Patent Publication Number: US-2016230328-A1

Title: Washing machine and method of controlling same

Description:
TECHNICAL FIELD 
     The present invention relates to a washing machine and a method of controlling the same, and more particularly, to a washing machine using an active balancer and a method of controlling the same. 
     BACKGROUND ART 
     Generally, a washing machine is a device including a tub for accommodating water and a drum installed to be rotatable in the tub, and washes laundry by rotating the drum while accommodating the laundry in the tub. The washing machine performs a washing cycle for washing laundry, a rinse cycle for rinsing the washed laundry, and a spin-dry cycle for spin-drying the wet laundry. 
     Particularly, in the spin-dry cycle, the washing machine rotates the drum at high speed. In this case, when the drum is rotated at high speed, the laundry is highly concentrated at a specific position rather than uniformly distributed in the drum, and thus a load imbalance is generated. Therefore, the load imbalance generates the vibration and noise of the washing machine. In a severe case, the load imbalance may cause damage to the washing machine. 
     DISCLOSURE 
     Technical Problem 
     The present invention is directed to providing a washing machine in which a balancer is positioned at a position where a load imbalance caused by laundry is offset during a spin-dry cycle. 
     Also, the present invention is directed to providing a washing machine in which a balancer is positioned to compensate for reduction of an imbalanced load by separating water from laundry during a spin-dry cycle. 
     Technical Solution 
     One aspect of the present invention provides a washing machine including a tub, a drum provided to be rotatable in the tub to accommodate laundry, a drive motor for rotating the drum, a balancer housing which is in a ring-shape and coupled to the drum, a balancer including a weight for offsetting an unbalanced load generated by the laundry during a spin-dry cycle and a moving unit moving the weight, and provided to be movable in the balancer housing, and a control unit for performing a balancing operation of moving the balancer to a balancing position where the unbalanced load is offset and a compensating operation of moving the balancer to a compensation position where the reduction of the unbalanced load is compensated for. 
     The balancer may include at least two balancers. 
     The control unit may rotate the drum at a predetermined balancing speed and move the at least two balancers to the balancing position. 
     The control unit may calculate an angle between the at least two balancers positioned at the balancing position and a compensation angle compensating for the reduction of the unbalanced load based on an angle between the least two balancers. 
     The control unit may move the at least two balancers so that the angle between the at least two balancers is increased by the compensation angle. 
     The control unit may perform a spin-dry operation of rotating the drum at a predetermined spin-dry speed. 
     Another aspect of the present invention provides a method of controlling a washing machine, including a tub, a drum provided to be rotatable in the tub, and at least two balancers for offsetting an unbalanced load while rotating the drum, which includes rotating the drum at a predetermined balancing speed; moving the at least two balancers to a balancing position where the unbalanced load is offset, moving the at least two balancers to a compensation position where the reduction of the unbalanced load during the rotation of the drum is compensated for, and rotating the drum at a predetermined spin-dry speed. 
     The moving of the at least two balancers to the balancing position may include detecting the vibration of the tub; moving the at least two balancers, re-detecting the vibration of the tub, and moving the at least two balancers in a direction opposite a direction of the moving when the re-detected vibration is greater than the detected vibration. 
     The moving of the at least two balancers may include moving the at least two balancers in the same direction. 
     The moving of the at least two balancers may include moving the at least two balancers in different directions from each other. 
     The moving of the at least two balancers to the compensation position may include calculating a compensation angle of compensating for the reduction of the unbalanced load based on an angle between the at least two balancers positioned at the balancing positions, and moving the at least two balancers so that the angle between the at least two balancers is increased by the compensation angle. 
     Still another aspect of the present invention provides a washing machine including a tub, a drum provided to be rotatable in the tub to accommodate laundry, a drive motor for rotating the drum, a balancer housing which is in a ring-shape and coupled to the drum, and a balancer provided to be movable in the balancer housing to offset an unbalanced load generated by the laundry during a spin dry cycle, wherein the balancer includes a weight and a moving unit for moving the weight, and moves to a compensation position where the reduction of the unbalanced load in the balancer housing is compensated for. 
     The balancer may move to a balancing position where the unbalanced load in the balancer housing is offset and moves to the compensation position. 
     The balancer may include at least two balancers. 
     The at least two balancers may move so that an angle between the at least two balancers is increased for compensating for the reduction of the unbalanced load. 
     When the spin-dry cycle is completed, the at least two balancers may move to be positioned in opposite directions from each other with respect to a rotation axis of the drum. 
     ADVANTAGEOUS EFFECTS 
     According to one aspect of the present invention, the washing machine can automatically offset an imbalanced load caused by laundry during a spin-dry cycle and can reduce the vibration and noise of the washing machine during the spin-dry cycle by compensating for the reduction of the imbalanced load due to spin-drying. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating an appearance of a washing machine according to one embodiment. 
         FIG. 2  is a view illustrating a configuration of the washing machine according to the embodiment. 
         FIG. 3A  is a perspective view illustrating a configuration of a drum included in the washing machine in  FIG. 2 . 
         FIG. 3B  is a perspective view illustrating a configuration of a flange included in the washing machine in  FIG. 2 . 
         FIG. 4  is a view illustrating a balancing module according to one embodiment. 
         FIG. 5  is a view illustrating a balancer according to one embodiment. 
         FIG. 6  is a view illustrating a coupling configuration between the balancer and a balancer housing according to one embodiment. 
         FIG. 7  is a view illustrating a balancer moving unit in  FIG. 5 . 
         FIG. 8  is a view illustrating the balancer housing and a bearing according to one embodiment. 
         FIGS. 9 and 10  are views illustrating operations of the balancer in the balancer housing. 
         FIG. 11  is a block diagram illustrating a control flow of the washing machine according to one embodiment. 
         FIGS. 12A and 12B  are flowcharts illustrating a method of performing a balancing operation and a water-removing compensating operation of the washing machine according to one embodiment. 
         FIGS. 13A to 14B  are views illustrating an example of the balancing operation of the washing machine according to one embodiment. 
         FIG. 15  is a view illustrating an example of the water-removing compensating operation of the washing machine according to one embodiment. 
         FIG. 16  is a view illustrating a change in a rotation speed of the drum during a spin-dry operation of the washing machine according to one embodiment. 
         FIGS. 17A and 17B  are flowcharts illustrating the spin-dry operation of the washing machine according to one embodiment. 
         FIGS. 18A to 18C  are views illustrating an example of the water-removing compensating operation during the spin-dry operation of the washing machine according to one embodiment. 
     
    
    
     MODES OF THE INVENTION 
     Embodiments described in this specification and configurations illustrated in drawings are only exemplary examples of the disclosed invention. It is to be understood that the invention covers various modifications that can substitute for the embodiments herein and drawings at the time of filing of this application. 
     Hereinafter, a washing machine according to one embodiment will be described in detail with reference to the attached drawings. 
       FIG. 1  is a view illustrating an appearance of a washing machine according to one embodiment,  FIG. 2  is a view illustrating a configuration of the washing machine according to the embodiment,  FIG. 3A  is a perspective view illustrating a configuration of a drum included in the washing machine in  FIG. 2 , and  FIG. 3B  is a perspective view illustrating a configuration of a flange included in the washing machine in  FIG. 2 . 
