Rejecting oscillatory, non-synchronous mechanical disturbances in hard disk drives

This paper describes a “testbook” technique for rejecting narrow-band disturbances to a hard-disk-drive servo loop, by including a model of the disturbance in the drive´s state-space controller, and then canceling it. Both numerical simulations and experimental evidence are presented which show significant reductions in tracking errors due to the targeted disturbance in steady-state operation. Simulations of the transient behavior of the augmented control loop, however, show some undesirable characteristics