Cloth bunching detection and adjustment for an automatic washer

Abstract

A method and apparatus for determining the bunching of fabric items during a wash process.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for detecting the degree of bunching of articles in an automatic clothes washer. The inventions further relates to methods of adjustment to reduce the degree of bunching.

2. Description of the Related Art

Automatic clothes washers are ubiquitous. Such appliances clean fabric items effectively, enabling the homeowner to complete other tasks or engage in more satisfying activities while doing the laundry. Modern clothes washers provide a multitude of options for matching a selected cleaning operation to the type of fabric comprising the laundry load and the degree of soiling of the laundry load. This includes setting a liquid level appropriate to the size and fabric type of the laundry load. Modern clothes washers also include sophisticated controllers that are programmed to maximize cleaning efficiency while minimizing water and power consumption. However, despite the capabilities of the modern clothes washer, the appliance remains limited in its ability to detect bunching and then adjust the wash cycle based on real-time information relating to the fabric items being washed.

One type of conventional automatic clothes washer may be provided with a drive motor, generally electrically powered, which may be used to drive a cylindrical perforate basket during a spin cycle, and a clothes mover during wash and rinse cycles for agitating the laundry load within the basket.

In a conventional automatic clothes washer, cleaning of the fabric items may be primarily attributable to three factors: chemical energy, thermal energy, and mechanical energy. These three factors may be varied within the limits of a particular automatic clothes washer to obtain the desired degree of cleaning.

The chemical energy relates to the types of wash aids, e.g. detergent and bleach, applied to the fabric items. All other things being equal, the more wash aid used, the greater will be the cleaning effect.

The thermal energy relates to the temperature of the fabric items. The temperature of the wash liquid typically constitutes the source of the thermal energy. However, other heating sources may be used. For example, one known way uses steam to heat the fabric items. All things being equal, the greater the thermal energy, the greater will be the cleaning effect.

The mechanical energy may be attributed to the contact between the clothes mover and the fabric items, the contact between the fabric items themselves, and the passing of the washing liquid through the fabric items. In washing machines with a fabric mover, the fabric mover tends to cause the fabric items to contact themselves, and for the wash liquid to pass through the fabric items. All things being equal, the greater the amount of mechanical energy, the greater will be the cleaning effect.

These three factors may be adjusted to obtain the desired cleaning effect. For example, while the direct contact between the clothes mover and the fabric items may be beneficial for laundering, it does cause greater physical wearing of the fabric items than the other two factors. Thus, for example, for more delicate clothing, it may be desired to reduce the direct contact. However with contemporary washing machines, it has not yet been possible to determine the mechanical energy imparted to the fabric items during the washing process. Thus, contemporary solutions are based on estimates or empirical data, both of which are typically determined based on a set of standard test conditions. Unfortunately, these standard test conditions are not guaranteed to be repeated when the consumer uses the clothes washer, resulting in a compromised cleaning result. It would be advantageous to the overall cleaning performance if the mechanical energy imparted to the fabric items could be determined during the washing process.

SUMMARY OF THE INVENTION

A method and apparatus for determining the degree of bunching of fabric items during a wash process.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a partially cut away elevational view of an automatic clothes washer according to the invention illustrating relevant internal components thereof, including a clothes basket, and a clothes mover.

FIG. 2 is a partially cut away perspective view of the clothes basket and clothes mover illustrated in FIG. 1.

FIG. 3 is a partially cut away enlarged view of the clothes basket and clothes mover illustrated in FIG. 2 showing an article of clothing in a first configuration relative to the clothes mover.

FIG. 4 is a view of the clothes basket and clothes mover illustrated in FIG. 3 showing the article of clothing in a second configuration relative to the clothes mover.

FIG. 5 is a view of the clothes basket and clothes mover illustrated in FIG. 3 showing the article of clothing in a third configuration relative to the clothes mover.

FIG. 6 is a schematic representation of fabric items in an un-bunched state in the cloths basket.

FIG. 7 is a schematic representation of fabric items in a bunched state in the cloths basket.

FIG. 8 is a first graphical representation of motor speed and motor current for the automatic clothes washer illustrated in FIG. 1 containing only liquid during a single cycle of the clothes mover consisting of a forward rotational stroke followed by a backward rotational stroke.

FIG. 9 graphically represents the motor speed and motor current for the automatic clothes washer illustrated in FIG. 1 containing liquid and a laundry load without bunching during a single cycle of the clothes mover consisting of a forward rotational stroke followed by a backward rotational stroke.

FIG. 10 graphically represents the motor speed and motor current for the automatic clothes washer illustrated in FIG. 1 containing liquid and a laundry load with bunching during a single cycle of the clothes mover consisting of a forward rotational stroke followed by a backward rotational stroke.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

The invention relates to a method of determining the degree of bunching of articles in a clothes washer based upon the mechanical energy imparted to the fabric items by the engagement of a clothes mover with fabric items in a laundry load. The invention may also include a method for adjusting the wash cycle based on the determined bunching. The method utilizes operational characteristics of a drive motor, such as current and speed, to determine the degree of bunching of the clothes articles. The degree of bunching of the clothes articles may be compared with pre-determined threshold for the degree of bunching to control the operating cycle by introduction of liquid to the clothes washer, by setting the agitator stroke, or by stopping the cycle.

Conventional automatic clothes washers enable a user to select one of several laundering options based upon the type of laundry load being placed in the clothes washer. For example, selectable options may include “normal,” “delicates,” “woolens,” and the like. These are typically referred to as “cycles.” As utilized herein, “laundering cycle” will refer to a specific cycle, such as “normal,” extending from the beginning of the cycle to its completion. A laundering cycle will generally consist of at least a wash cycle, a rinse cycle, and a spin cycle. The wash cycle, the rinse cycle, and the spin cycle may consist of several steps, such as a fill step, a drain step, a pause step, an agitation step, and the like. The invention may be used with any cycle regardless of the types and combination of steps.

FIG. 1 illustrates an embodiment of the invention consisting of a vertical axis automatic clothes washer 10 comprising a cabinet 12 having a control panel 14, and enclosing a liquid-tight tub 16 defining a wash chamber in which may be located a perforate basket 18. Thus, fabric items placed in the basket 18 are placed in the wash chamber. A clothes mover 20 adapted for imparting movement to a laundry load contained within the basket 18 may be disposed in the bottom of the basket 18. The clothes mover 20 illustrated has a low profile vertical axis impeller. However, the clothes mover 20 may also be a vertical axis agitator, with or without an auger, or a basket adapted with peripheral vanes. The clothes mover 20 and basket 18 may be coaxially aligned with respect to a vertically oriented oscillation axis 22.

