Modelling cloud data using an adaptive slicing approach

In reverse engineering, the conventional surface modelling from point cloud data is time-consuming and requires expert modelling skills. One of the innovative modelling methods is to directly slice the point cloud along a direction and generate a layer-based model, which can be used directly for fabrication using rapid prototyping (RP) techniques. However, the main challenge is that the thickness of each layer must be carefully controlled so that each layer will yield the same shape error, which is within the given tolerance bound. In this paper, an adaptive slicing method for modelling point cloud data is presented. It seeks to generate a direct RP model with minimum number of layers based on a given shape error. The method employs an iterative approach to find the maximum allowable thickness for each layer. Issues including multiple loop segmentation in layers, profile curve generation, and data filtering, are discussed. The efficacy of the algorithm is demonstrated by case studies.     

A virtual prototyping system for rapid product development

This paper describes a virtual prototyping (VP) system that integrates virtual reality with rapid prototyping (RP) to create virtual or digital prototypes to facilitate product development. The proposed VP system incorporates two new simulation methodologies, namely the dexel-based and the layer-based fabrication approaches, to simulate the powder-based and the laminated sheet-based RP processes, respectively. The dexel-based approach deposits arrays of solid strips to form a layer, while the layer-based approach directly forms a complete layer by extruding the slice contours. The layer is subsequently stacked up to fabricate a virtual prototype. The simulation approaches resemble the physical fabrication processes of most RP systems, and are therefore capable of accurately representing the geometrical characteristics of prototypes. In addition to numerical quantification of the simulation results, the system also provides stereoscopic visualisation of the product design and its prototype for detailed analyses. Indeed, the original product design may be superimposed on its virtual prototype, so that areas with dimensional errors beyond design limits may be clearly highlighted to facilitate point-to-point analysis of the surface texture and the dimensional accuracy of the prototype. Hence, the key control parameters of an RP process, such as part orientation, layer thickness and hatch space, may be effectively tuned up for optimal fabrication of physical prototypes in subsequent product development. Furthermore, the virtual prototypes can be transmitted via the Internet to customers to facilitate global manufacturing. As a result, both the lead-time and the product development costs can be significantly reduced.     

STL rapid prototyping bio-CAD model for CT medical image segmentation

This paper presents a simple process to construct 3D rapid prototyping (RP) physical models for computer tomography (CT) medical images segmentation. The use of stereolithography (STL) triangular meshes as a basis for RP construction facilitates the simplification of the process of converting CT images to an RP model. This is achieved by constructing the STL triangular meshes directly from data points without having to draw the curve model first. The grey prediction algorithm is used to sort contour point data in each layer of the medical image. The contour difference detection operation is used to sequence the points for each layer. The 3D STL meshes are then constructed by this proposed layer-by-layer sequence meshes algorithm to build the STL file. Once this STL file is saved, a 3D physical model of the medical image can be fabricated by RP manufacturing, and its virtual reality model can also be presented for visualization. CT images of a human skull and femur bone were used as the case studies for the construction of the 3D solid model with medical images. The STL models generated using this new methodology were compared to commercial computer-aided design (CAD) models. The results of this comparative analysis show that this new methodology is statistically comparable to that of the CAD software. The results of this research are therefore clinically reliable in reconstructing 3D bio-CAD models for CT medical images.     

Adaptive tool-path generation of rapid prototyping for complex product models

Rapid prototyping (RP) provides an effective method for model verification and product development collaboration. A challenging research issue in RP is how to shorten the build time and improve the surface accuracy especially for complex product models. In this paper, systematic adaptive algorithms and strategies have been developed to address the challenge. A slicing algorithm has been first developed for directly slicing a Computer-Aided Design (CAD) model as a number of RP layers. Closed Non-Uniform Rational B-Spline (NURBS) curves have been introduced to represent the contours of the layers to maintain the surface accuracy of the CAD model. Based on it, a mixed and adaptive tool-path generation algorithm, which is aimed to optimize both the surface quality and fabrication efficiency in RP, has been then developed. The algorithm can generate contour tool-paths for the boundary of each RP sliced layer to reduce the surface errors of the model, and zigzag tool-paths for the internal area of the layer to speed up fabrication. In addition, based on developed build time analysis mathematical models, adaptive strategies have been devised to generate variable speeds for contour tool-paths to address the geometric characteristics in each layer to reduce build time, and to identify the best slope degree of zigzag tool-paths to further minimize the build time. In the end, case studies of complex product models have been used to validate and showcase the performance of the developed algorithms in terms of processing effectiveness and surface accuracy.     

