Patent Publication Number: US-2023140507-A1

Title: Method for operating a washing machine, and washing machine

Description:
RELATED APPLICATIONS 
     The present disclosure claims priority to and the benefit of PCT Application PCT/EP2021/057237, filed on Mar. 22, 2021, which claims priority to and the benefit of German Application 10 2020 108 688.1, filed on Mar. 30, 2020, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to a method for operating a washing machine and to a washing machine. In particular, the disclosure relates to a method for operating a washing machine and to a washing machine having a non-ribbed drum. 
     BACKGROUND 
     Typically, washing machine drums have ribs inside. A rib, which is also referred to as an entraining element, is a part of the drum which, when the drum is moved, also causes the laundry inside the drum to execute a motion, i.e. it entrains the laundry. The rib is usually a plate in the drum on which the laundry located in the drum hangs up to a specific height when the drum rotates and then falls down again and in this way is swirled around and rearranged. Usually, there are a plurality of ribs in the drum, which are arranged at predetermined distances from one another. The ribs are substantial for the laundry to be rearranged while executing a washing program. However, the ribs are additional components that add cost. Therefore, a non-ribbed drum would be desirable. 
     In the development of a washing machine having a non-ribbed drum, however, it has been shown that there are practical laundry loads, such as laundry bags, which do not lie in contact with the drum casing, in particular at rotational speeds of the drum of 120 rpm and higher, but roll and/or slide in the drum due to the lack of ribs. We have found that this behavior is particularly problematic when the rolling and/or sliding laundry has a mass of 1 kg or more and is caused to lie in contact with the drum casing by a disturbance in the sliding and/or rolling motion, e.g., by the drum base, by the transparent glass door, or by other items of laundry inside the drum. This suddenly creates an imbalanced mass which, due to its size, can cause the drum unit to hit a housing of the washing machine and can also cause the entire washing machine to move. In extreme cases, this can destroy the washing machine. In addition, rolling and, in particular, sliding are problematic for delicate items of laundry. The longer an item of laundry slides on the drum casing, the greater the risk that the textile will be damaged due to the friction between the textile and the drum casing. 
     SUMMARY 
     The disclosure therefore provides a method for operating a washing machine and of providing a washing machine having a non-ribbed drum in which the occurrence of rolling and/or sliding laundry when the drum is rotating can be detected, in particular at a rotational speed in the subcritical rotational speed range. 
     According to the disclosure, the problem we discovered in the prior art is solved by a method having the features of claim  1  and by a washing machine having the features of claim  10 . Advantageous embodiments and developments of the disclosure can be found in the subsequent sub-claims. 
     The advantages that can be achieved with the disclosure are that it offers an important prerequisite for the reliable operation of a washing machine having a non-ribbed drum. It protects the washing machine from destruction by detecting imbalances caused by rolling and/or sliding laundry, and thus also protects a user of the washing machine from getting hurt and protects the laundry washed in the washing machine from being damaged. The method therefore makes it possible to protect the washing machine and the laundry from damage. As a result of detected rolling and/or sliding laundry, appropriate actions can be executed that are stored in the washing machine to prevent or at least reduce damage. 
     The disclosure 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 inventors have discovered that laundry rolling and/or sliding in the drum differs from laundry lying in contact with the drum in that rolling and sliding laundry exerts impulses on the drum casing. These impulses cause a braking of the peripheral speed of the drum and thus cause a deviation or difference between the target and actual rotational speed of the drum. The control device preferably has a controller of the motor for driving the drum, which is designed such that the torque is increased when the actual rotational speed of the drum is less than the target rotational speed of the drum and is reduced when the actual rotational speed is greater than the target rotational speed. The above variable can therefore be used to determine whether the laundry is sliding and/or rolling in the drum. 
     A non-ribbed drum is a drum that does not have a rib or entraining element inside it. However, it can have other elevations and/or depressions that do not have the shape of the plate-shaped rib or entraining element. The drum, preferably the drum casing, preferably has depressions and/or elevations other than a rib. It preferably has stamped portions, each of which is designed as an elevation or depression. 
     The sampling preferably takes place at a predetermined frequency. The predetermined frequency for sampling is preferably high and is, for example, 100 Hz. 
     In a preferred embodiment, the variable relating to the torque of the motor or the rotational speed of the drum is the torque, a signal fluctuation correlating with the torque, the rotational speed, or a signal fluctuation correlating with the rotational speed. More preferably, the variable is the torque of the motor or the rotational speed of the drum. More preferably, the variable is the torque. 
