Ultra-thin a-SiN_x protective overcoats for hard disks and read/write heads

This paper reports that amorphous silicon nitride （a-SiNx） overcoats were deposited at room temperature by microwave ECR plasma enhanced unbalanced magnetron sputtering. The 2 nm a-SiNs overcoat has better anti-corrosion properties than that of reference a-CNx overcoats （2 4.5 nm）. The superior anti-corrosion performance is attributed to its stoichiometric bond structure, where 94.8% Si atoms form Si-N asymmetric stretching vibration bonds. The N/Si ratio is 1.33 as in the stoichiometry of Si3N4 and corresponds to the highest hardness of 25.0 GPa. The surface is atomically smooth with RMS 〈 0.2 nm. The ultra-thin a-SiNx overcoats are promising for hard disks and read/write heads protective coatings.

OPTIMAL TRACK SEEKING CONTROL OF DUAL-STAGE ACTUATOR FOR HIGH DENSITY HARD DISK DRIVES

Based on generalized the variation method, by introducing Hamilton function and Lagrange multiplier, this paper proposed a linear quadratic optimal control strategy for an incomplete controllable system with fixed terminal state and time. Applying the proposed optimal control to the simple two-input dual-stage actuator magnetic head positioning system with three degrees-of-freedom, the simulation results show that the system has no residual vibration at the terminal position and time, which can reduce the total access time during head positioning process. To verify the validation of the optimal control strategy of three degrees-of-freedom spring-mass models in actual magnetic head positioning of hard disk drives, a finite element model of an actual magnetic head positioning system is presented. Substituting the optimal control force from simple three degrees-of-freedom spring-mass models into the finite element model, the simulation results show that the magnetic head also has no residual vibration at the end of track-to-track travel. That is to say, the linear quadratic optimal control technique based on simple two-input dual- stage actuator system with three degrees-of-freedom proposed in this paper is of high reliability for the industrial application of an actual magnetic head positioning system.

Vibration Response Characteristics against the Radial and Axial Shocks on Small Size Hard Disk Drive Spindle Supported by Oil Film Bearings

This paper describes the experimental study on shock response of FDB （fluid dynamic bearing） spindle for HDDs （hard disk drives）. The FDBs are widely used as rotating shaft support elements for HDD spindle motors. Recently, the opportunity for the HDD spindle motors exposed to external vibration has been increasing because the HDDs are used for various information related equipment such as mobile PCs （personal computers）, video cameras, car navigation systems and so on. Hence, the rotating shaft has a possibility to come in contact with the bearing by external shocks and it causes wear or seizure to the bearing surface. To avoid the problem, it is extremely important to know how the spindle moves against the large shock on HDDs experimentally. However, as far as the authors know, there are few experimental studies treating the shock response of HDD spindles. In this paper, firstly, we propose a new test rig and experimental method for shock response of FDB spindles. Then the shock tests against the radial and axial disturbance on FDB spindle for 2.5＂ HDD are conducted. Finally, the experimental results of shock response waveforms and maximum displacement of disk are shown.

Design of Intersample Response in a Hard Disk Control System

The present paper discusses a design method for the head position in a Hard Disk Drive （HDD） control system. In the HDD control system, the sampling interval of the head position is constrained because of the hardware specifications, but the hold interval of the control input is not constrained. In the present study, a multirate control system is designed, in which the sampling and the hold intervals are not equal. A multirate control law, which stabilizes a closed-loop system, is extended using newly introduced parameters such that the sample response of the plant output is maintained. Furthermore, intersample ripples in the steady state are eliminated using the new design parameters, which can be selected independently of the sample response. As a result, the intersample response can be improved independently of the sample response. The proposed method is applied to a benchmark problem of an HDD system, and its effectiveness is demonstrated.

