JP2010049946A - High frequency heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave oven in which an optional heated object of respective heated objects out of a plurality of the heated objects to be heated can be heated intensively, and the plurality of the heated objects can be subjected to heat treatment. <P>SOLUTION: A high frequency heating device is equipped with a connecting hole installed in the center part of the bottom face of a high frequency supply chamber in order to radiate high frequency energy guided to a wave guide tube mounted with a magnetron, an inner conductor installed penetrating through this connecting hole and facing the high frequency supply chamber nearly vertically, a metallic flat plate rotating antenna coupled with the high frequency supply chamber nearly horizontally at one end of this inner conductor, a dielectric shaft coupled in the wave guide tube of the inner conductor, and a driving part to rotate and drive this dielectric shaft. In the rotating antenna, a plurality of arc-shaped slits are installed, each of which has a length of λ/2 (λ: wavelength and here it is 122 mm) or more, and the center of each arc-shaped slit is installed so as to be positioned at the exterior of the rotating antenna. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a high-frequency heating apparatus that uses a rotating antenna to radiate high-frequency energy into a heating chamber to heat food or the like at high frequency.

  A conventional so-called turntableless high-frequency heating apparatus includes a rotating antenna under a heated object mounting plate in a heating chamber, scatters high-frequency waves supplied from the magnetron with the rotating antenna, and radiates the heated object into the heating chamber. The object to be heated placed on the placing plate is heated at high frequency.

  As a rotating antenna for supplying different amounts of high-frequency energy to a plurality of objects to be heated, a radiation port having a side longer than ½ of the wavelength used is provided in the rotating antenna, and the high-frequency energy is hardly attenuated. There is known a high-frequency heating device that radiates the light toward the heating chamber (see, for example, FIG. 2 and FIG. 3 in Patent Document 1).

JP 2003-86348 A

  When the rotating antenna shown in FIG. 2 of Patent Document 1 is used, high-frequency energy concentrates directly above the radiation port 9b. Therefore, the time required to position the radiation port 9b under the heated object having a high finishing temperature is lengthened, and the finishing temperature is increased. By shortening the time for positioning the radiation port 9b under the object to be heated, the finishing temperature suitable for each object to be heated can be obtained.

  However, in consideration of the feature of the rotating antenna of Patent Document 1 in which high-frequency energy is concentrated directly above the radiation port 9b, among the heated objects placed on the heated object placing plate, on the projection surface of the rotating antenna. Only the object to be heated can adjust the finishing temperature. In other words, when the heating chamber is widened, it is impossible to adjust the finishing temperature of the object to be heated if the rotating antenna is not enlarged, and the rotating antenna is reduced in size while widening the heating chamber. There was a problem that could not.

  Further, FIG. 3 of Patent Document 1 discloses a rotating antenna provided with a plurality of arc-shaped radiation openings having sides longer than ½ of the used wavelength. However, since any arc-shaped radiation aperture has the center of the rotating antenna as the center of the arc, it is difficult to provide a large number of radiation apertures having sides longer than ½ of the wavelength used. For this reason, if the size of the rotating antenna is reduced, the number of radiation openings having sides longer than ½ of the wavelength used is also reduced, which makes it difficult to reduce the size of the rotating antenna.

  The problems include a heating chamber that accommodates a heated object, a heated object mounting plate fixed to the bottom surface of the heating chamber, a magnetron that generates high-frequency energy of wavelength λ, and high-frequency energy generated by the magnetron. A transmission waveguide, a rotating antenna provided under the object-to-be-heated object mounting plate and diffusing high-frequency energy transmitted from the waveguide, a driving unit for rotating the rotation antenna, and the magnetron; A control circuit for controlling the driving, wherein the rotary antenna is provided with an arc-shaped slit having a length of λ / 2 or more, and the arc center of the arc-shaped slit is This can be solved by a high-frequency heating device outside the rotating antenna.

