Microwave Processing Equipment

Abstract

The microwave treatment device of an embodiment of the present disclosure is provided with a heating chamber, a microwave generation unit, an amplification unit, a power supply unit, a detection unit, a storage unit, and a control unit. The microwave generation unit generates microwaves having an arbitrary frequency within a predetermined frequency band. The amplification unit 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 incident power and reflected power returned 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 time elapsed since the start of heating. The control unit causes the microwave generation unit to perform frequency sweep over the predetermined frequency band. The control unit controls the microwave generation unit and the amplification unit on the basis of the incident power and the reflected power detected during the frequency sweep. According to the present embodiment, uniformity of heating can be improved.

Description

[Technical field]

[0001] The present disclosure relates to a microwave treatment device having a microwave generation unit. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there has been known a microwave processing apparatus that has a semiconductor oscillation element and controls the frequency and output level of microwaves to heat an object more uniformly (see, for example, 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 microwave wave and the reflected microwave wave. Conventional microwave processing devices adjust the microwave output level and oscillation time at each frequency based on this information to achieve uniform heating.

[0004] When the microwave frequency is changed, the microwave distribution in the heating chamber, i.e., the heating pattern for the heated object, changes. For this reason, in conventional microwave processing devices, it is important to make the power absorbed by the heated object at each frequency equal.

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

[0006] The conventional technique takes into account the microwave transmission path and the microwave dissipation on the walls of the heating chamber, which can improve the accuracy of the estimation of the power absorbed in the heated object at each frequency. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2009-527883 Summary of the Invention

[0008] However, even if the technology described in Patent Document 1 is applied to a microwave oven, it is difficult to achieve sufficient heating uniformity in actual cooking.

[0009] When food is heated in a microwave oven, the dielectric constant of the food changes with the temperature. In particular, in the case of frozen food, when a part of the food melts due to an increase in temperature, the dielectric constant of the melted part rises rapidly. For this reason, even if the microwave frequency and output level are controlled, it is difficult to prevent the microwaves from concentrating on the melted part of the frozen food. As a result, uneven heating occurs.

[0010] In the heating chamber of a microwave oven, microwaves tend to concentrate more on the parts of the object to be heated that are closer to the power supply than on other parts. Therefore, even if the microwave frequency and output level are controlled, it is difficult to prevent the microwaves from concentrating on the melting parts of the frozen food. As a result, uneven heating occurs.

[0011] An object of the present disclosure is to provide a microwave processing apparatus capable of heating an object to be heated more uniformly.

[0012] A microwave processing device according to one 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 memory unit.

[0013] The microwave generating unit generates microwaves having any frequency in a predetermined frequency band. The amplifying unit amplifies the microwaves and outputs the amplified microwaves as incident power. The power feeding unit feeds the incident power to the heating chamber. The detecting unit detects the incident power and the reflected power returning from the heating chamber to the power feeding unit. The memory unit stores the incident power and the reflected power in association with the microwave frequency and the elapsed time from the start of heating.

[0014] The control unit causes the microwave generating unit to perform a frequency sweep over a predetermined frequency band, and controls the microwave generating unit and the amplifying unit based on the incident power and the reflected power detected during the frequency sweep.

[0015] According to this aspect, the uniformity of heating can be improved. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic configuration diagram illustrating an example of a microwave processing apparatus according to an embodiment of the present disclosure. [Figure 2A] FIG. 2A is a diagram illustrating an example of temporal changes in frequency, output level, and stop time according to the first embodiment. [Figure 2B] FIG. 2B is a diagram illustrating an example of a stop time set for each frequency according to the first embodiment. [Diagram 3] FIG. 3A is a diagram showing an example of frequency characteristics of a reflected wave rate, and FIG. 3B is a diagram showing an example of a stop time set for each frequency according to the second embodiment. [Figure 4] FIG. 4 is a diagram showing (a) an example of the frequency characteristics of the reflected wave rate and a set threshold value, and (b) an example of the stop time set for each frequency when the threshold value is taken into consideration. [Figure 5A] FIG. 5A is a diagram illustrating an example of changes over time in frequency, output level, and duty ratio according to the fourth embodiment. [Figure 5B] FIG. 5B is a diagram illustrating an example of a duty ratio set for each frequency according to the fourth embodiment. [Figure 6] FIG. 6A is a diagram showing an example of frequency characteristics of a reflected wave rate, and FIG. 6B is a diagram showing an example of a duty ratio set for each frequency according to the fifth embodiment. [Figure 7] FIG. 7A is a diagram showing an example of frequency characteristics of a reflected wave rate, and FIG. 7B is a diagram showing an example of a duty ratio set for each frequency when a threshold value is taken into consideration. [Figure 8]FIG. 8 is a diagram showing an example of the change over time of the frequency and the reflected wave rate according to the seventh embodiment. [Figure 9] FIG. 9 is a diagram showing an example of the change over time of the frequency and the reflected wave rate according to the eighth embodiment. [Figure 10] FIG. 10 is a diagram showing an example of the change over time in frequency and reflected wave rate according to the ninth embodiment. [Figure 11] FIG. 11 is a diagram illustrating an example of the frequency characteristic of the reflected wave rate and a set threshold value. [Figure 12] FIG. 12 is a diagram showing an example of frequency characteristics of the reflected wave rate at each temperature in the heating chamber. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] (Findings on which this disclosure is based) In the above-mentioned conventional technology, the microwave frequency, output level, and oscillation time are controlled using the power absorbed by the object to be heated as an index. However, the conventional technology has a limited effect on the uniformity of heating and does not significantly suppress localized concentration of microwaves.

