UDE-Based Robust Output Feedback Control With Applications to a Piezoelectric Stage

In this article, an uncertainty and disturbance estimator (UDE)-based robust output feedback control technique without using a state observer is proposed for a general class of nonlinear single-input single-output systems that are bounded-input bounded-output stable and subject to input and output disturbances. Instead of designing a controller for the original system directly, an equivalent system consisting of a first-order linear system plus a lumped uncertainty term is used to represent the input-output relationship. Then, a UDE-based robust controller is designed only using the system output feedback and the bandwidth of the open-loop system, making the design almost modeling-free. A prominent advantage of the proposed approach is that it has converted a challenging robust control problem into an intuitive filter design problem. The effectiveness of the proposed approach is validated on an experimental piezoelectric stage in the presence of hysteresis nonlinearity.