  According to the present invention, even when a small-diameter rotating antenna is used, the directivity can be given to the diffusion of the high-frequency energy, and the directional high-frequency energy is irradiated to each of the plurality of heated objects for an arbitrary time. It becomes easy, and it becomes easy to heat a several to-be-heated material so that it may become a different finishing temperature.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a diagram illustrating a state in which the door 53 of the high-frequency heating device 50 according to the embodiment is opened. In FIG. 5, the upper cover and the side cover are omitted for explanation. In FIG. 5, reference numeral 1 denotes a heating chamber that accommodates an object to be heated. Reference numeral 2 denotes a heated object placing plate on which the heated object is placed, which is made of a dielectric material such as crystallized glass, for example, and is fixed to the bottom surface of the heating chamber 1. A magnetron 4 generates a 2450 MHz electromagnetic wave assigned to an ISM (Industrial, Scientific and Medical) frequency band. Reference numeral 8 denotes a rotatable rotating antenna made of a disk made of a highly conductive metal such as aluminum. An inverter power supply 51 supplies driving power to the magnetron 4. A control circuit 52 controls the rotation of the magnetron 4 and the rotating antenna 8. It is assumed that the rotating antenna 8 of the present embodiment is smaller than the conventional rotating antenna. Here, the description will be made assuming that the diameter of the rotating antenna 8 is 130 mm. Not limited to.

  FIG. 1 is a longitudinal sectional view of a main part of a high-frequency heating device 50. In FIG. 1, reference numeral 12 denotes an object to be heated accommodated in the heating chamber 1. Reference numeral 3 denotes a high-frequency supply chamber provided below the heated object placing plate 2. Reference numeral 5 denotes a waveguide having one end connected to the magnetron 4 and the other end opened to the high-frequency supply chamber 3, and high-frequency energy generated in the magnetron 4 is guided to the inner conductor 7 via the waveguide 5. The high-frequency energy guided to the inner conductor 7 is transmitted to the rotating antenna 8 by coaxial coupling, is diffused into the high-frequency supply chamber 3 by the rotating antenna 8, passes through the object mounting plate 2, and is radiated to the heating chamber 1. . Reference numeral 6 denotes a coupling hole in the opening on the high-frequency supply chamber 3 side of the waveguide 5, which is located at the approximate center of the bottom surface of the high-frequency supply chamber 3. The rotating antenna 8 is rotationally driven by a driving force applied from the driving unit 11 via the dielectric shaft 9 and the inner conductor 7. As shown in FIG. 1, the rotating antenna 8 is fixed horizontally to the upper end of the inner conductor 7 provided substantially vertically at a position penetrating the coupling hole 6. Further, the lower end of the inner conductor 7 and the dielectric shaft 9 are connected in the waveguide 5, and the dielectric shaft 9 is connected to the drive unit 11 through a hole 10 provided in the waveguide 5. If the rotating antenna 8 is a circular flat plate, the electric field is less likely to concentrate on the outer periphery of the rotating antenna 8 and the electric field strength is leveled, so that spark and abnormal heating are less likely to occur in this portion. Further, there is an advantage that when the rotating antenna 8 is rotated, a stable rotation can be obtained with less blur.

  Details of the rotating antenna 8 of this embodiment will be described with reference to FIG. FIG. 2 is a plan view of the rotating antenna 8 as seen from above. Reference numerals 8a to 8g denote a plurality of arc-shaped slits provided in the disk-shaped rotating antenna 8, and the arc-shaped slits excluding 8d have a length of 61 mm or more. Here, 61 mm is a length corresponding to λ / 2 when the frequency of the electromagnetic wave generated by the magnetron 4 is 2450 MHz, that is, when the wavelength λ is 122 mm. By providing a slit having a length of 2 or more, high-frequency energy transmitted to the rotating antenna 8 can be radiated into the heating chamber with almost no attenuation.

  The configuration of the arc slit will be described by taking the arc slit 8c as an example. As shown in FIG. 2, the arc-shaped slit 8c is an arc-shaped slit having a radius Rc composed of an outer arc, an inner arc, and two sides connecting both arcs. It is outside the antenna 8. The outer arc is designed to be longer than the inner arc. A straight line connecting the center of the rotating antenna 8 and the K point is referred to as a diameter axis 21.

