Method of operating an automatic washing machine and automatic washing machine

Abstract

The invention relates to a method for operating a washing machine comprising an outer tub for receiving a washing liquid, a rib-free drum (7) which is rotatably mounted in the outer tub and which is embossed (1-6) for receiving laundry, a motor for driving the drum (7), and a regulating device. The method has the following steps which are carried out while the drum (7) is being rotated in a sub-critical rotational speed range: sampling a variable, which relates to the drum (7) or the motor, over a specified period of time in order to determine time signals of the variable; carrying out a frequency analysis of the time signal of the variable in order to ascertain frequency components of the variable in a specified frequency range; adding the frequency components at specific frequencies of the specified frequency range; and on the basis of the sum of the added frequency components, detecting whether the drum exhibits a loading situation with sliding laundry. The invention additionally relates to a corresponding washing machine.

Description

[0001] The invention relates to a method for operating a washing machine and a washing machine itself. In particular, the invention relates to a method for operating a washing machine and a washing machine with a ribless drum.

[0002] Generic processes are known from EP 2 143 837 A1, US 2013 / 160216 A1, EP 3 412 823 A1, EP 3 453 795 A1, WO 2020 / 046076 A1 and EP 2 463 433 A2.

[0003] Washing machine drums typically have ribs inside. A rib, also known as a drum wheel, is a part of the drum that, as the drum rotates, sets the laundry inside in motion, i.e., pulls it along. The rib is usually a plate inside the drum against which the laundry gets caught as the drum rotates, up to a certain height, and then falls back down, thus being agitated and redistributed. There are usually several ribs in the drum, spaced at predetermined intervals. The ribs are essential for redistributing the laundry during a wash cycle. However, the ribs are additional components that increase costs. Therefore, a ribless drum would be preferable.

[0004] During the development of a washing machine with a ribless drum, it became apparent that some laundry loads do not rest against the drum wall but slide around due to the lack of ribs. This is particularly problematic when the sliding laundry weighs 1 kg or more and is disturbed by an obstruction, such as the drum base, the door viewing window, or other items inside the drum, causing it to press against the drum wall. This creates a sudden imbalance, which, due to its size, can cause the drum assembly to strike the washing machine's housing and potentially shift the entire machine. In extreme cases, this can destroy the washing machine. Furthermore, this sliding motion is problematic for delicate fabrics.The longer a piece of laundry slides on the drum shell, the greater the risk that the textile will be damaged due to friction between the textile and the drum shell.

[0005] The invention thus addresses the problem of providing a method for operating a washing machine and a washing machine with a ribless drum, in which the occurrence of laundry slipping when the drum is turned can be detected, particularly in the subcritical speed range.

[0006] According to the invention, this problem is solved by a method with the features of claim 1 and a washing machine with the features of claim 10. Advantageous embodiments and further developments of the invention are described in the following dependent claims.

[0007] The advantages achievable with the invention lie in the fact that it provides an important prerequisite for the safe operation of a washing machine with a ribless drum. It protects the washing machine from damage by detecting imbalances caused by shifting laundry, thereby also protecting the user of the washing machine and the laundry being washed from damage. The method thus makes it possible to protect both the washing machine and the laundry from damage. As a result of detected shifting laundry, a predetermined measure, stored in the washing machine, can be implemented to prevent or at least reduce damage.

[0008] The invention relates to a method for operating a washing machine with a tub for holding washing liquid, a ribless, embossed drum rotatably mounted in the tub for holding laundry, a motor for driving the drum and a control device, comprising the following steps during rotation of the drum in a subcritical speed range Scanning a quantity relating to the drum or motor over a predetermined period to determine time signals of the quantity; performing a frequency analysis of the time signal of the quantity to determine frequency components of the quantity 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 frequency components, whether the drum has a loading situation with shifting laundry.

[0009] The invention is based on the fundamental idea that when laundry slides over a raised area, the drum experiences a force impulse, albeit a potentially small one. This causes the drum to slow down. The control unit compensates for this braking action with a motor control system by briefly increasing the motor's torque. This oscillation of the motor torque is repeated each time the laundry slides over a raised area. Therefore, by sensing the parameters related to the drum or the motor and evaluating them using frequency analysis, it is possible to detect whether the drum is loaded with laundry that is sliding.

[0010] A ribless drum is a drum that has no rib or driver inside. However, it has other raised areas and / or depressions, such as embossing or indentations, which do not have the shape of a plate-like rib or driver.

