Nonuniform Multi-rate Sampled-data H∞ Following Control of HDDs

This paper is concerned with the use of the sampled-data H∞ servo controller with generalized hold for the track-following control of hard disk drives (HDDs). Conventional input multi-rate control normally utilizes a fast zero order hold that is uniformly time-divided piecewise constant function. However, there is no need to assume such an uniformity in hold duration. Elimination of this assumption increases the design degree-of-freedom. In this paper, we propose to invoke the sampled-data H∞ servo control theory to have an optimal piecewise continuous hold function. The derived function is used as a basis of our proposed nonuniformly time-divided piecewise constant function, which is introduced to implement it on standard systems with digital-toanalogue conversion devices. We conducted a set of simulations as well as experiments, and confirmed that the proposed method can improve the control performance.