JP5195255B2 - Microwave heating device - Google Patents

Description

  The present invention relates to a microwave heating apparatus that heats an object to be heated, which is an object to be heated, by irradiating microwaves.

  There is a microwave oven as a typical device of a microwave heating device that heats an object by using a microwave. In a microwave oven, microwaves are radiated into a metallic heating chamber in a microwave generator, and an object to be heated in the heating chamber is heated by the radiated microwaves.

Conventionally, as this microwave heating apparatus, a semiconductor oscillating unit, a dividing unit that divides the oscillation output of the semiconductor oscillating unit into a plurality, a divider that amplifies each divided oscillation output, and a divided oscillation output are each amplified. And a detecting unit for detecting a reflected wave between the combiner and the heating chamber, and changing the oscillation state of the oscillator according to the amount of the reflected wave detected by the detecting unit. (For example, see Patent Document 1).
JP-A-56-134491

  However, in the conventional configuration, since the semiconductor oscillation units are synthesized by the synthesis unit, the reflected wave related to the oscillation output from one power supply port is always monitored, and the reflected wave becomes larger than a certain level. By stopping the oscillation of the oscillator, changing the oscillation frequency, or changing and reducing the oscillation output, the semiconductor portion is not destroyed without using semiconductor element protection means such as an isolator.

  However, if a frequency with few reflected waves is selected at the time of oscillation and radio waves are not radiated there, the power of the reflected waves destroys the semiconductor element in the output section. In the conventional configuration, it is not described how to select a frequency with few reflected waves at the initial oscillation. During heating, the minimum frequency of the reflected wave is expected to change due to changes in the physical properties of the heated object, etc., but how to monitor and change the frequency to the optimum frequency at that time No realization means are described.

  The present invention solves the above-described problem, and even in a configuration having a plurality of semiconductor oscillation units, each reflection wave burden is always monitored for reflection or incident reflectance regardless of when oscillation starts or during heating, and any one output is achieved. An object of the present invention is to provide a highly reliable microwave heating apparatus that protects a semiconductor element from destruction by changing the frequency so that reflection is minimized when an excessive reflected wave is applied to the semiconductor element.

In order to solve the above conventional problems, the microwave heating apparatus of the present invention includes a semiconductor oscillation unit for transmitting an oscillating reference signal, and an output unit for creating a microwave, a plurality of the semiconductor oscillation unit connected to the output portion receiving a microwave generation part having a heating chamber for accommodating an object to be heated, and inputted and reflected wave monitoring unit that monitors the incoming reflected wave level located downstream of the output section, the signal of the inputted and reflected wave monitoring unit The control unit for controlling the output of the output unit, the detection circuit for detecting the detection signal of the incident / reflected wave monitor unit, and the incident / reflective monitor unit provided between the incident / reflective monitor unit and the detection diode of the detection circuit comprising a the detection signal and the attenuator for attenuating the desired low voltage, heating start the controller immediately after the detection (pre-search) the oscillation frequency having a minimum of the reflected wave to the time that is the output The attenuator function is stopped and the minimum reflection frequency is selected so that the detection signal level of the detection circuit becomes a detectable potential, and the power of the output unit is then heated at the minimum reflection frequency. The control unit detects the oscillation frequency that minimizes the reflected wave by increasing the output and functioning the attenuator to attenuate the signal level so that the detection signal level of the detection circuit becomes a detectable potential (this search) ). Since the microwave output is reduced in the pre-search, the voltage applied to the control unit via the reflected wave monitor unit is at an appropriate control level that can be controlled. When the microwave output emitted from the input / output unit greatly increases, the feedback signal in the control unit completely exceeds the voltage level in the uncontrollable region of the control unit. Therefore, a signal is sent from the control unit to the detection circuit, the signal level of the control unit is converted to a controllable signal level by limiting the feedback function.

  The microwave heating apparatus of the present invention detects a frequency at which the reflected output is minimized while suppressing the microwave output emitted from the output unit at the start of heating when the reflection state is completely unknown. At that time, although the voltage applied to the detection circuit is small, it is necessary to attenuate the signal to a level at which signal processing can be performed in the control circuit according to the incident / reflection level.

  When the microwave output emitted from the output unit is increased to perform the main heating at the frequency at which the incident / reflected output detected in this way is minimum (steady heating output), the signal level of the detection circuit naturally increases. At that time, the control circuit sends a signal to the detection circuit so that the feedback amount of the signal to the control circuit is reduced, and even the steady heating output is reduced to an output that can be processed in the control circuit. By such switching, the signal can be further attenuated to a level at which signal processing can be performed in the control circuit even during steady heating output.

