JPS6232595B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-frequency heating device provided with a detection means for detecting at least reflected power out of the incident power supplied to a heating chamber by a high-frequency heating heat source and the reflected power reflected from the heating chamber side. The purpose is to control the heating heat source based on the amount of change in reflected power and perform automatic heating.

Conventionally, methods for automatically heating in high-frequency heating equipment include those that detect the ambient temperature in the heating chamber with a temperature sensor, those that directly detect the temperature by inserting a temperature sensor into the heated object, and those that detect the temperature directly in the heated object. Temperature sensors are used to detect the amount of water vapor generated when an object is heated, and sensors are used to detect carbon-containing gas generated by heated objects. When performing automatic heating using a high-frequency heating device, the essence of a high-frequency heating device is the heating efficiency when the high-frequency power output from the high-frequency heating source is absorbed into the heated object (the high-frequency power absorbed by the heated object and the output of the high-frequency heating source). The ratio of high-frequency power) varies widely depending on the type and size of the object to be heated, which poses a major challenge in promoting automatic heating. This becomes clearer when looking at Figure 1. Figure 1 shows the light-load efficiency characteristics of high-frequency heating equipment. The horizontal axis is the amount of water (cc) that is the load, and the vertical axis is the heating efficiency when the water load is 2000 c.c. against the rated output. It expresses the heating efficiency with 100. For example, the water load is
If all 600W is absorbed by the load when the load is 2000c.c., then only about 380W is absorbed by the load when the water load is 100c.c.

In addition, the high-frequency power P absorbed by the heated object is calculated using the output high-frequency power Pi of the high-frequency heating heat source, its frequency, the relative dielectric constant ε _r of the heated object, and the dielectric power factor tan δ of the heated object. ...ε _r tanδ Here, K can be expressed as an absorption constant. By the way, ε _r tan δ changes with the frequency for the same object to be heated, but furthermore, ε _r tan δ changes depending on the temperature of the object at the same frequency, so the heating efficiency for the object is determined by the heating time. It will change accordingly. FIG. 2 is a characteristic diagram showing the relationship between the temperature of the heated object and ε _r tan δ. The horizontal axis is temperature [℃] and the vertical axis is ε _r tan δ, where the solid line is fish and the broken line is H ₂ O.
It is a characteristic for The figure shows that the amount of high-frequency power absorbed by frozen fish and ice is small, and it is rapidly absorbed when the temperature approaches 0℃, and after that, the absorbed high-frequency power gradually decreases as the temperature of the heated object increases. It is shown. This means that if the same amount of high-frequency power is supplied to the heating chamber, the reflected power reflected from the heating chamber side will change as the temperature of the heated object increases, especially for the thawing device. Applications and developments are possible.

The present invention has been made in view of the above points, and it controls a load impedance variable device based on the reflected power value at the start of heating, and thereafter controls the load impedance variable device based on the amount of change in the reflected power reflected from the heating chamber side. The present invention provides a high-frequency heating device that determines the heating state of an object to be heated and controls a heating heat source.

The explanation will be given below with reference to the drawings.

FIG. 3 is a configuration diagram of a high frequency heating device showing an embodiment of the present invention. The high-frequency heating source 1 is composed of an all-solid-state high-frequency generation source constructed using solid-state elements, and the output end thereof is composed of a microstrip line that detects the incident power Pi and the reflected power Pr. A two-way coupler 2 is connected, and the output end of the two-way coupler is connected to a coaxial-to-microstrip line converter and a coaxial transmission line 3, which is a high frequency power transmission line. An antenna 5 that excites high frequency waves in the chamber 4 is configured. The output high-frequency power of the high-frequency heating heat source, that is, the incident power Pi, is determined by the two-way coupler, coaxial transmission line,
The object to be heated 6 housed in the heating chamber is dielectrically heated by transmitting the antenna. A controller 7 controls the drive power source of the high-frequency heating heat source 1 and the load impedance variable devices 8 and 9. Further, the coaxial transmission line 3 includes stub tunnelers 8 and 9 for impedance matching arranged at an interval of λ _O /4 (λ _O =C/C: speed of light, _O oscillation frequency).

