Application of nonlinear PD learning control to a closed loop manipulator

In this paper, a new control method called nonlinear PD learning control (NPD-LC) is proposed and applied for the trajectory tracking control of a closed loop manipulator. The proposed control algorithm is a combination of a nonlinear PD feedback control and a directly iterative learning (feedforward) control. Consequently, this new control method possesses both adaptive and learning properties. One of the features of the NPD-LC controller is that the learning process is directly based on the previous torque profile of a repetitive trajectory tracking. It is proved that the asymptotic convergence for both tracking positions and tracking velocities is guaranteed based on the NPD-LC controller. Experimental studies are conducted for a closed loop manipulator under different operation conditions. It is demonstrated that the NPD-LC control method can achieve a fast convergence speed.