EP2765230A1 - A method of operating a washing machine and washing machine using such method - Google Patents

Abstract

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 comprises increasing the rotational speed of the drum by increasing the rotational speed of the motor and measuring at least one parameter related to the rotation of the drum in order to determine whether the laundry articles are retained in a substantially fixed position relative to the drum by centrifugal force, in order to perform a subsequent check of unbalance load. The above parameter, particularly motor torque or motor power, is monitored and the speed at which all laundry articles are retained against the wall of the drum by centrifugal force is assessed when said parameter reaches an absolute minimum value.

Description

• The present invention relates to 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. More specifically, the present invention relates to the above method comprising increasing the rotational speed of the drum by increasing the rotational speed of the motor and measuring at least one parameter related to the rotation of the drum/motor in order to determine the degree of the laying of the laundry articles against the inner wall of the drum.
• Even if the method according to the invention will be mainly used for washing machines, it can be used also for tumble dryers and washer-dryers as well.
• A known method is disclosed by EP 2379786 where the measured parameter (a measurement variable or a control variable) has a harmonic oscillation produced by an unbalance. Such known method requires a quite complex comparison between a theoretical sinusoidal oscillation of the parameter and the actual oscillation, so as to determine the degree of the laying of the laundry articles against the inner wall of the drum on the basis of the correlation. This known method requires a quite complex algorithm capable of carrying out such correlation. Moreover the degree of the laying 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 a too rich information for the actual purpose of washer control, since what matters is only the speed at which all clothes into 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 such speed, the unbalance determination can be safely and quickly carried out without the need of reaching a fixed predetermined value as in the old washing machines (i.e. saving cycle time and energy). Moreover carrying out unbalance 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.
• In view of the above, one object of the present invention is to provide a method as mentioned at the beginning of the description which allows a simple, reliable and inexpensive method to detect the speed at which laundry is entirely retained in a substantially fixed position relative to the drum by centrifugal force, so that no portion of load is allowed to tumble.
• According to the invention, the above object is reached thanks to the features listed in the appended claims.
• According to the invention, any signal related to the energy of the motor system, particularly torque or power thereof, is monitored during acceleration phase and the speed at which laundry articles are against the side wall of the drum due to centrifugal force is detected when said signal reaches an absolute minimum.
• The main advantage of the solution according to the present invention is that the complexity is dramatically reduced. Moreover, since the concept is based on the physical behavior of the laundry inside the drum (mechanical energy balance), the algorithm according to the invention is calibration free with respect to machine type/model variation. In few words, no additional effort is required to calibrate algorithm parameters.
• Further advantages and features according to the present invention will become clear from the following detailed description, with reference to the attached drawings, in which:
• Figure 1 is a diagram showing the acceleration of the drum which is the general phase used by the method according to the invention;
• Figure 2 shows the distribution of laundry inside the drum during three specific phases identified in figure 1;
• Figure 3 shows the balance of torque in a first phase;
• Figures 4-5 are similar to figure 3 and shows the balance of torques in the second and third phase of drum acceleration;
• Figure 6 shows the torque behavior during a distribution profile with laundry;
• Figure 7 shows the power signal behavior during a distribution profile with laundry;
• Figure 8 is a block diagram of an algorithm according to the invention; and
• Figure 9 shows the algorithm of figure 8 in details.
• Referring to figures 1 and 2, the technical solution according to the invention starts from the consideration that during an acceleration speed profile it is possible to identify three phases (I, II, III in figures 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 tumbling load amount decreases. This condition holds until the drum reaches a certain speed in which all clothes are stuck to the side of the drum (phase III). This speed is known in washing machines jargon as "satelization speed".
• This phenomenon is due to the increasing of centrifugal force due to drum rotational speed increasing. The mechanical torque that the motor delivers during the distribution phases shown in figure 2 will change according to the following findings, considering the drum rotating counterclockwise:
• Phase I ( figure 3 ) : laundry is tumbling; the motor torque must be enough to lift up all the amount of clothes inside the drum. Mechanical equation for this phase can be expressed as: $$T_{{\mathit{mot}}_I}=T_{{\mathit{laundry}}_I}+b_{\mathit{frict}}{\omega }_I+{\mathrm{<figure-callout\; id="0"\; label="J"\; filenames="imgf0006.png,imgf0007.png"\; state="\{\{state\}\}">J</figure-callout>}}_0\dot{\omega }$$
  
