Patent Publication Number: US-11021831-B2

Title: Washing machine and operating method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the Korean Patent Application No. 10-2017-0154073 filed on Nov. 17, 2017, which is hereby incorporated by reference as if fully set forth herein. 
     BACKGROUND 
     Field of the Invention 
     The present invention relates to a washing machine and an operating method thereof. 
     Discussion of the Related Art 
     Generally, washing machines are devices for removing pollutants from the polluted laundry through a washing process, a rinsing process, and a dehydrating process. Washing machines may each include a cabinet configuring an external appearance, a tub installed in the cabinet to store water, and a drum rotatably installed in the tub. 
     In a state where the laundry and washing water are put in the drum along with detergent, a washing machine rotates the drum to apply a physical impact to the laundry, thereby washing the laundry. At this time, in a washing process, the washing machine rotates a pulsator at a low speed to perform washing, and in a dehydrating process, the washing machine simultaneously rotates the pulsator and the drum at a high speed to perform dehydration. That is, washing machines have a structure which operates in two modes. 
     As described above, washing machines may each include a clutch for operating in the two modes, and an operation mode may be changed when a coupler included in the clutch is raised or lowered. 
     As the coupler is raised, the coupler may be detached from a pulsator shaft, and as the coupler is lowered, the coupler may be connected to the pulsator shaft. For example, in a case where the coupler is unstably connected to a motor, an abnormal value may be sensed in a subsequent washing process. Therefore, a method for increasing a fastening success rate between the coupler and the motor may be needed for washing machines. 
     SUMMARY 
     An aspect of the present invention is directed to providing a washing machine and an operating method thereof, which minimize a probability that a coupler is unstably coupled to a motor. That is, the present invention provides a washing machine and an operating method thereof, which compensate for a coupling defect between a coupler and a motor. 
     To achieve these and other advantages and in accordance with the purpose of the disclosure, as embodied and broadly described herein, there is provided a washing machine comprising a pulsator shaft configured to rotate a pulsator, a drum shaft configured to rotate a drum, a carrier connected to the drum shaft, a motor comprising a stator and a rotor, a coupler spline-coupled to the carrier and detachably connected to the rotor, a clutch motor configured to raise or lower the coupler, and a controller configured to perform a first mode of controlling the clutch motor to a clutching mode and rotating the drum clockwise or counterclockwise at least once, a second mode of rotating the drum at a higher speed than the first mode, and a third mode of accelerating the drum, maintaining a rotation speed of the drum, and decelerating the drum. 
     The controller sequentially performs the first mode, the second mode, and the third mode. 
     In the second mode, the controller rotates the drum in one direction of a clockwise direction and a counterclockwise direction. 
     In the second mode, the controller rotates the drum in a direction which is opposite to a rotational direction of the drum in a previous dehydrating process. 
     A maximum rotation speed of the drum in the second mode is faster than a maximum rotation speed of the drum in the first mode and is equal to or slower than a maximum rotation speed of the drum in the third mode. 
     In each of the second mode and the third mode, the controller accelerates a rotation of the drum, and an acceleration of the drum in the second mode is 0.8 to 1.2 times an acceleration of the drum in the third mode. 
     In the first mode, the controller alternately rotates the drum clockwise and counterclockwise, in the second mode, the controller accelerates the drum up to a first target speed which is faster than a maximum speed in the first mode, and decelerates the drum, and in the third mode, the controller accelerates the drum up to the first target speed, maintains the first target speed as a uniform speed for a predetermined time, and decelerates the drum up to a second target speed which is slower than the first target speed. 
     The controller sequentially performs the first mode and the second mode, and in the third mode, the controller senses an amount of laundry. 
     In the third mode, the controller senses the amount of laundry, based on a time required for deceleration from the first target speed to the second target speed. 
     In the second mode, the controller sequentially performs a first process of stopping and maintaining the drum, a second process of accelerating the drum up to a first target speed after the first process and decelerating the drum, and a third process of stopping and maintaining the drum after the second process. 
     In the second mode, a time taken in the third process is longer than a time taken in the first process. 
     There is provided an operating method of a washing machine, the operating method comprising operating a drum accommodating a laundry in a first mode of rotating the drum clockwise or counterclockwise at least once, operating the drum in a second mode of rotating the drum at a speed which is higher than a rotation speed in the first mode, and operating the drum in a third mode of accelerating the drum, maintaining a rotation speed of the drum, and decelerating the drum. 
