The tribology of linear tape/head interfaces and its impact on signal performance

The main application for data cartridge tape drives is backing-up data and thus it is imperative that the storage capacity of a single tape cartridge is significantly greater than the capacity of the latest rigid disk drives. Many of the recent improvements in capacity and data transfer rate have been achieved through the use of narrower tracks, higher linear densities and continuous servo tracking with multi-channel heads. These changes have made the tribological problems associated with tape storage systems of critical importance and this will continue to be the case as higher storage capacities and faster transfer rates are continually sought. The aim of the work described here was thus to understand the tribological phenomenon in linear tape systems that are responsible for signal loss and error growth in order that projected densities may be achieved in future systems.     

Interactions at the head–tape interface of a linear tape system

In this study, tape cycling experiments were performed using two different experimental metal particle media in combination with a Travan™ linear tape system. The aim was to investigate the effect of head/tape contact on the tribological properties and signal performance of the system. A combination of cycling at extreme environmental conditions, use of experimental media, and cycling beyond the normal limit of operation ensured a worst-case scenario for the head–tape interactions. Auger electron spectroscopy (AES) and atomic force microscopy (AFM) were used to characterize the chemical and physical surface changes that occurred on and in the head surfaces. X-ray photoelectron spectroscopy (XPS) was used to identify the chemical changes that occurred at the media surface and these changes were correlated to variation in signal dropout rate. Measurements were made as functions of number of cycles.The cycling experiments for the two different tapes were performed at conditions of 32°C, 80% RH and 5°C, 10% RH and transfer of material from the media to the head was observed at each condition for both tape types. The degree of material transfer was influenced by the environmental operating conditions, but was governed by localized heating effects, such as those originating from active magnetoresistive (MR) elements and frictional interactions between the head and media. XPS analyses of the surface of the media revealed a reduction of nitrogen with increasing number of cycles indicating binder depletion. Significant differences in elemental concentrations were also detected between areas corresponding to regions directly under the cartridge belt compared to those off belt.     

Effect of temperature,humidity and crystal directions on wear of rotary heads

In the advanced tape drive systems which achieve a higher recording density, the wear of rotary heads should be decreased to obtain a higher reproduced output signal by decreasing the ‘Gap depth’ of heads, keeping enough life time. By using the heads made by two kinds of crystal directions of Mn–Zn ferrite and metal evaporated tapes with DLC coating, temperature and humidity dependences of head wear are investigated. The wear rates of both crystal direction heads increase with the decrease in temperature. The wear rate of a (110) head increases very quickly at low temperature, compared with a (100) head. These temperature dependences of head wear are caused by the temperature dependence of the elastic modulus of the tape and the temperature dependence of the friction coefficient between the tape and the head.     

Characterization of surface changes to metal evaporated and metal particle media following durability tests in helical scan Hi-8 recorders at ambient and high humidity conditions

X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) have been employed in the surface characterization of two commercial tapes following durability tests in helical scan Hi-8 video recorders. Mechanical, physical and chemical changes to the surfaces of the metal evaporated thin film (ME) and metal particle (MP) tapes were compared to dropout errors and signal degradation under ambient and high humidity conditions. The signal measurements were correlated to changes in the physical and chemical structure of the surface with specific changes correlating well with dropout growth. Extensive surface analyses were used to identify the failure mechanisms in the ME and MP tapes and these were found to result from cyclic stressing and fatigue on the immediate substrate of the media. The durability of the tapes was assessed through stop motion (still-frame) and cycling tests, where error growth and signal degradation were measured as a function of running time. The signal performance of the ME tape was found to be quite different from that for the MP tape with dropout errors and signal degradation increasing at a much earlier stage.     

