Stability Analysis for the Head-Disk Interface in a Flexible Disk Drive

Abstract

This paper describes the modeling, theoretical formulation, and eigenvalue analysis for a combined system of a spinning flexible disk and a pair of head and suspension systems that contact the disk at opposing points on its two sides. In the analytical model a constant friction force between the sliders and disk and the slider pitch motion, as well as its transverse motion, are taken into account. From the eigenvalue analysis it is found that pitch stiffness and moment of inertia of the heads induce instability above the critical rotation speed similarly to the transverse stiffness and mass. This instability can be effectively stabilized by increasing the external damping which is spinning with the disk. It is also found that the friction force makes all forward modes unstable over the entire rotational speed range. The friction induced instability can be effectively suppressed by increasing the transverse stiffness and mass and it can be stabilized by the pitch damping and the external damping. The characteristics of instability due to the friction force qualitatively agree well with experimental results reported previously.