     Referring to  FIGS. 1 to 3B , a washing machine  1  includes a cabinet  10  forming an appearance, a tub  20  disposed in the cabinet  10 , a drum  30  disposed to be rotatable in the tub  20 , a drive motor  40  for driving the drum  30 , a water supply unit  50  for supplying water to the tub  20 , a drain unit  60  for discharging accommodated water in the drum, and a detergent supply unit  70  for supplying a detergent. According to circumstances, the tub  20  is integrally formed with the cabinet  10  or the tub  20  can be also omitted. 
     An introduction port  11  for introducing or discharging laundry is provided in the center of a front surface of the cabinet  10 , and a door  12  for opening or closing the introduction port  11  is provided at the introduction port  11 . Also, a control panel  13  for receiving a handling command for the washing machine  1  from a user and displaying operation information of the washing machine  1  is provided at an upper portion of the front surface of the cabinet  10 . 
     The door  12  has one side rotatably mounted on the cabinet  10  using a hinge (not shown) and opens or closes the introduction port  11  formed at the center of the front surface of the cabinet  10 . 
     The control panel  13  includes a dial  13   a  and a handling button  13   b  for receiving the handling command for the washing machine  1  from the user, and a display panel  13   c  for displaying the operation information of the washing machine  1  to the user. Specifically, the user may select any one of a plurality of predetermined washing courses using the dial  13   a , and may change detailed items (a temperature of water, the number of rinses, and the strength of spin-dry, etc.) of the washing course using the handling button  13   b . Also, the display panel  13   c  displays the operation information of the washing machine  1  such as a washing course selected by the user, the detailed items of the washing course changed by the user, washing time, and the proceeding operation, etc. The handling button  13   b  employs a microswitch or a membrane switch for detecting pressurization caused by the user, and a touch pad for detecting a touch operation of the user. The display panel  13   c  may employ a liquid crystal display (LCD) panel or a light emitting diode (LED) panel. 
     The tub  20  includes a tub body  21  which is provided in the cabinet  10  and has a cylindrical shape having a closed rear surface, and a tub front plate  22  disposed at the front of the tub body  21 . A bearing  25  and a bearing housing  24  for rotatably fixing the drive motor  40  to be described below are provided at the rear surface of the tub body  21 , and an opening  22   a  for introducing laundry into the drum  30  and discharging the laundry from the drum  30  is provided at the tub front plate  22 . Also, the tub  20  is connected with the water supply unit  50  and the detergent supply unit  60  through a connection tube  53  provided on an upper side of the tub  20  and connected with the drain unit  60  through a drain tube  61  provided at a lower side of the tub  20 . 
     Also, a vibration sensor  24  is provided at an outer side of the tub  20  to detect an amplitude of vibration when the tub  20  vibrates. The vibration sensor  24  may employ an acceleration sensor for detecting a change in acceleration by vibration of the tub  20 . 
     Also, position sensors  23  ( 23   a  and  23   b ) for detecting locations of balancers  200  ( 200   a  and  200   b  (see  FIG. 4 )) included in balancing modules  100  ( 100   a  and  100   b ) to be described below are provided at an inner side of the tub front plate  22  and an inner side of the rear surface of the tub body  21 . The position sensors  23  will be described below in detail. 
     The drum  30  is provided to be rotatable in the tub  20 . As shown in  FIG. 3A , the drum  30  includes a drum body  31  having a cylindrical shape, a drum front plate  32  provided at a front side of the drum body  31 , and a drum rear plate  33  provided at a rear side of the drum body  31 . 
     The balancing modules  100  ( 100   a  and  100   b ) for offsetting an imbalance of the drum  30  are provided at the front and rear sides of the drum body  31 . For example, when the drum  30  rotates, the laundry in the drum  30  is attached to an inner circumferential surface of the drum  30 , and thus the center of mass of the drum  30  deviates from a rotation axis of the drum  30 . A phenomenon that the center of mass of the drum  30  deviates from the rotation axis of the drum  30  refers to the imbalance. The imbalance causes vibration and noise from the washing machine  1  while the drum  30  is rotated. The balancing modules  100  ( 100   a  and  100   b ) located in a direction opposite the laundry with respect to the rotation axis of the drum  30  when the drum  30  rotates are provided at the front and rear sides of the drum  30  to offset the imbalance. The balancing modules  100  ( 100   a  and  100   b ) will be described below in detail. 
     Also, a through hole  34  for introducing water, accommodated in the tub  20 , into the drum  30  and a lifter  35  for lifting the laundry upward are provided at the drum body  31 . A first guide hole  35 a through which an electrical wire  122  for supplying power to the above-described balancing modules  100  ( 100   a  and  100   b ) and transferring a control signal for the balancing modules  100  ( 100   a  and  100   b ) passes is provided in the lifter  35 . 
     An opening  32   a  through which the laundry is introduced into or discharged from the drum  30  is provided in the drum front plate  132 , and a flange  36  connected with the drive motor  40  which rotates the drum  30  is installed at the drum rear plate  33 . Also, a second guide hole  36 a through which the electrical wire for supplying power to the above described balancing modules  100  ( 100   a  and  100   b ) passes is provided in the flange  36 . 
     The drive motor  40  includes a stator  41  fixed to a rear surface of the tub  120 , a rotor  42  which is rotated by a magnetic interaction with the stator  41 , and a rotating shaft  43  having one side connected with the rotor  42  and the other side connected with the flange  36  provided at a rear surface of the drum  30  through a rear surface of the tub  20 . Also, the rotating shaft  43  is rotatably fixed to the tub  20  by the bearing  25  provided at a rear surface of the tub  20  as described above. The drive motor  40  may employ a brushless direct current (BLCD) motor or an alternation current (AC) motor that easily controls a rotation speed. 
     The water supply unit  50  includes: a water supply tube  51  provided on an upper side of the tub  20  and connecting between an external water supply source (not shown) and the detergent supply unit  70  to be described below; and a water supply valve  52  provided on the water supply tube  51  to open or close the water supply tube  51 . Here, the water supply unit  150  supplies water to the tub  20  through the detergent supply unit  70  to be described below. 
     The drain unit  60  includes a drain tube  61  provided on a lower side of the tub  20  to guide discharging of the water of the tub  20  to the outside of the cabinet  10 , and a drain pump  62  disposed on the drain tube  61  to discharge the water through the drain tube  61 . 
     The detergent supply unit  70  is provided at an upper side of the tub  20  and is connected with the tub  20  through the connection tube  53 . Also, the detergent supply unit  70  includes a detergent housing  72  in a box shape having an open front surface, and a detergent container  71  coupled to be attachable and detachable through the open front surface of the detergent housing  72 . Also, the detergent container  71  is provided on an upper side of a front surface of the cabinet  10  so that the detergent container  71  protrudes from the housing  62  at the outside of the cabinet  10  to be opened and closed. The water supplied from the water supply unit  50  is supplied to the tub  20  through the detergent container  71 , and thus is supplied to the tub  20  along with the detergent. 
       FIG. 4  is a view illustrating the balance module according to one embodiment. The front balancing module  100   a  and the rear balancing module  100   b  have the same structure. Therefore, hereinafter, the front balancing module  100   a  and the rear balancing module  100   b  are generally referred to as the balancing module  100  to help understanding. 
