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中文譯文
計(jì)算機(jī)輔助制造
計(jì)算機(jī)輔助制造一詞涵蓋了信息處理、生產(chǎn)決策、及生產(chǎn)加工等諸多領(lǐng)域，給CAM下一個(gè)簡(jiǎn)單的定義極為困難。D.Kochan針對(duì)CAM的多樣性和廣泛的應(yīng)用范圍，給CAM下了一個(gè)非常合適的定義。CAM可定義為計(jì)算機(jī)輔助生產(chǎn)準(zhǔn)備，包括決策、工藝和作業(yè)計(jì)劃、軟件設(shè)計(jì)技術(shù)、人工智能、用不同類型的自動(dòng)機(jī)床（如數(shù)控機(jī)床、數(shù)控加工中心、數(shù)控加工單元、數(shù)控柔性制造系統(tǒng)），以及不同種類的實(shí)現(xiàn)方法（CNC——計(jì)算機(jī)數(shù)控技術(shù)、DNC——群控技術(shù)）。
由于CAM有如此廣泛的使用范圍。認(rèn)識(shí)CAM更好的方法是通過CAM技術(shù)。CAM技術(shù)覆蓋了群控技術(shù)、射干難產(chǎn)數(shù)據(jù)庫、自動(dòng)化、公差等。圖22-1所示的是CAM的一般框架結(jié)構(gòu)。
生產(chǎn)中計(jì)算機(jī)的基本職能就是獲取和處理與大量業(yè)務(wù)有關(guān)的數(shù)據(jù)，這些業(yè)務(wù)在企業(yè)內(nèi)各個(gè)部門中連續(xù)不斷地發(fā)生。CAM最初的研究是1953年麻省理工學(xué)院（MIT）對(duì)機(jī)床數(shù)字控制的研究。在MIT，出現(xiàn)懶得編程語言即自動(dòng)化編程工具（APT），它是后來進(jìn)一步發(fā)展的基本工具。當(dāng)前CAM涉及到的功能如下：
·數(shù)控技術(shù) （NC）
·計(jì)算數(shù)字控制 （CNC）
·計(jì)算機(jī)控制輸送系統(tǒng)
·計(jì)算機(jī)加工控制過程
·計(jì)算機(jī)輔助工藝過程監(jiān)控
·計(jì)算機(jī)輔助夾具設(shè)計(jì)
·計(jì)算機(jī)輔助刀具設(shè)計(jì)
·計(jì)算機(jī)輔助公差分析
·計(jì)算機(jī)輔助成本估算
·物料需求規(guī)劃 （MRP）
·計(jì)算機(jī)輔助加工工藝（CAPP）
·計(jì)算機(jī)化的可加工數(shù)據(jù)系統(tǒng)
·加工資源規(guī)劃 （MRPⅡ）
計(jì)算機(jī)數(shù)控技術(shù)
數(shù)控（NC）是可編程自動(dòng)化的一種表現(xiàn)形式，它以數(shù)字、字母和其他符號(hào)來控制加工設(shè)備。這些數(shù)字、字母、符號(hào)按適當(dāng)?shù)母袷骄幋a，形成用于某一工件或任務(wù)的加工程序。當(dāng)任務(wù)改變了，某一工件的加工程序也隨之改變。這種改變程序的能力使得NC適合于西歐挨批量生產(chǎn)，更新程序要比大量改變加工設(shè)備要容易得多。
數(shù)控原理首先用在銑削加工中，然后用在車削加工中、火焰切割、鉆削和磨削之中，數(shù)控技術(shù)越來越多地用在其他的機(jī)加工過程中，如成形加工（精密鍛造，液壓等）、雕刻或激光切割。
目前數(shù)控技術(shù)相對(duì)成熟，許多數(shù)控設(shè)備具有多種加工功能，如銑削中心可以進(jìn)行垂直和水平銑削、鉆削、鏜削、鉸孔、插削、成形和車削等加工過程，當(dāng)然，在配有大容量的自動(dòng)化刀庫后，CNC機(jī)床的功能將更加豐富。
可編程控制器
