Abstract: The Gough-Stewart parallel mechanism is chosen as the driving mechanism for the axisymmetrical vectoring exhaust nozzle (AVEN). However, this manipulator works at its singular position normally and obtains one degree-of-freedom rotation about the axis of the AVEN. In order to restrict this obtained freedom, the 3SPS-3PRS constraint kinematic chains are introduced. Through the configuration bifurcation characteristics investigation of the 3SPS-3PRS parallel manipulator, it is found that the singular points still exist in the 3SPS-3PRS parallel manipulator and the singular-free workspace of the manipulator is restricted by singular points. For the given vectoring requirements of the AVEN, the lengths of the input parameters can possibly overstep the singular-free workspace determined by the singular points, and lead a huge inner constraint force in 3PRS kinematic chains to be produced, as well as the motion of the top platform uncertainty while the manipulator passes through the singular points. Therefore, the singularities of the parallel manipulator still exist.

Key words: 3SPS-3PRS, Configuration bifurcation characteristics, Parallel manipulator, Singularity