JPS628919B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-frequency heating device that heats an object to be heated such as food using high-frequency energy.
In particular, the present invention relates to a door equipped with a chiyoke groove for preventing radio wave leakage.

Conventionally, small, multi-functional electronic components such as ICs and microcomputers have been actively incorporated into the control circuits of high-frequency heating equipment, and operation panels have become smaller and thinner. A thin door with a flat profile is requested. Furthermore, there is a growing tendency to automate complex operations, and as electronic circuits become more expensive, there is a demand for lower costs for mechanical parts, especially door structures.

Conventional doors often use a combination of chiyolk grooves and ferrite, which is a radio wave absorbing material, but this is disadvantageous in terms of cost because ferrite is attached to the entire circumference of the door. Furthermore, proposals have been made to increase the damping effect of the chiyoke groove itself and to eliminate ferrite. This proposal is as follows.

A proposal has been made to increase the attenuation effect of the chiyoke groove by periodically arranging λ/4 length conductor pieces, so-called slits, on one side of the chiyoke groove, which has a depth of 1/4 of the used wavelength λ, as a radio wave propagation direction regulating device. US Patent 2772402
(1956.11.27 patent) and 2850706 (1958.9.2 patent)
It is done in Alternatively, a radio wave leakage prevention structure similar to the above patent is disclosed in Patent No.
81146, Japanese Patent Publication Publication No. 53-4660), but in this proposal, the slit is one side of the radio wave propagation path before entering the chiyoke groove, and the distance between the slit and the opposing metal surface is This is a method that is forced by filling it with dielectric material. This is because when the slit partially contacts the opposing metal surface, the length of the slit becomes substantially shorter than λ/4, and its function as a radio wave propagation direction regulating device (electromagnetic energy mode maintenance structure) decreases. be. With this method, a large number of radio waves enter the gap between the door and the heating chamber opening, and to prevent leakage of fundamental waves and harmonics, it is necessary to add conductive rubber or to complicate the propagation path of leaked radio waves. It is necessary to produce a damping effect, and it is not suitable for making doors thinner and lower in cost.

In addition, many proposals have been made, such as British Patent No. 1392498 and Japanese Patent Publication No. 1983-22663, to increase the damping effect by dividing the choke groove into two with a metal wall having a slit of approximately λ/4, but this method does not However, the yoke groove becomes large, making it unsuitable for making doors thinner and lower in cost.

Furthermore, a structure in which a periodic structure other than the above-mentioned slits is inserted into the chiyoke groove has been proposed in Japan Patent Publication No. 54-21574 and Japanese Patent Publication Publication No. 52-40461, but the surface forming the chiyoke groove itself In addition, since high frequencies are not considered, it is necessary to add ferrite and the like in order to put it into practical use, which is disadvantageous in terms of cost.

Note that Japanese Patent Laid-Open No. 55-41679 proposes a door in which metal claw-like bodies are provided at predetermined intervals on the peripheral edge of the door. As is well known, the electric field is at the maximum position at the entrance of the cheese yoke, and at this position, the end cut of the sealer plate that makes metal contact with the opening edge of the heating chamber and the triangular tip cut of the claw-shaped body mentioned above are in contact with the opening edge of the heating chamber. Since these are opposed to each other, significant electromagnetic field concentration occurs, which tends to cause sparks and abnormal heating near the entrance of the choke section. In addition, since the configuration is such that the 1/4 wavelength of the radio waves, which is the length required for the front yoke, is taken only in the direction parallel to the opening edge of the heating chamber, the size of the yoke becomes large, making it unsuitable for downsizing the door. It is.

As mentioned above, conventional doors are not suitable for miniaturization, thinning, and cost reduction.

Therefore, the present invention provides a radio wave attenuation cavity with one entrance at the periphery of the door by arranging the fundamental wave channel groove and the second harmonic channel groove in opposite directions, and provides a radio wave attenuation cavity with one entrance at the periphery of the door. It has a simple radio wave leakage structure that minimizes radio wave leakage to the fundamental wave and harmonics by dividing the groove wall itself into multiple corrugated plates and giving specific relationships to the shape and dimensions of the corrugated plates. An object of the present invention is to provide a high-frequency heating device equipped with a door that can be made smaller, thinner, and lower in cost.

Next, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an external view showing an example of the high frequency heating device of the present invention. 1 is an outer box, 2 is a door, and 3 is an operation panel whose thickness is balanced with the thickness of the door 2. Although the operation panel 3 can be changed in various ways depending on the application, the case of automatic heating will be explained as an example.
4 is a display device that shows high frequency output, residual heating time, etc., 5 is a menu selection button that determines the optimal heating pattern for each menu, 6 is a finish adjustment knob that allows you to select the degree of finish according to your preference, and 7 is when to start heating. 8 is the heating button to press, and 8 is the door open button to open the door.

