JPS59219890A - Electromagnetic cooking device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an electromagnetic cooker that heats and cooks food by heating an object to be heated, such as a pan, by electromagnetic induction, and particularly,
The present invention relates to an electromagnetic cooker that accurately detects the temperature of an object to be heated and controls the temperature of the object.

[Technical background of the invention]

2. Description of the Related Art As a conventional electromagnetic cooker, for example, those shown in FIGS. 1 to 3 are known.

FIG. 1 is an external view of an electromagnetic cooker, showing the cooker main body 1 which houses electric circuit parts and the like shown in FIG.

It includes a top plate λ on which a heated object A made of a metal conductor is placed. Here, the top plate is made of, for example, heat-resistant crystallized glass.

As shown in FIG. 2, a heating coil 3 is disposed below the top plate.

The circuit that supplies coil current to the heating coil 3 is comprised of a rectifier circuit S that converts a commercial power source into direct current, and an inverter circuit that converts this direct current into high-frequency current. The inverter circuit section is composed of a transistor connected in series to the heating coil 3, a resonant capacitor, a diode, etc. connected in parallel to the transistor, and inputs a control signal given from the control circuit 7 via the driver g, The current is converted into a high-frequency current with a predetermined frequency and applied to the heating coil 3, and the heating coil 3 generates a high-frequency magnetic field to heat the object A. Here, the control circuit 7 is composed of a sawtooth wave generation circuit, a pulse width modulation circuit, etc., and supplies a control signal with a predetermined pulse width to the inverter circuit B via the driver g.

In addition, a temperature detection element IO consisting of a thermistor or the like is arranged on the back surface of the top plate (see Fig. 3), which detects the temperature of the heated object A conducted through the top plate and responds accordingly. outputs an electrical signal. This electric signal is given to the control circuit 7 via the temperature detection circuit //,
The output pulse width of the control circuit 7 is changed.

Figure 1 is a circuit diagram of the control circuit 70. This control circuit 7 is composed of a comparator 20, a variable resistor for setting a reference voltage connected to this input terminal, a temperature detection element /θ, and the like. At that point, the temperature of the heated object A rises and the temperature detector I
When the output signal of O becomes large and exceeds the reference voltage set by the variable resistor 2/, a signal corresponding to this deviation is outputted from the comparator 20 and given to the control circuit 7. Then, the threshold level of the control circuit 7 rises and the output pulse width becomes narrower, thereby reducing the coil current and suppressing the temperature rise of the object to be heated to a predetermined value. Here, it is also possible to configure the circuit so that the coil current is cut off when the heated object A rises to a set temperature.

[Problems with the Background Art] However, in this type of electromagnetic cooker, the temperature of the object to be heated, which is conducted through the top plate 2, is detected by the temperature detection element 10, and the temperature is detected based on this detection signal. Since temperature control is performed, the temperature detection of the heated object A is affected by the temperature state, heat capacity, etc. of the heated object A, resulting in poor detection accuracy. For example, if the top plate is at a high temperature, there is a risk that the control circuit 7 will operate and the coil current will be suppressed to a low level below the set value even if the heated object A has not risen to the set temperature. Ta.

[Summary of the invention]

The present invention has been made in order to eliminate the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide an electromagnetic cooker with high accuracy in detecting the temperature of a heated object and controlling the temperature based on the detected temperature.

[Summary of the invention]

In order to achieve this object, the present invention provides a temperature sensor that includes a detection coil that generates a magnetic field, and changes in the temperature of a heated object in a magnetic circuit formed by the detection coil and the heated object. The temperature sensor is arranged to be magnetically shielded from the alternating magnetic field generated by the heating coil, and the temperature sensor is configured to extract the magnetic resistance change caused by the heating coil as an electric signal. The coil current supplied to the heating coil is controlled.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings. Note that the same elements as in FIGS. 1 to 3 are given the same reference numerals.

FIG. S is a partial sectional view of the electromagnetic cooker according to this embodiment. In the figure, 3θ is a temperature detector that detects the temperature of the heated object A, and this temperature detector 30 has a coil 32 connected to the iron core 3/.
It is attached to the back surface of the top plate via a heat insulating material 33, and is shielded from the alternating magnetic field generated by the heating coil 30 by a magnetic shield plate 3t/. Then, the temperature detector 3θ and the object to be heated A form a magnetic circuit. The magnetic resistance R of this magnetic circuit is expressed by the following equation.

