Rapid surface reconstruction from a point cloud using the least-squares projection

A new approach for the rapid and robust surface reconstruction from a point cloud is presented based on the distance field and the least-squares projection (LSP) algorithm. This novel approach works directly on the point cloud without any explicit or implicit surface reconstruction procedure. First, a coarse base polygonal model was created directly from the distance field for the given point cloud through the iso-surface extraction. After acquiring a rough base polygonal model, we obtain a quality polygonal model through the iterative refinement and least-squares projection which projects current working polygonal model onto the point cloud in a least-squares sense. The main contribution of this work is the robust and fast surface reconstruction from randomly scattered 3D points only without any further information. We demonstrate the validity and efficiency of this new approach through a number of application examples.     

Evaluation of point cloud registration using Monte Carlo method

Supervision and control are one of the most important steps while executing a construction project and their automation remains an area of growing interest. LiDAR systems provide accurate point clouds with geometric information that can help to improve the automation of survey control. Alignment of the point clouds acquired from a number of scan positions is a fundamental issue regarding surveying accuracy and is frequently carried out in two steps: coarse and fine registration. Fine registration can be achieved automatically by means of an Iterative Closest Point (ICP) procedure. This work presents a Monte Carlo based method to quantify the reliability of a coarse registration step that would enable the automation of the alignment. The method consists of verifying the tolerance of a particular ICP implementation to coarse registration errors. Results show that the ICP alignment used works fine when coarse registration errors are lower than 18° for rotations and 1 m for translations. These values were similar for four case studies analysed. Quantifying these limits is crucial for operations such as robotic stop & go surveying, where coarse alignment is based on Simultaneous Location and Mapping (SLAM) and fine alignment is achieved through ICP.     

区域逻辑运算实现复杂形状目标区域孔径填充

本文研究了图像的区域编码和区域逻辑运算，并利用此运算在保持目标轮廓不变的情况下实现了目标区域孔径的填充。研究结果表明，该算法可以广泛应用于复杂轮廓目标区域的填充和图像检测。     

Statistical point cloud model to investigate measurement uncertainty in coordinate metrology

In this work an approach to investigate measurement uncertainty in coordinate metrology is presented, based on fitting Gaussian random fields to high-density point clouds produced by measurement repeats. The fitted field delivers a depiction of the spatial distribution of random measurement error over a part geometry, and can incorporate local bias information through further measurement or with the use of an external model to obtain a complete, spatial uncertainty map. The statistical model also allows the application of Monte Carlo simulation to investigate how error propagates through the data processing pipeline ultimately affecting the determination of features of size and the verification of conformance to specifications. The proposed approach is validated through application to simulated test cases involving known measurement error, and then applied to a real part, measured with optical and contact technologies. The results indicate the usefulness of the approach to estimate measurement uncertainty and to investigate performance and behaviour of measurement solutions applied to the inspection and verification of industrial parts. The approach paves the way for the implementation of automated measurement systems capable of self-assessment of measurement performance.     

基于自由曲面点云的RPM自适应分层研究

针对由激光三维扫描设备获取的点云数据及其后续RPM操作,提出基于栅带的自由曲面点云自适应分层方法.以栅带为基元,将点云投影栅带化,从中获取特征点集,结合相邻栅带距离最小值点找寻构建层间轮廓.定义投影点云栅带面积比为表面误差,建立其与堆层厚度的关系,通过表面误差逼近定值最终确定堆层厚度.经实例验证,此方法得到的分层模型充分满足RPM的要求.     

