Identification and Control of a Compact Disc Mechanism Using Fractional Representations

This paper discusses the approximate and feedback relevant parametric identi cation of the radial servo system present in a Compact Disc player. In this application the problem of approximate identi cation based on data from closed loop experiments will be analyzed to nd a nite dimensional linear time invariant discrete time model, suitable for model-based control design. The feedback relevant identi cation in this paper is based on the algebraic theory of fractional representations, which has lead to a framework for equivalent open loop identi cation of (normalized) coprime plant factors and a manageable approximate transfer function estimation of the feedback controlled plant. A mixed worst-case/probabilistic approach to model uncertainty quanti cation is used to construct an upper bound on the uncertainty of the normalized coprime factors being estimated. Both the nominalmodel and the uncertainty description are used to design an enhanced robust controller.