Achieving ultra-high magnetic-recording density in hard disk drives (HDDs) requires clarification of flow-induced vibration issues. In particular, it is necessary to reduce the flow-induced disk vibration called disk flutter. Thus far, however, there has been no experimental research related to disk flutter in actual HDDs. For this study, therefore, the disk-flutter issues have been studied experimentally, using an actual 2.5-in. HDD with one disk and two magnetic heads. The aim was to study the effect of operating magnetic-head mechanisms on flow-induced disk flutter. This study evaluated disk flutter as well as static pressure distribution in the actual HDD, by taking measurements while changing the operating modes of the magnetichead mechanism as well as the number of operating air-bearing sliders. The study demonstrated that the disk-flutter amplitude increases and its frequency decreases when the magnetic-head mechanisms are operating. It was also found that the amount of decrease in the disk-flutter frequency depends on the number of operating air-bearing sliders whose amplitude increase varies with the specific operating mode of the head mechanisms, such as whether it is in trackfollowing or seek modes. In addition, operation of the magnetic-head mechanisms generated non-uniform static pressure distribution within the HDD. These factors suggest that a decrease in disk-flutter frequency results from the slider-coupled vibration and an increase in disk-flutter amplitude results from the static pressure changes as well as air-following changes, as these vary with the actual operation of the disk head mechanism. From these experimental results, it appears that the disk-flutter issues in actual HDDs should be considered as a system that includes the operation of the magnetic-head mechanisms and disk-coupled vibration.
In recent storage boxes, fan vibrations have become a major vibration source because of increasing processing power and storage capacity. The fan vibration causes high frequency vibration up to 10 kHz in the head positioning error (PES) of HDDs, and the FEM simulation method for them have been required from the viewpoint of the HDD developments. In this paper, we conducted PES simulation by using rigid-body accelerations as the input, which were measured by using a surrogate drive. The surrogate drive has six accelerometers inside and its rigid-body motion in a box was calculated by using the least-square method. Comparing simulation and measurement results, it was found that surrogate drive measurement was effective to understand characteristics of box vibrations. The simulations also showed a problem of under-estimation at low frequencies from 1 to 2 kHz. Improvement of the boundary condition and input of the simulation model will be necessary.
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