浊点萃取在原子吸收光谱分析中的应用进展

浊点萃取(Cloud Point Extraction,CPE),是基于非离子型表面活性剂溶液的浊点现象和胶束增溶效应而建立的一种萃取技术。大部分金属螯合物具有微溶于水的特性,与表面活性剂的疏水基团结合,富集于小体积的富胶束相内,亲水性物质仍留在水相中。再经两相分离,即可实现样品中的目标化合物的分离和富集。浊点萃取法的优点:避免使用对人体有害的挥发性有机溶剂,不污染环境,安全;试剂消耗少,经济;减少萃取时间,快速高效;操作比较简便;对各种分析物具有高的萃取效率,富集倍数大;易于与仪器分析方法联用等。浊点萃取是分离和富集痕量金属离子的有效方法,是一种有发展前途的环境友好的分离富集技术。     

On-line three-dimensional point cloud data extraction method for scan-tracking measurement of irregular surface using bi-Akima spline

Point cloud data extraction is an important process in scan-tracking measurement. In this paper, a new method of on-line three-dimensional point cloud data extraction for scan-tracking measurement is proposed for reducing extremely dense sampled data while maintaining data accuracy during the real-time scan-tracking measuring process. It is inspired from sketch paintings: First outlining the broad contour of the curve and then revising local details till the interpolated curve satisfies the required accuracy. This method adopts bi-Akima spline interpolation for connecting acquired points in NC machining or for point data fitting in reverse engineering. It can reduce efficiently the amount of point data with a smaller data reduction ratio and a smoother machined/fitted surface than conventional three-dimensional chordal method.     

反求工程中点云数据的曲线拟合技术

针对反求工程中的激光随机扫描所产生的散乱点云数据,提出一种曲线拟合方法。该方法能有效地对点云数据进行三角剖分、精简、平滑去噪处理等操作,并能最终得到满足要求的拟合曲线。     

曲面重构中散乱点云数据曲率估算算法的研究

获取测量点云数据的几何特征信息是曲面重构的基础,估算数据点方向矢量和曲率是点云数据处理中必须面对的问题。这里针对散乱测量数据点云,以局部数据点协方差矩的最小特征向量作为数据点的方向矢量,并根据实际测量情况,对基于二次曲面拟合的数据点曲率估算算法进行了改进。对实际测量点云数据,能够较准确地估算出点云方向矢量和曲率,并能形象显示出数据点云的曲率分布。     

A robust approach to edge detection of scanned point data

In reverse engineering, segmentation is used to divide a point data set into subsequent regions according to its shape. It is vital for interpretation of discrete scanned data since surface reconstruction can be accomplished one-by-one on a given region. Edge detection is crucial to the segmentation process. The level of edge detection depends on the complexity of the part, and it determines the eventual success or failure of the reverse engineering (RE) process. This paper proposes a novel approach to the edge detection of 3D points based on a region growing technique. The proposed algorithm consists of two parts. First, polygonal meshes are generated to the scanned point data using the Delaunay triangulation algorithm. Second, the normal vector and the area of a polygonal mesh are checked to find boundary meshes using cost criteria (angle criterion and area criterion) based upon a region growing technique. The region growing technique aggregates meshes into a region until the area of aggregated meshes reaches an area threshold from a series of seed meshes. The proposed edge detection method is found to be effective when compared with other methods.     

The development of a technique for 3D complex surface reconstruction from unorganized point cloud

In this paper, we propose a new neural network based on our two-level adaptive hierarchical clustering algorithm. The algorithm is to manage unorganized points, so that the triangular mesh models can be correctly obtained by applying the triangular mesh creation algorithm. We also develop adaptive self-flipping triangle edges to improve triangular mesh structure. Only one parameter, the maximal edge length of triangle, is needed in the neural network. The proposed two-level consists of the first level for clustering the cloud of points that has same order of the maximal edge length into a same cluster and the second level for generating triangular surface model or drape surfaces over the points of the same cluster. The normal vector for the generated triangular 3D surface model can be obtained from the second level. This helps to generate the STL file or stereolithography format. From the experimental results it can be shown that the proposed method is very effective for clustering unorganized point clouds for generating a triangular mesh of complex surfaces.     

Acquisition of point cloud in CT image space to improve accuracy of surface registration: Application to neurosurgical navigation system

Journal of Mechanical Science and Technology - One important technique of surgical navigation is surface registration that matches coordinates in two different spaces. We proposed a novel method to...     

