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Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

DOI： 10.2474/trol.17.110

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/jamdsm.2022jamdsm0010

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Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

DOI： 10.2474/trol.16.309

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s11249-021-01482-2

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Other Link： https://link.springer.com/article/10.1007/s11249-021-01482-2/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media Deutschland GmbH  

The formation of head smears during the heat-assisted magnetic recording is a significant problem that must be addressed to ensure the reliability of the head-disk interface. In this study, the formation of a head smear by diamond-like carbon (DLC) films on magnetic disks was analyzed through simulated heating experiments. DLC films with a thickness of 100 nm were prepared and heated on a hot plate in an environmental gas chamber. A smear was observed on a silicon wafer placed 3 mm above the DLC surface film after the heating of the film. The smear amount was quantified based on the intensity of the carbon peak of the smear, which was measured by X-ray photoelectron spectroscopy. In air, the carbon concentration decreased with the heating temperature, while in nitrogen, it increased. Further, the carbon concentration of the smear formed in air was lower than that in nitrogen. A comparison of the smears formed by DLC films with different hydrogen concentrations showed that a greater amount of the decomposition gases was generated from the DLC films with a higher hydrogen concentration and that this value increased at lower temperatures. This result suggests that DLC films with low hydrogen concentrations generate smaller amounts of the decomposition gases during heating than those with high hydrogen concentrations. In addition, the results of Raman spectroscopy suggested that the DLC films get degraded during heating, resulting in the generation of hydrocarbon gases because the films contain carbon and hydrogen. Moreover, since peaks related to fragments with atomic masses of 250–500 atomic mass units were observed in the time-of-flight secondary ion mass spectrometry spectra of the smears, it can be concluded that the smears consist of hydrocarbons with relatively higher molecular weights.

DOI： 10.1007/s00542-020-05041-y

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/tmag.2020.3012979

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Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

DOI： 10.1080/10402004.2020.1815919

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Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

DOI： 10.2474/trol.17.32

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society of Mechanical Engineers (ASME)  

We propose a novel electromagnetic energy-harvesting device (EHD) for structural health monitoring systems of transportation infrastructures. The EHD is embedded in the road surface and uses the tread force of cars as the input force when tires of cars pass over it. Because the input force is very fast, the proposed EHD can generate a large amount of energy. The footprint of the device is 20× 20 mm, its height is 7.5 mm, and its volume is 2.4 cm3. We measured the energy generated when a bicycle passed over the EHD 34 times at various speeds between 5 and 15 km/h. Subsequently, we obtained the regression curve from the results, which showed the relationship between the bicycle speed and generated energy, and estimated the electric energy generated by car at higher speeds. The results showed that, even though the size of the EHD was small, electric energies of 100 ?J, and 1.0 mJ could be generated at car speeds of 17 km/h, and 52 km/h, respectively.

DOI： 10.1115/ISPS2021-63672

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society of Mechanical Engineers (ASME)  

In this study, the dependence of the electric field between the magnetic disk and Si wafer, used as the counter surface, on the hydrocarbon smear generated from the diamond-like carbon (DLC) overcoat was investigated. As a result, the positive electric field from the disk to the Si wafer increased the amount of smear, and the negative field reduced it. The positive electric field was estimated to extract hydrocarbon ions from the thermal plasma toward the Si wafer, and the opposite field attracts the hydrocarbon ions to the DLC surface. Therefore, the electric field between the slider and disk possibly controls the smear generation from the DLC overcoat, which is heated by laser irradiation in the heat-assisted magnetic recording).

DOI： 10.1115/ISPS2021-63202

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00542-020-04806-9

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Other Link： http://link.springer.com/article/10.1007/s00542-020-04806-9/fulltext.html

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/sensors47125.2020.9278840

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s11249-020-01333-6

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Other Link： https://link.springer.com/article/10.1007/s11249-020-01333-6/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：MYU K.K.  

DOI： 10.18494/sam.2020.2827

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Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

DOI： 10.2474/trol.15.186

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00542-018-4259-6

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Other Link： http://link.springer.com/article/10.1007/s00542-018-4259-6/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00542-019-04447-7

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Other Link： http://link.springer.com/article/10.1007/s00542-019-04447-7/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00542-019-04398-z

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Other Link： http://link.springer.com/article/10.1007/s00542-019-04398-z/fulltext.html

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society of Mechanical Engineers (ASME)  

The formation of head smear from DLC films on magnetic disks was confirmed by a simulated heating experiment. DLC films of 100-nm thickness were prepared and heated on a hot plate in an environmental gas chamber. Smear on a silicon wafer placed 3 mm above the DLC surface was observed after heating of the DLC film. The smear amount was quantified using the carbon intensity of the smear measured by XPS. In air, the carbon concentration decreased with the heating temperature
however, the carbon concentration increased with temperature in nitrogen. The carbon concentration of the smear in the air environment was smaller than that of nitrogen. As the result of comparison of smears on DLCs with various hydrogen concentrations, more decomposed gas is generated from the DLC film as the amount of hydrogen contained in the DLC increases, and this value increases at lower temperatures. This result suggests that DLC films with low hydrogen concentrations generate a smaller amount of decomposition gas than those with high hydrogen concentrations during heating. In addition, Raman spectra suggest that the DLC degraded by heating and the hydrocarbon gas-like materials were generated from the DLC film because the DLC films include carbon and hydrogen. Because fragments of 250–500 atomic mass units were observed in the TOF-SIMS spectra of smears, the smear is estimated to consist of a hydrocarbon of relatively high molecular weight.

DOI： 10.1115/ISPS2020-1902

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Lubricants that are used in miniaturized moving mechanical components generally serve under severe conditions, such as high temperature, high speed, and high load. Although alkyldiphenylethers (ADEs) are used as base oils for high-temperature greases, their tribological properties remain unclear. This study investigated the influence of the alkyl chains on the tribological properties of ADEs. Longer and more attached alkyl chains decreased the friction coecient of ADEs under both reciprocating and continuous sliding conditions. Wear was found to be independent of the alkyl chain under reciprocating sliding conditions due to abrasion being caused by debris that was not readily removed. ADEs showed good anti-wear properties when used as either a lubricant or an additive under continuous sliding conditions. Much smoother surfaces in the friction track were observed in comparison to poly--olefin. Fourier-Transform infrared spectroscopy analysis suggested that the ether groups were attracted to the worn steel surface, phenyl groups became consequently perpendicular, and the attached alkyl chains repelled other substances and prevented further wear of the surface. Moreover, ADEs showed a high adaptability with traditional additives.

DOI： 10.3390/LUBRICANTS7120112

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

In this study, we developed the new deposition method of Perfluoropolyether(PFPE) lubricant on diamond like carbon(DLC) overcoat by the photoelectron assisted chemical vapor deposition(PAcvd).Pfpe lubricant in vapor phase was deposited on DLC surface of magnetic disks with a RF pulse bias voltage between a disk surface and a counter electrode above disk surface during the ultra violet(UV) irradiation. Then, we evaluated the thermal stability for the laser beam heating and the corrosion resistance of magnetic disks with lubricant film deposited by PACVD. These disks showed higher thermal stability and high corrosion resistance than Z-tetraol lubricant film, because the lubricant film deposited by PACVD has no hydrocarbon segment in the molecular structure and has much high water repellency.

