ASME Conference Presenter Attendance Policy and Archival Proceedings

2013;():V001T00A001. doi:10.1115/ISPS2013-NS.

This online compilation of papers from the ASME 2013 Conference on Information Storage and Processing Systems (ISPS2013) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Tribology, Head/Media Interface

2013;():V001T01A001. doi:10.1115/ISPS2013-2803.

Storage of 10 Tb/in 2 in hard disk drives within the next decade requires a significant change to reduce the physical spacing as little as 0.25 nm at the read-write transducer location. A lot of tribology issues exist to such a low flying height, the touch down and take off instability and hysteresis, the flying height avalanche, the influences of surface topography and morphology, the lubricant modulation and pick-up, robust air bearing surface and suspension design, just to name a few. Understandings of the complex tribo-dynamics issues in the near contact and contact states are very important to further reduce the flying height. At such a small spacing intermittent contact between the slider and disk surface becomes inevitable and the current MEMS-based thermal fly-height control (TFC) technology needs further improvement to satisfy the future needs. How to control the slider to reduce touchdown instability and eventually eliminate bouncing has been a pressing and challenging research topic. Most of existing work on touchdown dynamics applied conventional nonlinear dynamics theory and spectrum as well as harmonics analysis, which could suffer from the assumptions of small nonlinearity and stationary. This study presents a concurrence plot and Lyapunov exponent analysis which could offer an insight to the problem in the context of contemporary nonlinear dynamics theory.

Commentary by Dr. Valentin Fuster
2013;():V001T01A002. doi:10.1115/ISPS2013-2805.

Current hard disk drives (HDD’s) use thermal fly-height control (TFC) during read/write operations. In this study, we use TFC technology during the disk glide process to determine sub-5nm height defects. We also utilize TFC to measure the height of the defect during glide operation. Addtionally, we magnetically mark the disk locations where defects are detected for further post-processing of the defects using optical surface analysis (OSA), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The defect height estimation during the glide was confirmed to be accurate by AFM and SEM analysis. Finally, we will present the TFC glide sensitivity showing capability of detecting smaller defects than conventional non-TFC glide technologies.

Topics: Disks , Flaw detection
Commentary by Dr. Valentin Fuster
2013;():V001T01A003. doi:10.1115/ISPS2013-2813.

The areal data density of magnetic recording hard disk drives (HDDs) increases year by year, following a trend similar to Moore’s law. However, the increase is not unbounded and there are some physical limits. As the density increases, the size of each magnetic grain shrinks. Finally the magnetic grain will be no longer thermally stable due to what is termed superparamagnetism. Above this point, the magnetic storage would be not reliable because the magnetic grains’ orientations fluctuate randomly. To increase magnetic recording density to more than 1 Tb/in2 and break this limit, heat assisted magnetic recording (HAMR) is proposed. In HAMR systems, a more thermally stable magnetic material, one with higher coercivity, will be used as a recording layer. But the coercivity of this material at room temperature is so high that it is difficult for the writer to switch the magnetic orientation with current magnetic transducers. However, the coercivity drops sharply if the temperature is raised close to the Curie temperature. In HAMR systems, a laser is proposed as the means to heat the disk to the Curie point. Simultaneously the magnetic field is applied from the writer to switch the magnetic bits. The success of the magnetic switching is very sensitive to the media temperature [2]. If the temperature is too low compared with the Curie point, it will not be able to write any information into the media. Conversely, heating the media over the Curie point requires more energy and may bring a greater challenge for the head disk interface (HDI). It is very important to understand the local temperature distribution during the laser heating and to calibrate the laser power input for HAMR writing. Some work has been done to evaluate the temperature increase using both numerical and experimental methods [3, 4]. Tagawa et.al. observed the disk refractive index change during laser heating and compared it with the change under conventional oven heating. This is a good method to calibrate the laser power and get the average temperature but it has some limitations for getting the accurate temperature distributions because of the averaging effect for the refractive index measurement by ellipsometry.

Commentary by Dr. Valentin Fuster
2013;():V001T01A004. doi:10.1115/ISPS2013-2814.

In order for the data areal recording density in the hard disk drive (HDD) to be further increased, the spacing between slider and disk must continue to be decreased. Some light sliding contact is unavoidable, and eventually it could result in the demagnetization of data stored in the HDD.

Commentary by Dr. Valentin Fuster
2013;():V001T01A005. doi:10.1115/ISPS2013-2817.

A concoction of various forces and physical effects (both mechanical and chemical) come into play in the depletion and evolution of the lubricant on the media during a heat-assisted magnetic recording (HAMR) process. They include the air-bearing shear and pressure, capillary pressure, thermo-capillary stress, disjoining pressure, lubricant desorption and the vapor recoil mechanism. The effects of these mechanisms and their complex interplay to stabilize/destabilize the lubricant interface is studied here numerically. Results for Z-type perfluropolyether (PFPE) lubricants with different polydispersity indices (PDI) are summarized.

Commentary by Dr. Valentin Fuster
2013;():V001T01A006. doi:10.1115/ISPS2013-2837.

In magnetic recording, the hard disk rotates at a high speed, with the slider flying above it. To protect the disk and slider from corrosion damage, contact scratching, high friction and wear, a thin lubricant layer is coated on the disk surface. With the continuous increase in the hard disk drive (HDD) areal density, the spacing between the head and the media is rapidly approaching the sub-nanometer regime, which demands the thickness of lubricant to be molecularly-thin. At such a nanoscale head-disk interface, the short-range forces and the air shear force may cause significant lubricant migration [1, 2]. The lubricant may pile up, and/or be picked up by the slider [3], which in turn affects the flyability of the slider. Meanwhile, the short-range forces such as Van de Waals forces may cause lubricant instability issues [1].

Commentary by Dr. Valentin Fuster
2013;():V001T01A007. doi:10.1115/ISPS2013-2840.

Carbon nano-tubes (CNTs) have certain desirable mechanical properties such as high tensile strength and high flexibility. The frictional properties of non-lubricated CNTs have been previously investigated by certain researchers [1], [2]. In their studies, oriented CNT samples were prepared by chemical vapour deposition (CVD). However, CNTs prepared by CVD generally exhibit weak adhesion with the substrate because, in CVD, a seed layer is required for the growth of CNTs. In this study, we prepared CNTs by the surface decomposition of SiC. CNTs prepared in this manner exhibit stronger adhesion with the SiC substrate because the carbon atoms of the CNTs form a chemical bond with the SiC atoms [3]. On the other hand, the application of dynamic flying height (DFH) control technology to a hard disk drive (HDD) reduces the clearance of magnetic heads above the disk surface to a few nanometers. Further, a little bit of particles, small asperities, and small amount of smear disturb the flyability of magnetic heads. Therefore, the cleanliness of disk surfaces is the important factor for head flyability. Generally, the final tape polishing and the slider burnishing are applied in order to improve the cleanliness of disk surface in manufacturing process. In this study, we focused on the improvement of the burnishing efficiency of burnishing slider by an application of the vertically-aligned CNT for burnishing slider surface.

Topics: Carbon , Disks , Nanotubes
Commentary by Dr. Valentin Fuster
2013;():V001T01A008. doi:10.1115/ISPS2013-2845.

The van der Waals (vdW) dispersion pressures between a half-space consisting of a uniform material and a half-space with one-dimensional material distribution in the in-plane direction have been theoretically derived. Two patterns of material distribution were considered here, i.e., a periodic distribution of materials (Pattern 1) and a distribution of two materials with single interface (Pattern 2). The vdW pressure for Pattern 1 was derived based on a Fourier series, while the vdW pressure for Pattern 2 was derived as elementary functions. The basic characteristics of these vdW pressures were clarified.

Commentary by Dr. Valentin Fuster
2013;():V001T01A009. doi:10.1115/ISPS2013-2853.

Thermally assisted magnetic recording (TAMR) has been studied to achieve high magnetic recording densities. Thus far, we have investigated the depletion of a thin lubricant film on a disk surface subjected to rapid laser heating in TAMR and elucidated the fundamental characteristics and the mechanisms related to lubricant depletion due to laser heating, theoretically and experimentally. A DLC thin film on a disk surface is damaged when it is heated to high temperatures of approximately 200∼400°C using laser beams in TAMR. These concerns may also be a critical technical issue in TAMR. Thus far, experimental research has been carried out to understand the DLC damage due to laser heating[1][2]. However, existing knowledge regarding the abovementioned issue is still limited. Therefore, in this study, experimental studies have been conducted to understand the structural stability of DLC thin films under heating using CVD and FCVA DLC films.

Commentary by Dr. Valentin Fuster
2013;():V001T01A010. doi:10.1115/ISPS2013-2860.

Heat-assisted magnetic recording (HAMR) is a promising technology for overcoming the superparamagnetic limit, and thereby enabling the achievement of a recording density beyond 8 Tb/in2 in a hard disk drive (HDD) [1]. The HAMR head gimbal assembly (HGA) consists of a HAMR head slider, a suspension, and a laser diode (LD) mounted on the slider. An optical near-field transducer (NFT) and a waveguide are near the write-pole in the head slider. During the writing process, light energy is delivered from the LD to the NFT through the waveguide, and the NFT forms a nano-size thermal spot on the recording medium, thereby reducing its coercivity. Development of an HAMR-HGA requires solving several thermal problems. There are two heat sources. One is the LD, which transforms electrical energy into light energy and heat energy. The heat energy increases the temperature of the LD itself, which reduces the laser power and deforms the slider. The other is the NFT, which absorbs light energy. The absorbed energy is transformed into heat energy. This increases the temperature of the NFT and causes the head to protrude. The thermal deformation and protrusion cause a change in the flying-height (FH). The head thermal protrusion problem has been solved using finite-element method (FEM) simulation [2]. We have developed a novel experimental set-up for measuring the temperature increase and FH change simultaneously.

