Rejection of repeatable and non-repeatable disturbances for disk drive actuators

Presents an application of two-parameter robust repetitive control (TPRRC) in disk drive servo control, where the repeatable runout (RRO) and non-repeatable runout (NRRO) are rejected simultaneously. The repeatable disturbances are rejected by the internal model structure of TPRRC, while the non-repeatable disturbances are attenuated by the robust performance specification. The design procedure of TPRRC is given. A simple structure of the robust performance weighting function W _p(jω¯) is proposed and the relationship between the coefficients of W_p(jω¯) and the performance specification over the non-repeatable disturbance is discussed too. The simulation results using the measured position error signals 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