FIG. 4 is a configuration diagram of a two-way coupler for detecting incident power and reflected power, showing one embodiment of the present invention.
The output high frequency power of the high frequency heating heat source, ie the incident power Pi, is transmitted through the microstrip main line 10. The output end of this main line 10 is connected to a coaxial transmission line 3 via a coaxial-to-microstrip line converter 11. Microstrip sub-line 12 stretched parallel to the main line 10 at desired intervals
The amount of power proportional to the incident power Pi and the reflected power Pr transmitted through the main line 10 is detected by the detection diode 1, respectively.
3 and 14 into electrical signals, and input the incident powers Pi and 2 to the two output terminals 15 and 16 of the two-way coupler 2, respectively.
It outputs signals Pi′ and Pr′ equivalent to the reflected power Pr. Further, a terminal resistor 17 is connected to the center of the sub-line 12.

FIG. 5 is a block diagram of an impedance matching stub tuner showing an embodiment of the present invention.

The stub tuners 8 and 9 are composed of coaxial lines, and their internal conductors 18 and 19 are in contact with or integrally formed with the internal conductor 20 of the coaxial transmission line 3, which is a high frequency power transmission line. Movable shorting plates 21 and 22 are configured to short-circuit the inner conductors 18 and 19 with the outer conductor, and impedance matching is performed by moving the shorting plates 21 and 22 to desired positions.

FIG. 6 is a control signal flow block diagram of a high frequency heating device showing one embodiment of the present invention.

Incident power obtained by the two-way coupler
Based on Pi, the reflected power Pr, and correspondingly the signals Pi′, Pr′(t), the relative value detector 23 determines that V(t)=
A signal Pr'(t)/Pi' is output. Here, the reflected power signal Pr'(t) is expressed as a function of the time variable t since it changes moment by moment. When heating is started at the current time t _O , the initial relative value holder 24 holds a signal amount of V(t _O )=Pr'(t _O )/Pi' during the heating time. Also, the difference V between V(t) and the above V(t _O ), which changes moment by moment as the heating time elapses.
(t _O )−V(t) is the heating heat source controller 25
is input. On the other hand, the reference signal generator 26 generates a heating time control reference signal V _S for controlling the heating time based on the incident power signal Pi and the MANUAL signal selected depending on the object to be heated. The heating heat source controller 25 compares the signal V(t _O )−V(t) with the control reference signal V _S and outputs a control signal V _C for controlling the heating source. This control signal V _C
This changes the output high frequency power of the high frequency heating heat source or terminates the high frequency generation operation.

In the following explanation, the matching state of the load impedance viewed from the output end of the two-way coupler, which is the reference plane when considering matching toward the heating chamber side, and the source impedance viewed from the high-frequency heating heat source side is within the preset matching range. This is an explanation of the operation in the case of . The operation in the case outside the set matching range will be explained below. This is a case where the load impedance changes greatly depending on the type and size of the object to be heated housed in the heating chamber, resulting in a matching state outside the set matching range. In such a case, as is clear from the explanation with reference to FIG. 1, the high frequency heating efficiency decreases. The load impedance variable devices 8 and 9 are used to improve this problem.

In this case, the variable impedance signal generator 27
is the shorting plate 2 of the stub tunnelers 8 and 9 in order to shift the matching state of the load impedance and power supply impedance to a preset matching range based on the incident power signal Pi and the initial relative value signal V _O (t).
₁ and ₂₂ to desired positions are generated. The shorting plate can be moved automatically using a servo mechanism, or manually using a variable load impedance lever provided on the operation panel.

