Lateral motion of magnetic tape is measured on roller and porous air-bearing type tape drives. The lateral tape motion signal is high-pass filtered and the spectral components are analyzed. Time-frequency analysis is also performed. The effect of lateral motion of tape on tape pack winding is investigated and the frequencies observed during edge contact are analyzed. The effect of dynamic tension changes during high frequency lateral motion events is examined, and the tension difference across a section of tape is found to be correlated to the lateral motion of that section. LDV data of out-of-plane (transverse) tape motion is presented and its relationship to lateral tape motion and edge contact is discussed.

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In hard disk drives, vibration suppression is very important for achieving a high performance of information-processing equipments. It has been expected that technology of smart structure will contribute to the development of small and light-weight mechatronics devices with the required performance. A design method of the actuator placement [1] with high controllability is studied to enhance the control performance [2] on the structural vibration suppression.

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The objective of this paper is to present a concept of structural dynamic design considering controllability for smart structures. The actuator, which is a base of the smart structure, is composed of a thin piezoelectric film in this study. To achieve high controllability for suppressing vibration of the objective mode, structural optimization is applied for the smart structure. The effectiveness of the proposed method is verified by simulation and experimental results.

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A new air bearing linear actuator with a VCM (Voice Coil Motor) was investigated for a precise head track following in a magnetic recording system. The actuator has a servo bandwidth of two times as wide as that of a conventional HDD (Heard Disk Drive). When a D-MIG (Double Metal In Gap) of 4 μm track width loaded on a 2.5 inch disk system, the tracking error was compressed down to a half of the general design value of one tenth of the track width.

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With the aim of increasing the track density in a hard disk drive by widening servo bandwidth, the authors have developed a new design concept based on lowering the major resonance gain in the transfer function of the actuator. A head actuator based on this design concept was constructed and fitted in an actual disk-drive assembly and evaluated. The test results show that the measured servo bandwidth is wider by more 300Hz than that of a typically designed actuator.

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In high-capacity disk drives with ever-growing track density, the allowable level of position error signal (PES) is becoming smaller and smaller. A substantial portion of the PES is caused by disk vibration. This can be reduced by using a head gimbal assembly that does not confine the movement of slider roll center to the vertical direction to disks, but allows movement to the radial direction of disks with respect to disk vibration.

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This paper is concise review on vibration of hard disk drives (HDD) spindle motors that carry multiple disks spinning at constant speed. The spindle motors could have ball bearings or fluid dynamic bearings (FBD). Theoretically, vibration of spindle motors consist of disk modes and unbalanced modes. Disk modes only involve disk deformation. In contrast, unbalanced modes involve deformation from the disks, hub, bearings, and the base. Experimentally, unbalanced modes are difficult to measures. Accurate measurements of unbalanced modes require careful considerations of excitation/measurement methods and locations.

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The purpose of this paper is to present a thorough study on coupled vibration of multiple co-rotating disks stacked on a hub, which are the basic configuration of computer hard disk drives (HDD). The paper has two specific goals. The first goal is to demonstrate experimentally that presence of air will lead to exactly N distinct natural frequencies for each propagating wave with two or more nodal diameters, where N is the number of disks. The second goal is to illustrate experimentally and numerically that flexibility of spacers between the corotating disks can also lead to coupled disk vibration in the same manner.

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We analyzed the stability of disk spindle supported by a full cylindrical fluid journal bearing and pivot bearing. We found that a half frequency whirl of vertical spindle caused by the full cylindrical journal fluid bearing becomes stable if the gyro factor of the rotor is larger than 0.5. We clarified that the bottom of the spindle shaft should be supported by a spherical grooved pivot bearing.

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A design of experiment (DOE) method for a practical implementation of squeeze-film aeroelastic disk vibration damping and its optimal performance are presented to provide a solution method to meet the tight TMR (Track Mis-Registration) design budget of 80GB/platter high-TPI (track per inch) HDDs. The squeeze-film disk damping effect is implemented by using the circular shape aluminum plate with the constant 0.5mm level gap between disk and plate which are practically implementable in mass-production HDDs.

