Design and experimental study of an observer-based controller for a three-DOF four-wire type optical pickup head

This study presents a servo scheme synthesized via methods of sliding-mode control and high-gain observer for a newly-designed three degree-of-freedom four-wire-type lens actuator which is installed in the pickups of optical disc derives to perform data-reading. The optical pickup considered herein is a particular one that owns three degrees of freedoms, focusing, tracking and tilting. The virtual work and Lagrange's equation are used to derive the equations of motion. The sliding-mode control design is performed to conduct precision positioning of the objective lens in directions of focusing, tracking and simultaneously annihilate possible tilting for faster data-reading and better accuracy. The full-order high-gain observer is next designed to estimate the velocities of the lens to provide low-noised feedback signals for sliding-mode control. Simulations are carried out to verify the theoretical model and the predicted performance of designed controller and observer. Finally, experiments are conducted to validate effectiveness of the proposed controller/observer scheme.