Patent Publication Number: US-8522380-B2

Title: Control method of washing machine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part of prior U.S. application Ser. No. 11/785,889, filed on Apr. 20, 2007, now pending, to which the benefit is claimed under 35 U.S.C. §120. This application also claims the benefit of Korean Patent Application No. 2006-0054933, filed on Jun. 19, 2006, and Korean Patent Application No. 2006-0084407, filed on Sep. 1, 2006, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     Embodiments of the present invention relate to a control method of a washing machine that performs washing using bubbles. 
     2. Description of the Related Art 
     Generally, a washing machine (normally, a drum washing machine) is an apparatus, including a water tub to receive water (wash water or rinse water), a cylindrical drum rotatably installed in the water tub to receive laundry, and a motor to generate a drive force to rotate the drum, to lift the laundry in the drum along the inner wall of the drum and drop the lifted laundry, during the rotation of the drum, thereby washing the laundry. 
     The washing machine performs washing through a series of operations, e.g., a washing operation to separate contaminants from laundry with water containing detergent (specifically, wash water), a rinsing operation to rinse out bubbles or residual detergent from the laundry with water containing no detergent (specifically, rinse water), and a spin-drying operation to spin-dry the laundry at high velocity. In the washing operation, when a user selects a washing course, the washing machine detects the weight (load) of the laundry to decide the amount of wash water, supplies detergent and water sufficient to wet the laundry into the water tub according to the decided amount of wash water, and performs a washing operation by transmitting detergent water (water+detergent) to the laundry and dropping the laundry through the rotation of the drum. 
     During the washing operation, however, a large amount of water is used to sufficiently wet the laundry. Also, a large amount of detergent is used to perform high-concentration washing. For laundry requiring delicate washing, such as wool or silk, the laundry may be damaged due to dropping of the laundry and friction between the laundry and water and between laundry articles by the rotation of the drum. 
     SUMMARY 
     Therefore, it is an aspect of the present invention to provide a control method of a washing machine that generates a large number of bubbles using a small amount of water to reduce water consumption and improves washing efficiency through washing using high-concentration detergent on the surfaces of the bubbles. 
     Additional aspects of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     In accordance with one aspect of the present invention, a control method of a washing machine includes supplying water and detergent into a water tub to form detergent water, generating air bubbles using the detergent water, injecting the air bubbles into the detergent water to generate bubbles, and washing laundry using the bubbles. 
     A level of the detergent water supplied into the water tub may be lower than the bottom of a drum. 
     The control method may further include detecting a level of the detergent water initially supplied into the water tub, and a supply of the detergent water may be stopped when the level of the detergent water reaches a predetermined bubble generation level. 
     The bubble generation level may be a level to generate bubbles while not wetting at least some of the laundry. 
     The bubble generation level may be a level about 5 cm or less higher than a bottom of the drum in which the laundry is placed. When the generation of the bubbles is stabilized, the level of the detergent water may be lowered to below the bottom of the drum. 
     The generating the air bubbles may include injecting the air bubbles into a space between the water tub and the drum through a circulation channel to circulate the detergent water. 
     The control method may further include dispersing the air bubbles injected into the space between the water tub and the drum into the drum through holes formed in the drum. 
     The air bubbles injected into the space between the water tub and the drum may rise to the surface of the detergent water between the water tub and the drum to form bubbles, and the bubbles may be dispersed into the drum through holes formed in the drum while moving up to an upper part of the space between the water tub and the drum. 
     The generating the bubbles may include generating bubbles at a surface of the detergent water through combination between the air bubbles dispersed into the drum and the detergent. 
     The generating the bubbles may include generating the bubbles to raise a level defined by the bubbles such that the level defined by the bubbles is higher than that of the detergent water initially supplied into the water tub. 
     The control method may further include counting bubble generation time, and generation of the bubbles may be stopped when a predetermined time has elapsed as a result of counting the bubble generation time. 
     The control method may further include detecting the level defined by the bubbles, and generation of the bubbles may be stopped when the level defined by the bubbles reaches a predetermined bubble detection level. 
     The bubble detection level may be a level to sufficiently wet the laundry. 
     The control method may further include rotating the drum when the level defined by the bubbles reaches the bubble detection level. 
     The control method may further include stopping the generation of the bubbles during the rotation of the drum. 
     The control method may further include continuing the generation of the bubbles during the rotation of the drum. 
     In accordance with another aspect of the present invention, a control method of a washing machine includes supplying water and detergent into a water tub to form detergent water, generating air bubbles in the water tub using the detergent water, allowing the air bubbles to pass through a plurality of holes formed in the drum, combining the air bubbles with the detergent to form bubbles, stacking the bubbles on a surface of the detergent water, and allowing the bubbles to be absorbed into laundry. 
     The control method may further include driving a bubble generating device to generate the bubbles, and the bubble generating device may circulate the detergent water in the water tub to generate the bubbles. 
     The control method may further include forming the bubbles in a space between the water tub and the drum, and the bubbles formed in the space between the water tub and the drum may be introduced into the drum through the holes of the drum. 
     The control method may further include introducing the bubbles formed in the space between the water tub and the drum into the drum through rear holes formed in a rear of the drum, and the bubbles may be introduced into the drum from a bottom, a side, and the rear of the drum. 
     In accordance with another aspect of the present invention, a method of a washing machine includes supplying water and detergent into a water tub to form detergent water, mixing air bubbles in detergent water being circulated via a pump, injecting the air bubbles mixed detergent water into the water tub via the pump to generate bubbles, and washing laundry using the bubbles. 
