Integrated servo/mechanical design of HDD actuators and bandwidth estimation

An optimal design technique of both the actuator dynamics and the servo controller is presented. The actuator dynamics are characterized by the time delay created by the unstables zeros of the actuator transfer function. The achievable bandwidth is a simple function of the time delay and the sampling frequency. The feedback controller, including the notch filter, is designed simultaneously. The performance with dynamics variations can also be evaluated by the time delay. It is shown that the variations of the high-frequency modes play an important role in the bandwidth improvement of the dual-stage system.