Modelling the focus error characteristic of a DVD player

This paper presents a new approach to focus error modelling in a DVD player, applied to an industrial system, developed in STMicroelectronics laboratories. First, two mathematical models, based on astigmatic method and on opto-geometrical analysis, are given. A numerical model is given too. Then a curve fitting method is applied, using real data from the industrial system, in order to estimate the unknown parameters of these models. They will be further included in the focus error control loop in order to improve the performance analysis.