JPS6142397B2 - - Google Patents

Description

Detailed Description of the Invention The present invention is a high-frequency thawing system equipped with a control device that automatically thaws frozen foods, etc. (brings the object to be thawed to a temperature above the ice zone and to about the temperature of a refrigerator). It is related to the device.

Conventional high-frequency thawing equipment supplies high-frequency power to the thawing chamber containing frozen foods (hereinafter referred to as thawed items) to thaw the thawed items, using a timer to defrost the items. The timer was set appropriately to ensure proper defrosting. That is, a timer is used to set an appropriate thawing time estimated in advance according to the quality and quantity of the object to be thawed, and thawing is continued until the timer expires. However, with this method, the optimal setting time of the timer varies greatly due to differences in the density, moisture content, shape, freezing temperature, etc. of the material to be thawed, making it difficult for the user to set it correctly, and often resulting in insufficient or excessive thawing. cause.

Therefore, in order to perform proper decompression, considerable skill is required in setting the timer.

Attempts have also been made to detect the temperature of the object to be thawed using a thermosensor and thaw it appropriately, but this method requires waiting until the temperature of the thermosensor becomes lower than the appropriate thawing temperature. The disadvantage is that you cannot start defrosting unless you do so.

An object of the present invention is to provide a high-frequency thawing device that can properly thaw objects to be thawed, regardless of differences in density, moisture content, shape, freezing temperature, etc. of the objects, while eliminating the drawbacks of the prior art described above. be.

In order to achieve the above object, in the high frequency thawing device of the present invention, outside or inside the thawing chamber,
A temperature-sensitive element shielded from high-frequency power is attached to detect the temperature of the object to be thawed, and thawing is automatically stopped when the detected temperature reaches a predetermined set value.

Further, in order to start thawing without waiting for the temperature of the temperature sensing element to become low, the above set value is changed over time.

Hereinafter, the present invention will be explained using the drawings. FIG. 1 shows an embodiment of the high frequency decompression device of the present invention. In Fig. 1, 1 is a thawing cabinet, 2 is an object to be thawed, 3 is a flat plate electrode, 4 is a high frequency oscillation source, 5 is a temperature sensing element, 6
is a heat insulating material, and 7 is a control device. When the object 2 to be thawed is placed on the bottom of the thawing chamber 1 and the control device 7 is activated,
The control device 7 drives the high frequency oscillation source 4, and the high frequency oscillation source 4 supplies high frequency power between the flat plate electrode 3 and the wall surface 30 of the thawing chamber 1. The thawed object 2 placed on the bottom of the thawing chamber 1 absorbs high frequency power and begins to be thawed. The temperature of the object 2 to be thawed is detected by the temperature sensing element 5 through the bottom of the thawing chamber 1, and when the detected temperature reaches a preset temperature, the control device 7 stops driving the high frequency oscillation source 4. , the decompression is finished. The heat insulating material 6 reduces the heat dissipation from the bottom of the thawing chamber 1, and also allows the temperature sensing element 5 to absorb the thawing material 2.
It is provided to make it difficult for other heat to be transmitted.

FIG. 2 shows the temperature of the thawed object 2 and the temperature sensing element 5 when thawing is started immediately after the thawed object 2 is placed on the bottom of the thawing chamber 1 in the high-frequency thawing apparatus shown in FIG. This is a characteristic diagram in which the detected temperature is plotted against the thawing time, and the solid line is the temperature of the object to be thawed 2.
T ₀ and the broken line indicate the detected temperature T _D of the temperature sensing element 5. Furthermore, range A shown in FIG. 2 is an ice crystal zone generated by the latent heat of the material to be thawed. Although the temperature of the object 2 to be thawed rises in the early stage of thawing, the temperature sensing element 5
The temperature T _D detected by the cell decreases and begins to rise as the thawing progresses. This temperature rise characteristic becomes correlated with the temperature rise characteristic of the object 2 to be thawed as the thawing time progresses. This phenomenon is caused by the fact that the initial temperatures of the thawing chamber 1 (wall surface 30) and the temperature sensing element 5 are usually the same as the ambient temperature of the thawing chamber 1 and higher than the temperature To of the object 2 to be thawed, and that the temperature sensing element 5 is This is due to the fact that the temperature detection mechanism involved has a thermal time constant.

