Development and Kinematics Optimization of a Human-Compatible Rope-Driven Ankle Rehabilitation Robot Based on Foot-Ankle IFHA Identification

To address the mismatch between current ankle rehabilitation robots and natural human motion, which affects rehabilitation efficacy, this paper uses screw theory and motion capture experiments to identify the instantaneous finite helical motion axis (IFHA) of the human ankle joint. It determines the distribution law of the IFHA and twist pitch (TP) of the ankle, and designs a human-machine motion compatible rope-driven ankle joint rehabilitation robot that meets the needs of human ankle joint rehabilitation. Firstly, human ankle motion trajectories are captured using the VICON system and IMU, and the experimental data are processed according to screw theory to obtain the distribution law of the IFHA and the range of TP. Secondly, the ankle joint's motion characteristics from the experiment inform the constraint characteristics of the rehabilitation mechanism, which are then mapped into a novel parallel rope-driven ankle rehabilitation robot to meet rehabilitation needs. Thirdly, the kinematic model of the novel mechanism is established, and its kinematic performance and singular configurations are analyzed based on the motion/force transmission index, guiding the optimization of the driving rope layout and mechanism scale parameters. Finally, an experimental platform is built to validate the human-machine motion compatibility, safety, comfort, and effectiveness of the rehabilitation robot.