JPH0824066B2 - High frequency heating equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency power feeding method for a high-frequency heating device, and is intended to prevent abnormal heating phenomenon due to high frequency in a heating chamber in a device having high-frequency power feeding means on the upper and lower walls of the heating chamber. It is something to suppress.

2. Description of the Related Art In general, in order to obtain a high output device in this kind of heating device, a plurality of high frequency generating means are provided and the high frequency generated by each high frequency generating means operated in parallel in the same heating chamber. A method of providing a guiding structure is adopted. Especially for the purpose of high output and uniform heating, as an example of a structure that guides high frequency waves to the heating chamber, power supply means to the high frequency heating chamber is provided in the upper wall and the bottom wall of the heating chamber and the object to be heated is placed from above and below. Means of heating are also used.

FIG. 3 schematically shows a lateral cross section of a high frequency generator having such a structure.

Circular power supply ports 4 and 5 for supplying a high frequency wave to the heating chamber are provided in a part of the upper wall 2 and the bottom wall 3 constituting the heating chamber 1, respectively. At the center of the power feed ports 4 and 5, antennas 6 and 7 for power feeding, which are rotatably supported by dielectrics, are rotatably supported around the centers of the power feed ports 4 and 5. Each of the antennas 6 and 7 has one end protruding into the heating chamber 1 and is provided with stirring plates 8 and 9 near the end faces thereof for stirring the electric field. The stirring plates 8 and 9 may be directly fixed to the antennas 6 and 7, or may be coupled via a dielectric. Above the lower stirring plate, a mounting table 11 for a heated object 10 made of a dielectric material such as glass is supported by a support piece 13 provided on a side wall 12 forming a heating chamber.
The ends of the antennas 6 and 7 outside the heating chamber are coupled in high frequency by two magnetrons 14 and 15 and waveguides 16 and 17 as a high frequency generator provided at the rear of the heating chamber. Also,
The ends of the antennas 6 and 7 on the side of the waveguides 16 and 17 are
The output shafts of drive motors 18 and 19 provided outside are coupled, and the antennas 6 and 7 are configured to rotate about the centers of the power supply ports 4 and 5 while the magnetrons 14 and 15 generate high frequencies.

With the above configuration, the object to be heated 10 is placed on the mounting table 11 in the heating chamber 1.
It is possible to heat the object to be heated from above and below and with a maximum output of twice by supplying electric power to the magnetrons 14 and 15 as needed.

Problem to be Solved by the Invention One problem of the high-frequency heating apparatus having such a configuration is an abnormal overheating phenomenon of a portion of the mounting table on which the object to be heated is not mounted. The presence of the dielectric loss due to the high-frequency energy heats the mounting table 11 at the same time as the object to be heated, and the heat is absorbed by the object to be heated in the part where the object to be heated exists, but the part without the object to be heated. Then, even a highly heat-resistant dielectric such as crystallized glass having a melting point of 1000 ° C. or higher is sometimes locally melted. As a result, the entire mounting table will be destroyed due to the generation of thermal stress.
If repeated heating operations are performed, the possibility becomes very high due to the heat storage effect. There is a possibility of causing a burn to the user, eventually causing a fire from the inside of the refrigerator, and causing an extremely dangerous state that may cause a fire of the entire body. Conventionally, as a countermeasure against this, for example, as a means for preventing overheating in the wall of the heating chamber, if a thermostat 20 or the like is provided and the temperature inside the chamber rises abnormally, this switch shuts off the input power of the magnetrons 14 and 15 to perform the heating operation. Although it was stopped, the local heating phenomenon became more severe as the high-frequency output increased, for example, even if a part of the mounting table exceeds 1000 ° C, the temperature of the thermostat is 100 ° C or less, so that malfunctions during normal operation can be prevented. However, there is a problem that the operating temperature of the thermostat set to 1 is not reached and the thermostat does not function sufficiently.

Means for Solving the ProblemsThe present invention is intended to prevent abnormal heating of such a mounting table, and compares the distance between the mounting table and the bottom wall facing the rotating area portion of the stirring plate where the electric field changes, By shortening the other parts, weaken the high-frequency electric field outside the rotation area,
The high-frequency energy is concentrated in the placement area of the object to be heated, and ventilation between the placing table and the bottom wall is performed to suppress abnormal heating of the part of the placing table other than the object placing area. is there.

