JPH0443593A - High frequency heating device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high-frequency heating device that performs thawing of objects such as frozen foods by all-dielectric heating.

2. Description of the Related Art In recent years, with the spread of frozen foods, there is a need for a high-frequency heating device that can thaw the entire amount of frozen foods almost uniformly.

Conventionally, this type of high-frequency heating device is a so-called microwave oven that uses a micro fl.
Large-scale high-frequency defrosting devices such as those shown in the figure above are used, and in particular, many small, easy-to-handle, and inexpensive microwave ovens are in use. In particular, this type of microwave oven is the most commonly used for household use.

The configuration will be explained below with reference to FIG. 6.

As shown in the figure, the microwave oven 1 includes a ferro-resonant transformer 2,
An electric pumping device 5 consisting of a capacitor 3 and a diode 4, a magnetron 6 which generates radio waves of 2450 htl+ with all electric power by this power supply device 6, an oven 7 to which the radio waves from the magnetron are fed, and a commercial power supply to the power supply device 6. power supply 8
The heating control device 9, etc., which opens the power supply from the heating control device 9, etc. is used.

The heating control device 9 receives a signal from a weight sensor 11 that detects the weight of an object 10 to be thawed, such as a frozen product in the oven 7, and performs intermittent control of a switch 12 such as a relay according to a predetermined thawing control sequence. It was configured to thaw the object 10 to be thawed.

In the above configuration, the operation will be explained using the decompression sequence shown in FIGS. 7(a) to (C). FIG. 7(a) shows the heating time area Th (heat area) and the non-heating time area Ts.
Heating area diagram showing (7-Tanzoing area), Fig. 7 (
b) is a control diagram B of the radio wave output Po of the magnetron 6 that was previously controlled using the control sequence shown in this heating area diagram, and FIG. tfjl It is an average output state g diagram showing the average heating output that changes as output control Q is performed. As is clear from this figure, the thawing of the object 10 using microwaves is as follows:
Heating time area T'h (heat area) and non-heating time area T
s (nutanding region), and the average heating output was controlled according to the size of the object 10 to be thawed and the elapse of heating time. This t'L is for improving the defrosting performance due to the heating distribution of microwave heating. That is, in order to improve the defrosting performance through heating distribution, the cumbersome heating control sequence described above has been devised, and a defrosting method that slowly defrosts food over a considerably long period of time has been used for practical purposes.

Then, the thawing is completed by automatically setting the total heating time (sum of Th and τB) based on the weight of the object to be thawed 1o, etc., using a predetermined calculation method, or manually based on the user's experience. It was something to do.

Problems to be Solved by the Invention These conventional high-frequency heating devices have disadvantages in that the thawing time is too long and, moreover, sufficient thawing performance cannot be obtained.

That is, thawing by microwave heating is dielectric heating using a high frequency electric field of 2450 kh, similar to circumferential cutting. Therefore, the high frequency absorption coefficient of water is particularly large.

On the other hand, the high frequency absorption coefficient of ice is approximately 1/600 of that of water.
Therefore, the heating distribution due to dielectric heating is further expanded. FIG. 8 is an example showing the temperature distribution after thawing a rectangular piece of frozen fish meat in a general microwave oven 1. As shown in the figure, in the case of a rectangular shape, the electric field concentration at each corner portion A is strong, and the electric field strength at the edge portion B is also high. On the other hand, the electric field strength is weak in the part indicated by D, and even if corner part A is heated to a temperature of 70°C or higher, part D will remain at 16°C.
There are cases where the thawing performance is extremely poor, below °C.

That is, when defrosting by microwave heating, it was inevitable that the heating distribution would be based on the shape and the physical property of the difference in high frequency absorption coefficient between ice and water. In order to suppress this inconvenience as much as possible, a configuration is adopted in which the data is decompressed using a decompression sequence as shown in FIG.

However, if the heating control is even slightly inappropriate, the defrosting performance often becomes severely inadequate as shown in Figure 8, and microwave defrosting cannot gain the trust of users in terms of its performance. It was not something that could be done.

