Head-tape Interface Research Articles

The Self-Acting, Subambient Foil Bearing in High Speed, Contact Tape Recording with a Flat Head

The mechanics and tribology of a flat head for high-speed, contact tape recording is presented. Experiments performed on a “row-bar” of thin-film disk heads where the tape is wrapped only on the edge opposite to the heads showed very stable contact for a wide range of tape speeds and very low wear. A model of the interface showed that a self-acting, subambient air bearing forms near the leading wrapped corner. This suction is caused by the expansion of air into the diverging gap on the upstream side of the head-tape interface, which is unique to this wrap geometry, and it is responsible for the stability and low contact pressures. A bidirectional version of a flat head geometry is analyzed via modeling and suggestions are made for that design. This work also showed strong evidence of a threshold of contact pressure below which wear becomes negligible.

Bending stiffness measurements of magnetic tapes and substrates

Magnetic coatings are made up of either magnetic particles dispersed in a polymeric matrix or thin continuous films of magnetic material. Magnetic tape stiffness, in both the machine and transverse directions, influences the way in which tapes conform to magnetic heads in magnetic tape drives. For this reason tape stiffness plays an important role in the friction, stiction and wear characteristics of a magnetic head–tape interface. In this study, a test method for measuring bending stiffness is developed. A tape segment is pressed against a load cell to measure the change in force as a function of the tape's normal displacement. Stiffness values are obtained from load vs. displacement data and a derived analytical model for the displacement of the tape segment in terms of load and geometry. Stiffness measurements of finished tapes and tape substrates are presented. The correlation between tape stiffness in the machine and transverse directions, and read/write head contouring and edge wear, is also presented.

Full-field interferometric measurement of head-tape contact spacing

Interferometry is the preferred measurement method for the contact spacing of the head-tape interface, due to its ease of use and high accuracy. Full-field techniques provide spacing data at all points in the field of view as opposed to a single measurement point. Dynamic interferometric measurement necessitates the use of a strobed illumination source, and thus prohibits the alteration of the fringe field to resolve the ill-constrained nature of the analysis problem. In addition, the head-tape contact problem is further complicated by the low phase gradient in the region of head-tape contact, which is often large in comparison to the field of view. In this paper two algorithms are compared which do not require alteration of the fringe field and therefore can easily be applied to the dynamic head-tape interface. The first technique is a two-dimensional implementation of a biquadratic fit to the fringe extremes, while the second is a pseudo-spatial heterodyne technique using the two-dimensional Fourier transform. Theoretical implementation and results are presented.

The Effect of Surface Roughness on the Head-Tape Interface

The effect of tape surface roughness on the head-tape interface is investigated for typical head contours using tapes with different surface roughness characteristics. Intensity-based monochromatic interferometry is used to obtain the asperity compliance curves for tapes of different roughness by relating contact pressure to the spacing between the head and the tape. A parabolic model and the Greenwood-Williamson model for contact between rough surfaces are used to “curve fit” experimental results for contact pressure versus spacing, and numerical calculations for the head-tape spacing of a cylindrical head with and without transverse slots are presented for two tapes with different roughness characteristics. The numerical calculations for the head-tape spacing are compared with experimental measurements showing excellent agreement between numerical and experimental results. It is concluded that the head-tape spacing for high recording density applications is limited by tape surface roughness.

Design of a head-tape interface for ultra low flying

A novel tape head contour is proposed that allows very small head tape spacing at high velocities using three transverse bleed slots and a single radius cylindrical head. A finite element based numerical model is used to determine the head-tape spacing as a function of physical design parameters including tape roughness, tape speed and tape tension. The Greenwood-Williamson theory of contact between rough surfaces is applied to account for asperity contacts as the head-tape spacing decreases below the peak-to-valley surface roughness. The sensitivity of the new head design on geometrical parameters is studied and the variation of spacing and contact pressure is determined as a function of physical and geometrical design parameters. The numerical results are compared with interferometric measurements of the head-tape spacing using head contours based on our numerical design. Excellent agreement is found between numerical predictions and experimental measurements and it is concluded that the spacing at the head-tape interface is limited by surface roughness.

映像機器のメカトロニクス ヘッド窓なしドラムにおけるヘッド・テープインタフェースの検討

To design a low-tape-tension mechanism, the differences in the head-tape interface between a window-type drum and a non-window-type drum (without the head windows) in a rotating head system were investigated. The head-tape spacing was observed using a transparent dummy head instead of the actual magnetic one, and tape deformation was measured using a non-contact displacement meter. In addition, tape deformation near the head was simulated numerically. We found that tape was deformed at the drum gap, and tape tension at the head-tape contact was lower in the non-window-type drum than in the window type. We concluded that a low-tape-tension mechanism useful for thin tapes can be constructed using a non-window-type drum.