     In accordance with another aspect of the present invention, a method of a washing machine includes supplying water and detergent into a water tub to form detergent water, circulating detergent water in the water tub via a pump, introducing air using pressure differential generated via the circulating detergent water, mixing the introduced air with detergent water being circulated via the pump, injecting the air bubbles mixed detergent water into the water tub via the pump to generate bubbles, and washing laundry using the bubbles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a sectional view illustrating the structure of a washing machine according to an embodiment of the present invention; 
         FIG. 2  is a control block diagram of the washing machine of  FIG. 1 ; 
         FIG. 3  is a flow chart illustrating an overall bubble washing control process of the washing machine of  FIG. 1 ; 
         FIG. 4  is a flow chart illustrating a control process of a washing operation using bubbles in the washing machine of  FIG. 1 ; 
         FIG. 5  is a flow chart illustrating a first operation to remove bubbles after bubble washing in the washing machine of  FIG. 1 ; 
         FIG. 6  is a flow chart illustrating a second operation to remove bubbles after bubble washing in the washing machine of  FIG. 1 ; 
         FIG. 7  is a flow chart illustrating a third operation to remove bubbles after bubble washing in the washing machine of  FIG. 1 ; 
         FIG. 8  is a sectional view illustrating the structure of a washing machine according to another embodiment of the present invention; 
         FIGS. 9 to 13  are views illustrating a bubble generation process in the washing machine of  FIG. 8 ; 
         FIG. 14  is a view illustrating the shape of a bubble generated through the bubble generation process of  FIGS. 9 to 13 ; 
         FIG. 15  is a control block diagram of the washing machine of  FIG. 8 ; 
         FIG. 16  is a flow chart illustrating a bubble washing control process of the washing machine of  FIG. 8 ; 
         FIG. 17  is a graph illustrating a shrinkage rate of laundry when washing the laundry in such a way as to reduce an amount of water and using bubbles at the same concentration in the same washing operation; and 
         FIG. 18  is a graph illustrating a cleaning degree of artificially contaminated laundry of 60 MU (Make Up), comparing a case of using detergent water with a case of using bubbles at the same detergent concentration. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. 
       FIG. 1  is a sectional view illustrating the structure of a washing machine according to an embodiment of the present invention. 
     In  FIG. 1 , the washing machine includes a drum-type water tub  11  mounted in a machine body  10  to receive water (wash water or rinse water) and a cylindrical drum  12  rotatably mounted in the water tub  11 . The drum  12  has a plurality of holes  12 ′. 
     The water tub  11  is provided with a motor  13  positioned therebelow to rotate the drum  12  in the clockwise or counterclockwise direction to perform washing, rinsing and spin-drying operations, a washing heater  16  positioned at a lower portion of the water tub  11  to heat water (specifically, detergent water) supplied into the water tub  11 , and a level detection unit  17  to detect an amount (level) of the water (specifically, detergent water) supplied into the water tub  11 . 
     The level detection unit  17  includes a first level sensor  17 - 1  to detect the maximum level (hereinafter, a first level) to prevent the detergent water from flowing into the drum  12 , in which laundry is placed, to perform washing with bubbles and a second level sensor  17 - 2  to detect the minimum level (hereinafter, a second level) necessary to generate bubbles. Through detection of the level detection unit  17 , supply of liquid detergent concentrate and water is controlled to be stopped to prevent the detergent water from flowing into the drum  12  when the detergent water reaches the first level upon washing or to be performed to resupply detergent water necessary to generate bubbles when the detergent water is gradually lowered to the second level due to the generation of bubbles. 
     The level detection unit  17  allows the detergent water to be maintained at a bubble generation level which permits generation of bubbles while preventing the detergent water from contacting the laundry through continuous detection of the level in addition to the detection of the first and second levels. In addition, with help of the level detection unit  17 , liquid detergent concentrate and water are supplied at amounts necessary to generate bubbles having a predetermined detergent concentration by measuring a reduced level through flow or time control during bubble washing. 
     The machine body  10  has an opening  14  in front of the water tub  11  and the drum  12  such that laundry may be removed from the front of the machine body  10  and a door  15  to open or close the opening  14 . 
     The washing machine further includes a detergent supply device  19  positioned above the water tub  11  to supply detergent, a detergent dissolving device  30  to generate and store a predetermined amount of liquid detergent concentrate used to generate bubbles having a predetermined detergent concentration, and a water supply device  20  to supply water into the detergent supply device  19  and the detergent dissolving device  30 . 
     The detergent supply device  19  has a plurality of partitioned spaces. The detergent supply device  19  is mounted at the front side of the machine body  10  such that a user may easily place detergent and rinse in the respective partitioned spaces. 
     The water supply device  20  includes a water supply pipe  22  to supply water and a water supply valve  24  positioned on the water supply pipe  22  to control supply of water through the water supply pipe  22 . The water supply pipe  22  is connected to the detergent supply device  19  such that water is supplied from an outside to the detergent supply device  19 . The detergent dissolving device  30  is connected between the detergent supply device  19  and the water tub  11  such that water passes through the detergent supply device  19  and is then supplied along with detergent into the detergent dissolving device  30  to generate liquid detergent concentrate (in a state wherein the detergent is concentrated in the water) to generate bubbles having a predetermined detergent concentration. A separate connection pipe  25  is connected between the detergent dissolving device  30  and the water tub  11 , and has a water supply nozzle  26  positioned at an exit of the connection pipe  25  to allow the liquid detergent concentrate to be supplied from the detergent dissolving device  30  to the water tub  11 . This is for the purpose of allowing the liquid detergent concentrate in the detergent dissolving device  30  to be supplied together with the water into the water tub  11  and form detergent water used to generate bubbles having a predetermined concentration between the water tub  11  and the drum  12 . 