  Since it is unclear what kind of reflection state is in the initial stage of heating, the power at the output section is kept low and the frequency at which the reflected output is minimized is detected. On the other hand, even when the steady heating output is entered, the attenuation level of the detection circuit is switched to a voltage level that can be processed in the control circuit, and the steady heating output is shifted to an output that can be processed in the control circuit.

  By doing so, the feedback voltage can be set to the optimum controllable voltage in the control unit with a low microwave output according to the initial stage of heating, so that the object of detecting the minimum reflection frequency can be achieved. Also, in the steady heating output state, the feedback voltage can be kept lower and the reflected signal and incident signal can be detected at all times even in the high output state. When the reflected wave becomes excessive, an immediate pre-search is performed to minimize the reflection. The frequency can be corrected.

A first aspect of the present invention is housed a semiconductor oscillation unit for transmitting an oscillating reference signal, and an output unit for creating a microwave, a microwave generation part having a plurality of the semiconductor oscillation unit connected to the output unit, an object to be heated a heating chamber for a inputted and reflected wave monitoring unit that monitors the incoming reflected wave level located downstream of the output section, and a control unit for controlling the output of the output unit receives the signal of the inputted and reflected wave monitoring unit, wherein A detection circuit for detecting a detection signal of the incident / reflected wave monitor unit; and an attenuator provided between the incident / reflected monitor unit and the detection diode of the detector circuit for attenuating the detected signal of the incident / reflected monitor unit to a desired low voltage; The control unit immediately after the start of heating reduces the power of the output unit to a level at which the semiconductor element of the output unit is not destroyed, and detects the oscillation frequency at which the reflected wave is minimized. At that time, the attenuator function is stopped and the minimum reflection frequency is selected (presearch) so that the detection signal level of the detection circuit becomes a detectable potential. Thereafter, the control unit reflects the output signal at the minimum reflection frequency so that the output signal is increased to the main heating output and the attenuator functions to attenuate the signal level so that the detection signal level of the detection circuit becomes a detectable potential. The oscillation frequency that minimizes the wave is detected (main search). In this way, the detection signal level of the detection circuit can be set to a detectable potential both during pre-search and during this search, and the minimum frequency of the reflected wave can always be selected. Thus, fail-safe control can be performed in a direction in which the semiconductor element of the output unit is not destroyed as appropriate.

According to a second aspect of the invention , in particular, in the first aspect of the invention, the reflected wave monitor unit is composed of a directional coupler and receives a signal of the output unit, and a port for transmitting the output of the output unit to the antenna with very little attenuation And a port for receiving the signal Pf attenuated and a port for detecting and attenuating the reflected wave to obtain the signal Pr, and detecting the minimum oscillation frequency based on the Pr / Pf signal. By performing the calculation of Pr / Pf, the parameter representing the reflectance can be normalized regardless of the level of the high frequency output, the absolute value can be normalized, and the minimum frequency of the reflected wave can be detected. It is possible to increase the accuracy by making the accuracy to be more uniform.

The third aspect of the invention is particularly effective in the first or second aspect of the invention when the attenuator is always functioned during the main heating to monitor the behavior of the reflected wave during the main heating and an excessive reflection is detected. If there is no time to detect the minimum frequency of the reflected wave by performing pre-search again, it is possible to immediately perform the safety-off, so that the semiconductor elements in the output section can be destroyed. Can be prevented.

In the fourth invention, in particular, in the first or second invention, the behavior of the minimum frequency is monitored by monitoring the behavior of the reflected wave during the main heating by always functioning the attenuator during the main heating. If Pr / Pf) becomes excessive, the process returns to the sequence at the start of heating, the power of the output section is reduced, and the function of the attenuator is stopped so that the detection signal level of the detection circuit becomes a detectable potential. The minimum frequency is set again. The heating chamber is viewed from the power supply section, such as the tipping of the object being heated during the heating, the change of the dielectric constant due to the temperature rise due to the heating, and the expansion of the food wrap often used in the microwave oven. Even if the impedance changes and the minimum frequency of the reflected wave changes, the set frequency can be changed again. State can be avoided.

In the fifth invention, in particular, in any one of the first to fourth inventions, the microcomputer function of the device of the present invention on the microcomputer that controls the entire device is transplanted to greatly reduce the redundancy. In addition to exhibiting economic effects, the number of parts can be reduced from the viewpoint of making two parts into one part, and the entire system can be simplified.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a configuration diagram of a microwave heating apparatus according to the first embodiment of the present invention.