Topics: Temperature
Commentary by Dr. Valentin Fuster
2013;():V001T01A011. doi:10.1115/ISPS2013-2864.

The present paper analyzes the static lubrication characteristics of a slider flying over a running boundary wall with arbitrary local temperature distributions using the thermo-molecular gas-film lubrication (t-MGL) equation. We obtain two approximate solutions: (i) a linearized solution when the temperature deviation is small (τW ≪1) and arbitrarily distributed, and (ii) a solution for the case with a very large bearing number (Λ → ∞). We herein numerically calculate the static lubrication characteristics and verify the validities of these two approximate solutions. Moreover, we calculate the characteristics for various temperature distributions produced by laser heating.

Commentary by Dr. Valentin Fuster
2013;():V001T01A012. doi:10.1115/ISPS2013-2871.

Bit patterned media (BPM) is considered as a revolutionary technology to enable further increase of areal density of magnetic recording beyond 1 Tbits/in2 [1]. Implementing BPM technology, however, significantly increases the complexity of the recording process, but also poses tremendous tribological challenges on the head-disk interface (HDI) [2]. One of the major challenges facing BPM is touchdown detection by thermal flying-height control (TFC), in which a minute heater located near the read/write transducers is used to thermally protrude a small portion of the slider into contact with the disk, and the contact is then detected by directly or indirectly measuring the friction, temperature rise or vibration caused by the contact [3]–[7]. Most recording heads rely on touchdown detection to achieve a desired flying height (FH), which approaches sub-1-nm regime for many of today’s commercial drives. As a result sensitive and accurate touchdown detection is of critical importance for a reliable head-disk interface by reducing contact duration and unnecessary interaction between the slider and the disk. However, the impact of touchdown on the mechanical robustness of the media has not been properly studied.

Topics: Robustness
Commentary by Dr. Valentin Fuster
2013;():V001T01A013. doi:10.1115/ISPS2013-2872.

In order to meet the demand to increase the areal density of magnetic recording, promising technologies such as heat-assisted magnetic recording (HAMR) are being extensively pursued [1–3]. However, the high transient disk temperature (400–500 °C, nanosecond time scale) required by this recording scheme might dramatically affect the reliability of the head-disk interface. Possible issues include overcoat oxidation and graphitization, both on head and disk, as well as lubricant evaporation, thermodiffusion, and decomposition. Although modeling and experimental studies have been published describing the lubricant film evaporation under thermal exposure, very few studies have been directed toward understanding the mechanisms of lubricant decomposition [4–7].

Commentary by Dr. Valentin Fuster
2013;():V001T01A014. doi:10.1115/ISPS2013-2886.

The evaluation of submonolayer lubricant mobility is becoming increasingly important in hard disk drives, in which the thickness of the lubricant has been reduced to one monolayer and that of the mobile lubricant layer has been reduced to less than 0.3 nm. To decrease the head–disk spacing significantly, a design concept of surfing–recording is proposed, in which a protruding small head’s surface slides on the mobile lubricant layer without solid–solid contact [1]. However, its feasibility has not yet been confirmed because the durability of the mobile and bonded lubricants with respect to the head–disk sliding contact has not been elucidated well.

Topics: Lubricants
Commentary by Dr. Valentin Fuster
2013;():V001T01A015. doi:10.1115/ISPS2013-2893.

A numerical model for the simulation of fretting wear at the dimple/gimbal interface of a hard disk drive suspension has been developed. The friction and wear coefficients used in the model are determined from experimental measurements. Archard’s wear equation is implemented numerically and the contact interface geometry is updated incrementally. The von Mises stress distribution and the worn surface profiles are determined.

Commentary by Dr. Valentin Fuster
2013;():V001T01A016. doi:10.1115/ISPS2013-2894.

For increasing areal density in hard disk drives (HDDs), the physical clearance between the read/write element and the surface of the disk has been continuously decreasing to 1 nm or below [1]. At such a low clearance, the contact between the head and the disk is inevitable to occur, so head wear is becoming a critical issue in the development of HDD. The contact between the head and the disk induces a frictional heating, which may generate an additional thermal protrusion in the contact area of the head, and causes more wear. On the other hand, the target clearance in a HDD is generally determined by pulling back a setting TFC power from the touchdown point, accurately identifying the touchdown point is very significant for the clearance control in hard disk drive. A thermal protrusion is caused by friction-heating in the status of touchdown. Therefore, it is very necessary to quantitatively understand on friction induced thermal protrusion and clearance loss.

Topics: Disks , Heating
Commentary by Dr. Valentin Fuster
2013;():V001T01A017. doi:10.1115/ISPS2013-2895.

A thermal contact sensor embedded in a magnetic-head slider was developed. The sensor has been used for contact detection between a head slider and a disk in hard disk drives, and, our previous research has shown that the sensor could successfully detect disk defects including asperities and pits. In this work, the sensor dimension effect and characterization of defect size was studied in order to better understanding of defect size. The results showed that the defect size can be clarified by considering sensor size and scan pitch.

Commentary by Dr. Valentin Fuster
2013;():V001T01A018. doi:10.1115/ISPS2013-2899.

Delamination between an ultra-thin amorphous carbon overcoat, a silicon adhesion layer, and permalloy substrate material of a hard drive recording head is studied during normal loading/unloading of the head disk interface. The effect of normal load and thickness of the silicon adhesion layer on delamination of the Si-permalloy and amorphous carbon-Si interfaces is quantified using a molecular dynamics model. No permanent delamination is found for contact pressures up to 100 MPa, except for the case where a silicon adhesion layer is absent.

Commentary by Dr. Valentin Fuster
2013;():V001T01A019. doi:10.1115/ISPS2013-2905.

During normal operations of a hard disk drive (HDD), a slider flies over the surface of a spinning disk lifted by a thin layer of air. The disk surface is coated by a molecularly-thin layer of lubricant to protect it against corrosion and reduce wear on the read/write head. The flying height of the slider should be as small as possible in order to achieve higher recording densities. In current HDDs the head-to-disk spacing is on the order of 1–3 nm [1]. At this ultra-low spacing lubricant from the disk often transfers to the slider’s air bearing surface (ABS) forming a thin film that imposes a significant degradation on its performance. Problems such as head instabilities, flying stiction, disk lubricant depletion and increase in head-disk spacing occur when lubricant is present on the ABS [2]. To avoid this condition, modern sliders should be able to remove the lubricant from the ABS as fast as possible. Hence, it is necessary to have a thorough understanding of the lubricant flow process and its driving forces.

Commentary by Dr. Valentin Fuster
2013;():V001T01A020. doi:10.1115/ISPS2013-2908.

The contact between a touchdown sensor and an asperity on a disk is investigated using finite element analysis. The touchdown sensor is embedded in the area of the thermal protrusion of a thermal flying-height control (TFC) slider. A transient thermo-elastic-plastic finite element contact model is developed to simulate the temperature rise of the touchdown sensor due to frictional heating.

Topics: Sensors , Disks
Commentary by Dr. Valentin Fuster
2013;():V001T01A021. doi:10.1115/ISPS2013-2909.

The head-disk spacing in current hard disk drives is approximately 1–2 nm. This distance is on the same order as the peak to valley surface roughness of a typical thin film disk. If one attempts to reduce the head-disk spacing even more, intermittent contacts between the slider and the disk are more likely to occur. Intermittent contacts are undesirable since they can result in slider and disk wear, lubricant transfer or degradation of the read and write elements.

Commentary by Dr. Valentin Fuster
2013;():V001T01A022. doi:10.1115/ISPS2013-2914.

Molecular dynamics (MD) simulations is an effective method to investigate the mechanical and tribological properties of amorphous carbon since the coordinates of all atoms can be calculated as a function of time. Several empirical potentials can be used to model the interatomic interactions of carbon atoms, including the Tersoff potential, the Reactive Bond Order (REBO) potential and its revised versions, and the Reactive Force Field (ReaxFF) potential. The choice of empirical potential is one of the fundamental and important assumptions in the MD approach since it can affect the properties of amorphous carbon during the MD simulations. In this study, liquid quenching method is used to model amorphous carbon for computational efficiency. We will study the influence of the three types of potentials, specifically the Tersoff potential, the 2nd REBO potential and the ReaxFF potential on DLC parameters. These parameters include the sp3 content as a function of density, the arrangement of the amorphous carbon atoms, hybridization and the radial distribution functions G(r).

Commentary by Dr. Valentin Fuster
2013;():V001T01A023. doi:10.1115/ISPS2013-2932.

New magnetic storage technology enhancements are being introduced into the HDD products to facilitate lower head media spacing and reliability. Recently, advanced components such as thermal protrusion devices, Head Disc Interface (HDI) proximity sensors, complex self-compensating AAB designs have been integrated into the recording heads. Component development and product integration teams evaluate performance of these critical head disc interfaces for tribological robustness. New HDI components could potentially bring new HDI wear mechanisms that occur under specific thermo-mechanical conditions. Characterization of recording head DLC overcoat nanoscale wear performance has always been a challenge. Historically, nano-wear tests evolved in conjunction with advances in Scanning Probe Microscopy (SPM) techniques [1] and wear resistive tools [2] like diamond tip cantilevers. Here, by controlling SPM, contact force specified wear patterns can be obtained in contact mode or dynamic mode. Decisions on DLC wear resistance can be made qualitatively by evaluating wear mark topographies.

Commentary by Dr. Valentin Fuster
2013;():V001T01A024. doi:10.1115/ISPS2013-2935.

