Notch filtering and multirate control for radial tracking in high-speed DVD-players

The problem considered in this paper is the radial tracking of the optical pick-up in a DVD-ROM player. For low-speed players, it is known that this problem can be solved by means of simple lead-lag regulators. For high-speed players, the servo design problem is more tricky, and a more sophisticated control architecture is required. The control scheme here proposed is constituted by a lead-lag filter and by two adapted notch filters. This set of filters is implemented in a parallel multirate structure. The resulting controller is simple, low-cost, and adequate to meet the required tracking-error specifications. The performance of the controller is tested on a real plant; experimental results are extensively reported.