Method for operating a washing machine, and washing machine

Abstract

A washing machine and method for operating a washing machine having a suds container for holding washing liquid, a non-ribbed drum provided with stamped portions rotatably mounted in the suds container for holding laundry, a motor for driving the drum, and a control device. During rotation of the drum in a subcritical rotational speed range, the method includes sampling a variable related to the drum or the motor over a predetermined period of time to determine time signals of the variable, executing a frequency analysis of the time signal of the variable to determine frequency components of the variable in a predetermined frequency range, summing the frequency components at predetermined frequencies of the predetermined frequency range, and detecting, depending on the sum of the summed up frequency components, whether a loading situation where laundry is sliding in the drum is present.

Claims

1. A method for operating a washing machine having a suds container for holding washing liquid, a non-ribbed drum provided with a plurality of stamped portions rotatably mounted in the suds container for holding laundry, a motor for driving the drum, and a control device, said method, during rotation of the drum in a subcritical rotational speed range, comprising the following steps: sampling a variable related to the drum or the motor over a predetermined period of time to determine time signals of the variable, the variable being a torque of the motor or correlating with the torque of the motor, or an actual rotational speed of the drum or correlating with the actual rotational speed; executing a frequency analysis of the time signal of the variable to determine frequency components of the variable in a predetermined frequency range; summing the frequency components at predetermined frequencies of the predetermined frequency range; and detecting, depending on the sum of the summed up frequency components in relation to a quantity and arrangement of the plurality of stamped portions, whether a loading situation where laundry is sliding in the drum is present.

2. The method according to claim 1, wherein a loading situation where laundry is sliding in the drum is detected when the sum of the added frequency components is greater than a predetermined limit value.

3. The method according to claim 1, wherein, if a loading situation where laundry is sliding in the drum is detected, a predetermined action is further executed, wherein the predetermined action is a redistribution of the laundry in the drum or a continuation of the rotation of the drum at a rotational speed of the drum which is below the subcritical rotational speed range.

4. The method according to claim 1, wherein the stamped portions are each designed as a depression and/or an elevation.

5. The method according to claim 1, wherein the predetermined period of time comprises an integer number of revolutions of the drum.

6. The method according to claim 1, wherein the predetermined frequencies are harmonic.

7. The method according to claim 1, wherein the drum is rotated at a constant rotational speed in the subcritical rotational speed range.

8. The method according to claim 1, wherein the frequency analysis is a Fast Fourier Transform.

9. 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 a method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 shows a development of a drum of a washing machine according to the disclosure;

(3) FIG. 2 shows a partial curve of a torque in a time sequence; and

(4) FIG. 3 shows the torque of the motor shown in FIG. 2 as a function of the frequency sampled over the predetermined period of time.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) FIG. 1 shows a development of a drum of a washing machine according to the disclosure. FIG. 1 shows in particular the development of the drum 1 with the depth t and the circumference u. The drum 1 has a plurality offor example sixstamped portions 1, 2, 3, 4, 5, 6. The stamped portions 1, 2, 3, 4, 5, 6 can each be designed as an elevation or depression in the drum 1.

(6) The washing machine (not shown) having a suds container (not shown) for holding washing liquid (not shown), the non-ribbed drum 7 which is provided with stamped portions 1-6, shown in development in FIG. 1 and which is rotatably mounted in the suds container for holding laundry (not shown), a motor (not shown) for driving the drum 7, and a control device (not shown), is designed to execute the method according to the disclosure, said method, during rotation of the drum 7 in a subcritical rotational speed range, comprising the following steps: sampling a variable related to the drum 7 or the motor over a predetermined period of time to determine time signals of the variable; executing a frequency analysis of the time signal of the variable to determine frequency components of the variable in a predetermined frequency range; summing the frequency components at predetermined frequencies of the predetermined frequency range; detecting, depending on the sum of the summed up frequency components, whether a loading situation where laundry is sliding in the drum is present.

(7) The control device has a control of the motor that drives the drum 7.

(8) If the drum 7 having the surface structure shown in FIG. 1 is used in the method, a subsequent signal evaluation of the motor torque is executed, for example, in order to be able to conclude that the laundry is sliding.

(9) A distinction is made in this case between three cases of how the sliding laundry can arrange itself in the drum 7. In a first case, the sliding laundry covers stamped portions 1 and 2; in a second case, stamped portions 1, 2, 3, and 4; and in a third case, all stamped portions 1-6. The preferred mode of operation of the drum 7, in order to detect sliding laundry, is a constant rotational speed above the contact rotational speed of approximately 70 rpm, for example 120 rpm. If there is no sliding laundry, i.e. the entire laundry is in contact with the drum casing, there is usually a fixed imbalance due to the uneven distribution of the laundry, the magnitude of which depends arbitrarily on the laundry distribution. This fixed imbalance produces a variation in motor torque with a rotational frequency of the drum, since the motor torque increases once per drum revolution to increase the fixed imbalance and decreases once when the fixed imbalance decreases again after 180 rotation.