In other words, as shown in Figure 7, Nutanding 8FF ff1
Even if you set up JTs and thaw slowly over time, the thawing result may be that the food is partially boiled, as shown in Figure 8, and thawing by microwave heating is very dissatisfying. It was a big one.

In addition, if thawing ends too quickly or too slowly, the thawing result may be impossible to cut with a knife or the temperature may become too high, so it is impossible to always achieve good thawing. It was difficult.

The present invention solves the above-mentioned problems, and aims to enable anyone to easily defrost an object with good defrosting performance.

Means for Solving the Problems In order to achieve the above object, the present defense provides a microwave oscillator such as a magnetron, an oscillator drive unit that energizes the microwave oscillator, and a device that is supplied with power by the microwave oscillator and that is used to store frozen food or the like. an oven for storing the thawed object, a pressure reducing means for reducing the pressure at least in the vicinity of the object to be thawed in the oven, and a heating control section for controlling the oscillator drive section and the pressure reducing means, the heating control section The first means for solving the problem is to start the oscillator drive section to drive the microwave oscillator after the pressure near the object to be thawed has decreased to a predetermined value.

Further, in addition to the first problem-solving means, the heating control section is provided with a release means for releasing the reduced pressure state by the pressure reduction means, and the heating control section operates the release means after the oscillator drive section is stopped, and controls the pressure near the object to be thawed. The second problem solving means is that the creation of the pressure reducing means is stopped after the pressure rises to a predetermined value.

Effect of the Invention The present invention, according to the first problem-solving means described above, adjusts the pressure near the object to be thawed to a desired pressure or lower pressure before at least a part of the object to be thawed is thawed and thawed. By adjusting the line of water contained in the object to be thawed, partial acceleration of thawing can be suppressed, and the entire object to be thawed can be thawed uniformly.

In addition, with the second problem-solving means, after the food to be thawed is almost uniformly thawed as described above, the reduced pressure state is automatically released to facilitate opening and closing of the oven, and the pressure is returned to a safe level. The decompression means can be automatically stopped from the start, allowing easy and safe termination of defrosting and heating.

EXAMPLE Hereinafter, an example of the present invention will be explained with reference to FIGS.

As shown in the figure, the electric heating section 20 is powered by a commercial power source, and an oscillator drive section 23 is connected to the power supply section 20, an inverter 21 that receives power from the power supply section 20, and an external pressure transformer 22.
and energizes the microwave oscillator 24. The output radio waves of the microwave 8 micrometer 24 are supplied to the oven 26.
, the object 26 to be thawed, such as frozen food, in the oven 26 is dielectrically heated.

On the other hand, the oven (or a vacuum container installed inside the oven)
26, the pressure is reduced to a predetermined pressure by a pressure reducing means 27. The heating control section 28 receives a signal from a pressure detection means 29 that detects the pressure of the oven (or pressure reduction container) 2517'', and operates the oscillator drive section 23 and the pressure reduction means 2.
7 to perform dielectric heating while controlling the pressure in the oven (or vacuum container) to a pressure that meets the desired thawing conditions. Here, when a vacuum container is used in the oven 26, the pressure is reduced only in the vicinity of the object to be thawed 26, which simplifies the groove construction of the entire device including the oven 26 and the like, and the pressure reduction capacity of the pressure reduction means 27. It has the advantage of being able to reduce The heating control unit 28 also includes a release means 3o for returning the pressure inside the oven (or vacuum container) 26 from a predetermined reduced pressure state to atmospheric pressure after the thawing of the object 26 by dielectric heating in the reduced pressure state is completed. is controlled so that the object to be heated 2e can be easily taken out from the oven (or vacuum container) 25.

Incidentally, the pressure reduction by the pressure reduction means 27 is configured to be performed for the purpose described below.

Microwave heating is dielectric heating using a high frequency electric field of 2450 j/h, and therefore absorbs the most significant energy from water, and is generally used to heat foods containing moisture. Therefore, when defrosting the object 26, if the negative portion is water, the thermal energy of the blade will be significantly concentrated in that portion, resulting in extremely uneven defrosting performance.

