JPH0261425A - Microwave oven - Google Patents

Abstract

PURPOSE:To enable appropriate thawing to be performed for any kind of material to be heated by mounting at least one electro-acoustic transducer on a wall surface of a heating chamber, supplying the heating chamber with a sound wave having a frequency equal to the resonant frequency of the system, and obtaining the driving-point impedance of the transducer. CONSTITUTION:With a high-frequency wave supplied into a heating chamber 3, a material to be heated 5 is heated and thawed, with a change in the hardness of the material 5 from a high hardness in a frozen state to a low hardness in a thawed state. This change has relation to a change in the absorption factor of a sound wave supplied into the chamber 3, and the driving-point impedance of an electro-acoustic transducer 6 is decreased with the progress of thawing, so that completion of the thawing can be recognized. The frequency of the sound wave to be oscillated is selected in the vicinity of a resonant frequency which is determined by the geometry of the inside space of the chamber 3 or the like.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention automatically recognizes the cooking state of the object to be heated, especially the thawing state thereof, thereby performing more appropriate cooking and thawing for each object to be heated. The present invention relates to high-frequency heating devices such as microwave ovens that are capable of high-frequency heating.

Conventional technology In recent years, high-frequency heating devices, especially microwave ovens, are equipped with various types of sensors such as temperature sensors, humidity sensors, and weight sensors for the purpose of automatic cooking. A cooking sequence is selected.

Defrosting is one of the items that is automated based on the information from the sensor.

Conventionally, for automation of defrosting, a method has been proposed in which the supply of high frequency waves is controlled using information from the humidity sensor.

The conventional decompression automation method described above will be described below with reference to the drawings.

FIG. 4 shows a conventional example of a method for automating decompression.

In Fig. 4, 1 is a magnetron, 2 is a waveguide, and 3 is a magnetron.
is the heating chamber, 4 is the tray, 5 is the object to be heated, 7 is the intake hole, 8
is a blower, 9 is an exhaust hole, 1o is an exhaust air path, 1) is a humidity sensor attached to the top of the exhaust hole 9, 12 is an air blow hole, and 13 is a circulating air connecting the exhaust hole 9 and air blow hole 12. 14.15 is a shield.

In the high-frequency heating device configured as described above, the shields 14 and 15 act to close the intake hole 7 and the exhaust air path 10, respectively, during thawing. When high frequency waves are supplied to the heating chamber 3 through the waveguide 2, the object to be heated 5 is heated and steam is generated. Since the air intake hole 7 and the exhaust air passage 10 are closed, the air in the heating chamber 3 circulates from the exhaust hole 9 to the circulation air passage 13 → the air blowing hole 12 → the heating chamber 3. The relative humidity of this air is detected by a humidity sensor 1), and the supply of high frequency waves is controlled based on the data, thereby realizing automation of defrosting.

Problems to be Solved by the Invention However, in the above configuration, the amount of water vapor generated differs depending on the object to be heated, so it is necessary to change the coefficient for controlling the supply of high frequency waves depending on the object to be heated. Therefore, it is necessary to have a coefficient for every object to be heated, and in the case of objects to be heated that generate a small amount of water vapor, the accuracy is poor and overheating is likely to occur. As a result, the problem was that it lacked versatility.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a high-frequency heating device that can automatically recognize the thawed state of any frozen food with high precision.

Means for Solving the Problems In order to solve the above problems, the high frequency heating device of the present invention has the following features:
An electroacoustic transducer is attached to the wall of the heating chamber, and the thawed state of food is recognized using the sound waves generated within the heating chamber.

Effect of the Invention With the above configuration, the present invention oscillates a sound wave within the heating chamber, and determines the thawed state of the object to be heated within the heating chamber as data based on the change in driving point impedance of the electroacoustic transducer. That is, by determining the state of the object to be heated in accordance with the impedance change, it is possible to control the supply of high frequency waves during thawing.

EXAMPLE Hereinafter, a high-frequency heating apparatus according to an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a longitudinal cross-sectional view of a high-frequency heating device in an embodiment of the present invention. In FIG. 1, 1 is a magnetron, 2 is a waveguide, 3 is a heating chamber, 4 is a tray, and 5 is an object to be heated, which is the same as in FIG.

Reference numeral 6 denotes an electroacoustic transducer, which is attached to the side wall surface of the heating chamber 3 to oscillate sound waves within the heating chamber 3, and is used as a sensor for determining the driving point impedance.

The operation of the high-frequency heating device configured as described above will be described below with reference to FIGS. 1, 2, and 3.

When high frequency waves are supplied to the heating chamber 3 through the waveguide 2, the object to be heated 5 is heated and thawed. At that time, the object to be heated 5
The hardness of the heated object 5 changes over time from the frozen hard state to the original hardness of the thawed object 5. A change in the hardness of the object to be heated 5 is related to a change in the absorption rate of the supplied sound waves, which results in a change in the driving point impedance of the electroacoustic transducer 6. FIG. 2 is a diagram showing changes in driving point impedance of the electroacoustic transducer before and after thawing of the heated object. The vertical axis shows driving point impedance, and the horizontal axis shows frequency. The solid line shows before thawing, and the dotted line shows after thawing. As this graph shows, the value of the driving point impedance near the resonance frequency becomes smaller as the hardness of the heated object 5 changes, that is, as the thawing progresses, and it becomes possible to recognize whether thawing has been completed based on this change. However, if the frequency of the oscillating sound wave deviates significantly from the resonant frequency, the change before and after thawing becomes small, making it impossible to accurately recognize the thawing state. Therefore, a sound wave with a frequency near the resonant frequency determined by the spatial shape of the heating chamber 3 is used. do. As a result, by measuring the change in the driving point impedance, the hardness of the object to be heated 5, that is, the thawing state can be recognized. By feeding back the results, the output of the magnetron 1 can be controlled, the heating time can be determined, and thawing can be automated.

FIG. 3 shows an example of a block diagram for determining a change in driving point impedance of an electroacoustic transducer. A bridge circuit is constructed with three resistors and an electroacoustic transducer 6, and a voltage is applied between A and B to drive the circuit, and a potential difference between C and D is determined to determine a change in driving point impedance.

Although the electroacoustic transducer is attached to the side wall of the heating chamber in Fig. 1, it may be attached to any other wall surface.Also, since the resonant frequency is shifted by placing the object to be heated in the heating chamber,
The optimum frequency for each object to be heated may be determined in the vicinity of the resonant frequency of the heating chamber, and the circuit may be configured to oscillate sound waves.

Effects of the Invention As described above, the present invention attaches at least one electroacoustic transducer to the wall surface of a heating chamber, supplies sound waves at the resonant frequency of the system into the heating chamber, and changes the driving point impedance of the electroacoustic transducer at that time. By determining this and recognizing the state of the object to be heated, an excellent high-frequency heating device can be realized that can perform appropriate thawing regardless of the type of object to be heated.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view showing a high-frequency heating device according to an embodiment of the present invention, Fig. 2 is a graph showing changes in driving point impedance of an electroacoustic transducer before and after thawing of the object to be heated, and Fig. 3 is a block diagram for determining the driving point impedance of an electroacoustic transducer, and FIG. 4 is a longitudinal cross-sectional view of a conventional high-frequency heating device. 1... Magnetron, 2... Waveguide,
3... Heating chamber, 4... Receiver is a plate, 5...
... Heated object, 6 ... Electroacoustic transducer. Name of agent Patent attorney Shigetaka Awano Haka 1 person 1-11 Mag ° Netron WE 2 Fig. 4 - Saucer 6 - Double # bowl food - - View, Kiff Mata Yoko-ku 1 Fig.

Claims (1)

[Claims] (1) It has a heating chamber and a high-frequency oscillator, and at least one electroacoustic transducer is attached to the wall surface of the heating chamber, and a sound wave is emitted from the electroacoustic transducer into the heating chamber, and the electricity generated at that time is 1. A high-frequency heating device comprising: means for measuring a change in driving point impedance of an acoustic transducer, and recognizing a cooking state of an object to be heated based on the measured data. (2) A claim characterized in that the electroacoustic transducer emits into the heating chamber a sound wave with a resonant frequency determined by the spatial shape of the heating chamber, the object to be heated placed in the heating chamber, the characteristics of the electroacoustic transducer, etc. (1) The high frequency heating device described.