Development and control of a large range XY⊖ micropositioning stage

The recent developments in micro/nano-positioning technologies have highlighted the demand for compact large range three-degrees-of-freedom (3-DOF) XY circle minus mechanisms for applications such as sample positioning in nanoimprint lithography, scanning probe microscopy, precision machining, and many more. However, this type of mechanisms suffers from a large footprint, sensing difficulties, and low motion accuracy due to the cross-coupling errors. In this paper, a compact design is proposed to achieve large workspace and high motion accuracy. Prismatic-Prismatic-Revolute (PPR) joints were used to construct this mechanism to yield deterministic large range motions. Laser-based measurement technique based on retroreflectors is proposed to sense large translations and rotation simultaneously with nanometer resolution. A prototype of the proposed mechanism was fabricated to investigate the static and dynamic properties of its structure, and compare these with the computational results. The motion accuracy of the mechanism was improved by using a sliding mode controller based on a nonlinear disturbance observer. The cross-coupling effects and modelling uncertainties were estimated and compensated in this control scheme, which consequently improved the tracking performance. The experimental results showed that the proposed design achieved large workspace, high resolution, improved tracking performance, and required level of compactness as compared with other designs reported in the literature.