     As shown in  FIG. 4 , the balancing module  100  includes a balancer housing  110  and balancers  200  ( 200   a  and  200   b ) provided in the balancer housing  110 . The balancers  200  include a first balancer  200   a  and a second balancer  200   b . The first balancer  200   a  and the second balancer  200   b  are configured in the same structure. Therefore, hereinafter, the first balancer  200   a  and the second balancer  200   b  are generally referred to as the balancers  200 . Also, the washing machine  100  according to the embodiment includes the first balancer  200   a  and the second balancer  200   b , that is, two balancers  200 , but is not limited thereto. The number of the balancers  200  may be less than or greater than two. 
     The balancer housing  110  includes a first balancer housing  115  which is in a ring shape with one open side and a second balancer housing  116  for covering the open part of the first balancer housing  115 . A ring-shaped channel through which the first balancer  200   a  and the second balancer  200   b  may move is formed by coupling the first balancer housing  115  and the second balancer housing  116 . 
     Also, a pair of electrodes  111  and  112  for supplying power to the balancers  200  are provided on an inner side of the second balancer housing  116 . The pair of electrodes  111  and  112  include a positive electrode  111  and a negative electrode  112 . The pair of electrodes  111  and  112  are provided in a circumferential direction of the ring-shaped second balancer housing  116 . And thus, even though the balancers  200  move in the balancer housing  110 , the balancers  200  may receive power or receive a control signal. The electrodes  111  and  112  of the washing machine  1  according to the embodiment are formed in the second balancer housing  116 , but is not limited thereto, and may be formed at another side of the balancer housing  110 . 
     A connector  120  for electrically connecting power with the pair of electrodes  111  and  112  is provided on an outer side surface of the balancer housing  116  of the balancer housing  110 . The connector  120  is connected with the electrical wire  122  to transfer the control signal and the power supplied through the electrical wire  122  to the pair of electrodes  111  and  112 . 
     Hereinafter, the balancers  200  (see  FIG. 4 ) accommodated in the balancer housing  110  (see  FIG. 4 ) will be described. 
       FIG. 5  is a view illustrating a balancer according to one embodiment,  FIG. 6  is a view illustrating a coupling configuration between the balancer and the balancer housing according to one embodiment,  FIG. 7  is a view illustrating a balancer moving unit in  FIG. 5 , and  FIG. 8  is a view illustrating the balancer housing and a bearing according to one embodiment. 
     Referring to  FIGS. 5 to 8 , the balancer  200  includes a main plate  210  which forms a basic form. 
     The main plate  210  includes a center plate  211  and side plates  212  and  213  bent at both sides of the center plate  211  to have a first angle θ 1  with the center plate  211 . 
     The center plate  211  and both side plates  212  and  213  have the predetermined first angle θ 1 . Therefore, the balancers  200  may easily move in the balancer housing  110 . 
     A balancer moving unit  220  is mounted on the center plate  211 , and the balancer moving unit  220  includes wheels  222  for moving the balancer  200  and a moving motor  221  for moving the wheels  222 . 
     Brushes  240  may be provided at the rear of the balancer moving unit  220 . The brushes  240  are electrically connected with the pair of electrodes  111  and  112  of the balancer housing  110 . The brushes  240  supply power or transfer the control signal to the balancer  200  by being in contact with the pair of electrodes  111  and  112  even through the balancer  200  moves. 
     As the pair of electrodes  111  and  112  include the positive electrode  111  and the negative electrode  112 , the brushes  240  ( 241  and  242 ) may also include a positive brush  241  and a negative brush  242 . The pair of brushes  241  and  242  are disposed to be in contact with the pair of electrodes  111  and  112 , respectively. Also, since the brush  240  is in contact with the electrodes  111  and  112  in the rotating and vibrating drum  30  (see  FIG. 2 ), the brush  240  may be damaged, and thus an end part in the brush  240  may be supported by an elastic material. 
     Gears  224  and  226  are disposed between the moving motor  221  and the wheels  222 , and thus a driving force of the moving motor  221  is transferred to the wheels  222 . Since the moving motor  221  and the wheels  222  are disposed to be perpendicular to each other, the first gear  224  and the second gear  226  are provided to transfer the driving force of the moving motor  221  to the wheels  222 . That is, the first gear  224  and the second gear  226  may be formed as a worm gear type. The first gear  224  is provided at a driving shaft  223  of the moving motor  221 , and the second gear  226  is disposed to be rotatably engaged with the first gear  224 . Also, a rotating shaft  225  is provided in the center of the second gear  226 , and the wheels  222  are mounted at both ends of the rotating shaft  225 . Also, the first gear  224  and the second gear  226  may be formed with a helical gear. The helical gear is a gear that has a twisted gear around a wheel. The first gear  224  and the second gear  226  are formed with the helical gear to restrain the wheels  222  from freely moving even when the moving motor  221  is not operated. Therefore, even when electric power is not supplied from a power source, the balancers  200  may be fixed to a destination without moving the balancers  200 . 
     Weights  270  are mounted to the side plates  212  and  213 , respectively. The weights  270  offset the imbalance by balancing the imbalance actually generated when the laundry in the drum  30  (see  FIG. 2 ) leans to one side, and thus the drum  30  may be rotated naturally. 
     A control substrate  230  on which various elements for operating the balancer moving unit  220  are mounted is installed at a front surface of one weight  270  of the two weights  270 . Also, a position identifying member  260  for detecting relative positions of the pair of balancers  200  is installed at the other weight  270  of the two weights  270 . The position identifying member  260  may employ a magnetic material including a permanent magnet, and a light emitting unit which emits light or a reflective plate which reflects light. 
     The position sensors  23  ( 23   a  and  23   b  (see  FIG. 2 )) are provided at the tub  20  (see  FIG. 2 ) to correspond to the position identifying members  260 . The position sensors  23  (see  FIG. 2 ) include a front position sensor  23   a  (see  FIG. 2 ) for detecting positions of the pair of balancers included in the front balancing module  100   a  (see  FIG. 2 ), and a rear position sensor  23   b  (see  FIG. 2 ) for detecting positions of the pair of balancers included in the rear balancing module  100   b  (see  FIG. 2 ). 
     The position sensors  23  (see  FIG. 2 ) are configured to determine where the balancers  200  are currently positioned by detecting positions of the balancers  200 . The position sensors  23  may be hole sensors, infrared sensors, or optical fiber sensors. When the position sensors  23  are the hole sensors, the position identifying member  260  may be the magnetic material, and when the position sensors  23  are the infrared sensors, the position identifying member  260  may be the light emitting unit which emits infrared light. Also, when the position sensors  23  are the optical fiber sensors, the position identifying member  260  may be the reflective plates. 
     Bearings  250  are coupled to end parts of side plates  212  and  213 , respectively. 
     The bearings  250  prevent the balancers  200  from colliding with an inner side surface of the balancer housing  110 . Also, the bearings  250  allow the balancers  200  to be accurately fixed to a position at which the imbalance is offset by restraining the balancers  200  from freely moving in the balancer housing  110 . The bearing  250  will be described below. 
     The bearing, as shown in  FIG. 8 , is formed to be in contact with an inner surface of the balancer housing  110 . 
