JPS58141768A - Device for detecting thawing state - Google Patents

Abstract

PURPOSE:To carry out properly thawing, by measuring the change of physical properties of a food in thawing by high frequency. CONSTITUTION:The frozen food 3 is put in the heating chamber 1, and a high- frequency signal having a frequency different from 2.45GHz generated from the oscillator 16 for high-frequency signal is radiated from the transmitting antenna 17 to the heating chamber 1. For example, the change 21 in the output voltage of the thawing of a frozen food at about -18--15 deg.C is gradually lowered by heating, and the absorption of electrical radiation is enlarged. The food temperature tmin to make the change in voltage minimum is approximately -3--1 deg.C, showing that the food is transferred to a state where it is in state of ice crystal. The thawing is detected by finding a point reaching the tmin.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on a thawing state detection device that detects the degree of thawing of frozen foods placed in a refrigerator. This invention relates to a thawing state detection device that measures changes in physical properties using high frequency waves and obtains clues for appropriate thawing.

Conventional defrosting methods for frozen foods include natural thawing, running water thawing, heating thawing, and thawing using high-frequency energy using a microwave oven in the home, and for industrial use, 2.45GH2 high-frequency energy or In either case, decompression is performed using high frequency energy of 10 MHz.

Due to the difference in the amount of frozen food and the temperature of the rice, it is not possible to thaw the food properly, resulting in over- or under-thawing, resulting in the food being boiled, or conversely, under-heating, which requires re-thawing. may occur.

It was extremely troublesome as it required constant monitoring of defrosting.

As a recent improvement in usability.

A device has been developed that detects thawing by measuring the temperature of food using infrared rays. As the principle diagram of this device is shown in FIG. 1, a food placing table 2 is placed inside a heating chamber 1 surrounded by metal, and a frozen food 3 is placed on this food placing table 2. Above the heating chamber 1 is a 2.45 GHz high frequency heating source 4. High frequency heating means constituted by a waveguide 5 is arranged. 6 is an excitation port for high frequency energy. At this point, the door (not shown) is opened and the food 3 is placed inside the heating chamber 1.

The high frequency energy oscillated by the high frequency heating source 4 is excited from the excitation port 6 through the 3P waveguide 5 to high frequency heat the food 3, and the infrared rays 7 from the food 3 that increase with heating are transmitted through the slit 8. This infrared ray 7
is detected by the infrared detector 9, and the detection signal is amplified.
The high frequency heating source 4 is controlled by signal processing in the converting and controlling device 10°.

This infrared detection method can measure the absolute temperature of 9 foods, so it can measure the thawing temperature, that is, around 0° C. However, even if this method is actually used, there are various problems. The first is that even if it is possible to measure temperature, it is not always possible to properly detect the thawing temperature, and the end point of thawing cannot be determined with certainty due to the melting of the ice.The second is that 2.
45 GHz HZ High frequency energy can only be measured in a narrow viewing angle range that cuts off the energy, and thirdly, because the amount of infrared signal is small, complex electronic circuit configurations are required for signal processing such as separating and amplifying noise components. It is necessary, and there is little possibility that it could be applied to anything other than microwave ovens.

The present invention eliminates the drawbacks of the prior art, and aims to accurately measure the changes in physical properties of frozen foods when they are thawed.When a wave is emitted, the food absorbs radio waves when the temperature of the frozen foods rises and approaches the thawed state. Thawing takes advantage of the rapid absorption change in the amount of ice, the phenomenon in which radio wave absorption is at its maximum in the crystalline state at the end of thawing, and the phenomenon in which the radio wave absorption rate decreases as the temperature rises from the ice crystal to room temperature or high temperature. The present invention relates to a thawing state detection device that can perform accurate thawing based on changes in the amount of radio wave absorption.

That is, this physical property change can be explained as follows.

Foods have a high water content, high dielectric constant and dielectric loss, and have the property of absorbing high frequencies.

This physical property has a temperature dependence; absorption is small when the substance is in a frozen state, and is maximum when it is in the '''' ice crystalline state.

When the temperature rises further after passing through the ice crystal, absorption tends to decrease again, and this change in state is a peculiar phenomenon that becomes more pronounced as the water content of the food increases.

The present invention utilizes the above phenomenon to indirectly, but accurately, detect and control defrosting.

An embodiment of the present invention will be described below with reference to the drawings.

Figure '2 is a perspective view of the present invention applied to a microwave oven. In the figure, 11 is a cabinet, 12 is a door, 15 is an exhaust port, 14 is a nailing device including a thawing detection function, a thawing completion indicator light, a thawing completion buzzer, etc., and 15 is a display unit including the control device 14.

FIG. 3 is a sectional view for explaining the present invention in detail. A door (not shown) is attached to the heating chamber 1, which is surrounded by a metal plate or a metal mesh, so that it can be opened and closed, and a food mounting table 2. Frozen food 3 is placed. The frozen food 5 is thawed by a heating source (none of which is shown) such as high frequency energy from a high frequency heating source, electricity, or the like. 16 is a high frequency signal generator used in the present invention, 17 is a transmitting antenna for high frequency signals, 18 is a receiving antenna, 19 is a converter that converts the received signal into a control signal, and 20 is a control device P device.

