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.     

Multi-resolution HDD contact detection technique for low SNR applications

The accurate calibration of active flying height in a hard disk drive (HDD) is an essential metrology for proper drive operation. Detecting head-disk contact of a head-disk-interface (HDI) is a critical step in calibrating the active fly height. Proposed is a head-disc contact detection technique that is an improved adaptive discrete wavelet transform (ADWT) methodology that can be integrated into an advanced HDD. The method is designed to process low SNR head/disc proximity probe data during a thermal protrusion pulse and extract HDI head modulation signatures correlating them with the contact event. The significance of the proposed ADWT implementation is in fact that thousands of DWT coefficients can be represented by a simple statistically derived data set of four parameters that can be tracked to declare the contact. This compact approach enables a practical, cost-effective ADWT implementation into the HDD hardware architecture using existing micro-processors and on-board memory.     

Ultra sensitive in-situ acoustic characterization system for HDD head disc interface defectoscopy

An ultra sensitive drive level acoustic characterization system has been developed for in-situ Head Disc Interface defectoscopy. Multimode acoustic emission (AE) sensor installed on the drive cover is designed for tracking air bearing (AB) and slider modes. Monitored modal changes at the AB and slider bandwidth correlate to the weak head disc interface (HDI) interactions such as lubricant modulation and particles induced defects. Two or three orders of magnitude increase in sensitivity can be achieved by a combination of advanced sensors, data acquisition hardware and digital signal processing algorithms. Continuous and Discrete Wavelet Transform and Joint Time-Frequency analyses are implemented for the AB modal data mining process. Performance of the newly developed technology is demonstrated on a normally operating hard disc drive (HDD).     

Experimental study on slider dynamics during touchdown by using thermal flying-height control

To investigate the possibility of further lowering the clearance in head?Cdisk interface systems, slider dynamic behavior during a touchdown sequence with a thermal flying-height control (TFC) function was investigated by using a spinstand-level evaluation utilizing an acoustic emission (AE) sensor and a laser Doppler vibrometer (LDV). Experimental results demonstrated that off-track vibration was easier to excite by head?Cdisk contact at the beginning of head?Cdisk contact. We then confirmed that the amplitude of pitch-mode vibration in the flying-height direction increased and sway-mode vibration in the off-track direction decreased when increasing heater power during the touchdown sequence. Moreover, we found that the peak frequency of pitch-mode vibration shifted to a higher frequency under over-push conditions. Time?Cfrequency domain analysis results showed that the peak shift occurred at several locations during a disk rotation. The mechanism of the peak shift is attributed to the increase in stiffness at the head?Cdisk interface (HDI) due to solid?Csolid contact or mode change occurred in such regions. During the touchdown sequence, the friction force at the HDI continues to increase, even though slider vibration and AE signal decrease when heater power is increased. The friction force at the HDI needs to be decreased to achieve further low-clearance HDI.     

基于小波分析的声发射刀具状态判析

提出了一种基于小波分析的声发射刀具状态判析方法,该方法通过多层小波分解对信号主能量所处频段进行局部特性刻画,利用小波分解系数2——范数表征信号的奇异性,在统计量与刀具状态间建立物理联系。实例表明:该方法能有效地判断刀具状态,并具有较好理论基础与操作性。     

基于CEEMD和改进小波阈值的机械密封声发射信号降噪方法

声发射作为一种无损检测结束被广泛应用于多个领域,针对声发射信号难以从背景噪声种分离的问题,提出了一种基于互补集合经验模分解（CEEMD）与改进小波阈值相结合的降噪方法。首先对声发射信号进行CEEMD分解,通过峰宽占比确定信噪分量分界点,对噪声分量进行改进的小波阈值降噪,将降噪后的分量与其余分量进行信号重构得到最终降噪结果。通过仿真信号和机械密封声发射实验信号论证了本文方法相较于传统小波降噪和CEEMD强制降噪更有效。     

