Method for operating a washing machine and washing machine

Abstract

In a method for operating a washing machine with a drum, a drive motor for the drum, a power supply for the drive motor and a washing machine control monitoring and detecting the motor current by means of the power supply, the following steps are performed where the motor current is constantly monitored while the drum rotates for at least three full revolutions. A full revolution of the drum is divided into three rotation sections of equal size, and the motor current is monitored and recorded for each of the rotation sections. An envelope curve of this motor current is calculated, and therefrom the standard deviation is calculated. The standard deviation is divided by the mean value of the envelope curve to determine the coefficient of variation for each rotation section. By comparing the determined coefficient of variation for each rotation section with stored values for the coefficient of variation, the behaviour of the laundry items is determined as to whether laundry items slide down the drum inner wall, fall from the drum inner wall or rotate together with the drum. From this behaviour, parameters are determined for a further operation of the washing machine with regard to the treatment of the laundry items.

1 . A method for operating a washing machine, said washing machine comprising:
 a drum,   a drive motor for said drum,   a power supply for said drive motor with monitoring of a motor current,   a washing machine control, wherein said washing machine control monitors and detects said motor current by means of said power supply,   with the steps of:   A said drum with laundry items in it is rotated by means of said drive motor and, in doing so, said motor current is constantly monitored and recorded, whereby a rotational position of said drum is also monitored and recorded,   B a full revolution of said drum is divided into at least three rotation sections and said motor current is monitored and recorded for each of said rotation sections,   C said drum is rotated for at least three full revolutions at a constant rotational speed,   D for said motor current determined for each rotation section, an envelope curve of said motor current is calculated, and from said envelope curve a standard deviation is calculated with a formula,   E then said respective standard deviation is divided by a mean value of said motor current or of said envelope curve to determine a coefficient of variation for each rotation section,   F by comparing said coefficient of variation for each rotation section that has been determined with stored values for said coefficient of variation, a behaviour of said laundry items is determined as to whether laundry items slide down said drum inner wall during rotation in said drum, fall from said drum inner wall or rotate together with said drum while remaining in substantially the same position on said drum inner wall, and   G from a determination of said behaviour of said laundry items, parameters are determined for a further operation of said washing machine with regard to a treatment of said laundry items, such as temperature, duration, rotational speed, type and quantity of additives used or the like.   
     
     
         2 . Method according to  claim 1 , wherein a formula for calculating said coefficient of variation is: 
       
         
           
             
               CV 
               = 
               
                 
                   
                     Standard 
                     ⁢ 
                         
                     Deviation 
                   
                   
                     Mean 
                     ⁢ 
                         
                     value 
                   
                 
                 = 
                 
                   σ 
                   μ 
                 
               
             
           
         
       
     
     
         3 . Method according to  claim 1 , wherein a formula for calculating said Standard Deviation is: 
       
         
           
             
               
                 σ 
                 = 
                 
                   
                     
                       
                         
                           ∑ 
                             
                         
                         
                           i 
                           = 
                           1 
                         
                         N 
                       
                       ⁢ 
                       
                         
                           ( 
                           
                             
                               x 
                               i 
                             
                             - 
                             μ 
                           
                           ) 
                         
                         2 
                       
                     
                     N 
                   
                 
               
               , 
             
           
         
       
       wherein x i  is a Datapoint value, μ is a samples mean value and N is a samples size. 
     
     
         4 . Method according to  claim 1 , wherein said drum is rotated for said three full revolutions at a rotational speed between 30 rpm and 90 rpm. 
     
     
         5 . Method according to  claim 1 , wherein said method with steps A to F is carried out several times for different rotational speeds in each case. 
     
     
         6 . Method according to  claim 5 , wherein said rotational speeds increase by 10% to 100%. 
     
     
         7 . Method according to  claim 1 , wherein said method detects whether said laundry items in said drum are sufficiently evenly distributed by using a predefined limit value for said coefficient of variation for comparison with a measured value for said coefficient of variation, and if said comparison falls below this predefined limit value, then said rotational speed for said drum is changed to redistribute laundry items in said drum for a more even distribution to compensate for imbalance of said laundry items in said drum. 
     
     
         8 . Method according to  claim 6 , wherein for said detection of a sufficiently even distribution of said laundry items in said drum the following is used: an initially determined weight of said laundry items, a stored value for said coefficient of variation for said determined weight of said laundry items and for a behaviour of said laundry items with falling from said drum inner wall, then said steps B to E are carried out in order to determine whether said value for said coefficient of variation determined in this way corresponds to said stored value, and
 if this is not the case, said rotational speed or direction of rotation of said drum is changed, and   if this is the case, said drum is rotated faster for a high speed for dry spinning.   
     
