Focusing control system for suppressing multi-harmonic disturbances in high speed optical disk systems

Recently, the size of digital content has continued to increase; therefore digital storage media have been required to increase capacity by narrowing the track pitch and the gap length between the optical head and the disk. On the other hand, anew optical disk has achieved a rotation speed of over 15,000 rpm. To meet these demands, several control systems for optical disks are proposed to achieve high-precision tracking control. In this paper, a high-precision focusing control system is proposed. The proposed control system consists of a feedback controller and a feedforward controller. The feedback controller design is based on a high-gain servo controller (HGSC). The feedforward controller design is based on a zero phase error tracking (ZPET) controller and an additional loop for suppressing multi-harmonic disturbances. The experimental results show the proposed control system has a fine focusing performance against fundamental periodic disturbances and high-order disturbances.