Geometrical Reconstruction and CNC Process of Spurious Tympanic Membrane Based on Reverse Engineering

Perforation of tympanic membrane is one of the main reasons for both deafness and dyssaudia.We could improve and restore audition by restoring or replacing the tympanic membrane.So,whether you can make the spurious tympanic membrane successfully is one of the keys to a successful operation.Utilizing CMM (Coordinate Measuring Machine) measurement equipment, we measured tympanic membrane model precisely and digitally.We also analysed the measured data by point to surface and we have successfully reconstructed the CAD model of the spurious tympanic membrane.Using the model we have got,we schemed out the mold of spurious tympanic membrane.In addition,we utilized MasterCAM compiling CNC (Computerized Numerical Con- trol) code and simulating the course of working.Ultimately,we obtained the mold of spurious tympanic membrane.Our research in this article has great significance to the success of spurious tympanic membrane grafting operation.

Slicing Method for Reverse Engineering Based on Image Mosaic

Reverse engineering dealing with images is traditionally based on image processing and contour recognition. A new method is presented based on the combination of sectional slicing with image mosaic. Sectional contours of the target object are generated by colorful liquid or laser scanning, these images from different views are fused into a set of complete cross-sectional images, thereby the whole practical model is reconstructed in 3D space.

MODEL RECONSTRUCTION FROM CLOUD DATA FOR RAPID PROTOTYPE MANUFACTURING

Model reconstruction from points scanned on existing physical objects is much important in a variety of situations such as reverse engineering for mechanical products, computer vision and recovery of biological shapes from two dimensional contours. With the development of measuring equipment, cloud points that contain more details of the object can be obtained conveniently. On the other hand, large quantity of sampled points brings difficulties to model reconstruction method. This paper first presents an algorithm to automatically reduce the number of cloud points under given tolerance. Triangle mesh surface from the simplified data set is reconstructed by the marching cubes algorithm. For various reasons, reconstructed mesh usually contains unwanted holes. An approach to create new triangles is proposed with optimized shape for covering the unexpected holes in triangle meshes. After hole filling, watertight triangle mesh can be directly output in STL format, which is widely used in rapid prototype manufacturing. Practical examples are included to demonstrate the method.

PHYSICS-BASED ILLUMINATION MODEL FOR METAL SURFACE RECONSTRUCTION IN RE

Representation of roughness is introduced and the rationality of applying thephysics-based model in RE is analyzed at first. Then the scattering theory of electromagnetic waveis simplified and deduced to a physics-based model according to the characteristics of the surfaceto be reconstructed in RE. At last, the intensity diagrams of reflected field distribution areprovided to prove the feasibility of the presented model and some spheres are rendered with thismodel.

Geometric Feature Extraction and Model Reconstruction Based on Scattered Data

A method of 3D model reconstruction based on scattered point data in reverse engineering is presented here. The topological relationship of scattered points was established firstly, then the data set was triangulated to reconstruct the mesh surface model. The curvatures of cloud data were calculated based on the mesh surface, and the point data were segmented by edge-based method; Every patch of data was fitted by quadric surface of freeform surface, and the type of quadric surface was decided by parameters automatically, at last the whole CAD model was created. An example of mouse model was employed to confirm the effect of the algorithm.

A New Algorithm for Feature Matching in Reverse Engineering

Feature recognition and surface reconstruction from point clouds are difficulties in reverse engineering. A new surface reconstruction algorithm for slicing point cloud was presented. The contours of slice were extracted. Then, the intersection of two adjacent curve segments in the contour was obtained and curves feature was extracted. Finally, adjacent section contours were matched directly with Fourier-Mellin curve matching method for feature extraction. An example of 3-D model reconstruction shows the reliability and application of the algorithm.

A novel model-based multivariable framework for aircraft gas turbine engine limit protection control

Control technologies are innovated to satisfy increasingly complicated control demands of gas turbine engines.In terms of limit protection control,a novel model-based multivariable limit protection control method,which is achieved by adaptive command reconstruction and multiplecontrol loop selection and switch logic,is proposed in this paper to address the problem of balancing smaller thrust loss and safe operations by comparing with widely-used Min-Max logic.Five different combination modes of control loops,which represent the online control loop of last time instant and that of current time instant,is analyzed.Different command reconstructions are designed for these modes,which is based on static gain conversion of amplitude beyond limits by using an onboard model.The double-prediction based control loop selection and switch logic is developed to choose a control loop appropriately by comparing converted amplitude beyond limits regardless of one or more parameters tending to exceed limits.The proposed method is implemented in a twin-spool turbofan engine to achieve limit protection with direct thrust control,and the loss of thrust is improved by about 30% in comparison with the loss of thrust caused by Min-Max logic when limit protection control is activated,which demonstrates the effectiveness of the proposed method.