     In the second mode, the drum rotates in one direction of a clockwise direction and a counterclockwise direction. 
     In the second mode, the drum rotates in a direction which is opposite to a rotational direction of the drum in a previous dehydrating process. 
     A maximum rotation speed of the drum in the second mode is faster than a maximum rotation speed of the drum in the first mode and is equal to or slower than a maximum rotation speed of the drum in the third mode. 
     Each of the second mode and the third mode comprises a process of accelerating a rotation of the drum, and an acceleration of the drum in the second mode is 0.8 to 1.2 times an acceleration of the drum in the third mode. 
     In the first mode, the drum rotates alternately and repeatedly in a normal direction and a reverse direction, in the second mode, the drum is accelerated up to a first target speed which is faster than a maximum speed in the first mode, and is decelerated, and in the third mode, the drum is accelerated up to the first target speed, maintains the first target speed as a uniform speed for a predetermined time, and is decelerated up to a second target speed which is slower than the first target speed. 
     The first mode and the second mode are sequentially performed, and in the third mode, an amount of laundry is sensed. 
     In the third mode, the amount of laundry is sensed based on a time required for deceleration from the first target speed to the second target speed. 
     The operating of the drum in the second mode comprises sequentially performing a first process of stopping and maintaining the drum, a second process of accelerating the drum up to a first target speed after the first process and decelerating the drum, and a third process of stopping and maintaining the drum after the second process. 
     A time taken in the third process is longer than a time taken in the first process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view schematically illustrating a structure of a washing machine according to the present invention. 
         FIG. 2  is an enlarged view of a driving mechanism of the washing machine according to an embodiment of the present invention. 
         FIG. 3  is a side view of the coupler illustrated in  FIG. 2 . 
         FIG. 4  is a partial cut-away perspective view of the coupler illustrated in  FIG. 3 . 
         FIG. 5  is a diagram illustrating an example where a coupler according to an embodiment of the present invention is normally fastened to a rotor of a motor. 
         FIG. 6  is a diagram illustrating an example where the coupler according to an embodiment of the present invention is not normally fastened to the rotor of the motor. 
         FIG. 7  is a diagram for describing a problem caused by a fastening defect of the coupler according to an embodiment of the present invention. 
         FIG. 8  is a block diagram for describing a washing machine for performing a coupling defect compensation operation according to an embodiment of the present invention. 
         FIG. 9  is a flowchart illustrating a method of performing, by the washing machine according to an embodiment of the present invention, the coupling defect compensation operation. 
         FIG. 10  is a graph illustrating a rotation speed variation of a drum when a motor operates, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Hereinafter, embodiments relating to the present invention will be described in detail with reference to the accompanying drawings. 
     &lt;Washing Machine&gt; 
       FIG. 1  is a cross-sectional view schematically illustrating a structure of a washing machine according to the present invention. 
     Referring to  FIG. 1 , the washing machine according to the present invention may include a cabinet  4  where a laundry entrance  2  is provided in an upper portion thereof, a lid  6  which opens/closes the laundry entrance  2 , a tub  8  which is installed in the cabinet  4  to store washing water, a drum  10  which is rotatably provided in the tub  8  to accommodate the laundry, a pulsator  12  which is installed in a lower end of the drum  10  and stirs from side to side to generate a water flow, and a driving mechanism  14  which is installed to rotate the drum  10  and the pulsator  12 . 
     The cabinet  4  may form an external appearance of the washing machine. The cabinet  4  may include a base  16 , a cabinet body  18  which is disposed on the base  16 , and a top cover  20  which is disposed on a top of the cabinet body  18  and where the laundry entrance  20  is provided. 
     A control panel  22  for controlling the washing machine and displaying information about the washing machine may be installed in the cabinet  4 . A plurality of water supply valves  30  through which water such as hot water and cold water is supplied may be installed inside the control panel  22 . 
     The lid  6  may be a type of door which opens the laundry entrance  2  in a laundry loading/unloading process and closes the laundry entrance  2  in a washing, rinsing, or dehydrating process. The lid  6  may be provided to be opened upward and closed downward with respect to a rear portion. 
     The tub  8  may be an external tank or a water storing tank in which washing water or rinsing water is put in washing or rinsing and which collects water flowing out from the drum  10  in dehydration. A top of the tub  8  may be opened for loading or unloading the laundry. 
