Abstract:
A washing control apparatus and method of a dish washing machine capable of detecting the turbidity of wash water during washing to determine a next washing operation. The washing control method includes detecting a turbidity of wash water while performing washing using the wash water, and determining a washing operation to be performed based on the detected turbidity of the wash water.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2006-0121632, filed on Dec. 4, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to washing control of a dish washing machine. More particularly, to a washing control apparatus and method of a dish washing machine capable of detecting the turbidity of wash water during washing to determine a next washing operation. 
         [0004]    2. Description of the Related Art 
         [0005]    A conventional dish washing machine washes food leftovers (hereinafter, referred to as “contaminants”) off dishes using cold wash water or hot wash water. The conventional dish washing machine includes a machine body having a washing tub, dish baskets mounted in the washing tub, injection nozzles to inject wash water to dish baskets, and a sump connected to the injection nozzles to pump wash water into the injection nozzles. 
         [0006]    When wash water is introduced into the dish washing machine while dishes to be washed are placed in the dish baskets, the dish washing machine washes the dishes through washing and rinsing operations in which a washing pump mounted at the sump is operated to forward wash water to the injection nozzles and the wash water is injected to dishes through the injection nozzles at high pressure. The washing and rinsing operations include a preliminary operation (preliminary washing or preliminary rinsing) and a main operation (main washing or final rinsing). The preliminary operation may be performed a predetermined number of times (normally, twice) before the main operation. 
         [0007]    Although the dishes can be completely washed by performing the preliminary operation (preliminary washing or preliminary rinsing) only once when the dishes are not excessively contaminated, however, the dish washing machine unconditionally performs the preliminary operation (preliminary washing or preliminary rinsing) a predetermined number of times. As a result, water consumption increases, and power consumption also increases. 
       SUMMARY 
       [0008]    Accordingly, it is an aspect of the present invention to provide a washing control apparatus and method of a dish washing machine capable of detecting the turbidity of wash water during washing, to thereby determine a next washing operation, thereby reducing the number of washing times and thus preventing waste of wash water. 
         [0009]    It is another aspect of the present invention to provide a washing control apparatus and method of a dish washing machine capable of detecting the turbidity of wash water before drainage of a previous washing operation and the turbidity of wash water after the initiation of a next washing operation twice, to thereby determine kinds of contamination, thereby accomplishing an appropriate washing process irrespective of kinds of contamination. 
         [0010]    It is a further aspect of the present invention to provide a washing control apparatus and method of a dish washing machine capable of changing a load action of a next washing operation based on the turbidity of wash water detected before drainage of a previous washing operation and the turbidity of wash water detected after the initiation of a next washing operation, thereby appropriately controlling washing time. 
         [0011]    Additional aspects and/or advantages will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
         [0012]    The foregoing and/or other aspects of the present invention are achieved by providing a washing control method of a dish washing machine including detecting a turbidity of wash water while performing washing using the wash water, and determining a washing operation to be performed, based on the detected turbidity of the wash water. 
         [0013]    According to an aspect of the present invention, detecting the turbidity of the wash water includes detecting a turbidity of wash water before drainage of a previous washing operation and a turbidity of wash water after the initiation of a next washing operation. 
         [0014]    According to an aspect of the present invention, the turbidity of the wash water after the initiation of the next washing operation is a turbidity of wash water after the performance of the next washing operation for a predetermined period of time after water supply for the next washing operation. 
         [0015]    According to an aspect of the present invention, the previous washing operation is a first preliminary washing of the dish washing machine, and the next washing operation is a second preliminary washing of the dish washing machine. 
         [0016]    According to an aspect of the present invention, the previous washing operation is a main washing of the dish washing machine, and the next washing operation is a preliminary rinsing of the dish washing machine. 
         [0017]    According to an aspect of the present invention, determining the washing operation to be performed includes comparing the detected turbidity of the wash water with a predetermined reference turbidity, and when the detected turbidity of the wash water does not exceed the reference turbidity, omitting at least one washing operation from a predetermined series of washing operations, and the omitting the at least one washing operation includes omitting a preliminary washing or a preliminary rinsing of the dish washing machine. 
         [0018]    According to an aspect of the present invention, the washing operation further includes changing the washing operation in progress into a subsequent operation when the detected turbidity of the wash water does not exceed the predetermined reference turbidity, and the changing the washing operation in progress into the subsequent operation includes changing the second preliminary washing in progress into a main washing. 
