A topological hierarchy-based approach to toolpath planning for multi-material layered manufacturing

This paper proposes a topological hierarchy-based approach to toolpath planning for multi-material layered manufacturing (MMLM) of heterogeneous prototypes. The approach facilitates control of MMLM and increases the fabrication efficiency of complex objects by generating multi-toolpaths that avoid redundant tool movements and potential collisions. It uses a topological hierarchy-sorting algorithm to group complex multi-material slice contours into families connected by a parent-and-child relationship. Subsequently, a sequential toolpath planning algorithm generates multi-toolpaths for sequential deposition of materials without redundant tool movements. To reduce build time further, a concurrent toolpath planning algorithm generates collision-free multi-toolpaths to control the tools that deposit materials concurrently. It uses parametric polygons to construct tool envelopes for contour families of the same material property to simplify detection of tool collisions. The tightness of polygons can be controlled to suit the processing speed and the optimality of the resulting concurrent toolpaths. The proposed approach has been implemented as an integral part of a multi-material virtual prototyping (MMVP) system that can process complex slice contours for planning, stereoscopic simulation, and validation of multi-toolpaths. It may be adapted for subsequent control of MMLM processes.     

A versatile virtual prototyping system for rapid product development

This paper presents a versatile virtual prototyping (VP) system for digital fabrication of multi-material prototypes to facilitate rapid product development. The VP system comprises a suite of software packages for multi-material layered manufacturing (MMLM) processes, including multi-toolpath planning, build-time estimation and accuracy analysis, integrated with semi-immersive desktop-based and full-immersive CAVE-based virtual reality (VR) technology. Such versatility makes the VP system adaptable to suit specific cost and functionality requirements of various applications.

The desktop-based VR system creates a semi-immersive environment for stereoscopic visualisation and quality analysis of a product design. It is relatively cost-effective and easy to operate, but its users may be distracted by environmental disturbances that could possibly diminish their efficiency of product design evaluation and improvement. To alleviate disturbance problems, the CAVE-based VR system provides an enclosed room-like environment that blocks out most disturbances, making it possible for a design team to fully concentrate and collaborate on their product design work.

The VP system enhances collaboration and communication of a design team working on product development. It provides simulation techniques to analyse and improve the design of a product and its fabrication processes. Through simulations, assessment and modification of a product design can be iterated without much worry about the manufacturing and material costs of prototypes. Hence, key factors such as product shape, manufacturability, and durability that affect the profitability of manufactured products are optimised quickly. Moreover, the resulting product design can be sent via the Internet to customers for comments or marketing purposes. The VP system therefore facilitates advanced product design and helps reduce development time and cost considerably.     

A virtual prototyping system with reconfigurable actuators for multi-material layered manufacturing

Proliferation of layered manufacturing (LM) in various sectors has been calling for fabrication of large, complex products with more materials and efficiency. We address this issue by integrating reconfigurable manufacturing (RM) with LM. This paper first analyses the benefits of such integration, and then presents a virtual prototyping system with reconfigurable actuators (VPRA) that can increase the number of materials, speed, and build volume to improve the efficiency and flexibility of multi-material layered manufacturing (MMLM). The VPRA system offers a test bed for design, visualization, and validation of MMLM facilities and processes. It takes advantage of the convenient graphics platform of SolidWorks™ for constructing a virtual MMLM facility by selecting reconfigurable actuators from predefined templates. The characteristics, including the dimensions and relative spatial constraints, of the actuators can be conveniently configured to suit design requirements. The mechanism and the operation process of the resulting MMLM facility can then be simulated and validated through digital fabrication of complex objects. Case studies are presented to demonstrate some possible applications of the VPRA system. Overall, the VPRA system gives insights into the characteristics of a reconfigurable MMLM system, which can be subsequently materialized for physical fabrication of multi-material objects. This approach highlights a possible direction for development of MMLM technology.     

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.     

