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附錄1中文譯文
柔性制造系統(tǒng)
介紹對(duì)制造系統(tǒng)和先進(jìn)的制造業(yè)的技術(shù)的討論，對(duì)定義制造系統(tǒng)這一術(shù)語是用的。
一個(gè)制造系統(tǒng)可以被定義為一系列的把原材料轉(zhuǎn)換成有用的形式和最終產(chǎn)品的增值的制造過程。
柔性是現(xiàn)代制造業(yè)的一個(gè)重要特性， 它的意思就是制造系統(tǒng)的工藝范圍廣、適應(yīng)生產(chǎn)的能力強(qiáng) ,有時(shí)候也能相對(duì)地提高生產(chǎn)率。柔性制造系統(tǒng)能很快地調(diào)整生產(chǎn)線以適應(yīng)不同零件的加工。
柔性制造系統(tǒng)是由一個(gè)或一組機(jī)床，在計(jì)算機(jī)控制系統(tǒng)和自動(dòng)化物料運(yùn)儲(chǔ)系統(tǒng)的協(xié)調(diào)控制下工作的。之所以把它叫做一個(gè)柔性制造系統(tǒng)，是因?yàn)樵谟?jì)算機(jī)控制下，這個(gè)系統(tǒng)能夠根據(jù)零件的不同進(jìn)行多樣性、廣泛地調(diào)整。
典型的FMS包括:
? 處理設(shè)備,例如：機(jī)床、工作站、和機(jī)械手
? 物料運(yùn)儲(chǔ)設(shè)備,例如：機(jī)械手、運(yùn)送裝置和 AGVs(自動(dòng)導(dǎo)向運(yùn)輸裝置)
? 一個(gè)交換系統(tǒng)
? 一個(gè)計(jì)算機(jī)控制系統(tǒng)
柔性制造系統(tǒng)業(yè)主要向著集成制造的目標(biāo)發(fā)展。 它包括自動(dòng)制造過程的集成， 在柔性制造業(yè)系統(tǒng), 那些數(shù)控機(jī)床 (例如 ,車床,鉆床)和自動(dòng)化的物料運(yùn)儲(chǔ)系統(tǒng)經(jīng)由計(jì)算機(jī)網(wǎng)絡(luò)控制系統(tǒng)進(jìn)行共享和及時(shí)的協(xié)調(diào)。 這就是一個(gè)小規(guī)模的集成。
柔性制造業(yè)系統(tǒng)向著能夠完全集成的制造目標(biāo)逐步形成了一些自動(dòng)化制造的觀念:
? 計(jì)算機(jī)對(duì)機(jī)床的數(shù)字控制 (CNC)
? 分配數(shù)字控制制造系統(tǒng) (DNC)
? 自動(dòng)物料運(yùn)儲(chǔ)系統(tǒng)
? 成組技術(shù) (部份的組合)
當(dāng)這些自動(dòng)化程序，將機(jī)器和人的思想進(jìn)行集成在一起成為一個(gè)系統(tǒng)，帶來了這些自動(dòng)化的過程，這就是FMS結(jié)果。 人和計(jì)算機(jī)是FMS的主要的角色。當(dāng)然，在這個(gè)系統(tǒng)中人的勞動(dòng)量要比用手工操作的制造系統(tǒng)少的多。 但是人仍然在FMS 的操作中扮演著一個(gè)重要的角色。 人所從事的工作主要包括以下幾項(xiàng):
? 修理和維護(hù)設(shè)備
? 工具更換和安裝
? 裝載和卸貨系統(tǒng)
? 數(shù)據(jù)輸入
? 部分計(jì)劃變更
? 計(jì)劃的實(shí)施
柔性制造系統(tǒng)的設(shè)備 , 像所有的制造業(yè)的設(shè)備一樣,也一定能被檢測(cè)出嚴(yán)重的故障, 和被破壞。當(dāng)有問題被發(fā)現(xiàn)的時(shí)候,一個(gè)人修理時(shí)必須認(rèn)清楚它的來源，并且能夠制定解決問題的措施。 人也可以根據(jù)那些制定的措施來維修那些發(fā)生故障的設(shè)備。 即使是所有的系統(tǒng)都能正常的運(yùn)作,也必須進(jìn)行周期的維護(hù)工作。