The increasing demanding for higher capacity storage devices continues to push the recoding densities of hard disk drivers to their limit. This has led to a significant decrease in the slider-disk spacing to less than 10 nm. The active-head slider technology has recently been implemented in magnetic recording disk. The thermal flying height control (TFC) sliders are to use a small resistance heater incorporated near the read/write element. By applying a current to the heater, it can change the contour of slider due to the Joule heat induced thermal deformation, thereby controlling the flying height of the slider. Improving the power efficiency and obtaining a large reduction of the flying height are important in the application of thermal flying height control slider.

Commentary by Dr. Valentin Fuster
2013;():V001T01A025. doi:10.1115/ISPS2013-2936.

A model for lubricant transfer from a rotating magnetic recording disk to a magnetic recording slider is developed using molecular dynamics simulation. The effects of disk velocity and local pressure changes on lubricant transfer are investigated.

Commentary by Dr. Valentin Fuster
2013;():V001T01A026. doi:10.1115/ISPS2013-2942.

A quick and reliable active flying height calibration is critical in today’s hard disc drive short product development and high volume production cycles. In addition to the servo signals, passive HDI acoustic and proximity monitoring techniques are tracking equilibrium of the head gimble assembly and air bearing modes. Passive acoustic HDI monitoring had been proven to be capable in active head protrusion detection applications [1] where derived passive and active Air Bearing flying profiles help to set active flying clearance. With enhanced sensitivity, passive acoustic techniques such as AE can detect embedded particles [2]. The drawback of this technique is that noisy HDD environment causes loss of detectability of the useful AE signal [3]. Special attention has to be paid for extracting desirable HDI information. On the other hand, recording head based proximity probes are immune to torsional HDI modes and operate on pitch mode induced modulation. Advanced HDD today uses a combination of recording head based proximity sensors that are designed to sense HDI modulation at close proximity to the disc. It has to be pointed out that interpretation of proximity probe contact signatures always has been challenging.

Commentary by Dr. Valentin Fuster
2013;():V001T01A027. doi:10.1115/ISPS2013-2945.

Thermal flying height control (TFC) has recently been implemented in magnetic recording disk drives to reduce the flying height at the read/write element for high areal density magnetic recording. In this work, we propose a novel thermal flying height control slider, by designing a slit near the thermal heater in the slider. The thermal-structure simulation coupled with air bearing simulation is used to simulate the actuation by the thermal actuator, as well as the effects on flying performance of slider being actuated.

Topics: Design
Commentary by Dr. Valentin Fuster
2013;():V001T01A028. doi:10.1115/ISPS2013-2947.

A pump-probe experimental technique that incorporated a 527nm wavelength pump laser and a 476nm probe laser was applied to a magnetic storage disk having a magnetic layer comprised of a FePt alloy and coated with a hydrogenated carbon overcoat (COC). The pump laser power was systematically increased while sweeping the applied field with an electromagnet to observe the temperature dependent magnetization, which is proportional to the change in the polarization of the reflected beam. In this way the laser power required to heat the media to the Curie temperature (Tc) was determined, with the Curie temperature of the media determined from a separate magnetometry measurement. Such a single point laser power-to-media temperature calibration allowed the determination of the media temperature over a small laser power range near Tc. The carbon over-coated FePt media was then irradiated for varying durations at temperatures pertinent to a Heat Assisted Magnetic Recording (HAMR) device [1]. The COC surface topography and carbon bonding structure within each irradiated zone was probed with AFM and micro-spot Raman. A subtle, systematic temperature and duration dependent change in the COC was observed. With increasing temperature and duration, the Raman D-peak became increasingly pronounced, signaling an increase of the sp2 (disorder) content in the film in the irradiated region. At incrementally higher temperatures, the loss of the carbon overcoat becomes apparent as a shallow depression in the COC film in the irradiated area. A clearer picture of the possible sensitivity and kinetics of the loss of COC on the HAMR media surface was obtained by measuring its loss over a range of irradiation temperatures and durations. The activation energy and COC loss rate were obtained and a possible mechanism for COC failure-loss was discussed within the bounds of the operating HAMR device [2].

Commentary by Dr. Valentin Fuster

Actuator/Suspension and Sensors

2013;():V001T02A001. doi:10.1115/ISPS2013-2824.

In machine tool industry, the current trend is to use magnetic scales instead of mechanical scales or optical scales for linear position identification and control. As the demand for more accurate precision in magnetic scale, more stable reading head suspension is thought. Magnetic media with grooves, such as patterned-media, are considered to achieve ultrahigh magnetic pitch density. Patterned-media consists of land parts for magnetized N pole and grooves parts for S pole. The higher magnetic pitch density on the media, the lower magnetic flux we can measure. In order to measure reliable magnetic flux signal, the distance between the media and reader head needs to be as close as possible. During the process, aerodynamics, which caused by the reader head passing through groove parts with tiny distance between reader head and media, have an impact on reader head suspension which leads to vibration and misjudgment of measured signals. In this paper, parameter studies are conducted with the goal placed on correlating response of certain suspension vibration modes to optimal parameters in reader head suspension design.

Commentary by Dr. Valentin Fuster
2013;():V001T02A002. doi:10.1115/ISPS2013-2891.

This paper reports a new rotary thermal micro-actuator. This new thermal actuator uses a pair of powerful silicon-polymeric composite benders to actuate a magnetic head slider into a rotation when the expandable polymer elements are resistively heated. The advantage is the rotary micro-actuator design can move the read/write head slider with a larger lateral displacement by using a new T-shape central hinge joint as compared to the previous translational design. The experimental results demonstrate that the prototyped device can reach up 314nm displacement by a 4V step voltage. The 1st mechanical resonance frequency has been pushed up to 35 kHz. Simulation shows that the micro-actuator can be subjected to 1000G shock loading under non-operation mode. The large displacement, high resonance frequency and robust shock resistance make the rotary thermal micro-actuator be very suitable for a wide range of precise positioning systems applications including dual-stage positioning systems in disk drives and resonance switches in microsystems.

Commentary by Dr. Valentin Fuster
2013;():V001T02A003. doi:10.1115/ISPS2013-2896.

Heat assisted magnetic recording (HAMR) and slim mobile hard disk drives (HDD) are being developed parallelly to maintain cost advantage over the solid state drive (SSD). Operational shock and non-operational shock capabilities are seriously challenged for the slim HDDs due to reduced stiffness (thickness). It is worse for slim HAMR drives due to additional laser diode (LD) and other necessities being added on slider. Shock tests are part of the key performance matrices that must be passed in HDD reliability tests, and the concerns for HAMR mobile drives are, 1) slider lift-off G-level degradation during op-shock, and 2) LD back-to-back hitting during non-operational shock. We studied a few potential HAMR HGA designs, also analyzed a design that improves drive op-shock performances.

Commentary by Dr. Valentin Fuster
2013;():V001T02A004. doi:10.1115/ISPS2013-2918.

The recording density of hard disk drives is achieving the physical limit due to the recording magnet size limitations. Therefore, the bit density BPI (Bits per inch) is saturated. The residual aim is to increase track density TPI (tracks per inch), because reducing mechanical track misregistration has a possibility of increasing TPI. The Dual Stage Actuator using a PZT microactuator which enables better positioning accuracy, is widely used in 3.5 inch high density drives. The latest PZT actuator called a “Milli” actuator drives the whole suspension. However, the mass of the suspension is around several milli-grams, thus the reaction force of PZT driving sometimes causes excitation to attached arm resonance at 8–9 kHz. In addition, the fundamental resonance frequency of a milli-actuator is around 20–25 kHz, the sway frequency of whole suspension.

Topics: Actuators
Commentary by Dr. Valentin Fuster
2013;():V001T02A005. doi:10.1115/ISPS2013-2920.

The magnetic spacing of Hard Disk Drives (HDD) needs to be reduced for high recording density. On the other hand, it is necessary to prevent contact between the slider and disk for reliability of HDDs. Various research was carried out for the flying stability of the slider [1–3]. Furthermore, the magnetic track width also needs to be narrowed for high recording density. The Dual Stage Actuator (DSA) servo system is used for high positioning accuracy [4]. The DSA servo system uses a piezoelectric actuator on a suspension in addition to Voice Coil Motor (VCM). In this study, we measured vibrations to the slider and suspension caused by the PZT and VCM actuations. Two Laser Doppler Vibrometers (LDV) were used for the measurement. Moreover, we performed a numerical analysis to estimate the roll moment of the Air Bearing Surface (ABS) of the slider caused by PZT actuation. As results, we confirmed that the ABS vibrated in vertical direction due to the suspension’s vibrations caused by PZT and VCM actuations.

Commentary by Dr. Valentin Fuster
2013;():V001T02A006. doi:10.1115/ISPS2013-2929.

The PZT motor is a critical component for dual stage actuation (DSA) in hard disk drives. When voltage is applied to PZT motors, the suspension with the motors can provide slider off-track motion. Servo control has been focusing on the slider off-track motion because the control loop is designed based on the position error signal (PES) in the off-track direction. However, along with PZT off-track actuation, gimbal and slider vertical motion is inevitably introduced, which may increase head-disk interference risks and even cause lube moguls and ABS (air-bearing surface) wear. In this paper, we present an experimental methodology to investigate the relationship of slider vertical motion and DSA voltage injection.

Commentary by Dr. Valentin Fuster
2013;():V001T02A007. doi:10.1115/ISPS2013-2941.

One of the issues in VCM rotary actuation in hard disk drives (HDDs) is the excessive sensitivity of the system to the skew angle. The rotation of the VCM from the inner diameter (ID) to the outer diameter (OD) of the disk results in an angle of skew between the read/write head and the track. The difference in skew angle, between the ID to the OD can be as large as 25 to 30 degrees in conventional 3.5″ and 2.5″ HDDs. A large skew angle affects the slider’s flying performance and off-track capability, causing an increase in side reading and writing, and thus reduces the achievable recording density. Large skewed actuation also complicates the position error signal calibration process in the hard disk drive servo loop. This paper presents a 4 link mechanism which can be designed to achieve near zero skew actuation in hard disk drives. The profiles of the arm, suspension, and links can be designed and optimized such that the skew angle is close to zero while the VCM actuator rotates from the ID to the OD. Study shows that the 4-link mechanism does not degrade the resonance performance along the tracking direction compared to a conventional actuator.

