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Flexible Manufacturing
As an introduction to the subsequent discussions of production systems 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 handling relatively high production runs. A flexible manufacturing system is versatile in that it can produce a variety of parts. It is adaptable because it can be quickly modified to produce a completely different line of parts.
A flexible manufacturing system is an individual machine or group of machines served by an automated materials handling system that is computer controlled and has a tool handling capability. Because of its tool handling 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 handling equipment e.g. , robots, conveyors, and AGVs (automated guided vehicles)
* A communication system
* A computer control system
Flexible manufacturing represents a major step toward the goal of fully integrated manufacturing. It involves integration of automated production processes. In flexible manufacturin , the automated manufacturing machine and the automated materials handling system share instantaneous communication via a computer network. This is integration on a small scale.
Flexible manufacturing takes 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 systems
* Automated materials handling systems
* Group technology (families of parts)
When these automated processes, machines, 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 systems are properly functioning, periodic maintenance is necessary.
Human operators also set up machines, change tools, and reconfigure systems as necessary. The tool handling capability of an FMS decreases, but does not eliminate 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 handling system, it is moved through the system in the prescribed manner. However, the original loading onto the materials handling system is still usually done by human operators, as is the unloading of finished products.
Humans are also needed for interaction with the computer. Humans develop part programs that control the FMS via computers. 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 key to the flexibility of an FMS.
1 Historical Development of Flexible Manufacturing
Flexible manufacturing was born in the mid-1960s when the British firm Molins, Ltd. Developed its System24. 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 point 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 remainder 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.
