Yasunaga Mitsuya

Nagoya Municipal Industrial Research Institute, Nagoya, Aichi, Japan

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Publications (105)76.44 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The friction properties of nanometer-thick lubricant films are crucial in the reliability and durability of miniaturized moving mechanical components in micro- and nanoelectromechanical systems and hard disk drives. In this work, gas cluster ion beam treatments were applied to prepare smoothed glass sliding pins and diamond-like carbon (DLC) coated sliding pins for pin-on-disk friction tests to study the effect of the surface roughness and the DLC coating on the friction properties of perfluoropolyether (PFPE) films. The effect of the texture of the solid surface on the friction properties was also investigated. The friction properties were not exclusively determined by the surface energies of the solids. The friction coefficients of the nanometer-thick PFPE films, confined between solid surfaces were sensitive to the surface roughness of the solids. The friction coefficient generally increased with an increasing surface roughness (the composite standard deviation of the surface roughnesses of the pair of solid surfaces). This tendency was reversed when there was a strong longitudinal roughness effect at the contact interface. Moreover, the DLC-coated sliding pins had lower friction coefficients than the glass sliding pins, indicating that the friction properties were noticeably affected by the hardness and Young׳s modulus of the contact materials. The mechanisms for the effects of the surface roughness, surface texture and contact materials on the friction properties are discussed.
    Wear 11/2014; 319(s 1–2):56–61. · 1.26 Impact Factor
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    ABSTRACT: For micro/nanoscale devices, surface functionalization is essential to achieve function and performance superior to those that originate from the inherent bulk material properties. As a method of surface functionalization, we dip-coated nanometer-thick liquid lubricant films onto solid surfaces and then patterned the lubricant films with ultraviolet (UV) irradiation through a photomask. Surface topography, adhesion, and friction measurements demonstrated that the patterned films feature a concave–convex thickness distribution with thicker lubricant in the irradiated regions and a functional distribution with lower adhesion and friction in the irradiated convex regions. The pattern linewidth ranged from 100 to as fine as 0.5 μm. The surface functionalization effect of UV-patterning was investigated by measuring the water contact angles, surface energies, friction forces, and depletion of the patterned, as-dipped, and full UV-irradiated lubricant films. The full UV-irradiated lubricant film was hydrophobic with a water contact angle of 102.1°, and had lower surface energy, friction, and depletion than the as-dipped film, which was hydrophilic with a water contact angle of 80.7°. This demonstrates that UV irradiation substantially improves the surface and tribological properties of the nanometer-thick liquid lubricant films. The UV-patterned lubricant films exhibited superior surface and tribological properties than the as-dipped film. The water contact angle increased and the surface energy, friction, and depletion decreased as the pattern linewidth decreased. In particular, the 0.5-μm patterned lubricant film even showed a larger water contact angle and lower friction and depletion than the full UV-irradiated film. These indicate that UV-patterning of nanometer-thick lubricant films with a minimized linewidth has a better surface functionalization effect than full UV irradiation. Enhancement of the surface functionalization effect may be attributed to a transition in the contact state, which was indicated by the different instantaneous friction behavior of the 0.5-μm patterned lubricant film.
    Applied Surface Science 01/2014; 320:102–111. · 2.54 Impact Factor
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    ABSTRACT: Friction properties of nanometer-thick lubricant films confined between two ultra-smooth solid surfaces are crucial to the practical performance of technologically advanced mechanical devices such as micro-electro-mechanical systems and hard disk drives. In this work, we applied argon gas cluster ion beam (Ar-GCIB) treatments to obtain ultra-smooth sliding pins for pin-on-disk tests of nanometer-thick perfluoropolyether (PFPE) lubricant films coated on magnetic disk surfaces. The GCIB treatments effectively smoothed the pin surfaces, and increases in the Ar dose decreased surface roughness. An ultra-smooth surface with a maximum peak height (Rp) less the monolayer lubricant film thickness was achieved when the Ar dose was increased to 8 × 1016 ions/cm2. We observed that both surface roughness and film thickness affected the friction coefficients of the PFPE films. To quantitatively describe the interplay of surface roughness and film thickness, we introduced two roughness characteristics: the ratio of film thickness to the surface's root-mean-square roughness (h/σ), and a surface-pattern parameter (γ), defined as the ratio of correlation lengths in two orthogonal directions. We infer that a fixed γ and higher h/σlead to lower friction coefficients, while a fixed h/σand higher γ induce higher friction coefficients.
