Adaptive Knee Joint Control for an Active Amputee Prosthesis

This work presents the design and evaluation of knee joint controllers for an above-knee prosthesis. The prototype is a three degree of freedom prosthesis which is planned to be controlled in part by EMG thigh signals, in part by a predictive trajectory generator based on multisensorial data such that the foot can be correctly positioned with respect the floor. There is described a simplified non-linear dynamic model for the knee opening angle. The model parameter identification is made using a least squares batch estimator. Based on the estimated non-linear model, two strategies for joint controllers are designed: PID and model reference adaptive controller. The PID design follows a root locus approach with experimental tuning. Preliminary tests were performed in a platform built for the prosthesis under development. The results discussed in this paper reveals the difficulty in controlling such a nonlinear plant.