[0001]    This application claims the benefit of Korean Patent Application No. 10-2015-0129959, filed on Sep. 14, 2015, which is hereby incorporated by reference as if fully set forth herein. 
       FIELD 
       [0002]    The present disclosure relates to a control method for a laundry treatment apparatus. 
       BACKGROUND 
       [0003]    A laundry treatment apparatus can include a cabinet defining the external appearance of the apparatus, a first reservoir placed inside the cabinet and configured to store water therein, and a second reservoir rotatably placed inside the first reservoir and configured to receive laundry therein. 
         [0004]    The laundry treatment apparatus having the above-described configuration is adapted to wash laundry using, for example, the emulsification of detergent and water streams produced by rotation of the second reservoir. In some cases, impurities may adhere to the inside of the first reservoir and the outer circumferential surface of the second reservoir after the long-term use of the laundry treatment apparatus. 
       SUMMARY 
       [0005]    According to one aspect, a control method for a laundry treatment apparatus—where the laundry treatment apparatus includes a first reservoir configured to hold water and defining a first opening for introduction of laundry, a second reservoir placed inside the first reservoir and configured to receive laundry, the second reservoir being configured to rotate about a rotation axis perpendicular to a bottom surface of the first reservoir and defining a second opening that is positioned under the first opening, a through-hole that is defined in the second reservoir, a spray unit configured to spray water to an inside of the second reservoir, and a drain unit configured to drain water inside the first reservoir—includes rotating the second reservoir to thereby apply force on laundry received in the second reservoir, spraying water to the inside of the second reservoir via the spray unit, and discharging the sprayed water in the second reservoir to an outside of the first reservoir via the drain unit. 
         [0006]    Implementations according to this aspect may include one or more of the following features. For example, the control method may further include draining the water in the first reservoir to the outside of the first reservoir via the drain unit, where the rotating, the spraying, and the discharging steps may be initiated after completion of the draining step. The rotating step and the spraying step may be implemented to at least partially overlap with each other during an overlapping period. The rotating, the spraying, and the discharging steps may be implemented to at least partially overlap with one another during an overlapping period. Additionally, in the spraying step, the spray unit may spray water that is supplied from a water source to a circumferential surface of the second reservoir. Also, in the spraying step, the spray unit may spray water that is supplied from a water source to a circumferential surface of the second reservoir and a bottom surface of the second reservoir. Further, in the spraying step, the spray unit may spray water to cover a region ranging from a first point to a second point, the first point being located between a corner, at which the circumferential surface of the second reservoir and the bottom surface of the second reservoir meet each other, and a center of rotation of the second reservoir, and the second point being located between the corner and the second opening. 
         [0007]    In some cases, the spraying step may include a first operation of spraying water and a second operation of stopping the spraying of water. The first operation may have an implementation time that is longer than an implementation time of the second operation. The spraying step may be performed as a sequence where the first operation is followed by the second operation, or where the first operation is followed by the second operation and then followed by the first operation. Additionally, the rotating step may include increasing the number of revolutions per minute of the second reservoir to a predetermined reference number of revolutions per minute, and maintaining the number of revolutions per minute of the second reservoir at the reference number of revolutions per minute, where the spraying and the discharging steps may be performed during the step of increasing the number of revolutions per minute of the second reservoir. The providing step may include primarily increasing the number of revolutions per minute of the second reservoir to a predetermined first number of revolutions per minute, maintaining the number of revolutions per minute of the second reservoir at the first number of revolutions per minute, and secondarily increasing the number of revolutions per minute of the second reservoir to a predetermined reference number of revolutions per minute, which is set to be higher than the first number of revolutions per minute. The spraying and the discharging steps may be performed during the step of maintaining the number of revolutions per minute of the second reservoir at the first number of revolutions per minute. The control method may further include measuring a magnitude of vibration generated at the second reservoir during rotation of the second reservoir, where the measuring step may be performed while the second reservoir is rotated at the first number of revolutions per minute and the step of secondarily increasing the number of revolutions per minute of the second reservoir may be initiated based on the vibration measured in the measuring being a predetermined reference value or less. 
