Practical robust loop-shaping design method for triple-stage HDD actuator control under stroke constraints in data-center storage applications

With the continuous growth of data storage demand, precise and stable magnetic-head positioning in hard disk drives (HDDs) remains essential. This paper proposes a disturbance-rejection-oriented control design for triple-stage actuator (TSA) systems. The approach employs Bode-plot analysis to achieve robust performance against plant perturbations while explicitly incorporating the stroke limits of Lead Zirconate Titanate (PZT) micro-actuators into controller synthesis. Stroke constraints are represented as forbidden regions on the Bode diagram, providing an intuitive feasibility criterion for controller design. The physical stroke limitation is formulated as an inequality condition and embedded directly in the loop-shaping procedure. Performance is evaluated through hybrid simulations in which numerical plant models identified from measured actuator frequency responses are driven by disturbance signals generated from measured disturbance characteristics. The results demonstrate that the proposed controllers significantly reduce the risk of micro-actuator saturation while preserving high positioning accuracy.