JPH02158084A - Induction heating cooker - Google Patents

Abstract

PURPOSE:To improve heat efficiency by providing an electrode for transferring a signal when an object to be heated is placed on a base, a circuit for determining the location or the size of the object by means of variation of the signal and a controller for changing heating area of a heating coil in response to the output of the circuit. CONSTITUTION:An electrode 10 is placed under a base plate 9 at the location where is almost the center of a heating coil 1. Electrodes 11a, 11b, 12a, 12b, 13a and 13b are disposed at the periphery of the electrode 10. Pulse signals are applied to the electrode 10 from a pulse generator 14. The pulse signals from the electrode 10 are received by the electrodes and a reception signal is supplied to a judging circuit 15. A signal from the judging circuit 15 is received by a heating coil controller 16 to change heating area of the heating coil 1. The heating area of the heating coil 1 is canceled to be non-heated state so as to inhibit heating under low heating efficiency when an object to be heated is displaced against the upper face of the heating coil 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an induction heating cooker that automatically detects the position or size of an object to be heated and automatically changes the heating area.

2. Description of the Related Art Conventionally, this type of induction heating cooker has detected the presence or absence of an object to be heated using a configuration as shown in FIG.

That is, when the object to be heated 3o is placed on the mounting plate 32 at the center of the heating coil 31 that heats the object to be heated 3o,
A magnet 33 is provided that moves in the direction of the mounting plate 32 in response to the object to be heated 30, and by moving the magnet 33 up and down, the system tip 34 is turned on.

The unit was turned off and the object to be heated was detected.

Furthermore, in recent years, there has been a structure shown in FIG. 6, for example, as shown in Japanese Patent Publication No. 59-32878. This electrically detects the presence or absence of a heated object and the size of the heated object.

That is, it is equipped with a heating coil/L' 35, a resonant capacitor 36, and a switching element 37, and is composed of an inverter circuit and a control circuit that convert DC power obtained by converting low frequency power 38 by a rectifier 39 and a smoothing capacitor 4o into high frequency power. The control circuit includes an input detection circuit 41 that detects the magnitude of the input current to the inverter circuit and outputs an output signal proportional to the magnitude, and an input detection circuit 41 that detects the voltage of the heating coil/v36 and outputs an output signal proportional to the magnitude. A voltage detection circuit 42 that outputs an output signal proportional to The configuration includes a small object load detection circuit 44 that supplies an output prohibition signal to the oscillation control circuit 43 when the output signal is smaller than the output signal of the voltage detection circuit 42, and detects the presence or absence of the object to be heated 45 and the object to be heated. It was detecting the size of objects.

Problems to be Solved by the Invention However, with such a structure, as shown in Fig. 5, a mechanical nib is used to detect the object to be heated, so foreign objects or the magnet may be installed at an angle. There are issues with operational reliability due to malfunctions caused by leakage and the lifespan of the switch contacts. In addition, even if a heated object with a small bottom diameter or a heated object with a large bottom diameter is placed offset from the heating coil, if the heated object is above the magnet, the heated object will be detected. Induction heating cookers that attempt to supply high-frequency power to objects to be heated using a fixed heating coil area have a problem in that heating efficiency deteriorates.

Furthermore, in the structure shown in FIG. 6, in order to detect the presence and size of the object to be heated, it is necessary to first drive the switching element 8 and supply high-frequency power to the inverter circuit, which reduces the heating efficiency mentioned above. In addition to the problem of deterioration, especially when an object to be heated with a small bottom diameter is placed, there is a problem that the object is heated until the small object load detection circuit determines that the object is a small object.

Therefore, the present invention detects the position or size of the object to be heated with high precision and high reliability, can efficiently heat the object even if the bottom diameter of the object is small compared to the heating coil, and can detect the object to be heated with high accuracy and reliability. Stops heating without wasting power when the object is not placed on the heating coil, or when the object to be heated is smaller than a certain value, or even if the object is large, it is placed out of alignment with the heating coil. Included for the purpose of obtaining an induction heating cooker.

Means for Solving the Problems In order to achieve the above object, the present invention provides a mounting plate on which an object to be heated is placed, a heating coil disposed below the mounting plate, and a heating coil disposed above the mounting plate. A plurality of electrodes are provided on the bottom surface of the device, and a heated object is placed on the top surface of the mounting plate at a position opposite to the plurality of electrodes, so that changes in the signal level generated at the plurality of electrodes can be avoided. a determination circuit that determines the position or area of the heated object based on the heating coil; and a heating coil control unit that controls the heating area of the heating coil; This is to change the area.

