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西安文理學(xué)院本科畢業(yè)設(shè)計(jì)（論文）中期檢查表 題 目 曲軸零件工藝規(guī)程及工裝設(shè)計(jì) 學(xué)生姓名 胡阿敏 學(xué) 號(hào) 08102080243 專業(yè)名稱 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 指導(dǎo)教師 趙竹青 檢查時(shí)間 班 級(jí) 08機(jī)械（2）班 畢 業(yè) 設(shè) 計(jì)（論文） 進(jìn) 展 情 況 1、對(duì)所要加工的曲軸零件做詳盡的分析，初步了解該零件的結(jié)構(gòu)特點(diǎn)和主要技術(shù)要求，以及零件加工工藝特性。由于該曲軸零件形狀較為復(fù)雜，剛度較差，而加工技術(shù)要求較高，所以需要專用夾具進(jìn)行零件的加工。經(jīng)過該時(shí)期查閱大量資料以及對(duì)零件的分析，已經(jīng)對(duì)本次設(shè)計(jì)的要求有所領(lǐng)悟。 2、設(shè)計(jì)工藝加工過程，分析加工過程中需注意的問題，提出夾具設(shè)計(jì)方案，并擬定曲軸加工的工藝規(guī)程，制作工藝卡片。 3、進(jìn)行夾具的整體設(shè)計(jì)，在設(shè)計(jì)中應(yīng)注意到連桿軸頸與主軸頸存在偏心距的問題。 4、熟悉并進(jìn)一步掌握Auto CAD軟件的使用.為下一階段繪制夾具裝配圖及零件工作圖做準(zhǔn)備。 以上是該階段的情況，在下一階段，將對(duì)各個(gè)部分進(jìn)行進(jìn)一步具體的設(shè)計(jì)分析，并著手撰寫設(shè)計(jì)說明書以及相關(guān)外文翻譯。 指 導(dǎo) 教 師 意 見 簽字： 年 月 日 教研室意見 簽字： 年 月 日 西安文理學(xué)院機(jī)械電子工程系 本科畢業(yè)設(shè)計(jì)（論文） 題 目 曲軸零件工藝規(guī)程及工裝設(shè)計(jì) 專業(yè)班級(jí) 08級(jí)機(jī)電（2）班 學(xué) 號(hào) 08102080243 學(xué)生姓名 胡阿敏 指導(dǎo)教師 趙竹青 設(shè)計(jì)所在單位 西安文理學(xué)院 年 月 西安文理學(xué)院本科畢業(yè)設(shè)計(jì)（論文）任務(wù)書 題 目 曲軸零件工藝規(guī)程及工裝設(shè)計(jì) 學(xué)生姓名 胡阿敏 學(xué) 號(hào) 08102080243 專業(yè)班級(jí) 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 08機(jī)電(2)班 指導(dǎo)教師 趙竹青 職 稱 副教授 教 研 室 機(jī)械 畢業(yè)設(shè)計(jì)（論文）任務(wù)與要求 任務(wù)：1、對(duì)曲軸零件的結(jié)構(gòu)特點(diǎn)和技術(shù)要求進(jìn)行分析 2、根據(jù)曲軸零件的結(jié)構(gòu)特點(diǎn)，選擇合適的機(jī)床、刀具，并進(jìn)行夾具設(shè)計(jì) 3、制定曲軸機(jī)械加工工藝規(guī)程 4、繪制夾具裝配圖和零件工作圖 5、撰寫相應(yīng)論文 6、相關(guān)外文翻譯。 要求：1、收集并整理關(guān)于曲軸零件工藝設(shè)計(jì)的相關(guān)資料，學(xué)習(xí)相關(guān)理論； 2、確定設(shè)計(jì)方案，并對(duì)各部分進(jìn)行設(shè)計(jì)； 3、完成相關(guān)圖文表達(dá)，撰寫畢業(yè)論文。 畢業(yè)設(shè)計(jì)（論文）工作進(jìn)程 起止時(shí)間 工作內(nèi)容 2012.1.10～2012.1.16 2012.1.17～2012.2.29 2012.3.1～2012.3.20 2012.3.21～2012.4.10 2012.4.11～2012.4.25 2012.4.26～2012.5.8 2012.5.9～2012.5.11 接受設(shè)計(jì)任務(wù)，明確設(shè)計(jì)內(nèi)容要求； 查（借）閱資料，學(xué)習(xí)關(guān)于曲軸零件加工的基礎(chǔ)理論和知識(shí)，了解所設(shè)計(jì)的曲軸零件結(jié)構(gòu)，撰寫開題報(bào)告； 進(jìn)行設(shè)計(jì)分析，包括機(jī)床、刀具的選擇，提出夾具的設(shè)計(jì)方案，并擬定曲軸加工的工藝規(guī)程； 完成曲軸零件的工裝設(shè)計(jì)； 用相關(guān)繪圖軟件繪制夾具裝配圖和零件工作圖； 撰寫畢業(yè)論文；論文定稿； 整理資料，準(zhǔn)備答辯。 開始日期 2012-1-10 完成日期 2012-5-11 教研室主任（簽字） 系主任（簽字） 西安文理學(xué)院本科畢業(yè)設(shè)計(jì)（論文）開題報(bào)告 題 目 曲軸零件工藝規(guī)程及工裝設(shè)計(jì) 學(xué)生姓名 胡阿敏 學(xué) 號(hào) 08102080243 專業(yè)名稱 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 指導(dǎo)教師 趙竹青 開題時(shí)間 班 級(jí) 08機(jī)電2班 一、 選題目的和意義 本課題研究的是曲軸零件的加工過程，并擬定工藝規(guī)程，進(jìn)行工裝設(shè)計(jì)。通過對(duì)該課題的研究，對(duì)加工曲軸所用到的工藝裝備：夾具進(jìn)行設(shè)計(jì)并選擇合適的刀具、機(jī)床。本設(shè)計(jì)從分析曲軸零件入手，闡明曲軸的功用和加工過程，以便對(duì)曲軸及其加工方法有一個(gè)明確的認(rèn)識(shí)；然后結(jié)合曲軸生產(chǎn)的實(shí)際情況，通過查閱大量資料確定曲軸加工的工藝規(guī)程及工裝設(shè)計(jì)。 曲軸是汽車發(fā)動(dòng)機(jī)的關(guān)鍵零件之一,其性能好壞直接影響到汽車發(fā)動(dòng)機(jī)的質(zhì)量和壽命.