JPS58141767A - Device for detecting thawing state - Google Patents

Abstract

PURPOSE:To obtain a key for proper thawing, by measuring the change of 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, and the thawing is detected by finding this point.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a thawing state detection device that detects the degree of thawing of frozen foods placed in a refrigerator, and more particularly, to 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 the physical properties of food using high-frequency waves to obtain clues for appropriate thawing.

Conventional defrosting methods for frozen foods include natural thawing, running water thawing, heating thawing, and high-frequency energy thawing using a microwave oven21) at home, and for industrial use, 2.45 GHz 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 was not possible to thaw it properly, resulting in over- or under-thawing, resulting in one food being overcooked, or on the other hand, under-heating, which required 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 in a microwave oven using infrared rays. This device is the first
As shown in the principle diagram in the figure, a food placing table 2f is placed inside the heating chamber 1 surrounded by metal, and a frozen food 3 is placed on the food placing table 2. Above is 2.
450Hz high frequency heating source4. High-frequency heating means constituted by a waveguide 5 are arranged. 6 is an excitation port for high frequency energy. Here, the door (not shown) is opened and the food 3 is placed in the 6P heating chamber 1, and the high frequency energy oscillated by the high frequency heating source 4 is excited from the excitation port 6 through the waveguide 5 to heat the food 3. is heated with high frequency, and the infrared rays 7 from the food 5, which increase with heating, are guided out of the heating chamber through the slit 8,
This infrared ray 7 is detected by an infrared detector 9, and the detected signal is subjected to signal processing in a device 10 for amplifying wave conversion and control, thereby controlling the high frequency heating 4.

This infrared detection method is capable of measuring the absolute temperature of a single food item, so it can measure the thawing temperature, that is, around 0° C., but 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 2.4
Thirdly, because the amount of infrared signal is small, complex electronic circuits are required to separate noise components and signal processing such as 11 and 4. It requires a special configuration and can be applied to things other than microwave ovens.
! 158-141767 (2) The possibility is small.

The present invention eliminates the drawbacks of the prior art, and aims to accurately detect changes in the physical properties of frozen foods when they are thawed by emitting radio waves. Thawing takes advantage of the rapid absorption change in absorption, 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 defrosting state detection device that detects defrosting conditions and can perform accurate defrosting based on changes in the amount of radio wave absorption.

That is, this physical property change is explained as follows. Foods have high water content, high dielectric constant and dielectric loss,
It has the property of absorbing high frequencies.

This physical property has little temperature dependence, and absorption is small when the substance is in a frozen state, and this is the maximum in ice crystals.

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

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

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

FIG. 2 is a perspective view of the present invention applied to a microwave oven. In the figure, 11 is a cabinet.

12Vi door, 13Fi exhaust port, 14 has thawing detection function,
Control device including defrost completion indicator light and defrost completion buzzer.

15 is a display section 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 a heating chamber 1 surrounded by a metal plate or a metal mesh so that it can be opened and closed, and a food loading table 2. Frozen food 3 is placed. The frozen food 3 is thawed using a heating source such as a high-frequency heating source, high-frequency energy, electricity, gas, etc. (none of which are shown). 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 for converting the received P-multiple signal into a control signal, and 20 is a control device. be.

By suppressing the high frequency signal of the concubine to the minimum level in the heating chamber 1 through the transmitting antenna 17, it is possible to reduce the size of the measuring device 2- due to complicated resonance. However, these radio waves are still reflected multiple times within the heating chamber, and either go out through the antenna or the air gap, or
Otherwise, it becomes heat loss, but if food with a large dielectric loss enters, a large amount is consumed by this food, and the amount that goes out from the antenna is small. 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 received signal when heating frozen food, that is, the relationship between food temperature and output voltage.The output voltage changes when thawing frozen food at -18 to -15°C. 21.22.25 gradually decreases with heating, indicating that radio wave absorption increases. The temperature of food at the point when the change in world pressure is at its lowest or almost constant t@H, t This tm indicates the temperature at which the water content changes from the ice state to the so-called ice crystal state where ice and water are mixed.
Decompression can be detected by finding the point at which tx is reached.

The pattern of output voltage change, ', mostly shows the change shown in Fig. 4, 21, but with so-called light loads (frozen buns, pizza pie, shumai) with little moisture, that is, little ice.

There are some cases showing changes such as those shown in Fig. 5, 22 and 23. It has been experimentally confirmed that if the food shown in Figures 4 and 5 is further heated after thawing, the output voltage will increase 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 rotating table 24 and heating it with high frequency by the high frequency heating source 4 in FIG. 3. FIG. The output voltage obtained in the figure is as shown in Figure 7.2 when output as is.
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 rotation of the motor 4 varies as shown in FIG. 827 due to the influence of the shape of the food, etc., and follows the temperature change with this waveform. 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 and measure only the same point during one rotation. There are two methods, 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 that detects the rotation of this rotation detection plate 300 every time it rotates. A synchronous detector 32 that detects the detection signal between these detection elements. The signal of this synchronous detector 32 is compared with the signal from the receiving antenna. The converter 33 is connected to 5Vc so that it receives the rotation detection signal only while the rotation detection signal is present. This converter 33
It is preferable to provide a control device 34 that obtains a signal from P and controls the heating source, and detects and controls the output voltage by these devices.
In this case, the change in the output voltage is intermittent as shown in FIG. 965, so when the output voltage reaches the minimum point in this state, thawing is complete and heating can be stopped. However, in FIG. 6, the transmitting and receiving antennas 17 and 18 will be replaced by the 2 and 45 parts that heat the food 6.
Since there is a risk that GH2O high frequency energy is transmitted and leaked to the outside, countermeasures are required to prevent this.

