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计算机辅助夹具设计技术回顾与发展趋势综述 计算机辅助夹具设计(Computer-aided fixture design，CAFD)技术从20世纪70年代发展至今，已经成为CAD/CAM集成技术的一个重要组成部分。文中从CAFD技术所包含的4个研究方面(安装规划，装夹规划，夹具构形设计，夹具性能评价)入手，对国内外CAFD技术的发展(主要对近10几年内的发展成果)进行了回顾，并对CAFD的未来发展趋势进行了分析。 随着制造技术的发展，产品的设计周期缩短，更新换代增快。传统的大批量生产模式逐步被中小批量生产模式所取代。机械制造业欲适应这种变化须具备较高的柔性，国外已把柔性制造系统作为开发新产品的有效手段，并将其作为机械制造业的主要发展方向。柔性化的着眼点主要在机床和工装两个方面，而夹具又是工装柔性化的重点。组合夹具的平均设计和组装时间是专用夹具所花时间的5%20%，可以认为组合夹具就是柔性夹具的代名词。由于组合夹具应变能力强、设计和制造周期短、成本低、适应产品更新换代的要求，提高了企业的竞争力，所以日益受到厂家的青睐。应用组合夹具的一项关键技术就是CAFD技术。我国从20世纪80年代中期就已经开始研究这项技术，并对如何将人工智能的理论应用到组合夹具计算机辅助设计(CAD)过程进行了探索。但由于组合夹具设计取决于被加工工件，而被加工工件又千变万化，造成组合夹具CAD难以实现智能化。经过30多年国内外众多学者的不懈努力，工作虽有进展，但离生产实际应用还有很大距离。1 CAFD技术概述从20世纪70年代开始夹具CAD研究至今，CAFD技术已经发展成为CAD/CAM集成技术的一个重要组成部分。目前，围绕CAFD技术所展开的研究主要包括4方面内容：安装规划，装央规划，夹具构形设计和夹具性能评价：(1) 安装规划。安装规划的任务是确定加工时所需的安装次数，每次安装中工件的方位及加工面。这部分也可以是CAPP(Computer-aided process planning)的一个子集，也是CAFD和CAPP集成的交互接口。安装规划的框架包括制造特征描述和特征库的开发、装夹特征的定义和定位表面的选择、安装规划算法、以及夹具设计和验证。安装规划由于与CAPP联系更为紧密，大多数CAFD领域内的研究都集中在装夹规划，夹具构形设计和夹具性能评价3方面，但目前在夹具构形设计中对夹具自动构形设计的研究仍然较少。(2) 装夹规划。装夹规划主要用来决定在某一特定安装条件下工件上的定位支撑面，支撑点以及夹紧点。装夹规划所考虑的主要问题包括：工件上可以选作为装夹表面的表面类型;装夹表面相对于刀具轴线的方位;候选装夹表面的精度要求;候选装夹表面的组合情况;装夹稳定性和装夹表面的可及性等。(3) 夹具构形设计。夹具构形设计的任务是选择夹具元件，构造夹具结构，并把它们装配成最终的夹具构形来夹持工件。CAFD中夹具构形设计的主要问题包括：夹具元件的选择如与工件直接接触的定位支承与压板等的选择;确定夹具组件的高度;夹具组件在基础板上的摆放;夹具元件之间的连接;夹具、工件及加工面之问的干涉检查等。(4) 夹具性能评价。夹具性能评价是对已经设计完成的夹具的有关性能进行评价和分析，定义、测量并对夹具设计进行优化处理，用以保证夹具设计的质量。性能评价的内容包括定位精度，加工表面精度，夹紧和加工稳定性，抵抗夹具元件变形的刚度，刀具路径的干涉检查，表面可及性等。2 国内外CAFD技术研究现状和成果文献5对CAFD从最初的起步到20世纪后的发展趋势作了回顾，这其中既包括最初的Latombe，Ingrand(1980)对于自动夹具推理的努力，也包括Markus(1984)和Miller(1985)开发一种半自动化的方法对给定的工件产生一种夹具设计的尝试，这种方法虽非自动，但提供了交互选择夹紧点，定位点和支撑点等功能，Chou等人(1989)基于工件稳定性和全约束要求的双重标准，重点研究了夹具设计中的夹紧过程。随着开发CAFD的剪要性被越来越多的学者所认可，人工智能和专家系统在夹具设计当中的应用也越来越多地被提出来，包括Davishi等人(1988)的开发专家系统的知识库表示，Nee等人(1992)基于特征的夹具分类模式，以及Pham等人(1990)的夹具CAD系统的开发等。纵观CAFD发展历程，其历经交互式计算机辅助夹具设计系统(ICAFD)，基于成组技术和知识的CAFD系统及20世纪90年代后的第3代CAFD系统3个阶段。而按照自动化程度划分，夹具设计系统又可分为交互，半自动和自动系统。20世纪90年代后，总结经验后认为，CAFD最终必须要生成夹具结构，而过去的系统只解决安装、定位、夹紧等问题或检索类似的结构，不能获得合乎工件实际应用的结构图，而且分析也不全面。所以，必须开发出以产生夹具结构为目的，实际生产为导向的商品化夹具设计软件上。下面着重对最近10几年来CAFD方面较新的研究进展和存在问题给予关注和总结。2.1 国外CAFD技术研究现状和成果国外CAFD研究内容在装夹规划，夹具构形设计及夹具性能评价等方面的研究如下：装央规划方面：Rong等人基于快速夹具构形设计系统研究了定位方法在自动组合装夹规划系统中对夹具元件和工件的几何关系进行了分析，对自动组合装夹规划中的夹装精度，夹紧规划，夹具可及性及夹紧稳定性进行了研究，一旦装夹规划确定了，分析结果会应用到夹具设计的性能评价中;除了机械加工用的组合夹具外，Wang等人将基于案例推理的方法(CBR)应用到了焊接夹具的研究中，提出了一种用于夹具设计信息表示的数据提取方法，在此方法基础上，提出了用于焊接夹具设计的多级CBR方法;Perremans开发了可以进行装夹规划如输入定位，夹紧，支撑表面等的专家系统，并可通过专家系统实现组合夹具元件的组装;Mervyn等人利用进化搜索算法提出了一种自动组合夹具分析方法;Varadarajan等人到为六轴定位和装夹精度设计了动力学模型和硬度模型。夹具构形设计方面：Rong等人从装夹规划到夹具构形设计，对CAFD进行了深入而广泛的研究，开发了基于孔系的自动组合夹具构形设计系统。在快速反应制造中开发了自动定制夹具构形设计系统;在夹具可重构方面，Kong等人将基于夹具工作区的结构合成及快速夹具校验的可视化分析应用于快速可重构组装夹具系统中;Shen等人纠以滑动副作为可重构夹具的基本结构，提出了用于可重构夹具系统的4种类型的机构;Ryll等人提出了一种快速可重构方法以及工件一夹具在智能装夹系统中的定位，可重构中应用了面向对象的方法来确保无需改变控制软件而保证夹具在不同的安装下工作;Culpepper，Varadarajan等人基于压力激励和弯曲轴承提出了一种双重目的的定位夹具(DPF)和偏心的球一轴夹具，用以弥补夹具元件的公差和轴承磨损，但并未涉及到工件公差对相关工件定位的影响;Ibrahim等人在综合考虑工件材料，工件表面粗糙度，夹具元件粗糙度，法向载荷等影响条件，通过实验方法确定工件、夹具元件接触表面之间的摩擦系数，通过静态方法来减少实验误差，以确保实验结果的可信度。结果对夹具构形设计至关重要;Martin等人针对夹具设计中应用专家知识所引起的不精确及不确定性等缺点，提出了模糊推理(fuzzy reasoning)的方法来支持来源于不同知识语义的造型;Surendra等人o开发了用于棱柱形工件的自动夹具生成系统，该自动夹具构形设计系统可以自动选择夹具元件并按照符合需要的组装关系放置在合适的位置;Hunter等人利用知识模板的重用，可以实现不同知识族中所定义知识的重用，并与模型结合起来，基于IDEFO和UML的功能方法表示夹具设计过程。