Action The electric field strength of the high frequency applied to the mounting table part depends on the high frequency standing wave generated in the heating chamber. That is, the electric field on the bottom wall surface is 0, and when looking up to the antinode of the standing wave, the electric field strength increases as the distance from the wall increases. In the present invention, the placement area of the object to be heated is set at a distance from the wall surface so that the strongest electric field is applied to the object to be heated. Further, a configuration in which the stirring means for the electric field is rotated is provided over almost the entire area to heat the object to be heated by a strong and uniform electric field. At the same time, the mounting table is also heated, but since the heat generated in the mounting table is absorbed by the object to be heated, the abnormal heating phenomenon of the mounting table does not occur in this part.

On the other hand, in the portion where the placing table faces the bottom wall other than the placing area of the object to be heated, there is little effect on the fluctuation of the electric field due to the rotation of the stirring means, and local heating due to standing waves tends to occur. The electric field applied to the part of the mounting table is weakened only by shortening the distance between the bottom wall and the mounting table as compared with the installation area of the object, thereby suppressing abnormal heating of the mounting table.

However, with this method alone, the outer peripheral portion of the object to be heated, particularly the upper surface portion, can hardly be heated because the high frequency generated from the bottom wall side is blocked by the bottom surface of the object to be heated. In the present invention, the high frequency electromagnetic wave is radiated to the vicinity of the heating chamber along the upper wall by the second power feeding means provided on the flat upper wall, reflected by each wall surface, and another high frequency electromagnetic wave is provided near the upper wall. It is possible to heat the upper surface or side surface of the object to be heated while stirring the electric field with the stirring plate. Further, heating of the portion other than the heated object placement area by high frequency is further suppressed by passing ventilation holes in the portion where the distance between the placement table and the bottom wall is short, and by applying cooling air. It

Embodiment An embodiment of the present invention will be described with reference to FIGS.
The same components as those in the conventional example are designated by the same reference numerals.

As shown in the figure, a circular high-frequency power supply port 5 is provided in the center of the heating chamber bottom wall 3 as a power supply means, and an antenna 7 and a flat plate-shaped stirring plate 9 fixed to the tip thereof are provided at the center of the power supply port 5 as in the conventional case. Is rotatably supported by a shaft, and the drive motor 19 causes the magnetrons 14 and 15 to rotate during oscillation.

The bottom wall 3 constituting the heating chamber 1 is provided with a circular throttle portion 21 having a size equal to or smaller than the placement area of the object to be heated and having a radius substantially similar to the radius of rotation of the stirring plate 9. In this embodiment, the bottom of the heating chamber has a width of 330 mm × 310 mm, and the diameter of the narrowed portion is 250 mm. The depth of the diaphragm is such that sufficient electric field strength can be obtained in the mounting area, that is, when the high frequency of the embodiment is 2450 MHz, the distance from the lower end (portion of the power supply port) surface of the diaphragm 21 to the mounting table. The height is about 25 mm. Around the narrowed portion 21 is a mortar-like 60 ° inclined surface 22
On the outside, the distance from the side wall of the heating chamber 1 to the mounting table 11 is about 10 mm. Similarly, the upper wall 2 of the heating chamber 1 is provided with a circular throttle portion 23 having a radius similar to the rotation radius of the stirring plate 9. Similarly, a power supply port 4 is provided in the center of the throttle portion 23, and the antenna 6 and the stirring plate 8 fixed to the tip thereof are provided.
Is rotatably supported around the center of the power supply port 4 as described above, and the drive motor 18 rotates the magnetrons 14 and 15 during oscillation to radiate a high frequency into the heating chamber 1 and stir it. There is. An inclined surface 24 of 50 ° is provided around the narrowed portion 23, and a surface lower than the surface provided with the power supply port 4 by 20 mm is formed on the outer side thereof and connected to the side wall portion.

