有界泊松曲面约束的曲面样点法向稳健估计

对存在噪声、非均匀采样等缺陷的曲面样本,基于样点及其邻近样点构成的局部样本通常无法稳健逼近曲面局部区域,导致样点法向难以准确估计。为抑制样本缺陷对样点法向估计的影响,提出一种以有界泊松曲面逼近局部样本作为约束的样点法向加权估计算法。对待估计法向的样点,该算法对其所属曲面局部样本作增益优化处理,使得曲面局部样本具备边界保护区域;在样点的Frenet标架中以泊松曲面逼近该样本,基于样本的边界保护区域将泊松曲面的离散网格转化为有界形式,从而建立样点邻域的曲面约束,以有界泊松曲面离散网格中距样点最近的网格面片作为样点的参考面片,基于顶点邻域面的正则度及邻域面到该顶点的测地距离估计参考面片顶点法向,将参考面片各顶点法向的加权求和结果作为样点法向的估计结果。实验结果表明:曲面样本噪声水平不高于20%时,可将法向计算误差控制在π/18以内,且所得法向过渡较为光滑。证明了该算法适用于复杂曲面样本,可稳健处理存在噪声以及采样不均匀等缺陷的曲面样本的样点法向估计问题,实现曲面样点法向的光滑过渡。     

样点邻域同构曲面约束的散乱点云法向估计

针对现有点云法向估计算法难以兼顾估计结果的精度与稳健性问题,以局部采样区域同构曲面作为样点邻域点集所反映曲面形状约束,提出一种散乱点云法向估计方法。该方法将目标样点的邻域点集作为局部样本进行曲面重建,获取插值于采样点集并与采样表面拓扑同构的局部网格曲面;对曲面局部区域高斯映射结果进行聚类分析,获取目标样点的各向同性邻域面;基于面片的正则度以及面片至目标样点的测地距离,确定目标样点各向同性邻域面片法向的加权均值,并将所得结果作为目标样点的法向估计结果。试验结果表明,该方法在点云数据信噪比为40 dB的情况下可保证98%以上样点法向估计偏差在以内,可稳健处理含有噪声以及采样不均匀等缺陷的散乱点云法向估计问题,对于含尖锐特征的点云亦能准确估计样点法向,且具有较高的计算效率。     

基于贝叶斯估计的测试性仿真评估方法研究

经典测试性参数估计方法仅利用了样本所提供的关于总体的信息,没有利用关于待估统计量的其他信息,例如装备在研制阶段的测试性摸底试验以及丰富的专家数据;因此,这种经典估计方法在小样本情况下,很难真实反映装备的测试性水平。针对以上问题,本文提出了一种在获取仿真试验数据的前提下,进行综合装备先验信息测试性评估的方法,即基于贝叶斯估计的测试性水平估计,研究了测试性参数先验信息获取方法,给出了测试性参数的点估计和区间估计方法。     

基于改进贝叶斯估计的水下地形匹配辅助导航方法

以多波束测深数据为依据,提出了一种基于贝叶斯估计的智能水下机器人(autonomous underwater vehicle,AUV)水下地形匹配辅助导航方法,针对在地形特征不明显区域该方法伪点增多的不足,引入了费希尔判据准则,提出了一种以最大有向特征参数作为二次判别依据的贝叶斯-费希尔估计方法,该方法有效地减少了伪点的个数,增强了地形平坦区域的识别率,对初始定位误差具有良好的鲁棒性。基于电子海图数据和多波束海上实验数据的仿真定位结果,表明了该方法的有效性和可行性。     

法向等厚旋转曲面体的模具型腔计算

在工业领域中,不少产品的零件结构采用法向等厚旋转曲面体.在航天航空领域,为适应飞行需要,一些飞行器如火箭、导弹的外形也大多采用法向等厚的旋转曲面.在制造生产这类零件时,常会碰到这些零件的模具型腔计算问题.为此,本文在理论曲面坐标下,经法向等厚条件,求出了实际模具型腔的坐标值,导出了获得实际模具型腔的精确计算算法和近似计算公式,并给出计算示例,说明对这些公式的具体应用.     

