Design and analysis of a dual-stage disk drive servo system using an instrumented suspension

This paper presents the design and analysis of a track-following controller using a mixed-objective optimization technique for dual-stage servo systems in hard disk drives (HDD). The objective of minimizing tracking error in the presence of plant uncertainties and operational variations is formulated into a framework of multi-objective minimization. The tracking error minimization is reasonably formulated as an H-2 norm minimization problem, while the robust stability issue is addressed by some H-infinity norm bounds. These norm minimization or constraints are then translated into a set of parametric feasibility conditions using linear matrix inequalities (LMI) which are readily solved by convex optimization solvers. To enhance tracking performance and stability robustness, attenuation of airflow excited suspension structural vibration is also explicitly taken into consideration by an inner-loop fast-rate damping and compensation controller utilizing a vibration sensor on the suspension surface. Analysis and simulation results show a noticeable improvement in tracking performance over a previous designs, while retaining acceptable robust stability under certain multiplicative and parameter uncertainties.