Abstract: An adaptive sliding mode control strategy based on nonlinear disturbance observer (NDO) is proposed for the displacement tracking control of the side roller of four roller bending machine, according to the uncertain problems such as varying load, parameter perturbation and un-modeled dynamics. The nonlinear disturbance observer is introduced to obtain and compensate the equivalent disturbance online. Subsequently, the backstepping design method is adopted to design an adaptive sliding mode controller (ASMC) for the system with nonlinear disturbance observer. The disturbance observation error is dynamically compensated with the adaptive law to reduce the switch gain of the sliding mode controller. This design method relaxes the prior requirement of the sliding mode switch gain to the upper bound of the system uncertainties, and reduces the influence of external disturbances and system uncertainties on the displacement tracking control performance of the side roller. Simultaneously, the stability of the closed-loop system is verified using the Lyapunov method. Numerical simulation is carried out according to actual engineering parameters, simulation results show that the proposed control strategy has strong robustness to the system uncertainty, especially to the variable load, and the requirement for precision and rapid tracking of the side roller displacement of the four roll bending machine can be satisfied.

Key words: displacement tracking, four roller bending machine, nonlinear disturbance observer, sliding mode control