Drive level acoustic defectoscopy for head disc interface (HDI) integration and manufacturing

A short product development cycle for modern hard disc drive (HDD) depends entirely on early defect characterization. However, deviations from desired HDI mechanical performance are not always manifested in electromagnetic read back or servo control signals. The best non-destructive tool to monitor HDI dynamics at the HDD level is a passive acoustic technique that tracks equilibrium of the head gimbal assembly and air bearing (AB) modes. This technique is capable of active head protrusion detection as well as detection of embedded particles. The drawback of the passive acoustic monitoring technique at drive level is that a noisy HDD environment makes the detectability of a useful signal challenging. The proposed HDD level in situ passive HDI acoustic monitoring technique consists of external AE sensors driven by adequate electronics. These are enhanced by advanced signal processing routines that include adaptive discrete wavelet transforms. The system is tuned to monitor acoustic HDI signatures during drive spin-up/spin-down cycles as well as during passive and active height across the data zones. In addition, integrated acoustic energy metrics can be used in AB design evaluation stages. In this work examples of HDD level passive acoustic monitoring applications for HDI development, and manufacturing defect tracking, are presented and supported by failure analysis results.     

Topology design to improve HDD suspension dynamic characteristics

In this paper, topology optimization in design of suspensions for high-density magnetic recording systems is studied. With the development of higher data density and the faster data streaming, a hard-disk drive (HDD) is required to move faster with greater positioning accuracy. At this situation, even small mechanical vibration induced by seeking motion may result in error in data reading. According to the operational characteristics of HDD suspension, the present work is focused on the topology design of HDD suspension for the dynamic shock response problem. As a result of this research, several new topological structures of HDD suspension are obtained, which are largely different from previous work, and dynamic response under shock force and stability of passive structure are also improved.     

Motor noise generation and prediction for high spinning speed hard disk drive

The acoustic level of a hard disk drive is an important specification. This is especially so for enterprise HDD which is required to operate under a high spinning speed. In order to reduce the acoustics level of a HDD, an in depth understanding behind the mechanisms whereby the noise is being generated in a HDD should be established. This paper will study the acoustics characteristics of a high speed permanent magnet brushless DC motor (PM BLDC) and investigate the physics underlying the generation of noise associated with a motor. An analysis procedure of the PM BLDC motor noise generating mechanisms is proposed. Through finite element analysis and experimental verification, the results indicate that the major noise source for the high speed PM BLDC motor is due to the presence of electromagnetic (EM) torque ripples. Furthermore, it has been observed that the noise radiated by a HDD can be amplified when its structural dynamics are close to the frequency components of the noise source. Finally, a methodology which discusses the steps involved in the prediction of motor radiated noise will be presented.     

Minimum weight design of solid annular plates under an assigned limit ring load

In this paper, topology optimization in design of suspensions for high-density magnetic recording systems is studied. With the development of higher data density and the faster data streaming, a hard-disk drive (HDD) is required to move faster with greater positioning accuracy. At this situation, even small mechanical vibration induced by seeking motion may result in error in data reading. According to the operational characteristics of HDD suspension, the present work is focused on the topology design of HDD suspension for the dynamic shock response problem. As a result of this research, several new topological structures of HDD suspension are obtained, which are largely different from previous work, and dynamic response under shock force and stability of passive structure are also improved.     

Differential evolution based high-order peak filter design with application to compensation of contact-induced vibration in HDD servo systems

Sensitivity loop shaping using add-on peak filters is a simple and effective method to reject narrow-band disturbances in hard disk drive (HDD) servo systems. The parallel peak filter is introduced to provide high-gain magnitude in the concerned frequency range of open-loop transfer function. Different from almost all the known peak filters that possess second-order structures, we explore in this paper how high-order peak filters can be designed to improve the loop shaping performance. The main idea is to replace some of the constant coefficients of common second-order peak filter by frequency-related transfer functions, and then differential evolution (DE) algorithm is adopted to perform optimal design. We creatively introduce chromosome coding and fitness function design, which are original and the key steps that lead to the success of DE applications in control system design. In other words, DE is modified to achieve a novel design for hard disk drive control. Owing to the remarkable searching ability of DE, the expected shape of sensitivity function can be achieved by incorporating the resultant high-order peak filter in parallel with baseline feedback controller. As a result, a seventh-order peak filter is designed to compensate for contact-induced vibration in a high-density HDD servo system, where the benefits of high-order filter are clearly demonstrated.     

