JP3203146B2 - High frequency heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to load matching of a high-frequency heating device using dielectric heating.

[0002]

2. Description of the Related Art In a high-frequency heating apparatus in which a load is placed between parallel heating electrodes and a high-frequency electric field is applied to perform dielectric heating, the output impedance of a high-frequency power supply that amplifies and outputs the oscillation output of an oscillation circuit and the parallel heating electrodes are controlled. If the impedance of the load including the load is different, that is, if the impedance is not matched, the high-frequency power supplied to the load from the high-frequency power supply will not be consumed by the load and most of it will be reflected back to the high-frequency power supply. In addition to heating the load, the high frequency power supply may be destroyed by the reflected power.

For this reason, in the conventional high-frequency heating device, an appropriate gap is provided between the parallel heating electrode and the load by operating the movable parallel heating electrode in accordance with the shape of the load, and then, from the high-frequency power supply to the parallel heating electrode via a tuning circuit. It is described in the prior art of Japanese Patent Publication No. 62-21238, for example, in which high-frequency power is supplied, and the coil 5a is variable in parallel with the load 11 placed between the parallel heating electrodes 7 as shown in FIG. The capacitor 5b and the variable capacitor 5b are connected in series with the load 11 as shown in FIG. 12 in parallel with the capacitor 5b, and the capacitance is adjusted by adjusting the capacity of the variable capacitor 5b. I have.

Further, as described in the invention of Japanese Patent Publication No. 62-21238, the terminal voltage of a series resonance circuit composed of a coil 5a connected in series to a load 11 and the load 11 as shown in FIG. There is also a feedback-type high-frequency heating device that feeds back to the switching element 5c and oscillates at a tuning frequency according to the load impedance to achieve matching.

[0005]

However, in the circuits shown in FIGS. 11 and 12, the reactance of the load can be reduced, but the impedance of the load cannot be adjusted. When the impedances are different, a mismatch occurs and high-frequency power cannot be efficiently supplied to the load.

In the circuit shown in FIG. 13, the impedance of the load cannot be similarly adjusted, and the oscillation frequency must be changed in order to match the impedance that changes with the shape and temperature of the load. It is very difficult to set the frequency to, for example, 27.12 MHz ± 162.72 MHz among the frequency bands of the ISM band permitted by the Radio Law. If the frequency deviates from this allowable range, the high-frequency heating device must be stopped.

Since matching by adjusting these circuit constants requires experience and skill, it is preferable to use a high-frequency heating apparatus for industrial applications in which the same load is continuously heated with a constant shape. In the case of general household use where the shape, material and weight of the load constantly change, it is necessary to frequently adjust the circuit constant.

An object of the present invention is to provide a high-frequency heating apparatus provided with a matching means capable of easily performing impedance matching even when the shape, size, and material of the object to be heated are different.

[0009]

According to the high frequency heating apparatus of the present invention, there is provided a high frequency power supply for outputting a high frequency voltage.
Parallel heating power for induction heating of load by high frequency electric field
In a high-frequency heating device having a pole and a tuning circuit , the load and the impedance of the tuning circuit are connected between the high-frequency power supply and the tuning circuit.
Match the dance equal to the impedance of the high frequency power supply
And a matching transformer provided with means for switching a winding ratio, and a (claim 2) standing wave ratio detection sensor is provided at an output terminal of the high-frequency power supply, and the standing wave ratio value is controlled by a control circuit. (3) The thickness of the load is detected by a distance sensor and the tap of the matching transformer is initially set from the characteristic curve of the load thickness and impedance obtained in advance. Means for controlling the matching; and (4) the initial setting of the tap of the matching transformer by measuring the distance between the parallel heating electrode on the movable side and the load and previously determining the characteristic curve of the distance and the impedance. And means for controlling, and detecting the area of the load facing the parallel heating electrode and initializing the tap of the matching transformer from the characteristic curve of the load area and the impedance determined in advance. Means for controlling the alignment with a constant,
(Claim 6) When tuning by adjusting the tuning circuit and when matching by switching the tap of the matching transformer by means of a high-frequency electromagnetic relay or the like, the output power of the high-frequency power supply is made lower than during normal heating and tuning is performed. Alternatively, there is provided a means for notifying that alignment is being performed.

