JPS62243282A - Induction heating 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] [Industrial application field] The present invention aims to improve the safety and use of induction heating cookers.

Especially when it comes to water and soups in induction heating cookers.

This article relates to an induction heating cooker that detects the finish and is safe, easy to use, and energy-saving.

[Conventional technology]

The conventional device f is described in Japanese Patent Application Laid-Open No. 58-95185, in which the water in the container of the induction + il buried vessel boils and spills out of the vessel, and the water boils over due to the thermal energy of the ceramic plate. makes a sound when it evaporates.

This sound was captured by a microphone and activated the heating coil's @twist circuit to stop heating. However, this method did not take into account the ability to capture the sound of water boiling inside the container.

The above conventional technology does not capture the sound of water boiling in a container and control the heating source of an induction cooker, but uses a microphone to capture the sound produced when boiling water evaporates on a ceramic plate. This is to control the heating source.

Therefore, with this method, (1) the water in the container must always boil over. (2) There were problems such as the need for heating and interrogation to some extent after the water had boiled.

[Inventiveness (problem to be solved)]

Therefore, in the present invention, the problem to be solved is to eliminate the above-mentioned drawbacks of the conventional technology and to be able to reliably detect the boiling status of water or soup in an induction heating cooker and control the heating source. Therefore, it is an object of the present invention to provide an induction heating cooker that is easy to use, safe, and energy-saving.

[Means for solving problems]

The above purpose is to closely attach and fix a vibration sensing element, such as an acceleration pick-up needle, to the ceramic plate on which the metal container is placed, so that the vibrations generated when water or soup boils in the container can be seen through the metal pot and ceramic plate. This is achieved by

[For production]

The vibration level when boiling water or soup will be described in detail later, but there is no vibration until the temperature of water or soup reaches about 80℃.
The vibration level gradually increases from 0℃ to 97~
It reaches a peak at about 98°C. After that, the vibration level stabilizes at a level slightly lower than the peak value.

Therefore, if the peak of the vibration level can be detected, that is, boiling can be detected, the heating source can be controlled. As for the method of capturing the peak of the characteristic, there is no problem if a peak value hold circuit or the like is used.

With this method, it is possible to detect the boiling of water or soup in the container, and the reliability of detection is high because the detection is not based on water droplets boiling out of the container as described in the conventional technology. .

〔Example〕

The following is part 1 of the present invention! An example will be explained using figures.

FIG. 1 is a system block diagram of an induction heating cooker according to an embodiment of the present invention. In Figure 1, -1 is gold 144
It is made of silk and magnetic material, and 2 is a soup such as miso soup mixed with water and various boiled foods. 5 is a ceramic plate on which the metal pot 1 is placed. 4 is a coil that generates magnetic force. The heating JfA of the induction heating cooker is connected to the magnetic force generating coil 4.
When a current flows, magnetic lines of force are generated around the coil. When a magnetic metal pot 1 is placed on the ceramic plate 5, magnetic lines of force pass through the bottom of the pot, generating eddy current. When a whirlpool occurs, the pot generates heat due to iron loss in the pot. This heat heats the food. Therefore, non-magnetic paper, cloth 9 hands, ceramic plate 5, etc. do not generate heat. However, the temperature of the ceramic plate 5 of the cooker increases due to heat conduction from the metal pot 1.

The above is a simple explanation of the principle of induction heating cooker-5.
A circuit drives the magnetic force generating coil 4, and 6 is a circuit that switches the outputs of the 11 embedders. 7 is a vibration sensing element that captures the vibration sound when water or juice 2 boils, and is equipped with a pressure-forming type acceleration pickup. 8 is an amplification circuit that amplifies the signal from the vibration sensing element 7, and 9 is a detection circuit that detects the amplified signal and extracts only the envelope of the signal. 10 is a peak value hold circuit that captures the peak of the signal. 10\This is a controller that controls the so-called buried implant system.

12 is a temperature sensor that measures the temperature of the ceramic plate 5, and 15 is a measurement processing circuit that enables temperature discussion based on the signal from the temperature sensor 12.

The operation of this cooking system will now be described.

A metal pot 1 containing water or juice 2 is placed on a ceramic plate 5, and when the power is turned on, temperature measurement and vibration measurement 5 are started.