Passive acoustic monitoring of head disc interface interactions

A hard disc drive (HDD) recording head thermal protrusion is monitored by the passive acoustic characterization technique where adaptive discrete wavelet (ADW) filtering has been introduced to declare the contact. A phenomenological model is built to demonstrate detectability of the passive acoustic monitoring. The model is based on the mechanical impedance approach where impedances of head disc interface (HDI) and acoustic emission (AE) sensor are compared for matching over air bearing/head gimble assembly frequency bandwidth. A synthesized HDI response signal derived from the HDI mechanical impedance function is compared to the real AE signal obtained during the thermal protrusion based contact detection. A methodology of HDD level AE signal characterization presented in this work consists of the ADW filtering technique where the fifth order DB7 wavelet base function is used in AE signal decomposition. The signal decomposition order is selected by the AE signal entropy minimization.     

Suppressing sensitivity hump in HDD dual-stage servo systems

In Hard disk drive (HDD) single-stage servo system that uses voice coil motor as the sole actuator, the sensitivity hump appears unavoidable due to the Bode’s integral theorem, resulting in amplification of disturbances at frequencies higher than the open-loop gain crossover frequency. This paper studies the sensitivity transfer function limitation in HDD dual-stage servo system. A compensation method for the micro-actuator dynamics, termed as “near-perfect modeling” (NPM), is proposed to generate an effective compensated plant model with zero relative degree in order to suppress the sensitivity hump of the dual-stage servo loop. Therefore, high-frequency disturbances would not be amplified by the servo loop. Experimental results show that the sensitivity hump of dual-stage servo loop can be reduced to very close to 0 dB without amplification of the corresponding measurement noise.     

一种基于多传感器的噪声信号分离方法

分析了工业现场噪声分布情况和噪声的传输特性,提出了一种将多点多传感器测量所得噪声值,再通过相关性分析进行噪声分离的新方法.各个传感器的测量信号都是混叠噪声信号,它们的自相关函数的波形与信号本身的波形无关,仅与信号所包含的频率成分亦即振幅谱有关,且互相关函数rxy(n)也只包含信号Xn和Yn所共有的频率成分.理论分析和计算机仿真证明可以有效的分离强干扰噪声,为噪声故障诊断提供可靠的真实数据.     

A design based on final-state control for residual vibrationless seeking in hard disk drives

A new design method - based on a final-state control (FSC) - for short-span seeking in a hard-disk drive (HDD) has been developed. The short-span seeking is performed by two-degree-of-freedom (2-DOF) control, which uses a feedforward (FF) control input along with a reference trajectory. The design method can directly generate the FF control input, whose derivative at a specified order is minimized and whose power spectrum amplitude is reduced at a specified frequency. The residual vibration caused by mechanical resonance can therefore be reduced by the generated FF control input. Test with a 2.5-in form-factor HDD experimentally confirmed that the developed seeking control significantly reduces the residual vibration in a HDD.     

MEMS存储设备的伺服设计

和硬盘相似,基于MEMS的存储设备读写数据时也采用伺服来定位.在分析MEMS存储设备固有特点的基础上,以硬盘的伺服原理为基础,提出了几种可行的伺服方式,分析并比较了各种伺服方式对数据布局、通道设计、服务时间和空间利用率的影响.结果表明,合适的伺服可以大幅度提高MEMS存储设备的性能.     

