Center-driven planar closed-loop mechanisms based on an angulated four-bar linkage

Abstract

Center-driven planar closed-loop mechanisms have a prospect in robotics yet are not synthesized easily. This paper generalizes an angulated four-bar linkage for a constant subtended angle and proposes three angulated derivatives, with which three novel center-driven planar closed-loop mechanisms are synthesized: a multi-bar mechanism (MBM), a center-driven double-ring mechanism (CD-DRM), and a deployable multi-arm mechanism (DMAM). A special MBM constructed using the angulated four-bar linkages is found to have extension and contraction shapes with a driving angle phase difference of π, and have a mirror symmetric shape sequence when the driving angle rotates from the extension shape to the contraction shape clockwise and counterclockwise, respectively. Based on the angulated derivatives, CD-DRMs and DMAMs with unique features are derived. Two special types of CD-DRMs have a mirror symmetric shape sequence like the special MBM while performing different motions, namely radial reciprocating and expansion motions, respectively. Moreover, the DMAMs realize a large deformation motion with all their end joints located along one circle and deployed simultaneously. Finally, model simulations and prototypes demonstrate the feasibility of the proposed mechanisms.