Application of kinematic geometry to computational metrology: distance function based hierarchical algorithms for cylindricity evaluation

This paper applies kinematic geometry to investigate the problem of determining the cylindricity error of a mechanical part by using measurement points obtained with a coordinate measuring machine. For a point expressed in the machine reference frame and a nominal surface represented in its own model frame, a signed point-to-surface distance function is defined, and its increment with respect to the differential motion of the surface is derived. On this basis, four commonly used cylindricity evaluation methods, i.e., minimum zone cylinder method, maximum inscribed cylinder method, minimum circumscribed cylinder method and least-squares cylinder method, are formulated as nonlinear constrained optimization problems and nonlinear least-squares problem, and efficient sequential approximation algorithms are developed to solve them. For enhancing the performance of the algorithms, two relevant optimization problems and corresponding algorithms, i.e., localization of cylinder and minimum variance fitting of cylinder, are introduced to analytically provide proper initial solutions. By organizing all involved algorithms in a hierarchical structure, four complete cylindricity evaluation algorithms are presented. Comparing with existing methods, they have the advantages of implementational simplicity, computational efficiency and robustness. Examples confirm the validity of the proposed hierarchical algorithms.     

Development of an automatic weld surface appearance inspection system using machine vision

In this paper, an automatic inspection system for weld surface appearance using machine vision has been developed to recognize weld surface defects such as porosities, cracks, etc. It can replace conventional manual visual inspection method, which is tedious, time-consuming, subjective, experience-depended, and sometimes biased. The system consists of a CCD camera, a self-designed annular light source, a sensor controller, a frame grabbing card, a computer and so on. After acquiring weld surface appearance images using CCD, the images are preprocessed using median filtering and a series of image enhancement algorithms. Then a dynamic threshold and morphology algorithms are applied to segment defect object. Finally, defect features information is obtained by eight neighborhoods boundary chain code algorithm. Experimental results show that the developed system is capable of inspecting most surface defects such as porosities, cracks with high reliability and accuracy.     

Determination of the parameters of the beam geometry in an electron beam welding installation

Abstract

With the aid of statistical methods, mathematical relationships between given technological parameters and installation dimensions are found. Using the algorithms obtained, the plant settings are calculated from the target quantities using a control computer (K1520) as required and for any value within the range of settings, and these are set in the EB installation.     

Image fusion of ultrasonic and thermographic inspection of carbon/epoxy patches bonded to an aluminum plate

Inspecting damaged structures repaired with composite patches is one of the most challenging issues of different industries, especially in aeronautical vehicles. Various inspection methods such as ultrasonic (UT) and thermographic methods are commonly applied to the patches and bondings. Although, both ultrasonic and thermographic inspections have their own capabilities, they are also associated with some limitations especially in the inspection of complicated structures such as multilayers. Different data fusion techniques can be used to overcome these limitations, by exploiting the advantages of each inspection technique to achieve the goal to have a more precise and reliable defects assessment. In this paper, different image fusion algorithms are used to fuse the UT C-scan and thermal images obtained from thermographic inspection of carbon/epoxy patches bonded to an aluminum plate. The inspected specimen contained several delaminations of various sizes and locations along with some disbond defects which were artificially embedded in five samples of composite patches. The resulting images of 28 fusion algorithms and the input images have been quantitatively compared using Average Differences (AD) to clarify the efficiency of the fusion algorithm. Comparing results revealed that contrast pyramid was selected as the best image fusion algorithms which can be used for NDE fusion of carbon/epoxy patches bonded to an aluminum plate.     

基于激光传感器的弧焊机器人焊缝跟踪研究

采用激光扫描式传感器,设计了一套机器人焊缝自动跟踪系统。开发了相应的焊缝跟踪算法,包括直线、圆弧和直线圆弧组合连续焊缝的跟踪算法。探讨实现这些算法的相关技术问题。计算机仿真结果表明,该算法合理有效,可用于弧焊机器人焊缝在线跟踪作业,改善和提高机器人的焊接精度和质量。     

摄像机标定中亚像素级角点检测算法

针对摄像机标定模板图像的角点检测问题,提出了两种简便而有效的亚像素级精度的提取算法.先用传统的Harris算子检测出像素级的角点坐标,然后再求取亚像素级角点坐标.一种方法是用二次多项式去逼近周围3×3领域内的角点反应函数,用线性解法求得亚像素级角点坐标;另一种方法是从亚像素角点到周围像素点的矢量应垂直于图像的灰度梯度这个观察事实得到的,通过最小化误差函数的迭代方法来获得亚像素级精度的坐标值.文中提出的亚像素级角点检测方法定位精度高,摄像机标定试验中,得到的重投影平均偏差小于0.15个像素.     