     The bearings  250 , as a friction bearing, are in contact with the inner surface of the balancer housing  110  to limit the movement of the balancers  200  to a predetermined range and prevent the balancer  200  from colliding with the inner side surface of the balancer housing  110 . 
     A surface of the bearing  250  includes a protruding contact part  251 , and a concave part  252  depressed inward from the contact part  251 . That is, the side surface of the bearing  250  is formed to be curved. 
     Thus, since foreign materials in the balancer housing  110  pass through between the concave parts  252  or gather in the concave part  252 , the movement of the balancers  200  is prevented from being interrupted due to the foreign materials. 
     Also, since a size of the contact part  251  is controlled, the balancers  200  are prevented from colliding with a side surface of the balancer housing  110 , and the brushes  240  may come in contact with the electrodes  111  and  112  of the balancer housing  110  while maintaining a predetermined distance. 
       FIGS. 9 and 10  are view illustrating an operation of the balancer in the balancer housing. 
     Specifically,  FIG. 9  is a view illustrating a state of the balancers  200  when the drum  30  (see  FIG. 2 ) rotates at low speed or stops. 
     As shown in  FIG. 9 , the center plate  211  and the side plates  212  and  213  of the main plate  210  maintain a second angle θ 2 , which is a greater angle than the first angle θ 1 , in the balancer housing  110 , and thus a restoring force in which the center plate  211  and the side plates  212  and  213  are restored to the first angle θ 1  is generated. 
     The bearings  250  provided at end parts of the side plates  212  and  213  are in contact with a first surface  113  formed on a radial inner side of the balancer housing  110  by the restoring force of the side plates  212  and  213  and the center plate  211 , and the wheels  222  provided in the center plate  211  are in contact with a second surface  114  formed at a radial outer side of the balancer housing  110 . 
     Also, since a small force F 1  by the restoring force between the side plates  212  and  213  and the center plate  211  is applied to the center plate  211 , the wheels  222  may be rotated and the balancers  200  may be moved. 
     That is, when the drum  20  (see  FIG. 2 ) stops or rotates at low speed, the balancers  200  may move along the balancer housing  110 . 
       FIG. 10  is a view illustrating a state of the balancer  200  when the drum  20  (see  FIG. 2 ) is rotated at high speed. 
     As shown in  FIG. 10 , both of the bearings  250  and the wheels  222  are in contact with the second surface  114  while the plates  212  and  213  are spread by a centrifugal force, and a third angle θ 3  formed by the center plate  211  and the side plates  212  and  213  becomes greater than the second angle θ 2  at the time of stopping. 
     As the third angle θ 3 , which is an angle between the center plate  211  and the side plates  212  and  213  when the drum  20  (see  FIG. 2 ) is rotated at high speed, is greater than the second angle θ 2 , which is an angle between the center plate  211  and the side plates  212  and  213  when the drum  20  (see  FIG. 2 ) is stopped or rotated at low speed, a centrifugal force F 2  is applied to the balancers  200  rather than the force F 1  generated by the restoring force between the center plate  211  and the side plates  212  and  213 . 
     According to the centrifugal force F 2 , a large frictional force is generated between the wheels  222  and the second surface  114 . When the frictional force is greater than torque of the moving motor  221  driving the wheels  222 , the balancers  200  may not be moved any more. 
     In the other words, when the drum  20  (see  FIG. 2 ) is rotated at high speed, the balancers  200  may not be moved in the balancer housing  110 . When the drum  20  (see  FIG. 2 ) is rotated at a speed of about 440 rpm or greater, the balancers  200  of the washing machine  1  according to the embodiment may not be moved. 
       FIG. 11  is a block diagram illustrating a control flow of the washing machine according to one embodiment. 
     Referring to  FIG. 11 , the washing machine  1  includes a handling unit  310 , a display unit  320 , a position detecting unit  330 , a vibration detecting unit  340 , a main driving unit  350 , a main storage unit  360 , a main communication unit  370 , and a main control unit  380  along with the drive motor  40 , the water supply unit  50 , the drain unit  60 , and the balancers  200  already described. Also, the balancer  200  includes a balancer driving unit  395 , a balancer storage unit  396 , a balancer communication unit  397 , and a balancer control unit  398  along with the moving motor  221 . 
     The handling unit  310  is provided on the control panel  13  (see  FIG. 1 ) and includes the dial  13   a  (see  FIG. 1 ) for receiving a handling command for the washing machine  1  from a user and the handling button  13   b  (see  FIG. 1 ). The display unit  320  is provided on the control panel  13  (see  FIG. 1 ) and includes the display panel  13   c  for displaying operation information. 
     The position detecting unit  330  includes the position identifying members  260  (see  FIG. 5 ) for detecting relative positions of the pair of balancers  200  (see  FIG. 5 ) and the position sensors  23  ( 23   a  and  23   b ) (see  FIG. 2 ). 
     The vibration detecting unit  340  includes the vibration sensor  24  which detects a magnitude of the vibration of the tub  20  (see  FIG. 2 ) due to the vibration. 
     The main driving unit  350  operates the drive motor  40 , the water supply unit  50 , and the drain unit  60  according to the control signal of the main control unit  380  to be described below. Particularly, the main driving unit  350  may include an inverter for controlling a rotation speed and a rotation direction of the drive motor  40 . 
     The main storage unit  360  may include not only a non-volatile memory (not shown), such as a magnetic disc and a solid state disk, that permanently store a program and data for controlling an operation of the washing machine  1 , but also a volatile memory (not shown), such as a dynamic random access memory (DRAM) and a static random access memory (SRAM), that temporarily store temporary data generated in a process of controlling an operation of the washing machine  1 . 
     The main communication unit  370  may include a wireless communication module (not shown) for performing wireless communication with the balancers  200  using a wireless communication method such as wireless fidelity (Wi-Fi), Bluetooth, Zigbee, near field communication (NFC), or a wired communication module (not shown) for performing wired communication with the balancers  200  through an electrical wire  122  ( FIG. 3B ) which provides power and a control signal for the balancers  200 . 
     The main control unit  380  performs washing, rinsing, and spin-drying, by controlling the drive motor  40 , the water supply unit  50 , and the drain unit  60  based on a handling command of a user input through the handling unit  310 . Particularly, the main control unit  380  controls movements of the balancers  200  based on the positions of the balancers  200  detected by the position detecting unit  330  and the vibration of the tub  20  (see  FIG. 2 ) detected by the vibration detecting unit  340 . 
     The balancer driving unit  395  operates the moving motor  221  to move the balancers  200  according to a control signal of the balancer control unit  398  to be described below. 
     The balancer storage unit  396  may include not only a non-volatile memory (not shown), such as a magnetic disc and a solid state disk, that permanently stores a program and data for controlling operations of the balancers  200 , but also a volatile memory (not shown), such as a DRAM and an SRAM, that temporarily stores temporary data generated in a process of controlling the operations of the balancers  200 . 
     The balancer communication unit  397  may include a wireless communication module (not shown) for performing wireless communication with the washing machine  1  using a wireless communication method, such as Wi-Fi, Bluetooth, Zigbee, and NFC, or a wire communication module (not shown) for performing wire communication with the washing machine  1  through an electrical wire  122  (see  FIG. 3B ) which provides the power and the control signal for the balancers  200 . 
