JPS6228553B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-frequency heater, and particularly in a microwave oven where the load is not constant, the present invention aims to improve the oscillation efficiency by adjusting the load impedance.

Generally, the oscillation efficiency of microwave oscillators such as magnetrons and semiconductors changes depending on the load impedance. Therefore, in a high-frequency heater using such an oscillator, especially one in which the load is not constant, such as a microwave oven, the oscillation efficiency varies greatly.

Figure 1 is a sectional view of the main parts of a commonly used conventional microwave oven. In the figure, 1 is the heating chamber, 2 is the main body case, 3 is the door that opens and closes the opening of the heating chamber, and 4 is the radio wave inside the heating chamber 1. 5 is the object to be heated, 6 is the wall of the heating chamber, 7 is the magnetron which is the radio wave oscillation source, 8 is the antenna thereof, 9 is the waveguide, 10 is the connection between the heating chamber wall 6 and the waveguide 9 It is a radio wave emission port.

In the above configuration, the radio waves emitted from the antenna 8 of the magnetron 7 pass through the waveguide 9 to the radio wave emission port 1.
0 into the heating chamber 1, and is absorbed by the object to be heated 5 while being stirred by the stirrer 4, thereby heating the object to be heated 5. The load impedance seen from the antenna 8 of the magnetron 7 is defined by the entire process of propagation and absorption of radio waves. However, the oscillation efficiency of the magnetron 7 varies depending on its load impedance.

FIG. 2 is a typical impedance chart showing load impedance versus oscillation output when a constant input is applied to the magnetron 7. In the figure, concentric circles indicate the voltage standing wave ratio, with the center being 1 and the outermost circle being 5. Also, radial straight lines passing through the center indicate wave numbers. With these two parameters,
The load impedance with the center FF' of the antenna 8 as a reference plane can be shown. The arc-shaped curve shown by the solid line shows the equal output line when a constant input is given to the magnetron 7. Depending on the load impedance, the output power is approximately 670W to 470W as shown.
It changes to. The black area indicated by L in the figure shows the load impedance when heating water 2, and in this case, it oscillates at almost the maximum output, but the area indicated by black area M is 100c.c. With the load impedance when water is added, the magnetron 7 oscillates in the range of about 640W to 550W, and the oscillation efficiency decreases.

The characteristics described above are typical examples, but in this way, in a conventional microwave oven, when heating 2 pieces of water and when heating 100 c.c. of water, in other words, when heating a large cake, The drawback is that the oscillation efficiency is significantly different from when heating a single egg.

The present invention solves the above-mentioned conventional drawbacks, and will be described below with reference to FIGS. 3 to 8.

FIG. 3 is a sectional view showing an embodiment of a microwave oven using the present invention. As for the numbers in the figures, the same functional parts are indicated by the same numbers in each figure, and the explanation thereof will be omitted.

Reference numeral 11 denotes a movable metal rod serving as a variable impedance element provided further from the radiation opening 10 of the waveguide 9 to the terminal end side of the waveguide 9, and it slides up and down tightly with a flange 12 provided on the waveguide wall. The insertion length of the movable metal rod 11 into the waveguide 9 can be made variable by operating the dial 14 from the front of the microwave oven via the gear mechanism 13. can.

Therefore, the load impedance of the antenna 8 of the magnetron 7 viewed from the reference plane FF' is the impedance D viewed from the antenna 8 to the right (D side) and the impedance D viewed from the left side (C side), as shown in Figure 5. The impedance on the C side is the impedance A when looking at the heating chamber 1 side from the radiation port 10,
Impedance B when looking at the movable metal rod 11 side of the waveguide 9.

Therefore, by changing the insertion length of the movable metal rod 11 by operating the dial 14, the impedance B can be changed. It can be adjusted to maximize the oscillation efficiency.

Therefore, even if the load impedance is as indicated by M in FIG. 2, by adjusting the insertion length of the movable metal rod 11, it can be changed to a high efficiency region as indicated by N indicated by the dotted line. I can do it.

In this way, by detecting the oscillation state of the magnetron 7 by some means and adjusting the insertion length of the movable metal rod 11 according to the detected state, the magnetron 7 can always be operated with optimum oscillation efficiency.

FIG. 4 shows a magnetron 7 having the above adjustment means.
The power supply circuit is shown. Reference numeral 20 denotes a high-voltage power transformer, and on its secondary side, a heater winding 21 that supplies heater power to the magnetron 7 and a high-voltage winding 22 that supplies high-voltage anode voltage to the magnetron 7 are provided. A capacitor 23 and a diode 24 are connected in series to form a voltage doubler rectifier circuit, and a high voltage for the anode voltage of the magnetron 7 is obtained from both ends of the diode 24.
A resistor 25 for detecting the anode current of the magnetron 7 and a voltmeter 26 in parallel with the resistor 25 are inserted into the anode circuit of the magnetron 7. Therefore, by looking at the voltmeter 26, the input to the magnetron 7 can be detected.

In general, a magnetron has the characteristic that its oscillation efficiency is highest when its anode input current is at its minimum. 7 can be oscillated with maximum efficiency.
For this purpose, a voltmeter 26 is mounted on the front panel as shown in FIG.

Of course, by using suitable electronic circuitry, the above operations can be performed automatically.