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In this paper, the aerodynamically dissipated power loss in hard disk drives is studied. The effects of rotational speed and form factor on the dissipation power loss are analyzed and compared to experimental results using 3.5", 2.5" and 1" disks. The torque coefficients for laminar and turbulent models are derived for various enclosure conditions. We implement experiments using a vacuum chamber and calculate frictional power loss by disk rotation. For a 1-inch disk, the power dissipation agree well with the laminar model, which is inversely proportional to the half power of Reynolds number. The frictional power consumption by 3.5-inch disk is similar to the air turbulent model. Finally, we propose the drive enclosure geometry to minimize the aerodynamic power loss based on the experimental results.

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Present study focuses on an interaction of flow instability and elastic vibration of a multiple disk system rotating with sub-critical speed. The simultaneous measurements of the flow velocity between disks and the transverse displacement of the disk reveal that the fluid-solid interactions are not negligible even in low speed range far below the flutter or critical speed.

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Two methods for investigating the flow inside an actual hard disk drive (HDD), namely, Particle-image-velocimetry (PIV) measurements and fluid simulation using tetrahedral elements have been developed. The HDDs used in the measurement have the same configurations as those of an actual product, but they are partly made of transparent acrylic resin. The measured velocity distribution clearly shows the flow characteristics induced by the arm or the base configuration. The fluid simulation considers most of an actual configuration between the two co-rotating disks. The simulated velocity distributions at the mid-plane between the disks agree well with those measured by the PIV. The developed PIV measurement technique and fluid simulation using tetrahedral elements more effectively determine the flow characteristics inside a HDD.

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The effects of E-block arm thickness on the head off-track vibration and the airflow in a modeled hard disk drive were investigated experimentally. Four arms with different thicknesses were tested. The Power spectra of the head vibrations were measured using laser Doppler vibrometry (LDV), and were used to compute the rms off-track vibrations and their components over selected frequency bands. The mean speed and flow fluctuation power spectra of the airflow downstream of the arm tip were measured using constant-temperature hot-wire anemometry (CTA), and these measurements were used to compute the rms dynamic head fluctuations and their components in the measurement region. A positive correlation was observed between the dynamic pressure fluctuation levels and the vibration levels.

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This paper summarizes functions and features of a new latch design, named as pawl latch from herein, for implementation on ramp loading disk drives, where a disk drive with a ramp would allow actuator to stay on the ramp outside the disk when not in use. The new latch system consists of two latch mechanisms : one is inertia latch and the other is magnetic latch. These two latches work together to obtain very reliable non-contact break free latch while maintaining high resistance during rotary shock condition. Simple control methods are also presented to alleviate audible noise issue generated using the pawl latch mechanism.

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The microdrive, 10 inch HDD compatible to compact flash type2,has been the smallest HDD in the world and epoch-making product, which opened new HDD application area like digital camera, PDA, etc. Since 1999,mass production has been carried out in newly developed manufacturing line in Thailand. Many of technical challenges had been overcome to establish microdrive dedicated manufacturing line. For example, in order to minimize manufacturing operator dependency and equipment cost, we adopted so-called mechanized concept that was neither automation line nor manual line.

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In order to realize a recording track density of 200kTPI in hard disk drives (HDDs), we set a control bandwidth target of 3.6kHz on the track following control in this study. The natural frequency of the lowest out-of-phase vibration mode of the positioning mechanism is required to be more than 11kHz. Considering recent trend of HDD we assumed a near-future type HDD with single 2.5-inch magnetic disk and single side recording. In the paper we presents a high natural frequency positioning mechanism. The FEM (finite element method) analysis result of the proposed head positioning mechanism shows that its first out-of-phase mode is 11.2kHz. It is experimentally confirmed that its first out-of-phase mode is about 9kHz.

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MoS_2-shot coating technology is recently focused as one of potential methods of surface modification to realized a low friction state. In this paper, performances of a small-sized journal bearing with MoS_2-shot coating, which we aim to apply to a spindle of magnetic recording storage system, are experimentally investigated from the viewpoints of frictional torque, durability against start-stop repetition, and run-out characteristics.

