Patent Publication Number: US-11377771-B2

Title: Washing machine and control method of the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Korean Patent Application No. 10-2018-0116365, filed on Sep. 28, 2018, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a washing machine for determining the position of a balancer that is actively movable, and a control method of the washing machine. 
     2. Description of the Related Art 
     In general, a washing machine is an apparatus that performs cleaning through a process such as washing, rinsing, dehydrating, and the like to remove contamination on clothes, bedding, etc. (hereinafter, referred to as ‘cloth’) by using water, detergent, and mechanical action. 
     Washing machines are classified into agitator type, pulsator type, and drum type washing machines. 
     The agitator type washing machine performs washing by rotating a laundry rod towering in the center of the washing tub from side to side, the pulsator type washing machine rotates a disk-shaped rotary blades formed in the lower portion of the washing tub from side to side to perform washing by using frictional force between the water flow and the cloth, and the drum type washing machine performs washing by putting water, detergent, and cloth into the drum, and rotating the drum. 
     The drum washing machine is provided with a tub, a drum, a motor, and a drive shaft. The tub, in which washing water is accommodated, is provided inside a cabinet forming an outer shape. The drum, which accommodates a cloth, is disposed inside the tub. The motor is mounted in the rear surface side of the tub so as to rotate the drum. The drive shaft which penetrates through the motor and is connected to the rear surface side of is built up in the drum. The inside of the drum is equipped with a lifter to lift the cloth when the drum rotates. 
     Such a washing machine has a phenomenon in which the cloth is biased to one side due to the entanglement of the cloth, which causes an eccentricity in which one side becomes heavy based on the center of the drum. When the cloth is eccentric and the drum rotates at high speed (e.g., when the cloth is dehydrated), vibration and noise are generated by unbalance where the geometric center of the drum&#39;s rotation axis itself and the actual center of gravity are not coincident. An apparatus, which is called a balancer, for reducing the unbalance of the drum is installed in order to reduce such vibration and noise. 
     A counter weight for counterbalancing eccentricity by attaching additional mass has been used as a balancer for drum type washing machines. Recently, as shown in Korean Utility Model Publication No. 1998-019360, a ball balancer that has a ring-shaped space, which is formed in the front surface or rear surface of the drum, having a certain width in the circumferential direction, inserts a ball therein, and then, fills liquid to completely seal by heat-welding is mainly employed. When the drum rotates at high speed, the balancer distributes the inner material to move away from the center of gravity of the cloth so that the center of gravity of the drum approaches the center of rotation. 
     Such a ball balancer scheme has a problem in that it cannot correctly resolve the unbalance actively. 
     In addition, there is a problem in that, in order to actively move the balancer to solve the unbalance, the eccentricity must be detected or the position of the balancer must be accurately detected while the eccentricity is solved. 
     A position sensor of the balancer has errors and failures that frequently occur, and if a large number of position sensors are not used, accurate detection is difficult. Accordingly, there is a problem of increasing unbalance in the balancing of the washing machine operation. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above problems, and provides a washing machine which actively moves to actively eliminate the unbalance, and a control method of the washing machine. 
     The present invention further provides a balancer and a washing machine which can operate by wireless power, have a simple structure, and can reduce the number of parts. 
     The present invention further provides a balancer and a washing machine which are stably fixed at the time of heat-welding of a guide case while a reception coil does not interfere with a moving balancing weight. 
     The present invention further provides a washing machine which can determine the position of the balancing weight moving along the circumference of the drum without a separate sensor, and a control method of the washing machine. 
     In order to achieve the above object, the present invention determines the position of the balancing weights based on the input current value of the transmission coil when the drum rotates. 
     In detail, the washing machine of the present invention includes: a tub for accommodating washing water; a transmission coil which is provided in the tub and transmits power wirelessly by generating a wireless power signal; an ammeter which measures an input current value of the transmission coil; a cylindrical drum which is disposed inside the tub to accommodate cloth and is rotatable; a balancer for reducing unbalance generated by a biasing of the cloth during rotation of the drum; and a controller for controlling the ammeter and the balancer, wherein the balancer includes; a reception coil which is provided in the drum and generates power from a magnetic field formed by the transmission coil; at least two drive modules which are driven by the power of the reception coil and provided in the drum; and at least one balancing weight which moves along a circumference of the drum by a driving force of each drive module, and changes a center of gravity of the drum, wherein the controller determines a position of the balancing weights based on the input current value when the drum rotates. 
     The controller controls the ammeter to measure an input current value for each unit time during at least one rotation of the drum, and determines a first time point at which the input current value is equal to or less than a preset first current value as a position of the reception coil. 
     The controller detects a second time point at which the input current value is equal to or greater than a preset second current value, and determines a phase difference between the reception coil and the balancing weight based on a time difference between the first time point and the second time point. 
     The controller controls the ammeter to measure the input current value for each unit time during at least one rotation of the drum, and determines a third time point at which the input current value becomes equal to or greater than a preset third current value as a position of the reception coil. 
     The controller detects a second time point at which the input current value is equal to or greater than a preset second current value and is less than or equal to the third current value, and determines a phase difference between the reception coil and the balancing weight based on a time difference between the third time point and the second time point. 
     The controller determines a minimum point of the input current value, on an input current curve showing a change in the input current value over time during at least one rotation of the drum, as a position of the reception coil, and determines a band section in which the input current value is equal to or greater than a preset reference current value as the position of the balancing weight. 
     The controller determines as a position of the drive module, when a width of the band section is smaller than a preset width. 
     The controller determines a phase difference between the reception coil and the balancing weight based on a time difference between the minimum point of the input current value and a peak of the band section. 
     The controller determines a maximum point of the input current value, on an input current curve showing a change in the input current value over time during at least one rotation of the drum, as a position of the reception coil, and determines a band section in which the input current value becomes a value between a preset reference current value and a preset second current value, as a position of the balancing weight. 
     The controller determines as a position of the drive module, when a width of the band section is smaller than a preset width. 
     The controller determines a phase difference between the reception coil and the balancing weight based on a time difference between the maximum point of the input current value and a peak of the band section. 
     The method of controlling a washing machine of the present invention includes the steps of: (a) supplying power to a transmission coil; (b) rotating a drum at least once; (C) measuring a change in an input current value of the transmission coil for each unit time during one rotation of the drum; and (d) determining a position of a balancing weight based on the input current value. 
     The step (d) includes determining a minimum point of the input current value as a position of a reception coil. 
     The step (d) includes determining a band section in which the input current value is equal to or greater than a preset reference current value as a position of a balancing weight. 
     The step (d) includes determining a phase difference between the reception coil and the balancing weight based on a time difference between the minimum point of the input current value and a peak of the band section. 
     The step (d) includes determining a maximum point of the input current value as a position of a reception coil. 
     The step (d) includes determining a band section in which the input current value becomes a value between a preset reference current value and a preset second current value, as the position of the balancing weight. 
     The step (d) includes determining a phase difference between the reception coil and the balancing weight based on a time difference between the maximum point of the input current value and a peak of the band section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a cross-sectional view of a washing machine according to an embodiment of the present invention; 
         FIG. 1B  is a block diagram of the washing machine shown in  FIG. 1A ; 
         FIG. 2  is a perspective view of a tub of the washing machine shown in  FIGS. 1A and 1B ; 
         FIG. 3  is a perspective view of a drum of the washing machine shown in  FIGS. 1A and 1B  and a balancer installed in the drum; 
         FIG. 4  is an exploded perspective view of a balancer according to an embodiment of the present invention; 
         FIG. 5A  is a perspective view of a balancer according to an embodiment of the present invention; 
         FIG. 5B  is a partially exploded perspective view of a balancer according to an embodiment of the present invention; 
         FIG. 5C  is a cross-sectional view of a balancer according to an embodiment of the present invention; 
         FIG. 5D  is a perspective view of a coil base from one direction according to an embodiment of the present invention; 
         FIG. 5E  is a perspective view of a coil base from another direction according to an embodiment of the present invention; 
         FIG. 6  is a plan view of a balancer according to an embodiment of the present invention; 
         FIG. 7  is a perspective view of a drive module according to an embodiment of the present invention; 
         FIG. 8  is a perspective view of a balancing weight according to an embodiment of the present invention; 
         FIG. 9  is a flowchart illustrating a dehydration process according to an embodiment of the present invention; 
         FIG. 10  is a graph showing the rotational speed of a drum in the dehydration process of  FIG. 9 ; 
         FIGS. 11A to 11D  shows each part of a balancer relatively moving with respect to a transmission coil when the drum rotates; 
         FIG. 12A  is a graph illustrating a change in an input current value of a transmission coil over time according to an embodiment of the present invention; 
         FIG. 12B  is a graph illustrating a change in an input current value of a transmission coil over time according to another embodiment of the present invention; and 
         FIG. 13  is a flowchart illustrating a control method according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present invention are described with reference to the accompanying drawings in detail. The same reference numbers are used throughout the drawings to refer to the same or like parts. Detailed descriptions of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present invention. As used herein, the singular form is intended to include the plural forms as well, unless the context clearly indicates otherwise. In the present application, it will be further understood that the terms “comprises”, includes,” etc. specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Unless defined otherwise, the terms including technical and scientific terms used in this specification may have the meaning that can be commonly apprehended by those skilled in the art. The terms, such as the terms defined in the commonly-used dictionary, must be interpreted based on the context of the related technology and must not be interpreted ideally or excessively. 
     Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1A  is a cross-sectional view of a washing machine according to an embodiment of the present invention,  FIG. 1B  is a block diagram of the washing machine shown in  FIG. 1A ,  FIG. 2  is a perspective view of a tub of the washing machine shown in  FIGS. 1A and 1B , and  FIG. 3  is a perspective view of a drum of the washing machine shown in  FIGS. 1A and 1B  and a balancer installed in the drum. 
     A washing machine  100  according to an embodiment of the present invention includes a cabinet  111  which forms an outer shape, a door  112  which opens and closes one side of the cabinet to allow the cloth to enter and exit the cabinet, a tub  122  disposed inside the cabinet and supported by the cabinet, a drum  124  disposed inside the tub and rotating with a cloth inserted therein, a drum motor  113  which rotates the drum by applying torque to the drum, a detergent box  133  which accommodates detergent, and a control panel  114  which receives a user input and displays a washing machine state. 
     The cabinet  111  has a cloth loading hole  111   a  formed to allow the cloth to enter and exit. The door  112  is rotatably coupled to the cabinet  111  to allow the cloth loading hole  111   a  to be opened and closed. The cabinet  111  is provided with the control panel  114 . The cabinet  111  is provided with a detergent box  133  to be withdrawn. 
     The tub  122  is disposed in the cabinet  111  to be buffered by a spring  115  and a damper  117 . The tub  122  accommodates washing water. The tub  122  is disposed in the outside of the drum  124  while surrounding the drum  124 . 
     The tub  122  includes a cylindrical tub body  122   a  having both sides opened, a ring-shaped front tub cover  122   b  disposed in an opened front side of the tub body  122   a , and a disk-shaped rear tub cover  122   c  disposed in an opened rear side of the tub body  122   a . Hereinafter, the front side means the door  112  side, and the rear side means the drum motor  113  side. 
     A tub hole  122   d  is formed in one side of the tub  122 . The tub hole  122   d  is formed to communicate with the cloth loading hole  111   a  to allow the cloth to enter and exit the drum  124 . The tub hole  122   d  is formed in the front tub cover  122   b.    
     A weight  123  is coupled to a portion of one side edge of the tub  122 . The weight  123  applies a load to the tub  122 . The weight  123  is preferably disposed around the tub hole  122   d . A plurality of weights  123  may be provided, and disposed in a portion of upper side and lower side of the front tub cover  122   b.    
     The plurality of weights  123  includes an upper weight  123   a  disposed above the front tub cover  122   b  and a lower weight  123   b  disposed below the front tub cover  122   b . The upper weight  123   a  is disposed above the tub hole  122   d  among the edge of the tub  122 , and the lower weight  123   b  is disposed below the tub hole  122   d  among the edge of the tub  122 . 
     A transmission coil  240  described later may be disposed in the edge of one side of the tub  122 . The transmission coil  240  wirelessly supplies power to the balancer  300 . 
     The drum motor  113  generates a rotational force. The drum motor  113  may rotate the drum  124  at various speeds or directions. The drum motor  113  includes a stator (not shown) wound around with a coil, and a rotor (not shown) that rotates by generating electromagnetic interaction with the coil. 
     The drum  124  accommodates the cloth and is rotated. The drum  124  is disposed inside the tub  122 . The drum  124  is formed in a rotatable cylindrical shape. The drum  124  is provided with a plurality of through holes so that the washing water can pass. The drum  124  rotates while receiving the rotational force of the drum motor  113 . 
     A drum hole  124   a  is formed in the front side of the drum  124 . The drum hole  124   a  is formed to communicate with the cloth loading hole  111   a  and the tub hole  122   d  so that the cloth can be loaded into the drum  124 . 
     The balancer is coupled to the edge of one side of the drum  124 . The balancer reduces the unbalance generated by the biasing of the cloth when the drum rotates. 
     A gasket  128  seals between the tub  122  and the cabinet  111 . The gasket  128  is disposed between the opening of the tub  122  and the cloth loading hole  111   a . The gasket  128  mitigates the shock transmitted to the door  112  when the drum  124  rotates, while preventing the washing water in the tub  122  from leaking to the outside. The gasket  128  may be provided with a circulation nozzle  127  for introducing washing water into the drum  124 . 
     The detergent box  133  accommodates a detergent such as laundry detergent, fabric softener or bleach. The detergent box  133  is preferably provided in the front surface of the cabinet  111  to be withdrawn. The detergent in the detergent box  133  is mixed with the washing water when the washing water is supplied, and introduced into the tub  122 . 
     It is preferable that a water supply valve  131  for controlling the inflow of the washing water from an external water source, a water supply flow path  132  through which the washing water introduced into the water supply valve flows into the detergent box  133 , and a water supply pipe  134  for introducing washing water mixed with detergent in the detergent box  133  into the tub  122  are provided inside the cabinet  111 . 
     It is preferable that a drain pipe  135  through which the washing water in the tub  122  is discharged, a pump  136  for discharging the washing water in the tub, a circulation flow path  137  for circulating the washing water, a circulation nozzle  127  for introducing the washing water into the drum  124 , and a drain flow path  138  for draining the washing water to the outside are provided inside the cabinet  111 . According to an embodiment, the pump  136  may be provided with a circulation pump and a drain pump, and may be connected to the circulation flow path  137  and the drain flow path  138 , respectively. 
     The balancer  300  is provided in the front side and/or rear side of the drum  124  and, in the present embodiment, is coupled to the edge of the front side of the drum  124 . The balancer  300  is preferably disposed around the drum hole  124   a.    
     The balancer  300  moves along the edge of the drum  124  and changes the center of gravity of the drum  124 . In this case, the center of gravity of the drum  124  does not mean the center of gravity of the drum  124  itself, but means a common center of gravity of objects including the drum  124 , the cloth accommodated in the drum  124 , the balancer  300 , and components attached to the drum  124  that rotate together with the drum  124  when the drum  124  rotates. 
     The balancer  300  moves along the circumferential direction of the drum  124  to adjust the center of gravity of the drum  124  when the cloth is eccentric. When the drum  124  rotates while the cloth is eccentric, vibration and noise are generated due to unbalance in which the geometric center of a rotation axis Ax itself and the actual center of gravity of the drum  124  are not coincident. The balancer  300  reduces the unbalance of the drum  124  by allowing the center of gravity of the drum  124  to approach the rotation axis Ax. 
     The control panel  114  may include an input unit (not shown) for receiving various operation commands such as a washing course selection, an operation time and reservation for each process through a user, and a display unit (not shown) for displaying the operation state of the washing machine  100 . 
     Referring to  FIG. 1B , the washing machine according to an embodiment of the present invention includes a power supply unit  210  for supplying electric power from the outside, an oscillation unit  220  for generating a voltage fluctuation range in the power supplied from the power supply unit  210 , an amplification unit  230  for amplifying the power, a transmission coil  240  for generating a magnetic field, a reception coil  310  for generating power due to electromagnetic induction from a magnetic field, a rectifier  321  for converting a power generated in the reception coil  310  into a direct power, an adjusting unit  322  for adjusting the power into a certain voltage and current, a drive motor  333  for generating power, and a current measuring device for measuring an input current value of the transmission coil  240 . 
