JPH0546677B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a leakage high frequency seal structure for a door that can be opened and closed in a high frequency heating device such as a microwave oven. 2. Description of the Related Art Generally, there are the following three types of door configurations in high-frequency heating devices such as microwave ovens. First, a chiyoke groove with a metal wall surface having a depth equal to 1/4 of the wavelength of the high frequency used is provided in the peripheral frame of the metal door body, and an opening is provided in this on the heating chamber side. It guides and attenuates high frequency waves leaking from the source. The second type has the same structure as above, but also includes a radio wave absorber such as ferrite. The third method, which is often used in combination with the first and second examples above, is a metal plate in which slits are provided at continuous intervals parallel to the longitudinal direction of the door frame in the cheese yoke groove. The damping effect is enhanced by the slit yoke structure. Among the configurations of the third method above, a metal plate having continuous slits (hereinafter referred to as a slit plate)
are processed into various shapes to optimize the individual characteristics of the heating device, but the depth of the chiyoke groove is mainly based on the length of 1/4 wavelength of the high frequency used. . Recently, a system has appeared in which the depth of the cheese yoke groove is smaller than 1/4 wavelength, and a system in which the outer wall of the cheese yoke groove, that is, the outermost periphery of the door frame, is replaced with the slit plate itself has appeared. Summer.
(Refer to PCT Patent International Publication W084-01083) Adoption of this compact chiyoke system has the advantage that the door body can be made smaller and thinner, and the overall size of the device can also be made smaller and lighter. has advantages. Problems to be Solved by the Invention However, even with the above configuration, the expected effect on the damping performance at the butt portions of the slit plates between the upper and lower sides and the left and right sides has not been achieved, and the mechanism of leakage waves has not been achieved. It is difficult to say that it has been explained theoretically. In the process of opening the door, there is usually a switch that stops the high-frequency generator, but at least in the process until the switch is activated, leakage waves from around the door increase; Leakage waves tend to concentrate at the corners of the door. The maximum value is not always shown when the tip of the detection probe of the leakage meter is placed against the corner of the door, but it is measured at the corner or near the corner, empirically at a point 1/4 wavelength away from the corner. It often shows a peak. Note that although the same conditions apply to the leakage of waves at the corners of the hinge side of the door, this is hardly a problem because there is little change in distance from the front of the heating chamber when the door is opened and closed. That is, the current situation is that no sufficient measures have been taken to attenuate the leakage waves at the two corners on the opening side of the door. However, when the door is closed, there is a problem in that the leakage of waves from the side edges of the hinge is also large. Means for Solving the Problems In order to solve the above-mentioned problems, in the door device of the high frequency heating device of the present invention, the shape of the slit plate provided in the door frame portion is approximately 7-shaped in cross section; The short sides of the door face toward the inside of the door on each of the four sides of the door, and the long sides with slits and square holes having a certain periodic dimension as described later are arranged on the outermost periphery of the door frame. , wherein the long side and the inner circumferential wall of the door body form a cheese groove having an opening on the heating chamber side, and an extension in the longitudinal direction of the short side of the slit plate that closely opposes the inner peripheral wall surface of the cheese groove. The lines intersect at right angles at the edge of the door, but in doing so, ensure that either the vertical or horizontal extension line does not directly collide with the other horizontal or vertical slit plate, and The horizontal and vertical spacing between the line and the slit plate perpendicular to the line is configured to be equal to or smaller than the width of the slit in the slit plate. In addition, the period in which the slits and square holes are formed in the longitudinal direction of the slit plate, that is, the dimension from one end of a slit to one end of an adjacent slit, or from one end of a square hole to one end of an adjacent square hole, is determined based on the high frequency used. 1/
