Disturbance-Observer-Based Sliding-Mode Control for a 3-DOF Nanopositioning Stage

To compensate for the nonlinear effects of nanopositioning stages and their model uncertainties, several control methods have been developed and reported in the literature. One promising method for compensation is the use of a proportional-integral-derivative (PID)-based sliding-mode control (SMC), in which the nonlinear effects are treated as an unknown disturbance to the system. If the nonlinearity and the model uncertainties can be completely or partially estimated, integration of their estimations into the control schemes may lead to improved performance. On this basis, this paper presents the development of a disturbance-observer-based (DOB) SMC, in which the nonlinearity of the nanopositioning stage is partially predicted through the use of an observer and then compensated by the PID-based SMC. Experiments were performed to verify the effectiveness of the proposed control schemes, and the results showed that the performance of the nanopositioning stage by employing the DOB-SMC was greatly improved, as compared to the PID-based SMC.