Microwave processing device

Abstract

A microwave processing device according to one embodiment of the present disclosure includes a heating chamber, a microwave generating unit, an amplifier, a power supply unit, a detection unit, a storage unit, and a control unit. The microwave generating unit generates microwaves having any frequency in a prescribed frequency band. The amplifier amplifies the microwaves and outputs the amplified microwaves as incident power. The power supply unit supplies the incident power to the heating chamber. The detection unit detects the incident power and the reflected power returning from the heating chamber to the power supply unit. The storage unit stores the incident power and the reflected power in association with the frequency of the microwave and the time elapsed from the start of heating. The control unit causes the microwave generating unit to perform a frequency scan over a prescribed frequency band. The control unit controls the microwave generating unit and the amplifier based on the incident power and the reflected power detected during the frequency scan. According to this embodiment, the uniformity of heating can be improved.

Description

Technical Field

[0001] The present disclosure relates to a microwave treatment device including a microwave generating unit. Background Art

[0002] Conventionally, there is known a microwave processing device which includes a semiconductor oscillating element and controls the frequency and output level of microwaves to heat an object to be heated more uniformly (for example, refer to Patent Document 1).

[0003] Conventional microwave processing devices calculate the amount of microwave power absorbed by the object to be heated at each frequency based on the difference between the incident wave and the reflected wave of the microwave. Conventional microwave processing devices adjust the output level and oscillation time of the microwave at each frequency based on this information, thereby achieving uniform heating.

[0004] When the frequency of the microwave changes, the microwave distribution in the heating chamber, that is, the heating pattern for the object to be heated changes. Therefore, in the conventional microwave processing apparatus, emphasis is placed on making the power absorbed by the object to be heated at each frequency equal.

[0005] Conventional microwave processing devices estimate the difference between incident and reflected microwave waves as the amount of power absorbed by the object being heated, and control the frequency, output level, and oscillation time of the microwaves so that the power absorbed by the object being heated at each frequency is equal.

[0006] Conventional technology takes into account the microwave transmission path and the microwave dispersion in the wall surface of the heating chamber, thereby improving the estimation accuracy of the power absorbed by the object to be heated at each frequency.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application No. 2009-527883 Summary of the invention

[0010] However, even if the technology described in Patent Document 1 is applied to a microwave oven, it is difficult to achieve sufficient uniformity of heating in actual cooking.

[0011] When food is heated in a microwave oven, the dielectric constant of the food changes as the temperature changes. In particular, in the case of frozen food, if part of it melts due to temperature rise, the dielectric constant of the melted part rises sharply. Therefore, even if the frequency and output level of the microwaves are controlled, it is difficult to suppress the concentration of microwaves on the melted part of the frozen food. As a result, uneven heating occurs.

[0012] In the heating chamber of a microwave oven, microwaves tend to concentrate more on the portion of the object to be heated that is closer to the power supply than on other portions of the object to be heated. Therefore, even if the frequency and output level of the microwaves are controlled, it is difficult to suppress the concentration of microwaves on the thawed portion of the frozen food. As a result, uneven heating occurs.

[0013] An object of the present disclosure is to provide a microwave processing device that can heat an object to be heated more uniformly.

[0014] A microwave processing apparatus according to one embodiment of the present disclosure includes a heating chamber for accommodating an object to be heated, a microwave generating unit, an amplifying unit, a power supply unit, a detecting unit, a control unit, and a storage unit.

[0015] The microwave generating unit generates microwaves having any frequency in a predetermined frequency band. The amplifier amplifies the microwaves and outputs the amplified microwaves as incident power. The power supply unit supplies the incident power to the heating chamber. The detection unit detects the incident power and the reflected power returning from the heating chamber to the power supply unit. The storage unit stores the incident power and the reflected power in association with the frequency of the microwaves and the elapsed time from the start of heating.

[0016] The control unit causes the microwave generation unit to perform frequency sweep over a predetermined frequency band. The control unit controls the microwave generation unit and the amplifier based on incident power and reflected power detected during the frequency sweep.

[0017] According to this aspect, the uniformity of heating can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic configuration diagram showing an example of a microwave processing device according to an embodiment of the present disclosure.

[0019] Figure 2A This is a diagram schematically showing an example of temporal changes in the frequency, output level, and stop time of Example 1.

[0020] Figure 2B This is a diagram showing an example of the stop time set for each frequency in the first embodiment.

[0021] Figure 3 (a) is a diagram showing an example of the frequency characteristics of the reflection wave rate. Figure 3 (b) is a diagram showing an example of the stop time set for each frequency in the second embodiment.

[0022] Figure 4 (a) is a diagram showing an example of the frequency characteristics of the reflection wave rate and the set threshold value, Figure 4 (b) is a diagram showing an example of a stop time set for each frequency in consideration of a threshold value.

[0023] Figure 5A This is a diagram showing an example of temporal changes in the frequency, output level, and duty ratio of Example 4.

[0024] Figure 5B This is a diagram showing an example of a duty ratio set for each frequency according to the fourth embodiment.

[0025] Figure 6 (a) is a diagram showing an example of the frequency characteristics of the reflection wave rate. Figure 6 (b) is a diagram showing an example of a duty ratio set for each frequency in Example 5.

