Patent Description:
In general, a laundry treatment machine is an apparatus which washes clothes, bedclothes, etc. (hereinafter, referred to as 'clothes') using water, detergents and mechanical action through a series of processes of washing, rinsing, spin-drying, etc., so as to remove contaminants from the clothes.

The laundry treatment machine generally performs a washing cycle, a rinsing cycle and a spin-drying cycle. Here, the spin-drying cycle includes rotation of a drum at the highest speed, and thus, a measure to overcome increased noise and vibration due to unbalanced rotation of the drum occurring during a process of rotating the drum at a high speed in the spin-drying cycle is required.

A laundry treatment machine has a balancer which reduces unbalance occurring due to unequal distribution of clothes accommodated in the drum, and a ball balancer or a liquid balancer may be used as the balancer of the laundry treatment machine. The ball balancer in which balls move to reduce unbalance occurring due to rotation of the drum, but if the drum is rotated at a designated speed or higher, movement of the balls in the ball balancer is difficult, and thus a measure to reduce unbalanced rotation of the drum caused by removal of water from the clothes in the spin-drying cycle is required.

<CIT> describes a washing machine with a balancer to counterbalance unbalanced load produced during rotation of a drum and a control method thereof. The washing machine with a balancer to counterbalance unbalanced load produced during rotation of a drum perform a ball distributing cycle of seating masses in a groove in the balancer before rotation of the drum possibly producing unbalance as in the spin-drying cycle begins to efficiently maintain balance of the drum, and a laundry untangling cycle of evenly distributing the laundry in the drum. Accordingly, vibration and noise may be reduced during the spin-drying cycle. In addition, in retrying the spin-drying, the ball distributing cycle is restricted based on the rate of rotation of the motor at the moment at which unbalance is sensed. Thereby, delay in cycle time in retrying the spin-drying cycle may be prevented.

<CIT> describes that when a dehydration process begins, a control unit senses the laundry weight in a drum. A control unit disperses the laundry in the drum. The control unit senses an eccentricity quantity of the drum. If the sensed eccentricity quantity is smaller than a reference eccentricity quantity, the control unit performs an excessive area passage stage.

The control unit rotates the drum at high speed in order to perform the dehydration process.

<CIT> describes a washing machine which includes a drum, a vibration sensor sensing vibration of the drum, a ball balancer installed in a portion of the drum and including at least one ball, and a controller controlling a rotation speed of the drum, wherein the controller detects information related to an eccentric amount within the drum and a position of the ball using a signal related to vibration of the drum obtained from the vibration sensor for a preset period of time, while maintaining a rotation speed of the drum, selects an acceleration pattern corresponding to the detected eccentric amount and position of the ball from a preset table, and rotates the drum according to the selected acceleration pattern.

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for controlling a spin-drying cycle of a laundry treatment machine, in which unbalanced rotation of a drum caused by removal of water from clothes during a spin-drying process is reduced.

It is another object of the present invention to provide a method for controlling a spin-drying cycle of a laundry treatment machine, in which unbalanced rotation of a drum occurring due to accelerating or decelerating rotation of the drum is reduced.

Objects of the present invention are not limited to the above-described objects, and other objects which are not stated above will be more clearly understood from the following detailed description.

The object is solved by the invention set out by the features of the independent claim.

In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a method for controlling a spin-drying cycle of a laundry treatment machine, including performing a plurality of spin-drying operations by rotating a drum above an adjusted rotational speed range configured to adjust disposition of balls within a ball balancer so as to correspond to a change in an amount of eccentricity, and adjusting the disposition of the balls within the ball balancer by rotating the drum within the adjusted rotational speed range, between the respective spin-drying operations, thereby coping with the change in the amount of eccentricity caused by removal of water in the respective spin-drying operations.

The method may include adjusting the disposition of the balls within the ball balancer by rotating the drum within the adjusted rotational speed range, prior to each of the spin-drying operations, thereby coping with the change in the amount of eccentricity caused by removal of water in the respective spin-drying operations.

The spin-drying operation includes a preliminary spin-drying operation performed by rotating the drum within a RPM range of a resonance point of a cabinet or lower, and a main spin-drying operation performed by rotating the drum within an RPM range of above the resonance point of the cabinet, and the disposition of the balls within the ball balancer is adjusted by rotating the drum within the adjusted rotational speed range, between the preliminary spin-drying operation and the main spin-drying operation, thereby coping with the change in the amount of eccentricity caused by removal of water in the preliminary spin-drying operation.

The main spin-drying operation may be divided into a first spin-drying operation performed by rotating the drum to a rotational speed of above the resonance point of the cabinet, a second spin-drying operation performed by rotating the drum at a maximum rotational speed higher than a maximum rotational speed of the drum in the first spin-drying operation, and a third spin-drying operation performed by rotating the drum at a maximum rotational speed for a longer time than in the second spin-drying operation, and the disposition of the balls with the ball balancer may be adjusted by rotating the drum within the adjusted rotational speed range, between the respective spin-drying operations, thereby coping with the change in the amount of eccentricity caused by removal of water between the respective operations divided from the main spin-drying operation.

In the first spin-drying operation, if the change in the amount of eccentricity due to removal of water is large during the rotation of the drum at a rotational speed of the resonance point of the cabinet or lower, the drum may be rotated at the rotational speed of the resonance point of the cabinet or lower, thereby preventing excessive vibration occurring from the drum.

In the first spin-drying operation, when a difference between a maximum vibration value within a first set rotational speed range set to the resonance point or lower, and a maximum vibration value within a second set rotational speed range set to be resonance point or lower, which is higher than the first set rotational speed range, exceeds a set value, the rotational speed of the drum may be maintained within the second set rotational speed range, and the first set rotational speed range and the second set rotational speed range may be set as sections in which removal of water is great, thereby preventing excessive vibration occurring during rotation of the drum at a rotational speed of above the resonance point of the cabinet.

The main spin-drying operation includes increasing the rotational speed of the drum to a maximum rotational speed, and decreasing the rotational speed of the drum from the maximum rotational speed, and the decreasing the rotational speed of the drum includes a ball disposition maintenance section configured to prevent excessive vibration of the cabinet occurring during a process of decreasing the rotational speed of the drum, thereby preventing excessive vibration of the drum occurring during the decelerating rotation of the drum.

