JPS6297286A - Detector of object not suitable to be heated in radio frequency 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 [Technical Field] This invention is directed to a high-frequency induction heating cooker that heats and cooks objects such as iron pots using eddy currents generated by a high-frequency magnetic field from a high-frequency heating coil. Regarding an object detection device.

<Summary of the Invention> The device for detecting unsuitable heated objects in a high-frequency induction heating cooker of the present invention detects whether heating of objects to be heated is appropriate by using the ratio of the magnitude of low-frequency alternating current to the magnitude of high-frequency alternating current as a judgment material. If the heating plate is determined to be inappropriate, the heating is stopped, and the danger and waste caused by placing small items such as spoons that may overheat, or pots made of materials that are difficult to heat, on the heating plate. Used as a safety device to avoid 0 <Prior art> If a small item such as a spoon is placed on the heating plate of a high frequency induction heating cooker and heated, there is a risk that the spoon etc. will overheat and cause burns. High-frequency induction heating cookers have traditionally been equipped with an unsuitable heated object detection device, which is a safety device to stop heating if an unsuitable heated object is placed on the heating plate. Ta.

A circuit diagram of this conventional high frequency induction heating cooker is shown in FIG.

First, the power circuit of the high frequency induction heating cooker will be explained. !
2 is a commercial low-frequency AC power supply, 2 is a rectifier circuit, and 3 is an inverter circuit. The rectifier circuit 2 rectifies the low-frequency AC from the power supply 1, and the inverter circuit 3 converts it into high-frequency AC. By passing this high-frequency alternating current to the induction heating coil 4 in the inverter circuit 3, a high-frequency magnetic field can be generated on a heating plate (not shown) to heat the object to be heated. Next, a circuit of the apparatus for detecting an unsuitable heated object for this high-frequency induction heating cooker will be explained. Reference numeral 5 denotes a power supply current detection circuit, which detects a low frequency AC current from the power supply 1 using a current transformer 6, converts this value into a DC voltage value, and outputs the same. 7 is a suitability judgment circuit that judges the suitability of the object to be heated by comparing the output of this power supply current detection circuit 5 with a reference value; 8Fi, when this suitability judgment circuit judges that the object is unsuitable, heating is stopped; This is the main control circuit for

The unsuitability of the conventional high-frequency induction heating cooker configured as described above is that when the inverter circuit 3 is driven with an arbitrarily set constant pulse width, a sufficiently large iron pot or the like is placed on the heating plate. When the object to be heated is placed, the output of the power supply current detection circuit 5 becomes larger than the reference value, so the suitability judgment circuit 7ij determines that the object is suitable and the heating is not stopped by the main control circuit 8. do not have. Next, if you place small items such as spoons on the heating plate, turn off the power
Since the low-frequency alternating current does not flow much and the output of the power supply current detection circuit 5 becomes smaller than the reference value, the suitability judgment circuit 7 judges that it is unsuitable, and the main control circuit 8 operates to stop heating. Ru. In this example, an iron pot with a diameter of about 100 W is the boundary for determining whether or not heating is appropriate.

However, if the power supply voltage fluctuates, the output of the power supply current detection circuit 5 will also fluctuate, and this will also affect the determination of whether or not heating is appropriate.

For example, a diameter of 200 m, which has sufficient suitability as a heated object.
In the case of a No. m iron pot, as shown by the black circle in Fig. 3, even if the power supply voltage fluctuates by 90v to 110vi degrees, the output of the power supply current detection circuit 5 is sufficiently larger than the reference value A, so heating is stopped. It will not be done. However, in the case of an iron pot with a diameter of 100 mm, the power supply voltage is 9
When the power supply voltage drops to 0V, it is determined that the object to be heated is inappropriate, and when the power supply voltage rises to 1Iov, it is determined that the object to be heated is suitable. For this reason,
Conventional high-frequency induction heating cooker apparatuses for detecting unsuitable heated objects have the disadvantage that when the power supply voltage fluctuates, the determination of whether or not heating is appropriate becomes unstable.

