MODEL-FOLLOWING DIGITAL SERVO USING MULTIRATE SAMPLING FOR AN OPTICAL DISK-DRIVE

In order to achieve faster seeks, a simple feedback method using classical control needs higher servo bandwidth to reduce the steady state tracking error and to maintain the stability of the objective lens positioning system. In a multi-input multi-output model-following servo controller, however, the tracking error and the instability of the objective lens positioning does not increase even when the faster seek is performed with the same actuators. Both simulation and experimental results show that the disturbances and the model mismatching are well reduced by the four feedback loops in the servo bandwidth. Although such multiple feedback loops makes the controller more complicated, a multi-rate sampling technique helps to decrease the load of the digital-signal-processing task without sacrificing the performance.