Thermal Fly-height Control Slider Dynamics and Slider-Lubricant Interactions in Hard Disk Drives PDF Download
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Author: Sripathi Vangipuram Canchi
Publisher:
ISBN:
Category :
Languages : en
Pages : 304
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Book Description
The storage industry's density target of 10 Tb/sq.in. in hard disk drives within the next decade requires a significant change in head-disk interface (HDI) architecture, and it likely involves a combination of new technologies such as Heat Assisted Magnetic Recording and Bit Patterned Media Recording to mention a few. Independent of the actual recording technology, it is necessary to reduce the magnetic spacing to within 2nm, which implies a physical spacing as little as 0.25nm at the read-write transducer location. At such a small spacing intermittent contact between the slider and the lubricant layer or hard overcoat surface on the disk becomes inevitable. A continuous lubricant-contact HDI may in fact be necessary to meet future magnetic spacing needs. While the new recording technologies impose a significantly tighter budget on the slider dynamics in all three directions (vertical, down-track and off-track), the contacting HDI must be reliable, ensuring no degradation of lubricant or disk overcoats even after prolonged operation. The current slider technology uses Thermal Fly-height Control (TFC) to bring the read-write portion of the slider closer to the disk by resistive heating induced thermal deformation/protrusion. While subnanometer level clearance can be achieved using the TFC, slider stability and HDI reliability at very small spacing remains to be understood. In order to further reduce the magnetic spacing using the TFC architecture, a recording strategy with a small portion of the thermal protrusion in intermittent or continuous contact with the lubricant layer of the disk has been proposed, but there is limited theoretical and experimental work to verify the feasibility of this technique. The focus of this work is to advance the understanding of TFC slider dynamics and slider-lubricant interactions at a HDI with contact through experiments and modeling. Slider-lubricant contact is experimentally established by carefully controlling the TFC heater power, and the three dimensional slider dynamics under lubricant-contact is investigated. The degree of slider-lubricant contact is shown to influence the slider's vibration modes. A simple two degree of freedom model that accounts for nonlinearities at the HDI through quadratic and cubic approximations is used to analytically investigate the interesting features of this problem. It is shown that the thermal protrusion induced by the heater power can cause the system modes to couple unfavorably for certain heater power ranges, and this condition can manifest itself as large amplitude slider vibrations. Experiments are conducted to understand the interplay between slider dynamics and disk lubricant evolution under the thermal protrusion for contact and near contact conditions. Slider dynamics and lubricant rippling are shown to be well correlated and a mechanism of lubricant transfer from the slider to the disk at the onset of contact is demonstrated. Parametric investigations are conducted to understand the effect of lubricant type and thickness on lubricant distribution, lubricant depletion and subsequent lubricant recovery behavior at a contacting HDI.
Author: Sripathi Vangipuram Canchi
Publisher:
ISBN:
Category :
Languages : en
Pages : 304
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Book Description
The storage industry's density target of 10 Tb/sq.in. in hard disk drives within the next decade requires a significant change in head-disk interface (HDI) architecture, and it likely involves a combination of new technologies such as Heat Assisted Magnetic Recording and Bit Patterned Media Recording to mention a few. Independent of the actual recording technology, it is necessary to reduce the magnetic spacing to within 2nm, which implies a physical spacing as little as 0.25nm at the read-write transducer location. At such a small spacing intermittent contact between the slider and the lubricant layer or hard overcoat surface on the disk becomes inevitable. A continuous lubricant-contact HDI may in fact be necessary to meet future magnetic spacing needs. While the new recording technologies impose a significantly tighter budget on the slider dynamics in all three directions (vertical, down-track and off-track), the contacting HDI must be reliable, ensuring no degradation of lubricant or disk overcoats even after prolonged operation. The current slider technology uses Thermal Fly-height Control (TFC) to bring the read-write portion of the slider closer to the disk by resistive heating induced thermal deformation/protrusion. While subnanometer level clearance can be achieved using the TFC, slider stability and HDI reliability at very small spacing remains to be understood. In order to further reduce the magnetic spacing using the TFC architecture, a recording strategy with a small portion of the thermal protrusion in intermittent or continuous contact with the lubricant layer of the disk has been proposed, but there is limited theoretical and experimental work to verify the feasibility of this technique. The focus of this work is to advance the understanding of TFC slider dynamics and slider-lubricant interactions at a HDI with contact through experiments and modeling. Slider-lubricant contact is experimentally established by carefully controlling the TFC heater power, and the three dimensional slider dynamics under lubricant-contact is investigated. The degree of slider-lubricant contact is shown to influence the slider's vibration modes. A simple two degree of freedom model that accounts for nonlinearities at the HDI through quadratic and cubic approximations is used to analytically investigate the interesting features of this problem. It is shown that the thermal protrusion induced by the heater power can cause the system modes to couple unfavorably for certain heater power ranges, and this condition can manifest itself as large amplitude slider vibrations. Experiments are conducted to understand the interplay between slider dynamics and disk lubricant evolution under the thermal protrusion for contact and near contact conditions. Slider dynamics and lubricant rippling are shown to be well correlated and a mechanism of lubricant transfer from the slider to the disk at the onset of contact is demonstrated. Parametric investigations are conducted to understand the effect of lubricant type and thickness on lubricant distribution, lubricant depletion and subsequent lubricant recovery behavior at a contacting HDI.
