High frequency thawing device and high frequency thawing method

Abstract

To perform thawing with high reproducibility by monitoring the end point of thawing on the basis of the transition to the latent heat region.SOLUTION: A high-frequency thawing device 1 includes a high-frequency power supply 11 that supplies high-frequency power between electrodes 21 and 22 that sandwich a moisture-containing thawing target W to thaw the target W, a matching circuit unit 12 that automatically matches the high-frequency power supply 11 with the electrodes 21 and 22, a timing detection unit (112, 30, 34) that switches off the automatic matching of the matching circuit unit 12 between the start of heating and the transition of the thawing state to the latent heat region, and detects the time point at which the high-frequency current peaks, and a thawing completion control unit 35 that monitors the time point at which thawing of the target W is completed, based on the detected peak time point.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a high-frequency thawing device and a high-frequency thawing method for thawing an object to be thawed, such as a frozen food, using high-frequency power. [Background technology]

[0002] Conventionally, when thawing frozen foods, etc., external heating by heat transfer tends to cause temperature differences between the inside and outside, resulting in uneven thawing. Therefore, a method of achieving more uniform heating by internal heating using high-frequency waves has been widely used. It is known that, as thawing progresses and the temperature of the frozen food rises to the latent heat region of -5°C or higher, the supplied power is used for phase transition (change of state), i.e., the consumption of latent heat, slowing the temperature rise (Patent Document 1). Patent Document 2 also describes a device that includes a matching circuit to match the load impedance with the power supply, because in the latent heat region, the frozen food becomes a mixture of ice and water, and the dielectric constants of the two materials differ. Furthermore, the balance of the mixture gradually changes (part of the ice becomes water). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4121258 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-12547 Summary of the Invention [Problem to be solved by the invention]

[0004] The high-frequency thawing device described in Patent Document 2 is configured to store in advance the high-frequency output corresponding to conditions such as electrode spacing and the weight of the frozen food, as well as the estimated thawing time from the start to the end of the thawing operation, and to set the high-frequency output corresponding to the conditions and the estimated thawing time in the device each time thawing is performed.However, since the estimated thawing time is from the start to the end of the thawing operation, there is a problem in that the estimated thawing time cannot be calculated when the initial temperature (freezing temperature) of the frozen food is unknown or when the set temperature conditions are not met.

[0005] The present invention has been made in consideration of the above, and provides a high-frequency thawing device and a high-frequency thawing method that enable highly reproducible thawing by monitoring the thawing end point based on the transition to the latent heat region. [Means for solving the problem]

[0006] The high-frequency thawing device of the present invention comprises a high-frequency power supply that supplies high-frequency power to thaw an object to be thawed placed between opposing electrodes, a timing detection means that detects the timing at which the thawing state transitions from the sensible heat region to the latent heat region from a predetermined change over time in a target electrical characteristic in a mismatched state, and a thawing completion control means that monitors the completion time of thawing of the object to be thawed based on the detected detection timing.

[0007] Furthermore, the high-frequency thawing method of the present invention, in which high-frequency power is supplied while an object to be thawed is sandwiched between opposing electrodes, includes the steps of detecting the timing at which the thawing state transitions from the sensible heat region to the latent heat region from a predetermined change over time in a target electrical characteristic in a mismatched state, and monitoring the end point of thawing of the object to be thawed based on the detected detection timing.

[0008] According to these inventions, the timing at which the thawing state transitions from the sensible heat region to the latent heat region is obtained by detecting a predetermined change over time in the electrical characteristic of interest in the mismatched state using a timing detection means. Then, the thawing completion control means monitors the thawing completion point of the object to be thawed, using the detected timing as the starting point. Because the thawing completion point is monitored using the transition to the latent heat region as the starting point, there is no need to consider variations in the initial temperature of the object to be thawed, the heating operation up to the current peak, or any of these, enabling highly reproducible thawing.

[0009] The high frequency power supply also includes a self-excited oscillator circuit having an electron tube, and the timing detection means detects the time when the anode current of the electron tube reaches a peak as a predetermined change over time in the target electrical characteristic. With this configuration, the time when the thawed state transitions to the latent heat region can be detected as the time when the anode current of the electron tube reaches a peak.

[0010] The high-frequency power supply also includes an externally excited oscillator circuit, and the timing detection means detects the time when the reflected wave from the electrode side starts to increase as a predetermined change over time in the target electrical characteristic. With this configuration, the timing when the thawing state transitions to the latent heat region can be detected as the time when the reflected wave from the electrode side starts to increase. Note that the time when the reflected wave rate (or reflection coefficient) starts to increase is technically essentially the same as the time when the reflection efficiency starts to decrease.

