Measurements and theoretical predictions of head/tape spacing over a flat-head

Experimental measurements and theoretical calculations of the head/tape spacing are presented for the self-acting subambient foil bearing phenomenon at the interface of a flexible tape and a flat surface (e.g., tape-head). The air entrained at the flat-head/tape interface forms a subambient pressure layer which creates suction on the tape to pull it down to contact the head. The head/tape spacing for flat-heads is measured with a commercially available, two-wavelength, digital interferometer by using transparent tape and Al₂O₃-TiC flat-heads. Measurements for a large array of tape speed, tension, wrap-angle values, and head-lengths are presented. The interferometric spacing measurements show that, in general, the tape contacts the flat-head in the central region of the head and forms displacement-bumps adjacent to the edges of the head in the upstream and downstream corners. Experiments also show that the length of the displacement-bump affects whether a central contact region will form. The length of the displacement-bump is proportional to tape tension and wrap angle and inversely proportional to tape speed. The experimental results compare favorably to results of a mathematical model of the flat-head/tape interface.     

A finite element simulation of the two-dimensional head/tape interface for head contours with longitudinal bleed slots

The two-dimensional (2D) steady-state linear head/tape interface with surface asperity contacts and tape shear deformations is analyzed using the finite-element method. A non-uniform mesh is utilized to improve the computational efficiency and to simulate cylindrical heads with longitudinal slots. Numerical results for the head/tape spacing and contact pressure are obtained for 2D head/tape interfaces using cylindrical heads with longitudinal slots. In addition, numerical examples are presented for the head/tape spacing and the pressure distribution using heads consisting of triple arc elements with and without longitudinal slots.     

Attenuation of lateral tape motion due to frictional interaction with a cylindrical guide

Lateral tape motion (LTM) is a function of tape path and tape properties, design parameters such as speed, tension, and friction between tape and tape path components. This investigation deals with the LTM of a tape moving over the surface of a cylindrical guide. Starting from the equation of motion for a moving tape on a cylindrical guide surface, the effects of friction, tape properties and design parameters are examined by calculating the ratio of LTM before and after a cylindrical guide. Attenuation of LTM is found to be mainly dependent on the guide radius and the wrap angle.     

Investigations of nano- and macro-wear of magnetic tape head materials

The nano- and macro-wear characteristics of calcium titanate, single crystal ferrite and polycrystalline ferrite were investigated using nano-scratch testing and wear bar testing. Nano- and micro-indentations were made to determine nano- and micro-hardness, and nano-scratch testing was used to evaluate relative wear rates on the nano-scale. The macro-wear characteristics of the various head materials against metal particle tapes was investigated as a function of tape speed using wear bars mounted in a DLT tape drive. The micro-indentation method was used to investigate wear of the head/tape interface in a linear tape drive. The results from nano- and macro-wear tests were analysed and correlated with the microstructure of the materials.     

Helical scan head and tape contact behavior: optimization of tribological and magnetic aspects

The tribology of a head/tape contact has been studied from the reconstitution of the life of the contact[1] (Souchon F., PhD Thesis, 1997). The mechanism of velocity accommodation between the head and the tape and the flows of the third bodies have been identified in this goal. The tape feeds a source flow of a third body because of an accommodation by shearing. The contact conditions materialised by the tent effect govern this flow, and are due to global solicitations on a large scale by the helical system, and to local solicitations on a small scale by the head and its housing. For the head, the shearing in the ‘skin' leads to a superficial tribological transformation for which the development is controlled by the third body coming from the tape. The superficial tribological transformation, initiated during the lapping of the head, ends on a detachment of particles which is the cause of the head wear.     

Effect of slot edge defects on the head/tape spacing

The effect of slot edge defects on the performance of the head/tape interface is studied for single and double module heads. A number of typical edge defects was created artificially on a glass replica of an actual head, and three-wavelength interferometry was used to study spacing changes caused by these defects. The results show that head edge defects have a small influence on the flying behavior of tape with the effects being localized to the immediate defect area.     

Simultaneous five-wavelength interferometry for head/tape spacing measurement

An improved five-wavelength interferometer with high-speed shutters in the light path was designed and implemented. The interferometer allows switching between two sets of three wavelengths, keeping one wavelength in each measurement in common. The set-up allows nearly simultaneous acquisition of fringe intensities and can be used to measure the head/tape spacing in a moving linear tape drive. The precision of the new five-wavelength interferometer was investigated and was found to be superior to the precision obtained with a three-wavelength interferometer.     

A Model for Magnetic Tape/Guide Friction Reduction by Laser Surface Texturing

The friction coefficient between a magnetic tape and a guide in a tape path can be minimized by creating micro dimples on the guide surface with laser surface texturing. The dimples enhance the formation of an air bearing and reduce the friction coefficient between the tape and the guide due to the increased spacing. A model is presented to optimize the geometry of the surface texturing parameters to maximize the average air bearing pressure and minimize the tape/guide friction coefficient.     

Tribology of metal evaporated tapes—for improvement of recording density

Increased recording density in video tape recorders and tape drives for data storage has been achieved by the increase in areal recording density and the decrease in tape thickness. Areal recording density can be increased by introducing high performance tapes, like metal evaporated tapes, with superior magnetic characteristics and smooth magnetic surfaces to reduce the spacing loss. However smoother surfaces often produce a higher friction coefficient, which could result in tape damage by the scanning heads and unstable runnability of tapes in VTRs or tape drives. Also thinner tapes show lower mechanical stiffness in general, which could result in damage of the tape edges during tape transportation. Superior durability and runnability are thus required of high performance tape in addition to magnetic characteristics, in spite of the trend towards smoother surface and thinner tapes. Therefore the development of practical new magnetic tapes requires research into their tribology. It was found that the durability and runnability of metal evaporated tapes with smoother surfaces can be improved by DLC coating, and that the edge damage of thinner tapes can be eliminated by decreasing the static friction coefficient, but not the kinetic one. Though the durability and the runnability of metal evaporated tapes themselves have been improved from the tape design point of view, as mentioned above, further improvement may be expected by integrating tape design with that of the VTR/tribo-elements tape drive design and thus further increasing recording density in the future.     

Enhancing tribological performance of the magnetic tape/guide interface by laser surface texturing

The friction coefficient is an important parameter in designing magnetic tape transports. We have introduced a novel approach to reduce the friction coefficient between guides and magnetic tape by laser surface texturing the cylindrical guides. The surface features enhance the formation of an air bearing and hence reduce the friction coefficient.     

Wear of tribe-elements of video tape recorders

The helical scan magnetic recording equipment, like the video tape recorders (VTR), consist of many tribe-elements. The wear of these tribe-elements is an essential problem affecting the reliability of the equipment. The rotating magnetic head in high-speed rubbing with the magnetic tape needs a self-cleaning effect by mild wear. A simple trial of reducing the head wear often brings partial recession, friction polymer and brown stain. The summary of the current study of head wear is given by dividing it into the head factors, the tape factors, the system factors and the atmosphere factors. The computational analysis of head contour change caused by wear is compared with the experimental results. The outline of the tribology of motor, capstan and tape path in the VTR is introduced.     

Resonance phenomenon and its effects of laser texture disk

To achieve lower flying height for high areal recording density, the laser zone texturing of the disk needs to be designed to reduce glide height. One problem of the laser bump design is that the regular laser bump pattern often produces glide resonance phenomenon, which leads to failure of the glide height test. However, it was found in this study that glide resonance is an intrinsic problem of the glide head used and resonance phenomenon depends on the type of the head slider, that is, the natural frequency of the slider body. Therefore, higher glide height or glide failure caused by glide resonance does not lead to head/media interface problem in the real drive operating conditions in which the data head is used. Pseudo- random bump pattern greatly reduces the glide resonance. Smaller bump pitch will also help to reduce the glide resonance. However, as bump spacing becomes smaller, glide height will be increased due to increased air pressure developed around the bumps. Lowering bump height is the most effect way to reduce glide avalanche.     

Numerical modelling of sub-surface stress in magnetic data tape heads due to the dynamic contact with a tape

The stress field at the subsurface of the ceramic used as a tape-bearing surface (TBS) in magnetic head construction is calculated by means of numerical methods taking into account roughness and friction forces at the head to tape interface (HTI). A two-dimensional model confirms the purely elastic character of the contact. However, only a three-dimensional model allows a quantitative interpretation, and thus to estimate the real area to apparent area of contact ratio—in agreement with a previous formal calculation—as well as the depth of the maximum von Mises stress—i.e. the depth at which a crack is more likely to form and extend—near 30 nm, comparable to the pullout depth observed at the surface of the ceramic used in actual heads.     

A study of three-body particle generation and subsequent pole tip recession in linear tape recording heads

The Pole Tip Recession (PTR) and transferred material (stain) are major causes of magnetic spacing losses in magnetic recording system. The recorded signal amplitude is only independent of the data being read if the spacing is zero. Thus, the level and more specifically the variation in head media spacing with device life must be a minimum to maximise signal output and minimised errors. It was the purpose of this research to isolate and identify the mechanisms responsible for pole tip recession using the Linear Tape Open format as an experimental platform, but the results have implications for any head where the tape-bearing surface is Al₂O₃/TiC (AlTiC).All experiments were conducted within a matrix of pressure and humidity, which encompassed the system operating extremes. Atomic force microscopy (AFM) was used to analyse the surface topography of the heads and monitor the development of PTR after 100, 1000 and 5000 passes of tape. Auger electron spectroscopy (AES) was employed to analyse the chemical changes on the surface of the heads after 5000 passes of tape and X-ray Photoelectron Spectroscopy (XPS) was used to identify the chemical changes that occurred at the head surfaces. Optical Microscopy was employed to identify the head surface changes before and after wear. Environment was found to have a significant influence on the head/tape interface. Head wear and PTR were highest at high temperature and humidity.Wear between the head and tape was found to transform the surface layers on the TiC grains in the tape-bearing surface to TiO₂. This process results in the production of TiO₂ fragments that become trapped in the recessed pole tip region, acting as three-body abrasive particles. The presence of Ti on the surface of head thin film region confirmed that the three-body particles originated from the head AlTiC ceramic. The TiO₂ (thickness and possible areal coverage) increased with the water content increase, wear of head increased in the high water content condition.     

Laplace pressure measurement on laser textured thin-film disk

To increase the recording density of hard disk drives (HDD), head and disk surfaces must be very flat. This will make the friction between them large when liquid bridges are formed. This is a result of Laplace pressure in the liquid bridge. Therefore, the study of Laplace pressure in real HDD interface is of an interest for head-disk interface engineers. However, Laplace pressure of perfluoropolyether (PFPE) lubricant on carbon coated thin-film disk surface was not clear until now.We measured Laplace pressure between transparent flat pins and carbon coated thin-film disks with laser texturing. Using laser textured disks, we could control the distance between two surfaces precisely by the bump height. The friction coefficient between the pin and the disk surfaces was determined when the interface was fully wet by liquids. It was 0.16 and 0.1 for water and a PFPE lubricant. The Laplace pressure was then calculated using the friction force and liquid wet area when the interface was partially wet by a liquid. The liquid wet area was measured by the observation of the contact point through the transparent pins.The results showed that the Laplace pressure at the lowest bump height (11 nm) was about 2.8 MPa for the PFPE lubricant. Results agreed well with calculated curves. We consider that PFPE acts as liquid down to 11 nm.     

Recent research of tape/drive tribology

Decreasing track width and tape thickness to increase the volumetric recording density of helical scan-tape-drive systems, which is suitable for higher volumetric recording density, will result in the failure of tracking. The displacement of tape forwarding position, which causes failure of tracking, is caused by static friction coefficient between a tape and a roller guide. It was found that surface roughness and materials of roller guides are very important to reduce static friction coefficient.     

Tribology of helical scan tape drive systems

The future direction of the designs of the metal evaporated tape for higher density recording in the helical scan tape drives which use MR heads was investigated. Static friction force between a tape and a roller guide increases the force with which the tape edge is pressed against the flange of the roller guide and wear debris is produced from the tape edge. The wear debris is driven to the recording area on the tape and increases a rewrite ratio, which indicates the ratio of failure of reading data. A solid lubricant at operating temperature was found to reduce the coefficient of static friction. However, the combination between the solid lubricant and MR heads which are heated by sense current may cause tape damage in dwell tests at low temperature. The increase in a melting temperature of the solid lubricant was found to improve the durability in dwell tests at low temperature.     

The Head/Tape Interface: A Critical Review and Recent Results

Modeling and measurement techniques for the head/tape interface are discussed. With the advent of contact between the head and tape, both the numeric models and experimental procedures need to be modified to account for the contact. In the field of head/tape interface modeling, the basic Green's function, finite difference, and finite element solution techniques are presented. The asperity compliance curve is introduced to calculate the contact pressure between the head and tape resulting from compression of surface asperities. Modern experimental measurements of head/tape spacing use monochromatic interferometry. The basic theory is presented, and the need for multi-wavelength interferometry is described to improve measurement resolution at extremely close spacings.     

Lubricant Effect on the Microtribological Behavior of Magnetic Coating Formulations 1-aliphatic Lubricants

Magnetic tape industry uses a mixture of fatty acids/fatty acid esters. This lubricant mixture transfers from the tape surface to the recording GMR head whereby they cause fouling the tape and enhances corrosion to the GMR head. The current study aims at finding a substitute lubricant that could make a bond with the binder and has no corrosive effect.     

Experimental and analytical studies of dynamic friction at the head/disk interface

Friction is an important parameter that critically impacts the tribological performance of a head/disk interface. The head/disk interface with laser zone texture affords a model system for the study of dynamic friction by virtue of its precisely-controlled contact geometry. By using two types of head sliders, i.e. the conventional slider and the padded slider, and a matrix of hard disks with a wide range of laser zone texture parameters, head/disk contacts involving a small number as well as a large number of bumps are realized. A rich variety of dynamic friction behaviors are observed with respect to bump height and bump density variations. To shed new light on the nature of HDI dynamic friction, an analytical model that treats both the deformational and the adhesive friction components on equal footings is formulated. It is shown that, based on the model analysis, the friction is deformation-dominated for HDIs involving a small number of contacting bumps and adhesion-dominated for HDIs involving a large number of contacting bumps. In the former case the friction decreases with bump density, whereas in the latter the friction increases with bump density.