Design and implementation of a gain scheduled controller for a compact disc player

In this work we present the design of a gain scheduled controller for a compact disc player. In this application we need a high-accuracy positioning of a laser spot on the track on the disc where the information is stored. The main source of disturbance is the eccentricity of the track that is modeled as a periodic signal with frequency components at the rotational frequency of the disc and its higher harmonics. As a feature of the CD mechanism, the rotational frequency varies during operating conditions, producing a shift of the disturbance spectrum along the frequency axis. Furthermore, the gain of the plant also depends on the operating condition. For these two reasons we derive a linear parametrically-varying (LPV) model of the system and we apply LPV-based techniques to design a gain scheduled controller. The resulting controller is implemented on the real system in a digital way using a multiprocessor system.