Function: With the above configuration, the position or size of the object to be heated is automatically determined and the heating area of the heating coil is automatically switched, so when the area of the object to be heated is small,
By reducing the heating area of the heating coil according to the area, the object to be heated can be efficiently heated. In addition, if the object to be heated is placed misaligned with respect to the top surface of the heating coil, it is possible to eliminate the heating area of the heating coil, set it in a non-heated state, and prohibit heating in a state where heating efficiency is poor. Of course, it is possible to detect a state in which there is no object to be heated or a state in which a small object such as a knife or fork is placed, and set the device to a non-heating state.

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings.

In FIGS. 1 and 2, 1 is a heating coil, and this heating coil 1 and a resonant capacitor 2 constitute a resonant circuit. 3 is a switching element which, together with a damper diode 4, supplies a high frequency current to the heating coil /l/1.

A smoothing capacitor 6 receives AC power from a commercial power supply 6, converts it into DC power through a rectifier 7, and supplies the power to the resonant circuit and the switching element 3. 8a and 8b are objects to be heated, which are placed on a placing plate 9 placed above the heating coil 1. On the lower surface of the mounting plate 9, an electrode 1o is placed approximately at the center of the heating coil, and electrodes 11a are placed around the heating coil.
11b, 12a, 12b, 13a.

13b is installed, and the pulse generator 1 is installed on the electrode 1o.
A pulse signal is supplied from 4. Electrode 11a.

11b, 12a, 12b, 13a, and 13b receive the pulse signal from the electrode 10 and supply the received signal to the determination circuit 16. A heating coil control section 16 receives a signal from the determination circuit 15 and switches the heating area of the heating coil 1.

Next, the operation of the configuration of this embodiment will be explained. By placing the object to be heated 8 on the mounting plate 9, as shown in FIG. Due to the capacitance generated between the object to be heated 1 and the electrode 13a, the voltage is transmitted to the electrode 13a as Vb and supplied to the signal detection means 26e in the determination circuit 15. 17 is a comparator and stain pole 1
Voltage V determined by signal vb from 3a and resistor 18.19. Compare with. Signals vb and V. As shown in FIG. 3, when the object to be heated 1 is placed on the electrode 13a, the pulse signal of Wb is kept constant. Therefore, the output of the comparator 17 is set to vd. When vd is HI, the transistor 2
0 is turned on and the capacitor 21 is charged. Vd is LOW
When the transistor is turned off, the capacitor 21 is discharged through the resistor 22, and the (+) input voltage of the comparator 23 is V. become that way. A resistor 24゜2 is connected to the (→) input of the comparator 23.
From K, supplying the voltage level v1 in the figure to 6,
The output Vq of the comparator 23 is at the Low level when the object to be heated is not placed on the top of the electrode 13a, and is at the HI level when the object is placed on the top.
The signal directly becomes the output of the signal detection means 26e.

In FIGS. 1 and 2, when the object to be heated is 8a, the object to be heated 8a is placed only on top of the electrodes 13a and 13b, and due to the operation of the signal detection means 26, Only the signal detection means 26e and 26f output HI. Here, the output of the signal detection means 26 is supplied to an AND circuit 27 and an OR circuit 28.
The output is supplied to the pan position determining section 29.

Therefore, the outputs of the signal detection means 26e and 26f are both H.
Since the signal is I, the output of the AND circuit 27c is at the Hl level, and the output of the OR circuit 28c is also at the HI level, and two HI level signals are supplied to the pan position determining section 29c.

Conversely, an electrode 11a on which the object to be heated 8a is not placed
, 11b and 12a, 12b, the signal detection means 26a, 28b and 26c, 26
All outputs of d are at LOW level. Therefore, AND circuits 27&, 27b, t7 circuits 28a, 28b
All outputs are at LOW level, and the pot position judgment section 29
LOW level signals are supplied to a and 2sb.

Here, for example, when the heating coil/I/1 and the heated object 8b are placed with their centers shifted as shown in the heated object 8b, only the electrodes 12a, 13a, and 13b are located below the heated object 8b. Therefore, by the above operation, HI level signals are output from the signal detecting means 26c, 26e, and 26f, and LOW level signals are output from the other means. Therefore, the outputs of the AND circuits 27a and 27b are at LOW level, the output of the AND circuit 27c is at Hl level, and the OR circuit 28
The output of a is at LOW level and is an OR circuit 28b.