操作員應(yīng)也能夠調(diào)整機(jī)器和工具, 并且給工作系統(tǒng)配置必需品。 增加工具能提高 FMS的能力, 但是不能除去人在工具變更中的作用。 FMS的裝載和卸貨是相同的。 一但原材料已經(jīng)被載入自動(dòng)化物料運(yùn)儲(chǔ)系統(tǒng),它將以被規(guī)定的方式由系統(tǒng)控制運(yùn)動(dòng)。 但是,在完成的產(chǎn)品卸貨之前進(jìn)行新材料的的載入。
人和那些計(jì)算機(jī)的也是相互作用的，人必須通過計(jì)算機(jī)來控制 FMS 的程序。當(dāng)再重新配置 FMS， 生產(chǎn)另外類型的零件的時(shí)候 , 他們也必須改變?cè)瓉淼某绦?。人在FMS 中扮演著小而且重要的角色，但是這個(gè)角色在關(guān)鍵時(shí)候仍然是十分重要的。
在 FMS 的所有控制系統(tǒng)都是由計(jì)算機(jī)提供。 個(gè)別的機(jī)床在 FMS 里面被 CNC 控制。 全部的系統(tǒng)被 DNC 控制。自動(dòng)化物料運(yùn)儲(chǔ)系統(tǒng)就象數(shù)據(jù)收集、系統(tǒng)監(jiān)聽、工具控制和交通控制的其他功能一樣,也是用計(jì)算機(jī)來控制的,人/ 計(jì)算機(jī)的相互作用這就是 FMS 的柔性。
一、 柔性制造業(yè)的發(fā)展歷史
柔性制造業(yè)最初是有英國的莫林公司在 1960 年提出的, 24小時(shí)無人值守自動(dòng)運(yùn)行 。 這個(gè)24小時(shí)的無人值守的系統(tǒng)就是真正的 FMS 。但是,由于自動(dòng)化，集成化和計(jì)算機(jī)控制技術(shù)仍未發(fā)展到可以能夠支撐系統(tǒng), 所以它一開始就有很多局限性。 首先FMS 是在支撐系統(tǒng)發(fā)展完善的時(shí)間之前發(fā)展的。它發(fā)展到最后被丟棄也是再所難免的。
在1960年到1970年間，柔性制造業(yè)的概念還只是存在與一些大學(xué)里。 然而，在 1970年后期和 1980年早期由于復(fù)雜的計(jì)算機(jī)控制技術(shù)的出現(xiàn)，柔性制造業(yè)發(fā)展迅速的概念。 在美國柔性制造業(yè)主要使用者在汽車，卡車和發(fā)動(dòng)機(jī)的制造業(yè)中。
二、柔性制造業(yè)的原理
在生產(chǎn)制造過程中制造的生產(chǎn)率和柔性之間總是存在著一定的不協(xié)調(diào)的關(guān)系。 一方面是生產(chǎn)線中有很高的生產(chǎn)率, 但是柔性非常低。另一方面是獨(dú)立的 CNC 雖然生產(chǎn)率低，但是能提供最大的柔性, 但是有能力的機(jī)器。 在這兩方面之間是柔性制造業(yè)發(fā)展最合適的方面。當(dāng)仍然維持柔性制造的情況下，能夠制造出在保持較高生產(chǎn)率，在以上兩方面總折中的制造系統(tǒng)制造嗎？
生產(chǎn)線能夠以高的生產(chǎn)率生產(chǎn)大量的零件。 這種生產(chǎn)需要采取很多的裝備, 但是可以把這些大量的設(shè)備的相同的部分關(guān)掉。 它的主要缺點(diǎn)就是在任何一個(gè)部份中，哪怕甚至十分小的設(shè)計(jì)的變化也能夠引起整個(gè)的生產(chǎn)線的停工或者是重新再配置。 這樣的生產(chǎn)線最主要的弱點(diǎn)就是在沒有寶貴的時(shí)間進(jìn)行重新配置的情況下，不能夠生產(chǎn)制造同一部機(jī)械的各個(gè)不同的部份的零件。
