G 2 curve design with planar quadratic rational Bézier spiral segments

Spiral segments are useful in the design of fair curves. They are important in computer-aided design (CAD) and manufacturing applications, the design of highway and railway routes, trajectories of mobile robots, and other similar applications. Quadratic rational Bézier curves are often used in CAD applications because they can be used to draw conic sections exactly. This paper shows how curvature continuous curves can be designed using quadratic rational Bézier curve segments of monotone curvature.     

A pipeline for computer aided polyp detection

We present a novel pipeline for computer-aided detection (CAD) of colonic polyps by integrating texture and shape analysis with volume rendering and conformal colon flattening. Using our automatic method, the 3D polyp detection problem is converted into a 2D pattern recognition problem. The colon surface is first segmented and extracted from the CT data set of the patient's abdomen, which is then mapped to a 2D rectangle using conformal mapping. This flattened image is rendered using a direct volume rendering technique with a translucent electronic biopsy transfer function. The polyps are detected by a 2D clustering method on the flattened image. The false positives are further reduced by analyzing the volumetric shape and texture features. Compared with shape based methods, our method is much more efficient without the need of computing curvature and other shape parameters for the whole colon surface. The final detection results are stored in the 2D image, which can be easily incorporated into a virtual colonoscopy (VC) system to highlight the polyp locations. The extracted colon surface mesh can be used to accelerate the volumetric ray casting algorithm used to generate the VC endoscopic view. The proposed automatic CAD pipeline is incorporated into an interactive VC system, with a goal of helping radiologists detect polyps faster and with higher accuracy.     

DEVELOPMENT OF AN INTELLIGENT PRODUCT DESIGN SYSTEM: INTEGRATION STRATEGIES

Conventional computer-aided design (CAD) packages have drastically reduced the workload of the human designer and shortened the product design cycle. However, the degree of effort and volume of information required to use these tools limit their use to the later stages of design. Intelligent computer-aided design (ICAD) systems have sought to provide a more complete design tool to assist the designer in all phases of design. ICAD systems incorporate conventional CAD elements as well as knowledge engineering constructs. The level of integration between different components of an ICAD system determines its usefulness. Most commercial intelligent CAD packages are tied to a specific set of CAD tools, restricting their application domains. This dependence on specific software tools can be reduced by using general purpose modules to interface with available CAD packages. This paper discusses a method of introducing knowledge engineering technology to help develop an advanced intelligent product design system by integrating ICAD's Concept Modeller with SDRC's l-DEAS package for engineering product design. This integration is necessary because neither the Concept Modeller nor the I-DEAS package provides any unified design environment where users can access both symbolic and numerical design tools as needed to carry out design synthesis and analysis activities. Interfacing engineering design and knowledge processing together is not an easy task. The task is further complicated since it needs to be done only by those who have enough knowledge of both technologies, and also because it may result in reorganization of the traditional design process altogether. The proposed intelligent product design system uses artificial intelligence techniques to take care of human experts knowledge and it advocates the use of several commercial software packages that come from a variety of sources (and are proven to be robust) to perform design synthesis in a cost-efficient and timely manner. The technique described here is relatively easy to implement and is well suited to industrial needs.     

A practical design procedure for circularly polarized printed arrays using high frequency CAE

A practical design procedure for a circularly polarized printed array antenna composed of strip dipoles and slots (CP-PASS) is presented. CP-PASS is a kind of series-fed array, and the equivalent circuit model of CP-PASS is simplified to be suitable for a computer-aided design (CAD) package. Some experimental results of a new strip element excited by a stripline and a 9-element set CP-PASS are also presented.     

