Abstract:
An apparatus and a method of controlling a microwave oven includes performing a first heating until detection values of a humidity sensor reach a reference value, wherein the humidity sensor senses humidity of water vapor discharged from a cooking chamber. A second heating is performed, lower than the first heating, after the detection values reach the reference value using an output power from a magnetron. A surrounding humidity condition of the microwave oven is determined. The reference value of the first heating is reset so as to cook food appropriately according to the determined humidity condition.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of Korean Application No. 2002-18377, filed Apr. 4, 2002, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to microwave ovens, and more particularly to an apparatus and a method of controlling a microwave oven, which can cook foods under optimal cooking conditions regardless of surrounding humidity conditions by compensating for variation of cooking conditions due to the surrounding humidity conditions.  
           [0004]    2. Description of the Related Art  
           [0005]    Generally, when rice is cooked in a conventional microwave oven, a first heating is performed until rice water reaches a boiling point of 100° C., and then a second heating is performed for a predetermined period of time after the rice water reaches the boiling point using an output power of a magnetron lower than that of the first heating.  
           [0006]    The microwave oven is not equipped with a temperature sensor and thus, detects the boiling of the rice water using a detection value from a humidity sensor, which senses a humidity value of water vapor discharged from a cooking chamber so as to detect the boiling point of the rice water.  
           [0007]    [0007]FIG. 1A is a waveform diagram showing a relationship between sensing voltages of a humidity sensor and time in the conventional microwave oven. FIG. 1B is a waveform diagram showing a relationship between output powers of a magnetron and time in the conventional microwave oven. FIG. 1C is a waveform diagram showing a relationship between boiling temperatures of water and time in the conventional microwave oven. As shown in FIG. 1A, at a beginning of heating food, the output power of the magnetron is maximized to rapidly heat the food, and then, the output power is gradually lowered while continuing to heat the food. If the rice water boils, rice continues to be heated using low output power suitable for steaming boiled rice, so the rice is cooked. Accordingly, the humidity value sensed by the humidity sensor is a constant value at the start of cooking, rapidly increasing when rice water reaches the boiling point, and gradually decreasing thereafter.  
           [0008]    A sensing voltage graph of the humidity sensor, as shown in FIG. 1A, shows a variation of the humidity value. A reference value (T1 FACTOR) of the humidity sensor, corresponding to the boiling point (100° C.) of the rice water, is estimated on a basis of sensing voltage values. Generally, the reference value is uniformly set at a value of, for example, 85% of a maximum voltage MAX of the sensing voltages on a basis of a normal surrounding humidity condition.  
           [0009]    However, a sensor for sensing relative humidity, not absolute humidity, is mainly used as the humidity sensor due to problems such as cost, etc. Then, if the surrounding humidity condition of the microwave oven is lower than that of a normal state, that is, a dry state, such as during Winter, the maximum voltage MAX sensed by the humidity sensor is relatively increased. Therefore, the voltage at 85% of the maximum voltage does not reflect the boiling point of rice water. Consequently, the output power of the magnetron is decreased to output a low output power suitable for steaming the rice before the rice water boils, thus causing rice to be half-cooked.  
         SUMMARY OF THE INVENTION  
         [0010]    Various objects and advantages of the invention will be set forth in part in the description that follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
           [0011]    Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a method of controlling a microwave oven to cook foods under optimal cooking conditions regardless of a surrounding humidity condition, by compensating for a variation of cooking conditions due to the surrounding humidity condition.  
           [0012]    To achieve the above and other objects, the present invention provides a method of controlling a microwave oven, including: performing a first heating until detection values of a humidity sensor reach a reference value, wherein the humidity sensor senses humidity of water vapor discharged from a cooking chamber; performing a second heating, lower than the first heating, after the detection values reach the reference value using an output power from a magnetron; determining a surrounding humidity condition of the microwave oven; and resetting the reference value of the first heating so as to cook food appropriately  
           [0013]    Further, to achieve the above and other objects, the present invention provides a method of controlling a microwave oven, including: performing a first heating until detection values of a humidity sensor reach a reference value, wherein the humidity sensor senses humidity of water vapor discharged from a cooking chamber; performing a second heating, lower than that of the first heating, for a set period of time after the detection values reach the reference value using an output power from a magnetron; determining a surrounding humidity condition of the microwave oven; and resetting a period of time for the second heating so as to cook food appropriately according to the determined humidity condition.  