夹具性能评价方面：Kulankara等人对工件尺寸和精度有较大影响的夹具布局过程进行了研究，提出了一种基于遗传算法(GA)的夹具布局优化技术，可以减少由于夹紧力和切削力所引起的加工表面的变形;Pelinescu等人基于多质量标准确定夹具布局设计并对所接受的夹具设计方案进行评估，选择一个最优的夹具设计方案来平衡多性能需求，文中给出了3个性能目标，即定位工件的精度，定位接触力的降低和定位接触力的平衡;Siebenaler等人重点研究了利用有限元方法分析预测工件变形的影响因素，仿真结果表明，基于表面对表面的工件一夹具接触模型可以对工件和反应力做出预测;Satyanarayana等人用有限元方法对不同边界条件导致的工件弹性变形和反作用力的预测进行了分析，并通过实验进行了性能评价;Amaral等人同样用有限元方法在夹具设计系统中对夹具设计进行了性能评价和优化;Song等人在确定定位状态的基础上，进一步分析和研究了非确定定位方案，用一种算法来检测几何约束状态，该算法可以识别欠约束状态并指出工件的非约束运动，也可以识别过约束状态及不必要的定位，这种信息可以帮助设计者分析和改善已有的定位方案;Subranmanian提出了一种基于遗传算法(GA)的优化方法，利用空间坐标来表示夹具元件的位置，集成了遗传算法中很多诸如实数编码，突变及共享等重要概念;Kaya也将GAs应用于夹具结构优化设计中，并利用有限元方法进行目标函数值的计算;Varadarajan等人对六轴定位原理和装夹精度进行了特性分析和评价;Kang提出了对夹具的定位性能、加工表面精度，稳定性及表面可及性等方面进行验证;Hurtado等人提出了一种用于优化柔性夹具设计的模型，该模型用于发现最优活动销的数目，所用算法目的在于获得夹具一工件的一致性和保持工件刚体运动稳定平衡，使夹具弹性变形保持在或低于用户指定的值;Ratchev等人基于FEA方法，提出了一种有效的性能评价方法，即用一种创新的仿真方法来预测夹具一工件系统中的动态行为，并兼容于任何商业化FEA平台;Wang和Kayaml提出了基于约束和遗传算法的定位和夹紧布局优化。2.2 国内CAFD技术研究现状和成果国内夹具CAD的研究起源于20世纪80年代中期，中国航空技术进出口公司应欧洲客户要求，设计了一套二维计算机辅助组装软件，拉开了我国开发夹具CAD系统的帷幕。从20世纪80年代中期开始，我国先后有lO余所高校对组合夹具CAD系统作了探索，但能长期坚持研究开发的有北京机械工业学院、河北工业大学、南京航空航天大学、西北工业大学和哈尔滨工业大学等。目前，对夹具CAD研究的内容越来越深入和具体，参与研究的学术单位和团体也越来越多，除上述单位外，四川大学、大连理工大学、天津大学、河海大学等众多的高校与研究机构参与到了夹具CAD的研究当中来，包括一些高校在ACIS。，Solidwork，ProE，UG等不同CAD平台上进行的夹具CAD系统的研发和不同平台下的夹具元件建库工作。近年来，国内夹具CAD研究的主要内容大部分集中在装夹规划和夹具构形设计(包括计算机辅助夹具系统的研究和开发)方面，部分对夹具性能评价的研究穿插于上述两方面。装夹规划方面：唐东等人将ANN算法(即Hopfield algorithm)用于自动装夹规划(automatic fixtureplanning)中，同时通过利用定位夹紧面的选择规则和确定工件定位的评估矩阵对定位和夹紧表面的选择进行了研究，并开发了从数据库中选择定位和夹紧元件进行夹具的组装方法;吴玉光，张坤明旧叫。针对孔系组合夹具采用了工件外轮廓规约化方法，确定工件可行夹紧点方案集合，对夹紧方案的自动规划方法进行了研究;吴玉光等人还就最优夹紧方案评价及定位方案的自动确定方法进行了研究，并利用关联(Linkage)机制进行工件定位候选点的识别，在评估可及性和装夹性的算法中采用了诸如IRC(instantaneousrotational center)三角形及定位可见圆锥等新概念;Zheng等人”副针对以往组合夹具装夹研究重点集中在2D和3D规则几何形状的对象方面，为3D复杂对象或者以任意位置放置的需要定位的对象夹具建立了数学模型，对3D组合夹具进行了系统研究。夹具构形设计方面：陈慰芳等人。提出了夹具装配模型分层的思想，实现了夹具元件的快速装配。融亦鸣等人设计的准商品化软件Fix-Des夹具自动结构设计系统;李剑峰等人将分解与重构原理和功能映射关系在组合夹具CAD系统中的应用做了介绍;徐雷将知识工程与夹具设计过程结合起来，对夹具知识描述、分类、发现及重用的基本原理和智能化夹具设计中的知识求解技术进行了重点研究并开发了基于集成知识资源的计算机辅助夹具设计支持系统;金天国等人针对组合夹具装配中顺序装配法的缺点，提出了自动求解装配体中零部件尺寸或位置的启发式算法;谢晓文等人以槽系组合夹具为例，利用人工智能的夹具设计方法和参数化的组合夹具建模技术结合粗糙集理论与夹具设计原理建立了计算机辅助组合夹具设计系统;刘惠英，刘琼等人利用PowerBuilder和Oracle研制了计算机辅助组合夹具管理系统;胡瑞飞等人将夹具元件库，典型组件库和典型结构库组成多层夹具实例库，提出了一种自顶向下的分层组合夹具智能辅助装配系统。河北工业大学是国内进行组合夹具CAD研究较早的单位之一，在20世纪80年代末与航天工业部保定向阳精密机械厂联合开发了组合夹具软件组装CAD系统，并在该系统基础上不断发展。段国林、齐红威等人将人工智能模块及基于案例推理(Casebased Reasoning，CBR)的方法加入到了组合夹具计算机三维软件组装及构形设计系统中。多年来对组合夹具计算机辅助构形设计系统的研究与开发经历了从最早的R14到AutoCAIY2002，历经了多次版本更新和软件架构的改善，已开发的组合夹具辅助设计软件包MFS CAD5.0版已在实际中得到了很好的应用，目前该CAFD软件已升级为6.0版本，并对软件功能进一步完善，开发了三维组合夹具CAD系统的图库管理系统，系统还进一步推广到了ACIS平台下，目的在于开发自主平台下的夹具CAD软件拼装系统并推广应用。并在以上研究基础上，对组合夹具元件库系统的异构平台应用展开了研究，目的在于提供可供不同CAD平台应用的组合夹具元件库系统。3 CAFD发展面临的问题和趋势以上按照CAFD的研究内容分别对CAFD近几年在装夹规划，夹具构形设计及夹具性能评价等几方面国内外的研究进展进行了回顾，可以看到，在CAFD发展过程中，针对不同的侧重点展开了多方位多角度运用多种方法(造型，模型分析等软件的应用，基于人工智能包括知识和专家系统的应用，算法，推理及功能分析方法等的应用)的计算机辅助夹具设计研究，为夹具CAD的研究提供了更多的借鉴和参考，也使夹具设计系统的自动化程度大大提高，但是至今仍然没有成熟的夹具CAD商品化软件。现有CAFD系统研究存在的主要问题有：夹具设计和装配手段仍未从计算机辅助工程中得到更多的受益，它仍是现代制造系统的瓶颈之一。对于CAFD的研究多，应用少，同CAD，CAM，PDM，MIS等相关计算机辅助技术相比，差距很大，CAFD应向着集成化，知识化，智能化和实用化方向发展。对于夹具构形设计当中针对不同CAD平台问夹具系统的信息传输和数据共享方面研究则更加缺乏，CAFD的网络化和异构平台应用作为夹具构形设计中一个很重要的发展和研究方向，应以能够满足网络时代下的信息交互和CAD系统间的数据共享为发展目标。某一特定平台下夹具设计系统的缺陷在于将用户局限于特定的CAD系统中，当CAD系统或者操作系统变化时，很难再重新利用该夹具系统，为了解决这种矛盾，克服单一平台的缺陷，亟需进行夹具设计系统如何独立于单一CAD平台的研究。一个有效的夹具设计系统应该便于在不同操作平台上进行数据传输，能够与其它制造系统交互并且为了达到最优设计应具备一定的柔性。使夹具设计及拼装系统的应用不再依附于某一特定平台，最终实现异构平台之间的数据转换和夹具CAD系统的重用。所以，CAFD技术目前仍然处于自动化和智能化程度不高，缺乏智能反馈应用功能，构形设计仍然对手工依赖较大，自动构形技术还非常缺乏，夹具设计和夹具组装系统大部分局限于某一特定平台而难以实现异构平台应用的这样一种现状。夹具构形中针对典型结构这种模块化夹具的研究，以及夹具元件库异构平台应用都相对较少，众多的研究重点集中在某特定平台下的夹具设计及夹具组装等研发工作中，而异构平台之间的数据共享和交瓦无疑是网络化制造和应用的研究重点，未来科技的发展更重视信息交流，没有信息交互的过程，协同将只是一种假设，而没有协同的设计环境，企业及行业在未来信息化的发展中将变得寸步难行，更无从谈竞争和发展。随着CAFD技术的进一步发展和现代生产的需求，对组合夹具的设计和构形自动化，智能化提出了更高的要求。在当今面向制造环境的虚拟企业中，规划和过程设计资源分布在全球各地，软件工具和其他虚拟企业资源来自于异构CAD平台，难以实现彼此间的无缝交互，在这种急剧变化的国际制造背景下，应发展创新夹具设计方法，实现远程分布合作伙伴在无缝协同方式下的交互，根据产品需求变化快速开发装夹规划，随着信息技术驱动下的制造环境已经发生了很大的变化，新的CAFD方法须瞩目于无缝数据交换，分布协同和集成规划等方面。