SETIT 2007 4 th International Conference: Sciences of Electronic, Technologies of Information and Telecommunications March 25-29, 2007 – TUNISIA 1 Sensitivity Function Loop Shaping Design For An Optical Disc Drive Lamir SAIDI * , Zohir DIBI * , Mohamed KADJOUDJ * and Fakhreddine ABABSA ** *Faculty of Electrical Engineering. University of Batna 05000 Batna, Algeria lamir_saidi@yahoo.fr zohirdibi@yahoo.fr kadjoudj_m@yahoo.fr **Laboratoire des Systèmes Complexes. Université d'Evry Val d'Essonne, France Fakhr-Eddine.ababsa@iup.univ-evry.fr Abstract: A new approach for active noise and disturbance rejection for an optical disk drive subject to periodic disturbances with time varying fundamental frequency is presented. We consider the problem of loop shaping of the sensitivity function by using estimators. The proposed method combines pole placement with sensitivity function loop shaping in the frequency domain. The approach is non adaptive and the frequencies are chosen according to the desired shape of the sensitivity function in the desired bandwidth. Damped sine wave models are introduced in the estimator for disturbance tuning reduction, for active damping rejection, and to achieve stability robustness. Keywords: CD-ROM, disturbance estimator, loop shaping, Multimedia. INTRODUCTION During the recent years, the reduction of noises, vibrations and loop shaping in various plants has become a main line of research and is the object of numerous publications. For many multimedia applications, it is desired to achieve a high speed in increasing data rate and reducing access time. Track following problem, for optical disk drive such as CD- ROM, is to control the position of the optical spot in such away that it follows the desired track (within 0,1 µm) of optical disk media which is usually deviated from the concentric circles due to the disk eccentricity. The displacement error caused by this last one amounts to 280 µm in the worst case. The optical disk drive measures the position of the spot by a relative position error between the desired track and the actual position of the spot. Therefore, the disc eccentricity affects this measure as a sinusoidal disturbance whose frequency is the one of the disk spindle motor [POL 92], [WAT 94]. The basic problem for the compact disc mechanism control is the huge variety of sources for disturbances and model errors which pose rather conflicting constraints on the control system in terms of bandwidth, precision, mechanical vibrations, and shocks …etc. Solutions to the problem have been actively studied in recent years in the literature [STE 02]. Many approaches are proposed. For example, repetitive structure has been shown to be very effective for rejecting repetitive disturbances [MOO 98]. However, this method requires an increased number of memory locations. Furthermore, plant uncertainty and bad knowledge of the disturbance frequency make it difficult to design a procedure providing good tracking performance. Recently a robust repetitive control was introduced in [STE 02] to solve such problem. ∞ H loop shaping is a popular design method to form the open loop (i.e. its singular values in the frequency range of interest) by introduction of weights, in order to fulfill certain aims as disturbance rejection, reference tracking, etc. However, weighting function selection is not an easy task and the order of the final controller, which is designed by this technique, is usually high [BLU 05]. The two-degree-of-freedom structure has been also shown to be very effective for rejecting disturbances and loop shaping design. The RST configuration (where R, S and T are polynomials to determine) is a widely used method in the design of controllers using classical pole placement [PAN 04]. However, it requires solving the equation of Bezout on one hand