Patent Publication Number: US-7223951-B2

Title: Cooking control method of microwave oven and apparatus for performing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Patent Application No. 2005-0000291, filed on Jan. 3, 2005, in the Korean Intellectual 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 a microwave oven for detecting the food position using a weight sensor, and more particularly to a method for controlling the microwave output depending upon a weight and food position to be cooked so as to implement optimized cooking performance in a microwave oven and an apparatus for performing the same. 
   2. Description of the Related Art 
   Generally, a microwave oven is a cooking device for rapidly heating food using microwaves at a frequency of about 2,450 MHz, which are generated when high voltage electricity is applied to a magnetron, a device for generating high frequency microwaves, and vibrate water molecules contained in food, so that the food is rapidly cooked by heat generated due to the vibration of the water molecules. 
   Such a microwave oven detects the food weight using a weight sensor, and a microwave oven using a weight sensor is disclosed in Korean Utility Model Registration No. 0118078. 
   The microwave oven in Korean Utility Model Registration No. 0118078 detects the food weight and controls cooking time and microwave output based on the detected food weight. 
   There are several types of weight sensors, such as a differential coil type weight sensor, a capacitance type weight sensor, a piezo-electric type weight sensor, a strain gage type weight sensor, and the like, and conventional weight sensors detect the food weight while the food is supported by a turntable. 
   Since a conventional microwave oven controls the microwave output only by taking account of the food weight without taking account of the fact that food is not cooked uniformly and microwave energy transmitted to the food varies according to the position of the food on the turntable, the cooking performance of the conventional microwave oven varies depending upon whether the food is located at the center or the side of the turntable. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an aspect of the present invention to provide a method for controlling the microwave output based on weight of food and food position so as to implement optimized cooking performance in a microwave oven and an apparatus for performing the same. 
   Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
   It is another aspect of the present invention to provide a method for precisely detecting the food position placed on a turntable using a weight sensor so as to supply a proper amount of microwave energy to the food and an apparatus for performing the same. 
   The foregoing and/or other aspects of the present invention are achieved by providing a control method for cooking food placed on a turntable in a microwave oven, including detecting a plurality of sensing values generated according to weight of food to be cooked during the rotation of the turntable, detecting a food position by comparing the detected sensing values, and controlling the microwave output based on the detected food position. 
   The sensing values are peak voltage values detected according to a pressure applied corresponding to the weight of food. 
   Further, the sensing values are peak voltage values detected for a period of one revolution or at least two revolutions of the turntable. 
   The food position is a distance of the food from a center of the turntable, and the output of the microwave is increased as the food position is farther from the center of the turntable. 
   The control method further includes detecting the weight of food based on the detected sensing values, and detecting the food position by classifying the detected weight of food. 
   The weight of food is a value corresponding to an average of the sensing values and is detected as a same value regardless of the food position. 
   The food position is estimated by obtaining a maximal value and a minimal value among the detected sensing values and by substituting a difference between the maximal value and the minimal value into a weight formula, wherein the weight formula is predetermined. 
   The maximal value is a maximal voltage value obtained by subtracting an initial voltage value from a greatest value among the sensing values, and the minimal value is a minimal voltage value obtained by subtracting an initial voltage value from a lowest value among the sensing values. 
   It is another aspect of the present invention to provide a controlling apparatus of a microwave oven for cooking food placed on a turntable, including a weight sensor to detect a plurality of sensing values generated corresponding to food weight, during a rotation of the turntable, and a controller to detect a food position of the food by comparing the detected sensing values, and to control the microwave output based on the detected food position. 
   The controller controls the microwave intensity and microwave output time based on the food position. 
   The sensing values are peak voltage values detected when a plurality of rollers that are installed in a lower side of the turntable passes by the weight sensor according to a pressure corresponding to the food weight is applied. 
