Abstract: Based on a particular representation of orientations of the 6/6-Stewart manipulator, a polynomial expression of thirteen degree that represents the orientation-singularity locus of the manipulator at a fixed position is derived and examples are given to illustrate the result. Using this particular orientation representation and the inverse kinematics solution of the 6/6- Stewart manipulator, a new discretization method is proposed for computing the nonsingular orientation-workspace of the manipulator by taking limitations of active and passive joints and the link interference into account, which can guarantee the manipulator is nonsingular in the whole orientation-workspace. Examples of a 6/6-SPS Stewart manipulator are given to demonstrate the results.

Key words: Nonsingular orientation-workspace, Nonsingular void, Orientation-singularity locus, Stewart manipulator