JPH05275167A - Microwave oven and its active load matching system - Google Patents

Abstract

PURPOSE:To make active load matching of a microwave oven by moving vertically a stab installed on the wall surface of a waveguide tube. CONSTITUTION:A recess 3-1 is provided at the wall surface of a waveguide tube 3. The lower part of a stab 5 intrudes in this recess 3-1, and a stab shaft 6 contacts a motor cam 9. The position of the stab 5 is sensed by a stab basic position sensing switch 10, and the data therefrom and the data given by an electric field sensor 11 are passed to a logic calculation control circuit 15. A motor drive circuit 18 rotates a motor 8 in accordance with the result from calculation, and the stab position is adjusted so that the output maximizes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active load control device for a microwave oven and its system.

[0002]

2. Description of the Related Art Even if the impedance of the heating chamber varies depending on the size and position of the food load in the heating chamber of the microwave oven,
As a conventional example of adjusting the impedance matching reflector to reduce the microwave reflected power inside the waveguide in order to maintain good impedance matching between the magnetron and the food load, see Japanese Utility Model Laid-Open No. 61-100897. Sho 5
6-160792 and the like. Further, as a conventional example in which impedance is controlled by moving a stub or a metal reflector according to the weight of food and the program content of a heating set time, Japanese Utility Model Publication 1-25513, JP-A-55-8828.
9 and the like. In both cases, the wall surface of the waveguide is almost flat.

[0003]

In order to reduce the reflected power from food, it is possible to expect a microwave power efficient operation by successively controlling and adjusting the position of the impedance matching device such as a stub or a reflector. But,
Inserting a metal part, which serves as an impedance matching device, inside a waveguide having a strong microwave electric field and controlling the position thereof has conventionally required solving the problems of discharge and microwave leakage.

Further, in order to solve these problems and adopt an impedance matching system in a mass-produced microwave oven, there are the following problems.

First, in the manufacturing stage, the structure of the impedance matching device, the structure of the members, and the adjustment region thereof are optimized, and the discharge inside the waveguide is dealt with, so that the rationality of assembly in mass production is improved. is necessary.

Immediately after the start of the cooking operation, information on the food load in the heating chamber is not obtained, but it is necessary to determine some kind of initial impedance mode of operation.

In light-duty food cooking, the cooking and heating time is usually short, but it takes several seconds to ten and several seconds to detect food information in the heating chamber by the electric field sensor or the weight sensor. Since the operating heating mode during this time has a great influence on the heating efficiency of lightly loaded foods, it is necessary to consider it separately from the case of relatively heavy loading.

Since a change in impedance is predicted due to a change in temperature before and during cooking of food or a change in weight due to water vapor scattering, it is necessary to appropriately detect and correct this.

When providing a stub in the waveguide for impedance matching, it is necessary to reduce the cost of the stub control mechanism component.

[0010]

The microwave oven according to the present invention has the following structure.

An electric field sensor provided in the microwave path including the wall surface of the heating chamber, a stub supported by a stub shaft inserted in the wall surface of the waveguide and matching impedance depending on the insertion degree, and a degree of insertion of the stub And a control means for adjusting the stub so that the stub is mounted in a recess extending outwardly of the waveguide at a portion closest to the waveguide wall.

Further, the waveguide wall is provided with an opening for mounting a component in which the stub and the stub, which can be inserted into and removed from the waveguide mounted on the wall surface of the waveguide, are mounted in the waveguide.

The active load control system according to the present invention is as follows. The basic position of the stub at the beginning of the cooking operation is the region where the impedance becomes the maximum output of the magnetron when a load equivalent to a light load of food is placed almost in the center of the bottom of the heating chamber. After the contents, the output level of the electric field sensor, the food weight, and other data were recognized, the stub was moved to the position to be controlled.

Further, when the set cooking operation time is shorter than the predetermined time, impedance control by moving the stub is not performed, and when the set cooking operation time is longer than the predetermined time, the magnetron operation is performed immediately after the start of the cooking operation. From the point of stabilization, sweep the stub position for at least half a cycle or more, and at the same time calculate the position information of the stub that gives the minimum value of the electric field sensor detection output, then move the stub position to the calculated electric field sensor output minimum position. A control means is provided for the control.

Further, according to the cooking menu and the cooking time set for the cooking operation of the food, the position control of the stub is performed according to the finished state of the food from the start of the operation until the end of the cooking.

The stub position control means used a unidirectional rotating synchronous motor and a cam as a drive source.

[0017]

In the portion where the stub and the wall surface of the waveguide are closest to each other, since the concave portion protruding outward from the wall surface of the waveguide is provided, the influence of the microwave electric field is weakened and the discharge is prevented.

