Title of Invention	"AN APPLIANCE FOR DETECTING AN OUT OF BALANCE CONDITION IN A ROTATING VESSEL OF APPLIANCES SUCH AS WASHING MACHINES AUTOMATIC DRYERS, CENTRI FUGAL LIQUID EXTRACTORS"
Abstract	A method and apparatus for determining load unbalance in an appliance is provided for an appliance having a vessel configured to receive a supply of material and rotatable about an axis. A control is arranged and configured to accelerate a rotation of the vessel between a series of constant rotational speeds, measure an amount of current with which the motor draws in rotating the vessel at each of the rotational speeds and during each acceleration period, compare the amount of current with a calculated threshold value for each speed and each acceleration period and send a signal indicative of an unbalance condition if the amount of energy exceeds the precalculated threshold value. The vessel may be rotated by use of an electric motor such as a controlled induction motor and the control can be used to measure the electric current drawn by the motor. The threshold values can further be adjusted by comparing the actual line voltage supplied to the motor with a predetermined nominal line voltage.

Title of Invention

"AN APPLIANCE FOR DETECTING AN OUT OF BALANCE CONDITION IN A ROTATING VESSEL OF APPLIANCES SUCH AS WASHING MACHINES AUTOMATIC DRYERS, CENTRI FUGAL LIQUID EXTRACTORS"

Abstract

A method and apparatus for determining load unbalance in an appliance is provided for an appliance having a vessel configured to receive a supply of material and rotatable about an axis. A control is arranged and configured to accelerate a rotation of the vessel between a series of constant rotational speeds, measure an amount of current with which the motor draws in rotating the vessel at each of the rotational speeds and during each acceleration period, compare the amount of current with a calculated threshold value for each speed and each acceleration period and send a signal indicative of an unbalance condition if the amount of energy exceeds the precalculated threshold value. The vessel may be rotated by use of an electric motor such as a controlled induction motor and the control can be used to measure the electric current drawn by the motor. The threshold values can further be adjusted by comparing the actual line voltage supplied to the motor with a predetermined nominal line voltage.