This is because ice absorbs radio waves (2450) compared to water's 17600.
This is because it is extremely small. Therefore, a partial boiling phenomenon occurs due to a partial temperature rise of the object to be thawed 26,
In many cases, the defrosting performance was insufficient. This is why the conventional high-frequency heating apparatus performs thawing sequence control as shown in FIG. If we consider the boiling point Tb of water here, it changes with pressure P as shown in FIG. That is, atmospheric pressure 760 wHg
Water boils at 100°C, and this boiling point (100°C) is maintained as long as water is present.

The present invention makes use of this phenomenon to control the heating temperature of the object 2e to be thawed by dielectric heating to a predetermined temperature or lower, and dramatically improves the delicate heating temperature control required for thawing compared to the conventional method. This is what we are trying to do. That is, as shown in FIG.
When controlled at 0 ffHg (66.4 mHcr to be exact) or 20 mHg, the boiling points of water are controlled at approximately 40'C and 20''C, respectively.Therefore, the maximum temperature of the material to be thawed 2e is below the temperature determined by the pressure P, and can be strictly controlled to below a predetermined desired temperature. Therefore, when thawing is performed where heating distribution is likely to occur, the maximum temperature of the object 26 to be thawed is set to the pressure P. The temperature can be maintained below the appropriate temperature, and the yield is extremely high! It is possible to thaw the object 26 to be thawed without changing its physical properties.

For example, if the pressure P is adjusted to about 50 smHgrc, the temperature of the thawed material will be maintained at about 40°C or less, and 20 smHgrc or less.
When adjusted to txHH, thawing and heating can be performed while maintaining the temperature at about 20"C or below. In particular, since the temperature is maintained at a temperature below 20"C at which denaturation of the object to be thawed 26 does not occur, thawing of raw materials is possible. Furthermore, if the inventors can set a sufficient capacity of the pressure reducing means 27 according to the weather conditions, it is possible to thaw raw materials by controlling the pressure P to about 10 fin Hq. It was also confirmed that the food could be thawed at a more suitable temperature of around 10°C.

It is clear that in order to achieve such good thawing, it is essential to maintain the pressure P at or below a desired value. However, when the object to be thawed 26 is heated and partial thawing based on the above-described heating distribution progresses, water evaporates, and the magnitude relationship between the generated volume of the evaporated water vapor and the exhaust capacity of the pressure reducing means 27 becomes a problem. If the exhaust capacity of the pressure reducing means 27 becomes lower than the volume of evaporated steam generated, the pressure will increase to P, and as a result, the boiling point Tb will increase, making it impossible to maintain a good thawed state.

Therefore, in this defense, as shown in Fig. 1, heating control @'S2
8 controls the output of one inverter 21 of the optical transmitter female part 23 so that the pressure P is maintained at a desired pressure. That is, the signal from the pressure detection means 29 is compared with the reference signal from the reference signal generator 31 and inputted to the microcomputer 33 as an output from the error term expander 32. The microcomputer 33 receives this signal and controls the output of the inverter 21 to maintain the pressure P below a predetermined desired threshold (for example, 20 wHg). One! 1. If the amount of evaporation of steam that exceeds the exhaust capacity of the pressure reducing means 27 increases, the inverter 2
As a result, the magnitude of the T-wave output of the microwave oscillator 24 is lowered to reduce the amount of water vapor evaporated. As a result, the occurrence of a phenomenon in which the exhaust capacity of the depressurizing means 27 is insufficient can be completely prevented, and the extremely good defrosting conditions described above can always be achieved.

On the other hand, the state of the exhaust gas produced by the pressure reducing means 27 is detected by the exhaust state detecting means 34 and sent to the heating control section 28 . Upon receiving this detection signal, the heating control section 2B
! ri optical oscillator drive unit 23 and microwave oscillator 2
This is to control the microwave heating output of step 4. That is, the heating control unit 28 can determine the magnitude of the microwave heating output or the heating time based on the result of the arithmetic processing of the signal from the exhaust state F5 detection means 34.
6 in a beautiful state at all times and can be automatically thawed.