DOI： 10.1109/APMRC.2018.8601076

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Czech Scientific Society for Mycology  

Lubricants that are used in miniaturized moving mechanical components generally serve under severe conditions, such as high temperature, high speed, and high load. Although alkyldiphenylethers (ADEs) are used as base oils for high-temperature greases, their tribological properties remain unclear. This study investigated the influence of the alkyl chains on the tribological properties of ADEs. Longer and more attached alkyl chains decreased the friction coefficient of ADEs under both reciprocating and continuous sliding conditions. Wear was found to be independent of the alkyl chain under reciprocating sliding conditions due to abrasion being caused by debris that was not readily removed. ADEs showed good anti-wear properties when used as either a lubricant or an additive under continuous sliding conditions. Much smoother surfaces in the friction track were observed in comparison to poly-α-olefin. Fourier-Transform infrared spectroscopy analysis suggested that the ether groups were attracted to the worn steel surface, phenyl groups became consequently perpendicular, and the attached alkyl chains repelled other substances and prevented further wear of the surface. Moreover, ADEs showed a high adaptability with traditional additives.

DOI： 10.3390/lubricants7120

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Pleiades Publishing  

Because the diamond-like carbon (DLC) thin film overcoat on either a hard disk surface or an air bearing surface plays an important role in maintaining the reliability and durability of the head-disk interface, nanoscale DLC wear and degradation is a critical issue in heat-assisted magnetic recording (HAMR). The use of helium in hard disk drives (HDDs) has been developed and put into practical use to decrease air-induced structural vibrations, and temperature rise. In this study, fundamental experiments were conducted to understand the wear and related degradation characteristics of an ultra-thin DLC overcoat subjected to laser heating in both air and inert gas environments, using a pin-on-disk tester. An inert gas environment was simulated using helium gas. The experiments were conducted using DLC-coated glass pins and actual magnetic disks without a lubricant film. The differences in the wear and degradation characteristics of a DLC overcoat on the pin and disk surfaces between inert gas and air environments were investigated after wear tests were performed, primarily through Raman spectroscopy. We found that wear and graphitization of DLC films became greater with laser heating, while the friction coefficients between the pin and magnetic disk became markedly smaller. However, our tests also revealed that wear and graphitization of the DLC film were significantly less in an inert gas environment than in an air environment. This is because the wear observed in this experiment was predominantly due to a wear mechanism that is based on tribo-chemical oxidation.

DOI： 10.1007/978-981-13-0411-8_62

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Vytautas Magnus University  

We investigated the smear characteristics upon laser heating in air and helium. We used magnetic disks coated with the perfluoropolyether (PFPE) lubricant D-4OH. The surface of the rotating disk was heated by laser irradiation using a pin-on-disk tester setup in a sealed chamber. The temperature was varied from 258°C to 540°C. When the lubricant film was heated by the laser, the lubricant evaporated from the surface of the disk by desorption or decomposition and adhered onto a hemispherical glass pin placed 5 μm above the disk surface as smears. The smears on the pin were analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS). It was found that the amount of smear under exposure to helium gas is greater than that to air at high temperatures. In addition, this interesting result may be attributed not only to the different lubricant depletion mechanisms due to laser heating under the two environmental conditions, but also to the diamond-like carbon (DLC) thin film at a relatively low temperature of approximately 260°C.

DOI： 10.15544/balttrib.2019.44

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

The lotus and taro leaf surfaces are superhydrophobic. We fabricated different surface patterns of lotus and taro leaves on Si surfaces and compared their contact angles and tribological properties. Three types of lotus patterns, consisting of a simple dot matrix of circular pillars with different pitches, and six types of taro patterns having the pillars distributed within a field of hexagonal ridges with different central pillar diameters and pitches, were prepared. The contact angles of water and hexadecane on these patterns were measured, and the wear resistance of each pattern was evaluated by reciprocating wear tests. The taro pattern showed a significantly higher contact angle for hexadecane and a lower coefficient of friction than the lotus pattern. The taro pattern ridges are supposed to contain air in the valleys between the ridges and pillars, which prevented sticking between the pillars and cloth fibers. Thus, the taro pattern exhibits better oleophobicity and a lower frictional force.

DOI： 10.2474/trol.13.311

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Verlag  

In this study, fundamental experiments were conducted to understand the wear and related degradation characteristics of an ultra-thin DLC overcoat subjected to laser heating in an air environment, using a pin-on-disk tester. The experiments were conducted using DLC-coated glass pins and actual magnetic disks without a lubricant film. The differences in the wear and degradation characteristics of a DLC overcoat on the pin and disk surfaces, both with and without laser heating, were investigated after wear tests were performed, primarily through Raman spectroscopy. We found that the wear on DLC films became greater with laser heating, while the friction coefficients between the pin and magnetic disk became markedly smaller. This is because the wear observed in this experiment was predominantly due to a wear mechanism that is based on tribo-chemical oxidation.

DOI： 10.1007/s00542-018-3875-5

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Other Link： http://link.springer.com/content/pdf/10.1007/s00542-018-3875-5.pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Verlag  

In this study, the smear by the lubricant and siloxane pickup at the laser heating in the heat assisted magnetic recording (HAMR) was evaluated using our developed noncontact pin-on-disk test. The smear area on the glass pin surface was measured on the disks with three types of different lubricant films prepared by changing the ultraviolet exposure condition, rinse condition, and lubrication process. The amount of siloxane adsorbed on disk surface relates with the siloxane wettability obtained from the contact angle of siloxane for disk surface and that increased as the siloxane wettability increases. On the other hand, the lubricant pickup increases as the physical and hydrogen bonding fractions increase. Overall, these data suggest that the sufficiently low surface free energy is needed by the lubricant film with only the chemical bonding fraction to reduce the lubricant and siloxane smear at the laser heating of HAMR, because the lubricant fractions of physical and hydrogen bonding increase the lubricant pickup and the much amount of siloxane adsorbs on disks with the large surface free energy.

DOI： 10.1007/s00542-018-3839-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

This paper examines the adsorption properties of the perfluoropolyether (PFPE) lubricant SNH2 with an ionic end-group (i.e., amine salt with a diphenylether moiety) for magnetic disk surfaces in heat-assisted magnetic recording (HAMR) drives. For comparison, the well-known lubricant Z-tetraol was used as a reference material. Initially, strong interactions between the ionic end-groups of SNH2 and an applied electric field in the lubricant solution were established. The surface free energy and bonding ratio were also compared before and after ultraviolet (UV) light exposure to diamond-like carbon (DLC) disk surfaces onto, which the lubricants were coated, with their photoelectron currents measured during UV exposure. In addition, the structural characteristics of the SNH2 lubricant on the DLC surface were analyzed using a time-of-flight secondary mass spectroscopy. Furthermore, the thermal stabilities of the lubricant films were compared following laser heating. Overall, SNH2 showed higher adsorption to the DLC surface than Z-tetraol and interacted more strongly with the electric field in the lubricant solution. Furthermore, although SNH2 without UV exposure showed a large polar surface energy, this energy decreased considerably after UV exposure. This decrease is attributed to interactions between photoelectrons emitted from the DLC surface and the ionic bonds of the SNH2 molecules
the cationic segments of the SNH2 ionic bonds dissociate, whereas the anionic main-chains chemisorb on the DLC surface at the electron holes generated from the ejected photoelectrons. SNH2 after the UV exposure showed high thermal stability because of its strong bonding to the DLC surface. Overall, these results demonstrate that a PFPE lubricant with ionic end-groups may be an effective lubricant for HAMR applications.

