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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 ( FMS) 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 :
(1) process equipment e.g., machine tools , assembly stations, and robots.
(2) material handling equipment eg, robots, conveyors, and AGVs (automated guided vehicles )
(3) a communication system
(4) 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 manufacturing, the automated manufacturing machine (i.e., lathe, mill,drill ) 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:
(1) computer numerical control (CNC) of individual machine tools .
(2) distributed numerical control (DNC) of ,manufacturing systems.
(3) Automated materials handling systems
(4) 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:
(1) equipment troubleshooting , maintenance, and repair.
(2) Tool changing and setup .
(3) Loading and unloading the system.
(4) Data input .
(5) Changing of parts programs.
(6) 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 system 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 materials handing 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 CNC. The overall system is controlled by DNC. The materials handing 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 history development of flexible manufacturing
flexible manufacturing was born in the mid-1986s 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 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 user 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 issue are transfer lines capable of high production rates, but low flexibility. At the other end of the issue are independent CNC machines that offer maximum flexibility, but are capable only of low production rates. Flexible manufacturing falls in the middle. 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 . Tts 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 tranfer 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 volume of parts that differ lightly in design .such machines are ideal for this purpose because they can be quickly reprogrammmed 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, it 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 this long standing void in manufacturing.
Flexible manufacturing ,with its ground capabilities, offers a number of advantages for manufacturers：
(1) flexibility within a family of parts.
(2) Random feeding of parts.
(3) Simultaneous production of different parts.
(4) Decresed setup time and lead time .
(5) More efficient machine usage.
(6) Decreased direct and indirect labor costs
(7) Ability to handle different materials .
(8) Ability to continue some production if one machine breaks down.
3 flexible manufacturing system components
A FMS has three major components:
(1) Machine tools
(2) Control system
(3) Materials handling system
3.1 machine tools
