Type Synthesis of a Class of Metamorphic Parallel Mechanisms for Wrist Rehabilitation Training

Aiming to address the problem of single motion mode for the general parallel mechanism, a type synthesis method of a class of metamorphic parallel mechanisms for wrist rehabilitation training is proposed. Two operation modes of the metamorphic parallel mechanisms are determined based on the physiological structure of the human wrist joint and the practical rehabilitation training requirements. Structural synthesis of the first three limbs is performed in terms of the displacement manifold theory, and structures of the fourth limb are synthesized via the virtual chain method and the screw theory. Type synthesis of the metamorphic parallel mechanisms is realized according to the given assembly conditions of the four limbs. Then, the structural evolution of the original parallel mechanisms is completed by replacing the rotational revolute joints at the ends of the first three limbs with a circular prismatic pair, and a plenty of novel metamorphic parallel mechanisms suitable for the wrist rehabilitation training robots are evolved. Finally, a 3RRUPc-1URS mechanism is taken as an example to validate that the moving platform can switch between the three-rotational and one-translational (3R1T) and the two-rotational and one-translational (2R1T) motion modes by releasing or locking the actuated joint of the fourth limb. Analysis results show that the type synthesis approach proposed is correct and feasible.