JPH0794264A - Electromagnetic induction heating device - Google Patents

Abstract

PURPOSE:To prevent overheating of a pan and generating temperature unevernness by measuring a temperature of a heated object through changing a resistance value of a resistor, and controlling electromagnetic induction based on a measured result. CONSTITUTION:Resistors 4A, 4B, 4C are connected to a temperature detecting circuit 3A, and based on changing a resistance value due to changing a temperature of the resistors 4A to 4C, the respective temperature is detected. In the circuit 3A, a signal corresponding to the largest temperature, detected by the resistors 4A to 4C, is output and applied to a comparator circuit 3C. In a circuit 3B, a desired temperature is left as preset, and a signal corresponding to this temperature is applied to the circuit 3C. Both the signals are compared in the circuit 3C, to apply a result compared signal to a coil control circuit 3D, and based on this compared signal, an AC current applied to an electromagnetic induction coil 1 is controlled. Then by generating a strong magnetic field in the periphery of the coil 1, a heated object 10, placed on a glass plate 2 to consist of ferromagnetic material, is quickly heated by electromagnetic induction action, and a resistance value is changed to control the current to the coil 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic induction heating device used for cooking, heating, drying and the like.

[0002]

2. Description of the Related Art An electromagnetic induction heating device is 25 to 30 kHz.
Is a device that heats an object to be heated by bringing the object to be heated made of a magnetic material such as iron close to the electromagnetic induction coil to which the alternating current is applied. In such an electromagnetic induction heating device, it is necessary to control the temperature of the object to be heated within a predetermined range. In a conventional technique for that purpose, a temperature measuring element such as a thermistor is provided on an isolation member such as a glass plate provided between the object to be heated and the electromagnetic induction coil. The thermistor is attached in contact with the surface of the glass plate of the isolation member on the electromagnetic induction coil side. Usually, the electromagnetic induction coil is provided in close contact with the glass plate in order to effectively obtain the electromagnetic induction effect. Therefore, there is no gap between the electromagnetic induction coil and the glass plate, and a thermistor cannot be attached between them.
Since the electromagnetic induction coil is usually a donut shape and has a hollow portion in the center, a thermistor is provided in the hollow portion.

When the object to be heated is heated, the heat is transmitted through the glass plate and raises the temperature of the thermistor attached to the glass plate. The detection output of the thermistor is input to the detection circuit, compared with a predetermined set value, and the control signal of the comparison result is output. This control signal is applied to an alternating current control circuit to control the magnitude of the current and consequently the temperature of the object to be heated.

[0004]

In the electromagnetic induction heating apparatus using such a donut-shaped electromagnetic induction coil, the heat generation of the object to be heated in the circumferential portion of the electromagnetic induction coil is large, but The heat generation of the object to be heated in the central space is relatively low. In the conventional temperature measuring method described above, the thermistor is provided in the center of the electromagnetic induction coil, so the thermistor detects the temperature of the portion of the object to be heated which is relatively low in heat generation. Cannot be detected. Even in this case, over time, the heat of the part of the object to be heated, which has a large amount of heat, is transmitted through the glass plate, raising the temperature of the glass plate in the part where the thermistor is attached and gradually approaching the correct temperature, but by then It takes a considerable amount of time and there is a time delay in detecting the temperature. In the electromagnetic induction heating method, unlike the heating method by heat conduction, there is no time delay or heat loss due to heat conduction during heating, so that the object to be heated is heated rapidly. Therefore, if there is a time delay in temperature detection, the object to be heated may be overheated, or the temperature may fluctuate so much that it cannot be controlled to a constant temperature. When a pot for cooking is used as the object to be heated, the pot bottom is generally not flat, and its central portion is convex toward the inside of the pot. Therefore, a space is formed between the bottom of the pan and the glass plate, and the center of the glass plate and the bottom of the pan do not come into direct contact with each other, so that the delay in temperature detection due to the above detection error is expanded. As a result, the pot is overheated,
In some cases, the temperature of the pot was partially different.

[0005]

The electromagnetic induction heating apparatus of the present invention is close to the electromagnetic induction coil to which the alternating current output from the electromagnetic induction coil control means is applied and isolates the electromagnetic induction coil from the object to be heated. A glass plate is provided, at least one resistor is provided on the glass plate, and temperature measuring means for measuring the temperature of the object to be heated is provided based on a change in resistance value of the resistor.