[0026] Figure 7 (a) is a diagram showing an example of the frequency characteristics of the reflection wave rate. Figure 7 (b) is a diagram showing an example of a duty ratio set for each frequency in consideration of a threshold value.

[0027] Figure 8 This is a diagram showing an example of temporal changes in the frequency and the reflection ratio of Example 7.

[0028] Fig. 9 This is a diagram showing an example of how the frequency and the reflection ratio change over time in Example 8.

[0029] Fig.10 This is a diagram showing an example of how the frequency and the reflection ratio change over time in Example 9.

[0030] Fig.11 It is a diagram showing an example of the frequency characteristics of the reflection factor and the set threshold value.

[0031] Fig.12 This is a diagram showing an example of the frequency characteristics of the reflection coefficient at each temperature in the heating chamber. DETAILED DESCRIPTION

[0032] (Insights that form the basis of this disclosure)

[0033] In the above-mentioned prior art, the frequency, output level and oscillation time of microwaves are controlled by taking the power absorbed by the heated object as an index. However, the prior art has limited effect on heating uniformity and cannot significantly suppress the local concentration of microwaves.

[0034] If the type, shape, size and placement of the heated object are limited, it is possible to achieve a certain effect on the uniformity of heating. However, it is difficult to apply the existing technology to actual cooking based on a microwave oven.

[0035] In order to heat the object to be heated more evenly, it is important to suppress the temperature difference in the food being heated. The inventors have come up with the following invention. The present invention controls the frequency, output level and oscillation time of microwaves based on the heat conduction of the object to be heated and the heat radiation from the surface of the object to be heated. As a result, the local temperature rise and the change of the local dielectric constant can be suppressed, and as a result, the object to be heated can be heated more evenly.

[0036] A microwave processing apparatus according to a first aspect of the present disclosure includes a heating chamber for accommodating an object to be heated, a microwave generating unit, an amplifying unit, a power supply unit, a detecting unit, a control unit, and a storage unit.

[0037] The microwave generating unit generates microwaves having any frequency in a predetermined frequency band. The amplifier amplifies the microwaves and outputs the amplified microwaves as incident power. The power supply unit supplies the incident power to the heating chamber. The detection unit detects the incident power and the reflected power returning from the heating chamber to the power supply unit. The storage unit stores the incident power and the reflected power in association with the frequency of the microwaves and the elapsed time from the start of heating.

[0038] The control unit causes the microwave generation unit to perform frequency sweep over a predetermined frequency band. The control unit controls the microwave generation unit and the amplifier based on incident power and reflected power detected during the frequency sweep.

[0039] In the microwave processing apparatus of the second aspect of the present disclosure, based on the first aspect, the control unit sets a stop time for stopping the output of the microwaves when changing the frequency of the microwaves. The control unit changes the stop time according to the frequency of the microwaves.

[0040] In the microwave processing apparatus of the third aspect of the present disclosure, based on the second aspect, the control unit calculates the reflection factor as the ratio of the reflected power to the incident power for each frequency in the frequency sweep. The lower the reflection factor, the longer the stop time is set by the control unit.

[0041] In the microwave processing apparatus of the fourth aspect of the present disclosure, based on the second aspect, the control unit calculates the reflection factor as the ratio of the reflected power to the incident power for each frequency in the frequency sweep, and does not set a stop time for microwaves of a frequency whose reflection factor exceeds a predetermined value.

[0042] In the microwave processing apparatus according to the fifth aspect of the present disclosure, based on the second aspect, the control unit changes the duty ratio in the output of the microwaves according to the frequency.

[0043] In the microwave processing apparatus of the sixth aspect of the present disclosure, based on the fifth aspect, the control unit calculates a reflection factor as a ratio of reflected power to incident power for each frequency in the frequency sweep. The higher the reflection factor, the higher the duty ratio is set by the control unit.

[0044] In the microwave processing apparatus of the seventh aspect of the present disclosure, based on the fifth aspect, the control unit calculates the reflection factor as the ratio of the reflected power to the incident power for each frequency in the frequency sweep, and sets the duty cycle to 100% for microwaves of a frequency whose reflection factor exceeds a predetermined value.

[0045] In the microwave processing apparatus of the eighth aspect of the present disclosure, based on the first aspect, the control unit causes the microwave generation unit to alternately generate microwaves of a frequency having a high reflection coefficient and microwaves of a frequency having a low reflection coefficient, wherein the reflection coefficient is a ratio of reflected power to incident power.

[0046] In a microwave processing device according to a ninth aspect of the present disclosure, based on the eighth aspect, the control unit causes the microwave generating unit to generate microwaves in descending order of frequency when the reflected wave coefficient is high. When the reflected wave coefficient is low, the control unit causes the microwave generating unit to generate microwaves in descending order of frequency.

[0047] In the microwave processing apparatus of the tenth aspect of the present disclosure, based on the first aspect, the control unit calculates the reflection factor as the ratio of the reflected power to the incident power for each frequency in the frequency sweep, and the control unit causes the microwave generation unit to generate microwaves in order from the frequency with the highest reflection factor.

[0048] In the microwave processing apparatus of the eleventh aspect of the present disclosure, based on the first aspect, the control unit calculates a reflection factor as a ratio of reflected power to incident power for each frequency in the frequency sweep, and controls the microwave generating unit to generate only microwaves of a frequency whose reflection factor exceeds a predetermined value.