     The detergent dissolving device  30  is connected to the detergent supply device  19  to form a predetermined amount of liquid detergent concentrate necessary to generate bubbles and to supply the predetermined amount of liquid detergent concentrate between the water tub  11  and the drum  12 , such that the liquid detergent concentrate (water with the liquid detergent concentrate dissolved at a high concentration therein) is supplied together with the water to prevent the concentration of the bubbles from varying from an initial concentration of the bubbles when water is additionally supplied through the water supply device  20  due to lack of the detergent water (water with the liquid detergent concentrate dissolved therein) resulting from generation of the bubbles. To this end, the detergent dissolving device  30  includes an assistant water supply pipe  31  connected to one side of the water supply pipe  22  connected to the detergent dissolving device  30  to allow water to be additionally supplied to the water tub  11  without passing through the detergent supply device  19 , an assistant water supply valve  32  mounted at the assistant water supply pipe  31  to control additional supply of water to the water tub  11 , and a detergent liquid input valve  33  to control liquid detergent concentrate of a high concentration in the detergent dissolving device  30  to be supplied by an amount necessary to generate bubbles having a predetermined concentration. 
     The assistant water supply valve  32  is a three-way valve to control the direction of water such that the water is supplied to the detergent supply device  19  or the assistant water supply pipe  31  through the water supply pipe  22 . The assistant water supply valve  32  adjusts the supplying direction of water in such a way that, after a small amount of water (that is, an amount of water sufficient to form the liquid detergent concentrate of the high concentration by dissolving the detergent of the detergent supply device  19 ) is supplied once into the detergent supply device  19  at an initial water supply stage, the water is directly supplied into the water tub  11  through the assistant water supply pipe  31  along with the liquid detergent concentrate formed in the detergent dissolving device  30 , to form the liquid detergent concentrate in the detergent dissolving device  30  by dissolving the detergent of the detergent supply device  19 . 
     The washing machine further includes a drying device  40  to dry laundry (clothes). The drying device  40  includes a drying fan  41  on the water tub  11 , a drying duct  42  connected between an outlet  48  of the drying fan  41  and an air induction port  45  formed on the opening  14  of the water tub  11 , and a condensing duct  43  mounted on the rear side of the water tub  11  and connected between an air discharge port  46  formed at a lower portion of the rear side of the water tub  11  and an inlet  47  of the drying fan  41 . 
     The drying device  40  includes a drying heater  44  positioned inside the drying duct  42  to supply hot air into the water tub  11  and a condensing device positioned on the condensing duct  43  to allow vapor generated when drying clothes to be condensed and removed while the vapor passes through the condensing duct  43 . 
     The condensing device includes a cold water injection nozzle  53  positioned at an upper portion inside the condensing duct  43  to inject cooling water into the condensing duct  43 , a cooling water supply pipe  54  connected to the water supply device  20  to supply cooling water to the cooling water injection nozzle  53 , and a cooling water valve  55  mounted on the cooling water supply pipe  54 . With this structure, the condensing device may enable an improvement in dehumidification effect to increase a contact area between humid air rising from a lower portion of the condensing duct  43  and the cooling water by allowing the cooling water from the cold water injection nozzle  53  positioned at the upper portion to flow to the lower portion of the condensing duct  43  along an inner surface of the condensing duct  43 . 
     The washing machine further includes a drainage device  50  to drain water from the water tub  11  to the outside. The drainage device  50  includes a drainage pipe  51  connected to a lower surface of the water tub  11  to guide the water from the tub  11  to the outside and a drainage pump  52  provided to the drainage pipe  51 . 
     The washing machine further includes an air supply device  60  to wash the laundry in the drum  12  with bubbles. The air supply device  60  includes an air motor  61  positioned below the water tub  11  to supply air, an air supply pipe  62  to transfer the air supplied from the air motor  61 , and a porous member  63  positioned at an end of the air supply pipe  62  to disperse the air. After being generated by the air motor  61 , air is dispersed through the porous member  63  via the air supply pipe  62 , and generates air bubbles in detergent water as a mixture of liquid detergent concentrate and water to form bubbles, so that the laundry may be washed with the bubbles in the drum  12 . 
     In addition, air holes  64  are formed through the water tub  11  in which the air supply device  60  is positioned, and allow air to flow from the air supply device  60  into the water tub  11  therethrough so that the air is introduced into a space between the water tub  11  and the drum  12  after being dispersed through the porous member  63 . 
       FIG. 2  is a control block diagram of the washing machine of  FIG. 1 . The washing machine further includes an input unit  100 , a temperature detection unit  110 , a dry detection unit  120 , a controller  130 , and a drive unit  140 . 
     The input unit  110  inputs operation information, such as a washing course (for example, a bubble washing course or a normal washing course), washing temperature, spin-drying RPM, and additional rinsing, which are selected by a user according to kinds of laundry to the controller  130 . In the bubble washing course, selected information such as bubble concentration is input to the controller  130 . 
     The temperature detection unit  110  serves to detect the temperature of water supplied into the water tub  11 , and the dry detection unit  120  serves to detect a dried state of laundry through detection of the temperature and humidity of the laundry. 
     The controller  130  is a microprocessor to control the washing machine according to operation information input from the input unit  100 , and stores motor RPM, motor operation rate (motor on-off time), and washing time, which are set depending on load (weight of laundry) in a selected washing course. 
     The controller  130  controls a motor  13 , the water supply device  20 , and the detergent dissolving device  30  to achieve optimum washing effect while reducing damage to the laundry by controlling supply amounts of water and liquid detergent concentrate together with generation of bubbles upon bubble washing, controlling the motor RPM and operation rate according to load, and by controlling a bubble concentration according to a contaminated degree of the laundry. 
     In addition, the controller  130  controls the motor RPM or driving of the water supply device  20  or drying device  40  to effectively remove bubbles after the bubble washing. 
