Novel Adaptive Global Observer-Based Sliding Mode Control of a 2-DOF Piezoelectric Nanopositioning System

This paper proposes a novel adaptive global sliding mode control strategy for a two-degree-of-freedom (2-DOF) piezoelectric nanopositioning system based on the integral extended state observer (IESO) technique. Its uniqueness is that a global robustness property is generated in the whole precision motion control process, which effectively circumvents sensitivity to the perturbations during the reaching phase. First, to generate an accurate disturbance estimation for compensation control, the IESO is constructed by incorporating an integral action into the observer design. Then, a global sliding mode control approach is developed for the nanopositioning system to ensure global robustness against the unknown hysteresis nonlinearity and cross-axis coupling motion. Moreover, an adaptive rule is established for the global sliding mode controller, which does not require a priori knowledge of the estimation error, hysteresis, and cross-coupling nonlinearity in the control design. Both simulation and experimental studies are conducted to demonstrate the effectiveness and superiority of the proposed motion control scheme over existing ones. Note to Practitioners-Nanopositioning systems actuated by piezoelectric actuators impose a great challenge to achieve precision motion tracking control. This work reports a global sliding mode control strategy of 2-DOF piezoelectric nanopositioning systems for the first time. By constructing a global sliding surface and control compensator, the global robustness to unknown hysteresis and cross-axis coupling effect can be improved in the whole process to achieve high-precision motion. To guarantee the estimation performance of unknown nonlinearities, an IESO is designed in this paper to suppress the total disturbance. Additionally, to suppress the effects of estimation errors and achieve high-precision motion tracking, two adaptive rules are established to approximate the upper bounds of estimation errors and the integral term in IESO. Compared to previous works, the proposed control scheme is easy to implement and provides superior results, as verified by simulation and experimental results.