傳統(tǒng)地CNC機(jī)床已經(jīng)開始用來生產(chǎn)那些在設(shè)計(jì)中微不足道的各種不同的的部份零件。因?yàn)檫@些設(shè)備可能被很快地就被重新調(diào)整、規(guī)劃，以適應(yīng)較小的或是甚至更主要的設(shè)計(jì)的改變 , 所以這些機(jī)床對(duì)這一個(gè)目的是十分理想的。 但是，這些機(jī)車設(shè)備不能夠獨(dú)立地或以較高的生產(chǎn)率來生產(chǎn)體積大零件。
FMS能夠生產(chǎn)體積大的和生產(chǎn)率高而優(yōu)越于獨(dú)立的CNC機(jī)床。 雖然這些機(jī)床和柔性十分不相配，但是它們也是閉合的。對(duì)于柔性制造系統(tǒng)特別地重要的、大概是最集中的能力就是在現(xiàn)在的生產(chǎn)制造形式下，能夠以很高的生產(chǎn)率、很大的柔性，為了生產(chǎn)另外的零件或產(chǎn)品快速地重新配置生產(chǎn)設(shè)備。柔性制造業(yè)就填充這一持續(xù)很久的制造業(yè)的空缺。
柔性制造業(yè)憑借自己的特有的能力，給生產(chǎn)者帶來了很多的便利:
? 柔性可以加工一系列的零件
? 加工零件的任意性
? 同時(shí)制造不同的零件
? 減少裝備時(shí)間和調(diào)試時(shí)間
? 高效率地應(yīng)用機(jī)床
? 減少直接的和間接的勞動(dòng)成本
? 能夠?qū)Σ煌牟牧线M(jìn)行識(shí)別處理
? 如果一部機(jī)床損壞，不影響零件的制造
三、柔性制造系統(tǒng)組成
FMS 主要有四個(gè)部分來組成:
? 機(jī)床工具
? 控制系統(tǒng)
? 材料處理系統(tǒng)
? 操作人員
1.機(jī)床工具
一個(gè)柔性制造系統(tǒng)和任何其他的制造業(yè)的系統(tǒng)一樣，使用的是同一類型的機(jī)床工具,它們是自動(dòng)化或用手操作的，用工具工作。這些機(jī)床包括車床，磨床，鉆床 , 鋸床, 等。
在 FMS 中所使用的機(jī)床的類型實(shí)際上是靠這些機(jī)床各自的用途來設(shè)定的，一些 FMS 需要被設(shè)計(jì)成符合定義明確要求的特性。在這些情況下，包括在系統(tǒng)中的機(jī)床的操作計(jì)劃都是必須的。 一個(gè)這樣的系統(tǒng)就是一個(gè)能夠很好提供服務(wù)的系統(tǒng)。
在一個(gè)車間的配置設(shè)定中,真實(shí)的請(qǐng)求不能被及時(shí)地識(shí)別任何其他的設(shè)定，或一定必然要有很高的可靠性、可能性, 機(jī)器系統(tǒng)會(huì)至少能夠包含標(biāo)準(zhǔn)的制造業(yè)的操作。這樣的系統(tǒng)就是一個(gè)用途一般的系統(tǒng)。
2.控制系統(tǒng)
控制系統(tǒng)是為FMS的其它系統(tǒng)提供了許多的不同控制功能:
? 規(guī)劃零件的運(yùn)儲(chǔ)和分配
? 控制和監(jiān)聽工作流程
? 控制加工過程
? 系統(tǒng)/工具控制/監(jiān)聽
在FMS的控制系統(tǒng)中運(yùn)行的計(jì)算機(jī)控制區(qū)域能夠?qū)θ魏我粋€(gè)FMS的部分的所有的活動(dòng)進(jìn)行控制和檢測(cè)。FMS 控制軟件是相當(dāng)復(fù)雜和煩瑣的，因?yàn)樗仨毻瑫r(shí)地執(zhí)行許多不同的任務(wù)。不管曾經(jīng)在這一區(qū)域中實(shí)行的什么樣的研究,都沒有和FMS軟件一樣的設(shè)計(jì)方案功能和結(jié)構(gòu)。
