Proposal for material viscoelasticity evaluation method under impact load

A novel practical method for evaluating the viscoelasticity of materials under impact load is proposed. The method is characterized by the fact that preparation of the test specimen is very easy and the testing time is very short. In the method, a mass that is levitated with a pneumatic linear bearing, and hence encounters negligible friction, is made to collide with a material under test. During the collision the Doppler frequency shift of a laser beam reflecting from the mass is accurately measured using an optical interferometer. The velocity, position, acceleration and inertial force of the mass are calculated from the measured time-varying Doppler shift. To demonstrate the high performance of the proposed method, the impact response of a gel block is highly accurately determined by means of the proposed method.     

移动硬盘磁头驱动臂的模态分析与脉冲响应

磁头驱动臂组件是硬盘驱动器内重要的机械部件,其冲击载荷下的动态响应是影响硬盘驱动器抗振性能好坏的主要指标。本文以2.5英寸移动硬盘驱动器组件为研究对象,在考虑枢轴轴承刚度影响的基础上,建立了驱动臂组件的三维有限元模型,分析了其各阶振动模态,并讨论了脉冲波形、脉冲幅值、脉冲宽度对磁头驱动臂组件动态响应的影响。     

A smooth impact rotation motor using a multi-layered torsional piezoelectric actuator

A smooth impact rotation motor was fabricated and successfully operated using a torsional piezo actuator. Yoshida et al. reported a linear type smooth impact motor in 1997. This linear motor demonstrated a high output force and a long stroke. A superior feature of the smooth impact drive is a high positioning resolution compared with an impact drive. The positioning resolution of SIDM (smooth impact drive mechanism) is equal to the piezo displacement. The reported positioning resolution of the linear type was 5 nm. Our rotation motor utilized a torsional actuator containing multi-layered piezoelectric material. The torsional actuator was cylindrical in shape with an outer diameter of 15 mm, an inner diameter of 10 mm, and a length of 11 mm. Torsional vibration performance was measured with a laser Doppler vibrometer. The obtained torsional displacement agreed with the calculated values and was sufficient to drive a rotor. The rotor was operated with a saw-shaped input voltage (180 V; 8 kHz). The revolution direction was reversible. The maximum revolution speed was 27 rpm, and the maximum output torque was 56 gfcm. In general, smooth-impact drives do not show high efficiency; however, the level of efficiency of our results (max., 0.045%) could be increased by improving the contact surface material. In addition, we are studying quantitative consideration, for example, about the optimum pre-load or frictional force.     

采用变换矩阵计算运动人体惯性参数

根据测量的25个人体形体指标,用Barter回归方程以及人体模型的定义计算得到人体环节的质量、几何尺寸和质量惯性矩等环节惯性参数。用Hanavan人体模型采用变换矩阵获得运动中人体环节相对惯性参考系的环节惯性参数,同时根据合力矩定理和平行轴定理计算运动中人体质心和主转动惯性等惯性参数,为研究人体运动提供可靠的定量分析依据。研究方法很好地体现了人体惯性参数的个体特征和任意姿态特征,其计算结果与国内报道用CT法和三线摆的研究结果相符。     

Noninvasive Vibration Diagnostics to Detect Head–Disk Contact in Hard Disk Drives

Reliability of modern hard disk drives (HDDs) is a major concern especially with decreasing head-to-disk spacing in order to attain higher recording densities. One of the reasons for HDD failure is the occurrence of intermittent or sustained head–disk contacts. It is therefore important to be able to detect such head–disk contacts early on so that backup safety schemes can be implemented before catastrophic HDD failure and permanent data loss. In the study reported here, we used noninvasive vibration diagnostics and multiaxial vibration measurements to assess the condition and functionality of HDDs. We chose a miniature triaxial accelerometer for the diagnostic study, given that it is relatively inexpensive and easy to use. We measured contact vibration, induced by a scratch on the top surface of the rotating disk, on the outside of the HDD by attaching an accelerometer on the actuator shaft. We found that contact vibrations between the head and disk inside the HDD can reliably be measured on the outside of the HDD with an accelerometer. We also found that a miniature accelerometer does not cause significant mass loading, as verified by noncontacting laser vibrometry.     

