Head actuator dynamics

Abstract

It is common in the present hard disk drives that there exist strong quasi-rigid (QR) system vibration modes between 3 and 5 kHz, which involve coupled vibrations of the slider, suspension, arm and bearing assembly. The system modes are caused by the stiffness of the ball-bearing assembly, and they are particularly troublesome for the servo system. Therefore, a thorough understanding of the dynamic behaviour of the head actuator especially the QR modes, is essential to control the vibration in future high-performance disk drives. In this paper the finite element model of a full head actuator is established. The detailed QR body modes are investigated and the transient response simulating the track seeking and settling is also involved. It is found that due to the stiffness of the pivot bearing in the axial and radial directions, the head actuator exhibits a series of QR body motions, among which the translation in the lateral direction and rotation about the longitudinal direction might contribute to the track misregistration (TMR). In the transient response simulating the track seeking, besides the QR modes, the suspension sway mode and first torsion mode might also be excited. Owing to the material damping, the sway mode attenuates very rapidly. The QR modes may be dampened gradually by the damping in the pivot bearing.