Patent ID: 8254222

Claim:
A disk drive comprising: a disk surface; a head coupled to a distal end of an actuator arm; a dual stage actuator (DSA) servo loop comprising a voice coil motor (VCM) servo loop and a microactuator servo loop operable to actuate the head over the disk surface; and control circuitry operable to: disable the microactuator servo loop; after disabling the microactuator servo loop: inject a sinusoid into the VCM servo loop, wherein the sinusoid comprises a target frequency; and compute a first open loop response of the VCM servo loop; enable the microactuator servo loop; after enabling the microactuator servo loop: inject the sinusoid into the DSA servo loop; and compute a second open loop response of the DSA servo loop; and tune a microactuator servo loop gain and a VCM servo loop gain in response to the first and second open loop responses.