JP2005056781A - High-frequency heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain a matching state by properly controlling a circuit constant of a matching circuit against impedance changes accompanying temperature rise of a heated object. <P>SOLUTION: The matching circuit 6 is composed of a variable inductor 6a and capacitors 6b-1 to 4, and it is so structured that the matching state is maintained as switching means 6c-1 to 3 change capacities of the capacitors so as to be increased sequentially after starting of heating by detected signals of a reflective power detection means 4. With this, down-sizing of the matching circuit 6 and the matching state necessary for cooking are satisfied to realize efficient defrosting of foods and heating. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-frequency heating apparatus that cooks food by high-frequency thawing or high-frequency dielectric heating.

  2. Description of the Related Art Conventionally, a high frequency heating apparatus that heats and cooks food by high frequency thawing or high frequency dielectric heating is known (see, for example, Patent Document 1).

  In general, in such a high-frequency heating apparatus, the high-frequency power source is configured to amplify the power necessary for heating the food through several power amplification circuits. For example, in order to obtain a defrosting capability equivalent to or higher than that of a home microwave oven, the power applied to the electrodes requires about 200 W or 300 W.

And the food used as the load to be heated has a wide variety of shapes and types, and the impedance between the electrodes when the food is inserted varies greatly depending on the type and shape. In addition, the impedance varies greatly depending on the thawing state of the food, and the impedance of the electrode in the state where the load is inserted is different between the initial thawing state and the state where thawing has progressed. In order to absorb this state and efficiently transmit power to the food, which is a load, a matching circuit is inserted between the power amplification circuit and the electrode, and the values of the variable inductor and variable capacitor, which are its constituent elements, are sequentially added. By changing, impedance matching is maintained.
Japanese Patent Application Laid-Open No. 08-255682

  However, since the impedance of food varies greatly depending on its shape and temperature, the matching circuit must have a considerably large variable width in order to cope with any food. On the other hand, when assuming a household heating device, the size of components that can be accommodated in the device is naturally limited. For this reason, the variable width of the variable inductor or the variable capacitor is also limited. In particular, as a configuration of the variable capacitor, a variable capacitor is known in which a plurality of semicircular electrodes are opposed to each other and the capacitance is changed by changing the mutual facing area. Since the electrode slides, a dielectric having a high relative dielectric constant cannot be inserted between the electrodes, and the size of the variable capacitor itself has to be increased in order to realize the capacity required by the device. . As a result, in addition to the size of the capacitor unit, a drive unit that slides the electrode is added, so that the size of the entire matching circuit increases, leading to an increase in size of the high-frequency heating device itself.

  The present invention solves the above-described problems of the conventional high-frequency heating device, and provides a high-frequency heating device that satisfies the matching state required for downsizing and cooking of the matching circuit and can efficiently thaw and heat food. The purpose is to do.

  In order to solve the above-described conventional problems, the high-frequency heating device of the present invention has a matching circuit having a variable inductor and a capacitor, and is heated by a detection signal of a reflected power detection means that detects power reflected from the matching circuit to the high-frequency power source. After the start, the switching means is switched so as to increase the capacitance of the capacitor sequentially, and the matching state is maintained.

  By this, even if the food is thawed and heated, even if the impedance of the food changes, the increase in the reflected power can be detected by the reflected power detection means, and the matching state can be maintained by switching the capacitance of the capacitor. The matching state required for downsizing and cooking of the matching circuit is satisfied, and the food can be thawed and cooked efficiently.

  In the high-frequency heating device of the present invention, the matching circuit includes a variable inductor and a capacitor, and when the temperature of the object to be heated measured by the temperature measuring unit that measures the temperature of the object to be heated exceeds a threshold value, the switching unit causes the switching circuit to The configuration is such that the matching state is maintained by sequentially switching the capacitance of the capacitor.

  As a result, even if the food is thawed and heated, and the impedance of the food changes, the temperature of the object to be heated is measured by the temperature measurement means, and the matching state is always maintained during heating by switching the capacitance of the capacitor. Therefore, it is possible to satisfy the matching state required for downsizing and cooking of the matching circuit, and to efficiently thaw and cook food.

  The high-frequency heating device of the present invention satisfies the matching state required for downsizing and cooking of the matching circuit, and can efficiently thaw and heat food.

