Head‐positioning control system for small‐sized hard disk drives

High track density has been achieved by adopting an H∞ controller with a feed-forward compensator using adaptive filter theory in a sector servo system. In applying the H∞ control theory, a state-space model of an augmented plant was constructed considering the input location of the disturbance. Moreover, to reduce repeatable runout, an experiment involving a feed-forward control system including an adaptive FIR filter was performed. As a result, the head-positioning accuracy was improved by approximately 15 percent compared to the case without feed forward. A 0.15-μm head-positioning accuracy was achieved. This level of accuracy means that a track density of 310 tracks/mm (8100 TPI) can be realized.