WO2015133845A1

WO2015133845A1 - Washing machine and control method of the same

Info

Publication number: WO2015133845A1
Application number: PCT/KR2015/002150
Authority: WO
Inventors: Sunho LEE; Bonkwon Koo; Sunku KWON; Sanghyun Lee
Original assignee: Lg Electronics Inc.
Priority date: 2014-03-05
Filing date: 2015-03-05
Publication date: 2015-09-11
Also published as: KR20150104426A; KR102280074B1

Abstract

The present invention relates to a control method of washing machine including an external tub to receive washing water, an internal tub rotatably disposed in the external tub to receive foams, and a motor to rotate the internal tub. The control method of the washing machine includes a water supply step of supplying washing water to the external tub and a change step of sequentially increasing or reducing target speed of the motor.

Description

WASHING MACHINE AND CONTROL METHOD OF THE SAME

The present invention relates to washing machine and a control method of the same. More specifically, the present invention relates to a washing machine for reducing noises and vibration by preventing foams from being united.

In general, a washing machine is a device which processes foams by applying a physical action and/or a chemical action to the laundry (hereinafter referred to as ‘foam’) such as clothes or bedding. The washing machine includes an external tub to receive washing water and an internal tub to receive the foams and rotatably installed inside the external tub. A pulsator is rotatably provided at a bottom of the internal tub. A motor rotates at least one of the pulsator and the internal tub. The foams conflict with the internal tub or the pulsator and flows in the internal tub to be separated from pollutions. According to the related art, in order to clean the foams, the motor is rotated at preset speed and a preset angle. However, if the forms are rotated in a united state, the internal tub is unstably rotated. Further, if the internal tub is eccentrically rotated, the internal tub collides with the external tub so that vibration and noises are generated.

Accordingly, the present invention has been made in an effort to solve the aforementioned problems, and it is an object of the present invention to provide a washing machine for stably rotating an internal tub by preventing the eccentricity of the internal tub, and a control method of the same.

It is another object of the present invention to provide a washing machine capable of minimizing vibration and noises thereof and a control method of the same.

It is still another object of the present invention to provide a washing machine capable of increasing a dehydration degree of the laundry when dehydration is terminated.

Objects of the embodiment may not be limited to the above and other objects and other objects which are not described may be clearly comprehended to those of skill in the art to which the embodiment pertains through the following description.

The present invention provides a control method of a washing machine, the control method including: (a) supplying washing water into an internal tub to receive foams; (b) alternately and repeatedly rotating the internal tub in both directions while controlling rotated speed of the internal tub when the internal tub is rotated in one direction to be increased as compared with speed of the internal tub upon previous rotation.

The control method of a washing machine of claim 1, wherein step (b) may include: setting target speed of the internal tub; and rotating the internal tub at the target speed, wherein the target speed is set to be gradually increased when a rotating direction of the internal tub is changed. The target speed may be increased with a constant ratio.

A rotated angle of the internal tub when the internal tub may be rotated in the one direction in step (b) is gradually increased corresponding to the target speed.

Step (b) may include: (b1) rotating the internal tub in a forward direction at predetermined speed; (b2) stopping rotation of the internal tub; and (b3) rotating the internal tub at speed higher than the speed of the internal tub in step (b1). Step (b) may include (b4) stopping the rotation of the internal tub after step (b3); and rotating the internal tub at a speed equal to the speed in step (b3) in the forward direction.

The control method of a washing machine may further include (c) alternately rotating the internal tub in the both directions while rotating the internal tub at constant speed every rotation after step (b). Rotated speed of the internal in step (c) may be equal to or greater than highest speed in step (b).

The control method of a washing machine may further include (d) alternately and repeatedly rotating the internal tub in the both directions after step (c) while controlling that the speed of the internal when the internal tub is rotated in the one direction is reduced as compared with previous rotated speed of the internal tub. Step (d) may include: setting target speed of the internal tub; and rotating the internal at the target speed, wherein the target speed is set to be gradually reduced when rotated direction of the internal tub is changed. The target speed in step (d) may be reduced with a constant ratio.

In step (d), rotated angle of the internal tub when the internal tub may be rotated in the one direction is gradually reduced corresponding to the target speed. The control method of a washing machine may further include: distributing water into the internal tub; and dehydrating the internal tub by rotating the internal tub at high speed, after step (d).

The present invention further provides a control method of a washing machine, the control method including: (a) alternately rotting an internal tub to receive foams in both directions in a state that water is supplied into the internal tub while controlling rotated speed of the internal tub when the internal tub is rotated in one direction to be reduced as compared with speed of the internal tub upon previous rotation; (b) distributing water into the internal tub; and (c) dehydrating the internal tub by rotating the internal tub at high speed.

Step (a) may include: setting target speed of the internal tub; and rotating the internal tub at the target speed, wherein the target speed is set to be gradually increased when a rotating direction of the internal tub is changed. The target speed is increased with a constant ratio.

A rotated angle of the internal tub when the internal tub may be rotated in the one direction is gradually increased corresponding to the target speed.

The washing machine and a control method of the same according to the present invention have one or more effects.

First, the laundry is uniformly spread so that the internal tub is stably rotated.

Second, a rotating shaft of the internal tub is vertically formed so that collision of the internal tub with the external tub is prevented.

Third, rotation of the internal tub is stabilized so that noises and vibration of the washing machine are reduced.

Fourth, since maximum possible rotation speed of the internal tub is increased, high speed rotation of the internal tub is possible so that a dehydration degree is increased.

Effects of the present invention are not limited to the above effects, but other various effects may be directly or indirectly disclosed in the following description of the embodiment of the present invention.

FIG. 1 is a cross-sectional view illustrating a structure of a washing machine according to an embodiment of the present invention;

FIG. 2 is a block diagram illustrating main constituent elements of the washing machine according to an embodiment of the present invention;

FIG. 3 is a flowchart illustrating a control method of the washing machine according to an embodiment of the present invention;

FIG. 4 is a diagram illustrating an agitating angle and target speed of a motor according to an embodiment of the present invention;

FIG. 5 is a graph illustrating variation of the target speed of the motor according to a time in a change step and a speed maintenance step;

FIG. 6 is a graph illustrating variation of the target speed of a real motor according to a time in a change step and a speed maintenance step; and

FIG. 7 is a diagram illustrating target speed and an agitating angle stored in a memory.

The details of other embodiments are contained in the detailed description and accompanying drawings. The advantages, the features, and schemes of achieving the advantages and features of the disclosure will be apparently comprehended by those skilled in the art based on the embodiments, which are described later in detail, together with accompanying drawings. The present inventive concept may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Hereinafter, exemplary embodiments will be described in more detail with reference to accompanying drawings. In the following description, for the illustrative purpose, the same components will be assigned with the same reference numerals, and the repetition in the description about the same components will be omitted in order to avoid redundancy.

In what follows, a washing machine and a control method of the washing machine according to preferred embodiments of the present invention will be described in detail with reference to the appended drawings.

FIG. 1 is a cross-sectional view illustrating a structure of washing machine according to an embodiment of the present invention, FIG. 2 is a block diagram illustrating main constituent elements of the washing machine according to an embodiment of the present invention, and FIG. 3 is a flowchart illustrating a control method of the washing machine according to an embodiment of the present invention.

Referring to FIGS. 1 and 2, a washing machine 100 according to an embodiment of the present invention includes: a cabinet 111 to form an outer appearance and including an open upper portion, a cabinet cover 112 disposed at the open upper portion of the cabinet 111 and formed therein with a laundry entrance in which the laundry enter, a door 113 to open/close the laundry entrance; an external tub 122 to receive washing water, hung inside the cabinet 111 by a support member 117 and buffered by a damper 118; and an internal tub 115 disposed at an inner side of the external tub and rotated based on a vertical shaft and to receive the laundry.

The internal tub 115 is formed a plurality of water holes (not shown) so that washing water may circulate between the external tub 122 and the internal tub 115. An external tub cover 114 is formed at an upper portion of the external tub 122. The external tub cover 114 is formed therein with a laundry entrance hole h through which the laundry may enter.

A pulsator 116 for forming a water stream in the washing water is provided at a bottom of the internal tub 115. A motor 130 for generating a rotating force in order to rotate the internal tub 115 and/or the pulsator 116 is disposed at a lower side of the external tub 122. Hereinafter, the internal tub 115 and/or the pulsator 116 generally refer to water

stream forming parts

115 and 116 for forming a water stream in the washing water.

The cabinet cover 112 includes a control panel 124 to receive a command from a user with respect to an overall operation of the washing machine 100. A detergent box 134 and a detergent box housing 136 are disposed at an inner side of the cabinet cover 112. The detergent box 134 may receive a detergent D. The detergent box housing 136 drawably receives the detergent box 134, and is formed therein with a fluid path so that washing water introduced from the water supply hose 119 is supplied into the internal tub 115 through the detergent box 134. The detergent box housing 136 may be formed therein with a distribution hole 136h to distribute washing water introduced from a water supply hose 119 to the detergent box 134.

A water distribution hose 142 and a water distribution pump 144 distribute washing water from the external tub 122. The cabinet cover 112 includes a control panel 124 to receive a command from a user with respect to an overall operation of the washing machine 100. A detergent box 134 and a detergent box housing 136 are disposed at an inner side of the cabinet cover 112. The detergent box 134 may receive a detergent D. The detergent box housing 136 drawably receives the detergent box 134, and is formed therein with a fluid path so that washing water introduced from the water supply hose 119 is supplied into the internal tub 115 through the detergent box 134.

The detergent box housing 136 may be formed therein with a distribution hole 136h so that washing water introduced from the water supply hose 119 is distributed to the detergent box 134. The motor 130 rotates water

stream forming parts

115 and 116. The motor 130 includes a stator 130a wound by a coil and a rotor 130b rotated by generating an electromagnetic interaction with the coil.

The stator 130a includes a plurality of wound coils and an internal resistor. The rotor 130b includes a plurality of magnets to generate the electromagnetic interaction with the coil.

The rotor 103b is rotated by the electromagnetic interaction between the magnets and the coil. A rotating force of the rotor 130b is transferred to the water

stream forming parts

115 and 116 to rotate the water

stream forming parts

115 and 116.

The motor 130 includes a Hall sensor 130c to measure a position of the rotator 130b. The Hall sensor 130c generates an on/off signal according to rotation of the rotor 130b. Rotating speed and a position of the rotor 130b are estimated based on the on/off signal generated from the Hall sensor 130c.

The controller 220 commands applying of a drive current to the motor 130. The drive current is determined according to target speed. If the target speed is increased, magnitude of the drive current is also increased. Conversely, if the target speed is reduced, the magnitude of the drive current is reduced.

An inverter 210 outputs power according to a PWM signal to supply the power to the coil of the stator 130a. When an agitated water stream is formed, the motor 130 is rotated in a predetermined direction to rotate the water

stream forming parts

115 and 116.

Referring to FIG. 3, an embodiment of the present invention relates to a control method of washing machine including an external tub 122 to receive washing water, an internal tub 115 rotatably disposed in the external tub 122 to receive foams, and a motor 130 to rotate the internal tub 115. The control method of the washing machine includes a water supply step S10 of supplying washing water to the external tub 122 and a change step S50 of sequentially increasing or reducing target speed of the motor 130.

In the water supply step S10, a controller 220 opens a water supply valve 135 to supply the washing water to the external tub 122. The washing water flows to the external tub 122 by passing through the detergent box 134 through the water supply hose 118.

The water supply step S10 is performed so that the laundry may be washed in a state that the external tub 122 is filled with the washing water. Such washing may include a step of alternately rotating the internal tub 115 in both directions. For example, in FIG. 3, a speed increasing step S20, a speed maintenance step S30, and a speed reducing step S40 are steps of performing the washing operation, and the internal tub 115 may be alternately rotated in the both directions in respective steps.

The internal tub 115 is alternately rotated in the both directions during washing. Each time a rotating direction is changed, the rotating speed is gradually increased so that the highest speed (for example, 120rpm in FIG. 5). Such a process corresponds to the speed increasing step S20.

The speed maintenance step S30 is performed after the speed increasing step S20. In the same manner as in the speed increasing step S20, the internal tub 115, the internal tub 115 is alternately rotated in the both directions, and is rotated at the highest speed every rotation. In the speed maintenance step S30, the rotating direction of the motor 130 may be changed at a predetermined period.

After the speed maintenance step S30, the speed reducing step S40 is performed. In the speed reducing step S40, the internal tub 115 is alternately rotated in the both directions. However, each time the rotating direction is changed, the rotating speed of the internal tub 115 is gradually reduced.

The change step S50 is a step of changing the rotating speed of the internal tub 115 with a predetermined tendency. The speed increasing step S30 is a step of changing the rotating speed of the internal tub 115 with an increasing tendency. However, the speed reducing step S40 of changing the rotating speed of the internal tub 115 with a decreasing tendency is an example of the change step S50. In the change step S50, a drive current applied to the motor 130 may be sequentially increased (case of step S20) or reduced (case of step S40) corresponding to change tendency of the rotating speed of the internal tub 115.

Hereinafter, for example, the change step S50 is performed in a state that the water is supplied to the internal tub 115. However, the present invention is not limited thereto. According to the embodiment, the change step S50 may be performed in a state that the washing water inside the internal tub 115 is all exhausted due to water exhaustion.

The target speed of the motor 130 in the speed increasing step S20 is not limited to follow values, but may be sequentially increased to 40rpm, 60rpm, 80rpm, 100rpm, and 120rpm as shown in FIG. 4(b). In this case, 120rpm corresponds to the highest speed.

Meanwhile, in the speed increasing step S20, when the target speed of the motor 130 is increased, an angle (hereinafter, agitating angle) of the motor 130 rotated at the target speed may be gradually increased. For example, as shown in FIG. 4(b), when the motor is rotated at target speed of 40rpm, 60rpm, 80rpm, 100rpm, and 120rpm, the agitating angle may be gradually increased to 60°, 120°, 270°, 300°, and 360°.

In contrast, in the speed reducing step S40, the target speed of the motor 130 may be sequentially reduced. For example, the target speed of the motor 130 may be sequentially reduced to an order of 120rpm, 100rpm, 80rpm, 60rpm, and 40rpm. The agitating angle of the motor 130 may be gradually reduced to 360°, 300°, 270°, 120°, and 60° corresponding to the speed of 120rpm, 100rpm, 80rpm, 60rpm, and 40rpm, respectively.

Meanwhile, the change step S50 may include a step of changing only a rotating direction while maintaining the target speed of the motor 130 constant. For example, in a case of the speed increasing step S20, each time the rotating direction of the motor 130 is changed, the target speed is not increased. That is, after the motor 130 is rotated in a forward direction at the target speed, the motor 130 may be rotated in a backward direction. FIG. 4(a) illustrates change in the target speed according to the above example. For example, in a case of the speed increasing step S20, the target speed of the motor 130 is gradually increased to 40rpm, 60rpm, 80rpm, 100rpm, and 120rpm in a state that the motor 130 is rotated in forward and backward directions with the target speed. (forward direction 40rpm rotation, backward direction 40rpm rotation, forward direction 60rpm rotation, backward direction 60rpm rotation...) Conversely, in a case of the speed reducing step S40, the target speed of the motor 130 is gradually reduced to 120rpm, 100rpm, 80rpm, 60rpm, and 40rpm in a state that the motor 130 may be rotated in forward and backward directions with the target speed. (forward direction 120rpm rotation, backward direction 120rpm rotation, forward direction 100rpm rotation, backward direction 100rpm rotation...)

In the change step S50, the controller 220 changes the rotating direction when the motor is rotated at a preset agitating angle. When the rotating direction of the motor 130 is changed, the rotating direction of the water

stream forming parts

115 and 116 are also changed. Accordingly, the foams may be uniformly distributed inside the internal tub 115. In detail, in the change step S50, if a rotated angle of the rotor 130b reaches a preset agitating angle, the controller 220 may stop rotation of the rotor 130b and again rotate the rotor 130b in an opposite direction. Each time the direction of a current applied to the motor 130 through the inverter 210, the rotating direction of the rotor 130b may be changed. To this end, the controller 220 obtains a position and a rotating angle of the rotor 130b based on a signal from the Hall sensor 130c. If the rotating angle of the rotor 130b reaches a preset agitating angle, the controller 220 may control the inverter 210 to rotate the rotor 130b in an opposite direction.

The agitating angle may be determined according to the target speed. The agitating angle and the target speed are stored in the memory 230. When the rotating direction of the motor 130 is changed, the motor 130 may be braked (plug brake) under control of the controller 220. The agitating angle may have directionality which is increased or reduced each time the rotating direction of the motor 130 is changed, and may be changed. For example, when the agitating angle has the increased directionality and is changed, the agitating angle may be increased in the order of 60°, 120°, 270°, 300°, and 360° according to change in the rotating direction of the motor 130.

As another example, when the agitating angle has the reduced directionality and is changed, the agitating angle may be increased in the order of 360°, 300°, 270°, 120°, and 60° according to change in the rotating direction of the motor 130.

The controller 220 may change the agitating angle each time a direction of a drive current applied to the motor 130 is changed. For example, the controller 220 may control the rotating direction of the motor 130 to rotate the motor 130 clockwise at 60°, counterclockwise at 80°, and again clockwise at 100° (see FIG. 4(b)).

As another example, the controller 220 may change the agitating angle if the applied direction of the drive current to the motor 130 is recovered to an initial state. For example, if it is assumed that the direction of the drive current is the initial state when the motor 130 is rotated clockwise, the controller 220 may control the rotating direction of the motor 130 so that the motor 130 is rotated counterclockwise at 60° after being rotated clockwise at 60° , and the motor 130 is rotated counterclockwise at 80° after being again rotated clockwise at 80° (see FIG 4.(a)).

As another example, the controller 220 may change the agitating angle every plug control of the motor 130. In contrast, if one period is terminated on the assumption that plug control of at least twice is the one period, the controller 220 may change the agitating angle.

FIG. 5 is a graph illustrating variation of the target speed of the motor according to a time in a change step and a speed maintenance step, and FIG. 6 is a graph illustrating variation of the target speed of a real motor according to a time in a change step and a speed maintenance step. In FIG. 6, a dotted line represents the target speed and the solid line represents real rotating speed of the motor 130.

In the change step S50, the target speed of the motor 130 is linearly increased or reduced.

In the change step S50, the target speed of the motor 130 may be linearly increased or may be increased with a constant rate. For example, the target speed may be increased to 40rpm, 60rpm, 80rpm, 100rpm, and 120rpm. As another example, the target speed of the motor 130 may be linearly reduced or may be reduced with a constant rate.

Meanwhile, the speed maintenance step S30 includes a step of changing the rotating direction of the motor 130. The rotating speed of the motor 130 up rotation may equally maintain.

If the target speed reaches preset highest speed (of 120rpm, see FIGS. 5 and 6) in the speed increasing step S30, the speed maintenance step S30 of alternatively rotating the motor 130 with the highest speed in both directions is performed and then the speed reducing step S40 may be performed.

In the speed maintenance step S30, when the motor is rotated by an agitating angle (for example, 360°) determined as the highest speed (for example, 120rpm), the rotating direction may be changed. In this case, the agitating angle upon every rotation of the motor 130 may be constant.

The control method of the washing machine according to an embodiment of the present invention includes a water distribution step S70 of distributing washing water received in the external tub 122 when the motor 130 stops after the speed reducing step S40 is terminated. In the water distribution step S70, the controller 220 may control the water distribution pump 144 to be driven. The water distribution step S70 may be terminated by stopping a drive of the water distribution pump 144 by the controller 220.

After the water distribution step S70, the dehydration step S80 may be performed. In the dehydration step S80, the foam is dehydrated by rotating the internal tub 115 at high speed in one direction.

Meanwhile, after terminating the speed reducing step S40, a bleach supply step S60 of supplying a bleach into the internal tub 115 before the water distribution step S70 may be further performed.

After the dehydration step S80 is terminated, the washing water is supplied into the internal tub 115 and a rinsing step S90 may be performed.

the change step S50 includes steps S51 of applying a plurality of currents which a drive current required at the target speed to the motor 130 and a pausing step S53 of stopping applying of the drive current to the motor 130, which is performed between steps S51.

In the speed increasing step S20, the target speed is increased by repeating the applying step S51. Accordingly, magnitude of the drive current may be increased. For example, the target speed may be increased to 60rpm, 80rpm, 100rpm, and 120rpm. Also, the drive current may be increased corresponding to the target speed.

Meanwhile, the control method of the washing machine according to an embodiment of the present invention includes agitating steps S20, S30, and S40 of alternately rotating the internal tub 115 to receive the foams in both directions. The agitating steps may include a step S20 of gradually increasing the agitating angle where the internal tub is rotated in one direction; a step S30 of rotating the internal tub 115 at a predetermined angle greater than the agitating angle in step S20; and a step S40 of gradually reducing the agitating angle of the internal tub 115.

The memory 230 may store target speeds and agitating angles corresponding to the target speeds, respectively.

The memory is divided into a volatile memory 230 which loses its data at power-off, and a nonvolatile memory 230which maintains its data even at power-off. The memory 230 may be divided into a Read Only Memory (ROM) and a Random Access Memory (RAM). Preferably, the memory 230 maintains the agitating angle and target speed information at power-off. The memory 230 may include an ROM.

Operations of the washing machine and a control method of the washing machine constructed as above according to the present invention are as follows.

The controller 220 opens a water supply valve to supply washing water to the external tub 115. The internal tub 115 receives the foams therein. The motor 130 rotates the internal tub 115.

After the water supply step, the controller 220 performs the speed increasing step S20.

The speed increasing step S20 gradually increase target step and an agitating angle. When the initial tub 115 is rotated at high speed from the beginning, the foams maintain the position by inertia and only the internal tub 115 is rotated so that uniting of the foams is deteriorated. However, according to the present invention, since the speed of the internal tub 115 is gradually increased, the foams are rotated together with the internal tub 115 to be distributed. Accordingly, a mass center of the internal tub 115 is closest to a rotating shaft of the motor 130. Further, since the agitating angle is sequentially increased to shake the foams. Accordingly, foams are distributed.

The speed maintenance step S30 is an interval when the target speed and the agitating angle maintain constant. In this case, washing out or washing is substantially performed. If a predetermined time elapses, the controller 220 performs the speed reducing step S40. The speed reducing step S40 is the purpose of removing uniting of the foams occurring during the speed maintenance step S30. The speed reducing step S40 gradually change the target speed and the agitating angle similar to the speed increasing step S20. However, since the speed reducing step S40 is performed until the drive of the motor 130 is terminated, the target speed is gradually reduced. In addition, the agitating angle is gradually reduced.

As described above, the uniting of the foams may be prevented by sequentially increasing or reducing the rotating angle and the target speed. Moreover, since the uniting of the foams is reduced, vibration and noises are reduced upon rotation of the internal tub 115. Further, since there is no great change in the mass center of the internal tub 115, the internal tub 115 is inclined to prevent the internal tub from colliding with the external tub. In addition, the internal tub 115 may be stably rotated so that the highest rotation possible speed of the internal tub 115 is increased. Accordingly, the dehydration degree is increased through high speed rotation of the internal tub 115.

Although the present invention has been described with reference to the illustrated drawings, it will be apparent to those skilled in the art that the present invention is not intended to be limited to the above-described embodiment and drawings, and various changes or modifications may be made therein without departing from the scope and the technical sprit of the present invention.

Claims

A control method of a washing machine, the control method comprising:

(a) supplying washing water into an internal tub to receive foams;

(b) alternately and repeatedly rotating the internal tub in both directions while controlling rotated speed of the internal tub when the internal tub is rotated in one direction to be increased as compared with speed of the internal tub upon previous rotation.
The control method of a washing machine of claim 1, wherein step (b) comprises:

setting target speed of the internal tub; and

rotating the internal tub at the target speed,

wherein the target speed is set to be gradually increased when a rotating direction of the internal tub is changed.
The control method of a washing machine of claim 2, wherein the target speed is increased with a constant ratio.
The control method of a washing machine of claim 1, wherein a rotated angle of the internal tub when the internal tub is rotated in the one direction in step (b) is gradually increased corresponding to the target speed.
The control method of a washing machine of claim 1, wherein step (b) comprises:

(b1) rotating the internal tub in a forward direction at predetermined speed;

(b2) stopping rotation of the internal tub; and

(b3) rotating the internal tub at speed higher than the speed of the internal tub in step (b1).
The control method of a washing machine of claim 5, wherein step (b) comprises:

(b4) stopping the rotation of the internal tub after step (b3); and

rotating the internal tub at a speed equal to the speed in step (b3) in the forward direction.
The control method of a washing machine of claim 1, further comprising (c) alternately rotating the internal tub in the both directions while rotating the internal tub at constant speed every rotation after step (b).
The control method of a washing machine of claim 7, wherein rotated speed of the internal in step (c) is equal to or greater than highest speed in step (b).
The control method of a washing machine of claim 1, further comprising (d) alternately and repeatedly rotating the internal tub in the both directions after step (c) while controlling that the speed of the internal when the internal tub is rotated in the one direction is reduced as compared with previous rotated speed of the internal tub.
The control method of a washing machine of claim 9, wherein step (d) comprises:

setting target speed of the internal tub; and

rotating the internal at the target speed,

wherein the target speed is set to be gradually reduced when rotated direction of the internal tub is changed.
The control method of a washing machine of claim 10, wherein the target speed in step (d) is reduced with a constant ratio.
The control method of a washing machine of claim 10, wherein in step (d), rotated angle of the internal tub when the internal tub is rotated in the one direction is gradually reduced corresponding to the target speed.
The control method of a washing machine of claim 12, further comprising:

distributing water into the internal tub; and

dehydrating the internal tub by rotating the internal tub at high speed, after step (d).
A control method of a washing machine, the control method comprising:

(a) alternately rotting an internal tub to receive foams in both directions in a state that water is supplied into the internal tub while controlling rotated speed of the internal tub when the internal tub is rotated in one direction to be reduced as compared with speed of the internal tub upon previous rotation;

(b) distributing water into the internal tub; and

(c) dehydrating the internal tub by rotating the internal tub at high speed.
The control method of a washing machine of claim 14, wherein step (a) comprises:

setting target speed of the internal tub; and

rotating the internal tub at the target speed,

wherein the target speed is set to be gradually increased when a rotating direction of the internal tub is changed.
The control method of a washing machine of claim 15, wherein the target speed is increased with a constant ratio.
The control method of a washing machine of claim 15, wherein a rotated angle of the internal tub when the internal tub is rotated in the one direction is gradually increased corresponding to the target speed.