Research On Electro-hydrostatic Based Intelligent Powered Ankle Prosthesis System

Millions of people around the world are suffering from lower-extremity amputation,adapting to an lower-limb prosthesis is their inevitable option to restore limited locomotion since current medical technology is not advanced enough to regenerate missing limb.Commercial available lower-limb prostheses are likely to be passive,with elastic or damping elements to provide basic body support,energy storage and terrain adaption but lack of net power output ability which leads to inferior counterparts far from the deserved functions of a sound ankle-foot complex.Human lower-limb is a multi-functional complex of shock absorption,body balance and energy delivery.According to the research findings in biomechanics,lacking of ankle push-off at step-to-step transition force the amputees to take advantage of the rest lower-extremity joint to generate requisite power compensating the mechanical energy lost during heel-ground collision,so that they are able to walk at a relatively constant speed.This compensation movement requires 30% more energy than ankle push-off,distorts the locomotion gait then negatively affects life quality of the amputees.Electro-hydrostatic Actuation System is a power-by-wire pump-controlled hydraulic servo system widely used in aeronautic and aerospace engineering.In this thesis,the author intends to take advantage of the high power to weight ratio,high efficiency and compact structure of electro-hydrostatic actuator to developed a powered lower-limb prosthesis which is capable of restoring the primary functions of a sound ankle to a great extant,rehabilitating the walking ability of the lower-limb amputees.Set out from the kinematics and biomechanics of human upright locomotion in level ground,the characteristics of ankle joint was piecewise studied in the form of gait phase division since the characteristics vary significantly within a complete gait cycle.Based on the pre-sampled biological joint motion profile,the author managed to reproduce basic human level ground locomotion in ADAMS platform,then studied the interaction among body,ground and ankle-foot complex as well as the ankle motion mechanism.The purpose of this study was to extract the essential functionality and technical specification of the ankle-foot prosthesis to be developed.The power kernel of the prosthesis consists of a brushless DC servo motor driving a reversible gear pump,and components like carbon fiber made foot-arch,integrated cylinder,hydraulic manifoldblock as well as the artificial Achilles tendon was designed based on Bionics.The whole system was modeled in Simulink to serve as a simulation experiment platform to verify the feasibility of the prosthesis designed.The control system of the prosthesis is based on the neuro-muscular feed-forward model which models the skeleton,muscle and local reflex around the ankle joint to build a mapping relation between ankle joint angle and torque.Under the supervision of a finite-state machine based high-level controller,the system is able to reproduce the nonlinear impedance characteristic of ankle joint.The simulation experiment of the prosthesis designed suggested that the EHA based powered prosthesis is capable of duplicating the primary characteristics of a sound ankle-foot complex in level ground walking to a great extent,providing effective power output and improving the locomotion gait of the lower-limb amputees.