    Applied Surface Science 09/2013; · 2.54 Impact Factor
  • Takefumi Hayashi, Hideyo Yoshida, Yasunaga Mitsuya
    Journal of Tribology-transactions of The Asme - J TRIBOL-TRANS ASME. 01/2009; 131(2).
  • Source
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    ABSTRACT: Monolayer perfluoropolyether (PFPE) films used for lubrication of magnetic disks are generally dip-coated from the PFPE solutions diluted by fluorinated solvents. In this paper, under lightly loaded (0-1 mN) and slowly rotated (2.1 mm/s) conditions that suppress disturbance of PFPE films during sliding, we investigate the effect of solvents on the friction properties of monolayer PFPE films coated on magnetic disk surfaces. The solvents include HFE-7200 and Vertrel-XF. For polar Zdol2000 and Zdol4000 films, friction fluctuated during one revolution of the disk immediately after film deposition, but became stable with elapsed time. Such transient friction behavior was not observed for nonpolar Z03 films, suggesting that the friction fluctuations exhibited by Zdol2000 and Zdol4000 films result from PFPE microstructure (such as film uniformity and molecular conformation) induced by the polar end groups. Despite of the higher solvent power of Vertrel-XF, the friction fluctuations in the transient state were noticeable for the films applied with Vertrel-XF as compared with those applied with HFE-7200. However, because the friction fluctuations were characterized by intermittent decrease of friction in narrow and sparsely distributed regions, the average value of the friction measured during one revolution of the disk was almost not affected by the friction fluctuations and showed weak dependence on the solvent.
    IEEE Transactions on Magnetics 01/2009; 45(10):3632-3635. · 1.42 Impact Factor
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    ABSTRACT: Monolayer films of functional perfluoropolyethers (PFPEs) that are partially bonded to disk surfaces are widely used to lubricate magnetic disks. The bonding ratio (i.e., ratio of bonded thickness to total film thickness) possibly impacts the tribological behavior of the lubricant films. In this work, under lightly loaded (0-1 mN) and slowly rotated (1 or 2 r/min) conditions that prevent disturbance of the lubricant bonding state, we measured the frictional properties of 2-nm-thick PFPE Zdol2000 and Zdol4000 films as a function of bonding ratio adjusted up to 100% by anneal treatment. The friction forces of both Zdol2000 and Zdol4000 increased with increasing bonding ratio, but the increase was less noticeable for Zdol4000. Additionally, the friction of the nonannealed (5%-bonded) Zdol2000 films exhibited a linear increase with external load as described by Amontons' law, and it increased with sliding speed. In contrast, the friction of the 100%-bonded Zdol2000 films increased nonlinearly with external load as predicted by the Johnson-Kendall-Roberts (JKR) model, and it showed no obvious speed dependency. These results suggest that mobile molecules show liquid-like frictional properties dominated by viscosity resistance, but bonded molecules exhibit elastomer-like frictional properties determined by energy dissipation during molecule deformation.
    IEEE Transactions on Magnetics 12/2008; · 1.42 Impact Factor
  • Y. Mitsuya, H. Zhang, J. Ohgi, K. Fukuzawa
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    ABSTRACT: To ensure the reliability and durability of the head-disk interface of magnetic disk drives, the lubricant film flow coated on the disk surface has become a significant concern because it is related to recovery performance when the film is damaged. In this study, the replenishment characteristics of perfluoropolyether (PFPE) polar lubricant films after lubricant depletion induced by a glass ball sliding on the disk were clarified by measuring the profile changes of the lubricant film. Lightly loaded and slowly rotated test conditions were selected to avoid strongly disturbing the molecular layering structure. We found that the replenishment process dramatically changed with increasing film thickness, and recoverable and unrecoverable features appeared depending on the coated and residual film thicknesses. The replenishment process was compared with the step-boundary flow, i.e., the flow from the step-shaped lubricant boundary and the disjoining pressure distributions. The diffusion coefficients calculated from the step-boundary flow were found to be ineffective for replenishment flow, and the disjoining pressure differences between the coated and residual film thicknesses bifurcate the replenishment flow into recoverable and unrecoverable features.
