System and method for detecting imbalance in a washing machine

1. A method for detecting an out of balance condition for a washing machine, the washing machine comprising a wash tub, a wash basket rotatably mounted within the wash tub, and a polyphase motor configured to rotate the wash basket within said wash tub, the method comprising:

rotating the wash basket at a predetermined rotational speed for a data collection period;

monitoring at least a single phase of motor current supplied to the motor while the wash tub rotates at the predetermined rotational speed during the data collection period;

monitoring the severity of tub strikes based at least in part on the single phase motor current; wherein monitoring the severity of tub strikes comprises comparing the single phase of motor current to a current threshold and determining the deviation of the single phase of motor current from the current threshold; and

detecting an excessive out of balance condition based at least in part on the severity of the tub strikes; wherein detecting an excessive out of balance condition comprises detecting an excessive out of balance condition if the deviation of the single phase of motor current exceeds a current deviation threshold.

2. The method of claim 1 , wherein the single phase of motor current is supplied from an inverter coupled to the motor.

3. The method of claim 1 , wherein the method comprises accelerating the wash basket to a second predetermined rotational speed if the single phase of motor current does not exceed the current threshold.

4. The method of claim 1 , wherein the method comprises estimating the out of balance mass of the washing machine based at least in part on the deviation of the single phase of motor current from the current threshold.

5. The method of claim 1 , wherein the single phase of motor current is monitored by a current sensor that is part of an inverter drive control system for the polyphase motor.

6. The method of claim 1 , wherein the predetermined rotational speed is selected such that the washing machine operates at about the first mode of suspension for the washing machine or the second mode of suspension for the washing machine.

7. The method of claim 1 , wherein the predetermined rotational speed is within a range of about 30 rpm to about 80 rpm or about 140 rpm to about 180 rpm.

8. A system for detecting an out of balance condition for a washing machine, the washing machine comprising a wash tub, a wash basket rotatably mounted within the wash tub, a polyphase motor configured to rotate the wash basket within the wash tub and an inverter coupled to the polyphase motor, the system comprising:

a controller coupled to the inverter, the controller configured to control the inverter to operate the polyphase motor to rotate the wash basket at a predetermined rotational speed for a data collection period;

a sensor configured to monitor at least a single phase of motor current supplied to the motor from the inverter, the sensor providing a signal associated with the single phase of motor current to said controller;

wherein said controller is configured to monitor the severity of tub strikes based at least in part on the single phase of motor current by comparing the single phase of motor current to a current threshold, and determining the deviation of the single phase of motor current from the current threshold; and

wherein said controller is further configured to detect an excessive out of balance condition if the deviation of the single phase of motor current exceeds a current deviation threshold.

9. The system of claim 8 , wherein the controller is configured to estimate the out of balance mass of the washing machine based at least in part on the deviation of the single phase of motor current from the current threshold.

10. The system of claim 8 , wherein the predetermined rotational speed is selected such that the washing machine operates at about the first mode of suspension for the washing machine or a second mode of suspension for the washing machine.

11. The system of claim 8 , wherein the predetermined rotational speed is within a range of about 30 rpm to about 80 rpm or about 140 rpm to about 180 rpm.

12. A washing machine, comprising:

a wash tub;

a wash basket rotatably mounted within the wash tub;

a polyphase motor configured to rotate the wash basket within said wash tub;

an inverter coupled to the polyphase motor;

a controller coupled to the inverter, the controller configured to control the inverter to operate the polyphase motor to rotate the wash basket at a predetermined rotational speed for a data collection period; and

a sensor configured to monitor at least a single phase of motor current supplied to the polyphase motor from the inverter, the sensor providing a signal associated with the single phase of motor current to the controller;

wherein said controller is configured to monitor the severity of tub strikes based at least in part on the single phase motor current by comparing the single phase of motor current to a current threshold; and determining the deviation of the single phase of motor current from the current threshold; and

wherein the controller is further configured to detect an excessive out of balance condition detect an excessive out of balance condition if the deviation of the single phase of motor current exceeds a current deviation threshold.

13. The washing machine of claim 12 , wherein the predetermined rotational speed is selected such that the washing machine operates at about the first mode of suspension or the second mode of suspension for the washing machine.