Design of controller for single axis knee using hydraulic damper

A prosthetic swing-phase control mechanism simulates the action of the upper leg musculature to aid in increased gait function. More specifically, swing-phase control mechanisms limit the maximum knee flexion and allow the shank to smoothly decelerate into full knee extension without excessive impact. In this work, a hydraulic damper is designed with the objective of controlling swing-phase damping in an above-knee prosthesis. A linear spring and damper model is used to represent the dynamic properties of the damper. Based on this model, three control parameters that govern the damping force and displacement of the damper have been identified. The parameters of the damper are determined through optimization of the prosthesis knee angle with a desired knee angle trajectory obtained from experimental data in normal level walking. Experimental data of thigh and hip motions are introduced as inputs into a dynamic system to find out a set of control parameters. A computer simulation is carried out. Comparison of the desired knee angle with that of the knee angle obtained from control parameters shows the effectiveness of the present design. Moreover, conditions of knee angle and shank velocity at the end of swing phase have been checked. The results obtained show a satisfactory performance of the system.