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This research investigates how the design variables of ball bearing change the bearing stiffness and the natural frequencies of a HDD spindle system in elevated temperature. It shows that large contact angle reduces the variation of the bearing stiffness and the natural frequencies in elevated temperature. It also proposes a robust design of the spindle motor, in which the wave spring maintains the constant preload even in elevated temperature. The theoretical investigation shows that the reduction of natural frequencies due to temperature rise is almost negligible in the proposed HDD spindle system.

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This research proposes a finite element method to determine the natural vibration characteristics of the spinning disk-spindle system in a HDD including the flexibility of supporting structure. Finite element equations of each substructure are derived with the introduction of consistent variables to satisfy the geometric compatibility at the internal boundaries. The natural frequencies and modes from the global asymmetric matrix equations of motion are determined by using the implicit restarted Arnoldi iteration method. The validity of the proposed method is verified by the experimental modal testing. It also shows that the flexibility of base plate plays an important role to determine the natural frequencies of the spinning disk-spindle system in a HDD.

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Diamagnetic levitation is known for a long time, but engineering applications have not yet been investigated. Modern permanent magnets make it possible to levitate an object of macroscopic size completely contact-free at room temperature without any energy input (passive levitation). Electrostatic glass actuators on the other hand are a promising new concept. Their stunning simplicity, together with their ability to outperform their electromagnetic counterparts at small size, make them potentially applicable for future HDD-type devices. Functional components have been demonstrated.

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A low-profile, small-diameter HDD motor for mobile application with fluid dynamic bearing had been developed. The thickness between the bottom of the motor and the top of the disk is 1.9mm. Although the radial bearing length is rather short, disk axial vibration can be reduced with optimization of thrust bearing structure. Magnetic noise from motor to head can be reduced with thin shield plate.

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Recent technological advances in magnetic storage suggest feasibility of extremely high density magnetic recording up to 1 Tbit/(in)^2 using conventional magnetic recording technology. However there are many challenging technological problems that need to be addressed before this areal density goal is realized. In this talk, there will be a general outline about the issues associated with achieving 1 Tbit/(in)^2 presented. The talk will then focus on the nano-tribological issues associated with head/disk interface relating to magnetic spacing of 6.5nm required for 1Tbit/(in)^2. This talk will also focus on air bearing design issues, slider dynamics and its flyability in near-contact regime, ultra thin carbon films and their interactions with the lubricant. Fly Height Modulation and its effects on the long term flyability will be discussed. Some latest data on the ultra thin carbon overcoats and their interactions with the flouro-carbon lubricants affecting the head/disk interface reliability will also be presented.

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The relation between hydrogen contents in DLC overcoat of a hard disk medium and its head flyability was studied. The effect of additional gasses such as N_2 and N_2O was also investigated. It was found that the hydrogen content in DLC affects the magnetic head flyability and it is effective to add N_2O in the atmosphere of DLC deposition process not only to obtain sufficient amount of functional groups but also to reduce hydrogen content of the DLC overcoat. The results of glide test showed drastic improvement of head flyability by decreasing the hydrogen/carbon ratio.

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Carbon over coat (COC) for head is one of important technologies in hard-disk-drive (HDD). Thickness of the film is about 4-5 nm. Evaluation of the film is quite important. In order to measure thickness of COC quickly and precisely in narrow area, we propose a new method by means of Auger electron spectroscopy (AES) without ion sputtering.

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Pico-sliders with nominal flying heights of 5 and 7 nm were etched using argon plasma etching. An island-type texture with a height of 4.5 nm was fabricated on the slider surface. The in-plane and out-of-plane vibrations of textured and untextured sliders were investigated using laser Doppler vibrometry (LDV) during contact start/stop. The results show that the amplitudes of both out-of-plane and in-plane vibrations are reduced as a consequence of the texture on the slider surfaces.

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The head flyability over a disk coated with the diamond like carbon (DLC) CH_x by the hot filament plasma enhanced chemical vapor deposition (HF-PECVD) was studied. The flyability was evaluated by measuring acoustic emission (AE) signals using a head attached a piezo transducer (PZT). Particularly, the noise level of AE signals during the head flying was focused, and it is called as the glide noise. As the results, the glide noise was changed by film characteristics of the DLC overcoat. The DLC overcoat was analyzed to clarify the difference of the glide noise using several analysis methods. From the analysis results of the DLC overcoat, it was found that the glide noise was changed by the hydrogen content in the DLC overcoat and the amount of the organic hydrocarbon onto the overcoat surface. It is important to control the hydrogen content in the DLC overcoat to keep the glide noise lower.

