Design and Kinematical Performance Analysis of a 3-RUS/RRR Redundantly Actuated Parallel Mechanism for Ankle Rehabilitation

In this paper, we present the design of a novel 3-RUS/RRR redundantly actuated parallel mechanism for ankle rehabilitation based on the principle from the conceptual design. The proposed mechanism can actualize the rotational movements of the ankle in three directions while at the same time the mechanism center of rotations can match the ankle axes of rotations compared with other multi-degree-of-freedom devices, owing to the structural characteristics of the special constraint limb and platform. A new actuator redundancy scheme is used, which not only still maintains all inherent advantages from actuator redundancy but also possesses the kinematic partially decouple feature that improves the flexibility of the robotic system. Kinematic performances, such as dexterity, singularity and stiffness, are analyzed based on the computed Jacobian. Then simulation is performed. All the results show that the redundant robot has no singularity, better dexterity and stiffness within the prescribed workspace in comparison with the corresponding 3-RUS/RRR nonredundant robot, and is suitable for rehabilitation exercise.