Variable structure identifier for servo systems under uncertain loading

A variable structure identification scheme is proposed to achieve fast and stable on-line parameter estimation of a servo system under uncertain loading. Theoretically, once the system starts up, the identifier attains to its 'steady' estimation of the uncertain loading after a short period required for the sliding variable to perform one oscillation about zero. The proposed scheme is combined with the boundary-layer method to control a magnetic levitation system with uncertain levitated mass. The preciseness of this identification scheme is verified through experiments.