Design reuse oriented partial retrieval of CAD models

As a huge number of 3D CAD models is generated each year, retrieval of 3D CAD models is becoming more and more important for achieving design reuse. However, the existing methods for partial retrieval of 3D CAD models are very few and far from the requirements of design reuse. In this paper, we present an approach to partial retrieval of 3D CAD models for design reuse. The criteria for determining whether a subpart of 3D CAD models is reusable for design is defined first. Based on the criteria defined, all the design reusable subparts involved in the 3D CAD models in the library are automatically extracted and stored in the library as reference models. Moreover, each design reusable subpart in the library is represented by all its local matching regions in a hierarchical way so as to support multi-mode partial retrieval. In our approach, three partial retrieval modes including normal retrieval, exact retrieval and relaxed retrieval are defined to meet various partial retrieval requirements of design reuse such as the incomplete and vague queries during the early design stage. And the multi-mode partial retrieval is achieved by performing multi-mode matching and similarity assessment between the query and the design reusable subparts in the library indexed by bitmap. Experimental results are presented to demonstrate the effectiveness of the approach.     

A flexible and effective NC machining process reuse approach for similar subparts

NC machining process reuse is widely accepted as an effective strategy for engineers to generate the process plan with less time and lower cost. However, there has been very little research on how to reuse the NC machining process of similar subparts. As a result, most reusable NC machining process still has to remain in the repository as tacit knowledge, which can easily get lost due to oblivion. This paper proposes a novel NC machining process reuse approach for similar subparts in which existing NC machining process cases are described in association with machining features. First, a feature-based parameter-driven model is established to formalize the links between information imbedded in the machining feature and the parameters of cutting tools, drive geometries, and machining strategies. Then, the NC process parameter-driven characteristic of similar feature is revealed from the perspective of machining geometry, machining precision of the feature, and cutter geometry. Moreover, an NC process reusability assessment approach of similar pocket/subpart is presented using the pocket’s medial axis transform. Finally, the NC machining process inheritance mechanisms are explored to implement the NC machining process reuse automatically and efficiently. A prototype system based on CATIA has been developed to verify the effectiveness of the proposed approach.     

基于网络本体语言的三维计算机辅助设计主模型相似性计算方法

为了提高三维计算机辅助设计(CAD)模型重用效率,针对当前三维模型检索系统中语义表达不足问题,提出了一种基于网络本体语言(OWL)表示模型语义的相似性计算方法。首先,将三维CAD产品主模型转化成以概念属性特征为基础语义对象的结构化表示模型;然后,从OWL表示模型中提取用于评价两个模型相似性的特征语义信息,构建可量化的相似元集,借助子图同构思想和Tversky算法给出了一种加权相似性计算方法;最后,通过实例验证了所提方法的有效性和可行性。实验的定量评价结果表明,该评价基准从对象本身转为两个对象特性的语义描述,能够客观反映两对比模型的相似程度。     

3D CAD model matching from 2D local invariant features

The matching of particular types of CAD models to existing physical models can provide invaluable support to the process of CAD design and reuse. To meet the demand for fast and robust algorithms to detect predefined models in database, an local invariant model matching approach is proposed in this paper. It first maps the 3D CAD model to 2D principal image plane by its first two principal components, and then finds affine invariant key points in the 2D image. The CAD model matching problem is implemented as key points matching. Experimental results show the proposed 3D model retrieval method performs fairly well in retrieving similar models from a database of 3D CAD models.     

New methods of creating MBD process model: On the basis of machining knowledge

Traditional machining process planning, which passes manufacturing information through 2D drawing, fails to meet the requirement of current 3D manufacturing environment. Thus, model based definition technology, which uses 3D technology to upgrade the current manufacturing capacity, comes into being. This paper focuses on the creation methods of 3D machining process model. In the first place, the relation between machining knowledge and 3D modeling knowledge has been analyzed, establishing machining ontology and modeling ontology. Then, forward creation method and reversed creation method of machining-knowledge-based 3D process model are proposed. In forward creation method, to drive 3D modeling with machining knowledge, process model is created in commercial CAD platform with modeling ontology transferred from machining ontology for knowledge reasoning through the decision tree constructed from training set and test set. Reversed creation method is established by identifying and suppressing the volumetric machining features and surface machining features after building attributed adjacent graph of process model, and the machining knowledge contained in 3D process model is extracted for subsequent reuse. Finally, the validity of this method is verified with the proposed prototype system.     

Saliency‐Preserving Slicing Optimization for Effective 3D Printing

We present an adaptive slicing scheme for reducing the manufacturing time for 3D printing systems. Based on a new saliency‐based metric, our method optimizes the thicknesses of slicing layers to save printing time and preserve the visual quality of the printing results. We formulate the problem as a constrained ?₀ optimization and compute the slicing result via a two‐step optimization scheme. To further reduce printing time, we develop a saliency‐based segmentation scheme to partition an object into subparts and then optimize the slicing of each subpart separately. We validate our method with a large set of 3D shapes ranging from CAD models to scanned objects. Results show that our method saves printing time by 30–40% and generates 3D objects that are visually similar to the ones printed with the finest resolution possible.     

