Design and evaluation of swing phase controllers for single-axis knee

A prosthetic swing-phase control mechanism simulates the action of thigh musculature to aid in increased gait function. In this work, a hydraulic damper and a magnetorheological (MR) damper are designed as controllers with an objective of evaluating their performance in controlling swing-phase damping in an above-knee prosthesis. Parametric models are utilized to represent dynamic properties of the dampers. Based on the models, control parameters that govern damping force and displacement of the dampers are identified. Parameters of the dampers are determined through optimization that minimizes the error between the prosthesis knee angle trajectories and a desired knee angle trajectory for normal level ground walking from experimental data. Experimental data of thigh and hip motions are introduced as inputs into a dynamic system to determine sets of control parameters. Furthermore, input thigh motion is also deviated to evaluate robustness of the controllers in real application. Comparison of the desired knee angle trajectory with those of the knee angle trajectories obtained from control parameters is done with respect to maximum achievable knee flexion angle, duration of swing phase, shank velocity at the end of swing phase and mean angle difference. Evaluation results of the dampers show a better competence of MR damper over hydraulic damper.