Shape optimization of heavy load carrying components for structural performance and manufacturing cost

This paper addresses the trade-off between structural performance and manufacturing cost of heavy load carrying components by incorporating virtual machining (VM) technique in computer-aided design (CAD)-based shape optimization problem. A structural shape optimization problem is set up to minimize total cost, subject to the limits on structural performance measures. For every design iteration, finite element analysis (FEA) is conducted to evaluate structural performance, and VM is employed to ascertain machinability and estimate machining time. Design sensitivity coefficients of objective function and constraints are computed and supplied to the optimization algorithm. Based on the gradients, the algorithm determines design changes, which are used to update FEA and VM models. The process is repeated until specified convergence criterion is satisfied. Application programs developed to integrate commercially available CAD/CAM/FEA/Design optimization tools enable implementation in virtual environment and facilitate automation. The application programs can be reused for similar design problems provided that the same set of tools is used.     

Predicting and evaluating the post-assembly shape of thin-walled components via 3D laser digitization and FEA simulation of the assembly process

Three-dimensional (3D) laser digitization has become a critical research field and a widely used technique for product quality inspection in the manufacturing and medical industries during the last decade. One common application of this technology is to analyze whether the final shape of an assembly component fulfills the designer’s geometric specifications. This task is currently performed by digitizing the component’s surface after mounting it into its final assembly or on a special testing frame. In order to speed up this process a new computational method is proposed for inspecting the final shape of an assembly component by virtually mounting it into the assembly, without the physical assembling process taking place. The developed computational method employs laser digitization to measure the initial shape of the assembly component and then finite element analysis (FEA) to predict its post-assembly shape. First, a laser-digitized dense mesh is smoothed and decimated to make it suitable for FEA. Material properties of the component, if not available, are then determined by a calibration process, and specific displacement boundary conditions are applied to reproduce the assembly process. After FEA is executed, the quality of the simulated post-assembly shape is checked using visualization tools such as light-reflection patterns and contour plots of the distance between the computed geometry and the target computer-aided design (CAD) geometry. Moreover, the accuracy of the proposed method is validated by comparing the simulated post-assembly shape with the actual post-assembly shape measured after physically assembling the component. Experiments show that the average distance between simulated shape and actual shape varies from 0.3 mm to 0.6 mm for objects with a characteristic size of a half meter, and that the isophotes and height fields of reflection (HFR) based indices are reduced up to 50%. The proposed method can thus predict the final shape of an assembled component well without assembling it, reducing the time and the cost of product quality inspection.     

Designing and assessing everyday objects: Impact of externalisation tools and judges’ backgrounds

Professional designers increasingly rely on IT-based systems in the course of their work. It is therefore crucial to know how such systems, especially computer-aided design (CAD) systems, influence both the design process and the final design, compared with the use of manual design methods. The objective of this paper is twofold: to address this issue and to suggest ways of improving IT-based systems specifically developed to support designers’ activities. In the first phase of a two-phase study, we investigated how the use of different tools can affect the design process. In the second phase, we conducted two complementary analyses to determine how the use of different tools affects the assessment of final designs, as well as the effect of the judges’ backgrounds on their assessments. We began by comparing the activities of two groups of designers: one group working with a CAD system, the other carrying out manual modelling. The results of this first phase revealed significant differences in the designers’ activities (changing the viewpoint, switching tools, correcting errors) according to the design method they used. We then asked judges from four different backgrounds (professional designers, design teachers, retailers and users), to assess the final designs according to specific assessment criteria (aesthetics, originality, functionality, marketability). The results of this second phase revealed a significant preference for objects designed with a CAD system. Furthermore, the judges attributed different levels of importance to each of the assessment criteria, depending on their background. This last result underscored differences in the mental models constructed by different groups of audiences involved in product development and marketing. In addition, it allowed us to identify their specific expectations about final designs. Based on the results of our analyses, we suggest ways of improving IT-based systems with a view to integrating design assessment more fully into CAD environments.     

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.     

