Estimating focus and radial distances, and fault residuals from CD player sensor signals by use of a Kalman estimator

Optical cross coupling between focus and radial loops in compact disc players is a problem both in nominal operations, but also in detection of defects such as scratches and finger prints. Using a Kalman estimator with an internal reference, the actual focus and radial distances are estimated. The sensor inputs to the Kalman estimator are computed focus and radial distances and are found by solving the inverse problem of an optical model of the compact disc player. Two pairs of decoupled fault features are found based on the optical model, estimated and calculated focus and radial errors.