JPS61188876A - Electromagnetic cooker - 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] [Field of Industrial Application] The present invention relates to an electromagnetic cooker that is provided with a heating coil that generates magnetic flux for induction heating the pot under a top plate for placing the pot. .

[Prior art]

FIG. 4 shows a conventional example of this type of electromagnetic cooker.

This electromagnetic cooker includes a top plate 2 on which a pot 1 is placed, a heating coil 3 that generates magnetic flux for induction heating the pot 1, and a coil holding stand 4 for holding the heating coil 3. The temperature rise of the top plate 2 is detected by a heat sensitive element 5 such as a thermistor or thermostat attached to the coil holding base 4, and when the temperature reaches a specified value, the operation of the electromagnetic cooker is automatically stopped. This structure is extremely effective in preventing the temperature of the pot 1 from becoming abnormally high.

By the way, the heating coil 3 that inductively heats the w41 generally has a heat resistance limit of 180°C, and if it is left in an overheated state, the insulator covering the coil will thermally deteriorate, causing premature damage. The electromagnetic cooker will be damaged. Therefore, preventing the heating coil 3 from overheating is an essential element for improving the durability of the electromagnetic cooker.

However, in order to prevent the heating coil 3 from overheating, using a heat-sensitive element such as a thermistor or thermostat as seen in the configuration for overheating prevention of the pot l in the conventional example, it is difficult to prevent the radiant heat from the pot l and the heating coil. Since the coil temperature is indirectly detected from the correlation with the temperature of No. 3, the temperature of the coil itself cannot be accurately detected, and the overheating prevention effect cannot be sufficiently exerted.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned problems in the conventional example, and accurately detects the overheating state of the heating coil to prevent thermal deterioration of the coil insulation due to overheating, thereby improving durability. The object of the present invention is to provide an electromagnetic cooker that is improved.

[Structure of the invention]

The electromagnetic cooker of the present invention includes a heating coil that is provided below a top plate for placing a pot and generates magnetic flux for inductively heating the pot, and a heating coil that is magnetically coupled to the heating coil and has a heat resistance limit temperature of the heating coil. A ferrite member whose vicinity has a Curie point, a detection coil that is magnetically coupled to this ferrite member and detects changes in the magnetic properties of the ferrite member as changes in induced voltage, and a detection signal from this detection coil that is processed by logical operations. The device is characterized by comprising a logic circuit.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 3.

FIG. 1 is a vertical cross-sectional view showing the main parts of the electromagnetic cooker of this embodiment, in which a magnetic flux for induction heating of the pot 6 is generated at a lower position of the top plate 7 on which the pot 6 is placed. A heating coil 8 is provided for this purpose. This heating coil 8 is held by a coil holding stand 9, and a rod-shaped ferrite member 10 formed by solidifying ferrite powder is disposed in the center of the coil holding stand 9, and the heating coil 8 is wound around this ferrite member 10. It's being passed around. Therefore, the top plate 7, the coil holding base 9, and the ferrite member 10 constitute a magnetic circuit for the magnetic flux generated by the heating coil 8.

The Curie point of the ferrite member 10 is determined by the heating coil 8
A detection coil 11 is separately wound around this ferrite member 10, and a detection coil 11 is separately wound around the ferrite member 10 to prevent the magnetic circuit from changing due to changes in the magnetic properties of the ferrite member 10. It is configured to detect a change in resistance as a change in voltage induced in this detection coil 11.

FIG. 3 shows the circuit configuration of the electromagnetic cooker of this embodiment, and the operation of this electromagnetic cooker is performed as follows under the control of the above-mentioned circuit.

A commercial power supply 12 (100V, 50V, 50V,
60 Hz) is rectified into direct current by the rectifying and smoothing circuit 13. The above-mentioned heating coil 8 and capacitor 14 are connected in series to this DC power source, and these constitute a resonant circuit. A switching circuit consisting of a diode 15 and a transistor 16 is connected between both terminals of the capacitor 14 of this resonant circuit, and as the transistor 16 turns on and off, a resonant current flows through the heating coil 8. 6 is heated by induction.

