Lowering the hump of sensitivity functions for discrete-time dual-stage systems

This brief is concerned with servo loop design in the discrete-time domain that aims to achieve a low-hump sensitivity function for dual-stage hard disk drive (HDD) systems. Sensitivity functions for the discrete-time dual-stage systems are analyzed on the basis of the Bode integral theorem. A 3-dB sensitivity function hump is achieved in simulation for the discrete-time dual-stage actuation system with a piezoelectric (PZT) microactuator (MA) using the H_∞ loop shaping method and the proposed linear matrix inequality (LMI) approach. Additionally, implementation is done for the PZT MA dual-stage system and a sensitivity function with the magnitude lower than 3 dB being achieved.