         [0019]    According to an aspect of the present invention, determining the washing operation to be performed further includes, completely performing the predetermined series of washing operations when the detected turbidity of the wash water exceeds the predetermined reference turbidity. 
         [0020]    It is another aspect of the present invention to provide a washing control apparatus of a dish washing machine including a turbidity detection unit to detect a turbidity of wash water while washing is performed using the wash water, and a control unit to determine a washing operation based on the detected turbidity of the wash water. 
         [0021]    According to an aspect of the present invention, the turbidity detection unit detects a turbidity of wash water before drainage of a previous washing operation and a turbidity of wash water after the initiation of a next washing operation. 
         [0022]    According to an aspect of the present invention, the control unit compares the detected turbidity of the wash water with a predetermined reference turbidity, and omits a preliminary washing or a preliminary rinsing from a predetermined series of washing operations when the detected turbidity of the wash water does not exceed the predetermined reference turbidity. 
         [0023]    According to an aspect of the present invention the control unit changes a second preliminary washing in progress into a main washing when the detected turbidity of the wash water does not exceed the predetermined reference turbidity. 
         [0024]    According to an aspect of the present invention the control unit completely performs the predetermined series of washing operations when the detected turbidity of the wash water exceeds the predetermined turbidity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    These and/or other aspects and advantages 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: 
           [0026]      FIG. 1  is a side sectional view illustrating the structure of a dish washing machine according to an embodiment of the present invention; 
           [0027]      FIG. 2  is a control block diagram of a dish washing machine according to an embodiment of the present invention; and 
           [0028]      FIGS. 3A-3C  are flow charts illustrating a washing control method of a dish washing machine according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0029]    Reference will now be made in detail to the embodiment of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
         [0030]      FIG. 1  is a side sectional view illustrating the structure of a dish washing machine according to an embodiment of the present invention. 
         [0031]    As shown in  FIG. 1 , the dish washing machine comprises a machine body  10  having a washing space defined therein, and a door  12  to open and close the front part of the machine body  10 . The machine body  10  and the door  12  constitute the appearance of the dish washing machine. 
         [0032]    A washing tub  20  is mounted in the machine body  10  and comprises a plurality of dish baskets  22  to receive dishes, racks  24  to slidably support the dish baskets  22 , an upper injection nozzle  26   a , a middle injection nozzle  26   b , and a lower injection nozzle  26   c . Specifically, the upper injection nozzle  26   a , the middle injection nozzle  26   b , and the lower injection nozzle  26   c  are mounted above and below the dish baskets  22  to inject wash water. 
         [0033]    The upper injection nozzle  26   a  and the middle injection nozzle  26   b  are connected to a sump  42 , which will be described below, via a first supply pipe  28   a . The lower injection nozzle  26   c  is connected to the sump  42  via a second supply pipe  28   b.    
         [0034]    A heater  30  to heat wash water is mounted at the bottom of the washing tub  20 . Specifically, the heater  30  is disposed in a heater receiving groove  32  formed at the bottom of the washing tub  20 . 
         [0035]    A machine compartment  40  is also mounted at the bottom of the washing tub  20 , in which the sump  42 , which pumps wash water introduced into the washing water  20  to forward the wash water to the upper, middle, and lower injection nozzles  26   a ,  26   b , and  26   c , is mounted. A turbidity sensor  44  is mounted in the sump  42 , to detect the turbidity of water used to wash the dishes (i.e., the contamination level of wash water) during a washing operation. 
         [0036]    The turbidity sensor  44  detects the turbidity of wash water using a photo coupler sensing light emitted from a light emitting part  44   a , transmitted through wash water used to wash the dishes, and received by a light receiving part  44   b.    
         [0037]    The sump  42  includes various flow channels. A washing pump  46  to pump water to the flow channels is also mounted at the sump  42 . Further, a drainage pump  48  and a drainage pipe  50  to drain contaminated wash water to the outside are mounted at one side of the sump  42 . 
         [0038]      FIG. 2  is a control block diagram of a dish washing machine according to an embodiment of the present invention. In addition to the components shown in  FIG. 1 , the dish washing machine further comprises an input unit  100 , a control unit  110 , a drive unit  120 , and a display unit  130 . 
         [0039]    The input unit  100  allows a user to input operation information such as a washing course, a wash water temperature, and addition of rinsing to the control unit  110 . 