     The balancer control unit  398  generates a control signal for controlling an operation of the moving motor  221  according to a control signal of the main control unit  380  received through the balancer communication unit  397  and transfers the generated control signal to the balancer driving unit  395 . 
     Hereinbefore, the configuration of the washing machine  1  according to one embodiment has been described. 
     Hereinafter, the operation of the washing machine  1  according to one embodiment, i.e., particularly, the operation of the balancer  200 , will be described. 
     A general operation of the washing machine  1  will be first described with reference to  FIG. 2  described above. The washing machine  1  performs a washing cycle for separating foreign materials attached to the laundry by rotating the drum  30  after supplying water and detergent to the tub  20 , a rinse cycle for removing the foreign materials separated from the laundry from the detergent by rotating the drum  30  after supplying a rinse agent to the tub  20 , and a spin-dry cycle for separating the water from the laundry by rotating the drum  30  at high speed. Also, the washing machine  1  performs a water supply operation of supplying the water to the tub  20  before the washing cycle and the rinse cycle, and performs an intermediate spin-dry operation after the washing cycle and the rinsing cycle are completed. 
     At the time of the washing cycle and rinse cycle, the washing machine  100  rotates the drum  130  (see  FIG. 3 ) at a speed of 45 to 60 rpm in a clockwise direction and a counterclockwise direction. Specifically, the washing machine  100  repeats stopping the drum  30  for 4 to 5 seconds (off-time) after rotating the drum  30  for about 20 seconds (on-time) in a clockwise direction, and stopping the drum  30  for 4 to 5 seconds (off-time) after rotating the drum  30  for about 20 seconds (on-time) in a counterclockwise direction. 
     At the time of the spin-dry cycle, the washing machine  100  separates the water absorbed in the laundry by the centrifugal force by rotating the drum  30  in any one direction of the clockwise or counterclockwise direction at a speed of hundreds to thousands of rpms and discharges the water to the outside of the drum  30  that is the tub  20 . 
     Particularly, at the time of the spin-dry cycle, as described above, since the laundry is attached to an inner surface of the drum  30  to generate the imbalance, the balancing operation of offsetting the imbalance is performed. Particularly, the washing machine  1  according to one embodiment includes the balancers  200  (see  FIG. 5 ) which change their positions by themselves according to the vibration of the tub  20 , and the balancers  200  (see  FIG. 5 ) move to optimal positions to offset the imbalance. 
     Also, after performing the balancing operation, the washing machine  1  performs a water-removing compensating operation to compensate for the water-removing phenomenon in which a weight of the laundry, that is a magnitude of the imbalance, is reduced when the water is separated from the laundry during the spin-dry cycle. As described below, the washing machine  1  according to one embodiment performs a spin-dry operation by increasing the rotation speed of the drum  30  up to a spin-dry speed (approximately hundreds to thousands of rpms) after the balancing operation when the drum  30  is rotated at a speed of about 400 rpm. At this time, since the balancing action is performed regardless of the water-removing phenomenon during the spin-dry action, an imbalance due to the balancers  200  is increased as the spin-dry proceeds. To compensate for the water-removing phenomenon, the washing machine  1  estimates the amount of the water separated from the laundry before the spin-dry operation and performs the water-removing compensating operation according to the amount of the estimated water. 
       FIGS. 12A and 12B  are flowcharts illustrating a method in which the washing machine according to one embodiment performs a balancing operation and a water-removing compensating operation, and  FIGS. 13A to 14B  are views illustrating an example of the balancing operation of the washing machine according to one embodiment. Also,  FIG. 15  is a view illustrating an example of the water-removing compensating operation of the washing machine according to one embodiment. 
     Referring to  FIGS. 2, 5, 12A, and 12B , the balancing operation and the water-removing compensating operation of the washing machine  1  will be described. Since operations of the front balancing module  100   a  and the rear balancing module  100   b  are the same, the front balancing module  100   a  will be described as an example. 
     As shown in  FIG. 5 , the balancers  200  include the first balancer  200   a  and the second balancer  200   b . The first balancer  200   a  and the second balancer  200   b  may be moved while the drum  30  is rotated. Also, when the washing machine  1  is stopped or performs operations other than the spin-dry cycle, the first balancer  200   a  and the second balancer  200   b  are positioned in the balancer housing  110  in the opposite directions to each other so that an imbalance is not generated by the first balancer  200   a  and the second balancer  200   b . That is, the first balancer  200   a  and the second balancer  200   b  are disposed to have an angle of 180° or less with respect to the rotation axis of the drum  30 . 
     Since the balancer  200  is rotated along with the drum  30 , a relative position between the balancer  200   a  and the second balancer  200   b  is not changed. Since the laundry is attached to an inner circumferential surface of the drum  30  when the drum  30  is rotated, the position of the laundry is also maintained without a change in position. Therefore, a coordinate system in which a straight line in which the first balancer  200   a  and the second balancer  200   b  are initially positioned becomes an x-axis and a straight line perpendicular to the x-axis becomes a y-axis may be defined. Of course, the coordinate system is a rotary coordinate system which rotates with the drum  30 . Hereinafter, the balancing operation will be described based on the rotary coordinate system which rotates with the drum  30 . 
     The balancing operation of the washing machine  1  is operated in a trial and error method. The balancing operation of the washing machine  1  includes positioning the balancers  200  so that a centrifugal force having the same magnitude as the laundry is generated in a direction opposite the centrifugal force by the laundry, and in this case, the washing machine  1  does not know the position of the laundry. So, the balancers  200  are moved in a direction in which vibration of the tub  20  is reduced by repeatedly moving the balancers  200  in a random direction and detecting the vibration of the tub  20 . Specifically, the washing machine  1  moves the first balancer  200   a  and the second balancer  200   b  and then, when the vibration is reduced as compared to the previous vibration of the tub  20 , maintains the positions of the first balancer  200   a  and the second balancer  200   b  and, when the vibration is increased, moves the first balancer  200   a  and the second balancer  200   b  in opposite directions. 
     Also, the balancing operation is divided into a closing operation in which the first balancer  200   a  and the second balancer  200   b  are moved in the different directions from each other to change an angle between the first balancer  200   a  and the second balancer  200   b  with respect to the rotation axis of the drum  30  and a shifting operation in which the first balancer  200   a  and the second balancer  200   b  are moved in the same direction to change a direction of the center line between the first balancer  200   a  and the second balancer  200   b . A magnitude of a resultant force due to the centrifugal forces of the first balancer  200   a  and the second balancer  200   b  is changed by the closing operation, and the direction of the resultant force due to the centrifugal forces of the first balancer  200   a  and the second balancer  200   b  is changed by the shifting operation. 
     In the balancing operation of the washing machine according to one embodiment, the closing operation and the shifting operation are repeated alternately. 
     During the spin-dry cycle, the washing machine  1  rotates the drum  30  ( 510 ). At this time, the drum  30  is rotated at a rotation speed at which the balancers  200  ( 200   a  and  200   b ) can be moved, and the washing machine  1  according to one embodiment rotates the drum  30  at a speed of about 400 rpm. 
