CA2132166A1 - Method for thawing food in microwave oven - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method for thawing a food in a microwave oven, capable of achieving an optimum thawing of the food by temporarily stopping heating of the food for a predetermined time after completion of an initial heating of the food, determining whether an additional heating of the food should be executed, on the basis of a variation of an output signal generated from a gas sensor, during the temporary stop interval, and calculating a time for the additional heating, during the temporary stop interval.

Description

METHOD FOR THAWING FOOD IN MICROWAVE OVEN

BACKGROUND OF THE INVENTION

Field of the Invention The present invention relates to a method for thawing a food in a microwave oven, and more particularly to a food thawing method capable of effectively thawing a small amount of food.
1~
Description of the Prior Art Referring to FIG. l, there is shown a thawing device equipped in a microwave oven. As shown in FIG. l, the thawing device includes a heating chamber 1 for heating a food 2 disposed therein. A turntable 3 is rotatably disposed in the heat1n~ chamber l. The turntable 3 supports the food 2 khereo~. Thawln~ device also includos a turntable motor 4 for ~ot~tlng the turntable 3 and an exhaust port 5 for exhausting water vapor and gas ~enerated in the heating chamb~r l. A gas 8en~0r 6 18 disposed near the exhaust port 5 so as to sense water vapor and ~a~ exhausted through the exhaust por~ 5. The thawlng device further includes a microcomputer 7 for calculatlng a thawing time for the food 2 based on an output 8ignal from the gas ~ensor 6 and controlling various parts of tho mlcrowavo oven, a display unit 8 for displaying the ~hawing time calculated by the microcomputer 7 and other in~ormation such as cooking time, a magnetron 10 for yeneratiny a radio frequency wave, an output control unit ~
for controlling driving of the magnetron 10 under a control of the microcomputer 7, and a key input unit 11 for selecting a function desired by a user.
Operation of the thawing device having the above-mentioned construction will now be described.
When a user 1QYS the food 2 to be thawed on the turntable 3 disposed in the heating chamber 1 for thawing the food and manipulates the key input unit 11, the microcomputer 7 determines whether an input key signal generated from the key input unit 11 corresponds to an automatic thawing key signal.
Where the generated input key signal does not correspond to the automatic thawing key signal, a ~unction accordiny to the lnput key signal is carried out. However, where the current in~ut key slgnal corresponds to the automatic thawing key ~l~nal, the mlcrocomputer 7 checks a door condition of the mlcrowave oven. When the door is at its closed state, the mlcrocomputer 7 sends a control signal to the output control unlt 9. Under the control o~ the mlcrocomputer 7, the output control unit 9 controls the magnetron 10 to oscillate, so that the magnetron 10 outputs radio ~requency waves. That is, the ma~netron 10 ls controlled to oscillate for 10 seconds and then 9top ~or 12 seconds repeatedly, as shown in FIG. 3.

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Now, the proc~dure of thawing the food will be described in tellrls of heating time. At an initial thawing step, the radio ~requency wave energy generated by the oscillation of the magnetron 10 permeates the food 2, thereby causing the freezed food 2 to ~e heated, as shown in FIG. 4A. As the food 2 is heated, the surface of food 2 is thawed, thereby forming a water film, as shown in FIG. 4B. At this time, the surf~ce temperature of the food 2 is in excess of 0/C, while the internal temperature of the food 2 is uniformly increased, as compared to the state shown in FIG. 4A. As the food is further heated, moisture and gas are generated from the water film on the surface of food 12, as shown in FIG. 4C. The generated moisture and gas are exhausted through the exhaust port 5. At this time, the internal temperature of food 2 is lncreased to a level approximate to 0~C. On the other hand, the ~agnetron 10 i8 controlled to output radio ~requency wave en~r~y corresponding to 30 to 50% of its maximum output. This output ran~e may be varied depending on the output grade of the mlcrowave range used.
When water vapor and gas generated from the ~ood 2 bein0 thawed are exhausted through the exhaust port 5, the ga~
~erlsor 6 sense~ them and generates an electrical signal indicatlve o~ the result of its sensing. The microcomputer 7 recelves the output signal from the gas sensor 16. When the ~a~ ~ensor 6 9ends a slsnal having a wave~orm shown in FIG. 5 . :, - " : ~ . , ~ :, .. .