When the short circuits 21 and 22 are moved by the signal that moves the short circuit plates 21 and 22, the initial relative value is determined by the movement completion signals V _M1 and V _M2 that notify the completion of movement and the signals V _IMP1 and V _IMP2 that move the short circuit plates. A control signal generator 28 outputs a reset signal RESET that resets the holding signal V(t _O ) of the holder 24. This reset signal RESET sets the initial relative value holder 24 to the time t ₁ after the shorting plate has completed its movement.
, the new initial relative value V(t ₁ ) is held and the heating heat source is controlled based on the operation described above. In addition, when moving the shorting plate to correct the load impedance, the variable impedance signal generator 27 outputs the driving power for the solid-state oscillator that constitutes the all-solid-state high-frequency generation source, which is the high-frequency heating heat source.
A stop signal STOP to turn off and stop the high frequency generation operation is sent to the heating heat source controller 25 to interrupt the high frequency generation operation. When the modification of the load impedance is completed, a clear signal CLEAR for canceling the stop signal STOP is sent from the control signal generator 28 to the variable impedance signal generator 27.
The interruption of the high frequency generation operation is canceled and the high frequency heating heat source becomes operational.

In the above explanation, an all-solid-state high-frequency generation source whose output high-frequency power can be easily and continuously changed was used as the high-frequency heating heat source. Since the output high frequency power is duty controlled, it is clear that it is possible to detect and control only the reflected power. Moreover, various modifications are possible within the scope of the present invention. For example, impedance can be varied by inserting an iris or the like into the wall of a high-frequency power transmission conductive tube, or a two-way coupler using two waveguides, or a two-way coupler using a waveguide and a coaxial line. There is.

As described above, the present invention provides a high-frequency heating device equipped with at least a detection means for detecting reflected power and an impedance variable device for matching load impedance and source impedance. The variable impedance is controlled based on the amount of reflected power or the relative ratio of reflected power and incident power, and the initial reflected power is maintained and changes as the heating progresses based on the amount of reflected power or the relative ratio of reflected power and incident power. The device controls the output power of the heating heat source, allows you to grasp the heating progress of the object to be heated from moment to moment, automatically sets the heating time according to the object to be heated, and performs so-called automatic heating. It is possible to increase the efficiency of high-frequency heating to the load as a fuel, save energy, and reduce reflected power to prevent damage to the high-frequency heating heat source and extend its life. This has the effect of making it easy to carry out.

[Brief explanation of the drawing]

Fig. 1 is a light-load efficiency characteristic diagram of a conventional high-frequency heating device, Fig. 2 is a characteristic diagram showing the relationship between the temperature of the heated object and ε _r and tan δ, and Fig. 3 is a high-frequency heating device showing an embodiment of the present invention. FIG. 4 is a block diagram of a heating device; FIG. 4 is a block diagram of a two-way coupler for detecting incident power and reflected power according to an embodiment of the present invention; FIG. 5 is a block diagram of a stub tuner for impedance matching according to an embodiment of the present invention. Diagram,
FIG. 6 is a control signal flow block diagram of a high frequency heating device showing one embodiment of the present invention. 1... High-frequency heating heat source, 2... Two-directional coupler (power detector), 4... Heating chamber, 6... Heated object,
7... Controller, 8, 9... Stub tuner (impedance variable device), 24... Initial relative value holder, 25... Heating heat source controller, 27... Impedance variable signal generator, Pi, Pi'... incident power,
Pr, Pr'... Reflected power, Pr', t _O ... Initial reflected power value, Pr'(t)/Pi'... Relative ratio of incident power and reflected power.

Claims (1)

[Scope of Claims] 1. A heating chamber that accommodates an object to be heated, a high-frequency heating heat source that generates microwave energy to supply power to the heating chamber, and a power source that controls incident power to the heating chamber and reflected power from the heating chamber. At least a power detector for detecting reflected power, a variable impedance device attached to a microwave energy transmission path between the power detector and the heating chamber, and a preset amount of reflected power at the start of heating. The variable impedance is controlled as follows, and the initial reflected power value after this control is held, and the power change amount is the difference between this initial reflected power value and the reflected power value that changes as the heating time elapses. and a controller that controls output power of the high-frequency heating heat source based on. 2 The power detector is configured to detect incident power and reflected power, and the variable impedance is controlled based on the relative ratio of reflected power and incident power so that the relative ratio becomes less than a preset value at the start of heating. At the same time, the initial relative value after this control was held, and the output power of the high-frequency heating heat source was controlled based on the relative ratio change amount of the difference between this initial relative value and the relative value that changed as the heating time elapsed. A high frequency heating device according to claim 1.