     While the drum  30  is rotated, the washing machine  1  detects the vibration of the tub  20  through the vibration sensor  24  ( 515 ). While the drum  30  is rotated, the wet laundry in the drum  30  is attached to the inner circumferential surface of the drum  30  to generate an imbalance, the imbalance causes the tub  20  to vibrate along with the drum  30 . The washing machine  1  detects the amplitude of the vibration of the tub  20 . 
     After the amplitude of the vibration of the tub  20  is initially detected, the following closing operation is performed. 
     The washing machine  1  moves the pair of balancers  200   a  and  200   b  in the different directions from each other by one step. That is, the first balancer  200   a  and the second balancer  200   b , as shown in  FIGS. 13A and 13B , are moved in the different directions from each other. Specifically, as shown in  FIG. 13A , when the first balancer  200   a  is moved in the counterclockwise direction, the second balancer  200   b  is moved in the clockwise direction. As shown in  FIG. 13B , when the first balancer  200   a  is moved in the clockwise direction, the second balancer  200   b  is moved in the counterclockwise direction. Consequently, the first balancer  200   a  and the second balancer  200   b , as shown in  FIGS. 13A and 13B , gather at one side of the drum  30 . That is, when the first balancer  200   a  is moved in the counterclockwise direction and the second balancer  200   b  is moved in the clockwise direction, as shown in  FIG. 13A , the balancers  200  converge to a lower side of the drum  30 , and the centrifugal forces of the first balancer  200   a  and the second balancer  200   b  are combined to generate a force  12  in a −y-axis direction. Also, when the first balancer  200   a  is moved in a clockwise direction, and the second balancer  200   b  is moved in a counterclockwise direction, as shown in  FIG. 13B , the balancers  200  converge to an upper side of the drum  30 , and the centrifugal forces of the first balancer  200   a  and the second balancer  200   b  are combined to generate a force f 3  in +y-axis direction. 
     Here, one step refers to a basic unit in which the balancers  200  are moved. 
     Afterward, the washing machine  1  detects the vibration of the tub  20  through the vibration sensor  24  ( 525 ). 
     Then, the washing machine  1  determines whether the amplitude of vibration of the tub  20  is reduced as compared to before ( 530 ). As the balancers  200  are moved, the vibration of the tub  20  may be reduced, or rather, the vibration of the tub  20  may be increased. As shown in  FIG. 13A , when the balancers  200  converge to the lower side of the drum  30 , a resultant force f 12  of the force f 2  and the centrifugal force f 1  of the laundry becomes greater than before. Therefore, when the balancers  200  converge to the lower side of the drum  30 , the imbalance is further increased, and thus the vibration of the tub  20  is increased. On the contrary, as shown in  FIG. 13A , when the balancers  200  converge to the upper side of the drum  30 , a resultant force f 13  of the force f 3  and the centrifugal force f 1  of the laundry becomes smaller than before. Therefore, when the balancers  200  converge to the upper side of the drum  30 , the imbalance is reduced, and thus the vibration of the tub  20  is reduced. 
     When the vibration of the tub  20  is not reduced, that is, the vibration of the tub  20  is increased (no in  530 ), the washing machine  1  moves the pair of balancers  200   a  and  200   b  in opposite directions to as before by two steps ( 535 ). In other words, the washing machine  1  moves the balancers  200   a  and  200   b  in the opposite direction to the direction in which the first balancer  200   a  and the second balancer  200   b  are moved in step  520  by two steps. For example, as shown in  FIG. 13B , when the vibration of the tub  20  is increased more by moving the first balancer  200   a  in the counterclockwise direction and the second balance  200   b  in the clockwise direction, the washing machine  1  moves the first balancer  200   a  in the clockwise direction and moves the second balancer  200   b  in the counterclockwise direction, and thus the vibration of the tub  20  is reduced. 
     Afterward, the washing machine  1  detects the vibration of the tub  20  through the vibration sensor  24  ( 540 ). 
     Then, the washing machine  1  determines whether the amplitude of the vibration of the tub  20  is equal to or less than an amplitude of a reference vibration ( 545 ), that is, determines whether the amplitude of the vibration of the tub  20  detected in step  525  or the vibration of the tub  20  detected in step  540  is equal to or less than the amplitude of the reference vibration. Here, the amplitude of the reference vibration refers to the amplitude of the vibration of the tub  20  in which noise due to the vibration of the tub  20  is less than or equal to an appropriate value. In other words, when the amplitude of the vibration of the tub  20  is less than or equal to the amplitude of the reference vibration, the imbalance is sufficiently compensated for by the balancers  200 . 
     In step  530  described above, when the vibration of the tub  20  is reduced (yes in  530 ), the washing machine  1  determines whether the amplitude of the vibration of the tub  20  is less than or equal to the amplitude of the reference vibration without additionally moving the balancers  200  ( 545 ). 
     When the amplitude of the vibration of the tub  20  is less than or equal to the amplitude of the reference vibration (yes in  535 ), the water-removing compensating operation to be described below is performed, and when the amplitude of the vibration of the tub  20  is greater than the amplitude of the reference vibration (no in  535 ), the following shifting operation is performed. 
     The washing machine  1  moves the pair of balancers  200   a  and  200   b  in the same direction by one step ( 550 ). That is, as shown in  FIG. 14A , both of the first balancer  200   a  and the second balancer  200   b  are moved in the same direction. Specifically, as shown in  FIG. 14A , both of the first balancer  200   a  and the second balancer  200   b  are moved in the counterclockwise direction, or as shown in  FIG. 14B , both of the first balancer  200   a  and the second balancer  200   b  are moved in the clockwise direction. Consequently, the first balancer  200   a  and the second balancer  200   b  are closer to or further away from the laundry. That is, when both of the first balancer  200   a  and the second balancer  200   b  are moved in the counterclockwise direction, as shown in  FIG. 14A , a force f 4  due to the centrifugal forces of the first balancer  200   a  and the second balancer  200   b  is rotated in the counterclockwise direction. Also, when both of the first balancer  200   a  and the second balancer  200   b  are moved in the clockwise direction, as shown in  FIG. 14B , a force f 5  due to the centrifugal forces of the first balancer  200   a  and the second balancer  200   b  is rotated in the clockwise direction. 
     Afterward, the washing machine  1  detects the vibration of the tub  20  through the vibration sensor  24  ( 555 ). 
     Then, the washing machine  1  determines whether the amplitude of the vibration of the tub  20  is reduced as compared to before ( 560 ). As shown in  FIG. 14A , when the balancers  200  are moved in the counterclockwise direction, the force f 4  is rotated in the counterclockwise direction, and thus an angle between the force f 4  and the centrifugal force f 1  of the laundry is reduced and a resultant force f 14  of the force f 4  and the centrifugal force f 1  of the laundry is increased as compared to before. That is, the imbalance is increased, and thus the vibration of the tub  20  is also increased as compared to before. On the contrary, as shown in  FIG. 14B , when the balancers  200  are moved in the clockwise direction, the force f 5  is rotated in the clockwise direction, and thus an angle between the force f 5  and the centrifugal force f 1  of the laundry is increased, and a resultant force f 15  of the force f 5  and the centrifugal force f 1  of the laundry is reduced as compared to before. Therefore, the imbalance is reduced, and thus the vibration of the tub  20  is also reduced as compared to before 
     When the vibration of tub  20  is not reduced, that is, the vibration of tub  20  is increased (no in  560 ), the washing machine  1  moves the pair of balancers  200   a  and  200   b  in the opposite direction from before by two steps ( 565 ). In other words, the washing machine  1  moves the first balancer  200   a  and the second balancer  200   b  in the opposite direction to a direction in which the first balancer  200   a  and the second balancer  200   b  are moved in step  550  by two steps. For example, as shown in  FIG. 14A , when the first balancer  200   a  and the second balancer  200   b  are moved in the counterclockwise direction and the vibration of the tub  20  is further increased, the washing machine  1  moves the first balancer  200   a  and the second balancer  200   b  in the clockwise direction to reduce the vibration of the tub  20 . 
