Abstract:
A refrigerator equipped with a door opening device opening doors by driving a motor and a method of controlling the same. In the method of controlling the refrigerator includes a door opening device including a plurality of sliding bars selectively opening first and second doors, a motor opening the first door or the second door by moving back and forth the sliding bars in directions opposite to each other, a plurality of position detectors detecting at least one protrusion provided at one side of the sliding bar, a switch unit inputting door opening signals, and a controller controlling operation of the first door and the second door according to the door opening signals. If door opening signals used to open the first and second doors, the door opening device is controlled so that the first and second doors are easily open/closed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2008-0122426 filed on Dec. 4, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to a refrigerator and a method of controlling the same. More particularly, the present invention relates to a refrigerator equipped with a door opening device enabling a user to easily open a door of the refrigerator and a method of controlling the refrigerator. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, a refrigerator cools articles stored therein through a cooling cycle of a compressor, a condenser, and an evaporator. The refrigerator is provided therein with a storage compartment to allow a user to store and take out the articles in the refrigerator. The refrigerator includes at least one storage compartment according to the capacity of the refrigerator. For example, the storage compartment may be divided into two compartments, such as a cooling compartment and a refrigerating compartment, or may be divided into four compartments, such as a cooling compartment, a refrigerating compartment, an auxiliary cooling compartment, and an auxiliary refrigerating compartment. 
         [0006]    Meanwhile, the refrigerator having at least one storage compartment includes a door, which opens/closes the storage compartment. The door is divided into a hinge coupling type door that is rotatably open/closed relative to the storage compartment and a drawer type door that is open/closed relative to the storage compartment like a drawer. 
         [0007]    Meanwhile, typically, a user must pull a door of a refrigerator when the user wants to manually open the door. In addition, when the user wants to close the door, the user must push the door using a hand or a foot such that the door can be closed by the weight thereof. 
       SUMMARY 
       [0008]    Accordingly, it is an aspect of the present invention to provide a refrigerator and a method of controlling the same, capable of automatically opening/closing a door using a motor. 
         [0009]    In addition, it is another aspect of the present invention to provide a refrigerator and a method of controlling the same, capable of reducing noise in the process of changing a direction of a motor when a door is open/closed. 
         [0010]    Further, it is still another aspect of the present invention to provide a refrigerator and a method of controlling the same, capable of setting a door in an initial position when the refrigerator is powered on. 
         [0011]    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. 
         [0012]    The foregoing and/or other aspects of the present invention are achieved by providing a refrigerator including first and second doors which open/close first and second storage compartments defined in a body, respectively, and a door opening device. The door opening device includes a plurality of sliding bars which selectively open the first and second doors, and a motor which opens/closes the first door or the second door by moving back and forth the sliding bars in directions opposite to each other. 
         [0013]    The door opening device may further include a switch unit inputting a door opening signal used to open the first door or the second door. 
         [0014]    The door opening device may further include a controller controlling the first door or the second door to be open according to the door opening signal input to the switch unit. 
         [0015]    The door opening device may further include a plurality of position detectors detecting at least one protrusion provided at one side of the sliding bars. 
         [0016]    The door opening device may further include a display unit displaying failure of the door opening device. 
         [0017]    According to another aspect of the present invention, there is provided a method of controlling a refrigerator including a door opening device, which includes first and second doors opening/closing first and second storage compartments defined in a body, a plurality of sliding bars selectively opening the first and second doors, a motor opening the first door or the second door by moving back and forth the sliding bars in directions opposite to each other, a plurality of position detectors detecting at least one protrusion provided in one side of the sliding bars, a switch unit inputting door opening signals, and a controller controlling operation of the first and second doors according to the door opening signals, and the method includes opening/closing the first and second doors by controlling the door opening device if the door opening signals are input in order to open the first door or the second door. 
         [0018]    The sliding bar may be moved by driving the motor for a first set time sufficient for enabling the at least one protrusion to deviate from a detection region of the position detector if the door opening signals are input. 
         [0019]    A time point, at which the at least one protrusion enters the detection region of the position detector, is recognized if the first set time elapses. 
         [0020]    The sliding bar may be moved by driving the motor for a second set time sufficient for enabling the at least one protrusion to enter a reliable detection region of the position detector if the at least one protrusion has entered the detection region of the position detector. 
