Adaptive time-delay estimation error compensation for application to robot manipulators

This paper introduces an adaptive time-delay estimation error compensation (ATDE2C) scheme that strategically reduces the difficult-to-predict tracking errors of time-delay control (TDC) for given reference trajectories. Specially, these tracking errors mainly come from the so-called TDE errors caused by one-sample delayed measurements associated with a time delay estimation (TDE) technique in TDC. ATDE2C enhances robustness of TDC against such inevitable TDE errors using a disturbance observer (DOB)-based approach, thereby enlarging the stable operational region and offering a more robust performance compared to the basic TDC. The ATDE2C scheme enhances tracking performance of robot manipulators by adaptively feeding back the difference between actual and estimated TDE errors using a disturbance observer. This approach is particularly effective in managing hard nonlinearities, such as Coulomb friction, encountered in high-degree-of-freedom robots during rapid joint movements. It minimizes frictional effects and prevents overshoots, ensuring precise control. Moreover, it allows for intuitive tuning of the controller through parameters focused on convergence speed, making it practical for application compared to existing controllers. Extensive testing, including simulations and experiments, confirms improved performance of ATDE2C in real-world applications.