A dual-stage control design for high track per inch hard disk drives

This paper proposes an optimization based control scheme for a dual-stage h ard disk drive servo system to maximize the tracking accuracy given the act uator bandwidth limitations without knowing the mechanical disturbance mode l. We proposed to add an outer loop, selected based on optimization of the Youla parameters, to the usual dual-stage controller for tracking accuracy improvement. The Youla parameters are bounded based on specifications of mi nimum bandwidth, phase margin, and gain margin, and maximum bandwidth limit ations, Time domain and frequency domain simulations were performed to show the effectiveness of the design. The tracking accuracy with respect to var ious noise and disturbance levels was considered, The results suggested tha t for the noise and disturbance model considered, the mechanical disturbanc e must be reduced considerably to achieve higher TPI.