A finite element model is used to study the transient thermo-elastic-plastic contact between a thermal asperity sensor and a thermal asperity. The temperature change of the thermal asperity sensor is determined during contact with an asperity. The results show that sensor temperature is a function of the operational temperature of the sensor and the friction coefficient between the sensor and the asperity.
An embedded contact sensor (ECS), which is a thermal sensor built into a head slider, has been used for contact detection between the head slider and the disk in hard disk drives. Our previous research showed that the ECS temperature effect caused by self-heating is smaller than by the thermal fly height control (TFC) heater. In this work, ECS sensitivity for head / disk contact detection was studied in the point of the distance between TFC and ECS. The results showed that the temperature caused by the TFC heater is a key factor for the contact detection.
The storage disk media substrate effect on contact/clearance sensor, also named embedded contact sensor (ECS), is addressed in this paper. The ECS exhibited different response on storage media comprising Aluminum and glass substrates. The response is attributed to cooling efficiency from the disk during a touchdown event. Aluminum substrates provided more effective cooling to the ECS as be measured by the DC component of the ECS signal. The AC component of the ECS signal was found to be less sensitive to media substrate than the DC component. The response dependence on bias applied to the ECS has also been characterized. Aluminum substrates showed larger sensitivity to bias compared to glass. By tuning the bias, both the AC and DC signals from ECS can be utilized as effective touchdown detectors.
In this investigation, we study head wear as a function of a dc bias voltage applied across the head-disk interface (HDI). Head-wear is determined by measuring the change in the heater touch-down power before and after 10 minute wear tests. It is found that applying a positive bias to the disk with respect to the slider results in reduced head wear.
Using a lateral force microscopy with a dual-axis micromechanical probe of our own design and fabrication, we measured the friction force of nanometer-thick films of perfluoropolyether (PFPE) lubricants with different bulk viscosities at low sliding speeds of 1-400 μm/s. With increasing sliding speed, the friction force decreased for the less viscous films, whereas it decreased initially and then increased for the more viscous films. From these results and our previous results at high sliding speeds, we infer that, in a wide range of sliding speeds, nanometer-thick PFPE films display a similar trend of an initial decrease followed by an increase in the friction force as the sliding speed increases, and the sliding speed at the inflection point decreases with increasing bulk viscosity of the PFPE.
This paper employs the coupled air bearing model and head stock assembly (HSA) modal order reduction (MOR) model to investigate the track-seeking process of a femto slider. Simulations indicate that the flying height may increase or decrease significantly, depending on the track-seeking directions. The most serious vibration is the off-track vibration, and it is highly related to the sweeping acceleration profile. A smooth acceleration profile is crucial to reduce all the vibrations of slider, especially the off-track vibration.
This paper presented a coupled field analysis method to integrate the air bearing model with the structural finite element (FE) model of the full hard disk drive (HDD), including the all major mechanical components, for operational shock simulations. The dynamics of head-disk interface (HDI) and mechanical components in HDDs during operational shock are then investigated by simulations. The effects of air bearing nonlinearity and the disk-ramp contact on the HDI responses to operation shocks are evaluated and understood by comparing to the linear simplified model. The results reveal that conventional de-coupled simulation methods are not valid anymore for the complicated nonlinear events, especially when the disk ramp contact or slider-disk contacts are considered. The newly developed coupled-field method is suitable for such operational shock simulations by considering the complexity of the system nonlinearity.
In order to understand the microwaviness (MW)-excited vibration of a thermal-flying-height control (TFC) head slider in the near-contact recording regime of hard disk drive (HDD) storage, the adhesion contact characteristics of a TFC head slider were investigated using various asperity adhesion contact models. The spacing variation of a single-degree-of (DOF) slider model with a second- pitch (P2) mode frequency was numerically simulated. It was found that if the total force acting on the slider has a negative stiffness region, the P2 mode frequency of 250 kHz shifts to a lower frequency of 〜100 kHz, and many frequency components are generated in a wide frequency range below 100 kHz. These frequencies could excite other modes of the slider-suspension system. The analytical results will help us understand MW-excited slider vibrations and spacing variations, which is critical in order to achieve the spacing of less than 1 nm that is necessary for high-density magnetic recording.
