Compensation for repeatable tracking errors in hard drives using discrete-time repetitive controllers

This paper presents the repeatable runout (RRO) compensation in disk file systems. We applied repetitive controllers for the tracking system. As experimental results, we obtained a high reduction ratio of 10/spl sim/45 dB for up to 10th harmonics of the RRO. Furthermore, by switching filter parameters between in the learning state and the steady state, we obtained fast learning of less than two disk rotations.