It is possible to minimize the formation of the heating chamber 1 by transmitting the high frequency signal of the wife from the transmitting antenna 17, thereby reducing measurement errors due to complex resonance. However, these radio waves are still reflected multiple times inside the heating chamber.

The heat either escapes through the antenna or the air gap, or becomes heat loss, but if food with a large dielectric loss enters, a large amount is consumed by this food, and the amount that escapes from the antenna becomes smaller. Furthermore, since dielectric loss is also temperature dependent, the received signal of the antenna also exhibits a unique change pattern.

Figures 4 and 5 show the relationship between the received signal, that is, the food temperature, and the output voltage when heating frozen food, and -18
When a frozen food is thawed at ~-15°C, the output voltage change 21, 22, 23 is drastically reduced by heating, indicating that radio wave absorption increases.

The food temperature tmin, tx at which this voltage change is at its minimum or becomes almost constant is approximately -3°C to -1°C as a result of determining it for nine different foods, and this temperature is approximately -3°C to -1°C, which is the temperature that is included in frozen foods. This indicates the temperature at which the water in the ice changes from an ice state to a so-called ice crystal state in which ice and water are mixed, and thawing can be detected by finding the point at which tmin and tx are reached. Most of the patterns of output voltage change are 4th
The changes shown in FIG. 21 are shown, but in so-called light loads (frozen ranman, pizza pie, shumai, etc.) with little moisture, that is, little ice, there are some that show changes as shown in FIG. 5, 22.25. In addition, in FIGS. 4 and 5, it has been experimentally confirmed that when the food is further heated after thawing, the output voltage increases slightly until the water boils.

FIG. 6 is an explanatory diagram of a means for uniformly thawing the food 3 by rotating it on the rotary table 24 in FIG. 3 and subjecting it to high-frequency heating by the high-frequency heating source 4. If the output voltage obtained in Fig. 1 is output as is, Fig. 7 2
5, and the average value (average of the rotating rotor of the rotary mounting table 241) is as shown in FIG. 26. Also, rotating mounting table 2
The fluctuation of the output voltage in one revolution of No. 4 fluctuates as shown in Figure 27 of No. 8 due to the influence of the shape of the food, and this waveform continues to follow the temperature change. Therefore, in such a case, either average the total output voltage during one rotation in accordance with the rotation of the rotary mounting table 24 shown in FIG. 6, or always monitor only the same point during one rotation.

There are two ways to measure it, but the latter is more accurate. That is, as shown in FIG. 6, an elongated rotation detection plate 30 is fixed to the shaft 29 of the motor 28 that drives the rotary mounting table 24 and rotates. A rotation detection element 31 detects the rotation of the rotation detection plate 30 every time it rotates. A synchronization detector 32 detects the detection signal of this detection element 51. A converter 33 that compares the signal from the synchronization detector 32 with the signal from the receiving antenna and receives the signal only while there is a two-rotation detection signal.The signal from the converter 33 is obtained to control the heating source.P It is preferable to provide a control device 34 that detects and controls the output voltage using these devices, and in this case, the change in the output voltage is determined by
This is because it is intermittent as shown in FIG.

Even in this state, when the output voltage reaches the minimum point, defrosting is complete, so heating can be stopped. However, in Figure 6, the transmitting and receiving antennas 17.18
There is a risk that the high-frequency energy of 2,451) H2 that heats the food 3 from the part will be transmitted and leak to the outside, so countermeasures are required to prevent this.

FIG. 10 is a circuit block diagram of a thawing state detection device including the radio wave leakage prevention means. In the figure, 36 is a sweep oscillation circuit, which is used in household microwave ovens.
It is preferable to sweep and oscillate radio waves with an output of several tens of mw. 57 is an oscillation signal. This oscillation signal is 2.4
Band re to prevent 5GHz frequency inflow
The signal is transmitted from the transmitting antenna 17 supported by the transmitting antenna support 39 via the injection filter 5B. At the same time, the reception number 4 is received by the reception anti-0P 18 supported by the reception antenna support 40, and Band rejection
filter 41.

Amplifier 42. Waveform shaping circuit 43. Differential circuit 44. The heating power supply control circuit 46 is reached via the storage and comparison circuit 45 and is operated. According to this means.

It is possible to distinguish between high-power high-frequency energy oscillated by the heating source and small-power high-frequency energy swept oscillated.

Problems such as malfunctions can be prevented. In the figure, the reason for the sweep oscillation on the transmitting side is that the maximum absorption wavelength changes depending on the food (9) and is not constant, so it is swept so that detection is always performed at the maximum absorption wavelength. Also, the differentiator circuit (4)
4 is used when there is no minimum point of the output voltage as shown in Figure 5, 22.25, to differentiate the received signal No. 4 and to control it when its absolute value approaches a certain value close to O. be. .