Efficient reconstruction of non-simple curves

We present a novel algorithm to reconstruct curves with self-intersections and multiple parts from unorganized strip-shaped points,which may have different local shape scales and sampling densities.We first extract an initial curve,a graph composed of polylines,to model the different structures of the points.Then a least-squares optimization is used to improve the geometric approximation.The initial curve is extracted in three steps:anisotropic farthest point sampling with an adaptable sphere,graph construction followed by non-linear region identification,and edge refinement.Our algorithm produces faithful results for points sampled from non-simple curves without pre-segmenting them.Experiments on many simulated and real data demonstrate the efficiency of our method,and more faithful curves are reconstructed compared to other existing methods.

Triangular Mesh Model Reconstruction from Scan Point Clouds Based on Template

For mesh reconstruction problems of point cloud models which have similar topological structure, a rapid and efficient method is presented to reconstruct triangular mesh surface. Based on projections of point cloud slicing that correspond to template sectional curves, the method constructs topological relevant information among discrete points, which makes unorganized points ordering and builds up optimal approximated B-spline curve, resamples every curve according to its curvature distribution and performes triangular mesh division on it. Finally, surface reconstruction is achieved. The experimental results demonstrate that the surface reconstruction is done as the point cloud hole is filled simultaneously.

Reconstruction of symmetric models composed of analytic curves and surfaces from point cloud

This paper presents a method to reconstruct symmetric geometric models from point cloud with inherent symmetric structure. Symmetry types commonly found in engineering parts, i.e., translational, reflectional and rotational symmetries are considered. The reconstruction problem is formulated as a constrained optimization, where the objective function is the sum of squared distances of points to the model, and constraints are enforced to keep geometric relationships in the model. First, the explicit representations of symmetric models are presented. Then, by using the concept of parameterized points (where the coor-dinate components are represented as functions rather than constants), the distances of points to symmetric models are deduced. With these distance functions, symmetry information, for both 2D and 3D models, is uniformly represented in the process of reconstruction. The constrained optimization problem is solved by a standard nonlinear optimization method. Owing to the explicit representation of symmetry information, the computational complexity of our method is reduced greatly. Finally, examples are given to demonstrate the application of the proposed method.

基于特征匹配的逆向工程模型重建方法

逆向工程(RE)也称反求工程,以实物、样件、软件(包括图样、程序、技术文件等)或影像(图片、照片等)为对象,应用产品设计方法学、系统工程学、计算机辅助技术方法进行系统分析和研究,探索掌握其关键技术,进而开发出同类或更先进产品。从数据采集、数据处理和模型构建3个阶段给出了RE中的模型重建过程。首先基于特征的点云匹配方法进行数据采集,获取物体表面的点云数据,然后采取降噪、平滑等方式进行预处理,最后通过曲面拟合、曲面特征提取和数据拼接完成实物到模型的建模。同时给出了各阶段的通用方法和实际应用的注意事项。RE可快速准确地确定实物的结构特点、内部构造等信息,并为后续设计提供参考。

WP10.5H柴油发动机三维数字模型重构

基于正/逆向混合建模技术对WP10.5H柴油发动机缸盖和缸体进行逆向重构,利用硅胶翻模技术获取发动机内部进、排气道和复杂水道结构的数据,分析了逆向过程中的误差来源,给出了提高模型重构精度的方法,研究结果可为大型复杂零件的模型重构提供参考。

CT用于非人体目标几何体的三维重建

当被扫描物体存在镂空、遮挡和狭小空间时,需要大量图像拍摄或激光扫描工作;利用三维点云构建三角网格时,需要大量人工交互操作,且三维面绘制容易丢失特征信息。为解决上述问题,提出了采用CT对非人体目标几何体进行三维重建,再用体绘制进行显示的方法。基于医用CT对瓷器、陶器、木器和青铜器等材质的工艺品进行三维扫描,直接基于体绘制算法进行三维显示,同时提取CT图像轮廓点实现面绘制建模。结果表明,CT扫描重建精度高、体绘制效果好且人工工作量小、速度快。因此CT扫描及体绘制在非人体目标的三维重建中具有可行性,并且可以提高效率和精度。

舰用倒车汽轮机技术特点及运行过程研究

概要介绍汽轮机的概念与分类,并由此引入其在水面舰船领域的应用。由于汽轮机的结构特点,以及喷嘴和工作叶片的相对位置,在完成安装后,汽轮机的转子只能实现单方向的转动。在水面舰船作机动航行时,汽轮机必须提高倒车功率以提高舰船的机动性,满足航行的需要,保证舰船的航行安全,从而引入倒车汽轮机的定义。重点介绍倒车汽轮机的结构特性、运作过程及工况特点,并将其与能实现反向旋转的柴油机进行对比。除传统的机械式结构外,汽轮机也可与电力推进系统实现搭配,从而提供倒车功率,该类方案则无须配备倒车汽轮机。

