This article proposes a discrete-time design for the robust control technique of uncertainty and disturbance estimator (UDE), with studies on applications to real-world systems. Despite the ease of implementation of discrete-time strategies, almost all prior work on UDE is for designing continuous-time control laws, with no general, complete research for discrete-time design. To design an appropriate discrete-time control law, a novel digital filter similar to the original analog filter for disturbance estimation is designed, a discrete-time error-based control law is derived, and a detailed stability analysis is provided. However, most real-world, physical systems are nonlinear and continuous-time in nature. Thus, the techniques of sampling and digital-analog (D/A) conversion are used, enabling the control of linear, time-invariant as well as a class of nonlinear, continuous-time systems using discrete-time UDE. The considered nonlinear system is for the phenomenon of wing-rock motion. Simulations are performed for the proposed techniques, and results indicate highly accurate stabilization and tracking performance, with excellent disturbance rejection. In particular, it is seen that the proposed control law is less sensitive to initial values of the error when compared to the original continuous-time UDE law.
This article presents the design of a robust observer based on the discrete-time formulation of Uncertainty and Disturbance Estimator (UDE), a well-known robust control technique, for the purpose of controlling robot manipulators. The design results in a complete closed-loop, robust, controller-observer structure. The observer incorporates the estimate of the overall uncertainty associated with the plant, in order to mimic its dynamics, and the control law is generated using an auxiliary error instead of state tracking error. A detailed qualitative and quantitative stability analysis is provided, and simulations are performed on the two-link robot manipulator system. Further, a comparative study with well-known control strategies for robot manipulators is presented. The results demonstrate the efficacy of the proposed technique, with better tracking performance and lower control energy compared to other strategies.
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