The areal density of magnetic storage needs to be increase so to meet the increasing demand for mass data storage. The application of the thermal fly-height control sliders allows a flying height lower than 3nm. State of art, the thickness of carbon overcoat thickness and lubricant are 1.8nm and 0.8nm, respectively. Further decrease in carbon thickness is difficult due to galvanic corrosion through exposure to air. We propose a way to decrease the head magnetic spacing. The PFPE lubricant will applied onto the magnetic head air bearing surface instead of the magnetic media. Reduction of the carbon over coat film thickness of the magnetic media is possible since nitration is not needed. Experiments were conducted to demonstrate the feasibility of this idea. The use graphene on magnetic hard disk is also disused.
In Micro Electro Mechanical Systems (MEMS) technology, a lift-off process with sputter deposition is one general patterning method for amorphous alloy thick film structure. However, a thickness of the structure is not uniform because sputtered particles are hindered by side a wall of the lift-off layer. In this paper, a new patterning method of amorphous alloy thick film structure with uniform thickness was proposed. Moreover, this patterning method was defined as "Reversed lift-off process". In reversed lift-off process, convex parts with the desired structure shape is formed on a top of a substrate. Thick film structure is deposited by the sputter deposition on the top surface of convex parts. A thickness of the structure is uniform because there is nothing which hinders sputtered particles in contrast to a conventional lift-off process. As a practical experiment of reversed lift-off process, we successfully fabricated Cu-Zr-Ti metallic glass thick film structure which has uniform film thickness, rectangular cross-sectional shape, and noncrystalline in a different width of the structure. Moreover, it was confirmed that reversed lift-off process is suitable for the fabrication of metallic glass thick film structure in the comparison with the conventional lift-off process.
In vitro microvascular models have been interested in the fields of regenerative medicine and drug development. Here, we successfully fabricated a 3D in vitro microvasculature composed by human umbilical endothelial cells completely surrounded by the collagen gel. We examined development of cell stress fibers, nucleus alignment and the diameter change of the microvasculature under shear stress.
We investigated characteristics of Ti-Ni-Zr thin film metallic glasses (TFMGs). The Ti-Ni-Zr amorphous thin films having Ni-content of more than 50 at.% and Zr-content of more than 11 at.% exhibited glass transition. Although the Ti_<39> Ni_<50> Zr_<11> sample had alloy composition at the boundary between TFMG and only amorphous, it showed the lowest glass transition temperature T_g of 703 K and wide width of supercooled liquid region (SCLR) ΔT of 57 K. Moreover, this sample showed a high thermal stability at the T_g . However, it is considered that viscosity of this sample was higher than those of other TFMGs
NiO nanoparticle solution film, which included NiO nanoparticles, ethylene glycol, and polyvinylpyrrolidone, was reduced to Ni to form Ni microstructures using femtosecond laser induced reduction. When the femtosecond laser pulses were focused onto the film and scanned, Ni microstructures were formed. The line width was uniform under the condition of low pulse energy and high scanning speed. This result indicates that the series of phenomena of NiO nanoparticle reduction, agglomeration, and sintering was completed by individual laser pulses. The lower scanning speed and higher scanning speed caused the re-oxidation of the microstructures and remained non-reduced NiO nanoparticles, respectively.
This paper describes the reliability of piezoelectric vibration energy harvesters (PVEHs) of Pb(Zr,Ti)O_3 (PZT) thin films on metal foil cantilevers. The PZT thin films were directly deposited onto the Pt-coated stainless-steel (SS430) cantilevers by rf-magnetron sputtering, and we observed their aging behavior of power generation characteristics under the resonance vibration condition for three days. During the aging measurement, there was neither fatigue failure nor degradation of dielectric properties in our PVEHs (length: 13 mm, width: 5.0 mm, thickness: 104 μm) even under a large excitation acceleration of 25 m/s^2 . However, we observed clear degradation of the generated electric voltage depending on excitation acceleration. The decay rate of the output voltage was 5% from the start of the measurement at 25 m/s^2 . From the decay curves, the output powers are estimated to degrade 7% at 15 m/s2 and 36% at 25 m/s^2 if we continue to excite the PVEHs for 30 years.
