JPH07282967A - Electromagnetic induction heating cooker - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a highly reliable electromagnetic induction heating cooker that is safe against no load and small loads without deteriorating usability and does not destroy the inverter circuit. [Structure] In an electromagnetic induction heating cooker having an inverter circuit including a resonance capacitor, a heating coil, a switching element, and the like, and an oscillation circuit that oscillates the switching element, whether the load induction-heated by the heating coil 4 is appropriate or not is determined. Two small object detection devices 7 and 8 for determination are connected to the oscillation circuit 6, and the oscillation circuit 6 switches the switching elements 5a and 5b when the first small object detection device 7 determines that the load is unsuitable such as when the pan is shaken. If the second small object detection device 8 determines that the load is unsuitable, such as when a knife or fork is used, the oscillation of the switching elements 5a and 5b is stopped for a certain period of time, and then intermittent oscillation is generated again. I decided to do it.

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 cooker for determining whether a load to be induction-heated is suitable or not and controlling the oscillation of an inverter circuit.

[0002]

2. Description of the Related Art An electromagnetic induction heating cooker receives an output of a rectifying / smoothing circuit by a commercial power source, a rectifying / smoothing circuit for rectifying / smoothing the commercial power source, and a resonance capacitor and a heating coil forming a resonance circuit. It consists of an inverter circuit configured by connecting the output of the resonance circuit to a switching element and an oscillating circuit that oscillates the switching element.The switching element sends a high-frequency current to the heating coil to generate a high-frequency magnetic flux for heating. An eddy current is induced in a load that is magnetically coupled to a coil, and the Joule heat causes the load to generate heat, which is widely used as an alternative to a heat source such as a gas table, a tabletop stove, or a rice cooker.

In an electromagnetic induction heating cooker, in order to prevent the user from accidentally heating a small load such as a knife or a fork, or to save power when a normal load such as a pot is removed from the heating coil. In addition, those equipped with a small object detection device for determining whether the load is appropriate or not have come to be used. As a small object detection method, it is common to judge the load by the balance of the input current to the inverter circuit and the current / voltage generated in the inverter circuit.
For example, as shown in Japanese Unexamined Patent Publication No. 2-114486, when it is determined that the load is unsuitable, heating is stopped for a certain period of time, and then intermittent oscillation is performed in which heating is performed again.

Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 58-155692, a no-load detection circuit for detecting the presence or absence of a load electromagnetically coupled to a heating coil, and whether the load is a small load such as a knife or a fork or an appropriate load. Equipped with a load detection circuit that determines whether a load is detected, an oscillation stop circuit when a no-load signal is detected, and a load detection inhibit circuit before oscillation stabilizes the power supply voltage. There is a method in which the oscillation of the inverter circuit is stopped in response to a signal and the inverter drive voltage is stabilized, and then the inverter is oscillated again.

[0005]

The problem in detecting small items of the conventional electromagnetic induction heating cooker will be described in the case of using a frying pan as a load in the former example. FIG. 2 is a characteristic curve diagram of a distance between a frying pan that is a load in a general electromagnetic induction heating cooker and a heating coil (hereinafter referred to as a gap), and input power input to the frying pan. It is shown that the input power to the load changes even if it is constant, depending on the positional relationship between the load and the heating coil.

When the load is a frying pan, if the operation level of small load detection is judged to be unsuitable when the gap becomes larger than a mm, the frying pan is vigorously shaken to stir the material, and the side portion of the frying pan is moved. As shown in FIG. 3, when the frying pan is tilted greatly with respect to the heating coil for quenching, the gap becomes amm or more, so that the small object detection device is activated and an intermittent oscillation state occurs, and cooking or quenching cannot be performed. .

This time, on the contrary, the operation level of small object detection is lowered,
In other words, in the case of a frying pan, if the gap is cmm or more, it is determined to be unsuitable, and if the frying pan is prevented from becoming an intermittent oscillation state even if it is tilted to some extent, the user will not be able to see the gap while heating at the oscillation frequency f1. Is a
When the cooking method in which the frying pan is vigorously shaken so as to have a value of mm is used, the input power supplied to the frying pan also drastically changes between W1 and W2. Therefore, an overcurrent or an overvoltage may occur in the inverter circuit, which may damage the circuit.

On the other hand, the latter example has two detecting means, and vigorously shakes the frying pan to stir the material, and quenches the side part of the frying pan.
When the frying pan is tilted greatly, the no-load detection device operates, and when small objects such as knives and forks are loaded, the small object detection device operates, and both stop oscillation and do not oscillate until the power supply voltage becomes stable, Although it is safe without causing overcurrent or overvoltage in the inverter circuit due to intermittent oscillation, the cooking method is too limited and the usability is poor.

An object of the present invention is to ensure safety against improper load without deteriorating usability.

[0010]

The present invention has been made to solve the above problems, and has an inverter circuit including a resonance capacitor, a heating coil, a switching element, and the like, and an oscillation circuit for oscillating the switching element. The electromagnetic induction heating cooker has two small object detection devices that judge whether the load induction heated by the heating coil is appropriate or not, and the oscillation circuit detects the first small object such as when the pan is shaken. If the device determines that the load is unsuitable, increase the oscillation frequency of the switching element, and if the second small object detection device determines that the load is unsuitable, such as when using a knife or fork, oscillate the switching element for a certain period of time. Intermittent oscillation that stops and then oscillates again is performed.

