Patent ID: 8780489

Claim:
A disk drive comprising: a head; a disk surface; a dual stage actuator (DSA) servo loop comprising a voice coil motor (VCM) servo loop comprising a VCM and a microactuator servo loop comprising a microactuator operable to actuate the head over the disk surface; and control circuitry operable to: generate a position error signal (PES) representing a position of the head over the disk surface; process the PES using a microactuator compensator to generate a first control signal; inject a disturbance sinusoid into the first control signal to generate a second control signal; control the microactuator in response to the second control signal; generate first feed-forward compensation corresponding to the injected disturbance sinusoid; generate a third control signal in response to the PES and the first feed-forward compensation; control the VCM in response to the third control signal; and estimate a gain of the microactuator in response to the first feed-forward compensation; wherein prior to injecting the disturbance sinusoid into the first control signal the control circuitry is further operable to adapt a second feed-forward compensation according to: A ( k+ 1)= A ( k )+μ·PES·cos( nk ) B ( k+ 1)= B ( k )+μ·PES·sin( nk ) where: n represents a frequency of the disturbance sinusoid; μ is a learning coefficient; and A and B are coefficients of a second sinusoid used to generate the second feed-forward compensation; and after injecting the disturbance sinusoid into the first control signal the control circuitry is further operable to adapt the first feed-forward compensation according to: a ⁡ ( j + 1 ) = a ⁡ ( j ) + ( 1 m ⁢ ∑ i = 1 m ⁢ A i ⁡ ( k ) post - inj ) - A 0 ⁢ ⁢ pre - inj b ⁡ ( j + 1 ) = b ⁡ ( j ) + ( 1 m ⁢ ∑ i = 1 m ⁢ B i ⁡ ( k ) post - inj ) - B 0 ⁢ ⁢ pre - inj where: a and b are coefficients of a first sinusoid used to generate the first feed-forward compensation; A 0 and B 0 are coefficients of the second sinusoid prior to injecting the disturbance sinusoid into the first control signal; and A i and B i are coefficients of the second sinusoid generated over m samples of the PES after injecting the disturbance sinusoid into the first control signal.