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to the microcomputer 7, the microcomputer 7 derives the re~istarlce ratio of the output signal of gas sensor 6 by the lap~e of time, as shown in FIG. 6. FIG. 6 shows graphs illustrating the resistance ratio of the output signal of gas sensor 6 by the lapse of time. In FIG. 6, the graph A
corresponds to a case where the food 2 is small in amount, while the graph B corresponds to a case where the food 2 is large in amount. As shown in FIG . 6, an infle*ion phenomenon occurs at the point of time when the freezed food is thawed more or less, namely the point of time, tl or t2. This is because absorption of the radio frequency wave energy is rapidly carried out at the portion of food 2 being thawed, thereby accelerating the generation of water vapor or gas.
After one of the graphs of FIG. 6 is obtained, the microcomputer 7 senses the inflexion point tl or t2 each indicative of a melting point of the freezed food 2, from the ~raph. Where the resistance ratio of the output signal of gas ~e~80r 6 i~ no~ le88 than 1.2, the microcomputer 7 operates to com~lete the thawing operation. On the other hand, where the r0sistance ratio is less than 1.2, the microcomputer 7 operate~ to execute an additional heating with decreased radio ~re~uenc~ wave energy for a predetermined time T2 in order to ~econdarlly thaw the,food 2. Upon secondarily heating the food 2 in the interval T2, the magnetron 10 is controlled to 2S osclllate for 4 seconds and then stop for 18 seconds :,! , ' ' ' ' ' ' . ' .. . . . . . . . . . .. .
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repeatedly. At this time, the gas sensor 6 generates an ou~put sigrlal havin~3 a waveform indica-ted in the interval T2 of FIG. 5 At the inflexion point, remarkable inflexion may not occur depending on the condition of the food 2 or the surrounding circumstance. In this case, the microcomputer 7 regards the thawing of food 2 to be completed when the output signal from the gas sensor 6 reaches a pred~termined value experimentally given, so as to complete the thawing operation.
In accordance with the prior art, however, where a small amount of food is subjected to a thawing treatment meeting a large amount of foodl a phenomenon that the food is partially ooiled. On the other hand, where a large amount of food is subiected to a thawing treatment meeting a small amount of food, a phenomenon that the food is insufficiently thawed.

, SUMMARY OF THE INVENTION

Therefore, an ob~ect of the invention is to provide a method Por thawing a food in a microwave oven, capable of e~ectively thawing a small amount of food.
In accordance with one aspect, the present invention provldes a method for thawing a food in a microwave oven, comprising: an initial heating step of initially heating the ~ood ~or a first predetermined time; an addltional heating -5- ~

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tlme calculating step of temporarily stopping the heating of the food for a second predetermined time after completion of the initial heating step, determining whether an additional heating of the food should be executed, on the basis of a variation of an output signal generated from a gas sensor adapted to sense a water vapor or gas generated from the food, during the temporary stop interval, and calculating a time for the additional heat1ng, during the temporary.stop interval;
and additionall~ heating the food for the additional heating time calculated at the additional heating time calculating step, and then completing thawing of the food.
In accordance with another aspect, the present invention provides a method for thawing a food in a microwavs oven, comprising: an initial heating step of initially heating the lS ~oed for a first predetermined time; an additional heating ~ime cal~ulating step of temporarily stopping the heating of ~he food ~or a second predetermined time after completion of the lnitial heating step, determining whether an additional heatlny o~ the food should be executed, on the basls of a r0~erence time taken for a variation of an outyut signal generated from a gas sensor adapted to sense a water vapor or gas generated from the food to reach a first predetermined value, and calculating a time for the additional heating on the basis of the reference time; and additionally heating the ~ood for the additlonal heatlng tlme calculated at tho r ,.,i ~,., 1 ~i' a~lditiorlal heating time calculating step, and then completing thawing o~ the food.

BRIEF DESCRIPTION OF THE DRAWINGS
:
Other objects and aspects of the invention will ~ecome ~:
apparent from th~ following description of embodiments with re~erence to the accompanying drawings in which: :
FIG. 1 is a block diagram of a conventional thawing device equipped in a microwave oven;
FIG. 2 is a flow chart illustrating a conventional method :~
for thawing a food using the thawing device shown in FIG. 1;
FIG. 3 is a waveform diagram of an output signal .;.
generated from a magnetron equipped in the conventional thawing device of FIG. 1;
FIGS. ~A to 4G are schematic views various conditions of ~h~ ~ood sub~ected to a thawing carried out in accordance with a conventional thawing method;
FIG. 5 i~ a waveform diagram of an output signal generated rom a ga~ ~en80r during a thawing operation in accordance with the con~entional method;
FIG. 6 ig a graph illustrating a resistance ratio of the gas 8ensor by the lapse o~ time during the thawing operation in accordance with the conventional method;
FIG. 7 is a flow chart illustrating a method for thawing .~