         [0040]    The control unit  110  is a microcomputer which controls the dish washing machine according to the operation information inputted from the input unit  100 . The control unit  110  detects the turbidity V 1  of wash water before drainage of a previous preliminary washing (i.e., preliminary washing  1 ) and the turbidity V 2  of wash water after water supply for a next preliminary washing (i.e., preliminary washing  2 ) (to be exact, after the performance of the next preliminary washing for a predetermined period of time after water supply) twice. When the detected turbidities V 1  and V 2  of the wash water exceed a predetermined reference turbidity Va, the control unit  110  determines that the contamination of the wash water is excessive, and completely performs the second preliminary washing (i.e., preliminary washing  2 ). When the detected turbidities V 1  and V 2  of the wash water do not exceed the reference turbidity Va, the control unit  110  changes the second preliminary washing (i.e., preliminary washing  2 ) into a main washing. 
         [0041]    Also, the control unit  110  detects the turbidity V 3  of wash water before drainage of the main washing and the turbidity V 4  of wash water after water supply for a next preliminary rinsing (i.e., preliminary rinsing  1 ) (to be exact, after the performance of the next preliminary rinsing for a predetermined period of time after water supply) twice. When the detected turbidities V 3  and V 4  of the wash water exceed a predetermined reference turbidity Vb, the control unit  110  determines that the contamination of the wash water is excessive, and completely performs a second preliminary rinsing (i.e., preliminary rinsing  2 ). When the detected turbidities V 3  and V 4  of the wash water do not exceed the reference turbidity Vb, the control unit  110  omits the second preliminary rinsing (i.e., preliminary rinsing  2 ). 
         [0042]    Also, when the control unit  110  changes the second preliminary washing (i.e., preliminary washing  2 ) into the main washing or omits the second preliminary rinsing (i.e., preliminary rinsing  2 ), the control unit  110  appropriately controls wash water temperature, detergent supply, and washing time. 
         [0043]    The drive unit  120  drives the heater  30 , the washing pump  46 , the drainage pump  48 , and a water supply valve  122  according to a drive control signal of the control unit  110 . The water supply valve  122  controls the supply of wash water into the washing tub  20 . 
         [0044]    The display unit  130  displays the operation state and error of the dish washing machine according to a display control signal of the control unit  110 . 
         [0045]    Hereinafter, a washing control method of the dish washing machine with the above-stated construction will be described in detail. 
         [0046]      FIGS. 3A-3C  are flow charts illustrating a washing control method of the dish washing machine according to an embodiment of the present invention. 
         [0047]    When a user selects operation information such as a washing course, wash water temperature, and addition of rinsing while dishes to be washed are placed in the dish baskets  22  mounted in the washing tub  20 , the operation information selected by the user is inputted to the control unit  110  through the input unit  100 . 
         [0048]    The control unit  110  performs a series of washing processes such as a washing operation, a rinsing operation, and a drying operation according to the operation information inputted from the input unit  100 . First, in operation  200 , the control unit  110  determines whether the operation is a preliminary washing operation. 
         [0049]    When the operation is the preliminary washing operation, the control unit  110  controls the water supply valve  122  through the drive unit  120 . Consequently, in operation  202 , wash water necessary for the preliminary washing is supplied into the washing tube  20  through wash water supply holes (not shown). 
         [0050]    The wash water supplied into the washing tub  20  is introduced into the sump  42  mounted at the bottom of the washing tub  20 . The introduced wash water is forwarded to the upper injection nozzle  26   a , the middle injection nozzle  26   b , and the lower injection nozzle  26   c  through the first and second supply pipes  28   a  and  28   b  by the pumping action of the washing pump  46  mounted at the sump  42 , and a first preliminary washing (i.e., preliminary washing  1 ) is performed to inject the wash water to the dishes placed in the dish baskets  22  at high pressure in operation  204 . 
         [0051]    As the first preliminary washing (i.e., preliminary washing  1 ) progresses, in operation  206 , the control unit  110  counts the progress time of the first preliminary washing to determine whether a predetermined preliminary washing time (i.e., approximately 15 minutes) has elapsed, i.e., the preliminary washing has been completed. When it is determined that the the preliminary washing has not been completed, the first preliminary washing is performed continuously Until the preliminary washing time elapses. 