[0011] The device also includes a matching circuit that automatically matches the high-frequency power supply side with the electrode side, and a switching unit that switches off the matching operation of the matching circuit during the period from the start of heating until the thawing state transitions to the latent heat region. With this configuration, heating is performed in a matched state during the initial stage, from the start of heating until the thawing state transitions to the latent heat region, so that initial heating is performed efficiently.

[0012] The matching circuit maintains the circuit state when the matching operation is switched off. With this configuration, when the automatic matching is switched off, the values of the electrical elements of the matching circuit at that time are maintained as set values, so that mismatching gradually occurs in response to changes in the load impedance accompanying the transition to the latent heat region, resulting in a change over time in the electrical characteristic of interest, such as a current peak.

[0013] The switching unit is also characterized by switching the matching operation on after the base point. With this configuration, when the automatic matching remains off, the high frequency output gradually decreases, enabling, for example, foodstuffs to be thawed slowly with less undercooking, while when the automatic matching is switched on, the thawing efficiency in the latent heat region can be improved.

[0014] The thawing completion control means monitors the thawing completion time corresponding to the property information of the object to be thawed. With this configuration, the thawing completion time is monitored based on the property information of the object to be thawed, thereby enabling appropriate thawing in accordance with the property information.

[0015] The thawing completion control means includes a setting unit that sets a target heat quantity required to thaw the object from the base point, a heat quantity integrating means that integrates the high-frequency power from the base point as an output heat quantity, and a thawing completion monitoring means that terminates the thawing operation when the integrated heat quantity reaches the target heat quantity. According to this configuration, the heat quantity required for thawing is set as the target heat quantity, and the completion of the thawing operation is monitored by integrating the actually measured output heat quantity and comparing it with the target heat quantity.

[0016] The thawing end control means is characterized in that it sets the end time of thawing in the latent heat region based on the property information of the object to be thawed, with the detection timing as a starting point, using a trained model. With this configuration, the use of the trained model enables thawing processing using the latent heat region. [Effects of the Invention]

[0017] According to the present invention, by monitoring the end point of thawing based on the transition to the latent heat region, there is no need to consider the initial temperature or the heating operation until a predetermined change over time occurs in the electrical characteristic of interest, making it possible to achieve thawing with high reproducibility. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a configuration diagram showing a first embodiment of a high-frequency thawing device according to the present invention. [Figure 2] 3 is a waveform diagram illustrating a high-frequency current peak, which is one of the electrical characteristics, showing the mechanism of high-frequency thawing when the self-excited oscillator circuit of the first embodiment is used. FIG. [Figure 3] 10 is a partially enlarged view showing an example of a display of input contents of a high-frequency defrosting device. [Figure 4] FIG. 10 is an explanatory diagram showing the state of high-frequency thawing when the frozen food is chicken. [Figure 5] FIG. 10 is an explanatory diagram showing the state of high-frequency thawing when the frozen food is beef. [Figure 6] 10 is a flowchart illustrating an example of high frequency decompression processing. [Figure 7] FIG. 10 is a waveform diagram showing the change over time in each electrical characteristic in a high-frequency thawing experiment when the separately excited oscillator circuit according to the second embodiment is used. [Figure 8] FIG. 8 is a partially enlarged waveform diagram of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] Fig. 1 is a block diagram showing a first embodiment of a high-frequency thawing device according to the present invention. The high-frequency thawing device 1 has a housing having a predetermined external shape, for example, a rectangular parallelepiped shape (see Fig. 3), and includes a power supply circuit unit 10 that outputs high-frequency power, a heating unit 20 that dielectrically heats an object W to be thawed, and a control unit 30 that is made up of a computer with a built-in processor that controls the thawing operation. Connected to the control unit 30 are a memory unit 301 that stores a control program related to the thawing process, a display unit 41 that displays images, and an operation unit 42 that allows necessary instructions and information to be input.

[0020] The power supply circuit unit 10 is capable of appropriately outputting power of, for example, several hundred W / kg, and includes a high-frequency power supply 11 that generates high-frequency power in the band of several MHz to several tens of MHz, for example, 40.68 MHz, and a matching circuit unit 12 interposed between the high-frequency power supply 11 and the heating unit 20, and further includes a power sensor 131 that detects traveling waves and reflected waves, and a matching sensor 132 that detects a matching error. In the first embodiment, the high-frequency power supply 11 uses a self-excited oscillator circuit 111 that uses an electron tube. The ammeter 112 detects the current flowing through the anode of the electron tube (hereinafter referred to as output current Io).

