Control Design for Self-Servo Track Writing Using a State-Space Disturbance Observer

Self-servo track writing is a process of writing servo bursts on a subsequent track using servo bursts from the previously written track as a reference. A fundamental obstacle in self-servo track writing is radial error propagation due to written-in repeatable runout (RRO) in the seed track and external disturbances. In this paper, we introduce a control scheme for the self-servo track writing process using a state-space disturbance observer. A linear quadratic Gaussian/loop transfer recovery controller with a state-space disturbance observer is designed for feedback control. In addition, feedforward control for the reference correction signal is designed to prevent radial error propagation. From simulation results, it turns out that the nonrepeatable runout (NRRO) component is a major source of AC track squeeze. The proposed disturbance observer is very effective in reducing the effect of the NRRO. The proposed control scheme is validated by simulation results which show improvement in the standard deviation and the AC track squeeze of the written tracks.