         [0052]    When it is determined that the preliminary washing has been completed, which means that the wash water and contaminants washed off the dishes by the wash water have been introduced into the sump  42 , the turbidity sensor  44  mounted in the sump  42  senses light emitted from the light emitting part  44   a , transmitted through the wash water used to wash the dishes, and received by the light receiving part  44   b  using the photo coupler to detect the turbidity V 1  of the wash water used to wash the dishes during the first preliminary washing (i.e., preliminary washing  1 ) before the drainage of the wash water in operation  208 . 
         [0053]    The control unit  110  compares the turbidity V 1  of the wash water detected by the turbidity sensor  44  with a predetermined reference turbidity (i.e., the turbidity of wash water to determine whether to progress from the preliminary washing) Va (operation  210 ). When the detected turbidity V 1  of the wash water exceeds the predetermined reference turbidity Va, the control unit  110  determines that the contamination of the wash water is excessive, and drains the wash water containing the contaminants through the drainage pipe  50  according to an operation of the drainage pump  48  (operation  212 ). 
         [0054]    The contaminants may be easily drained together with the wash water (contaminants having an intermediate specific gravity) or remain in the sump  42  after drainage (contaminants having a large or small specific gravity). 
         [0055]    In order that the washing process is appropriately performed irrespective of kinds of contaminants, therefore, the turbidity of the wash water is detected before the drainage of the first preliminary washing and after the drainage and water supply for a second preliminary washing twice to determine whether to progress the second preliminary washing. 
         [0056]    To this end, the control unit  110  controls the water supply valve  122  through the drive unit  120  to supply wash water necessary for the second preliminary washing (operation  214 ). As in the first preliminary washing (i.e., preliminary washing  1 ), the wash water supplied into the washing tub  20  is introduced into the sump  42 . The introduced wash water is forwarded to the upper injection nozzle  26   a , the middle injection nozzle  26   b , and the lower injection nozzle  26   c  by the pumping action of the washing pump  46 , and a second preliminary washing (i.e., preliminary washing  2 ) is performed to inject the wash water to the dishes placed in the dish baskets  22  at high pressure (operation  216 ). 
         [0057]    When the second preliminary washing (i.e., preliminary washing  2 ) is performed, the control unit  110  determines whether a predetermined period of time (i.e., time necessary to detect the turbidity of wash water based on kinds of contaminants after the initiation of the washing) T (i.e., approximately 1 minute) has elapsed after the initiation of the second preliminary washing (operation  218 ). When the predetermined period of time T has not elapsed, the second preliminary washing is performed continuously until the predetermined period of time T elapses. 
         [0058]    When it is determined that the predetermined period of time T has elapsed, which means that the wash water and contaminants washed off the dishes by the wash water have been introduced into the sump  42  for the predetermined period of time during the second preliminary washing, the turbidity sensor  44  detects the turbidity V 2  of the wash water used to wash the dishes during the second preliminary washing (i.e., preliminary washing  2 ) (operation  220 ). 
         [0059]    In  FIG. 3B , the control unit  110  compares the turbidity V 2  of the wash water detected by the turbidity sensor  44  with the predetermined reference turbidity Va (operation  222 ). When the detected turbidity V 2  of the wash water exceeds the predetermined reference turbidity Va, the control unit  110  determines that the contamination of the wash water is excessive, and completely performs the second preliminary washing (i.e., preliminary washing  2 ) (operation  224 ). 
         [0060]    As the second preliminary washing (i.e., preliminary washing  2 ) progresses, the control unit  110  counts the progress time of the second preliminary washing to determine whether the preliminary washing has been completed (operation  226 ). When the preliminary washing has not been completed, the second preliminary washing is performed continuously until the preliminary washing time elapses. 
         [0061]    When it is determined that the preliminary washing has been completed, the control unit  110  drains the wash water containing the contaminants according to the operation of the drainage pump  48  (operation  228 ). After that, the control unit  110  controls the water supply valve  122  to supply wash water necessary for a main washing such that the main washing is performed after the preliminary washing (operation  230 ). 
         [0062]    As in the first or second preliminary washing (i.e., preliminary washing  1  or  2 ), the wash water supplied into the washing tub  20  is introduced into the sump  42 . The introduced wash water is forwarded to the upper injection nozzle  26   a , the middle injection nozzle  26   b , and the lower injection nozzle  26   c  by the pumping action of the washing pump  46 , and a main washing is performed to inject the wash water to the dishes placed in the dish baskets  22  at high pressure (operation  232 ). 