[0021] Heating unit 20 has a structure in which opposing electrodes 21 and 22 are arranged, and high-frequency power is supplied between electrodes 21 and 22, thereby dielectrically heating an object to be thawed W placed between electrodes 21 and 22. In this embodiment, object to be thawed W is a chunk of chicken, beef, or other frozen food material frozen to an appropriate negative temperature, for example, about −20° C., as will be described later.

[0022] The matching circuit unit 12 is a circuit for matching the impedance on the power supply side with the impedance on the load side including the object to be thawed W and the heating unit 20. The matching circuit unit 12 includes a matching circuit 121 and a matching drive unit 122. In this embodiment, the matching circuit 121 has predetermined electric elements, for example, a variable capacitor C1 and an inductance element L1 connected in series between the power supply side and the heating unit 20, and further has a variable capacitor C2 connected between the connection point of the variable capacitor C1 and the inductance element L1 and ground. The variable capacitors C1 and C2 are configured to be able to change their respective capacitances by varying the distance between opposing electrodes using a drive source such as a motor or by varying the opposing areas of the electrode surfaces.

[0023] The matching driver 122 includes a motor driver or the like that drives a capacitance-varying motor or the like provided in the variable capacitors C1 and C2, and operates to maintain a matched state in response to instructions from the control unit 30. More specifically, the matching sensor 132 detects the current phase via a known magnetic circuit or the like (not shown) and the voltage phase via a capacitor (not shown) to detect the phase difference between the two and detect the impedance matching state. The matching sensor 132 outputs an output signal corresponding to the amount of phase difference between the two, and the control unit 30 receives this output signal and maintains the capacitance of the variable capacitors C1 and C2 in a matched state through feedback control via the matching driver 122.

[0024] Furthermore, the matching drive unit 122 controls the matching operation from the start of the thawing operation, and when it receives an instruction to switch to matching off from the matching switching control unit 33, which will be described later, it stops the motor drivers and stops driving each motor etc. so as to maintain the setting states (i.e., LC values) of the electric elements L, C1, and C2 at the time of switching off. Note that matching off can be achieved not only by completely turning off, which stops the movement of all electric elements, but also by semi-turning off, which stops the movement of only some of the electric elements, for example, capacitor C2, which has the same effect.

[0025] As described below, the control unit 30 functions as a data acquisition unit 31, a consistency control unit 32, a consistency switching control unit 33, a timing detection unit 34, and a decompression end control unit 35 by reading a control program from the memory unit 301 into the main memory and executing it on the processor.

[0026] In this embodiment, the thawing control by the control unit 30 starts when a predetermined anode voltage is applied to the electron tube of the oscillation circuit 111 while the matching operation is on, and continues after the matching operation is switched off when the output current Io detected by the ammeter 112 reaches a predetermined set current (see FIG. 2). Next, when a peak (Iop: see FIG. 2) of the output current Io is detected in the matching-off state (non-matching state), this current peak point tp (see FIG. 2) is regarded as the transition point to the so-called latent heat region, and the thawing end point is monitored using this current peak point as the base point.

[0027] The thawing mechanism according to the present invention will be described below with reference to Figures 2 and 3. Figure 2 is a waveform diagram illustrating a high-frequency current peak, which is one of the electrical characteristics, showing the mechanism of high-frequency thawing when a self-excited oscillator circuit according to the first embodiment is used. Figure 3 is a partially enlarged view showing an example of the display of input contents of the high-frequency thawing device.