調(diào)度程序功能包括計(jì)劃該如何生成FMS的命令通用的容量,考慮機(jī)床工具的現(xiàn)在工作狀態(tài)，工作進(jìn)程,工作工具,工作夾具,等等。 行程能夠自動(dòng)地安排，也可能在一個(gè)操作員的協(xié)助下進(jìn)行工作。 也有很多FMS的控制系統(tǒng)是聯(lián)合自動(dòng)機(jī)械和手工操作員操作的。發(fā)送功能包括實(shí)行程序調(diào)度和協(xié)調(diào)車間內(nèi)各部分的動(dòng)作，也就是說 , 能夠決定何時(shí)何地傳送一個(gè)貨盤, 什么時(shí)候該開始在在加工中心中處理, 等等。
監(jiān)視器的功能與監(jiān)聽工作進(jìn)展 , 機(jī)器狀態(tài) , 警報(bào)信息等等, 有關(guān)系,而且能夠給調(diào)度進(jìn)程和發(fā)送者提供輸入所產(chǎn)生各種不同的制造報(bào)告和警報(bào)信息。系統(tǒng)里面處理部份原料的運(yùn)輸由一個(gè)傳送控制模塊來管理。 用多點(diǎn)控制的運(yùn)輸工具由一個(gè) AGV 系統(tǒng)控制,控制邏輯就變的相當(dāng)?shù)貜?fù)雜，并成為FMS控制軟件的一個(gè)十分重要的部份。當(dāng)在載入?yún)^(qū)域的部分為它收集做好準(zhǔn)備時(shí)， 在一個(gè)終端機(jī)中的一個(gè)裝載/ 卸載模塊能夠在載入?yún)^(qū)域分別告知操作者進(jìn)入到系統(tǒng)，并且使他或她能夠更新控制系統(tǒng)的狀態(tài)。一個(gè)儲(chǔ)存控制模塊能夠中保留一個(gè)部份被儲(chǔ)存的帳戶在AS/RS 中的精確位置。 工具管理模塊維持所有的有關(guān)工具的賬戶數(shù)據(jù)的并保持工具在FMS中的真實(shí)的位置。工具管理模塊能夠管理遠(yuǎn)遠(yuǎn)勝過正常的數(shù)目，而且此外，模塊還能控制工具的準(zhǔn)備和流程。 DNC 功能是在生產(chǎn)車間中為FMS控制程序和工作機(jī)床和各種裝置之間提供接口技術(shù)。對(duì) FMS來說， 生產(chǎn)車間的裝備中DNC功能和作用是很重要的; 一個(gè)功能齊全的DNC通過通信的條款能夠控制在遠(yuǎn)處的機(jī)械的請(qǐng)求。關(guān)于以前的DNC 討論的片段)
事實(shí)上有很多機(jī)器工具的制造商已經(jīng)發(fā)展了專有的通信條款， 這些條款是很復(fù)雜的，因?yàn)樵贔MS中包含中很多設(shè)備的的發(fā)展和集成。 除此之外，那些多設(shè)備的物理的集成實(shí)際上是十分困難的；舉例來說，在托盤中各種各樣的裝載/ 卸載的機(jī)械裝置都是應(yīng)用很復(fù)雜的機(jī)械工具，它們來自各種不同的生產(chǎn)廠商。因此，僅僅可取的方法就是從主要的機(jī)械工具制造商中購買一個(gè)比較接近用具的關(guān)鍵系統(tǒng)，工具購買實(shí)現(xiàn) FMS 的唯一適當(dāng)?shù)姆绞揭徺I來自主要的工作母機(jī)制造業(yè)者之一的一個(gè)關(guān)鍵系統(tǒng)。這個(gè)系統(tǒng)必須是可靠的和能很好地進(jìn)行測(cè)試，并且應(yīng)該由多個(gè)廠商負(fù)責(zé)幫助這個(gè)系統(tǒng)進(jìn)行故障的處理。
3.物料運(yùn)儲(chǔ)系統(tǒng)
自動(dòng)化的物料運(yùn)儲(chǔ)系統(tǒng)的是一個(gè)的能夠協(xié)助獨(dú)立的 CNC 機(jī)床形成一組，并加入到全面的 FMS 之內(nèi)的基本的成分。系統(tǒng)必須能讓那些安裝在托盤上的工件從一個(gè)工作站移動(dòng)到另外一個(gè)工作站上。當(dāng)工件等待著去一個(gè)指定的工作站被處理的時(shí)候，這個(gè)系統(tǒng)必須盡可能地給它提供適當(dāng)?shù)奈恢谩?