基于三维实体特征的机械零件搜索引擎设计

随着各种三维CAD系统在产品设计和制造领域的普及应用,基于内容的三维模型检索技术应运而生。介绍了三维模型搜索引擎的发展概况,三维模型搜索引擎的关键技术。着重介绍三维实体模型中的归一化,特征提取,相似性比较的算法。     

三维CAD曲面模型距离-曲率形状分布检索算法

产品三维CAD模型检索对实现产品设计信息的有效重用具有重要意义和作用.针对在工程应用中存在大量含有曲面的产品,提出一种基于距离-曲率形状分布的三维CAD曲面模型检索算法.首先在模型表面随机取点,计算出所取点的曲率以及该点到模型质心的距离;然后以模型质心为球心,统计处在不同半径球壳间所取随机点的曲率分布,分别以球壳半径和曲率为坐标轴构建距离-曲率平面网格,并统计每个网格中随机点出现的频次,从而形成距离-曲率矩阵;最后利用特定的规则计算矩阵的相似值,用该值衡量2个模型的相似程度,实现模型的相似性检索.实验结果表明,文中算法的检索性能比传统的形状分布算法有较大提高,尤其适用于自由曲面模型的检索.     

Thesaurus-based 3D Object Retrieval with Part-in-Whole Matching

Research in content-based 3D retrieval has already started, and several approaches have been proposed which use in different manner a similarity assessment to match the shape of the query against the shape of the objects in the database. However, the success of these solutions are far from the success obtained by their textual counterparts. A major drawback of most existing 3D retrieval solutions is their inability to support partial queries, that is, a query which does not need to be formulated by specifying a whole query shape, but just a part of it, for example a detail of its overall shape, just like documents are retrieved by specifying words and not whole texts. Recently, researchers have focused their investigation on 3D retrieval which is solved by partial shape matching. However, at the extent of our knowledge, there is still no 3D search engine that provides an indexing of the 3D models based on all the interesting subparts of the models. In this paper we present a novel approach to 3D shape retrieval that uses a collection-aware shape decomposition combined with a shape thesaurus and inverted indexes to describe and retrieve 3D models using part-in-whole matching. The proposed method clusters similar segments obtained trough a multilevel decomposition of models, constructing from such partition the shape thesaurus. Then, to retrieve a model containing a sub-part similar to a given query, instead of looking on a large set of subparts or executing partial matching between the query and all models in the collection, we just perform a fast global matching between the query and the few entries in the thesaurus. With this technique we overcame the time complexity problems associated with partial queries in large collections.     

Topology based 2D engineering drawing and 3D model matching for process plant

Process plant models mainly include 3D models and 2D engineering drawings. Matching calculation between these CAD models has wide applicability in model consistency check and retrieval. In process plant, engineering design standards make 2D engineering drawing and 3D model differ in geometry, proportion and structure, leading to the inapplicability of current shape-feature based matching approaches. Since connection relationships between components are the core of a process plant, a topology based algorithm is proposed. Firstly, by exploiting components as vertices and relationships as edges, both 2D engineering drawing and 3D model are preprocessed into graph structures. Then each model’s relationship types are extracted from the graph. Finally, regarding the extracted relationship types as primary feature, feature similarity is calculated to measure the matching degree between their corresponding models. The proposed algorithm is geometric deformation invariant. Experiments with industrial applications are presented, which demonstrates the effectiveness and feasibility of the proposed algorithm.     

三维模型的基因匹配式检索方法研究

为了提高基于内容的3D模型检索效率,提出了一种通过基因匹配进行三维模型检索的方法。CAD底层的几何体API及拓扑API作为结构基因和协调基因构成三维模型基因组。基因组相似度主要是指等同基因块的数量、所有结构基因相似度的平均值。将排列次序相同的一系列基因符号串定义为基因块,基因块对应于产品结构的形状特征,基因块的甄别采用的是串模式匹配算法;结构基因相似度是基因欧氏距离的线性函数,采用基因遍历算法实现。参照目标基因组计算待评价基因组的相似度,相应的实例试验演示了这种三维模型检索方法的有效性。     

基于区域分割的三维自由曲面相似性评价算法

为了在工程应用中检索已有的三维CAD模型,以便重用相应零件的设计信息,节省设计和加工成本,提出一种基于曲面分割技术的CAD自由曲面相似性评价算法.依据曲面的曲率将自由曲面分割成具有相对固定曲率特征的不同区域;对每个分割得到的区域用一个7维向量表达其形状的几何特征和拓扑特征,一个自由曲面形状特征即可通过各分割区域所对应的7维向量组成的向量组表达;将该向量组作为自由曲面的形状描述子,2个自由曲面的相似性可通过相对应的形状描述子间的相似性表达.在评价2个曲面形状描述子的相似性时,将描述子中的每个向量看成是一个带有属性的节点,2个形状描述子所对应的2组属性节点可看成是一个二分图,2组属性节点间相应节点距离看成是二分图的权值,并利用赋权二分图最优匹配的算法求出2组属性节点的相似性,实现2个自由曲面之间的相似性评价.实验结果表明,该算法是有效、可行的.     