As described above, the present invention provides the movable metal body 11 in the waveguide 9 and detects the input current or power of the magnetron to detect the operating state of the magnetron 7, thereby detecting the movable metal body 11. metal body 1
By adjusting the impedance exhibited by the magnetron 1, the operating efficiency of the magnetron 7 can be maintained at a substantially constant high rate regardless of the object to be heated 5.

FIG. 6 shows another embodiment of the movable metal body used in the present invention. 31 is a movable metal body, which is inserted into the waveguide 9 and whose end face 34
The depth is approximately 1/4 at a distance of approximately 1/4 wavelength from
A chiyoke flange having wavelength grooves 32, 32' is constructed. The whole can be moved left and right by the operating rod 33. Therefore, since the end position of the waveguide 9 is defined by the end face 34, the load impedance seen from the antenna 8 can be made variable. Of course, a metal spring may be used instead of the chiyoke grooves 32, 32' to make metal contact with the waveguide wall.

FIG. 7 shows another embodiment of the movable metal body according to the present invention.

In FIG. 7, 40 is an antenna member made of a metal conductor, one end of which is connected to the waveguide wall and the heating chamber wall 6.
It projects into the heating chamber 1 through an opening 41 formed in the opening 41 , and the other end is inserted into the waveguide 9 . Therefore, the radio waves in the waveguide 9 are radiated to the heating chamber 1 via the antenna 40. A rod 42 made of dielectric material is fixed to the antenna 40,
One end thereof projects outwardly through a flange 43 provided on the waveguide wall and can be moved up and down by a suitable operating mechanism (not shown). Thereby, the height of the antenna 40 can be changed, so the load impedance of the magnetron 7 can be made variable.

FIG. 8 shows another embodiment of the invention. The embodiments so far have shown examples in which the radio wave radiating section to the heating chamber 1 is provided above the heating chamber 1, but FIG. 8 shows an example in which the radiating section is provided at the bottom of the heating chamber 1. . In this case, since the object to be heated 5 can be disposed near the radio wave emitting section, a design can be made to reduce changes in load impedance due to changes in the object to be heated 5. The waveguide 9 is attached to the bottom plate of the heating chamber, and an opening 57 communicating with the heating chamber 1 is provided in a part of the waveguide 9.
A spacer 55 made of a dielectric material that rotatably holds the antenna 54 is attached to the center of the antenna 54, and the antenna 54 is rotated by a motor 53 provided below, and has the function of uniformizing the heating inside the heating chamber 1. have. Reference numeral 56 denotes a dielectric radio wave transparent cover on which the object to be heated 5 is placed.

The end of the waveguide is defined by a movable member 51 made of a metallic spring material and making metal contact with the waveguide wall. This movable member 51 is connected to a rod 50 and is movable left and right by a suitable operating mechanism 52. Therefore, the load impedance of the magnetron 7 can be adjusted appropriately by moving the movable member 51.

The high frequency heater according to the present invention performs the above operations and has many effects described below.

(1) Since the load impedance of the radio wave oscillator can be adjusted according to the operating state of the radio wave oscillator, the radio wave oscillation source can always be operated with high efficiency even if the object to be heated changes.

(2) Energy saving can be achieved by increasing oscillation efficiency.

(3) The structure is simple because the metal body is simply inserted into the waveguide in a movable manner.

(4) As the radio wave radiating portion to the heating chamber, an opening can be used or an antenna made of a metal conductor rod can be used, so the design is easy.

(5) The operating state of the magnetron can be detected by the magnetron's anode current.

(6) The operating status of the magnetron is displayed on the front of the main unit, making handling convenient.

As described above, the high frequency heater of the present invention has many effects and is extremely effective when used in microwave ovens and the like.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a main part of a conventional microwave oven, Fig. 2 is an impedance chart showing the load impedance versus oscillation output of a magnetron, and Fig. 3 is a sectional view of a main part of an embodiment in which the present invention is used in a microwave oven. 4 is a magnetron power supply circuit implementing the present invention, FIG. 5 is an explanatory diagram of the load impedance at the magnetron reference plane FF' in FIG. 1, and FIG.
7 and 8 are sectional views of main parts of a microwave oven according to other embodiments of the present invention, respectively. DESCRIPTION OF SYMBOLS 1... Heating chamber, 5... Heated object, 7... Magnetron, 8... Antenna, 9... Waveguide, 10...
...Radio wave emission port, 11...Movable metal bar, 14...Dial, 25...Resistance for detection.

Claims (1)

[Claims] 1. A device comprising a magnetron, a heating chamber, and a waveguide connecting the magnetron and the heating chamber, and a display section for detecting an anode current of the magnetron and displaying the magnitude of the anode current. A high frequency device characterized in that a movable metal body is provided on the surface of the device, and a movable metal body is provided in the waveguide which is connected to the heating chamber through an opening, and an operating section for moving the metal body is provided on the surface of the device. Heater. 2 At one end of the waveguide, a magnetron antenna is attached to protrude into the waveguide, and the other end of the waveguide is short-circuited with a metal conductor, and the waveguide is connected to one wall of the heating chamber. are connected by a hole, and a metal body is movably disposed to connect the waveguide and the heating chamber in a radio wave manner through the hole. High frequency heater as described.