可編程控制器（PLC）廣泛地用于計(jì)算機(jī)輔助制造中。事實(shí)上，PLC用在企業(yè)有自動(dòng)化要求的每個(gè)環(huán)節(jié)上，PLC是電子工業(yè)快速發(fā)展的代表。從PLC誕生之起，就成為許多生產(chǎn)規(guī)劃中的重要輔助設(shè)備，而以往是依靠機(jī)電控制系統(tǒng)的。PLC是一個(gè)硬件裝置，用來實(shí)現(xiàn)以前繼電器完成的邏輯功能。大多數(shù)PLC的設(shè)計(jì)與計(jì)算機(jī)的設(shè)計(jì)相似。PLC基本上由固態(tài)數(shù)字邏輯元件組合而成，用于進(jìn)行邏輯判斷和提供輸出。可編程控制器可用來運(yùn)行和控制生產(chǎn)加工設(shè)備及其他機(jī)器設(shè)備。
計(jì)算機(jī)輔助物料處理
物料處理（MH）是體現(xiàn)工廠或公司運(yùn)營效率的非常重要因素，一個(gè)高效的MH系統(tǒng)有助于減少等待時(shí)間，它甚至有助于提高整個(gè)加工過程的安全性或效率。
Cabbert和Brown指出，生產(chǎn)成本的60%用于物料處理。事實(shí)也證明大多數(shù)離散加工的產(chǎn)品在加工過程中有90%的時(shí)間用于物料處理及儲(chǔ)存。由于MH在生產(chǎn)總成本中占有如此多的比例，顯然減少產(chǎn)品的物料處理時(shí)間一定能降低產(chǎn)品成本。幫助降低這些成本的途徑之一是應(yīng)用計(jì)算機(jī)做無聊處理的部分工作。
目前，有許多物料處理設(shè)備可供購買。并有許多種MH手段可供使用。一種手段就是采用計(jì)算機(jī)數(shù)據(jù)庫來記錄MH設(shè)備清單和輸入使用者因素植。計(jì)算機(jī)獲取使用者的需求水平、輕重緩急、各自的信譽(yù)度及擁有的MH設(shè)備完成任務(wù)的可行性，并且提供設(shè)備的種類，待使用者從中挑選適合的MH設(shè)備品種和模塊。
生產(chǎn)過程計(jì)算機(jī)監(jiān)控及故障診斷
在計(jì)算機(jī)監(jiān)控及故障診斷系統(tǒng)中，監(jiān)控的目的是發(fā)現(xiàn)錯(cuò)誤，而診斷的目標(biāo)包括故障定位和確認(rèn)。監(jiān)控和診斷都應(yīng)出現(xiàn)在各級(jí)監(jiān)控體系中。
幾乎所有監(jiān)控和診斷系統(tǒng)都要達(dá)到如下的基本要求：
(1) 具有測(cè)量和處理相當(dāng)多的模擬和數(shù)字信號(hào)的能力。
(2) 具有測(cè)量信號(hào)并進(jìn)行深層次的預(yù)處理能力，包括統(tǒng)計(jì)分析和頻率分析的能力。
(3) 具有復(fù)雜多參數(shù)的決策能力。
(4) 具有模塊化、可延展性和可重性的結(jié)構(gòu)。
(5) 所有功能的可編程能力。
(6) 有標(biāo)準(zhǔn)的軟件/硬件雙向接口與CNC/DNC控制器相連。
對(duì)診斷系統(tǒng)的要求如下：
(1) 當(dāng)出現(xiàn)差錯(cuò)時(shí)，系統(tǒng)應(yīng)能方便地提供關(guān)于該機(jī)差錯(cuò)的相關(guān)知識(shí)，使得甚至是對(duì)加工過程不熟悉的工人能知道差錯(cuò)發(fā)生在何處。
(2) 差錯(cuò)的影響結(jié)果在系統(tǒng)中能方便得到，因而能估計(jì)到已知差錯(cuò)后續(xù)生產(chǎn)影響的嚴(yán)重程度。
(3) 用戶該有獨(dú)自修復(fù)差錯(cuò)的可能性，即修復(fù)指令以一種合適的形式讓用戶能夠得到。
(4) 該專家系統(tǒng)能由那些先前在計(jì)算機(jī)方面沒有經(jīng)驗(yàn)的雇員來操作。
(5) 經(jīng)過短期培訓(xùn)之后，系統(tǒng)可由運(yùn)行設(shè)備的雇員來維護(hù)，這樣，專家工程師就沒有必要時(shí)刻在現(xiàn)場(chǎng)。