Author: Jinglin Zheng
Publisher:
ISBN:
Category :
Languages : en
Pages : 224
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Book Description
As a recent development to further reduce the flying height of a magnetic head in hard disk drives (HDDs) to nanometers, thermal flying-height (TFC) control technology is now widely applied in the HDD industry because it enables consistent read/write spacing, increased storage density and improved HDD reliability. The fast development of TFC technology presents new challenges to head designers because of the complicated structure of a TFC head, the thermo-mechanical-coupling effects and tribology issues arising at nanometer read/write spacing. A steady-state TFC solver dedicated to obtaining the steady-state flying attitude of a TFC slider is developed in this thesis. This solver uses a finite volume based solver (CML static solver) to solve the generalized Reynolds equation and obtain the pressure and spacing fields in the air bearing and a commercial coupled-field solver (ANSYS) to obtain the stress and strain fields due to internal heating. An iterative procedure is adopted to consider the cooling effect of the air bearing on the heater-induced protrusion. Accuracy of the solver is verified by drive-level magnetic tests on several combinations of air bearing and heater designs. TFC sliders' performances under different ambient conditions are investigated based on the TFC solver. It is found that the thermal actuation efficiency of a TFC slider increases with altitude because of the weakened cooling and reduced air bearing stiffness at the transducer area at a higher altitude. In addition, a TFC slider maintains a more consistent read/write spacing at different humidity levels, compared with a non-TFC slider, because the thermal actuation is able to compensate part of the pressure loss caused by water condensation. A TFC slider's flying height in air-helium mixtures is shown to be a highly nonlinear function of the fraction of helium in the gas mixture due to the combined effects of the gas mean free path, viscosity and heat conductivity. These results provide general guidelines for heater and ABS designers to reduce a TFC slider's sensitivity to ambient conditions and improve HDD reliability. A touchdown numerical model for predicting TFC sliders' dynamics at touchdown and over-pushed conditions is developed and implemented based on the CML dynamic simulator. It extends the solution of the time-varying generalized Reynolds equation to near-contact and contact conditions using a statistical multi-asperity approach. Various interfacial forces are considered by use and further development of a sub-boundary lubrication model to capture important tribological effects occurring at touchdown. This model is able to predict a TFC slider's unstable dynamics at the beginning of touchdown, which has been discovered in many related experimental studies. The effects of different head-disk interface factors are investigated using this numerical model. It is found that the suspension is actively involved in the TFC slider's bouncing vibrations and has a significant influence on the excited second air bearing pitch mode. It is also shown that adhesion force serves as an essential factor in exciting the second air bearing mode whereas other interfacial forces only affect details of the slider's bouncing behaviors. By changing the interfacial properties, namely, the interface roughness and lubricant thickness, the variation of interfacial forces with spacing reduction differs, which leads to very different touchdown patterns. With a rougher interface profile the slider smoothly transfers from a flying stage to a sliding stage. With a smoother interface profile the slider experiences a flying-bouncing-sliding transition. With the smoothest interface the slider goes through a flying-bouncing-surfing-sliding transition. The touchdown behaviors predicted by the numerical simulator are correlated with experiments conducted on industry-provided head parts with the same ABS and suspension design. Similar touchdown stages and excited modes are also discovered in the experiments. Though experiments showed a slider spectrum with richer frequency components, the modes missed from the numerical simulations are recovered by conducting a harmonic analysis on a full HGA model with air bearing included. The different touchdown dynamic patterns predicted here result in significant differences in the successful touchdown detection, which is very important for realizing reliable read/write operations, and therefore this work provides guidelines for head disk interface (HDI) optimization. The general approach proposed here is also applicable to studies on the effects of other important HDI factors, such as air bearing geometric features, heater-induced protrusion profiles, and suspension design parameters, and on the slider's touchdown dynamics behaviors, which will assist in obtaining solutions to performance and reliability issues in current hard disk drives.
Author: Rohit Pradeep Ambekar
Publisher:
ISBN:
Category :
Languages : en
Pages : 464
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Author: Sean N. Moseley
Publisher:
ISBN:
Category :
Languages : en
Pages : 386
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Author: Liming Dai
Publisher: Springer
ISBN: 3319694804
Category : Technology & Engineering
Languages : en
Pages : 472
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Book Description
This book analyzes the updated principles and applications of nonlinear approaches to solve engineering and physics problems. The knowledge on nonlinearity and the comprehension of nonlinear approaches are inevitable to future engineers and scientists, making this an ideal book for engineers, engineering students, and researchers in engineering, physics, and mathematics. Chapters are of specific interest to readers who seek expertise in optimization, nonlinear analysis, mathematical modeling of complex forms, and non-classical engineering problems. The book covers methodologies and applications from diverse areas such as vehicle dynamics, surgery simulation, path planning, mobile robots, contact and scratch analysis at the micro and nano scale, sub-structuring techniques, ballistic projectiles, and many more.
Author:
Publisher: ScholarlyEditions
ISBN: 1464963754
Category : Technology & Engineering
Languages : en
Pages : 2526
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Book Description
Issues in Mechanical Engineering / 2011 Edition is a ScholarlyEditions™ eBook that delivers timely, authoritative, and comprehensive information about Mechanical Engineering. The editors have built Issues in Mechanical Engineering: 2011 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Mechanical Engineering in this eBook to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Mechanical Engineering: 2011 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.
Author: YUNG-KAN CHEN
Publisher:
ISBN:
Category :
Languages : en
Pages : 125
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Book Description
The magnetic recording hard disk drive has been one of the most important storage strategies since 1956. Among all storage solutions, hard disk drives possess the unrivaled advantageous combination of storage capacity, speed, reliability and cost over optical strategies and flash memory. Unlike other storage solutions, hard disk drives utilize a mechanical interface to perform the magnetic read/write process, and therefore its success relies heavily on the stability of the head-disk interface (HDI) which is composed of a magnetic transducer carried by an air bearing slider, an air gap of a few nanometers thick, and a disk surface coated with multiple layers of molecularly-thin films. This dissertation addresses the physics of the interface in terms of contact detection, lubricant modulation and wear. Contact detection serves as one of the core requirements in HDI reliability. The writing process demands a strict spacing control, and its accuracy is based on a proper choice of a contact reference from slider dynamics and therefore the heads’ signal. While functioning in a real drive the only feedback signal comes from sensors neighboring the read-write transducer, and a high speed head-disk contact is associated with complex structural responses inherent in an air-bearing/suspension/lubricant system that may not be well explained solely by magnetic signals. Other than studying the slider-disk interaction at a strong interplay stage, this dissertation tackles the contact detection by performing component-level experimental and simulation studies focusing on the dynamics of air-bearing sliders at disk proximity. The slider dynamics detected using laser Doppler vibrometry indicates that a typical head-disk contact can be defined early as in-plane motions of the slider, which is followed by vertical motions at a more engaged contact. This finding confirms and is in parallel with one of the detection schemes used in commercial drives by magnetic signals. Lubricated disk surfaces play an important role in contact characteristics. As the nature of contact involves two mating surfaces, the modulation of disk lubricant films should be investigated to further understand the head-disk contact in addition to the slider dynamics. In this dissertation, the lubricant modulation is studied under various contact conditions with reference to slider dynamics. It is found that lubricant modulation can be directly associated with the slider’s dynamics in a location specific way, and its evolution is likely to affect the slider’s stable back-off fly-height as the contact is retracted. In addition to modulations at contact proximities, the lubricant response to passive flying and continuous contacting conditions are also addressed for different lubricant types and thicknesses. By integrating the observations from slider dynamics and lubricant modulations, we can establish an insightful understanding towards the transition from flying to the onset of contact. Head wear is also a concern when an erroneous contact detection occurs or imperfections from disk surface exists. Typically a protective diamond-like carbon (DLC) layer of thickness 1-2 nm is coated over the area of the reader/writer shields, and this film loss poses a threat to long term reliability. In this dissertation, in-situ methods of monitoring head wear is proposed in two ways. One method is to evaluate the touchdown power variations as a measure of spacing increase by DLC wear, which was verified by using Auger Electron Spectroscopy, and the other method studies the temperature contact sensor response to gauge mechanical wear. The later possesses the advantage of detecting wear without going into actual contact, but it may be affected by the location difference between the touchdown sensor and wear area.
Author: Jinglin Zheng
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Hao Zheng
Publisher:
ISBN: 9781267070210
Category :
Languages : en
Pages : 230
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Book Description
Many advanced technologies in the field of magnetic disk recording are being studied in order to achieve areal densities in excess of 1.6 gigabits per square millimeter (1 terabits per square inch). Bit patterned media (BPM) is one of these promising technologies. By using disks with physically separated magnetic patterns instead of conventional continuous media, bit patterned media avoid magnetic interference between adjacent bits and improve the thermal stability of the media. Currently, thermal flying height control (TFC) sliders are commonly used to compensate thermal effects during reading and writing and to maintain a stable and ultra-low head/disk spacing during drive operation. Heat assisted magnetic recording (HAMR) has been introduced in order to address difficulties in writing of information on magnetic media with high coercivity. By using a laser beam to locally heat the media above its Curie temperature, the magnetic material momentarily reduces its coercivity and permits writing of information on the disk. However, the method raises concerns about the stability of the lubricants on the disk. In this dissertation, we focus on the investigation of the head/disk interface for bit patterned media, the design of thermal flying height control sliders, and the implementation of heat assisted magnetic recording. In particular, we use a finite-element-based air bearing simulator to study the steady-state flying characteristics of sliders flying over bit patterned media. This air bearing simulator is then combined with a thermo-mechanical model of a slider in order to analyze thermal flying height control sliders featuring dual heater/insulator elements. Next, a finite element model of a thermal flying height control slider with an integrated heat assisted magnetic recording optical system is developed to study the effect of heat dissipation along the laser delivery path on the performance of the HAMR-TFC slider. The design parameters of the dual thermal flying height control heaters are optimized in order to minimize the dependence of the head/disk spacing on laser induced thermal effects. Finally, experimental techniques are developed to investigate the photo-thermo stability and tribological properties of HAMR-type lubricants which are designed to be resistant to the high temperatures experienced under laser exposure.
Author: Yan Li
Publisher: Springer Nature
ISBN: 9811950539
Category : Technology & Engineering
Languages : en
Pages : 628
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Book Description
This book provides a comprehensive reference for both academia and industry on the fundamentals, technology details, and applications of Advanced Driver-Assistance Systems (ADAS) and autonomous driving, an emerging and rapidly growing area. The book written by experts covers the most recent research results and industry progress in the following areas: ADAS system design and test methodologies, advanced materials, modern automotive technologies, artificial intelligence, reliability concerns, and failure analysis in ADAS. Numerous images, tables, and didactic schematics are included throughout. This essential book equips readers with an in-depth understanding of all aspects of ADAS, providing insights into key areas for future research and development. • Provides comprehensive coverage of the state-of-the-art in ADAS • Covers advanced materials, deep learning, quality and reliability concerns, and fault isolation and failure analysis • Discusses ADAS system design and test methodologies, novel automotive technologies • Features contributions from both academic and industry authors, for a complete view of this important technology
