Microwave oven

Details Microwave oven Microwave oven

2002-10-02

2003-12-30

Leung, Philip H. (Department: 3742)

Electric heating

Microwave heating

With control system

C219S719000, C219S492000, C099S325000

Reexamination Certificate

active

06670591

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Patent Application No. 2002-20269 filed on Apr. 13, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to microwave ovens, and more particularly, to a microwave oven which controls a variation in a cooking time period in accordance and proportionally with the quantity of food being cooked.
2. Description of the Related Art
Generally, microwave ovens are machines which cook food with the assistance of a variety of atmospheric sensors, such as a humidity sensor, a temperature sensor and a gas sensor, in addition to a weight sensor which measures the weight of the food to be cooked. A conventional cooking operation of such a microwave oven is described below.
To initiate a cooking operation, a user operates a start button of the microwave oven after laying the food on a turntable-type cooking tray installed in a cooking cavity of the microwave oven, and selecting a desired cooking mode in an automatic cooking menu provided on a control panel of the microwave oven. Thereafter, a microprocessor of the microwave oven receives a signal output from a humidity sensor of the microwave oven, and compares the signal output from the humidity sensor with preset reference data stored in a data storage unit of the microwave oven. Then, the microwave oven calculates a target cooking time period so as to control a magnetron of the microwave oven in accordance with the calculated target cooking time period.
In a conventional method of controlling the microwave oven, a first cooking time period is determined such that it is terminated at a time when a calculated slope of a sensor output value becomes equal to a preset reference slope. A second cooking time period is determined in accordance with the first cooking time period and factors preset in accordance with the kind of food to be cooked. When the second cooking time period expires, the total time period of the cooking operation ends.
In the conventional method, current atmospheric conditions obtained from signals output from the humidity sensor, temperature sensor and gas sensor during the cooking operation are different from previous atmospheric conditions. Therefore, the slope of a sensor output curve varies, and it is difficult for the microprocessor of the microwave oven to determine a precise first cooking time period. As such, it is necessary in the conventional method of controlling the microwave oven to provide an initial standby time period of, for example, about 20 minutes, before starting the magnetron of the microwave oven in a new cooking operation. During such an initial standby time period, the magnetron is stopped, and a fan installed in a machine room of the microwave oven is operated to reduce the temperature in the cooking cavity to near a predetermined point.
FIG. 1
shows a graph expressing a conventional method of controlling a cooking operation of the microwave oven described above. As shown in the graph, the method includes sectioning a total cooking time period into an initial standby time period TC, a first cooking time period T
1
, and a second cooking time period T
2
. That is, at an initial stage of the cooking operation, in a selected cooking mode, the temperature in a cooking cavity is reduced to near a predetermined point during the initial standby time period TC of, for example, about 20 minutes. The first cooking time period T
1
starts at a time when the initial standby time period TC ends, and is terminated when a calculated slope of a sensor output value becomes equal to a preset reference slope “A.”
The first cooking time period T
1
is determined in accordance with the quantity of food to be cooked. In such a case, measuring of the quantity of the food may be directly performed using a weight sensor. However, to avoid the use of expensive weight sensors in the microwave ovens, the measuring of the quantity of the food may be performed through an indirect method using an inexpensive humidity sensor. That is, the microprocessor of the microwave oven may measure humidity or the amount of moisture, i.e., in a form of steam, laden in air generated and discharged from the cooking cavity, and determine the quantity of food from the measured humidity.
To allow the microprocessor to determine the first cooking time period during the cooking operation, reference data of relationships between the amounts of food and humidity of discharged air is experimentally obtained from several cooking operations of specified foods, and stored in a data storage unit. Accordingly, the microprocessor controls the cooking operation of the food using the reference data stored in the data storage unit. Additionally, the first cooking time period T
1
is used as a variable when determining the second cooking time period T
2
. That is, the second cooking time period T
2
is determined in accordance with both the first cooking time period T
1
and factors preset in accordance with the kind of food to be cooked.
Therefore, when a cooking operation is started, the microprocessor primarily determines a first cooking time period T
1
in accordance with the quantity of food to be cooked. After the determination of the first cooking time period T
1
, the microprocessor determines another time period needed to complete the cooking after a termination of the first cooking time period T
1
, and sets the determined time period as a second cooking time period T
2
. In such a case, the determination of the second cooking time period is accomplished by searching the reference data, which is stored in the data storage unit and indicates the relationship between the first and second cooking time periods. When the second cooking time period T
2
is completed, the cooking operation is terminated.
In some of the models of the conventional microwave ovens, the transition from the first cooking time period T
1
to the second cooking time period T
2
is determined in accordance with output values of humidity sensors. Particularly, the above transition is determined by a characteristic curve of a sensor output value indicating sensed humidity (%) of discharged air, as a function of time. In the conventional control method of the microwave ovens, such a reference slope “A” is set by a slope of the characteristic curve at a point where the sensor output value, indicating sensed humidity of discharged air, initially exceeds a preset reference value. The above-mentioned preset reference value is experimentally obtained. That is, the preset reference value is set at a point of the characteristic curve of the sensor output value where the slope of the curve rapidly changes, ideally at a point with a slope of “A.”
However, even though the total cooking time period (T
1
+T
2
) can be automatically determined using the stored reference data in accordance with the quantity of food as described above, users may want to lengthen or shorten the cooking time periods to cook foods for periods of time which are longer or shorter than the automatically determined cooking time periods. In other words, some users may prefer lesser cooked food rather than medium- or well-done food, and may desire to shorten the cooking time period. On the other hand, others may prefer well-done food rather than the medium- or lesser cooked food, and may want to lengthen the cooking time period.
To allow the users to adjust the cooking time period of a cooking operation, which is different from the automatically determined cooking time period, the conventional microwave oven is provided with a mode-selecting unit through which the users adjust the cooking time period. Accordingly, when a user inputs a desired cooking mode by manipulating the mode-selecting unit, the cooking time period automatically determined in accordance with the quantity of food is lengthened or shortened, so as to cook the food to a user's taste.
FIG. 2
shows a graph illustrating charac

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