Disturbance Compensator for a Very Flexible Parallel Lambda Robot in Trajectory Tracking

Fatemeh Ansarieshlaghi, Peter Eberhard

Abstract

This research investigates the design of a nonlinear position controller and a disturbance observer to estimate and compensate disturbances on a very flexible parallel robot to improve trajectory tracking and control performance. The used robot has very flexible links and can be considered as an underactuated system since it has fewer control inputs than degrees of freedom for rigid body motions and deformations. Hence, these flexibilities must be taken into account in the control design. To obtain high performance in the end-effector trajectory tracking, an accurate and efficient nonlinear controller is required. This nonlinear controller includes a position controller and a disturbance observer. The nonlinear feedback controller is designed based on the feedback linearization approach and its stability is proofed by the Lyapunov candidate function. The disturbances that are investigated in this work are the friction forces of the drives of the robot, acting forces on the robot’s end-effector, and their combination. The designed nonlinear controller is implemented on the simulated model of the robot under different disturbances. The simulation results show that the end-effector tracks desired trajectories with higher accuracy and better performance in comparison to other controllers in previous works. Also, by the designed nonlinear position controller and the disturbance observer the robot tracks the desired trajectory with the highest robustness under disturbances in comparison to the previous work.

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