     The drive unit  140  drives the motor  13 , the washing heater  16 , the water supply valves  23  and  24 , the assistant water supply valve  32 , the detergent liquid input valve  33 , the drying fan  41 , the drying heater  44 , the drainage pump  52 , and the air motor  61  in response to a drive control signal from the controller  130 . 
     Hereinafter, a control method of the washing machine of  FIG. 1  will be described. 
     The control method of the washing machine of  FIG. 1  is to allow the washing machine to proceed a normal washing course to wash general laundry and a bubble washing course to wash delicate laundry (for example, wool or silk requiring delicate washing) through bubble washing. The input unit  100  of the washing machine includes a button with which a user may select the bubble washing course. 
       FIG. 3  is a flow chart illustrating an overall bubble washing control process of the washing machine of  FIG. 1   
     With laundry put into the rotational drum  12 , operation information such as a washing course (bubble washing or normal washing), a washing temperature, a spin-drying RPM, and additional rinsing, is selected by a user according to a kind of laundry, and is input to the controller  130  through the input unit  100 . 
     The controller  130  determines whether or not the selected washing course is a bubble washing course in response to the operation information input from the input unit  100  ( 200 ), and controls the washing machine to perform the normal washing course in the same manner as a conventional washing course when it is determined that the selected washing course is not the bubble washing course ( 210 ). 
     When the selected washing course is the bubble washing course, the controller  130  detects load (weight of the laundry) in the drum  12  ( 300 ), and sets an amount of water, motor RPM and operation rate (motor on-off time), and washing time based on the detected load ( 400 ). 
     Then, the controller  130  allows the washing machine to perform a washing operation through generation of bubbles with the set motor RPM, the motor operation rate, and the washing time ( 500 ), and to perform a bubble removal operation to effectively remove the bubbles remaining in the drum  12  after the bubble washing operation ( 600 ). 
     As for the washing operation through the generation of the bubbles, the bubbles act as a cushion upon friction between laundry articles to reduce damage to the laundry due to the friction between the laundry articles and between the laundry and the water. In addition, a high detergent concentration of the bubbles may enable dirt on the laundry to be effectively removed with only a small amount of water, thereby reducing energy consumption. 
     After performing the washing operation through the generation of the bubbles and the bubble removal operation, rinsing and spin-drying operations set corresponding to the load are performed ( 700 ). 
     Next, the process ( 500 ) of performing the washing operation through the generation of bubbles will be described with reference to  FIG. 4 . 
       FIG. 4  is a flow chart illustrating a control process of a washing operation using bubbles in the washing machine of  FIG. 1 . 
     When a bubble washing course is selected, the controller  130  controls the water supply device  20  to allow a small amount of water necessary to dissolve detergent to be supplied into the detergent dissolving apparatus  30  through the detergent supply device  19  via the water supply valve  24  and the water supply pipe  22 . At this time, the detergent in the detergent supply device  19  is introduced along with the water into the detergent dissolving device  30  while being dissolved by the water so that liquid detergent concentrate (that is, water with the detergent concentrated therein) is stored in the detergent dissolving device  30  ( 502 ). 
     Then, the controller  130  controls the detergent liquid input valve  33  to allow the liquid detergent concentrate in the detergent dissolving device  30  to be supplied into the water tub  11  through the water supply nozzle  26  via the connection pipe  25  ( 504 ), and controls the assistant water supply valve  32  to allow the water to be supplied into the water tub  11  through the connection pipe  25  and the water supply nozzle  26  via the assistant water supply pipe  31  without being supplied to the detergent supply device  19  ( 506 ). 
     As such, the control is performed in such a way that, after the small amount of water (that is, an amount of water sufficient to form liquid detergent concentrate of a high concentration by dissolving the detergent of the detergent supply device) is supplied once into the detergent supply device  19  at an initial water supply stage, the water is directly supplied into the water tub  11  through the assistant water supply pipe  31  along with the liquid detergent concentrate in the detergent dissolving device  30 . 
     Although the liquid detergent concentrate and the water are illustrated as being sequentially supplied in  FIG. 4  for easy understanding, operations of supplying the liquid detergent concentrate and the water may be performed simultaneously. 
     As the liquid detergent concentrate and the water are supplied into the water tub  11 , detergent water as a mixture of the liquid detergent concentrate and the water is formed between the water tub  11  and the drum  12 . At this time, a level of detergent water is detected by the level detection unit  17 , and the controller determines whether or not the level of the detergent water is a first preset level (the maximum level of the detergent water to prevent water supplied into the tub from flowing into the drum, and corresponding to about ¼ of a level of detergent water in a normal washing operation; a level detected by the first level sensor) ( 508 ). 
     When the level of the detergent water is not the first level, liquid detergent concentrate and water are continuously supplied into the water tub  11  until the level of the detergent water reaches the first level. When the level of the detergent water is the first level, the controller  130  turns off the water supply valve  24 , the assistant water supply valve  32 , and the detergent liquid input valve  33  to stop supply of liquid detergent concentrate and water ( 510 ). 
     Subsequently, to wash the laundry using bubbles in the drum  12 , air is supplied from the air supply device  60  to the detergent water formed of the mixture of liquid detergent concentrate and water to generate bubbles ( 512 ), followed by washing ( 514 ). At this time, the air supply device  60  generates the bubbles in such a way that, after being supplied from the air motor  61 , air is dispersed through the porous member  62  via the air supply pipe  62 , and is then forced into the detergent water as the mixture of liquid detergent concentrate and water through the air holes  64 , generating the bubbles. 
     After being generated between the water tub  11  and the drum  12  via the air supply device  60 , the bubbles are introduced into the drum  12  through the holes  12 ′ or the front of the drum  12 , and are finally dispersed into the overall space of the drum  12  after a predetermined time (about three minutes), enabling the laundry to be washed only with the bubbles in the drum  12 . 
