CAD模型转换到VR模型的实时可视性研究

实时3D 可视化是机械产品设计当中的一个主要问题,针对CAD几何学和装配以及机械产品的高可视化提出了MEMPHIS中间件框架,目的是连接实时虚拟现实应用,特别是CAD模型的管理操作设计。同时还保证了当进行模型转换时,在CAD模型上必须作相应的几何改变,系统会同步变化,这样避免了传统的从CAD模型转换到VR模型转换时人工加入虚拟现实特殊信息,如光照设置、材质、纹理、行为这些刻画VR模型可视化特性的信息属性后才能实现这种转换。从而大大提高了机械产品协同设计的效率和可视性性能。     

Content-based assembly search: A step towards assembly reuse

The increased use of CAD systems by product development organizations has resulted in the creation of large databases of assemblies. This explosion of assembly data is likely to continue in the future. In many situations, a text-based search alone may not be sufficient to search for assemblies and it may be desirable to search for assemblies based on the content of the assembly models. The ability to perform content-based searches on these databases is expected to help the designers in the following two ways. First, it can facilitate the reuse of existing assembly designs, thereby reducing the design time. Second, a lot of useful designs for manufacturing, and assembly knowledge are implicitly embedded in existing assemblies. Therefore a capability to locate existing assemblies and examine them can be used as a learning tool by designers to learn from the existing assembly designs. This paper describes a system for performing content-based searches on assembly databases. We identify templates for comprehensive search definitions and describe algorithms to perform content-based searches for mechanical assemblies. We also illustrate the capabilities of our system through several examples.     

A PDES/STEP-based model and system for concurrent integrated design and assembly planning

Product data exchange and interfacing between different CAD/CAM systems are of great importance to the development of concurrent integrated design environments and computer integrated manufacturing systems. This paper presents a STEP-based method and system for concurrent integrated design and assembly planning. An integrated object model for mechanical systems and assemblies is first defined by a hierarchy of structure, geometry and feature. The structure is represented as a component-connector or joint multi-level graph with both hierarchical functional and assembly relations. These hierarchical relation models are then used for uniformly describing their causal relations both for assembly level and feature based single part level. The generic product assembly model is organized according to STEP, using mostly the entities of integrated resources and partly self-defined entities, which are necessary for design and assembly planning. Based on the generic product assembly model, STEP-based strategies and agent concepts are used for agent-based concurrent integration of design and assembly planning. A prototype system, consisting of a CAD system, a product modeling system, an assembly planning system, and an assembly evaluation system is developed, in which product data can be exchanged between these subsystems. Details about the implementation of the system are addressed. The integrated design and assembly planning system can support the introduction of a new product. The results of assembly planning are feedback to the stage of assembly design to improve on the design. A case study is carried out for assembly-oriented design of a gearbox, to illustrate the proposed approach and to validate the developed system.     

Robot-enabled tangible virtual assembly with coordinated midair object placement

The assembly in Virtual Reality (VR) enables users to fit virtual parts into existing 3D models immersively. However, users cannot physically feel the haptic feedback when connecting the parts with the virtual model. This work presents a robot-enabled tangible interface that dynamically moves a physical structure with a robotic arm to provide physical feedback for holding a handheld proxy in VR. This enables the system to provide force feedback during virtual assembly. The cooperation between the physical support and the handheld proxy produces realistic physical force feedback, providing a tangible experience for various virtual parts in virtual assembly scenarios. We developed a prototype system that allowed the operator to place a virtual part onto other models in VR by placing the proxy onto the matched structure attached to a robotic arm. We conducted a user evaluation to explore user performance and system usability in a virtual assembly task. The results indicated that the robot-enabled tangible support increased the task completion time but significantly improved the system usability and sense of presence with a more realistic haptic experience.     

Collaborative virtual prototyping of product assemblies over the Internet

Product assembly design is a complex activity involving collaboration between several designers. Currently, many manufacturing firms out source the design and development of different portions of a product to different suppliers. Due to the absence of an integrated tool for collaborative product assembly design, designers currently follow an indirect approach. This makes collaboration an unorganized and inefficient activity. This paper discusses the architectural novelties and design considerations utilized to develop an integrated collaborative assembly design tool. Further, the scenarios of using such a tool are discussed in detail. This discussion highlights how the tool contributes towards making collaboration an organized and efficient activity and enables designers to rapidly design and prototype the product assembly.     

