US20140215725A1 - Methods of operating washing machines and washing machines using the same - Google Patents

Abstract

Example methods of determining the degree of satellization of laundry articles against an inner wall of a drum of a laundry treating appliance are disclosed. An example method of operating a laundry treating appliance having a rotatable drum defining a treating chamber for receiving laundry for treatment, and a motor rotating the drum includes increasing the rotational speed of the drum by increasing the rotational speed of the motor, and detecting when a parameter signal representing the rotation of the drum reaches substantially a minimum to determine the speed at which substantially all of the laundry is satellized.

Description

RELATED APPLICATION
• This application claims priority from European Patent Application No. 13154334.0 filed on Feb. 7, 2013, the entirety of which is incorporated herein.
FIELD OF THE DISCLOSURE
• This disclosure relates generally to washing machines and, more particularly, to determining the degree of satellization of laundry articles against an inner wall of a drum.
BACKGROUND
• A known method is described in EP 2379786, where the measured parameter (e.g., a measurement variable or a control variable) has a harmonic oscillation produced by an imbalance. This known method requires a complex comparison between a theoretical sinusoidal oscillation of the parameter and the actual oscillation, so as to determine the degree of the satellization of the laundry articles against the inner wall of the drum on the basis of the correlation. This known method requires a complex algorithm capable of carrying out such a correlation. Moreover, the degree of the satellization of the laundry articles against the inner wall of the drum, i.e., the percentage of load retained in a substantially fixed position relative to the drum by centrifugal force, may be considered too rich of information for the actual purpose of washer control, because what matters is only the speed at which all clothes in the drum of the washing machine are stuck to the side wall of the drum by means of the centrifugal force effect. At this speed, or at a speed incremented by a predetermined value with reference to this speed, the unbalance determination can be safely and quickly carried out without the need of reaching a fixed predetermined value as in prior-art washing machines (i.e. saving cycle time and energy). Moreover, carrying out imbalance detection at a speed identical or very close to the actual speed at which laundry is retained in a fixed position relative to the drum by centrifugal force has advantages also in view of the accuracy and robustness of unbalance detection.
SUMMARY
• In view of the above, this disclosure provides simple, reliable and inexpensive methods to detect the speed at which laundry is retained in a substantially fixed position relative to the drum by centrifugal force, so that substantially no portion of load is allowed to tumble.
• According to this disclosure, the above objects are reached thanks to the features listed in the appended claims.
• In this disclosure, any signal related to the energy of the motor system, particularly torque or power thereof, is monitored during an acceleration phase and the speed at which laundry articles are satellized against the side wall of the drum due to centrifugal force is detected when said signal reaches substantially a minimum.
• One advantage of the methods disclosed herein is that complexity is dramatically reduced. Moreover, because the disclosed methods are based on the physical behavior of the laundry inside the drum (mechanical energy balance), the disclosed methods are calibration free with respect to machine type/model variation. That is, no additional effort is required to calibrate algorithm parameters.
BRIEF DESCRIPTION OF THE DRAWINGS
• Further advantages and features of this disclosure will become clear from the following detailed description, with reference to the attached drawings, in which:
• FIG. 1 is a diagram showing an example acceleration of a drum used by the disclosed methods;
• FIG. 2 shows an example distribution of laundry inside the drum during the three specific phases identified in FIG. 1;
• FIG. 3 shows an example balance of torque in the first phase of FIGS. 1 and 2;
• FIGS. 4-5 are similar to FIG. 3 and show example balances of torque in the second and third phase of drum acceleration shown in FIGS. 1 and 2;
• FIG. 6 shows an example torque behavior during a distribution profile with laundry;
• FIG. 7 shows an example power signal behavior during a distribution profile with laundry;
• FIG. 8 is a block diagram of an example disclosed method; and
• FIG. 9 shows the example method of FIG. 8 in detail.
DETAILED DESCRIPTION
• This disclosure relates to methods of operating laundry treating appliances having a rotatable drum defining a treating chamber for receiving laundry for treatment, and a motor rotating the drum. More specifically, the disclosed methods comprise increasing the rotational speed of the drum by increasing the rotational speed of the motor, and measuring at least one parameter representing the rotation of the drum/motor in order to determine the degree of the satellization of the laundry articles against the inner wall of the drum.
• While the disclosed methods may be mainly used for washing machines, they can be used also for, among other things, tumble dryers and washer-dryers.
• FIGS. 1 and 2, show an example acceleration speed profile having three phases (I, II, III in FIGS. 1 and 2). During the first two phases I and II the laundry inside the drum is tumbling. The amount of laundry stuck on the side of the drum increases as the speed increases, while the amount of tumbling laundry decreases. This condition holds until the drum reaches the speed at which substantially all laundry is stuck to the side of the drum (phase III). This speed is known as “satellization speed”.
• This phenomenon is due to the increasing centrifugal force as drum rotational speed increases. The mechanical torque that the motor delivers during the distribution phases shown in FIGS. 1 and 2 will change according to the following findings, considering the drum rotating counterclockwise.
• Phase I (FIG. 3):
• Laundry is tumbling. The motor torque must be enough to lift up the amount of laundry inside the drum. An example mechanical equation for phase I can be expressed as:
• 
  T _{mot I} =T _laundryI +b _frictω_I J ₀{dot over (ω)}
• where T_{mot I} is the motor torque, b_frict is the viscous friction coefficient, ω is the rotational speed of the drum, J₀ is the inertia momentum of the machine with empty drum, and T_{laundry I} is the torque due to the gravity acceleration acting on non-satellized laundry and to the inertia momentum of the laundry. This last term can be considered as an additive friction torque amount that the motor need overcome.
• Phase II (FIG. 4):
• As the speed increases, the centrifugal force increases and laundry starts sticking on the drum side wall. The amount of laundry when rotating in the left side of the drum starts to “help” motor deliver the torque needed. So, the motor torque required (T_{mot II} ) decreases.
• 
  T _{mot II} +T _{laundry +} =T _{laundry −} +b _frictω_II +J ₀{dot over (ω)}
• 
  T _{mot II} =(T _{laundry −} −T _{laundry +} )+b _frictω_II +J ₀{dot over (ω)}
• 
  T _{mot II} =ΔT _laundry +b _frictω_II +J ₀{dot over (ω)}
• 
  where
• 
  T_{laundry −>T laundry +}