基于多尺度的声测量搅拌釜内物料特征

通过声波信号在线分析反应器内物料特征具有快速、无损、安全、不侵入流场的优点。讨论了利用声发射信号在线分析搅拌釜内物料浓度与粒度的方法。先通过小波变换多尺度分解原始声信号,然后以分解后各细节信号小波系数幅值绝对值加和为特征变量,釜内物料浓度或颗粒平均粒度和声发射信号的关系再用判别分析方法加以区分,考察了信号长度、分解尺度以及不同小波对判别准确性的影响,结果表明,当物料的浓度一定时,基于多尺度分析的声测量方法可以准确地对釜内物料的粒度进行分类。     

管道泄漏模拟声发射的压缩感知及经验模态分解

管道泄漏监测中常用到声发射信号检测技术。压缩感知理论是一种高效的信号采集压缩处理方法,将其应用到模拟声发射信号的采样重构中,可以使信号采样不再受Nyquist采样定理的限制,降低了数据采集成本,通过重构算法实现对原始信号的精确重构。进而对重构声发射信号进行分解,通过对比信号的经验模态分解,集合经验模态分解和掩膜信号法分解结果,表明掩膜信号法能有效抑制分解过程中存在的模态混叠现象,使分解结果更加精确有效。为声发射信号的特征提取打下坚实基础。     

小波分析在数控刀具磨损状态监测中的应用

研究了数控刀具切削过程中声发射(AE)信号的产生机理和特点,提出了利用小波分解和小波包分解技术提取AE信号特征参数的方法监测刀具的磨损状态,并通过实例验证了该方法在刀具磨损监测中的可行性.     

Acoustic emission (AE) measurements to determine the dynamic flying characteristics of optical sliders

Flying heads carrying a magnetic coil and a high numerical aperture lens for magneto-optic recording or a solid immersion lens for optical phase change recording, respectively, are promising approaches for increasing the data density. A classic approach to dynamically evaluate the flight attitude of flying heads in data storage is acoustic emission (AE) testing of the head/disk interaction using special glide heads. In our paper we introduce the application of AE test heads for measuring the flying characteristics of optical far field and near field sliders. In comparison to conventional external AE sensors, i.e. sensors mounted somewhere in the drive, these AE elements are directly mounted on the sliders thus yielding a higher pulse shape and a better signal to noise ratio. This set-up allows a clear identification of the head disk contact. To calibrate the sensor a bump disk was fabricated and used for AE measurements.     

水平定向对接穿越导向系统设计

水平定向对接穿越技术有效地解决了传统水平定向钻进无法进行长距离穿越,以及含砾石等复杂地层穿越的问题。在已有水平定向钻进工艺的基础上,实现对接穿越的关键在于成功进行导向孔对接。描述了一种水平定向对接穿越导向系统,系统采用三轴加速度计和磁阻传感器作为姿态敏感器件,以轴向磁铁产生的磁场作为对接磁源,介绍了系统的工作原理,以及系统的结构和功能。此系统具有体积小、成本低、精度和可靠性高等一系列优点,适用于水平定向对接穿越的导向。     

基于小波包与模糊聚类算法的声波法检测流化床内颗粒的平均粒度

平均粒径是气固流化床反应器运行时需要监控的重要参数之一,利用声波信号检测床内颗粒平均粒度的方法能克服传统方法不能实时在线测量的缺陷,安全环保不侵入流场.先用Db5小波包将声发射信号3尺度分解,求出各细节信号小波系数的绝对值加和,构成声信号的能量模式,标准化之后经主成分分析得出主成分,再用模糊均值聚类方法分类.由于不同粒度的声波信号经小波包分解后,其小波系数绝对值加和具有特定的模式,因而,这种方法分类准确性达98%以上.     

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。     

小波包分析在刀具声发射信号特征提取中的应用

分析了刀具的切削状态,介绍了刀具的声发射信号检测系统和小波、小波包分析技术,以及小波包频带能量分解方法,提出了小波包分解功率监测特征量提取技术.通过在刀具声发射的一个实例信号中的应用,有效地区分了刀具的两种切削状态,验证了小波包分解功率监测特征量提取方法的可行性.     

