Type synthesis of parallel mechanisms having 3T1R motion with variable rotational axis

Parallel mechanisms (PMs) having three translational (T) and one rotational (R) movement capability draw continuous attention from academia and industry. The existing 3T1R PMs can only generate Schoenflies motion and bifurcation of Schoenflies motion. This paper proposes a new 3T1R motion that features one rotation about a varying axis plus three pure translations. Drawing mainly on finite screw theory, a hierarchical approach for type synthesis of limb structures of the PMs having 3T1R motion with variable rotational axis is presented by developing the basic limb bonds first and then their equivalent substitutions using the properties of screw triangle product. The assembly conditions for the PMs of this kind are discussed. Consequently, numerous novel PMs consisting of four identical limbs are synthesized using this technique.