Full Text	BACKGROUND OF THE INVENTION The present invention relates to an appliance for detecting an out of balance condition in a rotating vessel of appliances such as washing machines, automatic dryers, centrifugal liquid extractors. Various appliances, such as automatic washing machines, automatic dryers, centrifugal liquid extractors, etc., utilize a rotating tub, basket or other vessel holding a load of material which may or may not be evenly distributed within the vessel. The condition of having the load unevenly distributed, or out of balance, creates a situation where the center of mass of the rotating vessel does not correspond to the geometric axis of the vessel. This leads to the generation of high loads and severe vibration of the vessel. In an appliance, this severe vibration may cause the phenomenon of movement of the appliance across the floor or other supporting surface. This can occur both in vertical axis rotating vessels as well as horizontal axis vessels and also in those appliances where the axis is arranged in-between vertical and horizontal. Various attempts have been provided in the prior art to provide mechanical arrangements to limit or reduce the possibility of unbalanced loads, which typically involve the addition of various masses, either fixed or movable, to the vessel which requires additional power for the motor to rotate the vessel. Approaches have also been disclosed in the prior art for detecting a load imbalance, for example, in an inverter driven motor for a washing machine, as disclosed in U.S. Patent No. 5,070,565, That patent discloses to examine a ripple in the de-inverter bus current, with a ripple value above a pre-determined level being indicative of load unbalance. If a load unbalance is detected, the washer controller would resume a redistribution cycle to attempt to re-balance the clothes. This would be attempted a pre-detennined number of times and, if the load is still unbalanced, the spin cycle would be aborted. If the ripple value falls below the pre-determined level before the maximum number of tries is reached, the spin cycle is started. Once a spin cycle has been initiated, the length of the spin cycle is determined on the basis of the magnitude of any remaining load unbalance. Spin rate and spin time may be adjusted based upon the degree of load unbalance detected. [1005] It would be an advance if a method and apparatus were provided in which the potential for a severe unbalance could be predicted in advance of it actually occurring so that appropriate steps could be taken to avoid the detrimental effects of such a condition. SUMMARY OF THE INVENTION [1006]} The present invention provides a method and apparatus for detecting a severe unbalance condition in a rotating device such as a basket, tub or other rotatable vessel of an appliance, for example an automatic washer. The method and apparatus provide the detecting by monitoring the motor current signature. When a severe unbalance condition is detected at a high rotational speed, the spin speed can be adaptively dropped down to a safe level, in which the appliance vibrations and mechanical stresses are tolerable. The appliance system can be continuously monitored so that, in the case of an appliance such as an automatic washer, clothes dryer or centrifugal water extraction, as water is extracted from the fabric load, and the load becomes less massive, the spin speed can be gradually increased to a desired level. If too great of an unbalance condition still persists, the spin speed can be adaptably limited or the cycle can be terminated and the user can be advised. [1007] The effect of unbalanced loads in a motor driven rotating component, such as arotatable vessel, translates into motor torque oscillations, which are proportional to the motor stator currents. Moreover, increased vibrations in certain appliances cause energy dissipation in passive components, such as in the suspension system, causing the average motor current to increase. In the case of a controlled induction motor (CIM), the stator currents are estimated by directly measuring the dc bus current of the inverter. [1008.1 In the present invention, motor torque oscillations are monitored as the vessel rotational speed is increased in a series of steps and a severe unbalance condition is detected as soon as it happens. f [1009] A stepped speed profile is commanded to the motor by the control system in order to obtain information about the load. The average energy that is required by the appliance to spin the vessel is monitored by means of averaging the motor stator current. Under normal conditions, the motor current can increase due to several conditions: acceleration torque due to speed profiles, mechanical drag in the system (i.e.,, bearings friction, viscous forces, etc.) or energy dissipation by the shock absorbers in the suspension system (i.e., when severe unbalanced loads are present). By carefully choosing the acceleration rates of the speed profiles and using self-referencing techniques, it is possible to minimize the effects of inertia and mechanical drag in the system. It is therefore possible to relate the motor average current to the mechanical dissipation of the shock absorbers and to the unbalance in the load. In a typical speed profile for a spin cycle, several regions can be identified, each characterized by a speed ramp during which the speed is increased, and a plateau where the speed is held constant. The speed ramps should be carefully chosen in order to avoid masking the effect of unbalanced loads on the motor current with the effect of acceleration torque and inertia (i.e., load size). At the beginning of each of these regions, thresholds are dynamically established for the motor current. When the motor current exceeds these thresholds, a severe unbalance condition for the load is assumed. In order to minimize the effect of mechanical drag, a base line for the motor current is acquired at the beginning of each region (end of previous speed plateau). In this condition there is no contribution due to the inertia (speed is constant) and the base line reflects the mechanical drag present in the system. The threshold for the motor current is established as a fixed offset (determined experimentally) above the base line. In order to increase the accuracy of the algorithm, the offset is higher during the speed ramp (to account for higher currents due to acceleration torque) and lower during the speed plateau (no acceleration, only mechanical drag). It is then possible to dynamically create a threshold profile that matches closely the speed profile and that accounts for the system mechanical drag (base line). The thresholds are determined separately for the ramp and for the plateau portions of the spin speed profile. (1010] To further improve the reliability of the algorithm, the thresholds are also adjusted to account for variations in line voltage. The motor current for a given torque-speed operating point depends on the voltage supplied to the motor. When driving the motor with an inverter, the maximum possible voltage is delivered to the motor during parts of the spin speed profile. This maximum voltage applied to the motor depends directly on the line supply voltage provided to the inverter and no regulation for the voltage supplied to the motor is possible in this condition. It has been experimentally determined that when the voltage is