Christopher Lacey

Measurement and Simulation of Partial Contact at the Head/Tape Interface

Partial contact at the head/tape interface is investigated as a function of changes in the head/tape spacing due to asperity compression during contact. A model of head/tape contact, based on measurements of average contact pressure versus average head/tape spacing, is developed and incorporated into a numerical simulation of the head/tape interface. Numerical calculations of head/tape spacing with partial contact are verified by interferometric measurements

A tightly coupled numerical foil bearing solution

Equations describing the steady-state flying height of magnetic tape over a recording head are solved using an algorithm that incorporates a linearized approximation of air bearing stiffness into the tape equation. The one-dimensional infinitely wide equations include compressibility and slip flow in the air bearing, as well as tension, momentum, and flexural rigidity in the tape. The stiffness coupling between the equations allows simulation of complicated head geometries and reduces the computational effort required to determine the steady-state flying height by more than an order of magnitude compared to previously published methods which are based on time-dependent equations. Two example problems are presented, both of which were solved on a personal computer in under one minute. >

Interferometric measurement of disk/slider spacing: the effect of phase shift on reflection

In an interferometric system for measurement of spacing between a transparent disk and a slider, the effect of phase shift on reflection off the slider surface must be considered to obtain an accurate measurement. Here, a theoretical treatment of the problem is described and typical measurements are provided of phase shift on reflection for several types of slider materials in use today. The technique used to measure phase shift utilizes an ellipsometric measurement of the sliders complex index of refraction from which the phase shift on reflection is calculated. Monochromatic interferometric theory is used to show that assuming the slider to behave as a dielectric with a phase shift on reflection of pi can result in flying height measurement errors on the order of 12 nm. The magnitude of the phase-shift effect is investigated for different slider materials. In addition, the variation in phase shift as a function of the wavelength of light is investigated. >

Simulation of wear of tape head contours

A procedure whereby head wear can be numerically simulated is described. Wear is assumed to be proportional to a material constant times the contact pressure. Based on this assumption, the change in head contour due to wear is calculated in incremental steps starting from any initial contour. Simulation data are compared to an experimental measurement of head contour change due to wear. It is noted that the simulation of mechanical wear allows the evaluation of head geometries for their performance after wear. Wear of composites can be modeled with the simulation as well as preferential wear of thin-film head elements. Additionally, the model gives insight into the final lapping process for head manufacture. >

Measurement of flying height with carbon overcoated sliders

Ellipsometry is used to characterize the phase shift on reflection off carbon-overcoated sliders in order to accurately determine slider flying height with interferometry. A simplified analysis is used to approximate the phase shift based on a single ellipsometric measurement of the finished slider. A rigorous analysis indicates that for the overcoating systems studied herein, the flying height error introduced by the simplified analysis of phase shift on reflection was less than one nanometer. Experimental measurements of spacing with an overcoated slider resting on deposited bumps on a stationary disk indicate that the average measured spacing was within one nanometer of the bump height. >

The Effect of Head Wear and Tape Shear on the Head/Tape Interface

The effects of transverse shear deformation in the tape and wear on the head profile are incorporated into a numerical simulation of the longitudinal head/tape interface. These effects can cause a significant change of the head/tape interface behavior for geometries that experience head/tape contact. The numerical implementation is described and results are compared to experimental measurements of head/tape spacing. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference In San Diego, California, October 19–21, 1992

Interferometric measurement of head/tape spacing in a high-speed R-DAT helical recorder

Head/tape spacing in a high-speed R-DAT helical recorder was interferometrically measured using a replica head made of fiber-optic material. For the head tested, observation of white light fringes indicates that the region where head/tape spacing is less than 100 nm changes significantly as a function of tape tension in the range of 0.05 to 0.15 N. However, the small spacing region was not significantly affected by changes in scanner speed in the range from 2000 to 100000 RPM. >

Tape dynamics in a high-speed helical recorder

Tape dynamics in a helical recorder were measured at head speeds up to 75 m/s. The onset and amplitude of transverse waves are studied as a function of head velocity, tape tension, and tape thickness. Wave patterns are plotted over a range of these parameters. The tape deflection directly behind the head, in front of the head, and at the tape edge is investigated and compared to theoretical predictions of tape deflections reported in the literature. For the range of parameters studied, damping of tape dynamics was increased in cases with lower head velocity, higher tape tension, and thinner tape. Chevron-shaped wave patterns were found to wrap around the head. The general deflection of the waves, particularly the short waves preceding the head and the dip trailing the head, correlate well with predictions existing in the literature. However, the chevron-shaped wave pattern that extends to the tape edges at high head speeds has not been predicted in the literature. The present measurements indicate that free tape-edge boundary conditions should be assumed in a high-speed model, and that the tape behavior in the vicinity of the head is a strong function of head speed, tape tension, and tape thickness. >