Patent ID: 7477471

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, the voice coil comprising a first end and a second end; a VCM control loop comprising a voltage detector operable to detect a back EMF voltage across the voice coil, a current detector operable to detect a current flowing through the voice coil, and a control voltage generator, responsive to a command input and the detected back EMF voltage, operable to generate a control voltage applied to the voice coil; and control circuitry operable to: (a) initialize the control voltage; (b) inject a transient into the control loop and detect a corresponding current flowing through the voice coil; (c) adjust the control voltage in response to a polarity of the detected current; (d) repeat elements (b) and (c) at least once; and (e) store an offset value in response to the adjusted control voltage.