Missing position-error-signal sampling data in hard disk drives (HDDs) results in their servo systems having irregular sampling rates. Due to the natural periodicity of HDDs, which is related to the disk rotation, HDD servo systems with missing samples can be modeled as linear periodically time-varying (LPTV) systems. Based on previous H_∞ control synthesis results for general LPTV systems developed by some of the authors, an optimal H_∞ track-following control algorithm for HDD servo systems with missing samples is proposed. A simulation and implementation study, which has been carried out on a set of hard disk drives, demonstrates that the proposed control synthesis algorithm is able to handle missing samples and can be used to achieve the robust performance of a desired error rejection function for disturbance attenuation. Implementation results on multiple real hard disk drives validate the predicted robust performance.
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