Polyphase motor drive imbalance detection

Claim 1

Apparatus comprising: a polyphase motor for propelling an object; a motor control and power supply for controlling and powering the motor; characterized in that the motor control comprises: means for operating the motor at a first speed; hall detector means comprising individual hall detectors associated with each motor winding for providing an output signal associated with each motor winding that manifests current magnitude and direction in the winding; means for summing output signals from the hall detectors and providing a first signal which manifests the magnitude of the ripple associated with the difference between the current flow in and out of the motor; means responsive to the first signal and a reference level signal for providing a second signal indicating that a ripple magnitude exceeding a predetermined magnitude associated with the reference signal; means responsive to said second signal for providing a third signal if the second signal is still provided following a predetermined time delay interval independent of the frequency of the motor current; means responsive to said third signal for causing the motor to operate at a speed less than said first speed until the object is at a preestablished location and then stopping the motor.