Research on design and trajectory tracking control of a variable size lower limb exoskeleton rehabilitation robot

Aiming at the problems of poor size adjustability and low joint tracking accuracy of lower limb exoskeleton rehabilitation robot (LLERR), a variable size lower limb exoskeleton rehabilitation robot (VSLLERR) was designed by UG NX software based on human body size data. Then, the kinematics model of VSLLERR was established by DH method, and the motion space of VSLLERR was analyzed. In addition, the dynamics model of VSLLERR was established by Lagrangian energy method, and the general nonlinear friction model was designed to modify and improve the accuracy of dynamics model. Then, the PID and reaching law (RL) controllers of VSLLERR were designed by SIMULINK. Furthermore, the joint tracking accuracy of the two controllers and the influence of RL controller parameters on tracking accuracy were studied by simulation experiment. The results indicate that the joint angle and joint angular velocity tracking accuracy of RL controller are higher than that of PID controller. In addition, appropriate parameters (c1, c2, k, ε, ϕ) can improve the tracking accuracy of VSLLERR.