[0006]

Since the resistor of the temperature detecting element is provided in the region of the glass plate with which the object to be heated contacts, the heat of the object to be heated is transferred to the resistor with almost no time delay.

[0007]

1 is a perspective view showing a cross section of an electromagnetic induction heating apparatus to which the present invention is applied. In this figure, a case where the electromagnetic induction heating device is applied to a cooking device is shown. In the figure, a glass plate 2 is provided in the upper part of a donut-shaped electromagnetic induction coil 1 so as to be in close contact with the electromagnetic induction coil 1, and an object to be heated 10 such as an iron pan and the electromagnetic induction coil 1 placed thereon.
The spaces are isolated. The glass plate 2 has a thickness of several millimeters, and its material is preferably lithium silicate glass, quartz glass or the like having a low coefficient of thermal expansion. Instead of the glass plate, a plate-shaped member obtained by coating the surface of the ceramic plate with the above-mentioned lithium silicate glass or quartz glass may be used. Glass plate 2
A resistor 4 which is, for example, a metal thin film is formed on the lower surface of the resistor 4, and the resistor 4 is covered with a glass layer 5 that is a protective film and has a thickness of about 100 microns. Since the resistor 4 is in the form of a film and is thin, it has a small heat capacity, and is not restricted by the mounting location unlike a thermistor having a large thickness. The glass layer 5 is preferably made of high-silica glass in terms of moisture resistance, abrasion resistance and electric insulation. The electromagnetic induction coil 1 is connected to the electromagnetic induction coil control device 3 and a predetermined alternating current is supplied thereto.

FIG. 2 is a plan view of the first embodiment of the resistor 4. In this embodiment, the resistor 4 is composed of a zigzag thin film resistor. The resistor 4 of the first embodiment is used when the temperature control of the object to be heated does not require very high accuracy. An example of a resistor that can perform temperature control with higher accuracy will be described below.

FIG. 3 is a plan view of the second embodiment of the resistor. In this embodiment, three arcuate resistors 4A, 4B and 4C having different radii are concentrically provided, and their respective terminals are connected to the electromagnetic induction coil control device 3 shown in FIG.

FIG. 4 is a plan view of a third embodiment of the resistor. In this embodiment, seven arc-shaped resistor elements having different radii are arranged concentrically, and the inner three resistor elements are connected in series to form the first resistor 4D. Next, the fourth and fifth resistor elements are connected in series from the innermost resistor element to form the second resistor 4E. Then, the two outer resistor elements are connected in series to form the third resistor 4F. In this third embodiment,
The length of each of the resistors 4D, 4E, 4F is about twice the length of the resistors 4A, 4B, 4C of the second embodiment. Therefore, the resistors 4D, 4E, 4F can be formed using a metal material having a relatively low electric resistivity. Further, in the third embodiment, the directions of the currents flowing through the resistor elements of the resistors 4D to 4F are opposite to each other in the adjacent resistor elements. Therefore, the current induced in the resistor element due to the external noise due to the electromagnetic wave or the like is canceled, and the occurrence of an error due to the influence of the external noise can be prevented. It is desirable that the radius of the arc of the outermost resistor 4C or 4F in the second and third embodiments is approximately equal to the maximum radius of the object 10 to be heated which is normally used such as a pot. The resistors 4A to 4F use noble metal resistors having a large temperature coefficient, and platinum, ruthenium or alloys thereof are suitable as the noble metal. As a method of forming the resistor, a printing method using a paste-like resistor, a vapor deposition method,
A sputtering method or the like is suitable. Further, in order to prevent the attenuation of the detection signal, the resistance value of the portion of the lead wire 6 other than the arc-shaped portions of the resistors 4A to 4F is lower than the resistance value of the resistors 4A to 4F (for example, 1 of the resistance value of the resistors is 1). / 50 or less), it is desirable to use another good conductive metal film.