[0010]

As described above, the matching transformer is provided between the high-frequency power supply and the tuning circuit. Therefore, if the tap is selected and the winding ratio is switched, the equivalent impedance seen from the primary side of the matching transformer becomes two. The impedance is determined by the impedance connected to the secondary side and the winding ratio between the primary and secondary windings. It can be matched equally to the impedance of the power supply.

When a load of an object to be heated is placed between the parallel heating electrodes, the impedance between the parallel heating electrodes mainly depends on the capacitance and resistance of the load itself, the capacitance between the movable parallel heating electrode and the load, and the parallel heating. It is determined from the capacitance between the electrodes. The impedance is proportional to the thickness of the load, inversely proportional to the distance between the load and the parallel heating electrode, and proportional to the area of the load, so that if the thickness of the load is detected, it is measured and stored in advance. The winding ratio for converting impedance can be calculated by referring to the characteristic curve of the impedance with respect to the thickness of the load. To start. (Claim 4) If the distance between the load and the parallel heating electrode is detected, the turns ratio can be calculated in the same manner, so that the turns ratio is initialized and matching is started. (Claim 5) If the area of the load is detected, the turns ratio can be calculated in the same manner, so that the turns ratio is initialized and matching is started. In this way, the control circuit calculates the approximate winding ratio and performs initial setting, and then sequentially switches the winding ratio while checking the standing wave ratio value to perform matching.

During tuning and matching, high-frequency power output from the high-frequency power supply to the tuning circuit is reflected back to the high-frequency power supply, and circuit elements such as switching elements of the high-frequency power supply may be overheated and damaged. So (Claim 6)
During tuning and during matching, the output power of the high-frequency power supply is set lower than during normal heating, and at the same time, the state during tuning or during matching is displayed.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

First, the outline of the present invention will be briefly described.

FIG. 7 is a diagram showing a main part of the present invention. The power of the commercial power supply 1 is output from the high-frequency power supply 3 as high-frequency power. A tuning circuit 5 composed of a coil 5a and a variable capacitor 5b is connected in series to one of the parallel heating electrodes 7 for dielectrically heating a load 11 to be heated by a high-frequency electric field. I do. The present invention is provided with a matching transformer 4 for matching impedance between the high-frequency power supply 3 and the tuning circuit 5. The matching transformer 4 is formed of a single-turn transformer and has a plurality of switches for switching the winding ratio. It has a tap.

Assuming that the coupling coefficient between the primary winding and the secondary winding of the matching transformer 4 is 1 and the winding ratio (the number of primary windings / the number of secondary windings is n), the matching transformer 4 is provided on the secondary side. The equivalent impedance Z1 viewed from the primary side when the impedance Z2 including the above impedance is connected is as shown in (Equation 1).

Z1 = Z2 × (1 / n) ² (Equation 1) This means that the impedance on the load side as viewed from the high frequency power supply 3 is changed by changing the winding ratio of the matching transformer 4, that is, a plurality of taps are appropriately switched. This means that the impedance on the load side can be adjusted by selecting and connecting.

Next, an equivalent circuit when the load 11 to be heated is placed between the parallel heating electrodes 7 will be described.

As shown in FIG. 8, the thickness of the load 11 is H _L , the area of the load 11 facing the parallel heating electrode 7 is S _L ,
The gap between the load 11 and the movable-side parallel heating electrode 7 is H _G , the distance between the parallel heating electrodes 7 is H _P , the area of the parallel heating electrode 7 is S _P , the equivalent resistance of the load 11 is R _L , and the relative dielectric constant. Assuming that the ratio is ε _L and the dielectric constant of air is ε ₀ , the capacitance between the load 11 and the movable-side parallel heating electrode 7 is C1, the capacitance C2 of the load 11 itself, and the floating between the parallel heating electrodes 7. Assuming that the capacitance is C _P , the equivalent circuit between the parallel heating electrodes 7 has C 1, C 2, and R _L connected in series as shown in FIG. 9, and C _P connected in parallel with them. The capacitance is represented by the following equation.