曲軸在發(fā)動(dòng)機(jī)中承擔(dān)著最大負(fù)荷和全部功率,并承受強(qiáng)大的方向不斷變化的彎矩及扭矩，同時(shí)經(jīng)受著長(zhǎng)時(shí)間高速運(yùn)轉(zhuǎn)的磨損，因此要求曲軸材質(zhì)具有較高的剛性、疲勞強(qiáng)度和良好的耐磨性能。發(fā)動(dòng)機(jī)曲軸的作用是將活塞的往復(fù)直線運(yùn)動(dòng)通過連桿轉(zhuǎn)化為旋轉(zhuǎn)運(yùn)動(dòng)，從而實(shí)現(xiàn)發(fā)動(dòng)機(jī)由化學(xué)能轉(zhuǎn)變?yōu)闄C(jī)械能的輸出。此設(shè)計(jì)的經(jīng)濟(jì)指標(biāo)高低對(duì)于機(jī)械加工企業(yè)具有十分重要的意義。 二、 本課題在國(guó)內(nèi)外的研究狀況及發(fā)展趨勢(shì) 在國(guó)內(nèi)，我國(guó)曲軸零件生產(chǎn)線多數(shù)由普通機(jī)床和專用機(jī)床組成，生產(chǎn)效率和自動(dòng)化程度相對(duì)較低。粗加工設(shè)備多采用多刀車床車削曲軸主軸頸及拐頸，工序的質(zhì)量穩(wěn)定性較差，容易產(chǎn)生較大的內(nèi)應(yīng)力，難以達(dá)到合理的加工余量。一般精加工采用MQ8260等曲軸磨床粗磨-半精磨-精磨-拋光，通?？渴止げ僮?，加工質(zhì)量不穩(wěn)定。其中，發(fā)動(dòng)機(jī)曲軸制造技術(shù)進(jìn)展最為迅速的是機(jī)械加工裝備，比較典型的加工工藝是銑削和磨削。 在國(guó)外，VDF 315 OM-4高速隨動(dòng)外銑床是德國(guó)BOEHRINGER公司專為汽車發(fā)動(dòng)機(jī)曲軸設(shè)計(jì)制造的柔性數(shù)控銑床，該設(shè)備可以一次裝夾不改變曲軸回轉(zhuǎn)中心隨動(dòng)跟蹤銑削曲軸的連桿軸頸。VDF 315 OM-4高速隨動(dòng)外銑使用SIEMENS 840D CNC控制系統(tǒng)，設(shè)備操作說明書在人機(jī)界面上，通過輸入零件的基本參數(shù)即可自動(dòng)生成加工程序，可以加工長(zhǎng)度450～700mm、回轉(zhuǎn)直徑在380mm以內(nèi)的各種曲軸，連桿軸頸直徑誤差為±0.02mm。 隨著貿(mào)易全球化的到來， 我國(guó)的發(fā)動(dòng)機(jī)曲軸生產(chǎn)已得到較快的發(fā)展，曲軸精加工采用國(guó)內(nèi)數(shù)控磨床磨削情況已相當(dāng)普遍，產(chǎn)品加工精度已有相當(dāng)程度的提高。曲軸在發(fā)動(dòng)機(jī)中是承受載荷傳遞動(dòng)力的重要零部件，也是發(fā)動(dòng)機(jī)五大零部件中最難以保證加工質(zhì)量的零部件，其性能、水平直接影響整機(jī)的性能水平及可靠性。因此，各工業(yè)發(fā)達(dá)國(guó)家十分重視曲軸的生產(chǎn)，不斷改進(jìn)其材質(zhì)及加工手段，以提高其性能水平，滿足發(fā)動(dòng)機(jī)行業(yè)的需要。先進(jìn)的加工工藝加工出的曲軸質(zhì)量好、效率高且穩(wěn)定，伴隨著汽車工業(yè)的發(fā)展，我國(guó)發(fā)動(dòng)機(jī)曲軸的生產(chǎn)發(fā)展較快，總量已具有相當(dāng)大的規(guī)模，無論是設(shè)計(jì)水平，還是產(chǎn)品品種、質(zhì)量、生產(chǎn)規(guī)模、生產(chǎn)方式都有很大的發(fā)展。隨著中國(guó)汽車產(chǎn)業(yè)的飛速發(fā)展，相應(yīng)的新工藝、新裝備、新材料也將不斷地涌現(xiàn)，高速、高效加工在曲軸制造業(yè)已有相當(dāng)程度的應(yīng)用，并成為主要發(fā)展方向，相信曲軸制造技術(shù)在將來會(huì)有更新、更快的發(fā)展。 三、 主要研究?jī)?nèi)容 1、對(duì)曲軸零件的結(jié)構(gòu)特點(diǎn)進(jìn)行分析，選擇合適的機(jī)床、刀具，并進(jìn)行夾具設(shè)計(jì)。 2、分析曲軸的加工過程，并結(jié)合曲軸生產(chǎn)的實(shí)際情況，查閱資料確定曲軸加工的工藝規(guī)程及工裝設(shè)計(jì)。 3、用相關(guān)繪圖軟件繪制夾具裝配圖和零件工作圖。 4、撰寫畢業(yè)論文。 指導(dǎo)教師意見及建議： 簽字： 年 月 日 教研室審核意見： 簽字： 年 月 日 注：此表前三項(xiàng)由學(xué)生填寫后，交指導(dǎo)教師簽署意見，經(jīng)教研室審批后，才能開題。 西安文理學(xué)院本科畢業(yè)設(shè)計(jì)（論文） 附錄A 外文翻譯-原文 Application and development Of case based reasoning in fixture design Fixtures are devices that serve as the purpose of holding the workpiece securely and accurately, and maintaining a consistent relationship with respect to the tools while machining. Because the fixture structure depends on the feature of the product and the status of the process planning in the enterprise, its design is the bottleneck during manufacturing, which restrains to improve the efficiency and leadtime. And fixture design is a complicated process, based on experience that needs comprehensive qualitative knowledge about a number of