1、精品 料推薦外文翻譯基于事例推理的夾具設(shè)計研究與應(yīng)用摘要 :根據(jù)基于事例的設(shè)計方法 ,提出采用工序件的特征信息和夾具的結(jié)構(gòu)特征信息來描述夾具的相似性 ,并建立了包括這 2 方面主要特征信息為基礎(chǔ)的事例索引碼 ,設(shè)計了事例庫的結(jié)構(gòu)形式 ,創(chuàng)建了層次化的事例組織方式 ;同時 ,提出了基于知識引導(dǎo)的夾具事例檢索算法 ,以及事例的修改和采用同族事例碼進(jìn)行相似事例的存貯 ,形成了基于事例推理的夾具設(shè)計 .所開發(fā)的原型系統(tǒng)在型號工程夾具設(shè)計等項目的設(shè)計過程中得到了應(yīng)用 ,并取得了令人滿意的使用效果 .關(guān)鍵詞 : 基于事例的推理夾具設(shè)計cad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

2、刀具或機(jī)床的位置一致不變。因為夾具的結(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)計是制造過程中的瓶頸 , 制約著效率的提高 . 夾具設(shè)計是一個復(fù)雜的過程 ,需要有從大量的設(shè)計論文中了解質(zhì)量知識的經(jīng)驗，這些設(shè)計論文包括工件的結(jié)構(gòu)設(shè)計、涉及加工工藝，和加工環(huán)境。當(dāng)用這些擅長繪制詳細(xì)設(shè)計圖的傳統(tǒng)的 cad 工具（如 unigraphics、catia 、pro/e)時,這仍然是一項非常耗時的工作，但是利用以往的設(shè)計經(jīng)驗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)以往個案解決的辦法 ,建立一個新問題的方法 ,主要有以下四步驟 :檢索

3、、利用、修改 ,并保留 .這是一個比用專業(yè)系統(tǒng)模仿人類思維有用的使用方法， 因為提出一個類似的情況 ,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、建筑設(shè)計、模具設(shè)計投死 , 規(guī)劃過程中 ,還有夾具設(shè)計 . 孫用六個數(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

4、，來區(qū)別不同的夾具. 使用他們能夠使操作方便 . 因為零件的形狀是多種多樣的 , 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)將會使搜索速度降低 ,其主要特征是不1精品 料推薦重要的 ,因 分配 每個特征的比重必 減少 . 另一方面 ,事例參數(shù)包含所有的特征是困 的。因此 ,考 到 和快速 的需求 ,事例參數(shù)要包含工件的主要特征和 具的 構(gòu)。事例參數(shù)代 由 16 位數(shù) 成： 13 位數(shù)是事例特征 3 位數(shù)是事例 數(shù)字。前 13 位數(shù)代表 13 個特征。 每個數(shù)字與特征的一個屬性相一致 , 可能是 * 、 ？ 、1 、2 ， a 、b, ，z ， ，等其中的一個。其中， *

5、是指任何一個 ,?代表不確定 ,0 代表沒有。系 定 : 具的 型，工件的形狀，位置模式不能是 * 和 ?。在 系統(tǒng)時 ,三個 目的屬性信息沒有 些 , 就意味著必 確定的屬性。最后三位數(shù)是事例 號 ,如果事例特征的 13 位數(shù)是一 的 , 三個數(shù)字就用來區(qū) 他 。 系 定 :000是用于修正的一個典型事例 ,其他事例 001 、002 、, 些是用于 找參考事例的 . 如果其中一個偶 需要改 成典型事例 ,首先它必 要求改成 000,前面的自 成參考事例 .事例索引 的 構(gòu)如 1 所示。1 具 型；6工件重量；11 模型；2工件形狀；7工件 度；12 具體；3工件材料；8加工內(nèi)容；13其他；

6、4批量；9 程所有物；14 到 16事例 ；5工件比例；10定位模型；圖 1事例索引 的 構(gòu)1.2 事例 事例 由 多 定 的事例 成。事例的描述是基于事例推理的最重要的 之一。所以由索引 復(fù)合。1.3 事例的 次化 具的 構(gòu)相似被 是整個 具，成分和內(nèi)容相似。所以，整個 具事例 ，成分事例 ， 具的成分事例 形成相同。整個 具的 料通常是由工件 料和工件加工 料 成 , 就意味著 具的 足特 功能的需求 .全部 具事例是由功能成分 成， 它是用功能成分的名字和數(shù)字來 行描述2精品 料推薦的。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)動參數(shù)，數(shù)字，和它們的約束關(guān)系）。成分事例（夾具的最低