FIG. 5 is a block diagram of the electromagnetic induction coil control device 3. In the figure, resistors 4A, 4B, 4C (or 4D, 4E, 4F) are connected to the temperature detection circuit 3A, and the respective temperatures are detected based on the change in the resistance value due to the temperature change of the resistors 4A to 4C. It In the temperature detection circuit 3A, a signal corresponding to the highest temperature detected by the three resistors 4A, 4B, 4C is output and applied to the comparison circuit 3C. On the other hand, in the temperature setting circuit 3B, a desired temperature is preset, and a signal corresponding to the temperature is similarly applied to the comparison circuit 3C. In the comparison circuit 3C, the above two signals are compared, and the resulting comparison signal is applied to the coil control circuit 3D. The coil control circuit 3D controls the alternating current applied to the electromagnetic induction coil 1 based on this comparison signal.

When an alternating current from the electromagnetic induction coil controller 3 is applied to the electromagnetic induction coil 1, the electromagnetic induction coil 1
A strong magnetic field is generated around the object, and the object to be heated 10 made of a ferromagnetic material such as an iron pot placed on the glass plate 2 rapidly generates heat due to the electromagnetic induction effect. This heat is transmitted to the resistors 4A to 4C via the glass plate 2 that is in contact with the object to be heated 10, and the temperature thereof rises and the resistance value changes. This change in the resistance value is detected by the temperature detection circuit 3A of the electromagnetic induction coil control device 3, compared with a desired set temperature preset in the temperature setting circuit 3B, and the electromagnetic wave is heated to the set temperature. Increase or decrease the current to the induction coil 1. In the temperature setting circuit 3B, for example, a desired "heating program" is set, the detection output of the temperature detection circuit 3A is compared and compared with this heating program, and the electromagnetic induction coil 1 is provided with the heating according to the program. The current can also be controlled. The heat generated by the object to be heated 10 diffuses into the glass plate, but the temperature thereof decreases as the distance from the heating portion of the object to be heated 10 increases.

An experimental example of the embodiment of the present invention will be described below in comparison with that of the above-mentioned conventional example. With the structure shown in FIG. 1, the resistors 4A, 4B having the shape shown in FIG. 3 are formed on the glass plate 2 having a thickness of 3 mm, a width of 28 cm, and a length of 28 cm.
4C from the center of the glass plate with a radius of 50 mm and 65 m, respectively
An example of the present invention formed at positions of m and 80 mm was compared with a conventional example using a glass plate of the same size.
Caliber 18c with 1 liter of water on both glass plates 2
The holo pot of m was placed, 1 kw of electric power was applied to the electromagnetic induction coil, and the detection delay time after the water in the pot boiled when each holo pot was heated was measured. In the case of the embodiment, the detection delay times of the resistors 4A, 4B, and 4C are 30 seconds, 26 seconds, and 46 seconds, respectively, and when this embodiment is used, boiling detection can be performed within 30 seconds. Further, since the outermost resistor 4C exhibits a large detection delay, information that the resistor 4C is close to the end of the pot is also obtained, and from this, the size of the pot can be detected. On the other hand, in the case of the conventional example, 126 seconds are required, which is 4th of the embodiment of the present invention.
Needed more than double the time.

According to the embodiment of the present invention, the temperature detecting resistors 4A to 4A are provided on the portion corresponding to the entire bottom surface of the object 10 to be heated.
Since 4C or 4D to 4F are provided, the object to be heated 1
The bottom surface of 0 is always in contact with either resistor. Therefore, the temperature of the bottom surface of the object to be heated 10 is set to the resistors 4A to 4C in a short time.
, And the temperature is detected. Also,
When the radius of the bottom surface of the object to be heated 10 is smaller than the radius of the resistor 4C and larger than the radius of the resistor 4B, the temperature of the resistor 4B changes according to the temperature of the object to be heated 10,
The temperature of the resistor 4C changes with a considerable time delay.
Therefore, the temperature of the resistors 4A, 4B, and 4C can be detected by the temperature detection circuit 3A and compared with each other to detect the radius of the object to be heated 10.
In this case, when the radius of the object to be heated 10 is small, the electromagnetic induction coil control device 3 can perform necessary control such as reducing the current applied to the electromagnetic induction coil 1. Even when the object to be heated 10 is not placed at the correct position in the center of the electromagnetic induction coil 1 and is displaced to either one, a large difference occurs in the detected values of the resistors 4A to 4C. Therefore, in such a case, an alarm signal can be generated to remind the user to place the article 10 to be heated in the correct position.