Metal Core Recession and Head Stain Studies of MIG Heads Sliding against Cobalt-Doped Gamma Iron Oxide and Metal Particle Tapes

Metal-in-gap (MIG) heads are commonly used for high-density magnetic recording. Metal core recession and head stains increase the gap between the tape and the head, resulting in signal loss. In this study, accelerated sliding wear tests of Co-γFe₂O₃, and metal particle (MP) tapes against MIC heads made of three different amorphous and, nanocrystalline metals were conducted under various operating conditions. Metal core recess and propensity for head staining were measured. The degree of tape contact with a recessed core was also measured by pressing the tape against a glass slide with Cr grids and using an optical interference technique. The authors found that the core recess was about the same for all three core metals. Core recess by MP tape was larger than that, by oxide tape. The tape speed appeared to have little effect on the recess value. The authors also found that significant recess may occur during initial contouring of the head surface; however, after sliding for about 250 km, core recess reaches a steady-stale value which may be either higher or lower than the initial values. The mechanism of core recession was studied. The authors believe that core recession occurs as a consequence of the debris trapped, between the tape and the core, in addition to that caused by some tape contact. Formation of head stains was observed in all combinations. The stains fanned on the metal cores were heaviest for CoNbZr metal, followed by CoTaZr and FeTaC. Co-γFe₂O₃ tape produced a more severe stain than the MP tape. The apparent roughening of head rubbing surface observed for CoNbZr heads sliding against Co-γFe₂O₃, tape was due to the formation of stains.     

Measurement and Origin of Tape Edge Damage in a Linear Tape Drive

Integrity of the magnetic tape edge is the key to maintaining high performance of modern tape drives. Damage to the tape edge under normal drive operation results in the change in tape dimensions and debris generation, both leading to degradation in the reproduction of the recorded signal. The objective of the present study is to develop a methodology for evaluation of tape edge quality and to apply the methodology to monitor tape edge degradation under normal drive operation. Optical microscopy, atomic force microscopy and scanning electron microscopy are employed to study and quantify the quality of the tape edge. AFM measure-ments were made on both individual tape layers and the tape reel. An edge quality measurement technique is used to quantify the damage to tape edge. A technique for the tape lateral motion measurement is used to study the effect of continuous sliding on tape guiding. A lateral force measurement technique is developed to measure the force exerted by the tape edge on the guide flange. The effect of normal drive operation on tape edge quality and on tape guiding in a linear tape drive is studied. It is shown that two edges of a factory-slit tape are imperfect and different, with cracking of the magnetic coating occurring at one edge. Under normal drive operation, one edge experiences more wear with larger amount of debris produced. This larger debris generation occurs on the edge with cracks developed during manufacturing. A possible mechanism of tape edge wear under normal drive operation is proposed.     

Failure Mechanisms of Advanced Metal Evaporated Tape in an Advanced Linear Tape Drive

Demand for increased data storage has resulted in the development of various types of magnetic tape. To achieve higher recording density, tape manufacturers are developing thin-film tapes, such as advanced metal evaporated (AME) tape, for use in linear tape drives. The structure of AME tape is fundamentally different from metal particulate (MP) tape. The goal of this study was to determine the methods and mechanisms associated with failure of AME tapes as well as to investigate the effect of tape cupping and initial edge quality on tape durability in an advanced linear tape drive. It is shown that AME tape exhibits a slightly lower coefficient of friction than the MP. The negatively cupped AME tape demonstrated a greater value of lateral tape motion peak-to-peak amplitude than both of the positively cupped AME samples as well as the MP tape sample. It was found that poor initial tape edge condition plays a large role in debris generation. For these reasons, positively cupped AME tapes with good initial relative edge contour are recommended for use in linear tape drives. The dominant mechanism of failure for the AME samples is adhesive wear resulting in removal of the DLC overcoats and sublayers.

     

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.     

The influence of peel angle on the mechanics of peeling flexible adherends with arbitrary load–extension characteristics

