Simulation and Analysis of a Full-Active Electro-Hydrostatic Powered Ankle Prosthesis

Abstract

This paper presents the design and control architecture of a novel full-active powered ankle prosthesis which uses integrated force-controllable electro-hydrostatic actuator (EHA) to provide both initiative compliance and sufficient positive power output at terminal stance to assist walking in whole gait cycle. A 100W brushless DC motor driving a 0.45 cc/rev bi-directional gear pump operates as the power kernel. Based on finite-state machine (FSM), a hierarchical controller was designed to ensure the control system performance while different control strategies were implemented on each individual gait phase. Three independent force sensing resistor (FSR) mounted under sole, two pressure transducers and a displacement sensor used as ankle rotation sensor provide feedback signal for both state detection and low-level impedance control. A simulation model of the ankle prosthesis system was established with the help of Matlab/Simulink to validate its feasibility. Using pre-sampled biomechanics profile as input variable and matched group, the conceptual ankle prosthesis turns out to be able to restore the dynamic interaction response of a wholesome ankle-foot to a great extent.