Abstract
A robust adaptive admittance control scheme using human-inspired virtual constraints was presented for a robotic knee prosthesis. The controller is able to deal with the wearer's motion intention as well as the partial unknown parameter values of the prosthesis dynamics. The desired trajectory of the prosthetic knee joint is parameterized by the amputee-driven thigh phase variable and implemented by human-inspired virtual constraints rather than the preprogrammed time-dependent trajectory or human data replaying. A reference admittance model was set up to make the prosthesis be more compliant in the presence of ground reaction forces impact. A composite reaching law is proposed to cope with the chattering phenomenon and the finite-time convergence problem. The controller is designed by the back-stepping method based on Lyapunov. The tracking performance and the stability of the closed-loop system are proven via Lyapunov stability analysis. The feasibility and effectiveness of the proposed control scheme are proved in simulation results.
Highlights
Amputee’s ambulation is usually slower, less stable, and more energy expenditure than able-bodied person [1]
In powered lower limb prosthesis field, the prevailing control strategy is by far the finite state impedance control (FSIC) [3]–[8]
The continuous control scheme brings many challenges that need to be solved. Such as i) how to generate a reference trajectory that can reflect the wearer’s motion intention; ii) how to achieve the flexibility or compliance of the prosthetic leg when it interacting with ground; iii) how to realize the adaptability and robustness of the controller so that the prosthesis can adapt to different wearers and adapt to more complex environments
Summary
Amputee’s ambulation is usually slower, less stable, and more energy expenditure than able-bodied person [1]. Trajectories of prosthetic joints would have a kind of humanlike characteristics of continuous and time-independent, that would potentially enable amputee subjects to walk at different gait speeds with the same controller. The continuous control scheme brings many challenges that need to be solved Such as i) how to generate a reference trajectory that can reflect the wearer’s motion intention; ii) how to achieve the flexibility or compliance of the prosthetic leg when it interacting with ground; iii) how to realize the adaptability and robustness of the controller so that the prosthesis can adapt to different wearers and adapt to more complex environments. At present, continuous control based on virtual constraints is often implemented by feedback linearization method which depends on an accurate mathematical model of the prosthetic leg and the precise interaction force between the prosthesis and the amputee. The specific forms of Y (q, q, v, v) and θ are given in Appendix B
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