Gait Planning And Control Of Stair Walking With A Powered Transfemoral Prosthesis

Powered transfemoral prosthesis have more advantages than passive prosthesis when stair walking.Due to lack of energy input,passive prosthesis can not help the transfemoral amputees to lift the body during stairs ascent,and provide stable support during stairs descent.But,the current stair gait control strategy of powered prosthesis still stays at the joint level,that is,to achieve the effect of assistance by imitating the torque output characteristics of human joints,without considering the comprehensive effect of powered prosthesis and residual limb on human body from the overall perspective.In order to solve the above problems,this paper proposes a control method based on virtual model,which can help amputees get better stair walking experience from the perspective of the whole lower limbs.The main work and achievements of this paper are as follows:(1)A virtual model of human lower limbs was constructed based on the center of pressure and the center of mass.According to the biomechanical data of the lower limbs collected in the stair walking experiment of the healthy people,this paper analyzes the data change rules of the center of mass power,the stiffness characteristics of the virtual leg,the swing angle ?,the horizontal angle ? of the foot during the support period of the human body going up and down the stairs,which provides the biomechanical basis for the design of the virtual model controller of the powered prosthesis stair.(2)The second generation of powered transfemoral prosthesis is designed,which provides a stable platform for the implementation of virtual model controller of stairs.This prosthesis combined the defects of the first generation of powered prosthesis and the needs of integration.Instead of the design of ankle joint based on SEA,the high power density torque motor with small reduction ratio reducer is used to reduce the control difficulty and increase the response bandwidth.In order to increase the stability and richness of the signal,the foot pressure is collected by six dimensional force sensor instead of the resistance strain gauge.The integration of the second generation of prosthetic hardware platform is realized by suing the embedded system based on STM32F427IIH6 framework instead of NI Compact RIO 9093 unit.(3)A virtual model controller of stair based on finite state machine is designed according to the biomechanical data of lower limbs obtained in the stair walking experiment of healthy people.The virtual model is applied to the prosthetic side by determining the substitution points of pressure center and mass center,and the virtual leg impedance controller is designed to adjust the output of virtual leg force.According to the slope of F_N-L_N curve along the relationship between leg force and leg length,i.e.the stiffness of virtual leg,the phase division of stair gait support period is carried out,and the linear fitting of each curve is carried out to obtain the simplified F_N-L_N curve.Then,using the good linear relationship between the swing angle and the gait period as the reference to control the phase switching of the prosthesis,the finite state machine design of the virtual model controller of stairs is completed.(4)A stair walking experiment is designed to test the effect of stair virtual model controller compare with the passive prosthesis and healthy people.According to the kinematic and dynamic data of the human lower limbs collected from the experiment,the influence of the dynamic prosthesis on the gait symmetry and the adjustment result of the force F_N are analyzed.The effectiveness of the controller is preliminarily proved.