基于神经网络方法的水声信号预测

由于海洋环境的复杂性和水声信道复杂的时变、空变特性，使得舰船辐射噪声是一种非平稳、非高斯过程。如能提前预测敌方舰船的辐射噪声，并有效地对敌进行水下对抗，先敌使用武器攻击，是克敌制胜的前提，也是我海军目前各型潜艇和水面舰艇急需解决的关键技术。文章根据水声信号的特点建立了预测模型和网络结构参数的设计。并分别采用BP神经网络和RBF神经网络对仿真信号和实际舰船水声信号进行预测。结果表明，利用神经网络预测水声信号达到了一定的效果，为今后进一步开展水声信号预测研究奠定了基础。     

基于AE-LSTM的多目标硬盘故障预测方法

硬盘故障预测是在故障发生前发出预警,避免数据丢失或服务中断,提高数据中心的可靠性和安全性。然而,大多数故障预测模型将硬盘故障问题转化为二分类任务,忽略了硬盘故障是渐变过程的,并且缺乏故障诊断功能。因此,提出了一种基于AE-LSTM的硬盘故障预测框架,实现多目标任务：硬盘健康状态分级、硬盘剩余使用寿命预测、硬盘故障诊断。首先,采用回归决策树模型智能化对硬盘健康状态进行标记;其次,通过AE-LSTM模型提取鲁棒的隐藏变量,并构建剩余使用寿命预测模型和硬盘健康状态分级模块;最后,根据AE模块的输入输出差异进行硬盘故障诊断。在Backblaze公开数据集上,对比了RF、LSTM和AE-LSTM三种算法,实验结果证实了AE-LSTM算法在多目标硬盘故障预测中的有效性和优势。     

粒子群算法在PID控制器参数整定中的研究与应用

针对自动化控制系统中PID控制器参数整定困难的问题,提出了基于粒子群算法的PID控制器的设计方法,给出了具体的实验架构。采用系统参数鉴定的方式得到直流伺服发电机的传递函数,并利用粒子群算法搜寻PID参数。实验采用MATLAB仿真证明了该方法的可行性和优越性。所得到模拟结果跟遗传算法搜索PID参数的结果做比较,结果显示用粒子群算法调整PID参数所得到的运算时间比用遗传算法的运算时间要短。     

神经网络PID控制器在硬盘磁头定位系统中的应用

针对硬盘驱动器难以建立准确对象模型的特性,提出了一种采用神经网络PID控制器的方法。该方法利用神经网络的自学习能力和任意非线性表达能力,实现实时、在线地调整PID控制器的比例、积分、微分系数,从而找到PID控制参数的最佳组合,以达到某种性能指标的最优化。作为常规BP神经网络的改进型,提出以从最初时刻到当前时刻的误差的平方和最小作为性能指标函数。仿真结果表明,采用这种控制方案进行硬盘伺服控制,系统收敛速度快、调节时间短、且几乎没有超调和稳态误差,性能优于常规神经网络PID控制,适用于实际的硬盘驱动器磁头定位。     

A patient transfer apparatus between bed and stretcher.

This paper presents a patient transfer apparatus between bed and stretcher. This apparatus makes it possible for the nurse to move weak, injured, or paralyzed patient from bed to stretcher, or vice versa, alone. Moreover, the suffering, stress, and uneasy feeling of the patient can be alleviated. This paper describes the specification, mechanical design, control system, and motion control of the apparatus. A special devised mechanism is developed, and a new servo system is used in this control system. The control principle and algorithm of the new servo system are proposed, and the motion-control method and safety function of the apparatus are described. The experimental results and evaluation indicated the effectiveness of this system.     

