Design and motion control analysis of a hybrid-powered ankle rehabilitation robot

This study presents a novel hybrid-powered ankle robot actuated from above (ARAA) designed to improve the smoothness and control of multiaxial movements in robot-assisted ankle rehabilitation. Addressing the limitations of existing systems, which often lack precise trajectory tracking and consistent force application, the proposed robot integrates pneumatic muscles for actuation along the X-axis and Y-axis, with a servo motor driving motion in the Z-axis. A PID-based posture controller is implemented to ensure accurate control during training, while a reconfigurable mechanism allows adjustment of motion parameters to accommodate individual physiological differences. Preliminary testing with a healthy participant demonstrated successful execution of both single-axis and multiaxial training protocols. The system achieved low trajectory tracking errors, with Root Mean Square Deviation (RMSD) and Normalized Root Mean Square Deviation (NRMSD) values of 0.0164 rad and 2.73 along the X-axis, 0.007 rad and 1.9 along the Y-axis, and 0.0012 rad and 0.31 along the Z-axis, indicating alignment with the requirements for effective rehabilitation. Force application by the pneumatic muscles closely followed the predefined trajectory, confirming high fidelity in force control. The results show that the hybrid-powered ARAA effectively meets the demands of controlled ankle training, offering enhanced precision and adaptability. This work contributes to advancing ankle rehabilitation technology by providing a more efficient and customizable solution for patient recovery.