Research On Design And Control Strategy Of Flexible Knee Joint Of Lower Limb Rehabilitation Robot

With the intensification of the population aging problem in our country and the improvement of people’s living standards,a large number of disabled patients and elderly people need rehabilitation medical equipment.Lower limb rehabilitation robots can effectively alleviate the shortage of rehabilitation medical resources in our country.Traditional robot joints adopt high-rigidity structural design and high-precision position control,which can achieve the high efficiency and high precision requirements of the robot in a structured environment,but such rigid joints are difficult to meet the requirements of human-robot interaction safety and environmental adaptability of lower limb rehabilitation robots in an unstructured environment.In response to this problem,we design a flexible knee joint of a lower limb rehabilitation robot that mimics the motion characteristics of the human knee joint and can realize active and passive variable stiffness in this paper.We analyze the variable stiffness characteristics of the flexible knee joint,and research its position tracking control method.Simulation experiments and physical prototype tests was carried out to verify the results.The main research contents of this subject are as follows:(1)Design of flexible knee joint structure of lower limb rehabilitation robot.In order to solve the problems of traditional rigid joint that cannot achieve impact resistance,energy storage and release,and compliance output,imitating the motion characteristics of human knee joints,according to the design requirements of the flexible knee joint variable stiffness scheme,a variable stiffness combining the advantages of the principle of cam and lever mechanism is designed.According to the designed variable stiffness scheme,a flexible knee joint with flexible force output that can realize active and passive variable stiffness is designed,and ANSYS software is used to check the strength of the cam disc of the weak part of the flexible knee joint.The results show that the cam disc satisfies its structure strength requirements.(2)Analysis of the variable stiffness characteristics of the flexible knee joint of the lower limb rehabilitation robot.In order to verify that the flexible knee joint designed in this topic can effectively achieve active and passive variable stiffness and compliance force output,the mechanical motion mathematical model of the flexible knee joint is established,and the mathematical model of the equivalent stiffness of the flexible knee joint system is deduced.MATLAB software is used for the flexible knee The joint’s variable stiffness characteristics and compliance force output characteristics are simulated.The simulation results show that the designed flexible knee joint can effectively achieve active and passive variable stiffness and compliance force output.(3)Research on the motion control strategy of the flexible knee joint of the lower limb rehabilitation robot.In order to realize the precise position tracking control of the flexible knee joint,the dynamic model of the flexible knee joint is established,the stiffness parameters of the flexible knee joint are added to the inversion controller,and the inversion controller for the motion control of the flexible knee joint is designed using nerves.The network realizes the approximation of the nonlinear unknown items,and the neural network inversion controller is designed for flexible knee joint motion control.MATLAB software is used to simulate the motion control method of the flexible knee joint.The simulation results show that the designed neural network inversion controller can effectively realize the precise position tracking control of the flexible knee joint.(4)Experimental research on the prototype of the lower limb rehabilitation robot flexible knee joint.According to the designed flexible knee joint structure,related parts are manufactured,processed and assembled,and a physical prototype test platform is built to test the output characteristics of the flexible knee joint.The test results show that the flexible knee joint designed in this project can effectively achieve active and passive variable stiffness and compliance force output.