一种降低微结构瞬态响应的方法

研究了机械结构的动力学快速减振方法。以硬盘读写头动臂为例，分析了其受驱动力激振后的瞬态响应。在其指导下，选择了作用力的作用时间和波形：该作用力的作用时间T应为机械结构一阶固有频率对应周期的2倍，且为关于T／2奇对称的单周期波形。通过实验，证明了这样的作用力可以有效减小系统的残余振动，实现快速减振。此方法可以引申到一般应用场合。     

轮带系统横向振动变结构控制方法

针对由主从动轮、作动器及皮带构成的典型轮带系统模型,皮带横向振动与主、从动轮及作动器振动相耦合,其横向位移受主、从动轮及作动器影响,给出皮带在谐波激励下横向振动位移精确表达式,利用变结构理论,采用指数趋近律设计出有效控制力以控制张紧臂方向,从而抑制皮带横向振动。在初始条件和与激励作用下,利用Matlab进行数值仿真。结果表明：在谐波激励下,皮带横向振动位移得到有效抑制,验证控制力的有效性。     

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。     

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.     

Application of nonlinear resonances for the diagnostics of closing cracks in rodlike elements

The vibrations of elastic bodies with closing cracks are essentially nonlinear. As a specific feature of these vibrations, one can mention the manifestation of so-called nonlinear effects, e.g., nonlinear (i.e., sub- and superharmonic) resonances and the nonlinearity of vibrations for these resonances. The proposed method for the evaluation of the parameters of cracks (their sizes and location) is based on the analysis of the nonlinearity of vibrations in the neighborhood of a superharmonic resonance of order 2/1 and/or a subharmonic resonance of order 1/2 in the case of variation of the site of application of the driving force because, as follows from the results of numerical and experimental investigations, the level of nonlinearity of the vibrations of rods with closing cracks for nonlinear resonances depends not only on the parameters of the crack but also on the site of application of the driving forces.     

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.     

A proximate-time-optimal-control design and its application to a hard disk drive dual-stage actuator system

We propose a compensator-based strategy for design of a track-seeking and track-following control system for a dual-stage servo actuator in hard disk drives. A well-known decoupling structure is employed to disconnect the control of the primary voice coil motor (VCM) actuator from the loop for a secondary high-bandwidth actuator. The compensator is placed in the secondary loop and suitably combined with a saturation nonlinearity in order to obtain actuator signal boundedness. The design procedure consists of four steps: 1) design of an established nonlinear seek-settle-track following controller for the VCM; 2) design of a linear track following controller for the secondary actuator; 3) observer design; and 4) design of a compensator to retain global stability and to improve performance. The proposed control system improves performance of both long-span seeking (proximate-time-optimal controller) and short-span seeking. In addition, it achieves high-bandwidth track following performance. The experimental results show good track-following performance, and short-span/long-span-seeking performance with fast settling time. The overshoot during track seeking can be made negligible for a suitably tuned VCM-actuator control loop.     

Diagnostics of closing cracks in rodlike elements at nonlinear resonances by the method of variation of the asymmetry of driving forces

The vibrations of elastic bodies with closing cracks are essentially nonlinear. As a specific feature of these vibrations, we can mention the manifestation of so-called nonlinear effects, in particular, sub- and superharmonic resonances and the nonlinearity of vibrations at these resonances. We propose a method for the diagnostics of cracks based on the variation of the asymmetry of driving forces. The static component of the concentrated harmonic driving force changes the state of a crack: it becomes partially or completely open or closed. Moreover, the degree of nonlinearity of vibrations for any nonlinear resonance varies from the maximum level (in the absence of static component) to its almost complete absence in the case where the crack becomes open or closed in the course of vibrations under the action of the static component. The proposed method enables one to detect the presence of cracks without any preliminary data on the analyzed object in the intact state.     