(10) If laundry slides over a stamped portion 1-6, the drum 7 experiences a relatively small force impulse. The drum 7 is braked. This braking is compensated for by the motor control in such a way that the motor torque briefly increases. This oscillation of the motor torque is repeated with each sliding of the laundry over a stamped portion 1-6. In the first case described above, the laundry slides twice per drum revolution, four times in the second case, and six times in the third case per drum revolution over the stamped portions 1-6 and generates an increase in the motor torque. This sliding can be recognized or detected by a frequency analysis, for example by Fast Fourier Transform (FFT) of the time signal of the motor torque, according to the following FIGS. 2 and 3, which are explained in more detail below.

(11) If all frequency components at the harmonic frequencies, as shown for example in FIG. 3, are summed up, which depend on the rotational speed of the drum and the number of stamped portions in the drum surface and the overlapping of the sliding laundry with the stamped portions, a sum is obtained with the help of which the situation where laundry is sliding in the drum is deduced, i.e. it becomes detectable. The first, second, and third cases do not have to be explicitly differentiated, since all cases are always taken into account in the cumulative value. A predetermined limit value for this variable can be stored in the washing machine, so that, if the total is greater than the predetermined limit value, sliding laundry is inferred and a loading situation where laundry is sliding in the drum is detected. This finding can in turn be used during the execution of a washing program in the washing process to decide that a predetermined action is to be executed in order to protect the laundry from wear and/or the washing machine from damage. This predetermined action can consist, for example, in redistributing the laundry or continuing the washing process without spinning.

(12) FIG. 2 shows a partial curve of a torque in a time sequence. The method according to the disclosure is executed with the washing machine of the drum shown in FIG. 1. FIG. 2 shows the time signal curve of the torque at a drum rotational speed of 120 rpm (2 Hz). The predetermined period of time is 3 seconds during which the drum completes six revolutions at two revolutions per second. The sampling is 100 Hz only as an example.

(13) In the case of the solid line, the laundry lies completely in contact with the drum casing, so that a loading situation where laundry is not sliding in the drum is present, 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 actual rotational speed, and to decrease it relative to a mean value, when decreasing the fixed imbalance causes an acceleration of the actual rotational speed.

(14) This fixed imbalance causes a sinusoidal actual rotational speed signal that fluctuates slightly around the value of a target rotational speed. If the imbalanced mass has to be raised, the rotational speed of rotation of the drum slows down. The motor control compensates for this by increasing the motor torque. If the drum has rotated by half a revolution, the fixed imbalance supports the rotational motion with its mass. The drum rotates slightly faster than the specified target rotational speed. Torque must be reduced to reduce actual rotational speed. This oscillation of the actual rotational speed occurs once per drum revolution and is very even, since the physical variables that determine it, such as fixed imbalance mass, lever arm, and drum rotational speed, do not change. Just like the rotational speed of the drum, the torque required to drive the drum also has a uniform sinusoidal curve in the case of a loading situation with a fixed imbalance and where laundry is not sliding in the drum.

(15) The torque waveform for the drum with fixed imbalance and where laundry is sliding in the drum and does not completely contact the drum casing but rather slides over one or more stamped portions 1-6, as shown by the dashed line, differs from the torque waveform for the loading situation where laundry is not sliding in the drum.

(16) FIG. 2 substantially reproduces the signal curve of the sampled torque over the predetermined period of time. The time signal of the torque determined in FIG. 2 is subjected to a frequency analysis which results in the spectrum shown in FIG. 3.

(17) FIG. 3 shows the torque of the motor shown in FIG. 2 as a function of frequency sampled over the predetermined period of time. The torques sampled over the predetermined period of time shown in FIG. 2 have been subjected to an FFT, resulting in the spectrum shown in FIG. 3. The predetermined frequency range is 0 to 15 Hz.

(18) In the case of a load of laundry that is completely in contact with the drum casing and where there is a fixed imbalance but no sliding laundry has formed, the FFT results in a frequency component at 0 Hz, which corresponds to the DC component of the motor torque. This is the average motor torque needed to overcome friction, such as bearing friction, in the system. The frequency component at 2 Hz is caused by the rotational speed-frequency torque oscillation of the fixed imbalance. In a loading situation where laundry is not sliding in the drum, no higher frequency components exist in the loading situation, or they exist only to a negligible extent. If, on the other hand, the first case described above is present, where sliding laundry slides over the stamped portions 1 and 2, a torque oscillation with two pulses per revolution or, at a rotational speed of 120 rpm, with four pulses per second is caused. In this case, the frequency analysis shows a frequency component in addition to the components at 0 Hz (friction component) and 2 Hz (fixed imbalance component) at 4 Hz and their harmonic multiple frequencies. The second case described above, where sliding laundry slides over stamped portions 1-4, generates further frequency components at 4, 8, and 12 Hz; the third case described above, where sliding laundry slides over stamped portions 1-6, also generates an additional frequency component at 12 Hz.

LIST OF REFERENCE SIGNS

(19) t Depth u Circumference 1-6 One stamped portion each 7 Drum