     The determination of whether the laundry is sliding and/or rolling in the drum based on the variable sampled over the period of time preferably includes a frequency analysis, with which frequency components of the variable are determined in a predetermined frequency range. Frequency analysis can be used to determine in a simple manner which frequency components or portions are represented to what extent in the signal of the determined variable at different frequencies. The frequency analysis is preferably a Fast Fourier Transform (FTT). 
     In a preferred embodiment, 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 of the variable that are in the predetermined frequency range. This makes it easy to calculate a single value that is comparable to another value. The predetermined frequency range can be segmented. 
     When the rotational speed of the drum is greater than the contact rotational speed, the predetermined frequency range preferably comprises higher and lower frequencies than the rotational frequency of the drum, i.e., the predetermined frequency range excludes the rotational frequency of the drum and includes frequencies unequal to the rotational frequency of the drum. In addition to these impulses, which are caused by the rolling and/or sliding laundry on the drum casing, a fixed imbalance that occurs in practice and is applied to the drum at rotational speeds greater than the contact rotational speed at which a fixed imbalance is applied on the drum causes a difference between the actual and target rotational speeds, which is compensated by the controller of the motor by increasing and decreasing the torque. This embodiment is therefore based on the idea that the regulation of the variable as well as the torque to compensate for the fixed imbalance formed due to rotation at a speed greater than the contact rotational speed causes an oscillation of the torque at the rotational frequency of the drum, while the impulses of the rolling and sliding laundry cause oscillations of the torque that occur at higher or lower frequencies than the rotational frequency of the drum. 
     In a preferred embodiment, 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 when the determined value is greater than the limit value. If the determined value is greater than the limit value, then there is a loading situation where laundry is sliding and/or rolling, i.e., laundry is located in the drum and is sliding and/or rolling. If the determined value is less than or equal to the limit value, then there is a loading situation where laundry is not sliding and/or rolling, i.e., there is no sliding and/or rolling laundry located in the drum. 
     A plurality of limit values can also be stored in the washing machine, which depend, for example, on the rotational speed of the drum at which the variable is sampled over the predetermined period of time and/or depend on the load amount. The larger the load amount, the greater the problems described above where the laundry is sliding and/or rolling. Furthermore, a plurality of limit values can also be stored in the washing machine, which depend, for example, on the textile type to be subjected to the washing program, which is defined by the user adjusting the washing program when the washing program is started. Sliding and/or rolling is much more problematic for delicate laundry such as silk or wool than for less delicate laundry such as cotton laundry because the risk of damage due to friction between the textile and the drum casing is greater for delicate laundry. 
     If it is determined in the method according to the disclosure that a loading situation where laundry is rolling and/or sliding in the drum is present, predetermined actions that are stored in the washing machine are preferably executed to prevent or at least reduce the sliding and/or rolling of the laundry. 
     In a preferred embodiment, the rotation of the drum is stopped 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. Preferably, when the rotation of the drum is stopped, the rotational speed of the drum is set to 0 rpm, and after setting the rotation speed of the drum to 0 rpm, the drum can then be rotated again. For example, after the rotation of the drum has stopped, the rotational speed is subsequently increased to a rotational speed below the contact rotational speed at which the centrifugal force acting on the laundry is greater than the force of gravity. 
     Preferably, the predetermined period of time comprises one complete revolution of the drum or an integer multiple of the complete revolution of the drum. The predetermined period of time is preferably an integer multiple of the complete revolution. This allows errors to be minimized. Preferably, the integer multiple is in the range of from 2 to 20, more preferably from 3 to 10. For example, if the rotational speed of the drum is 120 rpm, which corresponds to two complete revolutions of the drum per second, then the predetermined period of time may be, for example, 3 seconds, such that it comprises six complete revolutions of the drum. However, the method can also be carried out at any rotational speed, wherein the predetermined period of time is adapted accordingly and is stored accordingly in the washing machine. The longer an item of laundry is sliding and/or rolling on the drum casing, the greater the risk that the textile will be damaged due to the friction between the textile and the drum casing. The predetermined period of time is therefore preferably in the period of time of a few seconds. 
     In a preferred embodiment, the rotational speed at which the drum is rotated in the method is above the contact rotational speed. In a preferred embodiment, the rotational speed is in the subcritical range, i.e., a range of from 70 to 149 rpm. More preferably, the rotational speed of the drum at which the drum is rotated in the method is in the range of from 120 to 149 rpm. In this range, the problem of sliding and/or rolling laundry occurs particularly frequently. It occurs just as often at lower rotational speeds. The reason for this speed range of 120-149 rpm is that the method works more reliably in this rotational speed range; the signals that can be evaluated are better (keyword: signal-to-noise ratio). 