     Afterward, the washing machine  1  detects the vibration of the tub  20  through the vibration sensor  24  ( 570 ). 
     Subsequently, the washing machine  1  determines whether the vibration of the tub  20  is equal to or less than the amplitude of the reference vibration ( 575 ). That is, it is determined whether the amplitude of the vibration of the tub  20  detected in step  555  or the vibration of the tub  20  detected in step  570  is equal to or less than the amplitude of the reference vibration. 
     When the amplitude of the vibration of the tub  20  is greater than the amplitude of the reference vibration (no of  535 ), the closing operation is performed again. 
     The washing machine  1  alternately repeats the closing operation and the shifting operation until the amplitude of the vibration of the tub  20  becomes equal to or less than the amplitude of the reference vibration. 
     When the amplitude of the vibration of the tub  20  is equal to or less than the amplitude of the reference vibration (yes in  535 ), the following water-removing compensating operation is performed. When the amplitude of the vibration of the tub  20  is equal to or less than the amplitude of the reference vibration, as shown in  FIG. 15 , a resultant force of the centrifugal force of the laundry, the centrifugal force of the first balancer  200   a , and the centrifugal force of the second balancer  200   b  converges to 0. That is, the imbalance is offset. 
     First, a compensation angle compensating for water-removing in the spin-dry operation is calculated ( 580 ). A method of calculating the compensation angle will be described below in detail. 
     Afterward, the washing machine  1  is moved according to the compensation angle so that the pair of balancers  200   a  and  200   b  are further away from each other ( 585 ). That is, the balancers  200   a  and  200   b  are moved so that an angle between the pair of balancers  200   a  and  200   b  with respect to the rotation axis of the drum  30  is increased. For example, as shown in  FIG. 15 , the first balancer  200   a  is moved in the counterclockwise direction by a compensation angle θc, and the second balancer  200   b  is moved in the clockwise direction by the compensation angle θc. 
     After the water-removing compensating operation, as shown in  FIG. 15 , the angle between the first balancer  200   a  and the second balancer  200   b  is increased based on the rotation axis of the drum  30 , and a resultant force of the centrifugal force of the first balancer  200   a  and the centrifugal force of the second balancer  200   b  is reduced. Consequently, a small imbalance is generated due to the laundry. However, the imbalance disappears by the water-removing in the spin-dry operation, and the vibration of the tub  20  is reduced as the spin-dry proceeds. 
     Hereinbefore, the balancing operation and the water-removing compensating operation in the spin-dry operation have been described. 
     Hereinafter, a method of calculating the compensation angle of the water-removing compensating operation in the spin-dry operation will be described. 
       FIG. 16  is a view illustrating a change in a rotation speed of the drum during a spin-dry operation of the washing machine according to one embodiment. 
     Referring to  FIG. 16 , a spin-dry cycle of the washing machine  1  is largely divided into a first spin-dry step, a second spin-dry step, and a third spin-dry step. 
     In the first spin-dry step, the washing machine  1  increases a rotation speed of the drum  30  up to a balancing speed (approximately 400 rpm). When the rotation speed of the drum  30  reaches the balancing speed, the washing machine  1  performs a first balancing operation and a first water-removing compensating operation. Subsequently, the washing machine  1  increases the rotation speed of the drum  30  up to a first spin-dry speed (approximately 600 rpm). When the rotation speed of the drum  30  reaches the first spin-dry speed, the rotation speed of the drum  30  is maintained at the first spin-dry speed for a predetermined time, and thus the first spin-dry operation is performed. Subsequently, the washing machine  1  finishes the first spin-dry step by reducing the rotation speed of the drum down to the balancing speed. 
     In the second spin-dry step after the first spin-dry, the washing machine  1  performs the second balancing operation and the second water-removing compensating operation when the rotation speed of the drum  30  reaches the balancing speed. Subsequently, the washing machine  1  increases the rotation speed of the drum  30  up to the second spin-dry speed (approximately 850 rpm). When the rotation speed of the drum  30  reaches the second spin-dry speed, the rotation speed of the drum  30  is maintained at the second spin-dry speed for a predetermined time, and thus the second spin-dry operation is performed. Subsequently, the washing machine  1  finishes the second spin-dry step by reducing the speed of rotation of the drum  30  down to the balancing speed. 
     In the third spin-dry step after the second spin-dry step, the washing machine  1  performs the third water-removing compensating operation and the third balancing operation when the rotation speed of the drum  30  reaches the balancing speed. Subsequently, the washing machine  1  increases the rotation speed of the drum  30  up to the third spin-dry speed (approximately 1400 rpm). When the rotation speed of the drum  30  reaches the third spin-dry speed, the rotation speed of the drum  30  is maintained at the third spin-dry speed for a predetermined time, and thus the third spin-dry operation is performed. Subsequently, the washing machine  1  finishes the spin-dry cycle along with the third spin-dry cycle by reducing the rotation speed of the drum  30  down to the balancing speed. 
     The washing machine  1  performs the spin-dry step three times during the spin-dry cycle to accurately calculate the compensation angle in the third water-removing compensating operation. An amount of removed water in the spin-dry operation varies depending on various factors such as an amount of wet laundry and a material of the laundry. That is, the amount of removed water may not be entirely estimated based on the amount of the wet laundry. 
     For such a reason, the washing machine  1  determines the tendency of the water-removing by performing the first spin-dry operation and the second spin-dry operation with the first spin-dry speed (600 rpm) and the second spin-dry speed (850 rpm) that are relatively low speeds, and the third spin-dry operation is performed based on the tendency at the third spin-dry speed (1400 rpm) that is the final high speed. 
       FIGS. 17A and 17B  are flowcharts illustrating the spin-dry operation of the washing machine according to one embodiment, and  FIGS. 18A to 18C  are views illustrating examples of the water-removing compensating operation during the spin-dry operation of the washing machine according one embodiment. 
     Referring to  FIGS. 17A to 18C , the washing machine  1  rotates the drum  30  at a balancing speed (approximately 400 rpm) during the spin-dry cycle ( 610 ). 
     While the drum  30  is rotated at the balancing speed, the washing machine  1  performs the first balancing operation ( 615 ). Since the balancing operation was described in  FIGS. 12A to 15 , the description thereof will be omitted. As a result of the first balancing operation, an angle between the first balancer  200   a  and the second balancer  200   b  with respect to the rotation axis of the drum  30 , as shown in  FIG. 18A , becomes the first balancing angle θ 1 . At this time, the centrifugal force due to the laundry and the centrifugal force due to the first balancer  200   a  and the second balancer  200   b  are in equilibrium. 