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     

A novel laser Doppler velocimeter

The idea of using a reference-beam laser Doppler velocimeter (LDV) to measure the velocity of a vehicle for an inertial navigation system is proposed. In order to reduce the measurement error produced by the vehicle's jolt, a novel laser Doppler velocimeter (LDV) based on the Janus configuration is presented. The system mounted at the bottom of the vehicle is composed of two single reference-beam subsystems, one of the laser probes looks forward and the other looks backward. Each of the subsystems transmits a laser at 532?nm with the same inclination angle and detects its own Doppler frequency from the scattered light. The pitch angle of the vehicle is calculated by the two detected Doppler frequencies and the inclination angle, and then the measured velocity of the vehicle is compensated. The results of the theory analysis and experiments show that the vehicle's jolt affects conventional reference-beam LDV strongly. LDV with a Janus configuration is insensitive to the inclination angle, and its measurement accuracy is much better than that of a conventional reference-beam LDV. Comparing with the DZL-1 electronic speedometer, the measurement mean error is less than 0.9%, so it is suitable to offer the parameter of velocity for a vehicle self-contained inertial navigation system.     

Velocity measurement by vibro-acoustic Doppler

We describe the theoretical principles of a new Doppler method, which uses the acoustic response of a moving object to a highly localized dynamic radiation force of the ultrasound field to calculate the velocity of the moving object according to Doppler frequency shift. This method, named vibro-acoustic Doppler (VAD), employs two ultrasound beams separated by a slight frequency difference, Δf, transmitting in an X-focal configuration. Both ultrasound beams experience a frequency shift because of the moving objects and their interaction at the joint focal zone produces an acoustic frequency shift occurring around the low-frequency (Δf) acoustic emission signal. The acoustic emission field resulting from the vibration of the moving object is detected and used to calculate its velocity. We report the formula that describes the relation between Doppler frequency shift of the emitted acoustic field and the velocity of the moving object. To verify the theory, we used a string phantom. We also tested our method by measuring fluid velocity in a tube. The results show that the error calculated for both string and fluid velocities is less than 9.1%. Our theory shows that in the worst case, the error is 0.54% for a 25° angle variation for the VAD method compared with an error of -82.6% for a 25° angle variation for a conventional continuous wave Doppler method. An advantage of this method is that, unlike conventional Doppler, it is not sensitive to angles between the ultrasound beams and direction of motion.     

一种提高多普勒测速仪测频精度的方法

多普勒测速仪是水面或水下平台速度测量的主要设备。提出了利用随机样本一致(Random Sample Consensus,RANSAC)算法来估计多普勒频移,从而使速度测量具有更高的稳定性。多普勒测速仪信号处理的核心是测量多普勒频移,该方法利用回波复相关相位是多普勒频移的一次函数来估计多普勒频移,进而计算得到平台速度,在估计频移时采用RANSAC算法以提高测频精度。为了验证方法有效性,对信号形式为连续波(Continuous Wave,CW)脉冲对的情形进行了仿真。结果表明,提出方法的稳定性得到明显提高。     

Calibration of subnanometer motion with picometer accuracy

We have developed a method for calibrating subnanometer movements of a piezoelectric actuator with picometer accuracy and for a wide range of frequencies. This range make this calibration useful for scanning probe microscopes, particularly for an apertureless scanning near-field optical microscope in which the tip is dithered to modulate the optical signal. The setup consists of a Michelson interferometer that has a mobile arm capable of moving more than one fringe. The piezoelectric actuator to be calibrated vibrates at the desired frequency in the other arm. Net displacement can be calculated by simultaneous measurement of an interferometric signal and its derivative. Hysteresis of the system can be also measured. It will be shown that the actuator response is linear only for the low-frequency region (in our case as much as approximately 10 kHz). Above that frequency range, higher harmonics appear and cannot be neglected to obtain real displacement. Finally, it will be shown that the use of higher harmonics in calibration or detection schemes (that rely on the linearity of the response) must be validated, and this technique has proved adequate for that purpose.     

