Inversion-free design algorithms for multivariable quantitative feedback theory: an application to robust control of a CD-ROM

This paper describes an application of multivariable Quantitative Feedback Theory (QFT) to a robust performance design of a compact disc mechanism. Robust control design is based on new QFT design algorithms which do not involve loop transmission inversion found in present QFT design algorithms. Their advantage is that even when the designer prefers inversion-based QFT loop shaping, the associated bounds can still be computed more efficiently using our inversion-free design algorithms. Plant uncertainty consists of parametric variations in the natural frequencies of dominant mechanical resonances and a variation in the interaction between the focus and radial loops. Robust performance specifications were given in terms of the multivariable closed-loop sensitivity function. The QFT controller was! implemented in an experimental setup.