First, a method for controlling a spin-drying cycle of a laundry treatment machine in accordance with the present invention includes adjusting disposition balls within a ball balancer by rotating a drum within an adjusted rotational speed range, between a preliminary spin-drying operation and a main spin-drying operation, thus preventing excessive vibration of a cabinet occurring due to unbalanced rotation of the drum caused by removal of water in the spin-drying cycle.

Second, the method in accordance with the present invention includes adjusting disposition of the balls within the ball balancer by rotating the drum within the adjusted rotational speed range, among first to third spin-drying operations in which the drum is rotated at a rotational frequency of a resonance point or above, thus preventing excessive vibration of the cabinet occurring due to unbalanced rotation of the drum caused by removal of water in the spin-drying cycle.

Third, in the method in accordance with the present invention, when an amount of removed water is within or above a designated range during a process of spin-drying at the resonance point or lower in the first spin-drying operation, the rotational speed of the drum is not increased to a rotational speed of the resonance point or higher, and thus, excessive vibration of the cabinet occurring due to rotation of the drum at the rotational speed of the resonance point or higher may be prevented.

The effects of the present invention are not limited to the above-described effects, and various other effects of the invention will be directly or implicitly set forth in the following detailed description and the accompanying claims.

The advantages and features of the present invention and the way of attaining the same will become apparent with reference to embodiments described below in conjunction with the accompanying drawings. Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

Hereinafter, a laundry treatment machine and a method for controlling the same in accordance with embodiments of the present invention will be described with reference to the accompanying drawings.

<FIG> is a longitudinal-sectional view illustrating the configuration of a laundry treatment machine in accordance with a first embodiment of the present invention.

Referring to <FIG>, a laundry treatment machine <NUM> in accordance with one embodiment of the present invention includes a cabinet <NUM> which forms the external appearance of the laundry treatment machine, a door <NUM> which opens and closes one side of the cabinet so that clothes are put into and taken out of the cabinet therethrough, a tub <NUM> which is disposed within the cabinet so as to be supported by the cabinet, a drum <NUM> which is disposed within the tub so as to be rotated in a state in which the clothes are accommodated in the drum, a driver <NUM> which applies torque to the drum so as to rotate the drum, a detergent box <NUM> in which detergents are accommodated, and a control panel <NUM> which receives user input and displays the state of the laundry treatment machine.

A clothes entrance 111a is formed in the cabinet <NUM> so that clothes may be put into and taken out of the cabinet therethrough. The door <NUM> is rotatably coupled to the cabinet <NUM> so as to open and close the clothes entrance 111a. The control panel <NUM> is provided on the cabinet <NUM>. The detergent box <NUM> may be provided in the cabinet <NUM> so as to be capable of withdrawn.

The tub <NUM> is disposed within the cabinet <NUM> so as to be buffered using springs <NUM> and a damper <NUM>. The tub <NUM> holds washing water. The tub <NUM> is disposed outside the drum <NUM> so as to surround the drum <NUM>.

A tub hole 122a is formed through the front surface of the tub <NUM>. The tub hole 122a is formed so as to communicate with the clothes entrance 111a such that clothes may be put into and taken out of the drum <NUM> therethrough.

The driver <NUM> is disposed at the rear of the tub <NUM> and generates rotational force. The driver <NUM> is connected to a rotation shaft <NUM> and rotates the drum <NUM>. The driver <NUM> may rotate the drum <NUM> at various speeds or in various directions. The driver <NUM> includes a stator (not shown), on which a coil is wound, and a rotor (not shown), which is rotated through electromagnetic interaction with the coil.

The rotation shaft <NUM> connects the driver <NUM> to the drum <NUM>. The rotation shaft <NUM> transmits rotational force of the driver <NUM> to the drum <NUM>, thus rotating the drum <NUM>. One end of the rotation shaft <NUM> is coupled to the center of rotation of the rear portion of the drum <NUM>, and the other end is coupled to the rotor (not shown) of the driver <NUM>.

The drum <NUM> in which the clothes are accommodated is rotated. The drum <NUM> is disposed within the tub <NUM>. The drum <NUM> has a cylindrical shape which is rotatable. A plurality of through holes, through which washing water passes, is formed through the drum <NUM>. The drum <NUM> receives rotational force of the driver <NUM>, thus being rotated.

A drum hole is formed through the front surface of the drum <NUM>. The drum hole 124a is formed so as to communicate with the clothes entrance 111a and the tub hole 122a such that clothes may be put into and taken out of the drum <NUM> therethrough. A front ball balancer 140a is coupled to the front edge of the drum <NUM>, and a rear ball balancer 140b is coupled to the rear edge of the drum <NUM>.

Each of the front and rear ball balancers 140a and 140b includes balls <NUM> and a filling fluid therein. Further, each of the ball balancers 140a and 140b may further include a balancer housing <NUM> which defines a moving path of the balls <NUM> along the inner circumference or the outer circumference of the drum <NUM>. That is, the balancer housing <NUM> may be provided along the inner circumference or the outer circumference of the drum, and the balls <NUM> may move within the balancer housing <NUM>.

A gasket <NUM> seals a gap between the tub <NUM> and the cabinet <NUM>. The gasket <NUM> is disposed between the inlet of the tub <NUM> and the clothes entrance 111a. The gasket <NUM> relieves impact transmitted to the door <NUM> when the drum <NUM> is rotated, and simultaneously prevents washing water in the tub <NUM> from leaking to the outside. A circulation nozzle <NUM> which sprays washing water to the inside of the drum <NUM> may be provided at the gasket <NUM>.

A water supply valve <NUM> which adjusts inflow of washing water from an external water source, a water supply flow path <NUM> along which washing water flowing through the water supply valve flows to the detergent box <NUM>, and a water supply pipe <NUM> along which washing water mixed with a detergent in the detergent box <NUM> flows to the inside of the tub <NUM> may be provided within the cabinet <NUM>.

A drain pipe <NUM> to which washing water in the tub <NUM> is discharged, a pump <NUM> which pumps the washing water in the tub, a circulation flow path <NUM> which circulates washing water, the circulation nozzle <NUM> which sprays washing water to the inside of the drum <NUM>, and a drain flow path <NUM> along which washing water is drained to the outside may be provided within the cabinet <NUM>. According to embodiments, the pump <NUM> may include a circulation pump and a drain pump which are connected to the circulation flow path <NUM> and the drain flow path <NUM>, respectively.