[0018] Although it may be possible to achieve a certain degree of uniformity in heating by imposing certain restrictions on the type, shape, size, and location of the object to be heated, it is difficult to apply such conventional technology to actual cooking using a microwave oven.

[0019] In order to heat an object more uniformly, it is important to suppress the temperature difference within the food being heated. The inventors came up with the following invention. This invention controls the frequency, output level, and oscillation time of microwaves based on the thermal conduction of the object and the thermal radiation from the surface of the object. This suppresses local temperature rises and local changes in dielectric constant, and as a result, the object can be heated more uniformly.

[0020] A microwave processing device 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 supplying unit, a detecting unit, a control unit, and a storage unit.

[0021] The microwave generating unit generates microwaves having any frequency in a predetermined frequency band. The amplifying unit amplifies the microwaves and outputs the amplified microwaves as incident power. The power feeding unit feeds the incident power to the heating chamber. The detecting unit detects the incident power and the reflected power returning from the heating chamber to the power feeding unit. The memory unit stores the incident power and the reflected power in association with the microwave frequency and the elapsed time from the start of heating.

[0022] The control unit causes the microwave generating unit to perform a frequency sweep over a predetermined frequency band, and controls the microwave generating unit and the amplifying unit based on the incident power and the reflected power detected during the frequency sweep.

[0023] In a microwave processing device according to a second aspect of the present disclosure, based on the first aspect, the control unit sets a stop time for stopping the output of the microwave when changing the microwave frequency. The control unit changes the stop time according to the microwave frequency.

[0024] In the microwave processing device according to the third aspect of the present disclosure, based on the second aspect, the control unit calculates a reflection rate, which is a ratio of reflected power to incident power for each frequency in the frequency sweep. The control unit sets the stop time to be longer as the reflection rate is lower.

[0025] In the microwave processing device according to the fourth aspect of the present disclosure, based on the second aspect, the control unit calculates a reflection rate, which is a ratio of reflected power to incident power for each frequency in the frequency sweep. The control unit does not set a stop time for microwaves of a frequency at which the reflection rate exceeds a predetermined value.

[0026] In a microwave processing device according to a fifth aspect of the present disclosure, based on the second aspect, the control unit changes a duty ratio in the output of the microwave according to the frequency.

[0027] In a microwave processing device according to a sixth aspect of the present disclosure, based on the fifth aspect, the control unit calculates a reflected wave ratio, which is a ratio of reflected power to incident power for each frequency in the frequency sweep. The control unit sets a duty ratio higher as the reflected wave ratio is higher.

[0028] In a microwave processing device according to a seventh aspect of the present disclosure, based on the fifth aspect, the control unit calculates a reflected wave ratio, which is a ratio of reflected power to incident power for each frequency in the frequency sweep. The control unit sets a duty ratio of 100% for microwaves having a frequency at which the reflected wave ratio exceeds a predetermined value.

[0029] In a microwave processing device of an eighth aspect of the present disclosure, based on the first aspect, the control unit causes the microwave generating unit to alternately generate microwaves of a frequency having a higher reflectivity, which is the ratio of reflected power to incident power, and microwaves of a frequency having a lower reflectivity.

[0030] 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 ascending order of frequency when the frequency has a higher reflectivity, and the control unit causes the microwave generating unit to generate microwaves in descending order of frequency when the frequency has a lower reflectivity.

[0031] In a microwave processing device according to a tenth aspect of the present disclosure, based on the first aspect, the control unit calculates a reflection rate, which is a ratio of reflected power to incident power for each frequency in a frequency sweep. The control unit controls the microwave generating unit to generate microwaves in order from the frequency with the highest reflection rate.

[0032] In a microwave processing device according to an eleventh aspect of the present disclosure, based on the first aspect, the control unit calculates a reflection rate, which is a ratio of reflected power to incident power for each frequency in a frequency sweep, and causes the microwave generating unit to generate only microwaves having frequencies at which the reflection rate exceeds a predetermined value.

[0033] In a microwave processing device of a twelfth aspect of the present disclosure, based on the eleventh aspect, the control unit causes the microwave generating unit to generate only microwaves having a frequency at which the reflected wave rate exceeds a predetermined value, from the start to the end of heating.

[0034] In a microwave processing device according to a thirteenth aspect of the present disclosure, based on the eleventh aspect, the control unit calculates the reflected wave rate during the first half of the time from the start to the end of heating.

[0035] In a microwave processing device of a fourteenth aspect of the present disclosure, based on any one of the first to thirteenth aspects, the control unit causes the microwave generating unit to perform a frequency sweep based on the temperature inside the heating chamber, and resets the microwave frequency and output level, which are the microwave oscillation conditions.

[0036] In a microwave processing device of a fifteenth aspect of the present disclosure, based on the fourteenth aspect, the control unit causes the microwave generating unit to perform a frequency sweep and resets the microwave oscillation conditions each time the temperature inside the heating chamber changes by a predetermined value.