  
  Where T_motI is the motor torque, b_frict is the viscous friction coefficient, ω is the rotational speed of the drum, T_laundryI is the torque due to the gravity acceleration acting on non-satelized laundry and to the inertia momentum of the laundry. This last term can be considered as an additive friction torque amount that the motor should overcome.
  J ₀ is the inertia momentum of the machine with empty drum.
• Phase II ( figure 4 ) : as the speed increases, the centrifugal force is increasing and starts sticking laundry on the drum side wall. This 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_motII ) decreases. $$T_{{\mathit{mot}}_{\mathit{II}}}=T_{{\mathit{laundry}}_{+}}=T_{{\mathit{laundry}}_{-}}+b_{\mathit{frict}}{\omega }_{\mathit{II}}+{\mathrm{<figure-callout\; id="0"\; label="J"\; filenames="imgf0006.png,imgf0007.png"\; state="\{\{state\}\}">J</figure-callout>}}_0\dot{\omega }$$
  
  $$T_{{\mathit{mot}}_{\mathit{II}}}=\left(T_{{\mathit{laundry}}_{-}}-T_{{\mathit{laundry}}_{+}}\right)+b_{\mathit{frict}}{\omega }_{\mathit{II}}+{\mathrm{<figure-callout\; id="0"\; label="J"\; filenames="imgf0006.png,imgf0007.png"\; state="\{\{state\}\}">J</figure-callout>}}_0\dot{\omega }$$
  
  $$T_{{\mathit{mot}}_{\mathit{II}}}=\mathrm{\Delta }{T}_{\mathit{laundry}}+b_{\mathit{frict}}{\omega }_{\mathit{II}}+{\mathrm{<figure-callout\; id="0"\; label="J"\; filenames="imgf0006.png,imgf0007.png"\; state="\{\{state\}\}">J</figure-callout>}}_0\dot{\omega }$$
  
  
  Where T_{laundry_} > T _{laundry +} ⇒ T_motII < T_motI
  N.B: $$T_{{\mathit{laundry}}_I}>>b_{\mathit{frict}}\cdot {\omega }_I$$
  
  $$\mathrm{\Delta }{T}_{{\mathit{laundry}}_I}>>b_{\mathit{frict}}\cdot {\omega }_{\mathit{II}}$$
  
• Phase III ( figure 5 ) : motor torque continues to decrease from its initials values until the instant in which all the clothes are "plastered" or fixedly retained due to the fact that when the laundry is completely stuck, motor must lift up approximately half of the laundry amount (right side) while the other half (left side) "helps" the motor to deliver needed torque. $$T_{{\mathit{mot}}_{\mathit{III}}}=T_{{\mathit{laundry}}_{2+}}=T_{{\mathit{laundry}}_{2-}}+b_{\mathit{frict}}{\omega }_{\mathit{sat}}+J_{\mathit{sat}}\dot{\omega }$$
  
  $$T_{{\mathit{mot}}_{\mathit{III}}}=\left(T_{{\mathit{laundry}}_{2-}}-T_{{\mathit{laundry}}_{2+}}\right)+b_{\mathit{frict}}{\omega }_{\mathit{sat}}+J_{\mathit{sat}}\dot{\omega }$$
  
  $$T_{{\mathit{mot}}_{\mathit{III}}}=b_{\mathit{frict}}{\omega }_{\mathit{sat}}+J_{\mathit{sat}}\dot{\omega }+T_{\mathit{frict}}$$
  
Where T _{laundry 2-} ≅ T _{laundry 2+} ⇒ T_motIII < T_motII ,
• J_sat = J ₀ + J_{laundry_sat}, since when laundry is retained in a substantially fixed position relative to the drum geometry is fixed as well and remain approximately constant.
• T_frict is a constant friction torque.
• Just after clothes are retained in a substantially fixed position relative to the drum by centrifugal force, the motor torque (T_mot ) low frequency component increases linearly since the viscous friction term is increasing with rotational speed.
• The mechanical equation can be expressed as follows: $$T_{\mathit{mot}}=b_{\mathit{frict}}{\omega }_{\mathit{sat}}+J_{\mathit{sat}}\dot{\omega }+T_{\mathit{frict}}$$

