Internal model control for the dual-stage actuator in hard disk drives

Dual-stage actuator (DSA) is considered as the solution to meet the challenges of ever-increasing track density in hard disk drives (HDD). The low inertia of its secondary actuator makes it possible to reposition the read/write head fast to follow the variations in the data track. This allows better control of the position error during track-following mode of the servo system. Unfortunately, the physical characteristics of the secondary actuators vary widely because of imperfections in the manufacturing process and the variation in the material properties. Robustness is, therefore, a very important factor in the design of the servo controller. This paper presents the design and implementation of a dual actuator servo controller using internal model control (IMC) which is a well-known tool to design robust controller. The IMC is used for the piezoelectric secondary actuator only, and an observer-based controller is used for the primary stage. Effectiveness of the controller is verified through simulation and experiments.