Improved Terminal Sliding Mode Control for the Looper Tension System Under Matched and Unmatched Disturbances Using a Novel Reaching Law

During hot strip mill rolling, the looper tension system operates as a complex non-linear coupled system subject to both matched and unmatched disturbances, which can cause the strip tension to deviate from rolling requirements. In this study, the looper tension system is decomposed into two subsystems, and an improved terminal sliding mode control strategy is developed to enable each subsystem to adjust autonomously. The proposed method integrates virtual control technology with enhanced terminal sliding mode controllers for each subsystem, effectively suppressing both matched and unmatched disturbances to maintain the looper angle and strip tension within operational specifications. Furthermore, a novel reaching law is designed to enhance system stability and reduce convergence time. Simulation results confirm the feasibility of the proposed approach, demonstrating higher control accuracy and stronger disturbance rejection compared to conventional looper tension control schemes.