Patent Description:
A washing machine is a general term indicating a device for removing a contaminant stuck to clothes, bedding, etc. (hereinafter, referred to as 'the laundry') using a chemical disintegration of water and a detergent and a physical operation such as a friction between water and the laundry.

Washing machines may be classified largely into a top-loading washing machine and a front-loading washing machine.

In the top-loading washing machine, a laundry loading hole is located at the top and a washing tub and a pulsator are rotated on a vertical rotational center. The top-loading washing machine performs a washing operation as a water flow is formed by the rotation of the washing tub and/or the pulsator.

In the front-loading washing machine, a laundry-loading hole is located at the front and a washing tub is rotated on an approximately horizontal rotation center. A lifter is provided in an inner circumferential surface of the washing tub, and a washing operation is performed as laundry flows by the lifter in accordance with rotation of the washing tub.

A recently developed front-loading washing machine implements various motions by combining a direction of rotation of a washing tub and a rotational speed of the washing tub.

<CIT> discloses a rolling motion, a tumbling motion, a step motion, a swing motion, a scrub motion, a filtration motion, and squeeze motion by combining a direction of rotation of a drum and a rotational speed of the drum. <CIT> relates to top load washing machine appliances and methods for operating washing machine appliances.

Although the recently developed front-loading washing machine is capable of implementing various motions, a motion with enhanced washing power may cause damage to laundry and a motion causing less damage to the laundry provides insufficient washing power.

An object of the present invention is to provide a washing machine which implements a new motion different from a conventional motion applied to a front-loading washing machine.

Another object of the present invention is to provide a washing machine which implements a new motion that provides excellent washing power compared with a conventional motion applied to a front-loading washing machine.

Yet another object of the present invention is to provide a washing machine which provides excellent washing power and causes less damage to laundry compared with a conventional motion.

Yet another object of the present invention is to provide a washing machine which provides excellent washing power compared with a conventional motion even though the conventional motion and a flow of laundry implement an identical or similar motion.

Other objects of the present invention not mentioned herein will be clearly understood from the following description by those skilled in the art to which the inventive concept pertains.

In order to achieve the above-described objects, a washing machine according to the present invention is described in independent claim <NUM>.

Other details of embodiments are included in the following detailed description and accompanying drawings.

A washing machine according to the present invention has one or more effects, as below.

First, the drum is rotated in one direction by a preset rotation angle and then rotated in the opposite direction by the rotation angle, and thereby, a flow of laundry in the drum may realize a new motion that is different from a conventional motion.

Second, as a lifter having a height lower than that of a conventional lifter is provided, laundry is able to flow inside the drum at a speed at which the laundry can be rotated integrally with the drum in a conventional washing machine. Therefore, a washing cycle may be performed by rotating the drum at a speed faster than in a conventional washing cycle, and, even though not just the new motion, but also the conventional motion and a flow of laundry realize an identical motion or similar motions, washing power may improve.

Third, as the drum is rotated at a speed faster than in a conventional washing cycle, washing machine may improve, and, as rotation of the drum by a preset rotation angle in one direction and the other direction is performed alternately and repeatedly, laundry may be less damaged
Effects of the present invention are not limited to the aforementioned effects, and other effects of the present invention which are not mentioned above will become apparent to those having ordinary skill in the art from the claims.

Advantages and features of the present invention and a method of achieving the same will be clearly understood from embodiments described below in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments and may be implemented in various different forms. The embodiments are provided merely for complete disclosure of the present invention and to fully convey the scope of the invention to those of ordinary skill in the art to which the present invention pertains. The present invention is defined only by the scope of the claims. In the drawings, the thickness of layers and regions may be exaggerated for clarity. Throughout the drawings, like numbers refer to like elements.

Referring to <FIG>, <FIG>, and <FIG>, a washing machine according to an embodiment of the present disclosure includes a casing <NUM> forming an outer appearance of the washing machine, a tub <NUM> for storing wash water, a drum <NUM> rotatably installed inside the tub <NUM> to introduce laundry, and a motor <NUM> for rotating the drum <NUM>.

A front panel <NUM> having a laundry loading hole <NUM> formed therein may be disposed at a front of the casing <NUM>, a door <NUM> for opening and closing the laundry loading hole <NUM> may be disposed at the front panel <NUM>, and a dispenser <NUM> for introducing detergent may be installed at the front panel <NUM>.

In addition, a water supply valve <NUM>, a water supply pipe <NUM>, and a water supply hose <NUM> may be installed inside the casing <NUM> so that wash water supplied after passing through the water supply valve <NUM> and the water supply pipe <NUM> is mixed with detergent in the dispenser <NUM> and is then supplied to the tub <NUM> through the water supply hose <NUM>.

In addition, a pump <NUM> and a circulating water supply pipe <NUM> may be installed, the pump <NUM> and the tub <NUM> may be connected via a discharge hose <NUM>, and the circulating water supply pipe <NUM> and the pump <NUM> may be connected directly to each other or may be connected to each other via a connection pipe <NUM>. Thus, when the pump <NUM> operates, wash water stored in the tub <NUM> may be sprayed into the drum <NUM> through the circulating water supply pipe <NUM> and then circulated. The pump <NUM> may be connected to a drain pipe <NUM> and thus discharge wash water to an outside through the drain pipe <NUM>.

As such, the pump <NUM> according to an embodiment of the present disclosure functions as both a discharge pump for discharging wash water to the outside and a circulation pump for circulating wash water. On the contrary, a discharge pump and a circulation pump may be installed separately, and, in a case where the discharge pump and the circulation pump are installed separately, it is the discharge pump may be connected to the drain pipe <NUM> and the circulation pump may be connected to the connection pipe <NUM>.

Meanwhile, the tub <NUM> may be formed as a single tub body or may be formed as a combination of a first tub body <NUM> and a second tub body <NUM> coupled thereto.

An a front of the tub <NUM>, an opening is formed to correspond to the laundry loading hole <NUM> formed in the front panel <NUM>.

The gasket <NUM> may be disposed between a loading hole boundary of the front panel <NUM>, which defines the laundry loading hole <NUM>, and a boundary of the tub <NUM>, which defines the opening, so that wash water stored in the tub <NUM> is prevented from leaking from the tub <NUM>.

The drum <NUM> for accommodating laundry may be rotatably provided in the tub <NUM>. The drum <NUM> receives laundry, and is disposed such that an entrance hole through which laundry is loaded is disposed at a front surface. The drum <NUM> is rotated about an approximately horizontal rotation center line. In this case, "horizontal" does not refer to the mathematical definition thereof. That is, even in the case where the rotation center line is inclined at a predetermined angle relative to a horizontal state, the axis is more like in the horizontal state than in a vertical state, and thus, it is considered that the rotation center line is substantially horizontal. A plurality of through holes <NUM> may be formed in the drum <NUM> so as to introduce water contained in the tub <NUM> into the drum <NUM>.

A lifter <NUM> provided on the inner circumferential surface of the drum <NUM> and protruding toward the inside of the drum <NUM> may be included. A lifter 70b may be manufactured separately from the drum <NUM> and coupled to the inner circumferential surface of the drum <NUM> (see <FIG>). Alternatively, a lifter 70c may be formed integrally with the drum <NUM> (see <FIG>). When the drum <NUM> is rotated, an operation of lifting laundry by the lifter <NUM> and dropping the laundry may be performed repeatedly.

A driving unit for rotating the drum <NUM> may be further provided. A driving shaft to be rotated by the driving unit may penetrate the rear of the tub <NUM> to be coupled to the drum <NUM>.

The driving unit may include a wash motor <NUM> of which a speed is controllable. The wash motor <NUM> may be an inverter direct drive motor. The controller <NUM> may include a Proportional-Integral (PI) controller, a Proportional-Integral-Derivative (PID) controller, and the like. The controller <NUM> may receive an output value (e.g., an output current) of a pump motor, and control an output value of the driver based on the received output value of the pump motor so that the number of times of rotation of the pump motor follows a preset target number of times of rotation (or a target rotational speed). The controller <NUM> may control driving of the wash motor <NUM> in accordance with a driving pattern.

The wash motor <NUM> may include a stator fixed to a rear side of the tub <NUM>, and a rotor rotating by a magnetic force acting in relation with the stator. The driving shaft may rotate integrally with the rotor.

The controller <NUM> may not just control the wash motor <NUM> but also control overall operations of the washing machine. Constituent elements mentioned hereinafter may be controlled by the controller <NUM>.

Referring to <FIG>, a conventional washing machine includes a lifter 70a having a height equal to or higher than <NUM> on an inner circumferential surface of a drum. Such a lifter 70a may restrict flow of laundry, and accordingly, when a rotational speed of the drum is about 40rpm, the lifter 70a may implement a rolling motion, when a rotational speed of the drum is about 46rpm, the lifter 70a may implement a tumbling motion, and, when a rotational speed of the drum is about 60rpm, the lifter 70a may implement a filtration motion. When a rotational speed of the drum is about 60rpm in the conventional washing machine having the lifter 70a of about <NUM> in height, laundry may be attached to the inner circumferential surface of the drum, it is not possible to implement any other motion at a higher rotational speed, except for braking the drum from rotating.

<FIG> is a perspective view showing a part of an inner circumferential surface of a drum of a washing machine according to a first embodiment of the present disclosure, the washing machine which has a lifter of a height lower than that of a conventional washing machine. <FIG> is a plan view of a lifter shown in <FIG>, and <FIG> is a cross-sectional view of <FIG> taken away along line I-I'.

