A new class of foldable mechanisms with a circular rail—FoldRail mechanisms

Abstract

This article introduces a novel class of 6-DOF foldable parallel mechanisms with a circular rail—FoldRail mechanisms. The circular rail allows the mechanisms to perform an unlimited rotation around the rail axis, and the innovative design of the kinematic chains provides foldability to almost a planar configuration. First, the paper presents mechanisms with three to six kinematic chains and provides their mobility analysis using the instantaneous screw theory: this analysis allows determining the chain singularities and several inappropriate actuation schemes. Next, among the variety of different mechanisms with various actuation schemes, two mechanisms with three kinematic chains and identical actuation schemes in each chain are selected and compared. The rest of the article analyzes one of these two mechanisms, shows how its output link can achieve a reconfigurable spherical motion and a screw motion, and determines the singular configurations.