Patent ID: 7876522

Claim:
A disk drive comprising: a disk; a head; a voice coil motor (VCM) comprising a voice coil operable to actuate the head radially over the disk; a VCM control loop comprising: a voltage detector operable to detect a voice coil voltage across the voice coil; a current detector operable to detect a current flowing through the voice coil; an IR voltage detector, responsive to the detected current, operable to detect a resistive voltage due to a resistance of the voice coil; and a back EMF detector for subtracting the resistive voltage from the voice coil voltage to generate a back EMF voltage; and control circuitry operable to update the IR voltage detector by: measuring a first back EMF voltage; after measuring the first back EMF voltage, applying a first control current to the voice coil for a first interval and applying a second control current to the voice coil for a second interval; after the second interval, measuring a second back EMF voltage; computing a first delta voltage relative to a difference between the first back EMF voltage and the second back EMF voltage; and adjusting the IR voltage detector in response to the first delta voltage and at least one of the first and second control currents.