low, the current is higher for a given torque-speed point and vice versa. A simple inverse proportional compensation is used to adjust the thresholds to the line voltage. STATEMENT OF THE INVENTION According to the present invention there is provided an appliance for detecting an out of balance condition in a rotating vessel of appliances such as washing machines, automatic dryers, centrifugal liquid extractors comprising: a vessel mounted for rotation about an axis and configured to receive a supply of material; an electric motor drivingly connected to said vessel; a control operatively connected to the motor to operate said motor to rotate said vessel at a plurality of increasing predetermined speeds, to accelerate said vessel to each predetermined speed during an acceleration period, to measure an amount of current required by said motor to rotate said vessel at each of said predetermined speeds and during each of said acceleration periods to compare said measured current with a separately calculated threshold value for each predetermined speed and acceleration period, and to send a signal indicative of an unbalance condition if said amount of current exceeds the calculated threshold value for any predetermined speed or acceleration period. BRIEF DESCRIPTION OF THE DRAWINGS [1011] FIG. 1 is a perspective view of an automatic washer in which the present invention could be utilized. [1012] FIG. 2 is a graphic illustration of rotational vessel speed. [1013] FIG. 3 is a graphic illustration of motor current required to rotate the vessel at different speeds as well as representative thresholds for indicating an unbalance condition. [1014] FIG. 4 is a schematic illustration of an appliance embodying the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [1015] The present invention relates to a method and apparatus for detecting an out of balance condition in a rotating vessel and has applicability in a wide variety of devices in which materials are placed into a rotatable vessel, which materials maybe subject to an unbalanced distribution within the vessel [1016] For purposes of providing an explanation of the invention in a preferred embodiment, an automatic clothes washer has been identified as an appliance within which the invention can be utilized. It should be understood that the invention can be utilized not only in a vertical axis washer as illustrated, but also horizontal or tilted axis washers, clothes dryers, centrifugal extractors and separators, and other appliances and devices in which a rotatable vessel carries a material therein, which material is subject to being arranged in an unbalanced condition. [1017] In FIG. 1 there is illustrated at 20 generally a washing machine of the automatic type, i.e., a machine having a pre-settable sequential control apparatus for operating a washer through a pre-selected program of automatic washing, rinsing and drying operations in which the present invention may be embodied. Machine 20 includes a frame 22 carrying vertical panels 24 forming the sides 24a, top 24b, front 24c and back 24d of the cabinet 25 for the washing machine 20. A hinged lid 26 is provided in the usual manner to provide access to the interior or treatment zone 27 of the washing machine 20. The washing machine 20 has a console 28 including a timer dial 30 or other timing mechanism and a temperature selector 32 as well as a cycle selector 33 and other selectors as desired. (1018] Internally of the machine 20 described herein by way of exemplification, there is disposed an imperforate fluid containing tub 34 within which there is a spin wash basket 36 with perforations or holes 35 therein, while a pump 38 is provided below the tub 34. The spin basket 36 defines a wash chamber and includes an inside wall surface extending upwardly from a substantially flat bottom. A motor 100 is operatively connected to the basket 36 through a transmission to rotate the basket 36 relative to the stationary tub 34. All of the components inside the cabinet 25 are supported by struts 39 and there may also be provided various passive elements such as shock absorbers or springs to absorb vibrations and movements of the basket and tub relative to the frame and cabinet of the washing machine 20. The basket 36 comprises a vessel into which materials such as a fabric load may be charged. [1019] During the course of operation of an appliance such as an automatic washer, the wash basket 36 is rotated at relatively high speeds in order to extract water or other wash liquids from the clothes load. If the clothes load is not evenly distributed within the wash basket, an unbalance condition occurs which will cause the rotating basket to oscillate around the axis of rotation. Hence there will be some movement of the basket in a direction perpendicular to the axis of rotation. Depending upon the degree of unbalance and the speed of rotation, the oscillation may be small or it may be large enough to actually cause the basket 36 (and tub) 34 to engage the washer cabinet 25 or some other relatively stationary component of the appliance with some level of force. Continued operation in such a mode could cause severe damage to the washer and could cause the entire appliance to move from its otherwise stationary location, which could cause other damage or possibly hazardous conditions in the proximity of the appliance. [1020] The effect of unbalanced loads also causes motor torque oscillations which are proportional to the motor stator currents. Also, increased vibrations cause energy dissipation in passive components of the suspension system, in turn, causing the average motor current to increase. In a motor such as a controlled induction motor, the stator currents are estimated by directly measuring the de-bus current of the inverter. [1021] The present invention provides a method and apparatus for detecting an unbalance condition in a rotatable vessel as soon as a severe unbalance condition occurs. [1022] Typically an unbalanced condition becomes more severe as rotation speed increases. Therefore, the present method and apparatus contemplate monitoring the motor current after the vessel has been accelerated up to a predetermined minimum speed level which may depend on the particular appliance involved, the mass of its load, etc. However, the speed should be selected based upon a value, below which damage or severe vibration due to load unbalance is unlikely and above which damage or severe vibration could be likely. [1023] FIG. 2 illustrates graphically a spin profile showing rotational speed over time. A series of acceleration periods 50, or speed ramps, as well as a series of plateaus 52 or constant speeds are illustrated. [1024] FIG. 3 illustrates average motor current 53 during acceleration and constant speed modes. FIG. 3 also illustrates a varying threshold level 54 which is determined experimentally as a fixed offset above a base line, separately for each speed ramp and each speed plateau. A base line for the motor current is acquired at the beginning of each region (end of previous speed plateau) as shown at 56 in FIG. 2. In this condition, there is no contribution due to inertia and the base line reflects the mechanical drag present in the system. The threshold value for the motor current is established as a fixed offset (determined experimentally) above the base line. In order to increase the accuracy of the algorithm, the offset is higher during