Topics: Disks
Commentary by Dr. Valentin Fuster

Servo Control Technology

2013;():V001T03A001. doi:10.1115/ISPS2013-2839.

A mechanical structure embedded in a sampled-data system often contains several resonant modes above the Nyquist frequency of the system output’s sampling rate. Due to the notorious aliasing effect produced by the sampling operation, such resonant modes are difficult to be identified using conventional techniques.

Topics: Resonance
Commentary by Dr. Valentin Fuster
2013;():V001T03A002. doi:10.1115/ISPS2013-2901.

The fast growing areal density and continuous increasing demand of IOPS and throughput in hard disk drive present great challenges to servo systems on the performance of the track-follow accuracy and seek time. A high bandwidth servo system is required to meet the demand. However, the performance of the servo systems is ultimately limited by the resolution of the position signal which is demodulated form embedded servo sector. Inside the servo sector, the servo track address combining with the servo bursts provide a global position signal of read/write head. The servo track address, which is commonly encoded as gray code, provides coarse position information. Whereas the servo bursts carries the position error signal (PES) to determine the fine position information. There are multiple servo pattern schemes that have been used in hard disk drive, for example, amplitude based servo pattern, phase pattern, and dual frequency pattern [1]. The servo track address and servo bursts span multiple magnetic cycles. The head position is assumed to be unchanged when it travels through the servo sector. The assumption is valid when head is track-following or seeking at low velocity. However, when the head seeks with high velocity, the assumption induces large PE demodulation error, since the head can move as much as a few tracks when it travels through the servo sector. Thereby, it prevents us to use high servo bandwidth for pushing seeking performance. To tackle this problem, we proposed a robust PE demodulation algorithm which can eliminate the head velocity introduced error. The new demodulation algorithm can be generally applied to any servo pattern schemes. The paper is organized as follows. The servo burst modeling and problem formulations are introduced in section I. The velocity based PE demodulation algorithm is presented in section II. The paper concludes with simulation and experiment results.

Commentary by Dr. Valentin Fuster
2013;():V001T03A003. doi:10.1115/ISPS2013-2911.

This paper studies off-track write protection in HDDs. The system data integrity requirement is formulated based on the head/media and data track pitch configurations and a servo-mechanical system track misregistration (TMR) under various conditions. A write fault protection scheme is formulated based on position estimation through the current and predicted future PES (position error signal). The write fault trigger threshold determination and its impact on the system trade-offs are qualitatively discussed. The shock protection method applies to both conventional magnetic recording (CMR) and shingled magnetic recording (SMR).

Commentary by Dr. Valentin Fuster
2013;():V001T03A004. doi:10.1115/ISPS2013-2924.

Magnetic tape remains the medium of choice for long-term data storage at the lowest possible cost. Moreover, tape-cartridge capacities are expected to maintain a compound annual growth rate of about 40%, resulting in a 128 TByte tape-cartridge capacity by 2022, as forecast by the Information Storage Industry Consortium (INSIC) roadmap [1]. To achieve these capacities in future tape products, the data track width has to be aggressively reduced through ultra-precise tape head positioning.

Commentary by Dr. Valentin Fuster
2013;():V001T03A005. doi:10.1115/ISPS2013-2928.

This extended abstract summarizes a methodology along with the experimental results to adaptively reduce time-varying lateral tape motion (LTM) in a Linear Tape-Open (LTO) drive. For the adaptive regulation, the LTO actuator dynamics is modeled with a Linear Time Invariant (LTI) model and control of time-varying LTM disturbances is done via an adaptable linear feedback controller. Adaptive regulation is done via the direct estimation of a perturbation on the feedback controller. By simultaneously minimizing the variance of the Position Error Signal (PES) and the control output signal, the direct estimation of the controller perturbation is formulated as a weighted estimation problem that is implemented recursively for real-time implementation. The experimental results show a significant reduction of the variance of the PES over different tape cartridges and a constant PES variance during a complete reel-in/out operation of the tape drive.

Commentary by Dr. Valentin Fuster
2013;():V001T03A006. doi:10.1115/ISPS2013-2938.

In the realm of hard disk drives (HDD), dual-stage servo control has been shown to achieve increased control bandwidth and reduced power consumption compared to single-stage architectures [1]–[4]. Motivated by these results, we seek to apply dual-stage control to an analogous case of an optical pointing system, which has similar objectives of high-bandwidth control over a wide spatial range.

Topics: Servomechanisms
Commentary by Dr. Valentin Fuster
2013;():V001T03A007. doi:10.1115/ISPS2013-2948.

In hard disk drive (HDD) systems, disturbances commonly contain different frequency components that are time-varying in nature. Different HDD systems may subject to different excitation disturbances. In this case, it is difficult for fixed-gain PID controllers to maintain a good overall performance. When the characteristics of the disturbances change, or when servos are designed for different drive products, the PID gains have to be retuned. This paper presents automatic online gain tuning of PID controllers based on neural networks. The proposed control scheme can automatically adjust the PID parameters online in the presence of time-varying disturbances, or for different disturbances among different HDD products, and find the optimal sets of PID gains through the self-learning ability of neural networks.

Commentary by Dr. Valentin Fuster
2013;():V001T03A008. doi:10.1115/ISPS2013-2951.

This paper presents a novel robust H control design for linear systems with periodic irregular sampling and regular actuation rates. A three-step design algorithm is developed to design a controller that achieves high robustness in terms of disk margin, and high performance in terms of root mean square (RMS) of 3σ-value of performance signal. The proposed method is exploited to design a track-following controller for a hard disk drive (HDD) with 30% sampling time irregularity. The simulation study presented in this paper shows the effectiveness of the proposed control design for high-order systems with large periods.

Commentary by Dr. Valentin Fuster

Shock and Flow Induced Vibrations

2013;():V001T04A001. doi:10.1115/ISPS2013-2809.

Over the past decade, there has been an increase in the demand of hard disk drives (HDD) used in portable devices. In such applications HDDs are often subjected to mechanical shocks. Hence it is important to study the stability of mobile drives during operational shocks (op-shock) in order to improve their shock performance. Former numerical investigations [1–3] used either detailed structure models and simplified air bearing models or vice versa to understand the HDI response during an opshock event. In 2012, Rai and Bogy [4] proposed a method in which both the HDD components and the air bearing were modeled in detail and were coupled with each other. However, in this model the head actuator assembly (HAA) was assumed to be amounted on a fixed support and hence the flexibility of the base plate and those effects on the HAA were neglected. In this study, we model the HAA as mounted on the base plate to investigate the effects of HDD components on the shock performance of mobile drives.

Commentary by Dr. Valentin Fuster
2013;():V001T04A002. doi:10.1115/ISPS2013-2810.

This paper presents an experimental study of digital narrowband active control on the flow-induced vibrations (FIV) on the head gimbals assembly (HGA) in a working hard disk drive (HDD). Firstly, the modal testing on the HDD was carried out, in which the disk modes were analyzed with a 1-D laser Doppler vibrometer (LDV) and the HGA vibration modes with a 3-D LDV. Secondly, a digital feedback control close-loop was implemented in experiments to suppress the FIV spectrum peaks on the HGA. In this close-loop, the HGA vibrations detected by the LDV were used as feedback error signals, then the signals was passed through a digital controller to generate feedback signals to drive a piezoelectric disk to actuate feedback acoustic pressure around the HGA. Active control experiments were conducted in narrow bands on five principal peaks in the HGA off-plate vibration spectrum, around 1256Hz, 1428Hz, 2141Hz, 2519Hz and 3469Hz, respectively. It is shown that distinct suppression of at least 10 dB can be achieved on all these HGA vibration peaks.

Commentary by Dr. Valentin Fuster
2013;():V001T04A003. doi:10.1115/ISPS2013-2838.

The change of attitude of the spindle system can induce change in its resonance frequencies. The attitude of the spindle system is determined by each rotating event. The change in resonance frequency affects stiffness and damping ratio of the spindle system. Therefore, the dynamic behavior of a spindle system is affected by the change of dynamic coefficients of the spindle system under non-operational vibration.

Commentary by Dr. Valentin Fuster
2013;():V001T04A004. doi:10.1115/ISPS2013-2882.

One of the problems found in the 2.5-inch hard disk drives (HDD) in operation is its vibration. Aiming to find important information to help reduce the vibration transmitted to the outer shell of HDD, the parameters involving vibrational energy transmission among the main components of HDD are identified by the test-based Statistical Energy Analysis (SEA). First, the vibration tests of HDD in the idle mode are performed in order to identify the contribution of the main components; the platters and the top cover, to the overall vibration of HDD. Second, the SEA parameters including the dissipation loss factors of the components and coupling loss factors of the pairs of the components are then experimentally determined in order to calculate the vibration transmission power among the components.

Topics: Disks
Commentary by Dr. Valentin Fuster

Spindle Motor and Acoustics

2013;():V001T05A001. doi:10.1115/ISPS2013-2850.

Cogging torque of a brushless DC (BLDC) motor is a source of the vibration and noise of the hard disk drive (HDD) spindle motor, and the excitation frequencies of the cogging torques are the harmonics of the least common multiple of the poles and slots in ideal BLDC motors. However, manufacturing errors generate the additional harmonics to the cogging torque. Especially, the uneven magnetization of the permanent magnet (PM) in BLDC motors generates additional slot harmonics to the cogging torque. In small BLDC motors such as 2.5″ HDD spindle motors, the effect of additional slot harmonics is as serious as that of the fundamental harmonics of the cogging torque. A coil-positioning error of the magnetizer is a major source among the several potential sources of uneven magnetization of a ring-shaped PM in a HDD spindle motor [1]. It is difficult to estimate and to reduce the coil-positioning error when manufacturing a magnetizer. In addition, each magnetizer has different range of the coil-positioning error.

