Long-stroke tracking actuator for both coarse and fine motion in optical disk drives

Abstract

In an optical disk system, the tracking system consists of-a coarse actuator and a fine tracking actuator. This 2-stage actuator requires. many devices in order to obtain both a large stroke and precise movement. The moving parts also have a,heavy mass because of their complicated configuration. As a result, the inertia and friction forces caused by the large mass interfere with fast response and precise movement. This paper describes the design and construction of a one-dimensional tracking actuator that combines a fine tracking actuator with a coarse actuator. The system is designed in the following way: first, a voice coil motor (VCM) is used as the basic drive mechanism for high precision. The permeance method is used to obtain a large driving force for the actuator. The results of this analysis-are verified by simulation and experiment. Second, a focus spring is designed to enhance the stability of the tracking actuator and the sensitivity of the focusing actuator. Third, since friction is the dominant error source the friction force is reduced by a plastic coating, and friction identification is carried out. After the actuator is constructed based on the above design schemes, PD control is applied. The actuator has a resolution under +/-0.1 mum and a stroke over 33 mm. (C) 2003 Elsevier Science Ltd. All rights reserved.