     Subsequently, the washing machine  1  calculates a first compensation angle θ 1  based on the first balancing angle θ 1  ( 620 ). When the first compensation angle θc 1  is calculated based on the first balancing angle θ 1 , a table pre-stored by a designer of the washing machine  1  may be used. As described above, the amount of removed water in the spin-dry operation may be changed depending on various factors such as the amount of the wet laundry, a material of the laundry, a rotation speed of the drum, etc. But, a factor that mainly affects the amount of the removed water is the amount of the wet laundry. Therefore, the amount of the removed water may be approximately estimated from the amount of the wet laundry, the amount of the wet laundry may be calculated from the balancing angle, and the compensation angle may be calculated from the amount of the removed water. In short, the compensation angle may be approximately estimated from the balancing angle. But, when the compensating operation is performed with the calculated compensation angle, large vibration is not generated when the drum  30  is rotated at low speed. But since balancing is not accurately performed when the drum  30  is rotated at a speed equal to or greater than 1000 rpm, the large vibration may be generated. 
     When the first compensation angle θc 1  is calculated, the washing machine  1  performs the first water-removing compensating operation ( 625 ). In the first water-removing compensating operation, as shown in  FIG. 18A , the first balancer  200   a  and the second balancer  200   b  are moved by the first compensation angle θc 1  in a direction in which an angle between the first balancer  200   a  and the second balancer  200   b  is increased. 
     Subsequently, the washing machine  1  rotates the drum  30  at a first spin-dry speed (approximately 600 rpm) ( 630 ). That is, the washing machine  1  performs the first spin-dry operation during a predetermined first spin-dry time. 
     When the first spin-dry time elapses, the washing machine  1  rotates the drum  30  at the balancing speed ( 635 ). 
     While the drum  30  is rotated at the balancing speed, the washing machine  1  performs the second balancing operation ( 640 ). As a result of the second balancing operation, the angle between the first balancer  200   a  and the second balancer  200   b  with respect to the rotation axis of the drum  30 , as shown in  FIG. 18B , becomes the second balancing angle θ 2 . At this time, the centrifugal force due to the laundry and the centrifugal force due to the first balancer  200   a  and the second balancer  200   b  are in equilibrium. 
     Subsequently, the washing machine  1  calculates a second compensation angle θc 2  based on the first balancing angle θ 1  and the second balancing angle θ 2  ( 645 ). Specifically, the washing machine  1  calculates the first compensation angle θc 2  based on a difference between the first balancing angle θ 1  and the second balancing angle θ 2 . As described above, the amount of the wet laundry may be estimated from the balancing angle. In other words, the washing machine  1  may estimate the amount of the wet laundry before the spin-dry based on the first balancing angle θ 1 , and may estimate the amount of the wet laundry after the first spin-dry operation based on the second balancing angle θ 2 . Therefore, the washing machine  1  may estimate the amount of the removed water when the drum  30  is rotated at the first spin-dry speed based on the difference between the first balancing angle θ 1  and the second balancing angle θ 2 . Also, the compensation angle may be calculated from the amount of the removed water. Finally, the washing machine  1  may calculate the second compensation angle θc 2  in the drum  30  based on the difference between the first balancing angle θ 1  and the second balancing angle θ 2 . However, since the second compensation angle θ 2  is calculated based on the amount of the removed water when the drum  30  is rotated at the first spin-dry speed, the second compensation angle θc 2  may be different from a compensation angle required when the drum  30  is rotated at the second spin-dry speed. But, as described above, since the drum  30  is rotated at the second spin-dry speed of 1000 rpm or less during the second spin-dry operation, the large vibration is not generated by a slight difference of the compensation angle. 
     When the second compensation angle θc 2  is calculated, the washing machine  1  performs the second water-removing compensating operation ( 650 ). In the second water-removing compensating operation, as illustrated in  FIG. 18B , the first balancer  200   a  and the second balancer  200   b  are moved by the second compensation angle θc 2  in a direction in which the angle between the first balancer  200   a  and the second balancer  200   b  is increased. 
     Subsequently, the washing machine  1  rotates the drum  30  at the second spin-dry speed (approximately 850 rpm) ( 655 ). That is, the washing machine  1  performs the second spin-dry speed for a predetermined second spin-dry time. 
     When the second spin-dray time elapses, the washing machine  1  rotates the drum  30  at the balancing speed ( 660 ). 
     While the drum  30  is rotated at the balancing speed, the washing machine  1  performs a third balancing operation ( 665 ). As a result of the third balancing operation, the angle between the first balancer  200   a  and the second balancer  200   b  with respect to the rotation axis of the drum  30 , as illustrated in  FIG. 18C , becomes the third balancing angle θ 3 . At this time, the centrifugal force due to the laundry and the centrifugal force due to the first balancer  200   a  and the second balancer  200   b  are in equilibrium. 
     Subsequently, the washing machine  1  calculates a third compensation angle ®c 3  based on the first balancing angle θ 1 , the second balancing angle θ 2 , and the third balancing angle θ 3  ( 670 ). Specifically, the washing machine  1  calculates the third compensation angle θc 3  based on a difference between the first balancing angle θ 1  and the second balancing angle θ 2  and a difference between the second balancing angle θ 2  and the third balancing angle θ 3 . In other words, the washing machine  1  estimates an amount of removed water at the third spin-dry speed based on the amount of the removed water at the first spin-dry speed and the amount of the removed water at the second spin-dry speed. For example, the washing machine  1  obtains a relation between the spin-dry speed and an amount of removed water based on the amount of the removed water at the first spin-dry speed and the amount of the removed water at the second spin-dry speed, and estimates the amount of the removed water at the third spin-dry speed by applying the obtained relation to the third spin-dry speed. Also, the washing machine  1  may calculate the third compensation angle θc 3  based on the estimated amount of removed water. 
     Subsequently, when the third compensation angle θc 3  is calculated, the washing machine  1  performs the third water-removing compensating operation ( 6675 ). In the third water-removing compensating operation, as shown in  FIG. 18C , the first balancer  200   a  and the second balancer  200   b  are moved by the third compensation angle θc 3  in a direction in which the angle between the first balancer  200   a  and the second balancer  200   b  is increased. 
     Subsequently, the washing machine  1  rotates the drum  30  at the third spin-dry speed (approximately 1400 rpm) ( 680 ). That is, the washing machine  1  performs the third spin-dry operation for a predetermined third spin-dry time. 
     When the third spin-dry time elapses, the washing machine  1  stops the rotation of the drum  30  ( 685 ). At this time, the first balancer  200   a  and the second balancer  200   b  are moved to be positioned in opposite directions to each other with respect to the rotation axis of the drum  30 . 
     In short, the washing machine  1  performs three spin-dry steps to compensate for the water-removing during spin-dry, and calculates the compensation angle in the third spin-dry step in which the drum  30  is rotated at the highest speed based on the amount of the water removed in the first spin-dry step and the second spin-dry step. 
     The embodiments of the disclosed present invention have been described, but the disclosed invention is not limited to the above-described specific embodiment. It is possible for those skilled in the art to make various variations within the scope of the invention, and the variations should not be individually understood from the disclosed invention.