[0049] In a microwave processing apparatus according to a twelfth aspect of the present disclosure, based on the eleventh aspect, the control unit causes the microwave generation unit to generate only microwaves having a frequency whose reflection factor exceeds a predetermined value from the start to the end of heating.

[0050] In the microwave processing apparatus according to a thirteenth aspect of the present disclosure, based on the eleventh aspect, the control unit calculates the reflected wave factor before the first half of the time from the start to the end of heating has passed.

[0051] In the microwave processing apparatus of the fourteenth aspect of the present disclosure, based on any one of the first to thirteenth aspects, the control unit causes the microwave generation unit to perform frequency sweep based on the temperature in the heating chamber to reset the frequency and output level of the microwaves as oscillation conditions of the microwaves.

[0052] In the microwave processing apparatus according to a fifteenth aspect of the present disclosure, based on the fourteenth aspect, the control unit causes the microwave generation unit to perform frequency sweep and reset the oscillation conditions of the microwaves every time the temperature in the heating chamber changes by a predetermined value.

[0053] In the microwave processing apparatus according to a sixteenth aspect of the present disclosure, based on the fourteenth aspect, the control unit causes the microwave generation unit to perform frequency sweep and reset the oscillation conditions of the microwaves every time the temperature of the heating chamber exceeds a predetermined temperature.

[0054] With such a configuration, the influence of the change in the resonance frequency in the heating chamber accompanying the temperature change in the heating chamber is reduced, and by determining the reset timing under certain conditions, more uniform heating can be performed stably.

[0055] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0056] Figure 1 1 is a schematic diagram showing an example of a microwave processing device according to an embodiment of the present invention. Figure 1 As shown, the microwave processing apparatus of the present embodiment includes a heating chamber 1 , a microwave generating unit 3 , an amplifying unit 4 , a power supply unit 5 , a detecting unit 6 , a control unit 7 , and a storage unit 8 .

[0057] The heating chamber 1 accommodates a heated object 2 such as food as a load. The microwave generating unit 3 is composed of a semiconductor element. The microwave generating unit 3 can generate microwaves of any frequency in a predetermined frequency band, and generates microwaves of a frequency specified by the control unit 7.

[0058] The amplifier 4 is composed of a semiconductor element and amplifies the microwaves generated by the microwave generating unit 3 according to the instruction of the control unit 7, and outputs the amplified microwaves.

[0059] The power supply unit 5 functions as an antenna, and supplies the microwaves amplified by the amplifier unit 4 as incident power to the heating chamber 1. That is, the power supply unit 5 supplies the incident power based on the microwaves generated by the microwave generating unit 3 to the heating chamber 1. The power of the incident power that is not consumed by the heated object 2 and the like becomes reflected power that returns to the power supply unit 5 from the heating chamber 1.

[0060] The detection unit 6 is constituted by, for example, a directional coupler. The detection unit 6 detects the amounts of incident power and reflected power, and notifies the control unit 7 of the information. That is, the detection unit 6 functions as both an incident power detection unit and a reflected power detection unit.

[0061] The detection unit 6 has a coupling degree of about -40 dB, for example, and extracts about 1 / 10000 of the incident power and the reflected power. The extracted incident power and reflected power are rectified by a detector diode (not shown), smoothed by a capacitor (not shown), and converted into information corresponding to the incident power and the reflected power. The control unit 7 receives this information.

[0062] The storage unit 8 is composed of a semiconductor memory or the like, stores data from the control unit 7, reads out the stored data, and transmits it to the control unit 7. In particular, the storage unit 8 stores the incident power and reflected power amounts detected by the detection unit 6 together with the frequency of the microwaves and the elapsed time from the start of heating.

[0063] The control unit 7 is composed of a microprocessor including a CPU (Central Processing Unit). The control unit 7 controls the microwave generating unit 3 and the amplifying unit 4 based on information from the detecting unit 6 and the storage unit 8, and performs cooking control in the microwave processing device.

[0064] The control unit 7 causes the microwave generating unit 3 to perform frequency sweep. Frequency sweep is an operation of the microwave generating unit 3 to sequentially change the frequency at predetermined frequency intervals over a predetermined frequency band. In the present embodiment, the predetermined frequency band is 2400 MHz to 2500 MHz.

[0065] After the frequency sweep, the control unit 7 selects a frequency for heating the heated object 2 from a predetermined frequency band. Specifically, the control unit 7 calculates a reflection wave factor as a ratio (%) of the reflected power to the incident power based on the values ​​of the incident power and the reflected power detected during the frequency sweep. The control unit 7 controls the oscillation frequency of the microwaves in the microwave generating unit 3 and the amplification factor of the microwaves in the amplifier 4 based on the reflection wave factor, and supplies microwaves of a frequency for heating to the heating chamber 1.

[0066] The inner wall of the heating chamber 1 repeatedly reflects the microwaves supplied to the heating chamber 1. The heating pattern for the object 2 to be heated in the heating chamber 1 is determined by the interference between the microwaves generated at this time.

