Stroke-Constrained Positioning Controller Design for Quad-Stage Actuators in HDDs

With the growing demand for higher data storage capacities in hard disk drives (HDDs), achieving precise and reliable positioning of the magnetic head has become increasingly critical. To address this challenge, this paper proposes a control system design methodology tailored to the quadruple-stage actuator (QSA) system, a promising candidate for next-generation HDD architectures. The proposed framework leverages Bode plot analysis to incorporate stroke constraints of thermal actuators—the smallest elements in the QSA system—directly into the controller design. These constraints are visualized as forbidden regions on the Bode diagram, enabling intuitive evaluation of controller feasibility. Specifically, inequality conditions representing the physical stroke limitations are formulated and embedded into the design process. Validation was performed through hybrid simulations that integrated empirical measurement data into mathematical modeling. The results confirm that the enhanced controllers satisfy the stroke constraints while preserving high positioning accuracy and overall system responsiveness.