基于模糊聚类技术的肌电信号完全分解算法

肌电(EMG)信号分解是EMG信号产生的逆过程。通过EMG分解获取完整的运动单元(MU)的波形和发放信息,需完成复杂的叠加波形分解过程。首先,基于小波滤波和小波阈值估计技术去除EMG信号中的噪声;接着,利用幅度-斜率双阈值法检测出MUAP波形;然后,采用分类功能强的模糊K均值聚类技术对波形进行聚类,再利用最近邻法将未分配波形分类;最后,采用基于伪相关相似性度量的剥落法,进行叠加电位波形分解,实现肌电信号的完全分解,获取完整的MUAP波形和发放模式。利用对来自正常人的真实EMG信号和模拟EMG信号进行实验,系统平均正确率可达87%以上。     

声发射技术在高压输电塔锚杆腐蚀检测中的应用

在高压输电塔的锚杆顶端施加一瞬态激振力,由布设在锚杆顶端的声发射传感器接收反射的信号.对接收的声发射信号进行了时频分析和小波分析.通过对比可以看出,声发射信号的特征频率、能量与腐蚀的状况有很好的相关性.因此,声发射技术是一种可靠有效的检测高压输电塔锚杆腐蚀的方法.     

一种新的抑制光纤陀螺信号零漂的方法

介绍了光纤陀螺的基本原理和输出信号的数学模型,阐明了零漂的含义。分析了几种零漂抑制方法的原理,提出了基于小波分析的滤波方法。对于实测的光纤陀螺信号进行了多尺度小波分解和多分辨力分析,证明了该方法抑制光纤陀螺输出信号零漂的有效性。     

Dual track Wallace fly height measurement method to monitor slider motion in 2 dimension at near contact regime

Head media spacing of hard disk drive (HDD) is expected to continue its reduction in order to support areal density growth. At sub-nm clearance between the head and the disk, the intermittent head disk contact and interactions may happen. This does not only cause the fly height modulation but also induces the off-track motions as well. It is desirable to understand the characteristics of the 2D motions in the near contact regime, so as to enable further reduction of the clearance and to improve the reliability of HDD. This paper presents a method to measure instantaneous fly height (FH) motion and cross track motion concurrently by using read back signal from the dual data tracks written at different frequencies. The method is able to separate the FH motion and cross track motion of the head.     

An adaptive edge-preserving image denoising technique using patch-based weighted-SVD filtering in wavelet domain

Image denoising has always been one of the standard problems in image processing and computer vision. It is always recommendable for a denoising method to preserve important image features, such as edges, corners, etc., during its execution. Image denoising methods based on wavelet transforms have been shown their excellence in providing an efficient edge-preserving image denoising, because they provide a suitable basis for separating noisy signal from the image signal. This paper presents a novel edge-preserving image denoising technique based on wavelet transforms. The wavelet domain representation of the noisy image is obtained through its multi-level decomposition into wavelet coefficients by applying a discrete wavelet transform. A patch-based weighted-SVD filtering technique is used to effectively reduce noise while preserving important features of the original image. Experimental results, compared to other approaches, demonstrate that the proposed method achieves very impressive gain in denoising performance.     

Simulation of temperature around laser-heating media in heat-assisted magnetic recording

Heat-assisted magnetic recording (HAMR) is a new approach, which makes the head write data easily under a low magnetic field using a laser to heat the magnetic media to reduce its coercivity, thus, it is considered to be the next generation of higher recording areal density technology. In this paper, a three-dimensional HAMR finite-element model of hard disk drive (HDD) is developed. The temperature distributions around the laser-heating area on disk surface are investigated when the HDD is filled with air and helium. The cooling effects of the disk rotation and the heat convection in head-disk interface (HDI) are also analyzed.