         [0008]    In some implementations, the control method may further include supplying water to the first reservoir via a water supply unit connected to a water source, rotating the second reservoir so as to cause friction between the water and the laundry in the second reservoir, and draining the water inside the first reservoir to the outside of the first reservoir via the drain unit after completion of the rotating, wherein the providing, the spraying, and the discharging steps may be initiated after completion of the draining. The rotating step may include rotating the second reservoir such that the water inside the first reservoir is raised to a height of the second opening by centrifugal force. The rotating step may include controlling the number of revolutions per minute of the second reservoir so as to restrict the water from entering the second reservoir through the second opening. In some cases, the rotating step may include performing a primary rotation of the second reservoir, performing an intermediate draining of draining the water in the first reservoir, performing a secondary rotation of the second reservoir, performing an intermediate spraying of spraying water to the inside of the second reservoir via the spray unit while the secondary rotation step is being performed, and performing an intermediate discharging of discharging the water sprayed during the intermediate spraying to an outside of the first reservoir via the drain unit while the secondary rotation step is being performed. The number of revolutions per minute of the second reservoir in the secondary rotation step may be set to be higher than the number of revolutions per minute of the second reservoir set in the primary rotation step, and may be set to be lower than the number of revolutions per minute of the second reservoir set in the rotating step. 
         [0009]    According to another aspect, a control method for a laundry treatment apparatus—where the laundry treatment apparatus includes a first reservoir configured to hold water and defining a first opening for introduction of laundry, a second reservoir placed inside the first reservoir and configured to receive laundry, the second reservoir being configured to rotate about a rotation axis perpendicular to a bottom surface of the first reservoir and defining a second opening that is positioned under the first opening, a through-hole that is defined in the second reservoir, a spray unit configured to spray water to an inside of the second reservoir, and a drain unit configured to drain water inside the first reservoir—includes supplying water to the first reservoir via a water supply unit connected to a water source, performing a primary rotation of the second reservoir, draining the water stored in the first reservoir, performing a secondary rotation the second reservoir so as to apply force on the laundry inside the second reservoir, spraying water to the inside of the second reservoir via the spray unit, discharging the water supplied to the second reservoir in the spraying to an outside of the first reservoir via the drain unit, and performing a tertiary rotation of the second reservoir so as to apply force on the laundry inside the second reservoir. The number of revolutions per minute of the second reservoir in the secondary rotation step is set to be lower than the number of revolutions per minute of the second reservoir in the tertiary rotation step, and is set to be higher than the number of revolutions per minute of the second reservoir set in the primary rotation step. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In the drawings: 
           [0011]      FIG. 1  is a partial cross-sectional view illustrating an exemplary laundry treatment apparatus; 
           [0012]      FIG. 2  is a schematic view illustrating an exemplary spray unit; 
           [0013]      FIG. 3  is a flowchart illustrating an exemplary control method for a laundry treatment apparatus; 
           [0014]      FIG. 4  is a schematic view illustrating an exemplary motion that washes reservoirs while washing or rinsing of laundry is being performed; 
           [0015]      FIG. 5  is a schematic view illustrating an exemplary jet spray motion that washes reservoirs while dehydration of laundry is being performed; 
           [0016]      FIGS. 6A and 6B  are example plots illustrating variations in the number of the revolutions per minute (RPM) of a second reservoir in a centrifugal force providing operation; and 
           [0017]      FIG. 7  is an example plot illustrating another implementation of the control method. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  shows an exemplary laundry treatment apparatus  100  according to one implementation. The laundry treatment apparatus  100  according to the present disclosure may include a cabinet  1 , a first reservoir  3  which is placed inside the cabinet  1  and configured to store water therein, and a second reservoir  5  which is rotatably placed inside the first reservoir  3  and configured to receive laundry therein. 
         [0019]    The cabinet  1  may include a cabinet body  11  which provides a space in which the first reservoir  3  is received, and a cabinet cover  12  provided at the top of the cabinet body  11 . 
         [0020]    The cabinet cover  12  has a cabinet opening  121 , through which laundry may be introduced into or removed from the cabinet  1 . The cabinet opening  121  may be opened or closed by a door  13  provided at the cabinet cover  12 . 
         [0021]    In addition, the cabinet cover  12  may be further provided with an input unit  17  which allows a user to input a control command to the laundry treatment apparatus  100 , and a display unit  19  which allows the user to check the control command input via the input unit  17  or may indicate, for example, the implementation of the control command input by the user. 
         [0022]    The first reservoir  3  may include a first body  31  which provides a space in which water is stored. The first body  31  may be secured to the cabinet body  11  using a support unit  15 . The support unit  15  may be configured to alleviate vibration when the first body  31  vibrates. 
         [0023]    The first body  31  may take the form of a cylinder having an open top, and a cover  33  may be provided at the top of the first body  31 . The cover  33  has a first opening  35  which can fluidically communicate with the cabinet opening  121 . 
         [0024]    The second reservoir  5  may include a second body  51  which is placed inside the first reservoir  3  and provides a space in which laundry is received. The second body  51  may take the form of an empty cylinder. The second body  51  may fluidically communicate with the first opening  35  and the cabinet opening  121  via a second opening  53 . 