FIG. 3 shows another embodiment of the high frequency defrosting device such as a microwave oven according to the present invention. In Figure 3, the first
Objects that are the same as those in the figure are numbered the same. 3' is a cylindrical electrode, 8 is a probe for shielding the temperature sensing element 5 from high frequency power, and 9 is a saucer. When the object 2 to be thawed is placed on the saucer 9 in the thawing chamber 1 and the probe 8 equipped with the temperature sensing element 5 is brought into contact with the object 2 to be thawed, the control device 7 is driven. The high frequency oscillation source 4 supplies high frequency power between the cylindrical electrode 3' and the wall surface 30 of the defrosting chamber 1. The object 2 to be thawed placed on the saucer 9 absorbs the above-mentioned high frequency power and begins to be thawed. The temperature T ₀ of the object to be thawed 2 is detected by the temperature sensing element 5 via the probe 8, and when the detected temperature T ₀ reaches a preset temperature, the control device 7 stops driving the high frequency oscillation source 4. , the decompression is finished. This third
In the high-frequency thawing apparatus shown in the figure, the characteristics of the temperature T ₀ of the object 2 to be thawed and the detected temperature T _D detected by the temperature sensing element 5 with respect to the thawing time are similar to those shown in FIG. 2.

As mentioned earlier, in the early stage of thawing, the thawed object 2
Even though the temperature of the object 2 is increasing, the temperature detected by the temperature sensing element 5 decreases, and as the thawing progresses, it starts to rise, and as the thawing time progresses, there is a correlation with the temperature increase characteristic of the object 2 to be thawed. It becomes like this. Therefore, when performing automatic defrosting, control cannot be achieved simply by setting a desired defrosting temperature. For example, in FIG. 2, it is assumed that thawing is to be terminated when the temperature of the object 2 to be thawed reaches 0°C. Even when the object 2 to be thawed is placed in the thawing chamber 1 and the switch to start thawing is turned on, the high-frequency oscillation source does not start oscillating. This is because the initial temperature of the temperature sensing element 5 is the same as the ambient temperature of the thawing chamber 1, and is already at a temperature of 0° C. or higher. As described above, if the set temperature at which thawing ends is determined at the time of starting thawing, the high frequency oscillation source 4 does not immediately oscillate, and the object 2 to be thawed cannot be thawed. Therefore, the control device 7 of the present invention is configured to change the set value with a predetermined time constant so that oscillation always starts at the start of defrosting.

FIG. 4 is a circuit diagram showing one implementation of the circuit configuration of the control device 7 in the high frequency decompression device of the present invention.
In Fig. 4, 10 is a DC power supply, 11 is a switch, 12 is a resistor, 13 is a Zener diode, 1
4, 15, 16, 17 are resistors, 18 is a capacitor, 19 is a diode, 20 is a capacitor, 21
are comparators (hereinafter referred to as comparators) 22, 23
is the input terminal of the comparator 21, 24 is the diode, 25 is the resistor, 27 is the relay 28 is the relay 27
The coil 29 is a contact point of the relay 27. In addition, 5 is a temperature sensing element in FIG. 1 and FIG. 3, and uses a thermistor. switch 11
When connected, the constant voltage circuit consisting of the resistor 12 and the Zener diode 13 connects the current supplied from the DC power supply 10 to the series circuit of the resistor 14 and thermistor 5, and the series circuit of the resistor 15, resistors 16 and 17, and the capacitor 18. Supply a constant voltage to the parallel circuit. One of these constant voltages is divided by a resistor 14 and a thermistor 5, and is supplied to a positive input terminal 22 of a comparator 21. This voltage is thermistor 5
This is an electrical signal V _I (hereinafter referred to as temperature detection voltage) that detects the temperature of the object 2 to be thawed. This temperature detection voltage V _I decreases because the resistance value of the thermistor 5 decreases as the temperature increases. On the other hand, resistors 15, 16 and resistor 17,
A reference signal (hereinafter referred to as reference voltage) V generated by a time constant circuit constituted by the capacitor 18
_R is supplied to the negative input terminal 23 of the comparator 21. This reference voltage V _R has a resistance value obtained by adding the parallel resistance value of the resistor 15 and the resistor 16 to the resistance value of the resistor 17, and a time constant determined by the capacitance of the capacitor 18. The final voltage value of the reference voltage V _R is the constant voltage supplied by the resistor 12 and the Zener diode 13.
This is the voltage divided by . That is, the reference voltage V _R
is the time constant determined by resistors 15, 16, 17 and capacitor 18 from O _V to the final voltage (voltage corresponding to a predetermined temperature above the temperature of the ice crystal zone of the object to be thawed and below the temperature of the refrigerator). It will rise. FIG. 5 shows a characteristic diagram of the temperature detection voltage V _I and the reference voltage _VR , with the horizontal axis representing the thawing time and the vertical axis representing the voltage. The comparator 21 compares the input voltages V _I and _VR , and when V _I > _VR , sets the high level output voltage to V
When _I < V _R , the low level output voltage is relayed to the relay 27.
is supplied to the coil 28. Relay 27 closes contact 29 to which high frequency oscillation source 4 is connected when the output voltage of comparator 21 is at a high level. The high frequency oscillation source 4 is configured to oscillate when the contact 29 is closed and stop oscillating when the contact 29 is open. Note that the diode 19 is a diode for discharging the capacitor 18, and discharges the capacitor 18 with a time constant smaller than the time constant during charging when the switch 11 is turned from on to off. Further, the capacitor 20 is a capacitor for noise prevention, and short-circuits the two input terminals 22 and 23 of the comparator 21 in an alternating current manner to prevent malfunction due to noise. Also, comparator 2
1 is connected to a positive loop by a resistor 25 and a diode 24, and once the output voltage reaches a low level voltage, the voltage V _I at the input terminal 22 is lowered, so the output voltage of the comparator 21 becomes high. The voltage will never return to that level. In addition, resistance 25
When the capacitor 18 discharges with the output of the comparator 21 at a low level, the discharge current flowing into the output side of the comparator 21 via the diodes 19 and 24 flows into the output side of the comparator 21.
It is designed to ensure that the rating is not exceeded.