The length is 4 wavelengths or less, and the longitudinal dimensions of the slits and square holes at both ends are configured to have a period different from that of the other parts. Effect The door device configured as described above is effective in attenuating the amount of high frequency leaking from the heating chamber, especially the amount of leakage from the corners. That is, the leakage waves from the corner of the door leak from the corner of the front opening of the heating chamber or the vicinity thereof. It is thought that the characteristics of the leakage waves from this part and the characteristics of the leakage waves from around the center are slightly different, and it is necessary to have a chain structure that corresponds to each of these differences. The high-frequency attenuation effect of the chi-yoke structure, which is a periodic structure, is the attenuation of high-frequency energy propagating in the longitudinal direction (x direction) of the periodic structure, and the high-frequency energy propagating in the direction perpendicular to this (y direction). This is thought to be obtained in combination with energy attenuation. Now, when considering high-frequency leakage at any point in the yoke device, if it travels at a wavelength λ, a power density W, and an angle θ with respect to the x direction, then the apparent leakage in the x and y directions is The components are λ _x = λcosθ, W _x = Wcosθ, λ _y =
It can be regarded as λsinθ, W _y =Wsinθ. Near the longitudinal center of the chiyoke groove (same both vertically and horizontally)
The radio frequency leakage progression in must span almost all angles in the x and y directions. Optimization of the dimensions and shape of the slit plate for leakage high frequencies in all directions over these 180° angles was performed for λ _x , λ _y , W _x , W _y in the range from θ = 0° to θ = 90°. It will be. Normally, the position of the cheese yoke groove is located at least outside the heating chamber opening, so it is impossible for θ = 0°, but if θ = 0°, then the high frequency energy in the x direction is the highest, and the y When the direction is 0 and θ=90°, the energy in the y direction is maximum and the energy in the x direction is 0. On the other hand, the leakage traveling wave at the corner part is θ=45°
It can be considered as covering an angle range of ±45° centered on . In addition, it is unlikely that standing waves in the heating chamber will be concentrated at the aperture corners, and it is best to assume that the presence of standing waves at a point close to the aperture corner is closest at a point 1/4 wavelength away from the corner. is reasonable, and it must be considered that the end portions of the slit plates and the abutting portions of the vertical and horizontal slit plates are responsible for attenuating the leakage waves that proceed outward from this point.
And it must be assumed that the traveling wave in the 45° direction is at the highest energy level. As mentioned above, the properties of the high-frequency waves leaking from the edges of the door are different from those at the center, and the processing of the edges of the slit plate and the dimensions of the slit plate in the vicinity are structured to have a periodicity different from that of the center. Therefore, it becomes possible to deal with the problem, and by the combination thereof, it becomes possible to reduce the amount of leakage from the area around the door. Embodiment Hereinafter, a door device for a high-frequency heating device according to an embodiment of the present invention will be described with reference to the drawings. In FIGS. 1 and 2, the metal door body 1 consists of a door inner circumferential wall 3 located slightly outside the heating chamber front plate opening 2 (indicated by a dashed line), and slit plates 4 and 5 each having an approximately 7-shaped cross section. A chiyoke groove is formed by this.
The short sides 6 and 7 in the cross section of the slit plate are located between the cheese grooves and are provided facing the inner peripheral wall 3 of the door, and the area between the short sides 6 and 7 and the inner peripheral wall 3 is the high frequency cheese groove. It becomes an introduction opening to. Although not shown, a resin cover is usually provided at this portion. The slit plates 4 and 5 are provided with slits 8 and square holes 9 alternately and at regular intervals in the longitudinal direction. The lower end of the slit 8 and the lower end of the square hole 9 are on a line in the longitudinal direction, and the upper end of the square hole 9 and the short side 6,
7 is aligned with the lower end. The door opens horizontally, and there are hinge parts 1 on the top and bottom of one side of the main body.
0,11. A space 12 outside the slit plate 5 on the opening side of the door is used for attaching a key or the like for operating a door switch or the like. To reduce leakage waves from the corner portions by minimizing the distance between the corner portions of the vertical and horizontal slit plates 4 and 5, that is, the horizontal distance H and the vertical distance V in the figure. I can do it. However, as shown by dimension H' in FIG. 3, it is not desirable that the end of one slit plate extends to a position where the other slit plate overlaps. The actual measured values of the leakage power density when these dimensions H and V are changed are shown below.

[Table] In this table, the numbers in the upper row are for the worst combination of dimensional tolerances when the door is closed normally (i.e., the largest gap), and the numbers in the lower row are for stopping the high-frequency generator. The highest peak value is shown in both cases when the door is open until just before the switch is activated. The measurement target is a high frequency output of 500W.
