Kinematics characteristic analysis of a type of human-machine compatible ankle rehab robots based on human-ankle IFHA identification

Abstract

Existing ankle rehabilitation robots lack reference to the actual ankle motion posture of humans, leading to a mismatch with the natural motion of the ankle joint and affecting the rehabilitation outcome. This paper uses screw theory and motion capture equipment to identify the instantaneous finite helical motion axis (IFHA) of the human ankle and obtains the distribution law of the instantaneous rotational axis and translational pitch of the ankle, and based on this, design a human-machine motion compatible rope-driven ankle joint rehabilitation robot that aligns with human motion for ankle joint rehabilitation. Firstly, the experimental trajectories of human ankle dorsiflexion(DF) /plantarflexion(PF), inversion(IN)/ eversion(EN), and adduction(AD)/abduction(AB)/ are taken by using the VICON motion capture system, and the experimental data are analyzed and processed according to the screw theory. The distribution law of the IFHA and the range of twist pitch (TP) are obtained. Secondly, according to the motion characteristics of the ankle joint obtained from the experiment, the constraint characteristics of the ankle rehabilitation mechanism are obtained, and it is mapped into a series of parallel mechanisms to meet the rehabilitation needs. Select a configuration as the skeleton of the robot, design a prototype of the novel rope-driven rehabilitation robot, and establish its kinematic model. Then, analyze the kinematic characteristics of the mechanism by combining screw theory and spatial analytic geometry theory. Finally, the experimental platform of the ankle rehabilitation robot is built to verify the accuracy of human-machine motion fitting, safety, comfort, and effectiveness of the rehabilitation robot.