虚拟现实在CAD/CAM中的应用

简述了虚拟现实在ＣＡＤ中应用的产生背景,意义：介绍了目前研究的基本状况及其基本概念和基本内容;综述了当前的一些主要方法和关键技术;分析了目前存在的一些主要问题。最后展望了该研究领域的发展趋势。     

A framework for collaborative top-down assembly design

This paper presents a new system framework for collaborative top-down assembly design. Different from current computer-aided design (CAD) systems, the framework allows a group of designers to collaboratively conduct product design in a top-down manner. In our framework, a multi-level and distributed assembly model is adopted to effectively support collaborative top-down assembly design. Meanwhile, fine-granularity collaborative design functionalities are provided. First, the coupled structural parameters involved in the distributed skeleton models of the product can be collaboratively determined by the correlative designers based on fuzzy and utility theory. Second, agent based design variation propagation is achieved to ensure the consistency of the multi-level and distributed assembly model during the whole design process. Third, collaborative design of assembly interfaces between the components assigned to different designers is supported. The prototype implementation shows that our framework works well for supporting practical collaborative top-down assembly design.     

Geometric skeleton computation enabling concurrent product engineering and assembly sequence planning

This paper introduces a novel modelling approach to geometric skeleton computation enabling concurrent product engineering and assembly sequence planning. Current engineering vision has recently moved towards new modelling and management paradigms to maintain competitive edges all along the product lifecycle. Consistent with concurrent engineering and design for X stakes, this recent shift promotes cross-X and knowledge-intensive philosophies in the product development process, principally focused on lifecycle engineering.The main objective of this research is to integrate assembly process engineering information and knowledge in the early phases of the product development process in a top-down and proactive manner, in order to provide a geometric skeleton-based assembly context for designers. The definition of the product and its related assembly sequence requires both the enhancement and the entire understanding of product relationships between the various product components, and its related assembly rationale. As a consequence, this new modelling approach highlights the need to integrate various stakeholders’ viewpoints involved in the beginning of the product lifecycle. In such a context, earlier work has achieved the early generation of an optimal assembly sequence in the product development process, before the product geometry is completely defined. As a result, previous research has made possible to control and bind the product modelling phase through an assembly oriented product structure.The aim of the proposed approach is to compute and define a geometric skeleton model based on product relational information and the early-defined assembly sequence. The proposed approach–called SKeLeton geometry-based Assembly Context Definition (SKL-ACD)–enables the control of the product modelling phase by introducing skeleton entities consistent with product relationships and assembly sequence planning information. A prototype application within a CAD tool has been developed for aiding geometric skeleton computation and generation. Lastly, an industrial case study is introduced to highlight the feasibility and the relevance of the proposed modelling approach.     

Integrating VR and CAD

Suppliers of advanced computer-aided design and engineering applications (CAD/CAE) intend to make interactive, immersive visualization an integral part of their product offerings. Adding virtual reality (VR) capability helps reduce users' design-cycle time and cut costs. Advances in computing power and 3D visualization functionality enable this logical evolution of technology. While many VR companies have established procedures for importing data from CAD applications into VR applications, Dassault Systemes takes a different approach to integrating CAD with VR. Through collaboration with Fakespace, the company is developing native support for immersive visualization display devices within its Catia Version 5 applications. The paper discusses the functionality required to enable immersive visualization and hands-on interactivity within CAD applications. It also describes the joint development effort to bring this functionality into Catia     

基于VRML-JAVA的虚拟现实及其协同环境的开发

虚拟现实技术对于制造业信息化有着重要意义。为建立开放技术标准之上的可视化装配系统,该文对基于VRML-JAVA的虚拟现实技术在工程设计领域的应用进行了研究,提出一种新型的Web环境下3D交互仿真结构,复杂的运算和仿真在服务器上进行,从而实现服务器端装配模型和客户端显示模型的分离。并在此基础之上提出协同环境开发的系统结构。该模型不仅可用于网络环境下的可视化装配,也适合于其他领域基于Web的科学可视化。     

Cable harness design, assembly and installation planning using immersive virtual reality

