Patent ID: 8058826

Claim:
A method of compensating for misalignment of Hall-effect sensors that generate sensor signals providing motor position information to control commutation of motor drive current through windings of a motor, comprising: in a normal operating mode, (1) providing motor drive current to the windings based on the sensor signals such that sets of the windings are driven in a normal commutation sequence corresponding to forward rotation of the motor and a sequence of states of the sensor signals, and (2) monitoring for occurrence of a motor stall condition; and upon detecting the motor stall condition with the sensor signals in a given sensor signal state that in the normal operating mode results in driving the windings according to a corresponding given commutation state: (1) in a first driving step, momentarily driving the windings according to an advanced commutation state, the advanced commutation state following the given commutation state in the normal commutation sequence, (2) during the first driving step, detecting a reverse transition of the sensor signals to a preceding sensor signal state which precedes the given sensor signal state in the sequence of states of the sensor signals, and (3) upon completion of the first driving step when the reverse transition of the sensor signals has been detected, (a) in a second driving step driving the windings according to a preceding commutation state until the sensor signals are again detected to be in the given sensor signal state, the preceding commutation state preceding the given commutation state in the normal commutation sequence, and (b) in a third driving step momentarily continuing to drive the windings according to the preceding commutation state notwithstanding the sensor signals' being in the given sensor signal state.