Digital redesign and multi-rate control for motion control-a general approach and application to hard disk drive servo system

This paper is concerned with the digital redesign of continuous time controllers for motion control. Multirate digital control with a high order hold is utilized to better approximate the continuous time controller when the measurement sampling rate is relatively low. The proposed approach is illustrated for track following control of a hard disk drive (HDD) servo system. The HDD controller is first designed in the continuous time domain based on LQG/LTR method. It is redesigned as a single rate digital controller as well as multirate digital controllers with different holds. The redesigned controllers are evaluated by simulation, and the advantage of multirate control is demonstrated.