The heating control unit 28 is configured to adjust the magnitude of the microwave heating output based on the signals from both the pressure detection means 29 and the exhaust state detection means 34, and automatically terminate the heating based on the detection signal from the exhaust state detection means 34. However, pressure detection means 2
It is also possible to omit step 9 and adjust the magnitude li of the microwave heating output using only the signal from the exhaust state detection means 34.

FIG. 3 is a more detailed embodiment of the embodiment shown in FIG.
Components having the same configuration as in FIG. 1 are given the same reference numerals.

In the figure, a power supply unit 2o includes a commercial power supply 4o and a diode bridge 41, and supplies a full-wave rectified waveform voltage to an inverter 21. Inverter 21 is 1,000-1,000-ku coil 4
2. Capacitor 43, 44, insulated gate bipolar transistor (IGBT) 4es, diode 46, etc.
A high frequency voltage is generated in the primary winding of the external voltage transformer 22.

This high frequency voltage is connected to a capacitor 47 and a diode 48°4.
A high DC voltage is supplied to a microwave oscillator 24 made of a magnetron through a half-wave voltage doubler rectifier circuit made of 9. As a result, the p microwave oscillator 24 oscillates, and the oven 25
A high frequency radio wave of 245014 is supplied to the station.

The heating side portion 28 includes a power supply circuit 61 (outputs a stabilized voltage Vcc) that stabilizes the power voltage dropped through the resistor 6o, a microcomputer 52, a synchronous oscillator 63,
It is composed of an error amplifier 64, a reference voltage source 66, etc., and the synchronous oscillator 53 is connected to the capacitor 44 by resistors 66 and 67.
, the anode current of the microwave oscillator 24 changes the conduction pulse width of the transistor (IGBT) 45 in synchronization with the co-fitting operation of the resonant circuit consisting of the external pressure transformer 22.
PWM to achieve the target anode current given by
It is something that can be controlled. On the other hand, the microcomputer 62
controls opening/closing of switches 58, 69'i such as relays in response to commands from an operating section (not shown). That is, the microcomputer 62 controls the switches 58 and 59 in a predetermined sequence based on the signal from the pressure detector 29,
After the pressure reduction means 27 consisting of a vacuum pump is operated to perform the above-described pressure reduction process, the inverter 21 is operated to carry out microwave heating to achieve good thawing and heating.

The microcomputer 62 converts the difference signal between the signal from the pressure detection means 29 and the signal from the reference signal generator 31 into an error amplifier 32.
The reference voltage source 56 is controlled by the reference voltage source 56.

The synchronous oscillator 53 controls the conduction pulse width of the transistor (IGBT) 46 in accordance with the voltage generated by the reference voltage source 66, and controls the anode current of the microwave oscillator 24.

As a result, the output of the inverter 21 is controlled so that the pressure P becomes a desired pressure or less, and the microwave output of the microwave oscillator 24 is adjusted.

The microcomputer 62 is further inputted with a detection signal from the exhaust g detecting means 34, and a detection signal indicating the humidity or temperature of steam generated when a portion of the object 26 to be thawed is thawed and boils at, for example, 20°C. be done. The microcomputer 52 uses a reference voltage source 63 based on this standard.
and adjusts the size of the microwave pumping direction of the microwave oscillator 24 so that the steam output does not exceed the exhaust capacity of the pressure reducing means 27. As a result, the pressure P can be maintained below the desired pressure, so the object to be resolved 26 is thawed in a good condition.Furthermore, the microcomputer 62 performs a predetermined logical operation process based on the exhaust-like light detection signal. , it is possible to determine the end time of microwave heating and automatically end microwave heating, that is, thawing. In other words, microwave heating is automatically terminated according to this detection signal and the initial weight information of the object 26 to be thawed (which may be detected automatically or input by the user). This allows the user to perform defrosting very easily and without failure.