[0037] In a microwave processing device of a sixteenth aspect of the present disclosure, based on the fourteenth aspect, the control unit causes the microwave generating unit to perform a frequency sweep and resets the microwave oscillation conditions each time the temperature of the heating chamber passes a predetermined temperature.

[0038] With this configuration, the influence of changes in the resonant frequency within the heating chamber due to temperature changes within the heating chamber is reduced, and by determining the timing of resetting under certain conditions, stable and more uniform heating is possible.

[0039] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0040] Fig. 1 is a schematic diagram showing an example of a microwave processing device according to an embodiment of the present disclosure. As shown in Fig. 1, the microwave processing device according to 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.

[0041] The heating chamber 1 accommodates an object to be heated 2, such as food, which is a load. The microwave generating unit 3 is composed of a semiconductor element. The microwave generating unit 3 can generate microwaves of any frequency within a predetermined frequency band, and generates microwaves of a frequency specified by the control unit 7.

[0042] The amplifier 4 is composed of a semiconductor element. The amplifier 4 amplifies the microwave generated by the microwave generator 3 in response to an instruction from the controller 7, and outputs the amplified microwave.

[0043] 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 incident power based on the microwaves generated by the microwave generation unit 3 to the heating chamber 1. Of the incident power, the power that is not consumed by the object to be heated 2 or the like becomes reflected power that returns from the heating chamber 1 to the power supply unit 5.

[0044] The detector 6 is composed of, for example, a directional coupler. The detector 6 detects the amount of incident power and reflected power, and notifies the control unit 7 of the information. That is, the detector 6 functions as both an incident power detector and a reflected power detector.

[0045] The detector 6 has a degree of coupling of, for example, about -40 dB, and extracts about 1 / 10,000 of the incident power and 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 reflected power. The controller 7 receives this information.

[0046] 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 amount of incident power and reflected power detected by the detection unit 6, together with the microwave frequency and the elapsed time from the start of heating.

[0047] 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 detection unit 6 and the storage unit 8, and executes cooking control in the microwave processing device.

[0048] The control unit 7 causes the microwave generating unit 3 to perform frequency sweeping. Frequency sweeping is an operation of the microwave generating unit 3 to change the frequency in sequence at predetermined frequency intervals across a predetermined frequency band. In this embodiment, the predetermined frequency band is 2400 MHz to 2500 MHz.

[0049] After the frequency sweep, the control unit 7 selects a frequency to be used for heating the object 2 from a predetermined frequency band. Specifically, the control unit 7 calculates a reflected wave rate, which is the ratio (%) of reflected power to incident power, based on the values ​​of incident power and reflected power detected during the frequency sweep. Based on the reflected wave rate, the control unit 7 controls the oscillation frequency of the microwave in the microwave generation unit 3 and the amplification rate of the microwave in the amplification unit 4 to supply microwaves of a frequency for heating to the heating chamber 1.

[0050] 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 that occurs at this time.

[0051] The wavelength of microwaves changes depending on the frequency. The change in microwave wavelength changes the areas that are strongly heated by the microwaves and the areas that are weakly heated. This causes a change in the interference between the repeatedly reflected microwaves, and therefore a change in the heating pattern. In other words, by appropriately controlling the frequency and output level of the microwaves, the object 2 to be heated can be heated more uniformly.

[0052] Various control methods by the control unit 7 in this embodiment will be described below as Examples 1 to 11. At least two of the following examples may be arbitrarily combined as long as they are not contradictory to each other.

[0053] Example 1 Example 1 of the present embodiment will be described. Fig. 2A shows an example of a change over time in the microwave frequency, output level, and stop time according to Example 1. Fig. 2B shows an example of a stop time set for each microwave frequency according to Example 1.

[0054] 2A, in Example 1, when switching the microwave frequency, the control unit 7 stops the output of microwaves by the microwave generation unit 3. In the present embodiment, the period during which the microwave generation unit 3 outputs microwaves is called an output time, and the period during which the microwave generation unit 3 stops outputting microwaves is called a stop time.

[0055] Specifically, for example, as shown in Fig. 2A, 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.

[0056] According to this method, heat is transferred into the object 2 during the pause time, and heat is radiated from the surface of the object 2. Therefore, it is possible to reduce uneven heating caused by the heating pattern of the microwave of the immediately preceding frequency.

[0057] In this way, the unevenness of the dielectric constant of the object 2 caused by the uneven heating can be reduced before the supply of microwaves of the next frequency starts. As a result, the concentration of microwaves on the part of the object 2 with an increased dielectric constant can be suppressed, and the uniformity of heating can be improved.

[0058] The heating pattern and heating unevenness change depending on the frequency. The downtime to reduce the heating unevenness differs depending on the frequency.

[0059] As shown in Fig. 2B, the uniformity of heating can be improved by changing the stop time according to the microwave frequency. In the first embodiment, by setting the minimum necessary stop time, the cooking time can be prevented from being longer than necessary. Instead of the stop time, a low output time in which the microwave output level is significantly reduced may be provided.

[0060] Example 2 Example 2 of this embodiment will be described. Fig. 3(a) shows an example of frequency characteristics of reflected wave rate. Fig. 3(b) shows an example of a stop time set for each microwave frequency according to Example 2. As described above, the reflected wave rate is the ratio (%) of reflected power to incident power.