Commentary by Dr. Valentin Fuster
2013;():V001T05A002. doi:10.1115/ISPS2013-2857.

In order to achieve high area density of HDD to 10Tbit/in2, both radial and axial direction Repeatable Run-Out (RRO) and None repeatable Run-Out (NRRO) of spindle motor in HDD should be significantly reduced. That means the high performance spindle motor is need. Currently, the spindle motor used in HDD uses a rotating shaft FDB which structure likes slender cantilever beam to support the rotor and the problem of this kind of structure is reported in [1]. This structure cannot meet HDD high TPI requirements and should be replaced by the fixed shaft FDB spindle motor and the analytical model is shown in Fig. 1. Moreover, different types of Unbalance Magnetic Pull (UMP) of the Spindle motor and induced vibration should be fully studied. In order to fully understand motor vibration behavior, a thorough theoretical derivation of motor dynamics should be carried out as they can disclose clearly the global performance of the motor. Generally, four types of UMP reported in [1]–[3] can generate the motor lateral and axis vibration and produce motor acoustic noise. Researchers have studied vibration and acoustic signals in recent years[1]–[6]. In this paper, the PMSM mathematic model has introduced and validated by 12 slots and 5 pole-pairs PM surface mounting Synchronous motor M1 simulation case study. This type of Permanent Magnetic Synchronous motor (PMSM) is using in many applications, e.g.

Topics: Engines , Rotors
Commentary by Dr. Valentin Fuster
2013;():V001T05A003. doi:10.1115/ISPS2013-2863.

Fluid dynamic bearings (FDBs) have been applied to the spindle motor of a computer hard disk drive (HDD) because FDBs provide better dynamical characteristics of lower vibration and noise than ball bearings. However, one of the weaknesses of FBDs is the instability arising from the air bubble in oil lubricant of FDBs. Air bubbles are formed and trapped in oil lubricant by the inappropriate process of oil injection or the external shock. Trapped air bubbles decrease the rotational accuracy and the stability of a rotor-bearing system in such a way to generate non-repeatable run-out (NRRO) and to decrease the stiffness and damping coefficients of FDBs. It is important to predict the path of air bubbles in oil lubricant and to design FDBs in such a way to easily expel air bubbles out of operating FDBs.

Topics: Bubbles , Modeling
Commentary by Dr. Valentin Fuster
2013;():V001T05A004. doi:10.1115/ISPS2013-2865.

Both radial and axial direction Repeatable Run-Out (RRO) and none repeatable Run-Out (NRRO) of spindle motor in HDD is a big concern in high TPI requirement. Besides the reasonable spindle motor structure design which studied in [3]–[4], the fabrication tolerance of spindle motor parts should be controlled in order to minimum RRO and NRRO. As it is known, the vibration of spindle motor is mainly caused by unreasonable Unbalance Magnet Pull (UMP). Different motor parts faults (tolerance is out of the control) will generate different types of UMP which should be generate different vibration signals pattern. Though studying different vibration signals and acoustic noise pattern, the types of UMP or other faults should be detected and classified. then, the related out of tolerance controlled parts can be known. Researchers have studied vibration and acoustic signals in recent years [5][6]–[7]. In this paper, the 12 slots and 5 pole-pairs PM surface mounting Synchronous motor is modified as M1 to do experimental study. This paper can be a guideline of design high performance motor; it also can be the reference of general motor fault diagnosis.

Topics: Engines , Rotors , Vibration
Commentary by Dr. Valentin Fuster
2013;():V001T05A005. doi:10.1115/ISPS2013-2870.

Fluid dynamic bearings (FDBs) of a HDD spindle motor support the rotating disk-spindle system through the pressure generated in the fluid lubricant. The radial and axial clearances of a 2.5″ HDD spindle motor are approximately 2 and 30 micro-meters, respectively, and herringbone or spiral grooves are inscribed in the sleeve of journal or thrust bearings to provide pumping pressure. One of the difficult manufacturing processes is to inscribe uniform grooves, especially groove depth in the range of several micro meters. Grooves are inscribed on the surface of the stainless steel sleeve by the electro chemical machining (ECM) which generally generates rough surface of the sleeve in grooved bearing. Ball-sizing process is used to scrape down rough surface. When a ball passes through the sleeve of FDBs to make rough surface smooth, compressive pressure is generated between ball and sleeve inlet and between ball and sleeve outlet, respectively. It forms an hourglass-shape tapered sleeve as shown in Figure 1, and tapered sleeve generally decreases the static and dynamic performance of the FDBs and the HDD spindle system, consequently.

Commentary by Dr. Valentin Fuster
2013;():V001T05A006. doi:10.1115/ISPS2013-2885.

As recording area density increases, magnetic recording is approaching near contact regime. Disk deformations, both tangential and circumferential, affect magnetic head flight height (FH) significantly at this FH range, and it becomes increasingly important to magnetic reading and writing performances. Variation in manufacturing process, mechanical tolerance as well as design itself can affect disk deformation greatly. In this presentation, we present a few disk pack design improvements to minimize disk coning and disk crown. The designs are able to achieve consistent disk deformation even under significant manufacturing tolerances.

Commentary by Dr. Valentin Fuster
2013;():V001T05A007. doi:10.1115/ISPS2013-2946.

Cogging torque and UMF (unbalanced magnetic force) are major excitation sources of acoustic noise and vibration originated from HDD spindle motors. They are generally outer rotor type motors with fluid dynamic bearings (FDBs). The FDBs support and constrain the rotating disk-spindle system in five degrees of freedom except axial rotating direction. Unbalanced mass of the disk-spindle system generates whirling motion and changes the characteristics of UMF. Several researchers have investigated the harmonic contents of cogging torque and UMF by numerical and analytical methods [1]–[3]. Lee and Jang [4] experimentally and numerically investigated the characteristics of the UMF of a HDD spindle motor due to manufacturing errors such as the uneven magnetization of permanent magnet (PM) and the eccentricity of rotor and stator. However, they discussed only the cogging torque and UMF, and did not investigate the effect of the cogging torque and UMF on acoustic noise and vibration of a HDD spindle system.

Commentary by Dr. Valentin Fuster

Micro/Nano Technology

2013;():V001T06A001. doi:10.1115/ISPS2013-2820.

Bit patterned media (BPM) is being pursued by the disk drive industry as a way of extending magnetic recording densities beyond 1 Tbits/in2 [1]. As the patterned topography of an unplanarized BPM disk generates a tribology quite different than smooth, continuous media, it is important to assess how this topography will impact the tribology of head-disk interfaces (HDI). In this paper, we quantify the impact of BPM topography on flying height modulation.

Topics: Tribology , Disks
Commentary by Dr. Valentin Fuster
2013;():V001T06A002. doi:10.1115/ISPS2013-2846.

A minute optical sensor combined total analysis system (TAS) is thought to be one of the most powerful functional elements needed to realize a “ubiquitous human healthcare” system. In accordance with this concept, we have proposed a fundamental structure of detecting forward and side scattered light from a small cell or particle illuminating laser power through light waveguide formed in a thin resin layer. Based on this concept, we have demonstrated its effectiveness by using a trial-manufactured optical TAS chip, supplying and detecting visible laser power by using multiple optical fibers. Acquiring further various physiological properties created by an internal structure of a particles or cells, it is necessary to illuminate them with a small and arbitrarily-shaped light source placed close vicinity to them.

Commentary by Dr. Valentin Fuster
2013;():V001T06A003. doi:10.1115/ISPS2013-2913.

The recent advances in nanofabrication techniques have made it possible to engineer the magnetic and transport properties of thin magnetic films. The ability to design magnetic behavior is useful for technologies such as development of high-density hard disk drive (HDD) or magnetic random access memory (MRAM). In order to achieve high density in HDD, it is necessary to overcome the limit of super-paramagnetic effect. One way to solve this problem is to increase the anisotropic effect that can resist the external field and provide a net magnetic moment in remanence[1].

Commentary by Dr. Valentin Fuster

Mechatronics, Robotics, and Automation

2013;():V001T07A001. doi:10.1115/ISPS2013-2811.

Electromyogram (EMG) consists on the recording and measurement of the electrical potential generated by the activation of muscle fibers [1]. Electromyographic signals (EMGs) are directly linked to the movement performed by a person. Thus, the study of EMGs for the control prosthesis and exoskeletons has become increasingly popular in the past years. To provide a real time control of a prosthesis or exoskeleton (assistive device) to the user, the time between the movement performed by a healthy arm and the movement of the exoskeleton should be small as possible. The main objective of this paper is to map different movements of the upper limb. Moreover, detect the onset of the EMGs to determine which muscle is producing movement. Surface electrodes were used to perform the experiments in order to insure the comfort of the subjects. The analysis of the signal to detect the onset was done using Matlab. After mapping eight movements, results show that the EMGs recorded from the Trapezius muscle can be used as a discriminative to differentiate between movements performed by the arm and movements performed by the forearm and hand. This will reduce the time and number of EMG channels needed to correctly identify the movement performed by the upper limb of a subject.

Commentary by Dr. Valentin Fuster
2013;():V001T07A002. doi:10.1115/ISPS2013-2823.