A dynamic priority-based approach to concurrent toolpath planning for multi-material layered manufacturing

This paper presents an approach to concurrent toolpath planning for multi-material layered manufacturing (MMLM) to improve the fabrication efficiency of relatively complex prototypes. The approach is based on decoupled motion planning for multiple moving objects, in which the toolpaths of a set of tools are independently planned and then coordinated to deposit materials concurrently. Relative tool positions are monitored and potential tool collisions detected at a predefined rate. When a potential collision between a pair of tools is detected, a dynamic priority scheme is applied to assign motion priorities of tools. The traverse speeds of tools along the x-axis are compared, and a higher priority is assigned to the tool at a higher traverse speed. A tool with a higher priority continues to deposit material along its original path, while the one with a lower priority gives way by pausing at a suitable point until the potential collision is eliminated. Moreover, the deposition speeds of tools can be adjusted to suit different material properties and fabrication requirements. The proposed approach has been incorporated in a multi-material virtual prototyping (MMVP) system. Digital fabrication of prototypes shows that it can substantially shorten the fabrication time of relatively complex multi-material objects. The approach can be adapted for process control of MMLM when appropriate hardware becomes available. It is expected to benefit various applications, such as advanced product manufacturing and biomedical fabrication.     

单幅人体切片图像的多轮廓二维重构算法研究与实现

基于切片图像数据的轮廓曲线二维重构是轮廓表面三维重构的基础。单幅切片图像可能存在有单轮廓或多轮廓。本文对中国虚拟人切片图像进行分析,针对单幅切片图像里的多轮廓线情况,研究提出了多轮廓提取算法和拟合曲线建模算法。经编程实验,成功实现了单幅图像里的多轮廓二维重构。     

3D打印模型切片及路径规划研究综述

3D打印包括建模、分层切片、路径规划及打印等过程。对3D打印中三维模型数据处理技术核心--切片和路径规划进行综述。介绍3D打印切片软件中针对单材料不同格式的模型切片处理方法,阐明了3D打印中的不同工艺参数影响下的切片算法,包括各类分层切片算法和扫描填充算法,说明每种算法的优缺点,并对现有的单相均质模型切片算法进行对比分析与评价,总结模型切片处理算法的不足,提出改进方向以及未来研究多材料3D打印模型数据处理的切入点。     

Design evaluation and modification of mechanical systems in virtual environments

Design is one of the most important stages in the manufacturing cycle and influences all the subsequent stages of product development. In the context of today’s iterative design methodology, the modification of any design is a process involving many evaluations and improvements to the solutions chosen in earlier stages. For this purpose, in the most recent decade, 3D computer simulations have become common tools used within industry. Whilst virtual reality (VR) technology is seen as the interaction technology of the future, much of the current research in this area is carried out to explore the potential benefits and added value brought by the integration of this into standard software technologies currently used at various stages in manufacturing life cycle. A lot of attention has been given to exploring the usability and benefits of interactive VR for assembly planning, knowledge elicitation and design and simulation. However, little research has focussed on the analytical aspects of the design process, for example in the use of VR as an interface for simulation software in finite element methods and multi-body systems. This paper introduces research focussing on applications of virtual environments (VEs) for interactive design evaluation and modification adapted and used with standard simulation software. The use of such interactive visualisation offers the engineer more realistic real-time representations of the design and advanced facilities to interact with the model during the design process. While design evaluation is based mainly on visualisation; design modification requires interactive changes of the model during the simulation, and the interfaces described here highlights such applications. In this work, two software prototypes have been developed using VR technology. First, a software tool called design evaluation in virtual environments is presented together with an application in civil engineering to illustrate the mode of operation and added value of the use of an interactive visualisation environment. Linking the simulation software with the VE provides real time bi-directional communication of graphical information which can be successfully achieved even within the limits of current computer technology. The tool includes a suite of software modules and a user interface to facilitate the link between the simulation results and the VE. The second tool facilitates the design modification in virtual environments system by providing real time dynamic simulation. Two dynamic approaches are investigated in order to study the real time simulation issues in the context of design modification and system performance: the classic approach based on rigid interconnected bodies, and a new and novel approach developed by the authors based on particles dynamics. Both implementations have been tested and compared on a mechanism application under the same computing conditions. The research applications presented demonstrate the practicality, flexibility and versatility of the visualisation in virtual environment in design evaluation and modification. However, the computer efficiency whilst carrying out real time dynamic simulation is limiting the range of applications to models of moderate size; however, this is an improvement on previous similar applications.     

