In this thesis, an enhanced repetitive control is handled to apply to the track-following servo system of optical disk drives. For read / write operation in optical disk drives, the laser spot should be positioned on a target track which oscillates in the radial direction of a disk. The oscillation is originated from unavoidable eccentricity of the disk and regarded as an external disturbance whose period is related to the rotational speed of disk. Therefore, disturbance rejection is the major concern in the track-following servo system. Among various auxiliary controllers, repetitive control has been successfully utilized as an effective control algorithm for rejection of a periodic disturbance with an assumption that the delay constant is exactly set to a known constant period of disturbance. However, the disk rotation controlled in the constant linear velocity mode results in slow variation of the rotational speed of disk, which leads to varying period of the external disturbance. Therefore, it is required to adjust the delay constant to the exact period of disturbance to overcome the inherent drawback of the repetitive controller. As a remedy to get rid of the frequency-sensitivity, we propose a modified repetitive control structure to adjust the delay constant by measuring the rotational speed, which is directly related to disk rotation. The proposed method has been applied to simulations and experiments using a DSP-based digital control system, and some results are presented to show the validity. In addition, the relationship between measurement error of the rotational speed and tolerable error bound of the delay constant is analyzed based on the results.
