Method for operating a washing machine, and washing machine

Abstract

The invention relates to a method for operating a washing machine having a suds container for holding washing liquid, a non-ribbed drum rotatably mounted in the suds container for holding laundry, a motor for driving the drum, and a control device, wherein the method comprises a step for detecting when laundry is sliding and/or rolling, comprising, while rotating the drum, sampling a variable related to a torque of the motor or a rotational speed of the drum over a predetermined period of time; and determining whether the laundry is sliding and/or rolling in the drum based on the variable sampled over the period of time. The invention further relates to a corresponding washing machine.

1 . A method for operating a washing machine having a suds container for holding washing liquid, a non-ribbed drum rotatably mounted in the suds container for holding laundry, a motor for driving the drum, and a control device, wherein the method includes a step for detecting when laundry is sliding and/or rolling, the detecting step comprising, while rotating the drum:
 sampling a variable related to a torque of the motor or a rotational speed of the drum over a predetermined period of time; and   determining whether the laundry is sliding and/or rolling in the drum based on the variable sampled over the period of time.   
     
     
         2 . The method according to  claim 1 , wherein the variable relating to the torque of the motor or the rotational speed of the drum is at least one of the torque, a signal fluctuation correlating with the torque, the rotational speed or a signal fluctuation correlating with the rotational speed. 
     
     
         3 . The method according to  claim 1 , wherein the determination of whether the laundry is sliding and/or rolling in the drum, based on the variable sampled over the period of time, includes a frequency analysis, with which frequency components of the variable are determined in a predetermined frequency range. 
     
     
         4 . The method according to  claim 3 , wherein the frequency analysis is a Fast Fourier Transform (FTT). 
     
     
         5 . The method according to  claim 3 , wherein determining whether the laundry is rolling and/or sliding in the drum also includes a summation and/or an effective value formation of the determined frequency components that are in the predetermined frequency range. 
     
     
         6 . The method according to  claim 3 , wherein the frequency analysis is used to determine a value which is compared to a limit value stored in the washing machine, wherein it is determined that the laundry is sliding and/or rolling if the determined value is greater than the limit value. 
     
     
         7 . The method according to  claim 1 , wherein the rotation of the drum is stopped or the rotation of the drum is continued in a rocking process if, when determining whether the laundry is sliding and/or rolling in the drum based on the variable sampled over the period of time, it is determined that the laundry is sliding and/or rolling. 
     
     
         8 . The method according to  claim 1 , wherein the predetermined period of time comprises one complete revolution of the drum or an integer multiple of the one complete revolution of the drum. 
     
     
         9 . The method according to  claim 1 , wherein the rotational speed of the drum is in a subcritical rotational speed range. 
     
     
         10 . A washing machine having a suds container for holding washing liquid, a non-ribbed drum which is rotatably mounted in the suds container for holding laundry, a motor for driving the drum, and a control device that is designed and configured to execute the method according to  claim 1 .