任意拓扑三角网格模型的Loop细分曲面重建系统

提出一种从任意拓扑密集的三角网格模型拟合Loop细分曲面系统，包含对原网格模型进行特征识别，把保持了原有特征的简化网格和拓扑优化所获得的网格作为拟合初始控制网格。系统通过对控制网格顶点的循环修正和局部自适应细分来求解最终拟合细分曲面控制网格，避免了求解线性方程组，提高了拟合曲面的质量，实现了在给定精度下用较少的控制网格反映物体细节特征的分片光滑（片内除奇异点C^1外其余C^2连续）的Loop细分曲面重建。实例表明，Loop细分曲面重建系统对于任意拓扑海量三角网格测量数据的细分曲面重建是高效可行的。     

三维扫描点云优化网格重建与软件系统实现

物体经过三维扫描后获得大量的散乱点数据,为了能快速、准确的重建出网格曲面,提出了一种空间三角网格螺旋增长重建的算法。该算法首先利用包围球法对散乱点云进行优化,然后根据极坐标法确定螺旋增长的初始三角形,通过对生长的三角形最长边、最小内角和具有公共边的三角形所在面的二面角进行限制和对相应的新的网格边界点进行加锁和解锁操作,不断的寻找最佳扩展点,直到无可用的扩展点为止,最后再对有缝隙的网格边界进行缝合,完成三维扫描点云优化网格重建。     

散乱数据点云型面特征提取算法研究

提出一种新的散乱数据点云型面特征提取算法,该算法基于散乱数据点云的动态空间存取模型,应用WINDOWS APl和OpenGL技术拾取点云局部型面的曲率信息,根据点云型面特征的曲率性质,改进区域生长法实现产品点云型面特征的提取.实验证明该算法型面特征提取准确,可有效提高建模效率及重建模型精度.     

Loop细分曲面的自适应等距面生成算法与实现

提出一种精确快速生成有边界等距 L oop细分曲面的新算法 ,其核心思想是 :从控制网格顶点在 L oop细分曲面上的位置 ,按照给定的等距值 ,沿其法矢正 (反 )向等距 ,通过解线性方程组求出等距后的控制网格 ,然后检测等距误差 ,对部分超过给定等距精度的控制网格进行局部自适应细分 ,重新生成等距面并检测误差 ,直至整个细分等距曲面满足精度要求 ,所生成的等距细分曲面除局部 C1 外其余 C2 连续。实例表明 :本算法高效稳定 ,生成的等距细分曲面已完全满足实际工程需要。     

人字齿轮直线型对角修形设计及成形磨原理

为了降低承载传动误差波动产生的振动激励，提出了成形磨人字齿轮直线型对角修形优化设计。根据ISO对角修形定义，计算齿顶、齿根修形起始线在旋转投影面上的螺旋角，将修形曲线设计为直线型，给定最大修形量，确定对角修形的齿面方程。利用齿面接触分析和轮齿承载接触分析，以工作载荷下人字齿轮承载传动误差波动量最小为优化目标，采用遗传算法优化对角修形参数。确定以目标修形齿面法向偏差的平方和最小的目标函数，以螺旋角、模数、压力角为设计变量，采用遗传算法分别对齿顶和齿根修形区域进行逼近，从而实现对角修形的成形磨加工。结果表明，人字齿轮直线型对角修形可以将承载传动误差波动量降低到36.65%；采用三截面砂轮成形磨的理论误差控制在1μm以内，获得较高的齿面精度；试验人字齿小轮齿的检测结果控制在4级精度以内，并进行了齿轮副的滚检试验，从而验证该方法的有效性。     

基于“薄膜变形”的牙齿曲面重建算法研究与实现

牙齿曲面重建是口腔修复CAD/CAM系统的核心内容之一。本文提出了一种基于"薄膜变形包围"牙齿曲面重建算法,首先对简化后的牙齿三角网格模型进行Loop细分以提高模型的变形逼近的能力;然后对细分后的网格施加"吸引力"使细分网格逼近原始密集的网格模型;接着施加"松弛力"消除网格变形后的褶皱;最后通过不断的异步迭代循环调整网格顶点的位置,直到满足预设的误差精度后停止。通过对两类典型牙齿模型的网格重建的算例,验证了本文算法的可行性。     

基于空间点阵的齿轮精确修形方法

齿轮修形是改善啮合状态、提高传动精度和效率的一种重要工程技术,但现有的齿轮修形方式和工具性软件难以确保修形的齿面几何质量和效率。因此,提出了一种空间点阵的齿轮修形方法。首先,根据修形精度要求,将齿轮的齿面离散为规则空间点阵,并将修形量映射到对应的空间点上,再将调整后的空间点阵构建成规则的二次B样条曲线;然后,通过优化网格曲线,得到修形后的齿面,并自适应更新整个齿轮三维模型的齿面;最后,将该方法无缝集成到三维设计软件NX平台上,开发了齿轮精确修形设计系统。实例证明,该方法通过修形位置和修形量的双重控制,实现了齿面的精确修形,获得了高质量齿廓曲面,在保证精度的同时提高了齿轮修形的高效性和实用性。     

√3细分曲面的误差分析

针对细分控制网格与细分极限曲面的逼近度这一问题,基于细分控制网格的拓扑结构和细分模式的几何规则,提出一种√3细分曲面的误差估计方法并给出一个误差估计公式.利用该公式,根据给定的精度,可事先知道细分之后控制网格满足该精度的最少细分次数而不需要实际对一个模型细分.结合该误差估计方法,给出一种√3细分曲面数控加工刀具轨迹生成方法和一种用于直接在STL文件基础上提高精度的方法.试验结果表明这种误差估计方法的有效性.     

修形斜齿轮齿面误差的在机拓扑测量与表征

为全面表征拓扑修形斜齿轮的齿面误差信息,针对数控成形磨齿机的运动功能和修形齿面形成的机理,依据极坐标法测量的数学模型提出了在机拓扑测量方法。根据砂轮廓形与工件的接触迹线通过坐标变换推导出拓扑修形齿面理论点的数学方程,并对修形齿面进行网格划分。利用数控成形磨齿机的回转运动(C轴)、径向进给运动(X轴)和轴向进给运动(Z轴)形成理论渐开线点到点的拓扑测量。最后在成形磨齿机上进行测量实验,表征出齿面误差等值图。     

激光-机器视觉测量系统的数据采样及网格化

以激光-机器视觉测量方式得到的曲面数据云为基础,探讨基于给定精度的曲面密集散乱数据点群的数据压缩以及几何建模方法。其中,根据激光测量方式和三维点群分布的特点,提出一种在给定采样精度基于曲率的曲面自适应采样的方法;通过激光扫描曲线间的采样点匹配为进一步数据压缩提供依据;并由度量曲面的初步网格点阵对测量点逼近程度好坏来进一步完成对曲面模型的修正。通过实例验证这种方法的可行性。     

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.     

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....     

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.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.