DOI： 10.1109/TMAG.2017.2724038

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DOI： 10.2474/trol.13.157

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DOI： 10.1109/TMAG.2018.2835839

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

The tribocharge sensor to monitor the rotational speed and the temperature of ball bearing was fabricated and we studied the basic feasibility this tribocharge sensor. The tribocharge sensor was built up by the segmented electrode on rotor, the segmented electrode on stator. Electrode material is Cu of 35 μm thick and the material of base film is polyirude of 25 μm thick, This sensor was attached on the side on the ball bearing. This tribocharge sensor outputted the pulse voltage from the stator electrode. The output voltage was proportional to the rotational speed of ball bearing. The generated electric power was 0.2 μW at 2000 rpm, however, the electric power of 20 μW was expected by the reduction of PFTE film thic mess. On the other hand, the temperature of ball bearing was estimated by the envelope of negative voltage from the tribocharge sensor, and the estimated temperature approximately agreed with the temperature estimated by the friction force.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：euspen  

It is expected that, in the future, quadrotor helicopters (quadcopters) will be employed in many applications, several of which require the quadcopters to be extremely small. However, it is difficult for smaller quadcopters to achieve a sufficient lift force for flight because, with reduction in the propeller diameter, the lift force decreases more sharply than the mass does. To miniaturize flying robots, we developed a flapping-flight robot employing self-excited vibration based on dry friction, inspired by the flight mechanism of bees. The proposed structure uses a simple DC motor and is easy to control
a large flapping angle can be obtained by operating at the resonant frequency using dry friction-based self-excited vibration with robustness. The designed flapping-flight robot is similar to a hornet in size with a body length of 5.4 mm and wingspan of 57.2 mm
it weighs 970 mg, including the weight of a motor and battery.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society of Mechanical Engineers (ASME)  

The structural and molecular weight changes to lubricant picked up following laser heating in heat-assisted magnetic recording (HAMR) were analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The intensity of the ion mass fragments depended on the decomposition pathways and changed drastically, as did the average molecular weight of the picked-up lubricant as heating temperature increased. The fragment series formed by the dissociation of end groups with low molecular weights (CH3O+) showed a high intensity at temperatures under 300 °C, whereas at temperatures over 400 °C, the fragments series formed by the dissociation of the end-group component (C5H9O4F2+) increased. Overall, the results presented herein suggest that the chemical and thermal stability of the hydrocarbon terminal ends of lubricants should be improved in order to decrease depletion of the lubricant film and lubricant pickup by laser heating in HAMR.

DOI： 10.1115/ISPS-MIPE2018-8515

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We investigated the laser-heating-temperature dependence of the friction characteristics of magnetic disks coated with boundary lubricant films by using a pin-on-disk tester and discussed the fundamental characteristics observed. In the contact area of the glass pin and disk, we observed the area that showed a buildup and depletion of the lubricant film thickness. The amount of buildup and depletion increased with increasing heating temperature. It was found that the friction coefficient of each lubricant film initially decreased as the temperature increased. Thereafter, the minimum value of the friction coefficient of each test lubricant occurred at a specific temperature, resulting in an increase in the friction coefficient inversely as the temperature further increased. It was suggested that the specific temperature corresponds to the transition temperature at which the test lubricant film evaporates. In addition, it was also suggested that the thermal durability of the lubricant film improved because of ultraviolet treatment.

DOI： 10.1109/TMAG.2017.2697478

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Molecular alignment is key to achieving an ultra-low friction coefficient. We prepared associated carboxylic acids using oleic acid and p-pentylbenzoic acid via hydrogen bonding, involving a benzene ring and an eight-membered cyclic carboxylic acid in the molecules. We investigated frictional properties when these were added into a base oil and found that the associated carboxylic acids decreased the traction coefficient in EHL and boundary lubrication, although the viscosity increased. An in situ micro Fourier transform infrared spectroscope showed that both the eight-membered cyclic carboxylic acid and the benzene ring were oriented parallel to the shearing force, leading to the low friction coefficient.

DOI： 10.1016/j.triboint.2016.10.042

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Viscoelastic (VE) materials are widely used in daily life. For the effective utilization of VE materials, it is necessary to know their viscoelasticity with accuracy over a wide range of frequencies, especially for high frequencies. Currently, the viscoelasticity of solid-state materials is directly measured only in the low-frequency range; for high frequencies, it is estimated based on the time-temperature superposition (TTS) principle. However, it is generally recognized that the TTS principle is suitable only for estimating the viscoelasticity of rheologically simple materials for temperatures within a limited range that is higher than the glass-transition temperature. In this paper, we propose a device that can directly measure the shear modulus and tan delta values of solid-state VE materials at high frequencies. We also propose a method for compensating for the shear deformation mode resonance of VE materials based on the mass of the moving part, to gain a more accurate understanding of viscoelasticity in the high-frequency range, and discuss the causes of errors in the compensation method. Finally, we report the VE properties of natural rubber (NR 65 IRHD) measured using the developed device and compensation method, and compare the measured results with those obtained using commercial VE measurement equipment.

DOI： 10.1007/s00397-017-1010-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We developed a new method for using photoelectron-assisted chemical vapor deposition to deposit perfluoropolyether (PFPE) lubricant on a diamond-like carbon (DLC) overcoat. PFPE lubricant in the vapor phase was deposited on the DLC surface of a magnetic disk with a bias voltage between the disk surface and a counter electrode above the disk surface during ultraviolet irradiation. The bias voltage accelerated photoelectron emission from the DLC surface, and the photoelectrons partially dissociated the PFPE molecules in the vapor phase. The dissociated molecules then chemically bonded to the DLC surface. According to the experimental results, the bonded ratio of PFPE molecules to the DLC surface was approximately 100%. An ultrathin PFPE/DLC hybrid overcoat was produced as a monolithic film. This hybrid film exhibited a much lower surface energy than the reference Z-tetraol lubricant film and a high water contact angle of over 100 degrees. This hybrid film can increase the head-media clearance and improve some read/write characteristics by using the actual heads.

DOI： 10.1109/TMAG.2016.2626297

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To further increase recording density of disk storage drives, the heat assisted magnetic recording (HAMR) can solve the coercive force problem of thermal fluctuation and is regarded as the key technology for achieving recording density of more than 1Tb/in^{2 (1)(2)}. In this technology, it is suggested that there are serious issues for the diamond like carbon (DLC) overcoat on the disk surface. Because that is heated to high temperature with laser beams⁽²⁾. In this study, first, we measured temperature dependence of friction properties of non-lubricated DLC surface on magnetic disks. Second, we considered the influence of the accumulated smear on test pin surface during the friction test. As a result, it was estimated that the smear on pin surface accumulated by the laser irradiation was originated from the hydrocarbon contamination adsorbed on DLC surface.

DOI： 10.1299/jsmeiip.2017.A-12

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In recent years, the information society rapidly developed. It is required to increase density of hard disk drives （HDDs）. In order to achieve the high density HDDs, it is important to research details of magnetic disk surface and some properties related with the head-disk interface. However, diamond like carbon (DLC) film on disks have been too thin to analyze chemical structure of DLC surface using Raman spectroscopy. In this study, we fabricated the plasmon lens with the sliver thin film on the surface by the vapor deposition and evaluated the structure change of ultra-thin DLC after laser-heating using surface enhanced Raman spectroscopy with the plasmon lens.

