JPS6322439B2 - - 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, and is equipped with a chiyoke groove for preventing radio wave leakage. In recent years, small, multifunctional 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 well-fitting, thin door is desired. 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 mechanisms. The doors of these high-frequency heating devices often use a combination of a chiyoke groove and ferrite as a radio wave absorbing material, but this is disadvantageous in terms of cost because the 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 remove ferrite. This proposal is as follows. A proposal to increase the attenuation effect of the chiyoke groove by using one side of the chiyoke groove, which has a depth of 1/4 of the wavelength used, as a radio wave propagation direction regulating device in which λ/4 length conductor pieces, so-called slits, are arranged periodically. is a US patent
2772402 (1956.11.27 patent) and USP2850706
(4958.9.2 patent). It has the same radio wave leakage prevention structure as the above patent.
3767884 (Japanese Patent Publication Publication 1977-81146, Japanese Publication Publication 1973-
4660), but in this proposal, the slit is one side of the radio wave propagation path before entering the choke groove, and the gap between the slit and the opposing metal surface is filled with a dielectric. It is something that is taken forcibly. 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 sustaining structure) decreases. be. With this type, a large number of radio waves enter the gap between the door and the heating chamber opening, and in order to prevent the 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 create a damping effect,
It is unsuitable for making doors thinner and lower in cost. In addition, there have been many proposals such as British Patent No. 1392498 and Japanese Patent Publication No. 51-22663 to increase the damping effect by dividing the tee yoke groove into two with a metal wall having a slit of about λ/4, but these proposals do not effectively improve the damping effect. 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 Japanese Patent Publication Publication No. 54-21574 and Japanese Patent Publication Publication No. 52-40461, but the surface forming the chiyoke groove itself Moreover, since harmonics are not taken into account, it is also necessary to add ferrite etc. for practical use, which is disadvantageous in terms of cost. As mentioned above, conventional doors are not suitable for thinning and cost reduction. Therefore, in the present invention, a radio wave attenuation cavity with one entrance is provided at the periphery of the door by arranging the fundamental wave channel groove and the second harmonic channel groove in opposite directions, and providing a radio wave attenuation cavity with one entrance at the periphery of the door. A simple radio wave leakage prevention structure that minimizes radio wave leakage to the fundamental wave and harmonics by dividing the wall surface of the chiyoke groove itself into multiple corrugated plates and giving a specific relationship to the shape and number of these corrugated plates. An object of the present invention is to provide a high-frequency heating device equipped with a door that can be made 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 cross-sectional view of the main part of the high-frequency heating device 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. In addition to the turntable 12, the uniform heating device includes a stirrer, a rotating antenna, a fixed antenna, 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.
A door rear plate 16 is attached to the door front plate 15 with screws 17. Door front plate 15 and door rear plate 1
6 are both made of metal plates, and form a radio wave attenuation cavity 19 facing the opening periphery 18 of the heating chamber 11. 20 is a second transparent plate facing the heating chamber 11;
21 is a wire mesh (or perforated metal plate). The inside of the heating chamber 11 can be seen through the transparent plate 13, the wire mesh 21, and the second transparent plate 20. 2
2 is a satsushi surrounding door 2. FIG. 3 is an enlarged view of the vicinity of the radio wave attenuation cavity 19 shown in FIG. Dielectric heating frequency e.g.
Fundamental wave chiyoke groove 19a and second harmonic of the above frequency to prevent radio wave leakage for 2450MH
The second step to prevent radio wave leakage to 4900MHz
The harmonic wave grooves 19b are opposed to each other to form one radio wave attenuation cavity 19 having one inlet 23. Fundamental wave chiyoke groove 19
In a, the L-shaped radio wave propagation path from the inlet 23 to the short-circuit surface 15a is determined by the free space wavelength λ ₀ of the dielectric heating frequency.
It is set to approximately λo/4. The fundamental wave channel groove 19a is arranged on the side closer to the heating chamber 11, and one wall surface 16a of this groove 19a is connected to the heating chamber opening periphery 1.
This is the contact surface with 8. In the second harmonic chiyoke groove 19b, the length from the inlet 23 to the short circuit surface 15b is
The radio wave propagation path of the letter shape is approximately λo/4. The wall surface 15c of the second harmonic chiyoke groove 19b is divided into a plurality of tapered corrugated plates 15w as shown in FIG.
As shown in FIG. 7, they are arranged in the longitudinal direction with a gap size B larger than the entrance size A. Next, the operation of the high frequency heating device of the present invention will be explained. 4, 5, and 6 show that the wall surface 15c of the second harmonic chiyoke groove is connected to the alignment posts 24, 2.
5 to explain the process of transforming the corrugated plate 15w. Entrance 23 of the radio wave attenuation cavity 19 in FIG.
A plurality of conductor round bars 24, that is, matching posts known as matching elements in microwave theory, are arranged. By appropriately selecting the length, diameter, spacing, etc. of the conductor round rods 24, radio waves that would otherwise leak to the outside can be efficiently introduced into the radio wave attenuation cavity 19. Furthermore, as shown in FIG. 3, by setting the radio wave propagation path lengths in the two directions in the radio wave attenuation cavity 19 to approximately λo/4 and approximately λo/8, the fundamental wave and the second harmonic are A high impedance can be created at the inlet 23. Some of the radio waves pass through the entrance 23 of the radio wave attenuation cavity 19 and leak to the outside. In order to reduce the radio waves leaking to the outside, the average distance between the conductor surfaces of the conductor round rod 24 and the heating chamber opening periphery 18 is made small.
4 and 18 with low impedance, and the above-mentioned inlet 2
It is necessary to increase the reflection between the two high impedances. At this point, the conductor round bar 24 in FIG.
A square conductor bar 25 as shown in FIG. 5 is more suitable. However, if a large number of conductor square rods 25 are lined up and the second
When one wall surface of the harmonic channel groove 19b is formed, the spatial volume within the second harmonic channel groove 19b is reduced by the volume of the conductor square rod 25, so the Q of resonance is reduced and the damping effect is reduced. It will be disadvantageous. It is an object of the present invention to provide a high-frequency heating device that maintains the above-mentioned effective effects of the round conductor bar 24 and the square conductor bar 25, and is provided with something that functions as an alignment post with only the drawbacks removed. To achieve this purpose, the corrugated plate 15 shown in FIGS. 6 and 7 as an example
w is provided. Below, according to Figure 7 and the following table, radio wave attenuation cavity 1
The action of the corrugated plate 15w near the entrance 23 of FIG. 9 will be explained. λo: Free space wavelength (122.3mm at 2450MH) m: Cutoff wavelength of the maximum point of the electric field in the x direction of each mode (wavelength in the x direction) λc = 2a/m In-tube wavelength (wavelength in the z direction)

