Design And Control Strategy Of MRB-PAM Lower Extremity Exoskeleton Flexible Joint

With the aggravation of China ’s aging and the frequent occurrence of accidents,the number of patients with lower limb disability is increasing year by year.As a wearable intelligent system,the lower limb rehabilitation exoskeleton robot can assist patients to complete the corresponding training,which is of great significance to solve the current aging problem in China.As a new type of driving material,pneumatic artificial muscle is often used as the driving source of exoskeleton robot because of its good fault tolerance,strong flexibility and simple structure.However,when pneumatic artificial muscle is used as the driving source,there are often problems of poor stability and insufficient accuracy.Aiming at this problem,this paper introduces a magnetorheological brake and designs a MRB-PAM flexible joint.By controlling the damping stress of the magnetorheological brake,the stable control of the flexible joint with the pneumatic artificial muscle as the driving source is realized,and the problem of poor motion stability and insufficient accuracy of the pneumatic artificial muscle is improved.This paper focuses on the structural design of flexible lower extremity exoskeleton robot,the design and analysis of MRB-PAM antagonistic flexible joint,the control decision simulation and physical experiment verification of MRB-PAM antagonistic flexible joint.The research contents mainly include :(1)Structural design of flexible lower limb exoskeleton robot.Firstly,according to the basic situation of human biological lower limbs,the corresponding joint freedom and gait motion data of lower limb robot are obtained.According to the robot structure design criteria,a lower limb exoskeleton robot is designed.The kinematics and dynamics analysis are carried out,and the human-machine coupling simulation is carried out by Opensim.The corresponding human body angle and energy consumption comparison diagram are obtained to verify the feasibility and auxiliary effect of the designed exoskeleton robot.Combined with Matlab,the fitting curve equation of human lower limb joint is obtained.Finally,Adams is used to simulate the torque of the exoskeleton,and the theoretical torque and simulation torque of each joint are compared to verify that the designed exoskeleton and its driving torque meet the requirements.(2)Design and theoretical analysis of MRB-PAM flexible joint.According to the basic characteristics of the movement of pneumatic artificial muscle and magnetorheological brake,based on this,magnetorheological is used to improve the jitter and accuracy of pneumatic artificial muscle itself.Therefore,a MRB-PAM flexible joint driven by pneumatic artificial muscle and magnetorheological brake is designed,and its virtual prototype is established to explore its working principle and driving mechanism.Combined with the basic requirements,the selection of pneumatic artificial muscle and magnetorheological brake is completed.According to the basic properties of pneumatic artificial muscle and magnetorheological brake and the theoretical driving mechanics,the mechanical properties of MRB-PAM flexible joint are studied,and the relationship model between structural parameters and mechanical properties of MRB-PAM flexible joint is obtained.Finally,the kinematics and dynamics analysis are carried out respectively,which lays a theoretical foundation for subsequent verification.(3)Research on control strategy of MRB-PAM flexible joint.Aiming at the problem of high frequency jitter of MRB-PAM flexible joint,sliding mode control is selected for simulation analysis.However,the simulation results have large high frequency oscillation and poor convergence effect,which has a great influence on the flexible joint.Therefore,variable parameter admittance control is introduced.By obtaining the damping parameters and stiffness parameters of the system model,the dynamic stability of the flexible joint system and the flexibility requirements of the joint system are guaranteed respectively.It is verified that the flexibility and robustness of the flexible joint driven by pneumatic artificial muscle are improved after adding magnetorheological brake.(4)Physical experiment verification of MRB-PAM flexible joint.The control system of the flexible joint is designed,and the experimental hardware platform and software platform are built.The sliding mode control and variable parameter admittance control are used to carry out physical experiments on the joint.The comparative experiments of trajectory tracking and human knee joint gait tracking verify that the flexible joint has good flexibility and robustness.It proves the effectiveness of introducing magnetorheological.