[0028] A frozen object W to be thawed is placed between the opposing electrodes 21 and 22. It is desirable to position the upper electrode 21 with a small air gap relative to the top surface of the object W. Next, the anode voltage Vo is set, and the thawing operation begins at time ts. The object W receives power and its temperature gradually rises. In response, the output current Io gradually increases in accordance with the matching operation, eventually reaching the set current value (see the solid line rising from ts in FIG. 2 ). Once the output current Io reaches the set current value, the matching operation is switched off immediately, or after a predetermined time has passed. At this time, the water content of the object W is mostly ice, or ice has begun to melt. The water content remains in a nearly matched state, and the output current Io gradually increases. As the output current Io gradually increases, more ice in the object W begins to melt, increasing the amount of water, and changing the balance between the amount of ice and water. However, because water has a higher dielectric constant and dielectric loss than ice, the impedance rises and deviates from the matched state as the balance between the amount of ice and water changes, causing the output current Io to reach a peak Iop (see the current peak point tp in Figure 2). That is, up until the current peak point tp, the supplied high-frequency power acts as sensible heat that contributes to raising the temperature of the object to be thawed W (sensible heat region). On the other hand, after the current peak point tp is exceeded, the supplied high-frequency power is consumed as latent heat that contributes to melting the ice (latent heat region). Note that if an air gap is inserted, the thawing of the object to be thawed W will be slowed down by the amount of electric field applied to the air gap, and overheating can be suppressed.

[0029] When thawing control is monitored by the amount of heat, the current peak point tp is used as the base point to monitor whether a target amount of heat corresponding to the degree of thawing relative to the total thawing in which all the ice in the object to be thawed W is transformed into water, i.e., the target amount of heat as a ratio to the amount of latent heat required for total thawing, has been supplied to the object to be thawed W. That is, from the time when the current peak point tp is detected, the output high-frequency power is successively measured, converted into an amount of heat, integrated, and compared with the target amount of heat, and the thawing operation is terminated at the time te when the actual measured amount of heat reaches the target amount of heat.

[0030] By performing thawing control based on the current peak point tp in this way, the power supply (calorific value) from the start of thawing to the current peak point tp is not affected by the thawing control. This eliminates the need to consider the initial temperature of the object to be thawed W and the associated increase in error, and also eliminates the need for temperature management or other monitoring during that period. By performing thawing control in this manner within the latent heat region, high reproducibility is achieved. In the above, the actual measured power is measured periodically using the ammeter 112, and is calculated by multiplying the set anode voltage Vo by the output current Io and a preset device efficiency (e.g., approximately 0.7 to 0.8) and integrating them. The actual measured calorific value can be obtained by multiplying this by the heat of fusion of ice (e.g., 334 kJ / kg).

[0031] The target heat quantity varies depending on the thawing conditions, i.e., the properties of the object to be thawed W. Fig. 4 is an explanatory diagram showing the state of microwave thawing when the frozen food is chicken. Fig. 5 is an explanatory diagram showing the state of microwave thawing when the frozen food is beef.

[0032] The total thawing heat quantity varies depending on the type (including when the moisture content is known) and weight of the object W to be thawed, and a target heat quantity is set using a ratio corresponding to the degree of thawing depending on the application, as described below. Meanwhile, the target thawing temperature for the object W to be thawed is, for example, -2°C to 0°C, which is the general range for chicken, where a chicken block that has solidified due to freezing must be thawed to the point where it can be divided into small pieces (see FIG. 4). For beef, a large block of beef must be thawed with minimal drip loss within a temperature range that allows machining using a mixer or slicer (see FIG. 5). That is, as shown in FIG. 4, for chicken, the target heat quantity is between 70% and 100% of the total thawing heat quantity for the object W to be thawed. For beef, as shown in FIG. 5, the target heat quantity is between 5% and 10% of the total thawing heat quantity for the object W to be thawed. These ratios can be set in advance based on experiments, etc. In addition, in an embodiment where the moisture content can be set separately, the moisture content may be included as a setting item.

[0033] In the above description, the matching operation is turned on from the thawing start time ts, but the matching operation at the start of thawing is not limited to being on, and may be off, as long as it is off at least before the current peak point tp. Also, the setting for switching to the off state is not limited to a set current value, and may be based on the time from the start of thawing.

[0034] Next, the setting of property information of the object W to be thawed, the output current, etc. will be described. First, prior to the start of the thawing operation, as shown in FIG. 3, the output power is set by the operation unit 42 and the control unit 30. The output power is set via the operation unit 42 by inputting the product weight (weight of the object W to be thawed) (kg), weight output (W / kg), and thawing state (ratio of target heat amount to total thawing heat amount) (e.g., displayed as a percentage). If a weight scale is provided, the input may be automatic. Furthermore, if the moisture content is predetermined depending on the type of product, it may be treated as a predetermined percentage or may be input individually. In the example of FIG. 3, the total thawing heat amount is set to 10,000 kJ, calculated as 40 kg × moisture content (approximately 75%) × 334 kJ, and 7,000 kJ is displayed as the target heat amount. 1,234 kJ has currently been supplied. Note that the actually measured heat amount refers to the heat amount converted based on the actually measured power during thawing. When the measured calorific value reaches the target calorific value, the thawing operation ends, marking the end point of the thawing process. The storage unit 301 stores property information for various items W to be thawed, associated with output power and other factors. For example, the type of item W to be thawed (chicken, beef, pork, fish, etc.), weight, moisture content, and thawing state, along with output powers set in accordance with combinations of these. Additionally, the efficiency of the device and various values required for calorific value conversion are stored as appropriate. The output power may be fixed to one value or a predetermined number of values.