[Formula] Maximum position of electric field in x direction x _nax = Na/2m (N=1, 3, 2m-1)

【table】

[Table] Radio waves that are about to leak from the heating chamber 11 to the outside generally occur at several electric field maximum points E _nax in the longitudinal direction (x direction) of the contact area between the heating chamber opening periphery 18 and the door 2.
It is a higher-order mode with . For example, in the case of the heating chamber 11 having an opening of 365 x 260 mm, it is assumed that a 2450 MHz radio wave propagates in a waveguide whose propagation direction is the z direction corresponding to the radio wave leakage direction as shown in Table 1. In this case, when the longitudinal dimension a is 365 mm, five higher-order modes from TE ₁₀ to TE ₅₀ can propagate, and when a is 260 mm, TE ₁₀ to TE 50 can propagate.
Four higher order modes up to TE ₄₀ can be propagated.
The total number of electric field maximum points E _nax is 13 for a of 365 mm,
a is 10 for 260 mm. An electric field stirring device such as a turntable 12 or a rotating antenna is provided in the heating chamber 11 in order to reduce uneven heating, and the electric field maximum point E _nax changes with time.
Furthermore, which higher-order mode invades in the z direction as a leakage radio wave is determined by the resonance mode in the heating chamber 11,
Analysis is difficult because it depends on various factors such as the coupling position of the waveguide 10, the position and amount of load, and the operating point of the high-frequency oscillator. It is most effective to provide the corrugated plate 15w as an alignment post at the maximum electric field position x _nax . However, as mentioned above, its position is actually in flux. Therefore, if we decide to place them at equal intervals,
In order to make the corrugated plate 15w correspond to each electric field maximum position x _nax of all higher-order modes, if the longitudinal direction (x direction) of the opening of the heating chamber 11 is 365 mm, this length must be adjusted to the total number of electric field maximum points 13 It is necessary to arrange the corrugated sheets 15W at a pitch of 28mm or less. Similarly, if the longitudinal direction is 260 mm, it is necessary to arrange the corrugated plates 15w so that the length is equal to or less than 26 mm, which is calculated by dividing this length by the total number of maximum electric field points, 10. In other words, the same number or more of corrugated plates 15w as the total number of maximum electric field points are formed from one wall surface 15c of the second harmonic cheese yoke groove 19b itself. Furthermore, by making the gap size B between adjacent corrugated plates 15w larger than the entrance size A of the radio wave attenuation cavity 19 near the tip 15w' of the corrugated plate 15w,
The electric field tends to concentrate on the tip 15w' of the corrugated plate 15w. This is because, although the electric field is in a discontinuous state near the entrance 33, the electric field component in the direction of propagation into the radio wave attenuation cavity 19 (solid arrow in FIG. The corrugated plate 15 has the effect of reducing the electric field component (dotted line arrow in Fig. 7).
It means that w has. In other words, the corrugated plate 15w has the function of a matching post that efficiently introduces all high-order mode radio waves leaking between the heating chamber opening periphery 18 and the door 2 into the radio wave attenuation cavity 19, and the radio waves leaking to the outside. decrease. Furthermore, as shown in FIG. 3, the radio wave propagation path lengths in the two directions within the radio wave attenuation cavity 19 are set to approximately λo/4 and approximately λo/8 to provide high impedance for the fundamental wave and the second harmonic, respectively. ing. The peripheral edge 18 of the opening of the heating chamber and the wall surface 16a of the fundamental wave cheese yoke 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 cheese yoke groove 19a are designed to come into plane contact. 