DOI： 10.1299/jsmeiip.2017.H-01

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>PFPE/DLC hybrid overcoat was deposited by the photoelectron assisted CVD (PACVD) with RF pulse bias voltage. The properties of PFPE film on DLC surface deposited by PACVD was compared with those by the CVD with the glow discharge plasma. The deposition rate of PACVD was much lower than that of the glow discharge plasma. The surface energy of PFPE films by PACVD was approximately 15 mJ/m² and that by the glow discharge plasma was 50 mJ/m², and the estimated monolayer thickness of PFPE film deposited by PACVD was 7−8 Å. The PFPE film deposited by PACVD had much CF₂ structure at the surface, however, that deposited by the glow discharge plasma had much COO and CF structures. From these results, we estimated that the glow discharge plasma much dissociated the chemical structure of monomer PFPE gas molecules as precursor and the deposited film could not show low surface energy.</p>

DOI： 10.1299/jsmeiip.2017.A-08

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

Siloxane outgas is well known to cause smears on magnetic head sliders. Siloxane outgas is vaporized from certain components in hard disk drives (HDDs), that adsorbs on the magnetic disk surfaces, and SiO2 that is denatured from siloxane by flash temperature at a slider and disk contact gets accumulated on the slider surface. On the other hand, heat assisted magnetic recording (HAMR) is being developed to improve areal density. In HAMR, a laser light heats the magnetic disk surface to 400-500 K. Siloxane adsorbed on a disk surface easily gets desorbed from the disk surface owing to thermal evaporation and dissociation by laser heating. In this study, we have studied smear growth from siloxane outgas on laser heating. We observe that the siloxane adsorbed on the disk surface grew on the glass surface above the disk surface at the laser heating spot.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>To increase HDD capacity, the thickness of lubricant film on the magnetic disks need to be reduced. The lubricant film deposited by using the photoelectron assisted chemical vapor deposition (PACVD) with low molecular weight perfluoropolyether (PFPE) lubricant showed high bond ratio, low surface energy and high coverage. In this study, we compared the tribological performances on head-disk interface of PFPE lubricant films deposited by PACVD with DC bias voltage and RF pulse bias voltage. As the result, the lubricant film deposited by DC and RF pulse voltage showed very high touch down power (TDP). In addition, the lubricant film deposited by RF pulse voltage showed low slider wear.</p>

DOI： 10.1299/jsmeiip.2017.A-09

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Language：Japanese   Publisher：Japanese Society of Tribologists  

The contact type of tribocharge power generator was developed. This tribocharge power generator has a simple structure which two types of tribocharging films on electrode are laminated by silicon rubbers. That generated the volume density of electric power of 94 μW/cm³ under the condition of 40 Hz, 2 G, and 55 kPa. As the results, we confirmed that the tribocharge power generator was useful for the energy harvesting and sensing the acceleration.

DOI： 10.18914/tribologist.17-00015

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

The thermal decomposition of D-4OH lubricant thin film on an actual air-bearing surface under heating conditions was investigated using time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The substrates used in this experiment are those of actual magnetic head sliders with diamond-like carbon (DLC) thin-film coatings. Two kinds of surfaces were prepared
an undisturbed DLC thin-film surface and an AhO3 surface exposed by sputtering of the DLC thin film. Comparison of the changes in the positive mass spectra due to heating confirmed that thermal decomposition of the D-4OH lubricant thin-film occurred and that it could be accelerated by the catalysis of Al2O3 at heating temperatures below 150°C. This is despite the fact that the D-4OH lubricant thin-film on the undisturbed DLC thin-film surface did not decompose.

DOI： 10.1109/APMRC.2016.7524262

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this paper, we focused on the diamagnetism of grease oil for pivot bearings in hard disk drives (HDDs) and investigated the effect of a magnetic field on oil vapors. We vaporized the grease oil and compared the amounts of oil adsorbed on disk surfaces through two slits-one with magnets and the other without-in a preliminary experiment. As a result, we confirmed that it is possible to reduce the amount of oil adsorbed on a disk surface with the aid of a magnetic field. Based on the preliminary experiment, the grease oil vapor from the pivot bearing unit of HDDs was compared with regard to a narrow slit and clearance with and without the magnetic field gradient of permanent magnets. The amount of oil vapor was decreased by the magnetic field gradient, and the reduction ratio depended on the environmental temperature. The amount of oil vapor from the actual pivot bearing unit could be reduced by the ring magnet around the pivot unit. Finally, our results suggested the possibility of a gas seal generated by the magnetic field gradient for the pivot bearing unit in HDDs.

DOI： 10.1109/TMAG.2015.2511740

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

We studied the effect of bias voltage between slider and disk surfaces to reduce lubricant pickup by the slider. A perfluoropolyether (PFPE) lubricant film, which is coated on the disk surface, has been considered to be charged to a negative voltage by the airflow on the rotational disk surface. Because the PFPE lubricant film is negatively charged, the lubricant pickup should be reduced by a bias voltage with a negative voltage on the slider surface. We confirmed changes in the lubricant pickup in a lubricant pickup test conducted at different bias voltages. A positive voltage of the slider accelerated the lubricant pickup, whereas a negative voltage reduced it.

DOI： 10.1007/s00542-016-2814-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

Our previous study confirmed that the photo-electron-assisted ultraviolet (UV) irradiation with a bias voltage between the magnetic disk and the counter electrode above the disk surface increased the bonded ratio of a perfluoropolyether lubricant film on the disk surface. In this study, two types of lubricant materials (Fomblin Z-tetraol and Moresco ADOH) were prepared and coated on disks. After coating the lubricant films, UV irradiation of the lubricated disk surface was performed using the normal process and the photoelectron-assisted process, and the depletions of these lubricant films were compared using the pin-on-disk test with the laser heating function. The results showed that the lubricant film treated with normal UV irradiation without the bias voltage showed a deeper depletion of the lubricant film than that treated with photo-electron-assisted UV irradiation, and the ADOH film showed a shallower depletion than the Z-tetraol film. However, the molecular weight distributions of the ADOH films on DLC surfaces treated by UV irradiation were compared using time-of-flight secondary ion mass spectroscopy, and the film treated with photoelectron-assisted UV irradiation did not change owing to dissociation after photoelectron capture. Photoelectron-assisted UV irradiation led to the decomposition of the cyclo-triphosphazene end groups. Therefore, it is assumed that the depletion of lubricant films treated with photoelectron-assisted UV irradiation was reduced, since the bonding strength to the DLC surface increased because of the greater decomposition of end groups.

DOI： 10.1007/s11249-016-0668-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

A large skew angle in a hard disk drive (HDD) adversely affects the flying stability of the head sliders and the off-track capability of the read/write head. A novel actuator in the form of a separated pivot-shaft actuator (SPA) with a small skew angle is proposed in this paper. The SPA was particularly designed for a four-disk 3.5-in. HDD and has a skew angle of +/- 1.6A degrees, which is approximately one-tenth of that of a conventional voice coil motor. The SPA was numerically analyzed by a finite element method, and its mechanical characteristics were compared with those of a long-arm actuator (LAA) (which is a strong candidate for a small-skew-angle actuator) with respect to the seek performance and frequency response. It was found that the SPA had a higher resonant frequency, which enabled the achievement of a wider servo-bandwidth compared to the LAA, and that the average seek time of the SPA was significantly shorter than that of the LAA.