[0035] 1, the functional units of the control unit 30 will now be described. The data acquisition unit 31 acquires various pieces of information input via the operation unit 42 or the like and writes them to the storage unit 301. The data acquisition unit 31 acquires the incident wave and reflected wave detected by the power sensor 131, and acquires the phase information detected by the matching sensor 132.

[0036] Based on the phase information from the matching sensor 132, the matching control unit 32 drives the matching drive unit 122 to cause the matching circuit 121 to perform matching operations. The matching switching control unit 33 outputs a matching-on signal at the start of the thawing operation to turn the matching circuit 121 on (automatic matching), and then, when the output current Io rises to a set current value, switches to a matching-off signal, or continues heating in the matching state for a while, and then turns the matching circuit 121 off. In this case, the output current Io increases as the thawing progresses and the temperature of the object W to be thawed gradually rises, as shown by the solid line in FIG. 2. In this state, the ice gradually rises in the sensible heat region and partially undergoes a phase transition to water.

[0037] Next, the ice in the thawing target W gradually melts and turns into water, causing a change in the balance between the amounts of ice and water. Meanwhile, since it is known that the dielectric constants of ice and water are different, with water being approximately 20 times larger, as the balance changes and the amount of water increases relative to ice, the combined dielectric constant gradually increases, i.e., the impedance increases, gradually moving away from the matched state. As a result, the output current Io begins to plateau, peaking at the current peak point tp, and then gradually decreasing.

[0038] The timing detection unit 34 detects the transition from the sensible heat region to the latent heat region in the thawing state by acquiring the periodically detected output current Io and determining the current peak point tp, at which the current detected level drops below the previous detected level while the current is rising, as the transition timing to the phase transition. When the timing detection unit 34 determines that the current peak point tp has been detected, it outputs a current peak point detection signal to the thawing completion control unit 35.

[0039] In this embodiment, the thawing completion control unit 35 includes a target heat quantity calculation unit 351, an output heat quantity integration unit 352, and a thawing completion determination unit 353. The target heat quantity calculation unit 351 calculates the target heat quantity using property information about the object W to be thawed. The output heat quantity integration unit 352 periodically calculates the output power to the heating unit 20 taking into account device efficiency, using the current peak point signal as a base point, and then converts it into heat quantity and sequentially integrates it. The thawing completion determination unit 353 continues to monitor the integrated heat quantity, comparing it with the target heat quantity each time it is calculated, and determines that thawing is complete when the integrated heat quantity exceeds the target heat quantity. Note that the determination of the completion of thawing may be made by comparing the amount of energy, such as electric power, instead of the amount of heat.

[0040] Next, an example of the high-frequency thawing process will be described using the flowchart of Fig. 6. First, it is determined whether or not thawing conditions, such as property information about the object W to be thawed, have been input (step S1). If no input has been made, this flow is skipped. If input has been made, the target heat quantity is calculated and matching is turned on (step S3). Next, the thawing operation is started (step S5), and an operation of repeatedly detecting the output current Io at a predetermined cycle is started (step S7). Next, it is determined whether or not the output current Io has increased to a predetermined set current (step S9). After waiting until the output current Io has increased, or after waiting for a further predetermined time, the matching circuit 121 is switched to matching off (step S11).

[0041] Next, it is determined whether the output current Io has reached the current peak point tp (step S13). After it is detected that the current peak point tp has been reached, the output power is periodically measured, and then converted into an output heat quantity and integrated (step S15). Next, it is determined whether the integrated heat quantity has exceeded a target heat quantity (step S17), and once it has exceeded the target heat quantity, it is determined whether thawing has been completed (step S19). Then, when it is determined that thawing has been completed, the control unit 30 stops the operation of the high-frequency power supply 11.