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。     

弯振复合型超声驱动器振动特性研究

为了避免模态复合型超声驱动器中普遍存在的频率简并问题,作者在前期研究中提出了一种新型的弯振复合型超声驱动器。该驱动器采用压电金属复合梁两个正交弯振模态的复合在两个驱动足处激励出椭圆轨迹振动。本文对该驱动器的振动特性进行深入研究,旨在获得驱动区域质点的真实运动轨迹。首先,建立了矩形截面梁在弯振复合模态下末端区域质点振动轨迹的数学模型;然后,借助有限元瞬态分析,对驱动足振动轨迹进行仿真,实现对所建立振动轨迹数学模型的验证。振动轨迹方程和仿真结果均表明：两个驱动足表面质点振动轨迹均为三维的椭圆,垂直于驱动器轴线的平面内的椭圆振动更适合用于致动输出。最后,分析了该驱动器存在的不足之处,提出了一种改进方案,采用对称设置压电陶瓷片实现两个驱动足振动特性的一致;通过瞬态分析在两个驱动足处得到了一致的振动轨迹,改进的样机实现了输出特性的显著提高。     

Reduction of residual vibration in a rotating flexible beam

Summary. The reduction of residual vibrations of the position control of a rotating flexible beam is investigated. The control scheme is achieved by combining Input Shaping Technique (IST) with a piezoceramic actuator ( PZT ) attached to the surface of the beam. IST reduces residual vibration in the beam by convolving the desired torque with a sequence of impulses. A majority of the current IST is inherently open-loop where impulse application at an inaccurate instance can lead to system performance degradation. Thus, in order to improve the control performance of a flexible manipulator, the residual vibration generated due to those or the uncertainty model was further suppressed by the PZT. The optimal control voltage was determined by the Linear Quadratic Regulator (LQR) technique. The dynamic simulation shows that the proposed method has not only nice robustness properties for suppressing the vibration due to an inaccurate model or the instance of impulse application, but also the voltage applied on the PZT decreases 50% or more than only using PZT, in other words, the extra energy consumption is reduced significantly by the proposed method.     

有砟梯式轨枕轨道减振性能的理论分析与试验研究

为实验室铺设有砟、无砟两种梯式轨枕轨道,用自由落锤激励装置对两种梯轨减振性能进行对比研究。建立有砟梯轨、有砟普通轨道的数值模型,利用试验测试结果对模型进行验证。通过在模型中施加货运列车荷载对比两种有砟轨道减振性能。结果表明,有砟梯轨减振性能不及浮置式梯轨,在低频段有一定减振能力,20 Hz以下振动经道砟平均衰减25 dB,对控制重载货运列车环境振动具备潜在优势;梯式轨枕对分散列车冲击振动、降低时域内峰值有明显优势。     

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.     

Magnetic Circuit Design for Six-Wire Suspension Type Actuator in a Super Multioptical Pickup

We have developed a new magnetic circuit consisting of eight permanent magnets with special placement order. Here, we analyze the magnetic flux density distribution, the driving force distribution, and the interference force using the finite-element method. The driving sensitivity of the actuator at low frequency is nearly twice that of a conventional actuator. We have built several samples and compared their performance with simulation data. The results prove the validity of the proposed magnetic circuit and the design method.     

Impact force measurement of an actuator arm of a hard disk drive

Impact forces of an actuator arm of a hard disk drive (HDD) are measured by means of modifying the levitation mass method (LMM) whose basic concept was proposed by the first author. In the LMM, force is measured as the inertial force of a mass levitated with sufficiently small friction using an aerostatic linear bearing. The Doppler frequency shift of the laser beam reflecting from the mass is accurately calculated from the waveform recorded using a digitizer. The velocity, the position, the acceleration and the inertial force of the mass are calculated from the measured time-varying Doppler frequency shift. In the experiments, the mechanical response of an actuator arm of a HDD against an impact load and the inertial force of the actuator arm in free oscillation are measured. The importance and the problems concerning the present knowledge on the impact force of an actuator arm of a HDD are also discussed.     

Approximate analytical method for determining the vibration-diagnostic parameter indicating the presence of a crack in a distributed-parameter elastic system at super- and subharmonic resonances

An approximate method for calculating the vibration-diagnostic parameter indicating the presence of a crack in an elastic distributed-parameter system at super- and subharmonic resonances is considered. The method involves the finding of the non-linearity characteristic of an elastic system based on the analysis of its forced vibrations in the undamaged state and the use of results of the approximate analytical determination of parameters of nonlinearity for vibrations of an elastic body with a closing crack, which is simulated by a single-degree-of-freedom system with an asymmetric bilinear characteristic of the restoring force at the above-mentioned resonances.     