FIG. 2 is a schematic sectional view of a main part of the high-frequency heating device of the present invention corresponding to FIG. 1. 9 is a high frequency oscillator that generates high frequency energy, and 10 is a waveguide for transmitting the high frequency energy from the high frequency oscillator 9 to the heating chamber 11. 12 is a turntable for uniform heating, on which the object to be heated is placed. A turntable 12 is used as a uniform heating device.
In addition, there are stirrers, rotating antennas, fixed antennas, etc., and any of them may be used. Reference numeral 13 denotes a transparent plate attached to the front surface of the door 2, and the transparent plate 13 is fixed to the door front plate 15 by a door cover 14. The door front plate 15 is attached to the door rear plate 16 with screw 1.
It is attached by 7. Both the door front plate 15 and the door rear plate 16 are made of metal plates, and form a radio wave attenuation cavity 19 facing the heating chamber opening periphery 18. 20 is a transparent plate facing the heating chamber 11, and 21 is a wire mesh (or perforated metal plate). transparent plate 1
3. Heating chamber 1 through wire mesh 21 and transparent plate 20
You can see inside 1. 22 is a sash surrounding the door 2.

FIG. 3 is an enlarged view of the vicinity of the radio wave attenuation cavity 19 shown in FIG. A fundamental wave chuck groove 19a to prevent radio wave leakage at a heating frequency of, for example, 2450 MHz and a second harmonic of the above frequency of 4900 MHz.
The second harmonic channel grooves 19b for preventing radio wave leakage are made to face each other in opposite directions,
One radio wave attenuation cavity 19 having one entrance 23 is formed. In the fundamental wave channel groove 19a, the L-shaped radio wave propagation path from the inlet 23 to the short-circuit surface 15a is approximately λ ₀ /4 with respect to the free space wavelength λ ₀ of the heating frequency. The fundamental wave chiyoke groove 19a is arranged on the side closer to the heating chamber 11, and this groove 19
One wall surface 16a of a is used as a contact surface with the heating chamber opening periphery 18. Second harmonic chiyoke groove 19b
Here, the L-shaped radio wave propagation path from the inlet 23 to the short-circuit surface 15b is approximately λ ₀ /8. The corrugated plate 15w has a tip 15.
A tip surface 15T is provided by bending w' toward the inside of the radio wave attenuation cavity 19, and the fundamental wave chyoke groove 19 is arranged so as to face approximately parallel to the tip surface 15T.
A bending surface 16T is also provided at the end of one wall surface 16a of a, and both the fundamental wave cheese groove 19a and the second harmonic wave groove 19a are connected to the heating chamber opening periphery 1.
An L-shaped radio wave propagation path is formed in a direction perpendicular to 8 (y direction) and in a direction parallel to 8 (z direction). The maximum gap size B between adjacent corrugated plates 15w is set to λ ₀ /4 or less. This dimensional limit is the second
It corresponds to 1/2 wavelength or less of the wavelength of the second harmonic that entered the harmonic groove 19b, and becomes a shearing region, and once the second harmonic that entered the same groove 19b reaches the same groove 19b. This is a necessary condition to prevent the outside of the body.

The tip surface 15T of the corrugated plate 15w and the bent surface 16T at the end of the wall surface 16a of the fundamental wave chyoke groove 19a become the entrance 23 of the radio wave attenuation cavity 19 and are at the maximum electric field position, but the tip surface 15T and the bent surface 16T Since the planes face each other, there is no local electric field concentration. Therefore, it has been experimentally confirmed that no sparks or abnormal heating occur near the inlet 23.

Since the tip surface 15T and the bent surface 16T form a kind of parallel plate line whose width is sufficiently narrower than the wavelength, the direction of the electric field of the radio wave entering the radio wave attenuation cavity 19 is constant (in the yz plane). And the propagation mode is a TEM wave, and due to the properties of this TEM wave, the wavelength of the propagating radio wave is the free space wavelength λ
It becomes ₀ . Therefore, the leakage radio waves that have reached the entrance 23 through the gap between the heating chamber opening periphery 18 and the wall surface 16a of the fundamental wave channel 19a have a propagation direction and a wavelength (generally λ ₀ due to the higher order mode). ) is different, but the tip surface 15T of the corrugated plate 15w and the bent surface 16 at the end of the wall surface 16a
Since _the propagation directions are aligned with T and the wavelength is λ ₀ , _the fundamental wave and The inlet 23 has a high impedance with respect to the second harmonic, and a sufficient radio wave leakage prevention effect can be obtained. In this way, the corrugated plate 15w functions as a kind of matching post that efficiently guides the fundamental wave and the second harmonic that are about to leak into the radio wave attenuation cavity 19. The peripheral edge 18 of the opening of the heating chamber and the wall surface 16a of the fundamental wave groove 19a come into plane contact when the door 2 is closed, and since there is substantially little gap between them, the heating chamber opening periphery 18 and the wall surface 16a of the fundamental wave chiyoke groove 19a come into plane contact, and since the gap between them is small, There are also very few leaked radio waves. Further, since the contact portion has a low impedance (characteristic impedance as a transmission line) and is largely reflected from the high impedance of the inlet 23, the radio waves reaching the corrugated plate 15w are also very small. This minute radio wave is efficiently guided into the radio wave attenuation cavity 19 by the action of the matching post of the corrugated plate 15w, and is held as accumulated energy in the space inside this cavity 19, and a part is consumed as power loss on the wall surface. .