基于金属刚塑性/刚粘塑性不可压缩材料的无网格RKPM法

文章将刚塑性/刚粘塑性流动理论与再生核质点方法(RKPM)相结合,提出了基于刚塑性/刚粘塑性不可压缩材料的无网格RKPM法,进一步拓展了无网格RKPM法的应用范围。分别采用边界奇异权法和修正的罚函数法处理本质边界条件和体积不可压缩条件,推导了金属塑性成形过程无网格RKPM法数值模拟的刚度方程,给出了关键算法。对平面应变镦粗过程进行了数值模拟,并将模拟结果与刚塑性有限元体积成形商品化软件Deform 2D计算结果作了比较,二者吻合良好,表明了该文方法的正确性和有效性。     

金刚石微粉粒度不同检测方法的比较与研究

本文分析比较了不同型号激光粒度分析仪测量同一金刚石样品结果的差异。同时还比较了激光粒度仪与沉降管法对同一样品检测结果的差异。实验发现,由于不同型号的激光粒度分析仪设计原理、数据采集方式、算法不同,导致检测结果有所差别;另外,不同方法检测结果没有可比性。因此使用激光粒度分析仪检测粉状物料时,应注明所使用的仪器型号。该结论对超硬材料和磨料磨具行业微粉粒度组成检测有重要的参考价值。     

基于国产五轴超声装备的后置处理算法研究与应用

针对某自主研制的五轴超声装备,通过对该装备的多轴运动转换、控制系统、超声原理、超声专用刀具、刀具轨迹等进行深入研究,提出一套适用于该超声装备的后置处理算法,且基于Microsoft Visual Studio 2010开发工具,用C#语言开发出一套专用超声后置处理系统。选择C919型机某典型多自由度曲面零件开展应用验证,结果证明:该算法及系统稳定、可靠,能够满足生产需求,具有较强的适用性和推广性。     

Use of quasi-static nanoindentation data to obtain stress–strain characteristics for metallic materials

This paper concerns optimization of procedures and algorithms for extraction of stress–strain relationships from quasi-static nanoindentation experiments, using finite element method modelling. Several issues are highlighted, including the usefulness of incorporating residual indent shape in the comparisons, as well as load–displacement–time data, and the significance of creep and interfacial friction. The study is focused on extruded copper bar, using a spherical indenter and assuming transverse isotropy throughout. It is shown that, using the methodology presented here, experimental nanoindentation data could be used to estimate the yield stress and work-hardening rate, with good accuracy, i.e. the yield stress could have been obtained to a precision of about ±10%, and the work-hardening rate to about ±25%. Such inferred constitutive relations are more likely to be reliable if the comparisons are made in regimes within which creep does not significantly influence the behaviour, and in general the timescale of measurement is important.     

Mass balance calculations in copper flash smelting by means of genetic algorithms

This paper presents mass balance calculations using genetic algorithms for copper smelting in an Outokumpu flash furnace. Based on the elemental composition of the copper concentrates being fed to the reactor, the mineralogical composition of the concentrate mixture is adjusted by means of genetic algorithms. The macroscopic mass balance equations for the species entering and leaving the furnace are solved and the compositions and flow rates of matte, slag, and the off-gas stream are computed. Good agreement between the predicted and plant data was obtained in terms of matte and slag flow rates, matte grade, and copper, iron, magnetite, and silica contents in the slag. Predictions are more suitable and faster to obtain with this method than a conventional method in which the mineralogical composition of the feed is not adjusted. Future applications of the formulation are discussed. For more information, contact V.M. Sanchez-Corrales, Universidad de Sonora, Departamento de Ingeniería Química y Metalurgia, Blvd. Luis Encinas y Rosales, Hermosillo, Sonora, 83000, Mexico; +662-259-2105; fax +662-259-2105; e-mail vsanchez@guaymas.uson.mx.     