the ramp speed 54a to account for higher currents due to acceleration torque and lower during the speed plateau 54b where there is no acceleration, only mechanical drag. It is then possible to dynamically create a threshold profile that matches closely to speed profile and that accounts for the system mechanical drag. Also, a predetermined delay period is added following a drop in current demand following an acceleration period before the plateau threshold is implemented to permit the motor current to settle down following an acceleration. This can be seen in FIG. 3 where motor current 53 drops prior to the threshold value dropping from level 54a to 54b. [1025] The threshold values for ramp and plateau are calculated at the beginning of each new region as follows: Thresholdramp = base line + offset ramp Thresholdpiateau = baseline + offset piaWiu [1026] To further improve the reliability of the algorithm, the thresholds are also adjusted to account for variations in the line voltage. The motor current for a given torque-speed operating point depends on the voltage supplied to the motor. It has been experimentally determined that when the voltage is low the current is higher for a given, torque-speed point and visa-versa, A simple inverse proportional compensation is then used to adjust the thresholds to the line voltage. Thresholdramp - (base line + offsetramp) x (voltagenomjnai/voltageactun). • (base line +offsetp]ateau) x (voltagenominai/ voltageactuai). [1027] Thus, a standard constant level threshold above the motor current is not utilized, but rather a varying threshold based upon the condition of the rotating vessel, that is whether it is being accelerated or whether it is being rotated at constant speed. [1028] A still more accurate voltage compensation can be implemented, in which a different gain factor is used for voltages above and below nominal: If (voltageactuai Threshold = (base line + offset) x (voltagenomiT1ai/voltageactua\|) x Kl. Otherwise if (voltageactuai oltagenominai) then Threshold - (base line + offset) X (voltagenomjnai/voltageactuai) x K2. Kl and K2 are coefficients optimized experimentally. The precise initial threshold speed, rate of acceleration and speed after each acceleration may be varied, depending on the particular appliance involved, the size or mass of the typical load of material that the vessel is charged with, the severity of unbalance that may be expected, typical final rotational speeds for the vessel, and other parameters known to those skilled in the art. What is important is that the initial threshold rotational speed be chosen so that the speed is not so high as to cause damage to the appliance or damage to the user if an unbalance condition exists. [1029] If an out of balance signal is generated, this could lead to various further steps including a reduction of the spin speed to a lower level at which the appliance vibrations and mechanical stresses are tolerable. The control can continuously monitor the current draw so that as water is extracted from the clothes and load becomes lighter, the spin speed can be gradually increased to a maximum desired value. Alternatively, if the out of balance condition is too severe, the appliance user can be advised by an appropriate visible or audible signal and the cycle stopped until the user manually redistributes the material load and resets the control. [1030] Thus, the present invention provides an apparatus as shown schematically in FIG. 4 in which there is an appliance 60 which comprises a vessel 62 mounted for rotation about an axis and configured to receive a supply of material whereby the vessel 62 will vibrate in a severe unbalance loading condition of the material in the vessel while the vessel is rotating. The vessel is caused to rotate by a motor 64 which is operatively connected to the vessel to rotate the vessel. [1031] A control 66 is operatively connected to the motor to operate the motor at various predetermined speeds and to accelerate the motor between those speeds at predetermined rates. A current drawn by the motor at the various speeds and during the accelerations is measured by the control and compared to a pre-calculated threshold at each speed and acceleration period to determine whether the vessel is out of balance. If the threshold for a particular speed or acceleration period is exceeded, the control sends a signal indicative of an unbalance condition which can be used to provide a visible or audible signal to a user or to have the control take further steps to minimize the vibration of the vessel. [1032] As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art. WE CLAIM;- 1. An appliance for detecting an out of balance condition in a rotating vessel of appliances such as washing machines, automatic dryers, centrifugal liquid extractors comprising: a vessel mounted for rotation about an axis and configured to receive a supply of material; an electric motor drivingly connected to said vessel; a control operatively connected to the motor to operate said motor to rotate said vessel at a plurality of increasing predetermined speeds, to accelerate said vessel to each predetermined speed during an acceleration period, to measure an amount of current required by said motor to rotate said vessel at each of said predetermined speeds and during each of said acceleration periods to compare said measured current with a separately calculated threshold value for each predetermined speed and acceleration period, and to send a signal indicative of an unbalance condition if said amount of current exceeds the calculated threshold value for any predetermined speed or acceleration period. 2. An appliance as claimed in claim 1, wherein said electric motor is a controlled induction motor and an inverter is provided in the control connected to the motor, said control is having a current measuring device connected to a dc bus of said inverter. 3. An appliance as claimed in claim 2, wherein said current measuring device is connected to a digital filter in said control to receive an output signal representative of current used by said motor and to provide an output representative of an average current used by said motor. 4. An appliance as claimed in claim 1, wherein said signal is an audible or a visible signal to a user. 5. An appliance as claimed in claim 1, wherein said control is configured to accelerate said vessel at predetermined rates between each of the predetermined speeds. 6. An appliance as claimed in claim 1, wherein the control is configured to calculate the threshold value for each predetermined speed by adding a predetermined value to each measured amount of current at each predetermined speed. 7. An appliance as claimed in claim 6, wherein the control is configured to calculate the threshold value for each acceleration period by adding a predetermined value to each measured amount of current at each acceleration period. 8. An appliance as claimed in claim 6, wherein the control is configured to measure the actual line voltage being supplied to the motor and to adjust the threshold values by compensating for the actual line voltage as compared to a nominal line voltage. 9. An appliance for detecting an out of balance condition in a rotating vessel of appliances such as washing machines, automatic dryers, centrifugal liquid extractors, substantially as hereinbefore described with reference to the accompanying drawings.