In addition, even if the object is large enough to be heated, such as a +8-10 stainless steel pot,
Materials with low inductance against eddy currents are not suitable as objects to be heated, as the current in the inverter circuit 3 may become too large and the circuit may overheat.High-frequency induction heating is particularly recommended for thick objects. It may be better to refrain from using it in a cooker. However, in the conventional unsuitable heated object detection device, the current from the power supply 1 does not become so large even when such an unsuitable heated object is detected, so the output of the power supply current detection circuit 5 is as shown in FIG. As shown by the X mark in , it becomes almost the same as an iron pot of the same size, and the suitability judgment circuit 7 judges that the object to be heated has suitability and continues heating. In addition, for example, a pan made of 18-0 stainless steel, etc., which is made of a material with a high inductance against eddy current, may be of sufficient size and suitable as an object to be heated. Because it is difficult for the current to flow, as shown by the triangle mark in Figure 3,
The output of the power supply current detection circuit 5 was the same value as that of an iron pot with a diameter of 100 mm, and even if the power supply voltage decreased slightly, it was determined that the object to be heated was inappropriate and heating was sometimes stopped. . For this reason, the conventional high-frequency induction heating cooking device has a drawback in that it cannot accurately detect the suitability of the heated object depending on the material.

<Purpose of the Invention> This invention was made in view of the above circumstances, and it is possible to determine whether the object to be heated is suitable or not by using the ratio of the magnitude of low-frequency alternating current to the magnitude of high-frequency alternating current as a determining factor. The present invention relates to an improvement in a device for detecting an unsuitable heated object for a high-frequency induction heating cooker, which can stably and accurately determine the following.

<Configuration and Effects of the Invention> The unsuitable heated object detection device for a high frequency induction heating cooker of the present invention includes a low frequency AC detection means for detecting the magnitude of low frequency AC from a power source, and a low frequency AC detection means for detecting the magnitude of low frequency AC from a power source, a high-frequency AC detecting means for detecting the magnitude of the high-frequency AC in the inverter circuit by detecting; a calculating means for calculating the ratio of the output of the low-frequency AC detecting means and the output of the high-frequency AC detecting means; and calculating of the calculating means. The above-mentioned detection method comprises a suitability determining means for determining the suitability of the object to be heated by comparing the result with a reference value, and a heating control means for stopping heating when the suitability determining means determines that the object is unsuitable. It is characterized in that a value obtained by integrating the output of the secondary coil is used as the output of the high frequency AC detection means.

When the apparatus for detecting an unsuitable heated object in a high-frequency induction heating cooker according to the present invention is configured as described above, the influence of power supply voltage fluctuations is not limited to the output of the low-frequency AC detecting means but also the output of the high-frequency AC detecting means. Therefore, by calculating the ratio of these outputs, the influence of the fluctuation can be offset. In addition, since the magnitude of the high-frequency alternating current is taken into consideration when determining the suitability of the heated object, it is possible to avoid heating of unsuitable objects such as +8-10 stainless steel pots where the current of the inverter circuit is too large. It is possible to make an accurate judgment and stop heating. Furthermore, for example 18-0
It is possible to make accurate judgments and continue heating even objects to be heated, such as stainless steel pots, where the current from the power source does not increase, but has the appropriate properties.For this reason, The device for detecting unsuitable objects to be heated in a high-frequency induction heating cooker according to the present invention can accurately and stably judge whether or not the object to be heated is suitable for a high-frequency induction heating cooker, thereby improving the reliability of the high-frequency induction heating cooker and making it easier to use. It can be made very convenient even on the surface.

Further, by setting the value obtained by integrating the output of the detection secondary coil as the output of the high-frequency countercurrent detection means, it is possible to reliably prevent malfunction of the high-frequency induction heating cooker. In other words, the output of the high frequency AC detection means is sent as it is (without going through an integrating circuit).
When single-wave rectification is used as an input part of the calculation means (see Japanese Patent Application No. 60-46942 filed by the same applicant), even if the pot is the same, the input part of the calculation means may vary depending on the width of the driving pulse of the switching transistor. The disadvantage is that the output is different.

'For example, as shown in Figure 6, when using an iron pot with a diameter of 10 m (1 m), the larger the driving pulse width, the larger Vl/V2. That is, while heating an iron pot with a diameter of 100wn on the cooking surface at MAX, a pot with a diameter of about 70mm, which should not be heated, was placed next to the pot, and while moving this in parallel, a pot with a diameter of 70++m was heated. If the pot with a diameter of 100 m is removed when it comes to the heating surface, the diameter Tow
However, by using the integrated value of the output of the detection secondary coil as the output of the high-frequency AC detection means (as shown in Figure 7), such malfunctions can be prevented. can do.

<Embodiment> FIG. 1 is a circuit diagram of a high frequency induction heating cooker which is an embodiment of the present invention.

