JP7579740B2 - High Frequency Defrosting Device - Google Patents

Description

The present invention relates to a high-frequency dielectric heating device, and in particular to a high-frequency thawing device that applies a high-frequency electric field in the MHz range to frozen foods to rapidly thaw the frozen foods through dielectric heating.

In food processing factories and the like, frozen ingredients may be thawed to process the food. One type of thawing machine used in food processing factories and the like is a high-frequency thawing device that applies a high-frequency electric field in the MHz range to frozen food placed between opposing electrodes, thawing the frozen food through dielectric heating.

For example, the abstract of Patent Document 1 states, "The radio frequency thawing device comprises a heating chamber 1, upper electrode 2a and lower electrode 2b arranged in parallel within the heating chamber 1 with an object to be thawed 3 inserted between them, a radio frequency power supply 4 and matching circuit 6 which apply a radio frequency voltage between the upper electrode 2a and the lower electrode 2b, a power detection circuit 5 which detects the reflected power of the applied radio frequency voltage, and a control device 7 which estimates the progress of the object to be thawed based on changes in the detection signal of the power detection circuit 5 from the start of thawing, determines when thawing is complete, and controls the radio frequency power supply 4 based on the determination." Also, paragraph 0002 of the same document states, "There are known radio frequency thawing devices which apply radio frequency waves of 100 MHz or more to thaw objects to be thawed such as frozen foods by dielectric heating (e.g., Patent Documents 1 and 2). Radio frequency thawing devices comprise upper and lower electrodes within the heating chamber, and a radio frequency electric field is applied between the two electrodes from the radio frequency power supply to thaw the object by dielectric loss. The dielectric heating method is more suitable for thawing large objects to be thawed than thawing using microwaves in a microwave oven because the parallel electric field reaches the inside of the frozen food evenly." In other words, the high-frequency thawing device of Patent Document 1 uses a high-frequency electric field in the MHz range, which allows the inside of the item to be thawed to be thawed almost evenly compared to thawing with a microwave oven that uses microwaves (high-frequency electric field in the GHz range).

Here, during thawing by dielectric heating, the impedance of the load side, including the frozen food, changes significantly due to changes in the dielectric loss of the frozen food as the thawing progresses. Therefore, in the high-frequency thawing device of Patent Document 1, as explained in paragraph 0016 of the same document, "As shown in FIG. 2, the matching circuit 6 is equipped with variable capacitors 6a and 6b, and a variable coil 6c, etc., and offsets the reactance of the capacitor composed of the upper electrode 2a and the lower electrode 2b. In addition, by adjusting the values of the variable capacitors 6a, 6b and the variable coil 6c, the matching circuit 6 can match the input impedance to the matching circuit 6 and the output impedance to the amplifier. This allows a high-frequency electric field to be applied efficiently to the object to be thawed 3. The output of the matching circuit 6 is supplied to the upper electrode 2a and the lower electrode 2b in the heating chamber 1, and high-frequency dielectric heating is performed on the object to be thawed 3 inserted between the upper electrode 2a and the lower electrode 2b." By making the output impedance of the high-frequency power supply and the impedance of the load side including the object to be thawed approximately the same, the reflected power (reflected waves) returning to the high-frequency power supply is eliminated, and the heating efficiency of the food is improved. In order to constantly maintain impedance matching between the output side and the load side, a matching circuit composed of a capacitor and a coil is provided between the high-frequency power supply and the electrode (see FIG. 2 of the same document).

JP 2020-145114 A

However, as in Patent Document 1, if impedance matching is constantly maintained while thawing a frozen food, reflected power is eliminated, and almost all of the output power from the high frequency power source is continuously input to the food, even a high frequency electric field in the MHz band that tends to reach the inside of the frozen food evenly will gradually concentrate the electric field in the areas of the food where thawing occurs first (edges, corners, protrusions, etc.), causing parts of the food to become overheated. Temperature unevenness caused by overheating directly leads to a deterioration in the thawing quality of the food, so preventing overheating is an issue.