[0042] Next, a second embodiment will be described. In the first embodiment, a self-excited oscillator circuit is applied as the high-frequency power supply 11 that amplifies and generates high-frequency power, and the change over time of the high-frequency current is used as the electrical characteristic of interest. However, the second embodiment is a case where an externally excited oscillator circuit is used. The externally excited oscillator circuit is the oscillator circuit 111 shown in FIG. 1, and includes, for example, a quartz crystal element and a semiconductor amplifier circuit, and power-amplifies and outputs an oscillation signal of a set frequency.

[0043] In a separately excited oscillator circuit, when the matching operation is on, the output power (incident wave) from the power supply side is transmitted to the load side with high efficiency (the reflected wave is small), but if the matching operation is turned off during the sensible heat region in the early stages of thawing, the thawing state shifts from the sensible heat region to the latent heat region, as in the first embodiment, and the matching shifts with the change in impedance. The second embodiment focuses on the reflected wave as an example of an electrical characteristic that causes this mismatch, and employs its change over time.

[0044] Figure 7 is a waveform diagram showing the time-dependent changes in electrical characteristics in a high-frequency thawing experiment using a separately excited oscillator circuit. More specifically, the high-frequency thawing experiment was conducted by supplying a high-frequency power of 600 W (= 300 W / kg) and a frequency of 40.68 MHz to a 2 kg pack of chicken. In Figure 7, the horizontal axis represents elapsed time and the vertical axis represents power (W). Figure 8 is a partially enlarged waveform diagram of Figure 7, with the vertical axis representing percentage.

[0045] As shown in Figure 7, in the experiment, the matching operation was turned on at the beginning of the thawing operation, from 0 to 60 seconds. Then, after 60 seconds, the matching operation could be turned off completely (non-matching state), but in this experiment only the matching drive of capacitor C2 was stopped, i.e., a substantial non-matching state was established. During this period, the material temperature (e) gradually increased, and the reflected wave (b) measured by the power sensor 131 (Figure 1) decreased slightly. After a predetermined time from turning off the matching operation, i.e., about 60 seconds had elapsed in this experiment, the reflected wave (b) began to rise and gradually increase, and the rise in material temperature (e) slowed accordingly. Meanwhile, the voltage V across capacitor C1 C1The change in (c) gradually decreased, and stopped after about 300 seconds. At about 560 seconds, the reflected wave (b) reached 200 W, and output power drooping (waveform (a)) was observed to compensate for the operation.

[0046] In Figure 8, when the material temperature (e) rises to near -6°C, as in the first embodiment, the thawing state transitions from the sensible heat region to the latent heat region as the ice melts and the balance between the internal ice and water changes, slowing the rise in material temperature (e). This phase transition, along with the difference in the ice-to-water mass balance and the difference in the dielectric constant and dielectric loss between ice and water, increases the impedance on the load side, further deviating from the power supply side. As a result, the reflected wave (b) begins to increase. By detecting the time point tp at which this increase occurs, a reference point for monitoring the completion of thawing can be obtained. The time change in the reflected wave (b) can be detected by comparing the previous reflected wave level with the current reflected wave level each time the timing detector 34 periodically detects the reflected wave level, as in the first embodiment. Another method for detecting changes over time by the timing detection unit 34 is to detect the timing at which the level of the reflected wave (b) shows a slight downward trend after the matching operation is switched off (around 60 to 120 seconds), as shown in detail in Figure 8, and to detect the timing at which this downward trend turns to an upward trend as the starting point at which the thawing state transitions from the sensible heat region to the latent heat region.

[0047] Next, a third embodiment will be described. In the previous embodiments, for example, the first embodiment, the thawing end point was monitored by comparing the actually measured cumulative heat quantity with the target heat quantity in the latent heat region. However, the third embodiment controls thawing using AI generated by applying machine learning to, for example, a neural network (NN) or a C (convolutional) NN. More specifically, the third embodiment is a thawing device that, upon receiving property information (type (moisture content), weight, ratio, etc.) of the object W to be thawed, applies a trained model and outputs a preferred thawing time based on the current peak point tp as a target time. This enables thawing monitoring by detecting the current peak point tp and comparing the time being measured with the target time output by the trained model.

