A widely-practical model-free prescribed time control for trajectory tracking of n-DOF robot manipulators

Abstract

This paper proposes a novel, practical prescribed-time control (PTC) scheme for the trajectory tracking of n-degree-of-freedom (n-DOF) robot manipulators subject to external disturbances. Unlike existing approaches, the proposed PTC scheme is entirely model-free. It leverages a time-delay estimation (TDE) technique to compensate for unknown dynamics and disturbances, eliminating the need for upper bounds. A key innovation is the design of a new time-varying gain which increases only as the time approaches the prescribed value. This ensures the feasibility of the control signal and avoids saturation issues which often make practical deployment difficult. The controller also remains effective beyond the prescribed time, overcoming a significant limitation of previous studies. Rigorous Lyapunov analysis guarantees that position and velocity tracking errors will converge within the prescribed time. Comparative simulations on a parallel Delta robot demonstrate the superiority and practicality of the scheme over existing methods.