根據(jù)在制造系統(tǒng)中所處的位置和具備的功能，監(jiān)控診斷系統(tǒng)可有三種主要類型：
(1) 獨(dú)立監(jiān)控子系統(tǒng)：它僅從上級(jí)控制層獲得包含環(huán)境或條件描述的信息，為所有監(jiān)控處理單元提供測(cè)量、處理、分類及干預(yù)所需的指令、參數(shù)或配置。
(2) 輔助監(jiān)控子系統(tǒng)：僅僅完成測(cè)量和處理任務(wù)并向系統(tǒng)控制層傳輸分類和干預(yù)信息。
(3) 半獨(dú)立監(jiān)控系統(tǒng)：在同層中表現(xiàn)出獨(dú)立的簡(jiǎn)單快捷的監(jiān)控功能，并將復(fù)雜的分類和干預(yù)信息轉(zhuǎn)交給上層。
理想的計(jì)算機(jī)監(jiān)控和診斷系統(tǒng)可以概括為是一個(gè)專家不在現(xiàn)場(chǎng)即可使用的系統(tǒng)，例如當(dāng)專家休假、休息，或者公司要求有三班制，其中底三班沒什么人的情況下能使用的系統(tǒng)。
（A）計(jì)算機(jī)輔助設(shè)計(jì)
計(jì)算機(jī)輔助設(shè)計(jì)可定義為用計(jì)算機(jī)來通過有效的創(chuàng)造、修改，或證明零件的幾何模型來輔助工程設(shè)計(jì)過程。CAD是最普遍的人機(jī)交流的綜合系統(tǒng)的一種應(yīng)用。工程設(shè)計(jì)的對(duì)象被儲(chǔ)存和表現(xiàn)為幾何模型的形式。幾何學(xué)的模型和發(fā)展物體的幾何學(xué)的數(shù)學(xué)描述與CAD系統(tǒng)的使用有關(guān)。數(shù)學(xué)的描述叫做一個(gè)模型。有三種模型形式（線框架模型，表面模型和實(shí)體模型），它們被普遍用來表現(xiàn)一個(gè)實(shí)際的物體。線框架模型也被叫做邊緣——頂點(diǎn)或枝條——輪廓模型，是定義零件計(jì)算機(jī)模型的最簡(jiǎn)單和最常用的方法。表面模型可能被構(gòu)造在要使用一個(gè)表面面貌的大部分時(shí)。實(shí)體模型能比枝條——面的構(gòu)造更好地記錄計(jì)算機(jī)數(shù)學(xué)從面跳躍到體積。結(jié)果，它可能用來計(jì)算零件的大部分性能，就是要求經(jīng)常進(jìn)行工程分析的如有限元分析，動(dòng)力學(xué)分析，和大部分壓力轉(zhuǎn)移的檢查。
CAD模型也被分成二維（2D）模型，二又二分之一（2/1）模型，三維（3D）模型。一個(gè)2D模型表現(xiàn)一個(gè)平坦的部份，而一個(gè) 3D立體模型則提供零件整體的形狀。一個(gè)2/1模型可以用來描述不變的沒有邊——面部分的斷面。2/1模型的大部分優(yōu)點(diǎn)就是給一些3D立體模型的一部份一個(gè)大概的意思，而沒有產(chǎn)生完整 3D立體模型數(shù)據(jù)庫的必要。
在一部分選擇替代發(fā)展后，許多工程分析必須經(jīng)常被定義為設(shè)計(jì)過程的一部分。這個(gè)分析可以是壓力——拉力的計(jì)算，動(dòng)力學(xué)分析，有限元模擬實(shí)驗(yàn)等。一些在CAD系統(tǒng)的典型軟件上提供一些大部分性能分析和有限元分析的例子。大部分性能分析包含一個(gè)實(shí)體的外貌如它的體積，空間表面，重量和重心。有限元分析在大部分CAD系統(tǒng)中有效地輔助壓力轉(zhuǎn)移，拉——壓應(yīng)力分析，動(dòng)力學(xué)分析，和各種工程計(jì)算?，F(xiàn)在，各種CAD系統(tǒng)可以自動(dòng)地產(chǎn)生2D或3D有限元分析緊密配合這就是有限元分析的實(shí)質(zhì)。