[0067] The wavelength of microwaves changes according to the frequency. The change in the wavelength of microwaves changes the portion heated more strongly by the microwaves and the portion heated less strongly by the microwaves. Therefore, the interference between the repeatedly reflected microwaves changes, and the heating pattern also changes accordingly. That is, if the frequency and output level of the microwaves are appropriately controlled, the object 2 to be heated can be heated more uniformly.

[0068] Hereinafter, various control methods of the control unit 7 in the present embodiment will be described as Examples 1 to 11. At least two of the following Examples may be combined arbitrarily as long as they are not contradictory to each other.

[0069] (Example 1)

[0070] Example 1 of the present embodiment will be described. Figure 2A An example of temporal changes in the frequency, output level, and stop time of the microwaves in Example 1 is schematically shown. Figure 2BAn example of the stop time set for each microwave frequency in Example 1 is shown.

[0071] like Figure 2A As shown, in Example 1, when the frequency of the microwave is switched, the control unit 7 stops the output of the microwave from the microwave generating unit 3. In this embodiment, the period during which the microwave generating unit 3 outputs the microwave is called the output time, and the period during which the microwave generating unit 3 stops the output of the microwave is called the stop time.

[0072] Specifically, for example, Figure 2A As shown, the output times OT1 to OT5 are all 12 seconds. The stop times ST1, ST2, ST3, and ST4 are 6 seconds, 10 seconds, 2 seconds, and 15 seconds respectively. The frequencies F1, F2, F3, F4, and F5 are 2405 MHz, 2414 MHz, 2430 MHz, 2438 MHz, and 2445 MHz respectively.

[0073] According to this method, heat is transferred into the object to be heated 2 during the stop time, and heat is radiated from the surface of the object to be heated 2. Therefore, it is possible to reduce heating unevenness caused by the heating pattern based on the microwave of the frequency just before.

[0074] Thus, before starting to supply microwaves of the next frequency, the dielectric constant variation of the heated object 2 caused by uneven heating can be reduced. As a result, the microwaves can be prevented from concentrating on the portion of the heated object 2 where the dielectric constant increases, and the heating uniformity can be improved.

[0075] The heating pattern and heating unevenness change according to the frequency. The stop time for reducing heating unevenness varies according to each frequency.

[0076] like Figure 2B As shown, by changing the stop time according to the frequency of the microwave, the uniformity of heating can be improved. In Example 1, if the minimum necessary stop time is set, the cooking time can be prevented from being excessively prolonged. A low output time that greatly reduces the output level of the microwave can also be set instead of the stop time.

[0077] (Example 2)

[0078] Example 2 of this embodiment will be described. Figure 3 (a) shows an example of the frequency characteristics of the reflection coefficient. Figure 3 (b) shows an example of the stop time set for each microwave frequency in Example 2. As described above, the reflected wave rate refers to the ratio (%) of the reflected power to the incident power.

[0079] like Figure 3As shown in (a), generally, the reflection rate varies depending on the frequency. Most of the microwaves that do not return to the microwave generating unit 3 are dissipated in the object to be heated 2. However, a part of the microwaves are also dissipated in components of the microwave processing apparatus other than the object to be heated 2.

[0080] Such components include, for example, the inner wall of the heating chamber 1, a heater disposed in the heating chamber 1, components in the heating chamber 1 such as door glass, a waveguide, and an antenna (which correspond to the power supply unit 5), and the like.

[0081] As the reflected wave coefficient decreases, the microwaves in the object to be heated 2 are dissipated more. However, the microwaves are not necessarily dissipated uniformly in the entire object to be heated 2. That is, if the reflected wave coefficient decreases, there is a tendency for the heating unevenness of the object to be heated 2 to become larger.

[0082] Therefore, if Figure 3 (a) and Figure 3 As shown in (b), in Example 2, the control unit 7 makes Figure 3 The shape of the line graph of (b) is similar to Figure 3 The shape of the line graph of (a) is reversed vertically, that is, the stop time is set so that the stop time is inversely proportional to the reflected wave factor. According to Example 2, the uniformity of heating can be improved.

[0083] (Example 3)

[0084] Example 3 of this embodiment will be described. Figure 4 (a) shows an example of the frequency characteristics of the reflection wave ratio and the set threshold value. Figure 4 (b) means taking into account Figure 4 An example of the stop time set for each microwave frequency in the case of the threshold value shown in (a).

[0085] As the reflected wave rate increases, the dissipation of microwaves in the heated object 2 decreases. If the dissipation of microwaves in the entire heated object 2 decreases, the temperature of the heated object 2 will not rise locally. In other words, if the reflected wave rate increases, there is a tendency for the heating unevenness of the heated object 2 to decrease. Therefore, if the reflected wave rate exceeds a certain value, it is not necessary to set a stop time.

[0086] In the third embodiment, the control unit 7 sets the threshold value (refer to Figure 4 (a)), at a frequency where the reflected wave rate is higher than the threshold, the control unit 7 sets the stop time to zero (refer to Figure 4 (a) and Figure 4 (b)). According to Example 3, the uniformity of heating can be improved and the cooking time can be prevented from being excessively prolonged.

[0087] The threshold value needs to be set to different values ​​depending on the type and size of the object to be heated and the output level of the microwave. Experiments have shown that when the output level of the microwave is, for example, 250 W, if the threshold value is set within a specified range of the reflected wave rate (40% to 90%, 40% in Example 3), the uniformity of heating is improved.