基于UG的采煤机防爆盖板三维标注及数控工艺研究

随着三维CAD技术的发展,产品制造信息在三维模型和二维图纸之间的反复传递,严重影响了产品制造信息的正确、快速传递。基于三维产品制造信息技术,以采煤机防爆盖板为例,在UG NX10.0中建立了防爆盖板的三维模型并进行了三维标注,设计了加工工艺路线,规划了数控加工刀具轨迹,进行了加工仿真,验证了数控加工的正确性,在此基础上完成了采煤机防爆盖板的三维工艺式设计。该研究对基于模型定义的数字化设计与制造研究,实现制造业信息化具有重要意义。     

A deep learning approach to the classification of 3D CAD models简

Model classification is essential to the management and reuse of 3D CAD models. Manual model classification is laborious and error prone. At the same time, the automatic classification methods are scarce due to the intrinsic complexity of 3D CAD models. In this paper, we propose an automatic 3D CAD model classification approach based on deep neural networks. According to prior knowledge of the CAD domain, features are selected and extracted from 3D CAD models first, and then pre-processed as high dimensional input vectors for category recognition. By analogy with the thinking process of engineers, a deep neural network classifier for 3D CAD models is constructed with the aid of deep learning techniques. To obtain an optimal solution, multiple strategies are appropriately chosen and applied in the training phase, which makes our classifier achieve better per-formance. We demonstrate the efficiency and effectiveness of our approach through experiments on 3D CAD model datasets.     

Integration of product design,process planning,scheduling, and FMS control using XML data representation

An efficient model for communications between CAD, CAPP, and CAM applications in distributed manufacturing planning environment has been seen as key ingredient for CIM. Integration of design model with process and scheduling information in real-time is necessary in order to increase product quality, reduce the cost, and shorten the product manufacturing cycle. This paper describes an approach to integrate key product realization activities using neutral data representation. The representation is based on established standards for product data exchange and serves as a prototype implementation of these standards. The product and process models are based on object-oriented representation of geometry, features, and resulting manufacturing processes. Relationships between objects are explicitly represented in the model (for example, feature precedence relations, process sequences, etc.). The product model is developed using XML-based representation for product data required for process planning and the process model also uses XML representation of data required for scheduling and FMS control. The procedures for writing and parsing XML representations have been developed in object-oriented approach, in such a way that each object from object-oriented model is responsible for storing its own data into XML format. Similar approach is adopted for reading and parsing of the XML model. Parsing is performed by a stack of XML handlers, each corresponding to a particular object in XML hierarchical model. This approach allows for very flexible representation, in such a way that only a portion of the model (for example, only feature data, or only the part of process plan for a single machine) may be stored and successfully parsed into another application. This is very useful approach for direct distributed applications, in which data are passed in the form of XML streams to allow real-time on-line communication. The feasibility of the proposed model is verified in a couple of scenarios for distributed manufacturing planning that involves feature mapping from CAD file, process selection for several part designs integrated with scheduling and simulation of the FMS model using alternative routings.     

Similarity assessment of 3D mechanical components for design reuse

Duplicate designs consume a significant amount of resources in most new product development. Search of similar parts for a given query part is the key to avoid this problem by facilitating design reuse. Most search algorithms convert the CAD model into a shape signature and compute the similarity between two models according to a measure function of their signatures. However, each algorithm defines the shape signature in a different way, and thus has its own limitations in discriminating 3D parts. This paper proposes a search scheme that successfully complements various shape signatures in similarity assessment of 3D mechanical components. It considers form-feature, topological, and geometric information in component comparison. Such an integrated approach can effectively solve the feature intersection problem, inherited in any feature-based approaches, and capture the user's intent more precisely in the search, which geometry-based methods fail to accomplish. We also develop a set of algorithms that performs the component comparison in a polynomial time. The proposed scheme is implemented in a product design environment consisting of commercial CAD and PDM systems. The result demonstrates the practicality of this work in automatic search of similar mechanical components for design reuse.     

Indexing and retrieval in machining process planning using case-based reasoning

To reduce the manufacturing time of a product, one effective way to develop a machining process plan for a new part is to retrieve a relevant case of process planning similar to a new desired part and then adapt the retrieved case to meet the new requirements. This paper proposes a mechanism for retrieval of process planning cases. The core of the retrieval mechanism contains: (1) a feature-based representation of a part and cutting processes; (2) indexing of a part; (3) a feature hierarchical structure based on cutting processes; and (4) a similarity metric used to measure the similarity between a new desired part and any old part in the case base. The application domain here is for axisymmetric part machining. A prototype based on the retrieval mechanism is implemented on a Sun workstation using the ACIS 3D-Toolkit from Spatial Technology Inc.