Short-span seeking control for dual-stage servomechanism in hard disk drives

The dual-stage servomechanism is proposed to support ultra-high track density in hard disk drives. Narrower track width causes the seeking operation to occur within several tracks much frequently. Conventional seeking control methods may not achieve their optimal performance, because the actuator can not be boosted to the maximum speed in such a short-span distance. This paper proposes a new short-span seeking control scheme using two-degree-of-freedom configuration, which is composed of a dual-stage servo loop and two feed-forward control paths. The feed-forward control design utilizes a novel compensation method for nonminimum-phase zero, therefore the perfect reference tracking based on model inversion become practicable. Experiment results have shown that the proposed two-degree-of-freedom control scheme for dual-stage servo system can greatly improve the short-span seeking performance.