     When generating the bubbles, an RPM and operation rate of the drum  12  and washing time therein may be less than or equal to values set in each washing course corresponding to the load. 
     As such, dirt on the laundry may be effectively removed due to the high detergent concentration on the bubbles dispersed in the overall space of the drum  12 . At this time, the bubbles may act as a cushion with respect to dropping of the laundry and friction between laundry articles caused by rotation of the drum  12 , thereby preventing the laundry from being damaged due to the friction between the laundry articles. 
     Subsequently, it is determined whether or not the washing operation through the generation of the bubbles is completed ( 516 ). When the washing operation is completed, the procedure advances to Operation  600  to perform rinsing and spin-drying operations. 
     When the washing operation is not completed, the amount of detergent water is gradually reduced while the washing operation through the generation of the bubbles proceeds. At this time, the level detection unit  17  detects a level of the lowering detergent water, and determines whether or not the level of the detergent water reaches a second preset level (the minimum level of detergent water necessary to generate bubbles, corresponding to a level not less than the air supply device; a level detected by the second level sensor) ( 518 ). 
     When the level of the detergent water is not the second level, the procedure returns to Operation  512  to continue the washing operation through rotation of the drum  12  along with generation of the bubbles until the level of the detergent water reaches the second level. When the level of the detergent water is the second level, the procedure returns to Operation  504  to start supply of liquid detergent concentrate and water corresponding to a reduced amount of the detergent water. 
     Specifically, the water supply valve  24  and the assistant water valve  32  are opened with operation of the water supply device  20 , allowing water to flow through the assistant water supply pipe  31  instead of the detergent supply device  19 , and then to be additionally supplied into the water tub  11  through the water supply nozzle  26  via the connection pipe  25 . At the same time, the detergent liquid input valve  33  is opened, allowing liquid detergent concentrate of a high detergent concentration in the detergent dissolving device  30  to be also supplied into the water tub  11 . 
     That is, in the case where the amount of detergent water is reduced due to generation of the bubbles, if only water is supplied into the water tub without supplying detergent, it is difficult to generate bubbles having a predetermined detergent concentration due to a reduced detergent concentration on the bubbles. Thus, the predetermined amount of liquid detergent concentrate in the detergent dissolving device  30  is also supplied upon additional supply of the water. 
     The amount of the liquid detergent concentrate supplied from the detergent dissolving device  30  is determined so that, when 1 drop of liquid detergent concentrate having a predetermined concentration is supplied into the water tub  11 , the water is also supplied at an amount proportional to this liquid detergent concentrate. For example, assuming an amount of detergent water required by the water tub  11  is 10, the controller controls the washing machine to supply 1 drop of liquid detergent concentrate and an amount of water proportional to this liquid detergent concentrate into the tub  11 . Assuming an amount of detergent water required by the water tub  11  is 20, the controller controls the washing machine to supply 2 drops of liquid detergent concentrate and an amount of water proportional to this liquid detergent concentrate, that is, two times the above case, into the water tub  11 . 
     As such, the control method may enable the bubble washing operation to be effectively performed always using the bubbles having the predetermined detergent concentration by allowing the predetermined amount of liquid detergent concentrate to be supplied together with additional supply of water into the water tub. 
     Next, the process ( 600 ) of removing bubbles remaining in the drum  12  after bubble washing will be described with reference to  FIGS. 5 to 7 . 
       FIG. 5  is a flow chart illustrating a first operation to remove bubbles after bubble washing in the washing machine of  FIG. 1 . In the first operation, after the detergent water is drained to the outside upon completion of the bubble washing operation, a bubble removal operation is performed to remove the bubbles remaining in the drum  12  instead of directly performing a rinsing operation. 
     After draining the water upon completion of the bubble washing operation, the bubbles are removed by intermittent spin-drying during which the motor  13  is driven at a low RPM (for example, about 400 RPM) ( 602 ). 
     It is determined whether or not a preset intermittent spin-drying time (T 1 : the minimum time necessary to remove the bubbles in the drum through the intermittent spin-drying) has elapsed by counting time for which the motor  13  is driven at the low RPM ( 604 ). When it is determined the preset intermittent spin-drying time has elapsed, driving of the motor  13  is stopped ( 606 ). 
       FIG. 6  is a flow chart illustrating a second operation to remove bubbles after bubble washing in the washing machine of  FIG. 1 . In the second operation, after draining the detergent water upon completion of the bubble washing operation, the bubble removal operation is performed to remove the bubbles remaining in the drum  12  instead of directly entering the rinsing operation. 
     After draining the water or when blowing air through driving of the drying fan  41  simultaneously with water drainage, the drying heater  44  is driven to supply hot air, thereby removing the bubbles ( 612 ). 
     It is determined whether or not a preset drive time (T 2 : the minimum time necessary to remove the bubbles in the drum through air or hot air blowing) has elapsed by counting time for which the drying fan  41  or the drying heater  44  is driven ( 614 ). When it is determined the preset drive time has elapsed, the driving of the drying fan  41  or the drying heater  44  is stopped ( 616 ). 
       FIG. 7  is a flow chart illustrating a third operation to remove bubbles after bubble washing in the washing machine of  FIG. 1 . In the third operation, after draining the detergent water upon completion of the bubble washing operation, the bubble removal operation is performed to remove the bubbles remaining in the drum  12  instead of directly entering the rinsing operation. 
     While separately or simultaneously performing the driving of the motor  13  at the low RPM and the driving of the drying fan  41  or the drying heater  44 , the water supply device  20  is controlled to inject a small amount of water in the form of mist between the drum  12  and the water tub  11  through the water supply nozzle  26 , thereby removing the bubbles ( 622 ). 