While the invention will be illustrated with respect to a low profile impeller, other clothes movers may be utilized without departing from the scope of the invention. For example, it has been contemplated that the invention has applicability to horizontal axis washers as well as to the vertical axis washers. For purposes of this application, horizontal axis washer refers to those types of washers that move the fabric items primarily by lifting the fabric items and letting them fall by gravity, regardless of whether the axis of rotation remains primarily horizontal, and vertical axis washer refers to those types of washers that move fabric items by a clothes mover, regardless of whether the axis of rotation remains primarily vertical.

The clothes mover 20 may be operably coupled with a drive motor 28 through an optional transmission 26 and drive belt 30. One or more well-known sensors 31 for monitoring angular velocity, current, voltage, and the like, may be operably coupled with the motor 28. Outputs from the sensors 31 may be delivered to a machine controller 32 in the control panel 14. In many applications, the sensors 31 form part of a motor controller coupled with the machine controller 32. The machine controller 32 may be adapted to send and receive signals for controlling the operation of the clothes washer 10, receiving data from the sensors 31, processing the data, displaying information of interest to a user, and the like.

The clothes washer 10 may also be coupled with a source of water 34 which may be delivered to the tub 16 through a nozzle 36 controlled by a valve 38 operably coupled with the machine controller 32. The valve 38 and the machine controller 32 may enable a precise volume of water to be delivered to the tub 16 for washing and rinsing.

FIG. 2 illustrates an embodiment of the invention with the clothes basket 18 and the clothes mover 20 in coaxial alignment with the oscillation axis 22. The clothes mover 20 may be a somewhat circular, plate like body having a plurality of radially disposed vanes 40 extending upwardly therefrom. The vanes 40 may be adapted to contact and interact with fabric items and liquid in the basket 18 for agitating the fabric items and the liquid. During a wash cycle and a rinse cycle, the clothes mover 20 may be driven by the drive motor 28 for movement within the wash chamber. The basket 18 may be braked to remain stationary during the movement of the clothes mover 20, or the basket 18 may freely rotate during the movement of the clothes mover 20.

The drive motor 28 may drive the clothes mover 20 in an oscillating manner, first in a forward direction, referred to herein as a forward stroke, then in a backward direction, referred to herein as a backward stroke. The clothes mover 20 may move in a forward direction through a pre-selected angular displacement, for example ranging from 180° to 720°. The clothes mover 20 may move in a backward direction through a similar pre-selected angular displacement. A complete forward stroke and backward stroke are referred to herein as an oscillation cycle.

For clothes movers that move rotationally, the forward and backward strokes are often referred to as the clockwise and counterclockwise strokes. While typically the forward stroke constitutes the clockwise stroke and the backward stroke constitutes the counterclockwise stroke, these relationships may easily be reversed.

In a typical wash cycle, multiple fabric items, which collectively form a laundry load, are placed in the basket on top of the clothes mover 20. Some of the fabric items will be in direct contact with the clothes mover 20 and some will not. As the clothes mover 20 moves, the individual fabric items will be moved directly or indirectly by the clothes mover 20 to impart mechanical energy to the items, which will move the fabric items about the interior of the wash chamber.

In FIG. 3, an embodiment of the invention shows a single fabric item 50 in a lower portion of a laundry load will be in contact with the clothes mover 20. The illustration does not include liquid for clarity; however, it should be understood that liquid exists and it may be at any level from just wetting the fabric items to fully submerging the fabric items. The fabric item 50 may be represented by a downwardly directed weight factor 52. The vanes 40 terminate in an upper vane edge 54. All or part of the vane 40 may contact the fabric item 50 during the forward and backward strokes of the clothes mover 20. As the clothes mover 20 rotates in a forward stroke, represented by the motion vector 42, a vane 40 may be brought into contact with the fabric item 50.

FIG. 4 shows an embodiment where the contacting of the vane 40 with the single fabric item 50 tends to move the fabric item 50 in the direction of rotation of the clothes mover 20, represented by the pull vector 56. The illustration does not include liquid for clarity; however, it should be understood that liquid exists and it may be at any level from just wetting the fabric items to fully submerging the fabric items. Because of the weight of the fabric item 50, the weight of overlying fabric items, the frictional relationship between the fabric item 50 and the vane edge 54, the degree of wetting of the fabric item 50, and other factors, there may be intermittent grabbing and slipping by the vane 40 relative to the fabric item 50 which will be reflected in movement of the fabric item 50 that may not be the same rotational distance as the clothes mover 20, resulting in relative movement between the fabric item 50 and the clothes mover 20. As illustrated in FIG. 5, if sufficient slippage exists, at some point during the forward stroke the vane 40 may separate from the fabric item 50.

The intermittent grabbing and slipping of the vane 40 with respect to the clothes mover 20 results in an intermittent application of the weight of the fabric item 50 to the clothes mover 20, which amounts to a loading and unloading of the clothes mover 20. The loading and unloading present themselves as a change in speed of the clothes mover 20, this may be sensed by the sensors 31. In response, the controller 32, which typically tries to move the motor 28 at a predetermined set speed for the given cycle, will increase or decrease the current to the motor 28 to attempt to maintain the set speed.

The magnitude and frequency of grabbing and slipping may be impacted by several factors, only some of which will now be described. The greater the size laundry load, the greater will be the weight of other fabric items bearing on the fabric item in direct contact with the clothes mover 20. The increased volume of the greater laundry load will also tend to inhibit the free movement of the fabric items within the wash chamber.

Wet fabric items tend to create greater frictional resistance with the clothes mover than dry fabric items. However, as liquid level increases in the wash chamber to the point where the fabric items are fully submerged, the additional liquid brings into effect the buoyancy of the fabric items, which has an opposite effect than the weight force of the fabric items. In some instances, the liquid may be sufficiently deep and the clothes mover may sufficiently agitate the liquid that some or all of the fabric items are suspended in the liquid above the clothes mover 20, which will greatly reduce the loading of the clothes mover 20 by the fabric items. Thus, all things being equal, the deeper the liquid, the greater the degree of loading and unloading will be minimized.