         [0063]    When it is determined at operation  222  that the detected turbidity V 2  of the wash water does not exceed the predetermined reference turbidity Va, on the other hand, the control unit  110  determines that the contamination of the wash water is not excessive, and omits the second preliminary washing. Specifically, the control unit  110  changes the second preliminary washing into a main washing (operation  223 ). Consequently, the procedure advances to operation  232  to progress the main washing. 
         [0064]    The main washing is an operation in which detergent is introduced into the wash water through a detergent introduction unit (not shown), while the wash water is heated to a predetermined temperature (i.e., approximately 60 to 65° C.) by the heater  30 , before the washing water is injected at high pressure by the pumping action of the washing pump  46  such that hot wash water containing the detergent is injected to the dishes placed in the dish baskets  22  to wash the dishes. 
         [0065]    As the main washing progresses, the control unit  110  counts the progress time of the main washing to determine whether a predetermined main washing time (i.e., approximately 15 minutes) has elapsed, i.e., the main washing has been completed (operation  234 ). When the main washing has not been completed, the main washing is performed continuously until the main washing time elapses. 
         [0066]    When it is determined that the main washing has been completed, the turbidity V 3  of the wash water used to wash the dishes during the main washing is detected before the drainage of the wash water (operation  236 ). 
         [0067]    The control unit  110  compares the detected turbidity V 3  of the wash water with a predetermined reference turbidity (the turbidity of wash water to determine whether to progress a preliminary rinsing) Vb (operation  238 ). When the detected turbidity V 3  of the wash water exceeds the reference turbidity Vb, the control unit  110  determines that the contamination of the wash water is excessive, and drains the wash water containing the contaminants according to the operation of the drainage pump  48  (operation  240 ). 
         [0068]    The contaminants may be easily drained together with the hot wash water (contaminants having an intermediate specific gravity) or remain in the sump  42  after drainage (contaminants having a large or small specific gravity). 
         [0069]    In order that the rinsing process is appropriately performed irrespective of kinds of contaminants, therefore, the turbidity of the wash water is detected before the drainage of the main washing and after the drainage and water supply for a preliminary rinsing twice to determine whether to progress a first preliminary washing. 
         [0070]    To this end, the control unit  110  controls the water supply valve  122  to supply wash water necessary for the first preliminary rinsing (operation  242 ). As in the preliminary or main washing, the wash water supplied into the washing tub  20  is introduced into the sump  42 . The introduced wash water is forwarded to the upper injection nozzle  26   a , the middle injection nozzle  26   b , and the lower injection nozzle  26   c  by the pumping action of the washing pump  46 , and a first preliminary rinsing (i.e., preliminary rinsing  1 ) is performed to inject the wash water to the dishes placed in the dish baskets  22  at high pressure (operation  244 ). 
         [0071]    When the first preliminary rising (i.e., preliminary rinsing  1 ) is performed, the control unit  110  determines whether a predetermined period of time (i.e., time necessary to detect the turbidity of wash water based on kinds of contaminants after the initiation of the rinsing) T (i.e., approximately 1 minute) has elapsed after the initiation of the first preliminary rising (operation  246 ). When the predetermined period of time T has not elapsed, the first preliminary rinsing is performed continuously until the predetermined period of time T elapses. 
         [0072]    When it is determined that the predetermined period of time T has elapsed in operation  246 , which means that the wash water and contaminants washed off the dishes by the wash water have been introduced into the sump  42  for the predetermined period of time during the first preliminary rinsing, the turbidity sensor  44  detects the turbidity V 4  of the wash water used to wash the dishes during the first preliminary rinsing (preliminary rinsing  1 ) (operation  248  of  FIG. 3C ). 
         [0073]    The control unit  110  compares the detected turbidity V 4  of the wash water with the predetermined reference turbidity Vb (operation  250 ). When the detected turbidity V 4  of the wash water exceeds the predetermined reference turbidity Vb, the control unit  110  determines that the contamination of the wash water is excessive, and completely performs the first preliminary rinsing (i.e., preliminary rinsing  1 ) (operation  252 ). 
         [0074]    As the first preliminary rinsing (i.e., preliminary rinsing  1 ) progresses, the control unit  110  counts the progress time of the first preliminary rinsing to determine whether the preliminary rinsing has been completed (operation  254 ). When the preliminary rinsing has not been completed, the first preliminary rinsing is performed continuously until the preliminary rinsing time elapses. 
