This study presents a design of Variable Structure Control (VSC) scheme for a four-wire-type lens actuator that is installed in the structure of an optical pickup in DVD/CD derives. The objective of the control deign is the precision positionings in both directions of focusing/tracking and simultaneously annihilating tilting motion for a better data-reading speed and accuracy. To this end, a 3-DOF four-wire actuator is proposed and accompanied by a newly-designed nonlinear VSC scheme to achieve a quick vanish of tilting angle while the objective lens is controlled to desired positions. The design process of the controller is started with establishing a mathematical model to describe the dynamics of the 3-DOF four-wire actuator with consideration of assembling errors as uncertainty and unbalanced radial vibrations as disturbance. Based on this model, a robust VSC is synthesized to accomplish fast tracking, focusing and zero-tilting. Simulations are conducted for verifying effectiveness of the controller designed. The simulated responses show that the designed controller is able to achieve fast zero tilting with favorable tracking/focusing performances and robust to plant uncertainty and unbalanced radial vibrations.
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