地铁列车运行引起的振动对精密仪器影响的预测研究

采用一种动力有限元数值模型,并结合道路交通现场振动测试,对北京地铁8号线列车运行对邻近地铁线路的某科研楼内精密仪器的振动影响进行了预测研究,并比较了普通无砟轨道和浮置板轨道两种工况下楼内外的振动响应。提出了该有限元模型的网格划分、边界条件、阻尼施加等建模原则,采用实测的钢轨振动加速度计算而来的动态轮轨力作为该模型上的激励力。结果表明：采用该动力有限元模型可以有效地预测地铁列车运行引起的振动;浮置板轨道是一种有效的减振措施,在其工作频段内有显著的减振效果,但对低频振动没有减振效果,而且在其自振频率处还有一定的放大作用;地铁8号线开通后,地铁列车振动再叠加上道路交通引起的振动会对科研楼内部分精密仪器的正常工作造成一定的影响,仪器基座处可采取相应的隔振措施来减小这部分振动。     

High-speed actuation of a piezoelectric actuator by pulse driving and stopping of its residual mechanical vibration

The driving method for high-speed actuation and prevention of residual vibration of a piezoelectric actuator is described. The driving voltage is composed of a pulse voltage and a step voltage. As a result, the risetime of the piezoelectric actuator can be reduced to approximately 1/4 of its mechanical response period by setting the pulse width, and the residual vibration can be prevented by adjusting the step voltage. The high-speed stopping of a piezoelectric actuator driven by AC power at its resonance is discussed.     

Forced response of cylindrical shells coupled with nonlinear shape-memory-alloy (SMA) actuators regulated by sinusoidal and saw-tooth temperature profiles

Dynamic responses of cylindrical shells coupled with shape-memory alloy (SMA) ring segments placed at critical locations are investigated. Since the SMA actuators are highly nonlinear and governed by the temperate-dependent stiffness and martensite/austenite fraction, input shaping and phase shift of temperature profiles are incorporated to control the shell vibrations. Open-loop equations of an elastic cylindrical shell panel are defined first and then used with assumed mode-shape functions satisfying specified boundary conditions in the free-vibration analysis. Modal-analysis data are used to determine spatial strain distributions of natural modes. Distributed modal-signal characteristics suggest optimal placements of SMA actuator segment(s) for each given mnth mode. Based on the modal-expansion method, the open-loop control force induced by the SMA ring segments applied to a simply supported cylindrical shell panel is formulated. This formulation indicates that only the odd modes in the circumferential direction can be controlled. Longitudinal modes are controlled via placing specific number, depending on the mode, of actuator segments along the panel length. To predict control effects of the nonlinear SMA ring segments, the modal participation factor response is determined for an external harmonic excitation applied to the shell along with induced SMA control forces, via sinusoidal and saw-tooth temperature profiles to generate desirable control forces and to eliminate the unwanted effects. Analysis results suggest that with proper choice of temperature waveform function to the SMA ring segments and minor modifications to frequency and phase, the SMA ring segments can attenuate unwanted external vibrations of cylindrical shells.     

Deconvolution of blast vibration signals by wiener filtering

Ground vibration is one of the environmental concerns caused by mine blasts. The signature-hole technique, essentially the convolution of a single-hole signature with an impulse train function representing the timing of the blast, is one method used to predict and control ground vibrations. This method requires measuring a signature waveform from a singular blasting hole, which may be a limitation. Deconvolution of vibration signals, the inverse problem of signature-hole method, is still a frontier issue to solve that limitation in mining engineering. Wiener filtering deconvolution is used to compress the impulse train into a time-lagged spike, so that a normalized single-hole signature can be extracted from the full blast vibration waveform. The proposed methodology gives good results for a case study of mining blast using electronic detonators. Successful deconvolution will eliminate the need for measuring signatures by using all the seismograph information collected routinely in mine operations.