Midfrequency Runout Compensation in Hard Disk Drives Via a Time-Varying Group Filtering Scheme

Conventional add-on feedback filters that are designed to compensate for midfrequency (mid-f ) repeatable runout (RRO) in a hard disk drive (HDD) servo system either have a long filter transient or constitute a large sensitivity hump as well as poor stability margins. This paper presents a novel linear time-varying (LTV) group filtering scheme for the compensation of a few mid- f RRO harmonics. While having a short filter transient that ensures fast disturbance attenuation, the proposed filter does not constitute to any substantial unnecessary sensitivity function gain amplification at the steady state. Simulation and implementation results show the effectiveness of this group filtering scheme.