   The rollers are at least three rollers, which are disposed radially every 120 degrees. However, the number of rollers is not limited hereto, and may vary accordingly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a schematic perspective view illustrating a microwave oven including an embodiment of the present invention; 
       FIG. 2  is a sectional view illustrating main parts of the microwave oven of  FIG. 1 ; 
       FIG. 3  is a view illustrating a turning passage of rollers and a position of a sensor of the microwave oven according to an embodiment of the present invention; 
       FIG. 4  is a view illustrating a contact of the rollers with the sensor during the rotation of the rollers in the cavity of the microwave oven according to an embodiment of the present invention; 
       FIG. 5  is a block diagram illustrating the structure of a cooking control apparatus of a microwave oven according to an embodiment of the present invention; 
       FIG. 6  is a flowchart illustrating a cooking control method of a microwave oven according to an embodiment of the present invention; 
       FIG. 7  is a detailed flowchart illustrating a detection of the food position in the cooking control method in  FIG. 6 ; and 
       FIG. 8  is a graph illustrating waveforms outputted from a weight sensor of the microwave oven according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
     FIG. 1  is a schematic perspective view illustrating a microwave oven including an embodiment of the present invention. 
   As shown in  FIG. 1 , a cavity  12  is formed in a body  10 , a door  14  is installed to the front side of the cavity  12  to pivot, and a manipulation panel  16  is installed to the right side of the cavity  12 . When a user selects cooking function using the manipulation panel  16 , the manipulation panel  16  displays the selected cooking function. 
   At an inner lower side of the cavity  12 , a turntable  18  for rotating the food, on which food is placed, is installed. 
     FIG. 2  is a sectional view illustrating main parts of the microwave oven of  FIG. 1 ,  FIG. 3  is a view illustrating a turning passage of rollers and the position of a sensor of the microwave oven according to an embodiment of the present invention, and  FIG. 4  is a view illustrating the contact of the rollers with the sensor during the rotation of the rollers in the cavity of the microwave oven according to an embodiment of the present invention. 
   As shown in  FIGS. 2 to 4 , a turntable motor  20  for rotating the turntable  18  is installed at the lower side of a center shaft of the turntable  18  by a connecting shaft  20   a , and a center coupler  18   a , rotated on the bottom surface of the cavity  12 , for supporting the turntable  18 , is installed to the connecting shaft  20   a.    
   A plurality of rollers (i.e., approximately three rollers)  22  is rotatably installed to roller supporting shafts  22   a  (see  FIG. 4 ) on the lower surface of the turntable  18 . The rollers  22  rotate around the connecting shaft  20   a  during the rotation of the turntable  18 , and rotate about the roller supporting shafts  22   a . The rollers  22  are disposed radially every 120 degrees. 
   The rollers  22  travel along a rotating passage. At a lower side of the rotating passage, a weight sensor  24  penetrates the cavity  12 . The weight sensor  24  generates an output signal corresponding to the food weight whenever the rollers  22  travel over the weight sensor  24  while the rollers  22  generate a rotating force turn with a roller guide  22   b . The weight sensor  24  is a pressure sensor to generate voltage when a pressure corresponding to the food weight on the turntable  18  is applied thereto. 
   The food weight is detected by performing an algorithm for estimating the food weight, for example, by averaging three sensing values, which are generated by the three contacts of the rollers  22  for one revolution of the turntable  18  when the number of the rollers  22  is three or by using sensing values for two more revolutions of the turntable  18 . 
     FIG. 5  is a block diagram view illustrating the structure of a cooking control apparatus of a microwave oven according to an embodiment of the present invention. The cooking control apparatus includes the weight sensor  24 , a key input part  100 , a controller  110 , a magnetron driver  120 , a motor driver  130 , and a display  140 . 
   The key input part  100  is provided in the manipulation panel  16  and includes a plurality of keys (not shown) through which a user inputs cooking functions such as cooking time, menu, microwave output, start/stop, or the like, to the controller  110 . 
   The controller  110  is a microcomputer for overall control of the microwave oven, and controls the output of the microwaves by detecting the food weight W and food position L according to the sensing values, that is, peak voltages V MAX1 , V MAX2 , and V MAX3  generated by the weight sensor  24 , during one period (for example, when the number of rollers is three) for one revolution of the turntable  18 . 
   The magnetron driver  120  generates microwaves according to a control signal from the controller  110  and includes a relay for controlling a magnetron  121 . The motor driver  130  controls the turntable motor  20  according to the control signal from the controller  110 . 
   The display  140  displays the cooking time, the menu, or the like selected by the user on the manipulation panel  16  according to the control signal from the controller  110 . 
   Hereinafter, operation and effect of the cooking control apparatus of the microwave oven and the cooking control method according to an embodiment of the present invention will be described. 
