曲面模型重构方法比较及误差分析

三维CAD模型重建是逆向工程中的关键环节,在逆向设计中起到至关重要的作用。在运用Geomagic Studio软件进行点云处理、错误修复和曲面生成的基础上,重点讨论了曲面阶段的精确曲面重构和参数化曲面重构两种不同的曲面重构方法,并对同一种模型进行重构和误差分析。精确曲面重构方法可保证模型数据的完整性与精确性,从而生成高质量的模型;参数化曲面重构方法通过参数转换功能将初始曲面导入Solid Works软件中进行编辑,最后得到参数化模型。实际应用中可结合这两种方法各自特点及优势,高效优质地构建CAD曲面模型。     

基于实物的复杂曲面零件反求工程中未知区域测量数据补充及曲面重构技术

针对基于实物的复杂零件反求工程中含有部分形状未知区域（如裁减曲面中的被裁减部分、测量盲区等）的复杂曲面反求CAD建模问题,提出了三种测量数据补充方法:①局部区域实物填充法。②补充设计数据补充法。③基于逼近曲面或三角曲面的测量数据自动补充法。研究了基于三角曲面模型初始表达的复杂曲面分区NURBS曲面重构方法。最后,给出了结合上述方法和反求工程软件RE-SOFT所解决的摩托车塑料件反求CAD建模实例。实践表明,综合运用所提出的数据补充和曲面重构方法,能够大大缩短实物样件的反求CAD建模时间,提高复杂曲面产品的设计效率。     

G~2连续的A级曲面精确重构及光顺技术研究

A级曲面重构中拟合高精度曲面过程复杂繁琐,需要进行大量运算,且曲面拟合后没有保留参数特征,无法编辑修改,进而造成曲面逆向重构工作反复进行。针对上述问题提出一种高效准确的方法进行曲面重构。根据K-邻域搜索的离散点云,采用直线、圆弧等多方式分段插值拟合出曲率连续过渡的曲线,保留参数特征,方便修改;再利用NURBS理论拟合曲面,通过调整控制点、权因子和节点矢量等因素,确保曲面拟合精度和曲率连续过渡。经过实例分析,此方法拟合A级曲面快速准确,并保留了曲面形状参数,提高了曲面重构的精度和效率。     

保持参数分布状态的有限元变形网格B样条曲面重建算法

针对变形前后的有限元网格模型及原始曲面模型,提出一种保持参数分布状态的B样条曲面重建算法。在裁剪区域,通过对原始曲面进行平移、延伸、截取及重新参数化等操作,构造初始拟合曲面;在非裁剪区域,在垂直于大曲率边界的参数方向上插入截面线并重新参数化两条大曲率边界,用双向蒙皮的方法重建拟合曲面。然后进入重新参数化网格点和重新拟合曲面的迭代过程,直至满足终止准则。在曲面迭代修改过程中,通过计算基函数的极值点给出一种更精确的欠约束区域判定方法;利用插值四边/三角细分算法细化粗糙网格模型,补充约束条件,提高拟合曲面的光顺性;借助拟合曲面补充边界约束条件,结合网格点插值和形状保持约束,改进裁剪曲面的拟合精度。实验结果验证了算法的有效性。     

逆向工程中的参数化建模技术及应用

逆向参数化建模方法是在逆向工程的基础上,加入参数化技术形成的一种新的建模方法,该方法不仅有利于提取原始设计信息,重建更为精确的CAD模型;而且易于实现模型的参数化修改,推动产品的创新设计。简要介绍了逆向工程的概念和逆向参数化建模方法,以汽车后视镜为例,利用Geomagic Studio软件对扫描点云进行处理,拟合出特征识别后的初始曲面。通过参数转换功能把初始曲面导入Solidworks中进行编辑,最后得到汽车后视镜的参数化模型。实践表明这为反求模型的参数化建模提供了一种切实可行的方法。     

基于局部形状特征的自由曲面相似性评价方法

目前的三维CAD模型检索技术研究主要针对实体模型而较少考虑自由曲面,为此提出一种基于局部形状特征的自由曲面相似性评价方法,将两个自由曲面的相似性评价问题转化为两个曲面局部特征间的相似性评价。该方法首先在自由曲面的参数域内生成图像形式的曲率云图,然后从曲率云图中提取类Sift算子局部特征,最后通过比较局部特征的相似性实现自由曲面的相似性评价。实验结果表明,该方法有效可行,可以实现自由曲面的整体/局部相似性评价。     

任意拓扑结构复杂曲面模型重构新方法

分析了采用参数化方法进行复杂曲面模型重构时存在的缺点,给出了应用递归插值分割理论从离散测量点构成的初始控制网格直接构造任意拓扑结构复杂自由曲面模型时计算插值点的统一算法,设计了一种能充分体现这种曲面模型重构方法优点的四叉树型数据结构存储必要的信息,最后给出了复杂自由曲面模型重构的几个实例。从实例可以看出该方法能够避免参数化方法在复杂曲面模型重构时所必须的参数曲面片之间的拼接和裁剪等问题,为复杂自由曲面模型重构提供了有效的新方法。     

基于粒子群优化算法的三维点云NURBS曲面重构研究

针对Delaunay三角化等传统方法在逆向工程曲面重构过程中存在着精准度不足、处理高维非线性问题时效率低等问题,提出一种基于粒子群优化算法的三维点云NURBS曲面重构方法。通过曲面参数化和曲面拟合两个关键步骤,使用粒子群优化算法确定出控制点、节点矢量和权因子等NURBS曲面参数,实现了NURBS曲面重构。最后使用包含了开放、半封闭、封闭、实际扫描、多分支和自我交叉等5种不同类型具有代表性的曲面模型对算法进行验证。实验结果表明,该方法具有良好的鲁棒性、准确性和灵活性。     

基于逆向工程的人头像建模技术的研究

利用手持式激光扫描仪得到人头像雕塑的点云数据,通过基准点定位原理对点云数据进行拼合,经过多边形网格处理,最终实现NURBS曲面模型的重构。通过对重构模型进行偏差分析和修改,得到符合CAD/CAM要求的数字化模型。该方法能够快速地处理点云,建立复杂曲面的三维模型,满足CAM加工的要求。     

基于双测量设备的涡轮精确逆向重构方法

针对车用涡轮增压器中涡轮的结构特征,考虑不同测量设备的特性,提出了一种采用两种测量设备构建涡轮精确逆向模型的方法.通过非接触结构光三维扫描仪获取涡轮叶片点云数据,采用分区域处理法得到涡轮曲面模型,利用二维投影仪得到涡轮外轮廓边界形状和准确尺寸,将其与曲面模型进行数据匹配,在CAD软件中对匹配的曲面进行边界修整,完成涡轮三维建模.利用本方法能可靠重构涡轮三维模型,缩短设计开发的周期.     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

Limits of topographic measurement by the scanning tunnelling and atomic force microscopes

Parameters describing the topographic character of a surface (height, surface wavelength, slope and curvature) can be derived from equivalent sinusoidal profiles. The response of a surface-measuring instrument may be modelled in terms of instrument parameters such as stylus radius, and scanning range and resolution. The performance of the instrument may then be mapped as a zone in amplitude-wavelength (AW) space to show the sinusoidal profiles it is capable of measuring. In a first-order analysis the STM and AFM are considered as equivalent to contact-stylus instruments with a notional stylus radius equal to the tip radius plus the gap. Comparisons between different instruments and types of instrument are readily made by mapping in AW space. The error arising from convolution of the sinusoidal profile with that of the finite tip may be quantified and plotted as contours in AW space.