Coupling Controller Design for MISO System of Head Positioning Control Systems in HDDs

Abstract

Head positioning control systems are required to improve the positioning accuracy and thus increase the recording capacity of hard disk drives (HDDs). Existing head positioning control systems employ a dual-stage actuator system comprising a voice coil motor (VCM) and a piezoactuator. The control system is a multi-input single-output system, and positioning controllers must be designed for both actuators. In this article, we propose a coupling controller design method for head positioning control systems of HDDs. The proposed method designs the controllers by considering the interaction between the VCM and the piezoactuator. It is more complex than the decoupling controller design method, which is widely used to design the controllers for the dual-stage actuator system. Nevertheless, it provides greater freedom in the controller design. The main advantage is, when the entire feedback loop is stabilized, the feedback loop for each actuator does not need to be stabilized. The design results show that the proposed design method can improve the positioning accuracy with comparison to the decoupling controller design. Moreover, the amount of the required stroke of the piezoactuator is decreased by using the coupling controller design.