     It is determined whether or not a preset injection time (T 3 : the time necessary to remove the bubbles in the drum through mist injection) has elapsed by counting water injection time ( 624 ). When it is determined the preset injection time has elapsed, the mist injection is stopped ( 626 ), thereby completing the bubble removal operation. 
       FIG. 8  is a sectional view illustrating the structure of a washing machine according to another embodiment of the present invention. 
     In  FIG. 8 , the washing machine includes a drum-type water tub  11   a  mounted in a machine body  10   a  to receive water (wash water or rinse water) and a cylindrical drum  12   a  rotatably mounted in the water tub  11   a . The drum  12   a  has a plurality of holes  13   a.    
     Outside the rear of the water tub  11   a  is mounted a drive device, such as a motor  16   a , to rotate a rotary shaft  15   a  connected to the drum  12   a  such that washing, rinsing, and spin-drying operations are performed. At the inside bottom of the water tub  11   a  are mounted a washing heater  17   a  to heat water (specifically, detergent water) present in the water tub  11   a  and a level detection unit  18   a  to detect frequency variation depending upon the level and thus the amount (level) of water in the water tub  11   a.    
     The level detection unit  18   a  controls a level (an optimum level necessary to generate bubbles, which is a level 5 cm or less higher than the bottom of the drum; hereinafter, referred to as a bubble generation level) at which detergent water does not sufficiently wet laundry placed in the drum  12   a . When detergent water supplied during bubble washing reaches the bubble generation level, the supply of water (wash water) is stopped such that the detergent water is not introduced into the drum  12   a.    
     At the front of the machine body  10   a  is mounted a door  19   a  having an inlet through which laundry is put into or removed from the drum  12   a . Above the water tub  11   a  are mounted a detergent supply device  20   a  to supply detergent and a water supply device  30   a  to supply water (wash water or rinse water). 
     The detergent supply device  20   a  has a plurality of partitioned spaces. The detergent supply device  20   a  is mounted at the front side of the machine body  10   a  such that a user may easily place detergent and rinse in the respective partitioned spaces. 
     The water supply device  30   a  includes a first water supply pipe  32   a  connected between an external water supply pipe  31   a , through which water (wash water or rinse water) is supplied into the water tub  11   a , and the detergent supply device  20   a , a second water supply pipe  33   a  connected between the detergent supply device  20   a  and the water tub  11   a , a water supply valve  34   a  mounted on the first water supply pipe  32   a  to control the supply of water, and a water supply nozzle  35   a  mounted at the outlet of the second water supply pipe  33   a . In this structure, water is supplied into the water tub  11   a  via the detergent supply device  20   a  such that detergent is supplied into the water tub  11   a  together with the water. 
     Also, a circulation device  50   a  to circulate the water in the water tub  11   a  and a drainage device  60   a  to drain the water in the water tub  11   a  are mounted at a pump case  40   a  below the water tub  11   a  in a symmetrical fashion. Between the water tub  11   a  and the pump case  40   a  is connected a connection hose  41   a  to guide the water in the water tub  11   a  to the pump case  40   a.    
     The circulation device  50   a  includes a circulation pump  51   a  to supply the water guided to the pump case  40   a  into the water tub  11   a , a circulation pipe  52   a  mounted at the outlet of the circulation pump  51   a  to circulate the water, a circulation nozzle  53   a  mounted at the outlet of the circulation pipe  52   a  to supply the water into the lower part of the water tub  11   a , an air introduction hole  54   a  formed in the circulation nozzle  53   a  to introduce air necessary to generate bubbles into the water (specifically, detergent water) to be supplied into the lower part of the water tub  11   a , and an air guide pipe  55   a  to guide air in the drum  12   a  to the air introduction hole  54   a  through an air suction hole  56   a.    
     One side of the circulation pipe  52   a  is connected to the circulation pump  51   a , and the other side of the circulation pipe  52   a  is connected to the water tub  11   a . Upon driving the circulation pump  51   a , the water in the water tub  11   a  is guided to the pump case  40   a  through the connection hose  41   a . The water guided to the pump case  40   a  is resupplied into the water tub  11   a  through the circulation pipe  52   a . In this way, water circulation is achieved. The circulation pipe  52   a  connected to the water tub  11   a  is mounted at the lowest possible position such that the circulated water is smoothly supplied to the lower part of the water tub  11   a.    
     The circulation nozzle  53   a  is formed of a venturi that lowers the pressure of the circulated water. Air introduced through the air suction hole  56   a  is naturally introduced into the circulation nozzle  53   a  through the air introduction hole  54   a  via the air guide pipe  55   a  such that the detergent in the detergent water is formed into an aggregate to generate bubbles without an additional power device to supply air. 
     The drainage device  60   a  includes a drainage pump  61   a  to drain water guided to the pump case  40   a  to the outside and a drainage pipe  62   a  mounted at the outlet of the drainage pump  61   a  to drain the water. 
     In the washing machine of  FIG. 8 , the circulation device  50   a  to circulate water in the water tub  11   a  to generate bubbles may have the same effect as the air supply device  60  of  FIG. 1 . A bubble generation process in the washing machine of  FIG. 8  will be described in more detail with reference to  FIGS. 9 to 13 . 
       FIGS. 9 to 13  are views illustrating a bubble generation process in the washing machine of  FIG. 8 . 
     In  FIG. 9 , water, supplied through the water supply vale  34   a , is introduced into the lower part of the water tub  11   a  together with detergent via the detergent supply device  20   a , with the result that detergent water (water+detergent) is supplied into a space between the water tub  11   a  and the drum  12   a . When the supplied detergent water reaches a bubble generation level (for example, a level 5 cm or less higher than the bottom of the drum), the supply of detergent water is stopped. 
