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.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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:

[0029] 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

[0030] 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

[0031] 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.

[0032] 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,

[0033] sampling a motor torque over a predetermined period of time; and

[0034] determining whether the laundry is sliding and/or rolling in the drum based on the torque sampled over the period of time.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.