現(xiàn)實(shí)中的問題是，CAD系統(tǒng)的發(fā)展是成熟的。盡管如此，考慮到CAD和CAPP的相互配合工作，許多問題仍然存在。主要的問題是幾何模型的轉(zhuǎn)變，嚴(yán)格地說是，幾何模型的描述，從CAD到CAPP。例如，最簡(jiǎn)單的2D形式中，最初制圖明細(xì)表可以認(rèn)為是工程畫法，但是一個(gè)小的項(xiàng)比如尺寸可以用不同的方法定義。不同的設(shè)計(jì)系統(tǒng)用不同的技術(shù)把線組合成面。結(jié)果，在用IGES在不同的系統(tǒng)中間進(jìn)行數(shù)據(jù)捕捉時(shí)出現(xiàn)了很多問題。在三維中，這些問題更加突出因?yàn)樵S多整理表面和空間曲線的方法的不協(xié)調(diào)。一些另外的嘗試，比如分界線描述的接近和實(shí)體結(jié)構(gòu)模型上的接近在這些創(chuàng)造中被認(rèn)為是從最初的模型中得到特殊關(guān)系。不要提供任何可以和在局部信息的基礎(chǔ)上得出的機(jī)械加工相結(jié)合的警告信息。然而，在這一個(gè)區(qū)域中做了很多的努力，而且許多方法已經(jīng)與CAD一起提供到CAPP的接口中。
(B) 計(jì)算機(jī)輔助工藝規(guī)程計(jì)劃
CAPP被定義為使用計(jì)算機(jī)編制輔助加工工藝規(guī)程計(jì)劃工作的功能。輔助加工的水平程度依賴于不同的工作人員編制執(zhí)行不同的加工工藝規(guī)程計(jì)劃。對(duì)于將會(huì)用手被程序計(jì)劃者構(gòu)造的程序計(jì)劃為儲(chǔ)藏和數(shù)據(jù)的取回降低水平策略唯一的使用計(jì)算機(jī), 連同為供應(yīng)將會(huì)被用于計(jì)劃者的新工作的數(shù)據(jù)。和傳統(tǒng)的技術(shù)水平比較低的手工編制工藝規(guī)程的計(jì)劃相比，計(jì)算機(jī)輔助故意規(guī)程設(shè)計(jì)的水平大大的提高，許多簡(jiǎn)單規(guī)則的幾何學(xué)形狀可以自動(dòng)生成工藝規(guī)程計(jì)劃程序。CAPP 的終極目標(biāo)的是計(jì)算機(jī)能夠自動(dòng)生成加工工藝規(guī)程計(jì)劃的程序，取代工藝規(guī)程計(jì)劃編制者的地位，此時(shí)工藝規(guī)程知識(shí)和編制計(jì)劃的工作經(jīng)驗(yàn)已經(jīng)被電腦合并了。CAPP 已經(jīng)被認(rèn)為在 CIM 中扮演一個(gè)重要的角色。
計(jì)算機(jī)輔助工藝規(guī)程設(shè)計(jì)的研究已超過了20年，巨大的努力到今天才有現(xiàn)在的CAPP系統(tǒng)?，F(xiàn)在，對(duì)于 CAPP 系統(tǒng)的發(fā)展的研究興趣的重心集中在利用零件的相似性去檢索和修改工藝過程的形成相應(yīng)零件的工藝規(guī)程。增加 CAPP 系統(tǒng)的智能化，研究方向類于類神經(jīng)網(wǎng)路，模糊邏輯和機(jī)器學(xué)問。為增加 CAPP 系統(tǒng)的 智能化，工藝規(guī)程的計(jì)劃所起的主要角色就是合理安排加工的次序和程序編制的時(shí)序要完美的整合。而且制造業(yè)計(jì)劃的整合中心在資源計(jì)劃的整合。這一種現(xiàn)象是完全可以一起進(jìn)行的工程。
為什么要使用計(jì)算機(jī)輔助工藝規(guī)程的程序? 很顯然，CAPP發(fā)展已經(jīng)被許多大學(xué)、機(jī)構(gòu)、研究組織和企業(yè)的發(fā)展部門提出，已經(jīng)認(rèn)為是一個(gè)很好的課題在努力的研究了。然而, CAPP對(duì)現(xiàn)在的生產(chǎn)是如此重要仍然被人們懷疑。一般情況下，在這個(gè)課題上主要有三個(gè)爭(zhēng)論的觀點(diǎn)：