7、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)時間。根據(jù)夾具設(shè)計的需求，事例修改的策略使最接近的事例方法和知識指導(dǎo)結(jié)合起來。首先在深度上查找，然后在寬度上；知識指導(dǎo)策略意味著在來自客觀事物根源的知識規(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，第三查找一個平面兩個銷的定位方法。 如果沒

8、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事例碼匹配，然后計算相似尺寸的價值。3）整理相似尺寸的次序，最大的架子是最類似的事例。兩個事例之間的相似點(diǎn)是基于兩個事例特征之間的相似點(diǎn)。相似點(diǎn)尺寸的計算依靠特征的類型。相似點(diǎn)的價值可以通過數(shù)字化的價值來計算，例如比較重量分別是 50kg 和 20kg 的工件。非數(shù)字化的價值也能計算，例如，現(xiàn)在前13 位索引碼都是非數(shù)字化的價值。一個夾具的相似尺寸的計算公式如下：其中 s 表示通用夾具的相似尺寸， n 表示索引特性數(shù)，表示每個特性的

9、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，數(shù)值計算如下：3精品 料推薦其中表示第 i 個特征的索引特性值，表示事例庫中第j 個事例的第 i 個特征的特性值。所以有兩種方法選擇相似夾具。 一個方法是建立數(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 3.1 事例的修改夾具設(shè)計中相似事例的修改包括以下三個階段：1） 成分的替代2） 保持形式不變，調(diào)整成分的特

10、性3） 模型重新設(shè)計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)計好了。3.2 事例的存儲在將一個新的事例保存到事例庫之前， 設(shè)計者必須考慮保存是否有價值。 如果這個事例不能增加系統(tǒng)的知識，就沒有必要把它保存到事例庫里。如果它有價值的話，設(shè)計者在保存之前必須分析一下，看看這個事例是否作為標(biāo)準(zhǔn)事例或參考事例被存儲了。一個標(biāo)準(zhǔn)事例是一個描述同族事例主要特征的標(biāo)準(zhǔn)。一個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。一個標(biāo)準(zhǔn)事例的最后三位通常是 “000”。一個參考事例屬于同族標(biāo)準(zhǔn)事例，4精品 料推薦最后三位用不同數(shù)字區(qū)分。從被解釋的概念

11、中，可采用以下方法：1）如果一個新的事例和任何一個存在的事例族一致，和一個存在的標(biāo)準(zhǔn)事例的前 13 位數(shù)相同，那么這個事例就不能存儲因為已經(jīng)這種標(biāo)準(zhǔn)事例了。 或者只能作為一個參考事例保存（最后三位不是“ 000”，而且和其它的不一樣）在事例庫中。2）如果一個新的事例和任何一個存在的事例族一致， 并且被認(rèn)為代替這個事例族要比以前的標(biāo)準(zhǔn)事例好，那么這個標(biāo)準(zhǔn)事例就被這個新的事例代替，以前的標(biāo)準(zhǔn)事例作為一個參考事例保存。3）如果一個新的事例和任何一個存在的事例族不一致， 一個新的事例族將會自動產(chǎn)生，并作為標(biāo)準(zhǔn)事例保存到事例庫中。4 夾具設(shè)計中基于事例推理的過程根據(jù)夾具設(shè)計的特性，夾具設(shè)計的基本信息，例

12、如夾具的名字，零件，生產(chǎn)和設(shè)計者等等，必須先輸入。然后，輸入或設(shè)計工件的模型。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， 再存儲到事例庫中。程序流程圖如圖 2 所示圖 2基于事例推理的夾具設(shè)計流程圖5精品 料推薦5 基于事例推理的夾具設(shè)計說明這是一個工件如圖 3 所示。材料是 45 鋼，底座，形狀為塊狀，生產(chǎn)批量為中批等。需要設(shè)計成一個用來旋轉(zhuǎn)孔的旋轉(zhuǎn)夾具。圖 3 需要設(shè)計夾具的一個工件（最大尺寸 80mmx49mmx22mm）工件的特征值，屬性值，事例索引碼和重量在表1 中列出。表 1工

13、件的事例索引碼和重量特征名稱特性值索引碼重量夾具類型車床夾具1100工件形狀塊狀990工件材料中碳鋼370批量中批260工件比例小560工件重量輕560工件剛度硬度強(qiáng)160加工內(nèi)容孔380程序要求完成加工370定位方法三個平面1100夾緊方法不確定？90夾具體復(fù)合480其他沒有0606精品 料推薦通 過 查 找 和 計 算 相 似 點(diǎn) ， 最 相 似 的 事 例 的 事 例 索 引 碼 是19325513321402000，細(xì)節(jié)信息在表 2 中列出。表 2最相似事例的事例索引碼特征名稱特性值索引碼夾具類型車床夾具1工件形狀塊狀9工件材料中碳鋼3批量中批2工件比例小5工件重量輕5工件剛度硬度強(qiáng)1

