Patent ID: 7800857

Claim:
A disk drive comprising: a disk; a head connected to a distal end of an actuator arm; a voice coil motor (VCM) comprising a voice coil operable to rotate the actuator arm about a pivot 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 BEMF detector operable to subtract the resistive voltage from the voice coil voltage to generate a BEMF voltage; and control circuitry operable to calibrate a gain Gr of the IR voltage detector by: (a) adjusting a control current Im applied to the voice coil; (b) adjusting the gain Gr; (c) detecting and saving the BEMF voltage corresponding to the adjusted gain Gr; (d) repeating steps (b) and (c) at least once; (e) repeating steps (a) through (d) at least once; and (f) selecting an operating gain Gr of the IR voltage detector in response to the adjusted control currents, the adjusted gains Gr, and the saved BEMF voltages.