Time delay observer: a robust observer for nonlinear plants using time-delayed signals

Motivated by the idea of the time delay estimation used in the time delay control (TDC), an observer called the time delay observer (TDO) has been proposed. Owing to this idea, the observer turned out to be computationally quite efficient and robust to parameter variations, yet easy to design for nonlinear systems expressed in the phase variable form, even when the system dynamics is not well known. For this observer, the convergence property and the sensitivity to sensor noise has been analyzed. Then, in a simulation with a nonlinear dynamic system, and in an experiment with a two degrees of freedom robot, it was confirmed that TDO achieves a performance level similar to the sliding observer and higher than the linear observer.