Foam-Reducing Procedure in a Washing Machine During a Spinning Cycle

Abstract

The present invention relates to a method for operating a washing machine ( 10 ) adapted to perform a washing cycle and comprising a washing tub ( 24 ) in which a laundry drum ( 26 ) is contained, said method comprises the steps of: •—rotating said laundry drum ( 26 ) at a sticking speed (vst) at which laundry ( 28 ) clings at an inner periphery of said laundry drum ( 26 ), •—detecting a liquid level ( 44 ) in a washing tub ( 24 ) and/or in a draining region thereof while said laundry drum ( 26 ) is rotating at said sticking speed (vst), and •—starting a foam-reducing procedure if the detected liquid level ( 44 ) corresponds to a prefixed value or is within a prefixed range of values, or if the time dependent behaviour of said the detected liquid level ( 44 ) corresponds to a prefixed time dependent behaviour. Further, the present invention relates to a corresponding washing machine ( 10 ). Moreover, the present invention relates to a computer program product for performing the method for controlling a washing cycle in a washing machine ( 10 ).

1 . A method for operating a washing machine ( 10 ) adapted to perform a washing cycle and comprising a washing tub ( 24 ) in which a laundry drum ( 26 ) is contained, said method comprises the steps of:
 rotating said laundry drum ( 26 ) at a sticking speed (vst), at which laundry ( 28 ) clings at an inner periphery of said laundry drum ( 26 ),   detecting a liquid level ( 44 ) in a washing tub ( 24 ) and/or in a draining region to thereof while said laundry drum ( 26 ) is rotating at said sticking speed (vst), and   starting a foam-reducing procedure if the detected liquid level ( 44 ) corresponds to a prefixed value or is within prefixed range of values, or if the time dependent behaviour of the detected liquid level ( 44 ) correspond to a prefixed time dependent behaviour.   
     
     
         2 . The method according to  claim 1 , wherein:
 the method is performed during a spinning phase of the washing cycle and after a unbalancing detecting/reducing phase has been performed,   said step of rotating said laundry drum ( 26 ) at a sticking speed (vst) at which laundry ( 28 ) clings at an inner periphery of said laundry drum ( 26 ), is performed during or after said unbalancing detecting/reducing phase.   
     
     
         3 . The method according to  claim 2 , wherein:
 if, after said step of detecting a liquid level ( 44 ) in a washing tub ( 24 ) and/or in a draining region thereof while said laundry drum ( 26 ) is rotating at said sticking speed (vst), said foam-reducing procedure is not started, said laundry drum ( 26 ) is accelerated from said sticking speed (vst) to a final speed of said spinning phase without performing a further unbalancing detecting/reducing phase.   
     
     
         4 . The method according to  claim 1  or  2  or  3 , wherein the sticking speed (vst) of the laundry drum ( 26 ) is equal or marginally bigger than a minimum threshold value allowing that the laundry ( 28 ) clings at the inner periphery of said laundry drum ( 26 ). 
     
     
         5 . The method according to  claim 4 , wherein said minimum threshold value for the rotational speed (v) of the laundry drum ( 26 ) is between 80 rpm and 100 rpm. 
     
     
         6 . The method according to  claim 1 , wherein the method is performed during and/or before a dewatering phase and/or a spinning phase of the washing cycle. 
     
     
         7 . The method according to any one of the preceding claims, comprising the following steps:
 starting a predetermined monitoring period ( 54 ),   detecting the liquid level ( 44 ) in the washing tub ( 24 ) and/or in the draining region thereof during said predetermined monitoring period ( 54 ),   comparing the detected liquid level ( 44 ) with a lower threshold value ( 46 ) during the predetermined monitoring period ( 54 ), and   if the detected liquid level ( 44 ) does not decrease or drop below the lower threshold value ( 46 ) within the predetermined monitoring period ( 54 ), then starting said foam-reducing procedure.   
     
     
         8 . The method according to  claim 7 , wherein said predetermined monitoring period ( 54 ) is between five seconds and twenty seconds, preferably ten seconds. 
     
     
         9 . The method according to any one of the  claims 1  to  6 , comprising the following steps:
 detecting and storing the liquid level ( 44 ) in the washing tub ( 24 ) and/or in the draining region thereof during a drain pump ( 32 ) of said washing machine ( 10 ) is activated and the laundry drum ( 26 ) is rotating at said sticking speed (vst), 
 smoothing a signal of the stored liquid level ( 44 ), 
 determining gradient of the smoothed liquid level ( 44 ), 
 starting said foam-reducing procedure if the determined gradient corresponds to a prefixed range of values or is within a prefixed range of values. 
 
     
     
         10 . The method according to  claim 7  or  8 , wherein the drain pump ( 32 ) is switched on within the predetermined monitoring period ( 54 ) and, if said foam-reducing procedure is started, then the drain pump ( 32 ) remains activated, and, if said foam-reducing procedure is not started, then the drain pump ( 32 ) is switched off for a predetermined period and then switched on again. 
     
     
         11 . The method according to  claim 10  wherein said predetermined period for switching off the drain pump ( 32 ) is between 20 seconds and 40 seconds, preferably 30 seconds. 
     
     
         12 . The method according to any one of the preceding claims, wherein said foam-reducing procedure comprises reducing the rotational speed (v) of the laundry drum ( 26 ) or stopping the latter and switching off a drain pump ( 32 ) of said washing machine ( 10 ) for a predetermined period and then switching it on again. 
     
     
         13 . The method according to  claim 12 , wherein said predetermined period in which said drain pump ( 32 ) is switched off between a half minute and two minutes, preferably one minute. 
     
     
         14 . The method according to  claim 12  or  13 , wherein said foam-reducing procedure comprises, after reducing the rotational speed (v) of the laundry drum ( 26 ) or stopping the latter and switching off the drain pump ( 32 ) for a predetermined period and then switching it on again, the steps of:
 detecting again the liquid level ( 44 ) in the washing tub ( 24 ) and/or in the draining region thereof, and, 
 if the detected liquid level ( 44 ) does still not decrease or drop below the lower threshold value ( 46 ) within the predetermined period, adding water into in the washing tub ( 24 ), and draining the washing tub ( 24 ) and starting a balancing phase. 
 
     
     
         15 . A washing machine, wherein the washing machine is provided for the method according to any one of the  claims 1  to  14 .