Mechatronics Development and Control of a Lower Limb Exoskeleton With High-Torque Assistance

Abstract

Spinal cord injuries and strokes can lead to severe mobility impairments. Assistive devices, such as exoskeletons, can help individuals regain mobility and the strength to move their limbs. Developing these devices to be affordable and comfortable would make them more practical for home-based usage with a significant impact on people's lives. This work presents an optimized hip exoskeleton that is lightweight (10 kg) and cost-effective (under $3000) while maintaining high torque and strength capabilities. To enhance affordability and accessibility, the exoskeleton structure utilizes three-dimensional-printed materials, making it reproducible for a wider range of users. A mechatronic configuration was carefully selected to ensure portability, integrating high-torque DC motors, a mini-PC, a microcontroller, a rechargeable battery, and intermediate boards. The exoskeleton's motor delivers a nominal torque of 48 N·m and a peak torque of 120 N·m achieving a weight-to-torque ratio of 0.08 kg/N·m, which is lower than the ones for existing exoskeletons like Mina V2 (0.53 kg/N·m) and EksoNR (0.27 kg/N·m). The system was experimentally validated through walking and sit-to-stand motions, demonstrating high precision at varying speeds. The results showed a maximum tracking error of less than 0.09 rad and an assistive torque of up to 25 N·m, obtained by tuning the position controller gains. This mechatronic system design significantly improves exoskeleton efficiency, accessibility, and practicality, offering a transformative solution for lower-limb assistive devices.