The slider off-track motion is a growing concern for hard disk drives with higher densities. In the present study, a five-degree-of-freedom model was developed for the analysis of the slider off-track motion. The situations of a slider in contact with a single bump and multiple bumps were studied. For a single bump, the excitation to the transverse displacement of the slider is close to an impulse. However, for multiple bumps in a sequence, the excitation gives an effect of a step force function with its plateau value dependent on the circumferential spacing of the bumps, and the rotational speed of the disk. In the case of a bump spacing of 50 μm and a rotational speed of 7200 rpm, the transverse displacement may reach a steady-state of more than 1 μm within 10 ms. The off-track motion of the slider is dominated by the rotational mode of the actuator arm and the sway mode of the suspension, and is very weakly affected by other modes.

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