         [0021]    The motor may be stopped if the second set time elapses, so that the first door or the second door maintains an open state for a third set time. 
         [0022]    The sliding bar may be moved by driving the motor for a fourth set time sufficient for enabling the at least one protrusion to deviate from the detection region of the position detector if the third set time elapses. 
         [0023]    The time point, at which the at least one protrusion enters the detection region of the position detector, is recognized if the fourth set time elapses. 
         [0024]    The sliding bar may be moved by driving the motor for a fifth set time sufficient for enabling the at least one protrusion to enter the reliable detection region of the position detector if the at least one protrusion has entered the detection region of the position detector. 
         [0025]    If the door opening signals of the first and second doors are simultaneously input, the controller may determine an input sequence of the door opening signals to recognize only the door opening signal that is primarily input such that one of the first and second doors corresponding to the primary door opening signal is open. 
         [0026]    If the door opening signals of the first and second doors are simultaneously input, the controller may not recognize all the door opening signal, or recognizes only the door opening signal of a preset door. 
         [0027]    If the door opening signal for one of the first and second doors is input when a remaining one door is open/closed, the door opening signal may not be recognized. 
         [0028]    According to still another aspect of the present invention, there is provided a method of controlling a refrigerator equipped with first and second doors opening/closing first and second storage compartments partitioned in a body. The refrigerator includes a door opening device including a plurality of sliding bars selectively opening the first and second doors, a motor opening the first door or the second door by moving back and forth the sliding bars in directions opposite to each other, a plurality of position detectors detecting at least one protrusion provided at one side of the sliding bar, a switch unit inputting door opening signals, and a controller controlling operation of the first door and the second door according to the door opening signals. The method of controlling the refrigerator includes detecting a position of the at least one protrusion if the refrigerator is powered on, and controlling the first and second doors to be closed according to a position of the at least one protrusion. 
         [0029]    The method may further include rotating the motor in one preset direction if the position of the at least one protrusion is not detected. 
         [0030]    The method may further include controlling the first and second doors such that the first and second doors are closed according to the position of the at least one protrusion if the position of the at least one protrusion is detected due to the rotating of the motor. 
         [0031]    The method may further include recognizing that the at least one protrusion is placed at a preset position if the at least one position of the protrusion is not detected. 
         [0032]    The method may further include controlling the first and second doors such that the first and second doors are closed according to the at least one position of the protrusion. 
         [0033]    If the position of the at least one protrusion is not detected for a predetermined time when the first and second doors are controlled to be closed, the door opening device may be regarded as failed. 
         [0034]    The door opening device may further include a display unit, and the display unit displays failure of the door opening device if the door opening device is regarded as failed. 
         [0035]    As described above, according to one aspect, a plurality of doors can be open by moving two sliding bars using one motor, so that the manufacturing cost can be reduced. 
         [0036]    According to another aspect, when a door is open due to the rotation of the motor, or the door position is changed from the maximum open state to a closed state, the operation of the door is performed after a predetermined time has elapsed, so that noise can be reduced when the door is open/closed. 
         [0037]    According to still another aspect, when power is turned off and then turn on due to cut-off of electric current, a state of the door can be exactly determined by the position detectors, so that the door can return to a waiting state without an unnecessary operation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]    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: 
           [0039]      FIG. 1  is a view showing a refrigerator employing a door opening device according to one embodiment; 
           [0040]      FIG. 2  is a control block diagram showing the door opening device according to one embodiment; 
           [0041]      FIGS. 3A to 3C  are schematic views showing a door opening device according to a first embodiment; 
           [0042]      FIG. 4  is a view showing a table representing the detection state of position detectors based on the open state of doors according to the first embodiment; 
           [0043]      FIGS. 5A and 5B  are flowcharts showing the control procedure of the door opening device according to the first embodiment; 
           [0044]      FIG. 6  is a flowchart showing an initialization operation when the door opening device is powered on according to the first embodiment; 
           [0045]      FIGS. 7A to 7E  are sectional views schematically showing a door opening device according to a second embodiment; 
           [0046]      FIG. 8  is a table showing the detection state of position detectors when a door is open according to the second embodiment; and 
           [0047]      FIG. 9  is a flowchart showing an initialization operation of the door opening device upon a power-on state according to the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0048]    Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements. The embodiments are described below by referring to the figures. 