DOI： 10.1007/s00542-015-2516-5

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：euspen  

Viscoelastic (VE) materials are widely used in our daily lives. To utilize VE materials effectively, it is necessary to understand the accurate viscoelasticity over a wide frequency range, especially in the high frequency range. Currently, viscoelasticity is directly measured only in the low-frequency range, and viscoelasticity in the higher frequency is estimated based on the time- Temperature superposition (TTS) principle. However, it is generally recognized that estimation by the TTS principle is adequate only for rheologically simple materials in a limited range of temperatures above the glass- Transition temperature. In this study, we proposed a shear- Type measuring device that can directly measure the shear modulus and tan δ of VE materials. We also proposed a compensation method for the shear deformation mode resonance of the VE material based on the mass value of the moving part to gain a better and more accurate understanding of viscoelasticity in the high frequency range.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

We investigate the thermal behavior of the friction property of ultra-thin perfluoropolyether (PFPE) lubricant film on diamond-like carbon (DLC) overcoats of magnetic disks. We use a newly developed pin-on-disk tester with laser irradiation heating. Results show that the friction coefficient of a lubricated DLC surface with Z-tetraol decreased with increased temperature, while for lubricated disks with Z-03, it gradually decreased at around 120°C and increased over 120°C. This minimal point may indicate the transition temperature. The friction coefficient of both lubricant films on the DLC surface varied with the kinematic viscosity of the lubricant materials, and decreasing the kinematic viscosity decreased the friction coefficient.

DOI： 10.2474/trol.11.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

For dual-stage actuator systems in hard disk drives, stroke-saturation of the secondary actuator must be avoided to prevent the servo system from becoming unstable. In this study, a reduction in the secondary-actuator displacement was investigated by imparting a rotational stiffness to a voice coil motor (VCM). It is shown that an increase in the first resonant frequency of the VCM is largely effective for decreasing the secondary-actuator displacement in the general dual-stage actuator system. Then, an actuator, which can impart a rotational stiffness to the VCM, was designed and facilitated. A new control system for dual-stage actuators employing the actuator was also considered. It was confirmed that the proposed servo system reduced the head-positioning errors due to air-flow-induced carriage vibration by more than 35 % compared with a conventional dual-stage actuator system. Furthermore the secondary-actuator displacement was reduced 52 % on average.

DOI： 10.1007/s00542-014-2368-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

As part of the author's effort to optimize the design of the head-mounting blocks (HMBs) used in the head suspensions of hard disk drives, a parametric study was undertaken. First, the author derived a theoretical retention torque equation in preparation for this study. Then, eight design parameters, which are empirically believed to be important for controlling HMB deformation, were selected for the parametric analysis. Subsequently, the HMB deformation and retention torque after ball swaging were calculated using an analytical solution for HMB deformation, previously presented by the author, and the retention torque equation. As a result of this study, an optimal design for the HMB and its analysis results are presented, together with design guidelines for the HMB.

DOI： 10.1007/s00542-014-2365-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper investigates the depletion of a thin lubricant film subjected to laser heating in an inert gas environment, and we experimentally elucidate the fundamental characteristics and mechanisms related to lubricant depletion in air and inert gas environments. In addition, fundamental experimental studies are conducted to understand the structural stability or degradation, such as through oxidation and graphitization of diamond-like carbon (DLC) thin films subjected to laser heating, in an inert gas environment compared to air environment. The degradation and its mechanisms are investigated using Raman spectroscopy. The results suggest that less degradation would occur by oxidation for a DLC thin film in an inert gas environment than air environment. It is found that, from the view point of the reliability in the head/disk interface, the lubricant depletion issue is more crucial than DLC thin-film degradation for thermally assisted magnetic recording in an inert gas environment.

DOI： 10.1109/TMAG.2014.2359058

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The spring-back deformation of a head-mounting-block (HMB) after ball-swaging was analytically solved from equations of elasticity. The analytical solution helps to elucidate the mechanism of HMB deformation after swaging and provides insight for designing an adequate HMB with reduced spring-back. This study estimates the displacement of the HMB tip caused by spring-back after swaging, taking the plastic deformation of the HMB into consideration. A suitable boss radius is also discussed.

DOI： 10.1007/s00542-013-2047-x

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Language：Japanese   Publisher：Japanese Society of Tribologists  

<p>Thermal behavior of friction property on ultra-thin perfuruoropolyether (PFPE) lubricant film on diamond like carbon (DLC) overcoat of magnetic disks was studied using newly developed pin-on-disk tester with laser irradiation heating. Friction coefficient of lubricated DLC surface with Z-tetraol decreased with heated temperature. On the other hand, that of lubricated disks with Z-03 gradually decreased around 120°C and increased over 120°C. This minimal point might mean the transition temperature. Friction coefficient of both lubricant films on DLC surface depended on the kinematic viscosity of lubricant materials and the lubricant film with lower kinematic viscosity showed lower friction coefficient.</p>

DOI： 10.18914/tribologist.60.08_538

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper presents a disk-spacer damper (DSD), a new damper structure, for reducing disk flutter. Three types of DSD structures, which consist of an aluminum disk spacer having grooves embedded with viscoelastic (VE) films, have been developed in this paper. First, we investigated the material properties of the VE film, such as shear modulus and discrete relaxation spectra, and then carried out numerical analysis of the damping effect using the material properties. Further, we measured the damping effect of each DSD structure and confirmed that the proposed DSD reduces the disk flutter amplitude between the (0,1) mode and the (0,4) mode by 20%-30%.

DOI： 10.1109/TMAG.2014.2318032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this paper, we sought to determine if, during ultraviolet (UV) exposure, the external electric field could control the bonded lubricant thickness. During UV irradiation, the effect of the external electric field on both the bonded lubricant thickness and surface free energy was studied. The lubricant films after UV irradiation were analyzed using time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Because of the negative electric field, the polar component of the surface free energy was reduced, while the bonded lubricant thickness increased. Based on the results of the TOF-SIMS analysis, we concluded that these findings resulted from the negative electric field accelerating the photoelectron emission, and because of these photoelectrons, the bonding between the end groups and diamond-like carbon surface increased.

DOI： 10.1109/TMAG.2014.2318015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Because the diamond-like carbon (DLC) thin film overcoat on a hard disk surface plays an important role in maintaining the reliability and durability of the head-disk interface, DLC degradation is a critical issue in thermally assisted magnetic recording (TAMR). The use of helium in hard disk drives (HDDs) is being developed to decrease air-induced structural vibrations, windage loss, and temperature rise. TAMR technology is suggested to be put to practical use in a helium environment in HDDs. In this paper, fundamental experiments have been conducted to understand the structural stability or degradation of an ultrathin DLC overcoat subjected to laser heating in an inert gas environment. An inert gas environment was simulated using nitrogen gas. The degradation of DLC thin films fabricated through chemical vapor deposition was investigated by varying the laser irradiation duration and controlling the intensity of the laser, and it was evaluated through Raman spectroscopy. The differences in the damage mechanisms between an inert gas and air environments were elucidated. We found that the degradation of DLC thin films by oxidation would be significantly less in an inert gas environment than in an air environment.