[0061] As shown in (a) of Fig. 3, the reflectivity generally varies depending on the frequency. Most of the microwaves that do not return to the microwave generating unit 3 are dissipated in the object 2. However, some of the microwaves are also dissipated in components of the microwave processing device other than the object 2.

[0062] The parts include, for example, the inner wall of the heating chamber 1, a heater arranged in the heating chamber 1, parts 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.

[0063] As the reflection rate decreases, the microwave dissipation in the object 2 increases. However, the microwave does not necessarily dissipate uniformly throughout the object 2. In other words, as the reflection rate decreases, the heating unevenness of the object 2 tends to increase.

[0064] For this reason, as shown in Fig. 3(a) and Fig. 3(b), in Example 2, the control unit 7 sets the stop time so that the shape of the graph in Fig. 3(b) is upside down from the shape of the graph in Fig. 3(a), that is, so that the stop time is inversely proportional to the reflected wave rate. According to Example 2, it is possible to improve the uniformity of heating.

[0065] Example 3 Example 3 of this embodiment will be described. Fig. 4(a) shows an example of the frequency characteristic of the reflected wave rate and a set threshold value. Fig. 4(b) shows an example of the stop time set for each microwave frequency when the threshold value shown in Fig. 4(a) is taken into consideration.

[0066] As the reflected wave rate increases, the microwave dissipation in the object 2 decreases. If the microwave dissipation in the entire object 2 decreases, the temperature of the object 2 does not rise locally. In other words, as the reflected wave rate increases, there is a tendency for uneven heating of the object 2 to decrease. For this reason, once the reflected wave rate exceeds a certain value, there is no need to provide a stop time.

[0067] In the third embodiment, the control unit 7 sets a threshold value (see FIG. 4(a)), and at frequencies where the reflected wave rate is higher than the threshold value, the control unit 7 sets the stop time to zero (see FIG. 4(a) and FIG. 4(b)). According to the third embodiment, it is possible to improve the uniformity of heating and prevent the cooking time from being longer than necessary.

[0068] This threshold value must be set to a different value depending on the type and size of the object to be heated and the microwave output level. Experiments have shown that when the microwave output level is, for example, 250 W, setting the threshold value within a certain range of the reflected wave rate (40% to 90%, 40% in Example 3) improves the uniformity of heating.

[0069] When the frequency and the object to be heated 2 are unchanged, increasing the microwave output level increases the heating unevenness. In order to suppress the heating unevenness, it is necessary to use only microwaves with frequencies that have a higher reflected wave rate. Therefore, the control unit 7 sets the threshold value of the reflected wave rate to a large value in proportion to the output level.

[0070] Example 4 Example 4 of the present embodiment will be described. Fig. 5A shows an example of a change over time in the microwave frequency, output level, and duty ratio according to Example 4. Fig. 5B shows an example of a duty ratio set for each microwave frequency according to Example 4. The duty ratio is the ratio (%) of the output time to the sum of the output time and the stop time.

[0071] In the fourth embodiment, the control unit 7 performs duty control in which a predetermined output time and stop time are set for each frequency. The duty control is an on / off control of the microwave output with a predetermined or variable duty ratio.

[0072] For example, as shown in Fig. 5A, the duty ratio for microwaves of frequency F2 is set to be larger than the duty ratio for microwaves of frequency F1, and the duty ratio for microwaves of frequency F3 is set to be smaller than the duty ratio for microwaves of frequency F1.

[0073] Specifically, the frequencies F1, F2, and F3 are 2405 MHz, 2414 MHz, and 2430 MHz, respectively. The magnitude of the microwave of the frequency F2 may be set to be the same as that of the frequency F1, and the magnitude of the microwave of the frequency F3 may be set to be greater than that of the frequency F1.

[0074] According to this method, during the downtime when switching the frequency, heat is transferred into the object 2 and radiated from the surface of the object 2. Therefore, it is possible to reduce uneven heating caused by the heating pattern of the microwave of the immediately previous frequency.

[0075] In this way, the unevenness of the dielectric constant of the object 2 caused by the uneven heating can be reduced before the supply of microwaves of the next frequency starts. As a result, the concentration of microwaves on the part of the object 2 with an increased dielectric constant can be suppressed, and the uniformity of heating can be improved.

[0076] The heating pattern and heating unevenness change depending on the frequency. The duty ratio for reducing heating unevenness differs for each frequency. According to the fourth embodiment, as shown in FIG. 5B, the heating uniformity can be improved by changing the duty ratio according to the frequency. By not lowering the duty ratio more than necessary, the cooking time can be prevented from becoming longer than necessary.

[0077] Instead of duty control, the control unit 7 may cause the microwave generating unit 3 to alternately generate microwaves of a high output level and a lower output level close to zero having the same frequency at a predetermined time ratio.

[0078] Example 5 Example 5 of the present embodiment will be described. Fig. 6(a) shows an example of frequency characteristics of reflected wave rate. Fig. 6(b) shows an example of duty ratios set for each microwave frequency according to Example 5.

[0079] As shown in (a) of Fig. 6, the reflectivity generally varies depending on the frequency. As the reflectivity decreases, the microwave dissipation in the object 2 increases, and the object 2 tends to be heated more unevenly.

