Real-World Terrain-Dependent Variable Admittance Model for Amputee-Prosthesis System and Environment Interaction

Position-based prosthesis control strategies can reduce the tuning time of the finite-state machine impedance control strategies but often use high-out impedance for suitable motion tracking, precluding compliant interaction between the amputee-prosthesis system and the environment. This study focuses on enhancing dynamic interaction between the amputee-prosthesis system and real-world terrains in position-based prosthesis control strategies. A real-world terrain-dependent variable admittance model is proposed that integrates real-time force sensing to regulate the desired joint trajectories during the prosthesis-environment interaction in the stance phase. A trajectory tracking controller consisting of a proportional differentiation controller with a robust compensation controller is designed to deal with the system uncertainties and guarantee stability, enabling amputee-prosthesis walking on real-world terrains with a human-like motion. Experimental results show that the proposed control strategy reduces the torque of the prosthesis joints at the heel-strike phase and increases the torque at the push-off phase, enhancing the compliant interaction of the amputee-prosthesis system with the ground and achieving better tracking performance. To the authors' knowledge, this study is the first to investigate how to enhance dynamic interaction between the amputee-prosthesis system and the real-world environments in position-based powered prosthesis control strategies, offering a feasible solution for enhancing the compliant interaction and walking stability outside the laboratory.