古典家具复杂三维曲面数据测量与模型重建研究

本文旨在对古典家具全息三维信息进行数字化保护,以仿古典家具的陈列台座作为逆向建模案例,分析了逆向工程的特点、流程及关键环节,采用三维激光扫描设备对仿古典家具的表面三维数据进行非接触测量,采用逆向工程软件Geomagic Studio对测量数据进行处理,得到较完整的多边形数据模型;以NURBS曲面重建思想应用Solid Works软件进行实体重建,得到参数化实体结构装配模型,经测定,三维模型的尺寸和装配精度均符合样品原型,有利于对古典家具全息三维信息的数字化保护。

基于逆向工程的摩托车挡泥板的快速成型

以挡泥板为研究对象,运用逆向工程和快速成型技术,详细展示了其整个重构设计和快速成型过程。通过三维激光扫描设备进行实物数据采集,然后将点云数据导入Geomagic wrap软件进行处理,接着,利用Geomagic DesignX软件进行模型重构,最终,通过3D打印技术得到了与原件契合度较高的挡泥板样品。采用逆向工程设计的挡泥板能够显著缩短产品的设计研发周期,提高效率。本文的研究结果对其他产品的设计研发具有一定的参考价值。

基于逆向工程的航空发动机叶片三维重建模型构建

为精准控制航空发动机叶片型面数据,设计出更符合实际应用需求的发动机叶片,针对基于逆向工程的航空发动机叶片三维重建模型构建方法展开研究;按照逆向工程原理,采集三维数据样本,并根据误差修正条件,定义发动机叶片三维数据的拓扑关系,从而分析三维数据样点的邻域形式,实现航空发动机叶片三维数据的邻域构建;实施对三维数据的点云拼接处理,遵循三维拟合原则,提取完整的发动机叶片边界,再根据三维重建节点配置需求,确定重建四元数的取值范围,推导具体的重建模型表达式,完成基于逆向工程的航空发动机叶片三维重建模型的构建;实验结果表明,上述模型的应用可以保证建模时标志点、三维重建后标志点间的坐标误差不超过0.5 mm,符合精准构建航空发动机叶片的实际应用需求。

一种兼具强干扰背景噪声特征的轴承故障数据模拟生成方法

在对燃气涡轮发动机的轴承故障进行智能诊断时,存在着智能诊断难度大、实测案例稀缺等问题。为此,在考虑了非线性接触碰撞激励、发动机薄壁机匣支承结构复杂传递特性的基础上,提出了一种兼具发动机强干扰背景噪声特征的轴承故障数据模拟生成方法,并将其与实验数据进行了对比,验证了两者故障特征的一致性。首先,建立了典型发动机高压转子-轴承系统多体接触瞬态动力学模型,通过模拟故障轴承复杂接触碰撞过程,获取了非线性轴承故障激励力;其次,基于该发动机机匣高保真有限元模型,计算了故障轴承位置到测点的脉冲激励响应,并结合模态振型探明了发动机机匣的复杂传递特性;然后,在此基础上提出了基于非线性轴承故障激励与复杂传递的机匣测点信号时域离散卷积的重构方法,模拟了轴承故障在机匣测点的关键机理特征,并进一步融合了健康发动机的实测振动数据,构造了包含工作状态气流激振、非线性干扰等因素影响下的轴承故障仿真数据;最后,为了验证仿真数据故障特征的合理性,利用基于特征传递机理的包络解调方法提取了微弱轴承故障特征,并将其与发动机实测轴承故障实验数据进行了比较。研究结果表明:发动机轴承故障仿真数据与实验数据时域特征相似,二者包络谱中的故障特征频率误差小于1%,且故障特征频率及其倍频幅值大小相近,证明发动机轴承故障的仿真数据故障特征具有一定的合理性,可为基于机匣测点的发动机轴承故障特征提取、智能诊断算法训练等提供支撑。

反求工程CAD建模技术研究

将设计思想或实物原型迅速、直接、精确地转变为可以再加工的 CAD模型 ,是产品创新设计和快速原型制造面临的关键技术 .综合国内外反求工程 CAD建模的研究和应用现状 ,分析了反求工程 CAD建模问题的特点和需要进一步解决的主要问题 ,讨论了目前工程界普遍采用的反求工程 CAD建模技术与思路 。

基于逆向工程的D型打结器重构与运动仿真

打结器是方草压捆机的关键核心部件之一,直接影响打捆机的成结效率和捆形质量。以D型打结器为研究对象,基于逆向工程技术对其进行三维重构,进而对重构零件的关键工作曲面进行了偏差分析,发现所有关键工作面90%以上的区域达到了精确等级以上。基于Solidworks软件实现了重构部件装配,并进行了运动仿真研究,获取了卡线轮、打结嘴、脱绳杆角速度和驱动齿盘角位移数据,分析了卡线轮、打结嘴、脱绳杆与捆绳打结运动关系,为优化D型打结器提供了基础数据。