Computer Aided Fixture Design Technology Review and Trends SummaryComputer-aided fixture design (Computer-aided fixture design, CAFD) technology from the 1970s to now, has become an important part of integrated CAD / CAM technology. Article from the four research areas ( installation planning, fixture planning , fixture configuration design , fixture performance evaluation ) CAFD technology included start CAFD technology development at home and abroad (mainly for development results within the past 10 years ) were review , and future trends CAFD analyzed .With the development of manufacturing technology , product design cycles, faster replacement . The traditional mass production model gradually being replaced by small batch mode . To adapt to these changes machinery manufacturing industry should have higher flexibility, flexible manufacturing systems have already abroad as an effective means to develop new products , and the main development direction as machinery manufacturing . The main focus of flexibility in both the machine and tooling , tooling and fixtures is flexible focus. Average modular fixture design and assembly time is spent on special fixtures 5% -20 % of the time , can be considered synonymous with flexible modular fixture fixture . Due to a combination of strong adaptability fixture design and manufacturing cycle is short, low cost , to adapt to the requirements of replacement products , improve the competitiveness of enterprises, so growing manufacturers of all ages . A key technology is modular fixture CAFD technology. Our mid-80s from the 20th century had begun to study the technology , and how the theory of artificial intelligence applied to computer-aided modular fixture design (CAD) process are explored . However, due to a combination of fixture design depends on the workpiece , the workpiece has been changing , resulting in modular fixture CAD difficult to achieve intelligent. After 30 years of tireless efforts of many scholars at home and abroad , although the progress of the work , but from the practical application there is a great distance.1 CAFD Technical Overview From the 1970s began fixture CAD research to date , CAFD technology has developed into CAD / CAM integration is an important part of technology . Currently, the research commenced around CAFD technology mainly includes four aspects: installation planning, installation of central planning , design and fixtures fixture configuration performance evaluation :( 1 ) installation plan . Installation planning task is to determine the processing time required to install the number and orientation of each workpiece machined surface mounting . This part can also be CAPP (Computer-aided process planning) a subset is CAFD interactive interface and integrated CAPP . Installation planning framework , including the development of manufacturing and feature library characterization , definition and positioning choices clamping surface characteristics , installation planning algorithms, and fixture design and verification. Since the installation planning closer links with CAPP , most CAFD field of research has focused on planning clamping jig and fixture design configuration performance evaluation in three areas , but in the fixture configuration design, automatic configuration of the fixture design Research is still small .( 2 ) clamping planning. Fixture planning is mainly used to determine the condition of a particular installation support surface of the workpiece positioning , anchor and clamping points . The main problem considered by the planning fixture comprising: a surface can be selected as the type of clamping the workpiece surface ; clamping surface with respect to the tool axis orientation ; candidate precision clamping surface ; candidate combinations of clamping surfaces ; clamping stability and clamping surface can be and so on.