超声波流量检测中信号处理算法研究

通过对超声波流量测量中回波信号特征的分析，提出了回波自动搜索算法、以及用于时差测量的过零平均算法和插值相关算法，缩短了测量时间，提高了测量精度。通过测量数据说明了算法的有效性，并对两种算法进行了对比分析，并给出了算法的实现步骤。     

基于遗传算法的Al-5%Cu合金电脉冲孕育处理参数优化

以实验为基础,利用神经网络和遗传算法优化Al-5%Cu合金的电脉冲孕育处理工艺参数。神经网络的输入参数为脉冲电压、脉冲时间和电脉冲孕育处理时熔体温度,输出参数是合金凝固组织的晶粒度。在神经网络训练的基础上,采用遗传算法优化神经网络的输入参数。结果表明,神经网络和遗传算法的组合建模获得了较好的优化结果。     

管件液压成形加载路径的多目标优化

在管件液压成形过程中,加载路径对成形过程的影响最为重要。文章给出了一种新的加载路径优化方法,即精英保留非劣排序遗传算法(NSGA-Ⅱ)与成形数值模拟软件集成,实现对加载路径的自动寻优。该方法通过优化算法程序修改加载路径,自动调用数值模拟软件进行分析,在更大的解空间内自动寻找最优方案。文中以某汽车仪表板梁为例,采用该方法对液压成形中的加载路径进行优化分析。结果表明,通过该方法所获取的加载路径较通过人工寻优所获取的加载路径更趋于最优。另外,该方法一次运算能够同时获取多个Pareto最优解,可为加载路径的制订和设计人员的决策,提供更多的选择。     

Validating algorithms for calculation of the shape of a flexible blade

Methods and tools are developed to measure, analyze and compare physical and virtual blade shapes. An application is presented using measured data and the results of two blade shape calculation algorithms. A measuring method has been developed and a set-up for measuring physical blades was built. Tools were implemented to compare and evaluate the calculated and measured shapes. From the analysis of the measured data and the calculated results of the involved algorithms it could be concluded that none of the algorithms used initially could be applied directly for our shape calculations. The developed tools and methods have been found useful for the adaptation and fine-tuning of the algorithms, which is demonstrated in two examples.     

Multi-directional adjacent wave subtraction and shifted time point mapping algorithms and their application to defect visualization in a space tank liner

We propose the multi-directional adjacent wave subtraction (MAWS), shifted time point (STP) mapping and variable time window amplitude (VTWA) mapping algorithms for crack visualization based on our finding that the processing direction of the adjacent wave subtraction with respect to crack orientation can dramatically affect crack visibility. The proposed MAWS, STP and VTWA mapping algorithms were implemented in a laser ultrasonic propagation imaging system and were applied in a nondestructive evaluation of an Al-alloy tank liner for space applications. A crack and void on the fusion zone of a weld were more effectively visualized using the proposed algorithms, and the crack could be visualized regardless of its orientation. The multi-directional processing results of the anomalous wave propagation imaging were visualized as video clips. The STP mapping algorithm, which maps the number of shifted time points to minimize the difference between adjacent waves, was developed to enhance the crack visualization capability of the system. Additionally, the multi-directional VTWA mapping algorithm performed data projection using the residuals of MAWS processing and provided stationary mapping results of crack-induced anomalous waves. The presented results demonstrate that the proposed visualization algorithms are promising techniques that do not overlook unknown crack orientations.     

多维非平稳时间序列在机床主轴故障诊断中的应用

采用ARIMA模型将数控机床主轴故障初期的非平稳时间序列转化成标准平稳时间序列,然后利用多维自回归(AR)模型进行数据处理与趋势预测,并分析了基于多维自回归序列参数估计的Yule-Walker算法以及FPE阶次判定准则.实测数据的计算结果表明:经稳态处理后的多维AR时序模型能够很好地拟合数控机床主轴故障模型,预测的精度符合要求.     

Robust manifold learning with CycleCut

Many manifold learning algorithms utilise graphs of local neighbourhoods to estimate manifold topology. When neighbourhood connections short-circuit between geodesically distant regions of the manifold, poor results are obtained due to the compromises that the manifold learner must make to satisfy the erroneous criteria. Also, existing manifold learning algorithms have difficulty in unfolding manifolds with toroidal intrinsic variables without introducing significant distortions to local neighbourhoods. An algorithm called CycleCut is presented, which prepares data for manifold learning by removing short-circuit connections and by severing toroidal connections in a manifold.