JPS6057666B2 - induction heating cooker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction heating cooker that uses a magnet to detect whether or not the container is made of a magnetic material, and uses a thermistor to control the temperature of the container during cooking.

If a container made of non-magnetic material is used in an induction heating cooker, abnormal phenomena such as abnormal oscillation of the inverter due to a sudden change in coil impedance, excessive current application to the heating coil, and failure of commutation of the control element may occur. A magnet is installed so that the cooker can only be started when a magnetic container is placed on the top plate, and there is a risk that abnormally high temperatures caused by heating may cause deterioration of the coil insulation, so-called dry cooking. A thermistor is provided to detect the state or to control the temperature so that the optimum heating temperature of the food to be cooked is not exceeded.

The mounting state of the thermistor and the magnet was as follows.

That is, as shown in FIG. 1, the thermistor 2 is attached to the lower center surface of the top plate 1 in order to more accurately detect the temperature of the container 7, and the magnet 22 is provided with a cover 23 made of synthetic resin. This prevents the magnet 22 from directly hitting the thermistor 2 when it is attracted to the container 7 and raised.

However, even in this case, the magnet 22
When the cover 23 is attracted to the top plate 1, the cover 23 may be destroyed due to the impact, and after the cover 23 is destroyed, the magnet 22 will directly hit the thermistor 2. Therefore, there was a serious drawback that the thermistor 2 was destroyed.

The present invention eliminates the above-mentioned drawbacks by providing a hole in the magnet and providing a thermistor in a position corresponding to the hole in the top plate, and further improves safety by setting the Curie temperature of the magnet to a predetermined temperature. This is a further improvement.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings showing examples.
FIG. 2 is a longitudinal cross-sectional view showing the main parts of the induction heating cooker. A top plate 1 to be placed on the container 7 is provided at a predetermined position inside the induction heating cooker main body, and the top plate 1 is placed on the bottom surface of the center. A thermistor 2 is attached to the top plate 1, and a magnet support cylinder 4 supports a magnet 3, which will be described later, movably only in the vertical direction, between the lower surface of the center of the top plate 1 and the bottom plate 6 of the induction heating cooker main body. Furthermore, a microswitch 5 is provided at a predetermined height position inside the magnet support tube 4 to restrict the lowering of the magnet 3 and to be switched depending on the ascending and descending position of the magnet 3.

The magnet 3 has a cylindrical shape, and the thermistor 2 is accommodated in the cylindrical hole 31 when the magnet 3 is raised.

Further, the Curie temperature of the magnet 3 is set lower than the temperature of the lower surface of the top plate 1 when the induction heating coil 8 reaches the allowable limit temperature. In addition, 8 is an induction heating coil provided directly below the top plate 1 so as to surround the magnet support tube 4, 9 is a microswitch mounting plate, and 10 is a support rod that holds the thermistor 2 in pressure contact with the bottom surface of the top plate 1. It is.

FIG. 4 is an electrical wiring diagram of the induction heating cooker.

According to this, the first rectifying smoothing circuit 12 is connected between both terminals of the alternating current power supply 11, and the primary winding of the transformer 13 is connected, and the positive voltage terminal of the first rectifying smoothing circuit 12 and Induction between the negative voltage terminal and the negative voltage terminal. The heating coil 15 and the collector terminal and emitter terminal of the output transistor 16 are connected in series in this order.

Note that 17 is a protection diode connected in the opposite direction between the collector terminal and emitter terminal of the output transistor 16, and 18 is a capacitor connected in parallel with the protection diode 17.

Further, a second rectifying and smoothing circuit 14 is connected between the secondary winding terminals of the transformer 13, and the positive voltage terminal of the second rectifying and smoothing circuit 14 is connected to the monostable multivibrator 19 via the microswitch 5. In addition to connecting to the positive voltage terminal, it is also connected to the positive voltage terminal of the astable multivibrator 20, and further, the negative voltage terminal of the second rectifying and smoothing circuit 14 is connected to the ground terminal of the monostable multivibrator 19 and astable multivibrator 20. ing.

And the output terminal of the monostable multivibrator 19,
The base terminal I of the output transistor 16 is connected.

The thermistor 2 is connected to a temperature detection circuit 21, and uses the output signal of the temperature detection circuit 21 to control, for example, the base input signal of the output transistor 16, or to control the output/signal of the output transistor 16. I try to control it.

