Robust disturbance observer for the track-following control system of an optical disk drive

For track-following control in an optical disk drive, a compensator should be designed to satisfy conflicting specifications. The compensator design procedure usually requires numerous trial and errors. Utilization of a disturbance observer (DOB) for enhancing track-following precision simplifies the compensator design procedure by removing the requirement for disturbance attenuation from the compensator design specifications. However, the absence of DOB design guideline considering plant modelling uncertainty has hindered practical application of the DOB. In this paper, a robust stability condition for the DOB-based track- following control system is presented. A graphical design guideline based on frequency response analysis is proposed, and a DOB is designed to preserve the overall stability. To show the validity, simulation and experimental results are presented.