A time-optimal unified servo control method with a two-degree-of- freedom structure for a hard disk drive

In this paper, a time-optimal unified servo control (TOUSC) strategy with a two-degree-of-freedom (2DOF) structure is proposed for a hard disk drive. The feed-forward control signal in the 2DOF dominates in the track-seek phase while the TOUSC takes the main responsibility to maintain the track following performance. This unified design does not switch controllers in the transition from track seeking to track following. By using the saturation voltages of power amplifier in its profile generator, the track-seek performance is improved significantly over the single TOUSC scheme. The unified controller also achieves better disturbance suppression in track-following with superior tracking precision. Simulations show that the proposed 2DOF-based TOUSC provides satisfactory overall performances as a unified servo controller.