WO2008023997A1

WO2008023997A1 - Asymmetric load distribution in a washing machine

Info

Publication number: WO2008023997A1
Application number: PCT/NZ2007/000224
Authority: WO
Inventors: Adam John Darby
Original assignee: Fisher & Paykel Appliance Limited
Priority date: 2006-08-23
Filing date: 2007-08-21
Publication date: 2008-02-28

Abstract

The present invention relates to a washing machine 10 and method of controlling a washing machine 10 to reduce the effects of asymmetrical distribution in a wash load 18 during an agitate cycle. The invention comprises receiving a parameter indicative of water level in the washing machine 10 at a plurality of instants during an agitate stroke, and modifying the agitate cycle based on variation in the water level at the plurality of instants during the agitate stroke.

Description

"ASYMMETRIC LOAD DISTRIBUTION IN A WASHING MACHINE"

FIELD OF THE INVENTION

The present invention relates to a method and washing machine for controlling operation in response to asymmetric load distributions.

BACKGROUND TO THE INVENTION

In order to wash clothes, washing machines have an agitate cycle in which the spin basket or a wash-plate or agitator is oscillated in clockwise and counter-clockwise directions in order to agitate the wash load within the spin basket to clean items in the wash load. The wash load comprises all the items (eg. clothing) placed in the spin basket for washing.

Often, the items in the spin basket may not be distributed evenly. For example, the mass of the wash load might be asymmetrically distributed towards one side of the spin basket.

Alternatively, the volume might be distributed asymmetrically towards one side. This can be due to a user not loading the washing machine in an even manner. Also, movement of items during the washing process can cause asymmetric distribution. One form of asymmetric distribution is bunching, whereby the items become entangled and "bunch" in one portion of the spin basket.

Other types of asymmetric distributions can also occur.

When an asymmetric distribution occurs, this can cause a reduction in washing performance. Also, the spin basket assembly can hit into the outer housing or wrapper of the washing machine.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method or washing machine for at least partially alleviating the effects of asymmetric distribution in a wash load. For example, this might be by redistributing the items in the wash load, or by altering operation of the washing machine so the effects of an asymmetric distribution are reduced. In one aspect the present invention may be said to consist in a method of controlling a washing machine to reduce the effects of asymmetrical distribution in a wash load during an agitate cycle comprising: receiving a parameter indicative of water level in the washing machine at a plurality of instants during an agitate stroke, and modifying the agitate cycle based on variation in the water level at the plurality of instants during the agitate stroke.

Preferably the parameter indicative of water level is water level.

Preferably the parameter indicative of water level is water pressure in the washing machine. Preferably modifying the agitate cycle comprises one or more of: adding more water into the washing machine, increasing the agitation cycle time, aborting the agitate cycle, altering the speed vs. time profile of the agitate stroke.

Preferably the method further comprises normalising the water level variation based on a agitation stroke length.

Preferably the method further comprises comparing the water level or parameter indicative of water level to a reference at the multiple instants to obtain an indication of the variation in water level.

Preferably the reference is an average water level or one or more parameters indicative of average water level.

In another aspect the present invention may be said to consist in a washing machine adapted to reduce the effects of asymmetrical distribution in a wash load during an agitate cycle, the washing machine comprising: a spin basket adapted to hold a wash load , a motor for agitating the wash load in the spin basket, a sensor for detecting a parameter indicative of water level in the washing machine, and a controller coupled to control operation of the motor and coupled to receive information indicative of water level from the sensor, wherein the controller is programmed to control the washing machine to reduce asymmetrical distribution in a wash load during an agitate cycle by: receiving a parameter indicative of water level in the washing machine at a plurality of instants during an agitate stroke, and modifying the agitate cycle based on variation in the water level at the plurality of instants during the agitate stroke.

Preferably the parameter indicative of water level is water level.

Preferably the parameter indicative of water level is water pressure in the washing machine. Preferably the sensor is a water level sensor.

Preferably the sensor is a water pressure sensor.