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Lubricant-slider interaction was investigated by focusing on lubricant depletion during slider following or seeking over a magnetic disk. It was found that the decrease in lubricant film thickness mainly depends on asperity contact between the slider and disk. It was also found that lubricant depletes in nominally non-contact region at a following test. However, when the slider is seeking over the whole disk surface, lubricant depletes when the interference height is above a certain value. And the depletion saturates after the mobile layer of the lubricant is removed.

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This paper describes the effect of ultra-thin liquid lubricant films on air bearing dynamics and flyability of less than 10 nm spacing flying head sliders in hard disk drives. In particular, the effect of non-uniform lubricant film distributions on head/disk interface dynamics are studied. The dynamics of sliders is monitored using Acoustic Emission (AE) and the interactions between the slider and disk are investigated. The disks before and after test are also examined with a scanning micro-ellipsometer. Complicated slider responses were observed and clarified. In addition, it is found that the periodic lubricant film thickness modulations or re-distributions caused by the slider-disk contact interactions could be observed.

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Perfluoropolyether lubricants terminated with alkanolamine end groups were synthesized and the interaction between lubricants and several materials were examined. This study has revealed that the interaction between the lubricant and the disk can be estimated by the interfacial tension and work of adhesion. Besides the bonding property of alkanolamine-terminated lubricants mainly depends on the number of hydroxyl groups, and amine group performs the role to interact with functional groups on the disk surface as well, except OH site.

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The collision density of the evaporated lubricant molecules in the air with the hard disk surface was analyzed. It is found that the adsorption of the collided molecules may have significant contribution to the lubricant film replenishment, especially when the depleted area size is larger than 01. mm and the activation energy is high as in the immobile layer. It is proposed that the replenishment is carried out through and adsorbing-spreading mechanism.

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A molecular dynamic simulation with the Langevin equation using a coarse-grained, bead-spring model was performed. The spreading profile for the ultrathin lubricant films was investigated to examine temperature effects on the diffusive and spreading phenomena.

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Low-coherence phase-shifting interferometry is presented for direct visualization of thin film spreading over a magnetic disk surface. In this method, three-dimensional measurement is straightforwardly realized by introducing phase-shifting function to the interferometry, and image noise is remarkably suppressed by employing an incoherent white light source. The applicability of this method was demonstrated by experimental results.

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This paper deals with evaluation of ultraviolet rays-assisted bonding of PFPE lubricant to the DLC surface of a magnetic disk. Spreading of lubricant from quasi step-shaped boundary between lubricated and non-lubricated zones was measured with irradiation time as a parameter, and diffusion coefficients were obtained using a modified Boltzmann-Matano method, which enable us an approximate calculation under an initial condition of a non-step-shaped boundary. It is found that irradiation is effective for bonding the lubricant, while a very thin layer of the lubricant abutting the surface exhibits faster diffusion.

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Fiber wobbling method can be used to study nanotribological properties of head disk interface (HDI)[1]. In this study, the optical system for shear force measurement was optimized and the minimum force detection limit of sub-nano-newton was achieved.

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An accelerated wear test using a constant-area wear bar was developed to study the abrasivity reduction curve of various magnetic tape media. Effects of tape tension, tape speed, temperature, and relative humidity on tape abrasivity were also studied. Comparisons were made between constant-area abrasion test (CAAT) and square-bar abrasion test (SBAT).

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A contact mechanics based wear model is developed to investigate the head / disk interface wear due to the intermittent contact at low fly height. For the first time, a transient non-linear wear analysis based on this model is performed to predict the wear history of the head / disk interface. In this model, wear volume is calculated by extended Archard's wear law; the contact force is calculated with a two-dimensional suspension / air bearing model; and the associated contact area is calculated with a quasi-static contact model.

