JP2889442B2 - microwave - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave oven, and more particularly to an active load matching control for a microwave oven.

[0002]

2. Description of the Related Art The impedance of a heating chamber varies depending on the size and position of a food load in a heating chamber of a microwave oven, impedance matching between the magnetron and the heating chamber cannot be achieved, and the microwave reflected electric field increases. In order to reduce the microwave reflection electric field, a microwave oven capable of adjusting the position of a metal reflector for impedance matching has been disclosed (Japanese Utility Model Application Laid-Open No. 61-100).
897, JP-A-56-160792).

Further, there has been disclosed a microwave oven capable of controlling the impedance by moving a stub or a metal reflector according to the weight of food or a set heating time of a cooking program (Japanese Utility Model Publication No. 1-251313, Japanese Unexamined Patent Publication No. Sho 55-8828).
9).

[0004] These conventional microwave ovens can be expected to operate with good microwave power efficiency by sequentially controlling and adjusting the position of an impedance matching device such as a metal reflector.

[0005]

In order to effectively perform impedance matching by rotating a metal reflector inside a waveguide, a metal stub provided on a rotating plate (disk) of the metal reflector is required. The position of
It is necessary to move about λg / 4 (λg: wavelength inside the waveguide of the microwave) where the maximum and minimum values of the standing wave voltage of the microwave for microwave oven (2450 MHz) appear.

Accordingly, the diameter of the rotating plate of the metal reflector is required to be about 40 mm corresponding to λg / 4. On the other hand, it is necessary to provide a sufficient spatial distance from the wall surface of the waveguide in order to install a metal reflector inside the waveguide having a strong microwave electric field and to avoid discharge due to the microwave induced voltage. Also, the electric field concentration on the end of the metal reflector,
Considering the fluctuation of the reflected wave due to the load condition (light load) in the heating chamber, the size of the metal reflector must be reduced as much as possible in order to avoid air discharge inside the waveguide.

It is important that the active load matching device used in a home-use, particularly, an inexpensive type microwave oven has a low component cost. SUMMARY OF THE INVENTION It is an object of the present invention to reduce the size of a metal reflector and to provide an inexpensive active load matching device that can be used in commercial products.

[0008]

According to a first aspect of the present invention, there is provided a microwave oven comprising: a microwave generating means; and a microwave radiated from an antenna of the microwave generating means;
1, a dielectric rotating shaft 6 made of plastic, ceramic or the like inserted in the waveguide, and a metal stub supported by the dielectric rotating shaft and provided on the metal surface 5 a and the periphery of the metal surface And a control means for controlling the rotation of the metal reflector. The dielectric rotating shaft 6 is arranged to be inclined with respect to the microwave traveling direction. .

The microwave generating means is not limited to the magnetron currently in use, but may be one comprising an oscillation circuit using a semiconductor element and a power amplifier circuit. The microwave traveling direction is a direction perpendicular to the antenna in the waveguide and perpendicular to the waveguide opening surface. The metal surface includes a metal plate and a metal film formed on the surface of plastic, ceramic, or the like.

In the microwave oven according to a second aspect of the present invention, the angle of the metal stub 5b with respect to the metal surface 5a of the microwave oven of the first aspect is substantially equal to the inclination angle of the dielectric rotating shaft 6 with respect to the direction of microwave propagation. It is characterized by the following. Of course, it is preferable to make them equal.

[0011] microwave oven according to the invention of claim 3, wherein
Item 1. In the microwave oven according to Item 1, a weight sensor 25 for detecting the weight of the food placed in the heating chamber 21, memory means 14 for storing rotation position data of the metal reflector with respect to the weight of the food, and the weight Rotation control means 13 for comparing the weight input from the sensor 25 with the data in the memory means and controlling the rotation position of the metal reflector according to the weight of the food is provided.

The weight sensor is not limited to the piezoelectric weight sensor 25 disclosed in the embodiment described later, but may be a known capacitive weight sensor, vibration type weight sensor, or the like. .

