JPS6346551B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a power supply structure for a high frequency heating device such as a microwave oven.

Configuration of conventional example and its problems A conventional high-frequency heating device, for example, uses a magnetron to generate microwaves and a waveguide to supply the microwaves to the heating chamber, as shown in Fig. 1. This is a basic configuration in which an antenna 1-a of an oscillator 1 is projected into a waveguide 2, and microwaves are radiated through the waveguide into a heating chamber 4 from an opening 3 to heat an object to be heated. In high-frequency heating devices such as microwave ovens, it is important to have good heating distribution for various food menus, and this is called distribution performance. Experience has shown that a major factor that affects this distribution performance is the position of the opening 3 with respect to the heating chamber 4. That is, the position of the aperture 3 is determined based on the distribution performance requirements. Reference numeral 5 denotes a matching pin (projection) provided for impedance matching so that the magnetron 1 can operate with high efficiency. This protrusion 5 is generally made of aluminum and is constructed by fitting it into the waveguide 2. By the way, when this conventional high-frequency heating device is operated without putting an object to be heated into the heating chamber 4 or with a small amount of object to be heated, the above-mentioned protruding portion 5 and the upper plate 4 forming the upper surface of the heating chamber 4 The electric field generated between the opening cover 6 and the opening cover 6 causes a discharge and overheats the upper plate 4-a directly below the protruding portion, causing the opening cover 6 to become deformed.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional drawbacks, and aims to provide a highly reliable high-frequency heating device that can operate stably even under severe usage conditions such as dry firing.

Structure of the Invention In order to achieve the above object, the high frequency heating device of the present invention includes an antenna, an oscillator, a waveguide, an opening, and a plurality of protruding parts, and the antenna is protruded into the waveguide. The protruding portion is made of a metal body and protrudes into the waveguide,
The distance between each of the protruding parts is set to be an integral multiple of approximately λg/2 in the direction of propagation of the microwave,
The impedance matching function is changed from the conventional configuration in which a single protrusion is provided in the waveguide to the structure of the present invention in which multiple protrusions are provided at positions of 1/2 of the waveguide's internal wavelength, that is, an integral multiple of λg/2. By making each protruding part in the waveguide share the responsibility, the length of each protruding part protruding into the waveguide can be shortened. Therefore, the distance between the protruding portion of the waveguide and the opposing wall surface can be increased, which has the effect of alleviating the concentration of electric field and preventing discharge and overheating.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In Fig. 2, 1 is an oscillator, 1-a is an antenna, 2 is a waveguide, 3 is an aperture, 5-a, 5-b, 5
-c are respective protruding parts. 4 is a heating chamber in which the object to be heated is heated; 4-a is the heating chamber 4;
The upper plate forms the upper wall, and this upper plate also forms the lower wall of the waveguide 2. Reference numeral 7 denotes a table on which the object to be heated is placed, and is rotated by the driving force of a motor 8. Reference numeral 6 denotes an aperture cover for covering the aperture 3 and eliminating unevenness on the wall surface of the heating chamber, and is made of a low-loss dielectric material such as polypropylene so as to transmit microwaves. 9 is a transformer that supplies power for oscillating the oscillator. 10 is a body for safety and appearance, and 11 is a chassis. The antenna 1-a protrudes into the waveguide 2 as shown in the figure, and has a plurality of protruding parts 5-a, 5-.
b, 5-c are the waveguides 2 made of sheet metal bodies;
As shown in FIG.
The distance between b and 5-c is determined by the microwave oscillation frequency and waveguide dimensions in the microwave propagation direction, that is, in the left-right direction in Fig. 2 and in the arrow M-M direction in Fig. 3. It is set to an integral multiple of 1/2 of the determined pipe wavelength λg. That is, the protruding portion 5-a
and the protruding portion 5-b, the distance P ₁ is λg/2
The distance P ₂ between the protruding parts 5-b and 5-c
is set to λg/2. In addition, the antenna 1-a
The positions of the protruding portion 5-c and the protruding portion 5-c are made to coincide with each other as shown in the figure. Further, the distance Q between the opening 3 and the protruding portion 5-a is set to λg/4 in the direction of propagation of the microwave.

The operation of the above configuration will be explained below.
The oscillator 1 is operated by the high voltage generated by the transformer 9, and an electric field is generated between the antenna 1-a and the inner wall surface of the waveguide 2, thereby exciting microwaves into the waveguide. The microwave passes through the waveguide 2 and is radiated into the heating chamber 4 from the opening 3 to heat the object to be heated. However, in most high-frequency heating devices such as microwave ovens, the amount and shape of the objects to be heated vary widely, and as a result, the microwave impedance on the load side as seen from the antenna 1-a fluctuates. It causes fluctuations in wave power and efficiency. For this reason, the protruding portions 5-a, 5-
Impedance matching is achieved by b and 5-c. In this embodiment, as shown in FIG. 2, the protruding portions are provided at three locations at a pitch of λg/2, so unlike the conventional example shown in FIG.
The length of the protrusion into the waveguide can be made shorter than when the protrusion is provided in a concentrated manner. In the high frequency heating device of this embodiment, the protruding portion 5-c is eliminated, and the protruding portion 5-c is eliminated.
Experiments were carried out by varying the dimensions of a and 5-b and the distance _P1 between them, and the data shown in FIG. 4 was obtained.
In the figure, h ₁ is the protrusion dimension of the protrusion when impedance matching is achieved at only one protrusion, and h ₂ is the impedance matching when the protrusion dimensions of the protrusion 5-a and 5-b are the same. The protrusion dimension when the protrusions are removed, P ₁ is the distance between the protrusions at that time. Therefore, the vertical axis h ₂ /
h ₁ represents the degree of reduction when two protruding portions are provided compared to the case where one protruding portion is provided, and when the value is 1 or less, it indicates that the protruding dimension is shortened. Moreover, the horizontal axis P ₁ /λg indicates how many times the distance between the protruding parts is the wavelength inside the pipe.