design issues including workpiece configuration, manufacturing processes involved, and machining environment. This is also a very time consuming work when using traditional CAD tools (such as Unigraphics, CATIA or Pro/E), which are good at performing detailed design tasks, but provide few benefits for taking advantage of the previous design experience and resources, which are precisely the key factors in improving the efficiency. The methodology of case based reasoning (CBR) adapts the solution of a previously solved case to build a solution for a new problem with the following four steps: retrieve, reuse, revise, and retain [1]. This is a more useful method than the use of an expert system to simulate human thought because proposing a similar case and applying a few modifications seems to be self explanatory and more intuitive to humans .So various case based design support tools have been developed for numerous areas[2-4], such as in injection molding and design, architectural design, die casting die design, process planning, and also in fixture design. Sun used six digitals to compose the index code that included workpiece shape, machine portion, bushing, the 1st locating device, the 2nd locating device and clamping device[5]. But the system cannot be used for other fixture types except for drill fixtures, and cannot solve the problem of storage of the same index code that needs to be retained, which is very important in CBR[6]. 1 Construction of a Case Index and Case Library 1.1 Case index The case index should be composed of all features of the workpiece, which are distinguished from different fixtures. Using all of them would make the operation in convenient. Because the forms of the parts are diverse, and the technology requirements of manufacture in the enterprise also develop continuously, lots of features used as the case index will make the search rate slow, and the main feature unimportant, for the reason that the relative weight which is allotted to every feature must diminish. And on the other hand, it is hard to include all the features in the case index. Therefore, considering the practicality and the demand of rapid design, the case index includes both the major feature of the workpiece and the structure of fixture. The case index code is made up of 16 digits: 13 digits for case features and 3 digits for case identification number. The first 13 digits represent 13 features. Each digit is corresponding to an attribute of the feature, which may be one of“*”, “？”, “1”, “2”,…,“A”,“B”,…, “Z”,…, etc. In which, “*” means anyone, “?” uncertain, “0” nothing. The system rules: fixture type, workpiece shape, locating model cannot be “*”or“?”