Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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
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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
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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
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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
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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
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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
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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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