Research On Gait Planning And Control Of Lower Limb Rehabilitation Robot

With the aggravation of population aging,the number of patients with lower limb dysfunction is increasing gradually because of cerebral stroke and other reasons.It causes inconvenience to the patients themselves and increases the burden on the patients' families and society.At present,it has become a trend to use lower limb rehabilitation robot to carry out rehabilitation training for patients.However,the existing gait planning methods ignore the coordination of joint movement,and the designed gait trajectory leads to unstable walking.Due to some unreasonable controller design,the trajectory tracking error is large and the rate of convergence is slow,which affects the effect of rehabilitation training.Thus,a normalized gait planning method is proposed to improve coordination of joint movement and walking stability,which uses Levy flight particle swarm optimization.A novel fuzzy fast nonsingular terminal sliding mode control algorithm is dished to reduce the tracking error and improve the convergence speed as well as enhance the robustness of the system and suppress chattering effectively.The main research work is as follows:(1)The kinematics and dynamics models are established about lower limb rehabilitation robot.The five-links model is established for lower limb rehabilitation robot by the D-H method,then forward and inverse kinematics analysis are carried out.The correctness of model is verified by the Robotics Toolbox.The Lagrange method is used to construct the dynamics model of lower limb rehabilitation robot.The dynamics equation is deduced relying on the dynamics model.Then Sim Mechanics simulation is performed to certificate the accuracy.(2)The gait trajectory is planned for lower limb rehabilitation robot.According to the ZMP stability criterion,the coordinate calculation formula of ZMP point is deduced.A normalized gait planning method is proposed to improve the coordination of joint movement,which uses Levy flight particle swarm optimization.Other joint trajectories are planned making use of the x direction trajectory of the hip joint.The joint angle is got by inverse kinematics analysis.Compared with the three-point gait planning method,ZMP trajectory deviation of the proposed method is reduced by 43.1%,which proves that more stable walking can be achieved by the normalized gait planning method.(3)Research on control is developed about lower limb rehabilitation robot.A novel fast nonsingular terminal sliding mode controller is designed for solving the problems of large trajectory tracking error and slow convergence rate of some controllers.Constructing Lyapunov functions proves the stability and finite-time convergence of system.Compared with linear sliding mode controller,the maximum error of hip joint and knee joint is reduced by 23.9% and38.6% respectively.The average error of hip joint and knee joint is reduced by 36.0% and 26.4%respectively.MATLAB simulation results certificate that the designed controller can reduce the trajectory tracking error of the system and accelerate the convergence speed,and increase the robustness.The fuzzy control theory is introduced to solve the chattering problem of input torque.A fuzzy fast nonsingular terminal sliding mode controller is utilized to ensure the tracking effect and suppress the chattering phenomenon of input torque effectively.(4)Experimental platform is constructed and experimental verification is carried out.The lower limb rehabilitation robot platform is built to conduct the walking stability experiment and motion trajectory tracking experiment.The experimental results show that ZMP point is kept in the support domain during walking,and planned gait trajectory can ensure the stable walking of rehabilitation training.Trajectory tracking error is within 1°,and the designed controller can effectively track the given trajectory.