  The arc centers of the arc-shaped slits 8a to 8g are also set as the K point, and Ra to Rg, which are the radii of the arc-shaped slits 8a to 8g, are set so that the relationship Ra> Rb> Rc> Rd> Re> Rf> Rg is established. To do. The centers of the arc-shaped slits 8a to 8g are positioned on the diameter axis 21, respectively. Thereby, each arc-shaped slit 8a-8g turns into a concentric arc-shaped slit which does not cross | intersect with the adjacent arc-shaped slit. As a result, the arc-shaped slits 8 a to 8 c provided on the left side of the rotating antenna 8 and the arc-shaped slits 8 e to 8 g provided on the right side of the rotating antenna 8 are provided across the rotation center of the rotating antenna 8. The arc-shaped slits other than the arc-shaped slit 8c are also designed so that the arc on the inner peripheral side is shorter than the arc on the outer peripheral side.

  As described above, since the arc centers of the arc-shaped slits 8a to 8g are located at the point K outside the rotating antenna 8, the degree of freedom of arrangement of the number of arc-shaped slits having a length of λ / 2 or more is increased. Can do. That is, it becomes easy to provide a large number of arc-shaped slits having a length of λ / 2 or more even for a small rotating antenna.

  Since a plurality of arc-shaped slits having a length of λ / 2 or more are provided in the rotating antenna 8 as described above, the microwave energy transmitted to the rotating antenna 8 is transmitted from the arc-shaped slit near the center of the rotating antenna 8 to the outer periphery. In the process of successively propagating toward the arc-shaped slits, the phases of the microwaves emitted from the individual arc-shaped slits overlap with a slight delay, and microwave energy having strong directivity in the direction of the diameter axis 21 is radiated into the heating chamber 1. Will be.

  The result of calculating the radiation characteristics of the rotating antenna 8 of this embodiment by the TLM method, which is a kind of electromagnetic field analysis technique, will be described with reference to FIG. As shown in the lower part of FIG. 3, the X axis is an axis connecting the center of the rotating antenna 8 and the K point described above, and the K point direction is positive. The Z axis is an axis perpendicular to the X axis, and is provided on the plane of the rotating antenna 8 and at a position passing through the center of the rotating antenna 8. Further, as shown in the upper diagram of FIG. 3, the Y axis is an axis perpendicular to the X axis and the Z axis, and the height direction is a plus direction. The upper diagram of FIG. 3 shows the radiation characteristics of the rotating antenna 8 on the XY plane. As can be seen, stronger radiation was seen in the upper left side of the XY plane, that is, in the minus direction of the X axis.

Next, the results of calculating the temperature distribution when the article to be heated 12 is heated by the TLM method will be described with reference to FIG. In FIG. 4, in order to make the positional relationship between the object to be heated 12 and the rotating antenna 8 easy to understand, the rotating antenna 8 is superimposed on the object to be heated 12. In FIG. 4, the object to be heated 12 is a frozen pizza having a diameter of 170 mm and a thickness of 10 mm. The object to be heated 12 was decomposed into 174,000 cells, and the temperature rise value was calculated for each. The physical constants at the time of analysis were a relative dielectric constant of 4.4, a conductivity of 0.0722 s / m, and a density of 794 kg / m ³ . The lightness and darkness in FIG. 4 indicate the temperature distribution inside the object to be heated 12 (specifically, the temperature distribution in the cross section of the frozen pizza having a thickness of 5 mm). The bright portion has a high temperature rise, and the dark portion has a low temperature rise. Is shown. As can be seen from this, it was confirmed that the left side of the object to be heated 12, that is, the negative direction of the X axis was heated more strongly, and the temperature was increased.

  In this way, the object to be heated placed in the negative direction of the X axis is heated more strongly, and therefore, when a plurality of objects to be heated are placed in the heating chamber 1, the object to be heated that is to be preferentially heated. When there is an object, any object to be heated can be preferentially heated by lengthening the time in which the negative direction of the X axis is directed toward the object to be heated. On the other hand, when a plurality of objects to be heated are placed in the heating chamber 1 and it is desired to suppress uneven heating of the plurality of objects to be heated, the plurality of objects to be heated are rotated by rotating the rotating antenna 8 at a constant speed. Uneven heating of objects can be prevented.