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In order to solve in-use stiction problem, we have proposed a new method using square pyramids structure that are formed on the substrate. These square pyramids were made in sacrificial layers consisting of two qualitatively different silicon oxide films. According to etching rate difference between two sacrificial layers, the square pyramids can be obtained. We have fabricated capacitive actuators to confirm experimentally our newly proposed stiction free sacrificial layer releasing technique. As a result of experiment, it has revealed our double sacrificial layers process to be an effective method preventing in-use stiction.

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Integration of a grating-imaging-type encoder is proposed and the sensor for the encoder has been fabricated using Si micromachining technology. The sensor consists of the Si grids and line photodiodes. The Si grids work as the object grating The incoherent light emission through the Si grids and the light detection with the line photodiodes make the optical system compact. Moreover, the photodiode array based on the M-series arrangement is also installed on the same substrate for zero-point detection.

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We demonstrate a novel rotary vertical micromirror for fiber-optic switching. A very simple fabrication process which uses SOI wafer and DRIE technology has been employed to micromachine this electrostatically actuated mirror. Based on this one-mask process, 2N-switch-architecture cross-connects with all the components, including optic fiber couplers, electrostatic comb drives and reflective vertical mirrors, has been integrally fabricated on a monolithic silicon substrate.

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A MEMS mirror that we are developing for a three-dimensional MEMS optical switch module features a terraced electrode structure that enables low driving voltage. The mirror can tilt more than 4 degrees at less than 80-V driving voltage. A control method for the MEMS mirror achieves a short switching time. We demonstrate 3 msec switching time.

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Five year R&D project of optical disk systems finished in March, 2003. The project was funded by Japanese Government and carried out as the project of OITDA by 12 companies and one university. The recording density target of the project was 100Gb/(in)^2. To achieve them, four technologies : ultra high precision pit writing by using electron beam, ultra high precision pit measurement, three dimensional magneto-optical memory, and ultra high density ROM were developed. This paper introduces the outline of the project.

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An optical path for small form factor optical (SFFO) disk drives for the mobile devices is designed. The optical path includes a high NA objective lens (OL), a micro compensatory lens (MCL), and three mirrors. The tolerance of the designed optical path is analyzed by using Monte-Carlo simulation method. And, MCL is fabricated by micro molding process.

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In this paper, we propose a novel wafer-based optical pickup module with a micro objective lens having NA 0.85 and 405nm wavelength for a small form factor optical disk drive. The size of the optical pickup is 3mm[W] x 2mm[D] x 3mm[H] approximately, which is suitable for realizing a small form factor optical drive based on Blu-ray Disc. The objective lens consists of three layers that are a hologram plate for reducing the aberration and two partial ball lenses mounted in transparent fused silica for making optical power to achieve NA 0.85.

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Optical recording is currently used in a number of data storage formats, such as CDR, DVD and GIGAMO magneto-optical disks. In all cases the amount of data that can be stored is limited by the spot size of the focused laser beam. This is diffraction limited and gives rise to a spot size comparable with the laser wavelength. In order to overcome this limit a solid immersion lens (SIL) enables a significantly smaller spot to be realised. The design of an optical slider incorporating a SIL and a single galvanometer mirror will enable the dynamics of high-density near-field recording to be investigated.

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UP to recently, anti-vibration problem for CD or DVD deck has been mostly handled in one side standing direction. But consumer's various tastes have led to the stylish DVD player that can be laid in any directions, such as vertical, horizontal, hanging on the wall and even being arbitrary posture like a picture frame. So it is essential that we observe carefully this kind of deck mechanism and cope with vibration problems of deck in omnidirectional postures. In this paper, it is a goal to design anti-vibration system of stylish DVD deck that can be placed in all sides of direction and analyze its propriety with both simulation and experiment.

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A slim-type actuator mounted in notebook PCs is newly developed, which can make compensation for the radial inclination of optical disk. The proposed actuator adopts the moving magnet method for its tilt function but does the moving coil method for the other actuations, focusing and tracking. In order to find the optimal design for dynamic characteristics, we conduct some meaningful experiments and numerical simulations. The fabricated actuators following these guidelines show good tilt compensating ability and dynamic performances.

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