Repetitive operations are widely conducted by automatic machines in the industry, and the periodic disturbances induced by such operations are a concern as they hinder the proper functioning of these machines. A periodic-disturbance observer (PDOB) has been studied previously to compensate for the periodic disturbances. This observer is a two-degree-of-freedom controller based on the observer structure estimating a periodic disturbance. However, the PDOB does not take aperiodic disturbances into account because it focuses only on periodic disturbances. This paper proposes an enhanced PDOB to enable the PDOB also to compensate for aperiodic disturbances. The enhanced PDOB is constructed by combining the PDOB and disturbance observer. Experiments were conducted using a multi-axis manipulator to compare the PDOB with the enhanced PDOB. The experimental results demonstrate the validity of the proposed method.
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