Design and analysis of reconfigurable parallel robots with enhanced stiffness

Static redundancy in a parallel manipulator can enhance the stiffness of the end-effector, improve its fault tolerance, minimize its singularity loci, and reduce the internal loads experienced by the joints. Traditionally, this form of redundancy would be accompanied by actuation redundancy. Introduced in this paper is a new approach to statically enhance a manipulator without actuation redundancy. This is achieved through the use of lockable passive joints that are utilized in an alternating fashion to reconfigure the system into various isostatic and hyperstatic topologies without any external assistance. Although applicable to both kinematically non-redundant and constrained manipulators, this approach is especially effective for those with lower instantaneous mobility. The inherent redundancy in these reconfigurable robots is exploited to obtain full finite mobility with as few as one actuator through under-actuation with the use of virtual alternating constraints. The architecture design, kinematic analysis, and kinetostatic analysis of the proposed robots are addressed herein, followed by a case-study to demonstrate the effectiveness of the proposed design and analysis.