調(diào)查容易發(fā)現(xiàn)在制造業(yè)的整個(gè)系統(tǒng)中，加工工藝規(guī)程的計(jì)劃是最基本工作之一，因?yàn)橐粋€(gè)加工工藝規(guī)程的計(jì)劃決定其加工方法、設(shè)備、時(shí)序、工件材料、等其他一些必需條件的集合。那些比較困難的和有著詳細(xì)的工藝規(guī)程計(jì)劃的工作已經(jīng)廣泛地讓那些對(duì)制造業(yè)的輔助工藝規(guī)程很理解的工人去完成。熟悉工藝規(guī)程計(jì)劃程序的工人，大部分都要退休的或者接近退休，然而沒有年輕的了解工藝規(guī)程工人有資格去取代他們。計(jì)算機(jī)輔助工藝規(guī)程人才的短缺已經(jīng)產(chǎn)生，鑒于全球市場(chǎng)的強(qiáng)烈競(jìng)爭(zhēng)的高壓力，公司生存而且成功的方法就是整合完美的計(jì)算機(jī)工藝規(guī)程設(shè)計(jì)程序。CIM 在計(jì)算機(jī)自動(dòng)化編寫工藝規(guī)程計(jì)劃中扮演一個(gè)主要角色，它是許多公司借助計(jì)算機(jī)輔助工藝規(guī)程設(shè)計(jì)系統(tǒng)的原因。
計(jì)算機(jī)輔助工藝規(guī)程計(jì)劃的自動(dòng)化被大多數(shù)的公司解決和克服熟練計(jì)算機(jī)工藝規(guī)程工人不足方法。如美國機(jī)械師和自動(dòng)化制造業(yè)的社會(huì)已經(jīng)使用計(jì)算機(jī)軟件所寫的程序報(bào)告，提高準(zhǔn)確性和一致性,被用計(jì)算機(jī)處理的工藝規(guī)程設(shè)計(jì)本質(zhì)上有四個(gè)目標(biāo):
(1) 在制造業(yè)的工程師和熟練的工藝規(guī)程計(jì)劃者基礎(chǔ)上減少其勞動(dòng)量,計(jì)算機(jī)會(huì)及時(shí)的不給程序去完成。
(2)最優(yōu)的工藝規(guī)程計(jì)劃是利用現(xiàn)有的最新的信息，使用最好的機(jī)器、工具、速度等等。
(3)工藝規(guī)程劃分成若干個(gè)規(guī)范化的工作程序，藉此培養(yǎng)出多的熟練工藝規(guī)程計(jì)劃的工人
(4)規(guī)范化產(chǎn)品制造時(shí)間和費(fèi)用是工藝規(guī)程的重要組成部分。
英文原文
COMPUTER AIDED MANUFACTURING
The term Computer Aided Manufacturing (CAM) covers many areas from information processing and decision making to manufacturing and machining, which makes giving a single definition for CAM extremely difficult. D. Kochan gave fitting definition for CAM, with its diversity and wide range of use, in his book, “CAM can be defined as computer-aided preparation of manufacturing including decision-making, process and operational planning, software design techniques, and artificial intelligence, and manufacturing with different types of automation (NC machine, NC machine centers, NC machining cells, NC flexible manufacturing systems), and different types of realization (CNC single unit technology, DNC group technology).”
