment dial 8 or the like and the temperature of the pan P precisely estimated by the above equation [Equation 3]. Then, the drive circuit 60 can be controlled to heat with the optimum heating power. Moreover, since the actual temperature can be displayed in real time on the liquid crystal display unit 9 instead of the temperature of the pan P set as in the prior art, the thermal power adjustment suitable for the cooking method desired by the user is realized. And it can help you complete delicious dishes more easily.

  For example, if you want to cook thoroughly in cooking fried foods, set the temperature of the pan P set with the heating power adjustment dial 8 etc. to 160 ° C, and if you want to fry the surface, adjust it to 200 ° C to make milk or tea When heating etc., after making it boil once, it adjusts so that it may become about 70-90 degreeC. During stewed cooking, the stewed ingredients are adjusted to be maintained at 60 ° C., and when miso soup is heated, the temperature is adjusted so as not to boil. Thus, the user can set a temperature suitable for each cooking method, and does not need to adjust the heating power depending on the conventional user's feeling, and can cook delicious dishes. In the past, the heating power had to be adjusted based on the content of the food F contained in the pan P. However, since the temperature of the pan P can be estimated accurately and the heating power can be adjusted based on this, It is not necessary to adjust the heating power according to the content, and cooking can be performed more easily.

  In addition, when cooking eggs, fried eggs, hamburgers, crepes, dumplings, etc., when the ingredients are put into the preheated frying pan P, the temperature of the frying pan P is set in advance, thereby preventing airing that reaches an abnormal temperature. The frying pan P can be maintained at an appropriate and safe preheating temperature.

  Furthermore, the temperature of the pan P can be accurately estimated even when cooking a stewed dish such as oden, or when heated and kept at a low temperature such as hot salmon or milk, so that it can be reliably set to a desired temperature.

  The induction heating cooker 1 is provided with a menu selection device (not shown) that allows a specific menu such as rice cooking to be selected, and controls a cooking program in which cooking time and heating power are set for the selected menu. You may memorize | store in 50 built-in memories, and control a cooking time and a thermal power automatically according to this cooking program ("automatic cooking" is performed).

In the first and second embodiments, when the bottom plate temperature (T _p ) of the pan P is estimated, the temperature of the pan P is based on the temperature (T _g ) of the top plate 3 measured by the temperature sensor 30. The temperature (T _g ) of the top plate 3 is calculated by the equation [Equation 3]. The temperature (T _air ) of the cooling air that cools the top plate 3, the temperature (T _c ) of the heating coil 20, and the temperature sensor Also affected by the thermal contact resistance between 30 and the top plate 3.

That is, it is preferable to measure the temperature (T _air ) of the cooling air using a temperature sensor (not shown) provided separately. When the top plate 3 is sufficiently cooled, the temperature (T _g ) measured by the temperature sensor 30 is lowered, and the estimated temperature (T _p ) of the bottom plate B calculated based on this is expressed by the above equation [Equation 3]. It will be lower than the temperature calculated in. Therefore, in consideration of a decrease in the temperature (T _g ) of the top plate 3 due to the effect of the cooling _air , a correction term depending on the temperature (T _g ) of the top plate 3 and the temperature (T _air ) of the cooling air as shown in the following equation. (For example, the function F (T _g , T _air )> 0) may be added to the above equation [Equation 3], and the temperature estimation circuit 40 may estimate the estimated temperature (T _p ) of the bottom plate B.

Similarly, it is preferable to measure the temperature (T _c ) of the heating coil 20 using a temperature sensor (not shown) provided separately. The higher the temperature (T _c ) of the heating coil 20 is, the higher the temperature (T _g ) measured by the temperature sensor 30 is, and the estimated temperature (T _p ) of the bottom plate B calculated based on the temperature (T _g ) It becomes higher than the temperature calculated in 3]. Therefore, in consideration of the effect due to the temperature (T _c ) rise of the heating coil 20, a correction term (for example, depending on the temperature (T _g ) of the top plate 3 and the temperature (T _c ) of the heating coil 20 as in the following equation (for example, The temperature estimation circuit 40 may estimate the estimated temperature (T _p ) of the bottom plate B by adding the function G (T _g , T _c )> 0) to the above equation [Equation 3].