Preferably modifying the agitate cycle comprises one or more of: adding more water into the washing machine, increasing the agitation cycle time, aborting the agitate cycle, altering the velocity vs. time profile of the agitate stroke. Preferably the controller is further programmed to compare the water level or parameter indicative of water level to a reference at the multiple instants to obtain an indication of the variation in water level.

Preferably the reference is an average water level or one or more parameters indicative of an average water level. Preferably the controller is further programmed to normalise the water variation level based on agitation stroke length.

In another aspect the present invention may be said to consist in a method of determining asymmetrical distribution in a wash load in a washing machine during an agitate cycle comprising die steps of : receiving a water level characteristic by measuring a parameter indicative of water level at a plurality of instants throughout a period, obtaining a reference water level over die period, calculating a cumulative difference between the water level characteristic and the reference water level, and determining if there is asymmetry in the wash load from the cumulative difference between the water level characteristic and reference water level.

Preferably the period is an agitation stroke of a spin basket or agitator in the washing machine. Preferably if there is asymmetry in the wash load, the method further comprises modifying the agitate cycle based on the cumulative difference.

Preferably modifying the agitate cycle comprises one or more of: adding more water into the washing machine, increasing the agitation cycle time, aborting the agitate cycle, altering the velocity vs. time profile of an agitate stroke.

Preferably determining a cumulative difference between the water level chacteristic and the reference water level comprises integrating the difference between the water level characteristic and the reference water level.

Preferably the reference water level is an average water level or one or more parameters indicative of average water level.

Preferably the method further comprises the step of normalising die cumulative difference between the water level characteristic and reference water level.

Preferably the step of normalising the cumulative difference comprises the step of dividing the cumulative difference between the water level characteristic and the reference water level by an agitation stroke length.

Preferably the water level characteristic is a curve indicating die water level at various instants throughout the period and the cumulative difference between the water level characteristic and the reference water level is the area between die curve and the reference water level.

Preferably the step of determining a water level characteristic by determining a water level at a plurality of instants throughout a period comprises measuring the water level continuously throughout the period.

Preferably asymmetry in die wash load occurs due to one or more of: wash load bunching, wash load twisting, wash load engulfing, asymmetry in mass distribution.

In another aspect the present invention may be said to consist in a washing machine for determining asymmetry in a wash load during a agitate cycle, the washing machine comprising: a spin basket adapted to hold a wash load, a motor for agitating the wash load in the spin basket, a sensor for detecting a parameter indicative of water level in the washing machine, and a controller coupled to control operation of the motor and coupled to receive information indicative of water level from the sensor, wherein the controller is programmed to determine asymmetry in a wash load in the spin basket by: receiving a water level characteristic by measuring a parameter indicative of water level at a plurality of instants throughout a period, obtaining reference water level over the period, calculating a cumulative difference between the water level characteristic and the reference water level, and determining if there is asymmetry in the wash load from the cumulative difference between the water level characteristic and reference water level.

Preferably the period is an agitation stroke of the spin basket or agitator in the washing machine.

Preferably if there is asymmetry in the wash load, the method further comprises modifying the agitate cycle based on the cumulative difference.

Preferably modifying the agitate cycle comprises one or more of: adding more water into the washing machine, increasing the agitation cycle time, aborting the agitate cycle, altering die agitate stroke ramp time of the agitate cycle, altering the velocity vs. time profile of the agitate stroke.

Preferably determining a cumulative difference between the water level characteristic and the reference water level comprises integrating the difference between the water level characteristic and the reference water level. Preferably the controller is programmed to normalise the cumulative difference between the water level characteristic and reference water level.

Preferably normalising the cumulative difference comprises dividing the cumulative difference between die water level characteristic and die reference water level by an agitation stroke length. Preferably the water level characteristic is a curve indicating the water level a various instants throughout the period and the cumulative difference between the water level characteristic and the reference water level is the area between the curve and the average water level.

Preferably determining a water level characteristic by determining a water level at a plurality of instants throughout a period comprises measuring the water level continuously throughout the period.

Preferably the sensor is a water pressure sensor. Preferably the sensor is a water level sensor.

Preferably asymmetrical distribution in the wash load occurs due to one or more of: load bunching, load twisting, load engulfing, asymmetry in mass distribution.

Preferably the method further comprises wherein the water level characteristic is a curve indicating the water level a various instants throughout the period and the cumulative difference between the water level characteristic and the reference water level is the area between the curve and the average water level.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.

The term "comprising" as used in this specification means "consisting at least in part of. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will be described with reference to the following drawings, of which:

Figures Ia and Ib show a cross-section of a washing machine adapted to alleviate the effects of asymmetric load distribution,

Figure 2 shows a flow diagram of a method for alleviating the effects of asymmetric load distribution,

Figures 3a and 3b show a cross-section of a washing machine according to one embodiment of the invention,

Figure 4 shows a typical wash profile for an agitate stroke, Figure 5 shows an example of water level variation during an agitate stroke, Figure 6 shows a flow diagram of a method for alleviating the effects of asymmetric load distribution according to one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure Ia and Ib show in schematic form a washing machine 10 in accordance with a preferred embodiment of the invention. The washing machine comprises an outer wrapper 11 with and internal tub 12, a spin basket 13 rotatable within the internal tub 12, and a motor 14 for controlling rotation of the spin basket or an agitator or wash-plate 9. The spin basket 13 contains a wash load 18 comprising clothing and other items. As can be seen, the wash load is unevenly distributed such that it "bunches" 19 on one side. The load 18 is washed by oscillating the spin basket 13, or alternatively oscillating the agitator/wash-plate 9, depending on the particular design of the washing machine. In this case, the machine utilises a wash-plate to agitate and clean the wash load. The nature of a wash-plate will be known to those skilled in the art. While a low- profile wash-plate 9 is shown in the Figures, a central column or other type of agitator could alternatively be used. Use of the term wash-plate in this specification should not be considered to limit the invention to only that type of agitator. The term "agitator" can be used genetically to cover a wash-plate 9, central column agitator or any other agitation means. The wash-plate 9 in the Figures is shown in dotted lines, as generally it is obscured by the wash-load.

When the wash-plate 9 has rotated in one direction (Figure Ia) the bunching 19 is on the left hand side of the machine 10. When the wash-plate 9 has rotated in the opposite direction, the bunching 19 is on the right hand side. As can also been seen, the water level 17 varies as the wash- profile oscillates due to the asymmetry in die wash load.

The washing machine 10 also has a controller 15 for controlling the various functions of the washing machine, including the motor 14 to oscillate the spin basket 13. During an agitate cycle, the wash-plate 9 is oscillated a number of times. Each oscillation is an agitate stroke. An agitate stroke comprises to one clockwise and one counter-clockwise rotation or oscillation of the wash-plate 9. The washing machine 10 also includes a sensor 16 for determining water level 17 within die washing machine, which is coupled to the controller 15. The controller also operates a water pump (not shown) to introduce water into the machine via an inlet pipe in the usual manner. Only a selection of the components of a washing machine are shown. Other standard components of a washing machine will be known to those skilled in the art, and are not shown in detail here. The washing machine 10 carries out the usual functions of a washing machine for cleaning items. The functions include providing an agitate cycle whereby the wash-plate 9 oscillates between clockwise and counter-clockwise rotational directions in order to wash the items within the wash load. A spin cycle is also provided to remove excess water. The various other functions and cycles of a washing machine are also provided and will be known to those skilled in the art. In general terms, the controller 15 is programmed to receive a signal, data or other sampled information from the sensor 16 to determine variation in the water level 17, and then based on this, control the washing machine 10 to alleviate the effects of asymmetric load distribution in the spin basket 13. This might be by way of controlling the spin basket or wash- plate 9 itself via the motor 14, introducing additional water, or altering any other function of the washing machine 10. As seen in Figures Ia and Ib, the spin basket shows a typical asymmetric load distribution

17 that might occur during an agitate cycle in a washing machine. Asymmetry in a load distribution can occur for a range of reasons, including incorrect loading by user and movement of items in the wash load during the wash process. Asymmetric load distribution can manifest itself in a number of forms, including asymmetric mass distribution or asymmetric volume distribution. A typical example of such asymmetric distribution is bunching, whereby a number of items of clothing in the wash load become entangled and form a bunch or ball 19 in one portion of the spin basket such as shown in Figures Ia, Ib. Other forms of asymmetric load distribution can also occur, for example, through twisting, engulfing or a number of other means.

When asymmetry in the load distribution occurs this can cause unbalancing in the washing machine during an agitate cycle. Where asymmetric distribution exists, the spin basket can sway, rock or otherwise move from side to side due to the imbalance in the wash load. This can affect stability of the entire machine. Further, the items in the wash load might not be washed to an acceptable level.

As shown in Figure Ia, when the asymmetric load 18 rotates in a first direction, the water level in the machine rises and is higher at the side of the machine where the bulk 19 of the asymmetric distribution is positioned. The water level 17 on the opposite side of the spin basket is lower. Conversely, when the wash-plate 9 rotates in the opposite direction as shown in Figure Ib and moves the bulk of the asymmetric load distribution 17 to the other side of the washing machine 10, the water level 17 on that side of the washing machine then rises and is higher than that on the opposite side. The variation in the water level 17 throughout an agitate stroke can provide an indication of asymmetric load distribution. The controller 15 can be a microcontroller, microprocessor or any other suitable means and can be programmed in the usual way to carry out the usual functions of a washing machine 10. The controller also includes additional programming to operate the wash-plate 9 to reduce the effects of asymmetric load distribution 17 in accordance with the preferred embodiment of the invention. In particular, the controller 15 is coupled to receive a signal, data or other sampled information from the sensor 16, the signal, data or the like indicating a parameter indicative of the water level 17 in the washing machine 10. The sensor 16 may be a water level sensor which measures the water level direcdy and feeds a signal indicative of this to the controller 15. Alternatively, the sensor 16 might be a water pressure sensor that determines the water pressure in the washing machine and provides a signal indicating this pressure to the controller. The water pressure is indicative of the water level in the washing machine and therefore provides a parameter indicative of the water level in the machine. Other means for determining direcdy or indirecdy the water level in the machine could also be provided.

The controller 15 is programmed to operate the motor to agitate or oscillate the wash- plate 9 in accordance with a particular agitate regime. In a preferred embodiment of the present invention, the controller 15 is programmed to calculate or otherwise determine a variation in the water level throughout an agitate stroke of the agitate cycle.

To determine water level variation, the water level which is received, detected or measured at any particular point might be compared to a reference or threshold water level. This could be any one of a number of possible predetermined or measured water levels, such as an average water level in the wash basket or a measured water level based on the amount of water introduced into the washing machine 10. The controller 15 might also (as a further step) normalise the determined water level variation based on the agitate stroke length or other parameter.

A variation in the water level over a period, such as the agitate stroke or part thereof, provides an indication that asymmetrical distribution in the wash load has occurred. Upon calculating or otherwise determining a variation in the water level over the period, the controller 15 is programmed to modify the operation of the washing machine to alleviate the effects of asymmetric load distribution. One way to do this is to select or generate a different agitate regime and control the motor in order to operate the wash-plate 9 in accordance with the agitate regime. The agitate regime is selected or generated such that when put into action the effects of the asymmetric load distribution will be reduced. This could be by way of reducing the asymmetric distribution itself to provide a more symmetric distribution in the load. Alternatively this could be by way of operating the spin basket 13, wash-plate 9 or washing machine 10 in another manner such that even with an asymmetric distribution, the undesired effects caused by it are reduced or eliminated. A number of different actions could be implemented by the controller to reduce the effects. For example, the controller could control the washing machine to:

1. Introduce more water into the washing machine in order to redistribute the load.

2. Increase the agitate cycle time. This assists in achieving the desired level of cleaning.

3. Abort the agitate cycle, and provide the user with a warning to redistribute the load.

4. Alter the agitate regime. For example, various parameters of the agitate stroke might be altered to reduce the effects of asymmetric load distribution. For example, the agitate stroke could be made more or less vigorous.

One or a combination of these actions could be initiated by the controller in order to reduce the effects of asymmetric load distribution. Yet other possible actions could also be taken.

Referring to Figure 2 an overview of the preferred method for reducing the effects of asymmetric distribution is described. In summary, the controller carries out the method of receiving or obtaining, step 20, a parameter or other information from the sensor 16 that indicates water level at various points throughout a period in an agitate cycle. The controller then monitors or otherwise processes the water level information, step 21. If there is variation in the water level indicating asymmetry in the load, step 22, the controller modifies operation of the washing machine, step 23, by way of the spin basket 13, wash-plate 9 and/or other means to at least partially alleviate the effects of asymmetric distribution. Preferably the controller 15 receives the parameter indicative of water level from the sensor 16 at various instants throughout the agitate stroke.

An embodiment of a washing machine adapted to reduce the effects of asymmetrical distribution in a wash load and a method for doing the same will be described with reference to Figures 3a-5. It will appreciated by those skilled in the art that this is only one possible embodiment of the invention and other alternative means of implementing the invention are possible. Referring to Figures 3a and 3b, the washing machine includes a housing 11, an inner tub 12, and a spin basket 13 which is rota tab Ie in the inner tub 12, and a motor 14 for agitating the wash-plate 9. The washing machine also includes a sensor for providing a parameter indicative of water level in the washing machine. In this case the sensor is a water pressure sensor 30 that detects the water pressure at point A. The washing machine 10 also includes a controller 15 for controlling the various operations of the washing machine, including agitating the wash-plate 9 and introducing water into the washing machine. The controller 15 is coupled to the motor 14 and receives input from the water pressure sensor 30. In this embodiment, the controller 15 is programmed to operate the wash-plate 9 via the motor in accordance with a wash profile 40, such as shown in Figure 4. The wash profile is a rotate velocity vs. time profile of the agitate stroke. A wash profile 40 specifies the manner in which the basket is rotated clockwise and counter-clockwise during the agitate cycle. The controller 15 may generate this wash profile 40, or select it from one or more of a set of predetermined wash profiles depending on various input parameters.

A typical wash profile 40 is shown generically in Figure 4. This wash profile 40 specifies the speed of rotation of the wash-plate 9 at various stages throughout one half of the agitate stroke, for example the clockwise stroke. The wash profile 40 has a ramp portion A, which specifies the time taken B to reach a rotational speed C from a stationary point 0 (zero) in the agitate cycle. The stationary point is where the wash-plate 9 is between the clockwise and counter-clockwise rotations. The next section of the wash profile 40 specifies the plateau time D, namely the length of time the clockwise phase of the agitate stroke remains at the rotational speed C. The final stage is the ramp time E for slowing the clockwise agitate stroke from the plateau speed C down to 0. Once the wash-plate 9 is stationary, the direction of rotation reverses to counter-clockwise. The counter-clockwise stroke wash profile is the same as that for the clockwise stroke. By altering the various parameters A-E of the wash profile curve 40 the nature of the agitate stroke can be altered.

During operation, the controller 15 initiates an agitate cycle whereby the agitate stroke is controlled in accordance with a default, selected or generated wash profile curve 40. During the agitate stroke the controller receives a signal, data or other sampled information from the water pressure sensor 30 at multiple instants throughout the agitate stroke. At each of these instants, the controller 15 receives information defining a parameter that is indicative of the water level 17 in the washing machine at that time. The water pressure at point A is indicative of die water level in the spin basket 13. By monitoring or otherwise processing die water level information at multiple instants throughout the stroke, variation in the water level throughout the stroke can be determined. Where there is an asymmetric load distribution 19, the water level 17 will oscillate between high and low water level in time with the agitate stroke, as shown in Figures 3a, 3b. This is due to the water moving from one side of the spin basket to die odier under influence of the asymmetric load during oscillation. Figure 5 shows in schematic form how water level 50 might vary throughout die agitate stroke when load asymmetry has occurred. In this case, the water level 50 oscillates in a sinusoidal manner. It will be appreciated that the water level variations shown in

Figures 3, 3b and 4 are exemplary only, and die actual water level may vary in a different manner. Also, die controller samples at discrete times, so die samples will not be continuous. Also, diere may be noise on any such water level variation. Preferably, the controller 15 filters die samples received from the water pressure sensor 30 such diat the variation in water level detected is smoodied out to remove noise. In a preferred embodiment the received detected or measured water level is filtered with a 22 millisecond filter. The controller also determines, calculates, measures or otherwise obtains a reference water level from the water pressure sensor 30. For example, during the fill stage prior to the agitate stroke the controller 15 can sample the output of the water pressure sensor 30 to determine the initial reference water level 51. This water level can be used as the average, threshold or reference water level. The reference water level might be passed through a slow (for example 1.4 second) filter to provide a slow-moving average.

To obtain an indication of variation in water level 17 and from that infer or obtain an indication of asymmetric distribution, the controller 15 performs an integration to determine the area 52 under the curve between the varying water level 50 and the reference water level 51. An integration using the absolute value of curve 50 is undertaken. This provides an indication of the magnitude of the asymmetric distribution.

If the clothes are unevenly distributed, the agitate motion tends to make the entire spin basket 13 assembly sway from side to side in synchronisation with the period of the agitate stroke. By integrating the difference between the varying water level 50 and the reference (in this case average) water level 51 over one agitate stroke the magnitude of the spin basket 13, the sway and hence the magnitude of the asymmetrical distribution can be inferred. Typically, the greater the area under the curve, the greater the asymmetric distribution is. Therefore typically, the greater the magnitude of the integration, die greater the asymmetric distribution. Once the controller has performed the integration and has an indication of the degree of asymmetry in the load distribution, it then controls the washing machine to reduce the effects. It can do this by doing one or more of the following:

1. Introducing further water into the wash cycle in order to redistribute the wash load.

2. Abort the agitate stroke and provide a warning for the user to redistribute the load. 3. Increase the total agitation cycle time. This assists in achieving the desired level of cleaning. 4. Altering the agitate stroke ramp time. By decreasing the ramp time the stroke will become more vigorous, which may assist in redistributing the wash load. Alternatively, by increasing the ramp time the agitate stroke will be less vigorous and bowl sway may be diminished. 5. Altering the agitate stroke plateau speed. By increasing the speed, the stroke will be more vigorous and possibly loosen clothing. Alternatively, by reducing the speed the stroke will be less vigorous and may reduce bowl sway.

6. Altering the agitate stroke plateau time. By decreasing the plateau time bowl sway might be diminished. Alternatively, by increasing plateau time die stroke becomes more vigorous and may redistribute die load.

Various combinations of the above and any other washing machine functions can be modified in order to alleviate the effects of asymmetric load distribution.

The actual response to detection of bunch asymmetry depends on the severity or magnitude of the asymmetry. For example, for moderate asymmetric distribution the washing machine could be changed to operate a longer stroke (longer plateau time) to see if that alleviates the asymmetric distribution and effects. If the condition persists, or severe asymmetric distribution is detected, then the machine adds significandy more water. That is, a change to an immersion wash cycle. This immersion wash has its own set of wash profiles, so in effect the wash profiles will be recalculated for the new water level. Preferably, the agitate profile parameters in the machine are calculated from the bowl float level, which is related to load weight. This is the water level at which the bowl floats within the inner tub, in an embodiment where the spin basket can decouple from the wash-plate 9 and motor during agitation. These parameters are calculated in combination with options that are selected. A large number of combinations to alleviate the effects of asymmetric distribution are possible. As noted, the area 52 determined relates or otherwise corresponds to the magnitude of the asymmetric load distribution. However for any given level of asymmetric load distribution die determined area 52 will alter based on the length of the agitate strokes. The length of an agitate stroke relates to die arc dirough which die spin basket 13 rotates during one half cycle of an agitate stroke. In a short stroke, the wash-plate 9 will not rotate through as large an angle as a longer stroke. Therefore, a smaller amount of asymmetry in the load distribution for a longer stroke might produce the same area under the curve as a larger amount of load asymmetry distribution for a shorter stroke. Preferably, the controller 15 divides the area 52 by the stroke lengdi to produce a bunch severity parameter that is normalised for all stroke lengths. This adjusts the sensitivity of the detection system to make it work and provide meaningful results with long and short strokes for small and large loads. A multi stroke filter is generated using the bunch severity value and is compared to predefined thresholds to initiate the appropriate bunch recovery.

Referring to Figure 6, in summary, the controller carries out die following method. First it receives output, step 60, from the sensor 30, and determines a reference water level, step 61. Then it samples the sensor 30 throughout the agitation cycle, step 62, and integrates to find the area 52 between the varying water level 50 and reference water level 51, step 63. If die area indicates asymmetry is the load distribution, step 64, the controller 15 modifies the washing machine operates as per 1-6 above, step 65.

In an alternative embodiment the wash load might be cleaned in a machine that agitates the spin basket instead of an agitator/wash-plate 9. In diis case, the invention would operate in the same manner, except that it is the spin basket oscillation that is modified not the wash-plate 9 /agitator oscillation.

In another alternative, altering the agitate stroke comprises controlling the motor through on/off time control with fixed speeds. This would use a traditional AC induction motor with a gearbox and belt drive.

Claims

1. A method of controlling a washing machine to reduce the effects of asymmetrical distribution in a wash load during an agitate cycle comprising: receiving a parameter indicative of water level in the washing machine at a plurality of instants during an agitate stroke, and modifying the agitate cycle based on variation in the water level at the plurality of instants during the agitate stroke.

2. A method according to claim 1 wherein the parameter indicative of water level is water level.

3. A method according to claim 1 wherein the parameter indicative of water level is water pressure in the washing machine.

4. A method according to claim 1 wherein modifying the agitate cycle comprises one or more of: adding more water into the washing machine, increasing the agitation cycle time, aborting the agitate cycle, altering the velocity vs. time profile of the agitate stroke

5. A method according to claim 1 further comprising normalising the water level variation based on an agitation stroke length.

6. A method according to claim 1 further comprising comparing the water level or parameter indicative of water level to a reference at the multiple instants to obtain an indication of the variation in water level.

7. A method according to claim 6 wherein the reference is an average water level or one or more parameters indicative of average water level.

8. A washing machine adapted to reduce the effects of asymmetrical distribution in a wash load during an agitate cycle, the washing machine comprising: a spin basket adapted to hold a wash load, a motor for agitating the wash load in the spin basket, a sensor for detecting a parameter indicative of water level in the washing machine, and a controller coupled to control operation of the motor and coupled to receive information indicative of water level from the sensor, wherein the controller is programmed to control the washing machine to reduce asymmetrical distribution in a wash load during an agitate cycle by: receiving a parameter indicative of water level in the washing machine at a plurality of instants during an agitate stroke, and modifying the agitate cycle based on variation in the water level at the plurality of instants during the agitate stroke.

9. A washing machine according to claim 8 wherein the parameter indicative of water level is water level.

10. A washing machine according to claim 8 wherein the parameter indicative of water level is water pressure in the washing machine.

11. A washing machine according to claim 8 wherein the sensor is a water level sensor.

12. A washing machine according to claim 8 wherein the sensor is a water pressure sensor.

13. A washing machine according to claim 8 wherein modifying the agitate cycle comprises one or more of: adding more water into the washing machine, increasing the agitation cycle time, aborting the agitate cycle, altering the velocity vs. time profile of the agitate stroke

14. A washing machine according to claim 8 wherein the controller is further programmed to compare the water level or parameter indicative of water level to a reference at the multiple instants to obtain an indication of the variation in water level.

15. A washing machine according to claim 14 wherein the reference is an average water level or one or more parameters indicative of an average water level.

16. A washing machine according to claim 8 wherein the controller is further programmed to normalise the water variation level based on agitation stroke length.

17. A method of determining asymmetrical distribution in a wash load in a washing machine during an agitate cycle comprising the steps of : receiving a water level characteristic by measuring a parameter indicative of water level at a plurality of instants throughout a period, obtaining a reference water level over the period, calculating a cumulative difference between the water level characteristic and the reference water level, and determining if there is asymmetry in the wash load from the cumulative difference between the water level characteristic and reference water level.