    IEEE Transactions on Magnetics 12/2008; · 1.42 Impact Factor
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    ABSTRACT: An understanding of the viscoelastic properties of molecularly thin lubricant film is essential to clarify tribological issues of head-disk interface (HDI) in high-density recording hard disk drives. Characteristic conditions for the HDI occur when lubricant molecules are extremely confined in the gap between the head and the disk surfaces, and the surfaces slide at high speeds. The lower the flying height, the more this confinement affects the flying characteristics. However, a few attempts have been made at clarifying the dynamic viscoelastic properties of confined lubricant molecules. This is because a method of measuring the dynamic shear force has not yet been established. Fiber wobbling method enables us to measure the shear force with a detection limit of less than 1nN. Additionally, frequency of shear can be set at several kHz. Further, the gap which confines the lubricant is controlled with a resolution of 0.1nm. Using the FWM, we investigated the effect that confinement had on the dynamic viscoelastic properties of perfluoropolyether lubricants on a magnetic disk. We found that the viscosity started to increase at a gap width that was less than a few hundred nanometers, which is hundreds of times larger than the molecular size. On the other hand, elasticity suddenly appeared at a gap width that was less than a few nanometers, which is equivalent to a few molecular sizes. Both the viscosity and elasticity increased monotonically as the gap decreased.
    Tribology Letters 05/2008; 30(3):177-189. · 2.15 Impact Factor
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    ABSTRACT: We present a method for measuring head fly height in hard disk drives using phase comparison Michelson interferometry (PCMI), which compares the phases of two interference fringe patterns formed respectively on the inner surface of a glass disk and the air-bearing surface of a fly head slider through the glass disk. To suppress interference noise and further enhance measurement accuracy, we adopted a low-coherence light source as an illumination source to replace a high-coherence laser. The captured fringe images enabled us to extract ridge lines much more accurately than with a laser. We compared our measurements in the sub-10 nm spacing range with calculations and found excellent agreement.
    IEEE Transactions on Magnetics 03/2008; · 1.42 Impact Factor
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    ABSTRACT: We are developing an optical three-axis tactile sensor capable of acquiring normal and shearing force to mount on a robotic finger. The tactile sensor is based on the principle of an optical waveguide-type tactile sensor, which is composed of an acrylic hemispherical dome, a light source, an array of rubber sensing elements, and a CCD camera. The sensing element of the silicone rubber comprises one columnar feeler and eight conical feelers. The contact areas of the conical feelers, which maintain contact with the acrylic dome, detect the three-axis force applied to the tip of the sensing element. Normal and shearing forces are then calculated from integration and centroid displacement of the grayscale value derived from the conical feeler's contacts. To evaluate the present tactile sensor, we conducted a series of experiments using an x-z stage, a rotational stage, and a force gauge. Although we discovered that the relationship between the integrated grayscale value and normal force depends on the sensor's latitude on the hemispherical surface, it is easy to modify the sensitivity based on the latitude to make the centroid displacement of the grayscale value proportional to the shearing force. When we examined the repeatability of the present tactile sensor with 1,000 load/unload cycles, the error was 2%.
    Journal of Advanced Mechanical Design Systems and Manufacturing 01/2008; 2(5):860-873. · 0.49 Impact Factor
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    ABSTRACT: The authors developed advanced haptic displays capable of stimulating the muscles and tendons of the forearms and tactile receptors in fingers to investigate tactile and force effects on simultaneous presentation. Display A is comprised of a master hand with two sets of tactile display with a 4-by-6 array of stimulus pins driven by micro-actuators and an articulated manipulator. Display B is comprised of an articulated manipulator and an 8-by-8 array type tactile display developed in a previous paper. A series of experiments was performed using the above A and B displays to verify the presentation capability of this display type. In Experiment I, subjects grasped virtual pegs and judged their diameters. In Experiment II, subjects tried to insert the pegs into holes. In Experiment III, the crossed-angle of a comparison texture was adjusted to bring it as close as possible to the standard texture fixed during experiments. Since diameter discrimination and insertion precision of the virtual peg were increased by tactile information, tactile-force presentation was effective for peg-in-hole for relatively large clearance. On the other hand, recognition capability for virtual texture was not enhanced compared to a mouse-mounted tactile display previously developed. While the pressure display is effective for instant of touch and peg rotation representations, rotation tactile imaging is not always effective for texture recognitions.
    Journal of Advanced Mechanical Design Systems and Manufacturing 01/2008; 2(1):24-36. · 0.49 Impact Factor
  • Hedong Zhang, Yasunaga Mitsuya, Yuki Kudo, Kenji Fukuzawa
    Transactions of the Japan Society of Mechanical Engineers Series C. 01/2008; 74(740):970-977.