           [0014]    To achieve the above and other objects, the present invention provides a control method of a microwave oven, including: maximizing an output power; counting a first heating time; reading sensing voltages from a humidity sensor during the first heating time; comparing the sensing voltages sensed by the humidity sensor with each other to determine a maximum voltage; setting a first reference value at a predetermined voltage level from the maximum voltage; determining whether a current sensing voltage sensed by the humidity sensor has reached the first reference value; decreasing the output power to a low power; determining whether the current mode is in a dry mode or a normal mode; setting a preset time as a reference period of time for a second heating time corresponding to the counted heating time; outputting the low power for a predetermined period of time of the second heating time; increasing the output power of the microwave oven to perform a cooking operation after the predetermined period of time of the second heating time elapses; and stopping the cooking operation of the microwave oven after the second heating time has elapsed.  
           [0015]    To achieve the above and other objects, the present invention provides an apparatus to control a microwave oven, including: a control unit counting a time from a start of heating to a time point when a first reference value is detected, comparing the counted heating time with a predicted heating time preset; and determining a current mode as a dry mode when the counted heating time is shorter than the predicted heating time.  
           [0016]    To achieve the above and other objects, the present invention provides an apparatus to control a microwave oven, including: a control unit determining a surrounding humidity condition of the microwave oven, and compensating for a variation of heating time due to the surrounding humidity of the microwave oven according to seasons or areas in which the microwave oven is used to provide an optimal heating time enabling the microwave oven to optimally cook food, regardless of surrounding conditions.  
           [0017]    To achieve the above and other objects, the present invention provides a method of controlling a microwave oven, including: counting a time from a start of heating to a time point when a first reference value is detected; comparing the counted heating time with a predicted heating time preset; and determining a current mode as a dry mode when the counted heating time is shorter than the predicted heating time.  
           [0018]    To achieve the above and other objects, the present invention provides a method of controlling a microwave oven, including: determining a surrounding humidity condition of the microwave oven; and compensating for a variation of heating time due to the surrounding humidity of the microwave oven according to seasons or areas in which the microwave oven is used to provide an optimal heating time enabling the microwave oven to optimally cook food, regardless of surrounding conditions.  
           [0019]    These together with other objects and advantages, which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part thereof, wherein like numerals refer to like parts throughout. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0021]    [0021]FIG. 1A is a waveform diagram showing a relationship between sensing voltages of a humidity sensor and time in the conventional microwave oven when a surrounding humidity of the microwave oven is in normal and dry states;  
         [0022]    [0022]FIG. 1B is a waveform diagram showing a relationship between output powers of a magnetron and time in the conventional microwave oven when the surrounding humidity of the microwave oven is in the normal and dry states;  
         [0023]    [0023]FIG. 1C is a waveform diagram showing a relationship between boiling temperatures of water and time in the conventional microwave oven when the surrounding humidity of the microwave oven is in the normal and dry states;  
         [0024]    [0024]FIG. 2 is a top sectional view showing a construction of a microwave oven according to an embodiment of the present invention;  
         [0025]    [0025]FIG. 3 is a block diagram of the microwave oven of FIG. 2;  
         [0026]    [0026]FIG. 4 is a flowchart of a method of controlling the microwave oven according to an embodiment of the present invention;  
         [0027]    [0027]FIGS. 5A and 5B are graphs showing first and second reference values of FIG. 4;  
         [0028]    [0028]FIG. 6 is a flowchart of another microwave oven control method to change a second heating time in a dry mode, according to another embodiment of the present invention; and  
         [0029]    [0029]FIG. 7 is a waveform diagram showing sensing voltages of a humidity sensor to describe a method of determining a mode of FIGS. 4 and 6.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.  