Combustion and emission characteristics of HCNG in a constant volume chamber

Finding an alternative fuel and reducing environmental pollution are the main goals for future internal combustion engines. Hydrogenmethane (HCNG) is now considered an alternative fuel due to its low emission and high burning rate. An experimental study was carried out to obtain fundamental data for the combustion and emission characteristics of pre-mixed hydrogen and methane in a constant volume chamber (CVC) with various fractions of hydrogen-methane blends. A pre-mixed chamber was used to obtain a good mixture of these gases. Exhaust emissions were measured using a Horiba exhaust gas analyzer for various fractions of hydrogen-methane blends. The results showed that the rapid combustion duration was shortened, and the rate of heat release elevated as the hydrogen fraction in the fuel blend was increased. Moreover, the maximum mean gas temperature and the maximum rate of pressure rise also increased. These phenomena were attributed to the burning velocity, which increased exponentially with the increased hydrogen fraction in the fuel blend. Exhaust HC and CO₂ concentrations decreased, while NO_X emission increased with an increase in the hydrogen fraction in the fuel blend. Our results could facilitate the application of hydrogen and methane as a fuel in the current fossil hydrocarbon-based economy and the strict emission regulations in internal combustion engines.     

叶片机器人砂带磨抛点云匹配算法优化

为解决机器人磨抛路径中工件坐标系难以计算的问题及校正工件装夹误差,将三维点云配准技术应用到叶片机器人砂带磨抛系统中。由三维激光扫描仪扫描工件型面获得工件点云,采用基于主成分分析(PCA)的全局配准算法和改进的迭代最近点(ICP)算法完成了扫描点云和工件模型离散点云间以及不同工件扫描点云间的匹配,以获取工件坐标系和校正工件装夹误差。相关仿真和试验结果表明,优化后的算法在匹配速度与精度上有了长足改进,且加工后产品精度和质量都能满足实际加工要求。     

Predicting distribution of time to degradation limit using a weighted approach

One of the key elements in condition-based maintenance is to predict the distribution of time to a pre-specified degradation limit based on the observed degradation paths. The prediction accuracy strongly depends on the method to fit the observed degradation paths to a mean degradation model. Since the recent observations contain more information about the future degradation trend than the earlier observations, a weight function can be used to represent the importance of an observation. As such, the prediction accuracy can be improved through using a weighted parameter estimation method. A key issue with the weighted method is to appropriately specify the form of the weight function and its parameters. This paper aims to address this issue. We adopt the Gaussian kernel function with parameters mu and sigma as the weight function. The mu is set at the last observation time and the value of sigma is optimally determined using a cross-validation approach. The appropriateness and usefulness of the proposed approach are illustrated by a real-world example.     

An approach for reduction of the volume loss in the rigid-plastic FEM using two-step updating procedure

The volume loss, as a direct consequence of the geometry updating procedure used in the conventional penalty rigid-plastic finite element method (RPFEM), is primarily caused by the application of the widely used forward Euler time integration method. In order to decrease this undesired consequence, the combination of the two-step Adams-Bashforth time integration method and the volumetrically elastic and deviatorically RPFEM is proposed as a new approach. The cylinder upsetting process was simulated using in-house finite element code. The results of simulations, obtained for the various levels of friction factors and height reductions, show that the proposed method gives a significantly lower volume loss. Also, the results of the friction factor determination procedure utilising the ring compression test for three lubrication conditions demonstrate the capabilities of the proposed method.     

Scheduling decisions in FMS using a heuristic approach

The paper deals with the multilevel scheduling decisions of a Flexible Manufacturing System (FMS) to generate realistic schedules for the efficient operation of the FMS. The primary concern of an Operations Management System (OMS) for a FMS is production scheduling, Material Handling System (MHS) scheduling, Automated Storage/Retrieval System (AS/RS) operation and control and tool management. Scheduling is a critical issue and determines how efficiently the production resources are utilised and how the selected parts are affected in the system. In this paper, the integrated scheduling of FMS, namely, the production scheduling conforming with the MHS scheduling, is addressed. An enumerative heuristic is used, namely Giffler and Thompson, which is an evolutionary combining a Genetic Algorithm (GA) and a stochastic neighborhood search technique using a Simulated Annealing (SA) algorithm is employed.A. Noorul Haq received his PhD in Manufacturing Management from the Indian Institute of Technology (IIT), New Delhi, India, a Master of Engineering degree from Madras University, and a Bachelor of Engineering degree from Annamalai University, India. He is currently an assistant professor in the Department of Production Engineering, Regional Engineering College, Tiruchirappalli 620015, India. His research interests include aggregate production planning, facility layout and scheduling and optimisation techniques.T. Karthikeyan received his Master's degree from Bharathidhasan University. Currently, he is a research scholar in the Department of Production Engineering, Regional Engineering College, Tiruchirappalli 620015, India. His research interests includes facility layout, FMS and simulation.M. Dinesh received his bachelor's degree in engineering from Bharathiar University, India and is currently working on his master's degee in engineering in the Department Of Production Engineering, Regional Engineering College, Tiruchirappalli 620015, India. His current research interests are in optimisation techniques, facility layout and scheduling.     