A vibration sensor <NUM> which senses a magnitude of vibration of the tub <NUM> may be provided on the tub <NUM>. Vibration occurring due to unbalance of the drum <NUM> is transmitted to the tub <NUM> by the rotation shaft <NUM>, thus causing vibration of the tub <NUM>. The vibration sensor <NUM> senses the magnitude of vibration of the tub <NUM>, thus measuring a degree of unbalance of the drum <NUM>.

Vibration sensors may include a front vibration sensor which is disposed at the front portion of the tub <NUM> and senses a magnitude of vibration of the front portion of the tub <NUM>, i.e., a magnitude of front vibration, and a rear vibration sensor which is disposed at the rear portion of the tub <NUM> and senses a magnitude of vibration of the rear portion of the tub <NUM>, i.e., a magnitude of rear vibration. In the laundry treatment machine <NUM> in accordance with this embodiment, the vibration sensor <NUM> may be disposed at the rear portion of the upper region of the tub <NUM>.

An input unit (not shown) which receives selection of a washing course or various operation commands, such as operating times of respective cycles, reservation, etc., from a user, and a display unit (not shown) which displays the operating state of the laundry treatment machine <NUM> may be provided on the control panel <NUM>.

<FIG> is a partial exploded perspective view illustrating a laundry treatment machine in accordance with a second embodiment of the present invention, and <FIG> is an assembled sectional view of <FIG>.

Referring to <FIG> and <FIG>, in a laundry treatment machine <NUM>, a tub <NUM> is fixedly supported by a cabinet <NUM>. The tub <NUM> includes a tub front <NUM> which forms the front portion of the tub, and a tub rear <NUM> which forms the rear portion of the tub. The tub front <NUM> and the tub rear <NUM> may be assembled by screws. The tub <NUM> has an opening in the rear surface thereof. The inner circumference of the rear surface of the tub <NUM> is connected to the outer circumferential portion of a rear gasket <NUM>. The inner circumferential portion of the rear gasket <NUM> is connected to a tub back <NUM>. A through hole through which a rotation shaft passes is formed through the center of the tub back <NUM>. The rear gasket <NUM> is formed of a flexible material so as not to transmit vibration of the tub back <NUM> to the tub <NUM>.

The rear surface of the tub <NUM>, the tub back <NUM>, and the rear gasket <NUM> form a rear wall of the tub. The rear gasket <NUM> are respectively connected to the tub back <NUM> and the tub rear <NUM> so as to be sealed, thus preventing washing water in the tub from leaking. The rear gasket <NUM> may have a bellows part <NUM> which may extend a sufficient length so as to permit such relative motion of the tub back <NUM>.

A front gasket <NUM>, which prevents foreign substances from being introduced into a gap between the tub and the drum, is connected to the front portion of the tub <NUM>. The front gasket <NUM> is formed of a flexible material, and is fixedly installed at the front portion of the tub <NUM>. The front gasket <NUM> may be formed of the same material as the rear gasket <NUM>.

The cabinet <NUM> forms the external appearance of the laundry treatment machine <NUM>. The cabinet <NUM> includes a front cabinet (not shown), a rear cabinet <NUM>, side cabinets <NUM>, an upper cabinet (not shown) and a base cabinet <NUM>.

The drum <NUM> includes a drum front <NUM>, a drum center <NUM>, a drum back <NUM>, etc. The drum <NUM> accommodates clothes therein and is rotated. The drum <NUM> is disposed within the tub <NUM>.

Ball balancers 240a and 240b are installed at the front and rear portions of the drum <NUM>. Each of the front and rear ball balancers 240a and 240b includes balls <NUM> and a filling fluid therein. Further, each of the ball balancers 240a and 240b may further include a balancer housing <NUM> which defines a moving path of the balls <NUM> along the inner circumference or the outer circumference of the drum <NUM>.

The rear surface of the drum <NUM> is connected to a spider <NUM>, and the spider <NUM> is connected to a rotation shaft <NUM>. The drum <NUM> is rotated within the tub <NUM> by rotational force transmitted through the rotation shaft <NUM>.

The rotation shaft <NUM> passes through the tub back <NUM>, and is connected to a driver <NUM> in a direct connection manner. A bearing housing <NUM> is coupled to the rear surface of the tub back <NUM>. The bearing housing <NUM> between the driver <NUM> and the tub back <NUM> rotatably supports the rotation shaft <NUM>.

A stator <NUM> is fixedly installed at the bearing housing <NUM>. A rotor <NUM> is located so as to surround the stator <NUM>. The rotor <NUM> is directly connected to the rotation shaft <NUM>. The driver <NUM> is an outer rotor-type motor, and is directly connected to the rotation shaft <NUM>.

The bearing housing <NUM> is supported by the base cabinet <NUM> through a suspension unit. The suspension unit <NUM> includes three vertical supports and two inclined supports, which are inclined in forward and rearward directions.

The suspension unit <NUM> in accordance with this embodiment may include two front cylinder springs, one rear cylinder spring, and two cylinder dampers <NUM>.

The front cylinder springs <NUM> connect suspension brackets <NUM> to the base cabinet <NUM>. The rear cylinder spring <NUM> directly connects the bearing housing <NUM> to the base cabinet <NUM>. The cylinder dampers <NUM> are installed between the suspension brackets <NUM> and the rear portion of the base cabinet <NUM> so as to be inclined.

The cylinder springs <NUM> and <NUM> of the suspension unit <NUM> are not completely fixedly connected to the base cabinet <NUM>, and may be connected to the base cabinet <NUM> such that elastic deformation of the cylinder springs <NUM> and <NUM> is allowed to some degree and thus movement of the drum in the forward and rearward directions and in the leftward and rightward directions is possible. That is, the cylinder springs <NUM> and <NUM> are elastically supported so that rotation thereof about supporting points thereof connected to the base cabinet <NUM> in the forward and rearward directions and in the leftward and rightward directions is allowed to some degree.

Elements of the suspension unit <NUM>, which are vertically installed, may be configured to elastically buffer vibration of the drum, and elements, which are installed so as to be inclined, may be configured to reduce the vibration. That is, in a vibration system including springs and damping units, elements which are vertically installed may serve as the springs, and elements which are installed so as to be inclined may serve as the damping units.

The tub <NUM> is fixedly installed in the cabinet <NUM>, and vibration of the drum <NUM> is buffered by the suspension unit <NUM>. Substantially, support structures of the tub <NUM> and the drum <NUM> may be separated from each other. Further, even if the drum <NUM> is vibrated, the tub <NUM> may not be vibrated.

The bearing housing <NUM> and the suspension brackets <NUM> are connected by weights <NUM>.

A vibration sensor <NUM> which sense a magnitude of vibration of the tub <NUM> is provided on the tub <NUM>. Vibration occurring due to unbalance of the drum <NUM> may be transmitted to the tub <NUM> by the rotation shaft <NUM>, thus causing vibration of the tub <NUM>. The vibration sensor <NUM> senses the magnitude of vibration of the tub <NUM>, thus measuring a degree of unbalance of the drum <NUM>. The vibration sensor <NUM> may senses vibration of the tub <NUM> in the forward direction or in the leftward and rightward directions. Vibration sensors <NUM> may be disposed in plural at the front and rear portions of the tub <NUM>. The vibration sensor <NUM> in accordance with this embodiment may be disposed at the rear portion of the upper region of the tub <NUM>. Clothes are gathered in the rear portion of the drum <NUM> during the rotating process of the drum <NUM>, and thus, a large magnitude of vibration is sensed at the rear portion of the tub <NUM>.

The laundry treatment machine <NUM> in accordance with this embodiment further includes a control panel <NUM> including an input unit (not shown) which receives selection of a washing course or various operation commands, such as operating times of respective cycles, reservation, etc., through a user, and a display unit (not shown) which displays the operating state of the laundry treatment machine <NUM>.

<FIG> is a block diagram of a laundry treatment machine including a controller in accordance with one embodiment of the present invention.

A laundry treatment machine in accordance with this embodiment may include a controller <NUM> which controls the overall operation of the laundry treatment machine <NUM> or <NUM> according to an operation command input through the control panel <NUM> or <NUM>. The controller <NUM> may include a microcomputer which controls the operation of the laundry treatment machine, a storage device and other electronic parts. The controller <NUM> determines whether or not each cycle is performed, whether or not operations, such as water supply, washing, rinsing, draining, spin-drying and drying, are performed, times of these operations in each cycle, the number of repetitions of these operations, etc., according to on a washing course selected by a user, and thereby controls the water supply valve <NUM>, the driver <NUM> or <NUM> and the pump <NUM>.

The controller <NUM> controls the driver depending on the quantity of vibration of the tub <NUM> or <NUM> measured by the vibration sensor <NUM> or <NUM>, and thereby adjusts the rotational speed of the drum <NUM> and <NUM>. The controller <NUM> in accordance with this embodiment adjusts the rotational speed of the drum depending on each spin-drying operation.

<FIG> is a view illustrating a rotational speed of a drum during a spin-drying cycle of the laundry treatment machine in accordance with one embodiment of the present invention. <FIG> is a view illustrating a rotational speed of the drum during a spin-drying cycle of the laundry treatment machine, in which a first spin-drying operation of <FIG> is modified. <FIG> is a flowchart illustrating a method for controlling the spin-drying cycle of the laundry treatment machine in accordance with one embodiment of the present invention. <FIG> is a flowchart illustrating in detail an initial ball balancer adjustment operation in the method for controlling the spin-drying cycle of the laundry treatment machine in accordance with one embodiment of the present invention. <FIG> is a flowchart illustrating in detail a preliminary spin-drying operation in the method for controlling the spin-drying cycle of the laundry treatment machine in accordance with one embodiment of the present invention. <FIG> is a flowchart illustrating in detail a first spin-drying operation in the method for controlling the spin-drying cycle of the laundry treatment machine in accordance with one embodiment of the present invention.

A method for controlling a spin-drying cycle of the laundry treatment machine in accordance with this embodiment includes performing a plurality of spin-drying operations by rotating the drum above an adjusted rotational speed range configured to adjust disposition the balls within the ball balancer so that the balls correspond to a change in an amount of eccentricity, and adjusting disposition of the balls within the ball balancer by rotating the drum within the adjusted rotational speed range, between the respective spin-drying operations.

Alternatively, the method for controlling the spin-drying cycle of the laundry treatment machine in accordance with this embodiment includes a plurality of spin-drying operations by rotating the drum above an adjusted rotational speed range configured to adjust disposition of the balls within the ball balancer so that the balls correspond to a change in an amount of eccentricity, and adjusting disposition of the balls within the ball balancer by rotating the drum within the adjusted rotational speed range, prior to each of the spin-drying operations.

Referring to <FIG>, in each of the laundry treatment machines <NUM> and <NUM> in accordance with the above-described embodiments, when clothes are accommodated in the drum <NUM> or <NUM> and then the drum <NUM> or <NUM> is rotated, great noise and vibration may be generated depending on the position of the clothes.

If the clothes are gathered in a partial region of the drum <NUM> or <NUM>, an amount of eccentricity is generated when the drum <NUM> or <NUM> is rotated. Rotation of the drum <NUM> or <NUM> in the state in which the amount of eccentricity is caused by the clothes therein is referred to as eccentric rotation or unbalanced rotation. The eccentric rotation includes the case in which the drum <NUM> or <NUM> is rotated in a state in which the ball balancer does not correct the amount of eccentricity of the clothes, and the case in which the drum is rotated in a state in which the amount of eccentricity is changed due to removal of water during a spin-drying process.

Vibration occurring in the eccentrically rotated drum <NUM> or <NUM> may be reduced by the ball balancers <NUM> or <NUM> disposed at the front and rear portions of the drum <NUM> or <NUM>. The balls <NUM> and <NUM> disposed in the balancer housing <NUM> or <NUM> of the ball balancer <NUM> or <NUM> are rotated while balancing the clothes, thus reducing vibration occurring from the cabinet <NUM> or <NUM>. A plurality of balls <NUM> and <NUM> rotated along the inside of the balancer housing <NUM> or <NUM> is disposed in the balancer housing <NUM> or <NUM>.

In the method for controlling the spin-drying cycle of the laundry treatment machine in accordance with this embodiment, which will be described below, vibration of the tub occurring due to an increase in the rotational speed of the drum is reduced using the ball balancers. Therefore, movement of the balls disposed in the balancer housing of the ball balancer depending on the rotational speed of the drum will be first described, and the method for controlling the spin-drying cycle of the laundry treatment machine will then be described.

As the drum <NUM> or <NUM> is rotated, the balls <NUM> or <NUM> disposed in the balancer housing <NUM> or <NUM> are rotated due to frictional force. The balls <NUM> or <NUM> in the balancer housing <NUM> or <NUM> are not confined by the drum, and are thus rotated at a different speed from that of the drum when the drum <NUM> or <NUM> is rotated. However, laundry causing eccentricity is pressed against the inner wall of the drum, and may be rotated at almost the same speed as the drum due to sufficient frictional force and lifts provide on the inner wall of the drum.

The rotational speed of the laundry and the rotational speed of the balls may be different, and, at an initial stage in which the drum starts to be rotated at a relatively low speed, the rotational speed of the laundry is higher than the rotational speed of the balls. To be precise, it may be considered that the rotational angular speed of the laundry is higher than the rotational angular speed of the balls. Further, a phase difference between the balls and the laundry, i.e., a phase difference therebetween with respect to the center of rotation of the drum, is continuously changed.

When the rotational speed of the drum is gradually increased, the balls are pressed against the circumferential surface of the outer side of the moving path due to centrifugal force, and, when the rotational speed of the drum is a designated value or more, the centrifugal force is increased, frictional force between the circumferential surface and the balls is a certain value or more, and thus, the balls are rotated at the same rotational speed as the drum.

Hereinafter, movement of the balls within the ball balancer according to the increase in the rotational speed of the drum <NUM> or <NUM> will be described. Disposition of the balls <NUM> or <NUM> within the balancer housing <NUM> or <NUM> is varied according to the rotational speed of the drum. When the drum <NUM> or <NUM> is not rotated, the balls <NUM> and <NUM> are disposed in the lower portion of the balancer housing <NUM> or <NUM> in a state in which the balls <NUM> and <NUM> are in contact with one another.

As the rotational speed of the drum <NUM> or <NUM> is increased at an initial stage of rotation, the balls <NUM> or <NUM> are rotated within the balancer housing <NUM> or <NUM> in a state in which the balls <NUM> or <NUM> are spaced apart from one another by a designated distance. In this case, gravity is more strongly applied to the balls than centrifugal force due to rotation of the drum <NUM> or <NUM>, and thus, the rotational speeds of the balls may be different depending on the positions of the balls disposed in the balancer housing <NUM> or <NUM>.

Thereafter, when the rotational speed of the drum <NUM> or <NUM> is further increased, the balls <NUM> and <NUM> are rotated within the balancer housing <NUM> or <NUM> within a range within which centrifugal force is more strongly applied to the balls than gravity in the state in which the balls are in contact with one another. In the laundry treatment machine in accordance with this embodiment, when the drum <NUM> or <NUM> is rotated at a speed of <NUM> RPM, the balls in the mutually contacting state are rotated within the balancer housing.

Thereafter, when the rotational speed of the drum <NUM> or <NUM> is further increased, the balls are spaced apart from one another and disposed so as to correspond to an amount of eccentricity of clothes rotated within the drum. Further, when the rotational speed of the drum is increased so that the drum is rotated within the adjusted rotational speed range, disposition of the balls rotated within the ball housing may be finely adjusted.

The adjusted rotational speed range is a section in which the disposition of the balls is finely adjusted in the state in which the balls are spaced apart from one another within the balancer housing by further increasing the rotational speed of the drum within the range within which centrifugal force is more strongly applied to the balls than gravity. In the laundry treatment machine in accordance with this embodiment, the adjusted rotational speed range N1 may be about <NUM> to <NUM> RPM, particularly about <NUM> RPM.

When wet clothes are excessively dewatered through rotation of the drum, the drum <NUM> or <NUM> may be eccentrically rotated due to change in the amount of eccentricity by a designated amount or more. This eccentric rotation is severed if the rotational speed of the drum is increased to a resonance point or higher, thus causing excessive vibration of the cabinet.

Therefore, by rotating the drum <NUM> or <NUM> within the adjusted rotational speed range, the eccentric rotation of the drum <NUM> or <NUM> may be corrected even if the amount of eccentricity is changed due to removal of water from the clothes.

When the rotational speed of the drum <NUM> or <NUM> is increased above the adjusted rotational speed range, the balls rotated within the balancer housing <NUM> or <NUM> are rotated at the rotational speed of the drum <NUM> of <NUM>, and the disposition of the balls is almost fixed.

Therefore, it is difficult to adjust the disposition of the balls even if the amount of eccentricity is changed due to removal of water from the clothes. Thus, when the amount of eccentricity of the drum is changed by the designated range or more, the drum is eccentrically rotated and may thus cause vibration of the cabinet.

Hereinafter, the method for controlling the spin-drying cycle of the laundry treatment machine in accordance with this embodiment will be described with reference to <FIG>.

In the laundry treatment machine, the ball balancer is initially adjusted by draining water stored in the tub and increasing the rotational speed of the drum to the adjusted rotational speed range (operation S100). In the initial adjustment of the ball balancer, the controller <NUM> drains water remaining in the tub subsequent to the previous operation, and increases the rotational speed of the drum to the adjusted rotational speed range so that the balls disposed within the balancer housing <NUM> or <NUM> are disposed at a position corresponding to clothes.

In more detail, referring to <FIG>, water stored in the tub <NUM> or <NUM> is drained, and the rotational speed of the drum is increased (operation S110). In this case, the controller <NUM> increases the rotational speed of the drum <NUM> or <NUM> to the adjusted rotational speed range.

When the rotational speed of the drum <NUM> or <NUM> is increased to the adjusted rotational speed range, the adjusted rotational speed range is maintained for a designated time (operation S120), and whether or not vibration of a designated level or above occurs due to rotation of the drum <NUM> or <NUM> is determined (operation S130).

As vibration occurring due to rotation of the drum <NUM> or <NUM>, vibration of the tub in the forward and rearward directions or in the leftward and rightward directions is measured through the vibration sensor <NUM> or <NUM> disposed at the tub. When vibration sensed by the vibration sensor is the designated level or above, the controller <NUM> decreases the rotational speed of the drum to a designated speed or lower or stops the rotation of the drum, and then again increases the rotational speed of the drum (operation S110).

The reason for this is that, if the balls within the balancer housing <NUM> or <NUM> are not disposed at a position suitable for eccentricity of the clothes, excessive vibration of the cabinet occurs, and when the rotational speed of the drum is increased in this state, the vibration of the cabinet becomes severe due to eccentric rotation.

When the drum <NUM> or <NUM> is rotated at the adjusted rotational speed range, if vibration of the designated level or above does not occur, the controller <NUM> performs a preliminary spin-drying operation (operation S200).

In the preliminary spin-drying operation (operation S200) in which a considerable amount of water is removed from the clothes, the drum <NUM> or <NUM> is rotated to a speed range corresponding to the resonance point of the cabinet <NUM> or <NUM> or lower. In the preliminary spin-drying (operation S200), the rotational speed of the drum <NUM> or <NUM> is increased to the speed range corresponding to the resonance point or lower in a state in which the clothes contain a large amount of water. In the preliminary spin-drying operation (operation S200), a sufficient amount of water is removed from the clothes so that the amount of eccentricity of the clothes is reduced, prior to the main spin-drying operation in which the drum is rotated to a rotational speed exceeding the resonance point.

In the preliminary spin-drying operation (operation S200), the rotational speed of the drum is increased to a maximum rotational speed N2 corresponding to the resonance point or lower (operation S210). In the preliminary spin-drying operation, the maximum rotational speed N2 of the drum is set to an RPM range of the resonance point of the cabinet or below. In the laundry treatment machine <NUM> or <NUM> in accordance with this embodiment, on the assumption that the resonance point of the cabinet occurs at about <NUM> RPM, the maximum rotational speed N2 of the drum in the preliminary spin-drying operation is <NUM> RPM.

During the process of increasing the rotational speed of the drum <NUM> or <NUM>, whether or not vibration of the laundry treatment machine occurs when the rotational speed of the drum <NUM> or <NUM> is a vibration sensing rotational speed N3 is sensed (operation S220). The vibration sensing rotational speed N3 is set between the adjusted rotational speed range N1 and the maximum rotational speed N2 in the preliminary spin-drying operation. In this embodiment in which the maximum rotational speed N2 of the drum in the preliminary spin-drying operation is <NUM> RPM, the vibration sensing rotational speed N3 may be <NUM> to <NUM> RPM.

When vibration of the designated level or above occurs in the state in which the rotational speed of the drum <NUM> or <NUM> is the vibration sensing rotational speed N3, the controller <NUM> decreases the rotational speed of the drum to the adjusted rotational speed range N1. Thereafter, the rotational speed of the drum is again increased to the vibration sensing rotational speed N3, and whether or not vibration occurs is determined. Thereafter, when vibration sensed by the vibration sensor <NUM> or <NUM> is still the designated level or above, the controller <NUM> decreases the rotational speed of the drum to the designated speed or lower, or stops the rotation of the drum and then again perform the initial adjustment of the ball balancer (operation S100).

That is, upon determining that vibration of the designated level or above occurs at least once in the state in which the rotational speed of the drum <NUM> or <NUM> is the vibration sensing rotational speed N3, the controller <NUM> decreases the rotational speed of the drum to the designated speed or lower, or stops the rotation of the drum and then again perform the initial adjustment of the ball balancer (operation <NUM>).

Upon determining that vibration of the designated level or above does not occur in the state in which the rotational speed of the drum <NUM> or <NUM> is the vibration sensing rotational speed N3, the controller <NUM> increases the rotational speed of the drum to the maximum rotational speed N2 in the preliminary spin-drying operation (operation S230).

Thereafter, the rotational speed of the drum is decreased to the adjusted rotational speed range (operation S240). The controller <NUM> maintains the maximum rotational speed N2 for a designated time, and then decreases the rotational speed of the drum <NUM> or <NUM> to the adjusted rotational speed range N1. The maximum rotational speed N2 is maintained for the designated time so as to maximally remove water from the clothes in the preliminary spin-drying operation (operation S200).

Thereafter, the controller <NUM> decreases the rotational speed of the drum <NUM> or <NUM> to the adjusted rotational speed range N1, and then adjusts disposition o the balls within the ball balancer (operation S10).

In the laundry treatment machine in accordance with this embodiment, disposition of the balls within the ball balancer is adjusted several times during a process of the spin-drying cycle (operations S10, S20 and S30). In the adjustment of the disposition of the ball balancer (operations S10, S20 and S30), disposition of the balls <NUM> or <NUM> rotated within the balancer housing <NUM> or <NUM> is finely adjusted by rotating the drum <NUM> or <NUM> within the adjusted rotational speed range N1.

In the case of laundry having been subjected to the preliminary spin-drying (operation S200) or each spin-drying (operation S300, S400 or S500) which will be described below, the amount of eccentricity of the laundry is varied according to variables, such as the kind of the laundry, the amount of removed water, etc. The amount of eccentricity of the laundry having been subjected to each spin-drying operation (operation S200, S300, S400 or S500) is generally changed to be decreased, but in some cases, the amount of eccentricity of the laundry may be changed to be increased due to variables, such as the kind of the laundry, a region of the laundry from which water is removed, etc..

In each spin-drying operation (operation S200, S300, S400 or S500), the drum is rotated above the adjusted rotational speed range N1, and thus, it is difficult to change disposition of the balls within the balancer housing <NUM> or <NUM> to a position corresponding to the change in the amount of eccentricity. Therefore, in the method for controlling the spin-drying cycle of the laundry treatment machine in accordance with this embodiment, the disposition of the balls within the ball balancer is adjusted (operation S10, S20 or S30) between the respective spin-drying operations (operation S200, S300, S400 and S500), and thereby, the balls within the balancer housing <NUM> or <NUM> are finely adjusted so as to correspond to the change in the amount of eccentricity due to removal of water.

In the main spin-drying operation, the drum is rotated at a rotational speed of above the resonance point, after the preliminary spin-drying operation. In the main spin-drying, if a designated condition is satisfied, the drum is rotated at the rotational speed of above the resonance point. The main spin-drying operation includes accelerating rotation of the drum by increasing the rotational speed of the drum <NUM> or <NUM> to a maximum value of each operation, and decelerating rotation of the drum by decreasing the rotational speed of the drum <NUM> or <NUM> from the maximum value to the value corresponding to the adjustment of the disposition of the balls within the ball balancer. Further, the main spin-drying operation may further include maintaining the rotational speed of the drum <NUM> or <NUM> at the maximum value of each operation.

The main spin-drying operation in accordance with this embodiment may include a first spin-drying operation performed by rotating the drum at a rotational speed of above the resonance point of the cabinet (operation S300), a second spin-drying operation performed by rotating the drum at a maximum rotational speed higher than a maximum rotational speed of the drum in the first spin-drying operation (operation S400), and a third spin-drying operation performed by rotating the drum at a maximum rotational speed for a longer time than in the second spin-drying operation (operation S500).

Hereinafter, the respective spin-drying operations will be described in detail.

Referring to <FIG>, in the first spin-drying operation (operation S300), the drum <NUM> or <NUM> is rotated within an RPM range of above the resonance point of the cabinet. In the first spin-drying operation (operation S300), the drum is rotated within a range between the resonance point of the cabinet and a maximum rotational speed M2 or M3 in the second or third spin-drying operation. In the first spin-drying operation, the drum <NUM> or <NUM> is rotated within a range between the resonance point of the cabinet and a resonance point of the door <NUM>.

A maximum rotational speed M1 of the drum in the first spin-drying operation is set to be lower than the maximum rotational speed M2 or M3 of the drum in the second or third spin-drying operation. Since the amount of removed water in the first spin-drying operation is greater than in the second spin-drying operation or the third spin-drying operation and thus a change in the amount of eccentricity in the first spin-drying operation is relatively large, the maximum rotational speed M1 of the drum in the first spin-drying operation is set to be lower than the maximum rotational speed M2 or M3 of the drum in the second or third spin-drying operation. In the laundry treatment machine <NUM> or <NUM> in accordance with this embodiment, the maximum rotational speed M1 is within the range of about <NUM> to <NUM> RPM.

In the first spin-drying operation, when the change in the amount of eccentricity due to removal of water during rotation of the drum within the RPM range of the resonance point of the cabinet or lower is a set range or below, the drum is rotated to the maximum rotational speed M1, as shown in <FIG>. In the first spin-drying operation, when the change in the amount of eccentricity due to removal of water during rotation of the drum to the resonance point of the cabinet or lower is great, the drum is rotated to the resonance point of the cabinet or lower, as shown in <FIG>. The rotation of the drum to the resonance point or lower may serve to prevent excessive vibration of the cabinet occurring due to rotation of the drum at the resonance point or higher.

Referring to <FIG>, in the first spin-drying operation (operation S300), in detail, the rotational speed of the drum is increased (operation S310), after the adjustment of the disposition of the balls within the ball balancer (operation S10). The controller <NUM> increases the rotational speed of the drum which is rotated within the adjusted rotational speed range N1.

During the process of increasing the rotational speed of the drum <NUM> or <NUM>, a maximum vibration value V1 sensed within a first set rotational speed range N4 is stored (operation S320), and a maximum vibration value V2 sensed within a second set rotational speed range N5 is stored (operation S330).

The second set rotational speed range N5 is set to have a higher RPM range than that of the first set rotational speed range N4. The first set rotational speed range N4 and the second set rotational speed range N5 are set to be within an RPM range of the resonance point or lower. The first set rotational speed range N4 and the second set rotational speed range N5 may be set as sections in which removal of water is the greatest in the first spin-drying operation.

In the laundry treatment machine <NUM> or <NUM> in accordance with this embodiment, the first set rotational speed range N4 may be set to a range within which the rotational speed of the drum <NUM> or <NUM> is <NUM> RPM to <NUM> RPM, and the second set rotational speed range N5 may be set to a range within which the rotational speed of the drum <NUM> or <NUM> is <NUM> RPM to <NUM> RPM.

Thereafter, a difference between the maximum vibration value V1 within the first set rotational speed range N4 and the maximum vibration value V2 within the second set rotational speed range N5 is determined (operation S340). As the difference between the vibration values is increased, vibration of the cabinet of the designated level or above may occur when the rotational speed of the drum <NUM> and <NUM> is increased to resonance point.

Therefore, when the difference between the maximum vibration value V1 within the first set rotational speed range N4 and the maximum vibration value V2 within the second set rotational speed range N5 exceeds a set value, the controller <NUM> maintains the rotational speed of the drum <NUM> or <NUM> within the second set rotational speed range N5 (operation S350). The maintenance of the rotational speed of the drum <NUM> or <NUM> within the second set rotational speed range N5 includes maintaining one rotational speed of the drum within the second set rotational speed range N5, or changing the rotational speed of the drum within the second set rotational speed range N5. For example, the finally increased rotational speed of the drum <NUM> or <NUM> within the second set rotational speed range N5 may be maintained, the rotational speed of the drum <NUM> or <NUM> indicating a minimum vibration value among vibration values measured in the second set rotational speed range N5 may be maintained, or the minimum rotational speed of the drum within the second set rotational speed range N5 may be maintained. The maintenance of the rotational speed of the drum <NUM> or <NUM> within the second set rotational speed range N5 may be variously set in the same manner as in the satisfaction of the second set rotational speed range N5.

When the difference between the maximum vibration value V1 within the first set rotational speed range N4 and the maximum vibration value V2 within the second set rotational speed range N5 is the set value or less, the controller <NUM> increases the rotational speed of the drum to the maximum rotational speed M1 in the first spin-drying operation (operation S355). In this embodiment, whether or not the difference between the maximum vibration value V1 in the first set rotational speed range N4 and the maximum vibration value V2 in the second set rotational speed range N5 exceeds <NUM> is determined.

In the maintenance of the second set rotational speed range N5 (operation S350), a maintenance period may be set so that the same amount of water as the amount of water removed in the increase of the rotational speed of the drum to the maximum rotational speed (operation S360) may be removed. In accordance with this embodiment, the period to maintain the second set rotational speed range may be set to <NUM> seconds, and such a value is merely one embodiment and thus the maintenance period may be changed within a range within which the same amount of water as the amount of water removed in the increase in the rotational speed of the drum to the maximum rotational speed (operation S355) is removed.

Thereafter, the controller <NUM> decreases the rotational speed of the drum (operation S360). The rotational speed of the drum is decreased to the adjusted rotational speed range, and then the disposition of the ball balancer is adjusted (operation S20). The decrease of the rotational speed of the drum (operation S360) includes a ball disposition maintenance section S1. The ball disposition maintenance section S1 prevents excessive vibration of the cabinet occurring during the process of decreasing the rotational speed of the drum. When the rotational speed of the drum is rapidly decreased, the disposition of the balls within the balancer housing <NUM> or <NUM> is changed and thus excessive vibration of the cabinet may occur due to eccentric rotation of the drum, and therefore, the ball disposition maintenance section S1 is provided so as to prevent such a problem. The ball disposition maintenance section S1 in accordance with this embodiment may be formed within the range of <NUM> RPM. However, this is merely one embodiment, and the rotational speed range of the drum <NUM> or <NUM> in the ball disposition maintenance S1 may be variously set within a range within which the disposition of the balls within the balancer housing <NUM> or <NUM> is not changed during the decrease of the rotational speed of the drum.

The controller <NUM> adjusts the disposition of the balls within the ball balancer by decreasing the rotational speed of the drum to the adjusted rotational speed range N1 (operation S20).

In the second spin-drying operation (operation S400), the drum is rotated within an RPM range of above the resonance point. The maximum rotational speed M2 in the second spin-drying operation (operation S400) is set to be higher than the maximum rotational speed M1 of the drum in the first spin-drying operation (operation S300).

The maximum rotational speed of the drum in the second spin-drying operation (operation S400) in accordance with this embodiment is set within the range of about <NUM> to <NUM> RPM. The maximum rotational speed M2 of the drum <NUM> or <NUM> in the second spin-drying operation (operation S400) may be divided into a first maximum rotational speed M2a and a second maximum rotational speed M2b. The controller <NUM> may increase the rotational speed of the drum <NUM> or <NUM> to the first maximum rotational speed M2a, and then increase the rotational speed of the drum <NUM> or <NUM> to the second maximum rotational speed M2b when vibration sensed by the vibration sensor <NUM> or <NUM> is below the designated level. However, when the drum <NUM> or <NUM> is rotated at the first maximum rotational speed M2a and the vibration sensed by the vibration sensor <NUM> or <NUM> is the designated level or above, the controller <NUM> maintain the first maximum rotational speed M2a of the drum <NUM> or <NUM>. In this case, a section in which rotational speed of the drum is increased to the second maximum rotational speed M2b is omitted.

The second spin-drying operation includes increasing the rotational speed of the drum to the maximum rotational speed (operation S410), maintaining the rotational speed of the drum at the maximum rotational speed (operation S420), and decreasing the rotational speed of the drum from the maximum rotational speed to the adjusted rotational speed range (operation S430).

The decrease of the rotational speed of the drum (operation S430) in the second spin-drying operation includes a ball disposition maintenance section S2 to prevent excessive vibration of the cabinet occurring during the process of decreasing the rotational speed of the drum, in the same manner as in the first spin-drying operation.

In the third spin-drying operation (operation S500), the drum is rotated within an RPM range of above the resonance point. The maximum rotational speed M3 in the third spin-drying operation (operation S500) is set to be higher than the maximum rotational speed of the drum in the first spin-drying operation (operation S300).

The maximum rotational speed of the drum in the third spin-drying operation (operation S500) in accordance with this embodiment is set within the range of about <NUM> to <NUM> RPM. The maximum rotational speed M3 of the drum <NUM> or <NUM> in the third spin-drying operation (operation S500) may be divided into a first maximum rotational speed M3a and a second maximum rotational speed M3b. The controller <NUM> may increase the rotational speed of the drum <NUM> or <NUM> to the first maximum rotational speed M3a, and then increase the rotational speed of the drum <NUM> or <NUM> to the second maximum rotational speed M3b when vibration sensed by the vibration sensor <NUM> or <NUM> is below the designated level. However, when the drum <NUM> or <NUM> is rotated at the first maximum rotational speed M3a and the vibration sensed by the vibration sensor <NUM> or <NUM> is the designated level or above, the controller <NUM> maintain the first maximum rotational speed M3a of the drum <NUM> or <NUM>.

The third spin-drying operation includes increasing the rotational speed of the drum to the maximum rotational speed (operation S510), maintaining the rotational speed of the drum at the maximum rotational speed (operation S520), and decreasing the rotational speed of the drum from the maximum rotational speed to the adjusted rotational speed range (operation S530).

A time taken to maintain the rotational speed of the drum at the maximum rotational speed (operation S520) in the third spin-drying operation (operation S500) may be set to be longer than a time taken to maintain the rotational speed of the drum at the maximum rotational speed (operation S420) in the second spin-drying operation (operation S400). The amount of water removed from the laundry in the third spin-drying operation is less than the amount of water removed from the laundry in the second spin-drying operation, and thus, the time taken to maintain the rotational speed of the drum at the maximum rotational speed in the third spin-drying operation may be set to be longer than the time taken to maintain the rotational speed of the drum at the maximum rotational speed in the second spin-drying operation.

Claim 1:
A method for controlling a spin-drying cycle of a laundry treatment machine, the method comprising:
performing a plurality of spin-drying operations (S200, S300, S400, S500) by rotating a drum (<NUM>; <NUM>; <NUM>) above an adjusted rotational speed range (N1) configured to adjust disposition of balls within a ball balancer (140a, 140b; 240a, 240b) so as to correspond to a change in an amount of eccentricity; and
adjusting (S10, S20, S30) the disposition of the balls within the ball balancer (140a, 140b; 240a, 240b) by rotating the drum (<NUM>; <NUM>; <NUM>) within the adjusted rotational speed range (N1), between the respective spin-drying operations (S200, S300, S400, S500), wherein the spin-drying operations comprise:
a preliminary spin-drying operation (S200) performed by rotating the drum (<NUM>; <NUM>; <NUM>) within a RPM range of a resonance point of a cabinet (<NUM>; <NUM>) or lower; and
a main spin-drying operation (S300, S400, S500) performed by rotating the drum (<NUM>; <NUM>; <NUM>) within an RPM range of above the resonance point of the cabinet (<NUM>; <NUM>),
wherein the disposition of the balls within the ball balancer (140a, 140b; 240a, 240b) is adjusted by rotating the drum (<NUM>; <NUM>; <NUM>) within the adjusted rotational speed range (N1), between the preliminary spin-drying operation (S200) and the main spin-drying operation (S300, S400, S500);
characterized in that, the main spin-drying operation (S300, S400, S500) comprises:
increasing (S410, S510) the rotational speed of the drum (<NUM>; <NUM>; <NUM>) to a maximum rotational speed (M1, M2, M3); and
decreasing (S430, S530) the rotational speed of the drum (<NUM>; <NUM>; <NUM>) from the maximum rotational speed (M1, M2, M3),
wherein the decreasing the rotational speed of the drum (<NUM>; <NUM>; <NUM>) comprises a ball disposition maintenance section (S1, S2, S3) configured to prevent excessive vibration of the cabinet (<NUM>; <NUM>) occurring during a process of decreasing the rotational speed of the drum (<NUM>; <NUM>; <NUM>).