Referring to <FIG> and <FIG>, a lifter 70b made separately from the drum <NUM> and disposed on the inner circumferential surface of a drum <NUM> has a height equal to higher than <NUM> and equal to lower than <NUM>. The washing machine according to the first embodiment of the present disclosure includes the lifter 70b of a height lower than that of the conventional lifter 70a in order to implement various motions. The height of the lifter 70b may be between <NUM> and <NUM>. The term "between" refers to a value within a range equal to or higher than a lower limit value and equal to or lower than an upper limit value, and this term will be hereinafter used with the same meaning.

In a case where the height of the lifter 70a is <NUM>, if a rotational speed of the drum <NUM> is gradually increased, laundry may be attached to the drum <NUM> at a rotational speed of 56rpm and then start being rotated integrally with the drum <NUM> (see 15a1 in <FIG> and 16a1 in <FIG>), and this motion is referred to as a filtration motion. That is, in the case where the height of the lifter 70a is <NUM>, a rotational speed of the drum at which the filtration motion stats is 56rpm.

In a case where the height of the lifter 70b is <NUM> and there is a very small quantity of laundry contained in the drum (when the amount of laundry is less than <NUM>), the laundry is attached to the inner circumferential surface of the drum <NUM> at a rotational speed of 71rpm and then starts being rotated integrally with the drum <NUM>. In the case where the height of the lifter 70b is <NUM> and there is a small quantity of laundry contained in the drum <NUM> (for example, when the amount of laundry is between <NUM> and <NUM>), the laundry is attached to the inner circumferential surface of the drum <NUM> at a rotational speed of 56rpm and then starts being rotated integrated with the drum <NUM>.

Therefore, in a case where the height of the lifter 70b is equal to or lower than <NUM>, when a user washes a small amount of laundry, the washing machine according to the first embodiment of the present disclosure is able to implement a new motion that cannot be implemented by the conventional washing machine. In a case where the height of the lifter 70b is higher than <NUM>, the washing machine according to the first embodiment of the present disclosure may restrict a flow of laundry and thus cannot implement a new motion, in the same way as it does when the conventional lifter of <NUM> is given.

However, in a case where the height of the lifter 70b is equal to or lower than <NUM>, sufficient friction does not occur between the inner circumferential surface of the drum <NUM> and the laundry and thus various motions of the laundry are not made. That is, even though the drum <NUM> is rotated at a speed faster than 56rpm, the laundry slips at a certain height between the highest point and the lowest point and then flows while shaking upward and downward. In this case, if the rotational speed of the drum <NUM> is increased even faster, the laundry may be instantly attached to the inner circumferential surface of the drum at about <NUM> rpm and thus rotated integrated with the drum <NUM>. Since such a flow may significantly degrade washing performance, the height of the lifter 70b should be higher than <NUM>.

A side rake angle of the lifter 70b as well as a height of the lifter 70b influence in causing a flow of the laundry. If the inclination angle is small, this leads to a situation as the same as when the height of the lifter 70b is equal to or lower than <NUM>.

Thus, every lift 70b disposed in the inner circumferential surface of the drum <NUM> may be formed in a height between <NUM> and <NUM>. A more detailed description will be provided with reference to <FIG> and <FIG>.

A different amount of laundry may be allowed in the washing machine according to a diameter of the drum <NUM>. The greater amount of laundry, the less portion of laundry directly influenced by the lifter <NUM>. Therefore, in order to implement a rubbing motion according to an inner diameter of the drum <NUM>, the height of the lifter 70b can be changed, and the height of the lifter 70b may be set differently according to the inner diameter of the drum <NUM>. That is, the lifter <NUM> may have a height which is at a predetermined ratio to the inner diameter of the drum <NUM>.

The height of the lifter 70b may be equal to or higher than <NUM>% and equal to or lower than <NUM>% of the inner diameter of the drum <NUM>. In a case where the inner diameter of the drum <NUM> is between <NUM> and <NUM>, the height of the lifter may be about between <NUM> and <NUM>. In addition, in a case where the inner diameter of the drum <NUM> is between <NUM> and <NUM>, the height of the lifter 70b may be equal to or higher than <NUM> and equal to or lower than <NUM>.

Meanwhile, although the inner diameter of the drum <NUM> is increased, the amount of the laundry may be maintained at a constant level, and in this case, the height of the lifter 70b may be between <NUM> and <NUM>, irrespective of the inner diameter of the drum <NUM>.

The lifter 70b shown in <FIG> and <FIG> is illustrated as a linear shape in a forward-backward direction of <FIG> (hereinafter, referred to as a "depth direction of the drum"), but aspects of the present disclosure are not limited thereto. Instead, the lifter 70b may be formed in a non-linear shape in which one end and the other end of one side of the lifter 70b are twisted by a predetermined angle relative to a predetermined central axis, and a height of the lifter 70b may be increased within a range between <NUM> and <NUM> front a front surface toward a rear surface of the drum <NUM>.

Lifters 70b provided in the inner circumferential surface of the drum <NUM> may be spaced apart from each other at a predetermined interval along a circumferential surface of the drum. That is, in a case where three lifters 70b are formed in the inner circumferential surface of the drum <NUM>, the lifters 70b may be disposed to form an angle of <NUM>° relative to each other. Although <FIG> shows a part of the drum having three lifters 70b formed therein, three or more lifters 70b may be disposed and, even in this case, the lifters 70b may be disposed to form a predetermined angle relative to each other.

<FIG> is a perspective view showing a lifter integrally formed with a drum <NUM> of a washing machine according to a second embodiment of the present disclosure. <FIG> is a plan view and a cross-sectional view showing a developed shape of an inner circumferential surface of the drum of the washing machine according to the second embodiment of the present disclosure.

As shown in <FIG> and <FIG>, the washing machine according to the second embodiment of the present disclosure may include a lifter 70c integrally formed with the drum <NUM>.

Referring to <FIG> and <FIG>, the inner circumferential surface of the drum <NUM> may be divided into a lifter portion <NUM> and an embossed portion <NUM>. In the inner circumferential surface of the drum <NUM>, two or more lifters <NUM> spaced apart from each other at a predetermined interval along a circumferential direction of the drum may be formed. That is, in a case where three lifter portions <NUM> are formed in the inner circumferential surface of the drum <NUM>, the lifter portions <NUM> may be disposed to form an angle of <NUM>° relative to each other. As shown in <FIG>, in the lifter portions <NUM>, a lifter 70c having a height lower than that of the conventional lifter 70a may be formed integrally with the drum <NUM>.

In the washing machine according to the second embodiment, the lifter 70c may be formed in each of a plurality of liter portions <NUM>. The lifter 70c may be formed in plural in the forward-backward direction, and the plurality of lifters 70c may be spaced apart from each other in the forward-backward direction. In addition, the plurality of liters 70c may be formed in a line while spaced apart from each other in the forward-backward direction.

The embossed portion <NUM> may be formed between the plurality of lifter portions <NUM>. A width of the embossed portion <NUM> may be greater than a width of the lifter portion <NUM>.

Embossing portions <NUM>, <NUM>, and <NUM> may be formed in the inner circumferential surface of the drum <NUM> in order to assist the role of the lifter 70c for lifting laundry and to increase friction between the inner circumferential surface of the drum <NUM> and the laundry and thereby increase washing power. The embossing portions <NUM>, <NUM>, and <NUM> may include a first embossing portion <NUM>, a second embossing portion <NUM>, and a third embossing portion <NUM>. The first embossing portion <NUM>, the second embossing portion <NUM>, and the third embossing portion <NUM> may be formed to have a height lower than that of the lifter 70c. The embossing portions <NUM>, <NUM>, and <NUM> may be integrally formed with the drum <NUM>.

The lifter portion <NUM> may include the lifter 70c, and the first embossing portions <NUM> formed on both left and right sies of the lifter 70c. The first embossing portion <NUM> may be spaced apart from the lifter 70c. The first embossing portion <NUM> may be formed on the left and right sides between the lifters 70c are spaced apart from each other in the forward-backward direction. The first embossing portion <NUM> may be formed at a height lower than that of the lifter 70c. The first embossing portion <NUM> may have a bottom shape identical to that of the second embossing portion <NUM>, and may have a height higher than that of the second embossing portion <NUM>.

The second embossing portion <NUM> having a height lower than that of the lifter 70c may be formed in the embossed portion <NUM>. The first embossing portion <NUM> and the second embossing portion <NUM> may be formed such that a length thereof in the depth direction of the drum <NUM> is greater than a width thereof.

At an interval between the lifter 70c and the first and second embossing portion <NUM> and <NUM>, the third embossing portion <NUM> may be formed. The third embossing portion <NUM> may be formed in a circular or polygonal shape, as viewed from above. The third embossing portion <NUM> may be formed in an octagonal shape, as viewed from above.

The lifter 70c of the washing machine according to the second embodiment of the present disclosure may be formed in a height equal to or higher than <NUM> so as to lift laundry upon rotation of the drum <NUM> and then drop the laundry therefrom. The higher the height of the lifter <NUM> is, the greater the force acts on restricting laundry upon rotation of the drum <NUM>. This leads to vulnerability to durability in terms of structure. Therefore, the height of the lifter 70c of the washing machine according to the second embodiment should be equal to or lower than <NUM>.

In addition, in a case where the height of the lifter 70c is higher than <NUM> as does the lifter 70b of the washing machine according to the first embodiment, it is not possible to implement a new motion.

In a case where the height of the lifter 70c integrally formed with the drum <NUM> is <NUM>, durability is vulnerable and a rotational speed of the drum <NUM> at which a filtration motion starts is the same as the case where the conventional lifter 70a is provided.