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 introduced into the radio wave attenuation cavity 19 by the action of the matching post of the corrugated plate 15w, and is retained as energy stored in the space inside this cavity 19, and a part of it is consumed as power loss on the wall surface. be done. Leaked radio waves that do not enter the radio wave attenuation cavity 19 but pass through the inlet 23 and enter the gap between the heating chamber opening periphery 18 and the corrugated plate 15w and head to the outside are reflected to the heating chamber 11 side. By returning it, the effect of preventing radio wave leakage of the door 2 can be further improved. To do this, as is well known, the reflection at the connection point of two lines with different impedances increases as the difference in impedance between the two lines increases. For high impedance, the impedance (more precisely, the characteristic impedance) of the approximate parallel plate line formed between the conductors of the heating chamber opening periphery 18 and the corrugated plate 15w may be reduced. Furthermore, it is known that the impedance of parallel plate lines decreases as the width of the line increases. Therefore, by maintaining the dimensional relationship of gap size B>inlet size A at the tip 15w' of the corrugated plate 15w, and tapering the corrugated plate 15w so that the width becomes wider toward the base 15w', the heating chamber opening periphery 18 and the corrugated plate 15
The impedance of the line formed by w is reduced. That is, by increasing the reflection between the low impedance between the heating chamber opening periphery 18 and the conductors of the corrugated plate and the high impedance of the upper entrance 23, leakage radio waves passing through the entrance 23 and heading outside are further suppressed. . Figure 8 shows heating chamber 11 with an opening of 365 x 260 mm.
The amount of radio wave leakage is shown when a beaker containing 275 ml of water is placed on the turntable 12 and heated while supplying high frequency power of 700 W at a frequency of 2450 MHz. On the operation panel side, the gap at the contact portion between the heating chamber opening periphery 18 and the wall surface 16a of the fundamental wave cheese yoke groove 19a is defined as the gap on the lap side of the horizontal axis in FIG. Curve A indicates that the wall surface 15c of the second harmonic cheese yoke groove 19b facing the heating chamber opening periphery 15 is a corrugated plate 15 equivalent to the conventional slit or the alignment post of the above embodiment.
This is the radio wave leakage characteristic in the case of a so-called chiyoke alone (a perspective cross-sectional view is shown in figure A'), which is a plane without w. Curve B shows a case where a slit with a length of λo/12 (10 mm) is provided on the wall surface 15c (a cross-sectional perspective view is shown in Figure B'), and a curve C shows a case where the wall surface 15c is made of a corrugated plate 15w Figure C' shows a cross-sectional perspective view. It is clear from FIG. 8 that the amount of radio wave leakage is smaller in the order of curve C, echo line B, and curve A. That is, the high-frequency heating device of the present invention provided in the door 2 provided with the corrugated plate 15w has the least amount of radio wave leakage, and is suitable for cost reduction because it can remove ferrite, conductive rubber, etc. Furthermore, as shown in FIG. 3, the radio wave attenuation cavity 19 has a fundamental wave channel groove and a second harmonic channel channel facing each other in opposite directions, and the radio wave propagation path length in each channel groove is determined by heating. The required dimensions can be obtained by appropriately selecting the length in the direction parallel to the chamber opening periphery 18, and the thickness of the door 2 may be thin, so it can be balanced with the thin electronic operation panel. It is possible to achieve the desired appearance in terms of design. As described above, according to the present invention, one radio wave attenuation cavity is provided at the periphery of the door, and has one entrance in which the fundamental wave chiyok groove and the second harmonic chiyok groove are opposed in opposite directions. Depending on the chamber opening dimensions, a tapered corrugated plate equivalent to at least the same number of matching posts as the total number of electric field maximum points of several higher-order modes that may exist in the longitudinal direction of the contact area between the heating chamber opening periphery and the door is used. To provide a high frequency heating device equipped with a door that reduces radio wave leakage with a simple structure and is suitable for thinning and cost reduction by molding from one wall surface of the second harmonic chiyoke groove itself. Can be done.