According to experiments, as is clear from Figure 4, when the distance P ₁ between individual protruding parts is λg/2, the dimension of the protruding parts can be shortest, and the length is about 84% of that in the case of one protruding part. It turns out that the length of is sufficient.

Therefore, by shortening the protrusion dimension of the protrusion, electric field concentration at the protrusion is alleviated,
By increasing the distance between the protrusion and the top plate, electric discharge between the protrusion and the top plate and overheating of the top plate can be suppressed.

Further, the protruding portion 5-c is connected to the antenna 1-
By matching the positions of the antennas 1 and 1,
-a and the protruding portion 5-c are designed to an optimal dimension so that the microwave output from the oscillator 1 is high and the temperature of the antenna 1-a is low during dry firing. The protruding portions 5-a, 5
In addition to achieving the effect of shortening the protrusion dimension of -b, this becomes possible. The above antenna 1
FIG. 5 shows an example of the relationship between the distance between -a and the protruding portion 5-c and the antenna 1-a during dry firing, which was confirmed through experiments. In the figure, the vertical axis represents the temperature of the antenna during dry firing, and A, B, and C represent the state in which the distance l between the antenna 1-a and the protruding portion 5-c is 5.2 mm, 4.6 mm, and 4.0 mm, respectively. show. FIG. 5 shows the probability function by which the antenna temperature changes due to variations in the oscillator 1, the waveguide 2, and other factors, by plotting the frequency of occurrence on the horizontal axis. From the figure, the antenna 1-a
It can be seen that the distance between the antenna and the protruding portion 5-c has a large influence on the temperature of the antenna 1-a during dry firing.

Next, in this embodiment, the position of the opening 3 in FIG.
4, the protrusion 5-a is the maximum point of the electric field, and from that position λg/
The opening 3 is present at the farthest position from each of the positions separated by an integral multiple of 2, and the reduction in electric field concentration due to the shortening of the protrusion 5-a also reduces the area near the opening 3. The temperature rise of the upper plate 4-a is reduced and the discharge at the end face of the opening of the upper plate 4-a is suppressed.

As described above, according to this embodiment, the basic effect is that the plurality of protruding portions 5-a, 5-b, 5-c
By protruding into the waveguide 2 at a pitch of λg/2, each protrusion dimension is shortened, and electric field concentration at the protrusion is relaxed and the distance between the protrusion and the upper plate is increased, so that discharge near the protrusion is reduced. This prevents the top plate from overheating. Moreover, the antenna 1-a
By aligning the positions of the protruding portion 5-c with the oscillator 1, the temperature of the antenna 1-a can be lowered while increasing the basic effect.
can improve the output characteristics of Further, by providing the opening at a position λg/4 from the protruding portion 5-a, a synergistic effect with the above basic effect reduces the temperature rise of the upper plate 4-a and the opening of the upper plate 4-a. Electric discharge at the end face of the opening can be suppressed, thereby preventing the aperture cover 6 from burning or melting. Moreover, the plurality of protruding parts 5-
The configuration in which a, 5-b, and 5-c are provided at a pitch of λg/2 has the effect of reducing variations in impedance seen from the antenna 1-a due to variations in the oscillation frequency of the oscillator 1, and reduces the high-frequency output. Variations can be reduced.

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

(1) By reducing the protrusion dimension of the protruding part (alignment pin) inside the waveguide, it suppresses discharge inside the waveguide during dry firing and overheating of the upper plate, resulting in stable operation and safety and reliability. Increase sex.

(2) It is possible to improve the output characteristics of the oscillator and provide a highly efficient and highly durable high-frequency heating device.

(3) Lowering the opening temperature prevents the opening cover from burning or melting, increasing reliability.

(4) The effects of variations in high frequency output due to variations in oscillator frequency can be reduced.

(5) By shortening the length of the protruding part, the protruding part can be realized by drawing a part of the sheet metal waveguide, improving workability and workability.
It is advantageous in terms of cost.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the main parts of a conventional high-frequency heating device.
Fig. 2 is a cross-sectional view of a main part of a high-frequency heating device that is an embodiment of the present invention, Fig. 3 is a perspective view of a waveguide of the same device, and Fig. 4 shows the relationship between the distance between protruding parts and the protruding dimension. FIG. 5 is a diagram showing the gap between the antenna and the protrusion and the antenna temperature during dry firing. 1... Oscillator, 1-a... Antenna, 2... Waveguide, 3... Opening, 4... Heating chamber, 5-a, 5-
b, 5-c...Protruding portion, 6...Opening cover,
7... table, 8... motor, 9... transformer, 10... body, 11... chassis.

Claims (1)

[Claims] 1. An oscillator having an antenna, a waveguide for transmitting microwaves from the oscillator, an opening provided in the waveguide, and a plurality of protruding portions provided in the waveguide. The antenna is configured to protrude into the waveguide, and the protruding portion of the waveguide is made of a metal body, and the distance between the protruding portions is approximately an integral multiple of λg/2 in the direction of propagation of the microwave. high frequency heating device. 2. The high-frequency heating device according to claim 1, wherein the position of one of the plurality of protrusions substantially coincides with the position of the antenna. 3. The high-frequency heating device according to claim 1, wherein the opening is located at a distance from a position of λg/4 from the protruding portion in the direction of propagation of the microwaves to a distance approximately an integral multiple of λg/2.