[0088] If the microwave output level is increased while the frequency and the object 2 to be heated remain unchanged, the heating unevenness will increase. In order to suppress the heating unevenness, it is necessary to use only microwaves with a frequency having a larger reflection coefficient. Therefore, the control unit 7 sets the threshold value of the reflection coefficient to be larger in proportion to the output level.

[0089] (Example 4)

[0090] Example 4 of this embodiment will be described. Figure 5A An example of temporal changes in the frequency, output level, and duty ratio of microwaves in Example 4 is schematically shown. Figure 5B An example of the duty ratio set for each microwave frequency in Example 4 is shown. The duty ratio refers to the ratio (%) of the output time to the sum of the output time and the stop time.

[0091] In Embodiment 4, the control unit 7 performs duty ratio control in which a predetermined output time and stop time are set for each frequency. Duty ratio control refers to on-off control of microwave output at a predetermined or variable duty ratio.

[0092] For example, Figure 5A As shown, the duty ratio of the microwaves with frequency F2 is set to be larger than the duty ratio of the microwaves with frequency F1. The duty ratio of the microwaves with frequency F3 is set to be smaller than the duty ratio of the microwaves with frequency F1.

[0093] Specifically, the frequencies F1, F2, and F3 are 2405 MHz, 2414 MHz, and 2430 MHz, respectively. The magnitude of the microwaves of the frequency F2 may be set to be the same as that of the frequency F1, and the magnitude of the microwaves of the frequency F3 may be set to be larger than that of the frequency F1.

[0094] According to this method, during the stop time when the frequency is switched, heat is transferred inside the object 2 and heat is radiated from the surface of the object 2. Therefore, it is possible to reduce heating unevenness caused by the heating pattern based on the microwave of the frequency immediately before.

[0095] Thus, before starting to supply microwaves of the next frequency, the dielectric constant variation of the heated object 2 caused by uneven heating can be reduced. As a result, the microwaves can be prevented from concentrating on the portion of the heated object 2 where the dielectric constant increases, and the heating uniformity can be improved.

[0096] The heating mode and heating unevenness vary according to the frequency. The duty cycle for reducing heating unevenness varies according to each frequency. According to Example 4, Figure 5B As shown, by changing the duty ratio according to the frequency, the uniformity of heating can be improved. By not reducing the duty ratio excessively, the cooking time will not be unnecessarily extended.

[0097] Instead of the duty ratio control, the control unit 7 may cause the microwave generation unit 3 to alternately generate microwaves having a high output level and microwaves having a lower output level close to zero and having the same frequency at a predetermined time ratio.

[0098] (Example 5)

[0099] Example 5 of this embodiment will be described. Figure 6 (a) shows an example of the frequency characteristics of the reflection coefficient. Figure 6 (b) shows an example of the duty ratio set for each microwave frequency in Example 5.

[0100] like Figure 6 As shown in (a), generally, the reflection factor varies depending on the frequency. As the reflection factor decreases, the microwaves in the object 2 to be heated are dissipated more, and there is a tendency that the heating unevenness of the object 2 to be heated becomes larger.

[0101] In Example 5, Figure 6 (a) and Figure 6 As shown in (b), the control unit 7 makes Figure 6 The shape of the line graph of (b) is similar to Figure 6 The duty ratio is controlled in a manner that is the same as the shape of the line graph of (a), that is, the duty ratio is proportional to the reflected wave factor. According to Example 5, it is possible to reduce heating unevenness and improve heating uniformity.

[0102] (Example 6)

[0103] Example 6 of this embodiment is described. Figure 7 (a) shows an example of the frequency characteristics of the reflection wave ratio and the set threshold value. Figure 7 (b) means taking into account Figure 7 An example of a duty ratio set for each microwave frequency in the case of the threshold value shown in (a).

[0104] As the reflected wave index increases, the dissipation of microwaves in the heated object 2 decreases. If the dissipation of microwaves in the entire heated object 2 decreases, the temperature of the heated object 2 will not rise locally. That is, if the reflected wave index increases, there is a tendency for heating unevenness to decrease. In Example 6, the control unit 7 sets a threshold value, and when the reflected wave index exceeds the threshold value, the duty cycle control is stopped and the microwave generating unit 3 is always kept outputting microwaves.

[0105] For the threshold value set for the reflection ratio (refer to Figure 7 (a)) high frequency, the control unit 7 sets the duty cycle to 100% (refer to Figure 7 (a) and Figure 7 According to Example 6, the uniformity of heating can be improved and the cooking time will not be unnecessarily prolonged.

[0106] The threshold value must be a value that varies depending on the type and size of the object to be heated and the output level of the microwave. However, experiments have shown that when the output level of the microwave is, for example, 250 W, if the threshold value is set within a specified range of the reflected wave rate (40% to 90%, 40% in Example 6), the uniformity of heating is improved.

[0107] If the microwave output level is increased while the frequency and the object 2 to be heated remain unchanged, the heating unevenness will increase. In order to suppress the heating unevenness, it is necessary to use only microwaves with a frequency having a larger reflection coefficient. Therefore, the control unit 7 sets the threshold value of the reflection coefficient to be larger in proportion to the output level.