  The first invention includes a high-frequency power source, an electrode that dielectrically heats an object to be heated by an output of the high-frequency power source, a matching circuit that is connected between the electrode and the high-frequency power source and performs impedance matching with the high-frequency power source, Reflected power detection means connected between a high frequency power supply and the matching circuit for detecting power reflected from the matching circuit to the high frequency power supply, the matching circuit having a variable inductor and a capacitor, and the reflected power detection According to the detection signal of the means, after the start of heating, the switching means sequentially switches the capacity of the capacitor to increase so that the matching state is maintained, so that the food is defrosted and heated, and the impedance of the food changes. In addition, the increase in reflected power is detected by the reflected power detection means, and the matching state is maintained by switching the capacitance of the capacitor. It is possible, satisfy the matching condition required for a cooking miniaturization of the matching circuit efficiently food thawing, it is possible to heat cooking.

  In the second invention, in particular, in the high-frequency heating device of the first invention, when the value of the reflected power detected by the reflected power detection means exceeds a predetermined threshold value, the capacitance of the capacitor provided in the matching circuit is increased by the switching means. When the food is heated, the impedance changes, the reflected power increases, and when the value exceeds the threshold, the capacitor can be switched to maintain the matching state, so the food is efficiently heated. be able to.

  According to a third aspect of the invention, in particular, in the high-frequency heating device of the first or second aspect of the invention, the switching means for switching the capacitor capacity of the matching circuit is constituted by the contact means. Since the load matching can be maintained by switching the capacity and the capacitor capacity corresponding to the heating state of the food, the food can be efficiently heated. Further, by using the contact means for switching the capacitor, the size of the matching circuit can be reduced, and the high-frequency heating device can be reduced in size.

  The fourth invention is a high-frequency power source, an electrode that dielectrically heats an object to be heated by an output of the high-frequency power source, a matching circuit that is connected between the electrode and the high-frequency power source and performs impedance matching with the high-frequency power source, Temperature measuring means for measuring the temperature of the object to be heated between the electrodes, the matching circuit has a variable inductor and a capacitor, and switching means when the temperature of the object to be heated measured by the temperature measuring means exceeds a threshold value With the high-frequency heating device configured to maintain the matching state by sequentially switching the capacitance of the capacitor, the temperature of the object to be heated is measured by the temperature measuring means, and the capacitance of the capacitor is switched. Since the matching state can always be maintained during heating, the matching circuit meets the matching state required for downsizing and cooking, and during cooking It is possible to always maintain the alignment, it is possible to perform efficient cooking.

  According to a fifth aspect of the invention, in particular, in the high-frequency heating device of the fourth aspect of the invention, the temperature measuring means is configured by an infrared sensor that measures the temperature in a non-contact manner, whereby the temperature of the food can be measured without contacting the food. Therefore, it is possible to provide a hygienic high-frequency heating device and to change the capacitor capacity of the matching circuit while measuring the temperature of the food, so that an appropriate capacity can be selected. It can be maintained and efficient cooking can be performed.

  In a sixth aspect of the present invention, in particular, in the high-frequency heating device of the fourth or fifth aspect, when the temperature of the object to be heated measured by the temperature measuring means exceeds a predetermined threshold value, it is determined that cooking is finished and the high-frequency power supply is stopped. Thus, cooking is completed before the temperature of the food rises excessively, so that it is possible to prevent cooking errors due to overheating, particularly in thawing cooking.

  The seventh invention, in particular, in the high-frequency heating device according to any one of the first to sixth inventions, further comprises a timer means for measuring an elapsed time after switching the capacitance of the capacitor provided in the matching circuit, and the switching means. By switching from the capacity of the capacitor to the next time to reach the threshold for switching the capacity is determined to be the end of heating when the time set by the timer means is equal to or longer, and the high frequency power supply is stopped. Since cooking is finished before the temperature of the food rises excessively, it becomes possible to prevent cooking errors due to overheating, particularly in thawing cooking.

  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)
1 to 3 show a high-frequency heating device according to Embodiment 1 of the present invention.

  As shown in FIG. 1, a heated object 1 such as frozen food is placed so as to be sandwiched between electrodes 2, that is, a pair of electrodes 2 a and 2 b, and output from the high-frequency power source 3 to the electrode 2, for example, food Dielectric heating is performed by applying a high frequency electric field such as 13.56 MHz or 27.12 MHz suitable for thawing. The high-frequency power source 3 includes an oscillation circuit that determines an oscillation frequency by a crystal oscillator or the like, and a main power amplifier that amplifies the output of the oscillation circuit to a power necessary for thawing food.

