Study Of Control Strategy For Artificial Active Ankle Based On Electro-hydraulic Direct Drive Technology

There are millions of people around the globe who suffer from the lower leg extremity.Passive ankle prosthesis cannot fully restore the functionality like the natural gait.There are few artificial powered ankle prosthesis available in the market that can provide much better support during stance phase than the passive ankles prosthesis which is developed by the researchers but their power to weight performance is not very feasible.In this thesis,the artificial active powered ankle prosthesis proposed which uses electro-hydraulic direct drive technology.The purpose of this is to provide the sufficient torque at ankle joint during the gait cycle.Namely the plantarflexion(PF)before toe-off and dorsiflexion(DF)in the early swing phase after toe-lifting.In the rest of the gait,the ankle prosthesis actuation system can operate passively with controllable damping.A prototype of the artificial active powered ankle prosthesis has been developed.A 150 W Brushless DC motor is used to drive a 1.26 cc/rev bi-directional gear pump.The damping ratios of the ankle PF and DF are controlled by bypass restriction valves.The prosthesis is fully powered by wall socket AC power source.Walking characteristics for health subject lower limb were studied and in a trial gather Ankle-Foot ground reaction force for the controller design.A timing control method with a unique control strategy is proposed which uses the force sensing resistor(FSR)signals to detect heel strike.A middle stance time delay is added between the end of the heel strike and the start of the powered PF phase.This delay time length can be adjusted to fit different walking speeds.A hierarchical control strategy is designed to ensure the control system performance while the transition to different modes.A cascaded state machine logic is implement as control algorithm which is efficent while transits in between the four main ankle modes,sitting,standing,heel strike,walking mode and the gait phases in gai cycle.A hybrid simulation model was developed to help analyze the performance characteristics of the electro-hydraulic powered ankle.This includes a brushless DC motor model and asymmetric hydraulic actuation model.The hybrid simulation was achieved by combining AMESim and Simulink.Major control part was designed in Simulink.