Effect of Particulate Contamination on Pole Tip Recession in a Linear Tape Drive

Three-body abrasion is the cause of differential wear in magnetic tape heads resulting in recession of the magnetic poles with respect to the head substrate; this is called pole tip recession (PTR). The increasing head--tape spacing caused by PTR results in a lower write density, so the recession must be minimized. The three-body particles that may interact with the head--tape interface can originate from the operating environment (contaminant particles) and from the interface itself (debris particles). The effect of airborne particulate contaminants trapped at the head--tape interface (particle concentration, size, and hardness), which results in three-body abrasion, on PTR growth is studied experimentally. PTR increases with increases in any of the following: particle concentration, size, and hardness. Analytical modeling supports the experimental results. Possible mechanisms responsible for the observed behavior are discussed.     

The effect of hard coated metals on the thermo‐oxidative stability of a branched perfluoropolyalkylether lubricant

M‐50 and carburized Pyrowear 675® (Carpenter Technology, Reading PA, USA) steel coupons deposited with commercially available physical vapour deposited TiN, TiCN, TiAlCN, TiCrCN/TiB₄C multilayer, electroless Ni (E‐Ni) TiN and E‐Ni TiCN coatings were immersed in a branched perfluoropolyalkylether (PFPAE), Krytox AC® (E.I. du pont de Nemours and Company, Wilmington DE, USA), in an oxidative environment at temperatures ranging from 315 to 360 °C for a duration of 24 hours and compared with uncoated coupons. Coated and uncoated Pyrowear 675® coupons demonstrated superior corrosion resistance compared with coated and uncoated M‐50 respectively. The coatings most resistant to chemical attack in the PFPAE fluid were TiCN, E‐Ni TiN and E‐Ni TiCN. Copyright © 2006 John Wiley & Sons, Ltd.     

Effects of ultra-thin liquid lubricant films on contact slider dynamics in hard-disk drives

This paper describes the effects of ultra-thin liquid lubricant films on contact slider dynamics in hard-disk drives. In the experiments, the contact slider dynamics as well as ultra-thin liquid lubricants behavior are investigated using three types of lubricants, which have different end-groups and molecular weight as a function of lubricant film thickness. The dynamics of a contact slider is mainly monitored using acoustic emission (AE). The disks are also examined with a scanning micro-ellipsometer before and after contact slider experiments. It is found that the lubricant film thickness instability occurs as a result of slider–disk contacts, when the lubricant film thickness is thicker than one monolayer. Their unstable lubricant behavior depends on the chemical structure of functional end-groups and molecular weight. In addition, it is also found that the AE RMS values, which indicate the contact slider dynamics, are almost same, independent of the end-groups and molecular weight for the lubricants, when the lubricant film thickness is approximately one monolayer. The molecular weight, however, affects the contact slider dynamics, when the lubricant film thickness is less than one monolayer. In other words, the AE RMS values increase remarkably as the molecular weight for the lubricant increases. When the lubricant film thickness is more than one monolayer, the AE RMS values decrease because of the effect of mobile lubricant layer, while the lubricant instability affects the contact slider dynamics. Therefore, it may be concluded that the lubricant film thickness should be designed to be approximately one monolayer thickness region in order to achieve contact recording for future head–disk interface.     

Effect of relative humidity and disk acceleration on tribocharge build-up at a slider–disk interface

High performance disk drives require high spindle speed. The spindle speed of typical hard disk drives has increased in recent years from 5400 to 15000 rpm and even higher speeds are anticipated in the near future. The increasing disk velocity leads to increasing disk acceleration and slider–disk interaction. As the head-to-disk spacing continues to decrease to facilitate increasing recording densities in disk drives, the slider–disk interaction has become much more severe due to the direct contact of head and disk surfaces in both start/stop and flying cases. The slider–disk interaction in contact-start-stop (CSS) mode is an important source of particle generation and tribocharge. Charge build-up in the slider–disk interface can cause electrostatic discharge (ESD) damage and lubricant decomposition. In turn, ESD can cause severe melting damage to MR or GMR heads. We measured the tribocurrent/voltage build-up generated at increasing disk acceleration. In addition, we examined the effects of relative humidity on the tribocharge build-up. We found that the tribocurrent/voltage was generated during pico-slider/disk interaction and that its level was below 250 pA and 0.5 V, respectively. Tribocurrent/voltage build-up was reduced with increasing disk acceleration. Higher humidity conditions (75–80%) yielded lower levels of tribovoltage/current. Therefore, a higher tribocharge is expected at a lower disk acceleration and lower relative humidity condition.     

Toward structural/chemical cotailoring of phase‐change Ge–Sb–Te in a transmission electron microscope

Ge₂Sb₂Te₅, as the prototype material for phase‐change memory, can be transformed from amorphous phase into nanoscale rocksalt‐type GeTe provided with an electron irradiation assisted by heating to 520°C in a 1250 kV transmission electron microscope. This sheds a new light into structural and chemical cotailoring of materials through coupling of thermal and electrical fields.     

A numerical analysis of the interaction between the piston oil film and the component deformation in a reciprocating compressor

The piston secondary motion significantly influences the major characteristics of lubrication in a reciprocating compressor, such as the oil leakage, the piston slap phenomenon and the frictional power loss. Therefore, the design parameters governing piston dynamics should be carefully determined based upon a reliable dynamic characteristic investigation. As a preliminary research step, this paper is concerned with the finite element analysis for the piston dynamic response. By coupling FDM for the lubricating pressure field with FEM for the piston dynamic motion, we numerically approximate the lubricant–structure interaction in a reciprocating compressor. Numerical results illustrating the theoretical work are presented.     

A revised Hilbert–Huang transformation based on the neural networks and its application in vibration signal analysis of a deployable structure

A revised Hilbert–Huang method is proposed to deal with the non-linear and non-stationary signals generated from any kinds of the sensors, in order to overcome shortcomings of the Hilbert–Huang method, such as the end swings problem and the undesired intrinsic mode functions (IMFs) at the low-frequency range. Firstly, a radial basis function neural network is used as a pre-processor to extend the length of the signal at the both ends. Secondly, the empirical mode decomposition is applied to obtain IMFs. Thirdly, the selection process is employed to select the optimal IMFs. Finally, an energy–frequency–time distribution can be gained after the Hilbert transformation. Two simulated signals are analyzed to explain the pre- and the post-processor, respectively, by using the above two techniques. The efficiencies of the different bases are compared, and the length of signal extended is analyzed. The correlation coefficients between the analyzed signal and the IMFs are introduced to eliminate the undesired IMFs. In this paper, the revised HHT method has been applied to analyze vibration signals of a deployable structure. A simulated solar array setup is built, which contains six parts: the basal body, a locked mechanism, the synchronism mechanism, the connection joints, the driven parts, and two simulated panels. Vibration signals of the solar array setup in the deployed case that is knocked by a single impulse on the middle of the second panel are estimated, and the results show that the revised Hilbert–Huang method is efficient for non-linear and non-stationary signal analysis.