[0011] For a loading situation to involve shifting laundry, it is not necessary for all the laundry to shift within the drum; it is sufficient if some of the laundry shifts. A loading situation without shifting laundry is preferably present when all the laundry is in contact with the drum wall.

[0012] Sampling is preferably performed at a predetermined frequency. Preferably, the predetermined sampling frequency is high and is, for example, 100 Hz.

[0013] According to the invention, the physical quantity relating to the drum or the motor is a torque of the motor or a quantity correlated with the torque of the motor. Alternatively, and preferably, the physical quantity relating to the drum or the motor is an actual rotational speed of the drum or a quantity correlated with the actual rotational speed. More preferably, the quantity is the torque of the motor or the actual rotational speed of the drum. Even more preferably, the quantity is the torque.

[0014] In a preferred embodiment, the washing machine detects that the drum is experiencing a loading situation with shifting laundry when the sum of the summed frequency components exceeds a predetermined limit. Preferably, the predetermined limit is stored in the washing machine. Therefore, the method preferably further includes a comparison of the sum of the summed frequency components with the predetermined limit.

[0015] The washing machine may also have several preset limits, which, for example, depend on the drum's rotational speed at which the size is measured over a predetermined period, and / or on the load size. The larger the load, the more pronounced the aforementioned problems with laundry shifting become. Furthermore, the washing machine may also have several preset limits, each depending, for example, on the type of fabric being washed, which is defined by the user when selecting the wash program. Shifting is significantly more problematic for delicate fabrics like silk or wool than for less delicate fabrics like cotton, because the risk of damage due to friction between the fabric and the drum is greater.

[0016] If it is detected that the drum is loaded with shifting laundry, a predetermined action is preferably carried out. It is preferably decided that the predetermined action is carried out if the sum of the summed frequency components is greater than the predetermined limit.

[0017] In a preferred embodiment, the predetermined measure is a redistribution of the laundry in the drum or a continuation of the rotation of the drum at a drum speed that is below the subcritical speed range.

[0018] Redistributing the laundry can be achieved by stopping the drum's rotation. In a preferred embodiment, the drum's rotation is stopped when it is detected that the drum contains laundry that is rolling around. When the drum's rotation is stopped, the drum's speed is preferably set to 0 rpm. After this setting, the drum can then be rotated again, for example, in the opposite direction to the direction in which it was rotating before the rotation was stopped. For example, after the drum's rotation has stopped, the speed is subsequently increased to a speed below the initial spin speed, at which the centrifugal force acting on the laundry is greater than gravity. This avoids the need for a further spin cycle.

[0019] Alternatively, redistribution of the laundry can be achieved by continuing the drum's rotation in a pendulum motion. In another preferred embodiment, the drum's rotation continues in a pendulum motion when it is detected that the drum contains a load of rolling laundry. When the drum's rotation continues in a pendulum motion, the motor sets the drum into a right-left movement, causing the laundry to oscillate at a predetermined frequency. As a result, the drum does not complete a full rotation but oscillates from left to right and vice versa. The pendulum motion is executed in such a way that redistribution of the laundry is achieved, for example, by creating a tumble of laundry within the drum.

[0020] Alternatively, the predetermined measure can be to continue rotating the drum at a speed below the subcritical speed range. This prevents the laundry from being spun. This can at least reduce the deflection of the drum assembly compared to a spin cycle.

[0021] If the sum of the frequency components is less than or equal to the predetermined limit, it is preferably detected that the drum has a loading situation without shifting laundry. If it is detected that the drum has a loading situation without shifting laundry, the washing program is preferably continued without performing the predetermined action.

[0022] The drum, preferably the drum shell, has embossings or indentations other than ribs. Preferably, these embossings or indentations are formed as a depression and / or a raised area. More preferably, the drum, especially the drum shell, has honeycomb or circular patterns, each formed as a raised area or depression. The number of embossings is preferably between 2 and 20, more preferably between 4 and 10.

[0023] In a preferred embodiment, the predetermined period comprises an integer number of drum revolutions. Preferably, the predetermined period comprises one complete drum revolution or an integer multiple of a complete drum revolution. More preferably, the predetermined period comprises an integer multiple of a complete revolution. This minimizes errors. Preferably, the integer multiple is in the range of 2 to 20, more preferably 3 to 10. For example, if the drum speed is 120 rpm, which corresponds to two complete drum revolutions per second, then the predetermined period can be, for example, 3 seconds, thus comprising six complete drum revolutions.

