Hysteresis modeling and compensation of PZT milliactuator in hard disk drives

Dual-stage actuation consisting of a PZT Microactuator (MA) and a Voice Coil Motor (VCM) has been used to improve the servo bandwidth and the disturbance rejections of Hard Disk Drivers (HDDs). However, the hysteresis in PZT MA limits the performance that can be achieved. In this paper, a Hammerstein model structure consisting of static hysteresis nonlinear block and dynamic linear block is used to model the PZT MA in HDDs and the identification method is also given. The nonlinear subsystem in the Hammerstein model is represented by Modified Prandtl-Ishlinskii (MPI) hysteresis model. It is proved that the proposed model is equivalent to the physical system. A hysteresis compensator is designed based on the proposed model. By the hysteresis compensation, the effects of hysteresis on the frequency responses of the PZT MA are measured. It is shown that apparent phase lead is achieved by hysteresis compensation, which is useful to improve the performance of control system.