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


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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