[0108] (Example 7)

[0109] Example 7 of this embodiment is described. Figure 8 An example of temporal changes in the frequency and reflection rate of microwaves in Example 7 is schematically shown.

[0110] As the reflected wave coefficient decreases, the microwaves in the object 2 to be heated dissipate more, and there is a tendency for the heating unevenness of the object 2 to become larger. As the reflected wave coefficient increases, the microwaves dissipate less, and there is a tendency for the heating unevenness to decrease.

[0111] like Figure 8 As shown, in Example 7, after heating by microwaves of frequency F1 starts, the control unit 7 causes the microwave generating unit 3 to switch the oscillation frequency to frequency F2 so as to reduce the reflected wave rate. Thereafter, the control unit 7 causes the microwave generating unit 3 to switch the oscillation frequency to frequency F3 so as to increase the reflected wave rate. The control unit 7 causes the microwave generating unit 3 to repeatedly perform this operation.

[0112] That is, the reflection rate of microwaves of frequency F2 is lower than the reflection rate of microwaves of frequency F1. The reflection rate of microwaves of frequency F3 is higher than the reflection rate of microwaves of frequency F2. The reflection rate of microwaves of frequency F4 is lower than the reflection rate of microwaves of frequency F3.

[0113] The reflection rate of microwaves of frequency F5 is higher than that of microwaves of frequency F4. The reflection rate of microwaves of frequency F6 is lower than that of microwaves of frequency F5. The reflection rate of microwaves of frequency F7 is higher than that of microwaves of frequency F6. The reflection rate of microwaves of frequency F8 is lower than that of microwaves of frequency F7.

[0114] Specifically, the frequencies F1, F2, F3, F4, F5, F6, F7, and F8 are 2405MHz, 2414MHz, 2430MHz, 2438MHz, 2445MHz, 2459MHz, 2483MHz, and 2499MHz, respectively.

[0115] According to Example 7, when heating is performed by microwaves of a frequency with a high reflection coefficient, heat is transferred inside the heated object 2, and heat is radiated from the surface of the heated object 2. As a result, heating unevenness caused by heating by microwaves of a frequency with a low reflection coefficient can be reduced. That is, the uniformity of heating is improved.

[0116] As described in Examples 1 to 3, the uniformity of heating is improved by setting the stop time when switching the frequency. On the other hand, Example 7 is effective not only for uniform heating but also for shortening the heating time.

[0117] (Example 8)

[0118] Example 8 of this embodiment is described. Fig. 9 An example of temporal changes in the frequency and reflection rate of microwaves in Example 8 is schematically shown.

[0119] In Example 8, Fig. 9 As shown, the control unit 7 causes the microwave generating unit 3 to switch the frequency of the microwaves in the same manner as in the seventh embodiment so that the reflected wave rate increases and decreases alternately.

[0120] In addition, the control unit 7 causes the microwave generation unit 3 to generate microwaves in order from the highest frequency for frequencies with higher reflection coefficients, and causes the microwave generation unit 3 to generate microwaves in order from the lowest frequency for frequencies with lower reflection coefficients.

[0121] That is, the control unit 7 causes the microwave generating unit 3 to perform the following operations. The microwave generating unit 3 generates microwaves of the frequency F1 with the lowest reflection coefficient, and then generates microwaves of the frequency F8 with the highest reflection coefficient. Thereafter, the microwave generating unit 3 generates microwaves of the frequency F3 with the second lowest reflection coefficient, and then generates microwaves of the frequency F6 with the second highest reflection coefficient.

[0122] Then, the microwave generating unit 3 generates microwaves of frequency F5 with the third lowest reflection coefficient, and then generates microwaves of frequency F4 with the third highest reflection coefficient. Then, the microwave generating unit 3 generates microwaves of frequency F7 with the fourth lowest reflection coefficient, and then generates microwaves of frequency F2 with the fourth highest reflection coefficient.

[0123] Specifically, the frequencies F1, F2, F3, F4, F5, F6, F7, and F8 are 2405MHz, 2414MHz, 2430MHz, 2438MHz, 2445MHz, 2459MHz, 2483MHz, and 2499MHz, respectively.

[0124] According to Example 8, it is possible to simplify control and improve heating uniformity. Simplification of control means reducing the number of parameters required to determine the output level and oscillation time of microwaves at each frequency and the order of generated frequencies.

[0125] In this method, heating with large heating unevenness and heating with small heating unevenness are performed alternately in order according to their degree. Thus, for example, when microwaves of the same output level are used at all frequencies, the heating time at each frequency can be made the same. As a result, the control can be further simplified.

[0126] (Example 9)

[0127] Example 9 of this embodiment is described. Fig.10 An example of the change of the microwave frequency and the reflected wave rate over time in Example 9 is schematically shown. Fig.10 As shown, the control unit 7 causes the microwave generation unit 3 to generate microwaves of a frequency having a higher reflection coefficient in order.

[0128] In Example 9, microwaves of frequencies F1 to F7 increase the reflection coefficient in this order and reduce heating unevenness. That is, the reflection coefficient of frequencies F1 to F4 is higher than the reflection coefficient of frequencies F5 to F7. When heating is performed using microwaves of a frequency with smaller heating unevenness, heat is transferred inside the heated object 2 and heat is radiated from the surface of the heated object 2.