2 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 continuum. 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 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-consuming 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
3 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, and so on. The type of machine tools actually included in an FMS depends on the setting in which the machine will be used. Some FMS 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 include. 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 programs
* 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-process, tooling, and so on. The scheduling can be done automatically or can be assisted by an operator. Most FMS control systems combine automatic and manual scheduling; the system generates an initial schedule that can be changed 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 a 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.
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 mechanics 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.
（3）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. These include programming, operating, monitoring, controlling, and maintaining the system.
柔性制造
正如對(duì)制造系統(tǒng)和先進(jìn)的制造技術(shù)后來的討論，介紹制造業(yè)系統(tǒng)術(shù)語的定義是十分有用的。制造業(yè)系統(tǒng)的定義是一系列把原料轉(zhuǎn)換成較有用的形式，最后完成產(chǎn)品的，能夠使制造過程增值的系統(tǒng)。
在現(xiàn)代制造業(yè)的框架中，柔性是一個(gè)重要的特性。這意味一個(gè)制造系統(tǒng)是通用的和廣泛適應(yīng)的, 同時(shí)也有較高的生產(chǎn)能力。一個(gè)柔性的制造系統(tǒng)是通用的，它能生產(chǎn)多種零件。它具有適應(yīng)性是因?yàn)樗梢员缓芸斓卣{(diào)整，生產(chǎn)完全不同的零件。
一個(gè)柔性制造系統(tǒng)是一部單獨(dú)的或成組的，有自動(dòng)化材料處理系統(tǒng)服侍的，被計(jì)算機(jī)控制的，具有工具處理能力的機(jī)器。因?yàn)橛泄ぞ咛幚砟芰捅挥?jì)算機(jī)控制，這個(gè)系統(tǒng)可以被不斷地調(diào)整，制造廣泛和多樣的零件。這是它為什么叫做柔性制造業(yè)系統(tǒng)的原因。
一個(gè)FMS 典型地包括:
*比如有處理儀器，機(jī)器工具,集會(huì)安置,和機(jī)械手
*比如有材料處理設(shè)備，機(jī)械手，運(yùn)送裝置和 AGVs(自動(dòng)化信息處理系統(tǒng))
*一個(gè)信息傳輸系統(tǒng)
*一個(gè)計(jì)算機(jī)控制系統(tǒng)
柔性制造是制造業(yè)向完全整合的目標(biāo)邁進(jìn)的一個(gè)重要的階段。它包括自動(dòng)化制造程序的整合。在柔性制造過程中，自動(dòng)化的制造機(jī)構(gòu)和自動(dòng)化材料處理系統(tǒng)經(jīng)由一個(gè)計(jì)算機(jī)網(wǎng)絡(luò)被即時(shí)的溝通。這是在一個(gè)較小規(guī)模上的整合。
柔性制造對(duì)幾個(gè)自動(dòng)化制造概念的整合是實(shí)現(xiàn)完全整合的目標(biāo)過程中所采取的一個(gè)重要的步驟：
*計(jì)算機(jī)對(duì)機(jī)器設(shè)備分別的數(shù)字控制 (CNC)
*制造系統(tǒng)的分布式數(shù)字控制 (DNC)
*自動(dòng)化材料處理系統(tǒng)