1: induction heating cooker, 2: housing, 3: top plate, 4: IH heating unit, 5: radiant heating unit, 6: grill unit, 7: operation panel, 8: heating power adjustment dial, 9: liquid crystal display unit ,
20: heating coil, 30: temperature sensor, 40: temperature estimation circuit, 50: control circuit, 60: drive circuit, 70: setting device, 80: warning device,
P: heated body (pot, frying pan), B: bottom plate of heated body, A: air layer.

Claims (14)

A top plate on which the object to be heated is placed;
A heating coil disposed under the top plate for induction heating the object to be heated;
A drive circuit for supplying a high-frequency current to the heating coil;
A temperature sensor disposed below the top plate for detecting the temperature (T _g ) of the top plate;
a) A specified surface temperature (T _sh ) of the heated body when the rate of temperature increase of the heated body is equal to or less than a predetermined threshold, and a regulation until the heated body reaches a specified surface temperature (T _sh ) A memory for storing the relationship of the heating time (τ);
b) The specified surface temperature (T _sh ) at the specified heating time (τ) in the memory, the temperature (T _g ) of the top plate when the specified heating time (τ) has elapsed, and the rate of change with time ( A temperature estimation circuit that estimates a surface temperature (T _p ) of the object to be heated based on (ΔT _g / Δt);
An induction heating cooker, comprising: a control circuit that controls the drive circuit using the estimated temperature (T _p ) estimated by the temperature estimation circuit. The induction heating cooker according to claim 1, wherein the temperature estimation circuit estimates a surface temperature (T _p ) of the object to be heated by the following equation.

T _p : Heated object estimated temperature estimated by the temperature estimation circuit T _g : Top plate temperature detected by the temperature sensor t: Time from heating start τ: Specified heating time T _sh : Object to be heated in specified heating time Specified surface temperature T _{g, t = τ} : temperature of top plate when specified heating time has elapsed (ΔT _g / Δt) _{t = τ} :
Time rate of change in temperature of the top plate when the specified heating time has elapsed (ΔT _g / Δt):
Time change rate of the temperature of the top plate when the specified time after the specified heating time has elapsed The temperature estimation circuit includes:
The distance (δ _a ) between the object to be heated and the top plate is defined as the temperature (T _g ) of the top plate when the specified heating time (τ) elapses and the rate of change with time (ΔT _g / Δt). ), And the specified surface temperature (T _sh ),
Based on said distance (δ _a), the induction heating cooker according to claim 1 for estimating the surface temperature of the heated body (T _p). The induction heating cooker according to claim 3, wherein the temperature estimation circuit estimates a surface temperature (T _p ) of the object to be heated by the following equation.

