Composite hierarchical anti-disturbance control for nonlinear robotic systems with robust nonlinear disturbance observer

A new anti-disturbance control and estimation strategy is presented for a class of nonlinear robotic system subject to multiple disturbances. As a class of strong-coupled nonlinear system, the robotic models have measurement error, friction, varying load and un-modeled dynamics, which can be characterized as two types of disturbances in this framework. By integrating robust nonlinear disturbance observer with terminal sliding mode control, composite hierarchical anti-disturbance control scheme is proposed, where the nonlinear disturbance observers based on regional pole placement theory are constructed separately from the controller design to estimate and reject the first type of disturbance, and terminal sliding mode control is used to attenuate the second type of disturbance. Simulations for a two-link robotic manipulator are given to demonstrate the effectiveness of the proposed method.