Patent ID: 6867944

Claim:
A disk drive employing a velocity controlled servo loop, the disk drive comprising: (a) a disk; (b) a head; (c) an actuator arm for actuating the head radially over the disk; (d) a voice coil motor (VCM) for rotating the actuator arm about a pivot, the VCM comprising a coil comprising a VCM resistance R; (e) a back EMF voltage detector for measuring a back EMF voltage across the coil; (f) a current detector for detecting a current I flowing through the coil; (g) an IR voltage detector, responsive to the current I detected by the current detector, for detecting an IR voltage proportional to the current I times the VCM resistance R; (h) a voltage compensator for substantially canceling the IR voltage from the measured back EMF voltage to generate a compensated back EMF voltage; (i) a control voltage generator, responsive the compensated back EMF voltage, for generating a control voltage applied to the coil to generate the current I flowing through the coil; and (j) a stall detector for comparing the current I detected by the current detector to a threshold, wherein a VCM stall condition is detected if the current I exceeds the threshold for a predetermined interval.