According to a fourth aspect of the present invention, there is provided a microwave oven as a driving source of the rotational position control in the microwave oven according to the third aspect, wherein signal generating means for detecting a reference position for the rotational position control are provided. Characterized in that a synchronous motor 8 having the following is adopted. The signal generating means may be provided separately from the motor as disclosed in an embodiment to be described later, or may be integrally assembled with the motor.

According to a fifth aspect of the present invention, there is provided a microwave oven according to the first aspect.
Position detecting means for detecting the position of the food placed in the heating chamber in the microwave oven , and memory means 14 for storing rotation position data of the metal reflector 5 with respect to position information input from the position detecting means. And rotation control means 13 for comparing the position information input from the position detection means with the data in the memory means and controlling the rotation position of the metal reflector in accordance with the food placement position.

The position detecting means is not limited to the one detected by the piezoelectric weight sensor 25 disclosed in the embodiment described later, but is also determined by the detection of the infrared sensor provided above the turntable, which is already known. A device based on detection of a light receiving / emitting element provided on a side wall or the like can be applied.

According to a sixth aspect of the present invention, there is provided a microwave oven according to the first aspect.
In the above-mentioned microwave oven, a memory means 14 for storing rotation position data of a metal reflector corresponding to a cooking menu is provided, and rotation control means for controlling a rotation position of the metal reflector according to the cooking menu is provided. Features.

The microwave oven is not limited to one provided with an input means for designating a cooking menu, but also includes an auto-range which automatically determines a cooking menu and executes cooking.

The microwave oven according to claim 7 comprises a microwave generating means 1, a waveguide 3 for guiding a microwave radiated from an antenna 2 of the microwave generating means to a heating chamber 21,
A dielectric rotating shaft 6 inserted into the waveguide, an impedance matching metal reflector 5 having a metal surface 5a supported by the dielectric rotating shaft and a metal stub 5b provided around the metal surface; Control means 10 for controlling the rotation of the metal reflector, and no-load detecting means for detecting no-load of the food placed in the heating chamber; and a rotation for continuously rotating the metal reflector 5 when no-load is detected. A control means is provided.

The non-load detecting means may be a sensor based on the detection of an infrared sensor provided above the turntable, which is already known, in addition to a sensor based on the detection of the piezoelectric weight sensor 25 disclosed in an embodiment to be described later. A device based on detection of a light receiving / light emitting element provided on the side wall of the room can be applied.

According to an eighth aspect of the present invention, there is provided a microwave oven, comprising: a microwave generating means; a waveguide for guiding a microwave radiated from an antenna of the microwave generating means to a heating chamber;
A dielectric rotating shaft 6 inserted in the waveguide, an impedance matching metal reflector 5 having a metal surface 5a supported by the dielectric rotating shaft and a metal stub 5 provided around the metal surface; A control means 10 for controlling the rotation of the metal reflector is provided, and a rotation control means for continuously rotating the metal reflector 5 during thawing cooking is provided.

[0021]

According to the first aspect of the present invention, the rotating shaft 6 of the metal reflector 5 is disposed so as to be inclined with respect to the traveling direction of the microwave, so that the direction of the electric field of the metal stub 5b (the direction orthogonal to the traveling direction of the microwave). ) Changes, and the impedance adjustment width (adjustment degree) increases.

According to the second aspect of the present invention, the angle of the metal stub 5b with respect to the metal surface 5a of the metal reflector 5 is made equal to the angle of inclination of the rotating shaft 6 with respect to the microwave traveling direction, so that the direction of the electric field of the metal stub 5b is changed. The length component changes greatly, and the impedance adjustment width further increases.

In the microwave electric field inside the waveguide, a large voltage gradient exists at a high central portion and a low peripheral portion in a cross section (plane E) of the waveguide orthogonal to the direction of microwave propagation. For this voltage gradient, the length component of the metal stub 5b in the electric field direction affects the impedance.
As shown in FIG. 4, when the metal stub 5b is located on the opening cover 4 side, the entire length of the metal stub 5b is orthogonal to the microwave traveling direction, and when the metal stub 5b is located on the antenna 2 side, the metal stub 5b is located in the microwave traveling direction. On the other hand, when the inclination is large and the length component in the electric field direction is small, the impedance adjustment width is large.

According to the third aspect of the present invention, by controlling the rotational position of the metal reflector according to the weight of the food, impedance matching is performed according to the weight of the food. It is the best system as a system to monitor the reflected electric field component of microwaves and adjust the rotational position of the metal reflector according to the food load situation inside the heating chamber, but it requires an electric field sensor. In contrast, in the present invention, a cost advantage is obtained by using a weight sensor for automatic cooking of a microwave oven.

According to a fourth aspect of the present invention, a stepping motor or a direct current (DC) motor is provided by employing a synchronous motor having a signal generating means for detecting a reference position for rotational position control as a drive source for performing rotational position control. It offers a cost advantage over using a motor.

According to the fifth aspect of the present invention, by controlling the rotational position of the metal reflector according to the food placement position, impedance matching is performed according to the food placement position. Find the position information of whether the food placement position is the center part of the turntable or the peripheral part that is off the center, and select it from the data table on the rotation position of the metal reflector with respect to the food weight stored in advance and stored by experiment in advance. The operation is performed by driving and aligning the motor so that an appropriate rotational position is obtained.

According to the sixth aspect of the present invention, the impedance matching according to the cooking menu is performed by controlling the rotation position of the metal reflector according to the cooking menu. That is, the rotation position control of the metal reflector is incorporated in the program sequence for each cooking menu and executed, and depending on the program, the rotation position control of the metal reflector may be performed for each cooking stage. According to the invention of claim 7, when light load including no load is detected, the metal reflector continuously rotates to move the location of the local overheating, thereby dispersing the overheating. According to the eighth aspect of the present invention, the metal reflector is continuously rotated during the thawing cooking, so that the concentration of the microwave electric field inside the food is alleviated and the thawing is made uniform.

[0028]

FIG. 1 is a vertical sectional view showing an embodiment in which a waveguide is provided on the right wall surface of a heating chamber of a microwave oven according to the present invention.
FIG. 2 is an enlarged view of the waveguide portion of FIG. 1, and FIG. 3 is a perspective view of the metal reflector. This microwave oven has magnetron 1, magnetron antenna 2, magnetron antenna 2
3 that guides microwaves radiated from the heater to the heating chamber 21, a waveguide opening cover 4, a metal reflector 5 for impedance matching, and a motor that drives the metal reflector 5 via a plastic rotating shaft 6. 8, a detection switch 9 for detecting the rotation reference position of the metal reflector 5, a control circuit 10 for controlling the entire microwave oven including impedance matching control, an outer box 20, a heating chamber 21, a turntable 22, a support roller base 23, a turn Table motor 2
4, and the piezoelectric weight sensor 25, and openably instrumentation wearing been door opening surface of the heating chamber 21 (not shown) main components and the like. The metal reflector 5 for performing impedance matching, which is the subject of the present invention, is disposed in the waveguide 3 and is invisible from the heating chamber 21 side by the waveguide opening cover 4. The magnetron 1 is provided in the outer case 20 and radiates microwaves from the magnetron antenna 2 into the waveguide 3.

The microwave radiated from the magnetron antenna 2 passes through the waveguide 3 as a traveling wave, is radiated from the opening cover 4 into the heating chamber 21, reaches the food load, and is absorbed. However, some microwaves return to the inside of the waveguide 3 as reflected waves depending on the state of the food load. The standing wave mode inside the waveguide 3 changes depending on the ratio of the reflected wave and the traveling wave and the state of the phase, and the magnetron 1
Affect the operating efficiency of the system. The present invention relates to a magnetron 1
In view of the phenomenon that the impedance on the heating chamber 21 side as viewed from the side is influenced by the state of the food load, the technical idea of adjusting the impedance by rotating the metal reflector 5 to maintain the operating efficiency of the magnetron 1 high. It is.

