Disturbance rejection control of a HDD using mixed sensitivity approach

This paper describes designing a controller of a hard disk drive for rejecting disturbances using mixed sensitivity approach. Position error signal (PES) consists of repeatable runout (RRO) and nonrepeatable runout (NRRO); NRRO is decomposed into its contributing components which are force disturbance, mechanical vibration, etc, in the frequency domain. To simulate the behavior of the disturbance signals, the decomposed signals are transformed to the time domain. The H^∞ control design can eliminate such disturbances effectively. A mixed sensitivity approach is applied to the robust controller design of the track following control for the HDD. We compare the results with a conventional controller and the results with the proposed controller. It shows the validity of the proposed controller design method.