14、加工內(nèi)容孔3程序要求完成加工3定位方法三個平面1夾緊方法不確定？夾具體復(fù)合4其他沒有0相似點(diǎn)的計算如下：所以夾具的相似尺寸值是 0.806，這是在事例庫中用于設(shè)計的最相似的事例，最相似的事例的結(jié)構(gòu)如圖 4 所示7精品 料推薦圖 4最相似的夾具當(dāng)成分替代，修改定位模型和夾緊模型，以及調(diào)節(jié)相關(guān)尺寸之后，新的夾具被設(shè)計出來，圖形如圖 6 所示圖 5需要設(shè)計的新夾具因為在事例庫中沒有相似夾具，新夾具被儲存到事例庫中。事例索引碼是19325523311402000。6 結(jié)論基于事例推理， 作為一個問題解決的方法， 是一個比模仿人類思想的專業(yè)系統(tǒng)更有效的方法，已經(jīng)在很多難獲取知識的領(lǐng)域里得到發(fā)展。基于事例

15、推理的優(yōu)點(diǎn)如下：它和人類的思想很相似； 一個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，這和慣例庫有8精品 料推薦很大的不同?；谑吕评碇刑岢龅囊粋€夾具設(shè)計的框架已經(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。這個發(fā)展的標(biāo)準(zhǔn)系統(tǒng)，用于航空項目，幫助夾具設(shè)計者提高設(shè)計效率和重新使用先前的設(shè)計資源。9精品 料推薦附錄 2 英文原文application and developmentof case based reasoning in fixture designabstract:

16、 based on the case based designing (cbd) methodology, the fixture similarity is in two respects: the function and the structure information. then, the computer aided fixture design system is created on case based reasoning (cbr),in which the attributes of the main features of workpiece and structure

17、 of fixture as case index code are designed for the retrieve of the similar cases, and the structure and hierarchical relation of case library are set up for store. meanwhile, the algorithm based on the knowledge guided in the retrieve of the similar cases,the strategy of case adapt at ion and case

18、storage in which the case ident if cat ion number is used to distinguish from similar cases are presented. the application of the system in some projects improves the design efficiency and gets a good result .keywords: case based reasoning ;fixture design; computer aided design(cad)fixtures are devi

19、ces 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 desig

20、n is the bottleneck during manufacturing, which restrains to improve the efficiency and leadtime. and fixture design is a complicated process, based on experience that10精品 料推薦needs comprehensive qualitative knowledge about a number of design issues including workpiece configuration, manufacturing pr

21、ocesses 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 resourc

22、es, which are precisely the key factors in improving the efficiency. the methodology of case basedreasoning (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 t

23、han 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 areas2-4, such as in injection molding an

24、d design, architectural design, die casting die design, process planning, and also in fixture design. sun used six digitals to compose the index code that includedworkpiece shape, machine portion, bushing, the 1st locating device, the 2 nd locating device and clamping device5. but the system cannot

25、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 cbr6.1 construction of a case index and case library1.1 case indexthe case index should be composed of all features of the w

26、orkpiece, which11精品 料推薦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

27、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

28、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 anattri

29、bute 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 it

30、ems 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”

31、 is a prototype case, which is used for retrieval,12精品 料推薦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 theprototype case, first it must be required to apply to change the one “to 000”, and the fo

32、rmer is changed to referential case automatically.the construction of the case index code is shown in fig.1.1.2 case librarythe 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

33、hierarchical form of casethe 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 in

34、formation 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 function13精品 料推薦components

35、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 t

36、he 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 retrievalin the case based design of fixtures ,the most important thing is

37、 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

38、 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 typ

39、e, 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)accordin

40、g to the case index information of fixture case library, search the relevant case library;14精品 料推薦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

41、 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 an

42、d 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 theindex feature,i

43、s the weight of each feature,is the similaritymeasure of the attributeof the i2th feature with the attributeof relativefeature of the j-th case in the case library. at the same time,the value counts as follows:15精品 料推薦.whereis the value of the index attribute of the i-th feature, andis thevalue of a

44、ttribute 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

45、 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 sort

46、ed order.3 case adaptation and case storage3.1 case adaptationthe 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 form16精品 料推薦remains;

47、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 storagebefore saving a new fixture case in the case library, the designer must consider whether the saving is valu

48、able. 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

49、 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 thecase library. the last three digits of a prototype case are always“ 000”. a reference case belongs to the same family as

50、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 j