Design and control of nano precision dual servo actuator for near field optical recording system

Abstract

The objective of this study is the actuator design for the future optical disk drive. The conventional optical data storage devices such as CDs and DVDs are based on focusing propagating light with an objective lens. The maximum density in the conventional optical data storage devices is limited since the spot size cannot be less than the wavelength of the light due to diffraction limit. Near field recording (NFR) has been introduced as a new optical data storage method to realize higher data density beyond the diffraction limit. As the data density increases, the track pitch is reduced to about 400㎚. Compared with 1.6㎛ -track pitch of CD and 740㎚-track pitch of DVD, we recognize that track pitch is remarkably reduced and the more precise actuator for NFR is required. In this paper, dual servo actuator is proposed and manufactured to improve the accuracy of actuator. Actuator in data storage device plays a role to find and follow the destination track under several disturbances. These disturbances includes disk eccentricity, disk vibration, actuator vibration, and wobbling. The main disturbance among these is disk run-out by disk eccentricity. Thus, detail design specifications of actuator is derived from the disk run-out specifications. The target specifications of NFR actuator are listed in the contents. In this paper, rotary type voice coil motor (VCM) which is mainly used in HDD is selected as a coarse actuator. Generally, the rotary type VCM has faster seek characteristic than linear type VCM because of its lever structure. In design of VCM actuator, a novel magnetic circuit of VCM with multi-segmented magnet array (MSMA) is proposed. It can generate higher air gap flux density than the magnetic circuit of VCM with the conventional magnet array. High flux density in the air gap generates large actuating force and makes the seek time short. The comparative analysis is carried out to prove the effectiveness of MSMA in rotary type VCM. The result sh...