FIG. 10 is a circuit block diagram of a defrosting state detection device equipped with the above-mentioned radio wave leakage prevention means. In FIG.
It is preferable to oscillate radio waves with an output of several tens of mW for the pile. 67・is an oscillation signal 0 This oscillation signal is 2.4
Band re to prevent 5GHz frequency inflow
After passing through the injection filter 3B, the transmission antenna 17 supported by the transmission antenna support 69
1. be done. Similarly, the receiver number 4 is the receiver antenna support 40.
Band
l 'OP rejection filter 41. Amplifier 42
．． Waveform shaping circuit 43° differentiation circuit 44. The heating power supply control circuit 46 is operated via the storage and comparison circuit 45. According to this method, it is possible to distinguish between the high-power high-frequency energy oscillated by the heating source and the low-power high-frequency energy generated by sweep oscillation, and problems such as malfunction can be prevented. This is because the maximum absorption wavelength changes and is not constant, so it is swept so that detection is always performed at the maximum absorption wavelength, and the differentiator circuit 44 is used when there is no minimum point of the output voltage as shown in Fig. 5, 22° 230. , is used to differentiate the received signal 4 and control it when its absolute value approaches a certain value close to 0. The circuit 44 may be appropriately selected from well-known circuits.

Figure 11 shows an example in which an electric heater as a heating source is used in the transmitting/receiving antenna of the present invention. This shows a means of using one line for reception. Figure 11P The upper heater 47 is the transmitting antenna, and the lower heater 48
is the receiving antenna. Reference numeral 49 denotes a heater choke, which is used to prevent high frequency waves of 2.45 GHz excited in the heating chamber 1 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, so they can be regarded as independent antennas, but in fact they are sufficiently effective as antennas. I can do it.

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.

FIG. 12 is a sectional view of another embodiment showing a method of attaching 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 56.The other end is extended outside from the notch 55 of the heating chamber 1 to the converter 19. connected to. 56 is a cover made of insulating material. With such an antenna shape, the antenna does not protrude into the 5VC heating chamber unlike the case of the dipole antenna in other embodiments.

Cleanability 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. The figure shows that the smaller the output voltage, the greater the radio wave absorption from the food V. #Experience# = When a dielectric material that is relatively small compared to the volume of the box containing food, etc. enters, there is no change in the shape of the field, but it is preferable that there is a change in the amount of absorption, limited to one food item. If so, it is possible to limit the frequency to a specific frequency, and in this case, the transmitting circuit can be simplified.

As described above, according to the present invention, changes in physical properties, that is, changes in dielectric constant and dielectric loss during the thawing process of frozen food, are detected as changes in the level of radio waves absorbed by the food (3P), and a clear minimum value is detected at the end of thawing. Since the end of thawing can be detected using the characteristics of the reception level that indicates the point, by providing a control mechanism that stops heating at this point, thawing can be automatically completed or detected. It has the advantage of being able to defrost just the right amount. Also, according to this method &C, once the heating QIJ time until the minimum point of the received output is determined, the frozen food is replaced and thawed according to this optimum heating time (preferably, the weight is also constant). This makes it extremely convenient for industrial thawing. Furthermore, according to the present invention, if there is a food item that is better eaten at room temperature than at the thawing temperature, heating may be continued as appropriate after the thawing end point is detected. The temperature can be adjusted to room temperature, or the continuous heating time can be determined by calculating a certain ratio of the heating time required until the end of thawing.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a conventional defrosting device, FIG. 2 is an external view of a microwave oven equipped with a defrosting state detecting device according to an embodiment of the present invention, and FIG. Cross-sectional diagram for explaining the principle, No. 4.5.7.8, 9.
Fig. 13 is a characteristic diagram of the reception level, Fig. 6 is a sectional view showing an example of high frequency heating and defrosting, Fig. 10 is a sectional view with a block diagram illustrating the control method, and Fig. 11 is a heater used as the antenna. A cross-sectional diagram showing the structure when using
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. Sword, 64...control device. 21, 22.23.26.2 35.57. ...Output voltage change. 38, 41-Band rejection fil
ter, 42...Amplifier. 44... Differentiation circuit, 45... Memory and comparison circuit. 46, 51...Heating power supply control circuit, 47...Upper heater. 48... Lower heater, 54... Loop antenna 0 Applicant Hitachi Thermal Appliances Co., Ltd. Figure 6 Figure 7 Figure 8 Figure 12 Figure 13, 53 Frequency (MH2)

Claims (1)

[Scope of Claims] A high-frequency radio wave transmitting antenna and a receiving antenna are arranged in a refrigerator surrounded by a metal plate or a metal mesh, and a differential circuit is connected to the receiving antenna. Radio waves of a specific frequency are transmitted and received between the two antennas. Defrosting status detection characterized by measuring the differential value of this received output with respect to time and determining when the absolute value becomes smaller than a predetermined value to detect the thawing status of frozen food in the refrigerator. Device.