     The tub  8  may include a tub body  35  and a tub cover  36  installed on the tub body  35 . 
     The tub  8  may be connected to the cabinet  4  by a suspension mechanism  37 . 
     A drainage mechanism  38 , through which washing water, rinsing water, or water dehydrated from the laundry is drained, may be connected to the tub  8 . The drainage mechanism  38  may include a drainage valve controlled by the control panel  22  and a drainage hose connected to the drainage valve. 
     The drum  10  may be an internal tank or a washing tank, in which the laundry is put. A top of the drum  10  may be opened for taking in or out the laundry, and the drum  10  may be rotatably disposed inside the tub  8 . 
     The drum  10  may include a plurality of water holes  40  through which washing water or rinsing water moves to the inside or outside of the drum  10  and through which water dehydrated from the laundry is discharged to the outside of the drum  10 . 
     The drum  10  may be provided in a hollow cylindrical shape. The drum  10  may include a drum body  42  which forms a perimeter appearance of the drum  10  and a drum base  44  which is coupled to a lower portion of the drum body  42  and forms a lower appearance of the drum  10 . 
     A pulsator shaft  56  may pass through a center of the drum base  44 . A center hole  45 , through which washing water, rinsing water, and water dehydrated from the laundry passes, may be provided in the drum base  44 . 
     A hub  62 , which is connected to the driving mechanism  14  to transfer a rotational force of the driving mechanism  14  to the drum  10 , may be installed in the drum  10 . 
     A center of the hub  62  may be connected to a drum shaft  58  of the driving mechanism  14 , and a portion, other than the center, of the hub  62  may be connected to the drum base  44  by a plurality of fastening members. Therefore, the hub  62  may transfer the rotational force, transferred through the drum shaft  58 , to the drum base  44  through a plurality of portions other than the center. 
     The pulsator  12  may stir washing water, rinsing water, and the laundry while rotating inside the drum  10 . The driving mechanism  14  may be connected to the pulsator shaft  56 . 
     &lt;Driving Mechanism&gt; 
       FIG. 2  is an enlarged view of a driving mechanism of the washing machine according to an embodiment of the present invention. 
     As illustrated in  FIG. 2 , the driving mechanism  14  may rotate the pulsator  12 , or may rotate both the pulsator  12  and the drum  10 . The driving mechanism  14  may include a motor  54  which is a driving source, the pulsator shaft  56  which is connected to the pulsator  12 , the drum shaft  58  which is installed to rotate the drum  10 , and a clutch  60  which transfers a driving force of the motor  54  to the pulsator shaft  56  or transfers the driving force of the motor  54  to both the pulsator shaft  56  and the drum shaft  58 . 
     The motor  54  may include a stator  54 A coupled to the clutch  60 , a rotor  54 B rotated by the stator  54 A, and a rotational shaft  54 C connected to the rotor  54 B. 
     The drum shaft  58  may be configured as a hollow shaft in order for the pulsator shaft  56  to be rotatably located therein, and an upper portion thereof may be connected to the hub  11 . 
     The driving shaft may include the pulsator shaft  56  and the drum shaft  58  which is a hollow tube configuring a concentric circle with the pulsator shaft  56  and is connected to the drum  10 . 
     The clutch  60  may include a bearing housing  62  which is fixed to a lower portion of the tub  8 , a carrier  64  which is rotatably installed in the bearing housing  62  and is connected to the drum shaft  58 , a planet gear set  66  which is disposed in the carrier  66  so as to reduce a dynamic force of the motor  54  and is connected to the pulsator shaft  56 , and a clutch mechanism  68  which is installed under the carrier  64  to control dynamic force transfer between the motor  54  and the carrier  64 . 
     A plurality of ball bearings  70  may be provided in the bearing housing  62  and may rotatably support the carrier  64  and the drum shaft  58 . 
     The motor  54  may be equipped in the bearing housing  62  so that the stator  54 A is disposed under the carrier  64 , and the rotational shaft  54 C may pass through the stator  54 A and may be connected to the planet gear set  66  disposed in the carrier  64 . 
     The clutch mechanism  68  may include a clutch motor  72  which is provided on a bottom of the tub  8 , a clutch lever  74  which is connected to the clutch motor  72  at one side thereof, and a coupler  76  which is connected to the other side of the clutch lever  74  and is movably spline-coupled to a lower portion of the carrier  64  in order for the rotational force of the motor  54  to be selectively transferred/blocked to the carrier  64 . 