We developed a DNA separation chip utilizing micrometer-sized fence structures fabricated in a micro channel. The separation was achieved based on the principle of size exclusion chromatography (SEC). The smaller DNA molecules take longer time to pass through the molecular sieve of fences. In this study, we integrated a nano-slit structure for the pre-concentration of DNA samples in the same micro-channel. Since the pre-concentration was conducted just before the separation, we improved the resolution of DNA separation and succeeded in separating DNA molecules of 2 kbp and 10 kbp.
Plastic film are widely used for a lot of products, such as liquid crystal display monitors, lithium-ion secondary battery, and other high functional flexible materials related in the printed electronics fields. These devices re manufactured by web handling system (Roll-to-Roll system). Most of web handling industries are often encountered with the problems of wrinkling, slippage and gage band in the wound roll. Since the winding process is a final stage of the production, these web defects had been a cause of losing a lot of materials and being very high production costs, and wasting a lot of time to restore the wound roll. Recently, gage band which is a permanent strain occurring when there is thickness variation of the film across widthwise direction. Moreover, gage band is strongly related with the internal stress (radial stress) distributions in the wound roll. Therefore, in this study, internal stress was measured using a film with thickness variation. As a result, the tendency of internal stress distribution was similar to the thickness variation of the film.
Plastic film is often passed through roll-to-roll manufacturing processes such as coating, printing and slitting to convert to industrial products. The film is made into wound roll on the final stage of the process to ease handling and storage. And then it is usually transported and heat-treated under the various temperatures, which could be different from winding temperature. As a result, wound roll defects such as slippage and wrinkling occur, and then it leads to a risk of an economic loss. For preventing these problems, it is necessary to understand and predict the internal stress. In above situation, the internal stress may vary over time due to thermal strain and creep strain of the film. Furthermore, it is known that load stress and the temperature affect creep. Therefore, this paper describes a thermal-viscoelastic winding model considering the thermal elasticity and the viscoelasticity. To perform the numerical calculation of the internal stress which are radial and circumferential stress, an unsteady conduction analysis in radial direction was applied to evaluate time change of the in-roll temperature. The creep compliance change was measured by compression and tensile creep tests under various load stress and temperature conditions to investigate the creep behavior of a polypropylene film as test film. From the experimental results, magnitude of the change was affected by these conditions. In order to apply the effect into winding model, an empirical formula was obtained based on the experimental results. It was possible to estimate the creep compliance values on arbitrary stress/temperature condition and was expressed by generalized Voigt model. The predicted values generally correspond to the experimental values.
The devices based on plastic film such as optical film, lithium-ion secondary battery and fuel-cell stack have being manufactured by roll to roll system. In this system, the films are finally wound in the shape of roll. The wound roll is shipped to the store and transportation, in some cases, heat-treated under the various temperatures. Then internal stress of wound roll will be changed due to thermal strain and viscoelastic properties. As a result, those elements causes to wound roll defects such as slippage and wrinkling. For the problem, thermo-viscoelastic model of internal stress of wound roll was presented. In the present optimization method, the wind-up tension is gradually changed in the radial direction to minimize the tangential stresses under the constraint of nonnegative tangential stresses. At the same time, we consider the friction conditions to prevent the slippage between web layers due to a decrease of radial stresses and friction force. Successive quadratic programming, which is a typical mathematical programming method, is used as the optimization technique. The optimized wind-up tensions are obtained, and we confirmed theoretically and experimentally that the internal stress distributions are very much improved for preventing both wrinkling and slippage simultaneously.
To establish the new technology named Roll-to-Roll Printed Electronics, it is needed to combine the roll to roll transportation system and coating technology effectively. For that purpose one of important factors to be considered is the effect of friction characteristics between the film and steel roller because plastic film used for high functional devices has been becoming thinner. In past research, however, as far as authors know, there is no research which describes friction characteristics between thin plastic film and steel roller. On the other hand, in our past research, it was found that friction coefficient was increased with decrease in film thickness. In this study, the static friction between the plastic film and steel roller was measured by pulley method while changing the roller surface roughness, web tension, and relative humidity. As a result, the static friction coefficient between thin film and steel roller was significantly influenced by roller surface roughness, web tension and relative humidity. It was confirmed statistically that contribution ratio of three factors, relative humidity, web tension and surface roughness are 23.8 %, 32.6 % and 36.1 %, were very high.