基于砂轮法向跟踪的回转曲面磨削研究

在回转曲面的磨削中,采取小直径平行砂轮代替圆弧砂轮的方法,保证曲面磨削点的法向始终与砂轮表面垂直,实现砂轮法向跟踪磨削.根据磨削轨迹,建立了磨削表面残留高度模型,分析了砂轮半径、工件曲率和进给速度对残留高度的影响.并进行磨削试验,得出了砂轮半径、工件曲率及进给速度对表面粗糙度的影响曲线,其变化规律与残留高度的变化规律基本一致,证明在回转曲面磨削中,可以通过控制残留高度的大小来改善磨削表面粗糙度.     

基于激光距离传感器的机器人自动制孔设备的曲面法向找正方法研究

孔的垂直度对于孔的质量有很大的影响,为此提出了一种基于激光距离传感器的机器人自动制孔设备的曲面法向找正方法。该方法在调整传感器的位置和姿态后,通过选取特定传感器发射的光线在待测面上的光斑,建立坐标系,计算得到刀具轴线向量与待测面法向的夹角,进而得到了机器人需要旋转的角度。实验证明,该方法完全满足工艺要求。     

基于变量几何法的两种并联机床法向加工自由曲面仿真

采用CAD变量几何法,用两种新型5自由度3SPS+RRPU和2SPS+RRPRR并联机床对任意3D自由曲面进行法向加工。通过CAD几何约束和尺寸驱动技术,首先建立两种并联机床的模拟机构,再在并联机构动平台上构造任意3D自由曲面和刀具轨迹的引导平面,与并联机构合成,得到模拟并联机床。保持刀具与自由曲面垂直关系,给定加工路径,各驱动杆长和动平台的位置能自动求解和动态显示。结果表明:CAD变量几何法不仅简单直观,而且省去了大量的编程计算。     

考虑外法向的钣金零件展开方法研究

针对射线法展开钣金零件的不足，以几何映射原理和钣金零件三角网格信息为基础，兼顾零件带孔情况，建立了考虑外法向的射线法展开算法。展开实例表明，所提出的展开算法高效、实用，所得到的零件毛坯形状相对合理正确，为一步法快速分析优化提供了良好的初值。     

基于法向量区域聚类分割的点云特征线提取

针对逆向工程领域中散乱点云模型过渡线及细节特征线提取不完整问题,提出一种法向量区域聚类的特征线提取方法。采用自适应邻域的主成分分析法估算模型的法向量,利用萤火虫算法优化的模糊C均值聚类算法对法向量的进行聚类实现模型的有效分割。构造点集剔除与合并准则从各分割块边界点集中析取候选特征点,再以局部邻域主轴方向为基准提取特征点。实验结果表明：简单模型的特征线基本可准确完整提取,相对复杂模型的特征线数量提取率可达90%,长度提取率达到了85%。算法具有良好的自适应性和准确性,能有效提取点云模型尖锐特征和细节特征,并尽可能多地保留模型过渡特征。     

Implementation of the principal-axis method for machining of complex surfaces

In this paper a new strategy for 5-axis machining of complex surfaces is presented. The method uses curvature alignment and matching between the design surface and the cutting tool to improve surface finish and reduce machining time. The method is implemented on two configurations of 5-axis machines, and used to machine a test surface. The results of the tests show a considerable improvement over conventional 3-axis machining.     