In the past ten years, more and more robots are developed. Some are used for hazardous operation and others are used for industrial automation purposes, such as humanoid robot and industrial robot. However, there is another type of robot which is called assistive humanoid robot. The assistive humanoid robot looks very similar to human’s body that can help human to finish some daily tasks, such as moving heavy things, walking up stairs and raising your hand, etc. Besides, the assistive robot absolutely does a great help if it is applied to the patient who are suffering from the severe diseases, or who has difficulty to move his/her arm or leg. The robot can assist the disable arm or leg in moving again. So, people can use this device to manipulate the disable hand to do some easy tasks, such as holding cup for water drinking, or picking and placing some light items [2] Also, it can be used as a device to provide a safe and intensive rehabilitation training for the patients, and it has been proved that assistive robot is effective in assisting the therapist [1][6]. The assistive humanoid robot not only helps patients for recovery or assists patients for simple everyday tasks, but also effectively promotes human’s living quality. However, even though the assistive robot for elbow, wrist or leg has already been widely developed and used in hospital trials, few projects and assistive robotic devices for hand rehabilitation are found in the market [3][7].

Commentary by Dr. Valentin Fuster
2013;():V001T07A003. doi:10.1115/ISPS2013-2854.

Linear actuator has been widely used as vibration motor in mobile phones, and it generates a linear vibration through resonance in which the electromagnetic force with the application of a sinusoidal current excites the fundamental natural vibration mode of the moving mass-spring system. Figure 1 shows a linear actuator for mobile phones whose diameter and height are approximately 10 and 1 mm, respectively. The moving coil and mass are attached to a flat spring, and the radial magnetic field between the plate and the moving yoke is generated through a plate connected to the permanent magnet. The magnetic force in the air-gap between the plate and the yoke is generated according to Ampere’s law once the sinusoidal current is applied to the coil, and it excites the axial vibration mode of the linear actuator that generates the axial vibration. The linear actuators have a fast response time compared with other types of vibration motors. Currently, the response time of the linear actuators is approximately 50 msec, but the users and the application software of mobile phones are demanding increasingly faster response time. However, it is very difficult to reduce the response time while maintaining the vibration magnitude under the given constraints of volume and electric power.

Commentary by Dr. Valentin Fuster
2013;():V001T07A004. doi:10.1115/ISPS2013-2856.

Magnetic microrobots wirelessly manipulated by external magnetic field have been widely investigated as possible surgical alternatives for cardiovascular or intraocular surgeries [1, 2]. Since the principle of manipulation is based on the external magnetic field, the microrobot can be effectively simplified and miniaturized for the application in complex environments in the human body. Several researchers have investigated various types of single-body microrobots to achieve different mechanical motions [1, 2]. However, a magnetically coupled multibody magnetic microrobot (MMM) has not been proposed to improve the mechanical and therapeutic maneuverability to navigate through the blood vessels and to treat the diseased area.

Commentary by Dr. Valentin Fuster
2013;():V001T07A005. doi:10.1115/ISPS2013-2862.

Continuous blood pressure monitoring in daily life could contribute to early detection of strokes and heart attacks, as well as healthcare promotion. Understanding of what patients were doing when their blood pressure changes occurred would be much more helpful to check the causes of blood pressure changes. However, at present, patients should record their activities by filling the clinical activity record card. The activity record card is so inconvenient that handwriting all the activities becomes a burden and causes inaccuracy. Moreover, it is not able to record posture changes that are a major factor related to short-term blood pressure changes. From these reasons, automatic activities recognition method is strongly required.

Topics: Pressure , Sensors , Blood
Commentary by Dr. Valentin Fuster
2013;():V001T07A006. doi:10.1115/ISPS2013-2866.

Optical fiber sensor technology is more and more widely applied in the health monitoring testing of the major projects and infrastructure, because its sensing elements possess characteristics like the small size, high durability, absolute measurement and distributed monitoring. With the development of the optical fiber communication technology, several different kinds of passive devices appear continuously. Fiber Bragg Grating (FBG for short) develops continuingly and speedily in the field of optical fiber communication and sensing technology, owing to its good properties, such as low insertion loss, wavelength absolute coding, being independence on polarization, the flexible adjustment of wavelength and bandwidth and easily connect to fiber. But Fiber Bragg Grating is sensitive about two parameters — the changing temperature and the outside strain. Therefore, cross sensitivity becomes the hot issue. This paper will introduce the temperature compensation technology of the strain monitoring system for a quasi-distributed Fiber Bragg Grating.

Commentary by Dr. Valentin Fuster
2013;():V001T07A007. doi:10.1115/ISPS2013-2867.

The temperature compensation method of BOTDR strain monitoring system is proposed, which is based on Raman Optical Time Domain Reflectometer (ROTDR), aiming at temperature strain coupling effects of Brillouin Optical Time Domain Reflectometer (BOTDR) strain monitoring technology. Then the effectiveness of this method is proved on theoretical and experimental studies, which provides an effective means of improving the accuracy of BOTDR strain monitoring.

Topics: Temperature
Commentary by Dr. Valentin Fuster
2013;():V001T07A008. doi:10.1115/ISPS2013-2873.

In today’s world, there has been an increase in the usage of domestic purpose robots for assisting human activities. Such robots are more effective for physically handicapped people. Sometimes during an accident, person may suffer from a stroke. A stroke occurs when there is a blood clot which blocks the flow of blood due to which a blood vessel breaks, interrupting flow to a particular area of the brain. Functions performed by that area of the brain are lost which include speech, movement, and memory. This paper deals with recovery of human arm movement loss. The wearable exoskeleton robot for upper extremity rehabilitation is taken as the research object. The virtual rehabilitation system was generated in Simulink to carry out dynamic simulation. Robotic rehabilitation has been an effective method since the early 1990’s and is proving to have a significant effect on the fast recovery of stroke affected patients.

Topics: Simulation
Commentary by Dr. Valentin Fuster
2013;():V001T07A009. doi:10.1115/ISPS2013-2876.

This paper presents a novel approach to combine three powerful methods of control theory and fuzzy c-means clustering algorithm to build a robust learning control for nonlinear uncertain systems such as advance robot manipulators. It is worth noting that the combination not only encompasses the features and capabilities of its components but also the limitations attributed to these techniques (e.g, stability issues of fuzzy controller and poor performance of PID controller in the presence of time-varying uncertainties) may be remedied by each other. To date different combinations of the above mentioned methods presented in the literature each having its own merits and limitations. But, for advance robotics applications such as medical robot, and space applications and with increasing complexity of the robot’s tasks, there is a pressing need for the control systems that are able to learn systematically and efficiently during the course of operation, from its own experience, from the demonstration and also in an unsupervised fashion. The controller proposed in this paper aims at building such a control system using a novel approach to combine adaptive fuzzy modeling algorithm, fuzzy c-means clustering algorithm, adaptive sliding mode control and PID controller. Based on the simulations and experimental results, the proposed controller performs remarkably well in terms of the tracking error convergence and robustness against uncertainties.

Commentary by Dr. Valentin Fuster
2013;():V001T07A010. doi:10.1115/ISPS2013-2931.

The properties of fasteners as significant parts in varied engineering systems have been widely investigated [1–3], from hard disk drive devices to construction ground control. These problems are complex in nature because every bolting involves different sources of nonlinear and uncertainty characteristics. The interfaces forces such as contact forces, friction forces and bonding are not known in reality. The base forces and deformation could be redistributed non-uniformly in the presence of complex loadings such as shock and impact. Most of the reported studies focused on the design issues, characterization of the linear dynamic properties and energy dissipation of bolting system as well as using bolts with integrated detecting systems or dynamometers. The capability to assess the interface properties of bolting system is important for mechatronics, mechanical, civil and mining engineering [1–4]. Even though some conventional approaches have been used to infer bolting integrity, the diagnosis technology has been lacking. This study is conducted to explore the possibility of the diagnosis bolting interface integrity under impact by using accelerometer signal. The statistical pattern identification such as artificial neural network and support vector machine is used to diagnose the bolting integrity. By integrating the analysis and experimental data, an ANN is established as a nonparametric model to predict the system properties. Numerous numerical and experimental researches have been conducted to characterize the typical bolting system, which enables extraction of varied dynamic features from different mechanisms associated with the failures. This kind of database could be used as feature to characterizing the effect of complex loads on bolting for ANN training. To further illustrate the feature extraction, we investigated system models. Due to its adaptive and nonlinear input–output transformation capabilities, artificial neural network (ANN) has been widely applied in the field of pattern and system recognition. The proposed approach is capable of monitoring the stress/strain history and integrity of bolting interface with the goal of detecting structural damage and defects. The results from simulation, testing and ANN identification demonstrated the high performance of the proposed approach compared with conventional ones. In the following, an approach is proposed to reliably estimate the dynamic properties of a bolt-surrounding solid mass specimen using its impact response signal. The developed approach can be readily extended to the bolting connection in other systems such as mechanical and mechatronics systems.

Commentary by Dr. Valentin Fuster
2013;():V001T07A011. doi:10.1115/ISPS2013-2934.

Energy harvesting has generated great interest in recent years due to its usefulness in powering Wireless sensor networks (WSN). Energy harvesters are capable of harvesting energies from the environmental sources such as wind, solar, noise and vibrations [1]. They are an alternative source of power as batteries have a limited life and need constant replacing [2]. In hazardous or hard to reach places, energy harvesters are a feasible option as they are capable of providing constant source of power without any maintenance. Many energy harvesters developed mostly work on vibrational kinetic energy as vibrational energy is readily available even in closed environments as compared to solar or wind energies. The kinetic energy harvesters developed so far have been electromagnetic, piezoelectric or electrostatic and are capable of producing energy from micro watts to mili-watts at various frequencies [3, 4].

Commentary by Dr. Valentin Fuster
2013;():V001T07A012. doi:10.1115/ISPS2013-2940.