The present invention aims to improve the thawing quality of food by reducing overheating of the edges, corners, protrusions, etc. of frozen foods in a high-frequency thawing device that applies a high-frequency electric field in the MHz range to rapidly thaw frozen foods. In particular, it is intended to install the high-frequency thawing device in the back room of a retail store such as a convenience store or supermarket, and to rapidly thaw stored frozen foods such as boxed lunches and prepared meals to serve to customers.

The features of the present invention that solve the above problems are, for example, as follows:

A high-frequency thawing device comprising: a high-frequency power source that outputs high-frequency power in the MHz band; an electrode pair that applies a high-frequency electric field in the MHz band to a frozen food using the output power of the high-frequency power source; a matching unit that is connected between the high-frequency power source and the electrode pair and matches the output impedance of the high-frequency power source to a load impedance including the frozen food; and a power detection unit that detects the reflected power returning to the high-frequency power source, wherein the matching unit repeats a first step of automatically matching the output impedance to be substantially the same as the load impedance, and a second step of fixing the output impedance automatically matched in the first step until the thawing of the frozen food progresses and the reflected power reaches a predetermined threshold value, until the heating end time, and the high-frequency power source outputs an output power obtained by subtracting the threshold value from the previous output power from the first step onward following the second step.

The high-frequency thawing device of the present invention reduces overheating of the edges, corners, and protrusions of frozen foods, improving the thawing quality of the food.

1 is a schematic diagram of a high-frequency thawing device according to a first embodiment of the present invention; Graph showing time transition of output power and reflected power during thawing in Example 1 Flowchart of operation and decompression in the first embodiment Graph showing time transition of output power and reflected power during thawing in Example 2 Flowchart of operation and decompression in the second embodiment 11 is a flowchart of the operation when the decompression completion is automatically determined and the decompression operation in the third embodiment.

The following describes an embodiment of the high frequency thawing device 100 of the present invention with reference to the drawings. Note that the following description shows a specific example of the contents of the present invention, and the present invention is not limited to these descriptions. Various changes and modifications are possible by those skilled in the art within the scope of the technical ideas disclosed in this specification.

First, the high-frequency thawing device 100 according to the first embodiment of the present invention will be described with reference to Figures 1 to 3.

Figure 1 is a schematic diagram of the high-frequency thawing device 100 of this embodiment. As shown here, the high-frequency thawing device 100 mainly comprises a heating chamber 1, a high-frequency power source 2, a power detection unit 3, and a matching unit 4. Each unit will be described in turn below.

<Heating chamber 1>
The heating chamber 1 is a space for storing the frozen food 12 when the frozen food 12 is rapidly thawed by the high-frequency thawing device 100, and is provided with a door (not shown) for opening and closing the opening for putting in and taking out the food. The upper electrode 11a and the lower electrode 11b are non-magnetic metal materials arranged above and below in the heating chamber 1, such as plate-shaped aluminum alloy or stainless steel. The frozen food 12 is an object to be thawed that is placed on the lower electrode 11b, such as a frozen lunch box or side dish that is thawed by a retail store clerk at the request of a customer. Note that the high-frequency thawing device 100 is originally an apparatus that can rapidly thaw any object to be thawed, but in the following description, only frozen foods 12 of a type that have been registered in advance are to be thawed.

In this embodiment, at least one of the upper electrode 11a and the lower electrode 11b is configured to be movable in the vertical direction by a lifting mechanism (not shown). Therefore, the distance between the electrode pair can be appropriately adjusted according to the thickness and shape of the frozen food 12, and the upper electrode 11a can be brought close to the frozen food 12. This increases the heating energy (high-frequency electric field) input from the electrode pair to the frozen food 12, improving the heating efficiency, thereby shortening the time required to thaw the frozen food 12. Note that while FIG. 1 illustrates a configuration in which the frozen food 12 is placed directly on the lower electrode 11b, it is also possible to place a non-metallic container, dish, plate, etc. made of ceramics or heat-resistant resin on the lower electrode 11b, and then place the frozen food 12 on it.