Full Text

BACKGROUND OF THE INVENTION
The present invention relates to an appliance for detecting an out of balance condition in a rotating vessel of appliances such as washing machines, automatic dryers, centrifugal liquid extractors.
Various appliances, such as automatic washing machines, automatic dryers, centrifugal liquid extractors, etc., utilize a rotating tub, basket or other vessel holding a load of material which may or may not be evenly distributed within the vessel. The condition of having the load unevenly distributed, or out of balance, creates a situation where the center of mass of the rotating vessel does not correspond to the geometric axis of the vessel. This leads to the generation of high loads and severe vibration of the vessel. In an appliance, this severe vibration may cause the phenomenon of movement of the appliance across the floor or other supporting surface. This can occur both in vertical axis rotating vessels as well as horizontal axis vessels and also in those appliances where the axis is arranged in-between vertical and horizontal.
Various attempts have been provided in the prior art to provide mechanical arrangements to limit or reduce the possibility of unbalanced loads, which typically involve the addition of various masses, either fixed or movable, to the vessel which requires additional power for the motor to rotate the vessel.
Approaches have also been disclosed in the prior art for detecting a load imbalance, for example, in an inverter driven motor for a washing machine, as disclosed in

U.S. Patent No. 5,070,565, That patent discloses to examine a ripple in the de-inverter bus
current, with a ripple value above a pre-determined level being indicative of load unbalance.
If a load unbalance is detected, the washer controller would resume a redistribution cycle to
attempt to re-balance the clothes. This would be attempted a pre-detennined number of times
and, if the load is still unbalanced, the spin cycle would be aborted. If the ripple value falls
below the pre-determined level before the maximum number of tries is reached, the spin
cycle is started. Once a spin cycle has been initiated, the length of the spin cycle is
determined on the basis of the magnitude of any remaining load unbalance. Spin rate and
spin time may be adjusted based upon the degree of load unbalance detected.
[1005] It would be an advance if a method and apparatus were provided in which the
potential for a severe unbalance could be predicted in advance of it actually occurring so that appropriate steps could be taken to avoid the detrimental effects of such a condition.
SUMMARY OF THE INVENTION
[1006]} The present invention provides a method and apparatus for detecting a severe unbalance condition in a rotating device such as a basket, tub or other rotatable vessel of an appliance, for example an automatic washer. The method and apparatus provide the detecting by monitoring the motor current signature. When a severe unbalance condition is detected at a high rotational speed, the spin speed can be adaptively dropped down to a safe level, in which the appliance vibrations and mechanical stresses are tolerable. The appliance system can be continuously monitored so that, in the case of an appliance such as an automatic washer, clothes dryer or centrifugal water extraction, as water is extracted from the fabric load, and the load becomes less massive, the spin speed can be gradually increased to a desired level. If too great of an unbalance condition still persists, the spin speed can be adaptably limited or the cycle can be terminated and the user can be advised.

[1007] The effect of unbalanced loads in a motor driven rotating component, such as
arotatable vessel, translates into motor torque oscillations, which are proportional to the
motor stator currents. Moreover, increased vibrations in certain appliances cause energy
dissipation in passive components, such as in the suspension system, causing the average
motor current to increase. In the case of a controlled induction motor (CIM), the stator
currents are estimated by directly measuring the dc bus current of the inverter.
[1008.1 In the present invention, motor torque oscillations are monitored as the vessel
rotational speed is increased in a series of steps and a severe unbalance condition is detected as soon as it happens.
f [1009] A stepped speed profile is commanded to the motor by the control system in
order to obtain information about the load. The average energy that is required by the appliance to spin the vessel is monitored by means of averaging the motor stator current. Under normal conditions, the motor current can increase due to several conditions: acceleration torque due to speed profiles, mechanical drag in the system (i.e.,, bearings friction, viscous forces, etc.) or energy dissipation by the shock absorbers in the suspension system (i.e., when severe unbalanced loads are present). By carefully choosing the acceleration rates of the speed profiles and using self-referencing techniques, it is possible to minimize the effects of inertia and mechanical drag in the system. It is therefore possible to relate the motor average current to the mechanical dissipation of the shock absorbers and to the unbalance in the load. In a typical speed profile for a spin cycle, several regions can be identified, each characterized by a speed ramp during which the speed is increased, and a plateau where the speed is held constant. The speed ramps should be carefully chosen in order to avoid masking the effect of unbalanced loads on the motor current with the effect of acceleration torque and inertia (i.e., load size). At the beginning of each of these regions,

