光学小卫星振动夹具设计及动特性分析

夹具是卫星振动试验的传力部件,夹具性能的好坏直接影响到振动试验的真实性和可靠性。总结了卫星振动夹具设计的一般方法和思路,针对某光学小卫星振动夹具进行了设计工作,利用有限元软件MSC.NASTRAN对振动夹具动特性进行了分析,对其刚度、质量、固有频率及动特性响应间的关系进行了研究,完成了某光学小卫星振动夹具的设计工作,从其动特性响应分析结果看,带振动夹具后整星动特性响应平均偏差约为6%,最大响应偏差约为11%,振动夹具对整星动特性影响在合理范围内,目前该振动夹具已成功应用于某光学小卫星按GJB1032-90所规定的地面力学环境试验中,并取得了预期的效果,该方法可应用于其他卫星振动夹具的设计中。     

振动试验夹具的设计

夹具是振动试验常用的工件之一，它的刚度、质量、重心的定位等动态特性参数是影响产品试验真实再现的重要因素。介绍了夹具的设计原则，提出了夹具设计中常见的问题和注意事项，并介绍了相关夹具的测试方法。     

车载电子设备机柜通用振动试验夹具设计

根据车载电子设备振动试验条件和振动台性能，夹具模拟机柜的实际安装状态，由铝合金整体铸造而成，能用于大部分标准化机柜振动试验。经测试，夹具动态特性满足车载电子设备振动环境试验对夹具的要求，已用于多个型号产品的机柜振动试验。     

振动试验夹具设计研究

目前，振动试验中使用的夹具，其传递的应力往往存在较大的失真。通过对夹具设计技术现状的介绍，指出各设计方法存在的不足，并阐述了夹具类型、材料选择、制造加工等对夹具应力传递特性的影响。另外，还给出了夹具对振动台防过冲的设计方法和改进夹具设计的建议，并提出研究课题。     

结构振动试验转接器的设计及安装问题

一些产品及其相关部件在作振动试验时，由于产品的外形或特殊要求不能直接安装在振动台面上，需要通过特别设计的转接器（夹具）来进行连接，这种夹具实际上是一种附加结构，它作为台面与试件之间的中介，如设置不当将影响振动试验结果的可靠性。本文通过对某事例的分析与研究，从试验频带、允许误差、跟随条件以及安装共振频率等方面阐明与讨论了相关夹具的特性、设计原则与安装等问题。     

大型振动试验夹具设计探讨

振动试验是隔振研究和环境试验的一个环节,而振动试验夹具在振动试验中是不可缺少的,对大型试件尤其如此。本文对夹具的功能和要求、夹具的材料和制造方法、夹具谐振频率的计算等问题进行了探讨。指出夹具的谐振频率是夹具设计中的主要技术指标,夹具采用轻型材料可望得到较高的谐振频率,对比了用整块原材料机械加工夹具、栓接夹具、铸造夹具和焊接夹具等的优缺点及适用范围。文章着重介绍了一种工程设计中夹具谐振频率的计算方法,即把夹具分解为梁、板和连接构件等部分,通过对各部分     

空间光学遥感器振动夹具的设计与研究

力学振动试验是验证空间光学遥感器动力学特性的重要手段,而振动试验所需要的夹具在光学遥感器的振动试验中起着重要的作用,决定着振动试验的效果。本文运用振动理论分析了夹具对试验准确性的影响,并简要阐述了夹具设计的基本原则;针对空间光学遥感器,从材料选择、加工制造方法及结构形式等方面对夹具进行了设计,先后选择了两种结构方案形式;运用NASTRAN软件对两种方案的夹具的有限元模型进行了模态分析,最终选择了夹具方案二的结构形式,其一阶频率为451Hz;通过力学试验对夹具进行了鉴定,获得了夹具的正弦特征扫描曲线,试验得到夹具的一阶固有频率为398.7Hz,满足相机力学试验对夹具的要求。最后,对工程分析和试验的误差来源进行了分析,并提出了夹具设计时应该注意的一些问题。     