The metal reflector 5 comprises a disk 5a made of a non-magnetic metal plate such as aluminum and a metal stub 5b formed by bending the periphery of the disk 5a, and a low dielectric constant dielectric such as plastic or ceramic. It is fixed to a rotating shaft 6 made of a material. The rotating shaft 6 is provided with an inclination of an angle α with respect to the microwave traveling direction, and is connected to the motor 8 outside the bottom surface of the waveguide 3 provided with the inclined bottom surface 3a corresponding to the inclination. It rotates by driving.

The metal stub 5b of the metal reflector 5
The disk 5a is also inclined at an angle α, and as shown in FIG.
When b is orthogonal to the direction of microwave propagation and is located on the magnetron antenna 2 side, the stub 5b is inclined (angle 2α-90 °) with respect to the direction of microwave propagation. By doing so, the electric field direction (height direction) L of the metal stub 5b (Ls × Sin (2α−90)
°)), the position and length components will change significantly,
The impedance adjustment width (adjustment degree) increases. In the embodiment, the inclination angle α of the rotating shaft 6 and the metal stub 5b is set to 6
5 mm, the diameter of the disk 5a is 30 mm, and the height of the metal stub 5b is 18 mm.

By inclining the rotating shaft 6 and the metal stub 5b by 65 °, the diameter of the disk 5a can be reduced by 8 mm and the size of the metal reflector 5 can be reduced as compared with the case where the rotating shaft 6 and the metal stub 5b are not inclined. Can be downsized.

As shown in FIG. 5, if the portion of the magnetron antenna 2 is a rectangular waveguide and only the portion where the metal reflector 5 and the motor 8 are mounted is inclined, the inclination angle α of the rotating shaft 6 and the metal stub 5b is made large. As a result, the impedance adjustment width can be further increased, and the size of the metal reflector 5 can be further reduced.

Motor 8 for rotating metal reflector 5
Has a rotation speed of 15 rpm, the rotation direction of which is restricted to one direction.
It adopts a synchronous motor of m and has a cost advantage compared to the case of using a stepping motor or a DC motor.

A cam 7 for detecting a rotation reference position for controlling the rotation position is provided at the lower end of the rotation shaft 6 so that the detection switch 9 composed of a microswitch can detect the reference position. That is, when the position of the stub 5b of the metal reflector 5 reaches a reference position for controlling the rotational position by the rotation of the motor 8, the projection 7a provided on the cam 7 operates the detection switch 9 to turn on the ON / OFF signal. Is given to the control circuit 18. The control circuit 18 includes a peak hold circuit 11, an A / D converter 12, a logic operation control circuit 13 for controlling the rotational position of the metal reflector 5, and a memory 14 for obtaining food weight information from a piezoelectric weight sensor 10 described later. , A timing circuit 15, a motor drive circuit 16, and the like.

The logic operation control circuit 13 reads the weight and position information of the food obtained by the piezoelectric weight sensor 10 described later from the digital data obtained by the A / D converter 12 and converts the rotation position of the metal reflector 5 from the memory 14. The data is read, the energization time of the motor 8 is controlled, and the metal reflector 5 is stopped at a predetermined position. The rotation position data of the metal reflector 5 is obtained in advance by an experiment and written in the memory 14 as a data table of the metal reflector rotation position with respect to the load weight (the weight of the food) shown in FIG.

The numerals of the rotational position of the metal reflector shown in FIG. 12 represent the positions obtained by dividing one rotation into 16 (0 to 15), and the positional relationship of the numeral with respect to the magnetron antenna 2 is shown in FIG. 10 shows a state where the metal reflector 5 is stopped at the rotation position 10). In addition, two types of data tables are prepared, corresponding to the position information of the load, where the load is placed at the center of the turntable 22 and when it is placed at the periphery.

The rotation position control of the metal reflector 5 starts counting the time for the rotation position control from the time when the projection 7 a operates the detection switch 9 by the rotation of the cam 7 accompanying the rotation of the rotation shaft 6, and performs one rotation 4. Since a second motor is employed, 1/16 rotation can be achieved with 250 mSec current.