In a case where the height of the lifter 70c is <NUM> and there is a very small quantity of laundry contained in the drum (when the amount of laundry is less than <NUM>), the laundry is attached to the inner circumferential surface of the drum <NUM> at a rotational speed of 71rpm and then starts being rotated integrally with the drum <NUM>. In the case where the height of the lifter 70c is <NUM> and there is a small quantity of laundry contained in the drum <NUM> (for example, when the amount of laundry is between <NUM> and <NUM>), the laundry is attached to the inner circumferential surface of the drum <NUM> at a rotational speed of 56rpm and then starts being rotated integrated with the drum <NUM>.

In a case where the height of the lifter 70c is equal to or lower than <NUM>, when a user washes a small amount of laundry, the washing machine according to the first embodiment of the present disclosure is able to implement a new motion that cannot be implemented by the conventional washing machine. In a case where the height of the lifter 70c is higher than <NUM>, the washing machine according to the first embodiment of the present disclosure may restrict a flow of laundry and thus cannot implement a new motion, in the same way as it does when the conventional lifter of <NUM> is given.

However, in a case where the height of the lifter 70c is equal to or lower than <NUM>, sufficient friction does not occur between the inner circumferential surface of the drum <NUM> and the laundry and thus various motions of the laundry are not made. That is, even though the drum <NUM> is rotated at a speed faster than 56rpm, the laundry slips at a certain height between the highest point and the lowest point and then flows while shaking upward and downward. In this case, if the rotational speed of the drum <NUM> is increased even faster, the laundry may be instantly attached to the inner circumferential surface of the drum at about <NUM> rpm and thus rotated integrated with the drum <NUM>. Since such a flow may significantly degrade washing performance, the height of the lifter 70c should be higher than <NUM>.

Likewise to the lifter 70b in the first embodiment, a side rake angle of the lifter 70b as well as a height of the lifter 70c influence in causing a flow of the laundry. Thus, every lift 70b disposed in the inner circumferential surface of the drum <NUM> may be formed at a height between <NUM> and <NUM>. The height of the lifter 70c for implementing a rubbing motion may be changed according to an inner diameter of the drum <NUM>, and the height of the lifter 70c may be equal to or higher than <NUM>% and equal to or lower than <NUM>% of the inner diameter of the drum <NUM>.

The first embossing portion <NUM> is formed to protrude inward of the drum <NUM> from the lifter portion <NUM>, and assists the lifter 70c to restrict laundry so that laundry flows in accordance with rotation of the drum <NUM>. The first embossing portion <NUM> may be formed in a height of about <NUM> lower than the height of the lifter 70c.

The second embossing portion <NUM> is formed to protrude inward of the drum <NUM> from the embossing portion portion <NUM> formed in the inner circumferential surface of the drum <NUM>, and increases friction between laundry and the inner circumferential surface of the drum and thereby increases washing power. The second embossing portion <NUM> may be formed in a height of about <NUM> lower than a height of the lifter 70c and a height of the first embossing portion <NUM>.

The third embossing portion <NUM> is formed to protrude inward of the drum <NUM> from the entire inner circumferential surface of the drum <NUM>, and increase friction between laundry and the inner circumferential surface of the drum <NUM> and thereby increases washing power. The third embossing portion <NUM> may be formed in a height identical to that of the second embossing portion <NUM>.

<FIG> is a schematic view of a drum driving motion which is applied to a control method of a conventional washing machine. Hereinafter, a motion applied to the conventional washing machine will be described with reference to <FIG>.

<FIG> is a view showing a rolling motion. The rolling motion is a motion in which the washing motor <NUM> rotates the drum <NUM> in one direction and makes laundry on the inner circumferential surface of the drum <NUM> to fall from a point at less than <NUM>° in the rotation direction of the drum <NUM> to the lowest point in the drum <NUM>. In the rolling motion, the wash motor <NUM> rotates the drum <NUM> in one direction at about 40rpm, and in the case where the drum <NUM> is rotated in the clockwise direction, the laundry keeps rolling at the third quadrant of the drum <NUM> when the drum <NUM> rotates in a clockwise direction.

<FIG> is a view showing a tumbling motion. The tumbling motion is a motion in which the wash motor <NUM> rotates the drum <NUM> in one direction and makes the laundry positioned on the inner circumferential surface of the drum <NUM> to fall toward a lowest point in the drum from a point corresponding to about between <NUM>° and <NUM>° in the rotation direction of the drum <NUM>. In the tumbling motion, the wash motor <NUM> rotates the drum <NUM> in one direction at about <NUM> rpm. In a case where the drum <NUM> is rotated in a clockwise direction, a part of the laundry may move from the third quadrant of the drum to the second quadrant of the drum <NUM>, may be separated from the inner circumferential surface of the drum <NUM> and fall toward the lowest point in the drum and lifted again. This kind of laundry flow is repeatedly performed.

<FIG> is a view showing a step motion. The step motion is a motion in which the wash motor <NUM> rotates the drum <NUM> in one direction and controls laundry positioned on the inner circumferential surface of the drum to fall from the highest point in the rotation direction of the drum toward the lowest point in the drum. The step motion is controlled such that the wash motor <NUM> rotates the drum <NUM> at about 60rpm, and, if the laundry is positioned nearby the highest point in the drum, the wash motor <NUM> control to supply a reverse torque to the drum <NUM>. At a time when the drum <NUM> stops due to the reverse torque, the laundry falls from the highest point to the lowest point. Then, a torque is applied to the drum <NUM> again so that the laundry positioned at the lowest point in the drum to the highest point.

<FIG> is a view showing a swing motion. The swing motion is a motion in which the washing motor <NUM> rotates the drum <NUM> in both directions, and makes the laundry to fall from a position about less than <NUM>° in the rotation direction of the drum <NUM>. The wash motor <NUM> rotates the drum <NUM> in the counter-clockwise direction at about 40rpm, and stops the rotation of the drum <NUM> before laundry reaches a point in the drum <NUM> corresponding to about <NUM>° in the counter-clockwise direction, and thereby, the laundry flows toward the lowest point in the drum from the point in the drum <NUM> at an angle less than <NUM>° in the counter-clockwise direction. Thereafter, the wash motor <NUM> rotates the drum <NUM> at about <NUM> rpm in the clockwise direction, and stops the rotation of the drum <NUM> before falling laundry reaches a point in the drum at an angle of about <NUM>°, and thereby, the laundry falls toward the lowest point in the drum <NUM> from the point in the drum <NUM> at an angle less than about <NUM>° in the clockwise direction.

<FIG> illustrates a view of a step motion. The step motion is a drum motion in which the wash motor <NUM> rotates the drum <NUM> in both directions and makes the laundry to drop from a position at an angle of about <NUM>° in the rotational direction of the drum <NUM>. The wash motor <NUM> rotates the drum <NUM> at about <NUM> rpm in the counter-clockwise direction and then temporarily stops the rotation of the drum <NUM> by providing a reverse torque to the drum <NUM> after laundry positioned at the lowest point in the drum <NUM> passes through a point of the drum <NUM> at about <NUM>° in the counter-clockwise direction. As a result, the laundry positioned on the inner circumferential surface of the drum <NUM> may suddenly falls from the point of the drum <NUM> at about <NUM>° in the counter-clockwise direction. Then, the wash motor <NUM> rotates the drum <NUM> at about <NUM> rpm in the clockwise direction, and temporarily stops the rotation of the drum <NUM> by providing a reverse torque to the drum <NUM> after the fallen laundry passes through the point of the drum <NUM> at about <NUM>° in the counter-clockwise direction. As a result, the laundry positioned on the inner circumferential surface of the drum <NUM> may fall toward the lowest point in the drum from a point in the drum <NUM> at an angle equal to or greater than <NUM>° in the clockwise direction.

In <FIG> is a view showing a filtration motion. The filtration motion is a motion in which the wash motor <NUM> rotates the drum <NUM> at about 60rpm or more so that the laundry is prevented from being separated from the inner circumferential surface of the drum <NUM> due to a centrifugal force.

<FIG> is a view of a squeeze motion. The squeeze motion is different from the filtration motion in that the squeeze motion causes laundry to be stuck to the inner circumferential surface of the drum <NUM> and then separated therefrom by changing a rotational speed of the drum <NUM>.

Since a conventional washing machine has the lifter 70a of about <NUM> in height, the drum needs to be rotated at about 40rpm in order to implement the rolling motion and the swing motion. In the case of rotating the drum at about 60rpm, a filtration motion the laundry in which laundry rotates along with the drum while stuck to the inner circumferential surface of the drum may be implemented.

A control method of a washing machine configured as above according to the present disclosure will be described as below.

In the washing machine according to an embodiment of the present disclosure, the height of the lifter <NUM> is lower than the height of the lifter 70a provided in the conventional washing machine. Accordingly, in order to implement a filtration motion indicating laundry being along with the drum <NUM> while attached to the inner circumferential surface of the drum <NUM>, a rotational speed faster than 60rpm is required. Therefore, various motions different from a motion applied to the conventional washing machine can be implemented in a range higher than a rotational speed required for the conventional washing machine to implement the filtration motion.

<FIG> is a graph comparing washing power and a laundry worn-out level between a motion applied to the conventional washing machine and each motion implementable in a washing machine to which an embodiment of the present disclosure can be applied. A horizontal axis is an axis indicating a degree of damage to laundry, and less damage occurs in a rightward direction. A vertical axis is an axis representing washing power or a noise level, and the washing power increases in an upward direction, wherein a stronger washing power reduces a washing time for the same laundry. That is, a motion requiring a fast rotational speed of the drum <NUM> tends to have a strong washing power and reduce a washing time, but a conventional motion may cause severe damage to laundry.