Robust Optimum Design of Thrust Hydrodynamic Bearings for Hard Disk Drives

This paper describes the robust optimum design which combines the geometrical optimization method proposed by Hashimoto and statistical method. Recently, 2.5″ hard disk drives (HDDs) are widely used for mobile devices such as laptops, video cameras and car navigation systems. In mobile applications, high durability towards external vibrations and shocks are essentials to the bearings of HDD spindle motor. In addition, the bearing characteristics are influenced by manufacturing error because of small size of the bearings of HDD. In this paper, the geometrical optimization is carried out to maximize the bearing stiffness using sequential quadratic programming to improve vibration characteristics. Additionally, the bearing stiffness is analyzed considering dimensional tolerance of the bearing using statistical method. The dimensional tolerance is assumed to distribute according to the Gaussian distribution, and then the bearing stiffness is estimated by combining the expectation and standard deviation. As a result, in the robust optimum design, new groove geometry of bearing can be obtained in which the bearing stiffness is four times higher than the stiffness of conventional spiral groove bearing. Moreover, the bearing has lower variability compared with the result of optimum design neglecting dimensional tolerance.

Optimization of passive control performance for different hard disk drives subjected to shock excitation

Laptop personal computers(LPCs) and their components are vulnerable devices in harsh mechanical environments. One of the most sensitive components of LPCs is hard disk drive(HDD) which needs to be protected against damages attributable to shock and vibration in order to have better magnetic read/write performance. In the present work, a LPC and its HDD are modeled as two degrees of freedom system and the nonlinear optimization method is employed to perform a passive control through minimizing peak of HDD absolute acceleration caused by a base shock excitation. The presented shock excitation is considered as half-sine pulse of acceleration. In addition, eleven inequality constraints are defined based on geometrical limitations and allowable intervals of lumped modal parameters. The target of the optimization is to reach optimum modal parameters of rubber mounts and rubber feet as design variables and subsequently propose new characteristics of rubber mounts and rubber feet to be manufactured for the HDD protection against shock excitation. The genetic algorithm and the modified constrained steepest descent algorithm are employed in order to solve the nonlinear optimization problem for three widely-used commercial cases of HDD. Finally, the results of both optimization methods are compared to make sure about their accuracy.

Effect of AIBI as Free Radical Initiator on Abrasive-Free Polishing of Hard Disk Substrate

To optimize the existing slurry for abrasive-free polishing(AFP)of hard disk substrate,a water-soluble free radical initiator,2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride(AIBI)is introduced to the H2O2-based slurry.The polishing results show that,the material removal rate(MRR)of hard disk substrate polished with H2O2-based slurry containing AIBI is obviously higher than that without AIBI.The acting mechanism of the improved MRR is investigated.Electron paramagnetic resonances tests show that,by comparison with H2O2 slurry,H2O2-AIBI slurry provides higher concentration of hydroxyl radicals.Auger electron spectrometer analyses further demonstrate that the oxidation ability of H2O2-AIBI slurry is much greater than H2O2 slurry.In addition,potentiodynamic polarization tests show that the corrosion dissolution rate of hard disk substrate in H2O2-AIBI slurry is increased.Therefore that stronger oxidation ability and a higher corrosion dissolution rate of H2O2-AIBI slurry lead to higher MRR can be concluded.

Numerical Investigation of Flow Structure Interaction Coupling Effects in Hard Disk Drives

This paper studies the flow structural interaction (FSI) within a hard disk drive (HDD) through the use of a novel coupling method. The interaction studied was the fluid induced vibration in the HDD. A two step coupling approach was used, where the fluid and structural components were solved sequentially. The result obtained was a ratio of 0.65 between the vibration amplitudes of a fixed head stack assembly (HSA) and a moving HSA. The ratio was next applied on a real 3.5 inch HDD, to allow the parameter to be further improved upon. A new benchmark index of 0.69 was developed from this. This parameter may allow future researchers to model the out of plane vibrations of a HSA easily, saving precious time. A 31% more accurate simulation of FSI within 3.5 inch HDD at 15000 rpm is achieved by the use of this new coupling method and benchmark index.

Heat Source Analysis of Hard Disk Drives with Different Wall Conditions using Infrared System

Increasing performance parameters of hard disk drive (HDD) such as higher capacity and faster data access speed with decreasing physical size make HDD more susceptible to thermal effects. Contact temperature measurement using thermocouple is not suitable for the rotating platter of HDD. Heat analysis using simulation software requires accurate initial parameter setting such as thermal (initial & boundary) conditions of certain regions. Temperature measurement using infrared (IR) system avoids these limitations;it is non-contact, responsive and does not require initial parameter setting. Thermal pattern distribution can be studied from the thermal images. However, emissivity of the target has to be known and calibration of the system is essential for accurate temperature reading. This paper showed that temperature within the HDD increases with ambient temperature and time, but the thermal distribution pattern in the HDD was not affected by different ambient temperatures. Three wall boundary conditions were conducted to study the thermal distribution pattern in the HDD. A solution was then proposed based on the results obtained from the experiments to improve the heat transfer rate and steady state temperature, and reduce the detrimental effects from high thermal generation in future prototypes. Another important finding was that the averaged temperature of the head cap was generally higher compared to that of the disk, as the spindle motor is the primary heat source within the HDD. Heat source analysis of HDD with IR system allows designers to have better visibility of the temperature generated in different components of the HDD. Proper cooling may enhance disk life as well as ensure the stability and integrity of the system.

IDE Hard Disk Digital Image Record System Based on File Format

In this hard disk record system, the IDE hard disk is controlled by FPGA(Field Programmable Gate Array), and the image is recorded to file format directly. In the same time, the recorded image is real-time and lossless. All of this is convenient for subsequent processing.

Abrasive-free polishing of hard disk substrate with H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry

The effect of tert-butyl hydroperoxide-sodium pyrosulfite((CH3)3COOH-Na2S2O5)as an initiator system in H2O2-based slurry was investigated for the abrasive-free polishing(AFP)of a hard disk substrate.The polishing results show that the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry exhibits a material removal rate(MRR)that is nearly 5 times higher than that of the H2O2 slurry in the AFP of the hard disk substrate.In addition,the surface polished by the slurry containing the initiator exhibits a lower surface roughness and has fewer nano-asperity peaks than that of the H2O2 slurry.Further,we investigate the polishing mechanism of H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry.Electron spin-resonance spectroscopy and auger electron spectrometer analyses show that the oxidizing ability of the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry is much greater than that of the H2O2 slurry.The results of potentiodynamic polarization measurements show that the hard disk substrate in the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry can be rapidly etched,and electrochemical impedance spectroscopy analysis indicates that the oxide film of the hard disk substrate formed in the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry may be loose,and can be removed easily during polishing.The better oxidizing and etching ability of H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry leads to a higher MRR in AFP for hard disk substrates.

k-Dimensional hashing scheme for hard disk integrity verification in computer forensics

Verifying the integrity of a hard disk is an important concern in computer forensics,as the law enforcement party needs to confirm that the data inside the hard disk have not been modified during the investigation.A typical approach is to compute a single chained hash value of all sectors in a specific order.However,this technique loses the integrity of all other sectors even if only one of the sectors becomes a bad sector occasionally or is modified intentionally.In this paper we propose a k-dimensional hashing scheme,kD for short,to distribute sectors into a kD space,and to calculate multiple hash values for sectors in k dimensions as integrity evidence.Since the integrity of the sectors can be verified depending on any hash value calculated using the sectors,the probability to verify the integrity of unchanged sectors can be high even with bad/modified sectors in the hard disk.We show how to efficiently implement this kD hashing scheme such that the storage of hash values can be reduced while increasing the chance of an unaffected sector to be verified successfully.Experimental results of a 3D scheme show that both the time for computing the hash values and the storage for the hash values are reasonable.

HARD DISK DRIVES CONTROL IN MOBILE APPLICATIONS

In this paper, control design is investigated for hard disk drives in mobile applications with unknown external arbitrarily fast time-varying disturbances. The disturbances can be estimated with exponential accuracy using the proposed disturbance observer based on a series of integral filters. The position error signal will converge to zero with the proposed control technique for systems subjected to the unknown disturbances. The effectiveness of the proposed method is demonstrated by extensive simulation studies.

Influence of scanning velocity on the tribology performance of hard disk

The dependence of tribology behavior of hard disk on scanning velocity was investigated by friction force microscopy in both air and vacuum. It is found that the sur-face friction force decreases with increasing scanning velocity in air as well as in vacuum. In vacuum, due to the capillary force disappearing, the adhesive energy decreases signifi-cantly, and the friction force is much smaller than that in air.

Dynamic characteristics of hard disk drive spindles supported by hydrodynamic bearings

Most hard disk spindles currently used are supported by grease lubricated deep-groove ball bearings.However, in the trend of increasing spindle speed and reducing size and cost, the shortcomings of ball bearing spin-dles, such as high non-repeatable run out, high acoustic noise and short life time at high running speed, make themunsuitable for high performance hard disk drives (HDD). On the contrary, the dynamic characteristics of hydrody-namic bearing spindles are superior to that of ball bearing spindles. Therefore, they are considered to be the substi-tute of ball bearing spindles in HDD. In this paper, a simulative setup of HDD is build up. The dynamic characteristicsof liquid lubricated spiral groove bearing(SGB) spindles are studied. The effects of both operating condition andbearing clearance are investigated. It is found that running speed of the spindle has significant influence on its dy-namic performance, while the load has little influence. The effect of clearance is also evident.

基于随机森林的硬盘故障率预测研究

为了避免硬盘出现故障而造成大量数据丢失,文章提出一种基于随机森林的方法对硬盘的故障进行预测,降低其丢失数据的风险。首先,在数据预处理方面,对所采用的数据做特征映射预处理;其次,通过对决策树进行构建及选取等,构建随机森林预测模型,根据所选取的特征属性预测硬盘故障率所在的区间,并且特征属性的变化能反映出硬盘故障率的变化趋势;最后,对构建的随机森林模型参数进行调优,选取不同的n_estimators参数值进行测试和优化。实验结果表明,与XGBoost(Extreme Gradient Boosting)、LSTM(Long Short-Term Memory)等方法相比,本文方法的F1值(F-Measure)分别提高了0.93%和1.84%,并且对随机森林预测模型的参数值进行不同取值测试,最终准确率达到98.18%,比默认值提高了1.23%,证明该方法能更精确地预测硬盘故障率,反映出硬盘故障率基于特征属性的变化趋势。

存储系统性能测试技术研究

针对国产计算机硬盘I/O性能测试存在主要使用开源测试工具、缺少统一的基准测试工具问题,设计了一套专门适用于国产计算机上的硬盘I/O性能测试系统。与开源测试工具相比,该系统测试对象更明确,其图形界面简化了用户操作,能直观展示测试结果。该系统测试结果与开源测试工具Vdbench无异,证明了其可为评估国产计算机硬盘I/O性能提供可靠性依据,同时,在国产计算机上对其进行了应用测试,证明了其实用性。

大规模集群硬盘故障预测可迁移性研究

硬盘驱动器(HDD)仍然是大型数据中心与超算中心主要和重要的存储部件,而存储集群规模地持续扩大对硬盘故障预测的研究不断提出挑战.当前,前人已使用统计学、机器学习和深度学习等不同类型的故障预测方法用于大规模存储集群的硬盘故障预测,并取得不俗的研究结果.但是,对于故障模型的迁移性与数据集差异的相关研究还较少.我们收集了多种类型的HDD数据集与基于不同策略的模型,对其进行交叉实验验证,在模型迁移性、数据集预处理和模型参数方面获得了相关实验结果,例如:数据集在回溯时间与平衡度上的设置显著影响一定程度的预测模型性能,而模型参数设置则并不敏感;模型在不同数据集之间的可迁移性强弱不定,而数据集特征类型和数量的选择更影响预测模型性能.

噪声激励下的硬盘频响特性研究和性能预测模型

针对服务器硬盘在高噪声环境下性能下降问题,设计了一种试验方法来分析噪声激励下硬盘性能损失的敏感度特性。通过编程模拟不同频率和强度的1/9倍频程带宽的均匀随机噪声,测试硬盘在噪声激励下产生的性能损失。通过机理分析和试验数据分析,建立回归方程,提出敏感度(K)的数学模型。建立了预测硬盘性能损失的数学模型,基于服务器机箱内散热风扇产生的真实噪声信号可计算出硬盘性能损失率。在多种场景的检验中发现预测模型的结果非常接近实际结果,证明此方法是一种非常准确的分析和预测手段,为服务器系统的声学设计提供有效的量化参考。