[0024] However, the process can also be carried out at any desired rotational speed, with the predetermined time period adjusted accordingly and stored in the washing machine. The longer a garment slides on the drum, the greater the risk of damage to the fabric due to friction between the fabric and the drum. Therefore, the predetermined time period is preferably a few seconds. More preferably, the predetermined time period is in the range of 1 to 15 seconds. More preferably, the predetermined time period is in the range of 2 to 10 seconds. Even more preferably, the predetermined time period is in the range of 3 to 5 seconds.

[0025] Preferably, the predetermined frequencies are harmonic. If all frequency components of the harmonic frequencies are added or summed, depending on the drum's rotational speed during scanning and the number of indentations in the drum shell, the sum is determined, which can be used to identify whether the drum has a loading situation with shifting laundry.

[0026] The rotational speed at which the drum is to be turned during the process is in the subcritical range. Preferably, the target rotational speed is higher than the contact speed at which the laundry should be in contact with the drum shell. At a target rotational speed of 70 min⁻¹, the laundry is typically in contact with the drum shell. The subcritical rotational speed range is therefore preferably a range with target rotational speeds of 70 min⁻¹ or higher. The subcritical rotational speed range is preferably in the range of 70 to 149 min⁻¹. Preferably, the target rotational speed of the drum, at which the drum is to be turned during the process, is in the range of 120 to 149 min⁻¹. In this range, the problem of laundry slipping occurs particularly frequently. The target rotational speed is preferably kept constant during the size sensing process.

[0027] The actual drum speed can deviate from the target speed depending on the degree of imbalance. At actual speeds above approximately 70 rpm, the laundry is usually in contact with the drum shell. Since, in practice, the laundry is never distributed completely evenly across the drum shell, an imbalance of varying magnitude develops depending on the distribution of the laundry. This imbalance causes a sinusoidal actual speed signal that fluctuates slightly around the target speed. If the imbalance mass needs to be increased, the drum rotation speed slows down. The motor control compensates for this by increasing the motor torque. Once the drum has rotated another half turn, the imbalance mass assists the rotation. The drum then rotates slightly faster than the set target speed. The torque must be reduced to decrease the actual speed.This oscillation of the actual rotational speed occurs once per drum revolution and is very uniform, since the determining physical quantities, such as the unbalance mass, lever arm, and drum speed, do not change. Just like the drum's rotational speed, the torque required to drive the drum also exhibits a uniform sinusoidal curve. In a preferred embodiment, the motor torque is increased when the actual drum speed is lower than the target drum speed and decreased when the actual drum speed is higher than the target drum speed.

[0028] Frequency analysis is preferably based on a Fourier transform, or more preferably an FFT (Fast Fourier Transform). The FFT offers an efficient calculation method.

[0029] The invention further relates to a washing machine with a tub for receiving washing liquid, a ribless drum rotatably mounted in the tub for receiving laundry, a motor for driving the drum and a control device which is designed and configured to carry out a method according to one of the preceding claims.

[0030] The embodiments and advantages described for the method apply accordingly to the washing machine and vice versa.

[0031] A washing machine can be a front loader or a top loader. The term "washing machine" also includes combination appliances such as washer-dryers. The drum is preferably mounted horizontally within the tub so that it can rotate freely.

[0032] The control unit can be a single component or consist of multiple parts. In addition to controlling the motor speed to drive the drum, it includes other controls or regulators required to execute the washing program.

[0033] An embodiment of the invention is shown purely schematically in the drawings and is described in more detail below. It shows Fig. 1 a development of a drum of a washing machine according to the invention; Fig. 2 a partial curve of a torque in temporal sequence; Fig. 3 the in Fig. 2 The motor torque, sampled over a predetermined period, is shown as a function of frequency.

[0034] Fig. 1 shows a development of a drum of a washing machine according to the invention. In particular, shows Fig. 1 The development of the drum 1 with depth t and circumference u. The drum 1 has several – six by way of example – embossings 1, 2, 3, 4, 5, 6. The embossings 1, 2, 3, 4, 5, 6 can each be formed as a raised or recessed area in the drum 1.