FIG. 4 shows a metal stub 5b of a metal reflector.
Is a cross-sectional view for explaining the effect of the microwave on the electric field surface (E-plane). The microwave electric field on the electric-field surface (E-plane) is high in the center and low in the periphery, and is large in the vertical direction in the figure. A voltage gradient exists. When the metal stub 5b of the metal reflector 5 in the waveguide 3 is on the side of the opening cover 4, the height Ls of the metal stub 5b affects the voltage gradient of the microwave electric field. Conversely, when the metal stub 5b is located on the magnetron antenna 2 side, the component Ls × Sin (2α−90 °) in the height direction of the metal stub 5b has an effect, so that the metal reflector 5 is rotated. By
The electric field affects the standing wave electric field in the microwave traveling direction, and an impedance adjusting effect is produced.

On the other hand, as shown in FIG.
A turntable 22 and a support roller stand 23 for supporting the turntable 22 are provided. A turntable motor 24 is provided outside the heating chamber 21, and a piezoelectric type provided at a passing point of the support roller stand 23 with the roller 23 a is provided. The detection signal of the weight sensor 25 is input to the control circuit 18.

FIGS. 6 to 8 are explanatory views for explaining a piezoelectric weight sensor for obtaining information on the weight and the position of food. FIG. 6 shows a turntable support roller base 23 provided on the bottom surface of the heating chamber 21. FIG. 4 is a diagram showing a positional relationship of a piezoelectric weight sensor 25, wherein a support roller base 23 is coupled to a drive shaft of a turntable drive motor 24 via a coupling component, and the rotation of the drive motor 24 causes the support roller base 23 to rotate.
Are rotated between the turntable 22 and the bottom surface of the heating chamber 21, and the turntable 22 rotates. When the roller 23a passes over the piezoelectric weight sensor 25, the voltage signal shown in FIG. 7A is output from the weight sensor 25, and the peak hold circuit 11 in the control circuit 10 as shown in FIG. A peak voltage signal having a level exceeding the threshold voltage level is set to 20.
After holding from 0 msec to 300 msec, the voltage level of the signal is read by the A / D converter 12 and the data is sent to the logic operation control circuit 13. The applicant has already adopted the technology related to the piezoelectric weight detection in a microwave oven,
The technology has been disclosed and the rights have been obtained in Japanese Patent Publication No. Hei 3-20648 and Japanese Utility Model Publication No. Hei 3-17148.

When the food load is placed at the center of the turntable 22, a load of approximately one third of the weight of the food is applied to the three rollers 23a.
Output peak hold value V corresponding to each roller 23a of No. 5
a, Vb, and Vc have substantially the same value as shown in FIG.
The voltage conversion value Vx of the food load weight is represented by Va + Vb + Vc.

When the food load is placed on the periphery of the turntable 22, different loads are applied to the three rollers 23a depending on the position of the food load.
The output peak hold values Vl, Vm, Vn corresponding to the respective rollers 23a of the weight sensor 25 become different values as shown in FIG. 8B, and the voltage conversion value Vy of the food load weight is represented by Vl + Vm + Vn. Also, if the food load is the same, Vx = Vy.

If the output peak hold values Vl, Vm, Vn corresponding to the respective rollers 23a are all included within ± 30% of the voltage conversion value Vy of the food load weight, the food is placed at the center of the turntable 22. The output peak hold values Vl, V corresponding to the respective rollers 23a are determined within ± 30% of the voltage equivalent of the food load weight.
If at least one of m and Vn is not included, it is determined that the food is placed around the turntable 22. That is, the condition of Vy × 0.7 <Vl × 3 <Vy × 1.3 Vy × 0.7 <Vm × 3 <Vy × 1.3 Vy × 0.7 <Vn × 3 <Vy × 1.3 If the condition is satisfied, it is determined that the food is placed on the central portion of the turntable 22, and if the condition is not satisfied, it is determined that the food is placed on the peripheral portion of the turntable 22.