When the water or juice 2 boils and a signal is output from the peak value water hold circuit, the controller 11 outputs a signal to change the output to zero and stop the drive circuit.

Although not shown in Figure 1, the induction heating cooker has
It has a device to detect the presence or absence of the metal pot 1 and a thermoswitch to prevent abnormal heating. Detection of the presence or absence of a metal pot is generally performed using a switch using a magnet, since metal pots are magnetic.

The temperature measurement of the ceramic plate 5 is used when the object to be heated, such as water or juice, is kept warm after boiling has been detected, that is, when it is heated at low output.

The relative relationship between the temperature of the object to be heated and the temperature of the ceramic plate S is determined in advance through experiments, and the temperature of the object to be heated is determined from the temperature of the ceramic tooth 5.

This detection method can also be used for boiling detection, but it requires correction because it causes a time delay due to heat conduction. Also, its reliability is low compared to methods that detect vibrations.

Also, in this method, the user sets the temperature for keeping warm, and increases or decreases the output of the cooker to maintain that temperature.

FIG. 2 shows the vibration level characteristics of boiling water filled in a metal fi1, amplified and detected in degrees Celsius using a compression molded acceleration pickup.

The water temperature shown in Figure 2 is the temperature at the center of the water in the pot.

From FIG. 2, it can be seen that imaging does not occur until the water temperature reaches about 80°C, and the imaging level gradually rises from about 80°C.

Here I will briefly talk about boiling.

- When heating from the bottom, bubbles are generated from the heating wall. The core of these bubbles is a small amount of air that has adhered to the recesses or scratches on the heating wall. When heated, the bubbles grow and their diameter increases. The grown bubbles then separate from the heating wall due to buoyancy or other forces and float up. At this time, if the temperature of the upper part of the water is lower than that of the lower part, the bubbles disappear on the way to the surface and generate vibrations. As the bubbles float up and disappear, the imaging level becomes larger (.Also, when the bubbles leave the heating wall, they all detach (), the bubble nucleus remains and repeats the process of growing, detaching, and floating (as the water temperature increases) The diameter of the bubble becomes thicker as the height increases, and the state where the vibration level reaches its peak is
This is when the diameter of the bubble that disappears reaches its maximum. Water temperature is 1
When it reaches 00t, the bubbles no longer disappear and float to the surface of the water, and in this state, there are only vibrations due to the generation, growth, and levitation of the bubbles, so the imaging level is lowered and becomes -Level.

The above can be seen by looking at Figure 2. Therefore, there is a detection circuit that uses a peak value hold circuit as a detection circuit for detecting boiling based on the vibration characteristic curve shown in FIG.

FIG. 5 is a block diagram of a detection circuit based on a peak value hold circuit. 5, the vibration signal received by the vibration sensing element 7 is input to the input terminal 1.
4, the detection circuit 9 cuts off the alternating current component, and extracts the positive envelope signal (the signal shown in FIG. 2). In the signal shown in Figure 2, if you cut the high frequency part, that is, LPF
(low-pass filter) to obtain an even smoother curve.

The detected signal is directly input to the input terminal of the comparator 1B, and the other side is input to the comparator 18 via the peak value hold circuit. That is, the detected signal is charged to the capacitor C16 through the diode 15.The resistor 17 is a discharging resistor, and the time constant of the capacitor and the resistor is made large. The reason why the diode 15 is used is to provide a difference between the detected signal vI and the peak value hold voltage VIK and the voltage VD of the diode. The voltage VD is 0.5-0.5F for germanium diodes and about 0.7V for silicon diodes. That is, with the configuration shown in FIG. 5, the peak value hold voltage VJI is held with a voltage difference VD from the signal voltage vI in FIG. 2, so that the comparator 18 outputs an output at the crossing point. In other words, this output determines the boiling point.

Next, a specific example of a technology for measuring temperature will be described.

The temperature sensor 12 uses a thermistor. Generally, the resistance value of a thermistor tends to decrease as the temperature increases. RT the resistance value of the thermistor (double heat sink type)
If H, RTH=1'4m, Cape (B, (7-T,,))
-(11 Here, 1 (tl is the resistance value at 25°C, B is a constant, T is the temperature, and T□ is the absolute temperature at 25°C.