*成組技術(shù) (零件的系列)
當(dāng)這些自動(dòng)化程序，機(jī)器和觀念被引入一個(gè)整合的系統(tǒng)中的時(shí)候，F(xiàn)MS 就完成了。人和計(jì)算機(jī)在FMS中扮演重要的角色。人類的勞動(dòng)量當(dāng)然要比用手工操作的制造系統(tǒng)少。然而,人類仍然在FMS的操作中扮演著重要的角色。人類的工作包括下列各項(xiàng):
*儀器故障修理，維護(hù)和修理
*更換和調(diào)整工具
*載入和卸載系統(tǒng)
*數(shù)據(jù)輸入
*部分計(jì)劃的變更
*計(jì)劃的發(fā)展
柔性制造系統(tǒng)設(shè)備，像所有的制造業(yè)的設(shè)備一樣，一定會(huì)出現(xiàn)出錯(cuò)，故障,和崩潰。當(dāng)一個(gè)問題被發(fā)現(xiàn)的時(shí)候,修理它的人必須找出問題的來源，并提出糾正的方案。人也承擔(dān)著采取正確的措施修理那發(fā)生故障設(shè)備的任務(wù)。即使當(dāng)所有的系統(tǒng)正在正常地工作,周期的維護(hù)也是必需的。
人類的操作員有必要完成安裝機(jī)器，變換工具,重裝系統(tǒng)的工作。FMS工具處理能力的減少不包括更換和調(diào)整工具，載入和卸載FMS。一但原材料被裝入自動(dòng)化的材料處理系統(tǒng),它將被系統(tǒng)以規(guī)定的方式移動(dòng)。然而，最初是由人類的操作員把原材料裝入和把產(chǎn)品卸下材料處理系統(tǒng)的。
人也需要和計(jì)算機(jī)互動(dòng)。人經(jīng)由計(jì)算機(jī)控制FMS加工零件的程序。當(dāng)FMS生產(chǎn)另外類型的零部件的時(shí)候，人必須改變它的程序。人在FMS中扮演勞動(dòng)量很少但仍然是至關(guān)重要的角色。
FMS的所有標(biāo)準(zhǔn)都是由計(jì)算機(jī)提供的。FMS中單獨(dú)的加工工具都是由CNC控制的。而全面的系統(tǒng)是被DNC控制的。如同包括數(shù)據(jù)收集，系統(tǒng)監(jiān)視，工具控制和信息交換控制等其他功能一樣，自動(dòng)化的材料處理系統(tǒng)也是由計(jì)算機(jī)控制的。人機(jī)交互作用是FMS柔性的關(guān)鍵。
1.柔性制造的歷史發(fā)展
柔性制造在十九世紀(jì)六十年代中期出現(xiàn)在英國 Molins, Ltd公司。它發(fā)展System24。System24是真正的FMS。然而,因?yàn)樽詣?dòng)化，整合和計(jì)算機(jī)控制技術(shù)仍未發(fā)展到可以完全的支持系統(tǒng)的階段，所以從剛一著手開始，它的命運(yùn)就已被注定。第一個(gè)FMS超前于在它所在的時(shí)代。同樣，它最后就像難以實(shí)現(xiàn)的東西一樣被放棄。
柔性制造在六十年代和七十年代剩下的時(shí)間一直停留在理論和概念階段。然而，隨著七十年代后期和八十年代早期，復(fù)雜的計(jì)算機(jī)控制技術(shù)的出現(xiàn)，柔性制造變成一項(xiàng)可行的概念。美國的柔性制造最早的使用者主要是汽車，卡車和拖拉機(jī)制造業(yè)。
2.柔性制造的原理
在制造業(yè)中總是存在生產(chǎn)率和柔性之間的矛盾。一方面是流水線能夠?qū)崿F(xiàn)高的生產(chǎn)率,但是柔性低。另一方面是獨(dú)立的CNC機(jī)構(gòu)能提供最大的柔性,但是生產(chǎn)率低。柔性制造則在二者之間。制造業(yè)一直以來就有一個(gè)需求，就是一個(gè)系統(tǒng)有較高的生產(chǎn)率，獨(dú)立性，同時(shí)有柔性。
流水線以高的生產(chǎn)率能夠產(chǎn)生大量的零件。流水線需要很多的設(shè)備,但是失去其中的一部分能引起整個(gè)的流水線的停工，而且需要重新配置。這是它最為關(guān)鍵的缺點(diǎn)，因?yàn)檫@意味著流水線在沒有代價(jià)高昂的，長時(shí)間的關(guān)閉和重新裝配的情況下，不能生產(chǎn)不同的，即便是同一系列的零件。
傳統(tǒng)的CNC設(shè)備已經(jīng)用來小批量地生產(chǎn)在設(shè)計(jì)中有些微小差別的零件。 這是一種很理想的設(shè)備，因?yàn)樗鼈兡鼙煌ㄟ^重新編程很快的適應(yīng)較小的，甚至主要的設(shè)計(jì)變化, 然而作為獨(dú)立的設(shè)備，它們不能以較高的生產(chǎn)率大批量的生產(chǎn)零件。
FMS比獨(dú)立的CNC設(shè)備擁的更高的產(chǎn)量和生產(chǎn)率。它們的柔性還不能夠與獨(dú)立的CNC設(shè)備相比，但是已經(jīng)接近。柔性制造關(guān)于中間基本能力的顯著特點(diǎn)是，大多數(shù)的情況需要有足夠的柔性被迅速的改造用來生產(chǎn)別的零件或產(chǎn)品的前提下，能以中間的生產(chǎn)率生產(chǎn)中間數(shù)量的產(chǎn)品。柔性制造填補(bǔ)了制造業(yè)中的空白。
柔性制造是由它的基本能力為制造者提供許多的利益:
* 可以制造相似的零件
* 隨意更換零件
* 同時(shí)生產(chǎn)不同的零件
* 減少裝備時(shí)間和交貨期
* 有效率的機(jī)器用法
* 減少了直接的和間接的勞動(dòng)費(fèi)用
* 處理不同材料的能力