     A stopper  78  for restraining the coupler  76  may be installed in the bearing housing  62 . 
     A plurality of projections  80  may be provided on a top of the coupler  76 , and a plurality of projection inserting grooves  82  which the plurality of projections  80  are respectively inserted into and hung on may be provided in the stopper  78 . 
     A motor coupling part  84  which is coupled to or detached from the motor  54  (for example, the rotor  54 B) may be provided in the coupler  76 , and a coupler coupling part  86  which the motor coupling part  84  is lowered and inserted into and which the motor coupling part is raised and detached from may be provided in the rotor  54 B. 
     &lt;Coupler&gt; 
       FIG. 3  is a side view of the coupler illustrated in  FIG. 2 , and  FIG. 4  is a partial cut-away perspective view of the coupler illustrated in  FIG. 3 . 
     As illustrated in  FIG. 3 , the coupler  76  may include the plurality of projections  80  assembled or disassembled to or from the stopper  78 , the motor coupling part  84  coupled to or detached from the motor  54 , and a carrier coupling part  94  spline-coupled to the carrier  64 . 
     The carrier coupling part  94  may be provided in a spline tooth shape so that the coupler  76  engages with an outer circumference surface of the carrier  64  to rotate when the coupler  76  is coupled to the carrier  64 . The carrier coupling part  94  may be provided in a shape which engages with a spline groove provided in an outer circumference surface of the carrier coupling part  94 . 
     When the coupler  76  moves in an axial direction (i.e., an ascending direction), the carrier coupling part  94  may move while sliding along a spline groove provided in the carrier  64 , and when the coupler  76  rotates, the carrier coupling part  94  may rotate along with the carrier  64 . 
     The coupler  76  may be provided in a hollow cylindrical shape. The coupler  76  may include a cylindrical part  100 , where the carrier coupling part  94  spline-coupled to the carrier  64  is provided on an internal circumference surface of the coupler  76  and the motor coupling part  84  is provided in a lower portion thereof, and a horizontal part  102  which protrudes horizontally from an outer circumference of the cylindrical part  100  and where the plurality of projections  80  are provided on a top thereof. 
     &lt;Pulsator Rotation Based on Raising of Coupler&gt; 
     In a process of driving the motor  54 , when the clutch motor  72  is driven in a pulsator rotation mode, the clutch lever  74  may raise the coupler  76 . The coupler  76  may be raised along the carrier  64 , and the motor coupling part  84  may be detached from the rotor  54 A of the motor  54 . At this time, the plurality of projections  80  of the coupler  76  may be inserted into the projection inserting grooves  82  of the stopper  78  and restrained, and thus, without the projections  80  rotating, the drum  10  may not rotate. 
     At this time, the planet gear set  66  may rotate the pulsator shaft  56  in cooperation with driving of the motor  54 , and the pulsator shaft  56  may rotate the pulsator  12 . 
     &lt;Drum Rotation Based on Lowering of Coupler&gt; 
     In a process of driving the motor  54 , when the clutch motor  72  is driven in a drum simultaneous rotation mode, the clutch lever  74  may lower the coupler  76 . Since the coupler  76  is lowered, the plurality of projections  80  may be detached from the projection inserting grooves  82  of the stopper  78 , and the motor coupling part  84  may be coupled to the rotor  54 A of the motor  54 . 
     At this time, the coupler  76  may transfer a driving force of the motor  54  to the carrier  64 . When the carrier  64  rotates, the drum shaft  58  may rotate along with the carrier  64 , and the drum shaft  58  may rotate the drum  10 . 
     &lt;Coupler Unfastened&gt; 
     In a process of lowering the coupler  76 , the motor coupling part  84  may be unstably coupled to the rotor  54 B. 
       FIG. 5  is a diagram illustrating an example where a coupler according to an embodiment of the present invention is normally fastened to a rotor of a motor, and  FIG. 6  is a diagram illustrating an example where the coupler according to an embodiment of the present invention is not normally fastened to the rotor of the motor. 
     The coupler coupling part  86  selectively coupled/detached to/from the coupler  76  may be provided in the rotor  54 B of the motor  54 , and a coupler coupling groove  87  into which the motor coupling part  84  provided in the coupler  76  is inserted may be provided in the coupler coupling part  86 . 
