On Design and Analysis of Electrostatic Arch Micro-Tweezers

Abstract

This article provides criteria for the design of electrostatic arch micro-tweezers. The tweezers can be operated in two modes: a traditional quasi-static mode where a direct current voltage commands the tweezers arms along a trajectory to manipulate objects and dynamic mode where a harmonic signal commands release or characterization of objects. While the arms are rigid and move in tandem in the static mode, this is not guaranteed in the dynamic mode. To satisfy this, we carried out modal analysis of the tweezers using a finite element model (FEM) and a reduced-order model (ROM). The results show that the arms kinetic and potential energies divide the beam span into a middle sub-span between the arms and two outer sub-spans and result in significant changes in the relative compliance of the sub-spans. The changes in the platform compliance place limitation on the tweezers dynamic operation, such that only the first symmetrical mode shape of the tweezers satisfies the design criteria. We also investigate the adequacy of an ROM using straight unbuckled beam mode shapes as basis functions to represent the tweezers response by comparing its results with those of FEM. A five-mode ROM is found adequate to represent small motions in the vicinity of the tweezers initial curvature. It is inadequate for larger motions involving snap-though motions between the initial and counter curvatures. To capture larger motions, ROM should be improved by incorporating higher order straight beam modes or using the actual tweezers modes.