P.W. Smith

Effects of air bearing stiffness on a hard disk drive subject to shock and vibration

A finite element model of a hard disk drive (HDD) is developed to investigate the transient response of an operational HDD subject to shock and vibration. The air bearing stiffness of the head disk interface is determined from a finite element solution of the Reynolds equation and approximated with linear springs. The structural response is analyzed for several types of sliders with a wide range of air bearing stiffness. Results show the response of the head-disk interface subject to shock and the modes excited by vertical and lateral vibrations of the HDD.

Shock modeling of the head-media interface in an operational hard disk drive

In this paper, two finite element models are incorporated in the simulation of the operating HDD head-media interface. The first model is a structural model of the mechanical components of the interface. The second model is a finite element solution of the time dependent Reynolds equation.

Head slap simulation for linear and rotary shock impulses

A finite element model of a hard disk drive (HDD) is developed to investigate the response of the HDD to a shock impulse. Two types of shock are of interest, a linear shock and a rotary shock. The linear model corresponds to a HDD being dropped flat onto an impact surface. The rotary model is constrained to rotate about an axis and simulates a HDD standing on one edge that is allowed to drop and impact the opposite edge. The geometry is developed using Pro/E, a CAD package, and is then imported into Hypermesh, a pre- and post-processor. The transient solution is performed using LS-Dyna, a finite element solver. The three software packages are commercially available. Results are shown as animations and time series data. Comparison of the simulation results for the two models is used to develop a correlation between the linear and rotary shock tests.

Real-time tracking of the head-disk separation using laser heterodyne interferometry. I. Instrumentation

The design aspects of an optoelectronic probe that produces a real-time, DC coupled readout of the out-of-plane component of a flying head position relative to the disk are presented. The prototype implementation achieves nanometer resolution in a 50-kHz bandwidth. >

Accelerated Natural Convergence for Pivoted Slider Bearings

A solution technique is discussed which accelerates the convergence of the pivoted slider bearing problem. The technique is based on a fully populated, three-degrees-of-freedom stiffness matrix for the hydrodynamic lubricating film. This matrix is developed using a unique perturbation method which, when used in conjunction with a finite element formulation of the Reynolds equation, yields the bearing stiffnesses in a computationally efficient manner. The resulting natural convergence of this hydrodynamic stiffness approach is examined for a typical rigid disk magnetic recording slider. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Lahaina, Hawaii, October 16–20, 1994

Figures of Merit for Dynamically Unloaded Air Bearing Sliders

A modeling technique is described whereby a static air bearing solver can be used to predict the suitability of an air bearing design for dynamic load/unload applications. Several subambient pressure air bearings, with varying degrees of nominal suction force, are evaluated for their quasi-static unload trajectories. Experimental data, obtained using a high speed camera, are used to verify the predicted peak lift-off force during unload. Results from theory and experiment indicate that it is possible to design sub-ambient pressure air bearings to be suitable for dynamic load/unload applications, provided that the appropriate figures of merit are achieved. These include a non-negative net air bearing load, an increasing pitch attitude, and a non-excessive roll angle throughout the unload trajectory. A design that meets these criteria is described. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 26–28, 1998

Measurement of head-disk spacing using laser heterodyne interferometry. II. Simulation and experiments

For pt.I, see ibid., vol.29, pp.3909-3911 (Nov. 1993). Air bearing simulation and a laser heterodyne interferometer are used to investigate the air bearing features that may be effective in lowering takeoff velocity and thus reducing sliding wear. Slider dynamics, takeoff velocity and pitch angle of the slider during the initial stages are considered. The parameters studied include taper angle and load placement. Correlation between theory and experiment in the sub-0.25- mu m range is shown and discussed. >

Wear Measurements for Proximity Recording Heads

A focused ion beam is used to create wear fiduciary marks on subambient pressure air bearing sliders, and both atomic force microscopy and optical profilometry are used for localized wear measurement. Optical profilometry exhibits a σe (standard error) of 0.23-0.36 nm compared to 4.2-11.8 nm for the AFM, where the range results from differences in measurement location. Data from both measurement methods are used to examine wear behavior as a function of contact start/stop cycling. A group of test heads is oriented such that wear is expected to occur on an alumina surface at nominal operating speed. Wear results, evaluated by both AFM and optical profilometry, show patterns consistent with the flying attitude of the heads and excellent agreement between the two measurement techniques on the worn parts. Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997