An H-infinity nonlinear control approach for multi-DOF robotic manipulators

The paper proposes a new nonlinear H-infinity control method for multi-DOF robotic manipulators. At first stage local linearization of the robotic model is performed round its present operating point. The approximation error that is introduced to the linearized model due to truncation of higher-order terms in the performed Taylor series expansion is represented as a disturbance. The control problem is now formulated as a mini-max differential game in which the control input tries to minimize the state vector's tracking error while the disturbances affecting the model try to maximize it. Using the linearized description of the robot's dynamics an H-infinity feedback controller is designed through the solution of a Riccati equation at each step of the control algorithm. The inherent robustness properties of H-infinity control assure that the disturbance effects will be eliminated and the robot's state variables will converge to the desirable setpoints. The proposed method, stands for a reliable solution to the problem of nonlinear control and stabilization for multi-DOF robotic manipulators. It is also a novel approach, comparing to control of a robotic manipulator based on global linearization of its dynamics. Its efficiency is further confirmed through simulation experiments.