  In FIG. 1, microwave generation units 3a to 3d receive output from output units 2a to 2d configured using semiconductor elements and output units 2a to 2d and supply incident power to power supply units 7a to 7d. The incident wave reflection monitor units 6a to 6d are formed of directional couplers that detect the reflected power reflected from the heating chamber 5. Basic weak signals for generating microwaves are generated by the semiconductor oscillation units 1a and 1b. In order to realize the semiconductor oscillation units 1a and 1b with as few configurations as possible, the semiconductor oscillation units 1a and 1b are connected to the power distribution units 8a and 8d. In this case, each of them is divided into two, a total of four, and input to the microwave generators 3a to 3d.

  In addition, the microwave processing apparatus of the present invention has a heating chamber 5 having a substantially rectangular parallelepiped structure that accommodates an object 9 to be heated. The heating chamber 5 has a left wall surface, a right wall surface, a bottom wall surface, an upper wall made of a metal material. An open / close door (not shown) that opens and closes to store the wall surface, the back wall surface, and the object to be heated 9 and a mounting table on which the object to be heated 9 is placed so as to confine the supplied microwave inside. It is configured. And the output of the microwave generation parts 3a-3d is transmitted, and the electric power feeding parts 7a-7d which radiate | emit the microwave into the heating chamber 5 are arrange | positioned at the wall surface which comprises the heating chamber 5. FIG.

  In the present embodiment, the power feeding units 7a to 7d are arranged at the approximate center of the left wall surface and the right wall surface of the opposing configuration, respectively, and the power feeding unit 7c is arranged at the approximate center of the upper wall surface and the bottom surface of the heating chamber 5, respectively. , 7d are shown. The arrangement of the power feeding portions 7a to 7d is not limited to the present embodiment, and a plurality of power feeding portions may be provided on any wall surface, and are not opposed surfaces such as a right wall surface and a bottom wall surface. You may comprise the electric power feeding part used as a pair by the adjacent combination.

  The power amplifiers in the output units 2a to 2d are amplified by several tens of dB or more by a cascade amplifier on the printed circuit board. The circuit is formed by a conductor pattern formed on one side of a dielectric substrate made of a low dielectric loss material. In order to operate the semiconductor element which is configured and the amplifying element of each amplifying unit satisfactorily, matching circuits are arranged on the input side and the output side of each semiconductor element.

  The microwave transmission path connecting each functional block forms a transmission circuit having a characteristic impedance of about 50Ω by a conductor pattern provided on one surface of the dielectric substrate.

  The power distribution units 8a and 8b may be in-phase distributors that do not produce a phase difference between outputs such as a Wilkinson distributor, or may have a phase difference between outputs such as a branch line type or a rat race type. It may be the resulting distributor. The power distribution units 8a and 8b transmit approximately half of the microwave power input from the oscillation units 1a and 1b to the respective outputs.

  When the control unit 4 selects a frequency with as few reflected waves as possible, it can maximize the heat transfer power received by the article 9 to be heated, contribute to speed cooking, and reduce the heat loss of the semiconductor element due to the reflected wave power. This also improves the heat resistance reliability of semiconductors.

  However, it is inevitable that the object to be heated 9 is affected by the temperature of microwave heating during cooking. For example, it rarely occurs that the article 9 to be heated falls due to thermal expansion during heating or falls. It is also conceivable that the dielectric constant gradually changes as the food temperature rises. Moreover, although the habit of wrapping is often seen in the microwave heating apparatus, it can be seen that this also swells in the middle of heating and the volume of the article 9 to be heated increases.

In such a case, the impedance inside the heating chamber 5 as seen from the power feeding units 7a to 7d changes, and it is predicted that the minimum reflection frequency changes every moment as shown in FIG. Point a is the initial frequency characteristic. When a change in physical properties of the article 9 to be heated appears, a transition is made to a dotted line b-point curve. And, if the heated object 9 falls and rolls during the heating, rolls, the dielectric constant changes as the temperature of the food rises, or the heated heated object 9 wraps up, for example, It is predicted that the frequency characteristic changes up to a point c. At that time, the reflectance increases by d. That is, it is used in a state where there are many reflections. This increases the reflection duty of the semiconductor. For example, if the change is larger, the reflection is expected to increase and break down.

Therefore, as a means for avoiding this, it is necessary to always monitor the amount of reflection and the reflectance so that the reflected wave has the minimum frequency and follow the change.