An opening for inserting the combination product of the stub and the stub shaft into a predetermined position of the waveguide is provided, for example, on the wall surface of the waveguide opposite to the opening, to simplify the attachment to the waveguide. You can

As the operation heating mode after starting the cooking operation,
By setting the light load of the food as the optimum impedance in advance, it is possible to provide a microwave oven with good heating efficiency for the light load food.

After the stub is moved to the basic position where the light load is set after the cooking operation is started, if the program time set as the input is a predetermined time, for example, about 30 seconds or more, the stub position is moved and swept. The optimum position for the load can be detected in a short time, and the stub can be quickly moved to that position. The optimum position of the stub can be determined by monitoring the electric field for the impedance matching condition in the insertion range of the stub by an electric field sensor provided on the wall surface of the waveguide at an appropriate distance from the magnetron antenna.

In the food cooking program entered at the start of the cooking operation, the finish of the food is relatively high,
For example, if the program is expected to reach a temperature of about 80 ° C or higher, or if the program predicts that the shape will change significantly from the initial shape at the time of food finishing, or
If the magnetron operating time is longer than the amount of food that is a load due to the relationship with the food information obtained by detection means such as a weight sensor, the stub position should be changed periodically or as appropriate during the middle of the operating time until the end of cooking. By sweeping, the optimum position for the load can be detected, and the stub can be moved to that position quickly.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of the essential part of a microwave oven in which an embodiment of the present invention is provided.

A magnetron 1 is provided inside an outer box (not shown) of the microwave oven, and an antenna 2 of the magnetron radiates a microwave into a waveguide 3. The waveguide 3 radiates microwaves into the heating chamber from the opening covered with the power feeding opening cover 4 on the wall surface 19 of the heating chamber inside the microwave oven.

A recess 3-1 and an electric field sensor 11 are provided on the wall surface of the waveguide 3, and a stub 5 attached to a dielectric stub shaft 6 fitted therein is provided in the recess 3-1. ing. The stub shaft 6 is vertically inserted into a bearing portion of the bottom wall of the recessed portion 3-1 extending outward, and its tip is constantly pressed by a spring 7 to a cam 9 driven by a motor 8. The stub basic position detection switch 10 is in contact with the outer periphery of the cam 9. Stub basic position detection switch 1
0 and the output of the electric field sensor 11 are sent to the control circuit 20.

The mounting position of the electric field sensor is the wall surface of the waveguide in FIG. 1, but it may be the wall surface of the heating chamber. It is installed in a place that is easily affected by the reflected wave electric field that is experimentally obtained.

The control circuit 20 includes an A / D converter 14,
It is composed of a logic operation control circuit 15, a memory 16, a timing circuit 17, a motor drive circuit 18, etc., and is connected as shown in the figure. The operation of the control circuit 20 will be described later. A stub assembly insertion opening 12 is provided on the surface of the waveguide 3 that faces the stub 5 on the wall surface. A fixed stub 13 is provided at an appropriate portion of the waveguide wall surface, for example, by swelling the waveguide wall inward.

The impedance matching stub 5 is a non-magnetic metal, for example, aluminum or copper alloy having a diameter of 11 mm and a length of 15 mm is fixed to the tip of a stub shaft 6 made of a low dielectric constant dielectric material such as ceramic. ing. At the lowest point of the stub, an inner diameter of about 2 mm, which is about 8 mm larger than the diameter of the stub 5, is provided in order to prevent discharge from the approaching portion of the waveguide wall surface.
A recess 3-1 having a depth of 0 mm and a depth of about 8 mm is provided so as to project outside the waveguide wall surface, and a part of the stub 5 is housed in the recess 3-1.

A stub assembly insertion opening 12 is formed in the wall surface of the waveguide 3 facing the predetermined position of the assembly of the stub 5 and the stub shaft 6. The size of the opening is determined by the size of the combination of the stub 5 and the stub shaft 6, but for example, the inner diameter is about 12 mm and the height of the edge 12-1 is higher than the height of the peripheral edge provided to prevent microwave leakage. Is 3
mm. The opening 12 may be provided with other appropriate means for preventing microwave leakage.

The motor cam 9 is assumed to rotate once in about 4 seconds, and the basic position of the stub 5 is the motor cam 9
It is detected by the stub basic position detection switch 10 which is in contact with.

An AC power supply synchronous motor is adopted as a motor 8 for driving the stub 5, and an AC power supply of the main body and a control circuit 20 of this system are controlled by a control unit of the main body (not shown).
In order to separate the two, for example, a photo coupler switching element such as a photo triac or a relay is used.
N-OFF control is performed. As described above, the stub basic position detection switch 10 and the electric field sensor 11 each send a signal to the control circuit 20.

