Adaptive Backstepping Sliding Mode Control for a Hydraulic Knee Exoskeleton Robot

摘要

In the design of assisted exoskeleton robots, high load capacity, small volume size, compact structure and high-energy density are necessary. However, hydraulic actuator has inherently severe nonlinearities which make it difficult to be applied to exoskeleton robots. In addition, due to parameter uncertainties and external disturbances, traditional linear control is hard to achieve accurate position tracking. In this paper, based on assisted exoskeleton robots, driven by valve-controlled hydraulic cylinder, an adaptive backstepping sliding mode control (BSMC) scheme is utilized to resolve the nonlinearity problem of changes in the dynamic system. In order to obtain better parameter estimation, introducing a set of auxiliary filtered variables, then an expression of the parameter estimation is derived which is used in the parameter update law. The stability of the control system is verified by Lyapunov function. Finally, BSMC algorithm is modeled and verified with Simulink, and the results are analyzed. Compared with PID and SMC control scheme, BSMC has a better robust tracking performance.