         [0025]    The second body  51  may include through-holes  55  that are defined in at least one of the circumferential surface or the bottom surface thereof. As such, the through-holes  55  may allow water inside the second body  51  to move to the first body  31  therethrough, and may allow water supplied to the first body  31  to be supplied into the second body  51  therethrough. 
         [0026]    The second body  51  described above may be adapted to be rotated by a drive unit  57 . The drive unit  57  may include a stator  571  secured to the bottom surface of the first body  31  so as to be located outside the first body  31 , a rotor  573  configured to be rotated by a rotational magnetic field provided by the stator  571 , and a rotating shaft  575  penetrating the first body  31  to connect the bottom surface of the second body  51  and the rotor  573  to each other. 
         [0027]      FIG. 1  illustrates, as an example, the case where the rotating shaft  575  is perpendicular to the bottom surface of the first body  31 . In this case, the second opening  53  may be formed in the top of the second body  51 , so as to be located under the first opening  35 . 
         [0028]    The laundry treatment apparatus  100  having the above-described configuration may be adapted to supply water to the first reservoir  3  using a water supply unit and to discharge the water inside the first reservoir  3  to the outside of the cabinet  1  using a drain unit. 
         [0029]    The water supply unit may include a first supply pipe  71  connected to a water source to supply water to the first body  31 , and a value  77  to open or close the first supply pipe  71 . The drain unit may include a drain pipe  81  to guide the water inside the first body  31  to the outside of the cabinet  1 , and a pump  83  to move the water inside the first body  31  to the drain pipe  81 . 
         [0030]    In addition, the laundry treatment apparatus  100  may further include a spray unit  9  which sprays water, supplied from the water source, to the inside of the second body  51 . As exemplarily illustrated in  FIG. 2 , the spray unit  9  may include a connection pipe  93  secured to the cabinet cover  12  and a nozzle  91  configured to spray water supplied from the connection pipe  93  to the inside of the second body  51 . 
         [0031]    The connection pipe  93  may directly receive water from the water source, or may receive water through a second supply pipe  75  that diverges from the first supply pipe  71 . In the latter case, the valve  77  may be located at the point at which the first supply pipe  71  and the second supply pipe  75  diverge so as to control the opening or closing of the first supply pipe  71  and the second supply pipe  75 . 
         [0032]    The nozzle  91  may be provided at the edge of the cabinet opening  121  at a position spaced apart, by a prescribed distance, from a virtual line L 1  which passes through the rotating shaft  575  of the second body  51  and may be perpendicular to the rear surface of the cabinet  1  (or the front surface of the cabinet  1 ). 
         [0033]    The nozzle  91  may be located at any of the front side and the rear side of a virtual line L 2  which passes through the rotating shaft  575  and may be perpendicular to the side surface of the cabinet  1 .  FIG. 2  illustrates the exemplary case where the nozzle  91  is located at the rear side of the virtual line L 2 . In this case, the length of the second supply pipe  75  may be minimized, which may minimize loss in the pressure of water ejected from the nozzle  91 . 
         [0034]    In some cases, the nozzle  91  may be provided to spray water, supplied from the water source, only to the circumferential surface C 1  of the second body  51 , and may be provided to spray water to the corner at which the circumferential surface (C 1 , see  FIG. 5 ) and the bottom surface C 2  of the second body  51  meet each other. 
         [0035]    In the case where the nozzle  91  is provided to spray water to the corner of the second body  51 , the water spray range of the nozzle  91  may be set to a region from a first point (P 1 , see  FIG. 5 ), which is located between the corner and the rotating shaft  575  of the second body  51 , to a second point (P 2 , see  FIG. 5 ) which is located between the corner and the second opening  53 . 
         [0036]    To realize the spray range of the nozzle  91  described above, the cross sectional area of the nozzle  91  may increase with increasing distance from the connection pipe  93 . 
         [0037]      FIG. 3  shows an exemplary control method of a laundry treatment apparatus for the washing of the first reservoir  3  and the second reservoir  5 . 
         [0038]    The laundry treatment apparatus may be controlled such that the washing of the reservoirs  3  and  5  is implemented in response to the execution of a control command including an operation S 20  of rotating the second reservoir  5  in the state in which water is stored in the first reservoir  3  (e.g., a washing cycle or a rinsing cycle), or an operation S 41  of providing laundry stored in the second reservoir  5  with centrifugal force so as to separate water from the laundry (e.g., a dehydration cycle), even if the user does not input the reservoir washing course selection command to the input unit  17 . However, the control method of the present disclosure may be initiated only when the user inputs a control command for the washing of the reservoirs  3  and  5  (e.g., a reservoir washing course selection command) to the input unit  17 . 