     In addition, the washing machine may further include a controller for controlling the overall operation of the washing machine, such as the operations of the drive motor  333 , the power supply unit  210 , and the drum motor  113 . 
     The power supply unit  210  converts commercial power, which is AC supplied from the outside, into an appropriate power. In the present embodiment, the power supply unit is a switched-mode power supply to convert the commercial power into 14V DC. The power supply unit  210  may be provided in a certain position inside the cabinet  111  or in the control panel  114 . The power converted and supplied by the power supply unit  210  may also be supplied to the drum motor  113 . 
     The oscillation unit  220  is an oscillator, and generates a voltage fluctuation range in the power supplied from the power supply unit  210  to generate a magnetic field in the transmission coil  240 . The amplifier  230  amplifies the power so that the transmission coil  240  can acquire a sufficient current. 
     The transmission coil  240  generates a magnetic field, and the reception coil  310  generates power due to electromagnetic induction from the magnetic field in which the transmission coil  240  is generated. 
     The current measuring device measures the input current value of the transmission coil  240  to provide to the controller. A general ammeter may be used as the current measuring device. 
     The rectifier  321  converts the power generated from the reception coil  310  into DC power. The adjusting unit  322  adjusts the power rectified by the rectifier  321  into a certain voltage and current. 
     The drive motor  333  generates power from the power adjusted by the adjusting unit  322 . The drive motor  333  generate power from the power that is supplied from the outside and transmitted wirelessly through the transmission coil  240  and the reception coil  310 . Generally, the adjusting unit  322  and the rectifier  321  are disposed in a circuit board  370  described later. 
     According to an embodiment, a storage unit (not shown) for temporarily storing the power adjusted by the adjusting unit  322  may be provided, and the storage unit (not shown) may be configured of a capacitor or a battery. 
     The above-mentioned oscillation unit  220  and amplifier  230  are preferably provided in a certain position inside the cabinet  111  or in the control panel  114 , and the reception coil  310 , the rectifier  321 , the adjusting unit  322 , and the drive motor  333  are preferably included in the balancer  300 . 
     The transmission coil  240  is disposed in the edge of one side of the tub  122  as described above. 
     The transmission coil  240  is disposed in the tub  122  to correspond to the movement path of the balancer  300  and wirelessly supplies power to the balancer  300 . The transmission coil  240  may be disposed in the tub  122  in correspondence with a guide case  340  described later. 
     The transmission coil  240  may be formed in an arc shape and disposed in a portion of one side edge of the tub  122 , or may be formed in a ring shape and disposed in the entire of one side edge of the tub  122 . The transmission coil  240  is preferably disposed around the tub hole  122   d  which is an edge of the front side of the tub  122 . 
     The transmission coil  240  may be disposed in the front tub cover  122   b  or the rear tub cover  122   c . In the present embodiment, the transmission coil  240  is disposed in the front tub cover  122   b . The transmission coil  240  is preferably disposed in the front side of the front tub cover  122   b  to face a guide rail  125 . 
     The tub  122  is preferably coupled to a coil cover (not shown) surrounding the transmission coil  240 . The coil cover (not shown) is coupled to the front tub cover  122   b  to surround the transmission coil  240 . The coil cover (not shown) protects the transmission coil  240  from water or foreign matter together with the front tub cover  122   b.    
     The transmission coil  240  is preferably disposed in the front tub cover  122   b  in correspondence with the balancer  300 . The reception coil  310  is provided in one side of the balancer  300  and the transmission coil  240  is disposed to correspond to the reception coil  310 . The transmission coil  240  is disposed in a portion of the moving path of the reception coil  310  to allow the magnetic field generated in the transmission coil  240  to be converted into power in the reception coil  310 . 
     It is preferable that the distance between the transmission coil  240  and the reception coil  310  maintains a distance in which power can be transmitted wirelessly. The distance between the transmission coil  240  and the reception coil  310  is preferably within 30 mm. 
     When a plurality of balancers  300  are provided, a plurality of transmission coils  240  may be provided. 
     Referring to  FIG. 2 , the weight  123  is coupled to a portion of the edge of the drum  124 . The transmission coil  240  is preferably disposed in an area where the weight  123  is not disposed among the edge of one side of the tub  122 . At this time, the transmission coil  240  is preferably formed in an arc shape. 
     A plurality of weights  123  are provided and disposed in a portion of the upper and lower sides of the front tub cover  122   b . A plurality of transmission coils  240  are provided in both sides of the front tub cover  122   b  between the upper weight  123   a  and the lower weight  123   b.    
     Hereinafter, referring to  FIGS. 4 to 8 , the balancer  300  will be described in detail. 
     The balancer  300  may further include at least two drive modules  330  which provide driving force, at least two gear rails  350  which are formed in a ring shape and rotated while being gear-coupled with each drive module  330 , at least two balancing weights  360  which move along the circumference of the drum  124  by rotation of each gear rail  350  to change the center of gravity of the drum  124 , the reception coil  310  which generates power from a magnetic field formed by the transmission coil, a guide case  340  for receiving at least reception coil  310  and drive module  330 , and a coil base which supports the reception coil 
     Referring to  FIGS. 4 and 5 , the guide case  340  accommodates at least reception coil  310  and drive module  330 . Preferably, the guide case  340  may accommodate the circuit board  370  described later, the balancing weight  360 , and the gear rail  350 . The guide case  340  may be provided in the front side and/or rear side of the drum  124 , and in the present embodiment, the guide case  340  is provided in the front side of the drum  124 . When the drum  124  is rotated, the cloth accommodated in the drum  124  is generally collected in the inner side of the drum  124 , i.e., in the rear side. Accordingly, it is preferable that the guide case  340  is provided in the front side of the drum  124  so as to be balanced to the cloth collected in the rear side of the drum  124 . 
     According to the present invention, the drive module  330  and the circuit board  370  are not integrally formed with the balancing weight  360 , but separately fixed to the guide case  340 , so that the drive module  330  and the circuit board  370  do not move when the balancing weight  360  is moved, thereby reducing damage occurred during movement. 
     The guide case  340  has a ring shape corresponding to the circumference of the drum  124 , and may have a space in which the balancing weight  360  moves along the circumference of the drum  124 , a space for accommodating the drive module  330  and the reception coil  310 , and a space for accommodating the gear rail  350 . 
     In detail, the guide case  340  may include a case body  341  and a case cover  342  covering the case body  341 . 
     The case body  341  is provided with a guide part  341   a  which is a passage through which the balancing weight  360  passes. The guide part  341   a  is formed by recessing a cross section of the case body  341  downward so that the balancing weight  360  is movable therein. The guide part  341   a  may have a ring shape corresponding to the circumference of the drum  124  so as to guide a path along which the balancing weight  360  moves. 
     The guide case  340  may further include a drive module accommodating part  341   b  and  341   c  extended from the guide part  341   a  in the direction of the rotation axis Ax of the drum  124  to accommodate each drive module  330 . The drive module accommodating part  341   b  and  341   c  may be formed by recessing a portion of the case body  341  in the downward direction. In detail, the drive module accommodating part  341   b  and  341   c  may be defined as a recessed area communicating with the guide part  341   a.    
     The guide case  340  may further include a receiver accommodating part  341   f  extended from the guide part  341   a  in the direction of the rotation axis Ax of the drum  124  to place the reception coil  310 . The receiver accommodating part  341   f  may be formed by recessing a portion of the case body  341  in a downward direction (see  FIG. 4 ). In detail, the receiver accommodating part  341   f  may be defined as a recessed area communicating with the guide part  341   a.    
     Obviously, the reception coil  310  may be accommodated directly in the receiver accommodating part  341   f , or the coil base may be installed in the receiver accommodating part  341   f , and the reception coil  310  may be installed in the coil base  343 . The coil base  343  will be described later. 
     The guide case  340  may have a support part  341   g  for supporting the coil base  343  around the guide part  341   a . The support part  341   g  may support the coil base  343  and define a gap  21  that is a spaced space between the coil base  343  and the guide case  340 . The support part  341   g  may be formed in a part of the edge of the guide part  341   a , and in the edge of the receiver accommodating part  341   f.    