thresholds are dynamically established for the motor current. When the motor current
exceeds these thresholds, a severe unbalance condition for the load is assumed. In order to
minimize the effect of mechanical drag, a base line for the motor current is acquired at the
beginning of each region (end of previous speed plateau). In this condition there is no
contribution due to the inertia (speed is constant) and the base line reflects the mechanical
drag present in the system. The threshold for the motor current is established as a fixed offset
(determined experimentally) above the base line. In order to increase the accuracy of the
algorithm, the offset is higher during the speed ramp (to account for higher currents due to
acceleration torque) and lower during the speed plateau (no acceleration, only mechanical
drag). It is then possible to dynamically create a threshold profile that matches closely the
speed profile and that accounts for the system mechanical drag (base line). The thresholds
are determined separately for the ramp and for the plateau portions of the spin speed profile.
(1010] To further improve the reliability of the algorithm, the thresholds are also
adjusted to account for variations in line voltage. The motor current for a given torque-speed operating point depends on the voltage supplied to the motor. When driving the motor with an inverter, the maximum possible voltage is delivered to the motor during parts of the spin speed profile. This maximum voltage applied to the motor depends directly on the line supply voltage provided to the inverter and no regulation for the voltage supplied to the motor is possible in this condition. It has been experimentally determined that when the voltage is low, the current is higher for a given torque-speed point and vice versa. A simple inverse proportional compensation is used to adjust the thresholds to the line voltage.

STATEMENT OF THE INVENTION
According to the present invention there is provided an appliance for detecting an out of balance condition in a rotating vessel of appliances such as washing machines, automatic dryers, centrifugal liquid extractors comprising:
a vessel mounted for rotation about an axis and configured to receive a supply of material;
an electric motor drivingly connected to said vessel;
a control operatively connected to the motor to operate said motor to rotate said vessel at a plurality of increasing predetermined speeds, to accelerate said vessel to each predetermined speed during an acceleration period, to measure an amount of current required by said motor to rotate said vessel at each of said predetermined speeds and during each of said acceleration periods to compare said measured current with a separately calculated threshold value for each predetermined speed and acceleration period, and to send a signal indicative of an unbalance condition if said amount of current exceeds the calculated threshold value for any predetermined speed or acceleration period.
BRIEF DESCRIPTION OF THE DRAWINGS
[1011] FIG. 1 is a perspective view of an automatic washer in
which the present invention could be utilized.

[1012] FIG. 2 is a graphic illustration of rotational vessel speed.
[1013] FIG. 3 is a graphic illustration of motor current required to rotate the vessel at
different speeds as well as representative thresholds for indicating an unbalance condition.
[1014] FIG. 4 is a schematic illustration of an appliance embodying the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[1015] The present invention relates to a method and apparatus for detecting an out of
balance condition in a rotating vessel and has applicability in a wide variety of devices in which materials are placed into a rotatable vessel, which materials maybe subject to an unbalanced distribution within the vessel
[1016] For purposes of providing an explanation of the invention in a preferred
embodiment, an automatic clothes washer has been identified as an appliance within which the invention can be utilized. It should be understood that the invention can be utilized not only in a vertical axis washer as illustrated, but also horizontal or tilted axis washers, clothes dryers, centrifugal extractors and separators, and other appliances and devices in which a rotatable vessel carries a material therein, which material is subject to being arranged in an unbalanced condition.
[1017] In FIG. 1 there is illustrated at 20 generally a washing machine of the
automatic type, i.e., a machine having a pre-settable sequential control apparatus for operating a washer through a pre-selected program of automatic washing, rinsing and drying operations in which the present invention may be embodied. Machine 20 includes a frame 22 carrying vertical panels 24 forming the sides 24a, top 24b, front 24c and back 24d of the cabinet 25 for the washing machine 20. A hinged lid 26 is provided in the usual manner to provide access to the interior or treatment zone 27 of the washing machine 20. The washing

machine 20 has a console 28 including a timer dial 30 or other timing mechanism and a
temperature selector 32 as well as a cycle selector 33 and other selectors as desired.
(1018] Internally of the machine 20 described herein by way of exemplification, there
is disposed an imperforate fluid containing tub 34 within which there is a spin wash basket 36 with perforations or holes 35 therein, while a pump 38 is provided below the tub 34. The spin basket 36 defines a wash chamber and includes an inside wall surface extending upwardly from a substantially flat bottom. A motor 100 is operatively connected to the basket 36 through a transmission to rotate the basket 36 relative to the stationary tub 34. All of the components inside the cabinet 25 are supported by struts 39 and there may also be provided various passive elements such as shock absorbers or springs to absorb vibrations and movements of the basket and tub relative to the frame and cabinet of the washing machine 20. The basket 36 comprises a vessel into which materials such as a fabric load may be charged.
[1019] During the course of operation of an appliance such as an automatic washer,
the wash basket 36 is rotated at relatively high speeds in order to extract water or other wash liquids from the clothes load. If the clothes load is not evenly distributed within the wash basket, an unbalance condition occurs which will cause the rotating basket to oscillate around the axis of rotation. Hence there will be some movement of the basket in a direction perpendicular to the axis of rotation. Depending upon the degree of unbalance and the speed of rotation, the oscillation may be small or it may be large enough to actually cause the basket 36 (and tub) 34 to engage the washer cabinet 25 or some other relatively stationary component of the appliance with some level of force. Continued operation in such a mode could cause severe damage to the washer and could cause the entire appliance to move from