18. A method according to claim 17 wherein the period is an agitation stroke of a spin basket or agitator in the washing machine.

19. A method according to claim 17 wherein, if there is asymmetry in the wash load, the method further comprises modifying the agitate cycle based on the cumulative difference.

20. A method according to claim 17 wherein modifying die agitate cycle comprises one or more of: adding more water into the washing machine, increasing the agitation cycle time, aborting the agitate cycle, altering the velocity vs. time profile of the agitate stroke

21. A mediod according to claim 17 wherein determining a cumulative difference between the water level chacteristic and the reference water level comprises integrating the difference between the water level characteristic and the reference water level.

22. A method according to claim 17 wherein the reference water level is an average water level or one or more parameters indicative of average water level.

23. A method according to claim 17 further comprising the step of normalising the cumulative difference between the water level characteristic and reference water level.

24. A method according to claim 23 wherein the step of normalising the cumulative difference comprises the step of dividing the cumulative difference between the water level characteristic and the reference water level by an agitation stroke length.

25. A method according to claim 17 wherein the water level characteristic is a curve indicating the water level at various instants throughout the period and the cumulative difference between the water level characteristic and the reference water level is the area between the curve and the reference water level.

26. A method according to claim 17 wherein the step of determining a water level characteristic by determining a water level at a plurality of instants throughout a period comprises measuring the water level continuously throughout the period.

27. A method according to claim 1 or 17 wherein a symmetry in the wash load occurs due to one or more of: wash load bunching, wash load twisting, wash load engulfing, asymmetry in mass distribution.

28. A washing machine for determining asymmetry in a wash load during a agitate cycle, the washing machine comprising: a spin basket adapted to hold a wash load, a motor for agitating the wash load in the spin basket, a sensor for detecting a parameter indicative of water level in the washing machine, and a controller coupled to control operation of the motor and coupled to receive information indicative of water level from the sensor, wherein the controller is programmed to determine asymmetry in a wash load in the spin basket by: receiving a water level characteristic by measuring a parameter indicative of water level at a plurality of instants throughout a period, obtaining reference water level over the period, calculating a cumulative difference between the water level characteristic and the reference water level, and determining if there is asymmetry in the wash load from the cumulative difference between the water level characteristic and reference water level.

29. A washing machine according to claim 28 wherein the period is an agitation stroke of the spin basket or agitator in the washing machine.

30. A washing machine according to claim 28 wherein if there is asymmetry in the wash load, the method further comprises modifying the agitate cycle based on the cumulative difference.

31. A washing machine according to claim 28 wherein modifying the agitate cycle comprises one or more of: adding more water into the washing machine, increasing the agitation cycle time, aborting the agitate cycle, altering the velocity vs. time profile of an agitate stroke

32. A washing machine according to claim 28 wherein determining a cumulative difference between the water level characteristic and the reference water level comprises integrating the difference between the water level characteristic and the reference water level.

33. A washing machine according to claim 28 wherein die controller is programmed to normalise the cumulative difference between the water level characteristic and reference water level.

34. A washing machine according to claim 33 wherein normalising the cumulative difference comprises dividing the cumulative difference between the water level characteristic and the reference water level by an agitation stroke length.

35. A washing machine according to claim 28 wherein the water level characteristic is a curve indicating the water level a various instants throughout the period and the cumulative difference between the water level characteristic and the reference water level is the area between the curve and die average water level.

36. A washing machine according to claim 28 wherein determining a water level characteristic by determining a water level at a plurality of instants throughout a period comprises measuring the water level continuously throughout the period.

37. A washing machine according to claim 28 wherein the sensor is a water pressure sensor.

38. A washing machine according to claim 28 wherin the sensor is a water level sensor.

39. A washing machine according to claim 8 or 28 wherein asymmetrical distribution in the wash load occurs due to one or more of: load bunching, load twisting, load engulfing, asymmetry in mass distribution.

40. A method according to claim 1 or 17 wherein the water level characteristic is a curve indicating the water level a various instants throughout the period and the cumulative difference between the water level characteristic and the reference water level is the area between the curve and the average water level.