A New Reaching Law Based Nonsingular Terminal Sliding Mode Control Scheme for the Servo System With Periodic Uncertainties

A novel control strategy is introduced to optimize the position-tracking precision of the servo system in the face of disturbances and uncertainties, particularly periodic uncertainties that commonly exist in repetitively operating industrial equipment. Initially, in accordance with the tracking accuracy requirements, the position tracking error is divided into several error bands, and a new reaching law based on the error bands is established. The reaching law is composed of a linear term and a power term with variation coefficients. The proposed reaching law enhances the convergence rate of minor errors and mitigates inherent chattering. Subsequently, based on the new reaching law, a Non-Singular Terminal Sliding Mode Controller (NTSMC) with Periodic Adaptive Compensation (PAC) is developed. Amid periodic load torque variations and unmodeled system dynamics, the NTSMC component ensures rapid convergence of position tracking errors, while the PAC component improves tracking accuracy. The stability of the servo system under the proposed control law is analyzed using Lyapunov theory. Both simulations and experimental results demonstrate that high-precision tracking performance can be realized under various load situations.