A self-tuning control scheme for disk file servos

The authors present a self-tuning control scheme for disk file track-following servos. The scheme augments an existing fixed controller to recover a specified nominal performance in the presence of unmodeled dynamics. The compensator used in each disk file is individually tuned by inserting an add-on adjustable compensator to the nominal compensator, utilizing a linear fractional transformation (LFT) known as the Youla-Kucera parametrization. Similarly, the difference between the actual disk drive dynamics and the nominal model is characterized by an unknown transfer function, using the Youla-Kucera parametrization applied to the plant rather than the compensator. The algorithm consists of two steps: identification of the unmodeled dynamics transfer function, followed by the synthesis of the add-on compensator, utilizing the linear quadratic Gaussian (LQG) compensator methodology