FIG. 6 is a plan view showing the structure of the resistor according to the fourth embodiment of the present invention. In the figure, resistors 4D, 4E,
The shape of 4F is the same as that of the third embodiment. In this embodiment, a temperature detecting element 7 such as a thermistor is provided near the innermost resistor 4D. Temperature measuring element 7
Is preferably brought into close contact with the glass layer 5 shown in FIG.
Generally, the electrical resistivity of the resistors 4D, 4E, 4F varies to some extent depending on various conditions during manufacturing. This variation is caused by the individual resistors 4D in a certain glass plate 2,
Since it is easy to make the film thickness of each resistor the same between 4E and 4F, the value is so small that it can be almost ignored. However, it is difficult for the plurality of different glass plates 2 to have the same film thickness, and the above-mentioned variation becomes a large value that cannot be ignored. Therefore, based on the temperature detected by the temperature detecting element 7, an error between the resistance of the resistor 4D having substantially the same temperature as the temperature detecting element 7 and a predetermined reference resistance value is detected. Then, based on the detected error, the deviation of the electrical resistivity of the resistor 4D from the reference value is obtained, and the respective detection values of the resistors 4D, 4E, 4F in the temperature detection circuit 3A are based on this deviation. To correct. As described above, in the fourth embodiment, the temperature of any one of the plurality of resistors (4D in the above example) is detected by the temperature detecting element 7 to correct the error in the electrical resistivity of all the resistors. can do.

[0016]

According to the present invention, at the position where the object to be heated of the glass plate that separates the electromagnetic induction coil from the object to be heated is in contact, the temperature detection is performed on the surface of the glass plate opposite to the surface in contact with the object to be heated. Since the resistor is provided, the heat of the object to be heated is transferred to the resistor in a short time. Therefore, there is no time delay in detecting the temperature of the object to be heated. As a result, it is possible to provide an electromagnetic induction heating device that does not overheat the object to be heated and does not cause temperature unevenness where the temperature of the object to be heated is partially different.

[Brief description of drawings]

FIG. 1 is a perspective view showing a partial cross section of an electromagnetic induction heating apparatus to which an embodiment of the present invention is applied.

FIG. 2 is a plan view of a glass plate provided with a resistor according to the first embodiment of the present invention.

FIG. 3 is a plan view of a glass plate provided with a resistor according to a second embodiment of the present invention.

FIG. 4 is a plan view of a glass plate provided with a resistor and a temperature measuring element according to a third embodiment of the present invention.

FIG. 5 is a block diagram of an electromagnetic induction coil control device of the present invention.

FIG. 6 is a plan view of a glass plate provided with a resistor according to a fourth embodiment of the present invention.

[Explanation of symbols]

 1 Electromagnetic Induction Coil 2 Glass Plate 3 Electromagnetic Induction Coil Control Circuit 4A, 4D, 4C Resistor 4D, 4E, 4F Resistor 5 Glass Layer 7 Thermometric Element 10 Heated Object

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuichiro Sugita 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. An electromagnetic induction coil control means for outputting an alternating current, an electromagnetic induction coil to which the alternating current is applied, a glass plate which is provided in the vicinity of the electromagnetic induction coil and isolates the electromagnetic induction coil from the object to be heated. , At least one resistor provided on the glass plate, and temperature measuring means for measuring the temperature of the object to be heated based on a change in resistance value of the resistor, the electromagnetic wave based on the measurement result of the temperature measuring means An electromagnetic induction heating device comprising: a control unit that controls the induction coil control unit. 2. The electromagnetic induction heating device according to claim 1, wherein the resistor provided on the glass plate is covered with a glass layer. 3. The electromagnetic induction heating device according to claim 1, wherein the resistor is formed into a plurality of concentric arcs. 4. The electromagnetic induction heating device according to claim 3, wherein at least one resistor is provided with a temperature detecting element. 5. The electromagnetic induction heating device according to claim 3, wherein each of the resistors is configured by connecting a plurality of adjacent resistors of the plurality of resistors having the concentric arc shape in series.