         [0049]      FIG. 1  is a view showing a refrigerator employing a door opening device  20  according to one embodiment. 
         [0050]    As shown in  FIG. 1 , the refrigerator according to one embodiment includes a body  10  divided into a first storage compartment (not shown) and a second compartment (not shown). First and second doors  11  and  12  are installed at both sides of a front surface of the body  10  to open/close the first and second storage compartments. Generally, in such a refrigerator, the first storage compartment serves as a cooling compartment, and the second storage compartment serves as a refrigerating compartment. Upper and lower portions of the first and second doors  11  and  12  are pivotally coupled to the body  10  by a hinge assembly  13 . In addition, first and second handles  14  and  15  are provided on front surfaces of the first and second doors  11  and  12 . 
         [0051]    The door opening device  20  may be mounted on a top surface of the body  10  to push the upper portions of the first and second doors  11  and  12  forward and open the first and second doors  11  and  12 , so that a user can easily open the first and second doors  11  and  12 . 
         [0052]      FIG. 2  is a control block diagram showing the door opening device  20  according to one embodiment. 
         [0053]    As shown in  FIG. 2 , the door opening device  20  includes first and second switch units  16  and  17  allowing a user to input a door opening signal, first, second, and third position detectors  31 ,  32 , and  33  detecting positions of first and second sliding bars  40  and  41 , a memory  34  storing a program to control the operation of a motor  38 , a timer  35  measuring a driving time of the motor  38 , a controller  30  controlling the driving of the motor  38  using information from the first to third position detectors  31  to  33  and the timer  35 , a motor driver  36  driving the motor  38  under the control of the controller  30 , and a display unit  37  displaying the failure of the door opening device  20 . 
         [0054]    The first and second switch units  16  and  17  are provided at the first and second handles  14  and  15  of the first and second doors  11  and  12  to allow a user to control the operation of the motor  38 . The first and second switch units  16  and  17  may be detectors that detect touch of the user on the first and second handles  14  and  15 , or power switches that directly turn on/off power applied to the motor  38 . 
         [0055]    The first to third position detectors  31  to  33  may detect a rotation position of the motor  38 , that is, a position of the first and second sliding bars  40  and  41 . The first to third position detectors  31 ,  32 , and  33  may detect the rotation position of the motor  38  by detecting first, second, and third protrusions  42 ,  43 , and  44 . In addition, the first to third position detectors  31  to  33  may be a typical optical sensor. According to the present embodiment, the first to third position detectors  31  to  33  are turned on if a signal phase is changed due to the first and second protrusions  42  and  43 , and turned off if the signal phase is not changed. 
         [0056]    The memory  34  stores a program to control the operation of the motor  38 , and the timer  35  can measure the driving time of the motor  38 . 
         [0057]    The controller  30  can transmit an operational control signal for the motor  38  to the motor driver  36  according to the program previously stored in the memory  34  by using door opening signals of the first and second switches  16  and  17 , information delivered from the first to third position detectors  31  to  33 , and the timer  35 . 
         [0058]    The display unit  37  may be a display (not shown) positioned on the front surface of the body  10  of the refrigerator, and can display the failure of the door opening device  20 . 
         [0059]      FIGS. 3A to 3C  are schematic views showing the door opening device  20  according to a first embodiment of the present invention. 
         [0060]    As shown in  FIG. 3A , the door opening device  20  according to the first embodiment includes the first and second sliding bars  40  and  41  capable of selectively opening the two first and second doors  11  and  12 , the motor  38  moving the sliding first and second bars  40  and  41 , the first and second position detectors  31  and  32  capable of detecting the positions of the first and second sliding bars  40  and  41 , and the first and second protrusions  42  and  43  protruding from one side of the first sliding bar  40  to be detected by the first and second position detectors  31  and  32 . 
         [0061]    The first and second sliding bars  40  and  41  are geared with both sides of the motor  38  (e.g., a rack and a pinion assembly) to selectively push the two first and second doors  11  and  12 . The two first and second protrusions  42  and  43  are provided on the first sliding bar  40  to detect the position of the first sliding bar  40  by the first and second position detectors  31  and  32 . Meanwhile, as shown in  FIG. 3A , although the two first and second protrusions  42  and  43  are provided at one side of the first sliding bar  40 , the two first and second protrusions  42  and  43  may be provided at one side of the second sliding bar  41 . 