DOI： 10.1109/TMAG.2014.2321006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

The wear resistance of two types of nanotextured surfaces, fabricated on polyethylene terephthalate films and coated subsequently with a diamond-like carbon (DLC) layer and then a self-assembled monolayer (SAM) film with perfluoropolyether main chains, was compared. Nanotextures with hole and pillar patterns were fabricated by a nanoimprint process. The hole nanotexture with DLC and SAM films showed better wear resistance than the pillar nanotexture, and that film showed higher oil repellency than the pillar nanotexture with DLC and SAM films. The von Mises and shear stresses of the pillar nanotexture were concentrated on the center and at the bottom of the asperity surface, and it was estimated from finite element method calculations that these stresses accelerate the wear of asperities.

DOI： 10.1007/s11249-013-0218-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

In this study, the wear properties of a magnetic head slider on disks lubricated by ultra-thin perfluoropolyether (PFPE) lubricants with different molecular weights were evaluated by the continuous sliding of magnetic head sliders using the slider contact by the dynamic flying height control. Two types of PFPE lubricants (Z-tetraol and D-4OH) with different molecular weights were evaluated. Results show that the slider wear depended on the coverage of the lubricant film; i.e., the lubricant film with sufficient coverage reduced slider wear. The lubricant film with a low molecular weight (low-Mw), including a lubricant material with a Fomblin and Demnum main chain, exhibited better coverage on a diamond-like carbon surface. Sliders with a low-Mw lubricant film showed less wear than those of a high molecular weight (high-Mw), and the depletion of the low-Mw lubricant film was less than that of the high-Mw lubricant film.

DOI： 10.1007/s11249-013-0242-7

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

The drag friction of the laminar air flow in a steel pipe with permanent magnets attached was compared to that in a pipe without magnets. The drag reduction rate decreased as a function of the Reynolds number in the laminar flow regime, and it reduced to a low percentage when the Reynolds number was greater than 3000 in the turbulence air flow regime. These results suggest that the velocity of the boundary air flow on the pipe wall surface was accelerated by the magnetic field gradient produced by the permanent magnets attached to the outer pipe surface. The velocity of the boundary air flow, as roughly estimated by calculating the magnetic field distribution, could approximately express the experimental results.

DOI： 10.1109/TMAG.2013.2245106

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Politecnico di Torino (DIMEAS)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

One of the major contributors to head positioning errors is carriage vibration in low frequency due to an air flow caused by disk rotation. It is necessary to suppress the disturbance for Hard Disk Drives (HDDs) to have more capacity. We experimentally studied a reduction in the flow-induced carriage vibration using linear protrusion structures by putting wires on carriage arms. This study was carried out using 2.5 inch HDD which has high rotational speed of 10,000 rpm. We measured position error signals (PES) and compared with a conventional carriage. From the experimental results, we found that the linear protrusion structure was effective to reduce the carriage vibration. Leading edge wire configuration and 2 linear protrusion configuration improved average non-repeatable position errors (NRPE) by 6.9% and 6.4%, respectively.

DOI： 10.1007/s00542-011-1246-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

A novel slider-based micro-actuator for magnetic disk drive was designed and fabricated to improve the magnetic head positioning accuracy. The micro-actuator consists of a head slider, an actuator base, flexible hinge elements, and a pair of unimorph actuators which has piezo-electric transducers and actuator arms as components. The slider body is able to rotate around the center of mass, and the movable end of the actuator arms are contacted but not fixed to the slider body, so the arms won't constrain the slider rotation and results to a large stroke. The actuator arms are actuated by piezo-electic transducers to apply a rotation torque to the slider. The stroke of 0.16 mu m peak-to-peak was obtained under a drive voltage of +/-20V and the frequency response of the slider tip excited by the piezo-electric actuators was fairly well, with slider sway mode frequency of 21.8kHz. The evaluation results showed the micro-actuator is able to improve the servo bandwidth, implemented in the disk drive in the future.

DOI： 10.1299/jamdsm.5.45

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

To increase the recording density of hard disk drives, high accuracy of head positioning is required. But disk flutter, which is airflow induced vibration, is a major contributor to head positioning error. For detecting disk flutter, we proposed a suspension to which a PVDF film sensor was attached, and built the suspension into an actual HDD. Comparing the power spectrum of disk vertical vibration with that of the PVDF film sensor output, disk flutter was well detected. We also implemented a feedforward controller and confirmed that the influence of disk flutter on position error signal is considerably suppressed.

DOI： 10.1007/s00542-009-0797-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

A unique piezoelectric microactuator for the head-slider drive dual-stage actuator systems in magnetic disk drives has been developed. This microactuator is based on a rotating symmetrical structure and a symmetrical operation. The piezoelectric actuator elements used in the system have a simple rectangular multilayered structure. A prototype model with pico slider and head suspension has been tested to demonstrate 0.86 mu m displacement at a dc applied voltage of 30V and observed main resonant frequency of over 20kHz. No fluctuation in flying height was observed.

DOI： 10.1143/JJAP.45.7471

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We have developed a piezoelectric microactuator for dual-stage actuator systems in magnetic disk drives. We installed the microactuator in one of Fujitsu's 3.5-inch commercial drives for evaluation of the servo system of dual-stage actuator, The dual-stage actuator system achieved the nonrepeatable position error (NRPE) 3 sigma values of 0.036 mum. The dual-stage servo system reduced the NRPE by 35% compared with the conventional single actuator system even in HDD's which has a high rotational speed of 10 000 rpm.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We developed a novel piezoelectric microactuator for dual-stage actuator systems in magnetic disk drives. This microactuator is based on the shear deformation of piezoelectric elements, and drives the head suspension assembly. The actuator is suitable for thin devices, and is easily manufactured because bf its simple stack configuration. We installed the microactuator in a 2.5 " prototype drive, and evaluated the servo system of the dual-stage actuator. This paper describes the structure of our piezoelectric actuator, its mechanical characteristics, and the evaluation of the dual-stage actuator servo system.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We developed a new piezoelectric microactuator for dual-stage actuator systems in magnetic disk drives. This actuator exploits the shear mode of piezoelectric elements and drives the head suspension assembly.
This paper describes the structure of our piezoelectric actuator, its mechanical characteristics, and the experimental results of a life test after driving the piezoelectric elements in an atmosphere of high temperature and humidity.

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Language：English   Publishing type：Research paper (scientific journal)  

A new milli-scale piggyback actuator for magnetic disk drives with a high track density was developed. The movable part of this actuator is comprised of a head suspension assembly supported by a 'flexural' cross-shaped spring, driven in the rotary direction by electromagnetic force. The advantages are that the actuator moves over a long distance with small power and can be easily manufactured. Our dual-stage actuator system using the flexural milli-actuator can realize 25 kTPI. © 1996 IEEE.

DOI： 10.1109/20.539213

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Language：English   Publishing type：Research paper (scientific journal)  

A new type of rotary actuator for HDDs is presented. To suppress the resonance gain in quasi-rigid body mode caused by the stiffness of support bearings, we propose an orthogonal driving. The designed actuator for a 3.5-inch drive showed a quasi-rigid body mode gain of less than 5 dB, and a fundamental resonance frequency of approximately 10 kHz. These results agreed with that from finite element analysis. © 1996 IEEE.