[0048] In the learning phase of the third embodiment, actual thawing operations are performed at output powers set in accordance with the property information of a large number of objects to be thawed. Meanwhile, a timer is used to measure the elapsed time from when the current peak point tp is reached. Additionally, a contact thermometer, a radiation thermometer, or the like is used to measure the surface and internal temperatures of the objects to be thawed (W). The elapsed time until the desired thawing temperature is reached for each condition is acquired as a target time, which is sequentially input as a predicted target value. There is a correlation between the property information of the objects to be thawed (W), the set output power, and the target time in the latent heat region. For example, the target time is longer for larger weights, higher moisture contents, relatively higher thawing temperatures (e.g., −6°C to −4°C for chicken, compared with −1°C to 0°C for beef), and lower output power. Programs, trained model parameters, and the like are written to the memory unit 301. In the thawing control, upon receiving the input property information, the thawing completion control unit 35 inputs the trained model written to the memory unit 301 and outputs a target time corresponding to the thawing level. When the current peak point tp is detected, the thawing completion control unit 35 starts a timing operation, and when the timing time reaches the target time, performs a monitoring operation to terminate the thawing. In the third embodiment, steps S3, S15, and S17 in the flowchart of Fig. 6 are processed by replacing them with the target time and elapsed time.

[0049] In the above embodiments, for example, the current peak point tp is detected from consecutive detection data points before and after the current peak point tp. However, there are cases where the output power changes slowly and it is difficult to detect the peak using only three consecutive detection data points before and after the current peak point tp. In consideration of such cases, the peak point may be retroactively determined from four or more consecutive detection data points. In this case, for example, the output power may be continuously measured from the start of thawing, and the output power may be integrated using the retroactively determined current peak point as a base point.

[0050] After the start of thawing, it is desirable to switch the matching circuit 121 to matching off a little before the timing when the change in the composite dielectric constant, i.e., the load impedance, begins to occur and the current peaks. In the present invention, matching operation is not necessarily required, and the thawing process may be performed without matching operation for the entire period. In this case, the constants of the capacitors C1 and C2 and the inductance element L1 are preferably set to values equivalent to or close to the element constants when switching to matching off in the above embodiment.

[0051] In the above embodiment, for example, thawing is continued with the matching operation OFF even after the current peak point tp, but the matching operation may be changed to ON after the current peak point tp is exceeded to perform thawing. In this case, since matching can be achieved, the output current is maintained at a higher level than in the non-matching case, thereby improving thawing efficiency.

[0052] Furthermore, in the above embodiment, thawing is monitored based on the current peak point (phase transition point) by focusing on the latent heat consumed in the state change accompanying the phase transition from ice to water. However, this thawing technology is not limited to the case of water, and can also be applied to cases where the heating operation is monitored based on the latent heat of a material when heating an object to be thawed that contains a material whose dielectric constant changes before and after the phase transition from solid to liquid.

[0053] Next, in a fourth embodiment, for example, the peak point may be determined using a trained model generated using machine learning instead of the timing detection unit 34. When the high-frequency current transition is particularly gradual, a point in the past is recognized as the peak point after the peak point has passed, requiring a process to determine the peak point retroactively (by back-calculation). Therefore, in the third embodiment, the peak point is predicted and determined using AI generated by applying machine learning to, for example, a neural network (NN) or a C (convolutional) NN. More specifically, in the fourth embodiment, a trained model is created by, for example, supervised learning of data on the historical waveforms of multiple high-frequency current peaks (history) during the thawing process up to the peak point, and the peak point calculated from the entire historical waveform. In this way, the peak point can be predicted in advance, eliminating the need for retroactive processing.

[0054] The circuit configuration of the matching circuit is not limited to the matching circuit 121 of FIG. 1, and various known LC resonant circuits can be employed. For example, it may be a circuit in which one inductance element and one capacitor are connected in series or parallel, or it may be a circuit composed of one inductance element and two capacitors. The variable elements in the matching circuit are not limited to the variable capacitors C1 and C2 of the matching circuit 121 of FIG. 1. For example, when the matching circuit is composed of one inductance element and one capacitor, at least one of the one inductance element and one capacitor may be a variable element. When the matching circuit is composed of one inductance element and two capacitors, one or two of the three elements (the one inductance element and the two capacitors) may be variable elements. Matching is achieved by the matching operation using such variable elements. When a matching-off signal is received from the matching switching control unit 33, the matching operation of all the variable elements may be switched off, or it may be one of the two variable elements. In the above, a mismatched state is established when the two variable elements are switched to the off state in response to a matching-off signal from the matching switching control unit 33, and when one of the two variable elements is switched to the off state, a mismatched state is essentially established although matching tracking can be performed only by the other variable element. Note that the inductance of the inductance element can be adjusted by, for example, changing its shape.