     Therefore, in a process of lowering the coupler  76 , when the motor coupling part  84  is inserted into the coupler coupling groove  87 , the coupler  76  may be fastened to the motor  54 , and in a process of lowering the coupler  76 , when the motor coupling part  84  is not inserted into the coupler coupling groove  87 , the coupler  76  may not normally be fastened to the motor  54 . 
     In a case where a controller  90  lowers the coupler  76 , the controller  90  cannot know a position relationship between the motor coupling part  84  and the coupler coupling groove  87 . For this reason, as illustrated in  FIG. 5 , the motor coupling part  84  may be inserted into the coupler coupling groove  87 , or as illustrated in  FIG. 6 , the motor coupling part  84  may not be inserted into the coupler coupling groove  87 . 
     In this case, the motor  54  may be driven in order for the coupler  76  to be normally fastened. That is, the motor  54  may rotate the rotor  54 B at a predetermined rotation speed so that, when the coupler  76  is lowered, the motor coupling part  84  is inserted into the coupler coupling groove  87 . Based on the rotation of the rotor  54 B, the motor coupling part  84  which is not yet inserted into the coupler coupling groove  87  may be inserted into the coupler coupling groove  87 . 
     However, despite driving of the motor  54 , a fastening defect where the coupler  76  is not normally fastened may occur. 
     In this manner, in a state where a fastening defect where the coupler  76  is not normally fastened occurs, when a subsequent washing process is performed, the motor  54  may be driven and the rotor  54 B may rotate, whereby the coupler  76  may be fastened to the motor  54 . 
     However, if a washing process performed immediately after a fastening defect occurs is a washing process of sensing data such as sensing the amount of laundry, the coupler  76  may be fastened in a subsequent washing process, and an abnormal value may occur in the data. 
       FIG. 7  is a diagram for describing a problem caused by a fastening defect of the coupler according to an embodiment of the present invention. 
     A graph illustrated in  FIG. 7  represents a rotation speed of the drum  10  with respect to a time. 
     A fastening period may be a period where the clutch mode  72  operates in a clutching mode. That is, a fastening period may be a period where the clutch motor  72  lowers the coupler  76  in order for the coupler  76  to be fastened to the motor  54 . 
     The motor  54  may be driven in order for the motor coupling part  84  to be coupled to the rotor  54 B in the fastening period. A first graph  901  may show a rotation speed of the drum  10  in the fastening period. 
     According to the first graph  901 , in the fastening period, a maximum rotation speed of the drum  10  may be a first rotation speed. The first rotation speed may be 10 RPM, but this is merely an embodiment. 
     A laundry amount sensing period may be a period where the amount of laundry included in the drum  10  is sensed. The laundry amount sensing period may be a period where the motor  54  is driven at a certain driving speed to rotate the drum  10 , and thus, the amount of laundry is sensed. 
     Sensing the amount of laundry may be performed by rotating the pulsator  12 , or may be performed by rotating both the pulsator  12  and the drum  10 . In the present invention, an example where sensing the amount of laundry is performed by rotating both the pulsator  12  and the drum  10  will be described below. 
     The motor  54  may be driven for sensing the amount of laundry. A second graph  902  may show a driving speed of the motor  54  in the laundry amount sensing period. 
     According to the second graph  902 , in the laundry amount sensing period, a maximum rotation speed of the drum  10  may be a second rotation speed. The second rotation speed may be 50 RPM, but this is merely an embodiment. 
     Referring to the second graph  902 , the laundry amount sensing period may include a bounce period  910 . The bounce period  910  may denote a period where a rotation speed of the drum  10  temporarily varies by a certain value or more. In the bounce period  910 , when the coupler  75  is not normally fastened, a rotation speed of the drum  10  may increase, and due to this, the motor coupling part  84  provided in the coupler  76  may be inserted into the coupler coupling groove  87  provided in the rotor  54 B. 
     As described above, when the bounce period  910  occurs in the laundry amount sensing period, a laundry amount value which is a laundry amount sensing result may be sensed as an abnormal value. For this reason, since the amount of laundry is not accurately sensed, the amount of washing water, the amount of detergent, a washing intensity, and the like may be abnormally set, and due to this, energy may be wasted or a washing process may not normally be performed, causing the reduction in reliability. 
