Optimisation of a nano-positioning stage for a Transverse Dynamic Force Microscope

Abstract

This paper describes the optimisation of a nano-positioning stage for a Transverse Dynamic Force Microscope (TDFM). The nano-precision stage is required to move a specimen dish within a horizontal region of 1μm×1μm and with a resolution of 0.3nm. The design objective was to maximise positional accuracy during high speed actuation. This was achieved by minimising out-of-plane distortions and vibrations during actuation. Optimal performance was achieved through maximising out-of-plane stiffness through shape and material selection as well optimisation of the anchoring system. Several shape parameters were optimised including the shape of flexural beams and the shape of the dish holder. Physical prototype testing was an essential part of the design process to confirm the accuracy of modelling and also to reveal issues with manufacturing tolerances. An overall resonant frequency of 6kHz was achieved allowing for a closed loop-control frequency of 1.73kHz for precise horizontal motion control. This resonance represented a 12-fold increase from the original 500Hz of a commercially available positioning stage. Experimental maximum out-of-plane distortions below the first resonance frequency were reduced from 0.3μm for the first prototype to less than 0.05μm for the final practical prototype.