[Brief explanation of the drawing]

Fig. 1 is an external view showing an embodiment of the high-frequency heating device of the present invention, Fig. 2 is a schematic sectional view of the main part showing an embodiment of the high-frequency heating device in contrast to Fig. 1, and Fig. 3 is a radio wave diagram in Fig. 2. The enlarged cross-sectional views of the vicinity of the damping cavity 19, FIGS. 4, 5, and 6 show the process in which the wall surface 15c of the second harmonic choke groove 19b itself is transformed into a corrugated plate 15w by deforming the alignment posts 24 and 25. FIG. 7 is an explanatory diagram for explaining the radio wave attenuation cavity 19.
FIG. 8 is a diagram for explaining the action of the corrugated sheet 15w near the entrance 23 of the door. It is a figure comparing the amount of radio wave leakage in. 2... Door, 11... Heating chamber, 15c... One wall surface of the second harmonic chiyoke groove 19b, 15w... Corrugated plate, 1
8... Heating chamber opening periphery, 19... Radio wave attenuation cavity, 1
9a...Chiyok groove for fundamental wave, 19b...Chiyok groove for second harmonic wave, 23...Entrance of radio wave attenuation cavity 19.

Claims (1)

[Claims] 1 One radio wave attenuation cavity 19 having one entrance 23 is formed by arranging the fundamental wave groove 19a and the second high frequency wave groove 19b in opposite directions on the periphery of the door 2 that opens and closes the opening of the heating chamber. Depending on the heating chamber opening dimensions, the number of matching posts is equivalent to or more than the total number of electric field maximum points of several higher-order modes that may exist in the longitudinal direction of the contact area between the heating chamber opening periphery 18 and the door 2. A high frequency heating device characterized in that a tapered corrugated plate 15w is molded from one wall surface 15c of the second harmonic groove 19b itself.