Damping in a multitude of engineering applications has a variable threshold requirement based on system excitation. Since system excitation is also variable; dampers are designed such that a maximum amount of damping is provided (based on the worst case for a structure), opposed to an optimal amount as a function of excitation. By implementing a hybrid damper design based on a bias component provided through a hydraulic medium and a variable component provided by electromagnetics; an optimal damping quantity can be obtained for a given excitation.

Commentary by Dr. Valentin Fuster
2013;():V001T07A013. doi:10.1115/ISPS2013-2943.

A precision optical exposure process of lithography has become one of the essential processes to manufacture and develop micro electro mechanical system (MEMS) devices, flat panel display (FPD), and semiconductor. For a typical exposure process for the lithography, a photomask that is often very expensive is required to generate patterns[1]. So it is very inefficient not only in terms of cost but also the time due to the reliance on the photomasks in development. The alternative solution is the maskless lithography system, which does not use photomasks since the patterns are generated by using a digital mirror device (DMD). The unit mirror of a digital mirror device has two kinds of status which are on and off, then the status of unit mirrors configures a pattern called point array method. The maskless lithography system can reduce the amount of work forces significantly and save money as well. However, the maskless lithography system has a critical drawback, which is a low throughput since the patterns are generated in a line. This is an intrinsic problem of point array method. So in most volume production processes of maskless lithography system, a number of optical heads are used in order to maximize throughput of the expositing process. And to guarantee the exposure quality, multiple numbers of optical heads should be accurately aligned to each other, and then the focal plane of each optical head is also well aligned with chuck.

Commentary by Dr. Valentin Fuster

Imaging/Printing Technologies and Consumer Electronics

2013;():V001T08A001. doi:10.1115/ISPS2013-2927.

In this study, we analyze the acoustic noise generated by multi-layer ceramic capacitors with the modal test and acoustic noise test. And the relationship between dynamic characteristics of circuit board and acoustic noise was investigated.

Commentary by Dr. Valentin Fuster

Opto-Mechatronics and Optical Storage

2013;():V001T09A001. doi:10.1115/ISPS2013-2833.

Disc cartridge for archive data storage is made up of multi slots array and each slot keeping a disc. However, misalignment between slot and disc is caused by various disturbances sources. The archive data storage should be operated stably, able to cope with the misalignment. Because, misalignment can cause disc crash against slot walls, and miss positioning between transfer robot and disc slot. Therefore, proper detecting misalignment method should be adopted in archive data storage. In this paper, analyze allowable misalignment and propose dual sensing method based on vision system. Suggested method can simultaneously detect the upper and lower part of slots using only one detector. Each image is split by changing each optical path intentionally through lens shifting of 4f imaging system.

Commentary by Dr. Valentin Fuster
2013;():V001T09A002. doi:10.1115/ISPS2013-2848.

Custom image filter design method is suggested in this research for holographic data storage (HDS) system. While the previous research requires the high precise point spread function (PSF) as the deconvolution filter, proposed method calculated image restoration filter without the information of optical system. It could be possible because of the unique characteristic of HDS data page. We use the simple iteration method to obtain the image restoration filter. The performance of custom image filter is verified both simulation and experiment. As a result, it shows the acceptable performance in BER improvement in HDS system.

Commentary by Dr. Valentin Fuster
2013;():V001T09A003. doi:10.1115/ISPS2013-2851.

This research investigates to analyze the effect of ABB parameters on vibration reducing performance. Experiment was performed with respect to the parameters like number of ball, size of ball, mass of pickup base, and friction properties of ABB Race.

Topics: Disks , Friction , Vibration
Commentary by Dr. Valentin Fuster
2013;():V001T09A004. doi:10.1115/ISPS2013-2868.

In holographic data storage system, misalignment of optical components causes fluctuation of path and angle of laser. These phenomena generate data distortion like rotation, barrel, pincushion and mustache distortion, because holographic data storage system has very sensitive tolerance with incident angle of reference beam. Because it is difficult to align perfectly, data distortion occurs inevitably by misalignment. It is important to acquire accurate data page from holographic data storage system without distortion. In this paper, we propose intelligence compensation algorithm for data restoration in holographic data storage system. We used fuzzy system and sub-clustering algorithm to generate fuzzy rules for this compensation algorithm. This proposed algorithm acquires the value how much the data image has barrel distortion. With acquired data form this algorithm, data distortion can be compensated. Barrel image is used for this simulation and it shows good performance.

Commentary by Dr. Valentin Fuster
2013;():V001T09A005. doi:10.1115/ISPS2013-2869.

The performance of plasmonic lithography depends on how small the air gap is. In this paper, we focus on rejecting the dominant frequency of disturbance. In order to do this, frequency estimation and peak filter are used in this paper. We achieve about 12% and 10% reduction in the standard deviation and maximum peak to peak of Gap Error Signal (GES) respectively. This work will improve the quality of plasmonic lithography in the size and stability of patterns.

Commentary by Dr. Valentin Fuster
2013;():V001T09A006. doi:10.1115/ISPS2013-2874.

Today many media of information storage device are formed as disks. Hence, next generation removable data storage media are shaped as disk types too. The holographic data storage system also uses a disk type photopolymer media. And then, holographic data storage system is most advanced optical memory system. Tracking servo and tilt servo control are very important research in holographic data storage system. In this paper, we propose intelligent servo control by fuzzy rules in holographic data storage system. Hence, we have found pattern of tilt servo control in holographic data storage system through fuzzy system. Fuzzy rules were generated by Genetic algorithm for controlling tilt servo. Therefore, we control tilt servo using fuzzy rules in holographic data storage system. Consequently, practical pattern of tilt servo control was found by intelligence algorithm in holographic data storage system.[1]

Commentary by Dr. Valentin Fuster
2013;():V001T09A007. doi:10.1115/ISPS2013-2879.

The market of electronic products such as mobile phones and portable devices grows rapidly while the demand of lithium battery for fast charge, long duration, and long life cycle increases significantly as well. There are several charge methods for lithium battery, such as constant current (CC)/constant voltage (CV) charge [1], pulse charge [2] and reflex charge [3], etc. In general, a flyback converter has been widely adopted as the front-end converter of battery charger due to its low-cost, wide power range, and galvanic isolation between input and output stage. The battery charge controller with flyback converter has been developed in digital control with opto-coupler feedback [4]–[6]. The conventional flyback converter with CC or CV applications always requires two sensed ADC channels for regulating [7]–[9]. An improved control method is proposed in this study to achieve CC/CV by only one ADC channel. This study presents a battery charge mechanism with a flyback converter and associated trickle charge method for the temperature compensation. The PSR is adopted for switching the charge modes within trickle current (TC), constant current (CC) and constant voltage (CV). The TC charging method is used to avoid the rapid increase in the temperature of the battery which is based on the characteristics of the internal resistance of the battery [10]. The proposed system circuit contains two stages in topology. The first stage is a front-end flyback converter which operates in DC-DC discontinuous current mode (DCM) by using PSR to sense the output voltage from auxiliary winding. It is adopted to replace the opto-coupler for avoiding temperature limitation for operations and reducing cost. The software Powersim is used to simulate the proposed flyback converter and PSR method. The second stage is the digital feedback loop, which processes the controlled signal by a digital processor (DSP) TMS320F2812. The experimental results were compared with general CC/CV method. The results show favorable performance of the propose charging method.

Commentary by Dr. Valentin Fuster
2013;():V001T09A008. doi:10.1115/ISPS2013-2888.

The products in the market are mostly 2D sensing. The touch panel technology is used in the industry and the video game wisely. Many of the ATMs, cell phones and the vending machines have touch panel technology in these years. The touch panel technology grows up quickly. In recent years, there has been increasing interests in proximity sensing technology [1–3]. This study proposes the 3D proximity sensing can be used in un-touch screen, a 3D keyboard, or constructed on the robot’s hand for sensing the distance and position of an object. As the optical components advance, the optical system, optical touch panel, object sensing and medical system are growing up with it. A photo detector is the part of the optical component. However, the photo detector transfers the photon to the current (photocurrent). This study needs a circuit to be the rear end of the photo detector, transferring the current to the voltage. An active pixel sensor is the viable way to realize the function. For the large area object sensing and high resolution, one pixel should be designed as small as possible. A small pixel however gives small photocurrent. The efficient way to transfer the photon to the voltage is important. The aim of this study is to develop a 3D-position sensing technique for an arbitrary object. The schematic for illustration is shown in Fig. 1. Different from conventional 2D capacitance or resistance touch panels, the proposed proximity sensor array has third axis sensing and the 3D sensing. A new active pixel circuit is proposed for realizing the sensor array. The active pixel sensor is used to convert the light to the voltage, and it can improve the resolution and reduce the noise. The standard and official active pixel sensor is a 3T-structure APS (or 3T-APS). The drawback of 3T-APS is that the output range is limited by the original circuit design. The maximum output cannot be up to bias voltage. The new APS resolution is better than the standard 3T-APS resolution in this aspect. It is a good improvement in terms of not only the CMOS sensor but also the 3D optical proximity sensing circuit.

Topics: Sensors , Circuits
Commentary by Dr. Valentin Fuster
2013;():V001T09A009. doi:10.1115/ISPS2013-2915.

Commercial auto-stereoscopic display systems have equipped optical lenticular lens sheets in order to realize the function which is able to support two images or views to right and left eyes of viewers. In applications of auto-stereoscopic display, the method of using the lenticular lens sheet, also called time- or spatial-multiplexed method, is first proposed as a patent by Ichinose [1]. The method has more advantages, which includes high luminous performance, movable of eyes position with constant view distance and watchable of multi-viewer. Besides, it can be also easily manufactured to make it very popular. Owing to the superiority, some studies about lenticular lens sheets have been proposed. Berkel et al. [2] have proposed several researches about the method of using lenticular lens sheets on multi-view auto-stereoscopic displays, and he has also proposed that slanted lenticular lens sheets or pixels could be improved the effect of flipped image by boundaries of lens and pixel [3–5]. 2D/3D switchable display is first realized by a method of dual-lenticular lens sheets [6]. Moreover, the method of using lenticular lens sheets has been proposed to be replaced by liquid crystal, LC, lens arrays, [7–9] in order to control viewer distance based on a function of tunable focal length. For the method, some issues of LC lenses should be solved like non-smooth potential in the LC layer and to improve the lens power [10–12].