     In detail, referring to  FIG. 5C , the case body  341  may include a bottom surface  3411 , a flange  3415  positioned above the bottom surface  3411 , and an inner surface  3412  and an outer surface  3413  connecting the flange  3415  and bottom face  3411 . The bottom surface  3411 , the inner surface  3412  and the outer surface  3413  together define the receiver portion accommodating portion  341   f  and the guide part  341   a . That is, the bottom surface  3411  forms the bottom surface of the receiver accommodating part  341   f  and the guide part  341   a , and the inner surface  3412  and the outer surface  3413  form a side surface of the receiver accommodating part  341   f  and the guide part  341   a.    
     The flange  3415  extended in a direction away from both ends of the bottom surface  3411  at the upper end of each of the inner surface  3412  and the outer surface  3413 , thereby providing the case cover  342  and an adhesive surface. The flange  3415  is heat-welded with the case cover  342 . The flange  3415 , the inner surface  3412 , the outer surface  3413 , and the bottom surface  3411  are extended along the circumference respectively. 
     The support part  341   g  may be formed in a portion of the inner surface  3412  and the outer surface  3413  of the case body  341 . Alternatively, the support part  341   g  may be formed in the flange  3415 . Here, the inner surface  3412  of the case body  341  means a surface closer to the rotation axis Ax of the drum than the outer surface  3413 . 
     The support part  341   g  may be a groove formed by recessing the inner surface  3412  and the outer surface  3413  in a downward direction. Obviously, the support portion  341   g  may be defined as a groove communicating with the guide part  341   a  and/or the receiver accommodating part  341   f . An alignment groove  341   h  to which a fixing protrusion  35  of the coil base  343  is coupled may be formed in the support part  341   g.    
     The guide case  340  may further include a rail accommodating part  341   d  extended from the guide part  341   a  in the direction of the rotation axis Ax of the drum  124  to place the reception coil  310 . The rail accommodating part  341   d  may be formed by recessing a portion of the case body  341  in the downward direction. In detail, the rail accommodating part  341   d  may be defined as a recessed area communicating with the guide part  341   a.    
     The rail accommodating part  341   d  is positioned inside the guide part  341   a , and the drive module accommodating part  341   b  and  341   c  and the receiver accommodating part  341   f  are positioned spaced apart from each other inside the rail accommodating part  341   d.    
     The balancer  300  may further include a circuit board  370  which transmits power of the reception coil  310  to the drive modules  330 , and generates a control signal for controlling the drive module  330 . 
     According to the present invention, the manufacturing cost can be reduced by controlling the two drive modules  330  with a single circuit board  370 , and the circuit board  370  does not move together with the balancing weight  360 , thereby improving reliability. The circuit board  370  is accommodated in the guide case  340 . In detail, it is accommodated in the receiver accommodating portion  341   f  of the guide case  340 . 
     At least a portion of the circuit board  370  and the reception coil  310  may be disposed to be overlapped with each other when viewed in the rotation axis Ax direction of the drum  124 . This is because the power generated by the reception coil  310  is transmitted to the circuit board  370  in the shortest distance, thereby reducing the manufacturing cost. 
     The drive module  330  provides a driving force. The number of drive modules  330  corresponds to the number of balancing weights  360 . In detail, the drive module  330  may include a first drive module  330   a  and a second drive module  330   b.    
     Each drive module  330  may include a drive motor  333 , a pinion gear  332  engaged with the drive motor  333 , and each gear rail  350 , and a motor housing accommodating the drive motor  333  and the pinion gear  332 . 
     The drive motor  333  generates a driving force from the power which is supplied from the outside and is transmitted wirelessly through the transmission coil  240  and the reception coil  310 . Preferably, the drive motor  333  is a motor that generates a rotational force. The drive motor  333  rotates the pinion gear  332 . When the drive motor  333  is a motor, a worm gear is disposed between the motor and the pinion gear  332  so that the rotational force changes the axis of the motor to rotate the pinion gear  332 . 
     The pinion gear  332  is rotated by receiving power from the drive motor  333 . A rack gear  351   b  is disposed in the inner circumferential surface of the gear rail  350 , and the pinion gear  332  meshes with the rack gears  351   b ,  125   a.    
     The pinion gear  332  rotates by meshing with the rack gears  351   b ,  125   a  to rotate the gear rail  350 , and when the gear rail  350  rotates, the balancing weight  360  restrained by the gear rail  350  is moved. 
     The pinion gear  332  is engaged with the rack gear  351   b ,  125   a  to prevent the balancing weight  360  from moving by its own weight or by centrifugal force when the drum  124  rotates. 
     The motor housing  331  accommodates the pinion gear and the drive motor  333 , and is fixed to the guide case  340 . The motor housing  331  is fixed to the drive module accommodating part  341   b ,  341   c.    
     When the reception coil  310  and the first and second drive modules  330  are biased toward one side of the guide case  340 , the unbalance of the drum  124  may occur. Accordingly, is preferable that the reception coil  310  and the first and second drive modules  330  are disposed in consideration of the balance of the center of gravity of the drum  124 . 
     For example, the reception coil  310  and the first and second drive modules  330  are spaced apart from each other on an arbitrary circumference around the rotation axis Ax of the drum  124 , the separation distance between the reception coil  310  and the first drive module  330   a  is the same as the separation distance between the reception coil  310  and the second drive module  330   b , and the separation distance between the first drive module  330   a  and the second drive module  330   b  may be the same as the separation distance between the reception coil  310  and the first drive module  330   a.    
     For another example, the center angle between the reception coil  310  and the first drive module  330   a  may be the same as the center angle between the reception coil  310  and the second drive module  330   b . The center angle between the first drive module  330   a  and the second drive module  330   b  may be the same as the center angle between the reception coil  310  and the first drive module  330   a.    
     Here, the center angle between the reception coil  310  and the first drive module  330   a  may be referred to as a first center angle θ 1 , the center angle between the reception coil  310  and the second drive module  330   b  may be referred to as a second center angle θ 2 , and the center angle between the first drive module  330   a  and the second drive module  330   b  may be referred to as a third center angle θ 3 . 
     As shown in  FIG. 6 , the first center angle means the angle between a line connecting the center of the reception coil  310  and the rotation axis Ax of the drum  124 , and a line connecting the center of the first drive module  330   a  and the rotation axis Ax of the drum  124 , the second center angle means the angle between a line connecting the center of the reception coil  310  and the rotation axis Ax of the drum  124 , and a line connecting the center of the second drive module  330   b  and the rotation axis Ax of the drum  124 , and the third center angle means the angle between a line connecting the center of the second drive module  330   b  and the rotation axis Ax of the drum  124 , and a line connecting the center of the first drive module  330   a  and the rotation axis Ax of the drum  124 . 
     Here, the same does not mean the exact same in a mathematical sense, but means that the approximation is the same within a range including an error. The first center angle, the second center angle, and the third center angle may be 119 degrees to 121 degrees. 
     The gear rail  350  is gear-coupled and rotated with each drive module  330 . The gear rail  350  may have a ring shape having a diameter smaller than that of the guide part  341   a.    
     For example, the gear rail  350  may include a ring-shaped rail body  351   a , a rack gear  351   b  formed in an inner circumferential surface of the rail body  351   a , and a protrusion  351   c  that is protruded from the outer circumferential surface of the rail body  351   a  and restrains the balancing weight  360 . 
     The rack gear  351   b  is formed along the inner circumferential surface of the rail body  351   a . The inner circumferential surface of the rail body  351   a  means a surface relatively close to the rotation axis Ax of the drum  124  in the rail body  351   a , and the outer circumferential surface of the rail body  351   a  means a surface positioned farther from the rotation axis (Ax) of the drum  124  than the outer circumferential surface of the rail body  351   a  in the rail body  351   a . The inner circumferential surface of the rail body  351   a  and the outer circumferential surface of the rail body  351   a  may be disposed to face each other. The inner circumferential surface of the rail body  351   a  and the outer circumferential surface of the rail body  351   a  are disposed to surround the rotation axis Ax of the drum  124 . 
     The gear rail  350  may be provided to correspond to the number of drive modules  330 . The gear rail  350  includes a first gear rail  351  and a second gear rail  352 . The first gear rail  351  is rotated by the driving force of the first drive module  330   a , and the second gear rail  352  is rotated by the driving force of the second drive module  330   b . The rack gear  351   b  of the first gear rail  351  is engaged with the pinion gear  332  of the first drive module  330   a , and the rack gear  351   b  of the second gear rail  352  is engaged with the pinion gear  332  of the second drive module  330   b.    
     The gear rail  350  may be accommodated in the rail accommodating part  341   d . The gear rail  350  may rotate while sliding in the rail accommodating part  341   d.    
     The two gear rails  350  may be positioned at different heights. The first gear rail  351  and the second gear rail  352  may be disposed to be overlapped in the direction of the central axis of the drum  124 . In  FIG. 4 , the first gear rail  351  is disposed above the second gear rail  352 . 
     The balancing weight  360  moves along the circumference of the drum  124  by the driving force of the drive module  330 . In detail, the balancing weight  360  moves along the circumference of the drum  124  by the rotation of each gear rail  350  to change the center of gravity of the drum  124 . At least two balancing weights  360  are provided, and each balancing weight  360  is restrained by each gear rail  350 . The balancing weight  360  may include a first balancing weight  360  and a second balancing weight  360 . 
     The balancing weight  360  may include a balancing body  361  having a coupling groove  361   a  coupled to the gear rail  350 , and a roller  362  coupled to the balancing body  361 . 
     The balancing body  361  may include an object having a weight or mass. The balancing body  361  has an arc shape, and a coupling groove  361   a  may be formed in a surface facing the outer circumferential surface of the gear rail  350 . The protrusion  351   c  of the gear rail  350  is inserted into the coupling groove  361   a . The protrusion  351   c  is inserted into the coupling groove  361   a  of the balancing body  361 , so that the movement of the balancing body is restrained by the rotation of the gear rail  350 . 
     The roller  362  is provided in the balancing body  361  so as to be rotatable. The roller  362  is in close contact with the inner surface of the guide part  341   a  and is rolled. The roller  362  prevents the balancing body  361  from directly touching the inner surface of the guide part  341   a . It is preferable that a plurality of rollers  362  are provided in both ends of the balancing body  361 . 
     It is preferable each drive module  330  is positioned inside an arbitrary circumference formed by the gear rail  350 , and each balancing weight  360  is positioned outside of an arbitrary circumference formed by the gear rail  350  in terms of utilization of space. 
     Hereinafter, referring to  FIGS. 5A to 5C , the positional relationship between the coil base  343 , the reception coil  310 , and each component will be described in detail. 
     Since the reception coil  310  should be wired to the circuit board  370 , it should be disposed close to the circuit board  370 . In addition, the reception coil  310  should be positioned to avoid interference with the balancing weight  360  moving along the circumference. The reception coil  310  should be stably fixed when the guide case  340  is heat-welded. Accordingly, the coil base  343  is used so that the reception coil  310  is stably positioned to be close to the circuit board  370  and not to be interfered by the balancing weight  360 . 
     The coil base  343  is accommodated in the guide case  340  and supports the reception coil  310 . In detail, the coil base  343  is disposed at a different height from the balancing weight  360 , such that the reception coil  310  supported on the coil base  343  is disposed at a different height from the balancing weight  360 . In detail, the coil base  343  may be disposed at a height higher than the balancing weight  360 , and the reception coil  310  may be disposed above the coil base  343 . 
     Accordingly, since the balancing weight  360  and the reception coil  310  are positioned at different heights by the coil base  343 , interference between the balancing weight  360  and the reception coil  310  can be avoided. Here, the height reference is an up and down direction in  FIG. 5C . A higher one is positioned in a relatively upward direction, and a low one is positioned in a relatively downward direction. 
     When the circuit board  370  is disposed at a different height from the balancing weight  360 , the thickness of the balancer becomes too thick. Accordingly, preferably, the circuit board  370  and the balancing weight  360  are disposed at the same height. Since the reception coil  310  should be positioned close to the circuit board  370 , at least a part of the reception coil  310  overlaps with the circuit board  370  in the upper portion of the circuit board  370  of the reception coil  310 . 
     The coil base  343  may be disposed at a different height from the circuit board  370 . In detail, the coil base  343  may be positioned in the upper portion of the circuit board  370 , and the reception coil  310  may be disposed in the upper portion of the coil base  343 . Therefore, the thickness of the balancer can be reduced while adjoining the circuit board  370  and the reception coil  310 . 
     The reception coil  310  may be disposed at a different height from the drive module  330 . The reception coil  310  may be disposed at a height higher than that of the drive module  330 . The drive module  330  may be positioned at the same height as the circuit board  370  or the balancing weight  360 . 
     More specifically, the coil base  343  may be positioned above the receiver accommodating part  341   f  and the guide part  341   a . That is, the coil base  343  may be supported by the upper end of the case body  341  while covering at least a portion of the guide part  341   a  and a portion of the receiver accommodating part  341   f . Preferably, the coil base  343  may be supported by the support part  341   g  of the case body  341 . 
     The coil base  343  may be configured to prevent the inflow of slag into the receiver accommodating part  341   f  and the guide part  341   a , be fixed to the guide case  340  before heat-welding, and support the reception coil  310 . 
     For example, it may include a base plate  31 , an alignment protrusion  32 , an overflow preventing surfaces  33 ,  34 , and a fixing protrusion  35 . The base plate  31  supports the reception coil  310 . The base plate  31  may have a larger area than at least the reception coil  310 . 
     The overflow preventing surface  33 ,  34  may be extended in a direction intersecting the extension direction of the base plate  31  from both ends of the base plate  31 . Referring to  FIG. 5C , the base plate  31  is extended in the horizontal direction, and the overflow preventing surface  33 ,  34  may be extended in the up and down direction from the inner and outer ends of the base plate  31 . Here, the inner end is an end closer to the rotation axis Ax of the drum than the outer end. 
     The overflow preventing surface  33 ,  34  is supported by the support part  341   g , so that the base plate  31  is positioned above the receiver accommodating part  341   f  and the guide part  341   a . In addition, the overflow preventing surface  33 ,  34  may define a gap  21  in which slag is collected between the guide case  340  and the overflow preventing surface  33 . That is, the gap  21  is a separation space formed between one surface of the coil base  343  and at least three surfaces of the guide case  340 , and prevents the slag, which is generated when the case body  341  and the case cover  342  are heat-welded, from flowing into the guide part  341   a  and the receiver accommodating part  341   f.    
     The width of the overflow preventing surface  33 ,  34  is formed smaller than the width of the support part  341   g , and the gap  21  is positioned farther from the base plate  31  than the overflow preventing surface  33 ,  34 . The gap  21  may be positioned in the flange  3415 . By the overflow preventing surface  33 ,  34 , the slag which disturbs the movement of the balancing weight  360  does not flow into the guide part  341   a.    
     The fixing protrusion  35  protrudes from the base plate  31  to determine the position of the base plate  31 . In detail, the fixing protrusion  35  protrudes downward from the lower end of the overflow preventing surface  33 ,  34  to be coupled to the alignment groove of the case body  341 . The fixing protrusion  35  protrudes in the opposite direction to the alignment protrusion  32 . 
     The alignment protrusion  32  protrudes upward from the base plate to determine the position of the reception coil  310 . Two alignment protrusions  32  may be disposed spaced apart from each other, and the reception coil  310  may be disposed to surround the alignment protrusions  32 . 
     The melting point of the coil base  343  may be the same as the guide case  340  or higher than the guide case  340 . Preferably, the melting point of the coil base  343  may be higher than the guide case  340 . This is because if the melting point of the coil base  343  is higher than the guide case  340 , the coil base  343  does not melt during heat-welding of the guide case  340 , and the inflow of slag can be effectively prevented. 
     The noise and vibration of the washing machine may occur when the drum is rotated, particularly, in a dehydration process where the drum is rotated at high speed. Hereinafter, the driving of the drum in the dehydration process will be described. 
       FIG. 9  is a flowchart illustrating a dehydration process according to an embodiment of the present invention, and  FIG. 10  is a graph showing the rotational speed of a drum in the dehydration process of  FIG. 9 . 
     In the graph of  FIG. 10 , the horizontal axis indicates time, and the vertical axis indicates the rotational speed of the drum  30 , i.e., the change of RPM. 
     Referring to  FIGS. 9 and 10 , the dehydration process may briefly include a cloth dispersion step S 100  and a dehydration step S 200 . 
     In the cloth dispersion step S 100 , the drum  124  may be rotated at a relatively low speed to evenly disperse the cloth. In the dehydration step S 200 , the drum  124  may be rotated at a relatively high speed to remove moisture of the laundry. However, the cloth dispersion step and the dehydration step are named based on their main function, and the function in each step is not limited depending on the name. For example, in the cloth dispersion step, water may be removed from the cloth by the rotation of the drum  124 , in addition to the cloth dispersion. Hereinafter, each step will be described in detail. 
     Obviously, the cloth dispersion step S 100  may include a step of detecting the eccentricity of the drum  124  and releasing the eccentricity of the drum  124  by the balancer. 
     When a rinsing process is finished, the cloth inside the drum  124  is wet by moisture. When starting the dehydration process, a controller  260  may first detect the cloth amount inside the drum  124 , i.e., the amount of wet cloth (S 110 ). 
     The reason for detecting the amount of wet cloth is that the weight of the water-containing cloth is different from the weight of the dry cloth even if the amount of non-wet amount, i.e., the amount of dry cloth, is detected at the initial stage of the washing process. The detected amount of wet cloth serves as a factor that determines a permission condition for accelerating the drum  124  in a transient area passing step S 210  described later, or determines to perform the cloth dispersion step again by decelerating the drum  124  by the eccentric condition in the transient area passing step S 210 . 
     In detail, the amount of wet cloth inside the drum  124  may be measured when the drum  124  is accelerated to a first rotational speed (a first RPM), e.g., about 100 to 110 RPM to drive at a constant speed for a certain time and is decelerated. Power generation braking may be used when the drum  124  is decelerated. The amount of wet cloth can be detected by using the amount of rotation in an acceleration section during acceleration of the drive motor  40  for rotating the drum  124 , the amount of rotation in a deceleration section during deceleration, an applied motor DC power, and the like. 
     In the detection of the amount of wet cloth, in order to reduce the occurrence of error in the detection of the cloth amount by the balancer, the position of the balance weights  360  of the balancer is detected, and a plurality of balancing weights  360  have the same phase difference (phase difference between two balancing weights  360  is 180°. Detecting the position of the balancing weight  360  will be described later. 
     Meanwhile, after the detection of the amount of wet cloth, the controller  260  may perform a cloth untangling step for the cloth dispersion inside the drum  124  (S 130 ). The cloth untangling step intends to evenly disperse the cloths inside the drum  124  so as to prevent the cloths from being concentrated in a specific area inside the drum  124  and increasing the amount of eccentricity of the drum  124 . This is because noise and vibration increase when the RPM of the drum  124  is increased if the amount of eccentricity is increased. 
     In detail, the cloth untangling step may be performed until the drum  124  is accelerated in one direction by a certain inclination and reaches the rotation speed of an eccentric detection step described later. 
     Next, the controller  260  may detect an eccentricity of the drum  124  (S 150 ). When the cloth inside the drum  124  is not evenly dispersed and concentrated in a certain area inside the drum  124 , the amount of eccentricity is increased. Thus, when the RPM of the drum  124  is increased later, noise and vibration may be caused due to the eccentric rotation. Accordingly, the controller  260  may determine whether to accelerate the drum  124  by detecting the eccentric amount of the drum  124 . 
     Eccentricity detection may be performed by using an acceleration difference when the drum  124  rotates. That is, depending on the degree of eccentricity, when the drum  124  rotates, there is a difference in acceleration between a case where the drum  124  rotates downward according to the gravity and a case where the drum  124  rotates upward in the opposite direction to the gravity. The controller  260  may measure the acceleration difference by using a speed sensor such as a hall sensor provided in the drive motor  40 , and may detect an eccentric amount by the detected acceleration difference. 
     Therefore, in the case of detecting the eccentricity, even if the drum  124  rotates, the cloth inside the drum  124  should not fall and maintain the state of being attached to the inner wall of the drum  124 , which corresponds to a case where the drum  124  rotates at a rotational speed of about 100 to 110 RPM. 
     When the detected amount of eccentricity of the drum  124  is greater than or equal to a reference eccentricity in a certain amount of wet cloth, if the drum  124  is accelerated at a high speed, the vibration and noise of the drum  124  are significantly increased, which makes it difficult to accelerate the drum  124 . Therefore, the controller  260  may store the data, in the form of a table, in which a reference amount of eccentricity permitting acceleration is previously determined according to the amount of wet cloth. Therefore, it is possible to determine whether to accelerate by applying the detected amount of wet cloth and amount of eccentricity to the table. 
     That is, when the amount of eccentricity according to the detected amount of the wet cloth is equal to or greater than the reference amount of eccentricity, the eccentric amount is too large to accelerate the drum  124 , so that an eccentric reduction step is executed. 
     In the eccentric reduction step, the amount of eccentricity may be reduced by repeating the above-described wet cloth detection step, the cloth untangling step, the eccentric detection step or by moving the position of the balancing weight  360 . 
     In detail, the eccentricity reduction step by using the balancer may include a step of minimizing the phase difference between two or more balancing weights  360 . That is, prior to moving the two or more balancing weights  360  to minimize the eccentricity, firstly, the phase difference between the balancing weights  360  may be minimized, for example, the balancing weights  360  may be connected to each other. This is because when two or more balance weights  360  are provided and, if they are moved individually, it is time-consuming and complicated to reduce the amount of eccentricity. 
     Meanwhile, in order to minimize the phase difference between two or more balancing weights  360 , that is, to connect with each other, the position of the balancing weight  360  may be determined based on the amount of change in the input current value of the transmission coil  240 . 
     Therefore, in the case where the phase difference between the balancing weights  360  is to be minimized (or connected to each other), the controller  260  may move the balancing weights  360  in opposite directions, and when the distance between the balancing weights  360  is minimized, the movement of the balancing weight  360  may be stopped to minimize the phase difference. 
     Next, the eccentric amount of the drum  124  is detected while moving the two or more balancing weights  360  to be relatively moved with respect to the drum  124 . That is, when the drum  124  rotates at a certain rpm, for example, a rpm (a case where the drum  124  rotates at a rotational speed of about 100 to 110 RPM) at which the cloth inside the drum  124  does not fall and is attached to the inner wall of the drum  124 , the balancing weight  360  moves relatively with respect to the drum  124  and moves along the inside of the housing. In this case, the amount of eccentricity of the drum  124  may be reduced when the balancing weight  360  moves approximately to an eccentric corresponding position. Therefore, the controller  260  detects an eccentric amount of the drum  124  according to the movement of the balancing weight  360 . 
     Next, the controller  260  may stop the movement of the balancing weight  360  at a first position where a first minimum value of the eccentricity of the drum  124  is detected. The controller  260  may store the minimum value as the first minimum value when the minimum value of the eccentricity is detected according to the movement of the balancing weight  360 . In addition, the position of the balancing weight  360  in which the first minimum value is detected may be stored as the first position. Since the first minimum value corresponds to the minimum value of the eccentricity when the balancing weights  360  move in a minimum phase, i.e., in a connected state with each other, the controller  260  moves the balancing weight  360  to the first position to fix the position. Here, the first position may be changed according to various factors such as the dispersion of the cloth inside the washing machine, the cloth amount, the installation position of the balancer, and the like, and may correspond to an approximately eccentric corresponding position. 
     Meanwhile, in the case of having two or more balancing weights  360 , the eccentricity of the drum  124  can be further reduced than the first minimum value. That is, since the first minimum value is a value detected when two or more balancing weights  360  have a minimum phase difference (or state of being connected with each other), each of the two or more balancing weights  360  is moved from the first position where the first minimum value is detected, the amount of eccentricity can be reduced to a value smaller than the first minimum value. 
     When the amount of eccentricity according to the detected wet amount is equal to or less than the reference amount of eccentricity, the acceleration permission condition is satisfied, so that the subsequent transient area passing step S 210  may be performed. 
     Here, the transient area may be defined as a certain RPM band including one or more resonance frequencies in which resonance occurs according to a system of a washing machine. The transient area is an inherent vibration characteristic that occurs according to a determined system when the system of the washing machine is determined. The transient area is changed according to the system of the washing machine and, for example, may have a range of approximately 200 to 350 RPM. 
     That is, when the rotational speed of the drum  124  passes through the transient area, resonance occurs in the washing machine, and the noise and vibration of the washing machine may be significantly increased. In the washing machine, noise and vibration cause discomfort to the user, and further, disturb the acceleration of the drum  124 . In the case of passing through the transient area, the acceleration slope may be adjusted appropriately to reduce the noise and vibration when accelerating the drum  124 . 
     Meanwhile, as the drum  124  is accelerated while passing through the transient area, or due to an unexpected shock applied from the outside, the amount of eccentricity of the drum  124  may increase. When the amount of eccentricity of the drum  124  becomes larger than a certain value, the noise becomes remarkably larger, and it becomes difficult to continuously accelerate the drum  124 . Therefore, when passing through the transient area, the controller  260  can continue to detect the amount of eccentricity of the drum  124 . 
     In addition, the controller  260  may be provided with a vibration sensor in the drum  124  of the washing machine and may detect the vibration of the drum  124  when passing through the transient area. If the detected vibration and/or amount of eccentricity of the drum  124  in the transient area passing step becomes larger than a certain value, the controller  260  decelerates the drum  124  to repeat the above-described wet cloth detection step, the cloth untangling step, and the eccentric detection step, or to execute the eccentric detection step and the eccentricity reduction step S 170  using the balancer described above. 
     Subsequent to the transient area passing step, the controller  260  may perform a water extraction step (S 230 ). 
     The controller  260  removes water from a washing object by maintaining the rotational speed of the drum  124  at a second RPM (S 200 ). In detail, in the water extraction step, the drum  124  is accelerated to a relatively high speed up to a desired RPM and maintained to extract the water. 
     In the related art, since a plurality of position detection sensors (usually, ten or more sensors are disposed for accurate position detection) are used along the circumference of the drum  124 , manufacturing cost is greatly increased, and it is difficult to measure the exact position. 
     Hereinafter, a washing machine and a control method of the same for measuring the position of the balancing weight  360  which solves the conventional problem will be described in detail. In the eccentric reduction and cloth amount detection steps using the above-described balancer, a method of measuring the position (phase) of the balancing weight  360  of the present invention is used. 
       FIGS. 11A to 11D  shows each part of a balancer relatively moving with respect to a transmission coil  240  when the drum  124  rotates,  FIG. 12A  is a graph illustrating a change in an input current value of a transmission coil over time according to an embodiment of the present invention, and  FIG. 12B  is a graph illustrating a change in an input current value of a transmission coil over time according to another embodiment of the present invention. 
     In particular,  FIG. 12A  is a graph illustrating a change in an input current value of a transmission coil for each unit time according to one rotation of the drum  124  when the drive motor  300  of the drive module  330  is turned off.  FIG. 12B  is a graph illustrating a change in the input current value of the transmission coil for each unit time according to one rotation of the drum  124  when the drive motor  300  of the drive module  330  is turned on. 
     When the drum  124  is rotated while power is applied to the transmission coil  240 , the input current value of the transmission coil  240  is changed. When the transmission coil  240  is adjacent to (or overlapped with) the reception coil  310 , the input current value of the transmission coil  240  is changed rapidly because power is transmitted to the reception coil  310 , and when the transmission coil  240  is adjacent to other member, the change of the input current value of the transmission coil  240  becomes small. 
     Here, ‘the transmission coil  240  is adjacent to a certain configuration’ means that the transmission coil  240  is vertically overlapped with a certain configuration in the direction of the rotation axis of the drum  124  and is very close to each other. In this case, other configurations are spaced apart from the transmission coil  240  without being vertically overlapped with the transmission coil  240 . 
     In detail, as shown in  FIG. 11A , when the transmission coil  240  is adjacent to other configuration (guide case  340 ) excluding the balancing weight  360 , the drive module  330 , and the reception coil  310 , the input current value of the transmission coil  240  becomes a reference current value C 0 . Here, the reference current value C 0  may be a value preset by an experiment, or may be an average current value of a section A 5  having a rate of change of a certain time or less in an input current value curve. At this time, the guide case  340  is preferably formed of a resin material so as to change the input current value of the transmission coil  240  a little. 
     As shown in  FIG. 11B , when the drum  124  is rotated in the clockwise direction and the transmission coil  240  is adjacent to the drive module  330 , the input current value of the transmission coil  240  has a larger value than the reference current value C 0 , and has a value smaller than a maximum current value (Cmax). Since the drive module  330  has a material including magnetism, it changes the input current value of the transmission coil  240 . 
     As shown in  FIG. 11C , when the drum  124  is rotated in the clockwise direction and the transmission coil  240  is adjacent to the balancing weight  360 , the input current value of the transmission coil  240  has an intermediate current value that is larger than the reference current value C 0  and smaller than the maximum current value (Cmax). Obviously, the intermediate current value may be a value larger than the input current value of the transmission coil  240  when the transmission coil  240  is adjacent to the drive module  330 . 
     The balancing weight  360  may have a larger mass, a larger volume, and a larger length than the drive module  330 . Since the balancing weight  360  has a larger mass and size than the drive module  330 , it is easy to distinguish the balancing weight  360  from the drive module  330  on an input current curve. More preferably, the balancing weight  360  may contain a metal, or may contain a metal and a material including magnetism. 
     Referring to  FIG. 11D , when the transmission coil  240  is adjacent to (or overlapped with) the reception coil  310  and the drive motor  300  is in an off state, the input current value of the transmission coil  240  is decreased than the reference current value C 0  as shown in  FIG. 12A . In general, the input current value of the transmission coil  240  has a minimum current value Cmin, when the transmission coil  240  is adjacent to (or overlapped with) the reception coil  310  and the drive motor  300  is in an off state. 
     When the transmission coil  240  and the reception coil  310  are adjacent to each other and then are far away, the rate of change of the input current value of the transmission coil  240  is maximized. 
     When the transmission coil  240  is adjacent to (or overlapped with) the reception coil  310  and the drive motor  300  is in an on state, the input current value of the transmission coil  240  is increased larger than the reference current value C 0  as shown in  FIG. 12B . In general, the input current value of the transmission coil  240  has a maximum current value Cmax when the transmission coil  240  is adjacent to (or overlapped with) the reception coil  310  and the drive motor  300  is in an on state. 
     As described above, when each configuration of the balancer is adjacent to the transmission coil  240 , a change in the input current value of the transmission coil  240  occurs, so that the position of the configuration fixed to the drum  124  may be determined based on the input current value of the transmission coil  240 , and the position of the balancing weight  360  may be determined as a relative phase difference in the configuration fixed to the drum  124 . Hereinafter, it is illustrated that the relative position of the balancing weights  360  is determined based on the reception coil  310 . However, it is not limited thereto, and the position of the balancing weight  360  may be calculated based on the drive module  330 . 
     The controller  260  determines the position of the balancing weight  360  based on the input current value when the drum  124  rotates, while power is supplied to the transmission coil  240 . The controller  260  may vary the method of determining the position of the balancing weight  360  according to the on or off state of the drive motor  300 . 
     First, a method of determining the position of the balancing weight  360  according to the off state of the drive motor  300  will be described. 
     For example, the controller  260  controls an ammeter to measure the input current value for each unit time during at least one rotation of the drum  124 , and may determine a first time point at which the input current value becomes less than or equal to a preset first current value as the position of the reception coil. The first current value may be 0.5 times to 0.7 times the reference current value C 0 . 
     At this time, since the drum  124  is rotated at a constant speed, when the time from the rotation time point of the drum  124  to the first time point is measured, the phase difference between the initial position of the drum  124  and the reception coil may be obtained according to the ratio with respect to the time when the drum  124  is rotated once. Obviously, the first time point may be set as a reference time point and, at this time, the position of the reception coil  310  may be defined as a reference position (0°). Here, the first current value may be set smaller than the reference current value. 
     Obviously, in order to accurately calculate the first time point, the intermediate time point of a section A 6  in which the input current value becomes less than or equal to a preset first current value may be defined as the first time point. 
     Thereafter, the controller  260  determines a second time point at which the input current value is equal to or greater than a preset second current value, and may determine a phase difference between the reception coil and the balancing weight  360  based on a time difference between the first time point and the second time point. The second current value may be 1.1 times to 1.2 times the reference current value C 0 . Here, the second current value may be set to a value larger than the input current value when the drive module  330  is adjacent to the transmission coil  240 . Obviously, in order to accurately calculate the second time point, an intermediate time point of sections A 2  and A 3  in which the input current value becomes greater than or equal to the second current value may be defined as the second time points. 
     The operation of determining the phase difference between the reception coil and the balancing weight  360  based on the time difference between the first time point and the second time point may be calculated by multiplying a value obtained by dividing the time difference between the first time point and the second time point by one rotation time of the drum  124  by 360°. Accordingly, the relative position of the first balancing weight  360  and the second balancing weight  360  can be accurately calculated. 
     As another example, in the power-off state of the drive motor  300 , the controller  260  may calculate an input current curve showing a change in the input current value over time during at least one rotation of the drum  124 , and may determine the minimum point (C min) (within one period) of the input current value on the input current curve as the position of the reception coil. 
     The controller  260  selects a band section in which the input current value becomes greater than or equal to the preset reference current value C 0 . The controller  260  may distinguish the balancing weight  360  from the drive module  330  by a width (time) of the band section on the input current curve. In detail, the controller  260  determines the band section A 2 , A 3  as the position of the balancing weight  360  when the width of the band section is larger than a preset width, and determines the band section A 1  as the position of the drive module  330  when the width of the band section is smaller than the preset width. 
     The controller  260  may determine a phase difference between the reception coil and the balancing weight  360  based on a distance difference (in time axis) (or time difference) between the minimum point (Cmin) of the input current value and the peak of the band section A 2 , A 3 . The calculation of the phase difference based on the time difference or the distance difference is the same as described above. 
     Hereinafter, a method of determining the position of the balancing weight  360  according to the on state of the drive motor  300  will be described. 
     For example, the controller  260  controls the ammeter to measure the input current value for each unit time during at least one rotation of the drum  124 , and may determine a third time point at which the input current value is greater than or equal to a preset third current value as the position of the reception coil. The third current value may be 1.3 times to 1.5 times the reference current value C 0 . At this time, the drum  124  is rotated at a constant speed. Here, the third current value may be set larger than the reference current value. 
     Obviously, in order to accurately calculate the third time point, the intermediate time point of a section A 4  in which the input current value becomes greater than or equal to the preset third current value may be defined as the third time point. 
     Thereafter, the controller  260  determines a second time point at which the input current value is greater than or equal to the preset second current value and is less than or equal to the third current value, and may determine a phase difference between the reception coil and the balancing weight  360  based on the time difference between the third time point and the second time point. 
     Here, the second current value may be set to a value larger than the input current value when the drive module  330  is adjacent to the transmission coil  240 . The second current value is set to a value smaller than the third current value. Obviously, in order to accurately calculate the second time point, an intermediate time point of the section A 2 , A 3  in which an input current value is greater than or equal to the second current value and less than or equal to the third current value may be defined as the second time points. 
     The operation of determining the phase difference between the reception coil and the balancing weight  360  based on the time difference between the first time point and the second time point may be calculated by multiplying a value obtained by dividing the time difference between the first time point and the second time point by one rotation time of the drum  124  by 360°. 
     As another example, in the power-on state of the drive motor  300 , the controller  260  may calculate an input current curve showing a change in the input current value over time during at least one rotation of the drum  124 , and may determine the maximum point (C max) (within one period) of the input current value on the input current curve as the position of the reception coil. 
     The controller  260  selects a band section in which the input current value is greater than or equal to the preset reference current value C 0  and smaller than the second current value. The controller  260  may distinguish the balancing weight  360  from the drive module  330  by a width (time) of the band section on the input current curve. In detail, the controller  260  determines the band section A 2 , A 3  as the position of the balancing weight  360  when the width of the band section is larger than a preset width, and determines the band section A 1  as the position of the drive module  330  when the width of the band section is smaller than the preset width. 
     The controller  260  may determine a phase difference between the reception coil and the balancing weight  360  based on a distance difference (in time axis) (or time difference) between the maximum point (Cmax) of the input current value and the peaks of the band section A 2 , A 3 . 
     When the controller  260  specifies the position of the balancing weight  360  by the input current value of the transmission coil  240 , it is not necessary to mount a plurality of sensors to specify the position of the balancing weight  360 , but the burden on the controller  260  can be reduced by a simple operation. 
     Hereinafter, the control method of the balancer and the washing machine described above will be described in detail. 
       FIG. 13  is a flowchart illustrating a control method according to an embodiment of the present invention. 
     Referring to  FIG. 13 , the control method of the washing machine for determining the position of the balancing weight  360  of the present invention may include a step (a) of supplying power to the transmission coil  240  (S 310 ), a step (b) of rotating the drum  124  at least once (S 320 ), a step (c) of measuring the change in the input current value of the transmission coil  240  for each unit time during one rotation of the drum  124  (S 330 ), and a step (d) of determining the position of the balancing weight  360  based on the change in the input current value (S 340 ). 
     The control method of the washing machine for determining the position of the balancing weight  360  of the present invention can be accomplished at any step of the washing process described above. 
     First, the controller  260  controls the power supply unit  210  to supply power to the transmission coil  240  (S 310 ). 
     Next, the controller  260  controls the drum motor  113  in a state in which power is supplied to the transmission coil  240  to rotate the drum  124  at least once (S 320 ). 
     Next, the controller  260  controls the ammeter to measure the change in the input current value of the transmission coil  240  for each unit time during one rotation of the drum  124  (S 330 ). 
     Next, the controller  260  determines the position of the balancing weight  360  based on the change in the input current value (S 340 ). 
     For example, in step (d), the controller  260  may determine the minimum point (C min) (within one period) of the input current value as the position of the reception coil. More specifically, the controller  260  calculates an input current curve showing a change in the input current value over time during at least one rotation of the drum  124 , and may determine the minimum point (C min) (within one period) of the input current value, on the input current curve, as the position of the reception coil. 
     In step (d), a band section in which the input current value becomes equal to or greater than the preset reference current value C 0  is selected. The controller  260  may distinguish the balancing weight  360  from the drive module  330  by the width (time) of the band section on the input current curve. In detail, when the width of the band section is greater than the preset width, the controller  260  determines the band section A 2 , A 3  as the position of the balancing weight  360 . Then, the controller  260  may determine a phase difference between the reception coil and the balancing weight  360  based on the distance difference (in time axis) (or time difference) between the minimum point (Cmin) of the input current value and the peak of the band section A 2 , A 3 . 
     As another example, in step (d), the controller  260  may determine the maximum point (C max) (within one period) of the input current value as the position of the reception coil. In detail, the controller  260  may calculate an input current curve showing a change in the input current value over time during at least one rotation of the drum  124 , and may determine the maximum point (C max) (within one period) of the input current value on the input current curve as the position of the reception coil. Then, the controller  260  selects a band section in which the input current value is greater than or equal to the preset reference current value C 0  and smaller than the second current value. The controller  260  may distinguish the balancing weight  360  from the drive module  330  by a width (time) of the band section on the input current curve. In detail, the controller  260  determines the band section A 2 , A 3  as the position of the balancing weight  360  when the width of the band section is larger than a preset width. Then, the controller  260  may determine a phase difference between the reception coil and the balancing weight  360  based on a distance difference (in time axis) (or time difference) between the maximum point (Cmax) of the input current value and the peaks of the band section A 2 , A 3 . 
     According to the balancer and the washing machine of the present invention, there are one or more of the following effects. 
     First, even if the balancer rotates with the drum, a wireless power transmitter can wirelessly transmit sufficient power to the balancer in a short time. 
     Second, since the balancing weight that actively moves, the drive module, and the reception coil are separated from each other, and the drive module and the balancing weight are not manufactured integrally, so that manufacturing is easy and manufacturing cost is reduced. 
     Third, the interference of the balancing weight moving along the circumference with the reception coil can be eliminated, and the circuit board is positioned close to the reception coil. 
     Fourth, the position of the balancing weight can be accurately measured only by the input current value of the transmission coil, without the need to add a plurality of sensors. 
     Fifth, since a single ammeter is added instead of a plurality of sensors, manufacturing cost is reduced. 
     Sixth, the reception coil is positioned to be higher than the circuit board and the balancing weight by using the coil base, and the slag generated during heat-welding of the guide case can be prevented from overflowing into the moving path of the balancing weight. 
     Seventh, since each drive module and the circuit board for controlling each drive module and supplying power are separated from each other and a single circuit board and a single reception coil are used, so that manufacturing cost is reduced, and the reliability is improved as the drive module does not move together with the balancing weight. 
     Although the exemplary embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Accordingly, the scope of the present invention is not construed as being limited to the described embodiments but is defined by the appended claims as well as equivalents thereto.