Design and Robust Repetitive Control of a New Parallel-Kinematic XY Piezostage for Micro/Nanomanipulation

This paper presents mechanism and controller design procedures of a new piezoactuated flexure XY stage for micro-/nanomanipulation applications. The uniqueness of the proposed stage lies in that it possesses an integrated parallel, decoupled, and stacked kinematical structure, which owns such properties as identical dynamic behaviors in X and Y axes, decoupled input and output motion, single-input-single-output (SISO) control, high accuracy, and compact size. Finite element analysis (FEA) was conducted to predict static performance of the stage. An XY stage prototype was fabricated by wire electrical discharge machining (EDM) process from the alloy material Al7075. Based on the identified plant transfer function of the micropositioning system, an H_∞ robust control combined with a repetitive control (RC) was adopted to compensate for the unmodeled piezoelectric nonlinearity. The necessity of using such a combined control is also investigated. Experimental results demonstrate that the H_∞ plus RC scheme improves the tracking response by 67% and 28% compared to the stand-alone H_∞ for 1-D and 2-D periodic positioning tasks, respectively. Thus, the results illustrate the effectiveness of the proposed mechanism design and control approach.