     In  FIG. 10 , when the detergent water is supplied up to the bubble generation level, the circulation pump  50   a  is driven such that the detergent water discharged from the circulation pump  50   a  is introduced into the circulation nozzle  53   a  via the circulation pipe  52   a . While passing through the circulation nozzle  53   a , which is formed of a venturi that lowers the pressure of the detergent water, air in the drum  12   a  is introduced into the circulation nozzle  53   a  through the air introduction hole  54   a  by virtue of the expansion of a circulation channel. The air introduced into the circulation nozzle  53   a  is injected into a space between the water tub  11   a  and the drum  12  to generate air bubbles in the detergent water between the water tub  11   a  and the drum  12   a.    
     In  FIG. 11 , the air bubbles rise to the surface of the detergent water between the water tub  11   a  and the drum  12  to form bubbles. While moving up to the upper part of the space between the water tub  11   a  and the drum  12   a , the bubbles are introduced into the drum  12   a  through the holes  13   a  of the drum  12   a , and are dispersed in the drum  12   a  to generate bubbles as mixtures of the detergent and the air bubbles. The bubbles between the water tub  11   a  and the drum  12   a  pass through rear holes formed in the rear of the drum  12   a  or are introduced into the drum  12   a  from the bottom, the side, and the rear of the drum  12   a.    
     In  FIG. 12 , the bubbles as the mixtures of the detergent and the air bubbles are stacked from the surface of the detergent water, and start to rise in the drum  12   a . After a predetermined time (about three minutes), the bubbles are dispersed throughout the drum  12   a , with the result that a level defined by the bubbles rises. As the level defined by the bubbles rises, the bubbles surround laundry placed in the drum  12   a , and the high-concentration detergent on the surfaces of the bubbles is absorbed into the laundry. When the generation of the bubbles is stabilized, the level of the detergent water is lowered to below the bottom of the drum  12   a , i.e., a level between the water tub  11   a  and the drum  12   a.    
     In  FIG. 13 , when the detergent water reaches a level to sufficiently wet the laundry placed in the drum  12   a  (an optimum level necessary to perform bubble washing, which is a level higher than the level of the laundry; hereinafter, referred to as a bubble detection level), the drum  12   a  is rotated such that the high-concentration detergent on the surfaces of the bubbles is rapidly absorbed into the laundry, thereby achieving the bubble washing of the laundry placed in the drum  12   a.    
       FIG. 14  is a view illustrating the shape of a bubble generated through the bubble generation process of  FIGS. 9 to 13 . 
     In  FIG. 14 , a bubble is a mixture of detergent, water, and air. The bubble easily bursts and is easily absorbed. Consequently, the bubble is rapidly absorbed into the laundry to effectively remove contaminants from the laundry. 
       FIG. 15  is a control block diagram of the washing machine of  FIG. 8 . The washing machine further includes an input unit  70   a , a controller  72   a , and a drive unit  74   a.    
     The input unit  70   a  inputs operation information, such as a washing course (for example, normal washing or bubble washing), spin-drying RPM, and additional rinsing, which are selected by a user, to the controller  72   a.    
     The controller  72   a  is a microcomputer to control the overall operations of the washing machine, such as washing, rinsing, and spin-drying, based on the operation information input from the input unit  70   a . The controller  72   a  stores motor RPM, motor operation rate (motor on-off time), and washing time set according to the load (the weight of laundry) in the selected washing course. 
     For bubble washing, therefore, the controller  72   a  controls the motor RPM and the motor operation rate based on the load such that the motor  16   a  and the circulation pump  51   a  are driven to effectively perform the washing operation. 
     The drive unit  74   a  drives the motor  16   a , the washing heater  17   a , the water supply valve  34   a , the circulation pump  51   a , and the drainage pump  61   a  according to a drive control signal of the controller  72   a.    
     Hereinafter, a control method of the washing machine of  FIG. 8  will be described. 
       FIG. 16  is a flow chart illustrating a bubble washing control process of the washing machine of  FIG. 8 , which is an algorithm to effectively transmit detergent water to laundry placed in the drum  12   a  while minimizing the amount of water used through washing using bubbles. 
     When a user puts laundry into the drum  12   a  and selects operation information, such as a bubble washing course, spin-drying RPM, and additional rinsing, the operation information selected by the user is input to the controller  72   a  through the signal input unit  70   a.    
     The controller  72   a  determines whether the washing course selected by the user is a bubble washing course based on the operation information input from the input unit  70   a  ( 100   a ). When the washing course selected by the user is not the bubble washing course, a normal washing course is performed in the same manner as a conventional washing course ( 102   a ). 
     When the washing course selected by the user is the bubble washing course, the controller  72   a  detects the load (the weight of the laundry) placed in the drum  12   a  ( 104   a ), and sets motor RPM, motor operation rate, and washing time based on the detected load ( 106   a ). 
     Subsequently, the controller  72   a  controls the water supply valve  34   a  to supply detergent water necessary to generate bubbles such that water (specifically, wash water) is supplied into the water tub  11   a  through the detergent supply device  20   a  via the first water supply pipe  32   a . At this time, detergent in the detergent supply device  20   a  is dissolved in the supplied water (wash water), and is supplied into the water tub  11   a  through the water supply nozzle  35   a  via the second water supply pipe  33   a  together with the water (wash water). As a result, the detergent water (water+detergent) is supplied into the lower part of the water tub  11   a  (specifically, between the water tub and the drum) ( 108   a ). 
     At this time, the level of the supplied detergent water is detected by the level detection unit  18   a  to determine whether the level is a predetermined bubble generation level (for example, a level 5 cm or less higher than the bottom of the drum) ( 110   a ). When the level is not the bubble generation level, detergent water is continuously supplied until the level reaches the bubble generation level. When the level is the bubble generation level, the controller  72   a  controls the water supply valve  34   a  to be turned off such that the supply of water is stopped ( 112   a ). 