Product information visualization and augmentation in collaborative design

In this paper, a collaborative system for product information visualization and augmentation is presented. The developed system allows the users, who can be remotely distributed, to view a product model, which is a geometric representation of the product, from different perspectives. They can choose to view design and product history, such as previous modification processes and feature information of the product independently. The product models displayed to the users are immediately updated after any design modifications have been made to the CAD model. Product features being discussed can be highlighted to draw the users’ attention. In addition, modifications can be displayed dynamically for the users to evaluate the design effect. The product history document module in the system provides a user-friendly interface for retrieving design records. After a specific record has been chosen, the related product model is displayed, and it can be aligned with the current product model for the ease of comparison and evaluation. The feature information of the product is displayed using virtual “floating” annotations linked to the related features. A user interface to enter annotations is provided, and the annotations entered by different users can be shared in real time. A cluster-based greedy algorithm is implemented to avoid overlapping annotations in the field of view.     

基于灰色理论的家电产品造型评判系统的研究

为了保证设计质量,提高设计效率,并为设计改进提供依据,对计算机辅助造型评价进行了研究.探讨了工业产品造型设计的设计评价理论与方法,并对家电产品的分类及其特点进行了分析,依据工业设计评价内容和家电产品的特点建立了家电产品外观造型的评价模型,并采用灰色评价算法实现了评价过程,最后利用VC 结合数据库技术开发了一套家电产品造型评判系统,旨在为计算机辅助造型评价系统的开发提供一些思路和方法.     

虚拟装配环境支持下的产品可装配性评估

为了解决传统的产品可装配性评估研究需要结合实物模型或样机进行反复试验造成的评估周期长且成本高的问题,提出虚拟装配环境(VA)下的产品可装配性评估方法.从CAD模型及产品虚拟装配操作过程中分别得到产品装配中各零件的基本属性信息及主观属型信息,建立零件属性信息模型,通过Boothroyd-Dewhurst方法中的装配操作时间表计算得到产品装配效率,对产品可装配性进行评估.以减速箱产品装配为研究实例在虚拟环境下对产品可装配性进行了评估,验证了该方法的有效性和实用性.     

具有规整曲率线网的光滑曲面设计

为了设计具有规整曲率线网且无脐点的光滑曲面,提出一种曲面交互设计算法。 采用 Bézier 曲面片光滑拼接构成的复合曲面作为表达形式,通过交替曲率线网的优化和曲面细 分得到自由形状的设计曲面,所得曲面具有规整曲率线网而且没有脐点。以此复合 Bézier 曲面 为基础,通过圆纹样条曲面优化算法得到结构规整的圆纹样条曲面,同时也能得到圆锥曲面条 模型以及曲面多层支撑结构等自由建筑曲面设计中有重要应用的几何结构。     

An efficient GPU out‐of‐core framework for interactive rendering of large‐scale CAD models

Real‐time rendering of large‐scale engineering computer‐aided design (CAD) models has been recognized as a challenging task. Because of the constraints of limited graphics processing unit (GPU) memory size and computation capacity, a massive model with hundreds of millions of triangles cannot be loaded and rendered in real‐time using most of modern GPUs. In this paper, an efficient GPU out‐of‐core framework is proposed for interactively visualizing large‐scale CAD models. To improve efficiency of data fetching from CPU host memory to GPU device memory, a parallel offline geometry compression scheme is introduced to minimize the storage cost of each primitive by compressing the levels of detail (LOD) geometries into a highly compact format. At the rendering stage, occlusion culling and LOD processing algorithms are integrated and implemented with an efficient GPU‐based approach to determine a minimal scale of primitives to be transferred for each frame. A prototype software system is developed to preprocess and render massive CAD models with the proposed framework. Experimental results show that users can walkthrough massive CAD models with hundreds of millions of triangles at high frame rates using our framework. Copyright © 2016 John Wiley & Sons, Ltd.     

