Dynamics and Robust Control of a High Speed Optical Pickup

Abstract Recently there has been an increasing demand for optical disk drives to have higher speed as well as high information density, especially for applications like CD-ROM drives. To this end improvement of their optical pickup structure and control is recognized as a very challenging issue. In this paper, the pickup is first analytically modelled in a plane to describe its coupled auto-focusing and auto-tracking systems. With its immeasurable parameters being estimated based on experimental data, an approximate 1-DOF linear model is obtained neglecting the coupling terms. To design the high speed and robust positional servo controller realistic design specifications are addressed, and the H ∞ control method is employed. Finally taking as an exqample the pickup in a commercial CD-ROM drive, the performance of the designed controller is verified through realtime experiments.