         [0062]    The motor  38  is geared with the first and second sliding bars  40  and  41  (e.g., a rack and a pinion assembly) to rotate. When the motor  38  rotates in a first direction (clockwise), the first door  11  can be open by the first sliding bar  40 . When the motor  38  rotates in a second direction (counterclockwise), the second door  12  can be open by the second sliding bar  41 . 
         [0063]    The first and second position detectors  31  and  32  may be installed in order to detect the rotation position of the motor  38 , that is, the position of the first sliding bar  40 . The first and second position detectors  31  and  32  detect the two first and second protrusions  42  and  43  of the first sliding bar  40  through an optical sensor (not shown) to detect the rotation position of the motor  38 . In addition, the first and second position detectors  31  and  32  include typical optical sensors. According to one embodiment, the first and second position detectors  31  and  32  are turned on if the signal phase is changed by the two first and second protrusions  42  and  43 , and turned off if the signal phase is not changed. 
         [0064]    Meanwhile, the present invention is not limited to the first and second position detectors  31  and  32 , but can employ a lead switch to detect the positions of the first and second protrusions  42  and  43  and a limit switch to detect the positions of the first and second protrusions  42  and  43  in the contact with the first and second protrusions  42  and  43 . 
         [0065]    Hereinafter, the operation of the door opening device  20  will be described with reference to  FIGS. 3B and 3C . 
         [0066]    If a user grasps or pulls the second handle  15  of the first door  11  in order to open the first door  11 , the motor  38  operates with the manipulation of the second switch unit  17 . In this case, as shown in  FIG. 3B , the motor  38  rotates in the first direction (clockwise) to push the first sliding bar  40  geared with the motor  38  (e.g., a rack and a pinion assembly) forward so that the first door  11  can be opened. If the first position detector  31  detects the second protrusion  43  of the first sliding bar  40 , and the second position detector  32  does not detect any protrusion, it is determined that the first door  11  is at the maximum open state, and the motor  38  is stopped. Meanwhile, according to one embodiment, when open commands of the first and second doors  11  and  12  are issued, the first and second doors  11  and  12  are open through the driving of the motor  38 , and then, when a predetermined time elapses, the first and second doors  11  and  12  are closed. Details thereof will be described later. 
         [0067]    In addition, if the user grasps or pulls the first handle  14  of the second door  12  in order to open the second door  12 , the motor  38  rotates in the second direction (counterclockwise) with the manipulation of the first switch unit  16  to push the second sliding bar  41  forward, so that the second door  12  is open. In addition, if the second position detector  32  detects the first protrusion  42 , and the first position detector  31  does not detect any protrusion, it is determined that the door  12  has the maximum open state, and the motor  38  is stopped. 
         [0068]      FIG. 4  is a view showing a table representing the detection state of the first and second position detectors  31  and  32  based on the open state of the first and second doors  11  and  12  according to the first embodiment. 
         [0069]    As shown in  FIG. 4 , when the first and second position detectors  31  and  32  detect all of the first and second protrusions  42  and  43 , the first and second doors  11  and  12  of the refrigerator are in a waiting state, that is, a closed state. 
         [0070]    In addition, if the first position detector  31  detects a protrusion, and the second position detector  32  does not detect a protrusion, the controller  30  determines that the first door  11  is open. In contrast, if the first position detector  31  does not any protrusion, and the second position detector  32  detects a protrusion, the controller  30  determines that the second door  12  is open. 
         [0071]    If both of the first and second position detectors  31  and  32  do not detect the first and second protrusions  42  and  43 , the controller  30  may determine that the first door  11  or the second door  12  is open or is being opened. 
         [0072]      FIGS. 5A and 5B  are flowcharts showing the control procedure of the door opening device  20  according to the first embodiment. 