C1 = ε ₀ (S _L / H _G ) (Equation 2) C 2 = ε ₀ · ε _L (S _L / H _L ) (Equation 3) C _P = ε ₀ (S _P −S _L ) / H _P (Equation 4) On the other hand, as shown in FIG. 10, the impedance Z when tuning is performed by connecting the coil 5 a having an inductance suitable in series with these equivalent circuits of FIG. Become.

Z ≒ _RL · (C ₃ ) ² / (C _P + C ₃ ) (Equation 5) (where C 3 is the combined capacitance when C 1 and C 2 are connected in series) Eventually, Equation 2 and Equation 3 the area S _L and thickness H _L of the impedance Z load 11 of formula 5 from equation 4, the distance H _G of the parallel heating electrode 7 and the load 11, while the area S _P parallel heating electrode 7 parallel heating electrodes 7 will represented that as a function of the distance H _P of, since the parallel area S _P output heating electrodes 7 are known in advance, the thickness H _L and the area S _L of the load 11, parallel heating load 11 and the movable it is possible to determine the turns ratio of the matching transformer 4 matching by converting the impedance Z by providing a means for detecting the gap or distance H _G of the electrode 7.

Next, a specific description of the present invention will be given.

FIG. 1 shows a circuit block diagram of the present invention.
Is a commercial power supply, 2 is a DC power supply that can rectify the commercial power supply 1 and control a DC voltage value, 3 is a high-frequency power supply whose voltage value of high-frequency power changes according to the output voltage value of the DC power supply 2, 4
Is a matching transformer having a function of switching a winding ratio between a primary winding and a secondary winding, 5 is a tuning circuit including a serially connected coil and a controllable variable capacitor, 6 is a parallel heating electrode 7 And a distance sensor 8 for detecting the distance to the load 11 and the like.
WR value), a standing wave ratio detection sensor for detecting the WR value, 9
Is a display means for indicating whether matching or heating is being performed, and 10 is a control circuit, which receives a signal of the distance sensor 6 or a signal of the standing wave ratio detection sensor 8 and processes the data to perform a data processing. 5 and controls the display on the display means 9 and the operation and operation of the high-frequency heating device as a whole.

Referring to the tuning and matching according to the circuit block diagram of FIG. 1, first, a load 11 is placed between the parallel heating electrodes 7 and a heating start switch (not shown) of the control circuit 10 is provided.
When the control circuit 10 is pressed, the control circuit 10 displays the tuning or matching on the display means 9, drives the parallel heating electrode driving means (not shown), and moves the parallel heating electrodes to the vicinity of the load.
Control is performed so that the output voltage of the DC power supply 2 is set to a voltage value for tuning and matching lower than the voltage required for normal heating.

The high frequency power supply 3 is supplied with a constant voltage irrespective of the output voltage of the DC power supply 2 and generates an oscillation at a specific frequency in the ISM band (not shown). Since the output voltage of the DC power supply 2 is set to a lower value during the matching than during the heating, the high-frequency output voltage of the high-frequency power supply 3 also has a lower value. The signal is output to the tuning circuit 5 via the matching transformer 4.

When the high-frequency power is output, the tuning is not initially performed, so that the SWR value of the standing wave ratio detecting sensor 8 is large, but the control circuit 10 has the lowest SWR value. The tuning is completed by driving and adjusting the variable capacitor 5a of the tuning circuit 5 as described above.

Since the impedance of the equivalent circuit of the load constituted by the parallel heating electrode 7 and the load 11 is capacitive, the tuning circuit 5 has a large inductance coil 5a in order to tune to the oscillation frequency of the high frequency power supply 3. After that, the capacitance of the variable capacitor 5b is adjusted by the control of the control circuit 10.