物料運(yùn)儲(chǔ)系統(tǒng)必須能夠卸載在工作站上的工件，并且能夠裝載另外一個(gè)運(yùn)輸?shù)较乱粋€(gè)工作站上的零件。它還必須能夠適應(yīng)計(jì)算機(jī)的控制，并且完全地與柔性制造系統(tǒng)中的其他的成分相容。最后， 在FMS中物料運(yùn)儲(chǔ)系統(tǒng)必須能夠承受車間的嚴(yán)格環(huán)境。 一些 FMSs 配置的自動(dòng)化引導(dǎo)小車(AGVs)，如物料運(yùn)儲(chǔ)就是一個(gè)重要的方法。
在FMS中自動(dòng)儲(chǔ)存和取回系統(tǒng) (AS/RS) 常常集合在一起的。 這使系統(tǒng)能在無人操縱的情況下正常地運(yùn)行，降低了勞動(dòng)強(qiáng)度。在白天班將那些未加工的零件固定在貨盤中，載入系統(tǒng)并且儲(chǔ)存的AS/RS中，等待著機(jī)器可能的需要時(shí)的命令。當(dāng)工序完成的時(shí)候, 運(yùn)輸機(jī)就把零件運(yùn)回到AS/RS，在AS/RS里等待下一個(gè)工序或者被從 FMS 被卸載，F(xiàn)MSs 的完全無人值守的操作非常少見的；在大部份的情形下一或較多的操作員將會(huì)總是不在長場(chǎng)的, 他們很少在重要的情形下干涉系統(tǒng)，(這個(gè)被計(jì)算機(jī)控制系統(tǒng)正常地自動(dòng)地工作 ) ，但是系統(tǒng)能夠糾正那些較小的錯(cuò)誤，并且能讓系統(tǒng)高的效率運(yùn)行。
4. 人類的操作員
FMS 的最后成分是人的成分。 雖然柔性制造的觀念是盡量減少制造過程中人的參與次數(shù),但是它還不能完全不用人參與。而且,人在柔性制造業(yè)中所扮演的角色仍然是十分重要的。包括規(guī)劃,操作,監(jiān)聽,控制,和維護(hù)系統(tǒng)。
2.3.4 制造控制階層的性質(zhì)
當(dāng)描述和討論制造控制和在先進(jìn)制造系統(tǒng)自動(dòng)化工廠中應(yīng)用 FMS 和 CIM( 計(jì)算機(jī)整合的制造業(yè) ) 技術(shù)的時(shí)候，它對(duì)于安排許多計(jì)劃和在透視階層的控制活動(dòng)是很方便的,全部的策略計(jì)劃在頂部，和制造程序的操作控制在底部。
那兩個(gè)最重要的組織，NBS( 國家標(biāo)準(zhǔn)局 )現(xiàn)在被叫做NIST( 國家標(biāo)準(zhǔn)和技術(shù)的學(xué)會(huì) ) ，美國的(NBS模型) 和 ISO( 國際的標(biāo)準(zhǔn)化組織 ),提議為先進(jìn)的制造系統(tǒng)的控制水平的定義了一個(gè)國際的標(biāo)準(zhǔn)( ISO- 模型 )。 NBS模型識(shí)別五個(gè)層次，即工廠層，車間層，單元層、工作站和設(shè)備層。 ISO- 模型增加了一層，在它的模型中包括六個(gè)層次，即企業(yè)，工廠層/制造廠，部分層/區(qū)域，車間層，工作站，設(shè)備層。這些階層的模型在計(jì)劃和執(zhí)行計(jì)算機(jī)集成制造系統(tǒng)中主要地被當(dāng)作叁考的框架使用，但是他們也是可適用于討論生產(chǎn)計(jì)劃和大概的控制活動(dòng)。
這對(duì)討論制造業(yè)的控制水平的定義是有關(guān)系的，因?yàn)樵谖膶W(xué)和商業(yè)產(chǎn)品的描述中常常會(huì)用到一些自動(dòng)化工廠的專業(yè)術(shù)語。不同的級(jí)的典型的工作和職務(wù)在如下列各項(xiàng):
1)企業(yè)控制包括全部的企業(yè)的戰(zhàn)略計(jì)劃。 這是產(chǎn)品的需求計(jì)劃，市場(chǎng)策略 , 和區(qū)分企業(yè)內(nèi)部的各分區(qū)的工作。 制造業(yè)控制被運(yùn)用在企業(yè)的標(biāo)準(zhǔn)，就是負(fù)責(zé)的完成企業(yè)的使命; 這些年來規(guī)劃的水平在應(yīng)用中得到了衡量，并沒有常常發(fā)生變化。
2)設(shè)備控制負(fù)責(zé)實(shí)現(xiàn)企業(yè)策略。 它在制造設(shè)備控制和運(yùn)行方面有這樣的功能例如加工制造和產(chǎn)品工程學(xué)，數(shù)據(jù)管理和其他的長期活動(dòng)。
3)區(qū)域控制負(fù)責(zé)在車間內(nèi)的資源配置和制造的協(xié)調(diào)。 這一個(gè)典型的操作控制水平能夠在好幾個(gè)天或數(shù)個(gè)星期維持同一個(gè)狀態(tài)。 這一個(gè)層也經(jīng)常被稱為命" 車間層 " ，“車間控制層”術(shù)語包括區(qū)域控制和下一層的控制，在美國的著作中，車間控制經(jīng)常被稱為 "制造活動(dòng)控制 ",在 柔性制造系統(tǒng)中FMS控制軟件將會(huì)對(duì)區(qū)域?qū)嵭锌刂啤?
4)單元控制負(fù)責(zé)在制造單元里工作站間的作業(yè)調(diào)度。這包括資源分配, 作業(yè)指令的發(fā)放，工作路線的確定,分配給個(gè)別的工作站 , 對(duì)工作和工作站的工作情況的監(jiān)聽。
5)工作站控制負(fù)責(zé)協(xié)調(diào)工作站上被實(shí)行運(yùn)行分配到工作站的一個(gè)工作,這一個(gè)功能操作可以在幾秒到幾小時(shí)的時(shí)間內(nèi)完成
6)設(shè)備層是在一部機(jī)器上執(zhí)行具體的工作。 在一個(gè)工作機(jī)床上，這一層的特點(diǎn)是局部地的控制機(jī)床的主軸速度 , 冷卻等等。
附錄2外文文獻(xiàn)
Flexible Manufacturing System
As an introduction to the subsequent discussions of production system and advanced manufacturing technologies it is useful to present a definition of the term manufacturing system .A manufacturing system can be defined as a series of value-adding manufacturing processes converting the raw materials into more useful forms and eventually finished products.