Earlier research work using immersive virtual reality (VR) in the domain of cable harness design has shown conclusively that this technology had provided substantial productivity gains over traditional computer-aided design (CAD) systems. The follow-on work in this paper was aimed at understanding the degree to which various aspects of the immersive VR system were contributing to these benefits and how engineering design and planning processes could be analysed in detail as they are being carried out; the nature of this technology being such that the user’s activities can be non-intrusively monitored and logged without interrupting a creative design process or a manufacturing planning task. This current research involved the creation of a more robust CAD-equivalent VR system for cable harness routing design, harness assembly and installation planning which could be functionally evaluated using a set of creative design-task experiments to provide detail about the system and users’ performance. A design task categorisation scheme was developed which allowed both a general and detailed breakdown of the design engineer’s cable harness design process and associated activities. This showed that substantial amounts of time were spend by the designer in navigation (41%), sequence breaks (28%) and carrying out design-related activities (27%). The subsequent statistical analysis of the data also allowed cause and effect relationships between categories to be examined and showed statistically significant results in harness design, harness design modification and menu/model interaction. This insight demonstrated that poorly designed interfaces can have adverse affects on the productivity of the designer and that 3D direct manipulation interfaces have advantages. Indeed, the categorisation scheme provided a valuable tool for understanding design behaviour and could be used for comparing different design platforms as well as examining other aspects of the design function, such as the acquisition of design decision intent. The system also demonstrated the successful automatic generation of cable harness assembly and cable harness installation plans from non-intrusive user-system interaction logging, which further demonstrates the potential for concurrent design and manufacturing planning to be carried out.     

An object-oriented knowledge based Petri net approach to intelligent integration of design and assembly planning

Artificial intelligence can play an important role in the reduction of manufacturing costs and the enhancement of production efficiency and product quality. In order to assist designers in the early stages of a product development this paper develops an intelligent methodology for integration of design and assembly planning processes, including product design, assembly evaluation and redesign, assembly process planning, design of assembly system and assembly simulation, subjected to both econo-technical and ergonomic evaluations. A new unified class of object-oriented knowledge based Petri nets called OOKPNs, incorporating knowledge based expert systems and fuzzy logic into ordinary place–transition Petri nets, is defined and used for the representation and modeling of the distributed design processes. A prototype intelligent integrated design and assembly planning system (IIDAP) is implemented through distributed blackboard structure with concurrent integration of multiple cooperative knowledge sources and software. It consists essentially of the networked agents and the meta-system, each of which is a knowledge Petri net system with the capabilities of problem solving, learning and conflict resolution, and can be obtained through the inheritance, polymorphism and dynamic binding of instances of OOKPNs. In IIDAP system, both C/C++ language and COOL (CLIPS object-oriented language) are used to incorporate a Petri net tool, a geometric modeling and design tool, a planner and simulator and an evaluation tool. By use of this system, product design and assembly planning can be carried out simultaneously and intelligently in an entirely computer-aided concurrent design and assembly planning system. The design of manufacturable, cost-effective, usable products can therefore be achieved rapidly and flexibly. The developed methodology and system have been successfully applied to assembly design and planning of a micro switch.     

虚拟环境中装配设计语义的表达、传递与转化研究

研究了虚拟环境产品装配建模过程中装配语义的表达、装配语义与装配约束的转化技术,提出了采用语义－约束图对装配设计语义与约束进行维护。通过语义－约束图可以从语义层次和约束层次对产品装配模型进行编辑和维护。提出了采用模糊参量表达和处理产品装配设计中的模糊语义。基于模糊参量的语义表达不仅为设计信息输入提供了更大的自由度,而且扩展了计算机对模糊信息的处理能力,有利于产品设计意图的维护。通过产品装配信息从抽象到具体、从模糊到精确的转化,实现了虚拟装配设计系统对抽象、模糊设计信息的表达、传递与处理。     

VDVAS：一个集成的虚拟设计与虚拟装配系统

随着虚拟现实技术的逐渐成熟，研究者们已将其引入到工程领域，为实现虚拟设计与虚拟装配过程的集成，避免现有的虚拟装配系统中，虚拟环境与CAD系统间所必需进行的复杂的、无谓的数据传输，描述了一个基于多通道的、集成的虚拟设计与虚拟装配系统VDVAS。在该系统中，设计得可以通过直接三维操作和语音命令直观方便地建立机械零件及其装配模型，并通过交互拆装来得到零件的装配顺序和装配路径等信息，VDVAS的一个重要特征在于，可通过集成虚拟设计与虚拟装配过程，使设计者能在一个集成的虚拟环境中修改零件几何（假如在装配过程中发现零件存在设计缺陷的话）。     

A hierarchical approach on assembly sequence planning and optimal sequences analyzing

Assembly sequence planning (ASP) is a critical technology that bridges product design and realization. Deriving and fulfilling of the assembly precedence relations (APRs) are the essential points in assembly sequences reasoning. In this paper, focusing on APRs reasoning, ASP, and optimizing, a hierarchical ASP approach is proposed and its key technologies are studied systematically. APR inferring and the optimal sequences searching algorithms are designed and realized in an integrated software prototype system. The system can find out the geometric APRs correctly and completely based on the assembly CAD model. Combined with the process APRs, the geometric and engineering feasible assembly sequences can be inferred out automatically. Furthermore, an algorithm is designed by which optimal assembly sequences can be calculated out from the immense geometric and engineering feasible assembly sequences. The case study demonstrates that the approach and its algorithms may provide significant assistance in finding the optimal ASP and improving product assembling.     