[0011]

With the above-mentioned structure, the first small object detection device determines that the load is a little different from the heating coil when the pan is shaken, and the second small object detection device does not When it is far from the heating coil or when a small load such as a knife or fork is used, it is determined that the load is unsuitable, and the oscillator circuit receives the load unfit signal of the first small object detection device and raises the oscillation frequency of the switching element By suppressing the overvoltage and overcurrent of the circuit, receiving the load unsuitable signal of the second accessory detection device and stopping the oscillation of the switching element for a certain period, and then oscillating again intermittently, the inverter circuit is destroyed or the accessory load is reduced. Prevents heating and allows cooking by shaking or tilting the pot.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block circuit diagram of an electromagnetic induction heating cooker to which an embodiment of the present invention is applied.

In FIG. 1, a commercial power supply 1 is rectified and smoothed by a rectifying and smoothing circuit 2. The output of the rectifying / smoothing circuit 2 is connected to the resonance capacitors 3a and 3b,
The heating coil 4 is connected to the middle point of a and 3b to form a resonance circuit, and the output of this resonance circuit is used as the switching elements 5a and 5b.
b, and the other end is connected to the rectifying / smoothing circuit 2 side to form a closed circuit, thereby forming an inverter circuit.

An oscillating circuit 6 oscillates the switching elements 5a and 5b. When the load is appropriately heated, the oscillation circuit 6 outputs an oscillation pulse to the switching elements 5a and 5b. This oscillation pulse is generated by the switching elements 5a, 5
It is output so that b is alternately turned on and off.

Reference numeral 7 is a first small object detecting device, 8 is a second small object detecting device, and the detection results thereof are input to an oscillating circuit 6, and the oscillating circuit 6 receives a load from the first small object detecting device 7. When it receives a signal that the
When a signal indicating that the load is unsuitable is received from the small object detection device 8), intermittent oscillation is performed.

In FIG. 2 which shows the relationship between the distance from the heating coil 4 and the input current when the load is a frying pan, the first small object detection device 7 has a frying pan from the heating coils 4 to a.
The determination level is set so that it is determined to be inappropriate when the distance is more than mm. Similarly, the second small object detection device 8 is set with a judgment level so as to judge that the frying pan is unsuitable when the frying pan is separated from the heating coil 4 by cm or more. This judgment level is also set when a small object such as a knife or a fork is heated. This is an unsuitable judgment level.

Next, the operation of the first small object detecting device 7 and the second small object detecting device 8 will be described.

When attempting to heat a knife, a fork or the like, both the first small object detecting device 7 and the second small object detecting device 8 determine that the load is unsuitable and output it to the oscillation circuit 6. The oscillation circuit 6 intermittently oscillates in response to a signal from the second small object detection device 8 to prevent the knife or fork from being heated.

In FIG. 2, when the load is violently shaken during heating at the oscillation frequency f1 or floated from the heating coil 4, if the frying pan is violently shaken here, when the distance between the frying pan and the heating coil 4 is amm,
The first small object detection device 7 determines that the load is inappropriate and outputs it to the oscillation circuit 6. The oscillating circuit 6 raises the oscillating frequency to f2 (f1 <f2) to suppress the occurrence of overvoltage and overcurrent in the inverter circuit. This state is continued as long as the distance between the frying pan and the heating coil 4 is amm or more and less than cmm, and cooking can be continued.

When the distance becomes cmm or more, the second small object detection device 8 determines that the load is unsuitable, outputs it to the oscillation circuit 6, and the oscillation circuit 6 performs intermittent oscillation.

[0021]

According to the present invention, the oscillating circuit raises the oscillation frequency of the switching element when the first small object detecting device detects an unsuitable load such as the pan is shaken, and the second small object detecting device operates. When an unsuitable load such as when using a knife or fork is detected, the oscillation of the switching element is stopped for a certain period of time and then intermittent oscillation is performed again, so that there is no risk of destroying the inverter circuit and the frying pan etc. It also enables cooking methods such as shaking and floating,
In addition, it is possible to provide a safe and easy-to-use electromagnetic induction heating cooker capable of preventing heating of knives and forks.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an electromagnetic induction heating cooker showing an embodiment of the present invention.

FIG. 2 is a characteristic curve diagram of the input power and the distance between the heating coil and the load of a general electromagnetic induction heating cooker.

FIG. 3 is a diagram showing a state in which a load frying pan is greatly inclined to the heating coil.

[Explanation of symbols]

 4 Heating coil 5a, 5b Switching element 6 Oscillation circuit 7, 8 Small object detection device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuyuki Takeda 1-3, Shinjuyoji, Kashiwa-shi, Chiba 1

Claims (1)

[Claims] 1. An electromagnetic induction heating cooker having an inverter circuit including a resonance capacitor, a heating coil, a switching element and the like, and an oscillation circuit for oscillating the switching element, wherein a load induction-heated by the heating coil (4) is applied. Connect two small object detection devices (7), (8) to the oscillation circuit (6) to judge whether they are appropriate or not.
The oscillation circuit (6) has switching elements (5a) and (5b) when the first small object detection device (7) determines that the load is unsuitable.
If the second small object detection device (8) determines that the load is unsuitable, the switching element (5a),
An electromagnetic induction heating cooker, characterized in that the oscillation of (5b) is stopped for a certain period of time and then oscillated again.