3598 渦輪盤(pán)液壓立拉夾具設(shè)計(jì)
3598 渦輪盤(pán)液壓立拉夾具設(shè)計(jì),渦輪,液壓,夾具,設(shè)計(jì)
黑龍江科技學(xué)院畢業(yè)設(shè)計(jì)（論文）任務(wù)書(shū)姓名： 李 晶 任務(wù)下達(dá)日期： 2006 年 3 月 13 日設(shè)計(jì)（論文）開(kāi)始日期： 2006 年 3 月 14 日設(shè)計(jì)（論文）完成日期： 2006 年 6 月 20 日一、設(shè)計(jì)（論文）題目： 渦輪盤(pán)液壓立拉夾具 二、專題題目： 組合夾具技術(shù)的現(xiàn)狀與發(fā)展 三、設(shè)計(jì)的目的和意義： 我國(guó)汽車(chē)及相關(guān)零部件行業(yè)發(fā)展迅速，而連桿又是連桿是發(fā)動(dòng)機(jī)的五大主關(guān)件之一，是發(fā)動(dòng)機(jī)傳遞動(dòng)力的主要運(yùn)動(dòng)件。因而連桿檢測(cè)成了生產(chǎn)中頻繁而又不可缺少的環(huán)節(jié)。連桿平行度測(cè)量?jī)x是專門(mén)為檢測(cè)汽車(chē)連桿而設(shè)計(jì)的專用測(cè)量工具，其結(jié)構(gòu)簡(jiǎn)單、測(cè)量精度高。它極大地提高了檢測(cè)效率，同時(shí)也提高了檢測(cè)的精度，具有很好的市場(chǎng)前景。 四、設(shè)計(jì)（論文）主要內(nèi)容： 本設(shè)計(jì)的主要內(nèi)容是設(shè)計(jì)連桿平行度測(cè)量?jī)x的機(jī)械系統(tǒng)和控制系統(tǒng)，我設(shè)計(jì)的主要工作是機(jī)械系統(tǒng)的設(shè)計(jì)。 五、設(shè)計(jì)目標(biāo)： 本設(shè)計(jì)的設(shè)計(jì)目標(biāo)是將連桿平行度測(cè)量?jī)x的機(jī)械系統(tǒng)的每一個(gè)零件進(jìn)行三維造型，并進(jìn)行裝配和運(yùn)動(dòng)仿真。 六、進(jìn)度計(jì)劃： 2006年 3月 13日至 3月 31日進(jìn)行為期3周的生產(chǎn)實(shí)習(xí)；4 月 1日至 4月 10日完成對(duì)設(shè)計(jì)題目的資料收集與查詢；4 月 11日至 5月 20日完成各零件及圖紙的繪制；5 月 11日至 6月 10日完成運(yùn)動(dòng)仿真和畢業(yè)設(shè)計(jì)說(shuō)明書(shū)的編寫(xiě)；6 月 11日至 6月 20日最后的審稿及說(shuō)明書(shū)和圖紙的打印。 七、參考文獻(xiàn)資料： 趙松主編.機(jī)電一體化技術(shù)基礎(chǔ)及應(yīng)用.機(jī)械工業(yè)出版社.1996；王錫良主編.機(jī)械計(jì)量測(cè)試技術(shù).東北工業(yè)出版社.1995；李信主編.微型計(jì)算機(jī)原理與接口.南開(kāi)大學(xué)出版社.2002 等參考資料近 20 本。 指 導(dǎo) 教 師： 院（系）主管領(lǐng)導(dǎo)： 年 月 日 1附錄 1 外文翻譯基于事例推理的夾具設(shè)計(jì)研究與應(yīng)用摘要:根據(jù)基于事例的設(shè)計(jì)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(lái)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(jì)了事例庫(kù)的結(jié)構(gòu)形式,創(chuàng)建了層次化的事例組織方式;同時(shí),提出了基于知識(shí)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(jì).所開(kāi)發(fā)的原型系統(tǒng)在型號(hào)工程夾具設(shè)計(jì)等項(xiàng)目的設(shè)計(jì)過(guò)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(jì) 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(guò)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(guò)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(guò)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(wèn)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(lái)，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(guò)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(wèn)題,這在 CBR 中是非常重要的.1 事例參數(shù)和事例圖書(shū)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(lái)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 2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(méi)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(méi)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(lái)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(guò)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(kù)事例庫(kù)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(wèn)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(kù)，成分事例庫(kù)，夾具的成分事例庫(kù)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(lái)進(jìn)行描 3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(shū)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(lái)。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(lái)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(xiāo)的定位方法。如果沒(méi)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(kù)的事例索引信息，查找有關(guān)事例庫(kù)。2） 將事例索引碼與事例庫(kù)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(guò)數(shù)字化的價(jià)值來(lái)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(kù)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： 4其中 表示第 i 個(gè)特征的索引特性值， 表示事例庫(kù)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(lái)作相似事例。事例庫(kù)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(guò)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(kù)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(méi)有必要把它保存到事例庫(kù)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(kù)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。 5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。或者只能作為一個(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(kù)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(kù)中。