  
• Figure 6 shows the absolute minimum reached by the low frequency component of the torque when the "satelization speed" is reached. The applicant observed that after "satelization speed" the motor torque signal increases linearly due to the viscous term of the above mechanical equation.
• The algorithm according to the invention is the consequence of the above findings to detect the "satelization speed" in a simple and reliable way.
• According to a first embodiment of the invention, during a speed acceleration profile the torque low frequency component (or the average torque) is processed and, when the absolute minimum is found, the corresponding reached speed is the "satelization speed".
• According to a second embodiment of the invention, the signal processed by the algorithm to detect the "satelization speed" is the mechanical/electrical power as signal related to the energy of the motor.
• Such second embodiment, where the mechanical power is the chosen signal, is shown in figure 7.
• Since the power is the torque multiplied by the speed, the position of the absolute minimum according to the second embodiment is highlighted. That's because power (P_mot) shows a parabolic behavior: $$P_{\mathit{mot}}\triangleq T_{\mathit{mot}}\cdot \omega =\left(b_{\mathit{frict}}\omega +J_{\mathit{sat}}\dot{\omega }+T_{\mathit{frict}}\right)\cdot \omega =b_{\mathit{frict}}{\omega }^2+J_{\mathit{sat}}\dot{\omega }\cdot \omega +T_{\mathit{frict}}\cdot \omega$$

  
• On the other hand, the robustness of the algorithm with respect to the friction term (b_frict ω²) decreases.
• As mentioned above, the main signal processed by the algorithm according to the invention is preferably the low frequency component of the real signal. Accordingly, the algorithm finds the absolute minimum processing the real signal filtered with a low pass filter or with a "sliding moving average" or with any other method which eliminates the high frequency components. Since these methods are well known in the art, it is not necessary to describe them in details in the present specification.
• With reference to figure 8, the main algorithm steps are as follows: the algorithm monitors the input main signal (torque/power etc..), it waits until the absolute minimum occurs and, when the absolute minimum occurs, it gets the actual speed value and set it as "satelization speed". As shown above, a solution to detect the absolute minimum is to process the torque (or power) signal with a suitable digital filter (eg., "robust noise differentiator" technique well known in the literature) 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 local minima due to the laundry tumbling and inertia geometry variation during distribution. To avoid misunderstanding in the absolute minimum search, the algorithm according to the invention waits preferably a predefined time (machine model dependent) and monitors 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).
• Figure 9 shows such variant of the absolute minimum search algorithm in the details. Experiments carried out by the applicant on a washer machine have shown that the method according to the invention is very reliable and that the effect of variation of the viscous friction coefficient is negligible.

Claims (11)

1. 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 measuring at least one parameter related to the rotation of the drum in order to determine the degree of the laying of the laundry articles against the inner wall of the drum, characterized in that the above parameter is monitored and the speed at which all laundry articles are retained against the wall of the drum by centrifugal force is assessed when said parameter reaches a minimum value.
2. Method according to claim 1, wherein said parameter is related to the energy of the motor.
3. Method according to claim 2, wherein said parameter is the motor torque or the motor power.
4. Method according to any of the preceding claims, wherein only the low frequency component of said parameter is monitored.
5. Method according to any of claims 1-3, wherein said parameter is filtered in order to eliminate high frequency components.
6. Method according to any of the preceding claims, wherein after said minimum is detected, it comprises the step of waiting a predetermined time and monitoring if a new minimum is found after an intermediate maximum.
7. Laundry treating appliance having a rotatable drum defining a treating chamber for receiving laundry for treatment, a motor rotating the drum, a control unit adapted to increase the rotational speed of the drum by increasing the rotational speed of the motor and to measure at least one parameter related to the rotation of the drum in order to determine the degree of the laying of the laundry articles against the inner wall of the drum, characterized in that such control unit is adapted to monitor the above parameter in order to assess the speed at which all laundry articles are retained against the wall of the drum by centrifugal force, such speed corresponding to the speed at which said parameter reaches a minimum value.
8. Laundry treating appliance according to claim 7, wherein said parameter is related to the energy of the motor.
9. Laundry treating appliance according to claim 7, wherein said parameter is the motor torque or the motor power.
10. Laundry treating appliance according to any of claims 7 to 9, wherein such control unit is adapted to filter said parameter in order to eliminate high frequency components.
11. Laundry treating appliance according to any of claims 7 to 10, wherein said control unit is adapted to wait, after said minimum is detected, a predetermined time and to monitor if a new minimum is found after an intermediate maximum.

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