SUMMARY In this work, uncertainty and disturbance estimation (UDE) based robust trajectory tracking controller for rigid link manipulators was proposed. The UDE was employed to estimate the composite uncertainty that comprises the effects of system nonlinearities, external disturbances, and parametric uncertainties. A feedback linearization based controller was designed for trajectory tracking, and the same was augmented by the UDE‐estimated uncertainties to achieve robustness. The resulting controller however required measurement of joint velocities apart from the joint positions. To address the issue, an observer that employed the UDE‐estimated uncertainties for robustness was proposed, giving rise to the UDE‐based controller–observer structure. Closed‐loop stability of the overall system was established. The notable feature of the proposed design was that it neither required accurate plant model nor any information about the uncertainty. Also, the design needed only joint position measurements for its implementation. To demonstrate the effectiveness, simulation results of the proposed approach as applied to the trajectory tracking control of two‐link robotic manipulator and comparison of its performance with some of the well‐known existing controllers were presented. Lastly, hardware implementation of the proposed design for trajectory control of Quanser's single‐link flexible joint module was carried out, and it was shown that the proposed strategy offered a viable approach for designing implementable robust controllers for robots. Copyright © 2011 John Wiley & Sons, Ltd.

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In this work, uncertainty and disturbance estimation (UDE) technique is employed to robustify an input-output linearisation (IOL) controller. An IOL controller designed for a nominal system is augmented by the UDE estimated uncertainties to achieve robustness. In doing so, state dependent nonlinearities of the system are treated as a part of the uncertainties and thus, the controller does not require system states for its implementation. The resulting controller, however, needs derivatives of the output. To address the issue, a design of an observer that employs the UDE estimated uncertainties for robustness is proposed giving rise to the UDE based controller-observer structure. Closed loop stability of the overall system is established. The notable feature of the proposed design is that it neither requires accurate plant model nor system states or derivatives of output. Also the approach does not need any information about the uncertainty. To demonstrate the effectiveness, numerical simulation results of the proposed approach as applied to the wing-rock motion control problem are presented. Lastly, hardware implementation of the UDE based controller-observer structure for motion control of Quanser's DC servo motion control platform is carried out and it is shown that the proposed strategy offers a viable approach for designing implementable robust IOL controllers.

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.

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