Ellis Cha

A Numerical Scheme for Static and Dynamic Simulation of Subambient Pressure Shaped Rail Sliders

A numerical scheme based on the finite difference technique is developed to simulate the steady-state flying conditions and dynamic responses of subambient pressure sliders with shaped rails. In order to suppress numerical difficulties caused by the clearance discontinuities present in the subambient pressure sliders, the control volume formulation of the linearized generalized lubrication equation is utilized. For the shaped rail sliders, a method of averaging the mass flow across the rail boundaries is implemented. Furthermore, the power-law scheme by Patankar, is implemented in calculating the massflows. The resulting equation is solved using the alternating direction implicit method. For the simulation of steady-state flying conditions, a variable time step algorithm is implemented for the purpose of reaching the steady-state values as quickly as possible. This numerical scheme is very efficient in that the coarse finite difference mesh is sufficient for numerical stability, and that the time step changer very much improves the convergence rate. The static flying heights of the Transverse Pressure Contour and the «Guppy» slider are calculated for different disk velocities and slider skew angles. For the Guppy slider, the dynamic responses of the slider to a cosine bump and disk runout are simulated

Numerical Simulations of Slider Interaction With Multiple Asperity Using Hertzian Contact Model

A numerical simulation of slider-disk contact in a magnetic hard disk drive is studied using the Hertzian contact model. The slider-disk contact is caused by flying height fluctuation due to disk runout for very low flying sliders. The rough disk topography is generated numerically by combining a sinusoidal waviness and a Gaussian roughness. For each asperity contact, the radius of curvature is calculated from the disk topography, and the radius is used to calculate the contact force using the Hertzian contact model. The sliders response to a single asperity calculated using the Hertzian contact model agrees well with the result obtained using the impulse-momentum based contact model. The simulation results of slider-disk contact including suspension dynamics are calculated with and without friction for a nano-slider.

Slider Pitch Moment Associated With Dimple Friction

In the design of a magnetic recording disk file, pitch moment exerted by the flexure on the slider is usually treated as a product of flexure pitch static attitude and pitch-stiffness (k p ), both measured in the absence of preload (gram-load). However, a slider operates in the presence of preload, which permits a large dimple friction to exist. We shall show by elementary beam theory that the pitch moment due to dimple friction is appreciable. The lever-arm of dimple friction is proportional to the bow height, and is independent of the slope of the flexure. To minimize the pitch moment associated with dimple friction, hence improving fly-height distribution, the flexure must how toward the disk. These results are confirmed by optical fly-height tests.

Detection of Modulation and Contact at HDI With Electrical Current

In the present work, a novel technique for detecting head-disk contact and modulation is presented. The technique involves measuring electrical current at HDI in the ultra-low flying cases. It is found that the electrical current is very sensitive to head-disk contact and head modulation, which are confirmed with Guzik measurements. Acoustic emission (AE) is also used in the same measurements for contact detection and found to be less sensitive than the electrical current. The electrical current at HDI can be generated through either the tribo-charging/discharging at HDI or externally applied bias voltage. Potential applications of this technique for both head modulation/contact testing and disk glide testing are discussed.Copyright