     Therefore, the washing machine according to an embodiment of the present invention may sequentially perform the clutching mode of lowering the coupler  76 , a mode of compensating for a coupling defect of the coupler  76 , and the laundry amount sensing mode. 
       FIG. 8  is a block diagram for describing a washing machine for performing a coupling defect compensation operation according to an embodiment of the present invention, and  FIG. 9  is a flowchart illustrating a method of performing, by the washing machine according to an embodiment of the present invention, the coupling defect compensation operation. 
     The washing machine according to an embodiment of the present invention may include a coupler  76 , a clutch motor  72 , a motor  54 , a laundry amount sensing unit  81 , and a controller  90 . The controller  90  may control the clutch motor  72 , the motor  54 , and the laundry amount sensing unit  81 . Also, the washing machine according to an embodiment of the present invention may further include other elements in addition to the elements illustrated in  FIG. 8 . 
     The coupler  76 , the clutch motor  72 , and the motor  54  are the same as the above descriptions, and thus, their detailed descriptions are omitted. 
     The laundry amount sensing unit  81  may rotate the drum  10  to sense the amount of laundry included in the drum  10 . 
     According to an embodiment, the controller  90  may rotate the drum  10  at a laundry amount sensing rotation speed in a laundry amount sensing mode, and at this time, the laundry amount sensing unit  81  may measure a time for which a rotation speed of the drum  10  is decelerated, thereby sensing the amount of laundry. 
     The laundry amount sensing rotation speed may include a period where a rotation speed is accelerated to a first target speed, maintained as a uniform speed, and decelerated to a second target speed. 
     For example, the laundry amount sensing unit  81  may sense a laundry amount level in proportion to a time for which a rotation speed of the drum  10  is decelerated. That is, as a time for which a rotation speed of the drum  10  is decelerated becomes longer, the laundry amount sensing unit  81  may sense a laundry amount level as a high level. The laundry amount sensing unit  81  may sense that a first laundry amount level when a time for which a rotation speed of the drum  10  is decelerated is a first time is higher than a second laundry amount level when a time for which a rotation speed of the drum  10  is decelerated is a second time. 
     The laundry amount sensing unit  81  may measure a time for which a rotation of the drum  10  is accelerated when rotating the drum  10 , thereby sensing the amount of laundry. 
     However, a laundry amount sensing method is technology known to those skilled in the art, and thus, its detailed description is omitted. The present embodiment is not limited to the above-described laundry amount sensing method. 
     The controller  90  may control an overall operation of the washing machine. 
     In detail, the controller  90  may control the clutch motor  72  in order for the coupler  76  to be raised or lowered. Also, the controller  90  may perform control to rotate the motor  54 , or may perform control in order for the laundry amount sensing unit  81  to sense the amount of laundry. 
     According to an embodiment of the present invention, the controller  90  may control the clutch motor  72  to the clutching mode, and the clutch motor  72  may lower the coupler  76  in the clutching mode. 
     As illustrated in  FIG. 9 , the controller  90  may control the clutch motor  72  in order for the coupler  76  to be lowered (S 11 ). 
     At this time, based on a position of the coupler  76  and a position of the rotor  54 B of the motor  54 , the motor coupling part  84  provided in the coupler  76  may be inserted or not into the coupler coupling groove  67  provided in the rotor  54 B. 
     Therefore, the controller  90  may control the drum  10  to a first mode of clockwise or counterclockwise rotating the drum  10  (S 13 ). 
     That is, the controller  90  may control the clutch motor  72  to the clutching mode and may control the drum  10  to the first mode of clockwise or counterclockwise driving the drum  10  at a first rotation speed. In the first mode, the drum  10  may rotate at the first rotation speed, and the rotor  54 B may alternately and repeatedly rotate in a clockwise direction and a counterclockwise direction. In the first mode, the rotor  54 B may rotate in the clockwise direction and the counterclockwise direction at least once. In such a process, the motor coupling part  84  provided in the coupler  76  may be inserted into the coupler coupling groove  67  provided in the rotor  54 B. 
     The controller  90  may control the drum  10  to the first mode, and then, may control the drum  10  to a second mode of rotating the drum  10  at a higher speed than the first mode (S 15 ). 
     That is, the controller  90  may control the first mode to the second mode so as to compensate for a case where the coupler  76  is not normally fastened to the rotor  54 B in the first mode. 