         [0073]    As shown in  FIG. 5A , if an open command of the first door  11  or the second door  12  of the refrigerator according to one embodiment is input, the motor  38  is driven. In other words, if a user grasps or pulls the first or second switch unit  16  or  17  provided on the first or second handle  14  or  15  of the first or second door  11  or  12  to control the operation of the motor  38 , the motor  38  is driven with the operation of the first or second switch unit  16  or  17 . In detail, if the user manipulates the second switch  17  provided on the second handle  15  of the first door  11 , the motor  38  rotates in the first direction (clockwise). If the user manipulates the first switch  16  provided on the first handle  14 , the motor  38  rotates in the second direction (counterclockwise) (operation S 10  and S 20 ). 
         [0074]    Subsequently, if the motor  38  is driven due to the user manipulation of the first switch unit  16  or the second switch unit  17 , the controller  30  measures a time, in which the motor  38  is driven, to determine if a first preset time elapses. The first preset time is previously stored in the memory  34 , and is obtained by experimentally calculating a time spent until the first and second protrusions  42  and  43  of the first sliding bar  40  deviate from detection regions of the first and second position detectors  31  and  32  after the motor  38  in the waiting state is driven (operation S 30 ). 
         [0075]    Next, if the controller  30  determines that the first preset time has elapsed in operation S 30 , the controller  30  determines if a first state comes. In this case, the first state means an initial time point at which the first protrusion  42  enters the detection region of the second position detector  32  or the second protrusion  43  enters the detection region of the first position detector  31  due to continuous rotation of the motor  38  after the first and second protrusions  42  and  43  of the first sliding bar  40  have deviated from the detection regions of the first and second position detectors  31  and  32  (operation S 40 ). 
         [0076]    Thereafter, the controller  30  determines if a second preset time elapses after the first state is determined in operation S 40 . The second preset time is previously stored in the memory  34 , and means a time spent until the first protrusion  42  of the first sliding bar  40  or the second protrusion  43  moves into a reliable detection region of the second position sensor  32  or the first position sensor  31  from the initial time point at which the first protrusion  42  enters the detection region of the second position detector  32  or the second protrusion  43  enters the detection region of the first position detector  31  (operation S 50 ). 
         [0077]    Next, if the controller  30  determines that the second preset time has elapsed in operation S 50 , the controller  30  stops the motor  38  and determines if a third preset time elapses. In this case, the third preset time is previously stored in the memory  34 , and means a time, in which the motor  38  is stopped, in order to reduce noise created when the direction of the motor  38  is changed (operations S 60  and S 70 ). 
         [0078]    As shown in  FIG. 5B , if the third preset time has elapsed in operation S 70 , the controller  30  drives the motor  38 . In other words, the controller  30  rotates the motor  38  in directions opposite to a direction, in which the motor  38  has rotated in operations S 20  to S 50 , to commence to close the first door  11  or the second door  12  again (operation S 80 ). 
         [0079]    Then, if the motor  38  is driven, the controller  30  measures the driving time of the motor  38  to determine if a fourth preset time has elapsed. The fourth preset time is previously stored in the memory  34 . In addition, the fourth preset time is obtained by experimentally calculating a time spent until the motor  38  is driven in a door open state so that the first protrusion  42  or the second protrusion  43  of the sliding bar  40  deviates from the detection region of the second position detector  32  or the first position detector  31  (operation S 90 ). 
         [0080]    Thereafter, if the fourth preset time has elapsed in operation S 90 , the controller  30  determines if a second state comes. The second state means an initial time point at which the first and second protrusions  42  and  43  of the first sliding bar  30  enter the detection regions of the first and second position detectors  31  and  32  due to the continuous rotation of the motor  38  after the first protrusion  42  or the second protrusion has deviated from the detection region of the second position detector  32  or the first position detector  31  (operation S 100 ). 
         [0081]    Then, the controller  30  determines if a fifth preset time has elapsed after the second state has come in operation S 100 . The fifth preset time is previously stored in the memory  34 , and means a time spent until the first protrusion  42  or the second protrusion  43  of the first sliding bar  40  moves into the reliable region of the second position detector  32  or the first position detector  31  from the initial time point at which the first protrusion  42  or the second protrusion  43  enters the detection region of the second position detector  32  or the first position detector  31  (operation S 110 ). 
         [0082]    Thereafter, if the fifth preset time has elapsed in operation S 110 , the controller  30  stops the motor  38  to terminate a door opening/closing operation (operation S 120 ). 