[0035] The washing machine (not shown) with a tub (not shown) for holding washing liquid (not shown), the ribless, embossed (1-6) bearing, rotatably mounted in the tub, in Fig. 1 The drum 7 shown in the diagram, for holding laundry (not shown), a motor (not shown) for driving the drum 7 and a control device (not shown), is designed to carry out the method according to the invention, comprising the following steps during a rotation of the drum 7 in a subcritical speed range Scanning a quantity relating to the drum 7 or the motor over a predetermined period to determine time signals of the quantity; performing a frequency analysis of the time signal of the quantity to determine frequency components of the quantity 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 frequency components, whether the drum has a loading situation with shifting laundry.

[0036] The control device includes a control of the motor that drives drum 7.

[0037] If, during the process, drum 7 is connected to the Fig. 1 Using the surface structure shown, for example, a subsequent signal evaluation of the motor's torque is carried out to determine whether the laundry is slipping.

[0038] Three scenarios are distinguished regarding how the shifting laundry can arrange itself in drum 7. In the first scenario, the shifting laundry covers embossings 1 and 2; in the second scenario, embossings 1, 2, 3, and 4; and in the third scenario, all embossings 1-6. The preferred operating mode for drum 7 to detect shifting laundry is a constant rotational speed above the initial loading speed of approximately 70 rpm, for example, 120 rpm. If there is no shifting laundry, i.e., all the laundry is in contact with the drum shell, a fixed imbalance is typically present due to the uneven distribution of the laundry, the magnitude of which depends arbitrarily on the laundry distribution. This fixed imbalance creates a fluctuation in the motor torque with the drum rotation frequency, since for each drum revolution the motor torque increases once to raise the fixed imbalance, and decreases once when the fixed imbalance drops again after a 180° rotation.

[0039] When laundry slides over an indentation 1-6, the drum 7 experiences a relatively small force impulse. The drum 7 is decelerated. This deceleration is compensated for by the motor's control system by briefly increasing the motor torque. This oscillation of the motor torque repeats with each time the laundry slides over an indentation 1-6. Therefore, per drum revolution, the laundry slides over the indentation 1-6 twice in the first case described above, four times in the second case, and six times in the third case, generating an increase in the motor torque. This sliding can be analyzed by frequency analysis, e.g., using Fast Fourier Transform (FFT), of the motor torque time signal, according to the following... Fig. 2 und 3 which are recognized or detected and are explained in more detail below.

[0040] Are all frequency components present in the harmonic frequencies, such as in Fig. 3 The values ​​shown, summed, or added together, which depend on the drum's rotational speed, the number of indentations on the drum surface, and the overlap of the shifting laundry with these indentations, result in a sum that can be used to infer the case of shifting laundry, thus making it detectable. The first, second, and third cases do not need to be explicitly distinguished, as all cases are always considered in the sum. A predetermined threshold for this value can be stored in the washing machine, so that if the sum is greater than the predetermined threshold, the case of shifting laundry is inferred, and it is recognized that the drum is loaded with shifting laundry.This information, in turn, can be used during the washing process to decide whether to implement a predetermined action to protect the laundry from wear and tear and / or the washing machine from damage. This predetermined action could, for example, involve redistributing the laundry or continuing the washing process without spinning.

[0041] Fig. 2 shows a partial curve of a torque in temporal sequence. The method according to the invention is used with the washing machine of the in Fig. 1 performed on the drum shown. Fig. 2 This shows the time-dependent signal waveform of the torque at a drum speed of 120 min⁻¹ (2 Hz). The predetermined period is 3 seconds, during which the drum completes six full rotations at two revolutions per second. The sampling rate is 100 Hz for illustrative purposes only.

[0042] In the case of the solid line, the laundry lies completely against the drum shell, so that the drum has a loading situation without any shifting laundry, and a fixed imbalance has formed. This fixed imbalance ensures that the motor control increases the torque relative to a mean value for each drum revolution when raising the fixed imbalance causes the actual speed to decrease, and decreases it relative to a mean value when lowering the fixed imbalance causes the actual speed to increase.

[0043] This fixed imbalance generates a sinusoidal actual speed signal that fluctuates slightly around the target speed. If the imbalance mass needs to be increased, the drum's rotational speed slows down. The motor control compensates for this by increasing the motor's torque. Once the drum has completed half a revolution, the fixed imbalance, through its mass, assists the rotation. The drum then rotates slightly faster than the specified target speed. The torque must be reduced to decrease the actual speed. This oscillation of the actual speed occurs once per drum revolution and is very consistent because the determining physical parameters, such as the fixed imbalance mass, lever arm, and drum speed, remain constant.Just like the rotational speed of the drum, the torque required to drive the drum also exhibits a uniform sinusoidal curve in the case of a loading situation with fixed imbalance and without slipping laundry.