     In the second mode, the controller  90  may rotate the drum  10  in one of the clockwise direction and the counterclockwise direction. 
     In the second mode, the controller  90  may rotate the drum  10  in one of the clockwise direction and the counterclockwise direction once. 
     In the second mode, the controller  90  may sequentially perform a first process of stopping and maintaining the drum  10 , a second process of accelerating a rotation speed of the drum  10  up to a target speed after the first process and decelerating the drum  10 , and a third process of stopping and maintaining the drum  10  after the second process. 
     The first process may be a process of initializing a rotation speed value of the drum  10  after performing the first mode. 
     A rotation speed of the drum  10  may be more accurately measured in a case, where the first process is performed before the drum  10  is accelerated (the second process) to the target speed in the second mode after the first mode is performed, than a case where the first process is not performed before the drum  10  is accelerated (the second process) to the target speed in the second mode after the first mode is performed. That is, when the first process is performed, whether to reach the target speed may be accurately measured, thereby enhancing reliability. 
     The second process may be a process of rotating the rotor  54 B in order for the coupler  76  to be normally fastened to the rotor  54 B. 
     According to an embodiment, the controller  90  may rotate in a direction opposite to a direction in which the rotor  54 B rotates in a dehydrating process. In this case, the rotor  54 B may rotate in a direction opposite to a direction in which the rotor  54 B rotates at a high speed in a previous washing process, and thus, a relatively stronger torque may be applied thereto and the coupler  65  may be much better coupled to the rotor  54 B. 
     According to an embodiment, the controller  90  may perform control in order for the drum  10  to rotate at a faster second rotation speed than a first rotation speed in the second mode. In detail, a maximum rotation speed of the drum  10  in the second mode may be faster than a maximum rotation speed of the drum  10  in the first mode and may be equal to or slower than a maximum rotation speed of the drum in a below-described third mode. 
     When the drum  10  rotates at the faster second rotation speed than the first rotation speed in the second mode, the rotor  54 B may rotate at a high speed while a force is being applied in a downward direction in which the rotor  54 B is located, and thus, the coupler  76  may be coupled to the rotor  54 B. Accordingly, a probability that a bounce phenomenon occurs in the laundry amount sensing mode may be minimized. 
     Moreover, when the drum  10  rotates at the second rotation speed equal to or slower than a maximum rotation speed in sensing the amount of laundry in the second mode, the damage of the motor  54  or the coupler  76  caused by the very fast-speed driving of the drum  10  may be minimized. 
     According to another embodiment, the controller  90  may accelerate the drum  10  in each of the second mode and the below-described third mode, and at this time, the controller  90  may perform control so that an acceleration of the drum  10  in the second mode is equal to an acceleration of the drum  10  in the third mode. For example, an acceleration of the drum  10  in the second mode may be 0.8 to 1.2 times an acceleration of the drum  10  in the third mode. 
     For example, an acceleration of the drum  10  may be 24 rpm/s, but this is merely an embodiment. The present embodiment is not limited thereto. 
     As described above, driving may be performed similar to a driving pattern of the motor  54  in the laundry amount sensing mode before performing the laundry amount sensing mode, and thus, a possibility that a bounce phenomenon occurs in the laundry amount sensing mode may be minimized, thereby enhancing accuracy in sensing the amount of laundry. 
     The third process may be a process of initializing a driving speed value of the drum  10  after performing the second process. 
     A rotation speed of the drum  10  may be more accurately measured in a case, where the third process is performed before the drum  10  is driven (the third mode) at a laundry amount sensing rotation speed after the second mode is performed, than a case where the third process is performed before the drum  10  is driven (the third mode) at the laundry amount sensing rotation speed after the second mode is performed. That is, when the third process is performed, the laundry amount sensing rotation speed may be accurately measured, thereby enhancing reliability. 
     A time taken in the third process may be longer than a time taken in the first process. A rotation speed of the drum  10  before performing the third process may be faster than a rotation speed of the drum  10  before performing the first process, and thus, a time taken in the third process may be longer than a time taken in the first process. 
     Control may be performed so that a time taken in the first process is longer than a time taken in the third process, thereby minimizing a time taken in the second mode. 
     The controller  90  may control the drum  10  to the first mode and the second mode, and then, may control the drum  10  to the third mode of rotating the drum  10  at the laundry amount sensing rotation speed (S 17 ). 