         [0083]    Meanwhile, the above operational procedure prevents the motor  38  from erroneously operating due to chattering. The chattering refers to a phenomenon in which an electrical contact is abnormally turned on/off for a very short time due to mechanical vibration. According to the present embodiment, the above operation procedure is performed in order to drive the motor  38  for several times previously stored in the memory  34  and open/close the first door  11  or the second door  12 , so that the motor  38  moves the sliding bar  40  or  41  into a reliable detection region of the position detectors  31  and  32 . 
         [0084]      FIG. 6  is a flowchart showing an initialization operation when the door opening device  20  is powered on according to the first embodiment. 
         [0085]    As shown in  FIG. 6 , if power is applied to the refrigerator, the controller  30  turns on the timer  35  to set time (T) to ‘0’ (operations S 200  and S 210 ). 
         [0086]    Then, the controller  30  determines if the time (T) of the timer  35  exceeds a preset time T. If the time (T) does not exceed the preset time T, the controller  30  determines if the first door  11  or the second door  12  of the refrigerator stays in a waiting state. In other words, the controller  30  determines if the first and second protrusions  42  and  43  are simultaneously detected by the second and first position detectors  32  and  31 , respectively, to determine if both of the first and second doors  11  and  12  are closed (operations S 220  and S 230 ). 
         [0087]    Thereafter, if the first door  11  or the second door  12  of the refrigerator is in the waiting state in operation S 230  when power is applied to the first door  11  or the second door  12  of the refrigerator, the controller  30  determines the operational state of the motor  38 . If the motor  38  is driven, the controller  30  stops the operation of the motor  38  to terminate the initialization operation. However, if the first door  11  or the second door  12  is in the waiting state when power is applied to the refrigerator, since the motor  38  is in a stop state, the initialization operation is instantly terminated (operations S 260  and S 270 ). 
         [0088]    Meanwhile, if the first door  11  or the second door  12  is not in the waiting state in operation S 230 , the controller  30  determines if the first door  11  is open. In other words, the controller  30  determines if the second protrusion  43  of the sliding bar  40  is detected by the first position detector  31 . However, the first and second position detectors  31  and  32  do not detect the type of the first and second protrusions  42  and  43 . Accordingly, if the first position detector  31  detects a protrusion, and the second position detector  32  does not detect a protrusion, the controller  30  determines that the first door  11  is open through the program previously stored in the memory  34  (operation S 240 ). 
         [0089]    Thereafter, if the controller  30  determines that the first door  11  is open in operation S 240 , the controller  30  rotates the motor  38  in the second direction (counterclockwise) to move the first sliding bar  40  such that the first door  11  is closed (operation S 280 ). 
         [0090]    Then, if the controller  30  determines that the first door  11  is not open in operation S 240 , the controller  30  determines if the second door  12  is open. In other words, the controller  30  determines that the first protrusion  42  of the first sliding bar  40  is detected by the second position detector  32 . However, the first and second position detectors  31  and  32  do not detect the type of the protrusions  42  and  43 . Accordingly, if the second position detector  32  detects the protrusion, and the first position detector  31  does not detect the protrusion, the controller  30  determines that the second door  12  is open through the program previously stored in the memory  34  (operation S 250 ). 
         [0091]    Thereafter, if the controller  30  determines that the second door  12  is open in operation S 250 , the controller  30  rotates the motor  38  in the first direction (clockwise) to move the first sliding bar  40  such that the second door  12  is closed (operation S 290 ). 
         [0092]    Meanwhile, if the controller  30  determines that the first door  11  or the second door  12  is not in any one of the waiting state, a first door open state, and a second door open state in operations S 230  to S 250 , the controller  30  rotates the motor  38  in a reference direction stored in the memory  34 . In other words, in the case of an open state of a certain door as shown in the table of  FIG. 4 , that is, in the case in which the first and second position detectors  31  and  32  do not detect any protrusion, the controller  30  rotates the motor  38  in a preset direction and returns to operation S 220  to determine the state of the first door  11  or the second door  12  (operation S 300 ). 
