Nonlinear Control of a 3 DOF Articulated Manipulator using Nonlinear Transformation

The equations of motion for a 3 D.O.F. articulated manipulator are highly nonlinear equations with nonlinear coupling between the variables of motion. For these nonlinear equations, the control algorithm based on approximately linearized equation looses the efficiency as the real working processes deviate from the assumed conditions for the linearization. As one of the methods to design the control law for the manipulator, Hunt-Su's nonlinear transformation method and Marino's feedback equivalence condition are used with linear quadratic regulator (LQR) theory. By this feedback law, nonlinear terms of the system are eliminated and coupled terms are decoupled. This method is applied to a 3 D.O.F. articulated manipulator and compared with PID control which is widely used in the industry. The manipulator and the controller are made for experiments and analysis. From the results of experiments, we know that the performance of the nonlinear control law is better than PID control. Also the suggestions to choose the proper gains of the nonlinear control law are provided.