Robust control of a compact disc player

Summary form only given. Concerns mechanisms for positioning and track following in CD players. An electromechanical actuator is used to position the laser beam on the tracks of a CD. The maximum allowable track-following error is only 0.05 μm. Another actuator is used to focus the laser spot on the CD, with an error bound of 0.5 μm. The player is a multivariable system with high performance specifications. Based on detailed finite element models an accurate behaviour model is found. The model is of high order (>100 states). Model reduction is applied to arrive at relatively low order models (<30 states). The models are to be used for control system design, and it is important to account for this during the reduction. Using the models, robust controllers are designed for the CD player. The methods include fixed-order H₂ optimization, H_∞ control and mixed H₂/H_∞ control