Midfrequency disturbance suppression via micro-actuator in dual-stage HDDs

In hard disk drives (HDDs), it is difficult for the single-stage servo system to suppress the disturbance within the midfrequency band (1-3 kHz) because of the limited servo bandwidth. This article presents a dual-stage control design using a peak filter to deal with the midfrequency narrow-band disturbances caused by disk flutter or windage. The technique of initializing the states of the peak filter is proposed to preserve the smoothness of transient response when the dual-stage servo loop is switched on from track-seeking to track-following. Experimental results demonstrated that the proposed dual-stage control scheme could effectively suppress the midfrequency disturbance without compromising the settling performance. This method would enhance the disturbance attenuation of the dual-stage servo system for higher track density in HDDs.