JP2707768B2 - High frequency heating equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating device for achieving automatic thawing of food.

2. Description of the Related Art Conventionally, as an example of achieving an automatic thawing state of this type of high-frequency heating device (hereinafter referred to as a microwave oven), there is a sixth example.
As shown in the figure, the weight of the food on the turntable 12 was detected, and a heating sequence corresponding to the weight was controlled by a microcomputer, which is a control means, to control the output of the high-frequency radiation means. . That is, the weight sensor
In step 13, if the weight of a certain food is detected, the corresponding weight is heated with the maximum power for the initially determined time, and thereafter, the output of the high-frequency radiating means per unit time is repeated by repeatedly turning on and off the driving means. The control to lower was performed.

Further, as shown in JP-A-59-207595, the thawing state of food is indirectly grasped from the relationship between the temperature dependence of the dielectric loss of the food and the detection output in the oscillation frequency band of the high-frequency radiation means. There is also an example in which a control unit controls the output of the high-frequency radiation unit based on a change in a signal detected by an antenna provided in a heating chamber.

 Defrosting of food was realized by such control.

Problems to be Solved by the Invention However, in the above-described configuration, the above condition is satisfied only when the starting temperature of the food is a predetermined temperature (eg, freezer temperature −18 ° C.) or when the shape is standard (eg, square). Depending on the thawing start temperature and the shape of the food, the food was boiled or not thawed, so that the finish of the thawing was insufficient. In addition, the weight sensor for measuring the weight of food, a turntable is a necessary condition,
The configuration detects a change in the capacitance of the sensor due to the weight of the food and a distortion signal, and the configuration is complicated.

Also, when detecting the thawing by the detecting means, the power of the high-frequency radiating means is as high as 500 W, so that an excessive power cannot be supplied to the detecting means, so that an attenuator was separately required.

Therefore, an object of the present invention is to realize detection of thawing of food with a simple configuration.

Means for Solving the Problems In order to solve the above problems, the present invention is to detect the progress of thawing of food from the temperature characteristics of the dielectric loss of food in the frequency band of the high-frequency radiation means by the detection means, and to detect the microstrip line The antenna has an attenuation characteristic depending on the length, the permittivity of the substrate of the detection means, and the length of the antenna.

According to the present invention, the power input to the detection means has an effect that can be freely controlled by the length of the microstrip line or the like.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a structural view of a main body of a high-frequency heating device according to one embodiment of the present invention.

1 is a food, 2 is a heating room, 3 is a high-frequency radiation means (hereinafter referred to as a magnetron), 4 is a high-voltage transformer for operating the magnetron 3, 5 is a cooling fan for cooling the magnetron 3, and 6 is an antenna for the magnetron 3. The length is shorter than 1/4 wavelength of the oscillation frequency. In the present embodiment, by setting the length of the antenna to 3 to 5 mm, the matching of the antenna is lost, so that the attenuation characteristics can be obtained even in the antenna portion. That is, the oscillation frequency of the high-frequency heating device is 2.45 GHz, and one wavelength is 120 mm.
Since the length is one-twelfth the length of the case where matching is achieved with the half-wavelength antenna, the detected high-frequency power is an attenuated power of 40 dB or more. Therefore, a configuration having attenuation characteristics depending on the length of the antenna can be obtained. 8 is a detecting means, 9 is an amplifier for amplifying the detected signal, 10 is a driving means for varying the high-frequency power of the magnetron 3, 11 is a control of the driving means 10 in accordance with the amplified detection signal, and outputs the high-frequency power. It is a control means (a microcomputer in the present invention) for adjusting.

FIG. 2 is a circuit diagram of the detecting means 8 for detecting the oscillation signal of the magnetron 3. 14 is a 50 ohm resistor, 15 is a detection diode (for example, a Schottky barrier diode),
Reference numerals 16 and 17 denote resistors, and reference numeral 18 denotes a capacitor, which detects high-frequency power that is not absorbed by the food 1 in the oscillation frequency band of the magnetron 3 and is detected as a voltage Vs. In addition,
7 is a portion for attenuating high-frequency power, the high-frequency power emitted by the magnetron 3 into the heating chamber 2 is several hundred watts,
This is for preventing an excessive input from entering the detection means 8.

