Singularity analysis of a kinematically redundant (6+2)-DOF parallel mechanism for zero-torsion configurations

Abstract

The orientational workspace of parallel mechanisms is known to be restricted due to singular configurations of type II. Recently, a (6+3)-degree-of-freedom (DOF) kinematically redundant parallel mechanism was proposed based on the well-known Gough–Stewart platform. It was shown that, for the specific architecture proposed, a minimum of three redundant DOFs is necessary to guarantee the existence of a non-singular configuration for any pose of the platform. This work presents a different architecture with two redundant DOFs instead of three, and has for primary objective to derive the singularity locus for zero-torsion configurations. The results indicate that the mathematically possible singularities are outside of the reachable workspace, suggesting that for zero-torsion trajectories, two kinematically redundant DOFs are sufficient to greatly enhance the orientational workspace of the proposed architecture. An example path with large tilting angle is presented in a multimedia extension of the article in order to demonstrate the capability of the mechanism to reach such orientations without encountering inevitable singularities.