In this state, since the impedance of the equivalent circuit of the load does not always coincide with the output impedance of the high frequency power supply 3, the SWR value is still higher than 1 and the control circuit 10 sets the standing wave ratio detection sensor. The matching is completed by changing the turns ratio of the matching transformer 4 so that the SWR value of 8 is closest to 1 while checking the SWR value of 8.

FIG. 2 is a graph showing the relationship between the winding ratio and the impedance of the equivalent circuit of the load converted by the matching transformer 4 when the winding ratio is changed.

When the matching is completed in this manner, the control circuit 10 raises the output of the high-frequency power supply 3 by increasing the output voltage of the DC power supply 2 from a low voltage value for matching to a normal voltage for heating. Then, the display on the display means 9 is changed from during alignment to during heating, and normal heating is started.

Further, the high-frequency heating apparatus of the present invention can be used to quickly and easily perform the matching, so that the thickness and area of the load 11, the distance between the parallel heating electrodes 7, the load 11 and the parallel heating electrode
The control circuit 10 calculates the gap or distance from the matching transformer 4 based on the detection signal of the distance sensor 6 to calculate the winding ratio according to the size of the load 11 and the position of the parallel heating electrode 7. A tap that is close to the optimal one is selected from the taps to initialize and connect.

FIG. 3 shows a tuning transformer 4 which is tuned by the tuning circuit 5.
Shows the relationship between the pork thickness and the impedance at a temperature of -14 ° C when the winding ratio is set to 1, and the impedance increases as the load increases. This characteristic curve is stored in the control circuit in advance. Keep it.

Regarding the thickness of the load 11, first, a thickness of 2 cm
And the distance from the parallel heating electrode 7 is set to 1 cm. When the heating is started by pressing a heating start switch (not shown), the control circuit 10 controls and tunes the tuning circuit 5 in the same manner as described above, and then performs matching. However, the output impedance of the high-frequency power source 3 in the high-frequency heating apparatus of the present invention is adjusted. Is 50Ω
Therefore, the matching is performed at the point a in FIG.

Here, different thicknesses, for example, a thickness of 4.5 c
When the heating is started after placing the pork of m m, the distance sensor 6 measures the thickness of the pork. Assuming that the distance from the parallel heating electrode 7 is 1 cm, the impedance is about 6 at the point b in FIG.
Since it changes to 0Ω, the winding ratio n of the matching transformer 4 is obtained as shown in Expression 6 according to Expression 1, and the initial setting for matching is performed by selecting and connecting the tap having the winding ratio closest to this value. .

N = (60/50) ^1/2 (Equation 6) Then, the control circuit 10 can switch the tap of the winding ratio so that the SWR value becomes smaller while observing the signal of the standing wave ratio detecting sensor 8. I just need. The switching of the tap connection is performed by controlling the intermittent contact of a plurality of high-frequency relays (not shown) attached to the matching transformer by the control circuit 10.

FIG. 4 shows the relationship between the impedance or the gap or distance between the pork having a temperature of -14.degree. C. and the thickness of 5 cm and the parallel heating electrode 7 when the tuning circuit 4 is tuned and the winding ratio of the matching transformer is set to 1. The impedance decreases as the gap or distance increases.

Regarding the distance between the load 11 and the parallel heating electrode 7, pork having a thickness of 5 cm was separated from the parallel heating electrode 7 by a distance of 2.5 cm.
The control circuit 10 controls and tunes the tuning circuit 5 in the same manner as when mounting and starting heating. When matching is performed, the impedance of the high-frequency power supply 3 is 50Ω, so that the winding ratio of the matching transformer 4 is 1 As it is, it is matched at the point a in FIG.

Here, when pork having another thickness of 5 cm is added again, the distance from the parallel heating electrode 7 is set to 0.
When the impedance is changed to 5 cm, the impedance changes to about 68Ω at the point b in FIG.
The tap of the matching transformer 4 closest to the turns ratio n is selected and connected, and the initial setting of the matching is performed.