In the modern manufacturing setting，flexibility is an important characteristic It means that a manufacturing system is versatile and adaptable ,while also capable of handing relatively high production runs. A flexible manufacturing system is quickly modified to produce a completely different line of parts.
A flexible manufacturing is an individual machine or group of machines served by an automated materials handing system that is computer controlled and has a tool handing capability .Because of its tool handing capability and computer control, such a system can be continually reconfigured to manufacture a wide variety of parts. This is why it is called a flexible manufacturing system.
A FMS typically encompasses:
? Process equipment e.g., machine tools, assembly stations, and robots
? Material handing equipment e.g. , robots, conveyors, and AGVs(automated guided vehicles)
? A communication system
? A computer control system
Flexible manufacturing represents major step toward the goal of fully integrated manufacturing. It involves integration of automated production process. In flexible manufacturing, the automated manufacturing machine (i.e. ,lathe mill, drill) and the automated materials handing system share instantaneous communication via a computer network.
Flexible manufacturing tales a major step toward the goal of fully integrated manufacturing by integrating several automated manufacturing concepts:
? Computer numerical control (CNC) of individual machine tools
? Distributed numerical control (DNC) of manufacturing system
? Automated materials handing systems
? Group technology (families of parts)
When these automated processes, machine, and concepts are brought together in one integrated system, an FMS is the result. Humans and computers play major roles in an FMS. The amount of human labor is much less than with a manually operated manufacturing system, of course. However, humans still play a vital role in the operation of an FMS. Human tasks include the following:
? Equipment troubleshooting maintenance, and repair
? Tool changing and setup
? Loading and unloading the system
? Data input
? Changing of parts programs
? Development of programs
Flexible manufacturing system equipment, like all manufacturing equipment, must be monitored for bugs, malfunctions, and breakdowns. When a problem is discovered, a human troubleshooter must identify its source and prescribe corrective measures. Humans also undertake the prescribed measures to repair the malfunctioning equipment. Even when all system are properly functioning, periodic maintenance is necessary.