Furthermore, when the predetermined heating time ends and thawing is completed, the microcomputer 62 operates the release means 30 to automatically return the pressure in the oven 26 to atmospheric pressure.

Therefore, the operator of the high-frequency 710 heating device can easily move the object to be heated 26 from the oven 26 based on the completion information for releasing the reduced pressure state (via a buzzer, optical display, etc.) performed by the microcomputer 62 after the return to atmospheric pressure. It can be taken out.

FIGS. 4(a), (b), and (c) show the heating time Th and i Sakaideka Po when the object to be resolved 26 is thawed, respectively.
It shows the state of change in the detection voltage due to the change in resistance of the exhaust temperature sensor 34, which is the exhaust condition detection means 34. As is clear from this figure, the non-heating time region Tst is often not required at all in the high frequency yield heating device of the present invention. In Fig. 4(b), l@11 is controlled so that the radio wave output decreases (600W).
As mentioned above, since the pressure reducing ability of the pressure reducing means 27 is constant, the conduction time Ton of the transistor (IGBT) 46 is adjusted according to the detected voltage of the exhaust state transfer means 34 so that the reduced pressure P can be maintained at a predetermined value. This is because the heating radio wave output is adjusted. That is, by controlling the pressure P in this manner, the material to be thawed 26 is thawed by micro-numbers under a predetermined pressure or a pressure lower than the predetermined pressure.

Therefore, the occurrence of a state in which the depressurization capacity is insufficient is completely prevented, and complete thawing that does not occur to the food due to partial heating can be achieved. A high-frequency thermal device that incorporates the present invention in this way! This method achieves significantly better defrosting than conventional methods, without using the extremely inconvenient control method of greatly reducing the high-frequency output to compensate for the shortcomings in heating distribution and providing a non-heating time region Tsi. This makes it possible to realize the thawed state of the object 26, thereby significantly improving the usability and expanding the range of use of high-frequency equipment using dielectric heating. Then, the amount of evaporation of water vapor is determined by the pressure reducing means 2.
If the amount is too high compared to the exhaust capacity in step 7, the high-frequency heating output t should be adjusted so that the amount of steam generated is commensurate with the exhaust capacity.
- to control the pressure so that it is at or below the desired pressure.

Further, the mowing pressure of the exhaust state detection means 34 changes from Hl to H.
2, the subsequent heating time Tp is determined by the logical operation of the microcomputer 62, and the automatic defrosting and heating is terminated based on the signal from the exhaust state detection means 34. I can do it. Since this logical calculation can change the calculation formula depending on the amount of electricity and the type of the object 26 to be thawed, it is possible to perform the optimum heating control 81 according to the state of the object 26 to be thawed.

FIG. 6 shows the operating state of the pressure reducing means 27, the changing state of the pressure P, the changing state of the detected voltage of the exhaust state g forming means 34, and the microwave oscillator 2, respectively.
This is a sequence chart showing the changes in the microwave output voltage Po of No. 4.

At time 1-10, the pressure reducing means 27 is activated, and at tl the pressure P
When reaches a predetermined value P1 (for example, 50 ff1(q)), the microwave oscillator 24 is activated so that the microwave output Po becomes the maximum output of eooW.

Thereafter, the pressure P decreases to the next level P2 (for example, 20 mHg) due to the ability of the pressure reducing means 27. That is, the pressure P
By configuring the microwave heating to start after reaching Pl, when a part of the object to be heated 26 melts (at a time close to t2 between 11 and t2-J), the pressure P becomes 22, and it can be guaranteed that the boiling point has reached the desired value. When t=t2 is reached, steam starts to be generated from the thawing object 26, and the exhaust state detection means 3
The detection voltage starts to rise to 4 as shown in the figure. When this token is detected, the microwave output power P is reached at t=t3.

It is lowered at 1500Wi. Therefore, the pressure P is P=P3
(for example, 2 s w x Hq), but is maintained at this level. Therefore, 20°C to the boiling point
By maintaining the forward and backward movement, the object 26 to be thawed can be in a good thawed state.