Printed electronics is technology that produces electronic devices and circuits by printing functional ink on a web, which is flexible material like film. It is suitable for large-scaled and high-speed mass production, and is a next-generation process technology that can make electronic devices of flexible material. As precise measurement of positions of the web is required in order to commercialize such process of printed electronics, the measurement system with an optical encoder with the precision of micrometers has been proposed through the preceding research of this paper. However, in the preceding research, there is a limitation of not perceiving the phenomenon of the entire web being moved in the lateral when it happens. In this paper, a measurement system for the lateral positions of web, which utilizes the differences in the amount of light reflected from the alignment patterns depending on the web positions of the lateral direction, has been proposed. According to the proposed method, the noise caused by the printing quality degradation of the alignment patterns can generate measurement error. To reduce it, high measurement precision was obtained by adapting Hilbert transform method robust against noise.
We examined the behaviors of the paper sheet in the overlap-type isolation mechanism of the paper sheets. First, we introduced the formulation that can calculate the resistance force and feed force acting on the paper sheets in the mechanism. And, based on the calculation results of the resistance force and friction force between the paper sheets, we examined the behavior of the paper sheet. As a result, we found that the separation mechanism that can separate the paper sheets piled up to one piece exists in the overlap-type isolation mechanism, and that the separation mechanism is a superior factor than the other isolation mechanisms.
In this paper, we propose intelligence CGH method in Holographic 3D Display. Intelligence algorithm is fuzzy system and DNA coding method algorithm. Firstly, introduce our holographic Display and CGH. And then, explain a intelligence method in CGH, and then, you can see simulations and experiments, finally, explain conclusions in our system.
With monocular vision sensor, we try to constitute a sensing system, which is able to realize self-localization, navigation and collision avoidance at the same time. This paper proposes a novel sensing system with monocular vision sensor that is placed with a certain pitch angle in the front of the robot. The vision signal obtained by the monocular vision sensor, which is partitioned into the upper and lower images. Here, we will mainly describe the effort in visual odometry using the lower half of the image. With different pitch angles in experiments, the effects on odometry accuracy are investigated and evaluated under different conditions of the reflected light.
In this paper, an optimal switch-on strategy of dual-stage actuation (DSA) for hard disk drives (HDDs) is proposed. When DSA loop is switched on during the seek settling, the control performance can be compromised by saturation of the secondary-stage actuator. To address this issue, we have established a framework to derive the saturation boundary based on maximum output admissible set theory. In addition, the earliest switch-on of DSA is proposed to lower the overshoot and shorten the settling time. Numerical simulations show that our proposed method successfully lowers the overshoot by 59.4% and reduces the 5%-track settling time by 15.9%.
Dual-stage servo control loops are modeled for hard disk drives (HDDs) with the consideration of time delay which is due to the time taken for position error signal demodulation and controller computing. The time delays are involved in controller design and the closed servo control loop is investigated to show the effects of the time delay on servo control performance. The studied actuation system is a PZT milliactuator based dual-stage servo system. The delay time within and over the sampling interval is separately considered for 62.5kHz sampling rate. To show the effect of sampling rate on servo control performance, 40 kHz sampling rate is considered for comparison. The results tell us that increasing sampling rate gives more marked improvement of servo performance than reducing time delay for HDD dual-stage actuation servo systems.
An analytical enforced angular displacement function to control angle and angular velocity of a 1DOF rotational oscillator in arbitral operating time, called rotational vibration manipulation function (RVMF), is applied to design discrete target trajectory of a swing arm in HDD for suppression residual vibration of a magnetic head at desired angles. While the enforced angular displacement is a linear combination of basis functions with parameter α_p , arm trajectory can be chosen. In this study we show some simulations with trajectories of two or non-dwell rotation. Moreover, hence RVMF is the function of current and aimed angles and angular velocities of the target oscillator, it can be modified to realize sampled-data feedback control of the oscillator. The proposed sampled-data control can be utilized to manipulate the magnetic head of HDD device under short seeking mode either for short-distance track or long-distance one for high speed and high precision positioning.