     
         9 . Method according to  claim 6 , wherein for said detection of said sufficiently even distribution of said laundry items in said drum the following is used: said weight of said laundry items determined at a beginning, a stored value for said coefficient of variation for said determined weight of said laundry items and for said behaviour of said laundry items with falling from said drum inner wall, then steps B to E are carried out in order to determine whether said value determined in this way for said coefficient of variation corresponds to said stored value, and
 if this is the case, said drum is rotated faster for a high speed or for a dry spin, and   if this is not the case, a check is made as to whether said items of laundry rotate together with said drum, said weight of said laundry items being determined at said beginning, a stored value for said coefficient of variation for this determined weight of said laundry items and for said behaviour of said laundry items rotating with said drum being used, and then steps B to E are carried out to determine whether said value of said coefficient of variation thereby determined corresponds to said stored value for said behaviour of said laundry items with rotation together with said drum, and
 if this is the case, said drum is rotated more slowly and then it is checked again to see if said laundry items still fall from said drum inner wall at said lower rotational speed, and 
 if this is not the case, steps B to E are carried out at constant rotational speed to determine whether said determined value for said coefficient of variation corresponds to said stored value for said behaviour of said laundry items with sliding down said drum inner wall, and
 if this is the case, said drum is rotated faster and then checked again to see if said laundry still falls from said drum inner wall at said higher rotational speed, and 
 if this is not the case, a check is made in accordance with  claim 7  to see whether said items of laundry still fall from said drum inner wall while said rotational speed remains the same. 
 
   
     
     
         10 . Method according to  claim 7 , wherein, in the event that a distribution of said laundry items is considered to be sufficiently uniform, a treatment process of said laundry items is further carried out. 
     
     
         11 . Method according to  claim 10 , wherein said treatment process is a dry spinning process. 
     
     
         12 . Method according to  claim 1 , wherein a moistening of laundry items in said drum with water is monitored for said detection of a sufficiently uniform moistening of said laundry items in said drum: said weight of said laundry items determined at said beginning, a stored value for said coefficient of variation for said determined weight of said laundry items and for a behaviour of said laundry items with rotation together with said drum, then said laundry items are moistened by introducing water into said drum or onto said laundry items, then steps B to E are carried out to determine whether said value for said coefficient of variation determined in this way corresponds to said stored value for said behaviour of said laundry items with rotation together with said drum, and
 if this is the case, said drum is rotated faster for a high speed or for a dry spinning process, and   if this is not the case, said rotational speed and/or direction of rotation of said drum are changed.   
     
     
         13 . Method according to  claim 12 , wherein, in the event that said determined value for said coefficient of variation does not correspond to said stored value for a behaviour of said laundry items with rotation together with said drum, a check is made at constant rotational speed as to whether said laundry items fall from said drum inner wall, said weight of said laundry items determined at said beginning being used for this purpose, a stored value for said coefficient of variation for this determined weight of said laundry items and for said behaviour of said laundry items with falling from said drum inner wall is used, and then steps B to E are carried out in order to determine whether said value for said coefficient of variation determined in this way corresponds to said stored value for said behaviour of said laundry items with falling from said drum inner wall, and
 if this is the case, said drum is rotated faster and then it is checked again to see whether said laundry items are still rotating together with said drum at said higher rotational speed, and   if this is not the case, steps B to E are carried out at constant rotational speed to determine whether said determined value for said coefficient of variation corresponds to said stored value for said behaviour of said laundry items with sliding down said drum inner wall, and
 if this is said case, said drum is rotated faster and then it is checked again to see if said laundry items are still sliding down said drum inner wall at said higher rotational speed, and 
 if this is not the case, a check is made in accordance with  claim 7  to see whether said laundry items are still rotating with said drum at the same rotational speed. 
   
     
     
         14 . Method according to  claim 1 , wherein a washing process for said laundry items in said drum with water is monitored, using for said detection of an appropriate washing process for said laundry items in said drum one of the following: said weight of said laundry items determined at said beginning, a stored value for said coefficient of variation for said determined weight of said laundry items and for said behaviour of said laundry items desired for said washing process, then steps B to E are carried out to determine whether said value for said coefficient of variation determined in this way corresponds to said stored value for said desired behaviour of said laundry items, and
 if this is the case, said drum is rotated at the same rotational speed and in said same direction for a next wash cycle, and   if this is not the case, said rotational speed and/or direction of rotation of said drum is changed.   
     
     
         15 . Method according to  claim 1 , wherein a quantity or weight of said laundry items in said drum is determined in said beginning either by weighing or by monitoring said motor current as said drum with said laundry items in it rotates. 
     
     
         16 . Method according to  claim 1 , wherein said coefficient of variation is used in addition to said standard deviation and said mean deviation. 
     
     
         17 . Method according to  claim 1 , wherein in step B said rotation sections are of equal size. 
     
     
         18 . Method according to  claim 4 , wherein said drum is rotated for said three full revolutions at a rotational speed between 55 rpm and 65 rpm. 
     
     
         19 . Washing machine comprising:
 a drum,   a drive motor for said drum,   a power supply for said drive motor with monitoring of a motor current,   a washing machine control, wherein said washing machine control monitors and detects said motor current by means of said power supply,   wherein said washing machine control is designed to perform said method according to  claim 1 .