This paper presents an integral sliding disturbance observer (I-SDOB) to compensate for unknown disturbances for a class of nonlinear systems. To guarantee the existence of a sliding mode for disturbance estimation, the proposed I-SDOB needs only a small switching gain compared with conventional sliding disturbance observers, which leads to further alleviation of chatter. Moreover, the stability analysis of the controller-observer system is given based on the Lyapunov theory. Applications of the proposed scheme to a two-link robotic manipulator have been conducted, and experimental results confirm the effectiveness of the proposed scheme.

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We have developed a magnetic levitation system which uses an array of cylindrical actuation coils and a set of three position sensing photodiode assemblies for controlled levitation of a moving platform of permanent magnets. The novelty of this system is that low cost, standard off-the-shelf commodity hardware and software components are used for position sensing and feedback control, rather than costly motion tracking sensing systems and controllers. The design and function of the system are described and controlled motion in all directions is demonstrated through motion ranges of 30 mm horizontal and 20 mm vertical translation, and 26° of roll and 43° of yaw rotation.