[0080] In the fifth embodiment, as shown in (a) and (b) of Fig. 6, the control unit 7 performs duty control so that the shape of the graph in (b) of Fig. 6 becomes the same as the shape of the graph in (a) of Fig. 6, that is, so that the duty ratio is proportional to the reflected wave rate. According to the fifth embodiment, it is possible to reduce uneven heating and improve the uniformity of heating.

[0081] Example 6 Example 6 of the present embodiment will be described. Fig. 7(a) shows an example of the frequency characteristic of the reflected wave rate and a set threshold value. Fig. 7(b) shows an example of the duty ratio set for each microwave frequency when the threshold value shown in Fig. 7(a) is taken into consideration.

[0082] As the reflected wave rate increases, the microwave dissipation in the object 2 decreases. If the microwave dissipation in the entire object 2 decreases, the temperature of the object 2 does not rise locally. In other words, as the reflected wave rate increases, there is a tendency for uneven heating to decrease. In the sixth embodiment, the control unit 7 sets a threshold value, and when the reflected wave rate exceeds the threshold value, the control unit 7 stops the duty control and causes the microwave generating unit 3 to continue to output microwaves.

[0083] For frequencies with a reflected wave rate higher than the set threshold (see FIG. 7(a)), the control unit 7 sets the duty ratio to 100% (see FIG. 7(a) and FIG. 7(b)). According to the sixth embodiment, it is possible to improve the uniformity of heating and prevent cooking time from becoming longer than necessary.

[0084] This threshold value must vary depending on the type and size of the object to be heated and the microwave output level. However, experiments have shown that when the microwave output level is, for example, 250 W, setting the threshold value within a certain range of the reflected wave rate (40% to 90%, 40% in Example 6) improves the uniformity of heating.

[0085] When the frequency and the object to be heated 2 are unchanged, increasing the microwave output level increases the heating unevenness. In order to suppress the heating unevenness, it is necessary to use only microwaves with frequencies that have a higher reflected wave rate. Therefore, the control unit 7 sets the threshold value of the reflected wave rate to a large value in proportion to the output level.

[0086] Example 7 Example 7 of the present embodiment will be described below. Fig. 8 shows a schematic diagram of an example of the change over time in the microwave frequency and the reflected wave rate according to Example 7.

[0087] As the reflection rate decreases, the microwave dissipation in the object 2 increases, and there is a tendency for uneven heating of the object 2 to increase. As the reflection rate increases, the microwave dissipation decreases, and there is a tendency for uneven heating to decrease.

[0088] 8, in Example 7, after the start of heating with microwaves of frequency F1, the control unit 7 causes the microwave generating unit 3 to switch the oscillation frequency to frequency F2 so that the reflected wave rate decreases. Thereafter, the control unit 7 causes the microwave generating unit 3 to switch the oscillation frequency to frequency F3 so that the reflected wave rate increases. The control unit 7 causes the microwave generating unit 3 to repeatedly execute this operation.

[0089] That is, the microwave of frequency F2 has a lower reflectance than the microwave of frequency F1. The microwave of frequency F3 has a higher reflectance than the microwave of frequency F2. The microwave of frequency F4 has a lower reflectance than the microwave of frequency F3.

[0090] The microwave of frequency F5 has a higher reflectivity than the microwave of frequency F4. The microwave of frequency F6 has a lower reflectivity than the microwave of frequency F5. The microwave of frequency F7 has a higher reflectivity than the microwave of frequency F6. The microwave of frequency F8 has a lower reflectivity than the microwave of frequency F7.

[0091] Specifically, frequencies F1, F2, F3, F4, F5, F6, F7, and F8 are 2405 MHz, 2414 MHz, 2430 MHz, 2438 MHz, 2445 MHz, 2459 MHz, 2483 MHz, and 2499 MHz, respectively.

[0092] According to the seventh embodiment, when heating is performed using microwaves with a frequency having a high wave reflection rate, heat is transferred into the object 2 and is radiated from the surface of the object 2. As a result, it is possible to reduce uneven heating caused by microwaves with a frequency having a low wave reflection rate. In other words, the uniformity of heating is improved.

[0093] As described in Examples 1 to 3, the uniformity of heating is improved by setting a 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.

[0094] Example 8 Example 8 of the present embodiment will now be described. Fig. 9 is a schematic diagram showing an example of the change over time in the microwave frequency and the reflected wave rate according to Example 8.

[0095] In the eighth embodiment, as shown in FIG. 9, the control unit 7 controls the microwave generating unit 3 to switch the microwave frequency so that the reflected wave rate alternately increases and decreases, similarly to the seventh embodiment.

[0096] In addition, for frequencies with higher reflected wave rates, the control unit 7 causes the microwave generation unit 3 to generate microwaves in order from the highest frequency. For frequencies with lower reflected wave rates, the control unit 7 causes the microwave generation unit 3 to generate microwaves in order from the lowest frequency.

[0097] That is, the control unit 7 causes the microwave generating unit 3 to perform the following operation. The microwave generating unit 3 generates a microwave having a frequency F1 at which the reflectance is the lowest, and then generates a microwave having a frequency F2 at which the reflectance is the highest. F8After that, the microwave generating unit 3 generates a microwave of frequency F3 with the second lowest reflectivity, and then generates a microwave of frequency F4 with the second highest reflectivity. F6 It generates microwaves.

