Robust tracking control of an XY compliant nanomanipulator with variable loads

This paper presents a robust tracking control strategy for a newly-designed large range compliant XY nanomanipulator. The main objective of the proposed control strategy is to track periodic trajectories for the proposed XY parallel compliant nanomanipulating system with certain variable loads. The proposed control structure integrates a disturbance observer (DOB) based ${H}_{\infty }$ repetitive controller. Specifically, the outer loop is a plug-in repetitive controller combined with an ${H}_{\infty }$ controller, where the repetitive control is adopted for periodic trajectory tracking, and the ${H}_{\infty }$ control is utilized to deal with variable loads and to achieve robust stabilization. The inner loop is chosen as a disturbance observer for rejection purposes of periodic and non-periodic disturbances. The design prototype is fabricated and the proposed control algorithm is experimentally validated, where enhanced tracking performance with variable loads is demonstrated, achieving tracking errors from around 80 to 210 nm with a motion stroke over 1 mm.