JP4707765B1 - Induction heating cooker - Google Patents

Abstract

【Task】
Provided is an induction heating cooker with high detection accuracy that can reliably detect spillage and has few malfunctions.
[Solution]
A top plate on which the pan is placed; a heating coil provided under the top plate for heating the pan; a drive circuit for converting the AC voltage into a high-frequency voltage and causing the high-frequency current to flow through the heating coil; A control circuit for controlling the drive circuit, a plurality of electrodes provided around the coil, and a capacitance measuring means for measuring the capacitance between the electrodes. The control circuit drives the heating coil. If the capacitance between the electrodes changes, it is determined that a spill has occurred, and the drive circuit is stopped, or the drive circuit is controlled so as to reduce the high-frequency current flowing through the heating coil.
[Selection] Figure 1

Description

  The present invention relates to an induction heating cooker that detects spillage based on a change in capacitance.

As a conventional induction heating cooker, there is known a device that detects a spillage from a change in capacitance between an electrode installed around a heating coil and a predetermined potential (see, for example, Patent Document 1).

JP 2008-159494 A (FIG. 1)

Conventional induction heating cookers detect spillage from the capacitance value between the electrode and a predetermined potential.For example, from the viewpoint of improving the safety of the user and the convenience of cooking, the spillover detection is further improved. There is a need for improved detection accuracy.

An induction heating cooker according to the present invention includes a top plate on which a pan is placed, a heating coil that is provided under the top plate and that heats the pan, and an AC voltage is converted into a high-frequency voltage to the heating coil. A drive circuit for supplying a current, a control circuit for controlling the drive circuit so as to obtain a predetermined power, a plurality of electrodes provided around the coil, and a capacitance measuring means for measuring a capacitance between the electrodes. If the capacitance between the electrodes changes during driving of the heating coil, the control circuit determines that spillage has occurred and stops the driving circuit or reduces the high-frequency current flowing through the heating coil. The drive circuit is controlled.

According to the present invention, among the plurality of electrodes installed in the vicinity of the heating coil, the capacitance between two electrodes is measured to determine whether or not the spill has occurred, that is, when the spill has occurred. Since water with a high relative permittivity enters a short distance between the electrodes near the heating coil, it is possible to detect spillage more reliably than the conventional measurement of the capacitance between the electrode near the heating coil and a predetermined potential. An induction heating cooker can be provided.
In addition, although water was mentioned as an example here, it can detect more reliably similarly not only about water but the spill of cooking liquid, such as curry.

The induction heating cooking appliance which shows Embodiment 1 of this invention. The top view of the induction heating cooking appliance which shows Embodiment 1 of this invention. The induction heating cooking appliance which shows Embodiment 2 of this invention. The top view of the induction heating cooking appliance which shows Embodiment 3 of this invention.

Embodiment 1 FIG.
FIG. 1 is an explanatory diagram showing a schematic configuration of an induction heating apparatus 1 according to Embodiment 1 of the present invention.
In the figure, an induction heating apparatus 1 (induction heating cooker) controls a heating coil 2, a drive circuit 5 for driving the heating coil 2 by converting the AC voltage of the AC power source 4 into a high-frequency voltage, and the drive circuit 5. And a capacitance measuring circuit 7 (capacitance measuring means) for measuring the capacitance between the electrode 3a and the electrode 3b.

FIG. 2 is a schematic view when FIG. 1 is viewed from above. In FIG. 2, the heating coil 2 and the electrodes 3 a and 3 b are disposed under the top plate 8.

Next, the operation of this embodiment will be described together with a method for measuring the capacitance between two electrodes.
The relative dielectric constant (mainly air) between the electrode 3a and the electrode 3b of area A is K, the distance is d, and the vacuum dielectric constant is ε0. The formula for obtaining the capacitance C is:
C = K × ε0 × A / d
It becomes. The capacitance measuring circuit 7 applies an alternating voltage between the electrodes 3a and 3b. When the applied AC voltage has a large capacitance, the amplitude decreases, and the capacitance is measured from the attenuation of the amplitude.

When there is no spillage, air having a relative dielectric constant of 1 exists mainly between the electrodes 3a and 3b. However, when spillage occurs, water with a relative dielectric constant of 80 enters, and the capacitance increases. Therefore, by checking whether there is an increase in the capacitance, it is possible to determine the overflow.

When it is determined that the spilling has occurred, the operation of the drive circuit 5 is stopped, or the drive circuit 5 is controlled to reduce the current flowing through the heating coil 2.

As described above, according to the present embodiment, by measuring the capacitance between the two electrodes 3a and 3b installed in the vicinity of the heating coil 2, it is possible to avoid wasting electric power and the top plate 8 is spilled. It is possible to provide an induction heating cooker that can minimize contamination with the contents. In the present embodiment, since the capacitance is measured between the two electrodes 3a and 3b, the value of the distance d in the above equation is compared with the case where the capacitance between the electrode and the predetermined potential is measured. Decreases, and the capacitance to be measured increases. In other words, compared to the conventional measurement of capacitance between the electrode near the heating coil 2 and a predetermined potential, water with a high relative dielectric constant enters a short distance between the electrodes near the heating coil. A change in capacity can be detected with higher accuracy, and an induction heating cooker with high detection accuracy can be provided.

Further, when measuring the capacitance, the change rate of the capacitance within a predetermined time may be measured, and it may be determined that the spill has occurred when the change rate exceeds a predetermined value. When the spill occurs, the capacitance changes abruptly. Therefore, when spilling is determined based on the rate of change within a predetermined time, there is little malfunction and the spill can be detected more reliably.

