调谐质量阻尼器用于改善硬盘驱动器读写头动臂的动力特性

通常计算机硬盘中的读写头动臂在3～4kHz的频率范围内有一个准刚性模态，这个准则性模态限制了伺服带宽进而限制了硬盘存储密度的提高。设计了一种调谐阻尼器结构来降低准刚性模态导致的振动，该阻尼器安装在音圈马达的线圈内部，结构简单，不影响动臂移动。所使用的阻尼材料取材于硬盘本身的密封橡胶，也避免了可能的气体污染。实验证明，该阻尼器能够很好地降低动臂在准刚性模态下的振动，因而有利于存储密度的提高。     

爆炸振动作用下硬盘驱动器的安全性能分析

介绍了计算机硬盘驱动器的振动敏感性,分析了硬盘驱动器在振动环境下失效的机理,通过实验测定了硬盘驱动器振动环境下的短时工作失效判据中阈值[w].提出爆炸地震作用下硬盘驱动器工作失效的安全比距离计算方法.     

Failure Prediction,Lead Time Estimation and Health Degree Assessment for Hard Disk Drives Using Voting Based Decision Trees

Hard Disk drives (HDDs) are an essential component of cloud computing and big data, responsible for storing humongous volumes of collected data. However, HDD failures pose a huge challenge to big data servers and cloud service providers. Every year, about 10% disk drives used in servers crash at least twice, lead to data loss, recovery cost and lower reliability. Recently, the researchers have used SMART parameters to develop various prediction techniques, however, these methods need to be improved for reliability and real-world usage due to the following factors: they lack the ability to consider the gradual change/deterioration of HDDs; they have failed to handle data unbalancing and biases problem; they don’t have adequate mechanisms for health status prediction of HDDs. This paper introduces a novel voting-based decision tree classifier to cater failure prediction, a balance splitting algorithm for the data unbalancing problem, an advanced procedure for lead time estimation and R-CNN based approach for health status estimation. Our system works robustly by considering a gradual change in SMART parameters. The system is rigorously tested on 3 datasets and it delivered benchmarks results as compared to the state of the art.     

Evaluating Track-Following Servo Performance of High-Density Hard Disk Drives Using Patterned Media

In recent years, track densities of magnetic hard disks have continued to grow. A promising approach to continuing the trend to ultrahigh density is using bit-patterned media (BPM). However, the implementation of BPM in hard disk drives (HDDs) to achieve high recording density is challenging and requires various new techniques, such as new servo pattern designs and position error signal (PES) decoding schemes. In applying BPM in HDDs, it is important to select a servo pattern providing sufficient PES quality for head positioning. In this paper, we discuss evaluation of PES quality and servo pattern performance from a closed-loop (servo) point of view in order to evaluate the quality of several servo patterns. We consider three servo patterns (the amplitude pattern, chevron pattern, and differential frequency pattern) as case studies. We developed a PES simulation tool to provide a realistic HDD track-following simulation. Because of PES nonlinearity in the amplitude servo pattern, we considered time-based servo patterns as alternatives. For time-based servo patterns, we found that readback signal sampling and transition jitter greatly affect PES quality. Therefore, we conclude that the differential frequency servo pattern is superior to other patterns, since it is less sensitive to transition jitter and readback signal sampling.      

Direct Comparison of Computational and Experimental Head-Slap Data for a Nonoperating Hard Disk Drive

We refined a previously developed finite-element (FE) model of a Seagate Bali II hard-disk drive (HDD) to include compliance contributed by roller bearings at the spindle and pivot motors. We then performed drop-test simulations with the nonlinear structural dynamic codes LS-DYNA and ABAQUS/Explicit. In parallel, we subjected a nonoperating Bali II HDD to physical tilt-drop tests from drop angles of 10deg and 45deg, representing a mild and a substantial shock input, respectively. We measured velocity responses with a laser Doppler vibrometer (LDV) at two points on the HDD. The first point was on the topmost read/write head at the center of its trailing edge, and the second point was on the top surface of the baseplate directly above the line of contact with the impact bar. In the FE studies, the baseplate velocity histories measured during the tests were used to prescribe input motions at the corresponding baseplate nodes. We compared computed and measured head velocity histories in order to evaluate the effectiveness of present state-of-the-art simulation tools for modeling head-slap events     

Robust Controller Design of a Dual-Stage Disk Drive Servo System With an Instrumented Suspension