The power circuit of this high-frequency induction heating cooker includes a power source 1, a rectifier circuit 2, and an inverter circuit 3. The power source 1 is a commercial power source that supplies low frequency alternating current. It consists of a rectifier circuit 2Fi, a diode bridge circuit 9 for full-wave rectification of this low-frequency alternating current, a choke coil 10 and a smoothing capacitor 11 for smoothing the full-wave rectified direct current.

The inverter circuit 3 has a switching transistor 13 connected in series to a parallel circuit of an induction heating coil 4 and a resonance capacitor +2, and a diode 14 is connected between the collector and emitter of the switching transistor 13.
are connected in the opposite direction.

The power circuit of the high frequency induction heating cooker of this embodiment configured as described above rectifies the low frequency alternating current from the power source 1 in the rectifier circuit 2 and supplies it to the inverter circuit 3. In the inverter circuit 3, the switching transistor 13 performs a switching operation to convert the direct current from the rectifier circuit 2 into high frequency alternating current. The switching timing is synchronized with the resonance period of the inverter circuit 3 by the main control circuit 8 sending a drive pulse to the pace terminal of the switching transistor +3. That is, when the switching transistor 13 is turned on and the current flowing from the rectifier circuit 2 to the induction heating coil 4 becomes large to a certain extent, the switching transistor 13 is turned ON. 3 is set to OFF. Then, a current in the opposite direction will now flow through the diode 14.
When this reverse current becomes small to a certain extent, the switching transistor 13 is turned on again. By repeating this operation, direct current is converted to high frequency alternating current.

The unsuitable heated object detection device for the high frequency induction heating cooker of this embodiment includes a power supply current detection circuit (low frequency AC detection means) 5
．． High frequency magnetic field detection circuit (high frequency AC detection means) 15. It is comprised of an operational amplifier circuit (calculating means) 16° suitability judgment circuit (suitability judgment means) 7 and a main control circuit (heating control means) 8. The power supply current detection circuit 5 is a detection circuit that converts the secondary current of a current transformer 6 provided in the circuit from the power supply 1 into a DC voltage and outputs it, similar to the conventional inappropriate heated object detection device. . High frequency magnetic field detection circuit +5V! , is a detection circuit that includes a detection secondary coil 17 provided near the induction heating coil 4, converts the induced current excited in the detection secondary coil 17 into a DC voltage, and outputs the DC voltage. 17
It is provided with an integrating circuit 15A that integrates the input from. The operational amplifier circuit 16 is a circuit that calculates and amplifies the ratio between the output Vl of the power supply current detection circuit 5 and the output v2 of the high frequency magnetic field detection circuit 15. The suitability judgment circuit 7 uses this operational amplifier circuit I.
This circuit compares Vl/V2, which is the calculation result of No. 6, with a reference value C, and issues a stop signal when the calculation result Vl/V2 is smaller than the reference value C. 8 main control circuits,
By operating the operating unit 18, the switching transistor I3
When a stop signal is received from the suitability determination circuit 7, the driving pulse is stopped, the operation of the inverter circuit 8 is stopped, and the heating by the induction heating coil 4 is stopped.

The operation of the unsuitable heated object detection device for the high frequency induction heating cooker of this embodiment configured as described above will be explained. Here, the characteristics shown in FIGS. 3 to 5 represent the case where the inverter circuit 3 is driven with an arbitrarily set constant pulse width, and if this pulse width differs, the absolute value of each output characteristic will change. fluctuate. However, the correlation between the properties of each material hardly changes. The characteristics of the output v1 of the power supply current detection circuit 5 are as shown in FIG. 3, similar to the conventional inappropriate heated object detection device. That is, a 200 diameter iron pot (marked with a black circle) and an 18-10 stainless steel pot of similar size (
In the case of × mark), a voltage of a sufficiently high value is output even than the standard value A regardless of fluctuations in the power supply voltage, and the diameter is 10-0.
mm iron pot (white circle) and 18-0 with a diameter of 200 gourds
In the case of a stainless steel pot (marked with a triangle), the output voltage increases or decreases with respect to the standard value A due to fluctuations in the power supply voltage. As shown in Fig. 4, the characteristics of the output v2 of the high-frequency magnetic field detection circuit 15 are almost the same even if the size is different as long as the material is the same. In the case of an iron pot (marked with a white circle) having a diameter of 100 mm, the output voltage will rise and fall in almost the same way around the standard value B due to fluctuations in the power supply voltage.