     When the supply of the detergent water to the bubble generation level is completed, the controller  72   a  controls the circulation pump  51   a  to generate bubbles in the detergent water supplied to the lower part of the water tub  11   a  ( 702   a ). A process of generating bubbles by the circulation pump  51  is the same as the above description with reference to  FIGS. 9 to 13 . 
     When the circulation pump  51   a  is driven, water in the water tub  11   a  is guided to the pump case  40   a  through the connection hose  41   a . The water guided to the pump case  40   a  is resupplied to the lower part of the water tub  11   a  through the circulation pipe  52   a . In this way, water circulation is achieved. When the water passes through the circulation nozzle  53   a  via the circulation pipe  52   a , the water pressure is suddenly lowered. As a result, air is naturally introduced into the circulation nozzle  53   a  through the air introduction hole  54   a  and injects air bubbles into the water (detergent water) supplied to the lower part of the water tub  11   a  to form bubbles as mixtures of detergent and air bubbles at the surface of the detergent. 
     The bubbles as the mixtures of the detergent and the air bubbles start to rise in the drum  12   a . After a predetermined time (about three minutes), the bubbles are dispersed throughout the drum  12   a  to raise the level. At this time, the level is detected by the level detection unit  18   a  to determine whether the level is a bubble detection level (for example, a level higher than the level of the laundry) ( 116   a ). When the level is not the bubble detection level, the circulation pump  51   a  is continuously driven until the level reaches the bubble detection level. 
     When the level has reached the bubble detection level due to the generation of bubbles, the controller  72   a  controls the drum  12   a  to be rotated at the motor RPM and operation rate set to perform a washing operation using bubbles such that the high-concentration detergent on the surfaces of the bubbles surrounds the laundry placed in the drum  12   a  and is absorbed into the laundry ( 118   a ). 
     In addition, the controller  72   a  counts bubble generation time. When it is determined that a predetermined time has elapsed as a result of counting the bubble generation time, the controller  72   a  controls the drum  12   a  to be rotated at the motor RPM and operation rate set to perform a washing operation using bubbles such that the high-concentration detergent on the surfaces of the bubbles surrounds the laundry placed in the drum  12   a  and is absorbed into the laundry. 
     That is, the controller  72   a  controls the drum  12   a  to be rotated with the generation of the bubbles such that the washing operation is performed for a predetermined washing time to effectively and rapidly remove contaminants from the laundry using the high-concentration detergent on the surfaces of the bubbles dispersed throughout the drum  12   a  ( 120   a ). Meanwhile, the controller  72   a  controls the generation of bubbles to be stopped or continued during the rotation of the drum  12   a.    
     When the washing operation using the bubbles is completed, the controller  72  performs rinsing and spin-drying operations set based on the load to end the washing ( 122   a ). 
     In this embodiment, the circulation pump  51   a  and drainage pump  61   a  are mounted at the pump case  40   a  in a symmetrical fashion, to which, however, embodiments of the present invention are not limited. For example, the circulation pump  51   a  and drainage pump  61   a  may be mounted side by side at the lower front of the machine body  10   a . Also, the circulation pump  51   a  and drainage pump  61   a  may be applied to any structures to circulate and drain water. 
     In this embodiment, the water tub  11   a  is installed in parallel to an installation plane of the washing machine, to which, however, embodiments of the present invention are not limited. For example, the water tub  11   a  may be installed at a predetermined angle to the installation plane of the washing machine. 
     Results of the bubble washing operation are shown in  FIGS. 17 and 18 . 
       FIG. 17  is a graph illustrating a shrinkage rate of laundry when washing the laundry in such a way as to reduce an amount of water and using bubbles at the same concentration in the same washing operation. 
     In  FIG. 17 , “Conventional wool washing” indicates a shrinkage rate of wool when a washing operation is performed at an RPM of 25 and at an operation rate of 1 second-On and 78 seconds-OFF for a washing period of 10 minutes, “Bubble  1 ” indicates a shrinkage rate of wool when the washing operation is performed at an RPM of 25 and at an operation rate of 1 second-On and 78 seconds-OFF for a washing period of 10 minutes as in the conventional wool washing, and “Bubble  2 ” indicates a shrinkage rate of wool when the washing operation is performed at an RPM of 25 and at an operation rate of 2 seconds-On and 78 seconds-OFF for a washing period of 10 minutes, which is different from the conventional wool washing in terms of operation rate. 
       FIG. 17  reveals that Bubble  1  exhibits a noticeably reduced shrinkage rate of the laundry as compared with the conventional wool washing, and Bubble  2  exhibits a reduced shrinkage rate of the laundry as compared with the conventional wool washing in spite of its higher operation rate than that of the conventional wool washing. 
       FIG. 18  is a graph illustrating a cleaning degree of artificially contaminated laundry of 60 MU (Make Up), in terms of reflective index (%) at the same amount (2 g, 4 g, 10 g) of detergent, comparing a case of using detergent water with a case of using bubbles, both of which have the same detergent concentration. 
       FIG. 18  reveals that the cleaning degree of the laundry through the washing operation using the bubbles is noticeably higher than that using the general detergent water. 
     As is apparent from the above description, the control method of the washing machine according to the embodiment of the present invention may generate a large number of bubbles using a small amount of water to reduce water consumption and transmit detergent water to laundry placed in the washing machine effectively and rapidly using high-concentration detergent on the surfaces of the bubbles, thereby reducing time and energy consumption and improving washing efficiency. 
     The bubbles may act as a cushion to reduce friction between laundry articles, thereby preventing expensive laundry (such as wool or silk) from being damaged due to the friction between the laundry articles and between the laundry and water and preventing damage to and deformation of general laundry when washing the laundry. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.