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a ~ood in accordarlce with a first ~mbodiment of the present i,nv~ntien;
FIG. 8 is a waveform diagram of an output signal yenerated from the magnetron during a thawing operation in accordance with the method of FIG. 7;
FIG. 9 is a waveform diagram of an output signal generated from the gas sensor during the thawing operation in accordance with the method of FIG. 7; and FIG. 10 is a flow chart illustrating a method for thawing a food in accordance with a second embodiment of the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

i5 The thawing device shown in FIG. 1 i9 used a~ a thawing d0vice for carrying out a method for thawing a food in accordance with the present invention. Accordingly, de~cription o~ the thawi~g device for carrying out the method of the present invention will be omitted and elements of the thawin~ device 9hown in FIG. 1 will be incorporated in the followlng description.
Referring to FIG. 7, there is illustrated a thawing method in accordance with a first embodiment of the present invention. The thawing method of this embodiment lncludes an lnitial heating step S1, an additional heating time . ~, . . - . -. ~, -. , .. ~ . , calculating step S2 and an additional heating step s3. These steps will be described in detail, in conjunction with FIGS.
7 ~ 9.
Irl accordarlce with this method, at the initial heating step S1, when a user lays the food 2 to be thawed on the turntable 3 disposed in the heating chamber 1 for thawing the food and manipulates the key input unit 11 to generate an automatic thawing key signal, the microcomputer 7 drives a fan (not shown) in response to the automatic thawing key signal so as to achieve an initial thawing operation for a predetermined time of, for example, 16 seconds. After completion of the initial thawing operation, the microcomputer 7 sends a control signal to the output control unit 9. Under the control of the microcomputer 7, the output control unit 9 controls the magnetron 10 to generate radio frequency wave energy for a predetermined time T3, thereby causing the food 2 to be lnitially hqated. In this case, the magnetron 10 i8 cont~oll~d to generate the radio frequency wave energy for 10 sqconds and then stop for 12 seconds repeatedly, as shown in FIG. 8. As water vapor and gas generated upon thawing the ~ood 2 are exhausted through the exhaust port 5, the gas ~en~or 6 8en~es the exhausted water vapor and gas and ~enerates an electrical signal lndicative of the result of the ~ensing. The generated electrical signal is sent to the ~5 microco~puter 7. The output signal of the gas sensor 6 has a '; ,, ~ . ' .; ' . ' ' ., ' ' , ', , I , " , ';, , . ~ . . ', ",,,, ' ' . ', " ' , , ', , ! ", ,' ' " ' ., ', ""; "" ' ," ' " ;~ .. ' ' "' ' ".'; ', '," "' ~ " '' ' ' ' "" ' ' ' ' ' '' " '' ' wav~orm indicated in the interval T3 o~ FIG. 9.
~ Ihereafter~ the microcomputer 7 operates to stop the heating operation for a predetermined temporary stop interval TA of, for example, about one minute after completion of the initial heating step Sl, at the additional heating tlme calculating step S2. Under this condition, the microcomputer 7 checks a variation ~G of the output signal generated from the gas sensor 6 for the temporary stop interval TA, so as to determine whether the food 2 has to be additionally heated and the condition of the additional heating if the food 2 has to be additionally heated. Accordingly, the microcomputer 7 calculates an additional heating time T4 in accordance with the following eguation (1):

15T4 = ~G - a) x b (second) --------------------- (1) where, "a" and "b" are constants variable depending on ~he size o~ the heating chamber and e~perimentally given.
When "~G - a" in the e~uation (1) is not more than "0", lt is regarded as "0". In this case, the additional heating tlme T~ i8 ''O''. In this case, the thawing of the food 2 ls completed only by the lnltial heating for the predetermined time T3 wlthout any additional heating. This case corresponds i ~o the ca~e where the food 2 i8 small in amount. Where "~G -a" in the equatlon (1) is more than "0", the additional --1 0-- , , r~ s ~ ?;