         [0031]    [0031]FIG. 2 is a top sectional view showing the construction of a microwave oven according to an embodiment of the present invention. Referring to FIG. 2, the microwave oven of the present invention includes a body  10 , which constitutes an external shape of the microwave oven and defines a cooking chamber  12  and a machine room  11  separately partitioned. A door  13  is connected to the body  10  by a hinge to open and shut the cooking chamber  12 , a control panel  14  is installed on a front of the body  10  and provided with a plurality of functional buttons thereon, and a humidity sensor  17  senses a humidity of the cooking chamber  12 .  
         [0032]    The cooking chamber  12  opens at the front of the body  10 , where a cooking tray  12   a  in a form of a turntable is installed on a bottom portion of the cooking chamber  12  and a motor is installed under the cooking tray  12   a  to rotate the cooking tray  12   a.  Further, an inlet  15   a,  communicating with the machine room  11  to suck the external air into the cooking chamber  12 , is formed on a front portion of one sidewall  15  of the cooking chamber  12 . Further, an outlet  16   a  is formed on a back portion of another sidewall  16  of the cooking chamber  12  to discharge the air in the cooking chamber  12  to the outside.  
         [0033]    Further, in the machine room  11 , a magnetron  1   a  is installed to oscillate microwaves, a cooling fan  11   b  is installed to suck the external air to cool the machine room  11  and the cooking chamber  12 , and a guide duct  11   c  is installed to guide the air in the machine room  11  to the inlet  15   a.  The cooling fan  11   b  is disposed between a magnetron  11   a  and a back wall of the machine room  11 . A plurality of suction holes  11   d  are formed on the back wall of the machine room  11  to suck the external air into the machine room  11 .  
         [0034]    The humidity sensor  17  is mounted on the sidewall  16  of the cooking chamber  12  adjacent to the outlet  16   a  to be disposed along the air discharging path of the cooking chamber  12 . Therefore, the humidity sensor  17  senses the humidity of the air being discharged from the cooking chamber  12  through the outlet  16   a.  The humidity sensor  17  is electrically connected to a control unit formed on the control panel  14 , as will be described later.  
         [0035]    [0035]FIG. 3 is a block diagram of the microwave oven according to an embodiment of the present invention. Referring to FIG. 3, the microwave oven includes a control unit  30  to control operations of the microwave oven. The control unit  30  is connected to an input unit  14   a  arranged in the control panel  14  to allow a user to input operation commands, such as rice cooking for one person and two persons. Further, the control unit  30  is connected to the humidity sensor  17  to sense humidity.  
         [0036]    Further, the microwave oven has a storage unit  20  electrically connected to the control unit  30 , to store various data for cooking. Furthermore, the control unit  30  is electrically connected to a magnetron driving unit  41  to drive the magnetron  11   a,  a fan driving unit  42  to drive the cooling fan  11   b,  a motor driving unit  43  to drive a motor  12   b  for rotating the cooking tray  12   a,  and a display driving unit  44  to drive a display unit  14   b  arranged on the control panel  14  to display information. When the user manipulates the input unit  14 a of the control panel  14  to operate the microwave oven, the microwave oven according to an embodiment of the present invention cooks food placed on the cooking tray  12   a  by radiating microwaves that are oscillated by the magnetron  11   a  to the cooking chamber  12 .  
         [0037]    Further, the external air is sucked into the machine room  11  through the suction holes  11   d  to cool the machine room  11  by the action of the cooling fan  11   b  during a cooking operation of the microwave oven, and is provided to the cooking chamber  12  through the guide duct  11   c  and the inlet  15   a.  Then, the air in the cooking chamber  12  is discharged to the outside through the outlet  16   a,  together with water vapor generated from the food, as shown by an arrow in FIG. 3. Accordingly, odor and water vapor can be eliminated from the cooking chamber  12 . In this case, the air in the cooking chamber  12  is discharged to the outside while being brought into contact with the humidity sensor  17 , so the humidity sensor  17  senses water vapor contained in the discharged air and transmits the sensed water vapor to the control unit  30  as electrical signals. The control unit  30  recognizes such electrical signals as voltage values. The control unit  30  drives the magnetron  11   a,  the motor  12   b  and the cooling fan  11   b  to automatically cook the food based on the electrical signals received from the humidity sensor  17 .  