An adaptive process planning approach of rapid prototyping and manufacturing

This paper presents an adaptive approach to improve the process planning of Rapid Prototyping/Manufacturing (RP/M) for complex product models such as biomedical models. Non-Uniform Rational B-Spline (NURBS)-based curves were introduced to represent the boundary contours of the sliced layers in RP/M to maintain the geometrical accuracy of the original models. A mixed tool-path generation algorithm was then developed to generate contour tool-paths along the boundary and offset curves of each sliced layer to preserve geometrical accuracy, and zigzag tool-paths for the internal area of the layer to simplify computing processes and speed up fabrication. In addition, based on the developed build time and geometrical accuracy analysis models, adaptive algorithms were designed to generate an adaptive speed of the RP/M nozzle/print head for the contour tool-paths to address the geometrical characteristics of each layer, and to identify the best slope degree of the zigzag tool-paths towards achieving the minimum build time. Five case studies of complex biomedical models were used to verify and demonstrate the improved performance of the approach in terms of processing effectiveness and geometrical accuracy.     

Machine path generation for the SIS process

Because of the differences in the nature of rapid prototyping (RP) processes, there is no standard machine path code for them. Each RP process, based on its characteristics and requirements, uses the standard CAD file format to extract the required data for the process. Selective inhibition of sintering (SIS) is a new layered fabrication method based on powder sintering. Like other RP systems, SIS needs a specialized machine path generator to create an appropriate machine path file. Machine path (i.e., boundary path and hatch path) should produce the printing pattern that enables the SIS machine user to easily remove the fabricated part from the surrounding material. A new machine path algorithm, which generates appropriate boundary and hatch paths for the SIS process is proposed. The new machine path generator provides the ability to process CAD models of any size and complexity, the ability for machine path verification before sending the file to the SIS machine, and the ability to fix the possible STL files disconnection errors. In this system, very large STL files can be processed in a relatively small computer memory. The system has been successfully tested on STL files as large as 200 MB. The generated path files have been used in fabrication of several parts by the SIS process.     

Contour curve reconstruction from cloud data for rapid prototyping

In this study, a method for generation of sectional contour curves directly from cloud point data is given. This method computes contour curves for rapid prototyping model generation via adaptive slicing, data points reducing and B-spline curve fitting. In this approach, first a cloud point data set is segmented along the component building direction to a number of layers. The points are projected to the mid-plane of the layer to form a 2-dimensional (2D) band of scattered points. These points are then utilized to construct a boundary curve. A number of points are picked up along the band and a B-spline curve is fitted. Then points are selected on the B-spline curve based on its discrete curvature. These are the points used as centers for generation of circles with a user-define radius to capture a piece of the scattered band. The geometric center of the points lying within these circles is treated as a control point for a B-spline curve fitting that represents a boundary contour curve. The advantage of this method is simplicity and insensitivity to common small inaccuracies. Two experimental results are included to demonstrate the effectiveness and applicability of the proposed method.     

基于分层制作的三维汉字构建

目前 ,三维汉字图象的构建主要是基于“扫掠”原理 ,即用变化的截面沿汉字笔划中心线进行“扫掠”来形成立体笔划 ,它的主要缺点是难以表达变化丰富的汉字笔划 ,数据量也庞大 ,为此 ,基于快速成型的分层制作原理 ,提出了用二维汉字来构建三维汉字的一种新方法 ,即先将三维汉字笔划视为一些二维汉字笔划层面沿高度方向的叠加 ,然后通过采样二维汉字基本笔划轮廓线点列来构造它的 Voronoi图 ,由此来自动生成它的不同层面的等距线 ,再以这些不同层面的轮廓线作为骨架 ,采用三次 Bezier- B混合样条曲面拟合来形成立体笔划 ,最后将它们组合 ,构成三维汉字 ,并以一个三维汉字的构建实例来说明该算法的有效性 ,构建结果表明 ,该方法能更丰富地表现汉字笔划 ,同时能克服三维汉字构造中的数据量过大和放大处理的失真问题 .     

基于STL文件的快速成型分层算法与毗邻拓扑信息的快速提取

该文研究了实时的快速成型的分层算法,即从CAD模型转换成STL文件后,实时快速求出该模型与水平截面的轮廓线交线,为此,该文提出并建立了三角形网格的毗邻关系索引表,并构造相应的数据结构来表达STL文件的散乱三角形集合中的毗邻拓扑联系,而为了快速建立这种毗邻关系,该文进一步提出建立两套三角形网格的分组表,来缩小三角形网格的毗邻查找范围,为快速确定三角形网格的毗邻关系奠定基础。该文同时分析了该算法的时间与空间复杂度。计算实践表明,基于该文提出的毗邻关系索引表的分层算法能满足快速成型的实时要求。     

