High capacity of new magnetic material can be exploited only with a fine servo-positioning of the hard disk heads. This can be achieved by means of dual stage actuation, where the secondary actuator can be realized with different technologies. In this paper, the need for a secondary actuator is proven by explicitly including the nonlinear friction on the voice coil motor bearings. The use of a piezoelectric secondary actuator is analyzed, first by determining the dynamic model of piezo-based dual stage actuator system, then by including a detailed model of the piezoelectric actuator, comprehensive of the effects of voltage or charge driving. With this detailed model, different control strategies are evaluated. The results reported suggest that voltage-driven piezoelectric actuators should not be used in fine servo-positioning. Instead, charge driven actuators exhibit promising performances when used with the control strategies proposed.
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