<High frequency power source 2>
The high frequency power supply 2 is a power supply that oscillates a high frequency voltage in the MHz band, which is a lower frequency than the microwaves (high frequency electric field in the GHz band) used in a microwave oven, and supplies the voltage to the upper electrode 11a via the power detection unit 3 and the matching unit 4. As described above, a high frequency electric field in the MHz band has the characteristic that it can more easily reach the inside of the frozen food 12 than microwaves (high frequency electric field in the GHz band). Therefore, by using the high frequency power supply 2 of this embodiment, the thawing of the frozen food 12 can be promoted.

<Power detection unit 3>
The power detection unit 3 is a detection unit that detects both the output power P (incident wave) output from the high frequency power source 2 to the matching unit 4 and the reflected power R (reflected wave) returning from the matching unit 4 to the high frequency power source 2. Specifically, the power detection unit 3 is a combination of a voltage sensor and a current sensor.

<Matching unit 4>
The matching unit 4 is a circuit for matching the output impedance of the high frequency power supply 2 to the load side impedance including the frozen food 12, and for example, as shown in Fig. 1, is a circuit in which a series circuit of a variable coil 41 and a variable capacitor 42 is disposed between the upper electrode 11a and one terminal of the power detection unit 3, and a variable capacitor 43 is disposed between both terminals of the power detection unit 3. Although omitted in Fig. 1, the matching unit 4 also includes a control circuit for adjusting the reactance of the variable coil 41 and the capacitance of the variable capacitors 42, 43 in accordance with the reflected power R detected by the power detection unit 3.

When the amount of liquid water increases as the frozen food 12 thaws, the dielectric loss of the frozen food 12 changes significantly, and the impedance of the load side including the frozen food 12 also changes significantly. Therefore, the control circuit of the matching unit 4 adjusts the variable coil 41 and the variable capacitors 42 and 43 to make the output impedance from the high frequency power source 2 and the impedance of the load side including the frozen food 12 approximately equal, and by almost eliminating the reflected power R returning to the high frequency power source 2, the heating efficiency of the frozen food 12 is improved.

<An example of time transition of output power P and reflected power R>
2 is an explanatory diagram showing an example of the transition over time of the output power P and the reflected power R during thawing of a frozen food 12 in the high-frequency thawing device 100 of this embodiment. Note that the values of _Δt1 , _Δt2 , _Δt3 , _Δt4 , _ΔR1 , _ΔR2 , _ΔR3 , and _Tt in the diagram are parameters obtained by experiments for each type of frozen food 12 by the designer of the high-frequency thawing device 100 or a headquarters engineer of a convenience store chain, etc., and registered in advance so that a specific frozen food 12 (e.g., a standardized frozen lunch box) can be appropriately thawed, and are not parameters set by the user of the high-frequency thawing device 100 (e.g., a retail store clerk) when rapidly thawing the frozen food 12.

As shown in FIG. 2 , first, the output power of the high frequency power supply 2 is fixed at _P1 = _P0 (initial output power value set for each type of frozen food 12) and thawing of the frozen food 12 is started. In the initial first step (automatic matching), the matching unit 4 performs automatic matching so as to substantially eliminate the reflected power _R1 by making the output impedance of the high frequency power supply 2 and the impedance of the load side including the frozen food 12 substantially identical for a predetermined time _(Δt1 ) from the start of thawing.

Thereafter, in the first second step (fixed matching), the impedance matched in the preceding first step is temporarily fixed, and the thawing of the frozen food 12 is continued. Then, due to a change in dielectric loss as the thawing of the frozen food 12 progresses, the reflected power _R1 gradually increases, and the reflected power reaches a predetermined threshold value ( _ΔR1 ). When this threshold value is reached (time _t2S ), the high frequency power supply 2 reduces the subsequent output power P by the threshold value ( _ΔR1 ) corresponding to the increase in the reflected power R (output power _P2 = _P0 - _ΔR1 ), and starts the second first step (automatic matching).

In the first step (automatic matching) of the second time, the matching unit 4 performs automatic matching so as to substantially eliminate the reflected power _R2 by substantially equalizing the output impedance of the high frequency power source ₂ and the impedance of the load side including the frozen food 12 within a predetermined time (Δt2). As is clear from Fig. 2, the output power _P2 used in the first and second steps of the second time is suppressed to _P2 = _P0 - _ΔR1 , which is smaller than the output power _P1 = _P0 used in the first and second steps by the increase in the reflected power R, so that even if the frozen food 12 has thawed and is easily heated, it is possible to suppress the electric field from excessively concentrating on the edges, corners, protrusions, etc., which would otherwise be overheated.

