Attenuation and rejection for multiple disturbances of nonlinear robotic systems using nonlinear observer and PID controller

A hierarchical anti-disturbance strategy is designed for a class of robotic nonlinear systems. A new generalized disturbance observer is constructed and integrated with a conventional PID controller so that the desired dynamic performance can be guaranteed. The disturbances include two parts. One part is the norm bounded uncertain disturbance. The other part is supposed to be generated by an exogenous system with the modeling perturbation, and has nonlinear relations with system differential term. This method only involves design of linear parameters so as to avoid the heavy computation of Hamilton-jaccobi partial differential equations in nonlinear H_∞ control or the inversion of mass matrix. Simulations on a two-link robotic manipulator demonstrate the advantages of the proposed control scheme. Comparisons have been given with the classical disturbance observer based control (DOBC) strategy.