Design and implementation of a sliding-mode controller and a high-gain observer for output tracking of a three-axis pickup

Abstract

A novel decoupling actuation scheme applied to a new three-axis four-wire optical pickup is synthesized in this study based on theories of sliding-mode control and high-gain observer. The three-axis pickup owns the capability to move the lens holder in three directions of focusing, tracking and tilting. This capability is required particularly for higher data-density optical disks to annihilate the non-zero lens tilting. To achieve control design, Lagrange's equations are first employed to derive equations of motion for the lens holder. A sliding-mode controller is then designed to perform dynamic decoupling and nonlinearity cancellation with the aims of precision tracking, focusing and no tilting. A full-order high-gain observer is next forged to estimate the velocities of the moving lens holder in order to provide low-noised feedback velocity signals for the designed sliding-mode controller. Simulations are carried out to choose appropriate parameter values of the designed controller and observer. Finally, experiments are conducted to validate the effectiveness of the controller for annihilating lens tilting and the capability of the observer for reducing the effects of digital noises on pickup positionings.