The output of 28c becomes Hl level. Therefore, two LOW signals are supplied to the pot position determining section 29a, a LOW signal and a HI signal are supplied to 29b, and two HI times signals are supplied to 29c. The pot position determination unit 29 determines the status of the pot based on two input signals, and supplies the signal to the heating coil switching circuit 30 in the heating coil control unit 1 etc. In response to the signal, the heating coil switching circuit 3o The switch 31 is turned on and off, and FIG. 4 shows the signal transmission from the pot position determining section 29 to the switch 31. That is, when both inputs to one pot position determination section are HI, it is determined that the object to be heated 8 is placed at the center of the heating coil on the area surrounded by the electrodes connected thereto. If both inputs are LOW, it is determined that there is no heated object 8 in the area surrounded by the electrodes connected thereto.

Moreover, when one input is HI and the other is LOW level, it is determined that the object to be heated 8 is placed offset from the center of the heating coil.

As shown in FIG. 2, the heating coil 1 has an intermediate terminal 32.
a, 32b, 32c, and switches 31a, 31b,
31c is connected, and as shown in the signal transmission in FIG. 4, the output of the pan position determining section 29 turns on and off the switch 31 to change the heating area of the heating coil/L/1. This is possible.

In this embodiment, heating is prohibited when the object to be heated 8 is placed off the center of the heating coil 1, but there is no problem even if the heating area is changed to an appropriate one. Furthermore, in this embodiment, two electrodes are used as a pair to detect the heated object 8, but as shown in FIG. The central type [10 If the heated object 8 is detected by increasing the number of electrodes installed at substantially equal distances from the radial axis, the heated object can be detected with even higher accuracy.

Furthermore, assuming that the pulse signal generated from the pulse generator 14 has a frequency that is an integral multiple of the resonant frequency of the resonant circuit consisting of the heating coil 1 and the resonant capacitor 2,
The noise generated from the heating coil 1 is transferred to the electrodes 11a and 11b.
, 12a, 12b.

Even if signals 13a and 1sb receive the signal, it is not recognized as a signal from the electrode 1o, and there is no malfunction due to the above-mentioned noise, and stable signal detection can be performed.

Effects of the Invention As described above, according to the present invention, an electrode is provided on the lower surface of the mounting plate to transmit a signal when an object to be heated is placed on the upper surface.
The structure includes a determination circuit that determines the position or size of the object to be heated based on the change in the signal (1), and a heating coil control section that switches the heating area of the heating coil according to the output of the determination circuit. If the object to be heated is smaller than the heating coil, the area of the heating coil can be changed to be approximately the same as the area of the heating coil, so heating can be performed efficiently.Also, if the object to be heated is smaller than a certain value or when the object to be heated is placed off the center of the heating coil, the condition can be detected without passing high-frequency current through the heating coil, eliminating wasted power consumption and improving heating efficiency. This makes it possible to prohibit heating under bad conditions.

[Brief explanation of the drawing]

Fig. 1 is an electric circuit diagram of an induction heating cooker showing an embodiment of the present invention, Fig. 2a is an enlarged configuration diagram of the main parts, Fig. 2 is an electrode arrangement diagram of the mounting plate, and Fig. 3 a is a circuit diagram of the same signal detection means, FIG. 3 is an operational waveform diagram of the same main part, FIG. 4 is a diagram explaining the same operation, FIG. 6 is a configuration diagram of a conventional induction heating cooker, and FIG.
The figure is a circuit diagram of another conventional induction heating cooker. 1...Heating coil, 8...Heated object,
9... Placement plate, 10.11a, 11b, 12a
, 12b. 13a, 13b... Electrode, 16... Judgment circuit, 16... Heating coil control section. Name of agent: Patent attorney Shigetaka Awano and one other person

Claims (1)

[Claims] A placing plate on which an object to be heated is placed, a heating coil placed below the placing plate, a plurality of electrodes provided on the lower surface of the placing plate, and an upper surface of the placing plate. a determination circuit that determines the position or area of the heated object based on changes in signal levels generated at the plurality of electrodes by placing the heated object at a position facing the plurality of electrodes; and the heating coil. An induction heating cooker comprising: a heating coil control section for controlling a heating area of the heating coil, wherein the heating coil control section switches the heating area of the heating coil according to an output of the determination circuit.