Uncertainty modeling for hard disk drives

A modern hard disk drive uses a dual-stage actuator to read/write data on a track with width less than 100nm. The dual-stage actuator requires an advanced controller to achieve high performance on millions of hard disk drives. This paper presents a numerical algorithm utilizing convex optimization to create an uncertainty model, for the purpose of synthesizing a robust controller, from a set of experimental frequency response data. Furthermore several practical issues of constructing an uncertainty model for the dual-stage actuator are described. The proposed method is applied to a set of frequency response data of dual-stage actuators from numerous hard disk drives to create an uncertainty model of the actuator. Then the uncertainty model is used to synthesize a robust control law, which is implemented and experimentally tested on a hard drive.