  A matching circuit 6 for impedance matching with the high frequency power source 3 is connected between the electrode 2 and the high frequency power source 3, and the matching circuit 6 is connected to the high frequency power source 3 between the high frequency power source 3 and the matching circuit 6. A reflected power detection means 4 for detecting reflected power is connected. The reflected power is detected by the reflected power detecting means 4, and the control unit 5 appropriately sets the values of the variable inductor 6a and capacitors 6b-1 to 4 provided in the matching circuit 6 so as to minimize the reflected power. . Therefore, even if the impedance between the electrodes changes depending on the shape and type of the object to be heated 1 and the distance between the electrodes 2a and 2b, the impedance matching state with the high-frequency power source 3 is maintained, and the object to be heated 1 is efficiently high-frequency. Electric power can be transmitted.

  The matching circuit 6 includes a capacitor 6b-1 which is a fixed component and a capacitor 6b whose optimum value is appropriately selected by turning on / off the switching means 6c-1 to 3c depending on the impedance condition of the article 1 to be heated. -2 to 4. And the control part 5 is comprised so that the capacity | capacitance of the said capacitor may be switched so that it may increase sequentially by the switching means 6c-1 to 3 after a heating start by the detection signal of the reflected power detection means 4, and a matching state may be maintained. The switching means 6c-1 to 6c-3 are contact means such as a relay and switch the capacitor capacity.

  FIG. 2 shows what values the variable inductor 6a and capacitors 6b-1 to 4 provided in the matching circuit 6 should take in order to maintain the matching state from the start of heating of the article 1 to the end of cooking. Show.

  As shown in this figure, when heating of the article 1 to be heated starts, the inductance of the variable inductor 6a must be reduced to maintain the matching state. On the other hand, the value of the capacitor needs to be gradually increased after it is first decreased. Then, near the end of cooking, the amount of change in both the variable inductor 6a and the capacitor is small. However, in order to continuously change the capacitor in this way, for example, a so-called variable capacitor (variable capacitor) is required in which the area of electrodes facing the capacitor is continuously varied and the capacitance value is variable. In order to change the capacitance value of the variable capacitor, it is necessary to operate the electrode, and a motor capable of position control such as a stepping motor is required for driving the variable capacitor, and it is difficult to avoid an increase in the size of the matching circuit 6. It is. Therefore, in the first embodiment, the capacitance value of the capacitor is varied discretely using the switching means 6c-1 to 3c-1, that is, contact means such as a relay.

  FIG. 3 schematically shows how the capacitance and inductance values of the capacitor are changed in order to maintain the matching state. The switching of the capacitors 6b-1 to 6c-1 is performed by the control unit 5 reading the detection signal of the reflected power detection means 4, and when the value of the reflected power exceeds a predetermined threshold value, the switching means 6c-1 -3 are on / off controlled. For example, if the capacitors 6b-2 to 4 are configured to 50 pF, 100 pF, and 200 pF, respectively, it is possible to increase the initial capacitance value Co by 50 pF.

  As a result, the reflected power can always be kept below a predetermined threshold during cooking, so that the heating power can always be efficiently supplied to the article 1 to be heated, and an efficient high-frequency heating device can be realized. The effect that it can be done can be exhibited.

  Although not shown, the matching circuit 6 is provided with timer means for measuring the elapsed time after switching the capacitance of the capacitor. The switching means 6c-1 to 3 are used to change the capacitance of the capacitor. When the time from the last switching to the threshold for switching the capacity after the last switching is equal to or longer than the time set by the timer means, it is determined that the heating is finished, and the high frequency power source 3 is stopped. Thus, cooking is completed before the temperature of the food rises excessively, so that it is possible to prevent cooking errors due to overheating, particularly in thawing cooking.

  Further, the switching means 6c-1 to 6c-3 used for switching the capacitances of the capacitors 6b-2 to 4 of the matching circuit 6 are constituted by contact means such as general-purpose relays. The switching means 6c-1 to 3c are turned on / off after the output of 3 is reduced or stopped. By doing so, it is possible to prevent damage due to burn-in of the contacts of the switching means 6c-1 to 3c-3, and at the same time, it is not necessary to obtain excessive quality for the contacts, and the matching circuit 6 can be downsized. be able to.

(Embodiment 2)
4 and 5 show a high-frequency heating device according to Embodiment 2 of the present invention. The same elements as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In the second embodiment, as shown in FIG. 4, a temperature measuring unit 7 that measures the temperature of the heated object 1 between the electrodes 2 a and 2 b is provided, and the temperature of the heated object 1 measured by the temperature measuring unit 7. When the value exceeds the threshold value, the switching means 6c-1 to 3 are switched so as to increase the capacitance of the capacitor sequentially, and the matching state is maintained. And the temperature measurement means 7 is comprised with the infrared sensor which measures the surface temperature of the to-be-heated material 1 non-contactingly in this example, and is trying to monitor the heating state of the to-be-heated material 1. FIG.

