Model-based robust and adaptive control of transfemoral prostheses: Theory, simulation, and experiments

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Azimi, Vahid
Hutchinson, Seth
Simon, Dan
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This thesis presents and experimentally implements five different robust, adaptive, and robust adaptive controllers as the first steps towards using model-based controllers for transfemoral prostheses. The goal of this research is to translate these control methods to the robotic domain, from bipedal robotic walking to prosthesis walking, including a rigorous stability analysis. The human/prosthesis system is first modeled as a two-domain hybrid asymmetric system. The model upon which the controllers are based is a 5-link planar hybrid system (both continuous and discrete behaviors) with point feet, to represent a transfemoral amputee’s body and limbs. An optimization problem is formulated to obtain a stable human-like gait. The proposed controllers are then developed for the combined human/prosthesis model and the optimized reference gait. The stability of all five controllers is proven using the Lyapunov stability theorem and Barbalat’s lemma, ensuring convergence to the desired gait. The proposed controllers are first verified on a bipedal walking robot as a hybrid human/prosthesis model in simulation. Simulations show that the proposed controllers are capable of meeting specific performance requirements regarding trajectory tracking of the prosthetic knee, convergence to a stable periodic orbit, and robustness to force/obstacle disturbances while walking on flat ground. They are then experimentally tested on a treadmill with an able-bodied subject using AMPRO3 (the third iteration of Advanced Mechanical Prosthesis), a custom self-contained powered transfemoral prosthesis. Results show that all controllers provide humanlike walking and accurate tracking performance for a healthy human subject utilizing a transfemoral prosthesis. Finally, outdoor tests are carried out using AMPRO3 with three test subjects walking on level ground, uphill slopes, and downhill slopes at slope angles of 3 and 8 degrees, to demonstrate walking in different real-world environments.
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