Geometric design of triangulated bistable scissor structures taking into account finite hub size

Abstract

Pre-assembled scissor structures can be transformed from a compact bundle of elements to a fully deployed configuration, offering a considerable volume expansion. Intended geometrical incompatibilities during transformation can be introduced as a design strategy to obtain bistability, which allows instantaneously achieving some structural stability in the deployed state. Because of these incompatibilities, some specific members bend during transformation, resulting in a controlled potentially tunable snap-through behaviour. Geometric design methodologies were proposed in the literature to obtain a compatible geometry (i.e. with all of the beams straight) in the folded and the deployed configurations. However, most of these approaches do not consider finite hub sizes or introduce extra incompatibilities in the geometry by adding hub legs. In this contribution, deployability conditions are derived taking the finite hub size, i.e. the spacing between the connections of the different beams to the hub, into account to make triangulated bistable scissor modules fully geometrically compatible in the folded and the deployed configuration.