In addition, in the case of an 18-10 stainless steel pot (marked with an x), the inductance to eddy current is small, so it outputs an extremely large voltage even compared to the standard value B, and a +8-0 stainless steel pot (triangular In the case of mark), the inductance against eddy current is large, so a voltage smaller than the standard value B is output regardless of fluctuations in the power supply voltage. As shown in FIG. 5, the output Vl/V2 characteristics of the operational amplifier circuit 16 are such that the output in each case has the same value even if the power supply voltage changes, since the influence of fluctuations in the power supply voltage is canceled out. Become. In addition, in the case of an iron pot (marked with a white circle) with a diameter of +00o+, a value almost the same as the standard value C is output, and a diameter of 200o+ is output.
In the case of a mm iron pot (black circle) and 18-O stainless steel pot (triangle mark), a value that is sufficiently larger than the standard value C is output, and in the case of a +8-10 stainless steel pot (x). The output value is smaller than the reference value C.

For this reason, if the suitability judgment circuit 7 compares the output from the operational amplifier circuit z6 with the reference value C, and if the output is smaller than the reference value C, it issues a stop signal to the main control circuit 8. Without being affected by voltage fluctuations, it is possible to always set the judgment boundary for iron pots when the diameter is 100 m, making it possible to stably judge whether or not heating the object to be heated is appropriate. . In addition, in the case of an 18-0 stainless steel pot (marked with a triangle) that is suitable for heating,
Although the output Vl of the power supply current detection circuit 5 is small, the output v2 of the high frequency magnetic field detection circuit 15 is smaller, so the output V+/V2ij from the operational amplifier circuit 16 is sufficiently larger than the reference value C. There is no risk that heating will be stopped due to being judged as unsuitable. Furthermore, in the case of a pot made of 18-10 stainless steel (marked with an X), which is unsuitable for heating, the output v2 of the high-frequency magnetic field detection circuit 15 is higher than the output v1 of the power supply current detection circuit 5, even though the output v1 of the power supply current detection circuit 5 is larger. Since it becomes larger, the output vl/V2 from the operational amplifier circuit 16
becomes smaller than the reference value C, it can be judged as inappropriate, and heating can be stopped. Therefore, the unsuitable heated object detection device for the high frequency induction heating cooker of this embodiment can accurately determine whether the heated object is suitable or not.

By the way, the suitability of the object to be heated is basically determined based on the above-mentioned reasons. The output value of V2 is different. Therefore, in Fig. 6, the output of the high-frequency AC detecting means is directly rectified into single-wave rectification and inputted to the calculation means 6 (integrating circuit 1).
5A), the larger the driving nozzle width, the larger the value of Vl/V2, and as a result, when used in a special way, that is, when the diameter + While heating a 00rrrm iron pot at MAX, a pot with a diameter of about 70m, which should not be heated, was placed next to the pot, and while moving it in parallel, when the pot with a diameter of 70+ma came onto the heating surface, the above occurred. If the pot with a diameter of +00 mm is removed, a malfunction will occur in which the pot with a diameter of 70 mm will be heated.

However, in the present invention, since the high frequency AC detecting means 15 is provided with an integrating circuit +5A, by appropriately selecting the constant of the integrating circuit 15A, the value of 2' can be adjusted to the characteristic shown in FIG. Therefore, Vl/V2' can be kept at a substantially constant value, and as a result, the above-mentioned malfunction does not occur.

That is, since the output of the detection secondary coil I7 is integrated by the integrating circuit +5A, and the value rectified and smoothed by the half-wave rectifier circuit is input to the calculation means 16, the driving pulse width of the switching transistor is small. For example, since the frequency period is fast, the output of the integrating circuit J5A will be very small compared to the input, but if the drive pulse width is large, the frequency period will be slow, so the output of the integrating circuit will not be much smaller than the input. As shown in FIG. 7, the characteristic is 2', and therefore the ratio between vl and v2' remains the same regardless of the driving pulse width. Therefore, the slope of v2 shown in FIG. 6 is smaller than the slope of v2' in FIG. 7, and as a result, the above-mentioned malfunction does not occur.