Commentary by Dr. Valentin Fuster
2013;():V001T09A010. doi:10.1115/ISPS2013-2917.

Imaging technology has been in revolutionary progresses in decades with well-developed semiconductor and memory industries. Silicon sensors are used in most of camera and DV, since silicon is the best material for visible light imaging (wavelength from 400nm∼700nm). Short wave infrared (SWIR) requires indium gallium arsenide (InGaAs), composed of chemical compounds including indium arsenide (InAs) and gallium arsenide (GaAs), to cover SWIR spectrum. Wavelength of typical SWIR is defined between 0.7um and 2.5um; SWIR cameras focus on wavelength between 0.9um∼1.7um (In0.53Ga0.47As). Unlike Mid-Wave IR and Long-Wave IR, SWIR is reflected and absorbed by objects, which advantages SWIR imaging higher resolution due to better contrast. SWIR also has excellent imaging quality in low illumination environment and moon light or star light are good emitters outdoor at night. Another primary characteristic of SWIR is high penetration, providing effective imaging under hazy conditions. An Example for night vision between SWIR.

Commentary by Dr. Valentin Fuster
2013;():V001T09A011. doi:10.1115/ISPS2013-2921.

This study aims to develop an on-line tester machine for evaluating the image quality of a camera lens that is used in a lens module in a cell phone. This tester is not only suitable for conventional solid lens, but also applicable to the developing tunable liquid crystal lens by using the conoscopy approach to measure focus length and its quality. On the other hand, the approach using a commercial inspection chart along with a automatic feeding machine is also adopted for a quick estimate on the focusing quality that is primarily based on Modulation Transfer Function (MTF). In addition to the MTF, the proposed tester aims to has other functions of measuring Effect Focal Length (EFL), Back Focal Length (BFL), Field of View (FOV), Field curvature, Distortion, Astigmatism, Lateral/Axial Color, the distribution of index of refraction and phase retardation pattern. The constructed tester is capable of measuring varied optical performance indices for the next-generation tunable lens.

Topics: Lenses (Optics)
Commentary by Dr. Valentin Fuster

Flexible Media Mechanics and Tape Storage

2013;():V001T10A001. doi:10.1115/ISPS2013-2835.

A List–Viterbi detector produces a rank ordered list of the N globally best candidates in a trellis search. A List–Viterbi detector structure is proposed that incorporates the noise prediction with periodic state-metric updates based on outer error detection codes (EDCs). More specifically, a periodic decision making process is utilized for a non-overlapping sliding windows of P bits based on the use of outer EDCs. In a number of magnetic recording applications, Error Correction Coding (ECC) is adversely effected by the presence of long and dominant error events. Unlike the conventional post processing methods that are usually tailored to a specific set of dominant error events or the joint modulation code trellis architectures that are operating on larger state spaces at the expense of increased implementation complexity, the proposed detector does not use any a priori information about the error event distributions and operates at reduced state trellis. We present pre-ECC bit error rate performance as well as the post-ECC codeword failure rates of the proposed detector using perfect detection scenario as well as practical detection codes as the EDCs are not essential to the overall design. Furthermore, it is observed that proposed algorithm does not introduce new error events. Simulation results show that the proposed algorithm gives improved bit error and post-ECC codeword failure rates at the expense of some increase in complexity.

Topics: Noise (Sound) , Errors
Commentary by Dr. Valentin Fuster
2013;():V001T10A002. doi:10.1115/ISPS2013-2836.

In dynamic systems, motion transfer due to frictional effects could result in quasi-harmonic oscillations and stick-slip, with potentially undesirable effects. The track-following motion of a read/write (RW) head-assembly transfers frictional forced onto the translating tape. This, in turn, has the potential to introduce unwanted dynamic motion into the system, and to affect the track following operation. In extreme cases the tape could stick onto the head-assembly, which could then create the potential for sudden release (slip) of the tape, if the restoring forces exceed the static friction forces. Due to longitudinal tape motion, stick is only a possibility during start-stop operations. However, with increasingly smoother tape, the effects of friction induced vibration (FrIV) could become problematic for the next generation of tape drives.

Topics: Friction , Vibration
Commentary by Dr. Valentin Fuster
2013;():V001T10A003. doi:10.1115/ISPS2013-2875.

The Stribeck effect describes the velocity dependence of the friction coefficient between moving components [9]. In the case of an axially translating tape, supported by a roller, air entrainment can cause reduction in the contact pressure, and hence in the tractive capacity of the interface [5]. Grooved rollers are used to prevent excessive built-up of air pressure [6,7,8,1,2]. In this work, tribology and mechanics of a tape-grooved-roller interface is modeled in order to investigate the traction as a function of tape speed, tension and groove size.

Topics: Modeling , Rollers , Traction
Commentary by Dr. Valentin Fuster
2013;():V001T10A004. doi:10.1115/ISPS2013-2883.

The demand of raising recording density for hard disk has increased these years to achieve higher storage capacity of hard disk drive. This promotes the diminution in track size of hard disk nowadays to only hundreds of nanometers. Thus, more precisely-operated and robust actuation system for read/write heads in HDDs has been the research and development focus. Among mechanical contributors, Chang [1] indicated that flexible circuit in HDDs has been found to be a problematic vibration source that can interfere and reduce the operation accuracy of read/write arm. To perfectly eliminate the dynamic responses of flex cable, piezo-electric (PZT) film was adopted by attaching it onto flex cable to achieve the goal of vibration control. When an external electric field is applied to this PZT film, piezoelectricity effect is then taken place which results in induction of mechanical shear force in flex cable. The cable’s vibrations can then be controlled by this mechanism with the additional PZT film on the flex cable. With energized PZT film, this means that flex cable will turn harder and its stiffness will become larger, which makes the dynamic behavior of flex cable becomes an uncertainty. The mechanical model built in previous work [2] then fails to predict the dynamic response of the flex cable. Due to the problems mentioned above, modification for the mechanical model is imperative and it was elaborated by considering the shear effects produced by PZT in this paper. As reported by Kenji Uchino [4], Henno Allik [5] and many other researchers [6–8], finite element methods have been applied to many piezoelectric applications. Piezoelectricity includes electrical and mechanical behaviors of a material. Therefore, the piezoelectric constitutive equations were conducted in this paper to consider this combined electroelastic effects from PZT.

Commentary by Dr. Valentin Fuster
2013;():V001T10A005. doi:10.1115/ISPS2013-2925.

The potential for significant capacity and performance improvements in tape storage systems appears to be substantial [1],[2]. Advances in several areas, however, are necessary to foster increases in linear and track densities and consequently achieve higher cartridge capacities and improved performance [3],[4]. Reliable and precise tape transport and track-following servomechanisms are of fundamental importance to guarantee best read-channel performance on all parallel data channels during tape operation. In particular, tight control of tension and potentially of tape-dimensional stability (TDS) variations will be necessary for moving to thinner tape material, which in turn will enable an increase in volumetric density. Figure 1 shows the block diagram of conventional tape transport and track-following servomechanisms in a tape drive [5]. A digital dual servo channel provides estimates of the tape velocity, tape longitudinal position, and head lateral position, which are derived from signals read from dedicated servo bands [6]. Hall sensors provide tape velocity information from the individual reels, which typically is used in the absence of a valid velocity estimate from the servo channel. One of the main impairments affecting the performance of tape drives is the variation of tape tension [7],[8], which may be induced by, e.g., reel eccentricities.

Commentary by Dr. Valentin Fuster

Storage System and Future Technologies

2013;():V001T11A001. doi:10.1115/ISPS2013-2807.

In this paper an experimental study is reported to reduce the rotating inertia in a 2½″ HDD by replacing thick hard disk platters with thin, CP (commercially pure) titanium substrates in the range of 25 microns to 152 microns in thickness. The results of this work can be extended to other disk form factors [1]. The low inertia and thinness of the titanium foil platter can be exploited to allow disk drive products to be powered on/off rapidly, decreasing energy consumption. In addition, significantly faster rpms and data thru-put can be achieved. Also, many more disk platters can be housed in each unit, increasing storage capacity; while slimmer products that operate with low voltage battery power can be developed.

Topics: Disks , Titanium
Commentary by Dr. Valentin Fuster
2013;():V001T11A002. doi:10.1115/ISPS2013-2815.

As data center managers consider deployment of a Cloud Computing environment the most important issues they consider include critical application data availability, storage agility and data protection strategies. Early adopters of Cloud Computing have already deployed Virtualization as a key technology in their Infrastructure as a Service (IaaS) and Platform as a Service (PaaS) offerings. Cloud computing extends the benefits of virtualization by increasing the efficiency of server and storage utilization, reducing costs, improving operational efficiency and optimizing datacenter rack and floor space. It builds on first-generation system and storage virtualization with features such as application portability and storage agility to enable higher efficiencies and greater efficiencies across the enterprise. With recent innovation in storage, key features such as thin-provisioning, compression and de-duplication work in concert with virtualized infrastructure on the Storage Appliance to eliminate duplicate data blocks, compress data and allocate the amount of storage being consumed by users. Data services such as snapshots and clones provide instant and optionally, unattended backups that can be used in the short term for recovery of critical data. Disaster recovery is all the more important within the cloud computing environment and built in replication services enable a robust solution in case of a catastrophic event or simply for purposes of backup and recovery.

Commentary by Dr. Valentin Fuster

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