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    ABSTRACT: Using a coarse-grained molecular dynamics simulation based on the bead-spring polymer model, we reproduced the film distribution of molecularly thin lubricant films with polar end groups coated on the disk surface and quantified the film surface morphology using a molecular-probe scanning method. We found that the film surface morphology changed periodically with increasing the film thickness. The monolayer of a polar lubricant that entirely covers the solid surface provides a flat lubricant surface by exposing its nonpolar backbone outside of the monolayer. By increasing film thickness, the end beads aggregate to make clusters, and bulges form on the lubricant surface accompanying an increase in surface roughness. The bulges continue to grow up even though the averaged film thickness reaches or exceeds the bilayer thickness. With further increases in film thickness, the clusters start to be uniformly distributed in the lateral direction to clearly form a third layer. As for the formation of fourth-fifth layers, the process is basically the same as that for the second-third layers. Through our calculations of the intermolecular potential field and the intermolecular force field, these values are found to change periodically and are synchronized with the formation of molecule aggregations, which explains the mechanism of forming the layered structure that is inherent to a polar lubricant.
    Journal of Tribology-transactions of The Asme - J TRIBOL-TRANS ASME. 01/2008; 130(2).
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    ABSTRACT: Coarse-grained molecular dynamics (MD) simulations were applied to reproduce the surface morphology of lubricant films composed of perfluoropolyether (PFPE) Zdol and tri-functional PFPE, which has a functional group at the middle of a molecule as well as functional endgroups at the head and tail of the molecule. The molecular-mesh scanning method was introduced to detect the location of film surface. The effects of the number of polar groups and polymer length on a flat solid surface were studied as lubricant films with periodic boundary conditions. We clarified that the film surface of the tri-functional PFPE lubricant was smoother than Zdol 2000 when compared at the same film thickness condition.
    Micro-NanoMechatronics and Human Science, 2007. MHS '07. International Symposium on; 12/2007
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    ABSTRACT: We experimentally design a parallel typed two-axial micro actuator, which is utilized for the key part of the tactile display. The parallel typed two-axial actuator was composed of two bimorph piezoelectric elements and two small links connected by three joints. We formulated kinematics for the parallel typed two-axial actuator because the endpoint is controlled in the two-dimensional coordinate. Since relationship between applied voltage and displacement cause by the voltage shows a hysteresis loop in the bimorph piezoelectric element used as components of the two-axial actuator, we produce a control system for the two-axial actuator based on a multi-layered artificial neural network to compensate the hysteresis. The neural network is comprised of 4 neurons in the input layer, 10 neurons in the hidden layer and ones neuron in the output layer. The output neuron emits time derivative of voltage; two bits signal expressing increment or decrement condition is generated by two input neurons; one of the other two input neurons and the other calculate current values of voltage and displacement, respectively. The neural network is featured with a feedback loop including an integral element to reduce number of neurons. In the learning process, the network learns the hysteresis including a minor loop. In the verification test, the endpoint of the two-axial actuator traces the desired circular trajectory in the two-dimensional coordinate system.
    Micro-NanoMechatronics and Human Science, 2007. MHS '07. International Symposium on; 12/2007
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    ABSTRACT: In object handing, a robot should decide proper grasping force on the basis of the hardness of an object and the degree of surface slipperiness, which are estimated by three-axis tactile sensors mounted on its fingers. In the present paper, we produce a tactile sensor based on the principle of an optical waveguide-type tactile sensor, which is composed of an acrylic hemispherical dome, a light source, an array of rubber sensing elements, and a CCD camera. The sensing element of silicone rubber comprises one columnar feeler and eight conical feelers. The contact areas of the conical feelers, which maintain contact with the acrylic dome, detect the three-axis force applied to the tip of the sensing element. Normal and shearing forces are then calculated from integration and centroid displacement of the gray-scale value derived from the conical feeler's contacts. Two three-axis tactile sensors are mounted on the fingers of a three-joint articulated two-finger robotic hand. In the grasping tests, the robotic hand measures the hardness of an object to decide the proper grasping force before trying to move it. The robotic hand can move not only a hard aluminum block but also an easily crushed paper box.
