Limits of performance of an optical disk drive controller

The performance limitations of the focus controller in an optical disk drive are examined by looking at the plant uncertainty due to manufacturing tolerances, the controller complexity, the non-minimum phase limitations and the control design technique used. The uncertainty description is obtained by measuring the variation in the plant dynamics from five different disk drives and QFT is then used to design a controller with robust performance. The Poisson integral formula is used to calculate a lower bound on the peak sensitivity due to the plant non-minimum phase characteristics