[0044] The signal curve of the torque for the drum with fixed imbalance and slipping laundry, where the laundry does not fully rest against the drum shell but slips over one or more embossings 1-6, as shown by the dashed line, differs from the signal curve of the torque for the drum with the loading situation without slipping laundry.

[0045] Fig. 2 Essentially, it represents the signal curve of the sampled torque over the predetermined period. This is in Fig. 2 The determined time signal of the torque is subjected to a frequency analysis, which leads to the result in Fig. 3 The spectrum shown is shown.

[0046] Fig. 3 This shows in Fig. 2 The motor torque, sampled over a predetermined period, is shown as a function of frequency. The in Fig. 2 The torques shown, sampled over the predetermined period, were subjected to an FFT, resulting in the following: Fig. 3 The spectrum shown is produced. The predetermined frequency range is 0 to 15 Hz.

[0047] In the case of a laundry load that is fully in contact with the drum shell and where a fixed imbalance has formed but no shifting laundry has developed, the FFT results in a frequency component at 0 Hz, which corresponds to the DC component of the motor's torque. This is the average motor torque required to overcome friction in the system, such as bearing friction. The frequency component at 2 Hz is caused by the rotational-frequency torque oscillation of the fixed imbalance. Higher frequency components do not exist, or only to a negligible extent, in the loading situation without shifting laundry. In contrast, if the first case described above occurs, in which shifting laundry slides over the indentations 1 and 2, a torque oscillation with two pulses per revolution, or at a speed of 120 min⁻¹ < four pulses per second, is generated.The frequency analysis reveals an additional frequency component at 4 Hz and their harmonic multiples, in addition to the components at 0 Hz (friction component) and 2 Hz (fixed imbalance component). The second case described above, in which slipping laundry slides over embossings 1-4, generates further frequency components at 4, 8, and 12 Hz. The third case described above, in which slipping laundry slides over embossings 1-6, generates a further frequency component at 12 Hz. Reference symbol list

[0048] Depth and circumference 1-6, one embossing each, 7 drum

Claims

1. Method for operating a washing machine comprising a suds container for receiving washing liquid, a drum (7), which is rotatably mounted in the suds container, for receiving laundry, a motor for driving the drum (7), and a control device, comprising the following steps during a rotation of the drum (7) in a subcritical rotational speed range - sampling a variable relating to the drum (7) or the motor over a predetermined time frame to determine time signals of the variable; - carrying out 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; characterised in that the drum is rib-free and provided with impressions (1-6), and a step of detecting, depending on the sum of the summed frequency components, whether the drum has a loading situation with sliding laundry, and in that the physical variable relating to the drum (7) or the motor is a torque of the motor or a variable correlating to the torque of the motor or an actual rotational speed of the drum (7) or a variable correlating to the actual rotational speed.

2. Method according to any of the preceding claims, characterised in that it is detected that the drum has a loading situation with sliding laundry if the sum of the summed frequency components is greater than a predetermined threshold value.

3. Method according to any of the preceding claims, characterised in that in the event that it is detected that the drum has a loading situation with sliding laundry, a predetermined measure is further carried out, the predetermined measure being a redistribution of the laundry in the drum (7) or a continuation of the rotation of the drum (7) at a rotational speed of the drum (7) which is below the subcritical rotational speed range.

4. Method according to any of the preceding claims, characterised in that the impressions (1-6) are each formed as a depression and / or an elevation.

5. Method according to any of the preceding claims, characterised in that the predetermined time frame comprises an integer number of revolutions of the drum (7).

6. Method according to any of the preceding claims, characterised in that the predetermined frequencies are harmonic.

7. Method according to any of the preceding claims, characterised in that the drum is rotated at a constant rotational speed in the subcritical rotational speed range.

8. Method according to any of the preceding claims, characterised in that the frequency analysis is a fast Fourier transform.

9. Washing machine comprising a suds container for receiving washing liquid, a rib-free drum (7), which is rotatably mounted in the suds container, for receiving laundry, a motor for driving the drum (7), and a control device which is designed and configured to carry out a method according to any of the preceding claims.

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