The on/off control of the transistor 16 is performed by amplifying the output of the oscillation circuit 17 with the drive circuit 18 and inputting it to the base of the transistor 16.

When the resonant current flows through the heating coil 8, a voltage is induced in the detection coil 11. This induced voltage is converted into a DC voltage by the rectifying and smoothing circuit 19, and the comparator 20 in the next stage
is compared with the reference voltage Vrf. When the temperature of the heating coil 8 is lower than the Curie point of the ferrite member 10,
Since the magnetic properties of the ferrite member 10 do not change, the magnetic resistance of the magnetic circuit that passes the magnetic flux generated by the heating coil 8 does not change, and a voltage of a predetermined level is induced in the detection coil 11 as shown by symbol A in FIG. has been done. Therefore, at this time,
The level of the input signal to the comparator 20 is higher than the reference voltage Vrf, and the output of the comparator 20 becomes an H (high level) signal. The H signal output of the comparator 20 is input to an AND circuit 22 via an OR circuit 21. The AND circuit 22 performs a logical product of the output from the comparator 20 and the output from the oscillation circuit 17, and during this time, the output of the oscillation circuit 17 continues to be sent to the next stage drive circuit 18, and the heating coil 8 is energized. will continue.

On the other hand, when the temperature of the heating coil 8 exceeds the Curie point of the ferrite member IO, the magnetic properties of the ferrite member IO change, and the magnetic resistance of the magnetic circuit consisting of the top plate 7, coil holding base 9, ferrite member 10, etc. Due to the rapid increase, the induced voltage in the detection coil 11 suddenly decreases as indicated by the symbol B in FIG. Therefore, the level of the input signal provided to the comparator 20 is lower than the reference voltage Vrf, and the output of the comparator 20 is inverted to an L (low level) signal. For this reason, the AND circuit 22 no longer transmits the output of the oscillation circuit 17 to the drive circuit 18, the power supply to the heating coil 8 is stopped, and the electromagnetic cooker stops operating. This protects the heating coil 8 from insulation deterioration due to heating.

Note that when starting the electromagnetic cooker, the H signal from the comparator 20 cannot be obtained, so a separately prepared start circuit 23 is used.
A predetermined pulse signal is ANDed through the OR circuit 21.
The signal is applied to the circuit 22, thereby activating the electromagnetic cooker.

〔Effect of the invention〕

As described above, in the electromagnetic cooker of the present invention, the ferrite member whose Curie point is near the heating coil's heat resistance limit temperature is magnetically coupled to the heating coil, while the detection coil is magnetically coupled to the ferrite member. The device is configured to detect changes in the magnetic properties of the ferrite member, that is, overheating of the heating coil, as changes in the induced voltage of the detection coil, and to logically process this detection signal. Unlike the method of indirectly detecting the overheating of the heating coil from the radiant heat of the pot using an element, it is possible to accurately detect the overheating state of the heating coil itself, reliably preventing insulation deterioration of the heating coil, and improving the results. As a result, the durability of the electromagnetic cooker can be significantly improved.

Also, unlike conventional heat-sensitive elements, overheating is detected using only a ferrite member and a detection coil magnetically coupled to the ferrite member, so the structure is simple and costs can be reduced. It also has.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a main part showing an embodiment of the present invention, Fig. 2 is a graph showing changes in induced voltage of a detection coil, Fig. 3 is a circuit diagram of the embodiment, and Fig. 4 is a main part of a conventional example. FIG. 7 is a top plate, 8 is a heating coil, 9 is a coil holding stand, 10 is a ferrite member, and 11 is a detection coil. Figure 1 5; further “C)

Claims (1)

[Claims] 1. A heating coil that is installed below the top plate for placing the pot and generates magnetic flux to heat the pot by induction, and is magnetically coupled to the heating coil so that the Curie point is near the heat resistance limit temperature of the heating coil. a ferrite member; a detection coil that is magnetically coupled to the ferrite member and detects changes in magnetic properties of the ferrite member as changes in induced voltage;
An electromagnetic cooking device characterized by comprising a logic circuit that processes the detection signal from the detection coil by logical calculation.