# Patent

## Title
Washing machine and method of controlling a washing machine

## Abstract

The present invention relates to a washing machine and a method of controlling a washing machine. According to the washing machine and the method of controlling the washing machine in accordance with the present invention, the drum is operated at a first speed so that laundry tumbles within the drum. A laundry amount within the drum during the first speed operation is sensed. The drum is driven at a second speed so that part of the laundry tumbles within the drum and another part of the laundry adheres to the drum. Operation commands for driving the drum subsequent to the first speed operation are changed based on the sensed laundry amount. Accordingly, at the time of a dehydration cycle, stability of the washing machine and laundry balancing can be ensured.

## Background
This application claims priority from Korean Patent Application No. 10-2008-0048183, filed May 23, 2008, the subject of which is incorporated herein by reference.
BACKGROUND
1. Field
Embodiments of the present invention may relate to a washing machine and a method of controlling a washing machine and, more particularly, to a washing machine with improved stability and improved laundry balancing at the time of a dehydration cycle, and a method of controlling a washing machine.
2. Background
A drum-type washing machine of washing machines is configured to perform washing by employing a drum that rotates by driving force of a motor and frictional force of the laundry in the state in which a detergent, wash water, and the laundry are input to the drum. Thus, the drum-type washing machine does rarely damage the laundry, has the laundry rarely get entangled, and has knocking and rubbing washing effects.
After wash and rinse cycles are finished, a dehydration cycle is performed. In order to perform the dehydration cycle, laundry must be distributed effectively. To this end, a variety of methods have been used. For example, a method of determining an unbalance amount in the state in which laundry is adhered to the drum was used. However, this method is disadvantageous in that it has a long balancing time of laundry and the state of laundry is decided by sensing an unbalance laundry amount in the state in which the laundry is adhered to the drum. Further, in the case in which laundry is unbalanced with the laundry being adhered to the drum, it becomes problematic in the stability of a washing machine.



BRIEF DESCRIPTION OF THE DRAWINGS
Objects and features of arrangements and embodiments of the present invention may become apparent from the following description taken in conjunction with the accompanying drawings, in which like reference numerals refer to like elements and wherein:
FIG. 1 is a perspective view showing a washing machine in accordance with an embodiment of the present invention;
FIG. 2 is an internal block diagram of the washing machine shown in FIG. 1;
FIG. 3 is a graph showing an example of the relationship between a rotation speed and time of a drum within the washing machine of FIG. 1;
FIG. 4 is a diagram showing the states of laundry within the drum according to a second speed and a third speed;
FIG. 5 is a flowchart illustrating a method of controlling the washing machine in accordance with an embodiment of the present invention;
FIG. 6 is a flowchart illustrating a method of controlling the washing machine in accordance with an embodiment of the present invention; and
FIG. 7 is a flowchart illustrating a method of controlling the washing machine in accordance with an embodiment of the present invention.



DETAILED DESCRIPTION
Arrangements and embodiments of the present invention may be described in detail with reference to the accompanying drawings.
FIG. 1 is a perspective view showing a washing machine in accordance with an embodiment of the present invention.
Description is given below with reference to the accompanying drawing. A washing machine 100 includes a cabinet 110 forming an external shape of the washing machine 100, a tub 120 disposed within the cabinet 110 and supported by the cabinet 110, a drum 122 disposed within the tub 120 in which laundry is washed, a motor 130 for driving the drum 122, a wash water supply apparatus (not shown) disposed outside a cabinet main body 111 and configured to supply wash water to the cabinet 110, and a drain apparatus (not shown) formed under the tub 120 and configured to drain wash water to the outside.
A plurality of through-holes 122A for having wash water pass therethrough is formed in the drum 122. Lifters 124 can be disposed within the drum 112 so that the laundry is raised up to a specific height when the drum 122 is rotated and then dropped because of gravity.
The cabinet 110 includes the cabinet main body 111, a cabinet cover 112 disposed on the front side of the cabinet main body 111 and coupled thereto, a control panel 115 disposed on an upper side of the cabinet cover 112 and coupled to the cabinet main body 111, and a top plate 116 disposed at the top of the control panel 115 and coupled to the cabinet main body 111.
The cabinet cover 112 includes a laundry inlet/outlet hole 114 formed to have laundry pass therethrough, and a door 113 disposed rotatably left and right so that the laundry inlet/outlet hole 114 is opened and closed.
The control panel 115 includes a control button 117 for manipulating operating states of the washing machine 100, and a display device 118 disposed on one side of the control button 117 and configured to display operating states of the washing machine 100.
The control button 117 and the display device 118 within the control panel 115 are electrically connected to a controller (not shown). The controller (not shown) electrically controls respective constituent elements, etc. of the washing machine 100. An operation or the controller (not shown) is described later on.
FIG. 2 is an internal block diagram of the washing machine shown in FIG. 1.
Description is given below with reference to the accompanying drawing. First, a controller 210 operates in response to an operation signal received from the control button 117. Thus, actual washing, rinse, and dehydration cycles can be performed. For the actual washing, rinse, and dehydration cycles, the controller 210 controls the motor 130. Although not shown in the drawings, an inverter (not shown) can be used to control the motor. For example, when the controller 210 outputs a PWM switching control signal to the inverter (not shown), the inverter (not shown) can perform a high-speed switching operation in order to supply an AC power of a specific frequency to the motor 130.
Meanwhile, the controller 210 can display operating states of the washing machine 100 through the display device 118. For example, the controller 210 can display operating states, such as actual washing, rinse, and dehydration cycles, through the display device 118.
The motor 130 drives the drum 122. The drum 122 is disposed within the tub 120, as shown in FIG. 1, and has laundry for washing input therein. The drum 122 is driven by the rotation of the motor 130.
An unbalance amount sensing unit 220 senses an unbalance amount of the drum 122, that is, unbalance (UB) of the drum 122. The unbalance amount can be sensed based on a rotation speed variation of the drum 122, that is, a rotation speed variation of the motor 130. To this end, a speed sensor (not shown) for sensing a rotation speed of the motor 130 can be further included. Meanwhile, a rotation speed of the motor 130 can be calculated based on an output current value flowing through the motor 130, and an unbalance amount can be sensed based on the rotation speed. To this end, the motor 130 can include a current sensor (not shown), for example, an encoder.
Meanwhile, although it is shown that the unbalance amount sensing unit 220 is provided separately from the controller 210, the present invention is not limited to the above example. Alternatively, the unbalance amount sensing unit 220 may be included within the controller 210. In this case, a rotation speed and an output current value of the motor 130, which are respectively sensed by the speed sensor (not shown) and the current sensor (not shown), can be input to the controller 210.
Meanwhile, the washing machine can further include a laundry amount sensor 230. The laundry amount sensor 230 senses the laundry amount within the drum and inputs a sensed amount to the controller 210. Such sensing of the laundry amount can be performed based on sensing of the weight of laundry within the drum 122, a rotation speed of the drum 122, and so on while the drum is stopped or operated. The laundry amount sensor 230 is illustrated in FIG. 2 as being separate from the controller 210. However, the laundry amount sensor 230 may be included in the controller 210.
FIG. 3 is a graph showing an example of the relationship between a rotation speed and time of the drum within the washing machine of FIG. 1. FIG. 4 is a diagram showing the states of laundry within the drum according to a second speed and a third speed.
Description is given below with reference to the accompanying drawings. In relation to the dehydration cycle of the washing machine in accordance with an embodiment of the present invention, the speed of the drum 122 is first raised to a first speed V1 during a first period T1. Here, the first speed V1 is a speed at which laundry tumbles within the drum 122, that is, a speed at which the entire laundry are tumbled within the drum 122.
During a second period T2, the drum 122 is operated at the first speed V1. When the drum is operated at the first speed V1, the laundry amount sensor 230 senses the laundry amount. The controller 210 controls set values, which are subsequent to the first speed V1, to change according to a sensed laundry amount. The set values are operation command to decide the operating states of the drum 122. The set values can include a rising slope S2 of a second speed V2 (that is, a speed at which a part of laundry is tumbled within the drum and the other part of the laundry is adhered within the drum), the reference value of an unbalance amount at the second speed, a rising slope S3 of a third speed V3 (that is, a speed at which laundry are adhered), the reference value of an unbalance amount at the second speed V3, a rising slope S4 of a fourth speed V4 having a resonant speed or less at which a water drain process (simple dehydration) is performed, a reference value of an unbalance amount at the fourth speed V4, a rising slope S5 of a maximum speed of the drum at which full-scale dehydration is performed, a maximum speed Vmax, and so on. What the operation commands posterior to the first speed V1 are changed according to a sensed laundry amount is described later on.
Next, the speed of the drum drops to a stop speed during the third period T3, and is then stopped during the fourth period T4. As described above, after the laundry tumbling process, a laundry balancing process is performed again. Meanwhile, the laundry tumbling processes of the first period to the fourth period can be performed at least once.
The speed of the drum 122 is raised to the second speed V2 during the fifth period T5. Here, the second speed V2 is a speed at which a part 410 of the laundry is tumbled within the drum and the other part 420 of the laundry is adhered within the drum, as shown in FIG. 4(a). For example, the second speed V2 may be a speed at which 20 to 30% of a total of laundry is tumbled within the drum and 70 to 80% of the total of the laundry is adhered within the drum.
During a sixth period T6, the drum 122 is operated at the second speed V2. When the drum is operated at the second speed V2, an unbalance amount is sensed. A first specific value (that is, a reference value of the unbalance amount) can be changed according to the laundry amount sensed during the operation at the first speed V1. For example, as the sensed laundry amount increases, the first specific value may become small so as to stabilize the washing machine 100 and ensure laundry balancing. Alternatively, the first specific value may also change according to the type of laundry, the state of laundry, and so on as well as a sensed laundry amount.
When the unbalance amount sensed by the unbalance amount sensing unit 220 is the first specific value or less (that is, the speed of the drum has been stabilized), the speed of the drum 122 is raised to the third speed V3. Here, the third speed V3 is a speed at which the entire laundry 430 are adhered within the drum 122, as shown in FIG. 4(b).
The third speed rising slope S3 during a seventh period T7 may change according to a laundry amount sensed during the first speed (V1) operation as described above. For example, as the sensed laundry amount increases, the third speed slope S3 may become gentle (that is, small) so as to stabilize the washing machine 100 and ensure laundry balancing. Alternatively, the third speed slope S3 may also change according to the type of laundry, the state of laundry, and so on as well as a sensed laundry amount.
During an eighth period T8, the drum 122 is operated at the third speed V3. During the third speed (V3) operation, an unbalance amount is sensed. When the sensed unbalance amount is a second specific value or less, the operation speed of the drum 122 can be raised to the fourth speed V4 or a maximum speed Vmax. At this time, the second specific value can be changed according to a laundry amount sensed during the first speed (V1) operation. For example, as the sensed laundry amount increases, the second specific value may become small so as to stabilize the washing machine 100 and ensure laundry balancing. Alternatively, the second specific value may also change according to the type of laundry, the state of laundry, and so on as well as a sensed laundry amount.
The fourth speed rising slope S4 during a ninth period T9 can be changed according to a laundry amount sensed during the first speed (V1) operation, as described above. For example, as the sensed laundry amount increases, the fourth speed slope S4 may become gentle (that is, small) so as to stabilize the washing machine 100 and ensure laundry balancing. Alternatively, the fourth speed slope S4 may also change according to the type of laundry, the state of laundry, and so on as well as a sensed laundry amount.
During a tenth period T10, the drum 122 is operated at the fourth speed V4. The fourth speed V4 is a speed at which a water drain process is carried out. The fourth speed V4 can be set to a resonant speed or less.
During the fourth speed (V4) operation, an unbalance amount is sensed. A third specific value (that is, a reference value of the unbalance amount) can be changed according to a laundry amount sensed during the first speed (V1) operation. For example, as the sensed laundry amount increases, the third specific value may become small so as to stabilize the washing machine 100 and ensure laundry balancing. Alternatively, the third specific value may also change according to the type of laundry, the state of laundry, and so on as well as a sensed laundry amount.
During an eleventh period T11, the speed of the drum drops to the third speed V3. During a twelfth period T12, the drum is operated at the third speed V3. As described above, after the water drain process is performed, the speed of the drum 122 drops to the third speed V3 so that the laundry are adhered within the drum 122. The ninth period to the twelfth period T9 to T12 (that is, the water drain process) can be performed at least once.
Thereafter, when an unbalance amount during the third speed operation is the second specific value or less, the speed of the drum rises to the maximum speed Vmax during a thirteenth period T13. At this time, the maximum speed rising slope S5 during the thirteenth period T13 can be changed according to a laundry amount sensed during the first speed (V1) operation, as described above. For example, as the sensed laundry amount increases, the maximum speed rising slope S5 may become gentle (that is, small) so as to stabilize the washing machine 100 and ensure laundry balancing. Alternatively, the maximum speed rising slope S5 may also change according to the type of laundry, the state of laundry, and so on as well as a sensed laundry amount.
During a fourteenth period T14, the drum 122 is operated at the maximum speed Vmax. This operation is a process for full-scale dehydration. After laundry balancing within the drum 122 is completed, the full-scale dehydration process begins. Here, the maximum speed Vmax can be changed according to a laundry amount sensed during the first speed (V1) operation. For example, as the sensed laundry amount increases, the maximum speed Vmax may become small so as to stabilize the washing machine 100 and ensure laundry balancing. Alternatively, the maximum speed Vmax may also change according to the type of laundry, the state of laundry, and so on as well as a sensed laundry amount.
As described above, operation commands subsequent to the first speed V1 are changed according to a laundry amount sensed at the first speed V1. Accordingly, stability of the washing machine 100 and balancing of laundry at the time of a dehydration cycle can be ensured.
Meanwhile, in order to distribute laundry accurately and rapidly, the drum 122 can be driven at the second speed V2 at which a part of the laundry is tumbled not at a speed at which the entire laundry are tumbled as in the prior art, thus meeting the balancing state of the laundry to some extent, and the drum can be then operated at the third speed V3.
Meanwhile, the above-described second speed V2 may be about 60 rpm, the third speed V3 may be about 108 rpm, the fourth speed V4 may be 300 rpm or higher, and the maximum speed Vmax may be 500 rpm or higher.
FIG. 5 is a flowchart illustrating a method of controlling the washing machine in accordance with an embodiment of the present invention.
Description is given below with reference to the accompanying drawings. The controller 210 controls the drum 122 to operate at the first speed V1 in step S510. As shown in FIG. 3, the speed of the drum 122, being in a stop state, is raised to the first speed V1 and then operated at the first speed V1. The first speed V1 is a speed at which laundry tumbles within the drum 122 (that is, a speed at which the entire laundry are tumbled within the drum 122).
The controller 210 then senses a laundry amount during the first speed (V1) operation in step S515. The sensing of the laundry amount is performed by the laundry amount sensor 230.
Next, the controller 210 controls the drum 122 to operate at the second speed V2 in step S520. As shown in FIG. 3, the speed of the drum 122 being in a stop state is raised to the second speed V2 and then operated at the second speed V2. The second speed V2 is a speed at which a part of laundry is tumbled within the drum 122 and the other part of the laundry is adhered within the drum 122. For example, the second speed V2 may be a speed at which 20 to 30% of a total of laundry is tumbled within the drum and 70 to 80% of the total of the laundry is adhered within the drum.
The controller 210 then determines whether an unbalance amount sensed during the second speed (V2) operation is a first specific value or less in step S525. That is, the controller 210 determines whether an unbalance amount sensed by the unbalance amount sensing unit 220 is a first specific value or less.
If, as result of the determination, the unbalance amount sensed during the second speed (V2) operation is the first specific value or less, the controller 210 controls the drum 122 to operate at the third speed V3 in step S530. Here, the third speed V3 is a speed at which the entire laundry 430 are adhered within the drum 122 as shown in FIG. 4(b).
Meanwhile, if a reference value of the third speed is a second specific value or less, the speed of the drum 122 can be raised to the fourth speed V4 or the maximum speed Vmax. Here, the second specific value can be changed according to a laundry amount sensed at the time of the first speed V1. For example, as the sensed laundry amount increases, the first specific value may become small. Accordingly, the washing machine 100 can be stabilized and laundry balancing can be ensured.
Although not shown in the drawing, the second speed rising slope S2 and the second specific value can also be changed according to a laundry amount sensed at the time of the first speed V1.
FIG. 6 is a flowchart illustrating a method of controlling the washing machine in accordance with an embodiment of the present invention.
Description is given below with reference to the accompanying drawings. The control method of FIG. 6 is almost similar to that of FIG. 5 except that, in the control method of FIG. 5, the second specific value (that is, the reference value of an unbalance amount at the third speed) is changed according to a laundry amount sensed at the first speed V1, but, in the control method of FIG. 6, the third speed rising slope S3 is changed. The redundant description will not be given, for simplicity.
That is, in FIG. 6, a first speed operation (S610), a process (S615) of sensing a laundry amount at the first speed operation, a second speed operation (S620), and a process (S625) of determining an unbalance amount at the second speed operation are identical to those of FIG. 5.
If, as a result of the determination in step S625, the unbalance amount sensed during the second speed operation is the first specific value or less, the controller 210 controls the speed of the drum 122 to rise to the third speed in step S630. Here, the third speed rising slope S3 can be changed according to a laundry amount sensed at the first speed V1. For example, as the sensed laundry amount increases, the third speed rising slope S3 can become small. Accordingly, the washing machine 100 can be stabilized and laundry balancing can be ensured.
FIG. 7 is a flowchart illustrating a method of controlling the washing machine in accordance with an embodiment of the present invention.
Description is given below with reference to the accompanying drawings. The control method of FIG. 7 is almost similar to that of FIG. 5. In FIG. 7, a first speed operation (S710), a process (S715) of sensing a laundry amount during the first speed operation, a second speed operation (S720), a process (S725) of determining an unbalance amount during the second speed operation, and a third speed operation (S730) are almost similar to those of FIG. 5. Only processes subsequent to the third speed operation (S730) are described, and the redundant description will not be given, for simplicity.
The controller 210 determines whether an unbalance amount during the third speed operation is a second specific value or less in step S735. If, as a result of the determination, the sensed unbalance amount is the second specific value or less, the controller 210 controls the speed of the drum 122 to rise to the fourth speed V4 and then operate at the fourth speed V4 in step S740. The fourth speed V4 can be a speed having a resonant speed or less at which the water drain process (small-scale dehydration) is performed. The water drain process can be performed at least once (for example, three times).
Although not shown in the drawings, the fourth speed rising slope S4 or the third specific value (that is, the reference value of an unbalance amount during the fourth speed (V4) operation) can be changed according to a laundry amount sensed at the first speed V1. For example, as the sensed laundry amount increases, the fourth speed rising slope S4 or the third specific value can become small.
Next, the controller 210 controls the drum 122 to operate at the third speed V3 in step S745. The controller 210 then determines whether an unbalance amount sensed during the third speed (V3) operation is the second specific value or less in step S750. If, as a result of the determination, the sensed unbalance amount is the second specific value or less, the controller 210 controls the speed of the drum 122 to rise to the maximum speed Vmax and then operate at the maximum speed Vmax in step S755. The maximum speed Vmax is a speed at which a full-scale dehydration process is performed. The maximum speed Vmax can be changed according to a laundry amount sensed at the first speed V1. For example, as the sensed laundry amount increases, the maximum speed Vmax can become small.
Meanwhile, although not shown in the drawings, the maximum speed rising slope S5 can also be changed. For example, as the sensed laundry amount increases, the maximum speed rising slope S5 can become small.
As described above, several operation commands subsequent to the first speed V1 are changed based on a laundry amount sensed during the first speed (V1) operation. Accordingly, the washing machine 100 can be stabilized and laundry balancing can be ensured.
Meanwhile, the above second speed V2 may be about 60 rpm, the third speed V3 may be about 108 rpm, the fourth speed V4 may be 300 rpm or higher, and the maximum speed Vmax may be 500 rpm or higher.
Meanwhile, the method of controlling the washing machine in accordance with the present invention can be implemented as a processor-readable code in a recording medium, which can be read by a processor equipped in a washing machine. The processor-readable recording medium can include all kinds of recording devices in which data readable by a processor is stored. For example, the processor-readable recording medium can include ROM, RAM, CD-ROM, magnetic tapes, floppy disks, optical data storages, and so on, and can also be implemented in the form of carrier waves, such as transmission over the Internet. Further, the processor-readable recording medium can be distributed into computer systems connected over a network, so codes readable by a processor can be stored and executed in a distributed manner.
According to the washing machine and the method of controlling the washing machine in accordance with the embodiments of the present invention, operation commands (for example, a rising slope of each operation speed, the reference value of an unbalance amount at an operation speed, etc.) subsequent to the first speed may be changed according to a laundry amount sensed during the first speed operation. Accordingly, stability of the washing machine and balancing of laundry can be ensured.
Further, the drum may be driven at the second speed at which part of laundry is tumbled not at a speed at which the entire laundry are tumbled as in the prior art so as to meet the balancing state of the laundry to some extent, and the drum may be then operated at the third speed. Accordingly, laundry can be distributed accurately and rapidly.
Embodiment of the present invention may provide a washing machine with improved stability and improved laundry balancing at the time of a dehydration cycle, and a method of controlling a washing machine.
An embodiment of the present invention may provide a method of controlling a washing machine including a drum in which laundry are entered and rotated, including the steps of operating the drum at a first speed so that the laundry tumbles within the drum, sensing a laundry amount within the drum during the first speed operation, operating the drum at a second speed at which a part of the laundry is tumbled within the drum and the other part of the laundry is adhered within the drum, and changing operation commands for driving the drum subsequent to the first speed operation based on the sensed laundry amount.
An embodiment of the present invention may provide a washing machine, including a drum in which laundry are entered and rotated, a laundry amount sensor for sensing a laundry amount within the drum, and a controller for controlling the drum to operate at a first speed so that the laundry tumbles within the drum, controlling the drum to operate at a second speed so that a part of the laundry is tumbled within the drum and the other part of the laundry is adhered within the drum, and changing operation commands for driving the drum subsequent to the first speed operation based on a laundry amount sensed during the first speed operation.
Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments.
Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.

## Claims

1. A method of controlling a washing machine that includes a drum, the method comprising:
operating the drum at a first speed so that laundry tumbles within the drum;
sensing an amount of the laundry within the drum during the first speed operation; and
operating the drum at a second speed so that part of laundry tumbles within the drum and another part of the laundry is continuously forced toward the drum; and
when an unbalanced amount of the drum during the second speed operation is a specific value or less, operating the drum at a third speed so that substantially all the laundry is continuously forced toward the drum, wherein a reference value of the unbalanced amount of the drum during the third speed operation is changed based on the sensed laundry amount.

2. The method of claim 1, wherein the reference value is reduced as the sensed laundry amount increases.

3. The method of claim 1, wherein the second speed is approximately 60 rpm.

4. A method of controlling a washing machine that includes a drum, comprising:
operating the drum at a first speed so that substantially all laundry tumbles within the drum;
sensing an amount of the laundry within the drum during first speed operation;
operating the drum at a second speed so that part of the laundry tumbles within the drum and another part of the laundry is continuously forced toward the drum; and
when an unbalanced amount of the drum during the second speed operation is a specific value or less, increasing a rotational speed of the drum to a third speed so that substantially all the laundry is continuously forced toward the drum, wherein a rising slope corresponding to a rate at which the second speed is increased to the third speed is changed based on the sensed laundry amount.

5. The method of claim 4, wherein the rising slope decreases as the sensed laundry amount increases.

6. The method of claim 4, wherein the second speed is approximately 60 rpm.

7. A washing machine comprising:
a drum to rotate laundry;
a laundry amount sensor to sense an amount of the laundry within the drum;
a sensor to sense an unbalanced amount of the drum; and
a controller to control the drum to operate at a first speed so that substantially all the laundry tumbles within the drum, and to control the drum to operate at a second speed so that part of the laundry tumbles within the drum and another part of the laundry is continuously forced toward the drum, wherein:
when the sensed unbalanced amount of the drum during the second speed operation is a specific value or less, the controller controls the drum to operate at a third speed so that substantially all the laundry is continuously forced toward the drum, and to change a reference value of the unbalanced amount of the drum during the third speed operation according to the sensed laundry amount during the first speed operation.

8. The washing machine of claim 7, wherein the controller further controls the reference value to decrease as the sensed laundry amount increases.

9. The washing machine of claim 7, wherein the second speed is approximately 60 rpm.

10. A washing machine, comprising:
a drum to rotate laundry;
a laundry amount sensor to sense an amount of laundry in the drum;
an unbalance amount sensor to sense an unbalanced amount of the drum; and
a controller to control the drum to operate at a first speed so that substantially all the laundry tumbles within the drum, and to control the drum to operate at a second speed so that part of the laundry tumbles within the drum and another part of the laundry is continuously forced toward the drum,
wherein, when the sensed unbalanced amount of the drum during the second speed operation is a specific value or less, the controller controls the drum to operate at a third speed so that substantially all the laundry is continuously forced toward the drum, wherein the controller changes a rising slope corresponding to a rate at which the second speed is increased to the third speed based on the sensed laundry amount.

11. The washing machine of claim 10, wherein the controller further controls the rising slope to decrease as the sensed laundry amount increases during the first speed operation.

12. The washing machine of claim 10, wherein the second speed is approximately 60 rpm.