DOI： 10.1109/20.492861

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We have developed a high-performance moving-magnet rotary actuator for very low-profile magnetic disk drives. A small moving magnet and efficient low-profile magnetic circuit construction give high acceleration and reduce power consumption to 50% that of moving coil actuators. The arrangement of the coils and yokes increases the design flexibility. The actuator does, however, suffer from a magnetic bias force and large inductance.

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Language：Japanese  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In hard disk drives (HDDs), rotary-type voice coil motors (VCMs) are exclusively used for positioning head transducers on a target track. The rotary VCMs essentially have a skew angle, and its variation reaches more than 30° in the typical 3.5-in. HDDs. It is generally known that such a large skew angle deteriorates the flying stability of the head sliders and off-track capability. Recently, it has been considered that the large skew angle is capable of deteriorating the quality of the read-back signal in two-dimensional magnetic recording. The reduction in the skew angle, therefore, is strongly desired in HDDs. We previously proposed a new actuator structure, a separated pivot-shaft actuator (SPA), for reducing the skew angle, and its satisfactory capability for seeking and tracking actuations was demonstrated using finite element method analysis. In this study, we assembled a prototype SPA, measured the frequency response functions to reveal the actual mechanical characteristics.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

UV irradiation with the bias voltage between the magnetic disk and the counter electrode above disk surface increases the bonded ratio of the perfluoropolyether (PFPE) lubricant film on disk surface. In this study, two types of lubricant materials (Fomblin Z-tetraol and Moresco ADOH) were prepared and were coated on disk surface. After coating of lubricant film, the UV irradiation treatment with the bias voltage to lubricated disk surface was performed and the depletion of these lubricant films was compared by the pin-on-disk test with the laser heating mechanism. As the results, the lubricant film treated by UV irradiation without the bias voltage showed deeper lubricant depletion than that with the bias voltage, and the ADOH showed shallower lubricant depletion than Z-tetraol. On the other hand, the molecular weight distributions of ADOH film on disk surface treated by UV irradiation with and without the bias voltage were compared using the time of flight secondary ion mass spectroscopy (TOF-SIMS), and the bias voltage was estimated to increase the dissociation of hydroxyl end-groups and the chemical adsorption to disk surface.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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Reduction of the outgas from the pivot bearing of tracking actuator in hard disk drives (HDDs) by the diamagnetic repulsive force between the hydrocarbon gas and the magnetic field was studied. Outgas from the pivot bearing with and without permanent magnets was compared in several environmental temperature. It was observed that outgas from the pivot bearing with permanent magnets compared with that without magnet was reduced. This result suggests that the diamagnetic force affected to hydrocarbon outgas and the possibility of new magnetic seal technology to reduce outgas of hydrocarbon.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

When the magnetic head sliders contact with lubricant film on magnetic disks, the head sliders are vibrated by the friction force between the slider and disk surface. This vibration causes the decrease of HDD (Hard Disk Drive) reliability. In previous study, we confirmed that the vibration of head slider was reduced by vertical pattern on air bearing surface (ABS) on slider flow. Then, in this study, we focused on the reduction of slider vibration by the pattern on ABS, and evaluated the slider vibration with vertical / parallel / hole patterns.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

It is necessary to reduce the excitation force acting on the carriage arm in magnetic disk drives. In previous studies, it has been found that it is possible to reduce the excitation force by attaching a projection on the wall of the carriage arm. However, the principle has not been elucidated. I have attempted to elucidate the principle by numerical analysis.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, we prepared two types of PFPE lubricants (D-4OH and DDOH) with different end-groups. These lubricants have the same backbone, but D-4OH has two end-groups at both side of main chain and DDOH has a end-group at single side of main chain. The ultra-thin composite lubricant consisted by these lubricants were coated on magnetic disks. We studied the clearance between head and disk surface and the slider wear after touch-down cycles on the lubricant film with different bonding(as dip/UV/UV-rinse) and the D-4OH/DDOH composite lubricant film. As a result, we found that the UV-rinsed lubricant film showed the widest clearance in the lubricant film with three kinds of bonding and the D-4OH/DDOH composite lubricant film showed the possibility to reduce the slider wear.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Slider flying height has been reduced to less than 2 nm to increase the recording density of hard disk drives (HDDs). However, it is demanded that the flying height should be reduced more. On the other hand, the helium-filled HDD was proposed to resolve the positioning error and reduce the electricity consumption. In the helium-filled HDD, the wear properties of slider surface covered with diamond like carbon(DLC) may be different from the wear properties in air, because it has no oxygen. In this paper, we investigate wear properties of sliders as a function of relative amount of gases (water, Vertrel-XF, and ethanol) in atmospheric air and nitrogen.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, we prepared two types of PFPE lubricants (D-4OH and DDOH) with different end-groups of molecule. The D-4OH has two endgroups at both side of mainchain. On the other hand, the DDOH has one engroup at ingle side of mainchain. We coated the composite lubricant film by these lubricants on magnetic disks. First, we measured the friction force and the adhesion force on the disks with different lubricant thicknesses of D-4OH and DDOH by pin-on-disk test. Next, we measured these properties on the composite film and compared to these. We found that the adhesion force of D-4OH was lower than that of DDOH, and the friction coefficient of DDOH was lower than that of D-4OH. Composite lubricant film showed lowest the friction force in these lubricant films.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In Hard Disk Drives (HDDs), carriage vibration in low frequency due to an air flow caused by disk rotation is one of the factors that deteriorate the head positioning accuracy. Reduction of the disturbance is necessary for increasing capacities of HDDs. We proposed a new control strategy using a dual stage actuator mechanism and an additional electromagnetic actuator which provides a rotating stiffness to a carriage and suppresses the flow-induced carriage vibration. We measured a flow-induced carriage vibration when the additional actuator was working and carried out simulations of head positioning errors. It was confirmed that head positioning errors by flow-induced carriage vibration was reduced more than 30% compared with a dual stage actuator system.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Data recovery technology of the hard disk drives (HDDs) is important, because the HDDs may be sometimes troubled by unfortunate causes. However, it has been almost impossible to recover data from crushed HDDs. In this study, the data recovery method was studied by the tape cleaning of wear particles on the magnetic disk surface by the head-disk crush. The "process condition of tape cleaning for disk surfaces with the scratch by the head-disk crush was determined and the head flyability was compared on the disks with and without the tape cleaning. Finally, the data recovery was performed and confirmed the efficiency of the tape cleaning process for the crushed disks.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To achieve magnetic recording densities of more than 10 Tb/in^2, the head-disk interface (HDI) spacing should be less than 2-3 nm. Thus far, thermally assisted magnetic recording (TAMR) technology has been studied and developed to achieve such ultra-high magnetic recording densities. However, the use of ultra-thin liquid lubricant films as well as DLC thin films on the disk surface in TAMR leads to critical issues with regard to the HDI. In addition, HDD technology with head-disk assembly mechanism in which He gas is enclosed has been developed. In this study, the effect of lubricant bonding mechanisms on lubricant depletion has been studied. Furthermore, the mechanisms of lubricant depletion due to laser heating have bean investigated and discussed.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In recent years,the heat-assisted magnetic recording is suggested as the key-technology to achieve the recording density of more than lTb/in^2.In this technology,It may be problem for the depletion of lubricant film to occur by the laser irradiation,because that is heated to high temperature with laser beams.In this study,we focused on the thermal stability of the lubricant film with the different adsorption states on magnetic disks by the laser irradiation.As a result,it was found that the depletion of lubricant films by laser irradiation showed a different behavior from the reduction of lubricant thickness after heat treatment.The lubricant film with only chemical bonding showed lowest depletion by the laser irradiation