     FIG. 6  is a flowchart illustrating the cooking control method of the microwave oven according to an embodiment of the present invention. 
   In operation  100 , when the user places food on the turntable  18  in the cavity  12  and presses a start key of the key input part  100 , the key signal selected by the user is inputted to the controller  110  by the key input part  100 . 
   From operation  100 , the process moves to operation  200 , where the controller  110  outputs a control signal for rotating the turntable  18  to the motor driver  130  so as to drive the turntable motor  20 . 
   When the turntable motor  20  is driven, the center coupler  18   a  supporting the turntable  18 , rotates on the bottom surface of the cavity  12  and the rollers  22 , installed in the lower side of the turntable  18 , rotate and travel along the passage together the roller guide  22   b.    
   When the rollers  22  rotate with the roller guide  22   b , the weight sensor  24  disposed in the bottom surface of the cavity  12  generates a voltage V when a pressure corresponding to the food weight on the turntable  18  is applied (see  FIG. 8 ). 
   From operation  200 , the process moves to operation  300 , where from respective waveforms generated during one time period, for example, when the number of the rollers is three, a maximal value VMAX 1  generated from a first waveform, a maximal value VMAX 2  generated from a second waveform, and a maximal value VMAX 3  generated from a third waveform are detected based on the sensing values sensed by the weight sensor  24  whenever the rollers  22  travel over the weight sensor  24  (see  FIG. 8 ). 
   For more precise detection of the food weight, the maximal values for two more revolutions (approximately six values) can be detected. From operation  300 , the process moves to operation  400 , where it is determined if one revolution has been completed. However, the present invention will be described, for example, as if one revolution of the turntable  18  has been completed. 
   Therefore, when one revolution of the turntable  18  is completed in operation  400 , the process moves to operation  500 , where the controller  110  detects the food weight by estimating an average voltage value Vavg, an average value of three peak voltage values V MAX1 , V MAX2 , and V MAX3  generated during one revolution of the turntable  18 , and from operation  500 , the process moves to operation  600 , where the controller  110  determines the output of the microwave based on the detected food weight W. 
   The output of the microwave based on the food weight W (for example, 500 W, 2 minutes for 2 Kg of food) is inputted in a ROM table of the controller  110 . Since the food weight W is the average value of the three peak voltage values VMAX 1 , VMAX 2 , and VMAX 3 , and the detected food weight W is always identical regardless of the position of the food. 
   From operation  600 , the process moves to operation  700 , where the controller  110  finds a maximal value among the three peak voltage values VMAX 1 , VMAX 2 , and VMAX 3 , generated for one revolution of the turntable  18  and defines the found maximal value as VMAX, and finds a minimal value among the three peak voltage values VMAX 1 , VMAX 2 , and VMAX 3 , and defines the found minimal value as VMIN. 
   Further, in operation  700 , an initial value V 1  of the weight sensor  24  is subtracted from the defined maximal value VMAX and the defined minimal value VMIN, so as to obtain a maximal value Vmax and a minimal value Vmin of the weight sensor  24 , and to estimate a difference R between the maximal value Vmax and the minimal value Vmin. 
   Here, the initial value V 1  of the weight sensor  24  indicates an inherent initial voltage value peculiar to the weight sensor  24  and a reference value used to reduce the difference according to microwave ovens and weight sensors. 
   From operation  700 , the process moves to operation  800 , where when the estimated difference R is substituted into a formula for determining food weight, the distance from the center of the turntable  18  to food on the turntable  18 , i.e., the food position L can be precisely detected, and the formula is inputted to the controller  110  in advance. 
   The food position on the turntable may be changed, the roller  22 , near to the food position, transmits heavy food weight to the weight sensor  24 , and the roller  24 , far from the food position transmits light food weight to the weight sensor  24 , so that the distance of the food from the center of the turntable  18  can be estimated. 
   From operation  800 , the process moves to operation  900 , where the output of the microwave is determined based on the detected food position L. When the output of the microwave (for example, the output of the microwave is adjusted to 530 W and 2.5 minutes in the case that the food is positioned 60 mm from the center of the turntable  18  when the food weight is 2 Kg and the output of the microwave is set to 500 W and 2 minutes) is inputted to the ROM table of the controller  110  in advance. 