A control method of a washing machine according to an embodiment of the present disclosure provides a rubbing motion which has a relatively strong washing power while causing less damage to laundry. Referring to <FIG>, unlike conventional motions distributed from a left top to a right bottom, the rubbing motion causes relatively less damage to laundry while applying a strong washing power and thus the rubbing motion may be positioned at the right top in the graph of <FIG>.

Hereinafter, the rubbing motion according to an embodiment of the present disclosure will be described with reference to <FIG>.

Referring to <FIG>, the rubbing motion (hereinafter, also referred to as a "rubbing step") is performing a washing operation by rotating the drum <NUM> bidirectionally. The rubbing motion includes a first rotation step of rotating in a first direction and a second rotation step of rotating in a second direction, and the first rotation step and the second rotation step are performed repeatedly and alternately.

<FIG> shows a case where a counter-clockwise direction with the drum <NUM> viewed from front is referred to the first direction and a clockwise direction with the drum viewed from the front is referred to the second direction, but this is merely an example. That is, the clockwise direction may be the first direction and the counter-clockwise direction may be the second direction as long as the first direction and the second direction are opposite to each other.

Referring to <FIG>, at the first rotation step, the drum <NUM> is rotated one and a half times in the first direction and an operation of lifting and dropping laundry is repeatedly performed at least two times in each rotation step in accordance with rotation of the drum <NUM>. At the first rotation step, the drum <NUM> is rotated by a preset one-direction rotational angle in the first direction.

At the first rotation step, the drum <NUM> is rotated in the first direction in a manner in which the drum <NUM> is rotated at acceleration until reaching a preset target rotational speed and then rotated at the target rotational speed. The first step includes a constant-acceleration rotation step, at which drum <NUM> is rotated at a constant acceleration until reaching a target rotational speed, and a constant-speed rotation step, at which the drum <NUM> is rotated constantly at the target rotational speed after the constant-acceleration rotation step. In addition, the first rotation step includes a deceleration step for decelerating the drum <NUM> being constantly rotated at the target rotational speed until the drum <NUM> stops. The drum <NUM> is rotated by the one-direction rotational angle in the first direction over a section for rotation at acceleration until reaching the target rotational speed, a section for rotation at the target rotation speed, and a section for deceleration.

Referring to <FIG>, at the second rotation step, the drum <NUM> is rotated one or more times in the second direction, and laundry goes through a lift-and-fall operation two or more times at each rotation. At the first rotation step, the drum <NUM> is rotated by a preset one-direction rotational angle in the second direction.

At the second rotation step, the drum <NUM> is rotated in the first direction in a manner in which the drum <NUM> is accelerated until reaching a preset target rotational speed and then rotated at the target rotational speed. The first rotation step includes a constant-acceleration rotation step for rotating the drum <NUM> at a constant acceleration until the drum <NUM> reaches the target rotational speed, and a constant-speed rotation step of rotating the drum <NUM> constantly at the target rotational speed after the constant-acceleration rotation step. In addition, the second rotation step include a step for decelerating the drum <NUM> being rotated constantly at the target rotational speed until the drum <NUM> stops. The drum <NUM> is rotated by the one-direction rotational angle in the second direction over a section for rotation at acceleration until reaching the target rotational speed, a section for rotation at the target rotational speed, and a section for deceleration.

Meanwhile, referring to <FIG>, <FIG>, and <FIG>, the greater the angle by which the drum <NUM> is rotated in one direction, the greater the washing performance improves and the greater the abrasion of laundry is resulted.

In a case where an operation of rotating the drum <NUM> by less than one time in one direction and rotating the drum <NUM> by less than one time in the opposite direction is performed repeatedly, lifting and dropping of laundry may be performed once in one direction and only a slip occurs in the inner circumferential surface of the drum <NUM>. Referring to <FIG>, laundry in a state shown in <FIG> is lifted by slipping along the inner circumferential surface of the drum <NUM>, falls from a state shown in <FIG>, and in turn rendered into a state shown in <FIG>. Alternatively, the laundry may be lifted and fall in reverse order. Accordingly, the laundry may just slip or may be lifted to a low height and then fall and go through the same operation repeatedly in both directions, which leads to insufficient washing power.

As shown in <FIG>, if the drum <NUM> is rotated by more than two times in one direction, tension may applied to laundry in one direction. If tension keeps being applied to the laundry in one direction, the laundry may be stretched and deformed. Accordingly, abrasion of the laundry may increase. In addition, in a case where a ply of a laundry item is released, if intention keeps being applied in one direction, the ply may be pulled in one direction and cause more damage to the laundry item.

When the drum <NUM> is rotated more than once and less than twice in one direction, lifting and dropping of laundry may be performed two times in each of one direction and the other direction. A direction of force acting on laundry may be changed by the first operation of lifting and dropping the laundry in one direction, washing power may be applied to laundry by the next operation of lifting and dropping the laundry, and then another operation of lifting and dropping the laundry may be performed in the opposite direction, thereby changing the direction of force acting on the laundry.

As shown in <FIG>, in this case, it is possible laundry from being starched as a portion of laundry to which tension is applied is deformed. In addition, even when a ply is released, the play is prevented from being pulled constantly, thereby minimizing releasing of the ply. Accordingly, the rubbing motion renders the drum <NUM> to be rotated in both directions and thus causes less damage to laundry, compared to the rolling motion which causes the drum to be rotated constantly.

In an embodiment of the present disclosure, an angle of rotation in one direction of the rubbing motion may be set to an angle of rotation by which laundry can be lifted and dropped two times, by taking into consideration washing performance and abrasion of the laundry. The one-direction rotational angle may be in a range between <NUM>° and <NUM>°.

Meanwhile, referring to <FIG>, <FIG>, and <FIG>, the drum is in an approximate cylindrical shape, and the lowest point of the drum <NUM> is located vertically below a rotational center O. The drum <NUM> and the rotational center O of the drum <NUM> may be positioned to be inclined downward in a direction from a front toward a rear. A portion which includes the lowest point of the drum <NUM> and which is located vertically below the rotational center O is defined as a drum lower portion <NUM>.

The drum lower portion <NUM> is a portion located vertically below the rotational center O of the drum <NUM>, irrespective of rotation of the drum <NUM>. The drum lower portion <NUM> does not indicate a specific portion of the drum <NUM> and may change in accordance with rotation of the drum, and a location of the drum lower portion <NUM> is vertically below the rotational center O of the drum <NUM>.

When the drum <NUM> is in a stopped state, laundry is placed on the drum lower portion <NUM> or surroundings thereof due to a force of gravity. An area including the drum lower portion <NUM> and the surroundings thereof is defined as a first area <NUM>. Accordingly, when the drum <NUM> is not in a rotating state, laundry is placed on the first area <NUM> due to a force of gravity.

The first area <NUM> is an area of which a location is fixed even when the drum <NUM> such as the drum lower portion <NUM> is rotated, and which includes the drum lower portion <NUM>. The drum <NUM> may be divided into the first area <NUM> and other area, and the first area <NUM> is an area which is located lower in the two areas (the first area and the other area).

Meanwhile, the first area <NUM> may be defined in regard with a location of the lifter <NUM>. The washing machine according to an embodiment of the present disclosure may include three or more lifters disposed in the inner circumferential surface of the drum <NUM>. When the drum <NUM> is in a stopped state, a lifter positioned most adjacent to the drum lower portion <NUM> in the first direction among the three or more lifters <NUM> is referred to as a first lifter <NUM>, and a lifter positioned most adjacent to the drum lower portion <NUM> in the second direction among the three or more lifters <NUM> is referred to as a second flier <NUM>. That is, with reference to a vertical line passing through the rotational center O of the drum <NUM>, the first lifter <NUM> may be positioned on one side of the vertical line and the second lifter <NUM> may be positioned on the other side of the vertical line. The first are <NUM> may be defined as an area between the first lifter <NUM> and the second lifter <NUM> in a state in which the first lifter <NUM> and the second lifter <NUM> are located at the above-described positions.

Preferably, in a state in which the first lifter <NUM> and the second lifter <NUM> are symmetrical to each other with respect to the vertical line passing through the rotational center O of the drum, as shown in <FIG>, an area between the first lifter <NUM> and the second lifter <NUM> may be the first area <NUM>.

Hereinafter, a specific example in which a one-direction rotational angle of the rubbing motion is set to <NUM>° will be described with reference to <FIG> and <FIG>.

Referring to <FIG>, a rubbing motion step may include a step at which the three or more lifters <NUM> is positioned on an outer side of the first area <NUM> and laundry is positioned in the first area <NUM>. Before rotation of the drum <NUM> in the first direction, all of the three or more lifters <NUM> may be positioned on the outer side of the first area <NUM>. The first lifter <NUM> may be positioned on the outer side of the first area <NUM> in the first direction, and the second lifter <NUM> may be positioned on the outer side of the first area <NUM>. In this state, a lifter at the highest position among the three or more lifters <NUM> may be a third lifter <NUM>. In this state, the laundry may be positioned in the first area <NUM> due to a force of gravity.

Referring to <FIG>, in a state in which the three or more lifters <NUM> are positioned on the outer side of the first area <NUM> and the laundry is positioned in the first area <NUM>, the drum <NUM> is rotated at acceleration in the first direction. Accordingly, the laundry is lifted along the inner circumferential surface of the drum <NUM>. In a case where an acceleration gradient in a section for rotation at acceleration in the first direction is sufficient, a rotational speed of the drum <NUM> may reach a target rotational speed when the laundry is lifted to the highest point (which is a state shown in <FIG>).

In a state where the laundry (or the center of mass of laundry) is spaced apart from the second lifter <NUM>, the drum <NUM> may be rotated in the first direction and the laundry is not restricted by the lifter, and hence, the laundry may be lifted while slipping from the inner circumferential surface of the drum <NUM>. Accordingly, as the laundry is lifted, a distance between the laundry the second lifter <NUM> may be gradually reduced.

As the laundry is lifted from the drum lower portion <NUM>, a portion between the laundry and the inner circumferential surface of the drum <NUM> contact becomes a steep slope, and the laundry falls due to a force of gravity from a point where the laundry is lifted by an angle less than <NUM>° in the first direction. Before the drum <NUM> is rotated by <NUM>° in the first direction, the laundry is lifted to a point at the angle less than <NUM>° in the first direction and falls therefrom. In the case where the laundry is lifted to a point at the angle less than <NUM>° in the first direction and falls therefrom, a part of the laundry may fall to the drum lower portion while in contact with the inner circumferential surface of the drum <NUM>.

In the washing machine according to an embodiment of the present disclosure, a slip may occur as laundry falls because a height of the lifter <NUM> is lower than a height of the conventional lifter 70a, and thus the laundry may fall in a rolling manner. The slip refers to a flow of laundry slipping from the inner circumferential surface of the drum <NUM> because there is small friction (restriction) between the laundry and the inner circumferential surface of the drum <NUM>. The rolling of the laundry refers to a motion where the drum <NUM> and the laundry has different rotation directions and the same rotational speed at a portion of contact between the drum <NUM> and the laundry when a friction between the laundry and the inner circumferential surface of the drum <NUM> or restriction applied by the lifter <NUM> to the laundry is sufficient.

When the laundry falls, the laundry may completely slip without rolling or may completely roll without slipping. However, slipping and rolling of the laundry may occur at the same time.

Meanwhile, before the drum <NUM> is rotated in the first direction, a magnitude of friction between the laundry and the inner circumferential surface may vary according to a state of how the laundry is positioned inside the drum <NUM>. The greater the magnitude between the laundry and the inner circumferential surface of the drum <NUM>, the less the slip may occur when the laundry is lifted and the greater the distance between the second lifter <NUM> and the laundry may become when the laundry falls after being lifted. If the distance between the second lifter <NUM> and the laundry is longer, the laundry may fall with slipping from the inner circumferential surface of the drum <NUM>. If the distance between the second lifter <NUM> and the laundry is shorter, the laundry may be turned over by the second lifter <NUM> and the laundry may fall with rolling on the inner circumferential surface of the drum <NUM>.

Referring to <FIG>, the drum <NUM> keeps being rotated in the first direction in the course of the laundry is lifted and falls. In an initial stage where the laundry is lifted or falls, the second lifter <NUM> passes through the laundry and the laundry may fall slipping and/or rolling. While the laundry falls, the third lifter <NUM> may pass the first area and be positioned on a side of the first direction, rather than the first area. Accordingly, the laundry may fall in between the first lifter <NUM> and the third lifter <NUM>. Before the drum <NUM> is rotated by <NUM>°, laundry lifted from the first area to a point at an angle less than <NUM>° in the first direction may fall to the first area in a state where the drum <NUM> is rotated by an angle equal to or greater than <NUM>° and less than <NUM>°.

In a state where a part of the laundry is in contact with the first area, the drum <NUM> keeps being rotated. Since the laundry is not completely placed on the first area, the first lifter <NUM> may pass through the laundry.

Referring to <FIG>, after the first lifter <NUM> passes through the laundry, the laundry may slip from the inner circumferential surface of the drum <NUM> and be then lifted by the second lifter <NUM> in the first direction. In this case, the laundry is lifted with being restricted by the second lifter and thus the laundry may be able to be lifted to a higher point, compared to a case where the laundry is lifted along the inner circumferential surface of the drum <NUM> (see <FIG>). However, even in this case, the laundry may be lifted to a point at an angle less than <NUM>° in the first direction.

The rotational speed of the drum <NUM> may reach a target rotational speed at least before the second lifting of the laundry in the first direction. Accordingly, at a time when the laundry is lifted by the second lifter <NUM>, the rotational speed of the drum <NUM> may be the target rotational speed.

Referring to <FIG>, while the laundry lifted by the second lifter <NUM> falls, the drum <NUM> is rotated at the target rotational speed and stopped to cause the third lifter <NUM> to be positioned on the first area <NUM>. In a state in which the third lifter <NUM> is positioned on the first area <NUM>, the laundry may fall on the first lifter <NUM>. In a case where the laundry is lifted to a point at an angle less than <NUM>°, falls therefrom, and then is lifted again along the inner circumferential surface of the drum <NUM> (see <FIG>), a part of the laundry may fall toward the drum lower portion <NUM> while in contact with the inner circumferential surface of the drum <NUM>. That is, the laundry falls to the first area <NUM> with slipping and/or rolling.

At the first rotation step, after the drum <NUM> is acceleration at acceleration, the drum <NUM> is rotated at a target rotational speed. Then, the drum <NUM> is rotated at the target rotational speed, and then the rotation of the drum <NUM> is decelerated so that the drum <NUM> is stopped after being rotated by a preset one-direction rotational angle in the first direction. At the first rotation step, the drum is rotated by the one-direction rotational angle through accelerating rotation, constant-speed rotation, and decelerating rotation and stopped, and then the drum <NUM> immediately enters the second rotation step to be rotated in the second direction.

Referring to <FIG>, before the drum <NUM> is rotated in the second direction after rotation of the drum <NUM> one and a half time (which corresponds to <NUM>°) in the first direction, the third lifter <NUM> may be positioned on the first area <NUM> and the laundry may be positioned on the third lifter <NUM>.

Referring to <FIG>, in a state in which the third lifter <NUM> is positioned on the first area <NUM> and the laundry is positioned on the third lifter <NUM>, the drum <NUM> may be rotated at acceleration and accordingly the laundry may be lifted in the second direction along with the third lifter <NUM>. In this case, the laundry can be lifted to a point at an angle equal to or greater than <NUM>° in the second direction. In a case where the drum <NUM> is rotated in a state in which the laundry is positioned on the lifter <NUM>, the laundry may be restricted by the lifter <NUM> and thus the laundry may fall after being lifted to a point higher than when the drum <NUM> is rotated in a state in which the laundry is positioned on the inner circumferential surface of the drum <NUM>, rather than on the lifter <NUM>.

In a case where an acceleration gradient in a section of rotation at acceleration in the second direction is sufficiently great, a rotational speed of the drum <NUM> may reach a target rotation speed when the laundry reaches the highest point.

When the laundry falls after being lifted from the drum lower portion <NUM> by an angle equal to or greater than <NUM>°, the laundry may fall while separated from the inner circumferential surface of the drum <NUM>. In this case, the laundry may be distributed during the fall and thus uniformly mixed.

Therefore, when rotation in the second direction is performed after rotation in the first direction, a force acting on laundry changes in direction and entanglement of the laundry is prevented, thereby remarkably reducing damage to the laundry.

Referring to <FIG>, while laundry falls after being lifted by the third lifter <NUM>, the drum <NUM> keeps being rotated in the second direction, and the second lifter <NUM> and the first lifter <NUM> may pass through the first area <NUM>. Accordingly, the laundry may be positioned on the first area and, at the same time, positioned between the first lifter <NUM> and the third lifter <NUM>.

Referring to <FIG>, the drum <NUM> keeps being rotated in the second direction, and the laundry is lifted by the third lifter <NUM> in the second direction after slipping from the inner circumferential surface of the drum <NUM>. In this case, the laundry is restricted and lifted by the third lifter <NUM>, but a force of restriction is less than the state shown in <FIG>. Thus, the laundry may be at a position lower than in a state in which the laundry is lifted while positioned on the lifter (see <FIG>, and may be lifted to a position higher than in a case where the laundry is lifted along the inner circumferential surface of the drum <NUM> (see <FIG>. That is, the laundry may be lifted in a direction opposite to a direction shown in <FIG> and to a position similar to a position shown in <FIG>. Even in this case, the laundry can be lifted to a point at an angle less than <NUM>° in the second direction.

A rotational speed of the drum reaches a target rotational speed at least before the second lifting of the laundry in the second direction. Therefore, a rotational speed of the drum <NUM> at a time when the laundry is lifted by the third lifter <NUM> is the target rotational speed.

Referring to <FIG>€, while the laundry lifted by the third lifter <NUM> falls, the drum <NUM> is rotated, and the laundry falls on the first area <NUM> in a state where the three or more lifters <NUM> are positioned on the outer side of the first area <NUM>.

The laundry falls after being lifted to a point of an angle less than <NUM>°, and thus, even in this case, a part of the laundry may fall toward the drum lower portion while in contact with the inner circumferential surface of the drum <NUM>. That is, the laundry falls to the first area <NUM> with slipping and/or rolling.

Referring to <FIG> and <FIG>, a rotation position of the drum <NUM> in an initial stage of the first rotation step and a rotation position of the drum <NUM> in an initial stage of the second rotation step may be reversed. In a case where a one-direction rotational angle is set to an angle in a predetermined range including <NUM>°, this may bring the same effect as that can be achieved when the one-direction rotational angle is set to <NUM>°.

Accordingly, the reverse includes not just a case where a difference between a rotation position of the drum <NUM> in an initial stage of the first rotation step and a rotation position of the drum <NUM> in an initial stage of the second rotation step is <NUM>°, but also a case where the lifter <NUM> at the highest position in the initial stage of the first rotation step is placed on the first area <NUM> in the initial stage of the second rotation step and thereby there is a difference in angle by which the laundry can be positioned on the lifter <NUM> positioned on the third area <NUM>. That is, in a case where a difference between a rotation position of the drum <NUM> in an initial stage of the first rotation step and a rotation position of the drum <NUM> in an initial stage of the second rotation step is an angle in a predetermined range including <NUM>°.

The predetermined range may be set with reference to an angle (or distance) between two adjacent lifters. The predetermined range is smaller than a size of the first area <NUM>. In addition, the predetermined range is smaller than an angle (or distance) between the two adjacent lifters.

The predetermined range may be a half of an angle between the two adjacent lifters. In a case where the predetermined range is a half of an angle between the two adjacent lifters, the lifter <NUM> at the highest position in the initial stage of the first rotation step may be positioned on the first area <NUM> in the initial stage of the second rotation step and the laundry may be positioned on the lifter <NUM> positioned on the first area <NUM>.

For example, in a case there are three lifters and arranged at the same interval, an angle between two adjacent lifters may be <NUM>° and a half of the angle between the two adjacent lifters may be <NUM>°. Therefore, a difference between a rotation position of the drum <NUM> in an initial stage of the first rotation step and a rotation position of the drum <NUM> in an initial stage of the second rotation step may be in a range between <NUM>° and <NUM>°.

At the second rotation step, the drum <NUM> is rotated at acceleration to a target rotational speed, rotated at the target rotational speed, and then decelerated so that the drum <NUM> is stopped after being rotated by a preset one-direction rotational angle in the second direction. The drum <NUM> is stopped after being rotated by the preset one-direction rotational angle through an accelerating rotation, a constant-speed rotation, and decelerating rotation, and immediately enters the first rotation step to be rotated in the first direction.

If the first rotation step and the second rotation step are performed repeatedly and alternately, it is possible to implement a washing processing similar to hand washing. That is, after a part of laundry is rubbed to wash, change a part of the laundry to rub is changed and the changed part of the laundry is rubbed to wash, and, in this manner, it is possible to bring effects similar to that can be achieved when the entire laundry is uniformly rubbed to wash. Therefore, a motion of repeatedly performing the first rotation step and the rotation step may be referred to as a rubbing motion.

Meanwhile, even in a case where the one-direction rotational angle is set to <NUM>°, lifting and dropping of laundry may be performed twice at each of the first rotation step and the second rotation step. Hereinafter, rotation in the first direction and the second direction in a state in which the one-direction rotational angle is set to <NUM>° and laundry is positioned on the inner circumferential surface of the first area <NUM>, rather than on the lifter <NUM> (see <FIG>) will be described.

The first rotation step is performed in a manner in which lifting and dropping of the laundry is performed once through the steps shown in <FIG> and then the laundry is lifted by the second lifter <NUM>. Next, while the laundry falls with slipping and/or rolling, the drum <NUM> is rotated in the first direction and thereby the third lifter <NUM> passes through the first area <NUM>. Accordingly, the laundry can fall in between the first lifter <NUM> and the third lifter <NUM>.

In a state where a part of the laundry is in contact with the first area <NUM>, the drum <NUM> may be further rotated. In this case, since the laundry is not completely placed on the first area, the first lifter <NUM> is allowed to pass through the laundry. The first rotation step is terminated in a state in which the laundry and the lifter are arranged at the same positions as before the rotation in the first direction, and the second rotation step starts immediately.

In a case where the one-direction rotational angle is set to <NUM>°, the second rotation step is performed in a direction opposite to the direction in which the first rotation step is performed, while laundry flows in the same manner in the opposite direction.

Even though the one-direction rotational angle is set to <NUM>°, lifting and dropping of the laundry is repeatedly performed twice at the first rotation step and repeatedly performed twice at the second rotation step.

Hereinafter, there is provide a description about a case in which the one-direction rotational angle is set to <NUM>° and rotation is performed in the first and second directions in a state in which laundry is positioned on the lifter <NUM> positioned on the first area <NUM>, For convenience of explanation, rotation in a clockwise direction is defined as rotation in the first direction, a lifter positioned on the first area <NUM> is defined as the third lifter <NUM>, a lifter most adjacent to the third lifter <NUM> in the first direction is defined as the first lifter <NUM>, and a lifter most adjacent to the third lifter <NUM> in the second direction is defined as the second lifter <NUM>.

The first rotation step is performed such that laundry is lifted by an angle equal to or greater than <NUM>° in the first direction through the same steps as shown in <FIG>, falls therefrom, and is then lifted by the third lifter <NUM> by an angle less than <NUM>°. Next, while the laundry falls with slipping and/or rolling, the drum <NUM> may be rotated in the first direction and accordingly the second lifter <NUM> passes through the first area. Therefore, the laundry may fall in between the second lifter <NUM> and the first lifter <NUM>.

In a state in which a part of the laundry is in contact with the first area <NUM>, the drum <NUM> is further rotated in the first direction. In this case, since laundry is not completely placed on the first area <NUM>, the third lifter <NUM> goes into under the laundry. The first rotation step is terminated in a state in which the laundry and the lifter <NUM> are arranged at the same positions as before the rotation in the first direction, and the second rotation step is performed immediately.

Meanwhile, in the case where the one-direction rotational angle is set to <NUM>°, a rotation position of the drum <NUM> in an initial stage of the first rotation step and a rotation position of the drum <NUM> in an initial stage of the second rotation step may be identical. In a case where the one-direction rotational angle is set to an angle in a predetermined range including <NUM>°, this may bring the same effect as that can be achieved when the one-direction rotational angle is set to <NUM>°.

The predetermined range may be set with reference to an angle (or distance) between two adjacent lifters. The predetermined range is smaller than a size of the first area <NUM> and smaller than an angle (or distance) between the two adjacent lifters. The predetermined range may be a half of an angle between the two adjacent lifters. That is, a difference between a rotation position of the drum <NUM> in an initial stage of the first rotation step and a rotation position of the drum <NUM> in an initial stage of the second rotation step may be equal to or less than a half of a distance by which the two adjacent lifters are spaced apart from each other.

Hereinafter, there is provided a description about an acceleration gradient in a section of rotating the drum <NUM> in the first and second directions, a target rotational speed, and a decelerating section.

The acceleration relates to washing performance. Referring to <FIG>, <FIG>, in a case where lifting and dropping of laundry is to be performed twice, at a time when the laundry falls after the first lifting, the drum <NUM> may be in a state being rotated by an angle equal to or greater than <NUM>° and less than <NUM>°. The second lifting of the laundry is caused by the lifter <NUM>, and, the faster the rotational speed of the drum <NUM> is, the higher the laundry may be lifted, which leads to improvement in washing performance. Therefore, it is desirable that a rotational speed of the drum <NUM> reaches to a target rotational speed at least before the second lifting of the laundry.

As described in the following, the target rotational speed may be set to 60rpm, and the second lifting of the laundry is performed when a rotation position of the drum <NUM> is in a range between <NUM>° and <NUM>°. Thus, the acceleration at least in the acceleration section may be equal to or greater than a value by which the drum <NUM> reaches to the target rotational speed when being rotated by <NUM>°. Therefore, an acceleration gradient in an accelerating rotation section may be equal to or less than 30rpm/s. In an embodiment of the present disclosure, an acceleration gradient in a section for rotation at acceleration is set to 100rpm/s.

Meanwhile by taking into consideration not just a height for the second lifting of the laundry, but also a height for the first lifting of the laundry and friction between the laundry and the drum <NUM>, washing machine may improve if the acceleration is increased. Accordingly, the acceleration gradient in a section of rotating the drum <NUM> at acceleration may be set to a maximum value that can be output from the motor <NUM> that rotates the drum <NUM>.

The target rotational speed may be set by taking into consideration a height of the lifter <NUM>. The faster the target rotational speed is, the more the washing performance may improve. Since the lifter <NUM> of the washing machine according to an embodiment of the present disclosure is lower in height than the conventional lifter 70a, a speed at which a filtration motion starts may be faster than in a washing machine having the conventional lifter 70a, wherein the filtration motion is a motion where laundry is rotated integrally with the drum <NUM> while stuck to the inner circumferential surface of the drum <NUM> due to rotation of the drum <NUM>.

Accordingly, the target rotational speed may be set to be faster than a speed for a conventional rolling motion and a conventional swing motion. The target rotational speed may be a rotational speed between 56rpm and <NUM> rpm. The conventional rolling motion and the conventional swing motion rotate a drum, which has the lifter 70a of about <NUM> in height, at about <NUM> rpm. Thus, since the rubbing motion rotates the drum <NUM> at a speed faster than the speed for the conventional rolling motion and the conventional swing motion, the rubbing motion may provide strong washing power. A detailed description about the target rotational speed will be provided with reference to <FIG> and <FIG>.

In order to stop the drum <NUM> rotating at the target rotational speed or rotate the same in the opposite direction, the drum <NUM> may be decelerated to stop. The washing machine according to an embodiment of the present disclosure may decelerate and brake the drum <NUM> by applying reversing-phrase braking and/or dynamic braking. The reversing-phase braking is a braking method for braking the wash motor <NUM>, in which a phase of the current being supplied to the wash motor <NUM> is inverted in order to generate a rotation force in a direction opposite to a rotation direction. The rheostatic braking is a braking method for cutting off a current applied by the wash motor <NUM> so that the wash motor plays a role of a generator due to rotation inertia.

Hereinafter, an amount of supplied water required to more efficiently implement a rubbing motion will be described with reference to <FIG> shows that an amount of supplied water 14a required to more efficiently implement the rubbing motion is greater than an amount of supplied water 14b required for an existing motion.

In order to efficiently implement the rubbing motion, a height level of water supplied to the tub <NUM> may be higher at least than the drum lower portion <NUM> and may be determined by an amount of laundry in the drum <NUM>. An amount of supplied water may reach a height that is high enough to an extent where the level of the water can be checked from the outside of the washing machine.

By lowering a height of the lifter <NUM> compared to a height of a conventional lifter and increasing an amount of supplied water in the rubbing motion compared to an existing motion, it is possible to reduce a restricting force of the lifter <NUM> with respect to laundry flow. Accordingly, by rotating the drum <NUM> at a speed faster than the speed for the conventional rolling motion and the conventional swing motion, it is possible to improve washing power physically. In addition, water is supplied to a level higher than the drum lower portion <NUM>, and, if laundry is sufficiently wet by detergent-mixed water, it is possible to improve washing power chemically.

For example, in order to efficiently perform the rubbing motion, in a case where an amount of laundry is <NUM>, about <NUM> of water may be supplied. In a case where an amount of laundry is <NUM>, about <NUM> of water may be supplied. In a case where an amount of laundry is <NUM>, about <NUM> of water may be supplied. In a case where an amount of laundry is <NUM>, about <NUM> of water may be supplied.

In order to implement a motion applied to a conventional washing machine, it was necessary to supply about <NUM> of water for <NUM> of laundry and about <NUM> of water for <NUM> of laundry. The rubbing motion can be smoothly implemented by supplying a more amount of water compared to the above case. That is, conventionally, an amount of water three to eight times more than an amount of laundry needed to be supplied, and an amount of water eight to twelve times more than an amount of laundry needed to be supplied in order to implement the rubbing motion smoothly.

The rubbing motion may require a more amount of water than a conventional motion when the same amount of laundry is given. In addition, the drum <NUM> is rotated faster to implement the rubbing motion, and thus, the rubbing motion may lead to a great load to the wash motor <NUM>. Accordingly, the rubbing motion can be performed effectively when there is a small amount of laundry, and, especially when laundry is a small quantity being less than <NUM> (<NUM>), the effect of the rubbing motion may be maximized. The rubbing motion can be implemented when an amount of laundry is equal to or less than <NUM>. Accordingly, the amount of laundry is sensed at a laundry quantity sensing step, and a control operation may be performed such that the rubbing motion is implemented when the sensed amount of laundry is equal to or less than <NUM>. Accordingly, when the amount of laundry sensed in the laundry quantity sensing step is equal to or less than <NUM>, the rubbing motion is implemented in a washing cycle, and, when the amount of laundry is equal to or greater than <NUM>, a general motion of rotating the drum <NUM> in one direction may be implemented in the washing cycle. The general motion refers to implementing the washing cycle with a conventional tumbling motion, a conventional rolling motion, etc..

<FIG> and <FIG> are graphs showing a current applied to the wash motor <NUM> while a rotational speed ω of a drum is increased at a constant gradient. Hereinafter, the height of the lifter <NUM> and the rotational speed ω of the drum will be described with reference to <FIG> and <FIG>.

<FIG> is a graph showing a case where, when there is a very small quantity (less than <NUM>), a current is applied to the wash motor <NUM> and a rotational speed ω of a drum is increased constantly, and the lifter <NUM> is given at different heights. <FIG> is a graph showing a case where, when there is a small quantity (between <NUM> and <NUM>), a current is applied to the wash motor <NUM> and a rotational speed ω of a drum is increased constantly, and the lifter <NUM> is given at different heights. <FIG> and <FIG> are graphs showing a current applied to the wash motor <NUM> while the rotational speed ω of the drum is increased constantly when the lifter <NUM> is <NUM> in height. <FIG> and <FIG> are graphs showing a current applied to the wash motor <NUM> while the rotational speed ω of the drum is increased constantly when the lifter <NUM> is <NUM> in height. <FIG> and <FIG> are graphs showing a current applied to the wash motor <NUM> while the rotational speed ω of the drum is increased constantly when the lifter <NUM> is <NUM> in height. <FIG> and <FIG> are graphs showing a current applied to the wash motor <NUM> while the rotational speed ω of the drum is increased constantly when the lifter <NUM> is <NUM> in height. <FIG> and <FIG> are graphs showing a current applied to the wash motor <NUM> while the rotational speed ω of the drum is increased constantly when the lifter <NUM> is <NUM> in height (or when there is no lifter while a first embossing portion of <NUM> in height is given).

If the rotational speed ω of the drum <NUM> is increased, magnitude of a current may fluctuate at a certain value or may fluctuate while gradually increasing. In this section, a rolling motion, a tumbling motion, etc. may be implemented.

A current value may be remarkably reduced at a specific rotational speed ω. A value on a horizontal axis at a point (15a1, 15b1, 15c1, 15d1, 16a1, 16b1, 16c1, 16d1, and 16e) where the current value starts decreasing is a rotational speed ω at which laundry starts being stuck to the inner circumferential surface of the drum <NUM>. Since the laundry flows inside the drum <NUM>, a great force is required for rotation of the drum <NUM>. Once the laundry starts being stuck to the inner circumferential surface of the drum <NUM>, a current value decreases because there is no reaction to the force that causes the laundry <NUM> to flow.

The current value decreases and then fluctuates at a certain value. In this section, the filtration motion may be implemented. A value on the horizontal axis at a point (15a2, 15b2, 15c2, 15d2, 16a2, 16b2, 16c2, 16d2, and 16e) where the significant reduction in the current value is completed is a rotational speed w) at which the drum <NUM> is rotated with all the laundry stuck to the inner circumferential surface of the drum <NUM>.

If a height of the lifter <NUM> is reduced than a height of the conventional lifter, a rotational speed ω at which the laundry starts being stuck to the inner circumferential surface of the drum <NUM> and a rotational speed ω at which the filtration motion is implemented with all the laundry stuck to the inner circumferential surface of the drum <NUM> are increased, and this phenomenon may be called a filtration shift phenomenon. Accordingly, a new motion may be implemented in a section between a rotational speed ω of 56rpm at which laundry starts being stuck to the inner circumferential surface of the drum <NUM> in a washing machine having a lifter in height of about <NUM> and a rotational speed ω at which laundry starts being stuck to the inner circumferential surface of the drum <NUM> in a washing machine having the lifter <NUM> in height equal to or lower than <NUM>.

In a case where the height of the lifter <NUM> is <NUM>, the laundry starts being stuck to the inner circumferential surface of the drum <NUM> at 94rpm, and thus, a new motion may be implemented at a rotational speed ω equal to or greater than 56rm and equal to or less than 94rpm. Accordingly, a target rotational speed for the aforementioned rubbing motion in the washing machine having the lifter <NUM> in height equal to or less than <NUM> may be equal to or greater than 56rpm and equal to or less than <NUM> rpm.

Meanwhile, <FIG> does not show a section where a current value decreases, as described above. This means that, in a case where the height of the lifter <NUM> is equal to or less than <NUM>, laundry does not flow in accordance with rotation of the drum <NUM> and instead the laundry slips from a specific height in a rotational direction of the drum <NUM>. This happens even when the height of the lifter <NUM> is equal to or less than <NUM>. Therefore, the height of the lifter <NUM> may be greater than <NUM>. As described above, the height of the lifter <NUM> may be equal to or greater than <NUM> by taking into consideration of a side rake angle of the lifter <NUM>.

Therefore, every lifter 70b disposed on the inner circumferential surface of the drum <NUM> may be in height between <NUM> and <NUM>.

The target rotational speed may be equal to or greater than <NUM> rpm and equal to or less than <NUM> rpm. Preferably, when an amount of laundry is a small quantity, the target rotational speed may be equal to or greater than <NUM> rpm, which is a rotational speed 16b1 at which laundry starts being stuck to the drum when the height of the lifter is <NUM>, and may be equal to or less than <NUM> rpm, which is a rotational speed at which laundry starts being stuck to the drum when the height of the lifter is <NUM>.

Hereinafter, a control factor of the rubbing motion will be described with reference to <FIG>, <FIG>, and <FIG>. The control factor of the rubbing motion may take into consideration a rotational speed ω of the drum, a one-direction rotational angle θ, an acceleration gradient α, an accelerating rotation section of rotation, and a net acting ratio.

If the rotational speed ω of the drum increases, the washing performance may improve but washing power consumption and laundry abrasion increase. The one-direction rotational angle θ has the same tendency as that of the rotational speed ω. Meanwhile, if the acceleration α increases, washing performance improves and washing power consumption and laundry abrasion decreases, and therefore, a greater acceleration α has more advantageous effects.

The net acting ratio refers to a ratio of an ON-time of the wash motor <NUM> to a sum of the ON-time and the OFF-time of the wash motor <NUM>. If the net acting ratio increases, it takes a longer time to perform a washing operation compared to the same washing time, and thus, the net acting ratio has the same tendency as that of the rotational speed ω.

The rotational speed ω may be set to be equal to or greater than <NUM> rpm in order to improve washing performance compared to a rolling motion applied to a conventional washing machine. However, if the rotational speed ω is set to be excessively faster by taking into consideration only washing performance, it gives negative effects on washing power consumption and laundry abrasion. Therefore, the rotational speed ω may be set to <NUM> rpm.

The one-direction rotational angle θ may be set to be equal to or greater than <NUM>° in order to improve washing power compared to a conventional swing motion, and the one-direction rotational angle θ may be set to be less than <NUM>° by taking into consideration of washing power consumption and laundry abrasion, similarly as in the description about the rotational speed ω.

In a case where the one-direction rotational angle θ is set to <NUM>°, a rotation position of the drum <NUM> in the initial stage of the first rotation step and a rotation position of the drum in the initial stage of the second step may be reversed. In this case, as described above, one of the first rotation step and the second rotation step may include a section where laundry is rotated while positioned on the lifter <NUM>, has an effect of distributing the laundry. Therefore, the one-direction rotational angle may be set to <NUM>°.

The acceleration α may be set to be equal to or greater than 30rpm/s, as described above. In addition, if the acceleration α increases, washing performance may improve and washing power consumption and laundry abrasion may decrease, and therefore, the acceleration α may be set to a maximum value for controlling the wash motor <NUM>. In the present embodiment, the acceleration α is set to 100rpm/s.

The controller <NUM> may rotate the drum <NUM> in the first direction and in the second direction alternately and repeatedly a predetermined number of times, and then may temporarily stop operation of the wash motor <NUM> so that the net acting ratio has a preset value. The net acting ratio may be set to be equal to or higher than <NUM>% by taking into consideration washing performance, and the net acting ratio may be set to <NUM>% by taking into consideration washing power consumption and laundry abrasion, in the same manner regarding the rotational speed ω.

Hereinafter, a net acting ratio and a motor operating time will be described with reference to <FIG>. <FIG>, <FIG>, and <FIG> are data of experiments in which an operation stopping time of a motor is set to a constant value, and in which a motor is operated for a motor operating time of which a net acting ratio is <NUM>% and <NUM>%. <FIG> is data of experiment in which a predetermined washing time and a predetermined operation stopping time of motor are set, an operation time of the motor is set to cause a net acting ratio to become <NUM>%, <NUM>%, and <NUM>%, and the motor is operated and stopped repeatedly over the washing time. Accordingly, washing performance, laundry abrasion, washing power may have different data with respect to the same net acting ratio.

If the wash motor <NUM> operates continuously, washing power consumption may increase and temperature of the wash motor <NUM> and a driver <NUM> may increase excessively. In order to prevent this problem, the controller <NUM> may set the wash motor <NUM> to operate for a first time period and temporarily stopped for a second time period.

In order to prevent overheating of the motor <NUM> and the driver <NUM> and excessive increase in the washing time, the second time period may be set to <NUM> seconds. <NUM>(b) shows that, in a case where a time for temporarily stopping the motor is set to about <NUM> seconds, a degree of laundry abrasion is reduced when a net acting ratio is <NUM>% and <NUM>%, rather than when the net acting ratio is <NUM>%.

Accordingly, the second time period may be set to <NUM> seconds, and, if the first time period is set to <NUM> seconds, the net acting ratio is <NUM>%. In a case where the first time period is set to <NUM> seconds, the net acting ratio is <NUM>%. In a case where the first time period is set to <NUM> seconds, the net acting ratio may be <NUM>%. The net acting ratio may be set to between <NUM>% and <NUM>%, by taking into consideration washing power. The net acting ratio may be set to between <NUM>%, by taking into consideration laundry abrasion and washing power consumption.

Referring to <FIG> and <FIG>, the washing machine according to an embodiment of the present disclosure may include a nozzle <NUM> configured to spray water, discharged from the tub <NUM> (hereinafter, referred to as "circulation water"), into the drum <NUM>. The washing machine may include the gasket <NUM>, which forms the laundry loading hole <NUM> between the casing <NUM> and the tub <NUM>, and a circulation water supply pipe <NUM> disposed on an outer circumferential surface of the gasket <NUM> to supply the circulation water to the nozzle <NUM>. The nozzle <NUM> may include one or more nozzles.

The circulation water discharged from the tub <NUM> may be pumped by a pump <NUM>, supplied to the nozzle <NUM> through the circulation water supply pipe <NUM>, and then sprayed into the drum <NUM> after passing through the nozzle <NUM>. When a washing operation is performed as the drum <NUM> is rotated, the circulation water may be sprayed into the drum <NUM> through at least one nozzle <NUM>.

Hereinafter, a control method for a washing machine according to an embodiment of the present disclosure will be described with reference to <FIG>.

First, after the laundry is loaded into the drum <NUM> and the washing machine operates, a laundry quantity is sensed (S10). Various algorithms may be used to sense a laundry quantity, and there are various well-known laundry quantity sensing techniques, and thus a detailed description thereof is herein omitted.

Water is supplied into the tub <NUM> according to the sensed laundry quantity (s20). A level of supplied water may be higher than at least the drum lower portion <NUM>. An amount of supplied water may be eight to twelve times of the sensed laundry quantity. For example, in order to efficiently perform the rubbing motion, in a case where an amount of laundry is <NUM>, about <NUM> of water may be supplied. In a case where an amount of laundry is <NUM>, about <NUM> of water may be supplied. In a case where an amount of laundry is <NUM>, about <NUM> of water may be supplied. In a case where an amount of laundry is <NUM>, about <NUM> of water may be supplied.

After water is supplied into the tub <NUM>, a washing motion for washing laundry is determined based on the sensed laundry quantity (S30). When the sensed laundry quantity is equal to or less than a preset amount, the rubbing motion is selected. When the send laundry quantity is greater than the preset amount, a tumbling motion, a rolling motion, or the like which rotates the drum <NUM> in one direction is selected.

Being equal to or less than the preset amount may refer to a case where a laundry quantity is a small quantity (including a very small quantity) or a vast quantity. The case where the laundry quantity is a small quantity may correspond to a case where the laundry quantity is equal to or less than <NUM>. The case where the laundry quantity is a vast quantity may correspond to a case where the laundry quantity is between <NUM> and <NUM>. That is, the preset amount may be the vast quantity and may be specifically <NUM>.

After a washing motion to wash laundry is determined, a washing cycle (S100) is performed. In a case where the sensed amount of laundry is equal to or less than the preset amount, a washing operation is performed with a washing motion including the rubbing motion (S110 to S150). When the sensed amount of laundry is greater than the preset amount, a washing operation is performed with a washing motion including a tumbling motion and/or a rolling motion and not including a rubbing motion (S190).

The rubbing motion includes a first rotation step (S110) in which the drum <NUM> is rotated in the first direction, and a second rotation step (S120) in which the drum <NUM> is rotated in the second direction. The first rotation step (S110) and the second rotation step (S120) have been described above, and thus, a detailed description thereof is herein omitted.

A time for which the wash motor <NUM> is rotated in the first direction and the second direction and a time for which the wash motor <NUM> is temporarily stopped, thereby adjusting a net acting ratio (S130). The net acting ratio may be set to be between <NUM>% and <NUM>%. A driving time T1 of the wash motor <NUM> may be set to <NUM> seconds, and a time for temporarily stopping the wash motor <NUM> may be set to <NUM> seconds, so that the net acting ratio can be <NUM>%.

The controller <NUM> may control the wash motor <NUM> so that the drum <NUM> is rotated in the first direction and the second direction repeatedly. The controller <NUM> measures a driving time of the wash motor <NUM>. When the driving time of wash motor <NUM> has not yet reaches a preset driving time T1, the controller <NUM> may rotate the drum <NUM> in the first direction and in the second direction alternately and repeatedly. When the driving time of the motor <NUM> reaches the preset driving time T1, the controller <NUM> may determine whether a washing time T2 elapses (S140).

When the washing time T2 elapses, the controller <NUM> may terminate a washing cycle. When the washing time T2 has not yet elapsed, the controller <NUM> may temporarily stop driving of the wash motor <NUM> (S150). In a case where the driving time T1 of the wash motor <NUM> is <NUM> seconds and the temporary stopping time of the wash motor <NUM> is <NUM> seconds, the wash motor <NUM> rotates the drum <NUM> in a counter-clockwise direction and in a clockwise direction. When the washing time T2 has not been elapsed, the driving of the motor <NUM> is stopped for <NUM> seconds. After the driving of the wash motor <NUM> is stopped for <NUM> seconds, the first directional rotation and the second directional rotation S120 are repeated for the driving period T1. That is, the first rotation step and the second rotation step are performed for the driving time T1 alternately and repeatedly.

When the washing cycle (S100) is completed, a washing operation is terminated after passing through a rinsing cycle (S200) and a dewatering cycle (S300).

Claim 1:
A washing machine comprising:
a casing (<NUM>) including a front panel (<NUM>) which has a laundry loading hole (<NUM>) and is disposed at a front of the casing (<NUM>);
a tub (<NUM>) including an opening which is formed to correspond to the laundry loading hole (<NUM>) and is disposed at a front of the tub (<NUM>);
a drum (<NUM>) rotatably provided in the tub (<NUM>), wherein a rotation center of the drum (<NUM>) is horizontal or inclined horizontally more than vertically;
a lifter (<NUM>) provided on an inner circumferential surface of the drum (<NUM>); and
a wash motor (<NUM>) configured to rotate the drum (<NUM>);
wherein the drum (<NUM>) is configured to rotate in a first direction by a preset one-direction rotational angle and then to rotate in a second direction opposite to the first direction by the one-direction rotational angle,
wherein the lifter (<NUM>) protrudes from the inner circumferential surface of the drum (<NUM>) and has a height equal to or higher than <NUM> and equal to or lower than <NUM>, and
wherein the one-direction rotational angle is in a range within <NUM>° to <NUM>°.