. When the system is designed, the attribute information of the three items does not have these options, which means the certain attribute must be selected. The last three digits are the case identification number, which means the 13 digits of the case feature are the same, and the number of these three digits is used for distinguishing them. The system also rules: “000” is a prototype case, which is used for retrieval, and other cases are “001”,“002”,…, which are used for reference cases to be searched by designers. If occasionally one of them needs to be changed as the prototype case, first it must be required to apply to change the one to “000”, and the former is changed to referential case automatically. The construction of the case index code is shown in Fig.1. 1.2 Case library The case library consists of lots of predefined cases. Case representation is one of the most important issues in case based reasoning. So compounding with the index code,. 1.3 Hierarchical form of Case The structure similarity of the fixture is represented as the whole fixture similarity, components similarity and component similarity. So the whole fixture case library, components case library, component case library of fixture are formed correspondingly. Usually design information of the whole fixture is composed of workpiece information and workpiece procedure information, which represent the fixture satisfying the specifically designing function demand. The whole fixture case is made up of function components, which are described by the function components’ names and numbers. The components case represents the members. (function component and other structure components， main driven parameter, the number, and their constrain relations.) The component case (the lowest layer of the fixture) is the structure of function component and other components. In the modern fixture design there are lots of parametric standard parts and common non standard parts. So the component case library should record the specification parameter and the way in which it keeps them. 2 Strategy of Case Retrieval In the case based design of fixtures ,the most important thing is the retrieval of the similarity, which can help to obtain the most similar case, and to cut down the time of adaptation. According to the requirement of fixture design, the strategy of case retrieval combines the way of the nearest neighbor and knowledge guided. That is, first search on depth, then on breadth; the knowledge guided strategy means to search on the knowledge rule from root to the object, which is firstly searched by the fixture type, then by the shape of the workpiece, thirdly by the locating method. For example, if the case index code includes the milling fixture of fixture type, the search is just for all milling fixtures, then for box of workpiece shape, the third for 