Additional wash liquid also tends to interfere with the clothes mover's 20 ability to reverse the direction of the fabric items when the clothes mover 20 switches direction between the forward and backward strokes. For example, when the clothes mover 20 moves in a forward stroke, it causes not only the fabric items to move in the forward stroke direction, but also the liquid in the wash chamber to move in a forward stroke direction. Upon reversing to the backward stroke, fabric items in direct contact with the clothes mover 20 will tend to follow the reverse stroke direction of the clothes mover 20. However, the liquid, especially the liquid above the clothes mover 20, will tend to maintain movement in the forward stroke direction because of its momentum. Thus, the reversal of the clothes mover 20 does not necessarily result in all of the fabric items and liquid in the washer chamber reversing direction in time with the clothes mover 20.

FIG. 6 constitutes a schematic representation of a fabric load comprising fabric items 2 shown in an un-bunched state. Fabric items 2 are considered not bunched where they are relatively uniformly distributed in the wash liquid 4 in the wash basket 18. Uniform distribution may be desired for optimum efficiency and effective cleaning. The uniform distribution allows the cloth mover 20 to move forwards and backwards and allows for blooming of the fabric items. Blooming is the turning over of the fabric items in the wash load and is desired as it promotes uniform cleaning of the fabric items. A common form of blooming occurs when the fabric items move between the bottom of the basket to the top of the liquid. This movement can also include the fabric items moving radially inward and outward from the center of the basket to the peripheral wall of the basket.

In FIG. 7, fabric items 2 may become bunched during the wash cycle. During the wash cycle the bunched fabric items 3 become bunched to one side and are no longer uniformly distributed within the wash basket 18. Bunching may be thought of as several of the fabrics items operably coupled such that they effectively behave as a single mass. This may cause asymmetrical loading on the clothes mover. The operable coupling may arise for one or more reasons, examples include: the fabric items may be in an overlapped condition and their weight and/or frictional resistance tends to maintain the overlapped condition; the fabric items may be intertwined or wrapped around each other; and the fabric items may be twisted together.

Bunching of the fabric items in the wash basket 18 may have several different disadvantageous effects in the clothes washer 10. For example, one common disadvantage may be that the mechanical energy imparted to the fabric items by the clothes mover 20 may be focused primarily on the outside of the bunched fabric articles, which minimizes the cleaning effect to the interior fabric articles. The cleaning effect may be reduced because the wash liquid 4 may not pass through the bunched fabric items 3 as easily as if the clothes were more uniformly distributed. The cleaning effect may also be reduced because the bunched fabric items 3 are not able to move relative to each other and impart mechanical energy to each other.

The bunched clothes may also move asymmetrically within the wash basket even though the clothes mover typically rotates the same distance for both the forward and backward strokes. The phenomena of asymmetrically moving clothes occurs because the bunched clothes load has a greater inertia than an evenly distributed load and may be less likely to change direction of rotation along with the clothes mover. The phenomena may more easily occur as the liquid fill level increases in the wash chamber because the increase in the buoyancy force decreases the weight of the bunched clothes acting on the clothes mover, which makes it easier for the bunched clothes to separate from the clothes mover. The increased liquid further increases the likelihood of asymmetrical clothes movement because as the liquid rises farther above the clothes mover, the liquid may be less responsive to the movement of the clothes mover. For example, the liquid immediately adjacent the clothes mover may be very responsive to the movement of the clothes mover and tends to follow its direction. The further the liquid may be from the clothes mover, the less responsive it may be as the intervening liquid must transfer the forces from the clothes mover. The liquid also has its own inertia. Thus, once set in motion by the clothes mover the liquid as it gets farther away from the clothes mover will not be as greatly affected by the change of direction of the clothes mover. While either the bunched clothes or deeper fill may cause an asymmetrical movement of the clothes, the combined effect of bunched clothing in deeper fill wash cycles makes it more likely the bunched clothes will not follow the movement of the clothes mover. In some cases, the effect may be great enough that the bunched clothes generally move in only one direction in the wash tub. When the bunched clothing does not respond to the clothes mover, the cleaning of the bunched clothes may be reduced as there may be less mechanical energy imparted to the bunched clothes from the impeller, from reduced liquid flow through the clothes, and from less clothes-to-clothes contact.

Bunching may be further disadvantageous in that during either washing operations, where the clothes mover reciprocates, or spinning operations, where the wash basket rotates, but especially during the spinning operations, the bunched clothing may cause an out of balanced condition great enough for the wash basket to bottom out its suspension and/or contact a portion of the cabinet 12, which may be very undesirable.

Bunching may also slow the motor as the impeller blades of the clothes mover contacts the bunched fabric items. In response, the controller 32, which typically tries to move the motor 28 at a predetermined set speed for the given cycle, will increase the current to the motor 28 to attempt to increase the torque and maintain the set speed. The additional motor current results in increased costs to the consumer.

FIG. 8 graphically illustrates a waveform of the motor speed 70 and the motor current 72 during one oscillation cycle of the clothes mover 20 through a forward stroke, represented by a forward direction region 74, followed by movement in a backward stroke, represented by a backward direction region 76. The waveforms of FIG. 8 are generated by sampling the motor speed 70 and motor speed current 72 at a predetermined interval or sampling rate, which in this case constitutes 20 milliseconds.

As illustrated, in the forward direction region 74 the clothes mover 20 may be quickly accelerated to a predetermined set speed 74a, maintained at the predetermined set speed 74b, and then quickly decelerated 74c, which may include braking, prior to reversing. Region 74b may often be referred to as the plateau. The backward direction region 76 may be similarly divided into an acceleration step 76a, a plateau 76b, and a deceleration step 76c. Thus, when the clothes mover 20 transitions from the forward stroke to the backward stroke, the motor current 72 decreases to a zero value 94, and the motor speed 70 responsively decreases to a zero or nearly zero value 96. While the decrease in speed may not be shown going to zero in FIG. 8, this results from the sampling rate for the data points—the zero speed was not sampled—not an indication that the speed does not go to zero. In reality, whenever the clothes mover changes direction, there must be necessarily a point, which might be instantaneous, where the speed equals zero.

During the forward and backward strokes as illustrated in FIG. 8, the controller controls the speed of the motor in an attempt to maintain the motor speed at a predetermined set speed, which for the example in FIG. 8 constitutes 110 rpm. Thus, the speed of the clothes mover 20 remains essentially constant at approximately the 110 RPM set speed in the plateau 74b, 76b of the curve 70. There are nominal variations or ripples in the magnitude of the motor current and motor speed in the plateaus 74b, 76b due to the nominal loading and unloading of the liquid on the clothes mover 20 associated with the engagement of the clothes mover 20 with the liquid as the clothes mover 20 moves through the liquid. This loading and unloading transmits through the clothes mover 20 and the transmission 26 to the drive motor 28 where it may be sensed by the speed sensor 31. The loading and unloading causes temporary changes in the speed of the clothes mover 20 relative to the set speed. In response, the controller 32 adjusts the current to the motor 28 in an attempt to maintain the set speed, which results in the motor current leading the speed as may be easily seen in FIG. 8.

FIG. 9 graphically illustrates the waveforms for the motor current 72 and motor speed 70 signals attributable to the loading and unloading of the clothes mover 20 when there exists a load of generally well distributed fabric items 50 in the wash chamber for one oscillation cycle of the clothes mover 20. FIG. 9 illustrates the waveforms of the motor speed 70 and motor current 72 where the motor speed set point constitutes 120 rpm and the sampling rate equals 20 milliseconds. The intermittent grabbing and slipping of the fabric items 50 with the vanes of the clothes mover 20 transmits through the clothes mover 20 and the transmission 26 to the drive motor 28, where it manifests as ripples in the waveforms of both the motor speed and motor current. These ripples define a waveform having multiple peaks. The peaks have greater magnitude than those ripples in FIG. 8 because of the greater force associated with the laundry load as compared to the liquid alone. A peak in the waveform is an indication of the engagement between the clothes and the impeller and does not illustrate bunching.

Looking more closely at the ripples of the motor speed waveform in a fairly well distributed load, the ripples may be separated into peaks comprising both positive peaks 82a-d, 86a-d and negative peaks 84a-d, 88a-d. The amplitude or magnitude of the ripples may be determined by comparing the peaks to the motor speed set point. For example, the difference between the positive speed amplitude 82 and the target rotation speed may be a first amplitude value. Similarly, the difference between the negative speed amplitude 84 and the target rotation speed, expressed as an absolute value, may be a second amplitude value. The average frequency of the ripples may be determined by counting the number of positive/negative peaks for a given time period or by taking the speed of the wave and dividing by its wavelength. The motor speed and motor current waveforms have a quasi sinusoidal waveform for which a frequency may be determined using the positive/negative peaks for the time of the plateau 74b, 76b.

The motor current waveform in a fairly well distributed load shows a similar waveform to the motor speed with the current tending to lead the speed. The leading of the current relative to the motor speed results from the controller attempting to maintain the motor speed at the set speed. Because the magnitude of the current depends on the controller trying to maintain the set speed, the motor current does not have a corresponding set point in the way that the motor speed has a set point.

The amplitude values and frequency values for either or both of the motor speed and motor current may be stored by the machine controller 32 as individual data values as well as a cumulative value. The amplitude values may be averaged and, more preferably, a running average of the amplitude values may be determined and stored by the machine controller 32. The frequency values may also be averaged and, more preferably, a moving average of the frequency values may be determined and stored by the machine controller 32. The averages may be calculated over a set or variable time or a set or variable amount of movement of the clothes mover. The averages may be temporary averages or cumulative averages.

FIG. 10 shows an example of the current and speed waveforms that are indicative of bunching. Looking more closely at the ripples of the motor current waveform of FIG. 10, the forward stroke 74 has four positive peak points 92a-d while the backward stroke 76 has eight positive peak points 95a-h. It has been determined that the inconsistency between the number of peaks indicates bunching exists. This is because in the forward stroke the load is pushed in a forward or clockwise motion by the clothes mover 20. However, when the clothes mover 20 is in the backward stroke the bunched clothing may not be effectively pushed by the backward stroke. Instead, the clothes mover 20 skips underneath the bunched fabric items 3 and the bunched fabric items 3 do not immediately follow the clothes mover and may continue in the forward direction. This asymmetry in the clothes and basket motion manifests as asymmetry in the motor current waveforms between the forward and backward strokes.

More specifically, it is believed that the increased frequency of the backward stroke may be caused because the bunched fabric items are not traveling with the clothes mover to the same extent as on the forward stroke, resulting in a greater number of separations and contacts between the bunched clothes and the blades of the clothes mover, which correspondingly loads/unloads the clothes mover at a greater frequency, causing the motor to respond by increasing/decreasing current/speed in an attempt to maintain the set speed. In this way, the clothes mover can be thought of as skipping beneath the bunched fabric items, with the skipping resulting in an increased number of peaks in the backward stroke of the motor current and motor speed waveforms as well as a reduction in the magnitude of the peaks.

While the increased frequency in the backward stroke relative to the forward stroke indicates bunching, it has been determined that the frequency information can be used to quantify the degree of bunching in addition to the existence of bunching. The degree of bunching of the fabric items may be determined from the motor current data in real-time. In this way, the use of the data amounts to a real-time sensor placed in the wash chamber for determining the degree of bunching. Such a sensor has never before been available.

Applicants have also determined that the amplitude of the motor current may provide an accurate estimate of the degree of bunching of the fabric items, thereby enabling corrective action to be taken. The degree of bunching of the fabric items in a laundry load may be determined from the sample data of the waveforms of the forward and backward strokes, more specifically by comparing the determined amplitudes of the forward and backward strokes. For example, the sample data may be compared essentially on a point by point basis between corresponding points for the forward and backward strokes. The corresponding points may be thought of as paired points. The comparison may be done by determining the difference in amplitude between the corresponding paired points for the forward and backward strokes. This difference may be determined for all of the paired points or some of the paired points. The difference may be determined over one or multiple oscillation cycles. The difference may be tracked as a single difference, a running total that may be weighted or not, or as a trapped maximum difference. The difference of the amplitude may then be compared to a predetermined threshold and the degree of bunching may then be determined. The predetermined threshold may be a range of values or a single value. In most cases, it will be a single value that represents the threshold between acceptable and unacceptable bunching for the given washer.

Applicants have also determined that one type of difference which may accurately determine the degree of bunching is the asymmetry between the forward and backward strokes of the motor current waveform. This asymmetry can be computed from sample data of the waveforms from both the forward and backward strokes. This can be done using the entire waveform for the stroke or a part of the waveform. The asymmetry may be tracked as a single value, a running total that may be weighted or not, or as a trapped maximum value. The asymmetry can provide an estimate of the degree of bunching of the fabric items, thereby enabling corrective action to be taken. The more asymmetrical the waveforms are the greater the degree of bunching estimated.

A more detailed look at one implementation of determining the difference using the paired points should be helpful in further understanding the invention. It should be noted that the following implementation has been based on a mean squared difference method, which has been found to provide the desired resolution for determining the degree of bunching for the contemplated washer; however, it may be contemplated that other mathematical methods may also be used.

Looking to FIG. 10 as an example, the sample data of the clothes mover motor current for the forward stroke at the twenty-fifth sample is depicted as A. The sample data of the clothes mover motor current for the backward stroke at the twenty-fifth sample is depicted as B. Points A and B represent a set of paired points in the motor current waveform as each corresponds to the twenty-fifth sample during its respective stroke. In this manner the magnitude of each point on the forward stroke of the waveform may be compared to its counterpart on the backward stroke. In FIG. 10 the sampling rate results in there being fifty sets of paired points. The mean square difference may be taken between such paired points.

MSD_—I=1/NΣ_n=1^n=N{I(CW,n)−I(CCW,n)}²   (1)

where:

I is the current signal;

MSD_I is the mean squared difference for the current signal;

CW is a clockwise stroke of the clothes mover;

CCW is the counterclockwise stroke of the clothes mover;

“N” is the total number of paired data points; and

“n” is the paired data points of interest in the total number N of paired data points.

The number of paired points N may be across one complete oscillation cycle. Alternatively it may be across more than one cycle or less than one cycle. The MSD_I value may then be compared to a threshold T to determine the degree of bunching. The formulas below represent the comparison made between MSD_I and the threshold value.

MSD_—I>=T=Clothes are bunched   (2)

MSD_—I<T=Clothes are not bunched   (3)

The threshold value T will typically be empirically determined for different clothes washers, and established based upon factors such as fabric type, laundry load size, laundering cycle, clothes mover configuration, motor type, transmission type, and the like. An MSD_I greater than or equal to the threshold value T indicates the clothes are bunched. An MSD_I less than the threshold value T indicates the clothes are not bunched.

Another implementation takes the average of the mean squared difference determined by formula (1) for a number of mean squared difference determinations, which may be represented by the formula:

MSD_—IA=1/MΣ_m=1^m=MMSD_—I(m)   (4)

where:

M represents the number of mean squared difference determinations used to compute the average; and

m is the current mean squared difference determination.

It is currently contemplated that M will represent the number of oscillation cycles and the mean squared difference MSD_I will be calculated for paired points corresponding to a complete oscillation cycle. In that way, the MSD_IA will be an average of the mean squared difference for multiple oscillation cycles. However, as the MSD_I determination need not be on an oscillation cycle bases, the MSD_IA also need not be on an oscillation cycle basis.

This MSD_IA value may then be compared to its own threshold TA to determine the degree of bunching. The formulas below represent the comparison made between MSD IA and the threshold value.

MSD_—IA>=TA=Clothes are bunched   (5)

MSD_—IA<TA=Clothes are not bunched   (6)

An MSD_IA greater than or equal to the threshold value TA indicates the clothes are bunched. An MSD_IA less than the threshold value TA indicates the clothes are not bunched.

The methods represented by formulas (1) and (4) may also be implemented as a moving average over a predetermined set of values, sets of paired points or mean squared difference determinations as the case may be. For example, a moving average using formula (1) could be continuously calculated using the most recent specified number of paired points such as the most recent 5 points, 50 points, 500 points, or whatever number is chosen. The number of paired points would likely be based on the number of paired points required by a particular washing machine platform to provide the degree of bunching at a resolution needed for the operation of the particular washing machine platform. For formula (4), a moving average calculation could also be implemented by picking a predetermined number and sequence of the mean squared difference determinations from formula (1) such as the last 5, 10, or 15 mean squared difference determination. The number of mean squared difference determinations will likely be based on the number required by a particular washing machine platform to provide the degree of bunching at a resolution needed for the operation of the particular washing machine platform.

An illustrative example of the use of the bunch detection during the operation of the washing machine should be helpful in understanding the bunch detection within the washing operation. During a fill step in a wash cycle, the clothes mover 20 may be rotated through a pre-selected number of preliminary oscillation cycles, for example five, while water is added to the wash chamber, or after an initial filling of the clothes washer 10. Thus, the clothes mover 20 rotates through five forward strokes and five backward strokes while the machine controller 32 keeps track of the degree of bunching using the previously described method. This may be accomplished by the machine controller receiving data samples of the motor current from the sensor 31, storing the values of the magnitude at the same specific sampling time for each of the forward and backward strokes in the oscillation cycle, determining the mean square difference between the two points and maintaining an average of the mean squared differences. At the end of one cycle, the mean squared difference average, MSD_I, may be compared to a pre-selected threshold value, T. Alternatively or additionally, a comparison may also be made at the end of multiple cycles, where the value may be either a moving average or not. The machine controller 32 uses the determination of the degree of bunching to control the operation of the clothes washer. Specifically the machine controller 32 will take corrective action to separate the bunched clothing if the mean squared difference equals or exceeds than the threshold.

It should be noted that other types of threshold comparisons may exist. As described, the mean squared difference determined value is compared on a greater than or equal to basis. However, the threshold could be picked in such a way that the comparison may be done on a greater than basis, less than basis, or less than or equal to basis. The type of comparator may normally be controlled by how the threshold number is quantified. The predetermined threshold value may represent an optimal uniform distribution level reflecting an optimal combination of cleaning effort and cleaning efficiency. An optimal level has been reached when the mean squared difference or average of mean squared difference reaches the pre-selected threshold value.

Another way in which the current and motor speed information can be used to determine the degree of bunching is by using the ripple frequency of the current and motor speed waveforms. One manner of using the frequency is to use an average frequency, which may include determining the average frequency for each of the forward and backward strokes and then comparing the determined average frequencies of the forward and backward strokes. For example, the average frequency may be compared between corresponding samples for the forward and backward strokes. The corresponding samples may be thought of as paired sections of each stroke. The comparison may be done by determining the difference in the average ripple frequency between the forward and backward strokes. This difference may be determined for any useful time segment or operation segment, such as: multiple oscillation cycles, all of an oscillation cycle, or a portion of an oscillation cycle. The difference may be tracked as a single difference, a running total that may be weighted or not, or as a trapped maximum difference. The difference of the frequencies may then be compared to a predetermined threshold and the degree of bunching may then be determined. The predetermined threshold may be a range of values or a single value. In most cases, it will be a single value that represents the threshold between acceptable and unacceptable bunching for the given washer.

A more detailed look at an implementation of determining the difference using frequency data should be helpful in further understanding the invention. It should be noted that the following implementation has been based on an average ripple frequency difference method, which has been found to provide the desired resolution for determining the degree of bunching for the contemplated washer; however, it may be contemplated that other mathematical methods may also be used.

Using the data of FIG. 10 for the example, the frequency data of the clothes mover motor speed for the forward stroke is depicted as 74. Motor current may also be used to determine the degree of bunching but this explanation will use only motor speed. The frequency data of the clothes mover motor speed for the backward stroke is depicted as 76. The larger wavelengths in the forward stroke 74 correlates to the forward stroke 74 having a smaller frequency then the backward stroke 76 which has a much larger frequency and much shorter wavelengths. In this manner the average frequency for those samples may be determined from the waveform and may be compared to its counterpart on the forward or backward stroke.

Using the data of FIG. 10 for the example, the average may be calculated on a per stroke basis and then compared by taking the difference between the average frequencies for forward and backward stroke. In FIG. 10, the sampling rate was approximately fifty data points per stroke, resulting in fifty pairs of corresponding data points for the forward and backward strokes. The difference in the average frequency difference may be taken between such paired values using the formula:

delta_—F={Avg_—F(W(CW, n))−Avg_—F(W(CCW, n)}  (1)

where:

W is either the speed or current signal;

Delta_F is the difference between the average frequencies of the signal;

CW is a clockwise stroke of the clothes mover;

CCW is the counterclockwise stroke of the clothes mover;

“n” is the number of samples used to determine the average frequency in each of the clockwise and counterclockwise strokes; and

Avg_F is the average frequency of one of the forward or backward strokes for the “n” samples taken.

The delta_F value may then be compared to a threshold T to determine the degree of bunching. The formulas below represent the comparison made between delta_F and the threshold value.

delta_—F>=T=Clothes are bunched   (2)

delta_—F<T=Clothes are not bunched   (3)

The threshold value T will typically be empirically determined for different clothes washers, and established based upon factors such as fabric type, laundry load size, laundering cycle, clothes mover configuration, motor type, transmission type, and the like. A delta_F greater than or equal to the threshold value T indicates the clothes are bunched. A delta_F less than the threshold value T indicates the clothes are not bunched.

Another implementation takes the average of the frequency difference determined by formula (1) for a number of frequency difference determinations, which may be represented by the formula:

delta_—FA=1/MΣ_m=1^m=Mdelta_—F(m)   (4)

where:

M represents the number of frequency difference determinations used to compute the average; and

m is the speed or current frequency difference determination.

It is currently contemplated that M will represent the number of oscillation cycles and the frequency difference delta_F will be calculated for a sample corresponding to a complete oscillation cycle. In that way, the delta_FA will be an average of the frequency difference for multiple oscillation cycles. However, as the delta_F determination need not be on an oscillation cycle bases, the delta_FA also need not be on an oscillation cycle basis.

This delta_FA value may then be compared to its own threshold TA to determine the degree of bunching. The formulas below represent the comparison made between delta_FA and the threshold value.

delta_—FA>=TA=Clothes are bunched   (5)

delta_—FA<TA=Clothes are not bunched   (6)

A delta_FA greater than or equal to the threshold value TA indicates the clothes are bunched. A delta_FA less than the threshold value TA indicates the clothes are not bunched.

This implementation has two tunable parameters including M which represents the number of frequency difference determinations used to compute the average and may be varied to include a larger or smaller number of determinations. A larger amount of determinations would show the bunching over a greater period of time while a smaller number would be an average for a shorter time period. Furthermore, TA the threshold level may be tuned to allow bunching to be determined be the invention at lower or greater amounts.

By tuning these parameters the best performance can be extorted using this algorithm. The tunable parameter values may also differ between the speed based and current based algorithms. But irrespective of the signal used, the underlying algorithm metric and concept are the same. The main reason for choosing a moving average as a way to filter the data is to minimize embedded software implementation costs (i.e. memory/CPU usage); otherwise, a more expensive filter may be used to improve detection accuracy.

The methods represented by formulas (1) and (4) may also be implemented as a moving average over a predetermined set of samples, either parts of an oscillation cycle or multiple oscillation cycles as the case may be. For example, a moving average using formula (1) could be continuously calculated using the most recent specified number of samples for each of the forward and backward strokes such as the most recent 5 samples, 50 samples, 500 samples, or whatever number is chosen, of each of the forward and backward strokes. The number of samples would likely be based on the number of samples required by a particular washing machine platform to provide the degree of bunching at a resolution needed for the operation of the particular washing machine platform. For formula (4), a moving average calculation could also be implemented by picking a predetermined number and sequence of the frequency difference determinations from formula (1), such as the last 5, 10, or 15 frequency difference determinations. The number of frequency difference determinations will likely be based on the number required by a particular washing machine platform to provide the degree of bunching at a resolution needed for the operation of the particular washing machine platform.

An illustrative example of the use of the bunch detection during the operation of the washing machine should be helpful in understanding the bunch detection within the washing operation. During a fill step in a wash cycle, the clothes mover 20 may be rotated through a pre-selected number of preliminary oscillation cycles, for example five, while an addition of water to the wash chamber takes place, or after an initial filling of the clothes washer 10. Thus, the clothes mover 20 rotates through five forward strokes and five backward strokes while the machine controller 32 keeps track of the degree of bunching using the previously described method. This may be accomplished by the machine controller receiving data samples of the motor speed or motor current from the sensor 31, storing the values of the average frequency for each of the forward and backward strokes in the oscillation cycle, determining the difference between the two average frequencies and maintaining the differences of the average frequencies. At the end of one cycle, the frequency difference, delta_F, may be compared to a pre-selected threshold value, T. Alternatively or additionally, a comparison may also be made at the end of multiple cycles, where the value may be either a moving average or not. The machine controller 32 uses the determination of the degree of bunching to control the operation of the clothes washer. Specifically the machine controller 32 will take corrective action to separate the bunched clothing if the frequency difference equals or exceeds than the threshold.

It should be noted that other types of threshold comparisons may exist. As described, the frequency difference determined value may be compared on a greater than or equal to basis. However, the threshold could be picked in such a way that the comparison may be done on a greater than basis, less than basis, or less than or equal to basis. The type of comparator may normally be controlled by how the threshold number may be quantified. The predetermined threshold value may represent an optimal uniform distribution level reflecting an optimal combination of cleaning effort and cleaning efficiency. An optimal level has been reached when the difference between the average frequencies or average of the difference between the average frequencies reaches the pre-selected threshold value.

The ability to determine or sense the degree of bunching benefits the improvement of the wash performance as actions may be taken to reduce the bunching. Once one has the ability to determine the degree of bunching, one may then manipulate the wash cycle accordingly to control the degree of bunching. Controlling the liquid level in the clothes washer constitutes one way in which the degree of bunching may be controlled. As the liquid level increases in the wash chamber the fabric items may become more submerged. Even if the articles are not fully submerged the additional liquid adds to the buoyancy effect of the fabric items. This has an opposite effect than the weight force of the fabric items. In some instances, the liquid may be sufficiently deep and the clothes mover may sufficiently agitate the liquid that some or all of the fabric items become unbunched which will greatly reduce the loading of the clothes mover 20 by the fabric items. This in turn allows the clothes mover to move freely and increase its speed in comparison to when the fabric items were bunched. This allows the controller to reduce the motor current. Thus, the determined degree of bunching may be used to adjust the liquid level and thereby control the degree of bunching.

Another way of controlling the degree of bunching constitutes changing the length and speed of the forward or backward stroke of the clothes mover in the clothes washer. First, the speed of the cloth mover may be controlled. Additionally, the clothes mover may be controlled to increase or decrease the length of the forward or backward stroke. Shorter faster strokes of the cloth mover may more easily break up the bunched fabric articles. Once the fabric articles are more separated they may then continue to be more uniformly dispersed in the wash chamber by the forward and backward strokes of the cloth mover. Shorter strokes may also be used in combination with increased liquid levels in the wash chamber to reduce the amount of bunching of the fabric articles. Thus, the determined degree of bunching may be used to adjust the length and speed of the cloth mover stroke and thereby control the degree of bunching.

Furthermore, the machine may also be stopped if the degree of bunching happens to be high enough for safety reasons and so damage will not be done to the machine. Moreover, if the mean squared difference value or the moving average mean squared difference value become less than the threshold the current addition of liquid to the wash chamber will be stopped. Or if the mean squared difference value or the moving average mean squared difference value becomes less than the threshold the strokes may be lengthened and slowed as necessary.

The liquid level and stroke length and speed adjustments may be conducted at any time during the wash cycle. For example, it may be part of the filling step or it may be part of the wash or rinse steps. In this way, the fabric items may be unbunched as soon as bunch detection occurs. This also acts as a safety step if fabric items are irreparably bunched immediately upon a user loading the clothing into the washing machine. The machine may be immediately stopped before damage occurs to the machine.

The invention described herein provides an optimized laundering cycle by setting a liquid level, stroke length and stroke speed that are sufficient for satisfactorily cleaning a laundry load, thereby reducing the bunching of fabric items in the load. Thus, the items being laundered are cleaned more efficiently and cleaned better thereby saving the consumer costs related to cleaning and recleaning. Finally, the utilization of motor current in determining an optimal liquid level and stroke length and speed requires no additional instrumentation, thereby minimizing additional cost. The invention simply utilizes readily available information in a new manner to control an operation in order to optimize the laundering performance of a clothes washer.

While the invention has been specifically described in connection with certain specific embodiments thereof, understand that this constitutes an illustration and not a limitation. Reasonable variation and modification are possible within the scope of the forgoing disclosure and drawings without departing from the spirit of the invention defined in the appended claims.

Claims

1. A method for determining the degree of bunching of fabric articles in an automatic washer comprising a wash tub in which is disposed a wash basket defining a wash chamber configured to receive the fabric articles and an article mover located within the wash chamber and reciprocally driven by a motor between a forward stroke and backward stroke to impart mechanical energy to the fabric articles, the method comprising:

determining a characteristic of a waveform for at least one of the motor speed and motor current for each of the forward and backward strokes; and

determining the degree of bunching by comparing the determined characteristic for each of the forward and backward strokes.

2. The method according to claim 1 wherein determining the characteristic comprises determining an amplitude of the waveform for each of the forward and backward strokes.

3. The method according to claim 2 wherein the comparing of the amplitudes comprises determining the difference between the amplitudes of the motor current waveform.

4. The method according to claim 3 wherein the difference is compared to a threshold value to determine the degree of bunching.

5. The method according to claim 3 wherein the comparing of the amplitudes comprises determining the mean square of the difference between the amplitudes.

6. The method according to claim 3 wherein the difference between the amplitudes is determined for multiple pairs of the forward and backward strokes.

7. The method according to claim 6 wherein the comparing of the amplitudes comprises determining the mean square of the differences for the multiple pairs of forward and backward strokes.

8. The method according to claim 6 wherein the multiple differences are averaged.

9. The method according to claim 8 wherein the average is compared to a threshold value to determine the degree of bunching.

10. The method according to claim 3 wherein the determining the difference of the amplitudes comprises at least one of determining a difference between a current wave form for each of the forward and backward strokes and determining a difference between a point of each of the waveforms for the forward and backward strokes.

11. The method according to claim 2 wherein the determining of the amplitudes comprises determining amplitudes at the same relative time for each of the forward and backward strokes.

12. The method according to claim 11 wherein the comparing of the amplitudes comprises determining the difference between the amplitudes.

13. The method according to claim 12 wherein the difference is compared to a threshold value to determine the degree of bunching.

14. The method according to claim 12 wherein the comparing of the amplitudes comprises determining the mean square of the difference between the amplitudes.

15. The method according to claim 12 wherein the difference between the amplitudes is determined for multiple pairs of the forward and backward strokes.

16. The method according to claim 15 wherein the comparing of the amplitudes comprises determining the mean square of the differences for the multiple pairs of forward and backward strokes.

17. The method according to claim 15 wherein the multiple differences are averaged.

18. The method according to claim 17 wherein the average is compared to a threshold value to determine the degree of bunching.

19. The method according to claim 1 wherein determining the characteristic comprises determining a frequency of the waveform for each of the forward and backward strokes.