FIG. 9 is a graph showing the relationship between the weight of the food load placed on the turntable 22 and the output voltage, and shows that there is a proportional relationship. Turntable 22
Vw ₀ , the output voltage in the no-load state where no food is placed on
When the output voltage when put 1kg of food and Vw _1, obtained in the food weight g = 1000 × (Vx-Vw 0) / (Vw 1 -Vw 0).

FIGS. 10 and 11 are diagrams for explaining the impedance adjustment by controlling the rotational position of the metal reflector 5, and FIG. 10 shows the reference position (No. 0) for controlling the rotational position of the metal reflector 5. FIG. 1 is a horizontal sectional view showing predetermined positions (No. 0 to 15) obtained by dividing one rotation into 16 parts.
1 is a diagram in which the impedance on the heating chamber side when the metal reflector 5 is rotated is plotted on a Smith chart.

In the drawing, a shows a plot diagram when a 300 cc water load is placed on the center of the turntable 22, and b shows a 2000 cc water load when the turntable 2 is turned on.
2 shows a plot when placed in the center of FIG. If the structure of the waveguide 3 and the position of the magnetron antenna 2 are bilaterally symmetric with respect to the center line in the microwave traveling direction in the horizontal section of the waveguide 3, when the metal reflector 5 makes one rotation, the Smith of FIG. The locus of the impedance change (plot diagram) indicated by the predetermined positions No. 4 to 12 plotted on the chart and the locus from the predetermined position No. 12 to the No. 4 through the reference position (No. 0) are almost equal. In order to match, the position control of the metal reflector may be performed in either direction. However, in the embodiment, assuming that the waveguide is not symmetrical, the position control is performed in the rotation range of the predetermined positions No. 4 to 12 to improve the accuracy of the position control. ing.

In the Smith chart shown in FIG. 11, since the impedance in the state where the magnetron 1 operates efficiently and the maximum output operation area of the magnetron match,
By adjusting the impedance to the maximum output range according to the food load condition inside the heating chamber, a microwave oven with high power efficiency can be realized.

That is, according to the Smith chart of FIG.
For a light load of about 300 cc, the rotational position of the metal reflector 5 is preferably set to No. 9 to 11, and for a relatively large load of about 2000 cc, it is preferable to set it to No. 7 to 10.

FIG. 12 shows a metal stub (metal reflector).
FIG. 12 is a diagram showing high-frequency output in the case of a water load of 2000 cc and 300 cc using the rotational position of FIG. 11 as a parameter, and the rotational position in the high output state and the preferred rotational position of the metal reflector according to the Smith chart of FIG. .

In the graph of FIG. 12, the high-frequency output when the food load is placed at the center of the turntable is connected by a solid circle with a solid circle, and the high-frequency output when the food load is placed at the periphery of the turntable. Are indicated by white circles and broken lines. In the case of light load, it is necessary to consider that the size is small and it is not placed in the center part of the turntable, but in the case of a large food load exceeding 1.5 kg, the container used is also large and inevitably Since it is placed at the center of the turntable, it is not necessary to consider the case where it is not placed at the center.

Based on the graph of FIG. 12, the rotation position of the metal reflector 5 when the food load is equivalent to 2000 cc of water is No. 8, and the rotation position of the metal reflector 5 when the food load is equivalent to 300 cc of water is the turntable. No. 10 when placed at the center of the turntable, and No. 8 when placed around the turntable.

FIG. 13 is a graph showing the rotational position of the metal stub (metal reflector) obtained by measuring the data shown in FIG. 12 using another load weight as a parameter. Of the metal reflector with respect to the memory 14 of the control circuit 10
Is stored as a data table, and utilized by the logic operation control circuit 13 for controlling the rotational position of the metal reflector corresponding to the load weight. On the other hand, in the case of a heating operation of a food of 100 g or less (including a no-load operation), a large heat stress is applied to the microwave oven. That is, since large microwave power is injected into the heating chamber near no load, the magnetron 1 is heated up by local overheating of the turntable 22, the support roller base 23 and the wall of the heating chamber, and the microwave reflected power. Although the rotation position control of the metal reflector 5 can be alleviated to some extent, there is no object having a large microwave loss such as a food load, and this rotation position control is very critical. In addition, considering the variation in parts in mass production, it is judged that it is impossible to cope with all mass-produced products by this rotational position control, and the metal reflector 5 is continuously rotated at light load operation of 100 g or less. The control to move the location of the local overheating to disperse the local overheating was adopted.

