This paper investigates a factorization approach to sensitivity loop shaping for disturbance rejection in hard disk drives (HDDs). The advantage of the factorization approach is that the system sensitivity function can be expressed explicitly in terms of a unique design parameter. This greatly simplifies the control design process to make the system sensitivity function match a chosen target sensitivity function with guaranteed stability. By decomposing the stabilizing controller structure, we further present how to select the design parameter (also regarded as disturbance filter) to suppress the dominant disturbances at some specific frequencies. Simulation analysis and experimental results demonstrate that the proposed method can remarkably suppress the disturbances around the servo bandwidth and thus offers an improved tracking accuracy.
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