JPH0387520A - Microwave oven - Google Patents

Abstract

PURPOSE:To enable assured and easy detection of thawing, by detecting the progress of thawing of a food through an antenna shorter than one-quarter the wavelength corresponding to the oscillation frequency of a microwave- radiating means, and providing a detecting means in the vicinity of a cooling fan so that the detecting means is cooled. CONSTITUTION:An antenna 6 is shorter than one-quarter the wavelength corresponding to the oscillating frequency of a microwave-radiating means (magnetron) 3. Microwaves in the frequency band of the magnetron 3 are detected by the antenna 6 disposed in a heating chamber. A detecting means 8 detects those microwave power components in the oscillating frequency band which are not absorbed by a food 1, and outputs the detection result as a voltage VS. Repetition of thawing of foods causes a rise in the temperature of a substrate and variations in the dielectric constant and loss of the base plate, but the temperature rise can be prevented by blowing a cool airflow to the detecting means from a cooling fan 5, which is provided for cooling the magnetron 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high-frequency heating device that is closely related to the automation of defrosting food products.

BACKGROUND OF THE INVENTION Conventionally, as a distantly related example of automating the defrosting state of this type of high-frequency heating device (hereinafter referred to as a microwave oven), as shown in FIG. The heating sequence corresponding to the weight of the device was controlled by a microcomputer as a control device, and the output of the high-frequency radiation device was controlled. That is, when the weight of a certain food is detected by the weight sensor 21, the corresponding weight is heated at the maximum power for an initially determined time, and then the high-frequency radiation means per unit time is heated by repeatedly turning on and off the driving means. control to reduce the output. Furthermore, as shown in Japanese Patent Application Laid-Open No. 59-207595, the thawing state of food can be indirectly understood from the relationship between the temperature dependence of the dielectric loss of the food and the detected output in the oscillation frequency band of the high-frequency radiation means. There is also an example in which the control means is configured to control the output of the high-frequency radiating means by a change in a signal detected and controlled by an antenna provided in the heating chamber. Thawing of food was achieved through such control.

Problems to be Solved by the Invention However, in the above configuration, when the starting temperature of the food is a certain predetermined temperature (for example, the freezer temperature -
18°C) and the shape is standard (for example, square).Depending on the thawing start temperature and shape of the food, the food may be boiled or unthawed, resulting in poor thawing results. It was enough. In addition, a weight sensor for measuring the weight of food requires a turntable, and its configuration is complicated because it detects changes in the capacitance of the sensor due to the weight of the food and detects distortion signals.

Furthermore, when detecting thawing using a detection means, depending on the position where the detection means is placed, the temperature of the substrate increases when the food is repeatedly heated, and the detected voltage may differ even for the same weight due to the temperature characteristics. Therefore, an object of the present invention is to realize defrosting of food with a simple configuration.

Means for Solving the Problems In order to solve the above problems, the present invention detects the progress of defrosting of food using a detection means from the temperature characteristics of the dielectric loss of the food in the frequency band of the high-frequency radiation means. It is configured to be installed near the cooling fan and cooled.

Function According to the present invention, the detection means has the function of being kept at a constant temperature by the cold air from the cooling fan.

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings. FIG. 1 is a diagram showing the main body of a high-frequency heating device according to an embodiment of the present invention. 1 is food, 2 is a heating chamber, 3 is a high frequency radiation means (hereinafter referred to as magnetron), 4 is a high voltage transformer for operating magnetron 3, 5 is a cooling fan for cooling magnetron 3, and 6 is an antenna for magnetron 3. It is shorter than 1/4 wavelength of the oscillation frequency (3 to 5 in the present invention). 7 is an attenuator, 8 is a detection means, 9 is an amplifier for amplifying the detected signal, 10 is a drive means for varying the high frequency power of the magnetron 3, and 11 is for controlling the drive means 10 according to the amplified detection signal. ,
It is a control means (a microcomputer in the present invention) that adjusts the output of high frequency power.

FIG. 2 is a circuit diagram of the detection means 8 for detecting the oscillation signal of the magnetron 3. 12 is a 50 ohm resistor, 13 is a detection diode (for example, Schottky barrier diode), 14.15 is a resistor, and 16 is a capacitor. These detect the high frequency power that is not absorbed by the food 1 in the oscillation frequency band of the magnetron 3, and the voltage Detected as vS. Note that 7 is an attenuator, and the high frequency power that the magnetron 3 radiates into the heating chamber 2 is several hundred watts, and is used to prevent excessive human power from being applied to the detection means 8.

FIG. 3 is a diagram in which the detection means 8 is composed of a microstrip line. Dielectric substrate 1 having a certain dielectric constant ER
Patterns 18 and 19 of W4 foil are etched on the 7. 18 914 M part has characteristic impedance 50
It is ohm, and the 19 part is ground.

By configuring the detection means 8 on the microstrip line, it is easy to optimally design the length of the line according to the frequency band to be detected, and since it is performed by enching, the detection accuracy is improved. . FIG. 4 is a characteristic diagram showing the relationship between the signal level of the detection voltage vS and the minimum point T with respect to the weight of the minced beef meat. From this figure, it can be seen that there are large differences in the detection voltage immediately after the start of thawing and the detection time at the minimum point T, depending on the weight of the food. this is,
This is because if the weight of the food is small, less high frequency waves will be absorbed and relatively more high frequency waves will be detected by the antenna.

Figure 5 shows food 1 (frozen minced meat 100 min.
FIG. 3 is a characteristic diagram showing how the signal voltage detected by the detection means 8 changes due to changes in the temperature of the substrate when the sample (grams) is thawed.

In FIG. 5, it can be seen that as the substrate temperature increases, the detected voltage differs even for the same food. This is because the temperature of the substrate increases as the food is repeatedly thawed, and the dielectric constant and loss of the substrate change. However, if the configuration is such that the cooling fan 5 that cools the magnetron 3 blows cold air on it, the temperature of the substrate can be prevented from rising, so that the detected voltages will not differ.

Effects of the Invention As described above, according to the present invention, the following effects can be obtained.

The high frequency wave in the frequency band of the high frequency radiation means is detected by an antenna placed in the heating chamber, and the detection means is cooled by a cooling fan, so even if food is repeatedly thawed, stable thawing detection is possible. Since the influence of the temperature characteristics of the elements constituting the detection stage can also be prevented, thawing detection can be easily achieved without failure.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the main body of a high-frequency heating device according to an embodiment of the present invention, FIG. 2 is a circuit diagram of the detection means, FIG. 3 is a diagram of the detection means configured on a micro-string line, and FIG. The figure is a characteristic diagram of the change in the signal of the detection means with respect to the food weight during thawing, Figure 5 is a characteristic diagram showing the change in the signal when the same thawing is repeated, and Figure 6 is the main body configuration of a conventional high-frequency heating device. It is a diagram. 1... Food, 2... Heating chamber, 3...
... High frequency radiation means, 5 ... Cooling fan, 6
...Antenna, 8...Detection means, 10
. . . Drive means, 11 . . . Control means.

Claims (1)

[Claims] A heating chamber into which food is taken in and taken out, a high frequency radiation means which supplies high frequency power into the heating chamber, a driving means which drives the high frequency radiation means, a cooling fan which cools the high frequency radiation means and the driving means, and the driving means. an antenna shorter than 1/4 wavelength of the oscillation frequency of the high-frequency radiation means, and a detection means for detecting the progress of defrosting of the food through the antenna, and the detection means is configured to control the cooling. A high-frequency heating device configured to be installed near the fan for cooling.