Adaptive Non-Singular Terminal Sliding Mode Control for an Elbow Joint Orthosis System

This article introduces a non-singular terminal sliding mode technique designed for an upper-limb rehabilitation robot, ensuring robustness along with finite-time convergence by utilizing the nonlinear nature of the switching manifold. The tracking framework constitute of an equivalent control component derived from the estimated inverse dynamic model’s output, along with a continuous adaptive PI term that minimizes chattering effects. The integration of the super-twisting method, along with an adaptive uncertainty estimator, ensures the controller can handle unpredictable human operating conditions effectively. Additionally, the variable gain for the super-twisting algorithm is formulated using Lyapunov stability principles. Tracking performance highlight the effectiveness of the proposed method, demonstrating accurate trajectory tracking, finite-time stability, and resilience to disturbances of unknown magnitude while maintaining minimal chattering. The performance is quantitatively examined using Integral Absolute Error (IAE) and Integral Square Error (ISE) metrics, showing significant improvements in tracking precision across various operating conditions.