Since CAM has such a wide range of use, a better way too look at CAM is through CAM technologies. The CAM technologies covered are group technology, manufacturing database, automated and tolerancing. Fig.22-1 illustrates the general scope of CAM.
The essential role of the computer in the production function is to capture and process the data relating to a large number of transaction which continuously take place in different departments of the company. The initial research activity for CAM was Numerical Control (NC) for machine tools at the Massachusetts Institute of Technology (MIT) in 1953. The first programming language was Automatically Programming Tools (APT) created at MIT, and it was the pattern for many further developments. Currently, many manufacturing functions have been addressed by CAM including the following:
Fig.1 The general scope of CAM
·Numerical Control (NC)
·Computer Numerical Control (CNC)
·Direct Numerical Control (DNC)
·Computer controlled conveyor systems
·Computer controlled machining process
·Computer aided process monitoring
·Computer aided fixturing design
·Computer aided tooling design
·Computer aided tolerancing design
·Computer aided cost estimating
·Material Requirement Planning (MRP)
·Computer aided Process Planning (CAPP)
·Computerized machinability data system
·Manufacturing Resources Planning (MRPⅡ)
Computer Numerical Control
Numerical control (NC) is a form of programmable automation in which the processing equipment is controlled by means of numbers, letters, and other symbols. The number, letters, and symbols are coded in an appropriate format to define a program of instructions for the particular work piece changes. The capability to change the program is what makes NC suitable for low-volume and medium-volume production, and it is much easier to write new programs than to make major alteration to the processing equipment.
The principle of numerical control was first applied to the milling process, and then later to turning process, flame cutting , drilling, and grinding. NC technology is now used more and more for other manufacturing processes, such as forming (fine forging, rolling, etc.), engraving, and laser cutting.
The current NC equipment is relatively more mature. Many machines posses multiple processing function, such as milling centers which can perform vertical and horizontal milling, drilling, boring, reaming, slotting, shaping, and turning processes. Of course, with a high capacity automated tooling library, CNC machines’ functions can be considerably more abundant.
Programmable Logic Controller
Programmable logic controller are widely used in computer aided manufacturing. Actually, PLCs are used in virtually every segment of industry where automation is required. PLCs represent one of the faster growing segments of the electronics industry. Since their inception, PLCs have proved to be the salvation of many manufacturing plans which previously relied on electro-mechanical control system. A PLC is a solid-state device designed to perform logic functions previously accomplished by electro-mechanical relays. The design of most PLC is similar to that of a computer. Basically, the PLC is an assembly of solid-state digital logic elements designed to make logical decisions and provide outputs, programmable logic controllers are used for the control and operation of manufacturing process equipment and machinery.
Computer Aided Material Handing
Material handling (MH) is a very important factor in how efficiently a workshop or company can be operated. An efficient MH system will help reduce waiting time, and it may even help increase safety or the effectiveness of the entire manufacturing process.
Cabbert and Brown indicated that as much as 60% of the total production cost many be accounted for by material handing. It is also evidenced that most discrete manufacturing products spend 90% of their manufacturing lead time on the duration of material handing and storage.with MH accounting for such a large amount of the total production cost,it is obvious that reducing the amount of time a produce is handled will dramatically reduce production cost.One way of helping reduce these costs is by using computers to do some material handing.
There is a great variety of material handing equipment available commercially and there are many types of MH approaches used today. One of these approaches is to used a computer database to store listing of MH equipment and the user’s input of factor values. The computer takes the user’s required level of, and preferred importance for, each criterion, and the feasible MH equipment for the task at hand, and produces a category of equipment from which the user can choose the proper type or piece of MH equipment.
