Super twisting sliding mode incorporated with USDE for tracking control of nonlinear robotic systems

This study aimed to improve the control scheme incorporated into the unknown system dynamics estimator (USDE) to deal with unknown dynamics and external disturbances. In comparison with the nonlinear disturbance observer (NDO) that requires calculating the inverse of the inertia matrix, USDE can be easily implemented, and their parameter tuning is more straightforward. We use the super twisting sliding mode algorithm (STA) to achieve a faster convergence rate and increase tracking performance. The closed-loop stability of the new composite controller is proved. Finally, the improvement of the new hybrid proposed controller is confirmed by using numerical simulation and experimental tests on a DELTA robot. Then the performance of the new controller is compared with the previous method.