Reduction in Higher-order Resonance Amplitude of Objective Lens Actuator with Three-polar Magnetic Structure for Optical Disc Drives

Abstract

An electromagnetic objective lens actuator for optical disc drives has been developed in order to reduce higherorder resonance amplitude in frequency response characteristics of the actuator. The actuator has a configuration in which each set of three adjacent magnets is located to oppose each of the two sides of the lens holder and each polarization of the center magnet is set in reverse to those of the two outside magnets. The driving force in the positive focusing direction is generated at the focusing coil portions opposing the two outside magnets and the driving force in the negative focusing direction is generated at the focusing coil portions opposing the center magnet. This driving force distribution cancels the bending deformation of the vibration mode at the higher-order resonance. The resulting amplitude of the higher-order resonance in the focusing direction of the developed actuator with this three-polar magnetic structure for 9.5 mm-height Blu-ray Disc drives was successfully reduced to 2 dB or under.