PID‐Like Robust Control of Non‐Minimum Phase Robotic Manipulators

ABSTRACT This paper proposes an output‐feedback tracking controller for non‐minimum phase nonlinear systems with unknown uncertainties and external disturbances, where not all states are measurable, and the zero dynamics are unstable. The approach combines a backstepping‐based stabilizing state‐feedback law with a cascade extended high‐gain observer (EHGO): A fast observer estimates the measured output and its derivatives to generate a virtual output, while a slower observer estimates the unmeasured controlled output, its derivatives, and the lumped disturbance and uncertainty. For relative‐degree‐two systems, the controller exhibits a PID‐like control. This feature is rarely achieved for non‐minimum phase systems. Simulations of a wafer‐handling robot modeled as a flexible‐joint robot demonstrate accurate tracking, rapid disturbance rejection, smooth inputs, and improved robustness compared to existing methods.