         [0038]    Hereinafter, a method of controlling a microwave oven to cook rice according to an embodiment of the present invention will be described in detail. FIG. 4 is a flowchart of a method of controlling the microwave oven according to an embodiment of the present invention. Referring to FIG. 4, the user places a bowl, in which rice and a suitable quantity of water are mixed, in the cooking chamber  12  so as to cook the rice. The user then selects a cooking course for one person or two persons through the input unit  14   a.  At S 10 , the control unit  30  heats the food by driving the magnetron  11   a  to maximize its output power. At S 11 , the control unit  30  counts a first heating time.  
         [0039]    At S 12 , the control unit  30  reads sensing voltages from the humidity sensor  17  for a predetermined period of time of the first heating time. At S 13 , the control unit  30  compares the sensing voltages sensed by the humidity sensor  17  with each other and determines a maximum voltage.  
         [0040]    If the maximum voltage is determined, at S 14 , the control unit  30  sets a voltage at 85% of the maximum voltage as a first reference value. At S 15 , the control unit  30  determines whether a current sensing voltage determined from the humidity sensed by the humidity sensor  17  has reached the first reference value. In this case, the first reference value is a humidity value when the temperature of water reaches the boiling point (100° C.), the humidity value being obtained through experiments to determine the humidity and the temperature of water when a surrounding humidity condition of the microwave oven is normal.  
         [0041]    At S 15 , if the current sensing voltage has reached the first reference value, at S 16 , the control unit  30  determines whether a current mode is in a dry mode or a normal mode by a mode determining method to be described later.  
         [0042]    If it is determined that the current mode is in the normal mode, at S 19 , the control unit  30  decreases the output power of the magnetron  11   a  to a low power suitable for steaming boiled rice, and stops the counting of the heating time. Then, at S 20 , the control unit  30  sets a preset time as a reference period of time for a second heating (second heating time) corresponding to the counted heating time.  
         [0043]    If the second heating time is set, during the second heating time, at S 21 , the control unit  30  operates the magnetron  11   a  to output the low power required to steam boiled rice for a predetermined period of time of the second heating time, while the control unit  30  increases the output power of the magnetron  11   a  to perform a cooking operation after the predetermined period of time of the second heating time elapses. At S 22 , after the second heating time has elapsed, the control unit  30  stops the driving of the magnetron  11   a.  At S 23 , the control unit  30  finishes the cooking.  
         [0044]    Further, at S 16 , if the current mode is in the dry mode, at S 17 , the control unit  30  sets a second reference value (a voltage at 83% of the maximum voltage) lower than the first reference value, instead of the first reference value, so as to heat the food a little longer, as shown in FIGS. 5A and 5B. Accordingly, as shown in FIGS. 5A and 5B, a reference value is decreased to a voltage at 83%, lower that the previous 85%, of the maximum voltage, such that a time taken for the sensing voltage to reach the reference value is lengthened, thus allowing the food to be heated a little longer.  
         [0045]    At S 17 , if the second reference value is set, at S 18 , the control unit  30  determines whether the current sensing voltage has reached the second reference value. At S 18 , if the current sensing voltage has reached the second reference value, at S 19 , the control unit  30  decreases the output power of the magnetron  11   a  to the low power suitable to steam boiled rice, and stops the counting of the heating time. At S 20 , the control unit  30  sets a preset time corresponding to the counted heating time as the second heating time.  
         [0046]    During the second heating time, at S 21 , the control unit  30  operates the magnetron  11   a  to output the low power required to steam boiled rice for a predetermined period of time of the second heating time, while the control unit  30  increases the output power of the magnetron  11   a  to perform the cooking operation after the predetermined period of time of the second heating time elapses. At S 22 , after the second heating time has elapsed, at S 23 , the control unit  30  stops the driving of the magnetron  11   a  and finishes the cooking.  