快速原型虚拟逼真设计原理及体系结构

在分析设计的特点和发展趋势的基础上,提出快速原型虚拟逼真设计,并对其特点和原理进行了讨论,快速原型虚拟逼真设计是面向并行工具,基于虚拟原型和虚拟环境仿真的设计,强调虚拟原型的快速生成和演化,在关键技术,原型系统以及开发环境三个层次上论述了快速原型虚拟逼真设计的研究,提出快速原型虚拟逼真设计模型以及基于该模型的体系结构。     

基于WebGL技术的某升船机塔柱结构仿真可视化平台研究

在数字化技术应用于水利水电工程的大背景下,为在某升船机塔柱结构某升船机数字化升级项目中实现智慧化模拟,完善可视化和数据交互能力,研发一个结构仿真可视化平台。平台采用WebGL技术,在网页端对有限元网格模型进行重绘;提供云图及变形动画渲染功能用于展示前、后处理数据;研究有限元数据处理、模型面片和云图渲染优化技术,用于高效渲染。平台在某升船机数字化项目中得到了良好应用,可视化功能可用于常用结构分析,并基于平台接口开发监测对比功能,提高运行管理单位对结构安全的分析水平。相关技术可用于其他水利水电工程结构的仿真可视化平台当中。     

Web-based environment for mechanism simulation integrated with CAD system

The present work describes the architecture of a new approach addressing the sharing of virtual prototypes over the Web with standard programming tools. The usage of standard Web-based technologies leads to easier, effective and more general applications suitable for small and medium size companies with limited resources in that field of research. Designers not only exchange just geometry data, but also more information about design knowledge and design solutions, and collaboration is performed on remote locations. In this work the framework is proposed to model a mechanical product focusing on behavioural criteria. In order to avoid time-consuming virtual model preparation, product variety is defined in single configuration file. The configuration file is covering all the variations, with formalisation of the assembly structure and linking the parts and attributes in uniform way. It enables visualisation of the models from different modelling systems and allows interactive changes and evaluation of the virtual prototype.     

Neural clustering networks based on global optimisation of prototypes in metric spaces

The utilisation of clustering algorithms based on the optimisation of prototypes in neural networks is demonstrated for unsupervised learning. Stimulated by common clustering methods of this type (learning vector quantisation [LVQ, GLVQ] and K-means) a globally operating algorithm was developed to cope with known shortcomings of existing tools. This algorithm and K-means (for the common methods) were applied to the problem of clustering EEG patterns being pre-processed. It can be shown that the algorithm based on global random optimisation may find an optimal solution repeatedly, whereas K-means provides different sub-optimal solutions with respect to the quality measure defined as objective function. The results are presented. The performance of the algorithms is discussed.     

基于MSC Adams/Aircraft的飞机起落架着陆动态性能分析

以某支柱式起落架飞机为原型,在MSC Adams/Aircraft平台上建立起落架及全机虚拟样机模型并进行落震仿真分析、全机着陆仿真分析. 全机着陆仿真分析结果与落震仿真分析结果一致性较好,为在MSC Adams软件基础上进行飞机着陆过程虚拟技术研究奠定基础.     