     That is, the controller  90  may drive the drum  10  at the laundry amount sensing mode, and in the laundry amount sensing mode, the drum  10  may be driven at the laundry amount sensing rotation speed. 
     Here, the third mode may be a mode of rotating the drum  10  at the laundry amount sensing mode. In the third mode, the controller  90  may accelerate the drum  10  up to the first target speed, maintain the first target speed as a uniform speed for a predetermined time, and decelerate the drum up to a second target speed. Here, the second target speed may be a speed which is set slower than the first target speed. 
     The controller  90  may additionally perform a process of maintaining a rotation speed of the drum  10  at the second target speed. 
     That is, the laundry amount sensing mode may be a mode of accelerating a rotation speed of the drum  10  to the first target speed, maintaining the rotation speed of the drum  10  as a uniform speed, decelerating the rotation speed of the drum  10  to the second target speed in the middle of maintaining the uniform speed, and maintaining a decelerated rotation speed. 
     The second rotation speed of the second mode according to an embodiment of the present invention may be the same speed as the first target speed and may be a rotation speed within an error range (−10% to +10%) of the first target speed. 
     A drum acceleration of the second mode according to an embodiment of the present invention may be an acceleration the same speed as the first target speed and may be an acceleration within an error range (−20% to +20%) of an acceleration up to the first target speed in the third mode. 
     The controller  90  may control the drum  10  to the third mode, and then, may sense the amount of laundry (S 19 ). 
     That is, the controller  90  may sequentially perform the first mode, the second mode, and the third mode, and then, may sense the amount of laundry. 
     As described above, when the amount of laundry is sensed after compensating for a fastening defect of the coupler  76 , the amount of laundry may be accurately sensed, and thus, it is possible to more accurately control the amount of supplied water. Accordingly, the amount of wasted washing water may be minimized, and the laundry may be washed at an appropriate washing intensity. 
       FIG. 10  is a graph illustrating a rotation speed variation of a drum when a motor operates, according to an embodiment of the present invention. 
     The graph illustrated in  FIG. 10  shows a rotation speed of the drum  10  with respect to a time. 
     A fastening period may be a period where the drum  10  operates in the first mode. A first graph  901  may show the first rotation speed at which the drum  10  rotates in the first mode. 
     A compensation period may be a period where the drum  10  operates in the second mode. A second graph  903  may show the second rotation speed at which the drum  10  rotates in the second mode. 
     A laundry amount sensing period may be a period where the drum  10  operates in the third mode (the laundry amount sensing mode). A third graph  902  may show the laundry amount sensing rotation speed at which the drum  10  rotates. 
     As illustrated in  FIG. 10 , a maximum rotation speed of the second graph  903  may be faster than a maximum rotation speed of the first graph  901 , and a maximum rotation speed of the second graph  903  may be equal to a maximum rotation speed of the third graph  902 . Depending on the case, a maximum rotation speed of the second graph  903  may be slower than a maximum rotation speed of the third graph  902 . 
     Moreover, an acceleration period acceleration of the second graph  903  may be equal to an acceleration period acceleration of the third graph  902 . 
     As the drum  10  rotates as described above, the coupler  76  may be completely coupled to the rotor  54 B through a fastening operation and a fastening compensation operation in lowering the coupler, and a possibility that a bounce period occurs in the laundry amount sensing period may be minimized. That is, a possibility that the bounce period occurs in the first graph  901  and the second graph  902  may be greater than a possibility that the bounce period occurs in the third graph  903 . Accordingly, accuracy in sensing the amount of laundry may be enhanced, and an abnormal value in sensing the amount of laundry may be removed. 
     According to an embodiment of the present invention, a coupling defect where a coupler included in a washing machine is unstably coupled to a motor is minimized. Accordingly, an error occurrence possibility caused by a coupling detect of the coupler may be minimized in sensing the amount of laundry, and the amount of laundry may be more accurately sensed. 
     According to an embodiment of the present invention, without further adding a separate element, a fastening defect of the coupler may be compensated for by controlling the motor in the clutching mode, and thus, the increase in cost for enhancing a coupling rate of the coupler may be minimized and the reliability of a washing machine may be enhanced. 
     Moreover, according to an embodiment of the present invention, a probability that the coupler and the motor are damaged due to the excessive increase in a rotation speed of the motor may be minimized. 
     The description above is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. 
     Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. 
     The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as being included in the scope of the present invention.