         [0093]    Thereafter, if the motor  38  is rotated in operations S 280  to S 300 , the controller  30  returns to operation S 220  to determine if the time T of the timer  45  exceeds the preset time T 1 . If the time T of the timer  45  does not the preset time T 1 , the controller  30  determines if the doors  11  and  12  are adjusted to the waiting state due to the rotation of the motor  38 . In this case, if the doors  11  and  12  do not become the waiting state until the time T of the timer  45  exceeds the preset time T 1 , the controller  30  stops the operation of the motor  38 , determines that the door opening device  20  is failed, and displays the failure of the door opening device  20  on the display unit  37  (operations S 310  to S 330 ). 
         [0094]    If the door  11  or  12  becomes the waiting state within the preset time T 1  through the above procedure, the controller  30  determines the operational state of the motor  38  and then stops the motor  38  to terminate the initialization operation (operations S 260  and S 270 ). 
         [0095]      FIGS. 7A to 7E  are sectional views schematically showing the door opening device  20  according to a second embodiment, and  FIG. 8  is a table showing detection states of position detectors as a door is open according to the second embodiment of the present invention. Meanwhile, the same reference numerals will be assigned to elements identical to those of  FIG. 3A . 
         [0096]    As shown in  FIG. 7A , a door opening device  20  according to the second embodiment includes first and second sliding bars  40  and  41  capable of selectively opening two first and second doors  11  and  12 , a motor  38  moving the first and second sliding bars  40  and  41 , first, second, and third position detectors  31 ,  32 , and  33  capable of detecting positions of the first and second sliding bars  40  and  41 , and first, second, and third protrusions  42 ,  43 , and  44  protruding from one sides of the first and second sliding bars  40  and  41  to be detected by the first to third position detectors  31  to  33 . 
         [0097]    The sliding bars  40  and  41  are geared with both sides of the motor  38  (e.g., a rack and a pinion assembly) such that the two first and second doors  11  and  12  can be selectively pushed, and the two first and second protrusions  42  and  43  are provided on the first sliding bar  40  to be detected by the first and second position detectors  31  and  32 . One protrusion  44  is provided on the second sliding bar  41 , so that the position of the second sliding bar  41  can be detected by the third position detector  33 . 
         [0098]    The motor  38  is geared with the first and second sliding bars  40  and  41  (e.g., a rack and a pinion assembly) to rotate. When the motor  30  rotates in a first direction (clockwise), the first door  11  is open by the first sliding bar  40 . When the motor  38  rotates in a second direction (counterclockwise), the second door  12  can be open by the second sliding bar  41 . 
         [0099]    The first to third position detectors  31  to  33  detect the rotation position of the motor  38 , that is, positions of the first and second sliding bars  40  and  41 . In detail, the first to third position detectors  31  to  33  can detect magnets (not shown) provided in the three protrusions  42 ,  43 , and  44  to detect the rotation position of the motor  38 . 
         [0100]    Meanwhile, when both of the two first and second doors  11  and  12  are closed, that is, when both of the two first and second doors  11  and  12  are in a waiting state, the first and second position detectors  31  and  32  detect the second and third protrusions  42  and  43 , and the third position detector  33  does not detect the third protrusion  44 . 
         [0101]    Hereinafter, the operation of the door opening device  20  will be described with reference to  FIGS. 7B to 7E . 
         [0102]    As shown in  FIGS. 7B ,  7 C, and  FIG. 8 , if a user grasps or pulls a handle  15  of the first door  11  in order to open the first door  11 , the motor  38  is driven with the manipulation of a second switch unit  17 . In this case, as shown in  FIG. 7B , since the motor  38  rotates in the first direction (clockwise) to push the sliding bar  40  forward, the door  11  is open. Further, when the first to third position detectors  31  to  33  do not detect the first to third protrusions  42  to  44  of the first and second sliding bars  40  and  41 , the controller  30  recognizes an open state A of the first door  11 . 
         [0103]    As shown in  FIG. 7C , when the motor  38  rotates in the first direction (clockwise) so that the first position detector  31  detects the second protrusion  43 , and the second and third position detectors  32  and  33  do not detect any protrusions of the first and second sliding bars  40  and  41 , the controller  30  recognizes a maximum open state A of the first door  11 . 
