Design for Reducing the Off-Track Due to Arm Bending Considering DSA in HDDs

Abstract

This paper presents a strategy and approach to reduce the position error signal induced by arm bending mode, which is called arm-bending off-track in high density magnetic disk drives. In order to increase the data storage capacity of a hard disk drive (HDD), the track pitch keeps decreasing. This narrow pitch and its position error margin make the accuracy on track more challenging to meet the track misregistration (TMR) budget. To meet the requirements of hard disk drives, the mechanical component should be improved considering it. Among the enablers to meet the drive requirement, this paper is focused on a strategy to reduce the off-track due to arm bending under dual stage actuator system. Off-track due to arm bending mode becomes newly important parameter related to TMR with high density drives. The position error caused by the vertical motion owing to arm bending resonance, which can be neglected enough in the larger track pitch of old day, becomes a bottle neck of the TMR budget. Proposed arm design is introduced to reduce the arm-bending off-track by allowing the head to move in such as way that will compensated the off-track caused by arm bending mode. And, optimal bending frequency location under dual stage actuator can maximize the attenuate the off-track due to arm bending. Dual stage actuator is introduced for increasing the servo bandwidth. The dual stage actuator can extend the servo bandwidth using the additional fine actuator, which is located on suspension loadbeam or gimbal. And, there is also a special servo algorithm and its error sensitivity curve. In this paper, the optimal solution for reducing arm-bending off-track is proposed under dual stage actuator system is studied.