Study on Kinematics and Stiffness of a Cable-driven Ankle Rehabilitation Robot

Since the existing ankle rehabilitation robots are of poor human-machine structure matching, inferior compliance and weak adaptability, a novel cable-driven variable-stiffness ankle rehabilitation robot is proposed. Considering variable stiffness of the cable-driven robots due to unidirectional force transmission of the cable, a variable-stiffness device with simple, compact structure and high stiffness-tension linearity is designed based on flexible parallel mechanism theory, to improve the range and accuracy of variable-stiffness control. By modeling and analyzing the kinetictostatics and stiffness of the rehabilitation robot, it is found that the robot pose can be adjusted by regulating the cable lengths, and the robot stiffness can be adjusted by regulating the cable tensions. In order to achieve stiffness control, a stiffness-oriented cable tension distribution algorithm is proposed, and its effectiveness is verified by a simulation example. Finally, the control system and prototype of the cable-driven ankle rehabilitation robot are developed, and the motion control method is validated by an experiment. The results show that the proposed cable-driven ankle rehabilitation robot has the advantages of excellent human-machine structure matching and variable stiffness.