  FIG. 3 is a timing chart showing the sequence.

  This will be described with reference to FIG. First, it starts from the initial stage (t = 0). At this time, since the reflection spectrum characteristics (in the ISM band 2400-2500 MHz) are completely unknown, when a high output (steady output) is suddenly output, a large reflected wave returns, and the output units 2a--2 There is a possibility of destroying the 2d semiconductor element. Therefore, as a pre-search period, the ISM band 2400 to 2500 MHz is searched at a low output. Even if there is a large reflection, it oscillates with a low output of several tens of W so as not to destroy the semiconductor element. Therefore, the frequency that minimizes the reflected wave is selected. Next, at the selected frequency, the output is increased to a steady heating output and oscillates (main heating time).

  As a matter of course, when the output is increased, both the incident wave and the reflected wave are increased. Therefore, with the amount of feedback at the time of pre-search, an excessive incident wave / reflected wave that deviates from a range that can be detected and controlled by the control unit 4 is fed back, and there is a possibility that control becomes impossible. It is necessary to take some measures.

  If a large reflected wave returns during the heating time, it is necessary to pre-search again and reset the frequency at which the reflected wave is minimized. That is the second pre-search period shown in the figure. This is because it is necessary to carry out whether or not the reflected wave becomes large, and it is assumed in the figure that the reflected wave becomes large after heating. Fortunately, it is assumed that the state of reflection does not change during heating. At that time, this process is naturally skipped. However, when the impedance of the heating chamber 5 viewed from the microwave power feeding units 7a to 7d changes during heating and the minimum frequency of the reflected wave changes, this is a process that must be performed.

  If pre-searching is performed again and the minimum frequency is reset, the subsequent main heating time can be operated at the reset frequency. During this period, the incident wave and the reflected wave are always monitored as the main search.

  If the reflected wave is prominently large, there is no time to pre-search again, so it must be taken into consideration that the heating is stopped immediately. Naturally, it is also possible to see unusual reflections that have not been anticipated by previous experience. In this case, it is desirable to stop the progress of heating immediately without performing pre-search again.

  In the present invention, the incident wave Pf and the reflected wave Pr can be monitored at all times, so that the pre-search may be performed as necessary. As a matter of course, in the case of heating with a small impedance change, it is not necessary to pre-search again, so that the heating can be completed in the shortest time.

The reflectance (Pr / Pf) within the ISM band 2400-2500 MHz is shown using FIG. At point A, the reflectance is calculated by the ratio of the sum ΣPr of the reflected waves of the four power supply portions 7a to 7d and the sum ΣPf of the incident waves. It can be seen that the reflectance is the smallest at point A. Here, the power incident on the object to be heated is the largest, and the power reflected on the semiconductor element is the smallest. As a result of the pre-search, naturally, the frequency A point of the main heating of 2430 MHz should be selected.

The principle of detecting the incident wave Pf and the reflected wave Pr is shown in both the pre-search and the main search, using the circuit diagram of FIG. The reflected wave Pr from the incident / reflection monitor unit 6a is dropped by the resistor 13a, the resistor 14a, and the resistor 19a and inputted to the control unit 4, but is detected and peak detected by the detector diode 18a and the capacitor 16a. The potential is held for a certain period by the resistor 19a. A switch 15a connected in parallel to the resistor 14a and turned on / off by a command from the control unit 4 is also provided in the resistor 14a. This closes or opens the switch 15a in accordance with a command from the control unit 4 using an analog switch or the like. The diode 20 a is a clamp diode for overvoltage application protection to the control unit 4. Since the structures of the incident / reflective monitor units 6b to 6d are the same, the description is omitted.

  At the time of low output presearch, a close signal is transmitted from the control unit 4 to the switch 15a, and a low voltage dropped by the resistor 13a is applied to the control unit 4 to detect the signal. At this time, the clamp diode 20 a is not active, and a low voltage equal to or lower than the circuit power supply voltage Vcc 21 of the control unit 4 is processed by the control unit 4. The semiconductor oscillator 1a is swept from 2400 MHz to 2500 MHz to detect the minimum reflected wave frequency. The signals from the incident / reflection monitor units 6b to 6d are processed in the same manner.

  The incident / reflection monitor sections 6a to 6d also detect incident waves, and the isolation between the incident wave Pf and the reflected wave Pr is 20 dB to 30 dB, and the contact is almost completely prevented. The main power is transmitted from the input port to the output port with almost no loss and is transmitted to the antenna power feeding units 7a to 7d.

