Electric heating – Microwave heating – With control system
Reexamination Certificate
2003-07-31
2004-09-14
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
With control system
C219S719000, C219S716000, C099S325000, C426S243000
Reexamination Certificate
active
06791070
ABSTRACT:
This application claims the benefit of Korean Patent Application No. P2002-70916, filed on Nov. 14, 2002, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microwave oven. More particularly, the present invention relates to a method of automatically controlling a cooking operation such as a simmer or thawing operation in a microwave oven wherein, during cooking, food products containing moisture (either in a liquid or frozen form) such as broth, or the like, may be heated at a strong power and then slowly heated with a weak power, and wherein the automatically controlled cooking operation can be automatically performed regardless of the amount or type of food being cooked.
2. Description of the Related Art
Generally, microwave ovens automatically control the degree to which food is heated using sensors capable of detecting physical quantities that evolve as the food is heated. In particular, gas or humidity sensors, capable of detecting vapor generated when food is heated, are generally used by microwave ovens having automatic cooking features. Such related art sensors will now be explained in greater detail.
Generally, humidity sensors operate by measuring the increased voltage passing through an element when moisture, created within the microwave oven heating food and absorbed by the humidity sensor, decreases the electrical resistance of the element. Microwave ovens incorporating an automatic cooking feature using such humidity sensors are disclosed in, for example, U.S. Pat. Nos. 4,335,293, 4,336,433, and Re. 31,094. In view of the aforementioned patents, it can be understood that food is heated within microwave oven for an initial time period T
1
, measured from a starting point of the heating to a second point of time when humidity generated by the heated food changes abruptly, and for an additional time period AT
1
, wherein A is a constant specific to the type of the food being heated. Accordingly, the total time period during which the food is heated is T
1
+AT
1
.
A method and apparatus for simmering food in a microwave oven has been disclosed in U.S. Pat. No. 4,791,263 (herein referred to as the '263 patent).
FIG. 3
illustrates the consecutive output power levels applied over time in the microwave oven simmering method disclosed in the '263 patent.
FIG. 4
illustrates an operating process flowchart for controlling the simmering operation of the ‘263 patent.
Referring to
FIGS. 3 and 4
, a process for performing a simmer cooking operation in a microwave oven using a related art humidity sensor will now be explained.
First, a simmer key is pressed by a user to initiate a simmer cooking operation of a microwave oven. Next, a microwave cooking chamber (i.e. cooking chamber) is purged by ventilating the cooking chamber for a predetermined time period (e.g., 15 seconds) so that oven sensors can be stabilized (steps
101
and
102
). During steps
101
and
102
, signals generated by the humidity sensor cannot be used to control heating.
After the predetermined time period has elapsed, the microwave oven performs the simmer cooking operation using the humidity sensor. Accordingly, after the predetermined time period has elapsed, an initial level of the humidity within the cooking chamber, detected by the humidity sensor, is inputted into memory (step
103
). Next, heating commences at 70% of a maximum power level provided by the microwave oven (step
104
).
As heating progresses, the humidity sensor generates signals based on the detected humidity levels within the oven chamber. The generated signals are continuously read and compared with the initial level inputted into the memory. Accordingly, a difference in humidity value between the initial and detected humidity levels is calculated (step
105
). Next, a determination is made as to whether the calculated difference of values has reached a predetermined difference value (step
106
). The initial heating time T
1
is counted until a difference value reaches the predetermined value according to a determination result in step
106
. By setting T
1
according to the time period required to reach the predetermined difference value in initial and detected humidity levels, steps
103
to
106
determine the time period required to generate a predetermined level of humidity after the simmer cooking operation of a microwave oven has been initiated. The value of T
1
will generally be larger when a large amount of food is heated as compared to when a relatively smaller amount of the food is heated.
After it has been determined in step
106
that the calculated difference in humidity values reaches the predetermined difference value, the initial time period T
1
becomes fixed and the food is heated for a second time period T
2
, calculated on the basis of the initial heating time T
1
(step
107
). The second time period T
2
is determined by multiplying the initial time period T
1
by a predetermined constant value B, different from the aforementioned predetermined constant value A. During the second time period T
2
, the food is heated at 50% of the maximum power level (step
108
).
After the second time period T
2
has elapsed, heating at 50% of the maximum power level is stopped (step
109
). Subsequently, the food is heated for a third time period T
3
at 30% of the maximum power level (step
110
). A user must select a value to set the third time period. The third time period is set according to either the amount of food to be heated or according to a user's preference (step
111
). More specifically, if a specific key is pressed, the third time period is 210 minutes (step
112
). Otherwise, the third time period is 90 minutes (step
113
).
After the third time period T
3
has elapsed, the food is kept warm during a fourth time period T
4
whereby the food is heated at 10% of the maximum power level (step
114
). When initiated, the display unit indicates the ‘keep-warm’ operation is being performed. The ‘keep-warm’ operation is performed until the cooking is stopped. When the user stops heating the food, the simmer cooking operation is completed.
Referring to
FIG. 3
, the total amount of time required by the related art simmer cooking operation described above is divided into four stages. According to the related art, the heating power levels used during the four stages are set at predetermined power levels, the first and second amounts of time T
1
and T
2
, respectively, are determined automatically according to the amount of food within the cooking chamber, and the third time period T
3
is one of two values that must be selected by the user.
Use of the aforementioned related art simmer cooking operation is disadvantageous because the user is required to actively determine the value of the third time period T
3
. If the user does not select the third time period T
3
(by pressing a select key), the food is always heated for an additional 90 minutes, regardless of the amount of food within the cooking chamber. Accordingly, the effectiveness of the simmer cooking feature may be deteriorated.
Furthermore, use of the aforementioned related art simmer cooking operation is disadvantageous because the power levels applied upon heating within the first and second time periods T
1
and T
2
are not at the maximum power but at 70% and 50% of the maximum power level of the microwave oven. By not using the maximum power levels of the microwave oven, the total amount of time required to effectively perform the simmer cooking operation becomes prohibitively excessive.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a simmering control method in a microwave oven that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An advantage of the present invention provides a reduced cooking time compared to related art simmering control methods such as those described above.
Another advantage of the present inven
Leung Philip H.
LG Electronics Inc.
McKenna Long & Aldridge LLP
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