Further, based on the rate of change of the detection voltage of the exhaust state detection means 34 from t=t3 to t=t4, a time t6 for -Po=OW is determined by a logical operation, and at t=tS, the microwave heating is stopped. Ru.

Next, at t=t7, although not shown, the release means 3o is activated, so that at t=t8, the pressure P is returned to atmospheric pressure. As a result, the thawed object 26 can be easily taken out from the oven 26.

Furthermore, after the pressure P returns to atmospheric pressure, t = t
9, the pressure reducing means 27 is stopped, and the pressure reducing means 27 does not stop operating with a high pressure difference applied thereto.
High reliability can be guaranteed without causing failures due to this pressure difference.

In addition, when an oil rotary vacuum pump or the like is used as the pressure reducing means 27, it is possible to prevent a decrease in reliability due to backflow of oil or the like.

Effects of Investigation As is clear from the above examples, according to this investigation, part of the heating process is caused by starting the optical oscillator drive unit and activating the microwave oscillator after the pressure near the object to be thawed has decreased to a predetermined value. Therefore, before at least a part of the thawed object is thawed and thawed, the pressure near the thawed object can be partially reduced to the desired pressure or a pressure lower than the desired pressure. To provide a user-friendly high-frequency heat training device which allows anyone to defrost easily and reliably with good defrosting performance, and eliminates the drawbacks of the conventional ones.

Further, the heating control section is provided with a release means for releasing the state of pressure reduction caused by the pressure reduction means, and the heating control section operates the release means after the oscillator drive section has stopped, and after the pressure near the object to be thawed has increased to a predetermined value, the pressure reduction means is activated. I set it to stop, so after the decompression is complete,
It is possible to automatically release the pressure reduction state to make it easier to open and close the oven, and to automatically stop the pressure reduction means after returning to a safe pressure. Therefore, it is possible to provide a high-frequency heating device that can achieve good thawing performance, is easy to operate, is convenient to use, and can finish thawing and heating safely and with high reliability.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a high-frequency heating device according to a simple embodiment of the present invention, Fig. 2 is a characteristic diagram of the relationship between reduced pressure and the boiling point of water, Fig. 3 is a circuit diagram of the same high-frequency heating device, and Fig. 4 is the same. A sequence chart of the #freezing operation of the high-frequency heating tabletop, Figure 6 is a sequence chart of the defrosting operation of the high-frequency heating tabletop, Figure 6 is a circuit diagram of a conventional high-frequency heating device, and Figure 7 is a diagram of the same high-frequency heating device. A sequence chart of the thawing operation, FIG. 8, shows the temperature distribution of the object to be thawed by the same high-frequency heating device. 23... Optical vibrator drive unit, 24... Micro plate valve vibrator, 25... Oven, 26...
...Object to be thawed, 27...Decompression means, 28...
...Heating system (to) part. Name of agent: Patent attorney Takashi Kugeno and 1 other person 1st
Zujiru - Koushun 41r b---Fif D! Asashige 4 no L view 1 bar-opso 1 (r-棉解2!su2ku-3M+p; Fig. 4 Fig. 2 Fig. 5 Pan□H-J)

Claims (2)

[Claims] (1) A microwave oscillator such as a magnetron, an oscillator drive unit that energizes the microwave oscillator, an oven that is powered by the microwave oscillator and stores food to be thawed such as frozen food, and a pressure reducing means for reducing the pressure at least in the vicinity of the thawed object; and a heating control section for controlling the oscillator drive section and the pressure reducing means, the heating control section being configured to reduce the pressure near the thawing object to a predetermined value. After that, the high frequency heating device starts the oscillator driving section to drive the microwave oscillator. (2) A release means is provided for releasing the reduced pressure state caused by the pressure reduction means, and the heating control section operates the release means after the oscillator drive section has stopped, and the pressure reduction means after the pressure near the object to be thawed has increased to a predetermined value. 2. The high-frequency heating device according to claim 1, wherein the operation of the high-frequency heating device is stopped.