( 3 ) fixture configuration design . Fixture configuration design task is to select the fixture components, fixture structure constructed and assembled them into a final configuration of the fixture to clamp the workpiece . The main problem CAFD jig design configuration comprising: selecting a fixture element such as selection direct contact with the workpiece supporting and positioning the platen ; determine the height of the clamp assembly; placed in the base plate of the clamp assembly ; between the clamp element connection ; fixture, machined surface of the workpiece and ask interference inspection.( 4 ) Performance Evaluation fixture . Performance evaluation is a fixture on performance fixture has been designed to evaluate and analyze , define , measure and optimize fixture design process to ensure the quality of the fixture design. Evaluation of the content includes positioning accuracy , surface precision, clamping and processing stability , resistance to deformation of the clamp element stiffness , the tool path interference check , the surface accessibility and the like.2 CAFD study abroad technology status and results 5 for CAFD from the initial start-up to the development trend of the 20th century, made after a review , which includes both the original Latombe, Ingrand (1980) reasoning for automatic fixture efforts , including Markus (1984) and Miller (1985 ) developed a semi- automated method for a given workpiece try a fixture design , this approach , though not automatically , but provides interactive clamping points, anchor points and support points and other functions , Chou et al ( 1989 ) based on double standards workpiece stability and full restraint requirements , focusing on the design of the clamping fixture process . With the development of CAFD shear to be recognized by a growing number of scholars , artificial intelligence and expert systems applications in the fixture designs are also increasingly being proposed, including Davishi et al ( 1988 ) for the development of expert systems Knowledge Base said , Nee et al ( 1992 ) feature-based fixture classification model, and Pham et al ( 1990 ) developed CAD system and other fixtures .CAFD Throughout the development process , which experienced an interactive computer-aided fixture design system (I-CAFD), based on a set of skills and knowledge of CAFD systems and in the 1990s after the 3rd generation CAFD system three stages. And according to the degree of automation division, fixture design system can be divided into interactive , semi-automatic and automatic systems. After the 1990s , the experience gained, think , CAFD final fixture structure must be generated , and the system only resolved last installation , positioning, clamping and other issues or similar structure search , can not get in line with the practical application of the structure of the work , and analysis nor comprehensive . Therefore, we must develop a structure for the purpose to produce the fixture , the actual production on the commercialization of fixture design -oriented software .The following focuses on the last 10 years to a newer CAFD research progress and problems in terms of attention and summary.2.1 Foreign CAFD technology research status and results CAFD research study abroad planning in clamping jig and fixture configuration design and other aspects of performance evaluation as follows :Mounted central planning : Rong et al studied based on fast fixture configuration design system automatically