Other original circuit configurations of the microwave oven are the same as the conventional one. At the basic position of the stub 5 (the lowest point of the stub), when a light load of about 300 cc of water load is placed in the center of the turntable tray, the heating chamber impedance is adjusted to be the maximum magnetron output region. Therefore, the fixed stub 13 may be provided. The fixing stub 13 has a method of fixing a metal projection and a method of forming a projection on the wall surface of the waveguide as shown in the figure.

In order to obtain data for controlling the insertion amount of the stub 5, the electric field sensor 11 for detecting the electric field of the reflected wave inside the waveguide is about λg / 4 from the antenna 2 of the magnetron 1.
An opening 11-1 provided at a distance of (λg: wavelength in the waveguide)
The more leaked microwave is detected by the antenna of the electric field sensor 11, detected by the high frequency diode, smoothed by the high frequency capacitor, and the DC pulsating voltage obtained by the general high frequency detection circuit for removing the microwave noise by the low pass filter. Output, and at the timing about 4 msec to 4.5 msec delayed from the voltage zero cross point of the commercial power supply, A
The reflected wave level data converted by the / D converter 14 is sent to the logic operation control circuit 15.

The logic operation control circuit 15 sends a control signal based on a motor cam control flow chart shown in FIG. 3 described later to the motor drive circuit 18 to set the position of the stub 5 after the start of the cooking operation. The necessary data is stored in the memory 16, and the timing is the timing circuit 17
Given by.

FIG. 2 illustrates, on the Smith chart, the variation range of the heating chamber impedance when the stub 5 is raised from its basic position (bottom point of the stub) and the stub 5 is inserted inside the waveguide. .

As the basic position of the stub 5, the load on the heating chamber during the operation of the microwave oven is small (about 300 cc to 500 cc).
cc water load), so that the impedance becomes optimum when placed in the center of the turntable tray, that is, the impedance of the heating chamber is indicated by a thick broken line (a) “•” in the Smith chart of FIG. The state in which the stub 5 is inserted so that the maximum output can be obtained is used as a reference.

When the load inside the heating chamber increases, the impedance change range due to the insertion of the stub 5 changes as shown by the thick broken line (b) in FIG. 2, and the optimum position of the stub 5 is 2.
In the case of a 000 cc water load, the situation is close to the highest point, and the electric field sensor 11 detects the electric field of the reflected wave inside the waveguide.
The output of also shows a small value at this time. In the state where there is no load in the heating chamber, the reflected electric field inside the waveguide is high, and the impedance on the Smith chart is also as indicated by the thick broken line (c) in FIG.

In the broken lines (a), (b) and (c), the lowest point of each corresponds to the lowest point of the stub.

During the cooking operation, necessary data such as the type of food material, weight, finished state and, if necessary, operating time are input, these are stored in the memory 16 and the magnetron is driven with maximum efficiency. It

FIG. 3 shows a flowchart for the stub control immediately after the start of the cooking operation. The driving condition of the motor cam 9 is one cycle of stub up and down for one rotation of the cam and one rotation for 4 seconds at a power supply frequency of 60 Hz, the rotation cycle is 240 rotations of the INT (interval) cycle, and the lowest point of the stub 5. The position is the optimal basic position for light load of the oven. If the rotation cycle of the motor cam 9 is changed or the power supply frequency is 50 Hz, the INT count per rotation needs to be adjusted.

As an outline of the flow chart, the motor cam 9 is operated in parallel with the oscillating operation of the magnetron 1 when the operation is started.
Is started, the signal of the basic position detection switch 10 of the stub 5 is first detected, and if it is not the basic position, the motor cam 9 is rotated and the basic position detection switch 10 operates to move the stub 5. The basic position setting is completed (S1, S2). Next, it is determined whether the operating heating time input as the cooking program is long or short (S
3). For example, using about 30 seconds as a guide, if it is short, it is determined that the food is to be cooked with a light load, and the cooking operation for the set time is completed without controlling the position of the stub 5.

When the operating heating time of the inputted cooking program is longer than about 30 seconds, the position of the stub 5 is moved and swept to detect the optimum position for the load, and the stub 5 is quickly moved to that position. Adopt a program that lets you. Even if it takes a maximum of one rotation for the motor cam to detect the optimum position and set the position of the stub 5, the average microwave output is not significantly affected. Therefore, the motor cam 9 is driven according to the flowchart shown in FIG. 3 (S
4). The initial value of each data is stored in the memory 16 (S
5). The time lapse of 1/2 rotation (about 2 seconds) of the motor cam 9 and the A / D conversion value of the electric field level of the reflected wave inside the waveguide obtained from the electric field sensor 11 are monitored, and the electric field sensor 1
The time lapse timing at which the detection level of 1 is minimized is obtained (S6 to S10).