The peel test is commonly used to determine the strength of adhesive joints. In its simplest form, a thin flexible strip which has been bonded to a rigid surface is peeled from the substrate at a constant rate and the peeling force which is applied to the debonding surfaces by the tension in the tape is measured. Peeling can be carried out with the peel angle, i.e. the angle made by the peel force with the substrate surface, from any value above about 10° although peeling tests at 90 and 180° are most common. If the tape is sufficiently thin for its bending resistance to be negligibly small then as well as the debonding or decohesion energy associated with the adhesive in and around the point of separation, the relation between the peeling force and the peeling angle is influenced both by the mechanical properties of the tape and any pre-strain locked into the tape during its application to the substrate. The analytic solution for a tape material which can be idealised as elastic perfectly–plastic is well established. Here, we present a more general form of analysis, applicable in principle to any constitutive relation between tape load and tape extension. Non-linearity between load and extension is of increasing significance as the peel angle is decreased: the model presented is consistent with existing equations describing the failure of a lap joint between non-linear materials. The analysis also allows for energy losses within the adhesive layer which themselves may be influenced by both peel rate and peel angle. We have experimentally examined the application of this new analysis to several specific peeling cases including tapes of cellophane, poly-vinyl chloride and PTFE.     

Effect of Interchanging Tapes and Head Contour on the Durability of Metal Evaporated,Metal Particle and Barium Ferrite Magnetic Tapes

Interchanging metal evaporated in 120-minule cassettes (ME-120) and particulate [metal particle (MP) and barium ferrite (BaFeO)] tapes in a tape recorder caused excessive head and tape wear while a tape formed its preferred head shape in these experiments. The fundamental cause of this phenomenon was that the tapes formed different head shapes during tape recorder operation. To extend the usable lifetime of a rotary head recorder, and to minimize the extent of tape damage, as well, as to preserve the integrity of the recorded information, the authors recommend avoiding the practice of interchanging ME-120 and particulate tapes in a tape recorder. The interchanging of ME-180 (180-minute cassette) tape with ME-120 and particulate tapes is not recommended either, but apparently does not lead to excessive head and tape wear. Thin ME-180 tape was inefficient in significantly changing the head contour. This study suggests that the head contour is a determining factor for the performance of a tape in a tape drive. In the authors study of tape compliance using ME tapes, the highly compliant ME-180 tape gave more uniform head wear, lower fiction and slightly better durability than the lower compliance ME-120 tape.     

The measurement of in-situ wear of video heads

A method of measuring in-situ wear of video heads which determines the variation in wear along the surface of the video head is described. Knoop diamond indentations are positioned along the head, either side of the magnetic gap, enabling wear rate to be monitored at several positions. Virgin tape is run over the heads in the form of standard E180 cassettes and the wear occurring at each indentation position is derived from the reduction in length of the main diagonal. Wear rate is plotted against the position of the indentations. This describes the variation in wear along the head and therefore the conformation of the tape to the head. The technique has been used to study the wear of video heads with three types of tape sample: two iron-oxide-based formulations, with either Al₂O₃ or Cr₂O₃ added as head cleaning agents, and one chromium-dioxide-based tape. Little difference was found between the performances of the iron oxide tape samples. The chromium dioxide sample, however, produced wear some five to six times greater than the iron oxide tapes.     

Flexible media — recent developments from the tribology point of view

With the increase in the recording density of hard disk systems, the demand on the increase in the data recording capacity of tape drive systems as back-up systems is increasing. One of the advantages of the tape drive systems is high volumetric recording density, which is obtained by high areal recording density and thin tapes. The areal recording density can be increased by introducing high performance tapes, such as metal evaporated tapes, with superior magnetic characteristics and smooth magnetic surface to reduce the spacing loss. However, a smoother surface often produces a higher friction coefficient, which could cause tape damage by rotary heads and unstable tape runnability in the tape drives. Adoption of MR heads to tape drive systems is also effective in increasing the areal recording density. However, the wear allowance of the MR heads (shield type) is much smaller than that of the inductive heads. Thinner tapes show lower mechanical stiffness in general, which could cause damage to tape edges easily during tape transportation. In the second or later generation of tape drive systems, a thinner tape is often introduced. These thinner tapes should also have the interchangeability of the original thickness tape. New materials for a base film, such as PEN (polyethylene naphthalate) or aramid in which the elastic moduli are larger than those of PET, are required for thinner tapes. It was found that these side effects by the increase in the volumetric recording density can be improved by tribology. The tribological improvements from the drive design side is very important, as well as from the tape design side.     

