Stability Analysis of the Head-Disk Interface in Flexible Disk Drives (2nd Report, Instability Due to the Dynamic Components of Friction Forces)

Abstract

In order to clarify the unstable vibration of a flexible disk coupled with a head-suspension system, the effects of friction force between head sliders and the disk and other parameters of the head-suspension system are analyzed using a disk-head coupling model. In this model, it is assumed that the transverse motions of upper and lower head sliders interact with disk motion through transverse contact springs at the coupling point. It is found that the dynamic component of friction force, which is proportional to varying load on each disk surface, generates a bending moment about the coupling point on the neutral axis of the disk, and that this moment destabilizes some natural modes of the head-disk coupling system. These instabilities which due to frictional moment are hardly affected, by contact spring stiffnesses on upper and lower sides, but are proportionally dependent on the friction coefficient on the side where the dynamic contact force is larger. When the friction coefficients of the upper and lower surfaces are different from each other, strong instability appears at the resonance frequency of the upper and lower head-suspension system, the degree of which is proportional to the difference of friction coefficients of the upper and lower surface.