Electric heating – Microwave heating – With control system
Reexamination Certificate
2001-10-02
2002-12-31
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
With control system
C219S710000, C426S241000, C426S524000, C099S325000
Reexamination Certificate
active
06501058
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microwave oven, and more particularly, to a method for controlling defrosting in a microwave oven, in which an actual temperature of a surface of food is detected continuously during defrosting of the food, for controlling a defrosting process.
2. Background of the Related Art
The microwave oven heats food in a cavity by means of an ultra high frequency wave (2450 MHz) from a magnetron. In order to make an accurate food heating control in the microwave oven, an infrared sensor is fitted on one side of the cavity, for projection to the food, to detect a surface temperature of the surface of the food, and transmission of the information to a microprocessor in the microwave oven, so that the microprocessor can determine heating and control conditions thereafter based on the detected surface temperature of the food.
Referring to
FIG. 1
, a related art microwave oven is provided with a turntable
11
for placing food to be cooked thereon, a magnetron
12
for generating, and supplying a microwave to the food in the cavity
10
through a waveguide, a cooling fan
13
for cooling the heated magnetron
12
, an infrared sensor
14
for detecting a temperature of the food, and a control part (not shown) for controlling operation of the magnetron
12
.
The operation of the foregoing microwave oven will be explained. When the user provides a cooking command to the microwave oven, the control part puts the magnetron
12
into operation. A microwave generated at the magnetron
12
is directed to the cavity
10
through the waveguide, and heats the food. The infrared sensor
14
detects a surface temperature of the food, and provides a voltage for a surface temperature of the food, which signal is passed through a series of signal processing, and provided to the control part. According to this, the control part operates the magnetron
12
to heat the food until a cooking temperature reaches to a target temperature, and the cooling fan
13
during cooking for cooling the heated magnetron
12
. Positions of the infrared sensor
14
and the cooling fan
13
are not limited to the positions shown in
FIG. 1
, but may differ depending on types of the microwave oven; different from the positions shown in
FIG. 1
, the positions may be varied, such that the infrared sensor is fitted to a right side of the cavity, and the cooling fan is fitted to a top of the cavity.
A defrosting process of frozen food may differ from general food heating. A related art defrosting process of frozen food in the microwave oven will be explained, with reference to FIG.
2
.
FIG. 2
illustrates a graph showing time vs. a temperature variation of frozen food, wherein hatched blocks denote power turned on time periods during which a power is supplied into the cavity
10
as a heating energy. That is, the magnetron is operative in periods shown in hatched blocks to direct the microwave to the frozen food inside of the cavity
10
. In a case the frozen food is to be defrosted, the microwave oven is put into operation in a state a surface temperature thereof is below zero, when the infrared sensor
14
at one side of the cavity
10
detects a variation of the surface temperature of the frozen food. In the meantime, as the surface temperature of the frozen food is at a low temperature, even though the power turned on time period is long in an initial defrosting, the power turned on time period becomes shorter, gradually. That is, because a temperature of the frozen food rises gradually as the defrosting proceeds, the power turned on time periods become the shorter as a frozen food turn over time period ‘P’ approaches. At the turn over time ‘P’, the user opens a door on the microwave oven, turns the frozen food over, and proceeds the defrosting, again. When the defrosting is started again in a state the frozen food is turned over, a power turned on time period of the magnetron is controlled at fixed intervals baser on a time period taken from the initial defrosting to the turn over ‘P’, and a power condition until the turn over time period ‘P’ is reached. That is, after the frozen food is turned over, the defrosting is carried out in a certain time period and power, taking a time period taken in a first defrosting of the frozen food (a defrosting process until the turn over) and a power condition in the time period into account. Therefore, in the second defrosting process after the frozen food is turned over, a process proceeds, in which merely the magnetron
12
is turned on/off periodically based on the time period taken in the first defrosting and the power condition in the time period.
Consequently, the related art defrosting in the microwave oven has a problem in that defrosting of frozen food is not made properly in a case frozen states differ on both sides of the frozen food to be defrosted due to shape or other. In the related art defrosting, the defrosting after the frozen food is turned over is carried out regardless of the surface temperature of the turned over frozen food, that causes problems of a product reliability deterioration coming from pre-mature defrosting, or excessive defrosting, or inconvenience to the user.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method for controlling defrosting in a microwave oven that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for controlling defrosting in a microwave oven, which can control a second defrosting according to an actual temperature of frozen food.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method for controlling defrosting in a microwave oven having an infrared sensor, includes the steps of (a) controlling a first defrosting up to a preset temperature upon reception of defrosting key application from a user, (b) turning over frozen food upon completion of the first defrosting, and (c) periodically detecting a surface temperature of the turned over frozen food by using the infrared sensor, and controlling a second defrosting according to the detected surface temperature and temperature variation.
An initial voltage application time period in the step (a) or (c) is made relatively longer than the voltage application time period in a later half of each of the steps.
The step (a) includes the steps of calculating a turning over time point by using the presently progressive minimum temperature Min_T and a minimum temperature variation &Dgr;T, calculating a first defrosting voltage by using a greater value &Dgr;Tmax of the minimum temperature variation &Dgr;T and a maximum temperature variation &Dgr;Tm, and the presently progressive minimum temperature Min_T, and carrying out defrosting according to the calculation, and generating a signal sound if the minimum temperature Min_T or a maximum temperature Max_T is higher than a preset temperature, or if the turning over time point is over a preset time point.
The step (c) includes the steps of calculating a defrosting finish time point and a second defrosting time period upon reception of a starting key again after the frozen food is turned over, calculating a second defrosting voltage by using a smaller temperature variation value &Dgr;Tmin, and the presently progressive minimum temperature Min_T upon calculation of the defrosting finish time point and the second defrosting time period, the smaller temperature variation value &Dgr;Tmin being selected from the minimum temperature variatio
Fleshner & Kim LLP
Leung Philip H.
LG Electronics Inc.
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