Further, in the portion outside the inclined surface 22 of the bottom wall 3, there are two front and left and two rear and right and left portions, each having a diameter of 3 m.
Vent holes 25, 26, 27, 28 having a plurality of m holes are provided.
Further, in the side wall 12 of the heating chamber, a vent hole 29 having a plurality of holes of the same small diameter is provided in a portion below the mounting table 11 above the bottom wall and the joint portion. The magnetron 15 relating to high-frequency radiation from the bottom wall of the heating chamber has a configuration in which it is cooled by rotation of a blower motor 30 provided between the magnetron 15 and the side wall. Blower motor
An air intake guide 31 is provided in a part of the air intake portion of the air passage 30 to connect the air vents 27, 28 and 29, and the blower motor 30 rotates while high frequency is generated, cooling the magnetron 15 and venting the air. The air under the mounting table 11 is drawn out through the mouths 28, 29, 30. A part of the cooling air of the main body taken into the main body from the intake port 32 provided on the front surface of the main body is the ventilation port 25, 2
It has a structure in which it is replenished by flowing into the lower part of the mounting table from 6.

In addition, a front wall 33 forming the heating chamber 1 is provided with a door 34 for opening and closing an object to be heated and closed so as to prevent leakage of high frequency waves due to contact between the two. Also, magnetron 15
The cooled air is discharged from the exhaust port 35 to the outside of the main body.

According to the above configuration, the high frequency wave radiated to the narrowed portion 21 at the bottom of the heating chamber 1 through the antenna 7 passes through the mounting table 11 and is directly absorbed by the bottom of the object to be heated 10 or the inclined surface.
It is facing 22 and is reflected by this part. The direction of reflection depends on the angle of the inclined surface with respect to the bottom wall 3, but when the inclination of the inclined surface 22 with respect to the surface provided with the power supply port is 45 ° or more, the high frequency wave is directed toward the center of the heating chamber. It is reflected and faces the bottom surface of the object to be heated 10.

That is, the high frequency generated by the magnetron 15 is transmitted to the antenna 7
Is radiated toward the bottom of the article to be heated 10 via, and is less likely to travel to the outside of the inclined surface 22. The flat plate-shaped stirring plate 9 changes the direction of high-frequency irradiation centering on the rotation axis of the high-frequency antenna 7 according to the rotation, and also changes the standing wave standing on the wall surface as the starting point, and the diaphragm part The electric field of 21 is changed to prevent local heating of the bottom surface of the object 10 to be heated. Then, the mounting table 11 in this portion does not cause an abnormal heating phenomenon because the object 10 to be heated absorbs heat. Further, the high frequency wave that has exited from the inclined surface 22 passes through the mounting table 11 and is radiated into the heating chamber 1. However, as described above, the distance from the bottom wall 3 to the mounting table 11 is increased.
By making it 10 mm, the electric field strength due to the standing wave in this part becomes low, and it became possible to lower the part where the temperature was 300 ° C or more in the conventional body operation for 10 minutes to 140 ° C or less. .

Furthermore, the flow of air flowing from the vents 25, 26 between the bottom wall 3 and the mounting table 11 and discharged from the vents 27, 28, 29 is 10
Since it flows in a narrow space of mm, the flow velocity near the surface of the mounting table 11 is much faster than the mounting area of the object to be heated 10, that is, the narrowed portion 21, and the cooling effect on the surface is extremely high. As a result, the temperature rise of 10 minutes further decreased to around 110 ℃ at 140 ℃. Furthermore, the presence of air flow at all times prevents heat accumulation in this space,
Outside the placement area of the object to be heated 10 during long-term use
It is possible to eliminate the abnormal heating phenomenon that exceeds 200 ° C and prevent the mounting table 11 from being destroyed.

On the other hand, it is difficult to sufficiently heat the upper surface and the side surface of the object to be heated 10 only by this method. However, in the present invention, the antenna is provided by providing the power feeding port 4 in the central portion of the upper wall of the heating chamber. It can be sufficiently heated by the high frequency wave emitted from No. 6.

