Nonlinear robust internal loop compensator for robust control of robotic manipulators

Abstract

Robustness is a very classical issue in the robotics field. Disturbance observer (DOB) can be a good choice to improve the robustness of the system. It is easy to implement and shows successful results. DOB, however, cannot bring nonlinearity of the system into the formulation. To overcome this problem, nonlinear robust internal loop compensator (NRIC) is proposed in this paper. NRIC is attached to a existing controller and improves robustness of the system like DOB. NRIC makes an auxiliary input that compensates the difference between the output from the real plant and that from the nominal model. An auxiliary input is designed in a nonlinear h∞ optimal control framework and the resulting input is given as a simple PID form. The stability of a real plant is guaranteed if a controller is designed as an exponentially stable one (a sufficient condition). The benefit of NRIC is that it is easy to implement and it effectively brings nonlinearities of the system into the formulation successfully. The performance of NRIC is verified through the simulation and experiments.