硬盘驱动磁头偏置误差检测算法的研究

在硬盘装配过程中,通常需要对磁头间的磁头偏置误差进行预校准,并实施有效的补偿措施以减少磁头切换时的寻址误差,提高读写效率。然而,由于剧烈震动或不当操作等因素的影响,校准好的磁头偏置可能偏离预校准值,从而导致硬盘寻址或读写性能的下降以及伺服启动时间的延长。提出了一种在硬盘正常启动过程中快速有效的磁头偏置的检测和补偿算法,设计了与磁盘扇区绑定磁头偏置滤波方案。实验表明此方法可以快速有效地识别磁头偏置,并启动相应的校准操作,提高了硬盘在剧烈震动后的伺服性能。     

Circuit model for piezoelectric actuator with electrically conductive epoxy

Dual stage actuator (DSA) has been a critical component in hard disk drives to increase servo control bandwidth and thus storage capacity. The electrical properties of a typical DSA vary with the frequency, as piezoelectric materials (e.g., PZT) and electrically conductive adhesives (ECA) are commonly used. A circuit model is thus needed to capture such complexity for servo control design. In this paper, we review two typical DSA circuit designs and compare three circuit models with different simplifications. The model with parallel RC circuits can successfully capture DSA circuit characteristics up to 1 MHz. Impedance data measured from real parts show excellent agreement with simulation results based on the model. In addition, we investigate impacts of abnormal ECA on the overall DSA transfer function. This research can provide a practical yet valuable guideline for DSA related servo control.     

一种抑制硬盘自伺服刻写中径向误差传播的方法

磁头和数据道的相对位置是通过分析伺服信息得到的.因此伺服信息必须在硬盘生产过程中被写入.传统的伺服信息刻写过程需要借助伺服道刻写机和净房环境,这些都会使硬盘的生产成本增加.快速增长的磁道密度也给伺服信息的刻写带来很大压力.自伺服刻写能够使用硬盘自身的组件来完成伺服信息的刻写过程,因此提高硬盘的生产效率.讨论了硬盘自伺服刻写过程和其中的关键问题,分析了自伺服刻写原理及其带来的径向误差传递现象.径向误差是由于噪音扰动、"种子"磁道的缺陷和与上一磁道的高度依存性引起的.比较了现行的两种抑制自伺服刻写中误差传播的办法,分析了它们存在的问题,然后提出了一种加权型校正信号的产生方法,并从理论上和仿真条件下证明了该方法的正确性和优越性,它能同时减少磁道绝对径向误差和相对径向误差.     

球杆系统自适应遗传PID控制

遗传算法全局寻优参数,但训练时间较长;PID控制算法简单,却难以控制非线性复杂过程.将自适应遗传算法和PID相结合,可有效地改善控制效果.通过建立球杆系统机械部分模型、角度模型和电机模型,得到整个球杆系统的数学模型;设计基于遗传算法的自适应PID控制器,通过在线整定控制器参数,提高球杆系统的控制性能.仿真实验结果证明了该算法的控制效果良好,适应能力较强,具有算法简单、参数整定容易等优点.     

MEMS milliactuator for hard-disk-drive tracking servo

This paper describes the design, fabrication, and operational characteristics of a MEMS milliactuator designed for servo tracking in a hard-disk drive (HDD). The actuator is designed to increase the bandwidth of an HDD tracking servo and pack more recording tracks on a disk. An Invar (low thermal expansion metal) electrode position process was developed to meet the thermal stability requirement. The electroplated Invar's thermal coefficient of expansion is as low as 6.3×10^-6/K, which is almost half of that of pure nickel. For the plating mold pattern definition, a high-aspect-ratio polymer etching technique was developed. A high-aspect-ratio structure line-and-gap definition is required to achieve both a high directional stiffness ratio and electrode efficiency for the actuator. The etching technique described can etch through a thick (<40 μm) polymer layer with an aspect ratio of 16:1 at an etch rate of <2 μm/min. Low-cost/high-volume manufacturing is achievable by this batch fabrication technique. A milliactuator was fabricated and assembled with a suspension and a slider weighted at around 2 mg. The slider was successfully driven by the milliactuator while the slider was flying on a spinning disk. The operational characteristics (frequency response) of the in-flight milliactuator were measured, and the results indicate that the actuator is suitable for high-bandwidth HDD servo-tracking applications