Concept design for quality in virtual environment

The early identification of the optimal concept is a critical task of the design process in order to increase the chances of satisfying customers. The challenging aspect of the approach proposed in this work relies in the quality evaluation of virtual prototypes of new industrial products (i.e. concept designs) by adopting a statistical procedure previously applied to service industries. Following this approach, the optimal concept design is defined at the end of a process consisting of five phases: identification of the quality elements of the concept design, classification of the quality elements, generation and quality evaluation of product concepts and, finally, definition of the optimal concept. Currently, virtual reality (VR) environment offers the opportunity to evaluate the characteristics of different virtual prototypes by involving experts and/or customers, overcoming the need for several physical prototypes. On the other side, the dynamics of simulation and the stereoscopic visualization in VR environment provides a more realistic and impressive interaction with virtual prototypes than in CAD environment.

The proposed methodology is fully exploited through two case studies: the choice of the optimal design for a traditional Neapolitan coffee maker, addressed by the Italian designer Riccardo Dalisi, and for a subassembly of a new minicar.     

Computer-aided ergonomics: a case study of incorporating ergonomics analyses into workplace design

One of the primary goals of computer-aided ergonomics is to develop software tools that allow ergonomics information to be accessed at the earliest stages of design. This case study discusses a PC-based software program that allows a designer to quantify a worker's biomechanical risk for injury based on a proposed workplace design. The program couples an established software tool for biomechanical analysis, the Three-Dimensional Static Strength Prediction Program (3DSSPP), with a widely used computer-aided design software package, AutoCAD. The use of this "3DSSPP/AutoCAD interface" in the proactive analysis of an automotive assembly task is described and the results compared with an independent assessment using observations of workers performing the same task. Both studies yield similar conclusions, suggesting that proactive use of software such as the 3DSSPP/AutoCAD interface may be a valid tool in evaluating proposed workplace designs. In this context, issues in the analysis of workplace designs regarding the use of supporting ergonomic tools, assumptions, and posture selection are discussed.     

A virtual prototyping approach to product disassembly reasoning

An important aspect of Design for the Life Cycle is assessing the disassemblability of products. After an artifact has completed its useful life, it must be disassembled then recycled, remanufactured or scrapped. Disassemblability of a product can be evaluated by performing disassembly activities on prototypes. Virtual prototyping (VP) is an alternative to hardware prototyping in which analysis of designs can be done without manufacturing physical samples. In recent years, disassembly processes have been generated either by using interactive or automated approaches, but these approaches have limitations. Interactive approaches require extensive user input usually in the form of answering questions, whereas automated approaches can only be used to generate disassembly processes for products with simple component configuration and geometry. In this paper automated and interactive techniques are combined, using VP, to generate complete disassembly processes of a product design. To support generation of disassembly processes of a product, a virtual environment and VP method were developed that will support disassembly activities performed by a designer. The product model of the virtual prototype is generated from the CAD model. The disassembly process model for the prototype is generated using automated reasoning techniques and is completed by interactively disassembling the product in the virtual environment. Extensions to automatic reasoning techniques to compute ranges of feasible directions of component removal were developed to facilitate the generation of the disassembly process. A scheme to represent the disassembly process for disassemblability evaluation was developed and implemented. In this paper a Chrysler LHS center console has been used to illustrate our approach of generating disassembly processes via VP.     

Using requirement-functional-logical-physical models to support early assembly process planning for complex aircraft systems integration

The assembly line process planning connects product design and manufacturing through translating design information to assembly integration sequence. The assembly integration sequence defines the aircraft system components installation and test precedence of an assembly process. This activity is part of the complex systems integration and verification process from a systems engineering view. In this paper, the complexity of modern aircraft is defined by classifying aircraft system interactions in terms of energy flow, information data, control signals and physical connections. At the early conceptual design phase of assembly line planning, the priority task is to understand these product complexities, and generate the installation and test sequence that satisfies the designed system function and meet design requirements. This research proposes a novel method for initial assembly process planning that accounts for both physical and functional integrations. The method defines aircraft system interactions by using systems engineering concepts based on traceable RFLP (Requirement, Functional, Logical and Physical) models and generate the assembly integration sequence through a structured approach. The proposed method is implemented in an industrial software environment, and tested in a case study. The result shows the feasibility and potential benefits of the proposed method.