its otherwise stationary location, which could cause other damage or possibly hazardous conditions in the proximity of the appliance.
[1020] The effect of unbalanced loads also causes motor torque oscillations which are
proportional to the motor stator currents. Also, increased vibrations cause energy dissipation in passive components of the suspension system, in turn, causing the average motor current to increase. In a motor such as a controlled induction motor, the stator currents are estimated by directly measuring the de-bus current of the inverter.
[1021] The present invention provides a method and apparatus for detecting an
unbalance condition in a rotatable vessel as soon as a severe unbalance condition occurs.
[1022] Typically an unbalanced condition becomes more severe as rotation speed
increases. Therefore, the present method and apparatus contemplate monitoring the motor
current after the vessel has been accelerated up to a predetermined minimum speed level
which may depend on the particular appliance involved, the mass of its load, etc. However,
the speed should be selected based upon a value, below which damage or severe vibration due
to load unbalance is unlikely and above which damage or severe vibration could be likely.
[1023] FIG. 2 illustrates graphically a spin profile showing rotational speed over time.
A series of acceleration periods 50, or speed ramps, as well as a series of plateaus 52 or constant speeds are illustrated.
[1024] FIG. 3 illustrates average motor current 53 during acceleration and constant
speed modes. FIG. 3 also illustrates a varying threshold level 54 which is determined experimentally as a fixed offset above a base line, separately for each speed ramp and each speed plateau. A base line for the motor current is acquired at the beginning of each region (end of previous speed plateau) as shown at 56 in FIG. 2. In this condition, there is no contribution due to inertia and the base line reflects the mechanical drag present in the

system. The threshold value for the motor current is established as a fixed offset (determined experimentally) above the base line. In order to increase the accuracy of the algorithm, the offset is higher during the ramp speed 54a to account for higher currents due to acceleration torque and lower during the speed plateau 54b where there is no acceleration, only mechanical drag. It is then possible to dynamically create a threshold profile that matches closely to speed profile and that accounts for the system mechanical drag. Also, a predetermined delay period is added following a drop in current demand following an acceleration period before the plateau threshold is implemented to permit the motor current to settle down following an acceleration. This can be seen in FIG. 3 where motor current 53 drops prior to the threshold value dropping from level 54a to 54b.
[1025] The threshold values for ramp and plateau are calculated at the beginning of
each new region as follows:
Thresholdramp = base line + offset ramp Thresholdpiateau = baseline + offset piaWiu
[1026] To further improve the reliability of the algorithm, the thresholds are also
adjusted to account for variations in the line voltage. The motor current for a given torque-speed operating point depends on the voltage supplied to the motor. It has been experimentally determined that when the voltage is low the current is higher for a given, torque-speed point and visa-versa, A simple inverse proportional compensation is then used to adjust the thresholds to the line voltage.
Thresholdramp - (base line + offsetramp) x (voltagenomjnai/voltageactun).
• (base line +offsetp]ateau) x (voltagenominai/ voltageactuai).

[1027] Thus, a standard constant level threshold above the motor current is not
utilized, but rather a varying threshold based upon the condition of the rotating vessel, that is
whether it is being accelerated or whether it is being rotated at constant speed.
[1028] A still more accurate voltage compensation can be implemented, in which a
different gain factor is used for voltages above and below nominal: If (voltageactuai Threshold = (base line + offset) x (voltagenomiT1ai/voltageactua|) x Kl. Otherwise if (voltageactuai oltagenominai) then
Threshold - (base line + offset) X (voltagenomjnai/voltageactuai) x K2. Kl and K2 are coefficients optimized experimentally. The precise initial threshold speed, rate of acceleration and speed after each acceleration may be varied, depending on the particular appliance involved, the size or mass of the typical load of material that the vessel is charged with, the severity of unbalance that may be expected, typical final rotational speeds for the vessel, and other parameters known to those skilled in the art. What is important is that the initial threshold rotational speed be chosen so that the speed is not so high as to cause damage to the appliance or damage to the user if an unbalance condition exists.
[1029] If an out of balance signal is generated, this could lead to various further steps
including a reduction of the spin speed to a lower level at which the appliance vibrations and mechanical stresses are tolerable. The control can continuously monitor the current draw so that as water is extracted from the clothes and load becomes lighter, the spin speed can be gradually increased to a maximum desired value. Alternatively, if the out of balance condition is too severe, the appliance user can be advised by an appropriate visible or audible

