Nonlinear dynamic analysis and actuation strategy for a three-DOF four-wire type optical pickup

This study presents a scheme of sliding-mode control (SMC) for precisely positioning a newly designed three degree-of-freedom (DOF) four-wire type lens actuator which is installed in optical pickups of CD/DVD drives to perform data-reading. The SMC design aims to perform precision positioning of the objective lens in the directions of focusing/tracking and simultaneously to annihilate tilting motions for a faster data-reading and better accuracy. The design of the SMC controller is started with establishing a nonlinear dynamic model to capture the motions of the actuator with considerations of dimension/assembling errors as parametric uncertainty and unbalanced radial vibrations as disturbance. A robust SMC is then synthesized to accomplish fast tracking, focusing and zero tilting at steady state. Simulations are conducted for verifying the effectiveness of the controller designed, which show that the designed controller is capable of achieving fast zero tilting with favorable tracking/focusing performances and also robust to plant uncertainty and unbalanced radial vibrations.