  Here, the control unit 5 receives the output signal of the temperature measuring means 7 and measures the temperature of the object 1 to be heated, and appropriately switches the capacitors 6b-2 to 4 provided in the matching circuit 6 according to the value, thereby switching the high frequency power source 3 And maintain the impedance matching of the electrode 2.

  FIG. 5 shows the temperature change from the start of cooking of the article to be heated 1 to the end of cooking, the value of the capacitor of the matching circuit 6, and the value of the variable inductor 6a. As shown in this figure, when the temperature of the object to be heated 1 rises and reaches the threshold values 1 and 2, it is possible to maintain the matching state by switching the capacitance value of the capacitor so as to increase sequentially. Thereby, heating power is efficiently transmitted to the article 1 to be heated, and efficient cooking is possible.

  Moreover, the end of heating cooking always monitors the temperature of the article 1 to be heated, and when the threshold value 2 is exceeded, it is determined that the heating cooking is finished and the high frequency power supply is stopped, so that the food temperature rises excessively. Since cooking is completed, it is possible to prevent cooking errors due to overheating, particularly in thawing cooking. In addition, the effect | action by providing a timer means is the same as that of Embodiment 1.

  As described above, the high-frequency heating device according to the present invention satisfies the matching state necessary for downsizing and cooking of the matching circuit, and can efficiently thaw and cook food. This is useful for miniaturization of home-use high-frequency heating devices.

The circuit diagram which shows the high frequency heating apparatus in Embodiment 1 of this invention The figure which showed the time change of the value which should be taken of the capacitor and variable inductor with which the matching circuit was equipped in order to maintain a matching state in the high frequency heating device of the example The figure which showed the time change of the capacitor and inductor of a matching circuit in the high frequency heating device of the example The circuit diagram which shows the high frequency heating apparatus in Embodiment 2 of this invention The figure which showed the time change of the value of the capacitor | condenser and inductor of a matching circuit in the high frequency heating apparatus of the Example, and the temperature change of to-be-heated material

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heated object 2 Electrode 3 High frequency power supply 4 Reflected power detection means 5 Control part 6 Matching circuit 6a Variable inductor 6b-1-4 Capacitors 6c-1-3 Switching means 7 Temperature measurement means

Claims (7)

A high-frequency power supply; an electrode for dielectrically heating an object to be heated by an output of the high-frequency power supply; a matching circuit connected between the electrode and the high-frequency power supply for impedance matching; and the high-frequency power supply and the matching circuit And a reflected power detection means for detecting power reflected from the matching circuit to the high-frequency power source, and the matching circuit includes a variable inductor and a capacitor, and is heated by a detection signal of the reflected power detection means. A high-frequency heating apparatus configured to maintain a matching state by switching so that the capacitance of the capacitor is sequentially increased by switching means after the start. The high-frequency heating device according to claim 1, wherein when the value of the reflected power detected by the reflected power detection means exceeds a predetermined threshold, the switching means increases the capacitance of the capacitor provided in the matching circuit. The high-frequency heating device according to claim 1 or 2, wherein the switching means for switching the capacitor capacity of the matching circuit is configured by contact means. A high-frequency power source, an electrode that dielectrically heats an object to be heated by an output of the high-frequency power source, a matching circuit that is connected between the electrode and the high-frequency power source and performs impedance matching with the high-frequency power source, and an object to be heated between the electrodes The matching circuit has a variable inductor and a capacitor, and when the temperature of the object to be heated measured by the temperature measuring unit exceeds a threshold value, the capacitance of the capacitor is changed by the switching unit. A high-frequency heating device configured to maintain an aligned state by switching so as to increase sequentially. The high-frequency heating device according to claim 4, wherein the temperature measuring means is constituted by an infrared sensor that measures temperature without contact. The high frequency heating apparatus according to claim 4 or 5, wherein when the temperature of the object to be heated measured by the temperature measuring means exceeds a predetermined threshold value, it is determined that cooking is finished and the high frequency power supply is stopped. Timer means for measuring an elapsed time after switching the capacitance of the capacitor provided in the matching circuit, and the time until the threshold value for switching the capacitance is reached after switching the capacitance of the capacitor by the switching means is the timer means The high frequency heating device according to any one of claims 1 to 6, wherein the high frequency power supply is stopped when it is determined that the heating is finished when the time set in (1) is longer than the predetermined time.

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