Hard Disk Impact Dynamics abstract
Impact Dyamics and the Coefficient of Restitution
for the Eccentric Collision of a Slider onto a Disk
G.G. Adams
Summary
As slider flying heights continue to decrease below 100 nm, the
possibility of head-disk contact, during nominally steady flying, increases.
In this investigation, a theoretical model is presented for the slider-disk
impact process. It is found that because the impact is eccentric, a different
value of the coefficient of restitution must be used than for a
central collision. A simple relationship is given for an effective
approach velocity, for eccentric impacts, which is expressed in terms of the
actual approach velocity, friction, and the location of the eccentric impact
point. In particular, for parameters relevant to magnetic recording
situations in which a slider impacts the surface of a disk, eccentric impacts
are found to be elastic over a greater range of approach velocities than would
be indicated from a constant coefficient of restitution model.
The effect of the suspension constraint on the slider-disk impact is
investigated. It is found that the post-impact motion of the slider is
sensitive to the manner in which the constraint is modeled. In particular, it
is found that the impact is partially constrained by the suspension.
The result is that energy may be absorbed by the suspension, thus reducing the
rebound velocity and kinetic energy of the slider. Comparisons are made with
previous investigations which treated the suspension constraint in differing
manners. A constrained coefficient of restitution is defined which
allows the results of earlier papers to be utilized in conjunction with the
new model presented here.
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