[0054]

[Table 1]

Table 1 is a data table of the rotation control of the metal reflector corresponding to the cooking menu incorporated in the menu cooking program sequence incorporated in the microwave oven of the embodiment. Since the shape of the food and the shape of the container differ depending on the heating chamber side, the impedance matching control can be performed more appropriately by having the rotation control data of the metal reflector 5 corresponding to the cooking menu.

Regarding the thawing cooking, the electric field is concentrated on the thawed portion due to the difference in the dielectric constant of the unfrozen portion and the thawed portion of the frozen food with respect to the microwave, and the frozen food is easily heated. Since it is necessary, control for continuously rotating the metal reflector 5 is adopted. By doing so, the locally concentrated portion of the microwave can be dispersed, and the thawing time can be significantly reduced by supplying a large microwave power.

Next, the position control of the metal reflector from the start of the general heating cooking operation to the end of the heating will be described. In order to recognize the food weight, as described above, the support roller base 23 of the turntable 22 is connected to the weight sensor 2.
5 must be passed at least three times, and the weight of the food is not detected at the start of heating and cooking, and the control data of the metal reflector shown in FIG. Therefore, until the control based on the weight detection can be performed, the position of the metal reflector is set on the assumption that the food is lightly loaded (No. 10 shown in FIG. 10 in the initial position setting and embodiment). By doing so, the cooking time of the light-load food can always be reduced.

Next, based on three times of input information from the weight sensor 25 based on the rotation of the support roller base 23, the weight of the food is calculated and it is determined whether the food placement position is the central portion or the peripheral portion of the turntable 22. Next, the rotational position of the metal reflector 5 corresponding to the calculated weight is obtained from a data table corresponding to the determined food placement position (a data table relating to the rotational position of the metal reflector with respect to the food weight), and the motor 8 is rotationally driven. Then, the metal reflector 5 is rotated from the initial position to the position determined. At this time, the position control is performed by rotating the rotation shaft 6 so that the protrusion 7 a
The time counting is started from the passage of the reference position to operate the motor 8 and the energization time control to the motor 8 is performed. According to this position control, the position is set so as to pass through the reference position, so that even if there is a difficulty in the timing accuracy at the time of starting rotation of the motor 8, the stop position is very accurate.

In this impedance-matched state, heating with power efficiency is performed until the set heating time elapses.
Alternatively, the process is performed until the sensor detects the completion of the cooking. If the metal reflector 5 is set to the initial position corresponding to the light-load food after the heating is completed, the light-load food can be efficiently heated from the start of heating and cooking.

[0060]

According to the present invention, the size of the metal reflector for impedance matching can be reduced, and the possibility of a discharge phenomenon with the waveguide wall surface can be suppressed.

Further, it is possible to provide an inexpensive microwave oven that performs heating with high power efficiency in accordance with the weight and placement position of the food to be cooked or the cooking menu.

Furthermore, problems due to local overheating during light load operation including no load and during thawing cooking can be eliminated, and the thawing time can be shortened by increasing the microwave power during thawing cooking due to uniform thawing.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view showing one embodiment of a microwave oven according to the present invention.

FIG. 2 is an enlarged view of a waveguide portion of FIG. 1;

FIG. 3 is a perspective view of a metal reflector provided at the bottom of the waveguide.

FIG. 4 is a cross-sectional view illustrating an impedance change caused by a metal reflector.

FIG. 5 is a vertical sectional view showing another embodiment of the waveguide portion.

FIG. 6 is a plan view showing a positional relationship between a support roller base provided on the bottom surface of the heating chamber and a weight sensor.

FIG. 7 is an output voltage waveform diagram of the piezoelectric weight sensor.