In the high-frequency thawing device 100 of this embodiment, the above first and second steps are repeated until the set heating end time _Tt , and even in the third and fourth first and second steps, the output powers _P3 and _P4 of the high-frequency power source 2 are further suppressed according to the progress of the thawing. Therefore, at any time from the start of heating to the end of heating, an excessive electric field is not applied to the frozen food 12, and overheating of edges, corners, protrusions, etc. can be suppressed.

<Flowchart of operation and response action of high frequency thawing device 100>
Next, with reference to the flow chart of FIG. 3, an example of the operation of a user (e.g., a retail store clerk) and the thawing operation of the high-frequency thawing device 100 when rapidly thawing a given frozen food 12 will be described in detail.

First, in step S1, the user places the frozen food 12 in the heating chamber 1. Specifically, the user opens the door of the heating chamber 1, places the frozen food 12 on the lower electrode 11b, and then closes the door.

Next, in step S2, the user operates a menu button or the like of the high-frequency thawing device 100 to select from among previously prepared candidates for the object to be thawed, one corresponding to the frozen food 12 in the heating chamber 1. As a result, from among the thawing conditions previously prepared by the designer or the like, the thawing conditions corresponding to the frozen food 12 in the heating chamber 1 are selected and set in the high-frequency thawing device 100. The thawing conditions set here include the initial output power value P ₀ , the heating end time T _t , the automatic matching time Δt _i (i=1 to n), the increment threshold value ΔR _i (i=1 to n) of the reflected power, and the distance between the upper electrode 11a and the lower electrode 11b. When it is desired to thaw a frozen food 12 for which the thawing conditions are not registered, the user may set each parameter taking into consideration the material, shape, weight, temperature, etc. of the frozen food 12.

In step S3, the user issues a command to start thawing by operating a start button or the like on the high-frequency thawing device 100.

In step S4, the lifting mechanism of the heating chamber 1 is operated, and the upper electrode 11a or the lower electrode 11b moves up and down. This allows the distance between the electrode pair to be appropriately adjusted according to the thickness and shape of the frozen food 12, and the upper electrode 11a and the frozen food 12 are brought close to each other.

In step S5, the high frequency power supply 2 is started and thawing is commenced using the output power P ₁ =P _0. Thereafter, the high frequency thawing device 100 thaws the frozen food 12 while gradually reducing the output power P as described in FIG.

In step S6, the power detection unit 3 detects the reflected power _R1 returning from the matching unit 4 to the high frequency power source 2. As a result, automatic impedance matching is performed to substantially eliminate the reflected power _R1 by adjusting the variable coil 41 and the variable capacitors 42 and 43 of the matching unit 4 so that the output impedance of the high frequency power source 2 and the impedance on the load side including the frozen food 12 become substantially identical within a predetermined time ( _Δt1 ) from the start of thawing as shown in FIG.

In step S7, it is determined whether the time elapsed from the start of thawing of the frozen food 12 has exceeded the set heating end time Tt. If it has not yet exceeded the set heating end time _Tt , the process proceeds to step S8, and if it has already exceeded the set heating end time Tt, the process proceeds to step S11.

In step S8, the power detection unit 3 determines whether the reflected power _R1 is equal to or greater than the increment threshold value ΔR1. If the reflected power _R1 is not equal to or greater than the increment threshold value _ΔR1 , the process returns to step S6 and the reflected power R1 is detected again. On the other hand, if the reflected power _R1 is equal to _or greater than the increment threshold value ΔR1, the process proceeds to step S9.

In step S9, the output power _P2 to be used thereafter is reduced by the threshold value ( _ΔR1 ) from the current output power _P1 . As a result, the output power _P2 thereafter is set to _P0 - _ΔR1 , and the second first process (automatic matching) is started.

In step S10, i is incremented by 1. That is, the i-th first and second steps are completed, and the i+1-th first and second steps are started. This causes the reflected power _R2 to be detected in step S6, and the reflected power _R2 to be compared with the increment threshold _ΔR2 in step S8.