[0098] Thereafter, the microwave generating unit 3 generates a microwave having a frequency F5 with the third lowest reflectivity, and then generates a microwave having a frequency F6 with the third highest reflectivity. F4 After that, the microwave generating unit 3 generates a microwave of frequency F7 with the fourth lowest reflectivity, and then generates a microwave of frequency F8 with the fourth highest reflectivity. F2 It generates microwaves.

[0099] Specifically, frequencies F1, F2, F3, F4, F5, F6, F7, and F8 are 2405 MHz, 2414 MHz, 2430 MHz, 2438 MHz, 2445 MHz, 2459 MHz, 2483 MHz, and 2499 MHz, respectively.

[0100] According to Example 8, it is possible to improve the uniformity of heating while simplifying the control. Simplifying the control means reducing the number of parameters required to determine the microwave output level and oscillation time at each frequency, as well as the order of the frequencies to be generated.

[0101] In this method, heating with large heating unevenness and heating with small heating unevenness are alternately performed in order of the degree of unevenness. This makes it possible to make the heating time at each frequency the same when using microwaves with the same output level at all frequencies, for example. As a result, the control can be simplified.

[0102] Example 9 Example 9 of the present embodiment will be described. Fig. 10 shows a schematic example of a change over time in microwave frequency and reflected wave rate according to Example 9. As shown in Fig. 10, the control unit 7 causes the microwave generating unit 3 to generate microwaves in order of frequency to reflect wave rate.

[0103] In Example 9, microwaves of frequencies F1 to F7 have higher reflectivity and less heating unevenness in that order. That is, the reflectivity for frequencies F1 to F4 is higher than that for frequencies F5 to F7. When heating with microwaves of frequencies with less heating unevenness, heat is transferred into the object 2 to be heated and radiated from the surface of the object 2 to be heated.

[0104] Specifically, the frequencies F1, F2, F3, F4, F5, F6, and F7 are 2405 MHz, 2414 MHz, 2430 MHz, 2438 MHz, 2445 MHz, 2459 MHz, and 2483 MHz, respectively.

[0105] As a result, uneven heating caused by heating with microwaves of a frequency with a low wave reflection rate is reduced when heating with microwaves of a frequency with a high wave reflection rate, i.e., the uniformity of heating is improved.

[0106] In Example 9, the heating time per frequency is set shorter than the control method of setting a stop time when switching the frequency as described in Examples 1 to 3. This tends to improve the uniformity of heating.

[0107] This is because the longer the heating time per frequency, the greater the heating unevenness in heating with microwaves of a frequency with a smaller reflectance, resulting in localized denaturation of proteins.

[0108] Example 10 Example 10 of the present embodiment will be described below. Fig. 11 shows an example of the frequency characteristic of the reflected wave rate and a set threshold value.

[0109] As shown in Fig. 11, in the tenth embodiment, the control unit 7 uses only microwaves of frequencies in frequency bands (frequency bands FB1, FB2, FB3, FB4) in which the reflected wave rate is higher than a predetermined threshold value. This means that only microwaves of frequencies that cause relatively small heating unevenness are used. Therefore, the longer this control is performed, the more uniform the heating is improved.

[0110] This threshold value must be set to a different value depending on the type and size of the object to be heated and the microwave output level. However, when the microwave output level is, for example, 250 W, experiments have shown that the uniformity of heating is improved by setting the threshold value within a certain range of the reflected wave rate (40% to 90%, 40% in Example 10).

[0111] When the frequency and the object to be heated 2 are unchanged, increasing the microwave output level increases the heating unevenness. In order to suppress the heating unevenness, it is necessary to use only microwaves with frequencies that have a higher reflected wave rate. Therefore, the control unit 7 sets the threshold value of the reflected wave rate to a large value in proportion to the output level.

[0112] The control unit 7 uses only microwaves having a frequency with a wave reflection rate higher than the threshold value from the start to the end of the operation of the microwave generation unit 3, that is, from the start to the end of heating. This further improves the uniformity of heating.

[0113] If only microwaves having a frequency with a wave reflection rate higher than a threshold value are used from the start to the end of heating and this control is performed at least some time during the first half of heating, the uniformity of heating is improved.

[0114] This is because uneven heating can be suppressed in the early stages of heating, which have a large impact on uneven heating at the end of heating. If uneven heating is large in the early stages of heating, microwaves are locally concentrated in the part of the heated object 2 with a high dielectric constant for a long period until the end of heating.

[0115] Example 11 Example 11 of the present embodiment will be described below. Fig. 12 shows an example of the frequency characteristics of the reflected wave rate at each temperature inside the heating chamber 1.

[0116] 12, the frequency characteristics of the reflected wave coefficient change depending on the temperature of the heating chamber 1. Specifically, as the temperature of the heating chamber 1 increases, the frequency characteristics of the reflected wave coefficient shift to the left toward lower frequencies while maintaining almost the same waveform.

[0117] This is because the resonant 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 in the wall of the heating chamber 1 expands, causing a slight increase in the volume inside the heating chamber 1. Another reason is that the compression rate of the microwave wavelength inside the door glass increases due to an increase in the dielectric constant of the door glass.