After detecting the reflected wave minimum frequency, it shifts to the main heating at this frequency. At this time, since the power detected by the reflection monitor units 6a to 6d also increases, attenuation is necessary to reduce the voltage level to allow signal processing in the control unit 4. Therefore, a signal is transmitted from the control unit 4 to the switch 15a, the switch 15a is opened, and the voltage is dropped by the resistors 13a and 14a, and the dropped low voltage is applied to the control unit 4 and the signal is detected. . At this time, the clamp diode 20 a is not active, and a low voltage equal to or lower than the circuit power supply voltage Vcc 21 of the control unit 4 is processed by the control unit 4.

  With such a configuration, the voltage level is such that signal processing can be performed in the control unit 4 during pre-search and during the main search, and the configuration is such that the incident wave Pf and the reflected wave Pr can always be processed.

  In order to simplify the system, there is a microcomputer that controls the entire existing equipment, but by inserting this task into it, the task can be performed in parallel by one microcomputer, and the system is greatly improved. It is also possible to reduce the number of parts and achieve an economic effect.

  As described above, the microwave heating device according to the present invention can provide a device that has a plurality of power supply units and prevents the destruction of a semiconductor from reflected waves from a power supply unit that radiates microwaves. It can also be applied to uses such as a heating device using dielectric heating, a garbage disposal machine, or a microwave power source of a plasma power source which is a semiconductor manufacturing device.

The system block diagram of the microwave heating apparatus in embodiment of this invention The characteristic view which shows the change of the frequency spectrum accompanying the change of the to-be-heated material of this invention The time chart which shows the processing sequence of each part in embodiment of this invention The characteristic view which shows the reflectance in the ISM band in embodiment of this invention Circuit diagram of the detection circuit in the embodiment of the present invention

DESCRIPTION OF SYMBOLS 1 Semiconductor oscillation part 2 Output part 3 Microwave generation part 4 Control part 5 Heating chamber 6 Incident reflection monitor part 12 Detection circuit

Claims (5)

A semiconductor oscillating unit for transmitting an oscillation reference signal; an output unit for creating a microwave; a microwave generating unit having a plurality of the semiconductor oscillating units connected to the output unit; a heating chamber for storing an object to be heated; and inputted and reflected wave monitoring unit that monitors the incoming reflected wave level located downstream of the output section, the control section for controlling the output of the output unit receives the signal inputted and reflected wave monitoring unit, the entering-reflected wave monitoring unit A detection circuit for detecting a detection signal, and an attenuator provided between the incident reflection monitor unit and the detection diode of the detection circuit for attenuating the detection signal of the incident reflection monitor unit to a desired low voltage, immediately after the start of heating When the control unit detects a minimum oscillation frequency of the reflected wave, the power of the output unit is reduced so that the detection signal level of the detection circuit becomes a detectable potential. The function of the attenuator is stopped and the minimum reflection frequency is selected. Thereafter, the power of the output unit is increased to the main heating output at the minimum reflection frequency and the signal level is attenuated by the function of the attenuator. A microwave heating apparatus configured such that the control unit detects an oscillation frequency at which a reflected wave is minimized such that a level becomes a detectable potential. The incoming / reflected wave monitoring unit is composed of a directional coupler, and receives a signal from the output unit, a port that transmits power from the output unit to the power feeding unit with very little attenuation, and power sent to the power feeding unit 2. The configuration according to claim 1, wherein a minimum oscillation frequency is detected on the basis of the reflectance Pr / Pf, comprising a port for obtaining a signal Pf in which the signal is attenuated and a port for obtaining a signal Pr by detecting and attenuating a reflected wave. Microwave heating device. 3. The micro of claim 1 or 2, wherein the attenuator is always functioned during the main heating to monitor the behavior of incident / reflected waves during the main heating, and the output section is immediately stopped when excessive reflection is detected. Wave heating device. During the main heating, the attenuator is always functioned to monitor the behavior of the incident / reflected wave during the main heating to monitor the behavior of the minimum frequency. If the reflectance Pr / Pf becomes excessive, the output is returned to the initial stage. The microwave heating device according to claim 1 or 2, wherein the function of the attenuator is stopped and the minimum reflectance frequency is reset so that the detection signal level of the detection circuit becomes a detectable potential by reducing the power of the detection circuit. The microwave heating apparatus according to any one of claims 1 to 4, wherein the control circuit uses a microcomputer, and the microcomputer is configured to perform processing in combination with a microcomputer that controls the microwave heating apparatus.