FIG. 3 is a diagram in which the detection means 8 is constituted by a microstrip line.

Copper foil patterns 7, 20, 21 and the like are etched on a dielectric substrate 19 having a certain dielectric constant εr. The copper foil portion of No. 7 has a characteristic impedance of 50 ohms. this is,
It is constant regardless of the length of the microstrip line.
(Literature, Z ₀ as described on page 55 of the overall electronic publisher "Fundamentals and Applications of Microwave Circuit", the characteristic impedance of the dielectric constant of air, Ipushirondaburyu the effective permittivity of the microstrip line, the εr When the dielectric constant of the dielectric substrate, h is the thickness of the dielectric substrate, and the width W of the microstrip line is , The characteristic impedance is constant because the parameter relating to the length of the microstrip line is not included. 21 is the 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 the detection accuracy is improved because etching is performed. .

FIG. 4 is a characteristic diagram showing the relationship between the level of the signal of the detection voltage Vs and the minimum point T with respect to the weight of the food. From this figure, it can be seen that there is a large difference between the detection voltage immediately after the start of thawing and the detection time of the minimum point T according to the weight of the food. This is because if the weight of the food is small, the high frequency absorbed by the antenna is small and the high frequency detected by the antenna is relatively large.

FIG. 5 shows that food 1 (frozen beef mince 100
FIG. 6 is a characteristic diagram showing a state in which a signal voltage detected by the detection means 8 when the gram is decompressed is freely controlled by the length of the microstrip line.

 This is based on the following relational expression (1).

Z = ZO · tan (B · L) (1) where L is the length of the microstrip line in the portion shown in FIG. 3, ZO is the characteristic impedance of the substrate, B
Is a phase constant, using a wavelength λ, B = (2π / λ), and Z is an input impedance viewed from the antenna.

It can be seen that the input voltage becomes infinite depending on the length of L, and the detection voltage Vs decreases accordingly. Therefore, according to this relational expression, a configuration having an attenuation characteristic in the detection unit becomes possible. If the antenna is also configured to be shorter than a quarter wavelength, the high-frequency power input to the detection unit is attenuated, and No destruction.

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

(1) A high frequency in the frequency band of the high frequency radiating means is detected by an antenna arranged in the heating chamber, and the power input to the detecting means can be prevented from being excessively input by the length of the microstrip line. , And decompression detection can be achieved with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram of the main body of a high-frequency heating apparatus according to one embodiment of the present invention, FIG. 2 is a circuit diagram of the detection means, FIG. 3 is a view in which the detection means is formed on a microstrip line, and FIG. FIG. 5 is a characteristic diagram showing a change in signal with respect to the food weight of the detecting means 8 during the thawing, FIG. 5 is a characteristic diagram showing a relationship between the signal voltage and the microstrip line length, and FIG. FIG. 1 ... food, 2 ... heating room, 3 ... high frequency radiation means, 6
... antenna, 7 ... attenuator, 8 ... detection means, 10 ...
Driving means, 11 control means, 18 microstrip line.

Claims (2)

(57) [Claims] 1. A heating chamber for taking food in and out, a high-frequency radiating means for supplying high frequency to the heating chamber, a control means for controlling the high-frequency radiating means, an antenna for detecting the high frequency, and Detecting means for detecting the progress of thawing of the food, wherein the detecting means has a microstrip line, and is attenuated by a length of the microstrip line, a guide rate of a substrate of the detecting means, and a length of the antenna. A high-frequency heating device having a configuration having characteristics. 2. The high-frequency heating apparatus according to claim 1, wherein the length of the antenna is shorter than a quarter wavelength of the frequency of the high-frequency radiation means.