Design and experimental equilibrium stability assessment of a RFRFR continuum parallel robot

Continuum parallel robots (CPRs) are mainly constituted by flexible links arranged in parallel between a rigid platform and a rigid base, and they promise remarkable performance in human–robot collaboration applications. New CPRs modelling strategies and their experimental validation are continuously investigated due to the nonlinear phenomena complexity and the high computational effort required to solve them. This work focuses on the experimental validation of CPRs equilibrium stability prediction. We demonstrate that models based on planar displacement assumptions may fail in the equilibrium stability prediction, even though the CPR is nominally planar. A new CPR prototype for planar applications is proposed, designed, and tested for the scope. Unstable configurations that limit the robot workspace are theoretically and experimentally investigated. A singularity type, related to out-of-the-plane uncontrolled motions of the planar CPR, is experimentally identified for the first time. Experiments demonstrate that, even though the prototype is theoretically planar, a planar model neglecting out-of-the-plane phenomena is inadequate to assess equilibrium stability limits.