The hard disk drive (HDD) industry continues to meet the ever growing demand for storage capacity by increasing both the number of tracks on the disk surface and the number of bits recorded per track. Basically, the contact dynamics of slider involves strong nonlinearity and uncertainty. How to control slider to reduce touchdown instability and eventually eliminate bouncing has been a pressing and challenging research topic. To improve the active slider system performance, it is necessary to reduce or eliminate vibration induced by the uncertain dynamics. There are many control methods dedicated to address this challenging issue. Fewer results are available in the case when not all states are directly measured. The velocity is usually measured by a velocity tachometer, which is expensive and often contaminated by noise. One possible solution is to implement a velocity estimation, so it is very meaning to study state estimate- based dynamics control of active slider in touchdown. This paper aims to develop a state estimate- based adaptive fuzzy control techniques for controlling active slider in touchdown. A fuzzy state estimator is proposed to estimate the state variables for velocity variable. Under some conditions, it is shown that such a state estimator guarantees the uniformly ultimate bounded (UUB) of the estimate error. Based on system input-output data and our proposed state estimator, a robust adaptive fuzzy output-feedback control scheme is presented to control uncertain active slider in touchdown. The adaptive fuzzy output-feedback controller can guarantee the uniformly ultimate bounded of the tracking error of the closed-loop system. The results demonstrate that our proposed techniques have good potential in controlling active slider with uncertainty and unknown state.
In the conventional reproduction system, minimum resolutions of the environmental haptic memories depend on a resolution of the encoder. The force command is generated by the differential form of the step function when a resolution of an encoder is less than the change in the position. Therefore, the force command value diverges to infinity. Thus, this paper shows that the system cannot reproduce the high-stiffness environment if the encoder resolution is considered. In addition, this paper indicates that the reproduction method based on admittance control realizes of reproducing the high-stiffness environment. The effectiveness of the reproduction method based on admittance control is confirmed by simulation and experimental results.
This paper proposes the force control using the instantaneous state observer (ISOB). In a two-inertia system, a conventional disturbance observer (DOB) is widely used to achieve the robust motion control. In general, the DOB is used for the force sensor-less force control. However, the DOB exhibits an estimation delay attributed to pole allocation. The estimation delay has influence on the performance of the controller. The ISOB using an acceleration sensor is proposed for the estimation load-side torque in this paper. The ISOB does not exhibit the estimation delay because the acceleration signal is used for the input signal of the observer. Therefore, the performance of the force controller is improved by using the ISOB. On the other hand, the measured acceleration signal is susceptible to the effect to noise. To address the noise problem, the variable noise-covariance (VNC) Kalman filter is used to the estimation of the load-side acceleration. Hence, the noise is suppressed by using the VNC Kalman filter. Thus, the high performance load-side torque response is achieved by using the VNC Kalman-filter-based ISOB. The effectiveness of the proposed method is confirmed by performing the numerical simulation using an industrial robot.
For the purpose of the strategic positioning of Information Intelligent and precision engineering (IIP) division technologies of mechanical research area, technology roadmap (TRM) committee of IIP is organized. This paper is described the integrated perspective of the technology of IIP and shows challenges.
Social needs for information storage are very high and will also be higher in the future. Needs for data storage are explosively increasing in cloud environment. A significant part of storage data is expected to be cold data with low-frequency access. Therefore, HDDs in position of in future storage systems are changing. The aim of this roadmap is to suggest the academic research fields needed for future HDDs and candidate fields where academic knowledge on HDDs can apply to. We focused on two key technologies for HDDs; positioning technologies and nano-tribology. Based on technology mapping of the technologies, roadmaps of the two technologies are discussed.
We have considered what kind of technology will be needed in the future in the field of apparatus that handle flexible sheet media. As for the technology that handles cut sheet, it is about to enter a transitional period, and the development of a new technology that can handle various media (unlike the conventional cut sheet) with high reliability is required. As for the technology that handles consecutive media (web), in order to apply Roll-to-Roll (R2R) process to printed electronics (PE), the technology that can transport and wind thin web on which electric circuits and sensors formed is required.