[0055] In the above embodiment, the starting point of the transition to the latent heat region was described as a change over time in the anode current peak of the high-frequency power supply 11 or an increase in the reflected wave. However, other embodiments may also be employed that utilize the following changes over time in the electrical characteristic of interest. For example, the supply power may be calculated from the forward and reflected waves detected by the power sensor 131, and the timing of the load-side impedance change associated with the transition to the latent heat region may be detected by detecting a decrease in the supply power. Alternatively, an increase in the reflected wave rate or an increase in the reflection coefficient may be used as the time-dependent change in the electrical characteristic of interest. Furthermore, the phase difference between the output current phase and the voltage phase detected by the matching sensor 132 may be detected, and the timing of the load-side impedance change associated with the transition to the latent heat region may be detected by detecting an increase in the phase difference. Alternatively, in a self-excited oscillator, the starting point of the transition to the latent heat region from a frequency that fluctuates depending on the load impedance deviation may be detected by measuring the oscillation frequency directly or from a leakage electromagnetic field.

[0056] Another possible configuration is to use the voltage between electrodes 21 and 22 as the electrical characteristic of interest, and detect and utilize its change over time using a known high-frequency voltmeter. A high-frequency voltmeter for measuring the interelectrode voltage divides the high-frequency voltage between electrodes 21 and 22 via a capacitor or a series capacitor circuit, extracts one side of the divided voltage, rectifies, smooths, and detects it. When the load-side impedance increases with the transition to the latent heat region, the interelectrode voltage exhibits a change over time in which it begins to decrease, making it possible to detect the base point. [Explanation of symbols]

[0057] 1. High-frequency defrosting device 11 High frequency power supply 112 Ammeter (timing detection means) 12 Matching circuit section (matching circuit) 131 Power Sensor 132 Matching Sensor 20 Heating section 21,22 Counter electrode 30 Control Unit 301 Storage section 32 Integrity control section 33 Matching switching control section 34 Timing detection unit (timing detection means) 35 Decompression end control section W Thawing target

Claims

1. a high frequency power supply that supplies high frequency power to an object to be thawed that is placed between opposing electrodes to thaw the object; a timing detection means for detecting the timing at which the thawing state transitions from the sensible heat region to the latent heat region from a predetermined change over time in the electrical characteristic of interest in a mismatched state; and a thawing completion control means for monitoring the completion time of thawing of the object to be thawed, based on the detected timing.

2. the high-frequency power supply includes a self-excited oscillator circuit having an electron tube; 2. The high frequency thawing apparatus according to claim 1, wherein said timing detection means detects a time point at which the anode current of said electron tube reaches a peak as the predetermined change with time of said target electrical characteristic.

3. the high frequency power supply includes an externally excited oscillator circuit, 2. The high-frequency thawing device according to claim 1, wherein said timing detection means detects a time point at which the reflected wave from said electrode side starts to rise as a predetermined change with time in said target electrical characteristic.

4. a matching circuit that automatically performs matching between the high frequency power supply side and the electrode side; 2. The high-frequency thawing device according to claim 1, further comprising a switching unit that switches off the matching operation of the matching circuit until the thawing state transitions to the latent heat region.

5. 5. The high-frequency thawing device according to claim 4, wherein the matching circuit maintains a circuit state when the matching operation is switched off.

6. The high-frequency thawing device according to claim 4 , wherein the switching unit switches the matching operation on after the base point.

7. 2. The high frequency thawing device according to claim 1, wherein said thawing completion control means monitors the time point at which thawing is completed in accordance with the property information of the object to be thawed.

8. The decompression end control means a setting unit that sets a target heat quantity required to thaw the object to be thawed from the base point; a heat quantity integrating means for integrating the high frequency power from the base point as an output heat quantity; 2. The high frequency thawing device according to claim 1, further comprising a thawing completion monitoring means for terminating the thawing operation when the integrated heat quantity reaches the target heat quantity.

9. The high-frequency thawing device according to any one of claims 1 to 7, wherein the thawing completion control means sets the completion time of thawing in the latent heat region based on the detection timing and using a trained model, based on property information of the object to be thawed.

10. A high-frequency thawing method in which high-frequency power is supplied to an object to be thawed while the object is sandwiched between opposing electrodes, detecting a timing at which the thawing state transitions from a sensible heat region to a latent heat region from a predetermined change over time in the electrical characteristic of interest in a mismatched state; and monitoring the completion time of thawing of the object to be thawed based on the detected timing.

Images