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Perfluoropolyether(PFPE) lubricants are coated on the surface of hard disks or touch screens in order to reduce adsorptions of various contaminations.In this study,the durability of PFPE lubricants with different chemical structures,which have a endgroup at single side of Demnum mainchain(DDOH),two endgroups at both sides of the mainchain(D-4OH),and two endgroups at both sides of Fomblin mainchain(Fomblin Z-tetraol),were evaluated by the reciprocating friction tester.Friction force of Z-tetraol and DDOH showed lower than that of D-4OH and the lubricant depletion of DDOH after test showed smaller than that of other lubricants.Therefore,DDOH showed best durability performance in these lubricants.It is estimated the flexibility of lubricant molecules affects to the durabolity.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Cleanliness should be important factor for the stable flying of the magnetic head slider in hard disk drives to improve the areal density.Generally,magnetic disk surface are burnished by the burnish slider at final process in manufacturing.However,the burnish sliders sometimes cause scratches on disk surfaces by the contact with disk surface.In this study,we fabricated the burnish slider with the burnishing surface of vertically aligned carbon nanotube,and studied the burnishing effect using that burnish slider.As a result,the patterned burnish slider of carbon nanotube improved the burnishing effect on magnetic disks.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In recent years,the light contact recording is proposed in order to reduce the flying height between magnetic head and magnetic disk.But,it is difficult to stably read and write data,because the magnetic head is contacting with magnetic disk rotating at high speed.In this study,we studied the slider vibration in the contact by vibration using 1 degree of freedom model.And,we analytically investigated the effects of the adhesion force between the slider and disk to slider vibration,thickness and viscosity of lubricant layer and roughness of disk surface.As the results,low viscosity lubricant and optimum adhesion force are needed in order to realize the stable light contact recording.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The light contact magnetic recording is suggested in order to reduce the flying height of head-disk interface (HDI). In light contact magnetic recording, the head slider vibrates by the friction occurs at contacting the slider and the disk surface. In this study, the vibration behaviors of the slider with the fabricated the dynamic flying height (DFH) protrusion by the focused ion beam (FIB) to reduce the friction force were measured by the acoustic emission (AE) and the friction at the touchdown process of the slider on disk surface. As the results, FIB fabrication reduced the friction force and the light contact regime of the slider with the FIB fabrication became longer than that without the fabrication.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, the wear behaviors of nano-texturing surface on PET films fabricated by nanoinprint. Two kinds of texture patterns, which were a pillar structure and a hole structure with 200 nm diameter, 500 nm pitch, and 200 nm height, were fabricated. DLC coating films were deposited on the nanotexturing surfaces of some samples. After wear tests, surface texture asperities of pillar samples without DLC coating were crushed and the asperities of samples with DLC coating were severe damaged at initial stage. On the other hand, the surface asperities of the hole samples without DLC coating were slightly crushed, and these samples with DLC coating showed higher durability than these without DLC coating.

CiNii Books

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Event date： 2018.3

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Event date： 2017.9

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Event date： 2016.9

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Event date： 2016.6

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Event date： 2016.3

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Event date： 2015.12

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Event date： 2014.9

Venue：東京  

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Event date： 2014.9

Venue：東京  

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Event date： 2014.9

Venue：東京  

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Event date： 2014.9

Venue：東京  

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Event date： 2014.5

Venue：Dresden, Germany  

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Event date： 2014.5

Venue：Dresden, Germany  

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Event date： 2014.5

Venue：Dresden, Germany  

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Event date： 2014.3

Venue：東京  

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Event date： 2014.3

Venue：東京  

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Event date： 2014.3

Venue：東京  

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Event date： 2014.3

Venue：東京  

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Event date： 2013.11

Venue：仙台  

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Event date： 2013.11

Venue：仙台  

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Event date： 2013.9

In head-stack assembly for Hard Disk Drives (HDDs), head-gimbal-assemblies are attached to E-block-arms by ball-swaging. After the ball-swaging process, mount-plates made to deform, and it decreases the fling stability and the reliability of load/unload. Therefore, the reduction of their deformations is strongly desired in HDD industry. In this paper, the analysis of bending deformation was carried out to understand the mechanism of the deformations by ball-swaging process. Also, the proper boss-hole diameter is discussed for the reduction of the HMB deformation.

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Event date： 2013.8

Venue：Osaka, Japan,  

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Event date： 2013.5

Venue：Busan, Korea  

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Event date： 2013.5

Venue：東京  

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Event date： 2013.5

Venue：東京  

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Event date： 2013

Venue：福岡  

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Event date： 2013

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Event date： 2013

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Event date： 2013

Venue：Tokyo, JAPAN  

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Event date： 2010.7

Venue：Bangkok  

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Event date： 2010.6

Venue：Santa Clara, California, USA  

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Event date： 2010.3

Venue：東京  

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Venue：Milpitas  

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Venue：グランフロント大阪  

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Venue：Sendai  

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Venue：Sendai  

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Venue：九州工業大学（北九州）  

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Venue：九州工業大学（北九州）  

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Venue：九州工業大学（北九州）  

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Venue：京都産業会館  

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Venue：Nagoya  

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Venue：Nagoya  

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Venue：Nagoya  

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Venue：Nagoya  

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Venue：Nagoya  

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Venue：Nagoya  

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Venue：Nagoya  

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Applicant：富士通株式会社

Application no：特願2002-235564  Date applied：2002.8

Announcement no：特開2004-079040  Date announced：2004.3

Patent/Registration no：特許第4170043号  Date registered：2008.8 

J-GLOBAL

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Applicant：富士通株式会社

Application no：特願2002-024597  Date applied：2002.1

Announcement no：特開2003-228928  Date announced：2003.8

Patent/Registration no：特許第4117723号  Date registered：2008.5 

J-GLOBAL

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Applicant：富士通株式会社

Application no：特願平11-217904  Date applied：1999.7

Announcement no：特開2001-043641  Date announced：2001.2

Patent/Registration no：特許第3678613号  Date registered：2005.5 

J-GLOBAL

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Applicant：富士通株式会社

Application no：特願平11-031745  Date applied：1999.2

Announcement no：特開2000-231767  Date announced：2000.8

Patent/Registration no：特許第3819170号  Date registered：2006.6 

J-GLOBAL

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Applicant：富士通株式会社

Application no：特願平9-234055  Date applied：1997.8

Announcement no：特開平11-073743  Date announced：1999.3

Patent/Registration no：特許第3933762号  Date registered：2007.3 

J-GLOBAL

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Applicant：富士通株式会社, エフ・ディ-・ケイ株式会社

Application no：特願平9-185385  Date applied：1997.7

Announcement no：特開平11-031368  Date announced：1999.2

Patent/Registration no：特許第3420915号  Date registered：2003.4 

J-GLOBAL

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Applicant：富士通株式会社

Application no：特願平5-258321  Date applied：1993.10

Announcement no：特開平7-111051  Date announced：1995.4

Patent/Registration no：特許第3705609号  Date registered：2005.8 

J-GLOBAL

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Patent/Registration no：特許第7256526号  Date registered：2023.4 

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