As can be seen from equation (1), the resistance of the thermistor changes exponentially with temperature.

This thermistor is used in the oscillation circuit. FIG. 4 shows an astable multivibrator that utilizes charging and discharging of Re using an inverter element 20, and a thermistor is connected to its resistance section.

With such a circuit configuration, a change in temperature, that is, a change in the resistance value of the thermistor can be converted into a change in the oscillation period T. The oscillation period T of an astable multivibrator is generally T=:
FL, FLT, CT, 12 is constant a (Z, Z ~ 2
．． 5). This oscillation circuit consists of a capacitor CTt! Since the capacitance of is fixed, the resistance value FLT of the samister is
As H, , becomes smaller, the period T becomes smaller according to the above equation. Further, the resistor R825 is a protection resistor for reducing the current flowing through the input protection diode in the inverter.

Next, a method for capturing the oscillation period will be explained.

In FIG. 4, the oscillation period T is determined by the temperature change range of the ceramic plate 5. And period from period T.

There is a method of counting the period T using another short pulse and finding the period T from the count value.

In the method using this oscillation circuit, the measurement error will be much smaller if the relationship between temperature and oscillation period is actually determined experimentally rather than by the above calculation formula.

Further, as for the method of determining the period from the above count value and the temperature, it is better to use a micromanipulator to determine the period using software rather than the above relational expression.

Next, a method of attaching the ceramic plate 5 to the outer frame chassis of the cooking appliance will be described.

FIG. 5 shows a partial sectional view of the end portion where the ceramic plate 5 is installed on the outer frame chassis 251C. Since electrical parts and the like are housed in the lower part of the ceramic plate 5, the structure must be designed to prevent water from entering.

Furthermore, since the S motion sensing element is fixed in a dense layer on the ceramic plate 3, it is preferable that the structure prevents the transmission of an image from the outside. As a structure that satisfies these requirements, as shown in FIG. 5, there is a method of sealing and fixing between the ceramic plate 5 and the outer frame 25 with silicone rubber 24 or the like.

〔Effect of the invention〕

As is clear from the above description, the present invention has the following effects.

+1) Since the vibrations of the water and juice are detected by the vibration detection element, the amount is irrelevant.

(2) The peak value of the imaging level during boiling can be captured with a simple circuit configuration, and the heating output can be controlled, resulting in excellent energy savings and safety.

(3) When capturing the sound of boiling with a microphone, signals such as the human voice enter as noise, but the human voice enters because vibrations transmitted through metal or ceramic plates are captured using an acceleration pickup, etc. (High resistance to noise.) (4) When boiling is detected, the heating power supply can be automatically stopped, improving usability.

[Brief explanation of drawings]

Fig. 1 is a system block diagram of an induction heating cooker as an embodiment of the present invention, Fig. 2 is a graph showing boiling water and vibration level characteristic curves at 5 o'clock, and Fig. 5 is a peak value of vibration level characteristics. Block diagram showing the boiling detection circuit section that detects
The figure is a circuit diagram showing an oscillator circuit using a thermistor, which constitutes a part of the temperature measuring section. Figure 5 is a partial structural cross-sectional view showing the structure of the installation of the ceramic plate 1 of the induction heating cooker. . DESCRIPTION OF SYMBOLS 1...Metal pot, 5...Ceramic plate, 4...Magnetic force generating coil, 7...Picture sensing element, 9...Peak value hold, 11...Controller, 12...Temperature Sensor, 18... Comparator, 24... Silicon rubber seal. Section 1 Section 2 Section 3 Section 3 Section 4 Section 5

Claims (1)

[Claims] 1. A heating means consisting of a metal pot placed on a ceramic plate and a magnetic force generating coil for generating heat in the metal pot;
In the induction heating cooker, a vibration sensing element is installed and fixed on the ceramic plate, the sensing element detects the level of vibration that occurs when the soup in the metal pot boils, and the heating is performed according to the detected level. An induction heating cooker characterized in that the means is controlled by a control circuit. 2. In the induction heating cooker according to claim 1, the temperature of the soup in the pot and the temperature of the ceramic plate are determined in advance, the temperature of the ceramic plate is measured, and the temperature of the soup is determined thereby. An induction heating cooker further comprising means for controlling heating to a temperature set by a user.