After the first 1/2 rotation of the motor cam, the remaining 1/2 rotation continues continuously (S11, S).
12) counts down from the full count of the remaining 1/2 rotation time. The motor cam 9 is stopped at the timing of the elapsed time of the minimum value of the electric field sensor detection level obtained in the previous 1/2 rotation (S13). Motor cam 9
If the structure of (1) has a relationship corresponding to the passage of time above and below the stub 5, this stub position corresponds to the minimum position of the reflected wave electric field obtained previously.

When the cooking time is long and the finish of the food is expected to reach a relatively high temperature (for example, about 80 ° C. or higher), it is expected that the finish of the food will change more than the initial shape. In this case, when the weight changes during cooking, the processing is performed as follows.

FIG. 4 shows an example of a flowchart for determining the timing for resetting the stub position control when the operating time input for the microwave cooking operation as described above is relatively long. .. Immediately after the start of operation, the stub shown in FIG. 3 is set (S20, S
21), depending on the remaining operating time and cooking menu (S2
2) Either maintain the current stub position, divide the cooking time into several times (set it to four in the example of FIG. 4), and reset the stub position several times, or perform frequent stub operation such as in the defrosting operation. The resetting is performed and it is determined whether the effect of microwave agitation is expected (S23 to S28).

[0045]

According to the present invention, the microwave power efficiency of the microwave oven is maintained, and impedance matching corresponding to variations such as the size of the food load, the position of the food load in the heating chamber, and the impedance change due to the food finish is achieved. At the time of carrying out, the structure of the parts can be simplified so as to be practically suitable for mass production, and the structure in which the problem of electric discharge and microwave radio wave leakage is unlikely to occur can be realized. Also,
The stub control method of the present invention can provide a microwave oven with high power efficiency in a light load of an oven. further,
Since the driving of the stub is a reciprocating motion by a single-direction rotating AC synchronous motor and a motor cam, an inexpensive stub driving mechanism can be constructed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts of a microwave oven according to an embodiment of the present invention.

FIG. 2 is a Smith chart showing a change in impedance when the stub is moved up and down in the apparatus of FIG.

FIG. 3 is a stub setting flowchart when the operating time is short.

FIG. 4 is a stub setting flowchart when a driving time is long.

[Explanation of symbols]

 1 magnetron 2 antenna 3 waveguide 4 feed opening cover 5 stub 6 stub shaft 7 spring 8 motor 9 motor cam 10 stub basic position detection switch 11 electric field sensor 12 stub assembly insertion opening 14 A / D converter 15 logic operation control circuit 16 Memory 17 Timing circuit 18 Motor drive circuit 20 Control circuit

Claims (6)

[Claims] 1. An electric field sensor provided on a microwave path including a wall surface of a heating chamber, a stub supported by a stub shaft inserted in a wall surface of a waveguide and matching impedance depending on the degree of insertion, and insertion of a stub. And a control means for adjusting the degree of the stub, wherein the stub is mounted in a recess extending outwardly of the waveguide at a portion closest to the waveguide wall. 2. The waveguide wall is provided with an opening for mounting a component, which is a combination of a stub and a stub that can be inserted into and removed from the waveguide mounted on the wall surface of the waveguide, into the waveguide. The microwave oven according to claim 1. 3. The basic position of the stub at the beginning of the cooking operation is set to a region where the impedance becomes the maximum output of the magnetron when a load equivalent to a light load of food is placed almost in the center of the bottom of the heating chamber. An active load control system for a microwave oven, which moves to a position to be controlled after data such as the contents of the prepared cooking program, the output level of the electric field sensor, and the food weight are recognized. 4. When the set cooking operation time is shorter than a predetermined time, impedance control by moving the stub is not performed, and when the set cooking operation time is longer than the predetermined time, the magnetron operation after the start of the cooking operation is performed. From the point of stabilization, sweep the stub position for at least half a cycle or more, and at the same time calculate the position information of the stub that gives the minimum value of the electric field sensor detection output, then move the stub position to the calculated electric field sensor output minimum position. 4. The active load control system for a microwave oven according to claim 3, further comprising control means for controlling the microwave oven. 5. The cooking menu and the cooking time set for the cooking operation of the food, from the start of the operation until the end of the cooking,
4. The active load control system for a microwave oven according to claim 3, wherein the position of the stub is controlled according to the finished state of the food. 6. The active load control system for a microwave oven according to claim 4, wherein the position control means of the stub includes a synchronous motor that rotates in a single direction as a drive source and a cam.