Computational steering of a multi-objective evolutionary algorithm for engineering design

The execution process of an evolutionary algorithm typically involves some trial and error. This is due to the difficulty in setting the initial parameters of the algorithm—especially when little is known about the problem domain. This problem is magnified when applied to many-objective optimisation, as care is needed to ensure that the final population of candidate solutions is representative of the trade-off surface. We propose a computational steering system that allows the engineer to interact with the optimisation routine during execution. This interaction can be as simple as monitoring the values of some parameters during the execution process, or could involve altering those parameters to influence the quality of the solutions produced by the optimisation process. The implementation of this steering system should provide the ability to tailor the client to the hardware available, for example providing a lightweight steering and visualisation client for use on a PDA.     

Genetic approaches for topological active nets optimization

The topological active nets (TANs) model is a deformable model used for image segmentation. It integrates features of region-based and edge-based segmentation techniques so it is able to fit the contours of the objects and model their inner topology. Also, topological changes in its structure allow the detection of concave and convex contours, holes, and several objects in the scene. Since the model deformation is based on the minimization of an energy functional, the adjustment depends on the minimization algorithm. This paper presents two evolutionary approaches to the energy minimization problem in the TAN model. The first proposal is a genetic algorithm with ad hoc operators whereas the second approach is a hybrid model that combines genetic and greedy algorithms. Both evolutionary approaches improve the accuracy of the segmentation even though only the hybrid model allows topological changes in the model structure.     

集装箱智能化最优布局的算法建模与仿真实现

在货物的包装、存储及装载过程中,如何提高集装箱的利用率,是提高物流效率的重要环节。针对布局问题,建立积分式分片的数学模型,基于这一模型,提出了一种虚拟布局模式的积分式分片算法:引入虚体的概念,虚构以某种模式将集装箱布局完毕,再把已布局完毕的集装箱切割成若干薄片,然后根据薄片的分类信息建立规划模型,以虚体的总体积最小为目标,获得集装箱布局模式的最优解。运用VC++编程完成一仿真模拟系统,以应用实例证明了算法的正确性与可行性。     

Direct slicing of STEP based NURBS models for layered manufacturing

Direct slicing of CAD models to generate process planning instructions for solid freeform fabrication may overcome inherent disadvantages of using stereolithography format in terms of the process accuracy, ease of file management, and incorporation of multiple materials. This paper will present the results of our development of a direct slicing algorithm for layered freeform fabrication. The direct slicing algorithm was based on a neutral, international standard (ISO 10303) STEP-formatted non-uniform rational B-spline (NURBS) geometric representation and is intended to be independent of any commercial CAD software. The following aspects of the development effort will be presented: (1) determination of optimal build direction based upon STEP-based NURBS models; (2) adaptive subdivision of NURBS data for geometric refinement; and (3) ray-casting slice generation into sets of raster patterns. The development also provides for multi-material slicing and will provide an effective tool in heterogeneous slicing processes.     

基于庐山三维场景的图算法虚拟仿真系统研究

为应对传统计算机算法教学中理论知识存在逻辑性强、抽象程度高、教学与实验脱节、缺乏交互性等现实问题,本文借助虚拟现实技术,基于江西知名旅游胜地庐山的三维场景,使用Unity3D引擎设计图算法虚拟仿真系统。该系统实现5种图算法的仿真实验过程,每种图算法均提供“自动展示”和“用户交互”这2种运行模式,还提供用户进入景点(对应图的结点)分场景的自由控制视角浏览庐山景观的功能;同时,探讨本虚拟仿真系统存在的理论问题,并给出解决这些问题的关键技术和实施方案;最后,通过Prim最小生成树算法验证本虚拟仿真系统的实用性和灵活性。与传统的算法讲授、个性化问题驱动教学方式相比,本文设计的图算法虚拟仿真系统具有趣味性、交互性、沉浸性,既能激发学生学习的探索性和主动性,又为算法与数据结构课程提供了一种新的教学和实验方法。