In this manner, the first and second steps are repeated, and when the elapsed time reaches the set heating end time _Tt (No in step S7), the process proceeds to step S11, the high frequency power supply 2 is turned off, and the heating of the frozen food 12 is terminated.

The parameters set in step S2 have been prepared in advance to properly thaw the frozen food 12 in the heating chamber 1, so by completing the process in Figure 3, the frozen food 12 can be thawed without overheating.

Note that if the automatic matching time Δt _i (i=1 to n) is set long and the increment threshold value ΔR _i (i=1 to n) of the reflected power is set small, the heating efficiency of the frozen food 12 is improved and the time required to complete thawing is shortened. On the other hand, if the automatic matching time Δt _i (i=1 to n) is set short and the increment threshold value ΔR _i (i=1 to n) of the reflected power is set large, the heating efficiency of the frozen food 12 is reduced and the time required to complete thawing is lengthened, but overheating of the edges, corners, protrusions, etc. of the food during thawing is less likely to occur, and deterioration of the thawing quality of the food can be suppressed.

Therefore, by appropriately setting the automatic matching time Δt _i (i=1 to n) and the increment threshold value ΔR _i (i=1 to n) of the reflected power, it is possible to prevent overheating of food without lengthening the time required for thawing.

In this embodiment, the upper electrode 11a and the lower electrode 11b are each a single electrode, but they may be divided electrodes formed by dividing multiple electrodes. In addition, the variable coil 41 and the variable capacitors 42 and 43 that constitute the matching unit 4 may have a configuration other than that illustrated in FIG. 1.

As described above, the high-frequency thawing device 100 of this embodiment reduces overheating of the edges, corners, protrusions, etc. of frozen foods, improving the thawing quality of the food.

Next, the high-frequency thawing device 100 according to the second embodiment of the present invention will be described with reference to Figures 4 and 5. Note that, in the following, overlapping explanations of points common to the first embodiment will be omitted.

Figure 4 is an explanatory diagram showing an example of the time progression of the output power P and the reflected power R during thawing in the high-frequency thawing device 100 of this embodiment. Also, Figure 5 is a flowchart showing an example of the operation and thawing action in the high-frequency thawing device of the present invention.

4, in this embodiment, thawing is also started with output power _P1 = _P0 (initial output power value), and the matching unit 4 performs automatic matching to substantially eliminate reflected power by making the output impedance of the high frequency power source 2 and the impedance of the load side including the frozen food 12 substantially the same for a predetermined time ( _Δt1 ) from the start of thawing (first step).The impedance matched in the first step is then temporarily fixed, and when the reflected power _R1 reaches a predetermined threshold value ( _ΔR1 ) (time _t2S ), the output power is reduced by the threshold value ( _ΔR1 ) (output power _P2 = _P0 - _ΔR1 ) and automatic matching is resumed (second step).

In the first embodiment, the thresholds _ΔR1 and the like are fixed values preset by a designer or the like, but the threshold ( _ΔR1 ) in the present embodiment is determined based on the output power _P1 and a predetermined ratio _N1 (%).

Next, an example of the operations and behavior when thawing frozen food will be described in detail with reference to Figures 4 and 5.

As is clear from a comparison of FIG. 3 of Example 1 and FIG. 5 of this embodiment, step S2 of Example 1 is replaced with step S2a, and step S8 of Example 1 is replaced with step S8a. Therefore, the following description will focus on steps S2a and S8a, which are not included in Example 1, and descriptions of other steps will be omitted as appropriate.

In step S2a, the user operates a menu button or the like of the high-frequency thawing device 100 to select from pre-prepared candidates for the object to be thawed, one corresponding to the frozen food 12 in the heating chamber 1. This sets the initial output power value P ₀ , heating end time T _t , automatic matching time Δt _i (i=1 to n), and threshold value N _i (i=1 to n) of the increment ratio (%) of the reflected power as the thawing conditions corresponding to the frozen food 12 in the heating chamber 1.

