Design of a time optimal variable structure controller for a disk drive actuator

This paper presents the design of a time optimal variable structure control (VSC) scheme for seeking and tracking the read/write heads of a computer hard disk. Seeking is performed through a proximate time optimal servo (PTOS) controller while a VSC controller with fixed linear switching hyperplane is used for tracking. The controller is robust to both parameter variations and unmodeled dynamics. It also introduces a sufficiently high bandwidth to enable accurate track following in the presence of runout. The tracking performance of the controller is evaluated against a conventional PID control structure. Time and frequency domain simulations provide proof of the superior robustness and runout performance of the VSC structure