   The intensity and amount of energy of the microwave in the cavity  12  are varied whenever food is positioned at the center or the edge of the turntable  18  even if food of same weight W is placed. Thus, since, cooking performance is varied even if the same microwave energy is supplied to food of the same detected food weight W, the food position L is precisely detected and optimized cooking performance is implemented. 
   From operation  900 , the process moves to operation  1000 , where the food position L is displayed on the display  140 . 
   Process for detecting the food position L in the cooking control method illustrated in  FIG. 6  will be described in detail by referring  FIG. 7 . 
   The weight and size of the turntable  18  are determined when a microwave oven is initially developed, and the food position L on the turntable  18  cannot be the same. For example, there is a possibility that, when food is placed at the edge of a turntable  18  of a large diameter, the roller  22 , positioned where food is placed on the turntable, transmits a large pressure to the weight sensor  24  during the revolution of the turntable  18 , but the roller  22 , positioned opposite to the food position, transmits a light food weight to the weight sensor  24 . Due to the difference of the diameter and the weight of the turntable  18 , there may be different formulas depending upon food (for example, the food weight). In the present invention, five cases will be described by increasing the food weight in 250 g increments. 
   In  FIG. 7 , in operation  810 , it is determined whether the food weight W is less than 250 g. If it is determined in operation  810 , that the food weight W is less than 250 g, the process moves to operation  811 , where the difference R of the sensor  24  is substituted to a weight formula (L=5×R−32) so that the distance from the center of the turntable  18  to the food position, that is, the food position L is detected. 
   If it is determined in operation  810 , that the food weight W is not less than 250 g, the process moves to operation  810 , where it is determined whether the food weight W is greater than 250 g and less than 500 g. If it is determined in operation  820 , that the food weight W is greater than 250 g and less than 500 g, the process moves to operation  821 , where the difference R of the sensor  24  is substituted to a weight formula (L=2×R−11) so as to detect the food position L. 
   However, if it is determined in operation  820 , that the food weight W is greater than 250 g and not less than 500 g, the process moves to operation  830 , where it is determined whether the food weight W is greater than 500 g and less than 750 g is determined. If the food weight W is greater than 500 g and less than 750 g, the process moves to operation  831 , where the difference R of the sensor  24  is substituted to a weight formula (L=2×R−15) so as to detect the food position L. 
   If it is determined in operation  830 , that the food weight W is greater than 500 g and not less than 750 g, the process moves to operation  840 , where it is determined whether the food weight W is greater than 750 g and less than 1000 g is determined. If it is determined in operation  840 , that the food weight W is greater than 750 g and less than 1000 g, the process moves to operation  841 , where the difference R of the sensor  24  is substituted to a weight formula (L=1×R−4) so as to detect the food position L. 
   If it is determined in operation  840 , that the food weight W is greater than 750 g and not less than 1000 g, the process moves to operation  850 , where the difference R of the sensor  24  is substituted to a weight formula (L=1×R−7) so as to detect the food position L. 
   Since the intensity and amount of energy of the microwave are different according to the food position, the cooking performance is changed when the same microwave energy is supplied even if the same food weight W is detected. As a result, consumers may be dissatisfied with the conventional microwave oven and manufacturers lose a chance to provide a better microwave oven. 
   Thus, if the microwave energy in the microwave oven is measured and programmed based on the food position when developing the microwave oven, the user can experience uniform and optimized cooking performance regardless of the food position. 
   Although, in the embodiment of the present invention, the detection of the food weight W and the food position L using the sensing values of the weight sensor  24  generated due to the three contacts of the weight sensor  24  for one revolution of the turntable  18  has been described as an example. The present invention is not limited to hereto and the same aspect and effect as those of the present invention can be achieved even when the food weight W and the food position L are detected using the sensing values for two revolutions or more. 
   Moreover, regardless of the food position, the boomerang effect that food is always positioned in front of the door  14  when the cooking is finished can be implemented by detecting the food position by the weight sensor  24 . 
   As described above, according to the microwave oven cooking control method and the apparatus for performing the same according to the present invention, optimized cooking performance can be implemented by controlling the microwave output based on the food weight and the food position, and microwaves of proper energy can be supplied to food based on the food position by precisely detecting the food position on the turntable using the weight sensor. 
   Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.