4 夾具設(shè)計(jì)中基于事例推理的過(guò)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(kāi)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(kù)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5 基于事例推理的夾具設(shè)計(jì)說(shuō)明 6這是一個(gè)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(jì)成一個(gè)用來(lái)旋轉(zhuǎn)孔的旋轉(zhuǎn)夾具。圖 3 需要設(shè)計(jì)夾具的一個(gè)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(chē)床夾具 1 100工件形狀 塊狀 9 90工件材料 中碳鋼 3 70批量 中批 2 60工件比例 小 5 60工件重量 輕 5 60工件剛度 硬度強(qiáng) 1 60加工內(nèi)容 孔 3 80程序要求 完成加工 3 70定位方法 三個(gè)平面 1 100夾緊方法 不確定 ？ 90夾具體 復(fù)合 4 80其他 沒(méi)有 0 60通過(guò)查找和計(jì)算相似點(diǎn)，最相似的事例的事例索引碼是 719325513321402000，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(chē)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 加工內(nèi)容 孔 3 程序要求 完成加工 3 定位方法 三個(gè)平面 1 夾緊方法 不確定 ？ 夾具體 復(fù)合 4 其他 沒(méi)有 0 相似點(diǎn)的計(jì)算如下：所以?shī)A具的相似尺寸值是 0.806，這是在事例庫(kù)中用于設(shè)計(jì)的最相似的事例，最相似的事例的結(jié)構(gòu)如圖 4 所示 8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(jì)出來(lái)，圖形如圖 6 所示圖 5 需要設(shè)計(jì)的新夾具因?yàn)樵谑吕龓?kù)中沒(méi)有相似夾具，新夾具被儲(chǔ)存到事例庫(kù)中。事例索引碼是19325523311402000。6 結(jié)論基于事例推理，作為一個(gè)問(wèn)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?；谑吕评淼膬?yōu)點(diǎn)如下：它和人類的思想很相似；一個(gè)事例庫(kù)通過(guò)保存新事例獲得自學(xué)能力，它比有慣例庫(kù)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 9庫(kù)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(kù)和典型夾具庫(kù)結(jié)合起來(lái)。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。 10附錄 2 英文原文Application and developmentOf case based reasoning in fixture design Abstract: 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 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 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 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 11needs 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 Library1.1 Case indexThe case index should be composed of all features of the workpiece, which 12are 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. 13The 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 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 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 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 14is 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 RetrievalIn 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 15relevant 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 attribute of relative feature of the j-th case in the case library. At the same time, , the value counts as follows: 16.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 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 form 17remains; 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 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 18case 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 DesignAccording 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. 195 Illustrating for Fixture Design by CBRThis is a workpiece (seeFig.4). Its material is 45# steel. Its name is seat. Its shape is block, and the product batch size is middle, etc. A fixture is turning fixture that serves to turn the hole, which needs to be designed.The value of feature, attribute, case index code and weight of the workpiece 20is show n in Tab.2.Through searching, and calculating the similarity, the case index code of the most similar case is 19325513321402000, and the detailed information is show n in Tab. 3.The similarity is calculated as follows: 21So the value of similarity measure of the fixture which needs to be designed with the most analogical case in case library is 0.806, and the structure of the most analogical case is shown in Fig.5.After having been substituted the component, modified the locating model and clamp model, and adjusted the relative dimension, the new fixture is designed, and the figure is show n in Fig.6. 22As there is not the analogical fixture in the case library, the new fixture is restored in to the case library. The case index code is 19325513311402000.6 ConclusionCBR, 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.
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