Stability Analysis of the Head-Disk Interface in Flexible Disk Drives (3rd Report, Effects of Pitching Parameters of Head-Suspension System on the Instability Due to Dynamic Friction Forces)

Abstract

In order to clarify the unstable vibration of a flexible disk coupled with head-suspension systems, the effects of dynamic 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 and pitching motions of the upper and lower head sliders interacts with the disk motion through transverse and pitching contact springs at the coupling point. The dynamic components of friction force produce a bending moment about the coupling point, and this moment destabilizes some natural modes of the head-disk coupling system in the entire frequency range. When pitching motion of the head-suspension system is coupled, a reacting friction force on the head slider produces a moment about the center of mass of the head slider, and this moment strengthens instabilities. Unless the friction moment is applied to the head slider, the pitching moment of inertia of the head slider has the effect of suppressing the instability due to the friction moment on the disk, except near the pitching resonance of the upper and lower head-suspension systems. From these two effects of pitching motions of the head-suspension systems, the degree of instability of the natural modes increases dramatically near the pitching resonance. If the pitching resonance of the upper and lower head-suspension systems approach their transverse resonance, strong instability appears at this frequency.