Adaptive Disturbance Observer-Based Local Fixed-Time Sliding Mode Control With an Improved Approach Law for Motion Tracking of Piezo-Driven Microscanning System

This study developed a local fixed-time sliding mode control (FTSMC) method based on a novel adaptive disturbance observer (NADOB) dedicated to motion tracking control for piezo-driven microscanning systems with unmodeled uncertainties and external disturbances. First, the NADOB was developed to precisely approximate and compensate for the lumped disturbance, which includes unmodeled uncertainties and external disturbances. The adaptive law of the NADOB method can estimate the upper-bound information of the lumped disturbance, assuming that it is bounded. Its convergence was strictly proven using the Lyapunov theorem. Subsequently, the local FTSMC method with an improved approach law was developed for the piezo-driven microscanning system to achieve high-precision trajectory tracking control. The stability of the tracking controller was proved using the fixed-time convergence theory. Finally, a series of comparative experiments were conducted on a piezo-driven microscanning experimental setup in the presence of a lumped disturbance, illustrating the robustness of the local FTSMC method with the NADOB. Comparative experimental results revealed that the proposed fixed-time tracking control scheme exhibits stronger robustness and higher tracking accuracy compared with existing sliding mode control methods.