20. The method according to claim 19 wherein the comparing of the frequencies comprises determining the difference between the frequencies.

21. The method according to claim 20 wherein the difference is compared to a pre-determined value.

22. The method according to claim 19 and further comprising repeating the determination of the frequencies for multiple forward strokes and backward strokes.

23. The method according to claim 22 and further comprising determining an average frequency for the forward strokes and an average frequency for the backward strokes.

24. The method according to claim 23 wherein the comparing the determined frequencies comprises comparing the average frequencies.

25. The method according to claim 24 wherein the comparing of the frequencies comprises determining the difference between the average frequencies.

26. The method according to claim 25 wherein the difference is compared to a pre-determined value.

27. The method according to claim 22 wherein the determining of the frequency comprises determining an average frequency for the forward strokes and an average frequency for the backward strokes.

28. The method according to claim 27 wherein the comparing the determined frequencies comprises comparing the average frequencies.

29. The method according to claim 28 wherein the comparing of the frequencies comprises determining the difference between the average frequencies.

30. A method for controlling the operation of an automatic washer comprising a wash tub in which is disposed a wash basket defining a wash chamber configured to receive fabric articles and an article mover located within the wash chamber and reciprocally driven by a motor between a forward stroke and backward stroke to impart mechanical energy to the fabric articles, the method comprising:

determining a characteristic of a waveform for at least one of the speed and current for the motor for each of the forward and backward strokes;

determining the bunching of the fabric articles from the determined characteristics; and

controlling an operating cycle of the automatic washer based on the determined characteristics.

31. The method according to claim 30 wherein the determining of the bunching comprises comparing the characteristics.

32. The method according to claim 31 wherein the determining a characteristic comprises determining an amplitude of the motor current waveform for each of the forward and backward strokes.

33. The method according to claim 32 wherein the comparing of the characteristics comprises comparing the amplitudes by determining the difference between the amplitudes.

34. The method according to claim 33 wherein the difference is compared to a threshold value to determine the degree of bunching.

35. The method according to claim 33 wherein the comparing of the amplitudes comprises determining the mean square of the difference between the amplitudes.

36. The method according to claim 33 wherein the difference between the amplitudes is determined for multiple pairs of the forward and backward strokes.

37. The method according to claim 36 wherein the comparing of the amplitudes comprises determining the mean square of the differences for the multiple pairs of forward and backward strokes.

38. The method according to claim 36 wherein the multiple differences are averaged.

39. The method according to claim 36 wherein the average is compared to a threshold value to determine the degree of bunching.

40. The method according to claim 36 wherein the determining the difference of the amplitudes comprises at least one of determining a difference between a current wave form for each of the forward and backward strokes and determining a difference between a point of each of the waveforms for the forward and backward strokes.

41. The method according to claim 32 wherein the determining of the amplitudes comprises determining an amplitude at the same relative time for each of the forward and backward strokes.

42. The method according to claim 41 wherein the comparing of the amplitudes comprises determining the difference between the amplitudes.

43. The method according to claim 42 wherein the difference is compared to a threshold value to determine the degree of bunching.

44. The method according to claim 42 wherein the comparing of the amplitudes comprises determining the mean square of the difference between the amplitudes.

45. The method according to claim 42 wherein the difference between the amplitudes is determined for multiple pairs of the forward and backward strokes.

46. The method according to claim 45 wherein the comparing of the amplitudes comprises determining the mean square of the differences for the multiple pairs of forward and backward strokes.

47. The method according to claim 45 wherein the multiple differences are averaged.

48. The method according to claim 47 wherein the average is compared to a threshold value to determine the degree of bunching.

49. The method according to claim 30 wherein the controlling of the operating cycle comprises adjusting at least one of the impeller stroke and water level in the wash chamber.

50. The method according to claim 49 and further comprises adjusting of the operating cycle after at least one pair of strokes and after many multiple pairs of strokes.

51. The method according to claim 49 and further comprises immediate adjustment of the operating cycle when the bunching is determined to be very high.

52. The method according to claim 51 wherein the adjustment of the operating cycle comprises stopping the cycle.

53. The method according to claim 49 wherein the adjusting of the impeller stroke comprises at least one of increasing the speed and shortening the length of the impeller stroke

54. The method according to claim 49 wherein the adjusting of the water level in the wash chamber comprises increasing the water level in at least one of the wash chamber and wash basket.

55. The method according to claim 31 wherein determining the characteristic comprises determining a frequency for each of the forward and backward strokes.

56. The method according to claim 55 and further comprising repeating the determination of the frequencies for multiple forward strokes and backward strokes.

57. The method according to claim 56 and further comprising determining an average frequency for the forward strokes and an average frequency for the backward strokes.

58. The method according to claim 57 wherein the comparing the determined frequencies comprises comparing the average frequencies.

59. The method according to claim 58 wherein the comparing of the frequencies comprises determining the difference between the average frequencies.

60. The method according to claim 55 wherein the determining of a frequency comprises determining an average frequency for each of the forward and backward strokes.

61. The method according to claim 60 wherein the determining of the bunching comprises comparing the determined average frequencies.

62. The method according to claim 61 wherein the comparing of the frequencies comprises determining the difference between the average frequencies.

63. The method according to claim 62 wherein the difference is compared to a pre-determined value.

64. An automatic clothes washer comprising:

a wash chamber for receiving fabric items;

a clothes mover located within the wash chamber;

a motor operably coupled to the clothes mover to move the clothes mover relative to the wash chamber; and

a sensor configured to determine the degree of bunching of the fabric items in the wash chamber.

65. The automatic clothes washer according to claim 64, wherein the sensor is a real-time sensor.

66. The automatic clothes washer according to claim 65, wherein the real-time sensor comprises at least one of a motor speed sensor and motor current sensor.

67. The automatic clothes washer according to claim 66, wherein the real-time sensor further comprises a controller configured to receive an output from one of the motor speed sensor and the motor current sensor.

68. The automatic clothes washer according to claim 67, wherein the controller is configured to determine the degree of bunching from the output.

69. The automatic clothes washer according to claim 70, wherein the output is a determined characteristic of a waveform for at least one of the motor speed and motor current for each of the forward and backward strokes.

70. The method according to claim 69 wherein determining the characteristic comprises determining the amplitude from the motor current sensor.

71. The method according to claim 69 wherein determining the characteristic comprises determining the frequency from at least one of the motor current sensor or the motor speed sensor.