         [0039]    In the former case, the washing of the reservoirs  3  and  5  may be performed only while the rotating operation S 20  is being performed, may be performed only while the centrifugal force providing operation S 41  is being performed, or may be performed during each of the rotating operation S 20  and the centrifugal force providing operation S 41 . 
         [0040]    Hereinafter, the case where the washing of the reservoirs  3  and  5  is performed during each of the rotating operation S 20  and the centrifugal force providing operation S 41  will first be described with reference to  FIG. 3 , and then the other cases will be described. 
         [0041]    When the user inputs, via the input unit  17 , a single control command including the operation S 20  of separating impurities from laundry and the operation S 41  of separating water from laundry, the control method proceeds to an operation S 10  of supplying water to the first body  31  via the water supply unit. 
         [0042]    After completion of the water supply operation S 10 , the control method proceeds to the rotating operation S 20  of rotating the second body  51  via the drive unit  57 . The rotating operation S 20  is an operation of rotating the second body  51  so as to cause friction between laundry and water stored inside the second body  51 . The rotating operation S 20  may be referred to as a washing cycle when it is performed in the state in which detergent and water have been supplied into the first body  31 , or may be referred to as a rinsing cycle when it is performed in the state in which no detergent has been supplied into the first body  31 . However, the rinsing cycle may be performed in the state in which rinsing detergent (e.g., a fabric conditioner) has been supplied. 
         [0043]    The laundry treatment apparatus may implement the motion illustrated in  FIG. 4 , in order to enable the washing of the reservoirs  3  and  5  while the rotating operation S 20  is being performed. That is, while the rotating operation S 20  is being performed, in the present disclosure, the number of revolutions per minute of the second body  51  is controlled to allow the level of water inside the first body  31  to be raised to a height H, at which the second opening  53  is located, by centrifugal force. 
         [0044]    However, in the rotating operation S 20 , the drive unit  57  may control the number of revolutions per minute of the second body  51  so as to prevent the water inside the first body  31  from being introduced into the second body  51  through the second opening  53 . In addition, in the rotating operation S 20 , the level W of water inside the first body  31  may remain lower than the height H of the second opening  53  for a predetermined time. 
         [0045]    In the rotating operation S 20  described above, even if the level of water inside the first body  31  is lower than the height of the second opening  53 , the water inside the first body  31  may be supplied to the upper circumferential surface of the second body  51  and the upper circumferential surface of the first body  31  by centrifugal force. Accordingly, in the rotating operation S 20 , the water, supplied for the washing or rinsing of laundry, may be directed to impurities adhering to the upper portion of the first body  31  and the upper portion of the second body  51 . 
         [0046]    When impurities are adhered to the upper portion of the first body  31  and the upper portion of the second body  51 , the impurities may be changed to the state of being easily separated from the respective bodies  31  and  51  while the rotating operation S 20  is being performed. Meanwhile, in the rotating operation S 20 , since the water S present between the outer circumferential surface of the second body  51  and the inner circumferential surface of the first body  31  will be rotated along with the second body  51 , the impurities remaining on the respective bodies  31  and  51  may be separated from the respective bodies  31  and  51  by water streams generated by the rotation of the second body  51 . 
         [0047]    As shown in  FIG. 3 , after completion of the rotating operation S 20  described above, the control method proceeds to an operation S 30  of draining the water inside the first body  31  to the outside of the first body  31 . 
         [0048]    The drainage operation S 30  may be performed via the drain unit  81  and  83 . Impurities separated from the laundry in the drainage operation S 30  and impurities separated from the respective bodies  31  and  51  may be discharged, along with the water, out of the first body  31 . 
         [0049]    When the rotating operation S 20  is a process that removes impurities from laundry using detergent and water (i.e. a washing cycle), the water supply operation, the rotating operation, and the drainage operation may be performed once more after completion of the drainage operation S 30 . The additionally performed water supply operation, rotating operation, and drainage operation may be referred to as a process whereby the detergent remaining on the laundry is removed (i.e. a rinsing cycle). 
         [0050]    After completion of the drainage operation S 30 , the control may proceed to the centrifugal force providing operation S 41  of separating water from laundry. The centrifugal force providing operation S 41  is an operation of providing laundry with centrifugal force by rotating the second body  51 , so as to separate water from the laundry. 
         [0051]    While the centrifugal force providing operation S 41  is being performed, the control method may proceed to an operation S 43  of spraying water to the inside of the second body  51  through the nozzle  91 . As exemplarily illustrated in  FIG. 5 , when water is sprayed to the inside of the second body  51  while the second body  51  is rotated, the water sprayed to the inside of the second body  51  may be discharged to the first body  31  through the through-holes  55 . 