新型惯性压电驱动机构的设计与初步实现

提出通过机械方式控制压电驱动机构和支撑面之间摩擦力的有序变化，形成有规律的新型惯性压电驱动机构．分析了机构的运动机理，建立了动力学模型，利用Matlab对机构进行了运动学仿真，设计并制作了驱动机构样机，对驱动机构动态特性进行了仿真分析和试验对比研究．两者结果吻合较好，表明采用简单的对称波形信号能驱动机构运动，直线驱动器最高速度可达1mm／s，最高步长分辨率为20nm，最大承载能力为1000g．     

微机械惯性开关的非线性动力学特性分析与设计

利用倾斜支撑微梁结构大挠度后屈曲的非线性横向刚度,设计了一种新型屈曲式微机械加速度开关．该开关采用倾斜微梁支撑敏感质量块,两折叠梁固定于质量块的上下表面,保证开关动作的方向性．当外界加速度达到设定的阈值时,梁发生屈曲使开关迅速闭合,加速度低于截至门限值时,屈曲微梁弹性力使开关断开．开关设计中分析了气膜阻尼力和触点接触力对系统性能的影响,建立了多力耦合作用下加速度开关系统的动力学模型,并运用数值方法对含有椭圆积分的强非线性系统进行动态仿真分析,开关响应时间低于6 ms,实验表明开关具有良好的闽值特性和接触可靠性,充分证实了屈曲梁结构应用于惯性微感应器件设计的可行性．     

A study on the efficacy of flow mitigation devices in hard disk drives

We report on large eddy simulations of the turbulent flow of air in hard disk drives (HDDs) using a commercial CFD code. In particular, we focus on HDD casings in which flow-induced vibrations are reportedly reduced by small geometrical modifications. The modifications investigated are M1: a blocking plate situated between the disks, M2: a spoiler (or deflector) located behind (downstream of) the actuator arm, and M3: a similar deflector upstream of the arm. We observed that M1, M2, and M3 significantly modify the mean flow patterns in the drives. M1 reduces velocity magnitudes in most parts of the drive, the modification of M2 causes How reversal in regions close to the hub, while M3 causes the shedding of vortices upstream of the actuator arm. Our analysis points to M1 as the best candidate for mitigating the effects of turbulent airflow. This is because M1 is more effective in reducing the root-mean-square velocity fluctuations near the suspension. M1 is also more effective in reducing the pressure fluctuations near the base-plate and suspension region. This reduction, however, is at the cost of approximately 20% higher windage. Finally, we note that M3 has the adverse effects of increasing velocity and pressure fluctuations and hence is not the ideal candidate for mitigating airflow effects, among the modifications considered here.     

Drop test simulation and power spectrum analysis of a head actuator assembly in a hard disk drive

This work aims to develop a method for predicting the displacement and failure of the Head Actuator Assembly (HAA) during a drop test. When a Hard Disk Drive (HDD) is dropped from a certain height, it will accelerate due to gravity until it hits the ground with a certain speed, and the head suspension system may lift off the disk and land onto it in a very short time. The impact during the head slap often leads to failure of the HAA. The pivot-bearing stiffness is a very important factor for the dynamic behavior of the HAA during a drop test. A simplified beam model with a torsional spring and a translational spring located at the end of the arm has been developed to analyze the effects of the pivot-bearing stiffness on the dynamic response of the arm in the present paper. Moreover, to further investigate a pseudo-resonance phenomenon observed by the authors in a previous work, three types of acceleration shocks different in pulse shapes (half-sine, triangular, and dual-quadratic acceleration pulses) were selected as input loadings. Dynamic analyses of the actuator arm subjected to these loadings were carried out. Numerical results show that a pseudo-resonance phenomenon occurs for the maximum relative displacement, but at different pulse widths for these different acceleration shocks. Power spectrum analyses were implemented for these different acceleration shocks. An explanation is given in terms of the acceleration power at the resonant frequency of the arm. A corollary has been derived based on a theorem developed previously by the authors. A prediction is made by the corollary and confirmed by numerical results.     

大质量法在多点激励分析中的应用、误差分析与改进

为检验多点激励分析中广泛应用的大质量法(LMM)的计算精度和适用性,基于瑞利阻尼,以2自由度有限元模型为例,在4组不同的地震动输入下,分别用LMM和相对运动法(RMM)进行了多点激励分析.比较了两种方法的结果,从理论上分析了LMM误差产生的原因,指出了LMM的适用条件,进而提出了改进措施--基于地震动输入阻尼项修正(α...     

