Reset Control for Midfrequency Narrowband Disturbance Rejection With an Application in Hard Disk Drives

A reset disturbance compensation scheme is developed to reject midfrequency narrowband disturbances, with an application to the hard disk drives (HDDs). Generally, disturbance at the midfrequency band is not effective to reject through the feedback control based on the internal-model principle or high gain control due to phase stability. This paper investigates a reset control scheme and its favorable approximate frequency response using the describing function. The reset control makes its gain-phase frequency response break through the fundamental Bode´s constraint of linear time-invariant system and provides a maximal phase lead at desired frequencies without affecting gain´s characteristic. With additional phase lead, the issue of phase stability can be solved. A reset midfrequency narrowband compensator is designed by incorporating the reset controller and a narrowband filter. The implementation on a real HDD servo system shows the removal of midfrequency disturbance due to disk vibration is improved by 50% compared with the linear control scheme, resulting in a track misregistration (TMR) reduction of 32%.