However, μ = “0/μs μ0; Vacuum permeability μ8; 80% magnetic permeability of the heated object l; Length of the magnetic circuit B; Cross-sectional area of the magnetic circuit In the above equation, l and S are Since it remains constant unless it changes, the magnetic resistance R changes in proportion to the relative magnetic permeability μ8.Also, the relative magnetic permeability μ changes depending on the temperature, so if the temperature of the heated object A changes, the magnetic resistance R changes. Therefore, if an alternating current or the like is passed through the detection coil 3.2, and the detection coil 32 detects the change in magnetic resistance of the heated object A and extracts it as an electrical signal, the This means that temperature changes can be detected.
In the figure, the cross-sectional material 33 is provided for the temperature sensor 30.
The reason why the magnetic shield plate 3t is provided is to prevent the temperature sensor 30 from being affected by the magnetic field from the alternating magnetic field of the heating coil 3.

FIG. 6 shows a temperature detection circuit f/ using the temperature detector 30.
An example of the circuit configuration is shown. In this temperature detection circuit, the resistor '12. A current voltage of 1N is applied to the temperature detector 30 through the resistor 30, and the voltage across the resistor 30 is converted into a DC voltage by the bridge rectifier U, smoothed by the capacitor 4'J-, and then the voltage divided by the voltage dividing resistor 4' A.Give '77. Then, the voltage across the voltage dividing resistor 770 is applied to the input terminal of the differential amplifier qg, and the reference voltage set by the variable resistor q9 is applied to the input terminal of the differential amplifier /Ig.

In the temperature detection circuit ll/ constructed in this way, the (+) side voltage 2 of the capacitor frame . is expressed by the following formula.

V(1'''IN xR+R) However, the resistance value of R1; resistance q. Therefore, when the heated object A is heated by the alternating magnetic field of the heating coil 3 and the magnetic resistance R changes, the voltage vo changes. Therefore, the (+) side potential of voltage dividing resistor q7 changes,
The deviation between this (+) side potential and the reference voltage is amplified by the differential amplifier lIg and provided to the control circuit 7. Then, the control circuit 7 outputs a control signal with a pulse width that suppresses the input voltage, and supplies it to the inverter group via the driver g. Therefore, the coil current is controlled and the temperature of the heated object A is maintained at the set value. For example, if the set temperature of the heated object is 90°C, the heated object A is set by the heating coil 3.
When the temperature rises from 0°C and reaches qo°C, an output signal is output from the differential amplifier yg, the control circuit 7 is activated, the on time of the inverter base is shortened, the coil current is reduced, and the The heating temperature of heating object A is maintained at 90°C.

Note that it is also possible to configure the circuit so that the coil current is cut off when the heated object A reaches the set temperature wqo''C.Also, in FIG. 6 above, the temperature detection circuit q/
may be configured by a microcomputer consisting of a CPU or the like.

In the above embodiment, since the temperature detector 30 directly detects the temperature of the heated object from the change in magnetic resistance R, the temperature of the heated object is not affected by the ambient temperature, for example, the temperature of the top plate. Since the temperature of object A can be detected with high accuracy and the coil current is controlled based on this detection signal, the accuracy of temperature control is significantly improved.

〔Effect of the invention〕

As explained above, according to the present invention, the temperature of the object to be heated is detected from the change in magnetic resistance using the temperature detector, so that the temperature of the object to be heated can be detected without being affected by the surrounding temperature of the top plate, etc. The temperature of the object to be heated can be accurately detected, and the temperature of the object to be heated can be accurately controlled based on this detection signal.

[Brief explanation of the drawing]

2i! Figure 1 is an external view of a conventional electromagnetic cooker, Figure 1 is a sectional view showing the main parts of an electromagnetic cooker according to an embodiment, and Figure 2 is an electric circuit diagram of Figure 5. /...Cooker body, λ...Top plate, 3...
・Heating coil, 6... Inverter circuit, 7... Control circuit, 30... Temperature detector, 3/... Iron core, 32...
...Detection coil, 33...Insulating material, 3G...Magnetic shield plate, Kuha...Temperature detection circuit. Applicant's agent Kiyoshi Inomata

Claims (1)

[Claims] (11) An electromagnetic cooker in which an object to be heated made of a metal conductor is placed in an alternating magnetic field generated in a heating coil by an alternating current, and the object to be heated is heated by the alternating magnetic field. A magnetic circuit is provided with a detection coil that generates a magnetic field, and a change in magnetic resistance due to a temperature change of the object to be heated in a magnetic circuit formed by the detection coil and the object to be heated is detected by electricity from the detection coil. An electromagnetic cooking device in which a temperature sensor for the object to be heated, which is taken out as a signal, is arranged to be magnetically shielded from the alternating magnetic field, and the alternating current is controlled based on the output signal of the temperature sensor.