Patent ID: 7068463

Claim:
A disk drive comprising: (a) a disk comprising a plurality of tracks; (b) an actuator arm; (c) a head connected to a distal end of the actuator arm; (d) a voice coil motor (VCM) for rotating the actuator arm about a pivot to actuate the head over the disk; and (d) disk control circuitry for controlling the VCM by: applying a driving current to the VCM; detecting a back electromotive force (EMF) voltage generated by the VCM; estimating a velocity of the VCM in response to the back EMF voltage; comparing the estimated VCM velocity to a target velocity in a velocity profile, wherein the velocity profile comprises at least an acceleration component and a coast component; adjusting the driving current in response to the comparison so that the velocity of the VCM substantially follows the velocity profile; and estimating a latch distance corresponding to a distance the actuator arm travels during a latch operation by: performing an unlatch operation to unlatch the actuator arm; integrating the estimated VCM velocity during the unlatch operation to estimate an unlatch distance; detecting an unlatch track ID corresponding to a position of the head after the unlatch operation; performing a seek operation to seek the head from the unlatch track to an inner diameter track; integrating the estimated VCM velocity during the seek operation to estimate a seek distance; and subtracting the estimated seek distance from the estimated unlatch distance to estimate the latch distance.