Composite Control of Nonlinear Robotic System With Exogenous Disturbance

This paper studies disturbance estimation and attenuation problem for a multi-input-multi-output nonlinear robotic system subject to the disturbance generated by an exogenous system. A composite control approach is proposed which consists of three parts. A backstepping controller is designed to achieve position tracking performance under the assumption that there is no disturbance. A nonlinear disturbance observer is constructed to estimate the exogenous disturbance. Finally, the composite control law is derived integrating with the nonlinear disturbance observer and the backstepping controller previously designed, so that both disturbance attenuation and position tracking performance are achieved simultaneously for a multi-input-multi-output nonlinear robotic system. Stability of the overall system is studied via a Lyapunov function analysis. The effectiveness of the proposed approach is verified by the experiments on the phantom omni robots.