FIG. 8 is a voltage waveform diagram showing an output value of a weight sensor for each roller depending on a place where a food is placed on a turntable.

FIG. 9 is a relation diagram showing a relation between a converted value of an output voltage and a food load weight.

FIG. 10 is an explanatory diagram for explaining a rotational position for impedance adjustment of a metal reflector.

FIG. 11 is a Smith chart in which a heating chamber side impedance when a metal reflector is rotated is plotted;
a indicates a water load of 300 cc, and b indicates a water load of 2000 cc.

FIG. 12 is a diagram showing high-frequency outputs when the water load is 2000 cc and when the water load is 300 cc, using the rotational position of the metal reflector as a parameter.

FIG. 13 is a data table showing a rotation position of a metal stub (metal reflector) with respect to a load weight.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 magnetron (microwave generating means) 2 magnetron antenna 3 waveguide 5 metal reflector 5a disk (metal surface) 5b metal stub 6 dielectric rotating shaft 7 cam 8 motor 9 detection switch 10 control circuit 13 logic operation control circuit (rotation) Control circuit) 23 Roller support stand 25 Weight sensor

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Kinoshita 22-22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-4-245192 (JP, A) Shokai Sho 61- 38797 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H05B ^6/ 64-6/80

Claims (8)

(57) [Claims] 1. A microwave generating means, a waveguide for guiding microwaves radiated from an antenna of the microwave generating means to a heating chamber, a dielectric rotating shaft inserted in the waveguide, In a microwave oven, comprising: a metal reflector for impedance matching having a metal surface supported by a body rotation axis and a metal stub provided on a periphery of the metal surface; and control means for controlling rotation of the metal reflector. A microwave oven characterized in that a body rotation axis is inclined with respect to a microwave traveling direction. 2. The microwave oven according to claim 1, wherein the angle of the metal stub with respect to the metal surface of the impedance matching metal reflector is substantially equal to the angle of inclination of the dielectric rotation axis with respect to the microwave traveling direction. 3. In the microwave oven according to claim 1, and a weight sensor for detecting the weight of the placed into the heating chamber food, a memory means having stored the rotational position data of said metal reflector for food weight , microwave oven, characterized by comprising a rotation control means for controlling the rotational position of the metal reflector according to the collated food weight data of the weight and said memory means input from said weight sensors. 4. The microwave oven according to claim 3, wherein a synchronous motor having a signal generating means for detecting a reference position for controlling the rotational position is adopted as a drive source for controlling the rotational position. A microwave oven with features. 5. In the microwave oven according to claim 1, a position detecting means for detecting the position of the placed into the heating chamber food, prior to the location information input from the position detection means
Memory means having stored the rotational position data of the serial metal reflector, depending on the collated food placed position and data of the positional information input from the position detecting means and said memory means
Microwave oven, characterized by comprising a rotation control means for controlling the rotational position of the metal reflector. 6. The microwave oven according to claim 1 , further comprising memory means for storing rotation position data of said metal reflector corresponding to a cooking menu, and controlling the rotation position of said metal reflector according to said cooking menu. A microwave control device for performing rotation control. 7. A microwave generating means, a waveguide for guiding microwaves radiated from an antenna of the microwave generating means to a heating chamber, a dielectric rotating shaft inserted in the waveguide, A heating chamber in a microwave oven provided with a metal reflector for impedance matching having a metal surface supported on a body rotation axis and a metal stub provided on a periphery of the metal surface, and control means for controlling rotation of the metal reflector; A microwave oven provided with a no-load detecting means for detecting a no-load of the food placed on the metal reflector, and a rotation control means for continuously rotating the metal reflector when the no-load is detected. 8. A microwave generating means, a waveguide for guiding microwaves radiated from an antenna of the microwave generating means to a heating chamber, a dielectric rotating shaft inserted in the waveguide, Thawing cooking in a microwave oven provided with a metal reflector for impedance matching having a metal surface supported on a body rotation axis and a metal stub provided around the metal surface, and control means for controlling the rotation of the metal reflector In a microwave oven, a rotation control means for continuously rotating the metal reflector is provided.