* 如果一部機(jī)器崩潰繼續(xù)生產(chǎn)的能力
3 柔性制造系統(tǒng)的組成
FMS 有四個(gè)主要的組成部分:
*機(jī)器工具
*控制系統(tǒng)
*原料搬運(yùn)系統(tǒng)
*人類的操作
(1)機(jī)器工具
柔性制造系統(tǒng)同任何其他的制造系統(tǒng)一樣，使用相同類型的機(jī)器,是被自動(dòng)控制或用手操作。這些包括車床，磨床，鉆床，插床,等等。這些典型的機(jī)器實(shí)際上被FMS控制著，當(dāng)系統(tǒng)需要哪個(gè)時(shí)就調(diào)用那個(gè)機(jī)器。一些FMS被設(shè)計(jì)成符合一種特性，能夠定義明確的需要。在這樣情況下機(jī)器工具在系統(tǒng)中將會(huì)只是調(diào)用那些必需的為了計(jì)劃的操作。這樣的系統(tǒng)成為被人們所關(guān)注的系統(tǒng)。
在一個(gè)工作環(huán)境設(shè)定中,或?qū)嶋H的應(yīng)用中，應(yīng)用之前不知道的任何設(shè)定或一定必然地包含寬范圍的可能性,至少能夠控制或操作機(jī)器完成標(biāo)準(zhǔn)的制造。這樣的系統(tǒng)成為知名的普通用途的系統(tǒng)。
(2)控制系統(tǒng)
控制系統(tǒng)是FMS服侍控制許多的不同功能:
*零配件程序表的倉儲(chǔ)和分布
*工作流程的控制和監(jiān)測
*生產(chǎn)管理
*系統(tǒng)/工具控制/監(jiān)測
計(jì)算機(jī)不斷的對(duì)FMS的發(fā)出指令進(jìn)行面積控制，這是從控制中心到 FMS的所有活動(dòng)被控制和檢測的范圍。FMS控制軟件程序復(fù)雜，因?yàn)樗仨毻瑫r(shí)地進(jìn)行許多不同的操作。不管是已經(jīng)在這一個(gè)面積中的，還是正在進(jìn)行研究的,沒有普通答案設(shè)計(jì)功能和FMS軟件的體系機(jī)構(gòu)。
調(diào)試程序功能包括在FMS中計(jì)劃該如何執(zhí)行當(dāng)前大量的命令，現(xiàn)在的容積,同時(shí)考慮機(jī)器工具的當(dāng)前狀態(tài)，工進(jìn)步驟,所用工具,等等。行程安排能夠自動(dòng)地做或可能被一個(gè)操作員控制操作。大多數(shù)的FMS控制系統(tǒng)能夠結(jié)合自動(dòng)的和手動(dòng)的行程安排；系統(tǒng)所執(zhí)行的初次預(yù)定計(jì)劃可以被操作員用手改變。發(fā)送信息功能包括實(shí)行預(yù)定計(jì)劃并且協(xié)調(diào)工作環(huán)境中的活動(dòng),也就是說 , 決定何時(shí)和該向哪里傳送一個(gè)托板, 何時(shí)開始在加工中心上處理一個(gè)程序, 等等。
監(jiān)控功能隨著監(jiān)控工作的進(jìn)行而進(jìn)步 ,與機(jī)器狀態(tài) 、警報(bào)信息等有關(guān)系,倘若輸給調(diào)試中心和傳輸系統(tǒng)不同的信息將會(huì)使系統(tǒng)發(fā)生混亂。在系統(tǒng)里，一個(gè)傳送控制組能夠處理零配件和調(diào)色板的運(yùn)輸。用AGV系統(tǒng)可以達(dá)到成倍傳輸?shù)男Ч?控制邏輯的工作路線是FMS控制軟件的一個(gè)具決定性的部分。一個(gè)終點(diǎn)的負(fù)載/ 卸載組件在負(fù)載面積上分開連接到系統(tǒng)而且使他或她能夠更新控制系統(tǒng)的狀態(tài)。一個(gè)倉儲(chǔ)控制組件能夠維持一個(gè)零配件所儲(chǔ)存的帳戶，在當(dāng)時(shí)/之后R 能夠精確確定他們的位置。工具管理組件能夠維持所有的相關(guān)工具數(shù)據(jù)的帳戶并維持FMS工具的實(shí)際位置。當(dāng)工具的數(shù)目正常地超過系統(tǒng)的零配件的數(shù)目之后，工具管理可能包羅萬象。此外，組件能夠控制一定數(shù)量和流量的工具。DNC功能是為車間提供在FMS控制程序表和工作機(jī)與裝置之間的接口。車間設(shè)備對(duì)DNC的接受能力對(duì)FMS來說是很重要的;機(jī)器的遙控能夠記錄所需要的"全部"DNC的溝通記錄。
實(shí)際上大多數(shù)的廠商所使用的機(jī)器已經(jīng)發(fā)展成為專有的設(shè)備，溝通記錄是復(fù)雜的,包括眾多設(shè)備FMSs的發(fā)展和整合。此外，眾多設(shè)備的整合實(shí)際上是很困難的；舉例來說托板負(fù)載 / 卸載力學(xué)的差別很是復(fù)雜，因?yàn)樗褂玫臋C(jī)器來自不同的廠商。因此，實(shí)現(xiàn)FMS的唯一適當(dāng)?shù)姆绞骄褪且徺I一個(gè)來自主要的工作機(jī)器造業(yè)者的系統(tǒng)轉(zhuǎn)換系統(tǒng)。
(3)人類的操作
FMS中最重要的因素是人類。雖然柔性制造這一觀念能夠減少人類勞動(dòng)在制造業(yè)中的比重，但是它不能完全地脫離人類的勞動(dòng)。進(jìn)一步說,人類在柔性制造中扮演著極其重要的起決定性作用的角色。 這些包括規(guī)劃設(shè)計(jì),操作,追蹤監(jiān)測,控制以及維護(hù)系統(tǒng)。
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