positioning method in combination clamping fixture components of the planning system and the workpiece geometry is analyzed, a combination of automatic clamp fixture planning accuracy clamping planning and sexual and clamping fixtures can conduct stability studies , once established fixture planning , the results will be applied to the performance evaluation of the fixture design ; addition to the combination of mechanical machining fixture outside , Wang et al. methods case based Reasoning (CBR) is applied to the study of welding fixture , the proposed data extraction method for fixture design information representation , in this method , based on a multi -level CBR method for welding fixture design ; Perremans fixture planning can be developed as input positioning, clamping , expert systems and other supporting surface , and to achieve a combination of fixture elements assembled by expert systems ; Mervyn , who use evolutionary search algorithm presents a method for automatic analysis of modular fixture ; Varadarajan and others to the six -axis precision positioning and clamping kinetic model was designed and hardness models. Fixture configuration design : Rong et al from fixture to fixture configuration design plan for CAFD depth and extensive research and development based on the automatic system configuration design of modular fixture hole system. In the development of rapid response manufacturing automatic configuration of custom fixture design system ; reconfigurable areas in the fixture , Kong et al will rapidly reconfigurable assembly fixture system based on visual analysis is applied to the structure of the fixture workspace synthesis and verification of fast fixture in ; Shen et al correct sliding vice reconfigurable fixture as a basic structure , the proposed four types of institutions for reconfigurable fixture system ; Ryll , who proposed a method for rapid reconfiguration of a fixture and workpiece positioned in the smart clamping system , reconfigurable application of object-oriented approach to ensure that the need to change control software to ensure that work at different fixture installation ; Culpepper, Varadarajan and others bent on incentives and pressures bearing presents a dual purpose of positioning fixture (DPF) and an eccentric shaft ball jig fixture elements to compensate for tolerances and bearing wear , but not related to the impact of the workpiece positioning tolerances of related artifacts ; Ibrahim and others in considering the workpiece material , surface roughness , roughness fixture elements , such as the impact of normal load conditions to determine experimentally the workpiece fixture element contact surface friction coefficient between to reduce experimental error by static methods to ensure the credibility of the experimental results . The results of the configuration is crucial fixture design ; Martin et al imprecise and disadvantages for fixture design uncertainty caused by the application of expert knowledge , a fuzzy reasoning (fuzzy reasoning) approach to support semantic knowledge from different modeling ; Surendra et al o developed a system for automatically generating fixture prismatic workpieces , the automatic fixture configuration design system can automatically select the fixture elements and in accordance with the assembly to meet the needs placed in the right position ; Hunter , who use knowledge templates reuse , you can achieve different knowledge reuse of knowledge as defined by the tribe , and combined with the model , which means that the fixture design process is based on a functional approach IDEFO