A novel hybrid observer-based model-free adaptive high-order terminal sliding mode control for robot manipulators with prescribed performance

Although widely used in industrial applications, strong nonlinearity and coupling, high computational complexity prevent high precision tracking control of manipulator. In this paper, to overcome the rely on system model and achieve prescribed convergence, a novel hybrid observer-based model-free adaptive high-order fast terminal sliding model control scheme (HO-MHTSMC) with prescribed performance is proposed for trajectory tracking control of robot manipulators in the existence of friction and external disturbance. The ultra-local model is used to approximate the original complex system in a model free form in a short sliding time window, which avoid the accurate modeling of the manipulator system. To compensate for the lumped uncertainties, a hybrid observer based on adaptive time-delay estimation and adaptive second order sliding mode observer (SOSM) is proposed to achieve finite-time observation and zero estimation error. Besides, a transformation using prescribed performance function is applied to the system to ensure the transient and steady-state performance of the trajectory tracking in joint space. Furthermore, a high-order fast terminal sliding mode control algorithm with backstepping control strategy is used to stabilize the whole system and reduce the chattering problem in conventional sliding mode control. The stability analysis of the system is provided by Lyapunov theorem. Finally, numerical study and co-simulations show that the proposed control scheme has better performance in tracking accuracy and robustness compared with conventional control schemes.