Track-following Control Using Resonant Filter in Hard Disk Drives

A design method to suppress disturbances using resonant filters for a track-following control in hard disk drives was developed. The resonant filter can realize a stable resonant mode by a filter with a circular vector locus that recedes from the critical point on the Nyquist diagram. By using the proposed method, a stable resonant filter in the control system can be designed with accuracy to suppress the disturbances above the servo bandwidth. Application of the proposed method to a hard disk drive showed greatly suppression of the disturbances at the frequencies higher than the servo bandwidth.