Patent Publication Number: US-2013239336-A1

Title: Method For Controlling The Operation Of  A Washing Machine, And System For Controlling Freezes For A Washing Machine

Description:
TECHNICAL FIELD 
     The present invention relates to a method for controlling the operation of a washing machine and a system for controlling freezes for a washing machine. 
     BACKGROUND ART 
     In general, washing machines include an outer tub to contain wash water and an inner tub to contain clothing (hereafter, referred to as ‘fabrics’), rotatable in the outer tub, and wash the fabrics as the inner tub rotates. 
     The washing machines can be classified into a top loading type with an inner tub that is vertically mounted such that fabrics can be loaded from the tops of the machines, and rotates about the vertical axis and a front loading type with an inner tub that is horizontally mounted such that fabrics can be loaded through the fronts of the machines, and rotates about the horizontal axis. 
     The top loading type of washing machines can be largely classified into an agitator type and a pulsator type, then, the agitator type washes by rotating a wash bar standing at the center of an inner tub and the pulsator type washes by rotating a circular plate shaped-pulsator formed on the bottom of an inner tub or the inner tub. 
     The front loading type of washing machine, generally called a drum washing machine, includes a lifter on the inner side of a drum, which is an inner tub, and washes by lifting and dropping fabrics with the lifter as the drum is rotated. 
     There are various types of washing machines, as described above, but any one of them is equipped with a water supply system that supplies wash water to the outer tub and/or the inner tub and drain system that exhausts wash water from the outer tub after washing, rinsing, and spinning. 
     The washing machines of the related art has a problem in that the water supply system or the drain system cannot normally operate due to freeze of wash water under the environment such as wintertime where the external air drops in temperature to zero or less. 
     DISCLOSURE 
     Technical Problem 
     The present invention has been made in an effort to solve the aforementioned problems and it is an object of the present invention to provide a method of a washing machine which can prevent a washing machine from freezing. 
     Further, it is another object of the present invention to provide a method of controlling a washing machine which suspends the operation of a washing machine, depending on freeze conditions that are set in consideration of the internal temperature of the washing machine. 
     Further, it is another object of the present invention to provide a method of controlling a washing machine which can preclude a washing machine from freezing, by allowing a user to immediately recognize the temperature drop, when the internal temperature of the washing machine dropped to a predetermined level or less. 
     Further, it is another object of the present invention to provide a method of controlling a washing machine that can accurately sense whether a washing machine freezes, by determining several times whether the washing machine freezes at each of operational steps of the washing machine. 
     Further, it is another object of the present invention to provide a method of controlling a washing machine that can sense whether a washing machine freezes. 
     Further, it is another object of the present invention to provide a method of controlling a washing machine which can prevent wash water from freezing by removing the water remaining inside the washing machine. 
     Further, it is another object of the present invention to provide a method of controlling a washing machine which can improve convenience in the use by allowing a user to selectively remove the water remaining inside the washing machine. 
     Further, it is another object of the present invention to provide a system for managing freeze of a washing machine that can sense and prevent freeze at a short distance or a long distance by using a communication system. 
     Technical Solution 
     A method of controlling a washing machine of the present invention includes: a step (a) that senses the internal temperature of a washing machine through a temperature sensor; and a step (b) that operates a heater in the washing machine, when the temperature sensed in step (a) is lower than a set-temperature. 
     Alternatively, a method of controlling a washing machine including at least one of a water supply pump, a drain valve, and a drain pump of the present invention, includes: a step (a) that senses temperature by means of a temperature sensor disposed in the water supply valve, the drain valve, or the drain pump in the washing machine; and a step (b) that operates the water supply valve, the drain valve, or the drain pump which is equipped with the temperature sensor. 
     Alternatively, a method of controlling a washing machine of the present invention includes: a step (a) that performs draining, when the water level in an outer tub is a set-water level or more, before supplying wash water; a step (b) that compares the internal temperature of the washing machine with a reference temperature, draining takes a reference time or more in step (a); and a step (c) that outputs a first error message, when the internal temperature of the washing machine is lower than the reference temperature in step (b). 
     Alternatively, a method of controlling a washing machine of the present invention includes: a step (a) that performs draining, when the water level in an outer tub is higher than a first set-water level that is set to determine whether an overflow has occurred, before supplying wash water into the outer tub; a step (b) that performs draining, when the water level in the outer tub is higher than a second set-water level set to be lower than the first set-water level, after step (a); a step (c) that compares the internal temperature of the washing machine with a predetermined reference temperature, when the time taken to discharge the water to a predetermined level in step (b) is larger than a predetermined drain-set time; and a step (d) that outputs a first error message, when the internal temperature of the washing machine is lower than the predetermined reference temperature in step (c). 
     Alternatively, a method of controlling a washing machine of the present invention includes a step (a) that supplies water into an outer tub; a step (b) that compares the internal temperature of the washing machine with a third reference temperature, when the water level in the outer tub is lower than a first water supply-set water level, after wash water is supplied for a first water supply-set time; and a step (c) that outputs a first error message, when the internal temperature of the washing machine is lower than the third reference temperature in step (b). 
     Alternatively, a method of controlling the operation of a washing machine of the present invention includes: a step (a) that senses temperature before water is supplied into an outer tub; a step (b) that supplies water into the outer tub; a step (c) that senses the water level in the outer tub; and a step (d) that outputs a fifth error message, when the water level in the outer tub does not reach a first set-water level within a first set-time. Alternatively, a method of controlling a washing machine of the present invention includes: a step (a) that senses the amount of change in output voltage of a water supply valve, when power is applied to the water supply valve; and a step (b) that performs unfreezing, when it is sensed that the output voltage of the water supply valve has reduced by a predetermined value or more in step (a). 
     Alternatively, a method of controlling a washing machine of the present invention includes: a step (a) that senses the amount of change in output voltage of a drain pump, when power is applied to the drain pump; and a step (b) that performs unfreezing, when it is sensed that the output voltage of the drain pump has reduced by a predetermined value or more in step (a). 
     Alternatively, a method of controlling a washing machine of the present invention includes: a step (a) that senses the amount of change in output voltage of a drain valve, when power is applied to the drain valve; and a step (b) that performs unfreezing, when it is sensed that the output voltage of the drain valve has reduced by a predetermined value or more in step (a). 
     A system for controlling freezes for a washing machine of the present invention includes: a washing machine that determines whether wash water freezes, and transmits a signal about whether the wash water freezes to the outside through a communication medium; and a remote controller that receives whether the wash water freezes from the washing machine. 
     Alternatively, a system for controlling freezes for a washing machine of the present invention includes: a remote controller that allows a user to input a signal about anti-freezing of wash water and transmits the anti-freezing signal to a washing machine through a communication medium; and a washing machine that receives the anti-freezing signal from the remote controller and performs anti-freezing for the wash water. 
     Advantageous Effects 
     The method of controlling a washing machine of the present invention has the effect of being able to prevent a washing machine from freezing even under an environment at a low temperature such as a hard winter season. 
     Further, the method of controlling a washing machine of the present invention can effectively perform anti-freezing or unfreezing for the parts of a washing machine, which may freeze, by directly heating the parts. 
     Further, the method of controlling a washing machine of the present invention has the effect of being able to prevent freezing by using self-heating that is generated when the parts operate, without a specific heater for heating the parts that frequently come in contact with wash water. 
     Further, the method of controlling a washing machine of the present invention has the effect of being able to accurately sense whether to freeze. 
     Further, the method of controlling a washing machine of the present invention has the effect of being able to accurately sense whether a washing machine freezes, by determining several times whether the washing machine freezes at each of operational steps of the washing machine. 
     Further, the method of controlling a washing machine of the present invention has the effect of being able to determine whether to freeze, before a predetermined operation such as washing, rinsing, and spinning. 
     Further, the method of controlling a washing machine of the present invention has the effect of being able to ensure safety by stopping the operation of a washing machine when the washing machine freezes, and to induce taking appropriate measures by outputting an error that says that freezing has occurred to the outside. 
     Further, the method of controlling a washing machine of the present invention has the effect of being able to prevent water from remaining and freezing in the washing machine. 
     Further, the method of controlling a washing machine of the present invention has the effect of being able to prevent the washing machine from being left frozen for a long time, by performing unfreezing when it is sensed that the washing machine has frozen. 
     Further, the method of controlling a washing machine of the present invention has the effect of being able to simply and accurately sense whether to freeze, by sensing whether to freeze through a change in output voltage or output current of electric components of the washing machine, such as a water supply valve, a drain valve, or a drain pump. 
     Further, a system for controlling freezes for a washing machine of the present invention has the effect of being able to provide information about freezing of the washing machine to a user at a long distance. 
     Further, a system for controlling freezes for a washing machine of the present invention can check whether the washing machine has frozen at a long distance through a communication network. 
     Further, a system for controlling freezes for a washing machine of the present invention can allow an operation for preventing the washing machine from freezing at a long distance through a communication network. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side cross-sectional view of a washing machine according to an embodiment of the present invention. 
         FIG. 2  is a partial enlarged view showing the bottom of the outer tub shown in  FIG. 1 . 
         FIG. 3  is a block diagram illustrating the configuration of controlling a washing machine according to an embodiment of the present invention. 
         FIG. 4  is a diagram illustrating an example of the configuration of supplying power to prevent freeze in a washing machine according to an embodiment of the present invention. 
         FIG. 5  is a flowchart illustrating a method of controlling a washing machine according to a first embodiment of the present invention. 
         FIG. 6  is a flowchart illustrating a method of controlling a washing machine according to a second embodiment of the present invention. 
         FIG. 7  is a flowchart illustrating a method of controlling a washing machine according to a third embodiment of the present invention. 
         FIG. 8  is a flowchart illustrating a method of controlling a washing machine according to a fourth embodiment of the present invention. 
         FIGS. 9   a  to  9   c  are flowcharts illustrating a method of controlling a washing machine according to a fifth embodiment of the present invention. 
         FIG. 10  is a diagram illustrating another example of the configuration of supplying power to prevent freeze in a washing machine  100  according to an embodiment of the present invention. 
         FIG. 11  is a flowchart illustrating a method of controlling a washing machine according to a sixth embodiment of the present invention. 
         FIG. 12  is a flowchart illustrating a method of controlling a washing machine according to a seventh embodiment of the present invention. 
         FIG. 13  is a flowchart illustrating a method of controlling a washing machine according to an eighth embodiment of the present invention. 
         FIG. 14  is a flowchart illustrating a method of controlling a washing machine according to a ninth embodiment of the present invention. 
         FIG. 15  is a flowchart illustrating a method of controlling a washing machine according to a tenth embodiment of the present invention. 
         FIG. 16  is a flowchart illustrating a method of controlling a washing machine according to an eleventh embodiment of the present invention. 
         FIG. 17  is a flowchart illustrating a method of controlling a washing machine according to a twelfth embodiment of the present invention. 
         FIG. 18  is a flowchart illustrating a method of controlling a washing machine according to a thirteenth embodiment of the present invention. 
         FIG. 19  is a flowchart illustrating a method of controlling a washing machine according to a fourteenth embodiment of the present invention. 
         FIG. 20  is a flowchart illustrating a method of controlling a washing machine according to a fifteenth embodiment of the present invention. 
         FIG. 21  is a flowchart illustrating a method of controlling a washing machine according to a sixteenth embodiment of the present invention. 
         FIG. 22  is a flowchart illustrating a method of controlling a washing machine according to a seventeenth embodiment of the present invention. 
         FIG. 23  is a graph showing an output voltage change (a) when a water supply valve is unfrozen and an output voltage change (b) when a drain valve is unfrozen. 
         FIG. 24  is a flowchart illustrating a method of controlling a washing machine according to an eighteenth embodiment of the present invention. 
         FIG. 25  is a block diagram illustrating the flow of control in a system for controlling freezes for a washing machine according to an embodiment of the present invention. 
         FIG. 26  is a flowchart illustrating a first embodiment of a system for controlling freezes for a washing machine. 
         FIG. 27  is a flowchart illustrating a second embodiment of a system for controlling freezes for a washing machine. 
         FIG. 28  is a flowchart illustrating a third embodiment of a system for controlling freezes for a washing machine. 
     
    
    
     BEST MODE 
     The advantages and features of the present invention, and methods of achieving them will be clear by referring to the exemplary embodiments that will be describe hereafter in detail with reference to the accompanying drawings. However, the present invention is not limited to the exemplary embodiments described hereafter and may be implemented in various ways, and the exemplary embodiments are provided to complete the description of the present invention and let those skilled in the art completely know the scope of the present invention and the present invention is defined by claims. Like reference numerals indicate like components throughout the specification. 
       FIG. 1  is a side cross-sectional view of a washing machine  100  according to an embodiment of the present invention.  FIG. 2  is a partial enlarged view showing the bottom of the outer tub shown in  FIG. 1 .  FIG. 3  is a block diagram illustrating the configuration of controlling the washing machine  100  according to an embodiment of the present invention. 
     Referring to  FIGS. 1 to 3 , the washing machine  100  according to an embodiment of the present invention includes a cabinet  1  that forms the outer appearance, an outer tub  2  that is disposed inside the cabinet  1  and contains wash water, an inner tub  3  that is rotatably disposed inside the outer tub  2  and contains wash water, and a pulsator  4  that is rotatably disposed on the bottom inside the inner tub  3 . A plurality of holes  3   h  is formed through the inner tub  3  such that wash water can flow between the outer tub  2  and the inner tub  3 . The outer tub  2  may be equipped with, at the top, a top cover with substantially the center portion open such that laundry can be loaded into the inner tub  3 . Operation keys allowing a user to input various commands for controlling the operation of the washing machine and a control panel  11  providing a user interface by being equipped with a display that displays the operational status of the washing machine may be disposed on a side of the cabinet  1 . 
     Further, the washing machine  100  according to an embodiment of the present invention a water supply channel  5  connected with an external water source such as a faucet and supplying wash water to the inner tub  2  and the outer tub, a water supply valve  6  opening/closing the water supply channel  5 , a detergent box  7  containing a detergent, a drain channel  9  for discharging the wash water in the outer tub  2 , a drain valve  8  opening/closing the drain channel  9 , a drain pump  10  disposed in the drain channel  9 , and a driving unit  13  selectively rotating the inner tub  3  or the pulsator  4 . 
     The driving unit  13  may include a motor (not shown) that generates a rotational force and a clutch (not shown) that selectively transmit the rotational force of the motor to the inner tub  3  or the pulsator  4 . 
     Further, the washing machine  100  according to an embodiment of the present invention may further include a control unit  4  that controls the overall operation of the washing machine, an anti-freezing selection unit  16  through which control commands for performing anti-freezing are inputted, a water level sensor  20  that senses the level of the wash water in the outer tub  2 , a display unit  22  that displays the operational status of the washing machine, and a heater  28 . 
     The heater  28  may be disposed on the bottom of the outer tub  2 , and as shown in  FIG. 2 , on the bottom of the outer tub  2 , a heater seat that forms a predetermined space for receiving the heater  28  is recessed and a heater cover  71  that covers the top of the heater seat may be disposed. 
     A hole  71   h  may be formed through the heater cover  71  such that the wash water in the outer tub  2  can be discharged and a drain hole  74  may be formed through the heater seat such that wash water can be discharged to the drain channel  25 . 
     The temperature sensor  18  may be disposed on the bottom of the outer tub  2 . The temperature sensor  18  measures the temperature of wash water or the temperature of air in accordance with the level of the wash water in the outer tub  2 . That is, it is apparent that the temperature sensed by the temperature sensor  18  is the temperature of the medium that is in contact with the temperature sensor  18 , such that the temperature will be the temperature of wash water, when the temperature sensor  18  is submerged by wash water at a predetermined level or more in the outer tub  2 , and it will be the temperature of air in other cases. 
       FIG. 4  is a diagram illustrating an example of the configuration of supplying power to prevent freeze in the washing machine  100  according to an embodiment of the present invention. 
     Referring to  FIG. 4 , the washing machine  100  according to an embodiment of the present invention may include a first power supply unit  24  and a second power supply unit  26 . 
     The first power supply unit  24  supplies power with a predetermined magnitude or less with the washing machine in a standby status, not washing, rinsing, or spinning, and the display unit  22  can be operated even with the washing machine in the standby status by the power supplied from the first power supply unit  24 . 
     The second power supply unit  26 , which can supply power with a predetermined magnitude or more, supplies power for operating the heater  28 . Further, the second power supply unit  26  can supply power to the driving unit  13 , for washing, rinsing, or spinning. 
     In the washing machine  100  according to an embodiment of the present invention, the temperature sensor  18  senses temperature and the heater  28  operates, when the sensed temperature is lower than set-temperature, in order to prevent various parts of the washing machine from freezing with the washing machine in the standby status, not washing, rinsing, or spinning. 
     The set-temperature is reference temperature where the parts of the washing machine freeze, if they are left under a condition that is lower than the set-temperature, and preferably, it may be set at a subzero temperature. 
     Meanwhile, the power to be supplied to the temperature sensor  18  and the heater  28  can be supplied from any one of the first power supply unit  24  or the second power supply unit  26 , but it is preferable that the first power supply unit  24  supplies power to the temperature sensor  18 , when the washing machine is in the standby status without washing, rinsing, or spinning, and the first power supply unit  26  supplies power to operate the heater  28 , when the temperature sensed by the temperature sensor  18  is lower than the set-temperature. There is an effect that it is possible to reduce the amount of power consumed by the temperature sensor  18  with the washing machine in the standby status. 
     When anti-freezing starts, the control unit  14  may control the first power supply unit  24  to supply power in order to operate the temperature sensor  18  and may control the second power supply unit  26  to supply power in order to operate the heater  28 , when the temperature sensed by the temperature sensor  18  is lower than the set-temperature. 
     The start of anti-freezing means that a predetermined algorithm is executed to prevent the parts of the washing machine from freezing, and may be implemented in the following two ways. 
     First, anti-freezing automatically starts, when the washing machine is in the standby status without washing, rinsing, or spinning. It offers the advantage that it is not necessary to take a specific measure for preventing freeze of the washing machine. 
     Second, as shown in  FIG. 3 , as the anti-freezing selection unit  16  that allows selection of anti-freezing is provided in the washing machine, anti-freezing starts, only when there is a selection through the anti-freezing selection unit  16  by a user. 
     It should be noted that the starts (S 501 , S 601 , S 701 , and S 801 ) of anti-freezing shown in  FIGS. 5 to 8  can be implemented in any one of the two ways. 
     Further, the temperature sensor  18  will suffice as long as it can measure the internal temperature of the washing machine and may be a temperature sensor that is disposed inside the outer tub  2 , a temperature sensor that is disposed in the water supply valve  6 , a temperature sensor that is disposed in the drain valve  8 , or a temperature sensor that is disposed in the drain pump  10 , in order to measure the temperature of the wash water. 
     Meanwhile, the driving unit  13  may include a driving driver that controls the rotation of the motor by applying a driving signal to the motor. An IPM (Intelligent Power Module) may be exemplified as the driving driver and may be implemented by a driving circuit of a power device such as a power MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor), or a power module provided with a self-protection function. 
     The IPM may be equipped with a temperature sensor in itself and the temperature sensor of the IPM may be used in the temperature sensing steps (S 502 , S 602 , S 702 , and S 802 ) in  FIGS. 5 to 8 , which is described below. 
     On the other hand, though not shown in the drawings of the application, it should be construed that a washing machine for both washing and drying which has a function of drying too is included in the category of the washing machine of the present invention, and common washing machines for both washing and drying are equipped with a dry duct for supplying high-temperature air into the inner tub  3  with laundry loaded in order to dry the laundry and a temperature sensor that measures the internal temperature of the dry duct, so it should be noted that the temperature sensor  18  may be the temperature sensor that measures the internal temperature of the dry duct. 
     Further, the heater  28  may be disposed in the various parts of the washing machine  100 . For example, freezing is likely to occur in the water supply valve  6 , the drain valve  8 , and the drain pump  10  through which wash water flows, such that the water supply pump  6 , the drain valve  6 , and/or the drain pump  10  may be equipped with the heater  28 . 
       FIG. 5  is a flowchart illustrating a method of controlling a washing machine according to a first embodiment of the present invention. 
     As anti-freezing starts (S 501 ), the temperature sensor  18  senses temperature (S 502 ), and the heater  28  operates (S 503  and S 504 ), when the temperature sensed by the temperature sensor  18  is lower than a set-temperature. As long as freezing does not occur even after the heater  28  operates (S 505 ), the temperature sensor  18  repeats measuring temperature (S 506 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature, the heater  28  suspends the operation (S 507  and S 508 ). Thereafter, in accordance with whether freeze-sensing stops (S 505 ), the temperature sensor  18  senses temperature (S 506 ), and when the sensed temperature is lower than the set-temperature, the heater  28  operates again (S 507  and S 504 ). 
     The repeat of operating (S 504 ) and suspending (S 508 ) of the heater  28 , based on the temperature sensed by the temperature sensor  18 , as described above, keeps until the anti-freezing stops. Stopping the anti-freezing may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
       FIG. 6  is a flowchart illustrating a method of controlling a washing machine according to a second embodiment of the present invention. 
     As anti-freezing starts (S 601 ), the temperature sensor  18  senses temperature (S 602 ), and the heater  28  operates when the temperature sensed by the temperature sensor  18  is lower than a set-temperature (S 603  and S 604 ). As long as freezing does not occur even after the heater  28  operates, the temperature  18  repeats measuring temperature (S 605 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature, the heater  28  suspends the operation (S 606  and S 608 ). 
     Further, the heater  28  suspends the operation when a set-time has passed (S 606 , S 607 , and S 608 ), even though the temperature sensed by the temperature sensor  18  is not larger than the set-temperature in the present invention. The set-time may be set within a range where the heater  28  is not overheated, in consideration of the degree of heating of the heater  28 . 
     Thereafter, in accordance with whether freeze-sensing stops (S 609 ), the temperature sensor  18  periodically senses temperature (S 602 ), and when the sensed temperature is lower than the set-temperature (S 603 ), the heater  28  operates again (S 604 ). The repeat of operating (S 604 ) and suspending (S 608 ) of the heater  28 , based on the temperature sensed by the temperature sensor  18 , as described above, keeps until the anti-freezing stops. Stopping the anti-freezing may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
       FIG. 7  is a flowchart illustrating a method of controlling a washing machine according to a third embodiment of the present invention. 
     As anti-freezing starts (S 701 ), the temperature sensor  18  senses temperature (S 702 ), and the heater  28  repeats operating and suspending (S 704 ), when the temperature sensed by the temperature sensor  18  is lower than a set-temperature (S 703 ). As long as freezing does not occur even after the heater  28  operates, the temperature  18  repeats measuring temperature (S 705  and S 706 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature, the heater  28  stops the operation (S 707  and S 708 ). 
     The reason that the section where the heater  28  does not operate is referred to as ‘suspending’ in step S 704  and as ‘stopping’ in step S 708  is because there is a difference in the way of operation of the heater  28  in steps S 704  and S 708 . That is, the heater  28  repeats operating and suspending for a predetermined time in step S 704 , while the heater  28  that has stopped the operation in step S 708  returns to step S 705  from step S 708 , performs steps S 706  and S 707 , and stands by without operating until it is operated again. 
     Meanwhile, in step S 707 , when the temperature sensed by the temperature sensor is lower than the set-temperature, the process returns to step S 704  and the heater  28  repeats operating and suspending. 
     The third embodiment is different from the first embodiment described above in that when the temperature sensed by the temperature sensor  18  (S 702 ) is lower, the heater  28  does not continuously operate but repeats operating and suspending (S 704 ). 
     Stopping the anti-freezing in step S 705  may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
       FIG. 8  is a flowchart illustrating a method of controlling a washing machine according to a fourth embodiment of the present invention. 
     As anti-freezing starts (S 801 ), the temperature sensor  18  senses temperature (S 802 ), and the heater  28  repeats operating and suspending (S 803  and S 804 ), when the temperature sensed by the temperature sensor  18  is lower than a set-temperature. As long as freezing does not occur even after the heater  28  operates, the temperature sensor  18  repeats measuring temperature (S 805 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature, the heater  28  stops the operation (S 808 ). 
     Further, the heater  28  stops the operation when a set-time has passed (S 806 , S 807 , and S 808 ), even though the temperature sensed by the temperature sensor  18  is not larger than the set-temperature in the present invention. The set-time may be set within a range where the heater  28  is not overheated, in consideration of the degree of heating of the heater  28 . 
     Thereafter, in accordance with whether freeze-sensing stops (S 809 ), the temperature sensor  18  periodically senses temperature (S 802 ), and when the sensed temperature is lower than the set-temperature, the heater  28  operates again (S 803  and S 804 ). 
     The reason that the section where the heater  28  does not operate is referred to as ‘suspending’ in step S 804  and as ‘stopping’ in step S 808  is because there is a difference in the way of operation of the heater  28  in steps S 804  and S 808 . That is, the heater  28  repeats operating and suspending for a predetermined time in step S 804 , while the heater  28  that has stopped the operation in step S 808  returns to step S 802  from step S 809  and stands by without operating until it is operated again in step S 804 . 
     Stopping the anti-freezing in step S 809  may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
       FIGS. 9   a  to  9   c  are flowcharts illustrating a method of controlling a washing machine according to a fifth embodiment of the present invention. 
     The washing machine  100  according to an embodiment of the present invention can perform a process of sensing whether the washing machine has frozen after operating for washing, rinsing, or spinning. 
     The washing machine  100  according to an embodiment of the present invention can accurately determine whether the washing machine freezes by primarily determining whether to freeze, which determines whether there is an overflow on the basis of comparison between a first set-water level with the water level in the outer tub  2  after power is supplied to the washing machine, and then performs draining on the basis of the result of the determination, through the series of flow shown in  FIG. 9   a , by secondarily determining whether to freeze which performs draining when the water level in the outer tub  2  is a second set-water level or more by comparing the water level in the outer tub  2  with the second set-water level, through the series of flow shown in  FIG. 9   b , and by thirdly determining whether to freeze through the series of flow shown in  FIG. 9   c  after supplying wash water into the outer tub  2  to perform the operations such as washing, rinsing, and spinning. 
     The process of primarily determining whether to freeze is described hereafter in detail with reference to  FIG. 9   a.    
     As power is supplied and the washing machine starts operating (S 901 ), the water level in the outer tub  2  is sensed by the water level sensor  20  and whether an overflow has occurred in the outer tub  2  is determined by comparing the sensed value with the first set-water level (S 902 ). The reason that the process is performed in for sensing whether wash water has overflowed the outer tub  2 , rising in the outer tub  2 , by exceeding a predetermined level by a specific situation before the washing machine operates. For example, it may be the case when wash water keeps supplied into the outer tub  2  even with the power of the washing machine off due to a problem with the water supply valve  6 . Therefore, it is preferable to set the first set-water level in consideration of the water level where the wash water overflows the outer tub  2 . 
     When it is determined that the water level in the outer tub  2  is higher than the first set-water level in step S 902 , the control unit  14  controls the display unit  2  to output a third error message (S 903 ). The third error message is a message that allows the user to recognize that an overflow has occurred. 
     Thereafter, the control unit  14  operates the drain pump  10  such that the wash water in the outer tub  2  is discharged (S 904 ), and it turns off the third error message (S 906 ), when the water level in the outer tub  2  drops down under a second set-water level within a predetermined time (S 905 ). It is preferable to set the second set-water level to a zero water level with wash water in the outer tub  2  completely discharged. It is assumed that the second set-water level is a zero water level in the following description. 
     Meanwhile, when the water level in the outer tub  2  does not reach the second set-water level in step S 905 , the drain pump  10  keeps operating, and a when the water level in the outer tub  2  does not reach the second set-water level until the drain set-time reaches a first drain set-time (S 907 ), the control unit  14  compares the temperature sensed by the temperature sensor  18  with a first reference temperature (S 908 ). When it is determined that the sensed temperature is lower than the first reference temperature, as the result of comparing, the control unit  14  controls the display unit  22  to display a first error message, and when it is determined that the sensed temperature is higher than the first reference temperature, it controls the display unit  22  to output a second or a third error message (S 910 ). 
     The process of secondarily determining whether to freeze is described hereafter in detail with reference to  FIG. 9   b.    
     The process of secondarily determining whether to freeze is performed under the condition that the water level in the outer tub  2  is lower than the first set-water level. That is, this is for determining whether to freeze in the following processes, when it is determined that the water level sensed by the water level sensor  20  is lower than the first set-water level in step S 902  or when the water level in the outer tub  2  drops down under the second set-water level through steps S 902 , S 903 , S 904 , S 905 , and S 906 . 
     The process of secondarily determining whether to freeze includes comparing the temperature sensed by the temperature sensor  18  with a second reference temperature. When the sensed temperature is the second reference temperature or less in step S 911 , the control unit  14  controls the display unit  22  to output the first error message (S 912 ). 
     The water level in the outer tub in step S 911  may be the first set-water level or less (which is possible when the process enters step S 911  right after step S 902 ) or the second set-water level (for example, the case when the water level in the outer tub  2  becomes the zero water level after steps S 903 , S 904 , S 905 , and S 906  are sequentially performed). When the water level in the outer tub  2  is higher than the second set-water level and lower than the first set-water level, the temperature sensor  18  would sense the temperature of the wash water in the outer tub  2 . In contrast, when the water level in the outer tub  2  is lower than the second set-water level (for example, the zero water level), the temperature sensor  18  would sense the temperature of the air in the washing machine. It is preferable that the second reference value is set at a subzero value in consideration of the freezing point of the wash water, or may be set as a several degrees under zero or less, considering that the temperature of the air is sensed by the temperature sensor  18 . 
     When it is determined in step S 911  that the temperature sensed by the temperature sensor  18  is lower than the second reference temperature, the control unit  14  determines that the temperature inside the washing machine is low enough for freezing and immediately controls the display unit  22  to output the first error message (S 912 ). In sensing whether to freeze through steps S 911  and S 912 , whether to freeze is determined or estimated on the basis of the sensed value by the temperature sensor  18 , regardless of the features of discharging the wash water, and is not necessarily limited to the order shown in  FIG. 9   b  and may be performed at any point of time in the operation of the washing machine. 
     In particular, it is preferable to set the second set-temperature at an appropriate value through an experiment in step S 911  to make it possible to estimate that the parts of the parts of the washing machine such as the water supply valve  6  or the drain pump  10  will freeze, with sufficient accuracy, when the temperature sensed by the temperature sensor  18  is the second temperature sensor or less. 
     On the other hand, when it is determined that the temperature sensed by the temperature sensor  28  is higher than the second reference temperature in step S 911 , the control unit  14  compares the water level sensed by the water level sensor  20  with the third set-water level (S 913 ). 
     The case when the sensed water level is higher than the third set-water level means that there is wash water at the third water level or higher and at the first set-water level or less, in which the control unit  14  operates the drain pump  10  to drain (S 915 ), determines that drain is normally performed, and senses the laundry weight, when a change in water level in the outer tub  2  is a reference value or more by draining for a second drain set-time (S 916 ), compares the temperature sensed by the temperature sensor  18  with the third reference temperature (S 918 ) when the change in water level is the reference value or less even though the second drain set-time has passed in step S 916  (S 917 ), controls the display unit  22  to output the first error message when the sensed temperature is lower than the third reference temperature (S 919 ), and controls the display unit  22  to output the second error message (S 920 ) when the sensed temperature is higher than the third reference temperature. The process of thirdly determining whether to freeze is performed under the condition that the water level in the outer tub  2  is the third set-water level or less, and may be performed after a laundry weight sensing step (S 914 ) shown in  FIG. 9 . 
     When the laundry weight in the inner tub  6  is sensed in step S 914 , the patterns of the operation such as washing, rinsing, and spinning, which are performed later in accordance with the sensed laundry weight, are determined. 
     Water supplying (S 921 ) is a step of supplying wash water into the outer tub  2  and the amount of the supplied wash water is set in accordance with the laundry weight sensed in step S 914 . 
     Step S 923  that compares the water level in the outer tub  2  with the first water supply set-level to determine whether water is normally supplied is performed, when the first water supply set-time has passed (S 922 ) after water starts to be supplied in step S 912 , and the control unit  14  determines that water is normally supplied when the water level sensed by the water level sensor  20  is the first water supply set-level, and compares again the water level in the outer tub  2  with the second water supply set-level (S 928 ), after the second water supply set-time passes (S 924 ). The first water supply set-level means a water level that is expected to be reached, when water is normally supplied for the first water supply set-time and the second water supply set-level means a target water level of the water that is supplied in to the outer tub  2  in accordance with the laundry weight sensed in step S 914 . 
     On the other hand, when it is determined that the water level in the outer tub  2  does not reach the first water supply set-level, the control unit  14  compares the temperature sensed by the temperature sensor  18  with a fourth reference temperature, when the sensed temperature is lower than the fourth reference temperature as the result of comparing, it controls the display unit  22  to display the first error message, whereas when the sensed temperature is higher than the fourth reference temperature, it controls the display unit to output a fourth error message. The fourth error message is a message that informs the user that water fails to be normally supplied due to a breakdown of the water supply valve  6  or the like. 
     Further, even if the water level sensed by the water sensor  20  does not reach the second water supply set-level in step S 928 , the control unit  14  can control the display unit  22  to display the fourth error message (S 929 ). 
     By contrast, when the water level sensed by the water level sensor  20  is higher than the second water supply set-level in step S 928 , it means that water is normally supplied, and then the control unit  14  performs the washing operation through first washing by means of a predetermined algorithm, heating of the wash water in the outer tub  2  (S 911 ) by operating the heater  28 , second washing (S 932 ), and draining (S 933 ). In the first washing  930  and the second washing  933 , the inner tub  6  and/or the pulsator  4  rotate and draining (S 933 ) is achieved by the drain pump  10 . 
     When the water level in the outer tub  2  does not reach a drain completion level even after draining ( 933 ) is performed for a third drain set-time (S 939 ), the control unit  14  controls the display unit  22  to display the second error message (S 940 ). On the contrary, when it is determined that the water level in the outer tub  2  is the drain completion level or less in step S 934 , it means that draining has been normally performed, and then the washing machine is turned off (S 938 ), after rinsing (S 935 ), provisional spinning (S 936 ), and main spinning (S 937 ) are performed, thereby finishing the operation of the washing machine. 
       FIG. 10  is a diagram illustrating another example of the configuration of supplying power to prevent freeze in a washing machine according to an embodiment of the present invention. 
     Referring to  FIG. 10 , a washing machine according to the present embodiment includes a first power supply unit  24  and a second power supply unit  26 . 
     The first power supply unit  24  supplies power with a predetermined magnitude or less with the washing machine in a standby status, not washing, rinsing, or spinning, and the display unit  22  can be operated even with the washing machine in the standby status by the power supplied from the first power supply unit  24 . 
     The second power supply unit  26 , which can supply power with a predetermined magnitude or more, supplies power for operating the water supply valve  6 , the drain valve  8 , and the drain pump  10 . Further, power can be supplied to the driving unit  13  from the second power supply unit  26  in washing, rinsing, or spinning. 
     The washing machine according to the present embodiment is prevented from freezing through self-heat generated when various parts operate, by sensing temperature with the temperature sensor  18  and operating the parts of the washing machine, when the sensed temperature is lower than a set-temperature, in order to prevent the parts of the washing machine from freezing with the washing machine in a standby status without washing, rinsing, or spinning. 
     The set-temperature is reference temperature where the parts of the washing machine freeze, if they are left under a condition that is lower than the set-temperature, and preferably, it may be set at a subzero temperature. 
     Meanwhile, the power to be supplied to the temperature sensor  18  and the heater  28  can be supplied from any one of the first power supply unit  24  or the second power supply unit  26 , but it is preferable that the first power supply unit  24  supplies power to the temperature sensor  18 , when the washing machine in the standby status, not washing, rinsing, or spinning, and the second power supply unit  26  supplies power to operate the heater  28 , the water supply valve  6 , the drain valve  10 , or the drain pump  10 , when the temperature sensed by the temperature sensor  18  is lower than the set-temperature. There is an effect that it is possible to reduce the amount of power consumed by the temperature sensor  18  with the washing machine in the standby status. 
     When anti-freezing starts, the control unit  14  may control the first power supply unit  24  to supply power in order to operate the temperature sensor  18  and may control the second power supply unit  26  to supply power in order to operate water supply valve  6 , the drain valve  8 , or the drain pump  10 , when the temperature sensed by the temperature sensor  18  is lower than the set-temperature. 
     The start of anti-freezing means that a predetermined algorithm is executed to prevent the parts of the washing machine from freezing, and may be implemented in the following two ways. 
     First, anti-freezing automatically starts, when the washing machine is in the standby status without washing, rinsing, or spinning. It offers the advantage that it is not necessary to take a specific measure for preventing freeze of the washing machine. 
     Second, as shown in  FIG. 10 , as the anti-freezing selection unit  16  that allows selection of anti-freezing of the washing machine is provided, anti-freezing starts, only when there is a selection through the anti-freezing selection unit  16  by a user. 
     It should be noted that the starts (S 1101 , S 1201 , S 1301 , S 1401 , S 1501 , S 1601 , S 1701 , and S 1801 ) of anti-freezing shown in  FIGS. 11 to 18  can be implemented in any one of the two ways. 
     Further, the temperature sensor  18  of the present invention may be provided in any one of the water supply valve  6 , the drain valve  8 , or the drain pump  10  and is described in more detail in the following embodiments. 
     Embodiments of a method of preventing the water supply valve  6  from freezing are described hereafter with reference to  FIGS. 11 to 18 . However, the anti-freezing method illustrated in  FIGS. 11 to 18  can be applied in the same way to prevent the drain valve  8  from freezing, in which it should be noted that the temperature sensor  18  is disposed in the drain valve  10  and there is a difference only in that whether to operate the drain valve  10  is determined in accordance with a sensed value of the temperature sensor  18 . 
       FIG. 11  is a flowchart illustrating a method of controlling a washing machine according to a sixth embodiment of the present invention. The temperature sensor  18  is disposed in the water supply valve  6  in the present embodiment. 
     As anti-freezing starts (S 1101 ), the temperature sensor  18  senses temperature (S 1102 ), and the water supply valve  6  operates when the temperature sensed by the temperature sensor  18  is lower than a set-temperature (S 1103  and S 1104 ). As long as freezing does not occur even after the water supply valve  6  operates, the temperature  18  repeats measuring temperature (S 1106 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature, the water supply valve  6  suspends the operation (S 1107  and S 1108 ). Thereafter, in accordance with whether freeze-sensing stops (S 1105 ), the temperature sensor  18  senses temperature (S 1106 ), and when the sensed temperature is lower than the set-temperature, the water supply valve  6  operates again (S 1103  and S 1104 ). 
     The repeat of operating (S 1104 ) and suspending (S 1108 ) of the water supply valve  6 , based on the temperature sensed by the temperature sensor  18 , as described above, keeps until the anti-freezing stops. Stopping the anti-freezing may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
       FIG. 12  is a flowchart illustrating a method of controlling a washing machine according to a seventh embodiment of the present invention. 
     The temperature sensor  18  is disposed in the water supply valve  6  in the present embodiment. 
     As anti-freezing starts (S 1201 ), the temperature sensor  18  senses temperature (S 1202 ), and the water supply valve  6  operates when the temperature sensed by the temperature sensor  18  is lower than a set-temperature (S 1203  and S 1204 ). As long as freezing does not occur even after the water supply valve  6  operates, the temperature  18  repeats measuring temperature (S 1205 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature, the water supply valve  6  suspends the operation (S 1206  and S 1208 ). 
     Further, the water supply valve  6  suspends the operation when a set-time has passed (S 1206 , S 1207 , and S 1208 ), even though the temperature sensed by the temperature sensor  18  is not larger than the set-temperature in the present invention. The set-time may be set within a range where the water supply valve  6  is not overheated, in consideration of the degree of heating of the water supply valve  6 . 
     Thereafter, in accordance with whether freeze-sensing stops (S 1209 ), the temperature sensor  18  periodically senses temperature, and when the sensed temperature is lower than the set-temperature (S 1203 ), the water supply valve  6  operates again (S 1204 ). 
     The repeat of operating and suspending of the water supply valve  6 , based on the temperature sensed by the temperature sensor  18 , as described above, keeps until the anti-freezing stops. Stopping the anti-freezing may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
       FIG. 13  is a flowchart illustrating a method of controlling a washing machine according to an eighth embodiment of the present invention. 
     The temperature sensor  18  is disposed in the water supply valve  6  in the present embodiment. 
     As anti-freezing starts (S 1301 ), the temperature sensor  18  senses temperature (S 1302 ), and the water supply valve  6  repeats operating and suspending (S 1304 ), when the temperature sensed by the temperature sensor  18  is lower than a set-temperature (S 1303 ). As long as freezing does not occur even after the water supply valve  6  operates (S 1305 ), the temperature  18  periodically senses temperature (S 1306 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature (S 1307 ), the water supply valve  6  stops the operation (S 1308 ). 
     The reason that the section where the water supply valve  6  does not operate is referred to as ‘suspending’ in step S 1304  and as ‘stopping’ in step S 1308  is because there is a difference in the way of operation of the water supply valve  6  in steps S 1304  and S 1308 . That is, the water supply valve  6  repeats operating and suspending for a predetermined time in step S 1304 , while it stands by without operating before it operates again, by returning to step S 1305  from step S 1308  and performing step S 1306  and S 1307 . 
     Meanwhile, in step S 1307 , when the temperature sensed by the temperature sensor is lower than the set-temperature, the process returns to step S 1304  and the water supply valve  6  repeats operating and suspending. 
     In the present invention, the water supply valve  6  is not continuously operated, but repeatedly operated and suspended, when the temperature sensed by the temperature sensor  18  (S 1302 ) is lower than the set-temperature. 
     Stopping the anti-freezing in step S 1305  may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
       FIG. 14  is a flowchart illustrating a method of controlling a washing machine according to a ninth embodiment of the present invention. 
     The temperature sensor  18  is disposed in the water supply valve  6  in the present embodiment. 
     As anti-freezing starts (S 1401 ), the temperature sensor  18  senses temperature (S 1402 ), and the water supply valve  6  repeats operating and suspending (S 1404 ), when the temperature sensed by the temperature sensor  18  is lower than a set-temperature (S 1403 ). As long as freezing does not occur even after the water supply valve  6  operates, the temperature  18  periodically senses temperature (S 1405 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature, the water supply valve  6  stops the operation (S 1406  and S 1408 ). 
     Further, the water supply valve  6  stops the operation when a set-time has passed (S 1406 , S 1407 , S 1406 , S 1407 , and S 1408 ), even though the temperature sensed by the temperature sensor  18  is not larger than the set-temperature in the present invention. The set-time may be set within a range where the water supply valve  6  is not overheated, in consideration of the degree of heating of the water supply valve  6 . 
     Thereafter, in accordance with whether freeze-sensing stops (S 1409 ), the temperature sensor  18  periodically senses temperature, and when the sensed temperature is lower than the set-temperature, the water supply valve  6  operates again (S 1403  and S 1404 ). 
     The reason that the section where the water supply valve  6  does not operate is referred to as ‘suspending’ in step S 1404  and as ‘stopping’ in step S 1408  is because there is a difference in the way of operation of the water supply valve  6  in steps S 1404  and S 1408 . That is, the water supply valve  6  repeats operating and suspending for a predetermined time in step S 1404 , while the water supply valve  6  that has operated the operation in step S 1408  stands by without operating before it operates again in step S 1403 , by returning to step S 1402  from step S 1409 . 
     Stopping the anti-freezing in step S 1409  may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
       FIG. 15  is a flowchart illustrating a method of controlling a washing machine according to a tenth embodiment of the present invention. 
     The temperature sensor  18  is disposed in the drain pump  10  in the present embodiment. 
     As anti-freezing starts (S 1501 ), the temperature sensor  18  senses temperature (S 1502 ), and the drain pump  10  operates when the temperature sensed by the temperature sensor  18  is lower than a set-temperature (S 1503  and S 1504 ). As long as freezing does not occur even after drain pump  10  operates, the temperature  18  repeats measuring temperature (S 1506 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature, the drain pump  10  suspends the operation (S 1508  and S 1508 ). Thereafter, in accordance with whether freeze-sensing stops (S 1505 ), the temperature sensor  18  senses temperature (S 1506 ), and when the sensed temperature is lower than the set-temperature, the drain pump  10  operates again (S 1507  and S 1504 ). 
     The repeat of operating (S 1504 ) and suspending (S 1508 ) of the drain pump  10 , based on the temperature sensed by the temperature sensor  18 , as described above, keeps until the anti-freezing stops. Stopping the anti-freezing may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
       FIG. 16  is a flowchart illustrating a method of controlling a washing machine according to an eleventh embodiment of the present invention. 
     The temperature sensor  18  is disposed in the drain pump  10  in the present embodiment. 
     As anti-freezing starts (S 1601 ), the temperature sensor  18  senses temperature (S 1602 ), and the drain pump  10  operates when the temperature sensed by the temperature sensor  18  is lower than a set-temperature (S 1603  and S 1604 ). As long as freezing does not occur even after drain pump  10  operates, the temperature  18  repeats measuring temperature (S 1606 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature, the drain pump  10  suspends the operation (S 1606  and S 1608 ). 
     Further, the drain pump  10  suspends the operation when a set-time has passed (S 1606 , S 1607 , and S 1608 ), even though the temperature sensed by the temperature sensor  18  is not larger than the set-temperature in the present invention. The set-time may be set within a range where the drain pump  10  is not overheated, in consideration of the degree of heating of the drain pump  10 . 
     Thereafter, in accordance with whether freeze-sensing stops (S 1609 ), the temperature sensor  18  periodically senses temperature, and when the sensed temperature is lower than the set-temperature, the drain pump  10  operates again (S 1603  and S 1604 ). 
     The repeat of operating and suspending of the drain pump  10 , based on the temperature sensed by the temperature sensor  18 , as described above, keeps until the anti-freezing stops. Stopping the anti-freezing may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
       FIG. 17  is a flowchart illustrating a method of controlling a washing machine according to a twelfth embodiment of the present invention. 
     The temperature sensor  18  is disposed in the drain pump  10  in the present embodiment. 
     As anti-freezing starts (S 1701 ), the temperature sensor  18  senses temperature (S 1702 ), and the drain pump  10  repeats operating and suspending (S 1703  and S 1704 ), when the temperature sensed by the temperature sensor  18  is lower than a set-temperature. As long as freezing does not occur even after drain pump  10  operates, the temperature  18  periodically measures temperature (S 1706 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature, the drain pump  10  stops the operation (S 1707  and  1708 ). The reason that the section where the drain pump  10  does not operate is referred to as ‘suspending’ in step S 1704  and as ‘stopping’ in step S 1708  is because there is a difference in the way of operation of the drain pump  10  in steps S 1704  and S 1708 . That is, the drain pump  10  repeats operating and suspending for a predetermined time in step S 1704 , while the drain pump  10  that has stopped the operation in step B 28  returns to step S 1705  from step S 1709 , performs steps S 1706  and S 1707 , and stands by without operating until it is operated again. 
     Meanwhile, in step S 1707 , when the temperature sensed by the temperature sensor is lower than the set-temperature, the process returns to step S 1704  and the drain pump  10  repeats operating and suspending. 
     In the present invention, the drain pump  10  is not continuously operated, but repeatedly operated and suspended, when the temperature (S 1702 ) sensed by the temperature sensor  18  is lower than the set-temperature. 
     Stopping the anti-freezing in step S 1705  may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
       FIG. 18  is a flowchart illustrating a method of controlling a washing machine according to a thirteenth embodiment of the present invention. 
     As anti-freezing starts (S 1801 ), the temperature sensor  18  senses temperature (S 1802 ), and the drain pump  10  repeats operating and suspending (S 1803  and S 1804 ), when the temperature sensed by the temperature sensor  18  is lower than a set-temperature. As long as freezing does not occur even after drain pump  10  operates, the temperature  18  periodically measures temperature (S 1805 ), and when the temperature sensed by the temperature sensor  18  is higher than the set-temperature, the drain pump  10  stops the operation (S 1806  and S 1807 ). 
     Further, the drain pump  10  stops the operation when a set-time has passed (S 1806 , S 1807 , and S 1808 ), even though the temperature sensed by the temperature sensor  18  is not larger than the set-temperature in the present invention. The set-time may be set within a range where the drain pump  10  is not overheated, in consideration of the degree of heating of the drain pump  10 . 
     Thereafter, in accordance with whether freeze-sensing stops (S 1809 ), the temperature sensor  18  periodically senses temperature, and when the sensed temperature is lower than the set-temperature, the drain pump  10  operates again (S 1803  and S 1804 ). 
     The reason that the section where the drain pump  10  does not operate is referred to as ‘suspending’ in step S 1804  and as ‘stopping’ in step S 1808  is because there is a difference in the way of operation of the drain pump  10  in steps S 1804  and S 1808 . That is, the drain pump  10  repeats operating and suspending for a predetermined time in step S 1804 , while the drain pump  10  that has operated the operation in step S 1808  stands by without operating before it operates again in step S 1804 , by returning to step S 1802  from step S 1809 . 
     Stopping the anti-freezing in step S 1809  may be based on the condition that a stop command is inputted through the anti-freezing selection unit  16  or may be based on the condition that a user inputs a control command for washing, rinsing, or spinning. 
     The embodiments described above show that it is possible to prevent a washing machine from freezing, using the heat that is generated when the electric parts in the washing machine operate, particularly, that it is possible to prevent freezing by operating the water supply valve  6 , the drain valve  8 , or the drain pump  10 , which can be frequently frozen by remaining water. 
       FIG. 19  is a flowchart illustrating a method of controlling a washing machine according to a fourteenth embodiment of the present invention. 
     Referring to  FIG. 19 , the method of controlling a washing machine according to the fourteenth embodiment of the present invention senses the water level in the outer tub  2  before supplying wash water (S 1901 ). It is possible to sense a water level, using a water level sensor  20  in step S 1901 . 
     The control unit  14  compares the water level sensed in step S 1901  with a set-water level (S 1902 ), makes water be supplied when the sensed water level is lower than the set-water level, and then makes operations such as washing, rinsing, and spinning be performed (S 1903 ). The control unit  14  can make water be supplied by controlling the water supply valve  6  in step S 1903 . 
     On the other hand, when the water level sensed in step S 1902  is higher than the predetermined wash level, the control unit  14  makes wash water be discharged by operating the drain pump  10 , and when the water level in the outer tub  2  keeps sensed by the water level sensor  20  and the water level in the outer tub  2  sufficiently reduces before a drain set-time passes (S 1905 ), the control unit  14  makes the wash water be supplied into the outer tub  2  by opening the water supply valve  6  and the operations such as washing, rinsing, and spinning (S 1903 ). 
     In contrast, when the water level in the outer tub  2  does not sufficiently reduce and the drain set-time passes in step S 1905 , the control unit  14  controls the temperature sensor  18  to sense temperature (S 6 ) and compares the sensed temperature with a reference temperature (S 1907 ), and when the sensed temperature is lower than the reference temperature, the control unit controls the display unit  22  to output a first error message (S 1908 ), and when the sensed temperature is higher than the reference temperature, it controls the display unit  22  to output a second error message (S 1909 ). 
     Meanwhile, when draining is not enough even after the drain set-time passes in step S 904  (S 905 ), it may be assumed as one of the case when draining is not normally performed due to freezing of the drain system including the drain channel  9 , the drain pump  10 , and/or the drain valve  8  (first error message outputted) or the case when the drain pump  10  breaks down (second error message outputted). 
     Steps S 1906  and S 1907  are provided to determine which one it is of the two cases, and when it is determined that the temperature sensed in step S 1906  is lower than the reference temperature in step S 1907 , it can be considered as when the washing machine operates in an environmental condition with a low temperature such as the wintertime and the control unit  14  controls the display unit  22  to output the first error message such that the user can recognize freezing of the drain system. The reference temperature is a value which is set by an experiment and makes it possible to considerably accurately estimate freezing, when water remains in the washing machine. It is preferable to set the reference temperature as a subzero value. 
     In contrast, when it is determined that the temperature sensed in step S 1906  is higher than the reference temperature in S 1907 , it can be considered as the case when there is a low possibility that the water remaining in the washing machine freezes, so that the control unit  14  assumes that the reason for insufficient draining is the factors such as a breakdown of the drain pump  10  and clogging of the drain channel  9  or the drain valve  8 , and controls the display unit  22  to output the second error message such that the user can recognize the reasons. 
     On the other hand, the reason of performing step S 1902  before water is supplied while the washing machine operates is for determining whether to freeze using wash water when the wash water remains in the outer tub  2  before water is supplied for washing or rinsing, which has the advantage of being able to preclude unnecessary water supply by not supplying wash water thereafter, when freezing is sensed. 
     It is preferable that the control unit  14  controls the washing machine to stop the operation while outputting a corresponding error message in step S 1908  or S 1909  and the later operations are performed by specific operations of the user or under a stop condition that is output of the error message. 
       FIG. 20  is a flowchart illustrating a method of controlling a washing machine according to fifteenth embodiment of the present invention. 
     Referring to  FIG. 20 , as the washing machine is supplied with power and starts operating, temperature is sensed by the temperature sensor  18  before water is supplied into the outer tub  2  (S 2001 ). 
     The control unit  14  compares the temperature T sensed in step S 2001  with a reference temperature T 1  (S 2002 ). The reference temperature (S 2001 ) may be set as a subzero value. 
     When it is determined that the temperature T sensed in step S 2001  is lower than the reference temperature T 1 , that is, when the temperature of air sensed by the temperature sensor  18  is a subzero temperature, it can be considered that the washing machine is operating in a condition with a possibility of freezing, and accordingly, whether the washing machine freezes is determined the following steps S 2011  to S 2018 . 
     In contrast, when it is determined that the temperature T sensed in step S 2001  is higher than the reference temperature T, whether the water supply valve  12  or the drain pump  10  normally operates is determined in the following steps S 2021  to S 2030  and this process is discriminated from steps S 2011  to S 2018  which determine whether to freeze. 
     First, when it is determined that the sensed value T of the temperature sensor  18  is lower than a reference temperature T 1  in step S 2002 , laundry weight sensing (S 2011 ) for sensing the amount of laundry loaded in the inner tub  3  is performed, a target water level is set in accordance with the laundry weight, and water is supply (S 2012 ). 
     Thereafter, the water level in the outer tub  2  is sensed by the water level sensor  20  and the control unit  14  determines whether the sensed value W of the water level sensor  20  has reached a first set-water level W 1  within a predetermined first set-time. The first set-time W 1  may be set as a value lower than the target water level set in accordance with the laundry weight in step S 2011 . 
     The first set-time may be set to be shorter than the time that the water level in the outer tub  2  takes to reach the target water level set in step S 2011 , under the condition that the water supply valve  12  normally operates. 
     When the sensed water level W does not reach the first set-water level W 1 , the control unit  14  determines that water has not been normally supplied and stops the operation of the washing machine, including stopping water supply (S 2017 ), and controls the display unit  22  to display a fifth error message (S 2018 ). The fifth error message is for saying that the washing machine is not being able to operate due to freezing. 
     Meanwhile, washing S 2014  is performed, when it is determined that the sensed water level W has reached the first set-water level W 1  within the first set-time in step S 2013 . The washing S 2014  is a process of removing pollutants on the cloth by rotating the pulsator  4  or the inner tub  3 , in which the rotational pattern of the pulsator  4  or the inner tub  3  can be set in various ways. 
     Draining S 2015 , a process of discharging the wash water in the outer tub  2  to the outside after the washing (S 2014 ) is completed, is performed by the drain pump  10 . The control unit  14  operates the drain pump  10  in the draining S 2015 . 
     The water level in the outer tub  2  is sensed by the water level sensor  20  in the draining S 2015  and the control unit  24  determines whether the water level in the outer tub  2  has decreased to a second set-water level W 2  or less after the draining S 2015  (S 2016 ). 
     When it is determined that the sensed value W of the water level sensor  20  is higher than the second set-water level W 2  in step S 2016 , it means that draining has not been normally performed by the drain pump  10 , and it can be considered that there is large possibility the reason is freezing of the drain pump  10 , so that the control unit  14  stops the operation of the washing machine, including stopping draining (S 2017 ), and controls the display unit  22  to display the fifth error message (S 2018 ). 
     When it is determined that the sensed value W of the water level sensor  20  is lower than the second set-water level W 2  in step S 2016 , rinsing S 2003  that rinses out cloth by supplying again water into the outer tub  2  and spinning S 2004  that spins cloth dry by rotating the inner tub  3  at a high speed can be sequentially performed. 
     On the other hand, when it is determined that the sensed value T of the temperature sensor  18  is higher than the reference temperature T 1 , steps S 2021  to S 2030  can be performed. Steps S 2021  to S 2026  can be substantially considered as the same processes as steps S 2011  to S 2016 , but when the sensed value W of the water level sensor  20  is lower than the first set-water level W 1  in step S 2023 , the control unit  14  determines that water has not been normally supplied, stops the operation of the washing machine, including stopping water supply (S 2027 ), and controls the display unit  22  to display a sixth error message (S 2028 ). The sixth error message says that the water supply valve  12  is not being able to normally operate. 
     Further, when it is determined that the sensed value W of the water level sensor  20  is higher than the second set-water level W 2  in step S 2026 , it means that draining has not been normally performed, so that the control unit  14  stops the operation of the washing machine, including stopping water supply (S 2029 ), and controls the display  22  to display a seventh error message (S 2030 ). The seventh error message says that the drain pump  10  is not being able to normally operate. 
     Displaying error messages through the display unit  22  in steps S 2018 , S 2028 , and S 2030 , respectively, was described above as the method of outputting the fifth error message, the sixth error message, or the seventh error message and this is common visual display, but unlikely, the messages may be outputted by a sounding unit such as a buzzer or a speaker. 
       FIG. 21  is a flowchart illustrating a method of controlling a washing machine according to a sixteenth embodiment of the present invention. 
     A power supply unit  19  that will be described below is a device that applies or cuts power to supply to a washing machine. 
     Referring to  FIG. 21 , when a user loads cloth and turns on the power of the washing machine  100 , power is applied to the washing machine  100  from the power supply unit  19 . 
     The user can input control commands, such as a wash course, a wash time, the number of times of rinsing, intensity of spinning, and preset register, through an input unit  15 . Further, the user can make the washing machine  100  sense the laundry weight and determine an appropriate type of washing. 
     When the type of washing is determined, as described above, the washing machine  100  sequentially performs washing that removes the dirt on cloth, rinsing that rinses out the cloth, and spinning that spins the cloth dry (S 2101 , S 2102 , and S 2103 ). 
     When the spinning is completed, the washing machine  100  can stop all of operations and standby to wait for the water remaining on the wall of the outer tub  2  or the inner tub  3  to flowing down. 
     The standby process may be performed only when the user specifically inputs a standby command through the input unit  15 , or may be set to be always performed without input from the user. 
     The present embodiment is described under the assumption that a specific button for inputting a standby command is provided to the input unit  15  and the washing machine always performs the standby process if the button is pressed. For example, when the button is pressed once, the control unit  14  determines that a standby command has been inputted while the washing machine  100  is operating, and when the button is undone, the control unit  14  can determine that there is no standby command. 
     Therefore, the control unit  14  determines whether a standby command has been inputted through the input unit  14 , when the spinning is completed. The spinning includes intermittent spinning and main spinning and the control unit  14  determines whether a standby command has been inputted, after the main spinning is finished (S 2104 ). 
     When it is determined that a standby command has been inputted, the control unit  14  stops the operations of all the parts, including the water supply valve  6 , the drain pump  10 , and the driving unit  13  (S 2105 ). 
     When water remains on the wall of the outer tub  2  or the inner tub  3 , the remaining tub may freeze. Therefore, the washing machine stops all the operations and stands by until the water remaining on the wall of the outer tub  2  or the inner tub  3  completely flows down. 
     The standby may keep for a predetermined set-time and the control unit  14  determines whether the set-time passes during the standby (S 2106 ). The set-time is the time for the water remaining on the wall of the outer tub  2  or the inner tub  3  to completely flows down and is determined in advance by an experiment and stored. 
     The water flowing down for the set-time collects in the drain channel  9  or the drain pump  10 . 
     When the set-time has passed, it is possible to completely discharge the remaining water by driving the drain pump  10 . 
     The water level sensor  20  senses the water level in the outer tub during the draining. The water level sensor  20  senses the water level and transmits a signal showing the water level to the control unit  14 . 
     The control unit compares the water level sensed by the water level sensor  20  with a predetermined fully-drained water level (S 2108 ). 
     When the water level sensed by the water level sensor  20  reaches the fully-drained water level, the control unit  14  stops draining after a set-time (S 2109 ). The set-time may be set to a time for which a small amount of water can be discharged and may include zero, because a small amount of water may remain in the drain pump  10  even after the sensed water level reaches the fully-drained water level. 
     When draining is stopped, as described above, it is determined that the remaining water in the washing machine  100  has been completely discharged and the power is cut and turned off by controlling the power supply unit  19 . 
     As described above, it is possible to effectively remove the remaining water in the washing machine  100  and prevent the remaining water from freezing, by ensuring a standby time for which the remaining water in the inner tub  3  and the outer tub  2  can flow down before the power is turned off, after all of washing, rinsing, and spinning is finished. 
       FIG. 22  is a flowchart illustrating a method of controlling a washing machine according to a seventh embodiment of the present invention. 
     Referring to  FIG. 22 , the control unit  14  performs washing, rinsing, and spinning in accordance with a wash course that is set in advance (S 2201 , S 2202 , and S 2203 ). 
     When the spinning is finished, the washing machine performs cloth-unraveling for smoothly unraveling the raveled or gathered cloths (S 2204 ). 
     When the cloth-unraveling is finished, the control unit  14  determines whether a standby command for removing the remaining water has been inputted from the user (S 2205 ). 
     When it is determined that a standby command has been inputted, the control unit  14  stops the operations of all the parts, including the water supply valve  6 , the drain pump  10 , and the driving unit  13  (S 2206 ). 
     The control unit  14  determines whether the set-time passes while all the parts are stopped (S 2207 ). 
     When it is determined that the set-time has passed, the control unit  14  discharges all the remaining water that has flowed down, by operating the drain pump  10  (S 2208 ). 
     While the remaining water is discharged, the water level sensor  20  senses the water level and the control unit  14  determines whether the sensed water level has reached a predetermined fully-drained water level (S 2209 ). 
     When it is determined that the sensed water level has reached the fully-drained water level, the operation of the drain pump  10  is stopped (S 2210 ). 
     When draining is stopped, as described above, the control unit  14  determines that the remaining water in the washing machine  100  has been completely discharged and cuts and turns off the power by controlling the power supply unit  19 . 
     As described above, a washing machine that sequentially performs washing, rinsing, spinning, and cloth-unraveling can perform a standby step for removing remaining water after the cloth-unraveling. That is, it is the most effective to perform the standby step right before the power is turned off after all the operations for wash are finished. 
     As described above, although the embodiments of the present invention were described as being limited to performing a standby process when a standby command is inputted by a user, the present invention is not limited thereto, and the standby process may always be performed regardless of the number of times of operation of the washing machine until a user undoes the button after inputting the standby command once, and the standby process may always be performed too right before the power is turned off without specific information from the user, for a washing machine that is used under an environment with an extremely low temperature. 
     It should be understood that the sixteenth and seventeenth embodiments of the present invention, which were described above with reference to  FIGS. 21 to 22 , can be used to remove remaining water before the power of the washing machine is turned off in the other embodiments described herein. Obviously, the power of the washing machine can be turned off after any one of washing, rinsing, and spinning is completed. 
       FIG. 23  is a graph showing an output voltage change (a) when a water supply valve is unfrozen and an output voltage change (b) when a drain valve is unfrozen. 
     A washing machine according to an embodiment of the present invention can determine whether various electric components of the washing machine freeze, by sensing a change in output voltage that is outputted from the electric components, when power is supplied to the electric components. 
     A voltage sensing unit  18  (see  FIG. 2 ) senses output voltages that is outputted from various electric components of a washing machine, when power is supplied to the electric components. Hereafter, the voltage sensing unit  17  may be provided to sense the output voltage of the water supply valve  6 , sense the output voltage of the drain valve  8 , or sense the output voltage of the drain pump  10 . 
     In more detail, when the voltage sensing unit  17  is provided to sense the output voltage of the water supply valve  6 , whether the water supply valve  6  freezes can be determined in accordance with the amount of change in output voltage of the water supply valve  6 . 
     When the voltage sensing unit  17  is provided to sense the output voltage of the drain valve  8 , whether the drain valve  8  freezes can be determined in accordance with the amount of change in output voltage of the drain valve  8 . 
     When the voltage sensing unit  17  is provided to sense the output voltage of the drain pump  10 , whether the drain pump  10  freezes can be determined in accordance with the amount of change in output voltage of the drain pump  10 . 
     Meanwhile, the control unit  14  electrically communicates with the water supply valve  6 , the drain valve  8 , and the drain pump  10  and may sense whether to freeze through a change in output signal that is supplied to the control unit  14  from the water supply valve  6 , the drain valve  8 , and the drain pump  10 . 
     Further, the washing machine according to an embodiment of the present invention may determine whether to freeze through the amount of change in output voltage too, which is outputted from electric components, in accordance with the circuit configuration that applies power to the electric components such as the water supply valve  6 , the drain valve  8 , and the drain pump  10 . 
     Therefore, although sensing whether to freeze in accordance with the amount of change in output voltage of the water supply valve  6 , the drain valve  8 , or the drain pump  10  is described below, it should be understood that the present invention may sense the amount of change in output voltage of electric components such as the water supply valve  6 , the drain valve  8 , and the drain pump  10  and determine whether to freeze on the basis of the amount of change. 
     Further, the heater  28  may be disposed in the outer tub  2  to heat wash water. Alternatively, the heater  28  may be disposed in the water supply valve  6 , the drain valve  8 , or the drain pump  10 . Further, the water supply valve  6  or the drain valve  8  may be implemented by a solenoid valve. 
       FIG. 23  shows an output voltage (a) of the water supply valve  6  and an output voltage (b) of the drain pump  10  that have been measured by discharging water by operating the drain pump  10  after supplying water by opening the water supply valve  6 , by leaving a washing machine for a long time to freeze in a chamber set at a subzero temperature with the water supply valve  6  closed and the drain pump  10  stopping operation, and then by increasing the internal temperature of the chamber and applying a predetermined voltage to the water supply valve  6  and the drain pump  10 . 
     As shown in  FIG. 23(   a ), the water supply valve  6  rapidly drops in output voltage around T 1  and this is because the wash water remaining in the water supply valve  6  is unfrozen around T 1 . That is, the water supply valve  6  unfreezes around T 1 . Vvalve is an output voltage value with the water supply valve  6  frozen, Vvalve_ref is an output voltage valve with the water supply valve  6  completely unfrozen, and ΔVvalve is the difference between Vvalve and Vvalve_ref. 
     Similarly, as shown in  FIG. 23(   b ), the drain pump  10  rapidly drops in output voltage around T 2  and this is because the wash water remaining in drain pump  10  is unfrozen around T 2 . That is, the drain pump  10  unfreezes around T 2 . Vpump is an output voltage value with the drain pump  10  frozen, Vpump_ref is an output voltage valve with the drain pump  10  completely unfrozen, and ΔVpump is the difference between Vpump and Vpump_ref. 
     The reason that the unfreezing time T 2  of the drain pump  10  is longer than the unfreezing time T 1  of the water supply valve  6  is because the amount of wash water remaining in the drain pump  10  is relatively larger than that of the water supply valve  6 . 
     It can be seen from  FIG. 23  the amounts of change ΔVvalve and ΔVpump in output voltage when the water supply valve  6  and the drain pump  10 , which has frozen, unfreeze, but on the contrary, it can be expected that the amounts of change in output voltage which correspond to ΔVvalve and ΔVpump, respectively, will be sensed when the water supply valve  6  and the drain pump  10  freeze too. 
     Further, although a change in output voltage of the drain valve  8  is not shown in  FIG. 23 , the drain valve  8  may also show a similar type of change in output voltage, as shown in  FIG. 23(   a ). 
     According to the present invention, the amount of change in output voltage of various electric components of the washing machine, such as the water supply valve  6 , the drain valve  8 , and/or the drain pump  10 , is sensed, when predetermined power is applied to the electric components, and unfreezing is performed, when it is sensed that the output voltage has reduced by a predetermined value or more. 
       FIG. 24  is a flowchart illustrating a method of controlling a washing machine according to an eighteenth embodiment of the present invention. The method is described in more detail with reference to  FIG. 24 . 
     According to the present embodiment, whether a washing machine freezes is sensed and anti-freezing for preventing the washing machine from freezing is performed by performing unfreezing, when freezing is sensed. 
     The anti-freezing can be implemented in the following two ways. 
     First, anti-freezing automatically starts, when the washing machine is in the standby status without washing, rinsing, or spinning. It offers the advantage that it is not necessary to take a specific measure for preventing freeze of the washing machine. 
     Second, as shown in  FIG. 2 , as the anti-freezing selection unit  16  that allows selection of anti-freezing in the washing machine, anti-freezing is performed, only when there is a selection through the anti-freezing selection unit  16  by a user. 
     The flowchart shown in  FIG. 24  can be applied in the same way to any one of the water supply valve  6 , the drain valve  8 , and the drain pump  10 , and hereafter, the water supply valve  6  is described as an example to avoid repeat of description. 
     Referring to  FIG. 24 , the method of controlling a washing machine according to the present embodiment supplies predetermined power to the water supply valve  6  and senses an output voltage (S 2401 ). The output voltage V of the water supply valve  6  can be sensed by a voltage sensing unit  17 . 
     When it is sensed that the output voltage V of the water supply valve  6  has reduced by a predetermined value ΔV or more, freezing notice that says that the washing machine has frozen is displayed through the display unit  22  (S 2402  and S 2403 ). The display unit  22  may visually display the freezing notice or may aurally express it. An example of the display unit  22  in the former case may be an LCD, an LED, or a diode, and an example of the display unit  22  in the later case may be a buzzer or a speaker. 
     Meanwhile, when the amount of change in output voltage V is lower than the predetermined value ΔV in step S 2402 , the process returns to step Si and the output voltage V is sensed again. 
     Meanwhile, unfreezing S 2404  is performed, after the freezing notice is displayed in step S 2403 . The unfreezing S 2404  is a process of heating the water supply valve  6  by operating the heater  28  or may use the heat itself that is generated by the operation of the water supply valve  22 . The heater  28  may repeat operating and suspending with a predetermined period. 
     The heater  28 , as described above, may be provided to heat wash water (in which the heater  28  is preferably disposed in the outer tub  2 ), or may be disposed in the water supply valve  6  or in the drain valve  8  or the drain pump  10 . 
     It is preferable to dispose the heater  28  in the water supply valve  6  in order to directly heat the water supply valve  6 . 
     Meanwhile, as described above, the present embodiment can be applied to prevent the drain pump  8  or the drain pump  10  from freezing, in which it is preferable to dispose the heater  28  in the drain valve  8  in order to unfreeze the drain valve  8  and it is preferable to dispose the heater  28  in the drain pump  10  in order to unfreeze the drain pump  10 . 
     After step S 2402 , the output voltage of the water supply valve  6  is sensed again (S 2405 ), and when it is sensed that the amount of increase in output voltage V is a predetermined amount ΔV or more, the operation of the heater  28  is stopped and the freezing notice is removed (S 2406  and S 2407 ). The output voltage V of the water supply valve  6  can be sensed by a voltage sensing unit  17  in step S 2405 . 
     By contrast, when the amount of increase in output voltage V is within the predetermined value ΔV in step S 2406 , the process returns to step S 2405  and the output voltage V is sensed again. 
       FIG. 25  is a block diagram illustrating the flow of control in a system for controlling freezes for a washing machine according to an embodiment of the present invention. 
     Referring to  FIG. 25 , a system for controlling freezes for a washing machine according to an embodiment of the present invention includes a washing machine  100  that can perform wire/wireless communication, a remote controller  200  that can transmit/receive signals to/from the washing machine  100  at a short distance or a long distance, and a communication medium that transmits signals between the washing machine  100  and the remote controller  200 . 
     The washing machine can basically perform operations for washing cloth, and additionally, it can sense freezing of wash water therein and perform an operation for preventing freezing. 
     The washing machine  100  includes a freezing-sensing unit  110  that senses whether wash water freezes and a control unit  14  that transmits signals sensed in the freezing-sensing unit  110  to the remote controller  200 . 
     Further, the washing machine  100  may further include an anti-freezing unit  120  that prevents wash water from freezing and the control unit  14  may control the operation of the anti-freezing unit  120  in response to an anti-freezing signal received by the washing machine from the remote controller  200 . 
     The washing machine  100  may be equipped with any one of the freezing-sensing unit  110  and the anti-freezing unit  120  or may be equipped with both. In the following description of the present embodiment, the washing machine  100  is limited to having both of the freezing-sensing unit  110  and the anti-freezing unit  120 . 
     The freezing-sensing unit  110  measures the internal temperature of the washing machine or checks the degree of water supplied/discharged, and transmits the information to the control unit  14 , so the control unit  14  can sense freezing. 
     The freezing-sensing unit  110  may include a temperature sensor  18  that measures the temperature of air or the temperature of wash water in the washing machine  100  and a water level sensor  20  that senses the water level in the washing machine  100 . 
     The washing machine  100  may include an outer tub  2  to load cloth in and the temperature sensor  18  may be disposed in the outer tub  2 . When the outer tub  2  is filled with wash water at a set-water level or more and the temperature sensor  18  is submerged by the wash water, the temperature sensor  20  can sense the temperature of the wash water, and in other cases, it can sense the temperature of the air in the washing machine  100 . 
     Further, the washing machine  100  further includes an input unit that receives various commands about the whole operation of the washing machine  100  from a user. The input unit  15  may also be configured to allow a user to directly input a request command for sensing freezing or preventing freezing. 
     The anti-freezing unit  120  can prevent wash water from freezing by heating the air or wash water in the washing machine, using a heater  28  or other electric components. The heater  28  may be disposed on the bottom of the outer tub  2  and heat the wash water, or may be disposed in various parts of the washing machine  100  and heat them to prevent them from freezing. 
     Further, the washing machine  100  may have a built-in server (not shown) that transmits/receives control information through a telephone line or the internet line. 
     The remote controller  200  may include a mobile phone, a computer, and a telephone. The remote controller  200  may receive and display whether wash water freezes, which is sensed by the washing machine  100 , or transmits an anti-freezing signal to the washing machine  100 . 
     The remote controller  200  may include an input unit  210  through which a request command of a user about sensing whether wash water freezes is inputted, a display unit  200  that visually or aurally expresses whether wash water freezes, and a MICOM  230  that transmits the command inputted to the input unit as a signal to a communication network  150 , which is described below, or displays a signal received from the communication network  150  on the display unit  220 . 
     The communication medium means the communication network  150  that performs data communication between the washing machine  100  and the remote controller  200 . The communication network  150  may be a power line communication medium or a wireless frequency communication medium. The communication network  150  allows appropriate transmission/reception of information even though the washing machine  100  and the remote controller  200  are at a long distance, as well as a short distance. 
       FIG. 26  is a flowchart illustrating a first embodiment of a system for controlling freezes for a washing machine. 
     Referring to  FIG. 26 , a user may want to sense whether machine  100  in the house freezes, when being outside or traveling. In this case, the user can input a freezing-sensing command through the input unit  210  of the remote controller  200  carried (S 2601 ). 
     When a freezing-sensing command is inputted to the input unit  210 , the MICOM of the remote controller  200  converts the command into a signal and transmits the signal to the communication network  150 . The communication network  150  transmits a freezing-sensing signal to the washing machine  100  (S 2602 ). 
     The control unit  14  of the washing machine  100  can determine whether wash water in the washing machine freezes, using the freezing-sensing unit  110  (S 2603 ). The method of sensing whether wash water freezes can be implemented in various ways. 
     For example, by using the temperature sensor, it is possible to determined that wash water has frozen, when temperature sensed by a temperature sensor  18  is a set-temperature or less. Alternatively, water is supplied to a set-water level through the water supply valve  6  and then the wash water is discharged by operating the drain pump  10 . A change in water level is sensed by the water level sensor  20  in draining. When draining is not sufficient even though draining is performed for a set-time, it can be possible to determine that draining has not been normally performed due to freezing in the drain assembly including the drain pump  10  (S 2603 ). 
     The control unit  14  determines whether to freeze in the washing machine  100 , using the freezing-sensing method, and transmits a corresponding freezing determination signal to the remote controller  200 , using the communication network  150  (S 2604 ). 
     The MICOM  230  of the remote controller  200  can display the freezing determination signal received through the communication network  150  through the display unit  220  (S 2605 ). 
     When the information about whether to freeze is displayed through the display unit  200 , the user can know whether the washing machine  100  in the house has frozen, even at a long distance. When it is displayed that the washing machine has frozen, the user can rapidly take measures against the freezing, so that it is possible to reduce a breakdown of parts, including the drain assembly. 
       FIG. 27  is a flowchart illustrating a second embodiment of a system for controlling freezes for a washing machine. 
     Referring to  FIG. 27 , a user may want to sense whether machine in the house freezes, when being outside or traveling. In this case, the user can input a freezing-sensing command through the input unit  210  of the remote controller  200  carried (S 2701 ). 
     When a freezing-sensing command is inputted to the input unit  210 , the MICOM of the remote controller  200  converts the command into a signal and transmits the signal to the communication network  150 . The communication network  150  transmits a freezing-sensing signal to the washing machine  100  (S 2702 ). 
     The control unit  14  of the washing machine  100  can determine whether wash water in the washing machine has frozen, using the freezing-sensing unit  110  (S 2703 ). The freezing-sensing method using the freezing-sensing unit  110  is the same as that described in the first embodiment and the description is not provided. 
     The control unit  14  determines whether to freeze in the washing machine  100  and transmits a corresponding freezing determination signal to the remote controller  200  through the communication network  150  (S 2704 ). 
     The MICOM  230  of the remote controller  200  can display the freezing determination signal received through the communication network  150  through the display unit  220  (S 2705 ). 
     When the user sees the information displayed on the display unit  220  of the remote controller  200  and wants anti-freezing to be performed, the user can input an anti-freezing signal through the input unit  210  (S 2706 ). 
     When the anti-freezing signal is inputted to the input unit  210 , the MICOM  230  transmits the anti-freezing signal to the washing machine  100  through the communication network  150  (S 2707 ). 
     The washing machine  100  receiving the anti-freezing signal can perform anti-freezing through the anti-freezing unit  120 . The operation for preventing freezing can be implemented in various ways. 
     For example, it is possible to prevent freezing by increasing the internal temperature of the washing machine  100 , by heating wash water with the heater  28  after opening the water supply valve  6  and supplying water to a set-water level. Further, it is also possible to prevent various parts of the washing machine from freezing by operating the heaters  28  in the parts. The heater  28  may be operated until the temperature sensed by the temperature sensor reaches a set-temperature, or may be operated until a set-time has passed from the start of the operation of the heater  28 . 
     When the anti-freezing is finished, the control unit can transmit an operation completion signal to the remote controller  200  through the communication network  150  (S 2709 ). 
     The remote controller  200  can display the received operation completion signal through the display unit  220  (S 2710 ). 
     The user can recognize that displayed on the display unit  220  and can go outside or travel without a concern. 
       FIG. 28  is a flowchart illustrating a third embodiment of a system for controlling freezes for a washing machine. 
     Referring to  FIG. 28 , when a user wants to given an instruction of an operation for anti-freezing, regardless of whether the washing machine has frozen, at a short distance or a long distance, the user can input an anti-freezing command through the input unit  210  of the remote controller  200  (S 2801 ). 
     When the anti-freezing command is inputted, the MICOM  230  transmits the anti-freezing signal to the washing machine  100  through the communication network  150  (S 2802 ). 
     The control unit  14  of the washing machine  100  receiving the anti-freezing signal performs anti-freezing, using the anti-freezing unit  120  (S 2803 ). 
     The details of the anti-freezing are the same as those described in the second embodiment and the description is not provided. 
     When anti-freezing is completed, the control unit  14  transmits an operation completion signal to the remote controller  200  (S 2804 ). 
     The remote controller  200  can display the received operation completion signal through the display unit  220  (S 2805 ).