[0118] For example, such a state occurs in oven heating using radiant heating and convection heating in addition to microwaves.

[0119] Therefore, the control unit 7 performs frequency sweep based on the temperature of the heating chamber 1, and reacquires the frequency characteristic of the reflected wave rate. The control unit 7 resets the microwave oscillation conditions based on the frequency characteristic of the reflected wave rate.

[0120] The oscillation conditions refer to the frequency and output level of the microwave. The control unit 7 resets the oscillation conditions by causing the microwave generating unit 3 to change the microwave frequency and the amplifying unit 4 to change the microwave output level. This can improve the uniformity of heating.

[0121] In the three graphs shown in Fig. 12, the temperature rise in the heating chamber 1 is almost the same, and the frequency characteristics of the reflected wave rate shift to the left by almost the same frequency in response to the temperature rise. Therefore, the control unit 7 performs frequency sweeping every time the temperature of the heating chamber 1 changes by a predetermined value, reacquires the frequency characteristics of the reflected wave rate, and resets the microwave oscillation conditions. This makes it possible to improve the uniformity of heating.

[0122] The degree of temperature change in the heating chamber 1, which indicates the timing to reacquire the frequency characteristics of the reflected wave rate, depends on the shape and wall material of the heating chamber 1, as well as the type and size of the object to be heated 2. The measurement conditions for the frequency characteristics shown in Figure 12 are as follows: (1) The volume of the heating chamber 1 is 50 liters. (2) The wall surface is enameled steel plate. (3) No object to be heated 2 is placed in the heating chamber 1.

[0123] In the case of the frequency characteristic shown in FIG. 12, taking into consideration the degree of shift, the frequency characteristic of the reflected wave rate should be reacquired at most every 100° C., and preferably every 20° C.

[0124] The control unit 7 may reacquire the frequency characteristic of the reflected wave rate and reset the microwave oscillation conditions each time the temperature inside the heating chamber 1 exceeds or falls below the predetermined temperature. In other words, the case where the temperature inside the heating chamber 1 exceeds or falls below the predetermined temperature is the case where the temperature inside the heating chamber 1 passes through the predetermined temperature.

[0125] By clearly defining the conditions for the timing of resetting, it is possible to reduce the influence of changes in the resonance frequency in the heating chamber 1 that accompany changes in the temperature in the heating chamber 1. As a result, more uniform heating can be achieved stably.

[0126] The temperature of the heating chamber 1 at which the frequency characteristics of the reflected wave coefficient are to be reacquired is desirably set to half the set temperature in the oven heating using radiation heating and convection heating. The temperature may be half the difference between the set temperature and room temperature.

[0127] In Examples 1 to 11, the control unit 7 may use the dissipation factor of the microwave in the heating chamber 1 instead of the reflected wave rate. The dissipation factor of the microwave in the heating chamber 1 is the ratio (%) of the difference between the incident power and the reflected power to the incident power.

[0128] The control unit 7 may estimate the dissipation of microwaves in the inner walls of the heating chamber 1, the heater, parts inside the heating chamber 1 such as the door glass, the transmission path, etc., and correct the reflected wave rate based on the estimated value.

[0129] 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 the estimated value instead of the reflected wave rate. [Industrial Applicability]

[0130] The microwave processing device according to the present disclosure can be applied to drying devices, heating devices for pottery, food waste processors, semiconductor manufacturing devices, chemical reaction devices, and the like, in addition to the above-mentioned cooking devices. [Explanation of symbols]

[0131] 1 Heating chamber 2 Object to be heated 3. Microwave generator 4 Amplification section 5 Power supply unit 6. Detection section 7 Control section 8 Memory section

Claims

1. A heating chamber configured to accommodate an object to be heated; a microwave generating unit operable to generate microwaves having any frequency in a predetermined frequency band; an amplifier operable to amplify the microwave and output the amplified microwave as incident power; a power supply configured to supply the incident power to the heating chamber; a detector operable to detect the incident power and the reflected power returning from the heating chamber to the power supply; A control unit operable to control the microwave generating unit and the amplifying unit; a memory unit operable to store the incident power and the reflected power together with the frequency of the microwaves and the elapsed time from the start of heating; the control unit is operable to cause the microwave generating unit to perform a frequency sweep across the predetermined frequency band, is operable to control the microwave generating unit and the amplifier unit based on the incident power and the reflected power detected during the frequency sweep, and is operable to set a stop time for stopping output of the microwave when changing the frequency of the microwave, and to change the stop time according to the frequency of the microwave.

2. The microwave processing apparatus according to claim 1, wherein the control unit is operable to calculate a reflection rate, which is a ratio of the reflected power to the incident power for each of the frequencies in the frequency sweep, and to set the stop time to be longer as the reflection rate is lower.

3. 2. The microwave processing apparatus according to claim 1, wherein the control unit is operable to calculate a reflection rate, which is a ratio of the reflected power to the incident power for each of the frequencies in the frequency sweep, and not to set the stop time for the microwaves of the frequency at which the reflection rate exceeds a predetermined value.

4. The microwave processing apparatus according to claim 1 , wherein the control unit is operable to change a duty ratio in an output of the microwave in response to the frequency.