1plane+ 2pine of locating method. If there is no match of it, then the search stops on depth, and returns to the upper layer, and retrieves all the relative cases on breadth. Retrieval algorithms: 1)According to the case index information of fixture case library, search the relevant case library; 2)Match the case index code with the code of each case of the case library, and calculate the value of the similarity measure; 3)Sort the order of similarity measure, the biggest value, which is the most analogical case. Similarity between two cases is based on the similarity between the two cases. features. The calculation of similarity measure depends on the type of the feature. The value of similarity can be calculated for numerical values, for example, compareWorkpiece with the weight of 50kg and 20kg. The value can also be calculated between non numerical values, for example, now the first 13 digits index code is all non numerical values. The similarity measure of a fixture is calculated as follows: where S is the similarity measure of current fixture, n is the number of the index feature, is the weight of each feature, is the similarity measure of the attribute of the i2th feature with the attributeof relative feature of the j-th case in the case library. At the same time, , the value counts as follows: . Where is the value of the index attribute of the i-th feature, and is the value of attribute of the relative i-th feature of the j-th case in case library. So there are two methods to select the analogical fixture. One is to set the value. If the values of similarity measure of current cases were less than a given value, those cases would not be selected as analogical cases. When the case library is initially set up, and there are only a few cases, the value can be set smaller. If there are lots of analogical cases, the value should get larger. The other is just to set the number of the analogical cases (such as10), which is the largest value of similarity measure from the sorted order. 3 Case adaptation and Case Storage 3.1 Case adaptation The modification of the analogical case in the fixture design includes the following three cases: 1) The substitution of components and the component; 2) Adjusting the dimension of components and the component while the form remains; 3) The redesign of the model. If the components and component of the fixture are common objects, they can be edited, substituted and deleted with tools, which have been designed. 