         [0075]    When it is determined that the preliminary rinsing has been completed, the control unit  110  drains the wash water containing the contaminants according to the operation of the drainage pump  48  (operation  256 ). After that, the control unit  110  controls the water supply valve  122  to supply wash water necessary for a second preliminary rinsing such that the second preliminary rinsing is performed after the first preliminary rinsing, and performs the second preliminary rinsing in the same manner as the first preliminary rinsing (operation  258 ). 
         [0076]    After the preliminary rinsing is completed, and the wash water is drained, a final rinsing operation is performed (operation  260 ). 
         [0077]    The final rinsing is an operation in which gloss detergent is introduced into the wash water through a detergent introduction unit (not shown), while the wash water is heated to a predetermined temperature (i.e., approximately 73 to 75° C.) by the heater  30 , before the washing water is injected at high pressure by the pumping action of the washing pump  46  such that hot wash water containing the gloss detergent is injected to the dishes placed in the dish baskets  22  to wash the dishes. When the hot water heated to a temperature of approximately 73 to 75° C. is injected to the dishes, the dishes are heated, and then the dishes are dried by latent heat. Consequently, the final rinsing provides a drying effect. 
         [0078]    When it is determined at operation  250  that the detected turbidity V 4  of the wash water does not exceed the predetermined reference turbidity Vb, on the other hand, the control unit  110  determines that the contamination of the wash water is not excessive, and performs continuously the first preliminary rinsing (i.e., preliminary rinsing  1 ) with the omission of the second preliminary rinsing (operation  262 ). 
         [0079]    As the first preliminary rinsing (i.e., preliminary rinsing  1 ) progresses, the control unit  110  counts the progress time of the first preliminary rinsing to determine whether the preliminary rinsing has been completed (operation  264 ). When the preliminary rinsing has not been completed, the first preliminary rinsing is performed continuously until the preliminary rinsing time elapses. 
         [0080]    When it is determined that the preliminary rinsing has been completed, the control unit  110  drains the wash water containing the contaminants according to the operation of the drainage pump  48  (operation  266 ), and omits the second preliminary rinsing after the completion of the first preliminary rinsing. Consequently, the procedure advances to operation  260  to progress the final rinsing operation. 
         [0081]    When it is determined at operation  212  that the detected turbidity V 1  of the wash water does not exceed the predetermined reference turbidity Va, on the other hand, the control unit  110  determines that the contamination of the wash water is not excessive, and omits the second preliminary washing. Consequently, the process advances to operation  228  to drain the wash water and progress the main washing. 
         [0082]    When it is determined at operation  238  that the detected turbidity V 3  of the wash water does not exceed the predetermined reference turbidity Vb, the control unit  110  determines that the contamination of the wash water is not excessive, and drains the wash water with the omission of the preliminary rinsing (operation  239 ). After that, the process advances to operation  260  to progress the final rinsing operation. 
         [0083]    In the above description, the turbidity V 3  of the wash water before drainage of the main washing and the turbidity V 4  of the wash water after the performance of the first preliminary rinsing (i.e., preliminary rinsing  1 ) for the predetermined period of time are detected twice, and, when the detected turbidities V 3  and V 4  of the wash water do not exceed the reference turbidity Vb, the second preliminary rinsing (i.e., preliminary rinsing  2 ) is omitted. However, the present invention is not limited to this construction. In the rinsing operation, the contamination of the wash water is relatively low with the result that the difference between the detected turbidities and the reference turbidity may be small. In order to prevent misdetermination due to the small difference, therefore, the present invention may be constructed such that, when it is determined that the contamination of the wash water is excessive based on the turbidity V 1  of the wash water before drainage of the first preliminary washing and the turbidity V 2  of the wash water after the performance of the second preliminary washing for the predetermined period of time, the second preliminary rinsing (i.e., preliminary rinsing  2 ) is unconditionally performed to reliably remove even CU-level contamination. 
         [0084]    As apparent from the above description, the turbidity of wash water is detected during washing to decide a next washing operation. Consequently, the present invention has the effect of reducing the number of washing times and thus preventing waste of wash water. 
         [0085]    Furthermore, the turbidity of wash water before drainage of a previous washing operation and the turbidity of wash water after the initiation of a next washing operation are detected twice to determine kinds of contamination such that a load action of the next washing operation can be changed to accomplish an appropriate washing process irrespective of kinds of contamination. Consequently, the present invention has the effect of appropriately controlling washing time. 
         [0086]    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 this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.