         [0052]    Since the water, which is sprayed to the inside of the second body  51  during the rotation of the second body  51 , needs to pass through the laundry in order to move to the through-holes  55 , the spraying operation S 43 , which is initiated while the centrifugal force providing operation S 41  is being performed, may serve to remove impurities or detergent remaining on the laundry. 
         [0053]    In some cases, the water, which is discharged out of the second body  51  through the through-holes  55 , may collide with the inner circumferential surface of the first body  31 . In the course thereof, impurities remaining on the inner circumferential surface of the first body  31  may be separated from the first body  31  by the water discharged through the through-holes  55 . In addition, the water discharged from the through-holes  55  may collide with the first body  31  and, in turn, collide with the second body  51 . Therefore, the water discharged from the through-holes  55  may be used to remove impurities remaining on the second body  51 . Accordingly, the spraying operation S 43 , which is initiated while the centrifugal force providing operation S 41  is being performed, serves to wash the first body  31  and the second body  51 . 
         [0054]    To realize the effects described above, the time period during which the centrifugal force providing operation S 41  is performed and the time period during which the spraying operation S 43  is performed may be set to have an overlapping period. 
         [0055]    In addition, in the spraying operation S 43 , the nozzle  91  may spray water supplied from the water source only to the circumferential surface of the second body  51 , or may spray water to each of the circumferential surface and the bottom surface of the second body  51 . 
         [0056]    When it is desired to intensively wash the circumferential surface of the first body  31  and the circumferential surface of the second body  51 , the nozzle  91  may be provided to spray water to the circumferential surface of the second body  51 . 
         [0057]    However, in order to wash all of the circumferential surface of the first body  31 , the circumferential surface C 1  of the second body  51 , the bottom surface of the first body  31 , and the bottom surface C 2  of the second body  51 , the nozzle  91  may be provided to spray water to the circumferential surface C 1  of the second body  51  and the bottom surface C 2  of the second body  51  as exemplarily illustrated in  FIG. 5 . 
         [0058]    In this case, the nozzle  91  may be provided to spray water to a range from the first point P 1 , which is located between the corner of the second body  51  and the center of rotation (the rotating shaft  575 ) of the second body  51 , to the second point P 2  which is located between the corner and the second opening  53  of the second body  51 . 
         [0059]    In the centrifugal force providing operation S 41 , the laundry stored inside the second body  51  will remain densely gathered near the point (corner) at which the circumferential surface C 1  and the bottom surface C 2  of the second body  51  meet each other due to centrifugal force. Therefore, when the nozzle  91  sprays water to the space between the first point P 1  and the second point P 2 , most of the water discharged from the nozzle  91  will pass through the laundry and then be discharged to the first body  31 . Accordingly, the feature whereby the nozzle  91  sprays water to the space between the first point P 1  and the second point P 2  (i.e. sprays water toward the corner of the second body  51 ) serves to maximize the washing of each body  31  or  51  and the washing of the laundry stored in the second body  51 . 
         [0060]    In some cases, when the water discharged from the laundry in the centrifugal force providing operation S 41  and the water sprayed to the second body  51  in the spraying operation S 43  are not discharged out of the first body  31 , the water inside the first body  31  may prevent the rotation of the second body  51 , thus preventing the second body  51  from being rotated at high speed. 
         [0061]    To prevent the above-described problem, the control method of the present disclosure may further include an operation (S 45 , see  FIG. 3 ) of discharging the water inside the second body  51  to the outside of the first body  31  through the drain unit  81  and  83  while the centrifugal force providing operation S 41  and the spraying operation S 43  are being performed. That is, the time period during which the centrifugal force providing operation S 41  is performed, the time period during which the spraying operation S 43  is performed, and the time period during which the discharge operation S 45  is performed may be set to have an overlapping period. 
         [0062]    Despite the inclusion of the discharge operation S 45 , when a great amount of laundry is stored in the second body  51  or when the laundry contains a great amount of water, water exceeding a desired level may remain inside the first body  31  while the centrifugal force providing operation S 41  and the spraying operation S 43  are being performed. 
         [0063]    To prevent the problem described above, the spraying operation S 43  may include spraying water through the nozzle  91  (first operation) and temporarily stopping the spraying of water (second operation). That is, the spraying operation S 43  may be performed in the sequence of the first operation and the second operation, or may be performed by repeating the sequence of the first operation and the second operation. However, in order to achieve the desired effects of the spraying operation S 43 , the implementation time of the first operation may be set to be longer than the implementation time of the second operation. 
         [0064]    In addition, the spraying operation S 43  may be performed in the sequence of the first operation, the second operation, and the first operation, or may be performed by repeating the sequence of the first operation, the second operation, and the first operation. 
         [0065]    As described above, since the centrifugal force providing operation S 41  is an operation of providing laundry with centrifugal force so as to separate water from the laundry, the second body  51  may be rotated at a predetermined reference number of revolutions per minute for a given time or more, in order to achieve the desired effects. Therefore, a controller generally controls the number of revolutions per minute of the second body  51  as exemplarily illustrated in  FIG. 6A  in the centrifugal force providing operation S 41 . 
         [0066]    That is, as exemplarily illustrated in  FIG. 6A , the centrifugal force providing operation S 41  generally includes an acceleration operation T 1  of increasing the number of revolutions per minute of the second body  51  to a reference number of revolutions per minute R and a maintenance operation T 2  of maintaining the number of revolutions per minute of the second body  51  at the reference number of revolutions per minute R. 
         [0067]    In the case where the reference number of revolutions per minute R is the highest number of revolutions per minute of the second body  51  preset for the implementation of the centrifugal force providing operation S 41 , the spraying operation S 43  may be performed during the acceleration period T 1 . 
         [0068]    When water is sprayed to the second body  51  while the second body  51  is rotated at the reference number of revolutions per minute R, there is a likelihood that the water sprayed from the nozzle  91  may remain inside the second body  51 , rather than moving to the first body  31  through the through-holes  55 , due to the high number of revolutions per minute of the second body  51 . 
         [0069]    In some cases, when external force is input to the second body  51  while the second body  51  is accelerated to the reference number of revolutions per minute R, there may occur the problem whereby the load on the drive unit  57 , which rotates the second body  51 , increases, or the problem whereby the operation of the drive unit  57  becomes unstable. Accordingly, in the case where the spraying operation S 43  is performed during the acceleration operation T 1 , it may be necessary to appropriately select the number of revolutions per minute of the second body  51  at the beginning of the spraying operation S 43  in consideration of variables that determine the magnitude of centrifugal force (i.e., the diameter of the second body  51  and the amount of laundry stored in the second body  51 ). 
         [0070]    That is, the spraying operation S 43  may be provided to spray water to the second body  51  at a first number of revolutions per minute, which is set to be lower than the reference number of revolutions per minute R. The first number of revolutions per minute R 1  may be set to a range of revolutions per minute having a lowest value (lowest number of revolutions per minute) at which the spraying operation S 43  is initiated and a highest value (highest number of revolutions per minute) at which the spraying operation S 43  ends. 
         [0071]      FIG. 6B  illustrates a case in which the acceleration period T 1  includes a period during which the number of revolutions per minute of the second body  51  is maintained at the first number of revolutions per minute R 1 , such that the spraying operation S 43  is performed during the maintenance period so as to minimize the problem whereby the load on the drive unit  57  is increased due to the spraying operation S 43  or the problem whereby the operation of the drive unit  57  becomes unstable. 
         [0072]    That is, the centrifugal force providing operation S 41  of  FIG. 6B  includes the acceleration operation T 1  and the maintenance operation T 2  in the same manner as the case in  FIG. 6A . However, the acceleration operation T 1  includes a first acceleration operation T 11  of increasing the number of revolutions per minute of the second body  51  to a predetermined first number of revolutions per minute R 1 , an operation T 13  of maintaining the number of revolutions per minute of the second body  51  at the first number of revolutions per minute R 1 , and a second acceleration operation T 15  of increasing the number of revolutions per minute of the second body  51  to the reference number of revolutions per minute R, and the spraying operation S 43  is performed while the number of revolutions per minute of the second body  51  is maintained at the first number of revolutions per minute R 1  (T 13 ). 
         [0073]    In this case, when the operation T 13  of maintaining the number of revolutions per minute of the second body  51  at the first number of revolutions per minute is performed, the control method of may further include a vibration sensing operation along with the spraying operation S 43  and the discharge operation S 45 . 
         [0074]    When laundry is not distributed throughout the interior of the second body  51 , but is gathered in a certain region in the second body  51 , vibrations are generated during the rotation of the second body  51 . When the vibration generated at the second body  51  exceeds a given level, the second body  51  may collide with the first body  31  during the rotation thereof. That is, when laundry is gathered only in a certain region inside the second body  51 , the second body  51  has difficulty in rotating at high speed. 
         [0075]    The vibration sensing operation is an operation of predicting the magnitude of vibration that will be generated when the second body  51  is rotated at the reference number of revolutions per minute R by measuring the magnitude of vibration of the second body  51 , which is being rotated at a lower number of revolutions per minute than the reference number of revolutions per minute R. 
         [0076]    The vibration sensing operation may be performed by comparing the magnitude of vibration generated at the first body  31  during the rotation of the second body  51  with a predetermined reference value, or may be performed by comparing the magnitude of vibration generated at the second body  51  during the rotation of the second body  51  with the reference value. 
         [0077]    The measurement of the magnitude of vibration generated at the second body  51  may be implemented using various methods. For example, the vibration of the second body  51  may be directly measured using, for example, a vibration sensor, or the magnitude of vibration of the second body  51  may be estimated by monitoring the number of revolutions per minute of the rotor  573 . 
         [0078]    In the case when the vibration sensing operation is provided, the control method may proceed to the second acceleration operation T 15  of increasing the number of revolutions per minute of the second body  51  from the first number of revolutions per minute R 1  to the reference number of revolutions per minute R when the vibration measured in the vibration sensing operation is the predetermined reference value or less. 
         [0079]    As mentioned above, the above-described washing of the reservoirs  3  and  5  may be performed only while the rotating operation S 20  is being performed, or may be performed only while the centrifugal force providing operation S 41  is being performed. 
         [0080]    In the case where the washing of the reservoirs  3  and  5  is performed only while the rotating operation S 20  is being performed, the control method includes the water supply operation S 10 , the rotating operation S 20 , and the drainage operation S 30 , and the number of revolutions per minute of the second body  51  is controlled to maintain the level of water inside the first body  51  in the manner illustrated in  FIG. 4  while the rotating operation S 20  is performed. 
         [0081]    In some cases, in the case where it is desired to implement a control method S 40  of washing the reservoirs  3  and  5  only during dehydration (called a jet spray motion), the control method may include the centrifugal force providing operation S 41  of providing the laundry stored inside the second body  51  with centrifugal force by rotating the second body  51 , the spraying operation (S 43 ,  FIG. 5 ) of spraying water to the inside of the second body  51  through the nozzle  91 , and the discharge operation S 45  of discharging the water, supplied to the second body  51  in the spraying operation S 43 , to the outside of the first body  31  through the drain unit  81  and  83 . 
         [0082]    When the laundry treatment apparatus that performs the control method of the present disclosure is a washing machine and water is stored in the first body  31  prior to initiating the centrifugal force providing operation S 41 , the control method may be implemented in the sequence of the centrifugal force providing operation, the spraying operation, and the discharge operation, after the drainage operation of draining water inside the first body  31  through the drain unit  81  and  83  has been performed. However, when the laundry treatment apparatus that performs the control method of the present disclosure is an apparatus that is only for the purpose of dehydration, the control method may include the centrifugal force providing operation, the spraying operation, and the discharge operation without the drainage operation described above. 
         [0083]    As described above, since the washing of the reservoirs  3  and  5  is always possible while the laundry treatment apparatus is operated for the washing, rinsing, and dehydration of laundry, the control method may enable the sanitary management of the laundry treatment apparatus even if the user does not attempt to wash the reservoirs  3  and  5  by executing a separate course and even if the laundry treatment apparatus periodically executes a separate course for washing only the reservoirs  3  and  5 . 
         [0084]      FIG. 7  shows another implementation of the laundry treatment apparatus. The control method according to the present implementation also includes the water supply operation S 10 , the rotating operation S 20 , the drainage operation S 30 , and the centrifugal force providing operation S 41 . However, the present implementation has the feature that the motion of  FIG. 5  may be performed during the rotating operation S 20 . 
         [0085]    To execute the present implementation, the rotating operation S 20  may include a first rotating operation S 21  of rotating the second body  51  at the second number of revolutions per minute R 2  in the state in which water is stored in the first body  31 , an intermediate drainage operation (first intermediate drainage operation) S 23  of draining the water inside the first body  31  after completion of the first rotating operation S 21 , a second rotating operation S 25  of rotating the second body  51  at the first number of revolutions per minute R 1  which is set to be higher than the second number of revolutions per minute R 2 , an intermediate drainage operation (second intermediate drainage operation) S 26  of draining the water inside the first body  31  after completion of the second rotating operation S 25 , an intermediate water supply operation S 27  of resupplying water to the first body  31 , and a third rotating operation S 29  of rotating the second body  51  in the state in which water has been supplied to the first body  31 . 
         [0086]    In the control method according to the present implementation, the number of revolutions per minute of the second body  51  may be controlled such that the motion of  FIG. 4  is performed during the first rotating operation S 21 . The description related to the motion of  FIG. 4  has been given above in detail, and thus, a detailed description thereof will be omitted hereinafter. 
         [0087]    In addition, the control method according to the present implementation may control the spray unit  9  and the drain unit  81  and  83  so as to perform, during the second rotating operation S 25 , an intermediate spraying operation (i.e. an operation of spraying water into the second body  51  via the spray unit  9 ) and an intermediate discharge operation (i.e. an operation of discharging the water inside the first body  31  while the spraying operation S 43  is being performed). 