The above is an outline of the operation of the detection device, but in actual implementation, a pair of heaters for heating food is provided inside the refrigerator, and these are connected to the transmitting antenna 17 and the receiving antenna 18. It is something. The reason for this is to use the inside of the refrigerator effectively and to simplify the structure. As a pair of heaters, 11F uses sheathed heaters whose outsides are covered with metal pipes. An example thereof is shown in FIG. This figure shows an apparatus in which one of the upper and lower two heaters of a microwave oven with a heater, which is one form of a microwave oven, is used for transmission and the other one is used for reception. In the figure, the upper heater 47 is a transmitting antenna, and the lower heater 48 is a receiving antenna. 49
is the heater choke, which is excited in the heating chamber 1 at 2,45
This is to prevent GHz high frequency energy from transmitting through the heater and leaking out of the heating chamber. The surfaces of these heaters are electrically insulated from the heating chamber wall and the heater power supply, and not only can they be regarded as independent antennas, but they can actually fully function as antennas. can. In the figure, 50 is a heater power supply, 51 is a heater heating control circuit, and the heating is controlled by the receiver number 4. 51. .

FIG. 12 is a sectional view of an embodiment of the pond showing how to attach the transmitting and receiving antennas. The antenna used in the figure is a loop antenna 54 made of bent metal and fixed at one end to the heating chamber wall surface 52 with a stopper 53.The other end is extended outside from the cutout 55 of the heating chamber 1 and connected to the converter 19. Connected. 56 is a cover made of insulating material. With such an antenna shape, the antenna does not protrude into the heating chamber as in the case of dipole antennas in other embodiments, so that the cleaning inside the heating chamber is further improved.

FIG. 13 is a characteristic diagram showing the relationship between the transmission frequency and the reception level of the antenna. In the figure, 57 is a characteristic change curve when the received level is expressed as an output voltage. In the figure, the smaller the output voltage, the greater the absorption of radio waves by food. This method takes advantage of the fact that when a dielectric material, which is relatively small compared to the liquid, enters, there is no change in the shape of the field, but there is a change in the amount of absorption. Here, the sweep range Δf of the transmission frequency is 100 to W, although it depends on the size of the heating chamber.
It is preferably about MHz, and if two foods are limited, it is possible to limit the frequency to a specific 3 F frequency, and in this case, the signal circuit can be simplified.

As described above, according to the present invention, changes in physical properties, that is, changes in permittivity and dielectric loss during the thawing process of frozen foods, are detected as changes in the level of radio waves absorbed by the food, and furthermore, a clear minimum value is detected at the end of thawing. It is possible to announce the end of defrosting by using the characteristics of the reception level that indicates a track, so by providing a control mechanism that stops heating at this point, defrosting can be automatically completed or detected, making it possible to stop defrosting frozen foods. It has the advantage of being able to do just the right amount. In addition, according to this method, once the heating pre-heating period is determined until the minimum point of the received output is reached, the frozen food is replaced and thawed according to this optimum heating time (heavy electric power is also constant). preferred) and is convenient for industrial thawing. Furthermore, according to the present invention, if it is better to eat food at room temperature than at the thawing temperature, after detecting the end point of thawing, heating can be continued as appropriate to bring it to room temperature, and the continuous heating time can be extended until the end of thawing. It can also be determined by calculating 4 F as a certain percentage of the required heating time. Moreover, since a pair of heaters are especially provided and used as transmitting and receiving antennas, the inside of the refrigerator can be used effectively, and the structure is simple and easy to clean.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing a conventional thawing device, Fig. 2 is an external view of a microwave oven equipped with a thawing state detection device according to an embodiment of the present invention, and Fig. 3 is an explanation of the principle of the thawing state detection device. 4.5.7.8.9.13 is a characteristic diagram of the reception level, FIG. 6 is a sectional view showing an example of high frequency heating and thawing, and FIG. 10 is an example of the control method. FIG. 11 is a sectional view showing the structure when a heater is used as the antenna, and FIG. 12 is a sectional view showing the shape of the antenna. 1... Heating chamber, 3... Frozen food, 4... High frequency heating source. 16... High frequency signal generator, 17... Transmission antenna. 18...Receiving antenna, 19.33...Converter. 20.54...control device. 21, 22.25.26.27.35.57...Output voltage change. 15 P 51 41 ”' Band rejection
n filter. 42...Amplifier, 44...Differential circuit. 45...Memory and comparison circuit. 46, 51... Heating power supply control circuit. 47... Upper heater, 48... Lower heater 154...
loop antenna. Applicant: Hitachi Thermal Appliances Co., Ltd.? ! 58-141768 (5) Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. A pair of heaters for heating food is installed in a refrigerator surrounded by a metal plate or metal mesh, and these are used as a transmitting antenna and a receiving antenna that excite high-frequency radio waves, and radio waves of a specific frequency are transmitted between the two antennas. A thawing status detection device is characterized in that the thawing status detection device transmits and receives the thawing status of a frozen food and determines the thawing status of a frozen food based on a change in the received output.