Variable Structure Digital Repetitive Controller

Repetitive controllers as a new type of servo mechanism have been successfully applied to mechanical systems such as robot and disk drive track following. Many research in this field have been devoted to stability and robustness considerations of adding a repetitive signal generator in the feedback loop. In this paper, a variable-structure digital repetitive controller, which can adapt a slow varying period, is proposed. For accurately identified plant, it is shown that computations involved in identifying a period can be substantially reduced. Furthermore, an FIR filter is added to the period identifiers in order to cope with model uncertainties. It is shown that for small perturbations, unbiased estimate of period can be achieved by adding a low-order FIR filter.