  In addition, by widening the space | interval of each arc-shaped slit of the rotating antenna 8, the direction of strong radiation can be brought close to the minus direction of the X axis, and the position far from the center of rotation of the rotating antenna 8 can be warmed strongly. On the other hand, by narrowing the interval between the arc-shaped slits of the rotating antenna 8, the direction of strong radiation can be moved away from the minus direction of the X axis and closer to the plus direction of the Y axis. A close position can be warmed strongly. That is, by adjusting the distance between the arc-shaped slits, the radiation directivity of the microwave energy can be adjusted, so that any directivity can be obtained even when the small rotating antenna 8 is used.

  In the present embodiment, the arc-shaped slit 8d having a length less than λ / 2 is disposed between the arc-shaped slits 8c and 8e having a length of λ / 2 or more. This is to further increase the value. If there is no arc-shaped slit 8d, the high-frequency energy transmitted to the rotating antenna 8 via the inner conductor 7 is also radiated in the direction between the arc-shaped slits 8c and 8e. However, when the arc-shaped slit 8d is provided between the arc-shaped slits 8c and 8e, the high-frequency energy transmitted to the rotating antenna 8 through the inner conductor 7 is radiated in the direction of the arc-shaped slit 8d. It can prevent, and it can prevent that the directivity of radiation | emission of high frequency energy weakens.

  As described above, the high-frequency heating device of the present invention can install a plurality of arc slits of λ / 2 or more in parallel even with a small rotating antenna having a small diameter, and the length of the arc slit can be easily adjusted. . Moreover, directivity can be provided by arranging a plurality of arc-shaped slits in parallel, and directivity can be controlled because the directivity can be arbitrarily changed by adjusting the interval between the arc-shaped slits. Furthermore, by providing directivity, microwaves can be radiated in a concentrated manner by targeting any object to be heated with respect to a plurality of non-heated objects.

The principal part longitudinal cross-sectional view of the high frequency heating apparatus of one Example. The top view of the rotation antenna of one Example. The figure which shows the radiation characteristic of the microwave energy of a rotating antenna. It is a figure which shows the result of having analyzed the temperature distribution of to-be-heated material. 1 is an overall view of a high-frequency heating device according to one embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating chamber 2 To-be-heated object mounting plate 3 High frequency supply chamber 4 Magnetron 5 Waveguide 6 Coupling hole 7 Inner conductor 8 Rotating antenna 8a Arc-shaped slit 9 Dielectric shaft 11 Drive part

Claims (4)

A heating chamber for storing an object to be heated;
A heated object mounting plate fixed to the bottom surface of the heating chamber;
A magnetron that generates high-frequency energy of wavelength λ,
A waveguide for transmitting high-frequency energy generated by the magnetron;
A rotating antenna that is provided under the heated object mounting plate and diffuses high-frequency energy transmitted from the waveguide;
A drive unit for rotationally driving the rotating antenna;
The magnetron; and a control circuit for controlling the driving;
A high-frequency heating apparatus comprising:
The rotating antenna is provided with an arc-shaped slit having a length of λ / 2 or more, and the arc center of the arc-shaped slit is outside the rotating antenna. In the high frequency heating apparatus according to claim 1,
The rotary antenna is provided with a plurality of arc-shaped slits, and the plurality of arc-shaped slits are concentric arc-shaped slits. The microwave oven according to claim 2, wherein
The high frequency heating apparatus, wherein the plurality of arc-shaped slits are provided across a rotation center of the rotating antenna. A heating chamber for storing an object to be heated;
A heated object mounting plate made of a dielectric provided on the bottom surface of the heating chamber;
A high-frequency supply chamber provided in the center of the bottom surface of the heating chamber below the heated object placing plate,
A magnetron that generates high-frequency energy;
A waveguide to which this magnetron is attached;
A coupling hole provided in a central portion of the bottom surface of the high frequency supply chamber for radiating high frequency energy guided to the waveguide to the high frequency supply chamber;
An inner conductor provided substantially vertically through the coupling hole and into the high-frequency supply chamber;
A metal flat plate rotating antenna connected substantially horizontally in the high-frequency supply chamber at one end of the inner conductor;
A dielectric shaft connected within the waveguide of the inner conductor, and a drive unit that rotationally drives the dielectric shaft,
The rotating antenna is provided with a plurality of arc-shaped slits having a length of λ / 2 (λ: 122 mm) or more, and the arc center of each arc-shaped slit is outside the rotating antenna. .

Images