[0129] Specifically, the frequencies F1, F2, F3, F4, F5, F6, and F7 are 2405MHz, 2414MHz, 2430MHz, 2438MHz, 2445MHz, 2459MHz, and 2483MHz, respectively.

[0130] As a result, the uneven heating that occurs when heating is performed using microwaves of a frequency with a relatively low reflection coefficient is reduced when heating is performed using microwaves of a frequency with a relatively high reflection coefficient. That is, the uniformity of heating is improved.

[0131] As described in Examples 1 to 3, compared with the control method of setting the stop time when switching the frequency, in Example 9, the heating time for each frequency is set shorter. Thereby, there is a tendency for the uniformity of heating to be improved.

[0132] This is because the longer the heating time per frequency is, the greater the heating unevenness is in the heating by microwaves of a frequency with a smaller reflection coefficient, and the protein is locally denatured.

[0133] (Example 10)

[0134] Example 10 of the present embodiment will be described. Fig.11 An example of the frequency characteristics of the reflection factor and the set threshold value is shown.

[0135] like Fig.11 As shown, in Example 10, the control unit 7 uses only microwaves of frequencies in the frequency bands (frequency bands FB1, FB2, FB3, and FB4) where the reflected wave rate is higher than a predetermined threshold value. This is to use only microwaves of frequencies with relatively small heating unevenness. Therefore, if this control is performed for a longer period of time, the uniformity of heating is improved accordingly.

[0136] The threshold value needs to be set to different values ​​depending on the type and size of the object to be heated and the output level of the microwave. However, experiments have shown that when the output level of the microwave is, for example, 250 W, if the threshold value is set within a specified range of the reflected wave rate (40% to 90%, 40% in Example 10), the uniformity of heating is improved.

[0137] If the microwave output level is increased while the frequency and the object 2 to be heated remain unchanged, the heating unevenness will increase. In order to suppress the heating unevenness, it is necessary to use only microwaves with a frequency having a larger reflection coefficient. Therefore, the control unit 7 sets the threshold value of the reflection coefficient to be larger in proportion to the output level.

[0138] The control unit 7 uses only microwaves of a frequency having a reflection factor higher than a threshold value from the start to the end of the operation of the microwave generating unit 3, that is, from the start to the end of heating. Thereby, the uniformity of heating is further improved.

[0139] If only microwaves of a frequency having a reflection factor higher than a threshold value are used from the start to the end of heating, and this control is performed during at least an arbitrary time in the first half of heating, the uniformity of heating is improved.

[0140] This is because the heating unevenness can be suppressed in the initial stage of heating which has a great influence on the heating unevenness at the end of heating. If the heating unevenness is large in the initial stage of heating, the microwaves are locally concentrated on the part with high dielectric constant of the heated object 2 during the long period until the end of heating.

[0141] (Example 11)

[0142] Example 11 of the present embodiment will be described. Fig.12 An example of the frequency characteristics of the reflection coefficient at each temperature in the heating chamber 1 is shown.

[0143] like Fig.12 As shown, the frequency characteristic of the reflection factor changes according to the temperature of the heating chamber 1. Specifically, as the temperature of the heating chamber 1 rises, the frequency characteristic of the reflection factor shifts to the left side with a lower frequency while substantially maintaining its waveform.

[0144] This is because the resonance frequency of the microwaves in the heating chamber 1 decreases as the temperature in the heating chamber 1 increases. One reason for this phenomenon is that the metal of the wall of the heating chamber 1 expands and the volume in the heating chamber 1 increases slightly. Another reason is that the compression rate of the wavelength of the microwaves in the door glass increases due to the increase in the dielectric constant of the door glass.

[0145] For example, such a state is produced in oven heating or the like using radiation heating and convection heating, unlike microwaves.

[0146] Therefore, the control unit 7 performs frequency sweep based on the temperature of the heating chamber 1 to reacquire the frequency characteristics of the reflected wave factor. The control unit 7 resets the microwave oscillation conditions based on the frequency characteristics of the reflected wave factor.

[0147] The oscillation conditions refer to the frequency and output level of the microwaves. The control unit 7 causes the microwave generation unit 3 to change the frequency of the microwaves and the amplifier 4 to change the output level of the microwaves, thereby resetting the oscillation conditions. This can improve the uniformity of the treatment.

[0148] exist Fig.12 In the three graphs shown, the temperature rise in the heating chamber 1 is substantially the same, and the frequency characteristics of the reflected wave factor are shifted to the left by substantially the same frequency in accordance with the temperature rise. Therefore, the control unit 7 performs a frequency scan every time the temperature of the heating chamber 1 changes by a predetermined value, reacquires the frequency characteristics of the reflected wave factor, and resets the microwave oscillation conditions. This can improve the uniformity of heating.

[0149] The degree of temperature change in the heating chamber 1 indicating the timing at which the frequency characteristics of the reflected wave factor should be reacquired depends on the shape of the heating chamber 1 , the material of the wall surface, the type and size of the object 2 to be heated, and the like. Fig.12 The frequency characteristics shown were measured under the following three conditions: (1) The volume of the heating chamber 1 was 50 liters. (2) The wall surface was an enameled steel plate. (3) No object 2 to be heated was placed in the heating chamber 1.

