Robustness analysis on a high bandwidth disk drive servo system with an instrumented suspension

The magnetic disk drive industry is expected to reach track densities of 40,000 tracks per inch by early in the next century. Successful operation at such high track density requires an increase in the closed-loop bandwidth of the head positioning servo-system. Resonance modes in the suspension of hard disk drives limit the closed-loop bandwidth. A high bandwidth disk drive servo system with an instrumented suspension has been proposed by the authors. As an extension of the previous work, this paper presents analysis on stability robustness of the system. It is shown that although the proposed active vibration control scheme is a non-collocated problem, high frequency spillover does not cause instability. Furthermore, closed-loop stability is maintained when the actual frequencies deviate by as much as 40% of the nominal values for compensated flexible modes.