Model-free adaptive trajectory tracking control of robotic manipulators with practical prescribed-time performance.

Considering accurate model information of robotic manipulators is hard to obtain in real applications, this article proposes a model-free trajectory tracking control scheme for the robotic system with input saturation, where a pre-defined tracking precision within the prescribed time under any initial conditions is ensured. Firstly, to avoid a sharp corner when control input exceeds constraint, a new smooth function is used to approximate the saturated control torque, and then, a new robotic system model is built. Based on the rebuilt system, a time-delay estimation (TDE) method is used to estimate the lumped uncertainty containing unknown dynamics and external disturbance. Furthermore, a model-free adaptive controller is developed to ensure the tracking error converges to a preset small residual within a given time, where adaptive law and auxiliary system are used to cope with the TED estimation error and control input saturation, respectively. With the developed practical prescribed-time function, there is no constraint on the initial value of the tracking error, and thus, global stability is guaranteed. Finally, a planar two-link robotic manipulator is simulated to show the effectiveness of the developed control scheme. [ABSTRACT FROM AUTHOR]