Track-Following Control Using Resonant Filter in Hard Disk Drives

A design method to suppress the disturbances by using a resonant filter for track-following control has been developed. The resonant filter can realize a stable resonant mode by a filter to obtain a circular vector locus that recedes from the critical point on the Nyquist diagram. With this method, the control engineers can easily design and implement a controller to suppress the disturbances in head-positioning systems at a specific frequency by adding digital filters. Our experimental results show that the proposed method can greatly suppress the nonrepeatable runout and repeatable runout above the servo bandwidth.