  

  T_{mot II} <T_{mot I}
Note Well:
• 
  T _{laundry I} >>b _frict·ω_I
• 
  ΔT _laundry >>b _frict·ω_II
• Phase III (FIG. 5):
• Motor torque continues to decrease until the time at which substantially all of the laundry is “plastered,” “satellized,” or otherwise fixedly retained against the drum. The motor torque reaches substantially its minimum at the satellization speed due to the fact that when the laundry is completely stuck, the motor need only lift up approximately half of the laundry amount (right side) while the other half (left side) “helps” the motor to deliver needed torque.
• 
  T _{mot III} +T _{laundry 2+} =T _{laundry −} +b _frictω_sat +J _sat{dot over (ω)}
• 
  T _{mot III} =(T _{laundry 2−} −T _{laundry 2+} )+b _frictω_sat +J _sat{dot over (ω)}
• 
  T _{mot III} =b _frictω_sat +J _sat{dot over (ω)}+T _frict
• 
  where
• 
  T_{laundry 2−} ≅T_{laundry 2+}

  

  T_{mot III} <T_{mot II′}
• 
  J _sat =J ₀ +J _{laundry — sat},
• because when laundry is retained in a substantially fixed position relative to the drum, geometry is substantially fixed as well and remains approximately constant. T_frict is a constant friction torque.
• Just after the laundry is retained in a substantially fixed position relative to the drum by centrifugal force, the motor torque (T_mot) low frequency component increases linearly because the viscous friction term increases with rotational speed.
• The mechanical equation can be expressed as follows:
• 
  T _mot =b _frict ω+J _sat {dot over (ω)}+T _frict
• FIG. 6 shows the substantially minimum reached by the low frequency component of the torque when the “satellization speed” is reached. The applicants observed that after “satellization speed” the motor torque signal increases linearly due to the viscous term of the above mechanical equation.
• Disclosed example methods are the consequence of the above findings to detect the “satellization speed” in a simple and reliable way.
• In some disclosed examples, during a speed acceleration profile the torque low frequency component (or the average torque) is processed and, when the substantially minimum is found, the corresponding reached speed is the “satellization speed”.
• In some disclosed examples, the signal processed to detect the “satellization speed” is a mechanical/electrical power signal relative to the energy of the motor, where the mechanical power is, for example the signal shown in FIG. 7.
• Because the power is the torque multiplied by the speed, the position of substantially the minimum is highlighted in FIG. 7. That's because power (P_mot) shows a parabolic behavior:
• 
  P _mot