On the other hand, in order to maintain the dimensional relationship of gap dimension B>inlet dimension A, and to increase the conductor surface of the corrugated plate 15w facing the heating chamber opening periphery 18, to lower the impedance between both conductors, the corrugated plate 15w is root 1
It has a trapezoidal shape with a wide width of 5w'' and a narrow width at the tip 15w'.By increasing the reflection between the low impedance between these two conductors and the high impedance of the inlet 23, the conductor passes through the inlet 23 and goes to the outside. This further reduces the amount of leaked radio waves.

FIG. 5 shows a corrugated plate 15 at the corner 2a of the door 2.
The dimensional relationship between w is shown. At the corner 2a, the gap size C between the bases 15w'' of adjacent corrugated plates 15w is set to λ ₀ /4 or less. On the other hand, it corresponds to 1/2 wavelength and becomes a shearing region, which is a necessary condition to prevent the second harmonic that once entered the groove 19b from exiting to the outside of the groove 19b on the way.Furthermore, Corrugated plate 1 other than corner 2a
If the gap size B between the tips 15w' of the waveguides 5w is also set to λ ₀ /4 or less for the same reason as above, the damping effect of the second harmonic tooth yoke groove 19b will be improved. door 2
The gap size B is λ ₀ /4 or less over the entire circumference including the corner 2a.

As mentioned above, the radio wave attenuation cavity 19 is basically the second
Since it has a sufficient attenuation effect against harmonics, it is practically unnecessary to use auxiliary means such as ferrite or conductive rubber, which is advantageous in terms of cost reduction.

Furthermore, the radio wave attenuation cavity 19 has the sum of the lengths of the fundamental wave groove 19a and the second harmonic groove 19b in the parallel direction (z direction) and the perpendicular direction (y direction) facing the heating chamber opening periphery 18. are approximately λ ₀ /4 and approximately λ ₀ /8, respectively. Therefore, the dimensions of the radio wave attenuation cavity 19 in both the y direction and the z direction can be reduced, so the door can be made smaller and thinner, and the design is balanced with the smaller and thinner operation panel 3. A desirable appearance can be achieved.

As described above, the present invention provides a high-frequency heating device equipped with a door that can reduce radio wave leakage, does not generate sparks or abnormal heating, and is suitable for downsizing, thinning, and cost reduction. can do.

[Brief explanation of the drawing]

FIG. 1 is an external view showing an example of the high-frequency heating device of the present invention, FIG. 2 is a schematic cross-sectional view of essential parts showing an example of the high-frequency heating device of the present invention corresponding to FIG. 1, and FIG.
The figure is an enlarged sectional view of the radio wave attenuation cavity 19 in FIG. 2, and FIGS. 4 and 5 are perspective views for explaining the dimensional relationship and function of the corrugated plate 15w near the entrance 23 of the radio wave attenuation cavity 19. It is. 2...door, 2a...corner of door 2, 11...
...Heating chamber, 15c...Chiyoke groove 1 for second harmonic
Wall surface of 9b, 15w...corrugated plate, 15w'...tip of corrugated plate 15w, 16a...chiyoke groove 1 for fundamental wave
One wall surface of 9a, 18...Heating chamber opening periphery, 19
...Radio wave attenuation cavity, 19a...Chiyok groove for fundamental wave, 19b...Chiyok groove for second harmonic, 23...
...Entrance of the radio wave attenuation cavity 19, 24...Rotation shaft on the hinge side of the door 2.

Claims (1)

[Claims] 1 One radio wave attenuation cavity 19 having one entrance 23 with a fundamental wave chock groove 19a and a second harmonic wave chock groove 19b facing oppositely on the periphery of the door 2 that opens and closes the opening of the heating chamber 11. The wall surface 15c facing the heating chamber opening periphery 18 of the second harmonic chiyoke groove 19b is divided into a plurality of trapezoidal corrugated plates 15w.
A tip surface 15T is provided by bending w' toward the inside of the radio wave attenuation cavity 19, and a bent surface 16T is also provided at the end of the wall surface 16a of the fundamental wave chiyoke groove 19a so as to face the tip surface 15T substantially parallel to the tip surface 15T.
The fundamental wave channel groove 19a and the second harmonic channel channel 19b together form an L-shaped radio wave propagation path consisting of a direction perpendicular and a direction parallel to the heating chamber opening periphery 18, and a corrugated plate 15w. The gap size B between the adjacent tip surfaces 15T and the root 1 of the adjacent corrugated plates 15w at the corner 2a of the door 2
A high-frequency heating device characterized in that the gap size C between 5w'' is set to 1/4 or less of the free space wavelength of the heating frequency.