星载螺旋天线阵抗力学环境设计与分析

螺旋天线具有圆极化和宽波束特性,广泛应用于星载通信系统。文中介绍了一种星载螺旋天线阵结构,对其抗力学环境设计要求及技术难点进行了分析。在此基础上开展了抗力学环境设计,就其各部件具体形式、载荷特性、安装方式和材料选择进行了具体设计,并分别从结构的静强度、动刚度和动强度等方面进行了力学仿真,对结构基频和各部件安全裕度进行了计算,仿真结果表明产品满足抗力学环境设计要求。最后针对该螺旋天线阵试验件开展了随机振动和正弦振动环境试验,试验件通过了环境试验的考核,且试验与仿真分析数据一致性较好,该螺旋天线阵抗力学环境设计合理、有效。     

地面雷达动目标自动识别分类研究

本文介绍了地面雷达动目标自动识别分类研究成果，该成果在大量试验的基础上，运用回波多普勒信号的频谱特性，实现了动目标的自动识别与分类，其准确率达到８５％以上。     

振动试验夹具设计的几个问题

振动试验夹具,用以连接试件和振动台,进行振动试验,保证试件受到规定的振动激励。如果夹具将振动衰减,则造成试件欠试验,使本来不合格的产品通过试验;若夹具将振动放大(共振时),则造成试件过试验,使本来合格的产品也不能通过试验,造成盲目地修改设计。不论欠试验和过试验,都将造成严重的经济损失和时间浪费。因此,对振动试验夹具的设计问题,绝不可等闲视之。影响夹具设计的因素较多,但主要有:夹具装有试件时的自然频率;夹具阻尼大小;试验要求及试验系统的特性。以下简要说明夹具设计中的几个问题及目前有些振动试验夹具存在的问题。     

方位安装误差对调平性能的影响及对策

针对水平传感器存在较大方位安装误差角会导致调平时间延长的问题,该文简述了四点调平策略和动态水平传感器工作原理,建立了坐标矩阵、矩阵转换关系式,讨论了动态水平传感器的方位安装误差对调平系统的影响。试验结果表明,通过测试仪器使动态水平传感器的轴系与安装基座轴系平行的方法,可减小方位安装误差角,提高系统性能。     

Vibration reliability characterization of PBGA assemblies

Generally, the low-cycle fatigue induced by thermal cycling is the major concern in the reliability of surface mount technology for electronic packaging, but the high-cycle fatigue induced by vibration can also contribute significant effect, especially for applications in automobile, military, and avionic industries. To assess vibration induced fatigue failures, the dynamic properties of printed circuit board (PCB) assemblies play a very important role. In this paper, the dynamic properties of a plastic ball grid array (PBGA) assembly were characterized by using experimental modal testing and finite element analysis. The bare PCB and PCB assembly with PBGA modules mounted were tested and analyzed separately, so that the influence of PBGA modules on the PCB’s dynamic properties could be identified. It was found that mounting PBGA modules to PCB increased the stiffness of the PCB. Results of constant-amplitude vibration reliability testing of the PBGA assembly are also reported. It was found that the PBGA assembly was vulnerable to vibration, and fatigue failure always occurred at the corner solder balls of the PBGA module.     

An experimental study of scalability in shield-based on-wafer CMOS test fixtures

In this paper, the possibilities of employing full scalability to on-wafer complementary metal-oxide-semiconductor (CMOS) test fixtures is studied experimentally. Several test fixtures and in-fixture sets were fabricated and measured in order to find the significant parasitic components in shield-based fixtures. An improved method for applying bi-directional scaling to on-wafer shield-based test fixtures is proposed. This method takes into account the parasitic series resistance, series inductance, and parallel capacitance that are present in the test fixture. The proposed method can be used successfully in commonly known deembedding methods. This is verified through measurements. The test fixtures were fabricated on top of a lossy substrate using double-poly, three-metal-layer 0.35-/spl mu/m CMOS technology.     

