In recent years, the extended high-gain observer has proven valuable in its use with fully actuated mechanical systems. In this thesis we investigate the performance of the extended high-gain observer experimentally. First, we explore its use with underactuated mechanical systems. Using the extended high gain observer to estimate and cancel the disturbance in one link of an underactuated system results in adding that disturbance to other links. However, we show that the extended high gain observer can be used to reduce the effect of disturbances in a rotary pendulum system. We also compare the performance of the extended high-gain observer as a disturbance estimator in a fully actuated mechanical system with the performance of the sliding-mode observer when applied to the same system. We use a DC motor to demonstrate the simplicity of applying the extended high-gain observer compared to the complexity of the sliding-mode observer. We then highlight the advantages and drawbacks of using each observer. Overall, our experimental results provide a check, using the extended high-gain observer, for control engineers working with underactuated mechanical system that may simplify controller design. These results also underline the ease in implementation of the extended high-gain observer and its state of the art performance.
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