基于自组装成品率的球栅阵列焊点工艺参数分析

为了提高球栅阵列焊点封装器件的自组装成品率,研究了焊点体积偏差率及焊盘直径对器件自组装成品率的影响。考虑封装器件的温度翘曲变形、焊点体积的不可避免的制造误差及焊点位置的随机性,分析了器件自组装过程。通过求解不同体积焊点的形态,得到了不同体积焊点的液桥刚度曲线。基于不同体积焊点的液桥刚度曲线,仿真分析了焊点体积偏差率及焊盘直径对器件自组装成品率的影响。结果表明,焊点体积偏差率及焊盘直径的减小会增大焊点液桥刚度曲线的公共范围,从而提高器件的自组装成品率。     

Parallel heterodyne readout of information from three-dimensional superimposed holograms

A method is proposed for parallel (simultaneous) readout of information from threedimensional “coupled” Fourier holograms. The method is based on the principle of transformation of informational degrees of freedom of the optical signal with the use of moving diffraction gratings: the spectrum of spatial harmonics of superimposed holograms is transformed to a spectrum of time harmonics separated in terms of frequency. A method of formation of images of moving gratings with a prescribed orientation in the volume of the recording material is developed. Conditions of the frequency separation of the signals, resolution of the method over the material depth, and the number of detected bits as a function of grating parameters are obtained.     

复合材料瓦面推力轴承弹性模量的研究

对复合材料瓦面推力轴承表面弹性层进行了不同温度下的整体加压和局部加压测试试验,在测得弹性层的压缩弹性模量的基础上,给出了理论弹性模量和计算弹性模量的定义,研究了载荷和温度对弹性模量的影响规律及弹性模量的取值范围,提出了以弹性层压缩弹性模量作为轴瓦整体压缩弹性模量的观点.所得结果可用于轴瓦结构设计、润滑参数计算及瓦面修形.     

Effects of dissipative forces on Coriolis flowmeter readings

An indirect measurement method based on recording the phase difference of resonance vibrations of two symmetrical halves of the flow-carrying tube is used to quantify the mass flow rate of the current fluid in Coriolis mass flowmeters (CMFs). A variant of modeling the CMF vibration system is analyzed, which allows taking into account the influence of the dissipation of oscillations of a measuring tube with fluid flowing through it on the dependence between the mass flow rate of the fluid and the phase difference recorded by the sensor. The steady-state CMF vibration mode is considered as the result of the superposition of two principal vibrations of the measuring tube. The first principal coordinate corresponds to the deformation of the measuring tube along the lowest natural mode excited by an external driving force in the resonance mode. Vibrations of the other principal coordinate correspond to deformation in a natural mode corresponding to a higher natural frequency than the frequency of the exciting force. The relationship of the amplitudes of the principal coordinates is established on the basis of the gyroscopic coupling of the principal vibrations that occurs when a fluid flows through a tube. The coefficients of gyroscopic coupling are determined as a result of 3D finite-element simulation of the steady-state vibration mode of the measuring tube with a flowing fluid. The simulation is performed for five variants of the shape of the axis of the measuring tube, taking into account the distribution of the gyroscopic forces of the flowing fluid. Quantitative estimates of the influence of dissipative forces on the flowmeter readings are obtained on the example of dissipative forces of linear viscous friction. A comparison of the CMF simulation results for different tube axis shapes demonstrates how the phase shift arising in the vibration system is affected by the dissipation level and the proximity of the natural frequencies of the flowmeter measuring tube at a fixed mass flow rate of the fluid.     

Effect of the parameters of a material on the surface displacements caused by waves propagating in a layer

The amplitude—frequency characteristics of the vibrations of the surface of a free elastic layer are determined. These vibrations are caused by propagating Lamb waves under the action of a normal surface load. The changes in the spectra of surface displacements and in the tangential-to-normal displacement-amplitude ratios during changes in the Poisson ratio are studied. Studying the spectrum of surface displacements of an elastic layer is of interest owing to the necessity of discriminating modal components of the wave field [1] and as one of possible methods for determining some of the parameters of a material. The ratio of the amplitudes of the horizontal and vertical displacements as a function of the frequency of a vibration source is sensitive to the Poisson ratio of the material and the conditions of the contact with the base. The amplitude-frequency characteristics of the surface displacements of an elastic isotropic layer are plotted and compared to those obtained in the case of a layer that is in contact with a rigid base.     

Dependence of the results of classification of multispectral images of forest vegetation on wavelet-transform parameters

The problem of classification of space multispectral images of forest vegetation is considered. Features based on the wavelet transform and a classification method involving consideration of the importance of each feature are investigated. Dependence of the classification results on the wavelet function, the level of the transform, and the parameter of the classification method — the number of segments of the range of features — is given. Results of classification of multispectral images of six classes of forest vegetation in images obtained by a Rapid Eye shooting system are presented.     

双列调心凹面滚子轴承接触载荷分析

在考虑滚子与套圈、滚子与保持架以及保持架与引导套圈作用力的条件下,建立双列调心凹面滚子轴承动力学模型.以某双列调心凹面滚子轴承为研究对象,与静力学分析模型滚子最大接触载荷计算结果对比,验证了模型的正确性.并分析了工况条件(轴向载荷、径向载荷、倾覆力矩、转速)和结构参数(滚子数量、滚子长度、径向游隙)对滚子最大接触载荷的...     

基于UG的立铣刀铣削力的有限元分析

为提高加工精度,对立铣刀的应力场进行了有限元分析。通过铣削力试验,对不同切削参数下立铣刀的铣削力进行动态采集,利用UG中的建模模块进行立铣刀实体建模,根据切削力实验结果给出了边界条件,在立铣刀有限元模型上进行加载,利用UG有限元分析模块,获得了立铣刀切削过程中切入、切出的瞬时应力场云图,显示了切削中铣刀片应力场的变化规律。     

基于支持矢量聚类的机械故障诊断

针对无监督的支持矢量聚类方法由于样本类别数量未知带来的模型参数难以选择的问题,提出有监督的支持矢量聚类方法,并应用到机械故障诊断中.该方法首先以聚类区域个数及支持矢量个数作为模型参数的选择准则,以支持矢量为核估计样本分布的概率密度,并根据概率密度估计值选择不同聚类区域的类别代表样本,而后引入k近邻法实现对不同故障的分类.对测试样本的分类结果表明了该方法的有效性.