5. 5. The microwave processing apparatus according to claim 4, wherein the control unit is configured to calculate a reflection rate which is a ratio of the reflected power to the incident power for each of the frequencies in the frequency sweep, and to set the duty ratio higher as the reflection rate is higher.

6. 5. The microwave processing apparatus according to claim 4, wherein the control unit is operable to calculate a reflection rate which is a ratio of the reflected power to the incident power for each of the frequencies in the frequency sweep, and to set the duty ratio to 100% for the microwaves of the frequency at which the reflection rate exceeds a predetermined value.

7. A heating chamber configured to accommodate an object to be heated; a microwave generating unit operable to generate microwaves having any frequency in a predetermined frequency band; an amplifier operable to amplify the microwave and output the amplified microwave as incident power; a power supply configured to supply the incident power to the heating chamber; a detector operable to detect the incident power and the reflected power returning from the heating chamber to the power supply; A control unit operable to control the microwave generating unit and the amplifying unit; a memory unit operable to store the incident power and the reflected power together with the frequency of the microwaves and the elapsed time from the start of heating; The control unit is operable to cause the microwave generating unit to perform a frequency sweep across the predetermined frequency band, is operable to control the microwave generating unit and the amplifier unit based on the incident power and the reflected power detected during the frequency sweep, and is operable to cause the microwave generating unit to generate at least in sequence a frequency with the lowest reflectivity, a frequency with the highest reflectivity, a frequency with the second lowest reflectivity, and a frequency with the second highest reflectivity, which is the ratio of the reflected power to the incident power.

8. A heating chamber configured to accommodate an object to be heated; a microwave generating unit operable to generate microwaves having any frequency in a predetermined frequency band; an amplifier operable to amplify the microwave and output the amplified microwave as incident power; a power supply configured to supply the incident power to the heating chamber; a detector operable to detect the incident power and the reflected power returning from the heating chamber to the power supply; A control unit operable to control the microwave generating unit and the amplifying unit; a memory unit operable to store the incident power and the reflected power together with the frequency of the microwaves and the elapsed time from the start of heating; a control unit operable to cause the microwave generating unit to perform a frequency sweep across the predetermined frequency band, to control the microwave generating unit and the amplifier unit based on the incident power and the reflected power detected during the frequency sweep, to calculate a reflection rate which is a ratio of the reflected power to the incident power for each of the frequencies in the frequency sweep, and to cause the microwave generating unit to generate the microwaves in order from the frequency with the highest reflection rate.

9. A heating chamber configured to accommodate an object to be heated; Operable to generate microwaves having any frequency within a predetermined frequency band A microwave generating unit; an amplifier operable to amplify the microwave and output the amplified microwave as incident power; a power supply configured to supply the incident power to the heating chamber; a detector operable to detect the incident power and the reflected power returning from the heating chamber to the power supply; A control unit operable to control the microwave generating unit and the amplifying unit; a memory unit operable to store the incident power and the reflected power together with the frequency of the microwaves and the elapsed time from the start of heating; the control unit is operable to cause the microwave generating unit to perform a frequency sweep across the predetermined frequency band, to control the microwave generating unit and the amplifier unit based on the incident power and the reflected power detected during the frequency sweep, to calculate a reflection rate which is the ratio of the reflected power to the incident power for each of the frequencies in the frequency sweep, and to cause the microwave generating unit to generate only the microwaves of the frequencies for which the reflection rate exceeds a predetermined value.

10. A microwave processing device as described in Claim 9, wherein the control unit is operable to cause the microwave generating unit to generate only the microwaves of the frequency whose reflected wave rate exceeds the predetermined value from the start to the end of the heating.

11. A microwave processing device as described in claim 9, wherein the control unit is operable to calculate the reflected wave rate by the first half of the time from the start to the end of the heating has elapsed.

12. A heating chamber configured to accommodate an object to be heated; a microwave generating unit operable to generate microwaves having any frequency in a predetermined frequency band; an amplifier operable to amplify the microwave and output the amplified microwave as incident power; a power supply configured to supply the incident power to the heating chamber; a detector operable to detect the incident power and the reflected power returning from the heating chamber to the power supply; A control unit operable to control the microwave generating unit and the amplifying unit; a memory unit operable to store the incident power and the reflected power together with the frequency of the microwaves and the elapsed time from the start of heating; A microwave processing apparatus, wherein the control unit is operable to cause the microwave generating unit to perform a frequency sweep across the predetermined frequency band, and is operable to control the microwave generating unit and the amplifier unit based on the incident power and the reflected power detected during the frequency sweep, and the control unit is operable to cause the microwave generating unit to perform the frequency sweep and to reset the frequency and output level of the microwave, which are the oscillation conditions of the microwave, based on the temperature of the heating chamber.

13. A microwave processing apparatus as described in claim 12, wherein the control unit is operable to cause the microwave generating unit to perform the frequency sweep and reset the oscillation conditions of the microwaves each time the temperature of the heating chamber changes by a predetermined value.

14. A microwave processing device as described in claim 12, wherein the control unit is operable to cause the microwave generating unit to perform the frequency sweep and reset the oscillation conditions of the microwaves each time the temperature of the heating chamber passes a predetermined temperature.

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