and UML . Fixture Performance evaluation : Kulankara fixture layout process , who have a greater impact on the workpiece size and precision were studied, and fixture layout optimization technique based on genetic algorithms (GA) can reduce the clamping force and cutting force machined surface deformation caused ; Pelinescu et al fixture based on multiple criteria to determine the quality of the design and layout of acceptable fixture design to evaluate and select an optimal fixture design scheme to balance multiple performance requirements , the paper gives three performance objectives, namely the positioning accuracy of the workpiece, reducing the balance of the positioning of the contact force and positioning of the contact force ; Siebenaler , who focused on the factors analyzed using the finite element method to predict deformation of the workpiece , the simulation results show that the surface of the workpiece surface based on a fixture models can make contact with the workpiece and the reaction force projections; elastic deformation of the workpiece and reaction Satyanarayana , who predicted using the finite element method leads to different boundary conditions were analyzed through experiments carried out performance evaluation ; Amaral , who also using the finite element method in the fixture design system for fixture design performance evaluation and optimization ; Song et al determine the positioning of the state , based on further analysis and study of the non-deterministic positioning program , with an algorithm to detect geometric constraint condition, the algorithm can recognize that under-constrained state and the non-binding movement of the workpiece to be the recognized position constraint condition and unnecessary , this information helps designers to analyze and improve the existing location solutions ; Subranmanian proposed based on a genetic algorithm (GA) optimization method , the use of space coordinates to represent the position of the clamp element that integrates many important concepts of genetic algorithms , such as real-coded mutation and sharing ; Kaya also be applied GAs fixture structure optimization design and the use of limited element method to calculate the objective function value ; Varadarajan et al clamping six-axis positioning accuracy of the principles and characteristics of the analysis and evaluation ; Kang proposed fixture positioning performance , surface accuracy, stability and surface accessibility and other aspects verification ; Hurtado et al proposed a model for optimizing flexible fixture design , the model is used to find the optimal number of active sales , the use of the algorithm aims to obtain consistency of a workpiece and fixture to hold the workpiece rigid body motion stable equilibrium , so that jig elastic deformation remains at or below the user-specified value ; Ratchev et FEA based method , an effective performance evaluation method, which uses an innovative method to predict the simulation of a workpiece fixture in the dynamic behavior of the system , and compatible with any commercial FEA platform ; Wang and Kayaml proposed constraints and optimization based on genetic algorithms to locate and clamp layout.2.2 Domestic CAFD technology research status and results CAD study of the origin of domestic fixture in the mid- 1980s, China Aviation Technology Import and Export Company in Europe to customer requirements, a set of two-dimensional computer-aided design software assembly , opened the country to develop the curtain fixture CAD system . From the mid- 1980s , Chinas colleges and universities have