The operation of the induction heating cooker of the present invention having the above structure is as follows.

First, the container 7 is placed on the top plate 1.

Next, by turning on a switch (not shown) for starting heating cooking, the heating cooking operation is started. When the container 7 is made of a magnetic material, the magnet 3 attracts the container 7 and moves upward, so that the microswitch 5 is closed and a positive voltage is applied to the positive voltage terminal of the monostable multivibrator 19.

Therefore, the monostable multivibrator 19 outputs a rising pulse with a predetermined time width at the timing of the rise of the pulse periodically output from the astable multivibrator 20, and the monostable multivibrator 19 outputs a pulse with a predetermined width. By making the output transistor 16 conductive, the induction heating coil 15 is energized and an induction heating operation can be performed.

By continuing the induction heating operation, the temperature of the container 7 rises, and the resistance value of the thermistor 2 increases accordingly. When the container 7 reaches a predetermined temperature, the resistance value of the thermistor 2 reaches the preset value. When the temperature reaches a predetermined value, the temperature detection circuit 21 operates to cut off the input signal or output signal of the output transistor 16.

Therefore, it is possible to maintain the optimal heating temperature of the article to be adjusted stored in the container 7, and to reliably prevent the container 7 from being abnormally heated.

Also, for some reason, thermistor 2 or temperature detection circuit 2
1, the above operation will not be performed, but if the temperature of the container 7 rises further and the magnet 3 reaches the Curie temperature, the magnet 3 will lose its magnetic force and fall due to its own weight. However, since the microswitch 5 is opened, the monostable multivibrator 19 does not output any pulses, and the current to the induction heating coil 15 is cut off to stop the heating operation. Therefore, safety can be further improved.

Moreover, unlike the above case, when the container 7 is made of non-magnetic material, the magnet 3 does not rise at all and the microswitch 5
Since it is held in the open state, no cooking operation is performed.

FIG. 3 shows another embodiment, and the only difference from FIG. 2 is the support mechanism for the thermistor 2. FIG. That is, the bottom plate 6
The support tube 24 is erected in the support tube 24, the lower end of the support rod 10 is inserted into the cylindrical hole 25 of the support tube 24, and the support rod 10 is constantly biased upward by the spring 26, so that the thermistor 2 is placed at the top. It is made to come into pressure contact with the lower surface of the plate 1.

The configuration of other parts is the same as that shown in the second figure, and therefore will be omitted.

In terms of operation and effect, it is almost the same as that shown in the second figure, and the simple point is that it is biased by a spring 26, so
The only difference is that the adhesion of the thermistor 2 to the lower surface of the top plate 1 is improved.

The induction heating cooker of the present invention as described above has a magnet,
Since the hole capable of accommodating the thermistor is provided, the magnet will not come into contact with the thermistor when it rises, so there is no risk of damaging the thermistor.

Furthermore, the Curie temperature of the magnet is set lower than the temperature at the bottom of the top plate when the induction heating coil reaches its allowable limit temperature, so even if the thermistor fails, abnormal temperature rise due to cooking, especially dry cooking, can be prevented. It can definitely be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show embodiments of the present invention, FIG. 1 is a vertical cross-sectional view of main parts showing a conventional example, FIG. 2 is a longitudinal cross-sectional view of main parts showing one embodiment of the apparatus of the present invention, FIG. 3 is a vertical cross-sectional view of a main part showing another embodiment, and FIG. 4 is an electrical wiring diagram of the same.

1... Top plate, 2... Thermistor, 3... Magnet, 4... Magnet support tube, 5
...Micro switch, 7...Container, 8
...Induction heating coil, 31 ... Cylindrical hole.

Claims (1)

[Scope of Claims] 1. In an induction heating cooker in which an induction heating coil is provided below a top plate that supports a magnetic container, a thermistor that controls energization to the induction heating coil is provided on the bottom surface of the top plate. At the same time, a switch for controlling energization of the induction heating coil is provided below the top plate, and a magnet that is attracted and lifted by the magnetic container is provided above the switch, and at a predetermined position of the magnet, An induction heating cooker characterized by having a hole to prevent collision with a thermistor. 2. Induction heating according to claim 1, characterized in that a magnet is used that loses its magnetic force when the induction heating coil reaches a predetermined temperature that is not higher than the temperature of the lower surface of the top plate when the induction heating coil reaches its permissible limit temperature. Cooking device.