Optimal H∞ control for hard disk drives with an irregular sampling rate

This paper discusses the optimal H_∞ control syn thesis via discrete Riccati equations for hard disk drives (HDDs) with an irregular sampling rate. A HDD servo system with an irregular sampling rate, caused by missing position error signal sampling data, is modeled as a linear periodically time varying (LPTV) system. An optimal H_∞ track-following control algorithm for HDD servo systems with irregular sampling rates is proposed, which is based on the previous H_∞ synthesis results for LPTV systems developed by some of the authors. A simulation and implementation study demonstrates that the proposed control synthesis technique is able to handle the irregular sampling rate and can be used to conveniently design a loop-shaping track-following servo that achieves the robust performance of a desired error rejection function for disturbance attenuation. Implementation results on an actual hard disk drive validate the simulation results.