Reversible Shape Memory Alloy Film Fabricated by RF Sputtering

The fabrication and processing of an actuator with a TiNi Shape Memory Alloy (SMA) film are discussed and demonstrated. TiNi SMA films were deposited by using sputter deposition techniques, patterned and etched. These films were solution-treated and aging-treated, and then an inverse force layer of chromium was deposited on a SMA film. The frequency response of the beam type actuator was measured by resistance heating. The maximum amplitude was in proportion to the inverse force, and was therefore controlled by chromium thickness. The maximum displacement slightly decreased with an increase of frequency. The minimum displacement suddenly increased at more than 0.1 Hz, then showed a stability over 5 Hz. The maximum displacement was not decided by chromium thickness but TiNi thickness, because thickness of the latter was fifteen to forty times larger than that of the former. Because the frequency response depended on the heat radiation of an actuator, TiNi thickness was the most important factor to the actuation.     

受移动质量作用的一类变截面梁横向振动分析

采用半解析法计算了横截面积、横截面的惯性矩沿轴线方向以幂函数规律变化的一类变截面梁的固有频率和振型,通过与有限元法的计算结果比较说明了半解析解的精确性。在此基础上,考虑牵连惯性力、相对惯性力、科氏力和离心惯性力的影响,推导了变截面梁受移动质量作用的横向弯曲振动方程,并采用Newmark法进行数值求解。以某梁式结构受移动质量作用为例,将其简化为横截面积和惯性矩沿轴线按任意次幂函数变化的变截面梁,结果表明:该方法能够正确、有效地处理此类问题。     

新型谐振式硅微机械加速度计

制作出一种新型结构的谐振式硅微加速度计，其输出频率信号可以克服微机电系统器件输出微弱信号检测的困难、采用双端固定音叉作为谐振器，在加速度作用下，质量块的惯性力通过悬臂梁施加于音叉轴向，利用音叉谐振频率的变化测量加速度．在每个音叉臂上制作了梳齿结构，用梳齿间的静电力激励音叉产生谐振，并利用其构成的电容检测其振动频率．该加速度计采用体硅工艺制作，文中给出了工艺流程、用有限元方法仿真估算，得到传感器的灵敏度约为2／gHz．     

Laser doppler interferometry on magnetic recording systems

Laser Doppler interferometry is used to determine the six components of velocity of read/write heads in magnetic disk files. These measurements are made on production drives in which the only alteration is the installation of a window so that the laser beams can be directed onto any of the four corners of the slider. A laser Doppler vibrometer (LDV) is used to measure the out-of-plane velocity of the four corners from which we calculate the out-of-plane velocity of the geometric center as well as the pitch and roll of the slider. A laser Doppler anemometer (LDA) measures the in-plane velocity of the four corners, which gives the radial and tangential velocity of the geometric center and the yaw of the slider. We are also using the LDV for the measurement of disk runout and surface topography as well as suspension and actuator vibration. These measurements allow us to determine the natural frequencies of the slider bearing, the rotating disk, the actuator, and the suspension arm. In this paper we summarize some of the results we have obtained using this method on various 5-1/4" and 8" rigid disk drives that employ "Winchester" and "mini-Winchester" sliders together with stepper motor and servo controlled actuators of both the linear and swing arm designs.     

Shock Resistance of a Disk-Drive Assembly Using Piezoelectric Actuators With Passive Damping

Current dual-stage actuator design uses piezoelectric patches only, without passive damping. In this paper, we propose a dual-stage servo system using enhanced active-passive hybrid piezoelectric actuators. Because they incorporate passive damping, the proposed actuators will improve the existing dual-stage actuators, giving them higher precision and better shock resistance. We report finite-element analyses of different types of piezoelectric actuators in a disk arm assembly under external shock and vibration. We modeled the viscoelastic damping layers in the hybrid actuators with the Prony series, whose parameters we determined from the dynamic frequency data of a nomograph. In the analyses, a shock impulse (175 g, 1 ms half sine) and a vibration impulse (350 g and 1 ms full sine) are applied at one end of the base, while the other end of the base is fixed. We evaluated and compared the responses of the disk arm assembly with different configurations of the piezoelectric actuators. The simulation results show that the enhanced active-passive hybrid actuator design would reduce the residual in-plane vibration induced during the shock, resist liftoff motion, and reduce the impact damage when the head slaps.