T _p : heated object estimated temperature estimated by the temperature estimation circuit T _g : temperature of the top plate detected by the temperature sensor δ _a : distance between the heated object and the top plate ρ _g : top plate density c _g : Specific heat of the top plate δ _g : Top plate thickness λ _a : Thermal conductivity of air t: Time from the start of heating τ: Specified heating time T _sh : Specified surface temperature T _{g of the} object to be heated at the specified heating time _{t = τ} : Temperature of the top plate when the specified heating time has elapsed (ΔT _g / Δt) _{t = τ} :
Time rate of change in temperature of the top plate when the specified heating time has elapsed (ΔT _g / Δt):
Time change rate of the temperature of the top plate when the specified time after the specified heating time has elapsed   The induction heating cooker according to claim 2 or 4, wherein the specified heating time (τ) is set between 30 seconds and 90 seconds. At a plurality of time points after the elapse of the specified heating time (τ), the temperature (T _g ) of the top plate is detected, and the time change rate (ΔT _g / Δt) is calculated,
The temperature estimation circuit estimates the surface temperature (T _p ) of the object to be heated by using an average value of these temperatures (T _g ) and time change rates (ΔT _g / Δt). Or the induction heating cooking appliance of 4. Compare the temperature (T _g ) of the top plate after the start of heating with the specified surface temperature (T _sh ),
i) When the measured temperature (T _g ) of the top plate after the start of heating is higher than the specified surface temperature (T _sh ) (T _g −T _sh > 0), and when the measured temperature (T _{g of the} top plate after the start of heating) _g ) and the specified surface temperature (T _sh ) are smaller than a predetermined temperature difference (T _X ) (T _sh −T _g > T _X > 0), the interval (δ _a ) is not estimated,
ii) When the temperature (T _g ) of the top plate after the start of heating is larger than the specified surface temperature (T _sh ) and the temperature difference is equal to or higher than a predetermined temperature (T _sh −T _g > T _X > 0) The induction heating cooker according to claim 4, wherein the interval (δ _a ) is estimated. The induction heating cooker according to claim 2 or 4, wherein the temperature estimation circuit corrects the specified surface temperature (T _sh ) according to the heating power (W). The temperature estimation circuit determines the temperature of the food according to the estimated temperature (T _p ) of the heated object and the degree of superheat (ΔT _bf ) corresponding to the temperature difference between the heated object and the food contained in the heated object. The induction heating cooker according to claim 8, wherein the heating power (W) supplied to the heating coil is adjusted so as to maintain the temperature at 100 ° C. or lower. In the control circuit, the estimated temperature (T _p ) of the heated object exceeds the temperature obtained by adding the degree of superheat (ΔT _bf ) corresponding to the temperature difference between the boiling point of the food and the food contained in the heated object, The drive circuit is controlled so as to suppress or stop the high-frequency current supplied to the heating coil by determining that a bumping phenomenon occurs when the state continues for a predetermined period or longer. Induction heating cooker. A top plate on which the object to be heated is placed;
A heating coil disposed under the top plate for induction heating the object to be heated;
A drive circuit for supplying a high-frequency current to the heating coil;
A control method of an induction heating cooker that is provided below the top plate and includes a temperature sensor that detects a temperature (T _g ) of the top plate, the control method comprising:
a) A specified surface temperature (T _sh ) of the heated body when the rate of temperature increase of the heated body is equal to or less than a predetermined threshold, and a regulation until the heated body reaches a specified surface temperature (T _sh ) Storing the relationship of the heating time (τ);
b) The specified surface temperature (T _sh ) at the stored specified heating time (τ), the temperature (T _g ) of the top plate when the specified heating time (τ) elapses, and the rate of change over time (ΔT) _g / Δt) to estimate the surface temperature (T _p ) of the heated object,
And a step of controlling the drive circuit using the estimated temperature (T _p ) estimated. The control method according to claim 11, wherein the step of estimating the surface temperature (T _p ) of the object to be heated estimates the surface temperature (T _p ) of the object to be heated by the following equation.

T _p : Heated object estimated temperature estimated by the temperature estimation circuit T _g : Top plate temperature detected by the temperature sensor t: Time from heating start τ: Specified heating time T _sh : Object to be heated in specified heating time Specified surface temperature T _{g, t = τ} : temperature of top plate when specified heating time has elapsed (ΔT _g / Δt) _{t = τ} :
Time rate of change in temperature of the top plate when the specified heating time has elapsed (ΔT _g / Δt):
Time change rate of the temperature of the top plate when the specified time after the specified heating time has elapsed The step of estimating the surface temperature (T _p ) of the object to be heated includes
The distance (δ _a ) between the object to be heated and the top plate is defined as the temperature (T _g ) of the top plate when the specified heating time (τ) elapses and the rate of change with time (ΔT _g / Δt). ), And the specified surface temperature (T _sh ),
The control method according to claim 11, wherein a surface temperature (T _p ) of the heated object is estimated based on the interval (δ _a ). The control method according to claim 13, wherein the step of estimating the surface temperature (T _p ) of the object to be heated estimates the surface temperature (T _p ) of the object to be heated by the following equation.

T _p : heated object estimated temperature estimated by the temperature estimation circuit T _g : temperature of the top plate detected by the temperature sensor δ _a : distance between the heated object and the top plate ρ _g : top plate density c _g : Specific heat of the top plate δ _g : Top plate thickness λ _a : Thermal conductivity of air t: Time from the start of heating τ: Specified heating time T _sh : Specified surface temperature T _{g of the} object to be heated at the specified heating time _{t = τ} : Temperature of the top plate when the specified heating time has elapsed (ΔT _g / Δt) _{t = τ} :
Time rate of change in temperature of the top plate when the specified heating time has elapsed (ΔT _g / Δt):
Time change rate of the temperature of the top plate when the specified time after the specified heating time has elapsed

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