    Proceedings of the 13th IASTED International Conference on Robotics and Applications; 08/2007
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    ABSTRACT: A coarse-grained molecular dynamics simulation of the spreading of monolayer lubricant films on magnetic disks is presented. The simulated diffusion coefficient for various coverages of the bonded molecules was in good agreement with that obtained by an experiment using the half-dip method. The simulated relation between the coverage and bonding ratio was also in good agreement with the experimental one
    IEEE Transactions on Magnetics 07/2007; · 1.42 Impact Factor
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    ABSTRACT: To obtain specifications for a tactile display that would be effective in virtual reality and tele-existence systems, we have developed two types of matrix-type experimental tactile displays. One is for virtual figures (display A) and the other is for virtual textures (display B). Display A’s pad has a 4 × 6 array of stimulus pins, each 0.8 mm in diameter. Three pad configurations, in which distances between any two adjacent pins (pin pitch) are 1.2, 1.9, or 2.5 mm, were developed to examine the influence of distance on a human operator’s determination of virtual figures. Display B has an 8×8 array of stimulus pins, each 0.3 mm in diameter and with 1- or 1.8-mm pin pitch, because presentation of virtual textures was presumed to require a higher pin density. To establish a design method for these matrix-type tactile displays, we performed a series of psychophysical experiments using displays A and B. By evaluating variations in the correct answer percentage and threshold caused by different pin arrays and different pin strokes, we determined under what conditions the operator could best feel the virtual figures and textures. The results revealed that the two-point threshold should be adopted as the pitch between pins in the design of the tactile display, that a pin stroke should exceed 0.25 mm, and that the adjustment method is the most appropriate to evaluate the capabilities of tactile displays. Finally, when we compared the virtual texture with the real texture, we found that the threshold for the real texture is almost 1/3rd that of the virtual texture. This result implies that it is effective to present variations in patterns caused by rotation and variation in shearing force, itself produced by relative motion between the finger surface and object surface. Robotica. v.25, n.4, 2007, p.451-460
    Robotica 07/2007; · 0.88 Impact Factor
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    ABSTRACT: This article presents measurements of adhesion and friction of perfluoropolyether (PFPE) lubricant films dip-coated on magnetic disks covered with diamond-like carbon (DLC) film. We have developed a custom-built pin-on-disk type micro-tribotester to perform the tribological measurements. The adhesion tests were performed by pulling down/up a 1.5-mm-diameter glass ball on a stationary disk surface, and the friction tests were carried out by sliding the glass ball on a rotating disk surface without changing head-disk interface conditions from the adhesion tests. Experiments were performed for the different kinds of 2- and 6-nm-thick PFPE lubricants (polar: Zdol4000 and Zdol2000; nonpolar: Z03) under lightly loaded and slow sliding conditions to minimize disturbance against the molecular layered structure. The adhesive forces were found to decrease with increasing film thickness in the order of Z03>Zdol2000>Zdol4000 (decreasing rate), which closely corresponds to the order of monolayer thickness, and then to saturate to almost the same calculated values. As for the friction forces of 2-nm-thick films, Zdol2000 featured extraordinarily large friction in comparison with Zdol4000 and Z03, while Zdol4000 was slightly larger than Z03. The largest friction of Zdol2000 reveals that the 2-nm-thick Zdol2000 formed a monolayer that served as an immobile layer. With the increase in film thickness, the friction force of Zdol2000 decreased, indicating that extra lubricant molecules served as a mobile layer, while that of Z03 remained unchanged as the lowest value. By extrapolating the loading force versus friction force relationship into a negative loading force region, it is found that the friction force of Z03 tended to zero at zero net load (loading force plus adhesion force), while those for Zdol2000 and Zdol4000 exhibited finite values, indicating formation of an immobile layer, which shows similar characteristics to those of adhesive rubber material. The dewetted surface is found to feature violently changing friction force only at the first stage of sliding, and it then becomes stable after several sliding passes.
    Tribology Letters 06/2007; 27(1):1-11. · 2.15 Impact Factor
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    ABSTRACT: Characteristics of molecularly thin lubricant films are basically determined by their interactions with solid surfaces. Since these interactions can be modified by engineered microscopic surface textures, it is expected that rational design of the textures will make it possible to attain desired tribological functions and performance. In this research, with the aim of applying it to head-disk interface of hard disk drives, we propose a method based on diffraction simulations that enables thickness measurement of molecularly thin films coated on grooved solid surfaces. Using this method, we experimentally investigate the spreading characteristics of nanometer-thick polymeric liquid lubricant films on grooved surfaces. The results revealed that the average thicknesses of the films dip-coated on the grooved and smooth surfaces under identical conditions were approximately the same, whereas lubricant spreading on grooved surfaces was significantly faster than that on smooth surfaces.
    Microsystem Technologies 04/2007; 13(8):895-904. · 0.83 Impact Factor

Publication Stats

378 Citations
76.44 Total Impact Points

Institutions

  • 2014
    • Nagoya Municipal Industrial Research Institute
      Nagoya, Aichi, Japan
  • 1996–2008
    • Nagoya University
      • • Department of Micro-Nano Systems Engineering
      • • Department of Mechanical Science and Engineering
      Nagoya-shi, Aichi-ken, Japan