This paper proposes a robust track-following controller design method for a dual-stage servo system in magnetic hard disk drives (HDDs). The method formulates the problem of minimizing track misregistration (TMR) in the presence of plant uncertainty and variation as a multiobjective optimization problem. Tracking error minimization is naturally formulated as an$H_2$norm minimization problem, while the robust stability issue is addressed by some$H_infty$norm bounds. This mixed$H_2/H_infty$control problem can then be formulated as a set of linear matrix inequalities (LMIs) and be efficiently solved through convex optimization algorithms. To enhance the system's tracking performance and stability robustness, the method explicitly takes attenuation of airflow-excited suspension vibration into consideration by an inner loop fast rate damping and compensation controller that utilizes the output of a strain gauge sensor on the suspension surface. Analysis and simulation show that a system designed by this method can achieve good tracking performance while still keeping stability robustness to plant variation and high-frequency spillover.     

光盘振动模态的电视激光全息测量与分析

采用激光全息(TV—holography)振动测试技术测量和分析了CD光盘的固有频率、模态振型以及模态分布情况。采用非接触声激励和非接触式激光全息摄像精确地测量出了CD光盘从零节圆到三节圆五节径的振动模态，最高模态频率达6300Hz。分析了节径振型和节圆振型间的关系和出现规律。结果表明：光盘的振型节线是由中心对称和轴对称的节径和节圆组成的，它们对应的振型也是中心对称和轴对称的；光盘的各阶固有频率是按一定的顺序排列的，节径和节圆的出现是有规律的，文中给出了表示这些规律的表达式。     

Investigation of Fluid Structure Interaction of a Head Stack Assembly in a Hard Disk Drive

An analysis of three-dimensional, unsteady flow field is conducted in a 3.5-in, 7200 rpm hard disk drive (HDD) using FLUENT software. The analysis is carried out for the head stack assembly (HSA) positioned at the outer diameter (OD). A finite element model (FEM) of the HSA, built in ANSYS, is used for the forced vibration analysis. The flow field analysis yields the aerodynamic forces and moments which are applied to the HSA FEM. The effects of a damper plate and arm holes introduced to the HSA design are investigated. The analysis shows that a damper plate attenuates the root mean square (RMS) of aerodynamic loads acting on the HSA, resulting in a significant reduction of off-track displacement of the heads. It also shows that a weight-saving hole in the arm causes a complex vortex structure inside the hole. The vortex structure exhibits a forming/collapsing frequency of 7 to 9 kHz, which resonates with the structural modes of the HSA, causing additional off-track vibration of the heads.      

Feedforward Control Based on Neural Networks for Hard Disk Drives

We present a novel feedforward control based on neural networks to attenuate the effect of external vibrations on the positioning accuracy of hard disk drives. The neural network compensator, which is an add-on function on top of nominal feedback control, uses the accelerometer signals obtained from a sensor to detect external vibrations. Our feedforward control can be regarded as a nonlinear finite impulse response (FIR) that corresponds to linear FIR when the basis function of the neural network is linear. By neural network learning, the tracking performance of hard disk drives can be improved with no information on disturbance dynamics or sensor model. We have analyzed the stability of the proposed scheme by the Lyapunov criterion. Here, we give simulation results to demonstrate that our control scheme can eliminate the effect of external disturbances on positioning accuracy.      

摄动法研究硬盘磁头滑块动态飞行特性

硬盘工作时,磁头滑块飞行在磁盘上方,其动态飞行特性对硬盘工作性能有重要影响。该文利用摄动法推导了磁头滑块的气膜刚度和阻尼摄动方程,且通过有限体积法进行求解,获得了初始摄动条件下的气膜刚度和阻尼矩阵。结合磁头滑块动力学方程,研究了扰动速度、扰动俯仰角和扰动侧倾角对磁头滑块动态飞行特性的影响。研究结果表明:①扰动速度会导致磁头滑块向磁盘表面作竖直方向的移动,增加了与磁盘接触碰撞的风险;②扰动俯仰角或侧倾角的增加都会导致磁头滑块振动幅度的增加,但扰动俯仰角更容易引起磁头滑块的振动。     

U-type piezoelectric thin-film microactuator for hard disk drives

We have designed, fabricated, and investigated a new dual-stage actuator system based on a thin-film lead-zirconate-titanate (PZT) microactuator and a voice coil motor for positioning a magnetic head in a high-density hard disk drive (HDD). We made the PZT microactuator by using a modified sol-gel technique to deposit PZT thin film and applying reactive ion etching processes to shape the device. We studied the crystalline structure and growth behavior of the piezoelectric films by X-ray diffraction and scanning electron microscopy and found that the PZT material preferably has a composition of Pb(Zr/sub 0.52/Ti/sub 0/.48)O/sub 3/. We also tested and simulated the U-type SUS304 substrate integrated with two single-layer PZT elements in order to investigate the driving mechanics. The device performance is outstanding. With the peak-to-peak head displacement of 1.08 /spl mu/m at the applied voltage of /spl plusmn/20 V and the suspension response frequency higher than 12 kHz, both displacement/voltage sensitivity and resonant frequency are high enough for the device to be used in future high-density HDDs.     

薄壁圆盘裂纹的应变分形特征及诊断识别研究

运用有限元方法对裂纹圆盘进行动态特性分析,获得振型和应变响应。应用多重分形理论计算和分析裂纹圆盘应变响应的广义维数和敏感维数。把应变广义分形维数、敏感维数作为圆盘裂纹状态的特征量,对圆盘的裂纹诊断与识别进行定性及定量研究。通过计算得到圆盘裂纹的应变广义维数相关系数,用广义维数相关系数法对圆盘裂纹长度进行定量识别。通过对实例的识别分析,考查了裂纹长度的识别精度及广义维数相关系数法对裂纹长度的定量识别的实用性。     

Novel method for minimizing track seeking residual vibrations ofhard disk drives

Track access time is an important parameter for high-performance hard disk drives (HDDs). Presently, the resonances of the head actuator caused by the pivot-bearing stiffness are an even more urgent problem, since these resonances have become the main design factor that limits further reduction of track access time and improvement of the servo control bandwidth in HDDs. Our objective in this paper is to investigate, from a mechanics and dynamics viewpoint, the influence of the driving force waveforms on residual vibrations and to identify the characteristics of the waveform, which will lead to zero or very low residual vibrations. Using a simplified model of a head actuator assembly and finite-element simulation, we show that the residual vibration of the head actuator assembly depends strongly on the waveform and the time duration of the driving impulse force. If suitable waveform and time duration of the seeking impulse force are appropriately chosen, very low track seeking residual vibrations and quick track access can be achieved     

A Novel Threshold Accelerometer With Postbuckling Structures for Airbag Restraint Systems

Based on the postbuckling theory of large deflection beams, the nonlinear stiffness of a postbuckling beam is deduced and in agreement with the results of buckling experiments. Then, a novel post machined threshold accelerometer is designed, which consists of eight oblique post beams with an inertial mass in the middle to ensure its single moving direction and an electrical contact part fabricated on the bottom of the inertial mass. The threshold accelerometer is an integration of a threshold sensor and an inertial driven actuator used in airbag restraint systems. When the acceleration reaches the threshold, the beams buckle and close the threshold accelerometer, and when it gets down to be a certain value, the accelerometer opens quickly under the effect of the elastic force developed by the postbuckling beams. Compared with the design models of other threshold accelerometers with linear beam structures, the nonlinear postbuckling beams are introduced as threshold sensing elements. A number of design factors such as the air film damping and the contact force are taken into full consideration, thus establishing the dynamic equation of the accelerometer under coupled forces. The dynamical simulation for the strong nonlinear system with elliptic integrals indicates its good threshold characteristic and high contact reliability. The threshold accelerometer responds within 4 ms when it is triggered by a threshold acceleration ac = 20 g, and cuts off quickly when the cutoff acceleration is under ad = 5 g. Meanwhile, the unstable contact time is only 0.02 ms for the contact force to reach 50 mN, which guarantees the contact resistance to be less than 20 mOmega. With the results of the dynamic simulation, supported by previous buckling experiments, the accelerometer can provide accurate threshold sensing without false actuations under interferences outside, especially electromagnetic and vibration interferences, and hence their wide applications in safe-arming systems.     

Investigation of the fabric evolution and the stress-transmission behaviour of sands based on X-ray μCT images

This paper presents the use of X-ray micro-tomography (X-ray $\mu$CT) and image processing and analysis techniques to investigate the stress transmission and buckling of inter-particle contacts within a granular material. A triaxial testing of a miniature Leighton Buzzard sand (LBS) sample was carried out with full-field in-situ X-ray $\mu$CT scanning. High-spatial-resolution CT images of the sample were acquired at several loading stages of the test. Image processing and analysis techniques were used to quantify the inter-particle contact evolution (contact gain, contact loss and contact movement), fabric, contact duration and buckling of stress-transmission contacts based on the CT images. The results indicated that contact gain and loss, and contact movement played two competing roles in determining the overall fabric evolution of the sample. Contacts with a longer duration were more likely to orient in the major principal stress direction and form a stress-transmission contact network. A gradual decrease in the buckling rate of the stress-transmission contacts was observed outside of the shear band, and a relatively stable buckling rate was observed within the shear band during the shear. The results suggested that jamming occurred outside of the shear band and that unjamming occurred within the shear band.     

某航空发动机整体叶盘耦合振动特性分析

通过建立某航空发动机整体叶盘的三维实体模型,对整体叶盘结构的耦合振动特性进行了固有模态特性分析。根据有限元软件ANSYS的计算结果,绘制了叶片共振转速Campbell图,分析了整体叶盘结构模态振动的基本特性,得到了整体叶盘节径-频率图,分析的结果为进一步研究整体叶盘的结构设计优化和避免共振提供了依据。     

Contact-Type Vibration Sensors Using Curved Clamped PVDF Film

This paper describes a new type of contact vibration sensor made by bonding a piezoelectric polyvinylidene fluoride (PVDF) film to a curved frame structure. The concave surface of the film is bonded to a rubber piece having a front contact face. Vibration is transmitted from this face through the rubber to the surface of the PVDF film. Pressure normal to the surface of the film is converted to circumferential strain, and an electric field is induced by the piezoelectric effect. The frequency response of the device was measured using an accelerometer mounted between the rubber face and a rigid vibration exciter plate. Sensitivity (voltage per unit displacement) was deduced from the device output and measured acceleration. The sensitivity was flat from 16 Hz to 3 kHz, peaking at 6 kHz due to a structural resonance. A contact vibration sensor theory has been developed, which accounts for the effect of the radiation medium. It has been found that the imaginary part of the radiation impedance has an effect equivalent to the addition of mass to the curved PVDF film structure, which reduces the resonance frequency by about one order. Calculations predicting performance against human tissue (stethoscope or contact microphone) show results similar to data measured against the metal vibrator. This implies that an accelerometer can be used for calibrating a stethoscope or contact microphone. The observed arterial pulse waveform from the new PVDF sensor showed more low-frequency content than a conventional electronic stethoscope.     

基础激励下非线性碟簧减振系统的特性研究

详细研究了考虑静力载荷影响、具有弹性非线性和Coulmb摩擦阻尼非线性的磺簧元件的动力学特性。首先利用Fourier级数展开与平均法研究非线性碟簧系统的自由振动,讨论影响自由振动的振幅和频率的各种因素;然后利用Fourier级数展开与谐波平衡法研究基础激励下非线性簧系统的强迫振动,通过详细的参数研究考察非线性碟簧元件的减振性能特征;最后采用修正的稳定分析方法研究稳态响应的稳定性。     

Failure Analysis of Steam Turbine Rotor Disk

This article presents an investigation into causes of failure of rotor disk of an 8.25-MW capacity steam turbine, which failed catastrophically. Four pieces of the rotor disk detached from the tenth-stage disk of the turbine rotor during this failure. Visual inspection, chemical analysis, macro- and microscopic analysis of the failed rotor disk, analysis of the operational data, and the history of the rotor operation indicated that the failure could be attributed to stress concentrations at macropores and regions of segregation in the disk. Stress corrosion cracking (SCC) subsequently took place in the regions of stress concentration because the steam in the turbine contained chloride and potassium. The SCC produced a network of cracks associated with the macro- and microporosities. It was recommended that the disk fabrication processes ensure a high-quality microstructure and that operational monitoring of the composition of steam be initiated to ensure that the chlorides and potassium concentrations are maintained below a specified level.     

The pulse width effect on the shock response of the hard disk drive

A finite element model (FEM) of the ST drive from Seagate is developed in ANSYS to investigate the shock response of the hard disk drive (HDD). The FEM includes the pivot bearing, the head stack assembly (HSA) and the disk. The free state of the HSA is determined by an iterative procedure to produce the prescribed preloading force at the head–disk interface. The FE model is then verified by conducting a modal analysis over the HSA. The obtained mode shapes and resonant frequencies are compared with the modal testing results. An acceleration pulse is applied to the shaft and the whole disk surface at the same time to study the shock response of the HDD. The head slap behavior is examined at the slider–disk interface. The effect of the pulse width on the head slap behavior is studied. The duration of the acceleration pulse varies from 0.3 to 1 ms. It is found that the lift-up height of the slider reaches a peak value at different pulse widths when the amplitude of acceleration pulse changes. This is due to the nonlinear behavior introduced by the contact surfaces.