[0150] exist Fig.12In the case of the frequency characteristics shown, the frequency characteristics of the reflected wave rate should be re-acquired at intervals of 100° C. at most, preferably 20° C., in consideration of the degree of the shift.

[0151] The control unit 7 can re-acquire the frequency characteristics of the reflected wave factor and reset the microwave oscillation conditions each time the temperature in the heating chamber 1 exceeds or falls below the specified temperature. In other words, the case where the temperature in the heating chamber 1 exceeds or falls below the specified temperature means that the temperature in the heating chamber 1 passes the specified temperature.

[0152] By clearly defining the conditions indicating the reset timing, it is possible to reduce the influence of the change in the resonance frequency in the heating chamber 1 accompanying the temperature change in the heating chamber 1. As a result, more uniform heating can be performed stably.

[0153] The temperature of the heating chamber 1 for re-acquiring the frequency characteristics of the reflected wave factor is preferably set to half the set temperature in oven heating using radiation heating and convection heating. The temperature may be half the difference between the set temperature and room temperature.

[0154] In Examples 1 to 11, the control unit 7 may use the dissipation rate of microwaves in the heating chamber 1 instead of the reflected wave rate. The dissipation rate of microwaves in the heating chamber 1 refers to the ratio (%) of the difference between incident power and reflected power to the incident power.

[0155] The control unit 7 can estimate the dissipation of microwaves in the components in the heating chamber 1 such as the inner wall of the heating chamber 1, the heater, the door glass, and the transmission path, and correct the reflected wave factor based on the estimated value.

[0156] The control unit 7 may estimate the dissipation of microwaves in the object 2 based on the temperature of the object 2 obtained by using an infrared sensor or the like, and use this value instead of the reflected wave rate.

[0157] Industrial Applicability

[0158] The microwave processing device according to the present disclosure can be applied to a drying device, a ceramic heating device, a household garbage disposal device, a semiconductor manufacturing device, a chemical reaction device, and the like in addition to the above-mentioned heating cooker.

[0159] Description of Reference Numerals

[0160] 1: Heating chamber; 2: Object to be heated; 3: Microwave generating unit; 4: Amplifying unit; 5: Power supply unit; 6: Detecting unit; 7: Control unit; 8: Storage unit.

Claims

1. A microwave processing device, wherein: The microwave processing device comprises: A heating chamber configured to accommodate an object to be heated; A microwave generating unit capable of operating in the following manner: generating microwaves having any frequency in a predetermined frequency band; an amplifier capable of operating in the following manner: amplifying the microwave and outputting the amplified microwave as incident power; a power supply unit configured to supply the incident power to the heating chamber; a detection unit operable to detect the incident power and the reflected power returning from the heating chamber to the power supply unit; A control unit capable of operating in the following manner: controlling the microwave generating unit and the amplifying unit; as well as a storage unit operable to store the incident power and the reflected power together with the frequency of the microwave and the elapsed time from the start of heating, The control unit is operable to cause the microwave generating unit to perform frequency sweep over the predetermined frequency band, and the control unit is operable to control the microwave generating unit and the amplifier based on the incident power and the reflected power detected during the frequency sweep. The control unit can operate in the following manner: calculate the reflection wave factor as the ratio of the reflected power to the incident power related to each of the frequencies in the frequency scan, set a stop time for stopping the output of the microwave when changing the frequency of the microwave, and change the stop time in a manner in which the stop time is inversely proportional to the reflection wave factor.

2. The microwave processing device according to claim 1, wherein: The control unit may operate so as not to set the stop time for the microwaves of the frequency having the reflected wave index exceeding a predetermined value.

3. The microwave processing device according to claim 1, wherein: The control unit may operate to change a duty ratio in output of the microwave according to the frequency.

4. The microwave processing device according to claim 3, wherein: The control unit is configured to set the duty ratio to be higher as the reflected wave rate is higher.

5. The microwave processing device according to claim 3, wherein: The control unit may be operated so as to set the duty ratio to 100% for the microwave of the frequency for which the reflected wave factor exceeds a predetermined value.

6. The microwave processing device according to claim 1, wherein: The control unit may be operated so as to cause the microwave generation unit to alternately generate the microwaves of the frequency having a high reflection coefficient and the microwaves of the frequency having a low reflection coefficient.

7. The microwave processing device according to claim 6, wherein: The control unit can operate in the following manner: when the frequency has a high reflection coefficient, the microwave generating unit can generate the microwaves in the order of the frequencies from high to low, and when the frequency has a low reflection coefficient, the microwave generating unit can generate the microwaves in the order of the frequencies from low to high.

8. The microwave processing device according to claim 1, wherein: The control unit may operate to cause the microwave generation unit to perform the frequency sweep based on the temperature of the heating chamber, and to reset the frequency and output level of the microwaves as oscillation conditions of the microwaves.

9. The microwave processing device according to claim 8, wherein: The control unit may be operable to cause the microwave generation unit to perform the frequency sweep and reset the oscillation condition of the microwave every time the temperature of the heating chamber changes by a predetermined value.

10. The microwave processing device according to claim 8, wherein: The control unit may operate to cause the microwave generation unit to perform the frequency sweep and reset the oscillation condition of the microwave every time the temperature of the heating chamber exceeds a predetermined temperature.

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