Rejection of Repeatable and Non-repeatable Disturbances for Disk Drive Actuators

This paper presents an application of two-parameter robust repetitive control (TPRRC) in disk drive servo control, where the repeatable rrmout (RRO) and non-repeatable runout (NRRO) are rejected simultaneously. The repeatable disturbances are rejected by tbe internal model structure of TPRRC, while the nonrepeatable disturbances are attenuated by the robust performance specification. The design procedure of TPRRC is given. A simple structure of tbe robust performance weighting function WP(j@ is proposed and the relationship between the coefficients of WP@iS) and the performance specification over the non-repeatable disturbance is discussed too. The simulation results using the measured position error signals (PES) of a disk drive as output disturbance are presented to show the effectiveness of the disturbance rejection of disk drive servo control and demonstrate that it is a cost effective way to improve the track density of disk drives. Keyword Disk Drive Servo Control, Repetitive Control and Disturbance Rejection.