A new technique for the measurement of speeds of gigahertz digital IC's

We describe a new technique for the measurement of picosecond switching speeds and propagation delays in gigahertz digital IC's. This technique, based on logic-level sampling with pairs of ultrashort optical pulses at variable interpulse delays, provides accurate and reliable values of picosecond propagation delays without requiring the coupling of high-frequency electrical signals to and from the IC chip. Since this optical technique dispenses with the usual need for dicing and mounting the IC wafer in high-frequency (multigigahertz bandwidth) test fixtures, a promising application of its use is in the precise temporal characterization of multigigabit logic circuits in low-frequency (< 100-MHz) probe stations.     

Effects of fluid properties on dispensing processes for electronics packaging

The fluid dispensing process has been widely employed in electronics packaging manufacturing to deliver fluid materials (such as epoxy, encapsulant, adhesive) on substrates or printed circuit boards (PCBs) for the purpose of die attachment, encapsulation, coating, or surface mounting. In this process, the fluid properties such as How behavior, surface tension, and contact angle can have a significant influence on the How rate of the fluid dispensed and the profile of fluid formed on the substrate or PCB, thereby affecting the quality of electronics packaging. At present, massive measurements are always required to characterize the fluid properties by using specific instruments, and the procedure of measuring is time-consuming. This paper presents a method upon which the fluid properties and their influence on the dispensing process can be readily identified from a few measurements of the process. By experiments, this method was proven to be not only cost and time effective but also promising for the investigation into the effects of fluid properties on the dispensing process.     

Dynamic 3-D virtual fixtures for minimally invasive beating heart procedures

Two-dimensional or 3-D visual guidance is often used for minimally invasive cardiac surgery and diagnosis. This visual guidance suffers from several drawbacks such as limited field of view, loss of signal from time to time, and in some cases, difficulty of interpretation. These limitations become more evident in beating-heart procedures when the surgeon has to perform a surgical procedure in the presence of heart motion. In this paper, we propose dynamic 3-D virtual fixtures (DVFs) to augment the visual guidance system with haptic feedback, to provide the surgeon with more helpful guidance by constraining the surgeon's hand motions thereby protecting sensitive structures. DVFs can be generated from preoperative dynamic magnetic resonance (MR) or computed tomograph (CT) images and then mapped to the patient during surgery. We have validated the feasibility of the proposed method on several simulated surgical tasks using a volunteer's cardiac image dataset. Validation results show that the integration of visual and haptic guidance can permit a user to perform surgical tasks more easily and with reduced error rate. We believe this is the first work presented in the field of virtual fixtures that explicitly considers heart motion.     

MSC．ADAMS在贴片机动态精度研究中的应用

应用多体动力学方法模拟贴片机系统动态过程,仿真研究贴片机的动态精度问题。根据贴片机的结构形式,建立贴片机的数学模型和虚拟样机模型。用考虑结合部影响的刚柔耦合模型模拟实际系统,仿真分析影响贴片机动态精度的各种因素,根据分析结果建立优化模型,并对比分析原始模型与优化模型的动态精度。采用激光干涉仪对仿真分析结果进行试验验证．试验结果与仿真结果能较好地吻合,验证了该方法的正确性。     

Frequency limitation in the calibration of microwave test fixtures

The problem of frequency limitation arising from the calibration of asymmetric and symmetric test fixtures has been investigated. For asymmetric test fixtures, a new algorithm based on the thru-short-match (TSM) method is outlined. It is found that the conventional TSM method does not have any inherent frequency limitation, but using the same procedure with an unknown match may lead to the said problem. This limitation can be avoided by using a different algorithm. The various calibration methods for symmetric test fixtures using known standards are also discussed and the origin of the frequency limitation is identified. Several ways in avoiding the problem are proposed. There is good agreement between the theories and experimental data.