         [0047]    [0047]FIG. 6 is a flowchart of another microwave oven control method of changing the second heating time in a dry mode instead of the reference value during the first heating, according to another embodiment of the present invention.  
         [0048]    Referring to FIG. 6, at S 100 , the control unit  30  heats the food by driving the magnetron  11   a  to maximize the output power, and, at S 101 , counts the first heating time. At S 102 , the control unit  30  reads the sensing voltages from the humidity sensor  17  for a predetermined period of time of the first heating time. Further at S 103 , the control unit  30  compares the sensing voltages sensed by the humidity sensor  17  with each other, and sets the maximum voltage.  
         [0049]    If the maximum voltage is set, at S 104 , the control unit  30  sets a voltage at 85% of the maximum voltage as a first reference value. At S 105 , the control unit  30  determines whether the current sensing voltage determined from the humidity sensed by the humidity sensor  17  has reached the first reference value.  
         [0050]    At S 105 , if the current sensing voltage has reached the first reference value, at S 106 , the control unit  30  decreases the output power of the magnetron  11   a  to a low power suitable for steaming boiled rice, and stops the counting of the heating time. Then, at S 107 , the control unit  30  determines whether the current mode is in the dry mode or the normal mode by a mode determining method to be described later If the current mode is in the normal mode, at S 108 , the control unit  30  sets a preset time as the second heating time corresponding to the counted heating time.  
         [0051]    If the second heating time is set, at S 109 , during the second heating time, the control unit  30  operates the magnetron  11   a  to output low power required to steam boiled rice for a predetermined period of time of the second heating time, while the control unit  30  increases the output power of the magnetron  11   a  to perform a cooking operation after the predetermined period of time of the second heating time elapses. After the second heating time has elapsed, at S 110  and S 111 , the control unit  30  stops the driving of the magnetron  11   a  and finishes the cooking.  
         [0052]    Further at S 106 , if the current mode is in the dry mode, at S 120 , the control unit  30  sets the second heating time to be longer than the preset time. If the second heating time is set, at S 109 , during the second heating time, the control unit  30  operates the magnetron  11   a  to output low power required to steam boiled rice for a predetermined period of time of the second heating time, while the control unit  30  increases the output power of the magnetron  11   a  to perform a cooking operation after the predetermined period of time of the second heating time elapses. After the second heating time has elapsed, at S 110  and S 111 , the control unit  30  stops the driving of the magnetron  11   a  and finishes the cooking.  
         [0053]    Hereinafter, the dry mode determining method of FIGS. 4 and 6 is described. There are two methods to determine the dry mode of FIGS. 4 and 6.  
         [0054]    A first method is performed by determining the current mode as the dry mode if a voltage waveform between points A and B ascends as shown in FIG. 7, and by determining the current mode as the normal mode if the voltage waveform is constant or descends. That is, sensing voltages sensed by the humidity sensor  17  for a predetermined period of time are compared with each other, such that the current mode is determined as the dry mode if the sensing voltages are gradually increased. Alternatively, the maximum voltage is set by comparing sensing voltages sensed by the humidity sensor  17  for a predetermined period of time with each other, and if a voltage at the start of heating is less than the maximum voltage, the current mode is determined as the dry mode. This determination is due to a phenomenon where if the surrounding humidity of a microwave oven is decreased, the humidity within the cooking chamber is affected to cause the waveform of the sensing voltages of the humidity sensor  17  to ascend.  
         [0055]    A second method is performed by counting a time from the start of heating to a time point when the first reference value is detected, comparing the counted heating time with a predicted heating time preset for a case where the surrounding humidity of the microwave oven is normal, and determining the current mode as the dry mode if the counted heating time is shorter than the predicted heating time. The second method considers that, when the surrounding humidity of the microwave oven is in the dry mode, heating time becomes shorter than that of a normal mode.  
         [0056]    As described above, the present invention provides a method of controlling a microwave oven, which provides an optimal heating time by compensating for a variation of heating time due to surrounding humidity of the microwave oven according to seasons or areas in which the microwave oven is used, thus enabling the microwave oven to optimally cook food, regardless of surrounding conditions.  
         [0057]    Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.