been more than lO fixture CAD system made of a combination of exploration, but it can have a long-standing research and development of Beijing Institute of Machinery , Hebei University of Technology , Nanjing University of Aeronautics and Astronautics , Northwestern Polytechnical University and Harbin Institute of Technology , etc. Currently, research on the fixture CAD content more deeply and specifically involved in academic research institutions and organizations are more and more , in addition to the above units , Sichuan University, Dalian University of Technology , Tianjin University, Hohai University and many other colleges and universities and research institutions involved in the research were to clamp CAD , including some colleges and universities in the ACIS. Fixture component development and building a database to work on different platforms Solid work, Pro-E, UG different CAD platforms fixture CAD system under . In recent years, the main content fixture CAD mostly in clamping fixture configuration planning and design ( including research and development of computer-aided fixture system ) , the research part of the performance evaluation of the fixture interspersed in these two areas . Clamping planning : Don East , who will ANN algorithm ( ie Hopfield algorithm) for automatic clamping planning (automatic fixtureplanning) while positioning through the use of selection rules and determine the clamping surface of the workpiece positioning evaluation matrix for positioning and clamping select the gripping surface is studied and developed to select the positioning and clamping element from the database for the clamp assembly method ; Wu Yuguang ,Zhang Kunming old name . For a combination of holes in the outer contour of the workpiece fixture adopted the Statute of the method to determine the workpiece clamping point plan feasible set of clamping scheme for automatic planning methods were studied ;Wu Yuguang, who also had the best clamping and positioning program evaluation program automatically determines the method is studied , and the use of association (Linkage) workpiece positioning mechanism to identify candidate points in the assessment of accessibility and clamping uses algorithms such as IRC (instantaneousrotational center) triangle and positioning new concepts visible cone , etc. ; Zheng et al , deputy for the past modular fixture clamping study focused on 2D and 3D object geometry aspects of the rules for complex 3D objects or placed in any position of the object needs to locate a mathematical model of the jig , fixture combination for 3D systematically studied . Fixture configuration design : Chen Weifang et al . Fixture assembly model proposed hierarchical thinking , to achieve a rapid assembly fixture components. Rong -ming , who also designed commercial software Fix-Des quasi- automatic fixture design system ; Li Jianfeng , who will be functional decomposition and reconstruction principle and mapping in combination fixture CAD system application have been described ; Xu Lei knowledge engineering combined with the fixture design process , knowledge of the fixture description, classification , discovery and reuse of the basic principles and intelligent fixture design knowledge in solving techniques were the focus of research and development of an integrated knowledge- based resources, computer-aided fixture design support systems ; gold heaven and others for the shortcomings of the order of assembly of modular fixture assembly method is proposed to solve the auto parts size or location of the assembly heuristics ;Xie Xiaowen and others to