Hollowing objects with uniform wall thickness

In rapid prototyping, we can significantly reduce the building time and expensive RP material consumption by building a hollowed prototype instead of a solid model. Presented in the paper is a new method to hollow out solid objects with uniform wall thickness to speed up the part building processes in rapid prototyping systems. To achieve uniform wall thickness, it is necessary to generate internal contours by slicing the offset model of an STL model. Since computing an offset model of an STL model involves many difficulties, this paper proposes a new algorithm that computes internal contours without computing the offset model. The proposed algorithm is efficient and relatively easy to implement, because it employs well-known 2D geometric algorithms, such as planar curve offsetting and tracing innermost curves. Various examples have been tested with implementation of the algorithm, and some examples are presented for illustration.     

NURBS-based adaptive slicing for efficient rapid prototyping

This paper presents slicing algorithms for efficient model prototyping. The algorithms directly operate upon a non-uniform rational B-spline surface model. An adaptive slicing algorithm is developed to obtain an accurate and smooth part surface. A selective hatching strategy is employed to further reduce the build time by solidifying the kernel regions of a part with the maximum allowable thick layers while solidifying the skin areas with adaptive thin layers to obtain the required surface accuracy. In addition, it provides a generalization to the containment problem with mixed tolerances for slicing a part. The article also developed a direct method for computing skin contours for all tolerance requirements. Some case studies are presented to illustrate the developed algorithms and the selective hatching and adaptive slicing strategy. The developed algorithms have been implemented and tested on a fused deposition modeling rapid prototyping machine. Both the implementation and test results are discussed in the paper.     

结合纹理与形状的Tagged MR图像左心室分割算法

分割带标记线核磁共振(tagged MR)图像是左心室运动重建的前提.由于标记线的加载破坏了左心室的轮廓边缘和区域灰度一致性,再加上乳突肌的存在,使带标记线核磁共振图像的左心室内外轮廓分割变得相当困难.在变分框架下,将纹理分类信息与形状统计先验知识引入Mumford-Shah模型中,提出了一种改进的分割带标记线核磁共振图像的左心室内外轮廓的方法.该方法基于支持向量机对S滤波器组提取的纹理特征的分类结果,构造了一种新的图像能量表示;针对乳突肌及边缘断裂现象,引入形状统计先验信息来约束曲线的演化.因为分割过程利用了有监督学习策略,较好地克服了标记线对左心室区域灰度的影响,提高了分割精度.实验结果表明,该方法较以往方法具有更高的分割精度和更好的稳定性.     

Non-uniform deformation of an STL model satisfying error criteria

In this research, a method is presented for generating a deformed model satisfying given error criteria from an STL model in a triangular-mesh representation suitable for rapid prototyping (RP) processes. A deformed model is a non-uniformly modified shape from a base STL model. In developing a family product with various sizes such as a shoe, sometimes prototypes for all sizes should be made using an RP machine. Although an STL model is generated from a solid model, it is well known that creating a non-uniformly modified solid model from a base solid model is very difficult. Generally there are some gaps between surfaces after modification, and stitching the gaps is very difficult. To solve this problem, the authors explored the possibility of generating a deformed STL model directly from a base STL model. This research includes a data structure for modifying the STL model, checking the error of a modified edge compared with the exact non-uniformly scaled curve, checking the error of a modified facet compared with the exact non-uniformly scaled surface, and splitting a facet with an error greater than the allowable tolerance. Using the results of this research, the difficult work of creating solid models to build non-uniformly deformed STL models could be avoided.     

Surface roughness visualisation for rapid prototyping models

When considering the use of rapid prototyping (RP), there are many questions a designer might ask. One such question is “what build orientation should be used to minimise the adverse effects of surface roughness?” At present, this decision is often made in an intuitive way or sometimes overlooked completely. This paper describes a methodology and software implementation that provides the designer with a computer graphics based visualisation of RP model surface roughness. This enables the build orientation to be determined as a result of increased designer knowledge. The surface roughness values were obtained through an extensive empirical investigation of several RP techniques. These are used as the database for a visualisation algorithm that represents varying surface roughness of the RP model as colour shading within a CAD image. The nature of the empirical measurements is analysed and the functionality of the software algorithm is described. Examples are given that demonstrate the use and benefits of the methodology. Finally, conclusions are drawn as to the significance of the work and future research directions are outlined.     