Preliminary design and manufacturing planning integration using web-based intelligent agents

Software agents have been increasingly used in the product and process development in industry over the past years due to the rapid evolvement of the Internet technology. This paper describes agents for the integration of conceptual design and process planning. Agents provide mechanisms to interact with each other. This mechanism is important since both of those processes involve negotiations for optimization. A set of design and planning software agents has been developed. These agents are used in a computer-based collaborative environment, called a multi-agent platform. The main purpose of developing such a platform is to support product preliminary design, optimize product form and structure, and reduce the manufacturing cost in the early design stage. The agents on the platform have access to a knowledge base that contains design and planning rules. These rules are derived from an analysis of design factors that influence process and resource planning, such as product material, form, shape complexity, features, dimension, tolerance, surface condition, production volume, and production rate. These rules are used by process planning agents to provide process planners with information regarding selecting preliminary manufacturing processes, determining manufacturing resources, and constructing feedback information to product designers. Additionally, the agents communicate with WEB servers, and they are accessible by users through Internet browsers. During performing design and planning tasks, agents access the data pertinent to design and manufacturing processes by the programming interfaces of existing computer-aided design (CAD) and manufacturing system. The agents are supported by a developed prototype agent platform. The agents and the platform enable the information exchange among agents, based on a previously developed integrated design and manufacturing process object model.     

An integrated intelligent machining system for axisymmetric parts using PC-based CAD and CAM software packages

Machining process planning involves the formation of a set of directions describing the machining operations required to transform raw stock into a finished part. Conventional process planning, performed manually, relies on the knowledge and competence of an experienced process planner and tends to be time consuming and error prone. In the past two decades, much effort has been spent on improving process planning by utilizing the power of a computer to emulate the capabilities of an experienced planner. During the same period, computer-aided design (CAD) and computer-aided manufacturing (CAM) software has been developed to enhance design productivity and to assist the NC code generation facets of the machining process. The entire planning process may be automated be integrating CAD and CAM using computer-aided process planing (CAPP). The research described in this paper outlines the design and development of an intelligent CAPP system integrating two commercial CAD and CAM software packages, Autocad and Mastercam.     

Structural shape optimization integrated with CAD environment

The research work presented here is based on the concept of the integration of optimization techniques and numerical analysis with the finite element method (FEM) and computer-aided design (CAD). A microcomputer aided optimum design system, MCADS, has been developed for general structures. Certain techniques to be discussed in the paper, e.g. the semi-analytical method for design sensitivity analysis, optimization analysis modelling for shape design, application oriented user interfaces and the coupling of automated optimization and user intervention have rendered MCADS pratical and versatile in applications for engineering structures. The above techniques and an application are presented in this paper.     

Development of a CAD-based intelligent manufacturing system

This research proposes a CAD-based manufacturing system that embraces computer-aided design, design for manufacturing and assembly (DFMA), computer-aided process planning (CAPP), computer-aided assembly planning (CAAP), and vision-robot integration. The proposed system starts with the design of products using a commercial CAD software, Autocad. The design data is then extracted from the CAD database and organized into a standardized product model. Interface programs are used to translate the geometrical and topological information in the model into DFMA, CAPP, CAAP and vision image representations. Based on the results generated by the interface programs the applications using artificial intelligence techniques can automatically generate redesign advises, CNC part programs, assembly sequence and instructions for robots.     

Surface shape control using constrained optimization on the B-spline representation

Shape control for surfaces is an important problem in CAD/CAM design as well as in other areas. Until recently, shape control has required the use of skilled engineering labor. This paper presents methods that will help to make this shape control process automatic. The particular problem considered is that of controlling the curvature of isoparametric lines for parametric tensor product spline surfaces. Conditions for curvature control are presented in terms of the B-spline coefficients. These conditions allow the problem to be stated as a constrained optimization problem and to be solved using modern optimization techniques.     

计算机辅助概念设计研究

本文基于计算机辅助概念设计的重要性,首先介绍了产品设计的发展、相关软件CAD的开发与发展;以及产品设计的趋势,包括集成化、标准化、智能化和网络化等。接着又重点介绍计算机辅助概念设计的关键技术,主要包括产品信息建模和推理,从而说明计算机辅助概念设计具有重要的研究意义。