Comparison of Nonlinear Control Strategies for the UR3 Cobot Modeled in the SIMSCAPE MULTIBODY Environment

Since the Industrial Revolution, technologies have evolved at an ever-increasing rate, becoming increasingly useful for improving production efficiency and safety. Cobots have also become part of this ongoing progress. A cobot is a collaborative robot designed to assist humans with dangerous or repetitive tasks. Cobots interact with humans, and therefore, it is necessary to develop efficient control algorithms. With this in mind, this work develops a nonlinear control strategy and compares it with different trajectories. Specifically, these control algorithms are applied to the Universal Robots UR3 multibody model, created using the SIMSCAPE MULTIBODY toolbox. Trajectory generation is developed using the Robotic Toolbox. Using an inverse kinematics algorithm, joint variables are calculated for a specific trajectory. The control strategy used for tracking joint variables combines feedforward (FF) and feedback (FB) controllers. The feedforward controller solves the inverse dynamics problem, while the feedback controller uses two control strategies: the proportional-derivative (PD) and the linear quadratic (LQR) controllers. The main objective is to compare these two different feedback control strategies. To perform this comparison, the mean square error on the end-effector displacement and the six laws of motion with their first derivatives were evaluated.