Design and analysis of a two-DOF serial ankle rehabilitation robot

Abstract

To address the problems of limited rehabilitation resources, difficulty in ensuring sufficient training intensity, and insufficient individualized training schemes for stroke patients with ankle dysfunction, this paper proposes a two-degree-of- freedom independently driven serial ankle rehabilitation robot based on the physiological structure and motion characteristics of the human ankle joint. The robot can perform single-DOF training in plantarflexion/dorsiflexion and adduction/abduction, as well as coordinated two-DOF training, thereby satisfying the rehabilitation requirements of patients at different recovery stages. The reachable workspace of the robot is analyzed using the Monte Carlo method, and posture-coupling constraints are introduced to correct the workspace, making the simulation results more consistent with the physiological motion range of the human ankle joint. Furthermore, motion simulations are performed in Adams to verify the continuity and smoothness of the robot during operation. The control system is developed with a Siemens S7-200 SMART PLC as the core controller and an upper-level computer for training-mode selection and online parameter configuration. The system is designed to support passive, active, and resistive training modes. Single-DOF angle tracking experiments were further conducted to evaluate the motion tracking performance of the prototype. The experimental results showed that the root mean square error values were 1.650 deg for plantarflexion/dorsiflexion motion and 1.005 deg for adduction/abduction motion, indicating that the robot achieved stable tracking performance in both motion directions. The results show that the proposed robot can provide a reachable workspace suitable for ankle rehabilitation and exhibits stable motion performance, providing a feasible design solution for individualized ankle rehabilitation training.