         [0088]    The detailed control process of the intermediate spraying operation and the intermediate discharge operation may be identical to that of the spraying operation S 43  and the discharge operation S 45  described above, and thus a detailed description thereof will be omitted hereinafter. However, note that the first number of revolutions per minute R 1  set in the second rotating operation S 24  may be higher than the second number of revolutions per minute R 2  set in the first rotating operation S 21 , and may be lower than the reference number of revolutions per minute R set in the centrifugal force providing operation S 41 , which is initiated after completion of the drainage operation S 30 . 
         [0089]    In some cases, when the intermediate spraying operation and the intermediate discharge operation are executed while the second rotating operation S 25  is being performed, the intermediate drainage operation S 26  may be omitted. 
         [0090]    The first rotating operation S 21  may be referred to as a washing cycle of separating impurities from laundry when it is performed in the state in which detergent and water have been supplied into the first body  31 , and the third rotating operation S 29  may be referred to as a rinsing cycle of removing detergent or impurities remaining on laundry using the water supplied to the first body  31  via the intermediate water supply operation S 27 . 
         [0091]    In this case, the second rotating operation S 25 , which is performed between the first rotating operation S 21  and the third rotating operation S 29 , may serve to minimize the amount of water required in the third rotating operation S 29 , thereby reducing the implementation time of the third rotating operation S 29 , and may additionally serve to wash the reservoirs  3  and  5 . 
         [0092]    The control method proceeds to the drainage operation S 30  of draining the water inside the first body  31  via the drain unit  81  and  83  after completion of the third rotating operation S 29 . 
         [0093]    After completion of the drainage operation S 30 , the control method of the present disclosure may execute all of the centrifugal force providing operation S 41 , the spraying operation S 43 , and the discharge operation S 45 , or may execute only the centrifugal force providing operation S 41  after completion of the drainage operation S 30 . 
         [0094]    In the case where all of the centrifugal force providing operation S 41 , the spraying operation S 43 , and the discharge operation S 45  are executed after completion of the drainage operation S 30 , the spraying operation S 43  and the discharge operation S 45  may be performed during the operation T 13  of maintaining the number of revolutions per minute of the second body  51  at the first number of revolutions per minute R 1 . 
         [0095]    Similar to the implementation of  FIG. 3 , in the present implementation, when the operation T 13  of maintaining the number of revolutions per minute of the second body  51  at the first number of revolutions per minute R 1  is performed, the control method may further include a vibration sensing operation along with the spraying operation S 43  and the discharge operation S 45 . 
         [0096]    When the vibration sensing operation is provided and the vibration measured in the vibration sensing operation is equal to or less than a predetermined reference value, in the present implementation, the number of revolutions per minute of the second body  51  may increase to the reference number of revolutions per minute R which is the final target number of revolutions per minute in the centrifugal force providing operation (T 15  and T 2 ). 
         [0097]    As is apparent from the above description, the present disclosure may help realize the effect of providing and controlling a laundry treatment apparatus that enables the washing of a first reservoir in which water is stored and a second reservoir in which laundry is stored. 
         [0098]    In addition, the present disclosure may help realize the effect of providing and controlling a laundry treatment apparatus that enables the washing of a first reservoir and a second reservoir while washing or rinsing of laundry is being performed. 
         [0099]    In addition, the present disclosure may help realize the effect of providing and controlling a laundry treatment apparatus enables the washing of a first reservoir and a second reservoir while dehydration of laundry is being performed. 
         [0100]    In addition, the present disclosure may help realize the effect of providing and controlling a laundry treatment apparatus that implements the washing of a first reservoir and a second reservoir via a jet spray motion which sprays water into the second reservoir while the second reservoir is rotated. 
         [0101]    Although the example implementations have been illustrated and described above, it will be apparent to those skilled in the art that the implementations are provided to assist understanding of the present disclosure. The present disclosure is not limited to the above described particular implementations, and various modifications and variations can be made in the present disclosure without departing from the spirit or scope of the present disclosure.
A control method for a laundry treatment apparatus, where the laundry treatment apparatus includes a first reservoir for holding water and defining a first opening for introduction of laundry, a second reservoir placed inside the first reservoir, the second reservoir being rotatable about a rotation axis perpendicular to a bottom surface of the first reservoir and defining a second opening that is positioned under the first opening, a through-hole that is defined in the second reservoir, a spray unit for spraying water to an inside of the second reservoir, and a drain unit for draining water inside the first reservoir, includes rotating the second reservoir to thereby apply force on laundry received in the second reservoir, spraying water to the inside of the second reservoir via the spray unit, and discharging the sprayed water in the second reservoir to an outside of the first reservoir via the drain unit.