This is the case when 275ml of tap water is loaded in a microwave oven. Note that the combination of the butt dimensions of the slit plates 4 and 5 on the hinge side is omitted because, as mentioned above, there is almost no change in leakage due to the change in dimensions, and the values in the table above are all values for the corner on the opening side of the door. be. From this actual measurement result, it can be seen that the smaller the abutting dimension of the corner portions of the slit plates 4 and 5, the more the leakage of waves decreases. However, the value when H=-40mm is H=
There is a tendency for some wave leakage to become larger than the value at 5.0 mm. This seems to be because the high frequency waves that propagate in the longitudinal direction of the slit plates 4 and 5 and are attenuated interfere with each other and disturb the attenuation effect. The H and V dimensions are the width dimension A of the slit in the longitudinal direction of the slit plates 4 and 5 (10 mm in this measurement)
If it exceeds this value, it becomes a value that is hardly of practical use, so this width dimension A serves as a guideline, and making it smaller than this value is considered to be a condition under which appropriate effects can be expected. On the other hand, if dimension A of the slits 8 of the slit plate and dimension B between the slits are set at regular intervals in the longitudinal direction, the corner dimensions may not be optimized. That is, the vertical slit plate 5 may be just right, but the horizontal slit plate 4 may be undersized (or oversized), or vice versa, or one may be undersized and the other may be oversized. There are many things. However, from the viewpoint of wave leakage, it is desirable that the periodicity in the longitudinal direction be the same in both the vertical and horizontal directions. For these contradictory conditions, the widths A and B of both ends of the slit plates 4 and 5 and the outermost slit are set to 0.5 to 1.
It shall be different from the dimension near the center within the range of mm,
Therefore, it is assumed to be non-periodic near both ends. This is done by focusing on the fact that the nature of the leakage waves from the vicinity of the corner of the heating chamber opening is different from the leakage waves from other parts, as described above, and the period is set to 1/4 wavelength of the high frequency, and the slit plates 4, 5 It is non-periodic for only one period of the length of the longitudinal end, that is, a length of 1/4 wavelength at the maximum. Considering that it is difficult to imagine the existence of standing waves in the heating chamber unless the point is more far away, we believe that the attenuation of the leakage waves carried by the non-periodic portion of the slit plate is directed outward from the portion where the standing waves exist. It is possible to target only high-frequency leakage components with slightly different properties. Effects of the Invention As described above, in the cheese yoke device of the present invention, the distances in the horizontal and vertical directions at the corners of the vertical and horizontal slit plates are made at least smaller than the width of the slits, and are set to values that do not overlap with each other. At the same time, by making the length of one cycle at both ends of the slit plate different from the other cycles at the center, it is possible to reliably reduce the amount of leakage at the corners of the door sealing performance. It will be done.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway perspective view of a chiyoke device of a door according to an embodiment of the present invention, Fig. 2 is a back view of the door, and Fig. 3 is a partial back view showing an example of a combination of corner portions of the door. . 3... Inner peripheral wall of the door, 4... (horizontal) slit plate,
5... (vertical) slit plate, 6, 7... short side, 8
...Slit.

Claims (1)

[Scope of Claims] 1. In a high-frequency sealing device provided on the four surrounding frames of a metal door body, the cutout portions and square hole portions are arranged alternately, and the dimensions are 1/4 or less of the wavelength of the high frequency used. A slit plate with a cross section of approximately 7-shape formed at regular intervals is arranged in the cheese yoke, and one end of each slit plate on the upper and lower sides of the door and a 7-shaped slit plate on the left and right sides of the door that corresponds at right angles to the slit plate are arranged in the cheese yoke. The apparent horizontal distance when the short sides of the shaped cross section are extended in the longitudinal direction, as well as the distance between each end of the slit plates on the left and right sides of the door and the slit plates on the top and bottom sides of the door corresponding at right angles thereto. A high-frequency heating device configured such that the apparent vertical distance when the short sides of the figure-7 cross section are extended in the longitudinal direction is set to be larger than 0 and smaller than the width dimension of the notch of the slit plate. door device. 2. High-frequency heating according to claim 1, in which the longitudinal dimensions of the notch and the square hole of the slit plate on each of the four sides of the left, right, top, and bottom are different from other constant periodic dimensions only at each end. Device door device.