FOLDABILITY AND CONSTRAINT ANALYSIS OF TWO 3US PARALLEL MECHANISMS

摘要

Due to advantages of large-span, compact storage and high portability, foldable mechanisms have a promising prospect in aeronautics and astronautics applications. Two configurations of 3US parallel mechanisms with full foldability are constructed and their mobility and motion characteristics are further analyzed. This paper starts from geometrical arrangements of Hooke joints. Aimed at achieving full foldability, Hooke joints axes are placed along opportune directions, and lead to two configurations of 3 US parallel mechanisms with anticlockwise folding and clockwise deploying motions. The analytic expression of the deployable ratio is presented and a numerical example is evaluated. This paper then applies constraint analysis in two configurations. In particular, constraint-screw systems of three limbs and those of platforms are investigated, followed by twist systems of platforms being derived as reciprocals of their wrench systems. The similarity and difference of motions allowed by two configurations are further addressed by comparison of their platform twist systems.