In step S8a, the power detection unit 3 judges whether the ratio (%) of the reflected power _R1 to the output power _P1 is equal to _or greater than a preset threshold value N1. If the ratio is smaller than the threshold value _N1 , the thawing is continued in this state (return to step S6), and when the ratio reaches the threshold value _N1 (time _t2S ), the process proceeds to step S9.

In this embodiment, if the automatic matching time Δt _i (i=1 to n) is set long and the threshold value N _i (i=1 to n) of the increment ratio (%) of the reflected power is set small, the heating efficiency of the frozen food 12 is improved, and the time required for the completion of thawing can be shortened. On the other hand, if the automatic matching time Δt _i (i=1 to n) is set short and the threshold value N _i (i=1 to n) of the increment ratio (%) of the reflected power is set large, the heating efficiency of the frozen food 12 is reduced and the time required for the completion of thawing is lengthened, but overheating of the edges, corners, protrusions, etc. of the food during thawing is less likely to occur, and deterioration of the thawing quality of the food can be suppressed.

Therefore, by appropriately setting the automatic matching time Δt _i (i = 1 to n) and the threshold value N _i (i = 1 to n) of the increment ratio (%) of reflected power, it is possible to prevent overheating of food without lengthening the time required for thawing.

Here, by setting the threshold value N _i (i = 1 to n) of the increment ratio (%) of the reflected power to, for example, about 10%, the increase in the reflected power to the high frequency power source 2 can be suppressed, thereby reducing the failure rate of the high frequency power source 2 and lengthening its lifespan.

Next, the high-frequency thawing device 100 according to the third embodiment of the present invention will be described with reference to FIG. 6. Note that, in the following, overlapping explanations of points common to the second embodiment will be omitted.

In the second embodiment, in step S2a (FIG. 5), the heating end time _Tt corresponding to the frozen food 12 in the heating chamber 1 is preset, and the thawing is continued until the elapsed heating time reaches the heating end time _Tt (step S7).

In contrast to this, in this embodiment, as shown in step S2b of Fig. 6, a criterion M for thawing completion is set corresponding to the frozen food 12 in the heating chamber 1. Then, in step S7a, if the ratio of the threshold value (ΔR _i ) of the reflected power to the initial output power value _P0 becomes equal to or less than a certain threshold value M (%), it is determined that thawing is complete and the process proceeds to step S11, where heating is automatically terminated. In this case, the threshold value M (%) is the criterion for determining whether thawing is complete, and is, for example, about several percent.

100 High-frequency thawing device 1 Heating chamber 11a Upper electrode 11b Lower electrode 12 Frozen food 2 High-frequency power source 3 Power detection unit 4 Matching unit 41 Variable coil 42, 43 Variable capacitor

Claims (6)

A high frequency power source that outputs high frequency power in the MHz band;
an electrode pair for applying a high frequency electric field in the MHz band to the frozen food using the output power of the high frequency power supply;
a matching unit connected between the high frequency power supply and the electrode pair, for matching an output impedance of the high frequency power supply to a load impedance including the frozen food;
a power detection unit that detects reflected power returning to the high frequency power source,
the matching unit repeats a first step of automatically matching the output impedance to be substantially the same as the load side impedance and a second step of fixing the output impedance automatically matched in the first step until the thawing of the frozen food progresses and the reflected power reaches a predetermined threshold value, until a heating end time;
The high-frequency power supply outputs an output power obtained by subtracting the threshold value from the previous output power from the first step subsequent to the second step. 2. The high frequency thawing device according to claim 1,
The high frequency thawing device according to claim 1, wherein the threshold value is a value registered in advance for each type of the frozen food. 2. The high frequency thawing device according to claim 1,
A high-frequency defrosting device, wherein the threshold value is determined from a predetermined ratio to the output power. 4. The high frequency thawing device according to claim 3,
A high-frequency thawing device characterized in that heating is terminated when a ratio of the threshold value of the reflected power to the output power at the start of heating becomes equal to or less than a predetermined threshold value. The high frequency thawing device according to any one of claims 1 to 4,
A high-frequency thawing apparatus, wherein the duration of the first step is a value registered in advance for each type of frozen food. The high-frequency thawing device according to any one of claims 1 to 3,
The high-frequency thawing device is characterized in that the heating end time is a value registered in advance for each type of frozen food.

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