3.2 Case storage Before saving a new fixture case in the case library, the designer must consider whether the saving is valuable. If the case does not increase the knowledge of the system, it is not necessary to store it in the case library. If it is valuable, then the designer must analyze it before saving it to see whether the case is stored as a prototype case or as reference case. A prototype case is a representation that can describe the main features of a case family. A case family consists of those cases whose index codes have the same first 13 digits and different last three digits in the case library. The last three digits of a prototype case are always “000”. A reference case belongs to the same family as the prototype case and is distinguished by the different last three digits. From the concept that has been explained, the following strategies are adopted: 1) If a new case matches any existing case family, it has the same first 13 digits as an existing prototype case, so the case is not saved because it is represented well by the prototype case. Or is just saved as a reference case (the last 3 digits are not “000”, and not the same with others) in the case library. 2) If a new case matches any existing case family and is thought to be better at representing this case family than the previous prototype case, then the prototype case is substituted by this new case, and the previous prototype case is saved as a reference case. 3) If a new case does not match any existing case family, a new case family will be generated automatically and the case is stored as the prototype case in the case library. 4 Process of CBR in Fixture Design According to the characteristics of fixture design, the basic information of the fixture design such as the name of fixture, part, product and the designer, etc. must be input first. Then the fixture file is set up automatically, in which all components of the fixture are put together. Then the model of the workpiece is input or designed. The detailed information about the workpiece is input, the case index code is set up, and then the CBR begins to search the analogical cases, relying on the similarity measure, and the most analogical case is selected out. If needed, the case is adapted to satisfy the current design, and restored into the case library. The flowchart of the process is shown in Fig.3. 5 Conclusion CBR, as a problem solving methodology, is a more efficient method than an expert system to simulate human thought, and has been developed in many domains where knowledge is difficult to acquire. The advantages of the CBR are as follows: it resembles human thought more closely; the building of a case library which has self learning ability by saving new cases is easier and faster than the building of a rule library; and it supports a better transfer and explanation of new knowledge that is more different than the rule library. A proposed fixture design framework on the CBR has been implemented by using Visual C ++, UG/Open API in U n graphics with Oracle as database support, which also has been integrated with the 32D parametric common component library, common components library and typical fixture library. The prototype system, developed here, is used for the aviation project, and aids the fixture designers to improve the design efficiency and reuse previous design resources. 附錄B 外文翻譯-翻譯 基于事例推理的夾具設(shè)計(jì)研究與應(yīng)用 夾具是以確定工件安全定位準(zhǔn)確為目的的裝置，并在加工過程中保持工件與刀具或機(jī)床的位置一致不變。因?yàn)閵A具的結(jié)構(gòu)依賴于產(chǎn)品的特點(diǎn)和在企業(yè)規(guī)劃中加工工序的地位,所以它的設(shè)計(jì)是制造過程中的瓶頸,制約著效率的提高. 夾具設(shè)計(jì)是一個(gè)復(fù)雜的過程,需要有從大量的設(shè)計(jì)論文中了解質(zhì)量知識(shí)的經(jīng)驗(yàn)，這些設(shè)計(jì)論文包括工件的結(jié)構(gòu)設(shè)計(jì)、涉及加工工藝，和加工環(huán)境。當(dāng)用這些擅長(zhǎng)繪制詳細(xì)設(shè)計(jì)圖的傳統(tǒng)的CAD工具（如Unigraphics、CATIA、Pro/E)時(shí),這仍然是一項(xiàng)非常耗時(shí)的工作，但是利用以往的設(shè)計(jì)經(jīng)驗(yàn)和資源也不能提供一些益處,而這正是提高效率的關(guān)鍵因素. 基于事例推理 (CBR) 的方法適應(yīng)以往個(gè)案解決的辦法,建立一個(gè)新問題的方法,主要有以下四步驟:檢索、利用、修改,并保留.這是一個(gè)比用專業(yè)系統(tǒng)模仿人類思維有用的使用方法，因?yàn)樘岢鲆粋€(gè)類似的情況,和采用一些修改,似乎不言自明,而且比人類更直觀.所以支持不同事例的設(shè)計(jì)工具已經(jīng)在諸多領(lǐng)域中發(fā)展起來，如在注射成型及設(shè)計(jì)、建筑設(shè)計(jì)、模具設(shè)計(jì)投死, 規(guī)劃過程中,還有夾具設(shè)計(jì). 孫用六個(gè)數(shù)字組成代碼參數(shù),包括工件的形狀、機(jī)械部分、軸襯,第一定位裝置,第二定位裝置和夾緊裝置. 但這個(gè)系統(tǒng)不能用于除鉆床夾具外的其他夾具類型,不能解決儲(chǔ)存需要保留的同一參數(shù)代碼的問題,這在CBR中是非常重要的. 1、事例參數(shù)和事例圖書館的建立 1.1事例參數(shù) 事例參數(shù)應(yīng)該由工件的所有的特征組成，來區(qū)別不同的夾具. 使用他們能夠使操作方便. 因?yàn)榱慵男螤钍嵌喾N多樣的, 在生產(chǎn)企業(yè)中制造的技術(shù)要求也不斷發(fā)展,許多特征作被用做事例參數(shù)將會(huì)使搜索速度降低,其主要特征是不重要的,因?yàn)榉峙浣o每個(gè)特征的比重必須減少. 另一方面,事例參數(shù)包含所有的特征是困難的。 因此,考慮到實(shí)際和快速設(shè)計(jì)的需求,事例參數(shù)要包含工件的主要特征和夾具的結(jié)構(gòu)。事例參數(shù)代碼由16位數(shù)組成：13位數(shù)是事例特征 3位數(shù)是事例識(shí)別數(shù)字。 前13位數(shù)代表13個(gè)特征。 每個(gè)數(shù)字與特征的一個(gè)屬性相一致,這可能是"*"、"？"、"1"、"2"，…，"A"、"B",…，"Z"，…，等其中的一個(gè)。其中，"*"是指任何一個(gè),"?"代表不確定,"0"代表沒有。 系統(tǒng)規(guī)定:夾具的類型，工件的形狀，位置模式不能是"*"和"?"。在設(shè)計(jì)系統(tǒng)時(shí),三個(gè)項(xiàng)目的屬性信息沒有這些選擇,這就意味著必須選擇確定的屬性。 最后三位數(shù)是事例識(shí)別號(hào)碼,如果事例特征的13位數(shù)是一樣的,這三個(gè)數(shù)字就用來區(qū)別他們。 該系統(tǒng)還規(guī)定:"000"是用于修正的一個(gè)典型事例,其他事例"001"、"002"、…,這些是用于設(shè)計(jì)師查找參考事例的. 如果其中一個(gè)偶爾需要改變成典型事例,首先它必須要求改成"000",前面的自動(dòng)變成參考事例. 事例索引碼的結(jié)構(gòu)如圖1所示。 1—夾具類型； 6—工件重量； 11—夾緊模型； 2—工件形狀； 7—工件剛度； 12—夾具體； 3—工件材料； 8—加工內(nèi)容； 13—其他； 4—批 量； 9—過程所有物； 14到16—事例識(shí)別碼； 5—工件比例； 10—定位模型； 圖1 事例索引碼的結(jié)構(gòu) 1.2事例庫 事例庫由許多預(yù)定義的事例組成。事例的描述是基于事例推理的最重要的問題之一。所以由索引碼復(fù)合。 1.3 事例的層次化 夾具的結(jié)構(gòu)相似被認(rèn)為是整個(gè)夾具，成分和內(nèi)容相似。所以，整個(gè)夾具事例庫，成分事例庫，夾具的成分事例庫形成相同。整個(gè)夾具的設(shè)計(jì)資料通常是由工件資料和工件加工資料組成,這就意味著夾具的設(shè)計(jì)應(yīng)滿足特別功能的需求.全部夾具事例是由功能成分組成，它是用功能成分的名字和數(shù)字來進(jìn)行描述的。成分事例代表成員（成分功能和其他結(jié)構(gòu)成分，主要驅(qū)動(dòng)參數(shù)，數(shù)字，和它們的約束關(guān)系）。成分事例（夾具的最低層）是功能成分和和其他成分的結(jié)構(gòu)。在現(xiàn)代夾具設(shè)計(jì)中有很多參數(shù)化準(zhǔn)件和普通非標(biāo)準(zhǔn)件。所以成分事例圖書館應(yīng)記錄特殊參數(shù)和保持它們的方法。 2、事例修改的策略 在基于事例的夾具設(shè)計(jì)中，最重要的是相似點(diǎn)的修改，這樣能有助于獲得最相似的事例，以及縮短適應(yīng)時(shí)間。根據(jù)夾具設(shè)計(jì)的需求，事例修改的策略使最接近的事例方法和知識(shí)指導(dǎo)結(jié)合起來。首先在深度上查找，然后在寬度上；知識(shí)指導(dǎo)策略意味著在來自客觀事物根源的知識(shí)規(guī)則上查找，這就要首先查找固定類型，然后查找工件的形狀，第三查找定位方法。例如，如果事例索引碼包括夾具類型的磨削夾具，就只查找所有的磨削夾具，然后查找工件形狀的盒子，第三查找一個(gè)平面兩個(gè)銷的定位方法。如果沒有合適的，就查找深度標(biāo)點(diǎn)，然后回到最上層，然后再找所有與寬度相關(guān)的事例。 修改方法： 1） 根據(jù)夾具事例庫的事例索引信息，查找有關(guān)事例庫。 2） 將事例索引碼與事例庫的每個(gè)事例碼匹配，然后計(jì)算相似尺寸的價(jià)值。 3） 整理相似尺寸的次序，最大的架子是最類似的事例。 兩個(gè)事例之間的相似點(diǎn)是基于兩個(gè)事例特征之間的相似點(diǎn)。相似點(diǎn)尺寸的計(jì)算依靠特征的類型。相似點(diǎn)的價(jià)值可以通過數(shù)字化的價(jià)值來計(jì)算，例如比較重量分別是50kg 和 20kg的工件。非數(shù)字化的價(jià)值也能計(jì)算，例如，現(xiàn)在前13位索引碼都是非數(shù)字化的價(jià)值。一個(gè)夾具的相似尺寸的計(jì)算公式如下： 其中S表示通用夾具的相似尺寸，n表示索引特性數(shù)，表示每個(gè)特性的重量，表示事例庫中特性和相關(guān)夾具的特性的相似尺寸。同時(shí)， ，數(shù)值計(jì)算如下： 其中表示第i個(gè)特征的索引特性值，表示事例庫中第j個(gè)事例的第i個(gè)特征的特性值。 所以有兩種方法選擇相似夾具。一個(gè)方法是建立數(shù)值。如果通用事例的相似尺寸值比給定的數(shù)值小，這些事例就不能選來作相似事例。事例庫最初建立的時(shí)候，只有一些事例，數(shù)值可以建小一點(diǎn)。如果有大量的相似事例，數(shù)值就應(yīng)該建的大一些。另外一個(gè)方法是只建立相似事例的數(shù)字（例如10），這是類型單里相似尺寸的最大值。 3 、事例的修改和存儲(chǔ) 3.1事例的修改 夾具設(shè)計(jì)中相似事例的修改包括以下三個(gè)階段： 1） 成分的替代 2） 保持形式不變，調(diào)整成分的特性 3） 模型重新設(shè)計(jì) 如果夾具的成分是普通的物品，它們能通過使用工具被修改，代替以及刪除，這些已經(jīng)被設(shè)計(jì)好了。 3.2事例的存儲(chǔ) 在將一個(gè)新的事例保存到事例庫之前，設(shè)計(jì)者必須考慮保存是否有價(jià)值。如果這個(gè)事例不能增加系統(tǒng)的知識(shí)，就沒有必要把它保存到事例庫里。如果它有價(jià)值的話，設(shè)計(jì)者在保存之前必須分析一下，看看這個(gè)事例是否作為標(biāo)準(zhǔn)事例或參考事例被存儲(chǔ)了。一個(gè)標(biāo)準(zhǔn)事例是一個(gè)描述同族事例主要特征的標(biāo)準(zhǔn)。一個(gè)同族事例是有事例庫中索引碼前13位相同而最后三位不同的那些事例組成的。一個(gè)標(biāo)準(zhǔn)事例的最后三位通常是“000”。一個(gè)參考事例屬于同族標(biāo)準(zhǔn)事例，最后三位用不同數(shù)字區(qū)分。 從被解釋的概念中，可采用以下方法： 1）如果一個(gè)新的事例和任何一個(gè)存在的事例族一致，和一個(gè)存在的標(biāo)準(zhǔn)事例的前13位數(shù)相同，那么這個(gè)事例就不能存儲(chǔ)因?yàn)橐呀?jīng)這種標(biāo)準(zhǔn)事例了?；蛘咧荒茏鳛橐粋€(gè)參考事例保存（最后三位不是“000”，而且和其它的不一樣）在事例庫中。 2）如果一個(gè)新的事例和任何一個(gè)存在的事例族一致，并且被認(rèn)為代替這個(gè)事例族要比以前的標(biāo)準(zhǔn)事例好，那么這個(gè)標(biāo)準(zhǔn)事例就被這個(gè)新的事例代替，以前的標(biāo)準(zhǔn)事例作為一個(gè)參考事例保存。 3）如果一個(gè)新的事例和任何一個(gè)存在的事例族不一致，一個(gè)新的事例族將會(huì)自動(dòng)產(chǎn)生，并作為標(biāo)準(zhǔn)事例保存到事例庫中。 4、夾具設(shè)計(jì)中基于事例推理的過程 根據(jù)夾具設(shè)計(jì)的特性，夾具設(shè)計(jì)的基本信息，例如夾具的名字，零件，生產(chǎn)和設(shè)計(jì)者等等，必須先輸入。然后，輸入或設(shè)計(jì)工件的模型。輸入有關(guān)工件的細(xì)節(jié)信息，建立事例索引碼，然后CBR開始依靠相似尺寸查找相似事例，選出最相似的事例。如果需要的話，事例要滿足通用性設(shè)計(jì)，再存儲(chǔ)到事例庫中。程序流程圖如圖2所示 圖2 基于事例推理的夾具設(shè)計(jì)流程圖 6、 結(jié)論 基于事例推理，作為一個(gè)問題解決的方法，是一個(gè)比模仿人類思想的專業(yè)系統(tǒng)更有效的方法，已經(jīng)在很多難獲取知識(shí)的領(lǐng)域里得到發(fā)展。基于事例推理的優(yōu)點(diǎn)如下：它和人類的思想很相似；一個(gè)事例庫通過保存新事例獲得自學(xué)能力，它比有慣例庫更快更容易，它可以更好的傳遞和解釋新的知識(shí)，這和慣例庫有很大的不同。基于事例推理中提出的一個(gè)夾具設(shè)計(jì)的框架已經(jīng)被實(shí)行了，使用的是支持基礎(chǔ)數(shù)據(jù)的VC++，UG電腦繪圖軟件。這個(gè)框架也已經(jīng)和普通成分庫和典型夾具庫結(jié)合起來。這個(gè)發(fā)展的標(biāo)準(zhǔn)系統(tǒng)，用于航空項(xiàng)目，幫助夾具設(shè)計(jì)者提高設(shè)計(jì)效率和重新使用先前的設(shè)計(jì)資源。 第10頁