  

  T _mot·ω=(b _frict ω+J _sat {dot over (ω)}+T _frict)·ω=b _frict ω ² +J _sat{dot over (ω)}·

  

  T_frict·ω
• On the other hand, the robustness of the disclosed methods with respect to the friction term (b_frictω²) decreases.
• As mentioned above, the main signal processed by the disclosed methods is preferably the low frequency component of the real signal. Accordingly, the disclosed methods find substantially the minimum by processing the real signal filtered with a low pass filter, with a “sliding moving average,” or with any other method which eliminates the high frequency components.
• With reference to FIG. 8, an example method includes monitoring the input main signal (torque/power etc.), waiting until substantially the minimum occurs, and, when the minimum occurs, getting the actual speed value and setting it as the “satellization speed”.
• As disclosed above, a solution to detect substantially the minimum is to process the torque (or power) signal with a suitable digital filter (e.g., a “robust noise differentiator” technique) and compare values to get minima and maxima.
• However, FIG. 7 shows that the low frequency component of the power (or torque) signal could present a local minima due to the laundry tumbling and inertia geometry variation during distribution. To avoid misclassifying minima, disclosed methods wait preferably a predefined time (machine model dependent) and monitor if a new maximum is found (i.e., due to the physical behavior of the laundry inside the drum, if a maximum happens a new minimum will come).
• FIG. 9 shows such a variant of the minimum search algorithm in the details.
• Experiments carried out by the applicants on a washer machine have shown that the disclosed methods are very reliable, and that the effect of variation of the viscous friction coefficient is negligible.

Claims (13)

1-11. (canceled)

12. A method of operating a laundry treating appliance having a rotatable drum defining a treating chamber for receiving laundry for treatment, and a motor rotating the drum, the method comprising:

increasing the rotational speed of the drum by increasing the rotational speed of the motor; and

detecting when a parameter signal representing the rotation of the drum reaches substantially a minimum to determine the speed at which substantially all of the laundry is satellized.

13. A method as defined in claim 12, wherein the parameter signal represents the energy of the motor.

14. A method as defined in claim 13, wherein the parameter signal represents at least one of a motor torque and/or a motor power.

15. A method as defined in claim 12, wherein detecting when the parameter signal reaches substantially the minimum comprises monitoring a low frequency component of the parameter signal.

16. A method as defined in claim 12, further comprising filtering the parameter signal to substantially remove a high frequency component.

17. A method as defined in claim 12, further comprising after the minimum is detected, waiting a predetermined time, and detecting whether another minimum is found after detecting a maximum.

18. A laundry treating appliance comprising:

a rotatable drum defining a treating chamber for receiving laundry for treatment;

a motor rotating the drum; and

a control unit programmed to, at least, increase the rotational speed of the drum by increasing the rotational speed of the motor, and detect when a parameter signal representing the rotation of the drum reaches substantially a minimum to determine the speed at which substantially all of the laundry is satellized.

19. A laundry treating appliance as defined in claim 18, wherein the parameter signal represents the energy of the motor.

20. A laundry treating appliance as defined in claim 19, wherein the parameter signal represents at least one of a motor torque and/or a motor power.

21. A laundry treating appliance as defined in claim 18, wherein the control unit is programmed to detect when the parameter signal reaches substantially the minimum by monitoring a low frequency component of the parameter signal.

22. A laundry treating appliance as defined in claim 18, wherein the control unit is programmed to filter the parameter signal to substantially remove a high frequency component.

23. A laundry treating appliance as defined in claim 18, wherein the control unit is programmed to, after the minimum is detected, wait a predetermined time, and detect whether another minimum is found after detecting a maximum.

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