两种高聚物薄带的沙尘磨损特性研究

首次开展了ATM(Auto TellerMachine)高聚物部件在沙尘环境中的磨损研究。在实验室模拟降尘环境中使用ATM中的Tape-scraper摩擦系统,对PI(聚酰亚胺)和PEN(聚萘二甲酸乙二酯)两种高聚物薄带的磨损行为进行了研究,并利用扫描电镜对薄带的磨损表面进行了分析。实验采用了采集自沙漠的自然沙尘。实验结果表明:PI薄带比PEN薄带表现出更优良的耐沙尘磨损性能。PEN薄带的微观磨损机理主要是纤维组织的塑性流动和拉断,而PI薄带的微观磨损机理为裂纹的萌生、扩张和块状剥落。用材料的机械变形因子可以很好地解释两种聚合物薄带的磨损特性差异。     

基于硬盘的视频实时存储方法的研究

数字图像的实时存储是视频判读的基础,经常使用模拟录像机把视频信息记录在磁带上,由于磁带录像机的分辨率不高,影响判读的精度.本文针对数字图像的特点,提出了一种新型的、基于计算机硬盘的视频存储方法,其目的是简化判读系统的结构,提高判读的精度.它利用了数据压缩原理,对视频信号进行实时、无失真的压缩,再把压缩后的数据进行存盘,实现了视频图像实时存储.试验表明,用此方法可以完成512×512的视频图像的实时存储,且结构简单,方法实用,是一新型的视频存储方法.     

A study of tribology of Travan heads in linear tape recording

Tape cycling experiments were performed with a Travan™ linear tape system using metal particle (MP) media. The effects of various environmental conditions, particularly water content, on the tribology of the head/tape interface were studied. Auger electron spectroscopy (AES) and atomic force microscopy (AFM) were used to characterise the chemical and physical surface changes that occurred at the head surfaces. Transfer of material from the media to the head was observed at each condition. X-ray photoelectron spectroscopy (XPS) was used to identify the chemical changes that occurred at the media surface. This showed that in all areas of the tape, the amount of detected iron had increased, while the nitrogen (binder indicator) signal had decreased. Significant differences in elemental concentrations were also detected between areas directly in contact with the cartridge drive belt compared to those not in contact. Pole tip recession (PTR) was around 50–65 nm after 5000 passes, but increased at the higher water contents. AES results showed that stain is a function of water content, not relative humidity. It was noted that a larger ceramic grain size seemed to increase PTR.     

Lateral motion and edge wear of magnetic tapes

Lateral motion and edge wear are measured on magnetic tape, and the relationship between tape edge wear and tape lateral motion is investigated. Instrumentation for measuring tape edge force is described. Tape edge force is measured at the tape guiding position using a force-calibrated cantilever spring and a linear optical probe. Typical measurements of tape lateral motion are given as a function of tape tension, tape direction, and path position. A technique for measuring tape edge wear is introduced and wear measurements are presented as a function of load and the number of passes.     

直流无刷电机驱动曲柄压力机动态仿真与实验研究

研制了由直流无刷电机驱动的250kN伺服曲柄压力机试验样机,以直流无刷电机取代普通异步电机,取消了机械飞轮和离合器,驱动电路中配有大电容,以储存和释放电能。对压力机驱动和传动系统进行了理论分析,建立了机电系统的数学模型;根据样机参数进行了数值仿真和实验研究,二者结果十分接近,证明了数学模型的正确性;实验样机可以获得滑块的任意工作曲线,实现工作特性的柔性化;电容器可以起到“电子飞轮”储放能量的作用,在实验条件下,冲裁时电网瞬时峰值电流可减少86.3%。     

Investigation of tape edge wear of magnetic recording tapes

Tape edge wear is studied for polyethylene naphthalate-based magnetic tape as a function of tape speed, tape tension, and tape guide surface roughness. The results show that tape edge wear is on the order of 0.04 nm per cycle at a constant force of 45 mN and that edge wear increases with increasing tape speed, tape tension and tape guide surface roughness. In addition, tape edge wear of three coated tapes with polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyaramid (PA) substrate is studied. It is found that edge wear of polyaramid based tape is similar to that of PET-based and PEN-based tapes.     

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.     

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.