FIG. 5 shows a tuned circuit 4 tuned by the tuning circuit 5.
-14 ° C., thickness 4.5c when the winding ratio of 1 is 1.
m of pork was placed at a distance of 1 cm from the parallel heating electrode 7 and the relationship between the pork area and impedance was shown.
The larger the area, the higher the impedance.

Regarding the area of the load 11, the thickness is 4.5 cm,
The distance between the pork having an area of 40 cm ² and the parallel heating electrode 7 is 1c.
control circuit 1 in the same manner as
0 controls and tunes the tuning circuit 5, and when matching is performed, the impedance of the high-frequency power supply 3 is 50Ω, so that the winding ratio of the matching transformer 4 remains 1, and matching is performed at the point a in FIG.

Here, 70c having the same thickness but different areas is used.
When the pork of m ² is added again, the impedance becomes
Since it changes to about 80Ω at the point, the winding ratio n is determined in the same manner as in Expression 6, and the tap of the matching transformer 4 closest to the winding ratio n is selected and connected, and the initial setting of matching is performed.

As described above, the impedance shows different values depending on the thickness of the load 11, the gap or distance from the parallel heating electrode 7, and the area of the load 11, respectively.
4 and 5, the thickness of the load 11, the gap or distance with the parallel heating electrode 7, the area of the load, and the like, which are provided with a condition of passing an impedance value substantially equal to the output impedance of the high frequency power supply 3. When a load 11 is placed between the parallel heating electrodes 7 and heating is started, the control circuit 10 first looks at a signal from the distance sensor 6. Thus, the parallel heating electrode 7 is driven and fixed at a gap or a distance from the stored load 11, that is, a distance of 1 cm in the embodiment of the present invention. Is output from the high frequency power supply 3 to control the tuning circuit 5 so that the SWR value of the standing wave ratio detection sensor 8 becomes the lowest value.

After tuning, as an example of the matching method, the control circuit 10 measures the thickness of the load 11 by the distance sensor 6 and obtains the impedance corresponding to the thickness just measured from the characteristic curve of FIG. Then, the winding ratio n is obtained by Equation 3, the tap of the matching transformer 4 is selected, and the winding ratio is initially set. At this time, since the characteristic curve of FIG. 3 mainly uses only the thickness of the load 11 as a parameter, the load 11
Are not taken into account, and the taps are switched so that the SWR value of the standing wave ratio detection sensor 8 indicates a smaller value to complete the matching.

As another example of the matching method, the control circuit 10 measures the area of the load 11 by the distance sensor 6 and reads the impedance with respect to the area just measured from the characteristic curve of FIG. The alignment can be completed.

However, when the thickness of the load 11 is particularly large, for example, when the thickness exceeds 5 cm, matching cannot be performed by these methods, and the control circuit 10 sets the distance to the load 11 to 0 by the distance sensor 6. The impedance at this time can be read from the characteristic curve of FIG. 4 stored by measuring the distance between the load 11 and the parallel heating electrode 7, and matching can be completed in the same manner.

FIG. 6 shows the operation of the distance sensor 6. The distance sensor 6 has a plurality of distance measuring sensors arranged in an array, and is fixed from one end of the parallel heating electrode 7 to the other end. The distance of the entire area is detected while moving at a speed, and the detected data is subjected to data processing in the control circuit 10 to determine the distance between the parallel heating electrodes 7 and the gap or distance between the parallel heating electrodes 7 and the load 11. The area of the load 11 can be easily calculated.

[0047]

According to the present invention, by providing a matching transformer provided with a means for switching a winding ratio as described in claim 1, the material and dimensions which can be used for heating or thawing in ordinary households can be obtained. Even if the load is variously different, the impedance of the high-frequency power supply can be easily matched, and the range to be heated is greatly expanded.

As described in the second aspect, the tuning state of the tuning circuit and the matching state of the matching transformer by switching the winding ratio are known by checking the detection value of the standing wave ratio detection sensor, so that accuracy can be easily determined. Good tuning and matching.