     The disclosure further relates to 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 that is designed and set up to execute a method according to one or more of the embodiments described above. 
     Embodiments and advantages described for the method apply correspondingly to the washing machine and vice versa. 
     The washing machine can be a front loader or a top loader. The term “washing machine” also comprises a combination device such as a washer-dryer. The drum is preferably mounted in the suds container so that it can rotate horizontally. 
     The control device can be designed in one or more parts. In addition to regulating the rotational speed of the motor for driving the drum, it has other open or closed loop control means that are required to execute the washing program. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the disclosure is shown in the drawings in a purely schematic manner and will be described in more detail below. In the drawings: 
         FIG.  1    shows a curve of a torque of the motor over a predetermined period of time in a method according to the disclosure where laundry is or is not sliding and/or rolling; and 
         FIG.  2    shows the torque of the motor shown in  FIG.  1    as a function of frequency sampled over the predetermined period of time where laundry is or is not sliding and/or rolling. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG.  1    shows a curve of a torque of the motor over a predetermined period of time in a method according to the disclosure where laundry is or is not sliding and/or rolling. 
     The method according to the disclosure is 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 motor torque over a predetermined period of time; and 
     determining whether the laundry is sliding and/or rolling in the drum based on the torque sampled over the period of time. 
       FIG.  1    shows the time signal curve of the torque at a rotational speed of the drum of 120 rpm. The predetermined period of time is 3 seconds during which the drum completes six revolutions at two revolutions per second. 
     In the case of the solid line, the laundry lies completely in contact with the drum casing, so that the drum is free of rolling and/or sliding laundry, and a fixed imbalance has developed. This fixed imbalance causes the control of the motor per drum revolution to increase the torque relative to an average value when increasing the fixed imbalance causes a braking of the rotational speed and to decrease it relative to a mean value when decreasing the fixed imbalance causes an acceleration of the rotational speed. The torque waveform for the drum with fixed imbalance and where laundry is sliding and/or rolling in the drum, and where it does not completely contact the drum casing, as shown by the dashed line, differs from the torque waveform for the drum where laundry is not rolling and/or sliding in the drum. 
       FIG.  1    substantially reproduces the signal curve of the sampled torque over the predetermined period of time. The determination of whether the laundry is sliding and/or rolling in the drum based on the torque sampled over the period of time is explained in more detail in connection with  FIG.  2   . 
       FIG.  2    shows the torque of the motor shown in  FIG.  1    as a function of frequency sampled over the predetermined period of time where laundry is or is not sliding and/or rolling. The torques sampled over the predetermined period of time shown in  FIG.  1    have been subjected to an FFT, resulting in the spectrum shown in  FIG.  2   . The oscillation on the time signal of the torque caused by the fixed imbalance takes place at the rotational frequency of the drum as shown by the solid line. However, the signal of the torque having fixed imbalance and sliding and/or rolling laundry, as represented by the dashed line, also has frequency components or oscillation components which are different from the rotational frequency of the drum in comparison with the signal of the solid line. 
     These frequency components or portions are visible in  FIG.  2    in the frequency range of between approximately 0.5 and 1.5 Hz marked with the reference sign  1  and in the frequency range of from approximately 2.5 Hz marked with the reference sign  2 . Both loading situations, i.e., loading where laundry is or is not sliding and/or rolling, have a constant component at 0 Hz, which corresponds to the average torque for overcoming the friction in the overall system. The position of the frequency range marked with the reference sign  2  can depend on the geometric shape of the drum and the geometric shape of the sliding and/or rolling laundry. 
     Determining whether the laundry is sliding and/or rolling is executed in the method according to the disclosure explained with reference to  FIGS.  1  and  2    in that all frequency components of the torque at frequencies between, for example, 0.5 and 1.5 Hz and above 2.5 Hz are summed up, so that a value is determined, wherein, for example, a calculation method of effective value formation, in which all frequency components in the specified frequency ranges are squared and summed up and then their square root is formed, is equivalent. A limit value is predetermined for each of these calculation methods and stored in the washing machine. If the determined value is greater than the limit value, then this is a loading situation where laundry is rolling and/or sliding. If the determined value is less than or equal to the limit value, this is a loading situation where laundry is not rolling and/or sliding.