In general, before starting heating, a high-frequency induction heating cooker intermittently generates a narrow drive pulse, for example, about a 5μ hole, called a search pulse, and during the generation period it detects whether there is a pot or not. Appropriate pots and unsuitable pots are determined, and the drive pulse width at the time of this search pulse generally fluctuates, but in conventional circuits, the value of Vl/V2 changes as the drive pulse changes. However, according to the present invention, the detection level does not change at all, making it possible to make accurate judgments.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of the high frequency induction cooking device of the present invention, Fig. 2 is a circuit diagram of a conventional high frequency induction heating cooking device, and Fig. 3 is a circuit diagram of the conventional high frequency induction heating cooking device and Fig. 3 is a circuit diagram of the high frequency induction cooking device of the present invention. Figure 4 shows the basic output characteristics of the low frequency AC detection means in the apparatus, and FIG. Figure 5 is a basic output characteristic diagram of the calculation means in the same unsuitable heated object detection device, and Figure 6 shows the Vl, V2 and FIG. 7 shows a characteristic diagram of vI, 2', and V1/V2' when an iron pot with a diameter of 100 m is used in the high-frequency induction heating cooker of the present invention. - Power supply, 2- Rectifier circuit, 3- Inverter circuit, 4- Induction heating coil, 5- Power supply current detection circuit (low frequency AC detection means), 7- Suitability judgment circuit (suitability judgment means), 8- Main control circuit (heating control means), 15-high frequency magnetic field detection circuit (
High frequency AC detection means) +5A-integrator circuit, 16-operational amplifier circuit (calculation means), +7-secondary coil for detection,! 9-
Inverter circuit current detection circuit (High frequency AC agent Patent attorney Aihiko Fukushi (and 2 others) Figure 1 ^ 0 e's (O Shima! False ~
Nshi and Cao Kei Qianzhen - back ~ acupuncture beak bea mi to electric enemy kidney 剌 → 輯 acupuncture ÷ ~ 嘱≧ public - $1 hip roll - everyone rents Kusunobe (daughter and shi to makishi exclusive turn buttocks) Indication of 1985 January 1tJ-口I thing f1 Patent application 1987-240187 2. Name of the invention Unsuitable heated object detection device for high-frequency induction cooking device 3. Amendment Relationship with person f↑ Patent applicant 4, agent Address 22, Nagaike-cho, Abeno-ku, Osaka, 545); Voluntary amendment 6, subject of amendment 9 Le Jukut, Sai 1n) den Prize B7, Contents of amendment, 4 Misaki, 1) The scope of claims in the specification will be amended as shown in the attached sheet. 2) In the specification, "ratio to size" written on page 2, line 15 and page 7, line 8 will be corrected to "size and wo." 3) In the specification, "induced current" written on page 7, line 16 will be corrected to "induced voltage." 4) "By comparing the calculation means for calculating the ratio with the output and the calculation result of the calculation means and the reference value" described from page 7, line 19 to the last line of the same page in the specification. First, correct it "according to the output". 5) In the specification, "by calculating the ratio of outputs" written on page 8, line 10 to line 11 of the same page will be corrected to "by calculating the output." [1. The low-frequency AC from the power source is rectified once and converted into high-frequency AC using an inverter circuit, and the induction heating coil generates a high-frequency magnetic field to heat the heated object. In a high-frequency induction heating cooker Cζ that heats A suitability determining means for determining the suitability of the object to be heated according to the output of the AC detecting means and the output of the high frequency AC detecting means, and a heating control means for stopping heating when the suitability determining means determines that the object is unsuitable. An apparatus for detecting an inappropriately heated object in a high-frequency induction heating cooker, characterized in that a value obtained by integrating the output of the detection secondary coil is used as the output of the high-frequency AC detecting means. Ko

Claims (1)

[Claims] 1. In a high-frequency induction heating cooker that heats the object by rectifying the low-frequency alternating current from the power source and converting it into high-frequency alternating current with an inverter circuit and generating a high-frequency magnetic field with an induction heating coil, The magnitude of the high-frequency alternating current in the inverter circuit is determined by a low-frequency alternating current detection means that detects the magnitude of the low-frequency alternating current, and by detecting the induced current in the secondary detection coil excited by the high-frequency magnetic field from the induction heating coil. A high frequency alternating current detecting means for detecting, a calculating means for calculating the ratio of the output of the low frequency alternating current detecting means and an output of the high frequency alternating current detecting means, and a calculation result of the calculating means and a reference value are compared to detect the heated object. and a heating control means that stops heating when the suitability determining means determines that the heating is unsuitable. A device for detecting an unsuitable heated object for a high frequency induction heating cooker, characterized in that the output is an output of a means.