Design And Verification Of An Exoskeleton Reproducing Stiffness Characteristic Of Ankle

Since the beginning of the 21 st century,the emergence of exoskeleton for paraplegic has broken the situation that paraplegics can only rely on wheelchairs,bringing new hope for patients to walk again.However,the existing exoskeletons for paraplegic mostly adopt rigid structure in ankle joint design,and seldom design special driving system for ankle joint,which is different from the fact that the ankle joint of healthy people will adjust its stiffness periodically during walking,and can greatly affect the overall performance of exoskeleton.Therefore,this paper proposes an ankle exoskeleton which can reproduce the stiffness characteristics of human ankle joint at different stages of walking on the ground,so as to improve the limitation of ankle joint movement and function caused by rigid structure design,and reduce the impact on the ground while maintaining the human body to move forward stably.The main work is as follows:(1)Based on the stiffness characteristics of human ankle joint at different stages of walking on the ground,the mechanical model of exoskeleton which can reproduce the stiffness characteristics is built,and the transmission scheme of exoskeleton is determined.The characteristic parameters of key components are solved by taking the gait data of healthy people as reference,and then the mechanical structure of exoskeleton is designed through three-dimensional modeling.What’s more,the strength of important stress components is checked by finite element analysis,to ensure the rationality and safety of exoskeleton structure.(2)Combined with the gait data of healthy people and the mechanical model of exoskeleton,the displacement of transmission mechanism matching the stiffness characteristics of human ankle joint at different stages of walking on the ground is planned,and then the exoskeleton control system is built.Through the feedback of the starting point of gait cycle and characteristic angles of joint,the displacement of transmission mechanism in different stages of gait can be adjusted,so that the exoskeleton can reproduce the stiffness characteristics of human ankle joint at different stages of walking on the ground.(3)Through the simulation,the changes of physiological state of user caused by wearing exoskeleton can be analyzed,which confirmed that the exoskeleton will not bring extra burden to the muscle,and then experiments are carried out to verify the effect of exoskeleton.The experimental results show that,compared with wearing ankle foot orthosis,the changes of ankle joint angle and vertical ground reaction force when wearing this exoskeleton are more similar to those when normal walking,which indicates that this exoskeleton,which can reproduce the stiffness characteristics of human ankle joint,can effectively improve the limitation of ankle joint caused by rigid structure design of exoskeleton.