As described in the third aspect, it is only necessary to switch the winding ratio after the initial setting of the winding ratio according to the thickness of the load and to perform matching, so that the time required for matching can be reduced.

As described in claim 4, when the distance between the load and the parallel heating electrode changes, or when the thickness of the load is particularly large, the distance can be manipulated and then the matching can be achieved. The initial setting of the line ratio can reduce the time required for matching.

As described in the fifth aspect, the time required for the matching can be similarly reduced by initial setting of the winding ratio according to the area of the load.

As described in claim 6, the output power of the high-frequency power supply is reduced during tuning and during matching, so that the problem of destruction of the high-frequency heating device and unnecessary radiation is reduced, and this state is indicated by the display means. Since it is displayed, there is no possibility that the power is not increased at the start of heating, and that the malfunction is erroneously recognized.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a high-frequency heating device according to the present invention.

FIG. 2 is a characteristic diagram of impedance with respect to a turns ratio of the matching transformer of the present invention.

FIG. 3 is a characteristic diagram of impedance with respect to load thickness.

FIG. 4 is a characteristic diagram of impedance with respect to a distance between a load and a parallel heating electrode.

FIG. 5 is a characteristic diagram of impedance with respect to a load area;

FIG. 6 is an explanatory diagram showing an operation of the distance sensor.

FIG. 7 is an explanatory diagram showing a main part of the high-frequency heating device of the present invention.

FIG. 8 is an explanatory diagram showing a position of a load and a parallel heating electrode.

FIG. 9 is a circuit diagram showing an equivalent circuit viewed from a tuning circuit.

FIG. 10 is a circuit diagram showing an equivalent circuit after tuning.

FIG. 11 is a circuit diagram showing an example of a tuning circuit of a conventional high-frequency heating device.

FIG. 12 is a circuit diagram showing another example of the tuning circuit of the conventional high-frequency heating device.

FIG. 13 is a circuit diagram of a conventional high-frequency heating device.

[Explanation of symbols]

 2 DC power supply 3 High frequency power supply 4 Matching transformer 5 Tuning circuit 6 Distance sensor 7 Parallel heating electrode 8 Standing wave ratio detection sensor 9 Display means 10 Control circuit

Claims (6)

(57) [Claims] 1. A high-frequency heating apparatus provided with a parallel heating electrode for induction heating of the load by the high frequency power source and the high-frequency electric field for outputting a high-frequency voltage and the tuning circuit, between the high-frequency power source and the tuning circuit, a load and Tuning circuit impedance
To match the impedance of the RF
A high frequency heating device provided with a matching transformer having means for switching a turn ratio of the high frequency heating device. 2. A high-frequency heating apparatus according to claim 1, wherein a standing wave ratio detecting sensor for detecting a tuning state or a matching state is provided at an output terminal of the high-frequency power supply, and a control circuit is provided to provide the standing wave. Controlling the tuning circuit so as to minimize the ratio value, performing tuning, and sequentially switching the winding ratio of the matching transformer after tuning, and controlling the matching transformer so that the standing wave ratio value takes a smaller value. A high-frequency heating device characterized by the following. 3. The high-frequency heating apparatus according to claim 1, further comprising means for obtaining a load thickness by a distance sensor, and initial setting of a winding ratio of the matching transformer based on the load thickness. High frequency heating device. 4. The high-frequency heating apparatus according to claim 1, further comprising means for obtaining a distance between the load and the parallel heating electrode by a distance sensor, and initially setting a winding ratio of the matching transformer based on the distance from the load. A high-frequency heating device characterized by the following. 5. The high-frequency heating apparatus according to claim 1, further comprising means for determining a load area by a distance sensor, and initially setting a winding ratio of the matching transformer based on the load area. apparatus. 6. The high-frequency heating apparatus according to claim 1, wherein the output power of the high-frequency power source during tuning and during matching is reduced from that in a normal heating state, and a display during tuning or during matching is displayed on the display means. A high-frequency heating device, characterized in that: