Pole placement/sensitivity function shaping and controller order reduction in DVD players (Focus control loop)

The problem considered in this paper is the robust controller design for the focus control loop of DVD-video drive. For low-speed players, is known that this problem can be solved by means of simple lead-lag regulators. For high-speed players the disturbance rejection is more difficult problem than for CD players because of higher performance requirements. The control scheme proposed here is based on the design of robust digital controllers using the combined pole placement/sensitivity function shaping method to reduce the effect of repetitive disturbances. Controller order reduction is performed to allow its practical implementation. Experimental results, obtained on a real system in STMicroelectronics laboratories, illustrate the performance of the proposed algorithms for the focus control loop.