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Tracking Improvements for Nonlinear Systems Using Inversion-Based Feedforward Control and Feedback Control: A Robotic Arm Example

Abstract—This article seeks approaches to controlling the motion of a robotic arm that needs to follow a given time-profile trajectory within a required time period. The equation of motion of the robotic arm is derived and it exhibits a nonlinear behavior. This work proposes three different control methods: (i) feedback control approach, (ii) inversion-based feedforward control, and (iii) integration of feedforward control with feedback control. Each control approach is simulated to track time-profile trajectories. The tracking performance for each controller is evaluated through tracking errors. The contributions of this research work are to demonstrate that: (i) the feedback approach cannot properly track the trajectories, and tracking errors may be unacceptable in some applications, (ii) the feedforward approach can substantially enhance the tracking performance, compared to that of the feedback method, and (iii) integration of feedforward control with feedback control method can further improve the tracking and achieve the best tracking performance. The integration of feedforward control method with feedback control approach can perhaps be effectively implemented when very good tracking is required. 

Index Terms—feedback control, feedforward control, inversion-based control, manipulator, robotic arm, trajectory tracking, perturbation, relative degree