Design and Control of a Coarse-Fine Inverted Span-Scale Positioning Stage With Smooth Switching for Antagonistic Piezo-Actuation

Dual-servo systems are highly expected in span-scale manipulations where both large stroke and high positioning precision are required. This paper presents a new coarse-fine inverted span-scale positioning stage with antagonistic piezo-actuation configuration. Different from conventional designs for coarse-fine positioning stages, in the proposed stage, the coarse stage is mounted on the moving platform of the fine stage. This coarse-fine inverted configuration helps to utilize the high out-of-plane stiffness of the fine stage and to guarantee the workspace of the overall system. To address the measurement signal allocation and chattering problems in antagonistic actuation, a Sigmoid function is used instead of the common Step function. A prototype is fabricated and its positioning and tracking performances are assessed. Experimental results show that the stage achieves a positioning error of ±25 nm and a resolution of 8 nm across a centimeter scale stroke, showing excellent span-scale positioning performance. Further, different trajectories are used to assess the tracking performance. It is found that the root-mean-square tracking error can be reduced to several tens of nanometers, corresponding to a tracking error within 1% of the trajectory span. These results demonstrate the applicability of the stage in span-scale tasks, such as single-molecule manipulation.