A flexible manufacturing system uses the same types of machine tools as any other manufacturing system, be it automated or manually operated . there include lathes ,mills,drills,saws, and so on. The type of machine tools actually include in an FMS depends on the setting in which the machine will be used . some FMSes 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.
3.2 control system
The control system for an FMS serves a number of different control functions for system:
(1) Storage and distribution of parts programs
(2) Work flow control and monitoring
(3) Production control
(4) 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 task 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.
Some typical functions of a FMS control system are illustrated in fig.3.22
Fig.3.22 diagram of functions in advanced FMS Control 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 fixtures, 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 transporation 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 partes 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 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 shopfloor equipment are essential to a FMS,a “full” DNC communication protocols is 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 FMSes including multi-vendor equipment .further more,the physical integration of multi-vendor equipment is different; 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. These systems are reliable and well tested and should the system not function satisfactorily, a single vendor responsibility will facilitate remedy of malfunctions.
柔性制造
由于對生產(chǎn)系統(tǒng)和先進制造技術的隨后進行的討論的介紹，提出一個術語定義——制造系統(tǒng)是很有用的。制造系統(tǒng)可以被定義為一個增值工序，它將原材料轉(zhuǎn)換成更多有用的形式和最終成品。
? 在現(xiàn)代制造業(yè)的背景下，靈活性是一個重要的特征。這意味著制造系統(tǒng)靈活、適應性強，同時也有處理相對較高的生產(chǎn)運行的能力。一個柔性制造系統(tǒng)的通用性在于能生產(chǎn)各種零件。它適應性強是因為它可以迅速修改，以產(chǎn)生完全不同的零件線。
一個柔性制造系統(tǒng)（FMS）是一個單獨的機器或處理系統(tǒng)，由計算機控制，具有自動化的工具，材料處理能力擔任設備組。由于其處理能力和計算機控制的工具，這種系統(tǒng)可以不斷地重新配置，制造各種各樣的零件。這就是為什么它被稱為柔性制造系統(tǒng)。
一個柔性制造系統(tǒng)通常包括：
（1）工藝設備如機床，裝配站和機器人
（2）材料處理設備如機器人，輸送機，和AGV（自動導引車）
（3）通訊系統(tǒng)
（4）計算機控制系統(tǒng)
柔性制造向著完全集成制造目標邁出了重要一步。它包括生產(chǎn)過程自動化集成。在柔性制造，自動加工機（即，車床，銑，鉆）和自動化材料處理系統(tǒng)通過一個計算機網(wǎng)絡分享即時通信。這是一個小規(guī)模的整合。
柔性制造通過結合幾個自動化生產(chǎn)理念，朝著全面集成制造目標邁出了重要一步：
（1）單個機床的計算機數(shù)值控制（CNC）。
（2）制造系統(tǒng)的分布式數(shù)字控制（DNC）
（3）自動化物料處理系統(tǒng)
（4）成組技術
當這些自動化的過程，機械和概念弄成一個完整的體系，柔性制造系統(tǒng)就是它們的產(chǎn)物。人類和計算機在柔性制造系統(tǒng)發(fā)揮重大作用。當然，人類勞動量遠遠不如了手工操作的制造系統(tǒng)。然而，人類在柔性制造系統(tǒng)的運作上仍然起著至關重要的作用。人類的任務包括以下內(nèi)容：
（1）設備故障排除，維護和修理
（2）刀具更換和安裝
（3）裝卸系統(tǒng)
（4）數(shù)據(jù)輸入
（5）部分節(jié)目的變遷
（6）方案的發(fā)展
柔性制造系統(tǒng)設備像所有的生產(chǎn)設備，必須對錯誤，故障，以及故障進行監(jiān)控。當發(fā)現(xiàn)一個問題，一個人的疑難解答必須確定它的來源和記錄糾正的措施。人類也在采取記錄下的措施來修復損壞的設備。即使所有的系統(tǒng)都運轉(zhuǎn)正常，定期保養(yǎng)也是必要的。
人力經(jīng)營者還建立了機器，改變刀具，并在必要時重新配置系統(tǒng)。一個柔性制造系統(tǒng)處理能力工具增加，但并不能消除人類在換刀和設置方面的參與。柔性制造系統(tǒng)的裝卸同樣很真實。一旦原材料已加載到自動化物料處理系統(tǒng)，它就會通過系統(tǒng)按照已經(jīng)描述好的方式移動。然而，原裝載到自動化物料處理系統(tǒng)仍然通常由人工操作完成，這也是成品裝卸。
