Flow-induced vibration of a head gimbal assembly under various conditions
The flow-induced vibration of a head gimbal assembly (HGA), known as windage, is an obstacle to achieving higher track densities in hard disk drives (HDDs). We examine the characteristics of windage in this paper with the goal of enabling the development of smaller-windage HGAs. We used a 14.5-mm-length (from swage hole center to dimple) HGA in our study. The windage was measured by a laser Doppler vibrometer in a spin stand under various conditions, such as different slider radius locations (inner diameter, medium diameter, and outer diameter), disk-rotational speeds, Z heights (distance from arm to disk), and temperatures. With respect to the slider radius location, windage was much greater when the slider was on the outer diameter rather than at other positions. When the slider was positioned at a fixed location, the windage was proportional to the square of the disk rotational speed. At high temperatures, the resonant frequencies decreased and their amplitudes increased. For some resonance modes, there was an optimal Z height. These findings will be useful for evaluating HGAs and optimizing HGAs through experimental design.
Flow-Induced Slider Vibration in a Functional Hard Disk Drive: Influence of Air Shroud
An air shroud is designed and placed within a commercially available hard disk drive operating at 15 000 rpm. Large eddy simulations of the turbulent airflow characteristics resulting from both the models, with and without air shroud, are carried out by assuming the read/write head is at the disk middle diameter. The numerical model consists of about nine million tetrahedral cells with the largest and smallest sizes of the cell volumes being 2.5 mm3 and 0.35 mm3 , respectively. The dynamic Smagorinsky-Lily model is employed to mimic the effect of small-scale eddies in the turbulent airflow. Numerically predicted airflow characteristics are compared against the LDA measurements and found to be in good agreement. The wind blowing on the surfaces of the head gimbals assembly is converted into aerodynamic forces and the resulting slider displacement in the off-track and out-of-plane directions are investigated. It is inferred that the disk drive model with air shroud results in a maximum of 44% and 10% less off-track and out-of-plane slider displacements, respectively.
Air flow around magnetic-head-slider suspension and its effect on slider flying-height fluctuation
Flow around a Watrous-type suspension was measured using a hot-wire anemometer. Although three kinds of flow cells having characteristic frequencies are detected along the suspension span, no resonance of the suspension vibration with flow excitation having specific frequencies is observed in a uniform flow. In a rotating flow, no peak frequency component is observed, probably due to high-level upstream disturbance. Changes in the flow pattern and/or vibration of the suspension with changes in the distance between a flat plate and the flange edges of the suspension, changes in disk speed, and changes in distance between the disk and the suspension are investigated experimentally. The results suggest that not a periodic excitation but an irregular one due to separations, especially at the upper leading edge and the lower trailing edge, has a significant effect on the vibration. This is confirmed by reduction in flying-height fluctuation due to flow excitation of an aerofoil section suspension whose trailing edge is made as thin as possible and where the upper leading-edge separation reattaches before the trailing edge. >