基于DLP数字微镜的结构光三维扫描系统

为了提高现代化生产中的效率和满足三维扫描的需求,设计了一种能够准确提取物件表面三维轮廓信息的扫描系统。系统采用结构光三维成像方法,先通过普通白光将光栅投影到被测物体表面,利用工业相机采集变形光栅图,再根据变形光栅图像中的灰度值变化,用傅里叶变换轮廓法解调出三维坐标信息。实验结果表明,使用傅里叶变换轮廓法重构可获得效果理想的三维点云,其为三维轮廓扫描提供了实验方法,同时也为提高点云精度提供参考。     

发动机凸轮轴参数化建模与加工力学分析

针对发动机凸轮轴在数控磨削时产生弹性变形与振动的问题,提出了凸轮轮廓曲线相邻三点逐次样条拟合方法。并利用该方法在ANSYS有限元软件中对某凸轮轴进行了APDL参数化建模,对凸轮轴磨削时不同位置和不同转角下凸轮轴的弹性变形量进行了计算公式推导和有限元分析,对凸轮轴的固有频率和磨削约束条件下的振型、谐响应进行了分析。应用三点拟合方法可以快速、准确地建立凸轮轴的有限元模型,而适当选取磨削参数可以减小凸轮轴的弹性变形与振动,从而提高凸轮轴的轮廓精度和升程精度。     

流形网格上机构运动轨迹的参数化生成方法

在三角网格模型上操作机构的运动轨迹生成通常采用截面线法,当网格边界复杂时由此生成的运动轨迹很难保证与边界的一致性,从而产生较多较短的单条路径。基于调和映射技术,提出复杂网格曲面上机构运动轨迹参数化生成的一般方法。通过将复杂网格模型同胚映射到平面上的圆形区域或矩形区域,建立在参数曲面基础上的Zigzag型及轮廓型等参数轨迹线的具体规划模型,给出该种情况下轨迹离散点、行距及机构运动干涉的计算方法与解决方案。实例表明该轨迹生成方法具有良好的边界一致性,并因其固有的轨迹磨光性质提高了运动机构的动力学性能及运行效率。     

Contour-based algorithms for generating 3D CAD models from medical images

This paper concerns contour-based algorithms for generating a 3D CAD model from medical images. The 3D model generated by contour-based algorithms can be used to generate CAM data for fabrication where the accuracy is of most concern. The overall procedure includes: (1) contour data extraction from medical images, (2) smoothing of the extracted contours, and (3) creation of a surface model from contours. For this, various methods should be applied to generate a high-quality surface model. The main contribution of this paper is to propose a new contour smoothing method, called bi-directional smoothing. The basic idea behind the proposed bi-directional smoothing method is to refine contours along both (u, v) parametric directions. Compared to conventional smoothing methods, the recontouring that comprises the first part of the method can prevent the shape of a contour from shrinking with a large number of iterations. Along with recontouring, a vertical connectivity estimation and a vertical smoothing method are also proposed. The overall procedure for this approach is demonstrated with an application example using CT images of a femur.     

基于空间相移技术的平面干涉仪系统设计

时域相移技术由于需要在时域采集多幅干涉图而只擅长用于静态检测。为改善测量的动态特性,现提出了基于空间相移技术的平面干涉仪系统。采用基于偏振干涉和光栅分光的单CCD成像空间相移系统设计方案,设计了具有折叠式布局特点的干涉仪光路系统,建立了系统机械结构三维模型,结构紧凑、调整方便,并运用四步相移算法进行了模拟试验后数据处理。结果表明,所设计系统能够满足动态测量要求。     

OPTIMIZATION METHOD ON IMPELLER MERIDIONAL CONTOUR AND 3D BLADE

An optimization method for 3D blade and meridional contour of centrifugal or mixed-flow impeller based on the 3D viscous computational fluid dynamics (CFD) analysis is proposed. The blade is indirectly parameterized using the angular momentum and calculated by inverse design method. The design variables are separated into two categories: the meridional contour design variables and the blade design variables. Firstly, only the blade is optimized using genetic algorithm with the meridional contour remained constant. The artificial neural network (ANN) techniques with the training sample data schemed according to design of experiment theory are adopted to construct the response relation between the blade design variables and the impeller performance. Then, based on the ANN approximated relation between the meridional contour design variables and impeller performance, the meridional contour is optimized. Fewer design variables and less calculation effort is required in this method that may be widely used in the optimization of three-dimension impellers. An optimized impeller in a mixed-flow pump, where the head and the efficiency are enhanced by 12.9% and 4.5% respectively, confirms the validity of this newly proposed method.     

Calculation method of radial stress and deformation on conic threaded connections with interference fit

This paper presents a calculation method for radial stress distribution and deformation on conic threaded connections with interference fit. Based on elastic mechanics, a new calculation model is established using the thick-walled-cylindrical theory. A sample calculation for API 88.9 mm conic threaded connection indicates that the method proposed in this paper is reasonable, and the finite element analysis (FEA) method is used to validate the proposed method. The results obtained by the proposed method and FEA method are identical. The model offers a new way of calculating the radial stress and deformation on conic thread connections with interference fit.     

A method for planar development of free-form surfaces made of anisotropic materials

This paper presents a method for planar development of free-form surfaces especially made of anisotropic materials. A free-form surface is first tessellated into a set of triangular elements (i.e., facet model). If necessary, a facet refinement technique using Euler operators is applied to create a more reliable model that approximates the original surface as closely as possible. The facet model is then roughly flattened on a 2D plane. Next, the roughly flattened model is used as an initial guess for subsequent optimization during which the strain energy method using constant strain triangles (CST) is applied to yield an optimal 2D contour. In fact, various resulting 2D contours can be obtained while varying elasticity ratios between two material axes or development angles. To compare these resulting 2D contours, a contour alignment technique for error estimation is also presented. In this paper, anisotropic materials are considered to be orthotropic as a first approximation. A specific example (lateral surface of a shoe last) is shown to validate the proposed method.     

基于预分割轮廓的CT图像亚体素表面检测方法

针对基于CT(computed tomography)图像检测分析中的点云提取精度与完整性问题,提出一种基于预分割轮廓的高精度、高完整性的亚体素表面检测方法。首先采用Otsu分割算法提取CT图像的体素级轮廓点集,并以此作为粗定位轮廓自适应地生成用于亚体素表面检测的完备感兴趣区域(region of interest,ROI);然后提出一种基于梯度非极大值抑制的表面体素判定方法,避免了梯度阈值选择难题;最后基于3D Facet模型定位亚体素级表面点位置。实验结果表明,该方法能有效改善传统亚体素检测方法的轮廓丢失、伪边严重等问题,轮廓定位误差小于0.2个体素,同时能够取得3倍以上的计算加速比。     

基于窗口傅里叶变换的线性相位误差抑制

在窗口傅里叶变换(WFT)相位提取技术中,抑制线性相位误差和背景光强干扰对窗口尺寸的需求条件存在矛盾,无法对二者进行同时抑制,故提出一种通过改变输入信号频谱成分的线性相位误差抑制技术,该技术利用傅里叶空频分析法将输入信号进行背景光强滤除并保留基频成分,使测量结果不受背景光强影响;考虑到线性相位误差同样受到窗口尺寸选取的影响,通过仿真分析确定最优窗口尺寸判定依据;采用该方法重构抛物面形并以相移干涉技术所获面形结果为基准进行对比分析,结果表明,本文提出方法可实现线性相位误差与背景光强干扰的综合抑制效果并提高了传统WFT相位提取精度。