Computer Monitoring and Diagnostics for Manufacturing Processes
In a computer monitoring and diagnostic system, the aim of monitoring is to detect failure, while the aim of diagnostics includes fault localization and identification. Both monitoring and diagnostics should appear at all levels of the control-monitoring hierarchy.
There are some essential requirements that almost every monitoring and diagnostics system should posses. Some of the requirement for a monitoring system are : (1) the ability to measure and process relatively numerous analogue and digital signals; (2) the capability of profound preprocessing of measured signals, including statistical and frequency based analysis; (3) the ability for complex, multi-parameter decisions; (4) modular, extendable, reconfigurable structure; (5) programmability in all functions; and (6) standardized bi-directional software/hardware interfaces to the CNC/DNC controllers. Some of the requirements for a diagnostic system are : (1) the system should easily provide knowledge about the causal interrelationship when faults arise, to enable even worker who are not well acquainted with the process to localize faults ; (2) the consequences of faults should be readily available in the system so that the severity of a given fault for the further production process can be estimated ; (3) the user should have the possilibity of repairing the fault alone, I . e . repair instructions should be available to the user in a suitable form ; (4) the operation of the expert system should be possible by employees who have no previous experience with computer ; and (5) after a short training period, the system should be maintained by the employees running the facility so that the presence of expert engineers is no longer necessary.
There are three major types of M/D systems that can be classified by their place and function in the manufacturing system. These M/D systems are : (1) autonomous subsystem monitoring, which gets only messages containing environment or condition descriptions from upper levels of control, and supplies all of the elements of the monitoring process with instruction, parameters, or setting needed for measuring, processing, classification, and intervention ; (2) complementary subsystem monitoring, which undertakes only the task of measuring and processing and passes classification and intervention to system level; and (3) semi-autonomous monitoring, which performs only simple, quick monitoring functions autonomously on its own level, and turn to upper levels in case of sophisticated classification and intervention tasks.
The ideal computer monitoring and diagnostic system can be summed up as being a system that can be used during the absence of the human expert, for example, when the expert is on vacation, during breaks, or if a company wants to have three shift with few people on the third shift.
(A) COMPUTER AIDED DESIGN
Computer Aided Design(CAD) can be defined as using computer to aid engineering design process by means of effectively creating modifying, or documenting the part’s geometrical modeling. CAD is most commonly associated with the use of an interactive computer graphics system..The object of the engineering design is stored and represented in the from of geometric model. Geometric modeling is concerned with the use of a CAD system to develop a mathematical description of the geometry of an object. The mathematical description is called a model. There are three types of models (wire-frame,surface model, and solid models), that are commonly used to represent a physical object. Wire –frame model ,also called edage-vertex or stick-figure models,are the simplest method of modeling and ate most commonly used to define computer models of parts. Surface models may be constructed using a large variety of surface features. Solid models are recorded in the computer mathematically as volumes bounded by surfaces rather that as stick-figure structures. As a result, it is possible to calculate mass properties of the parts, which is often required for engineering analysis such as finite element methods, kinematic or dynamic studies studies, and mass or heat transfer for interference checking .
Models in CAD also be classified as being two-dimensional (2D) models, two-and-half-dimensional models , or three-dimensional (3D) models . A 2Dmodel represents a flat part and a 3D model provides representation of a generalized part shape . a 2.5D model can be used to respresent a part of constant section with no side-wall details . the major advantage of a 2.5D model is that it give a certain amount of 3D information about a part without the need to create the database of a full 3D model .
After a particular design alternative has been developed, some from of engineering analysis must often be performed as a part of the design process .The analysis may take the form of stress-strain calculations, heat transfer analysis, dynamic simulation etc. some examples of the software typically offered on CAD systems are properties and Finite Element Method analysis .Mass properties analysis involves the computation of such features of a solid object as its Volume、surface area、weight、and center of gravity. FEM analysis is available on most cad systems to aid in heat transfer, stress-strain analysis, dynamic characteristics, and other engineering computations. Presently, many CAD systems can be automatically generate the 2D or 3D FEM meshes which are essential to FEM analysis.