heating time T~ is determined using the equation (1). This case corresponds to the case where the food 2 is large in amourlt .
Thereafter, the additional heating step S3 is executed.
That is, the microcomputer 7 displays the additional heating time T4 calculated at the additional heating time calculating step S2 on the time display unit 8. The microcomputer 7 also controls the output control unit 9 so that the magnetron lO
operates to additionally heat the food 2 for the additional heating time T4. After completion of the additional heating operation, the microcomputer 7 completes the thawing operation.
FIGS. 8 and 9 are waveform diagrams of output signals of the magnetron 10 and gas sensor 6 for the temporary stop interval TA and additional heating interval T4, respectively.
Referring to FIG. 10, there is illustrated a thawing method in accordance with a second embodiment of the present invontlon. The thawing method of this embodiment includes an lnltlal heatin~ step S4, an additional heating time calculating step S5 and an additional heating step S6, in ~lmilar to the thawing method of the first embodiment. These ~ep~ wlll be described in detail, in con~unction wlth FIG.
10 .
In accordance with this method, at the initial heating ~tep S4, the food 2 to be thawed is initially heated for a --11-- , '~ '.! ` ' ' , , . .. . . . .` , . . . . . , . " , . `, J i3 predetermined time T5 in the same manner as in the initial hf3aking step S1 of the first embodiment.
Thereafter, the additional heating time calculating step S5 is executed. At the additional heating time calculating step S5, the heating of food 2 is temporarily stopped. During the heating of food 2 is temporarily stopped, a time TB taken for a variation ~G of the signal generated from the gas sensor 6 to reach a predetermined value c is measured. That is, the microcomputer 7 measures a time Ti taken for the variation ~G
of the output signal of the yas sensor 6 to correspond to the predetermined value C. The microcomputer 7 takes the measured time Ti as the temporary stop time TB. Subsequently, the microcomputer 7 multiplies the temporary stop time TB by a constant L experimentally given, thereby obtaining a value T6.
Thereafter, the microcomputer 7 compares the value T6 with a prsdetermined value N. When the vaule T6 is less than the ~re~et0rmlned value N, the thawing operation is completed without any additional heating. That is, the food 2 is thawed enly by the initlal heating for the time T5. On the other hand, when the value T6 is not less than the predetermined value N, the value T6 is re~arded as the addltional heatlng ti~e. In thi~ case, the additional heating step S6 is executed.
At the additional heating step S6, the food 2 is additionally heated for the calculated additional heating time ~, ~ , , . . , ., .:
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T6. A~teI completion o the additional heating step S6, the thawirl~ c)~?eration is completed.
As apparent from the above description, the present invention provides a method for thawing a food in a microwave 5 oven, involving the steps of determiring whether the food is additionally heated in a temporary stop interval after an~
initial heating of the food and calculating an additional heating time, thereby capable of preventing the food from being partially boiled where the food is small in amount and, 10 thus, achieving an optimum thawing.
Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the ;~
art will appreciate that rarious modifications, additions and substitutions are possible, without departing from the scope 15 and spirit of the invention as disclosed in theiaccompanying claim~. For example, the gas sensor 6 as means for sensing the de~ree of' thawing may be replaced by a humidity sensor or a temperature sensor.

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Claims (4)

1. A method for thawing a food in a microwave oven, comprising:
an initial heating step of initially heating the food for a first predetermined time;
an additional heating time calculating step of temporarily stopping the heating of the food for a second predetermined time after completion of the initial heating step, determining whether an additional heating of the food should be executed, on the basis of a variation of an output signal generated from a gas sensor adapted to sense a water vapor or gas generated from the food, during the temporary stop interval, and calculating a time for the additional heating, during the temporary stop interval; and additionally heating the food for the additional heating time calculated at the additional heating time calculating step, and then completing thawing of the food.

2. A method in accordance with claim 1, wherein the additional heating time calculating step comprises:
checking the variation of the output signal from the gas sensor for a predetermined time;
calculating a difference between the checked variation of the output signal from the gas sensor and an experimentally determined first constant; and completing the thawing of the food when the calculated difference is not more than "0", while multiplying the calculated difference by an experimentally determined second constant when the calculated difference is more than "0", thereby determining the additional heating time.

3. A method for thawing a food in a microwave oven, comprising:
an initial heating step of initially heating the food for a first predetermined time;
an additional heating time calculating step of temporarily stopping the heating of the food for a second predetermined time after completion of the initial heating step, determining whether an additional heating of the food should be executed, on the basis of a reference time taken for a variation of an output signal generated from a gas sensor adapted to sense a water vapor or gas generated from the food to reach a first predetermined value, and calculating a time for the additional heating on the basis of the reference time;
and additionally heating the food for the additional heating time calculated at the additional heating time calculating step, and then completing thawing of the food.

4. A method in accordance with claim 3, wherein the additional heating time calculating step comprises:
measuring a time taken for the variation of the output signal from the gas sensor to reach the first predetermined value;
multiplying the measured time by a first constant; and completing the thawing of the food when the resultant value obtained at the multiplying step is less than a second predetermined value, while determining the second predetermined value as the additional heating time when the resultant value obtained at the multiplying step is not less than the second predetermined value.