signal and the cycle stopped until the user manually redistributes the material load and resets the control.
[1030] Thus, the present invention provides an apparatus as shown schematically in
FIG. 4 in which there is an appliance 60 which comprises a vessel 62 mounted for rotation about an axis and configured to receive a supply of material whereby the vessel 62 will vibrate in a severe unbalance loading condition of the material in the vessel while the vessel is rotating. The vessel is caused to rotate by a motor 64 which is operatively connected to the vessel to rotate the vessel.
[1031] A control 66 is operatively connected to the motor to operate the motor at
various predetermined speeds and to accelerate the motor between those speeds at
predetermined rates. A current drawn by the motor at the various speeds and during the
accelerations is measured by the control and compared to a pre-calculated threshold at each
speed and acceleration period to determine whether the vessel is out of balance. If the
threshold for a particular speed or acceleration period is exceeded, the control sends a signal
indicative of an unbalance condition which can be used to provide a visible or audible signal
to a user or to have the control take further steps to minimize the vibration of the vessel.
[1032] As is apparent from the foregoing specification, the invention is susceptible of
being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.

WE CLAIM;-
1. An appliance for detecting an out of balance condition in a
rotating vessel of appliances such as washing machines,
automatic dryers, centrifugal liquid extractors comprising:
a vessel mounted for rotation about an axis and configured to receive a supply of material;
an electric motor drivingly connected to said vessel;
a control operatively connected to the motor to operate said motor to rotate said vessel at a plurality of increasing predetermined speeds, to accelerate said vessel to each predetermined speed during an acceleration period, to measure an amount of current required by said motor to rotate said vessel at each of said predetermined speeds and during each of said acceleration periods to compare said measured current with a separately calculated threshold value for each predetermined speed and acceleration period, and to send a signal indicative of an unbalance condition if said amount of current exceeds the calculated threshold value for any predetermined speed or acceleration period.
2. An appliance as claimed in claim 1, wherein said electric
motor is a controlled induction motor and an inverter is provided
in the control connected to the motor, said control is having a
current measuring device connected to a dc bus of said inverter.
3. An appliance as claimed in claim 2, wherein said current
measuring device is connected to a digital filter in said control
to receive an output signal representative of current used by

said motor and to provide an output representative of an average current used by said motor. 4. An appliance as claimed in claim 1, wherein said signal is an audible or a visible signal to a user.
5. An appliance as claimed in claim 1, wherein said control is
configured to accelerate said vessel at predetermined rates
between each of the predetermined speeds.
6. An appliance as claimed in claim 1, wherein the control is
configured to calculate the threshold value for each
predetermined speed by adding a predetermined value to each
measured amount of current at each predetermined speed.
7. An appliance as claimed in claim 6, wherein the control is
configured to calculate the threshold value for each acceleration
period by adding a predetermined value to each measured amount of
current at each acceleration period.
8. An appliance as claimed in claim 6, wherein the control is
configured to measure the actual line voltage being supplied to
the motor and to adjust the threshold values by compensating for
the actual line voltage as compared to a nominal line voltage.
9. An appliance for detecting an out of balance condition in a
rotating vessel of appliances such as washing machines, automatic
dryers, centrifugal liquid extractors, substantially as
hereinbefore described with reference to the accompanying
drawings.

Documents:

683-del-2001-abstract.pdf

683-del-2001-claims.pdf

683-del-2001-correspondence-others.pdf

683-del-2001-correspondence-po.pdf

683-del-2001-description (complete).pdf

683-del-2001-drawings.pdf

683-del-2001-form-1.pdf

683-del-2001-form-19.pdf

683-del-2001-form-2.pdf

683-del-2001-form-26.pdf

683-del-2001-form-3.pdf

683-del-2001-form-5.pdf

683-del-2001-gpa.pdf

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Patent Number

230876

Indian Patent Application Number

683/DEL/2001

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

28-Feb-2009

Date of Filing

20-Jun-2001

Name of Patentee

WHIRLPOOL CORPORATION

Applicant Address

2000 N M-63 BENTON HARBOR, MICHIGAN 49022, UNITED STATES OF AMERICA.

Inventors:

#	Inventor's Name	Inventor's Address
1	ROSARIO CIANCIMINO	2585 LAKE PINE DRIVE APT. #29, SAINT JOSEPH, MICHIGAN 49085.
2	BRENNER MARTIN SHARP	9771 WEKO DRIVE, BRIDMAN, MICHIGAN 49106 .
3	GERALD CLARENCE STENGER	634 SOUTH 600 EAST, MILL CREEK, INDIANA 46365.

PCT International Classification Number

D06F 37/20

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA