Geometrical modeling of granular structures in two and three dimensions. Application to nanostructures

A granular structure can be modeled by a parallelepiped containing spherical balls in three dimensions or by a rectangle filled with disks in two dimensions. These grains (spherical balls or disks) are separated by interfaces called grain boundaries and their size correspond to a size distribution, which is obtained experimentally. The geometrical modeling of such a structure consists in determining the repartition of the set of disjoint grains according to these specifications. In this paper, a new constructive algorithm based on an advancing‐front approach, usually used in the context of mesh generation, is proposed. This algorithm is nearly linear in complexity, robust and fast in both two and three dimensions. Enhancements in computing time and density are observed and reported via comparisons with existing methods. Moreover, we propose a method to transform spherical balls (disks) into polyhedral (polygonal) cells similar to the real grain shapes. Examples of nanostructure modeling in two and three dimensions are presented. Copyright © 2009 John Wiley & Sons, Ltd.     

Finite Element Analysis of sheet metal bending process to predict the springback

Springback remains a major concern in sheet metal forming process. Springback, shape discrepancy between fully loaded and unloaded configuration due to elastic recovery of material, is mainly affected by geometrical parameters, material properties of sheet and lubrication condition between the blank and the tool. A total-elastic–incremental-plastic (TEIP) algorithm, for large deformation and large rotational problems, was incorporated in indigenous Finite Element software. This software was used to predict the springback in a typical sheet metal bending process and to investigate the influence of these parameters on springback. The results of simulation are validated with own experiments and published experimental results.     

Investigation of a multi-ball, automatic dynamic balancing mechanism for eccentric rotors

This paper concerns an analytical and experimental investigation into the dynamics of an automatic dynamic balancer (ADB) designed to quench vibration in eccentric rotors. This fundamentally nonlinear device incorporates several balancing masses that are free to rotate in a circumferentially mounted ball race. An earlier study into the steady state and transient response of the device with two balls is extended to the case of an arbitrary number of balls. Using bifurcation analysis allied to numerical simulation of a fully nonlinear model, the question is addressed of whether increasing the number of balls is advantageous. It is found that it is never possible to perfectly balance the device at rotation speeds comparable with or below the first natural, bending frequency of the rotor. When considering practical implementation of the device, a modification is suggested where individual balls are contained in separate arcs of the ball race, with rigid partitions separating each arc. Simulation results for a partitioned ADB are compared with those from an experimental rig. Close qualitative and quantitative match is found between the theory and the experiment, confirming that for sub-resonant rotation speeds, the ADB at best makes no difference to the imbalance, and can make things substantially worse. Further related configurations worthy of experimental and numerical investigation are proposed.     

Fabrication and MFM study of 60 nm track-pitch discrete track media

Discrete track magnetic recording media with a 60 nm track pitch and prewritten servo patterns were fabricated and tested for read/write performance, and a feasibility analysis of the embedded servo was performed. The fabrication process consisted of ultraviolet nanoimprint lithography (UV-NIL) and sequential ion beam etching on a conventional perpendicular magnetic recording medium. Magnetic patterns were written to the fabricated tracks at 700 kilo flux changes per inch (kFCI) using a spin stand and were read using magnetic force microscopy (MFM), with a resulting signal-to-noise ratio (SNR) of 12.15 dB. The servo pattern was also visualized with MFM. These results demonstrated the feasibility of writing to a 30 nm wide discrete data track and the workability of the embedded servo pattern.     

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.      

Collinear technology for a holographic versatile disk

A novel reading and writing technology for a holographic versatile disk (HVD) system called collinear technology is developed. With this method a two-dimensional data page can be recorded as volumetric holograms generated by a reference beam and a signal beam that are bundled on the same axis and that are irradiated on the recording medium through a single objective lens. The multiplex recording and reconstruction process is demonstrated, and it is shown that the optical configuration and the dichroic medium disk structure are suitable for a compact system. With the HVD's special structure, the system can use a servo to focus, track, and locate the reading and writing addresses. A unique selectable-capacity recording format of a HVD and its standardization activity are also introduced. This method willenable us to construct a small HVD system with CD and DVD upper compatibilities.     

Longitudinal recording in a stray field

We have studied the sensitivity of soft error rate (SER) to an external magnetic field in longitudinal hard disk drives. We found that during writing SER is generally quadratic with field amplitude and symmetric with field direction. The application of an external field during writing also shifts the center of the track. In contrast, during reading SER is predominantly linear with field amplitude and antisymmetric with field direction. There is no shift in the track center when the field is applied during reading up to 100 Oe. We explain the difference in the track center shift between writing and reading in terms of the effect of the stray field on the servo positioning system.     

数控瓦楞纸板印刷模切机伺服配置设计与评价研究

在综合考虑数控瓦楞纸板印刷模切机生产、运行、服务过程中的特征参数基础上,研究了数控瓦楞纸板印刷模切机伺服配置评价体系结构,并采用了模糊集、层次分析法和区间分析法,实现了瓦楞纸板印刷模切机伺服配置评价指标分析与计算。构建了基于iSIGHT的瓦楞纸板印刷模切机伺服配置设计系统,实现了数控瓦楞纸板伺服配置需求与伺服配置候选方案的映射。最后,采用逼近于理想解法方法,进行了候选瓦楞纸板印刷模切机伺服配置方案的优选研究。实验结果表明,提出的方法可以有效、合理实现数控瓦楞纸板印刷模切机伺服配置评价。     

头/盘界面均匀化Reynolds方程及其高效数值求解

当硬盘工作时,磁头滑块飞行在高速旋转的磁盘上方,头/盘界面产生了一层只有几个纳米的气膜,该气膜润滑方程为考虑气体稀薄效应的修正Reynolds方程。为了提高磁记录密度,人们正在考虑用离散磁道（Discrete Track Recording,DTR）磁盘取代传统的光滑磁盘。由于这种DTR磁盘表面磁道和沟槽的影响,在数值求解修正Reynolds方程的过程中,就需要足够多的离散网格来分辨出DTR磁盘表面几何形状,从而带来了计算效率问题。基于均匀化理论和修正Reynolds方程的线性流率（Linearized Flow Rate,LFR）模型,该文推导了一个适合分析DTR磁盘气体润滑特性的均匀化Reynolds方程,并采用有限体积法对均匀化Reynolds方程进行了求解和验证。其结果显示:相对于修正Reynolds方程,求解均匀化Reynolds方程只需要很少的离散网格,从而节省了大量的计算时间,大幅提高了计算效率,且两者压力分布、压力中心和承载力的最大相对误差都小于3.5%。     

光电平台伺服系统自抗扰滑模控制

提出一种基于参考模型的自抗扰滑模控制器,它包括一个自抗扰控制器和一个全局滑模控制器.根据参考模型,利用跟踪微分器设计自抗扰控制器,控制参考模型的输出精确跟踪指令输入信号.全局滑模控制器控制伺服系统被控对象的输出高精度跟踪参考模型的输出.光电平台伺服系统的实验结果证明该新型控制器能有效补偿系统的参数不确定性和非线性扰动,提高了伺服系统的跟踪精度.系统具有全局鲁棒性.     

Mechanical and servo design of a 10 inch disk drive

Design concepts of the mechanical and servo system of a newly-developed compact disk drive are discussed. This new drive features 10 inch diameter disks with a capacity above 400 Mega-bytes. The mechanical structure, with its own closed self-circulating air system , is designed to minimize thermal offtrack and undesired vibration. A new rotary type head actuator is accommodated, and servo system design is based on an optimal control theory to achieve fast, precise positioning.     

Dependence of the tracking performance of an optical disk on the direction of the incident-light polarization

In optical-disk data-storage systems, the signal that provides tracking information is dependent on the groove shape, the optical constants of the materials involved, and the polarization state of the incident light. In this paper, we show that the tracking signal can be described by two measurable quantities, both of which are largely independent of aberrations in the optical system. Using these two quantities, we match the tracking performance of a given disk to an equivalent disk having rectangular grooves-the adjustable parameters being the rectangular groove depth and the duty cycle. By assumption, these rectangular grooves modulate only the phase of the incident beam and disregard its state of polarization. The effective groove depth and the duty cycle thus become dependent on the polarization state of the incident beam. We examine these dependences for various disks having different groove geometries and different combinations of materials.     

全数字电液伺服新型万能材料试验机的研制

论述了高能效、高精度、低成本和低油质手动／自动双控全数字伺服新型万能试验机的研发理念。采用四立柱可调框架结构、活塞深置调心装置、变流量技术、无泄漏技术和全数字多通道闭环测控系统等新技术。经用户使用证明,该机造型新颖、结构紧凑、试验空间可调、操作极为便捷。该机已实现高新技术成果转化,成为适销对路的试验机换代产品。     

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.     

大型盘件辗轧工艺及坯料设计

合理的毛坯尺寸设计是获得精确的盘件尺寸和良好的性能的关键.本文进行了盘件辗轧试验,并根据体积不变原理和变形协调理论提出了一种非矩形截面盘件辗轧用毛坯的设计方法,给出了毛坯尺寸计算公式.试验表明辗轧出的盘件尺寸合格,坯料设计是其中的关键.根据毛坯设计方法通过对燃气轮机压气机盘进行实例设计计算,表明与辗轧成功试验用坯料相吻合,证明了本文设计方法是适用的.     

Synchronous servo scheme using maximum-likelihood detectors

For magnetic disk drives, we have developed a scheme for synchronous servo with maximum-likelihood (SSML) detection that is synchronous around the entire circumference of the track and utilizes ML estimation to detect head position, clock mark phase, and track addresses. Compared to the conventional asynchronous sector servo scheme, the SSML scheme has many, much shorter, servo areas-typically several hundred-distributed on the disk. This results in higher servo information rate, which will be needed for future high-track-density disk drives with a wide servo bandwidth. We analyze the performance of the SSML scheme, including the format efficiency. We discuss a limitation of the synchronous servo scheme with respect to the number of servo areas, and we show an appropriate region for its application. Feasibility of the SSML scheme has been demonstrated in prototype 2.5-in hard disk drives.     

Study of Lithographically Defined Data Track and Servo Patterns

We report on fabrication of discrete tracks on perpendicular magnetic recording (PMR) media with an e-beam lithographical process. We studied the recording performance of the e-beam media on a spinstand in parallel with conventional PMR media. Discrete track media show significant reduction in adjacent track erasure (ATE). We studied and quantitatively measured the source of the ATE improvement, and developed a triple track geometrical model to calculate achievable track density for both discrete track recording (DTR) and continuous media. From the model, we identify two factors of DTR that contribute to reaching a higher TPI. Using the same fabrication technique, we also studied servo burst design and its playback waveform quality. At 250 ktpi, we compare DTR servo bursts with servo bursts written with a conventional method. DTR servo bursts show better edge definition, which can translate to better position error signal sensitivity and support higher TPI in the future.Discrete tracks are fabricated on conventional PMR media with an e-beam litho graphical process. The recording performance is studied on a spinstand in parallel with conventional PMR media. Discrete track media shows significant reduction in adjacent track erasure (ATE). The source of the ATE improvement is studied and quantitatively measured. A triple track geometrical model is developed to calculate achievable track density for both DTR and continuous media. From the model, we identify two factors of DTR, which contribute to reaching a higher TPI. Using the same fabrication technique, we also study servo burst design and its playback waveform quality. At 250 ktpi, we compare DTR servo bursts and servo bursts written with a conventional method. DTR servo bursts show better edge definition, which can translate to better PES signal sensitivity and support higher TPI in the future.     

Head positioning servo design for the IBM 3344/3350 disk files

The 3344/3350 disk files have significantly increased both the recording areal density and total storage capacity per spindle in comparison to previous disk file products, such as the 3340. Parameters directly related to the head positioning systems are compared. Three areas of the head positioning servo system that required design changes for increased performance are described: (1) the encoding used on the servo disk to obtain position information, (2) the compensation technique employed in the track following controller to reduce steady state positioning error and (3) implementation of the phase plane trajectory for improved accuracy and settling as well as decreased access time.     

Constitutive relations for a planar,simple shear flow of rough disks

Stresses developed in a rapid simple shear flow of disks are quantified. Collisional momentum transfer is considered to be the dominant stress generating mechanism. The disks are inelastic and frictional. The restitution coefficient and the coefficient of friction together determine the transfer of momentum and dissipation of energy during a collision. The frictional coefficient generates and maintains a rotational motion of disks. The total fluctuation motion of disks consists of two translational modes and one rotational mode. The rotational mode is found to depend on both the restitution and the friction coefficient. Equipartition of energy among all modes of motion is absent. The mean rotation depends only on the mean flow gradient. The analysis assumes fluctuation modes all have constant magnitudes. Comparison with a computer simulated disk flow shows good agreement. This implies that the distribution of velocity magnitude may not be crucial to the quantification of stresses.     

高速滚珠丝杠副的碰撞噪声控制

滚珠丝杠副是数控机床的关键功能部件,返向器是提供滚珠循环的通道,滚珠进入返向器时的碰撞力会引起较大的噪声。通过分析影响滚珠丝杠副中滚珠与返向器碰撞力的因素,寻找降低该碰撞力的方法,对返向器结构进行改进,并对两种结构丝杠副进行噪声对比试验。研究表明通过减小返向器滚道与丝杠滚道切线的夹角,采用弹性模量较小的工程塑料制作返向器,可以达到降低滚珠与返向器的碰撞力,进而降低滚珠丝杠副噪声的目的。