基于水平集的扫描点云简化算法及在人体模型上的应用

简化是计算机图形学的一个重要课题.针对真实性建模技术在图形领域的迅速发展和三维扫描设备的广泛应用,提出一种基于水平集的扫描点简化算法,对高密度的扫描点模型作简化处理,并能解决扫描点模型中普遍存在的重影与空洞问题.该方法具有自动排序特点,并且使筒化结果保留原扫描点模型按层划分的特性.通过指定不同的简化半径,该算法自动生成多分辨率的层次细节模型.实验结果显示,新方法在高简化精度下具有好的保形性,所得模型的误差优于角度简化结果.该方法对于高曲率细节显示的特殊需求可作自适应拓展.简化所得的点模型可通过多边形或曲线、曲面重建.三维人体模型重建工作是服装仿真、计算机动画等方面研究的基础性工作.经简化方法处理所得不同精度的人体模型能作为后续应用的基础.     

数控机床远程智能故障诊断系统设计

为了解决机床远程故障诊断中有线网络布线干涉、设备成本高等问题，同时满足大数据存储、多样化数据接入的需求，提出基于物联网(The internet of things,IoT)无线网络和IoT云平台的故障诊断系统。系统模型设计为4层：采集层、传输层、运算层和应用层。采集层采用基于应用过程的对象连接与嵌入(Object linking and embedding for process control,OPC)和多传感器融合的数据采集方法，获得故障诊断所需数据；传输层基于窄带物联网(Narrow band internet of things,NB-IoT)无线通信技术和IoT云平台，实现数据远程传输、通信和存储；运算层基于BP神经网络在前、专家系统在后的串行反馈控制机制，建立故障诊断算法模型。以机床的主轴伺服系统为实例，分析其故障现象并获得故障样本，对诊断算法模型进行误差仿真分析，预测结果与期望相吻合，验证了该模型的有效性。     

贪心算法优化云数据中心的虚拟机分配策略

如何将云客户端的大量虚拟机均匀的分配到云数据中心的物理主机上执行是一个关键问题.提出了贪心算法优化云数据中心的虚拟机分配策略,首先设计一个用于企业的云数据中心的工作场景,该场景包括三层云计算系统结构,包括用户层、云服务提供者层和云数据中心集合层.用户层用来生成虚拟机的请求集;云服务提供者层通过经典的装箱问题算法完成用户层的大量的虚拟机请求集到底层的云数据中心的分配.然后建立虚拟机分配过程中各种约束因素的数学模型;最后利用贪心算法优化云数据中心之间的虚拟机分配.利用某个企业的大数据中心作为云端测试环境,测试结果表明,经典的最好适应算法Best-Fit-Algorithm具有比较的虚拟机分配效果,云平台的能量消耗比较少,该实验结果对于其他企业构造云数据中心有比较好参考价值.     

Optimum part orientation in Rapid Prototyping using genetic algorithm

Part orientation is an important parameter in the planning of a Rapid Prototyping (RP) process as it directly governs productivity, part quality and cost of manufacturing. This paper reports the design and implementation of a system for obtaining optimum orientation of a part for RP. Developed in a modular fashion, the system comprises of functional modules for CAD model preprocessing, shelling (hollowing), part orientation and optimization. CAD part model in STL format is an input to the system. The oriented CAD model is sliced and hollowed with desired shell thickness. Genetic algorithm based strategy is used to obtain optimum orientation of the parts for RP process. The objective criteria for optimization is considered to be a weighted average of the performance measures such as build time, part quality and the material used in the hollowed model. The developed system has been tested with several case studies considering SLS process.     

Motif analysis for automatic segmentation of CT surface contours into individual surface features

This paper presents a new layer-based technique for automatic high-level segmentation of 3-D surface contours into individual surface features through motif analysis. The procedure starts from a contour-based surface model representing a composite surface area of an object. For each of the surface contours, a relative turning angle (RTA) map is derived. The RTA map usually contains noise and minor features. Algorithms based on motif analysis are applied for extracting a main profile of the RTA map free from background noise and other minor features. All feature points on the extracted profile are further identified from the extracted main profile through further motif analysis. The original contour is thus partitioned into individual segments with the identified feature points. A collection of consecutive contour segments among different layers form an individual 3-D surface feature of the original composite surface. The developed approach using motif analysis is particularly useful for the identification of smooth joins between individual surface features and for the elimination of superposed noise and unwanted minor features.     

基于PSO-ELM算法的三维激光点云处理研究

为找出用于三维激光点云数据的处理方法,本文基于无人机装载激光扫描仪技术,以粒子群算法优化极限学习机(ELM)算法(PSO-ELM),得出最新算法处理点云数据,并与ELM模型计算结果对比,结果表明:PSO-ELM模型最优隐含层个数为50,在此情况下模型精度最高;PSO-ELM算法的处理效果明显更好,其生成的DEM和地形数据可清晰反映研究区域实际地形,证明了该算法的科学性。