Human operators also set up machines, change tools, and reconfigure systems as necessary. The tool handing capability of an FMS increases, but does not eliminate human involvement in tool changing and setup. The same is true of loading and unloading the FMS. Once raw material has been loaded onto the automated materials handing system, it is moved through the system in the prescribed manner. However, the original loading onto the unloading of finished products.
Humans are also needed for interaction with the computer .Humans develop part programs that control the FMS via computer .They also change the programs as necessary when reconfiguring the FMS to produce another type of part or parts .Humans play less labor-intensive roles in an FMS, but the roles are still critical.
Control at all levels in an FMS is provided by computers. Individual machine Tools within an FMS are controlled by CNC. The overall system is controlled by DNC. the automated materials handling system is computer controlled, as are other functions including data collection, system monitoring, tool control, and traffic control, Human/computer interaction is the flexibility of an FMS.
一、Hisorical Development of Flexible Manufacturing
Flexible manufacturing was born in the mid-1960s when the British firm Molins, Ltd. Developed its System 24. System 24 was a real FMS. However, it was doomed from the outset because automation, integration, and computer control technology had not yet been developed to the pont where they could properly support the system. The first FMS was a development that was ahead of its time. As such, it was eventually discarded as unworkable.
Flexible manufacturing remained an academic concept through the remained of the 1960s and 1970s. However, with the emergence of sophisticated computer control technology in the late 1970s and early 1980s, flexible manufacturing became a viable concept. The first major users of flexible manufacturing in the United States were manufacturers of automobiles, trucks, and tractors.
二、 Rationale for Flexible Manufacturing
In manufacturing there have always been tradeoffs between production rates and flexibility. At one end of the spectrum are transfer lines capable of high production rates, but low flexibility. At the other end of the spectrum are independent CNC machines that offer maximum flexibility, but are capable only of low production rates. Flexible manufacturing falls in the middle of the spectrum. There has always been a need in manufacturing for a system that could produce higher volume and production runs than could independent machines, while still maintaining flexibility.
Transfer lines are capable of producing large volumes of parts at high production rates. The line takes a great deal of setup, but can turn out identical parts in large quantities. Its chief shortcoming is that even minor design changes in a part can cause the entire line to be shut down and reconfigured. This is a critical weakness because it means that transfer lines cannot produce different parts, even parts from within the same family, without costly and time-cinsuming shutdown and reconfiguration.
Traditionally, CNC machines have been used to produce small volumes of parts that differ slightly in design. Such machines are ideal for this purpose because they can be quickly reprogrammed to accommodate minor or even major design changes. However, as independent machines they cannot produce parts in large volumes or at high production rates.
An FMS can handle higher volumes and production rates than independent CNC machines. They cannot quite match such machines for flexibility, but they come close. What is particularly significant about the middle ground capabilities of flexible manufacturing is that most manufacturing situations require medium production rates to produce medium volumes with enough flexibility to quickly reconfigure to produce another part or product. Flexible manufacturing fills this long-standing void in manufacturing.
Flexible manufacturing, with its ground capabilities, offers a number of advantages for manufacturers:
? Flexibility within a family of parts
? Random feeding of parts
? Simultaneous production of different parts
? Decreased setup time and lead time
? More efficient machine usage
? Decreased direct and indirect labor costs
? Ability to handle different materials
? Ability to continue some production if one machine breaks down
三、Flexible Manufacturing System Components
An FMS has four major components:
? Machine tools
? Control system
? Materials handling system
? Human operators
1、 Machine Tools
A flexible manufacturing system uses the same types of machine tools as any other manufacturing system, be it automated or manually operated. These include lathes, mills, drills, saws, an so on. The type of machine tools actually included in an FMS depends on the setting in which the machine will be used. Some FMSs are designed to meet a specific, well-defined need. In these cases the machine tools included in the system will be only those necessary for the planned operations. Such a system would be known as a dedicated system.