Visual Investigation of the Head-Tape Interface in an HDTV Digital Baseband VCR

Visual Investigation of the Head-Tape Interface in an HDTV Digital Baseband VCR

Tape dynamics following an impact

The dynamic response of a tape caused by an impact load is analytically modeled. The solution is obtained using modal expansion techniques. Results from examples illustrate the model's potential for design of the head-tape interface in magnetic recording. Parametric changes may be assessed under dynamic loading conditions for the localization of deflection and the dispersion of energy. An interesting result is that desirable, near-steady conditions may be achieved even without the benefit of an explicit damping mechanism. Numerical simulations indicate that the transient displacements decrease when the tape thickness is reduced, when the damping coefficient is increased, when the foundation stiffness is increased, when the point of application of the load is moved away from the free edges, and when the tension is increased. Parameter studies showed that the stiffness k was very important to the dynamic response. >

A study by scanning electron microscopy of magnetic head-tape interface sliding

A test apparatus was designed and built which would allow direct observations of a sliding experiment between a magnetic tape and a ceramic head material. The tests were performed inside the chamber of a scanning electron microscope. The resulting observations and energy-dispersive analysis are discussed in this paper.

Magnetic Head-Media Interface Temperatures: Part 2—Application to Magnetic Tapes

An analytical model has been used to predict the interface temperature of a typical magnetic head-tape contact and of isolated (exposed) magnetic particles in contact with the head. Average and maximum interface temperatures for the assumed head-tape interface are about 7° and 10° C, respectively. If the exposed magnetic particles contact the head surface, the average and maximum temperture rises could be about 600° and 900° C, respectively. The duration of an asperity contact is about 2 to 4 μs and the thermal gradients perpendicular to the sliding surface are very large (a temperature drop of 90 percent in a depth of less than the radius of an asperity contact or a few micrometers). The predicted temperatures are compared with the temperatures previously measured using an infrared radiometric technique.

Frictional Properties as a Function of Physical and Chemical Changes in Magnetic Tapes During Wear

Some computer tapes exhibit excessive friction after repeated use or through use in some tape drives. An objective of this study was to develop methodology for monitoring the physical and bulk-chemical changes of tapes during wear and correlating any changes with increases in friction. From simulated head-tape interface tests and tape-drive tests, we have generally observed an increase in friction during tape wear. Bulk-chemical properties were monitored and did not change during wear. Changes in surface smoothness were not found significant enough to account for the increase in friction, but a noticeable increase in the real area of contact was measured and indicated mechanical and/or chemical changes in the tape surface. Techniques for monitoring surface chemistry need to be developed before specific changes in tape surface that lead to an increase in friction can be fully understood. Methods for measuring tape-debris generation were developed. Tapes having a high propensity for debris generation, in ad...

A predictive analysis for optimum contour-after-wear for magnetic heads

Reliable reproduction of recorded signals is dependent upon a good head-tape interface, and particularly, upon adequate contact pressure at the gap. In the case of grooved magnetic heads the pressure profiles are complex 3-dimensional surfaces. The head contours, as machined, may cause pressure profiles which are unfavorable to good signal reproduction. A mathematical analysis is outlined, which forecasts the progressively changing head contours and pressure profiles in terms of the average depth of head wear due to passage of tape (magnetic or lapping tape). The analysis indicates the amount of wear needed to substantially improve the pressure profile. Good correlation is shown between the theoretical predictions and actual test values.

Capacitance Probe Study of Rotating-Head/Tape Interface

A modified version of the capacitance probe technique is used to investigate the head-tape interface in a rotating head configuration. The relationship between air-bearing spacinga nd contour design is studied as a function of tape tension, head protrusion, and velocity; in addition, the effect of wave dynamics on flying height is examined.

Hygroscopic properties of magnetic recording tape

Relative humidity has been recognized as an important environmental factor in many head-tape interface phenomena such as headwear, friction, staining, and tape shed. Accordingly, the relative humidity is usually specified in many applications of tape use, especially when tape recorders are enclosed in hermetically sealed cases. Normally, the relative humidity is believed regulated by humidification of the fill gas to the specification relative humidity. However, this study demonstrates that the internal relative humidity in a sealed case is completely controlled by the time-dependence of the hygroscopic properties of the pack of magnetic recording tape. Procedures for the humidity conditioning of sealed cases must be established on the basis of the tapes' hygroscopic properties, and not on humidification of the fill gas. Without taking the tape into account, the final, stabilized, relative humidity can be significantly different from the specification requirement. Additionally, this same study finds differences in the hygroscopic properties of the same brand of tape, which apparently results from aging, and which may have significance on the long-term humidity-regulating behavior in a sealed case, and on the occurrence of head-tape interface phenomena from the long-term use of the tape. This article presents results on the basic hygroscopic properties of tape, its humidity-regulating behavior in a sealed case, and includes a theoretical commentary on the relative humidity dependence of head-wear by tape.