Robust control of a compact disc mechanism

A compact disc (CD) player is an optical decoding device that reproduces high-quality audio from a digitally coded signal recorded as a spiral-shaped track on a reflective disc [2]. Apart from the audio application, other optical data systems (CD ROM, optical data drive) and combined audio/video applica tions (CD-interactive, CD-video) have emerged. An important research area for these applications is the possibility of increasing the rotational frequency of the disc to obtain faster data readout and shorter access time. For higher rotational speeds, however, a higher servo bandwidth is required that approaches the resonance frequencies of bending and torsional modes of the CD mechanism. Moreover, the system behavior varies from player to player because of manufacturing tolerances of CD players in mass production, which explains the need for robustness of the controller. Further, an increasing percentage of all CD-based applications is for portable use. Thus, additionally, power consumption and shock sensitivity play a decisive role in the performance assess ment of controller design for CD systems. In this chapter we concentrate on the possible improvements ofboth the track-following and focusing behavior of a CD player, using robust control design techniques.