In a job-shop setting, or any other setting in which the actual application is not known ahead of time or must necessarily include a wide range of possibilities, machines capable of performing at least the standard manufacturing operations would be included. Such systems are known as general purpose systems.
2. Control System
The control system for an FMS serves a number of different control functions for system:
? Storage and distribution of parts program
? Work flow control and monitoring
? Production control
? System/tool control/monitoring
The control area with the computer running the FMS control system is the center from which all activities in the FMS are controlled and monitored. The FMS control software is rather complicated and sophisticated since it has to carry out many different tasks simultaneously. Despite the considerable research that has been carried out in this area, there is no general answer to designing the functions and architecture of FMS software.
The scheduler function involves planning how to produce the current volume of orders in the FMS, considering the current status of machine tools, work-in-pocess, tooling, fixtures, and so on. the scheduling can be done automatically or can be assisted by an operator. Most FMS control systems combine automatic and manually by the operator. the dispatcher function involves carrying out the schedule and coordinating the activities on the shop floor, that is, deciding when and where to transport a pallet, when to start a process on machining center, and so on.
The monitor function is concerned with monitoring work progress, machine status, alarm messages, and so on, and providing input to the scheduler and dispatcher as well as generating various production reports and alarm messages. A transport control module manages the transportation of parts and palettes within the system. Having an AGV system with multiple vehicles, the routing control logic can become rather sophisticated and become a critical part of the FMS control software. A load/unload module with a terminal at the loading area shows the operators which parts to introduce to the system and enables him or her to update the status of the control system when parts are ready for collection at the loading area. A storage control module keeps an account of which parts are stored in the AS/RS as well as their exact location. the tool management module keeps an account of all relevant tool data and the actual location of tools in the FMS .Tool management can be rather comprehensive since the number of tools normally exceeds the number of parts in the system, and furthermore ,the module must control the preparation and flow of tools. the DNC function provides interfaces between the FMS control program and machine tools and devices on the shop floor. the DNC capabilities of the shop floor equipment are essential to a FMS; a “full” DNC communication protocol enabling remote control of the machines is required (see the discussion on DNC in the previous section).
The fact that most vendors of machine tools have developed proprietary communication protocols is complicating the development and integration of FMSs including multi-vendor equipment. Furthermore, the physical integration of multi-vendor equipment is difficult; for example, the differences in pallet load/unload mechanisms complicate the use of machine tools from different vendors. Therefore, the only advisable approach for implementing a FMS is to purchase a turn-key system from one of the main machine tool manufacturers. there systems are reliable and well tested and should the system not function satisfactorily a single vendor responsibility will facilitate remedy of malfunctions.
3. Materials Handing System
The automated materials handing system is a fundamental component that helps mold a group of independent CNC machines into a comprehensive FMS. The system must be capable of accepting workpieces mounted on pallets and moving them from workstation to workstation as needed. It must also be able to place workpieces on hold as they wait to be processed at a given workstation.
The materials handing system must be able to unload a workpiece at one station and load another for transport to the next station. It must accommodate computer control and be completely compatible with other components in the flexible manufacturing system .Finally, the materials handing system for an FMS must be able to withstand the rigors of a shop environment. Some FMSs are configured with automated guided vehicles (AGV s) as a principal means of materials handling.
An automated storage and retrieval system (AS/RS) is very often integrated in the FMS. This enables the system to run one or two unmanned shifts with reduced workforce. In the day shift raw parts are fixed on pallets loaded into the system and stored in the AS/RS waiting for available capacity on the machines required. When the process is finished, the transporter can move the part back to the AS/RS where it waits for the next process or to be unloaded from the FMS when the workforce reports for workforce reports for work next morning. The fully unmanned operation of FMSs is very rare; in most cases one or more operators will always be present, not so much to intervene in critical situations ( this is normally done automatically by the computer control system ) but to correct minor faults and keep the system running with highest possible utilization.
4. Human Operators
The final component in an FMS is the human component. Although flexible manufacturing as a concept decreases the amount of human involvement in manufacturing, it does not eliminate it completely. Further, the roles humans play in flexible manufacturing are critical. There include programming, operating, monitoring, controlling, and maintaining the system.
四、The Hierarchical Nature and discussing production control
When describing and discussing production control and facto