slot modular fixture , for example, the use of artificial intelligence methods and fixture design parametric modeling technology combined with modular fixture rough set theory and computer aided fixture design principles established modular fixture design system ; Liu Huiying , Liu Qiong , who use PowerBuilder and Oracle developed a computer-aided modular fixture management system ; Hurui Fei et al. fixture elements library , libraries, and the typical structure of a typical component library consisting of multi- instance database fixture presents a combination of top-down hierarchical assembly fixture intelligent assistance systems .Hebei University of Technology is one of the units of modular fixture CAD study conducted earlier , in the late 1980s with the Ministry of Aerospace Industry Sunningdale Precision Machinery Factory Baoding joint development of modular fixture assembly CAD software system , and continue to develop on the basis of the system . Duan Guolin , Qi Hongwei , who will artificial intelligence module, and case-based reasoning (Case-based Reasoning, CBR) method is added to the combination of three-dimensional computer software fixture assembly and configuration design system. Over the years, a combination of computer-aided fixture design system configurations experienced research and development from the earliest R14 to AutoCAIY2002, after several versions updated and improved software architecture has been developed modular fixture aided design packages MFS CAD5.0 Edition has been in practice a very good application , now the CAFD software has been upgraded to version 6.0 , and software features to further improve the development of three-dimensional CAD system modular fixture library management system, the system was further extended to the next ACIS platform , purpose lies in the development of CAD software fixture assembly system independent platform and application. In the above study , based on a combination of fixture elements for heterogeneous database system platform application launched a study aimed at providing a platform for the combination of different CAD applications fixture library system available .Issues and trends facing the development of 3 CAFD Above in accordance with the contents of each of the CAFD CAFD research progress in recent years, several aspects of fixture planning , fixture design and fixture configuration performance evaluation carried out in the review, you can see that in the CAFD development process, for different launched a multi-faceted focus angles using various methods ( application modeling, model analysis software based on artificial intelligence applications , including applications , algorithms, methods of reasoning and functional analysis and expert knowledge of the system ) computer-aided fixture design research for the study of CAD fixture provides more useful reference , but also the degree of fixture design automation system greatly improved, but still not mature commercialization fixture CAD software. The main problem with existing research CAFD systems exist are: fixture design and assembly methods still get more benefit from computer-aided engineering , it is still one of the bottlenecks of modern manufacturing systems. For CAFD research , less applications , compared with CAD, CAM, PDM, MIS and other related computer-aided technologies differ greatly , CAFD should be toward integration , better educated , intelligent and practical direction. Fixture system for information transfer and data sharing among research asked fixture configuration design for different CAD platforms is even more lack