Research On Torque Coupling And Compliance Control Of Lower Extremity Exoskeleton

The key to the control of lower extremity exoskeletons is to collaborate with operators,exerting the carrying capacity of robot on basis of the fully understanding to human subjective control ability and action-orienting ability.The lower extremity exoskeleton follows desired trajectory to accomplish a series of movements in human's daily life by understanding the wearer's intention of movement.However,due to the certain motion ability the wearer retains,and the situation that wearer's active torque and the exoskeleton control torque are coupling with each other,the uncertainty of active torque provided by exoskeleton may have a significantly affection to the exoskeleton control.The exoskeleton can be affected by external forces during operation,so it is necessary to comply compliance control to exoskeleton,in order to reduce the influence of external forces in time and ensure the comfort and safety of the wearer.This paper mainly studies the torque coupling and compliance control of exoskeleton.The main research contents are as follows:1.The lower extremity EMG signal and motion information of the wearer are collected during the walking process,which is then feed to a Extreme Learning Machine to obtain the desired motion trajectories of hip joint and knee joint.Simplify the lower extremity exoskeleton system nto a two-link model,and adopt the Lagrange dynamics to analyze it afterward,by which can we establish the lower extremity exoskeleton dynamic model of its swing phase and support phase respectively.2.Aiming at the uncertainty of active torque provided by wearer during the operation of the lower extremity exoskeleton,the control method based on the disturbance observation technique is studied.Considering the nonlinear and strong coupling characteristics of the model,the sliding mode controller is designed.The wearer's active torque is estimated based on the disturbance observer which is compensated to sliding mode controller.The stability analysis and simulation experiment design are carried out.The experimental results show that the designed closed-loop system has good follow-ability to the desired joint angle and can suppress the influence of interference effectively.3.The exoskeleton angle dynamics model is transformed into the Cartesian coordinate system,the relationship mode between exoskeleton position control and the end constraint surface is established.The calculation of end contact force based onimpedance model is completed;On the basis of giving full considerration to model nonlinearity and strong coupling,the impedance sliding mode control system based on fuzzy estimation is designed,and the stability analysis and simulation experiment design are carried out.The experimental results show that the control system can reduce the contact force effectively when the swing phase of exoskeleton collides with obstacle and improve the comfort and safety of exoskeleton wearer.