Minimum destructive interference design of dual-stage control systems for hard disk drives

This paper presents the design of a dual-stage actuator control system consisting of a voice coil motor and a microactuator (MA). A dual-stage actuator model is developed to include a dominant MA flexible mode and the interaction between both actuators. Fundamental observations and design strategy are followed by a proposition of a dual-stage actuator control system to be used for track-seek in the MA range, track-follow, and settle. A new performance index, destructive interference, is introduced to express the degree of cooperation between both actuator systems with very different specifications and characteristics. In the dual-stage actuator control design, the measure of destructive interference is minimized to determine a MA controller so as to attain desired time and frequency responses. Robustness analysis is conducted using the structured singular value method on the resulting dual-stage actuator control system. Through an application example, it is demonstrated that minimizing the destructive interference produces a dual-stage actuator control system with desired time and frequency responses.