3D printer was now applied to fabricate not only anime figures but also industrial products those were parts of vehicle and airplane. Actually, the machining accuracy is less than the ultraprecision machining's. However, relatively complex structures are easy to fabricate utilizing commercial 3D printer. In this paper, we would like to introduce the development of originally developed micro 3D printer and its future applications of biotechnology field and green technology field.
Human motion-assist and rehabilitation systems such as orthoses, prostheses, human assist systems, etc. have been developed to make the human life better. Especially, the studies on the human assist systems such as power-assist robots and rehabilitation robots are actively performed in these days. Although simple motion generation systems such as CPM (continuous passive motion) systems are widely used for rehabilitation at present, rehabilitation robots are expected to realize more advanced rehabilitation. Many kinds of rehabilitation robots have been developed for upper-limb and lower-limb rehabilitation. Human motion-assist robots are also expected to help daily motion of physically weak persons. In this paper, state of the art technology of motion-assist and rehabilitation systems is explained and their future technology is prospected.
With low birthrate and aging, staying healthy and the maintenance and improvement of the quality of life (QOL) are strongly desired. To stay healthy, early detection, treatment and recovery of diseases is important. In this paper, we report a trend of the recent medical equipment and what is demanded and how they advance in a future
Academic roadmap for intelligent machines came from the output of studying activities in Information, Intelligence and Precision Equipment Division of the Japan Society of Mechanical Engineers. Technology Trends on Intelligent machines to 2080 are explained.
To balance performance and cost, binary gas mixtures such as air-helium are currently being investigated as candidates for use in advanced drives. The amount of accumulated lubricant is determined by evaporation from the disk and slider, condensation on the slider and lube transfer. The increase in helium fraction ratio leads to the decrease in lube transfer and the amount of total lube pick-up is increased dramatically. Therefore, the HDI problems induced by the lubricant pick-up should be considered in helium-filled drive.
In the head-disk interface (HDI) of a hard disk drive (HDD), the effects of lubricant deformation on the flying characteristics of a head slider increase as the flying height decreases. Therefore, it is very important to investigate the deformation and flow characteristics of lubricant on a recording disk. In particular, in heat-assisted magnetic recording (HAMR), laser heating of the lubricant induces surface tension distribution and evaporation of lubricant, which may cause deformation of the lubricant film. In this study, flow characteristics of a liquid nano-step of perfluoropolyether (PFPE) on a solid substrate were investigated experimentally. Two types of PFPE lubricants (Z03 and Z-dol) were evaluated. Using the modified Boltzmann-Matano method, diffusion coefficients of the liquid nano-step, which shows the flow characteristics, were calculated from experimental data. As a result, change of flow characteristics of the liquid nano-step due to heating were clarified.
In recently developed magnetic storage systems, the spacing between the slider and the disk has been decreased to less than 2 nm. This ultra-small spacing results in the slider picking up the liquid lubricant on the disk. The small amount of the transferred (picked-up) lubricant affects the flying characteristics. In this study, we experimentally investigated the basic characteristics of liquid transfer due to the breakage of a liquid meniscus bridge. Furthermore, the force curves of the meniscus bridge were measured. The effects of the surface roughness on the liquid transfer and the force curves were discussed.
Dynamic characteristics of a liquid meniscus bridge were experimentally investigated using a dynamic meniscus force apparatus we developed. Especially, effects of solid surface roughness on vibration transfer characteristics of liquid meniscus bridge were examined.
An entrapped particle in the slider air bearings causes various damages on the surface of slider or the disk, the study of particle movement and adhesion mechanism on the slider surface is critical to reduce the contamination. In this paper, it investigates the interaction between the particles and slider surface. The particle trajectories in the far-field region are calculated using the classical Runge-Kutta method. In the near-field region where the distance between the particle and slider surface less than mesh size (about 1 μm), a novel model for particle velocity and adhesion criterion was proposed to judge whether the particle will be rebounded or captured subsequent to collision on the slider surface. Then the particle trajectory and velocity in the near-field region were presented.