In this circuit, at the start of defrosting, the temperature of the thermistor 5 is the same as the ambient temperature of the defrosting chamber 1, so the resistance value is small and the temperature detection voltage V _I is low.
However, the reference voltage V _R of the comparator 21
is O _V because no charge is stored in the capacitor 18. Therefore, since V _I > V _R , the comparator 21 is connected to the coil 28 of the relay 27.
Outputs high level voltage. As a result relay 2
7 closes and the high frequency oscillation source 4 starts oscillating. As mentioned in Fig. 2, the temperature detected by the thermistor 5 drops once, then starts to rise,
As the thawing progresses, a correlation with the temperature rise characteristic of the object 2 to be thawed can be taken. Therefore, the resistance value of the thermistor 5 increases once and then decreases, so the temperature detection voltage V _I increases once and then decreases. The reference voltage V _R is OV at the start of defrosting, but increases as the capacitor 18 is charged, and eventually the resistors 15 and 1
A constant voltage determined by 6 is reached. When thawing further progresses and V _I <V _R , the output voltage of the comparator 21 is reversed from a high level to a low level, the current flowing through the coil 28 of the relay 27 decreases, the contact 29 opens, and the high frequency oscillation source The oscillation of 4 stops and the decompression ends.

Note that the time constant given to the reference voltage V _R must be appropriately determined in consideration of the output of the high frequency oscillation source, the initial temperature of the object to be thawed, and the like. The thawing output of the high frequency oscillation source 4 is 50 watts (W), and the initial temperature of the thawed object is -18
Since the time required to thaw the object at a temperature of about 100° C. is about 5 to 20 minutes, sufficiently appropriate thawing can be achieved by setting the time constant to about 100 seconds (Sec).

Furthermore, although the above embodiment describes the case where the oscillation of the high frequency oscillation source is stopped, the present invention can also be implemented when the high frequency power is reduced to continue defrosting. Furthermore, in the circuit configuration of the control device shown in FIG. 4 of the above embodiment, variable resistors can be used for the resistor 16 and the resistor 17 to make it possible to adjust the attained voltage and time constant of the reference voltage _VR .
Furthermore, instead of using a fixed resistor as the resistor 14, a thermistor or the like may be used to compensate for variations in thawing of the object due to changes in ambient temperature.

As described above, in the high-frequency thawing device of the present invention, thawing can be started without waiting for the temperature of the temperature sensing element to reach a low temperature. Since thawing is stopped when the temperature of the object reaches the appropriate temperature, no skill is required to properly thaw the object regardless of the density of the object, moisture content, freezing temperature, etc.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing one embodiment of the high-frequency thawing device according to the present invention, Fig. 2 is a characteristic diagram of the temperature of the object to be thawed and the temperature detected by the thermosensor, and Fig. 3 is the high-frequency thawing device according to the present invention. FIG. 5 is a characteristic diagram showing changes in temperature detection voltage and reference voltage in the control device of FIG. 4. FIG. 1: Thawing chamber, 2: Item to be thawed, 4: High frequency oscillation source, 5: Temperature sensing element, 7: Control device, 21: Comparator 27: Relay, V _R : Reference signal (reference voltage).

Claims (1)

[Scope of Claims] 1. A thawing refrigerator having a thawing chamber and a high-frequency oscillation source that supplies high-frequency power into the thawing chamber, and capable of thawing objects in a frozen state at a temperature lower than the initial temperature of the thawing chamber or the ambient temperature. , in the high-frequency thawing device that defrosts using the high-frequency power, the temperature-sensing means is shielded from the high-frequency power and detects the temperature of the object to be thawed, and the temperature is higher than the temperature detected by the temperature-sensing means at the start of thawing. As the thawing time progresses, a second set value corresponding to a predetermined temperature that is higher than the temperature of the ice crystal zone of the object to be thawed and lower than the refrigerator temperature is outputted. a reference signal generating means for outputting a reference signal; a comparing means for comparing an output signal of the temperature sensing means with a reference signal output by the reference signal generating means; A high-frequency decompressor having a control device comprising means for changing the high-frequency power generated by an oscillation source.