Embodiment 2. FIG.
FIG. 3 is an explanatory diagram showing a schematic configuration of the induction heating apparatus according to Embodiment 2 of the present invention.
Note that the same portions described in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
In FIG. 3, the induction heating apparatus 1 includes an input current measuring unit 10, a heating coil voltage measuring unit 11, and a heating coil current measuring unit 12.

Next, the operation of the present embodiment will be described. When a heating start command is issued by an operation unit (not shown), the control circuit 6 causes a weak current to flow, and the input current measured by the input current measuring means 10 or the heating coil current measured by the heating coil current measuring means 12 and The impedance viewed from the heating coil 2 is calculated from the heating coil voltage measured by the heating coil voltage measuring means 11, and it is determined whether or not the pan 9 is placed on the top plate 8. When the pan 9 is placed, the impedance viewed from the heating coil 2 is increased. Therefore, when the impedance is equal to or higher than a predetermined value, it is determined that the pan 9 is placed.

When the pan 9 is placed, the capacitance between the electrodes 3a and 3b is changed by the capacitance between the electrode 3a or 3b and the pan 9. That is, the capacitance of the electrode 3a or 3b and the pan 9 is added in parallel to the capacitance between the electrodes 3a and 3b. In the present embodiment, the control circuit 6 stores the capacitance between the electrodes 3a and 3b when it is determined that the pan 9 is placed, and if the capacitance increases with reference to this capacitance, the control circuit 6 is blown out. When it is determined that the spillage has occurred, the operation of the drive circuit 5 is stopped or the drive circuit 5 is controlled so as to reduce the current flowing through the heating coil 2.

As a result, the control circuit 6 does not erroneously determine that a change in capacitance that occurs when the pan 9 is placed has caused a spill, thus preventing a user's cooking convenience from being lowered due to a detection error. be able to.

As described above, according to the present embodiment, since the overflow is determined based on the capacitance when the pan 9 is placed, detection accuracy is high, and malfunctions such as erroneous detection can be reduced.

In addition, while the pan 9 is being heated, the input current, the heating coil current, and the heating coil voltage are continuously measured, and the control circuit 6 changes the stored capacitance when any of the measured values changes. It may be determined that a spill has occurred when the capacitance increases based on the newly replaced capacitance.

When the user moves the pan 9 during cooking, since the impedance viewed from the heating coil 2 changes, the input current, the heating coil current, and the heating coil voltage change. At this time, since the distance between the electrodes 3a and 3b and the pan 9 also changes, the capacitance between the electrodes 3a and 3b also changes. Since the capacitance after the change is determined as a new standard, the control circuit 6 erroneously determines that the capacitance has changed when the pan 9 is moved during cooking. Therefore, it is possible to prevent the user's cooking convenience from being lowered due to erroneous detection of overflowing.

Embodiment 3 FIG.
FIG. 4 is a top view of induction heating apparatus 1 according to Embodiment 4 of the present invention.
In addition, the same number demonstrated in Embodiment 1, 2 attaches | subjects the same number, and abbreviate | omits description.
In FIG. 4, the heating coil 2 and the electrodes 3 a, 3 b, and 3 c are disposed under the top plate 8.

Next, the operation of the present embodiment will be described. The capacitance measuring circuit 7 measures the capacitance between the electrodes 3a and 3b and the capacitance between the electrodes 3c and 3b using the electrode 3b sandwiched between the electrodes 3a and 3c as a reference potential. The control circuit 6 determines that a spill has occurred when the capacitance between the electrodes 3a and 3b or between the electrodes 3c and 3b increases. When it is determined that the spilling has occurred, the operation of the drive circuit 5 is stopped, or the drive circuit 5 is controlled to reduce the current flowing through the heating coil 2.

As described above, according to the present embodiment, an electrode sandwiched between a plurality of electrodes is used as a reference potential, so that it is possible to detect the spillage at a plurality of locations with a small number of electrodes.

1 induction heating device, 2 heating coil, 2 heating coil, 3a electrode, 3b electrode, 3c electrode, 4 AC power supply, 5 drive circuit, 6 control circuit, 7 capacitance measurement circuit, 8 top plate, 9 pan, 10 input Current measuring means, 11 heating coil voltage measuring means, 12 heating coil current measuring means.

Claims (3)

A top plate on which the pan is placed;
A heating coil provided under the top plate for heating the pan;
A drive circuit for converting an alternating voltage into a high frequency voltage and flowing a high frequency current through the heating coil;
A control circuit for controlling the drive circuit to have a predetermined power;
A plurality of electrodes provided around the heating coil;
A capacitance measuring means for measuring a capacitance between the electrodes;
Means for measuring the heating coil current or drive circuit input current or heating coil drive voltage,
Wherein the control circuit, the change rate that put a predetermined time of the electrostatic capacitance between the electrodes the heating coils during driving was measured, it is determined that the change rate is boiling over not less than a predetermined value occurs, the drive Controlling the drive circuit to stop the circuit or reduce the high frequency current flowing through the heating coil;
If any of the heating coil current or the drive circuit input current or the heating coil drive voltage changes, it is not determined that a spill has occurred even if the capacitance increases, and the capacitance at this time is As a new reference capacitance, it is determined that a spill has occurred when an increase in capacitance of a predetermined value or more occurs with respect to this value, and the drive circuit is stopped or the heating coil is turned on. An induction heating cooker characterized by controlling the drive circuit so as to reduce a high-frequency current to flow. Claims plurality of electrodes disposed on the heating coil outside the above three, the reference potential electrodes sandwiched between the plurality of electrodes, and measuring the capacitance between the reference potential electrode 1 serial induction heating cooker of the mounting. The induction heating cooker according to claim 1 or 2 , wherein the control circuit applies an AC voltage to the electrode and measures the capacitance based on an attenuation level of the applied voltage.

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