The interaction stresses acting between a half-space consisting of a uniform material and a half-space with one-dimensional material distribution in the in-plane direction have been derived. Two patterns of material distribution are considered here, i.e., a periodic distribution of materials (Pattern 1) and a distribution of two materials with a single interface (Pattern 2). The interaction stresses for Pattern 1 was derived by using a Fourier series, while the interaction stresses for Pattern 2 was derived as elementary functions. The basic characteristics of these interaction stresses were clarified.
A method has been developed for calculating the interaction pressure between a half-space consisting of a uniform material and a half-space with a spatially periodic material distribution based on the Lennard-Jones potential. The periodic material distribution is two dimensional in the x- and y-directions. The periodically distributed material property function is expanded as a complex Fourier series. The interaction pressures consist of both the attractive and repulsive pressures. The interaction pressures for a distribution of two materials were then calculated as a typical example of a periodic material distribution. The basic characteristics of the interaction pressure are clarified.
Hertz contact theory was first derived 133 years ago which prescribes the contact behavior of normal contact between elastics. Furthermore, many studies and applications are based on it. However, Hertz contact theory still exists many uncertainties. This study first focused on the contact of a rigid sphere and an elastic half-space, and found that Hertz theory predicts well at large indentation. Besides, the critical contact central angle is 47.8° with maximum von Mises strain of 0.51. This large indentation result is independent of Young's modulus of the elastic half-space and the radius of the sphere, and it could be explained by the conformation of the pressure distribution at contact surface. Results were yielded by finite element method (FEM) and nanoindentation of polydimethylsiloxane (PDMS).
Static and dynamic flying characteristics of a slider in hard disk drives have become an important issue owing to increase in recording density. In the present paper, the characteristics of a step slider flying in either air or He over a running boundary wall with local temperature distributions and thermal deformation (projection) of the slider are analyzed using the thermo-molecular gas-film lubrication (t-MGL) equation. The decreases in minimum spacing for the slider flying in He are significant, because the mean free path of He is approximately three times that of air. The increases in minimum spacing due to laser heating are negligibly small in both air and He, because the heat spot size is very small. Moreover, the decrease in minimum spacing produced by thermal deformation in TFC slider is reduced by total additional pressure of i) MGL pressures produced by the air-film wedge effect, ii) t-MGL pressures by the temperature distribution and iii) van der Waals attractive pressure by small spacing. The spacing fluctuation caused by running wavy disk is reduced, because the inlet to outlet spacing ratio (h_1/h_0) increases.
Perpendicular recording media samples were exposed at 65 ℃ and 90 % RH for 6 days to trigger corrosion growth. Several corrosion spots were selected by optical surface analyzer, and then analyzed by scanning electron microscope, transmission electron microscope, and element energy dispersive X-ray spectrometry. By scanning electron microscope images, the spots were classified to the following corrosion patterns: "Rod type" and "Whisker type". Transmission electron microscope with element energy dispersive X-ray spectrometry analysis revealed that the "Rod type" was made of nickel oxides with micrometers in size, while the "Whisker type" was made of metallic cobalt with sub-micrometers in size. The nickel and cobalt were eluted from nickel-alloy layers and cobalt-alloy layers to media overcoat surface, respectively. In cross-sectional transmission electron microscope images of the samples with "Rod type", considerable deformation of media layer structures was observed, which was due to the lack of the nickel-alloy layers. Such corrosion induced the fatal error because of huge corroded materials and recording layer distortions.
Turbulent flow in a HDD model which contained two disks and a RW (Read and Write) arm was numerically analyzed at a disk rotation Reynolds number of about 10^5 . The evaluation of the fluctuating torque revealed that the RW arm may be oscillated at a frequency which has only weak correlation with the disk rotation speed. The fluctuating pressure was stronger on the leeward surface of the RW than that of the windward. It was further indicated that the fluctuating torque on the RW arm is well correlated with the surface pressure fluctuation on the shroud wall.
The present study aims at investigating details of turbulent fluid flow structure inside a hard disk drive. The measurements of fluctuating pressure are performed simultaneously at different locations on the inner surface of the shroud. The correlation between the signals taken at different locations indicate the existence of rotating vortex structure, which is in good agreement with the results of preceding numerical simulation which was conducted under the equivalent condition.