Program-combinatorial approach to solving problems of error-free readout of random point images

A novel approach is proposed for solving probability problems arising in studying reliability of readout of random point structures. The essence of this approach is based on combining specialized program-analytical and discrete-combinatorial methods of research seldom used in academic practice. The efficiency of the proposed approach is demonstrated by an example of solving a particular problem that involves two-threshold readout of random point images.     

An improved closed-form solution to interfacial stresses in plated beams using a two-stage approach

Shear stress and normal stress in the thickness direction at interfaces (referred to as interfacial shear and transverse normal stresses, respectively, hereafter) have played a significant role in understanding the premature debonding failure of beams strengthened by bonding steel/composite plates at their tension surfaces. Due to the occurrence of dissimilar materials and the abrupt change of cross-section, the stress distribution at plate ends becomes singular and is hence considerably complicated. Extensive experimental and analytical analyses have been undertaken to investigate this problem. Large discrepancies have been found from various studies, particularly from experimental results due to the well-acknowledged difficulty in measuring interfacial stresses. Numerical analyses, e.g. 2-D or 3-D finite-element analysis (FEA), may predict accurate results, but they demand laborious work on meshing and sensitivity analysis. Analytical solutions, in particular those in a closed form, are more desirable by engineering practitioners, as they can be readily incorporated into design equations. This paper reports an improved closed-form solution to interfacial stresses in plated beams using a two-stage approach. In this solution, beams and bonded plates can be further divided into a number of sub-layers to facilitate the inclusion of steel bars or multiple laminae. Thermal effects may also be considered by using equivalent mechanical loads, i.e. equivalent axial loads and end moments. Numerical examples are presented to show interfacial stresses in concrete or cast iron beams bonded with steel or FRP plates under mechanical and/or thermal loads. The effect of including steel reinforcements with various ratios in the RC beam on interfacial stresses is also investigated. Compared with previously published analytical results, this one improves the accuracy of predicting the transverse normal stresses in both adhesive-beam and plate-adhesive interfaces and the solution is in a closed form.     

点云频域配准的双目双线结构光列车轮对检测

针对单线结构光测量因范围有限以及遮挡等原因而无法检测整个车轮的轮缘及踏面的问题,提出了一种列车轮对双目双线结构光检测方法。该方法采用两组双线结构光传感器进行测量和数据采集。在两传感器产生的点云进行配准的过程中使用截面点云数据还原点云矩阵,然后对其进行傅里叶变换,在计算旋转角度时先进行极坐标转换,最后求取两矩阵的互功率谱,从而得到点云的旋转和平移矩阵。在此过程中考虑到点云噪声的存在,将辛格函数近似代替无噪声的互功率谱傅里叶反变换,从而确定在频域配准时噪声对配准参数的确定并无影响。接着采用相对值比较的算法和主成分分析拟合基准平面,对轮对直径方向进行标定。利用标定值对扫描数据进行处理,得出包括车轮直径、车轮滚动圆径向跳动等对尺寸参数。实验表明:点云频域配准的双目双线轮对检测技术对车轮直径的测量尺寸误差≤±0.05mm,车轮端跳的测量误差≤±0.06mm,车轮径跳的测量误差≤0.04mm。与标准轮对检测数据相比可知,该系统满足轮对检测精度的要求。