As a matter of fact , development of CAD systems is now quite mature . however, considering the interface between CAD and CAPP , many problems still remain .the main problem is transformation of geometrical mode or ,more strictly , geometrical model representations, from CAD to CAPP . for instance ,in the simplest 2D form , Initial Graphics Exchange Specification (IGES) can represent an engineering drawing ,but items such as dimensions can be represented in different ways . Also different drawing systems use different technologies to group lines into profiles. As a result, there appear to be major problems in using IGES to transfer data between different systems . In 3D, The problems are worse because many ways of sorting surface and space curvese are incompatible. Some other attempt, such as the approach of Boundary Representation (B-Rep) and the approach of Constructive solid Geometry (CSC) tress in which the cavities are recognized from the special relationships between the primitive volumes, do not provide any semantic which could be associated with the machined volumes and are based on local information . Nevertheless, great efforts have been made in this area , and many approaches have been provided to interface CAPP with CAD .
(B) COMPUTER AIDED PROCEDD PLANNING
Computer Aided Process Planning (CAPP) can be defined as the functions which use computers to assist the work of process planners. The levels of assistance depend on the different strategies employed to implement the system. Lower level strategies only use computers for storage and retrieval of the data for the process plans which will be constructed manually by process planners, as well as for supplying the data which will be used in the planner’s new work. In comparison with lower level strategies, higher level strategies use computers to automatically generate process plans for some workpieces of simple geometrical shapes. Sometimes a process planner is required to input the data needed or to modify plans which do not fit specific production requirement well. The highest level strategy, which is the ultimate goal of CAPP, generates process plans by computer, which may replace process planners, when the knowledge and expertise of process planning and working experience have been incorporated into the computer programs. The database in a CAPP system based on the highest level strategy will be directly integrated with conjunctive system , e . g. CAD and CAM . CAPP has been recognized as playing a key role in CIM.
More than 20 years have elapsed sine the use of computers to assist process planning tasks was first proposed. Tremendous efforts have made in the development of CAPP system. For the time being, the research interests for development of CAPP system are focused on intelligent and integrated process planning systems. For increasing the intelligence of CAPP systems, some new concepts, such as neural networks, fuzzy logic, and machine learning have been explored for the new generation of CAPP system. For increasing the integrability of CAPP system, feature based design, the roles of features, integrating process planning with scheduling, and integrating process planning with manufacturing resources planning have been focused on . this phenomenon is entitled concurrent or simultaneous engineering.
Why computer aided process planning? It is obvious that CAPP development has been addressed by many universities, institutions, research organization and corporate development departments. A great effort has been made on the subject. However, the question of why CAPP is so important for the current production environment still needs to be answered. In this section the issues will be addressed. In general, there are three main arguments that are involved in the subject.
Since a process plan determines the methods, machines, sequences, fixturing, and tools required in the fabrication and assembly of components, it is easy to see that process planning is one of the basic tasks to be performed in manufacturing systems. The task of carrying out the difficult and detailed process plans has traditionally been done by workers with a vast knowledge and understanding of the manufacturing process. Many of these skilled workers, now considered process planners, are either retired or close to retirement, with no qualified young process planners to take their place. An increasing shortage of process planners has been created. With the high pressure of serious competition in the world market, integrated production has been pursued as way for companies to survive and succeed. Automated process planning systems have been recognized as playing a key role in CIM. It is for reasons such as these that many companies look for computer aided process planning systems.
Computer aided process planning is the way in which most companies are solving the problem of automating process planning and overcoming the shortage of skilled process planners. As the American Machinist and Automated Manufacturing Society has reported in the paper Process Planning Software Enhances Accuracy and Consistency, a computerized process planning system has essentially four goals:
(1) reduces the clerical load of plan preparation on the manufacturing engineers and skilled process planners, who are in short supply;
(2) optimize existing plans using the best available information on machines, tools, speeds, etc. ;
(3) standardize what are known to be the ‘best’ process plans for families of components within a company, thereby capturing the knowledge of the skilled planners;
(4) standardize production time/costs for particular families of components.