         [0104]    In addition, as shown in  FIGS. 7D ,  7 E, and  FIG. 8 , if the user grasps or pulse a first handle  14  of the second door  12  in order to open the second door  12 , the motor  38  is driven with the manipulation of a first switch unit  16 . In this case, as shown in  FIG. 7D , since the motor  38  rotates in the second direction (counterclockwise) to push the second sliding bar  41  forward, the second door  12  is open. Further, if the first and second position detectors  31  and  32  do not detect the first and second protrusions  42  and  43 , and the third position detector  33  detects the third protrusion  44 , the controller  30  recognizes the open state B of the second door  12 . 
         [0105]    In addition, as shown in  FIG. 7E , the motor  38  rotates in the second direction (counterclockwise), so that the second and third position detectors  32  and  33  detect the first and third protrusions  42  and  44 , and the first position detector  31  does not detect the second protrusion  43  of the sliding bar  40 , the controller  30  recognizes the maximum open state A of the second door  12 . 
         [0106]      FIG. 9  is a flowchart showing an initialization operation of the door opening device  20  upon a power-on state according to the second embodiment. 
         [0107]    As shown in  FIG. 9 , if the refrigerator is powered on, the controller  30  turns on a timer  35  to set a time T of the timer to 0 (operations S 400  and S 410 ). 
         [0108]    Then, the controller  30  determines if the time T of the timer  35  exceeds a preset time T 1 . If the time T does not exceed the preset time T 1 , the controller  30  determines if the first and second doors  11  and  12  of the refrigerator are in the waiting state. In other words, the controller  30  determines if the first and second protrusions  42  and  43  of the first sliding bar  40  are detected by the first and second position detectors  31  and  32 , and the third position detector  33  does not detect the protrusion  44 , to determine the closed state of the first and second doors  11  and  12  (operations S 420  and S 430 ) 
         [0109]    Next, if the controller  30  determines that both of the first and second doors  11  and  12  are in the waiting state when the refrigerator is powered on in operation S 430 , the controller  30  determines the operational state of the motor  38 . Accordingly, if the motor  48  is operating, the controller  30  stops the rotation of the motor  38  and terminates the initialization operation. However, if the first and second doors  11  and  12  are in the waiting state when the refrigerator is powered on, since the motor  38  has been stopped, the initialization operation is instantly terminated (operations S 450  and S 460 ). 
         [0110]    Meanwhile, the controller  30  determines that both of the first and second doors  11  and  12  of the refrigerator are not in the waiting state in operation S 430 , the controller  30  determines if the third protrusion  44  is detected by the third position detector  33 . In other words, the controller  30  determines if the third protrusion  33  of the second sliding bar  41  is detected by the third position detector  44 . 
         [0111]    Thereafter, the controller  30  determines that the door  12  is open if the third protrusion  44  is detected by the third position detector  33  in operation S 440 , and rotates the motor  38  in the first direction (clockwise) to move the second sliding bar  41  such that the second door  12  is closed (operation S 470 ). 
         [0112]    Therefore, the controller  30  determines that the first door  11  is open if the third protrusion  44  is not detected by the third position detector  33 , and rotates the motor  38  in the second direction (counterclockwise) to move the first sliding bar  40  such that the first door  11  is closed in operation S 470 . In other words, the controller  30  determines that the second door  12  is open if the third protrusion  44  is detected by the third position detector  33 , and the first door  11  is open if the third protrusion  44  is not detected by the third position detector  33  according to the program stored in the memory  34 . Accordingly, the controller  30  rotates the motor  38  such that the two first and second doors  11  and  12  are regulated to be closed, that is, be in the waiting state (operation S 480 ). 
         [0113]    If the motor  38  rotates in operations S 470  to S 480 , the controller  30  returns to operation S 420  to determine if the time T of the timer  35  exceeds the preset time T 1 . If the time T of the timer  35  does not exceed the time T 1 , the controller  30  repeats operations S 430  to S 440 . In this case, if the first and second doors  11  and  12  do not reach the waiting state until the time T of the timer  35  exceeds the time T 1 , the controller  30  stops the motor  38 , determines that the door opening device  20  is failed, and displays the failure of the door opening device  20  on the display unit  37  (operations S 490  to S 510 ). 
         [0114]    However, if the first and second doors  11  and  12  reach the waiting state within the preset time T 1  through the above procedure, the controller  30  determines the operational state of the motor  38  and then stops the motor  38 , thereby terminating the initialization operation (operations S 450  and S 460 ). 
         [0115]    Although few embodiments 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.