An inclined surface by the stirring plate 8 provided at the tip of the antenna 6.
The high frequency wave toward 24 is reflected by this inclined surface 24. The high frequency reflected by setting the angle with respect to the upper wall 3 of the inclined surface to 50 ° goes slightly inward from below and enters the object to be heated 10. The distance between the mounting table 11 and the power supply port 4 is
Compared with the distance to the power supply port 5, the space for placing the article to be heated 10 is larger by a necessary amount, and the high-frequency focusing property is deteriorated, so that the object placed directly below the inclined portion 24 is placed. The object to be heated is also sufficiently heated, and as a result, the object to be heated is sufficiently heated from above and below,
Further, the high frequency does not enter the peripheral portion of the mounting table 11 on which the object to be heated 10 is not mounted outside, and abnormal heating of the mounting table 11 does not occur even by the high frequency irradiated into the heating chamber from the power supply port 4.

In this embodiment, the inclination angles of the inclined portions 22 and 24 are 60 ° and 50 °.
Although it is set to a value of °, this angle depends on the size of the heating chamber 1, the size of the narrowed portion, or the heating condition of the heated object 10 and the peripheral part of the mounting table 11 depending on the type and shape of the heated object. The optimum value is set according to how the temperature rises.

In addition, the mounting table 12 does not have to be provided with the diaphragm 23 provided on the upper wall.
It is possible to suppress the rise in the temperature to a certain degree. That is, as described above, since the outer peripheral portion of the mounting table is closer to the rotation area of the stirring plate 9 than the wall surface, a sufficient high-frequency electric field for heating is not generated.

Further, in this embodiment, in order to perform ventilation between the mounting table 11 and the bottom wall 3, a method of drawing out the air in this space by the negative pressure generated by the rotation of the blower motor 30 has been shown. Ventilation of the space is the reverse blower motor
It is possible that, for example, air is forcibly sent to this space from the vent hole 29 or the like by means of 30 to make it a positive pressure, and is discharged to the outside of the heating chamber wall from the other vent holes 25, 26 or the like. In this case, as compared with the embodiment, the flow velocity of air is higher, the mounting table is further cooled, and it is effective in suppressing abnormal heating.

Effects of the Invention With the above configuration, the present invention makes it possible to prevent abnormal heating in the outer peripheral portion of the mounting table of the object to be heated as originally intended, and at the same time, the following effects can be obtained together. It became like.

(1) Reduction of high-frequency leakage from this part by reducing the high-frequency intrusion to the contact part of the front wall of the heating chamber facing the door that moves the heated object in and out of the heating chamber and weakening the electric field I was able to measure. Furthermore, it is possible to significantly reduce the heating phenomenon due to high frequency in this part, and to prevent burns caused by touching this contact part when moving in and out of the object to be heated, thus improving safety. Was completed.

(2) By providing a circular throttle and an inclined part, and rotating the stirring plate in this, the fluctuation of the load impedance seen from the antenna is extremely reduced compared to the past, and the high frequency that was previously absorbed by the mounting table. In addition to being absorbed by the object to be heated from the bottom surface, the heating efficiency could be greatly improved. This tendency was especially remarkable at light loads. In the embodiment, when a constant input power is applied to the magnetron, the ratio of the high frequency output at the time of 250 cc of water load to the water load of 2 is 80% in the conventional 60 to 65%.
With the above values being obtained, it has become possible to heat an object to be heated in 45 to 50 seconds, which conventionally required a heating time of 1 minute.

[Brief description of drawings]

FIG. 1 is a plan sectional view showing an essential part of an embodiment of the present invention.
FIG. 3 is a side sectional view showing an embodiment of the present invention, and FIG. 3 is a side sectional view showing a conventional example. 1 ... heating chamber, 3 ... bottom wall, 5 ... power supply port, 7 ... antenna, 9 ... stirring plate, 10 ... object to be heated, 11 ... mounting table,
21 …… throttle part, 22 …… slanted surface, 25, 26, 27, 28, 29 …… vent.

Claims (1)

[Claims] 1. A heating chamber is provided in a main body, and high-frequency power feeding means and a stirring plate which rotates around the power feeding means are provided at central portions of wall surfaces of an upper wall and a bottom wall which form the heating chamber, respectively. At least the bottom wall has an outer shape which is substantially the same as the rotating area of the stirring plate which is equal to or smaller than the placement area of the object to be heated, and is located on the side of the object to be heated around the rotating shaft of the stirring plate. A circular throttling part having a mortar-shaped inclined surface open toward the periphery is provided, and a vent is provided further outside the throttling part to ventilate the part outside the throttling part during heating operation. High frequency heating device characterized by having.