Hierarchical roughness optimization for biomimetic superhydrophobic surfaces

Superhydrophobic surfaces should have high contact angles (CA) with water and low contact angle hysteresis (CAH). High CA may be achieved by increasing surface roughness, while in order to have low CAH, superhydrophobic surfaces should be able to form a stable composite interface with air pockets between solid and liquid. Capillary waves, nanodroplets condensation, hydrophilic spots due to chemical surface inhomogeneity, and liquid pressure can destroy the composite interface. These destabilizing factors have different characteristic length scales, so a hierarchical roughness is required to resist them. It is shown that convex rather than concave profile enhances stability, so nanoscale convex bumps should be superimposed over microasperities, in order to pin the liquid-air interface. In addition, the nanoroughness is required to support nanodroplets. The ability of the interface to support high pressure requires high asperity density and size, so it is in conflict with the requirement of low fractional solid-liquid contact area for low CAH and slip length. The new parameter, spacing factor for asperities, is proposed, and requirements for optimum design, which combines conflicting conditions, are formulated and discussed. Remarkably, biological superhydrophobic surfaces satisfy these requirements.     

存在约束条件的复杂曲面三角网格剖分方法

针对存在特征约束条件的复杂曲面三角剖分提出了一种新的算法，该算法首先将该类复杂曲面划分成平面参数域，产生较为均匀的参数域，进而对各子平面参数域进行平面参数域的三角剖分，然后将所得到的各子平面参数域映射为空间Beizier网格结点，形成粗网格三角剖分后进行各子曲面片间G^1连续的拼接运算，最后动用曲率标准和细分规则进行三角剖分质量的优化。该方法不但可以较好处理复杂曲面，而且能克服曲面网格产生裂缝。     

Research on real time feature extraction method for complex manufacturing big data

Big data related to manufacturing applications has the traits such as great quantity, multi-sources, low value density, high complexity, and dynamic state. Traditional feature extraction methods are incapable of meeting real-time demands. Therefore, a robust incremental on-line feature extraction method based on PCA (Principal Component Analysis), RIPCA (Robust Incremental Principal Component Analysis), is proposed. RIPCA adopts a sliding window to update new coming data stream and to filter outliers. The proposed method could ensure the accuracy of data analysis and meet real-time demands of big data processing for manufacturing applications. A test data set based on a semiconductor manufacturing process containing 1567 records with 590 features is used to demonstrate the availability of the proposed method. Experimental results show that the method can effectively extract features of the data stream in real time with high accuracy.     

一种图像边缘特征提取算法

边缘作为一个重要特征是图像目标检测中基础而又困难的一个问题.用常规方法进行边缘检测时,噪声会影响到边缘特征提取的准确性.为了减小噪声对图像边缘特征的影响,改善边缘特征的定位精度,本文提出了一种新的图像边缘特征提取算法.该方法利用小波变换天生的多尺度特性,对小波变换各尺度下的细节图像用互能量交叉的方法进行噪声抑制和边缘识别.最后作了实例验证.     

Chebyshev fitting of complex surfaces for precision metrology

The form qualities of precision components are essential for their functionalities. The Peak-to-Valley parameters are widely adopted to assess the form accuracies of optical components. The commonly used least squares method is prone to over-estimation, thus the Chebyshev fitting should in turn be implemented. In this paper the original minimax optimisation problem is converted into an unconstrained differentiable minimisation problem by the exponential penalty functions. The fitting accuracy and numerical stability are balanced by employing an active-set strategy and adjusting the configuration parameters adaptively. Finally some benchmark data sets are applied to demonstrate the validity and efficiency of this method.     

An adaptive uniform toolpath generation method for the automatic polishing of complex surfaces with adjustable density

During automatic polishing process, path trajectory is an important factor affecting the quality of machining. In this paper, a path generation algorithm based on adaptive Hilbert curves which can cover the curved surface evenly is proposed. The generated path not only makes the coverage density adjustable but also is able to pass through the points on the curved surface in more directions which is helpful to get a finished part without stripes. Using the proposed algorithm, the uniform distributed grid points are obtained in the parameter domain and then these node points with adjustable density can be calculated accordingly. Thus, according to the construction rule of adaptive Hilbert curve, the objective toolpaths are subsequently obtained. After that, by means of a mapping strategy, the path trajectory can be obtained on the physical space. To verify the proposed algorithm, uniform polishing paths with variable density are planned on two typical curved surfaces. The result of the machining experiment shows that the curved mirror-like surface can be achieved, and it also indicates the applicability of the proposed method.