人類也需要與電腦互動。人類開發(fā)通過計算機控制柔性制造系統(tǒng)工件程序。當重新配置柔性制造系統(tǒng)以加工不同的工件時，他們還根據(jù)需要更改程序。人類在柔性制造系統(tǒng)上起著一個少勞力密集的作用，但作用仍然至關重要。
在各級的柔性制造系統(tǒng)控制是由電腦提供的。在柔性制造系統(tǒng)中單獨的機床是由CNC控制的。整個系統(tǒng)是由DNC控制的由于其他功能，包括數(shù)據(jù)采集，系統(tǒng)監(jiān)控，控制工具，以及交通管制，因此自動化物料處理系統(tǒng)是有計算機控制的。對一個柔性制造系統(tǒng)的靈活性的關鍵是人與電腦互動。
1 柔性制造的發(fā)展歷史
當英國莫林斯公司開發(fā)了其系統(tǒng)24時，柔性制造便產(chǎn)生于19世紀八十年代中期。系統(tǒng)24是一個真正的柔性制造系統(tǒng)。然而，從一開始就注定失敗，因為自動化，集成和計算機控制技術尚未發(fā)展到可以正確地支持系統(tǒng)的地步。第一個柔性制造系統(tǒng)是一個發(fā)展領先于它的時間的。因此，它最終也因行不通而丟棄。
通過對20世紀60年代和70年代的其余部分，柔性制造仍然是一個學術概念。但是，隨著先進的計算機控制技術在20世紀70年代末和80年代初出現(xiàn)，柔性制造成為一個可行的概念。柔性制造的第一個在美國的主要用戶是各國汽車制造商，卡車，和拖拉機。
2 柔性制造的原由
在制造業(yè)一直存在生產(chǎn)效率和靈活性之間的權衡。在1月底的問題是傳輸線的高生產(chǎn)率的但靈活性低的能力。在這個問題的另一端是獨立的數(shù)控機床能夠提供最大的靈活性，但唯一缺陷是生產(chǎn)率低。柔性制造在中期下跌。在制造上一直需要一個系統(tǒng)，它可以比獨立的機床產(chǎn)生更高的容量和生產(chǎn)運行量，同時仍保持靈活性。
傳輸線具有以高生產(chǎn)率生產(chǎn)大量零部件的能力。這線需要大量的安裝程序，但可以打開了大量相同的部件。它的主要缺點是，即使在一小部分設計變更也可能會導致整個傳輸線被關閉和重新配置。這是一個關鍵的弱點，因為這意味著即便是同組工件，無需進行昂貴，費時的關機和重新配置，傳輸線也不能加工不同的工件。
傳統(tǒng)上，數(shù)控機床已被用于生產(chǎn)在設計稍微不同的小型零件。為此這種機器是理想的，因為他們能夠迅速重新編程以適應小的甚至是主要的設計變化。然而，作為獨立的機器，他們不能以大量或高生產(chǎn)率生產(chǎn)零部件。
一個柔性制造系統(tǒng)可以比獨立數(shù)控機床處理更高的產(chǎn)量和生產(chǎn)率。它不能完全匹配這種靈活性的機器，但他們接近。柔性制造的中間環(huán)節(jié)極其重要的是大部分制造環(huán)境用需要中型生產(chǎn)速率以足夠的靈活性和迅速重新配置加工另一個工件或產(chǎn)品的方式生產(chǎn)中批零件。柔性制造填補了制造業(yè)在這方面長期存在的空白。
具有打基礎能力的柔性制造，為制造商提供了許多優(yōu)點：
（1）同一組工件的靈活性。（2）隨機零件供給。
（3）不同零件的同時生產(chǎn)。
（四）減輕設定時間和前置時間。
（5）更有效的機器使用。
（6）減少直接和間接的勞動力成本。
（七）處理不同材料的能力。
（八，如果一臺機器上壞了繼續(xù)一些生產(chǎn)的能力。
3 柔性制造系統(tǒng)組件
一個柔性制造系統(tǒng)有三個主要部分組成：機床、控制系統(tǒng)、材料處理系統(tǒng)
3.1 機床
一個柔性制造系統(tǒng)無論是自動或手動操作都像其他任何制造系統(tǒng)一樣，使用同一類型的機床。這些包括車床，磨，鉆，鋸等。實際上包含柔性制造系統(tǒng)的該類型機床，依賴于使用的該機床的設置。一些FMS旨在滿足特定的，定義良好的需求。在這些情況下，包含該系統(tǒng)的機床將只有那些必要的行動計劃。這種系統(tǒng)將稱為一個專用系統(tǒng)。
在工作車間，或不知道時間提前或必然包括各種可能性的實際應用的其他任何環(huán)境中，機器能執(zhí)行的標準至少制造業(yè)務將被包括在內(nèi)。這種系統(tǒng)被稱為通用系統(tǒng)。
3.2 控制系統(tǒng)
對于一個柔性制造系統(tǒng)來說孔子系統(tǒng)服務于許多不同的系統(tǒng)控制功能：（1）工件程序的儲存和分配（2）流量控制和監(jiān)測工作（3）生產(chǎn)控制（4）系統(tǒng)/工具控制/監(jiān)測
計算機運行FMS控制系統(tǒng)控制的領域是在柔性制造系統(tǒng)中的所有活動進行控制和監(jiān)測的中心。 FMS的控制軟件是相當復雜和精密的，因為需要進行大量的研究。盡管已經(jīng)在這一領域進行了許多不同的研究，但是對設計功能和柔性制造系統(tǒng)軟件的體系結構沒有普遍性的答案。柔性制造系統(tǒng)的體系結構。
一個典型的FMS控制系統(tǒng)的一些功能說明在例圖3.22
例3.22圖 先進的柔性制造系統(tǒng)控制軟件圖標功能
考慮到機床當前狀態(tài)，加工過程中，工裝夾具等，調(diào)度功能涉及計劃如何在柔性制造系統(tǒng)中生產(chǎn)目前的訂單。調(diào)度，可自動完成，也可以由經(jīng)營者協(xié)助。最大多數(shù)的柔性制造控制系統(tǒng)把自動和手動調(diào)度相結合，系統(tǒng)生成一個初步的時間表，它可以由操作員手動改變。涉及的調(diào)度功能進行日程安排和協(xié)調(diào)在車間的活動，，即決定何時何地的運輸托盤，什么時候開始加工中心的進程等等。
該監(jiān)控功能在于監(jiān)測工作進展情況，機器狀態(tài)，報警信息等和提供投入的調(diào)度，以及各種生產(chǎn)報表和報警信息。一個傳輸控制模塊管理系統(tǒng)內(nèi)的部件和調(diào)色板的輸送。有多個車輛自動導引車系統(tǒng)，路由控制邏輯可以變得相當復雜，成為柔性制造系統(tǒng)控制軟件的關鍵部分。加載/卸載終端模塊在裝載區(qū)顯示了操作者把那種工件傳輸?shù)较到y(tǒng)，使他或她當工件在加載區(qū)準備接收信息時更新了控制系統(tǒng)的狀態(tài)。存儲控制模塊保持一定數(shù)量的工件信息存儲在AS&RS中當，以及他們的確切位置。該工具管理模塊保留了所有有關的刀具數(shù)據(jù)資料和刀具在柔性制造系統(tǒng)的實際位置的賬戶。
刀具管理是比較全面，因為通常的刀具數(shù)量超過了在系統(tǒng)中工件數(shù)量，而且，該模塊必須控制刀具的準備和流動。DNC功能是在FMS的控制程序和機床與車間設備之間提供接口。車間里的設備的DNC功能對一個柔性制造系統(tǒng)是必不可少的，一個能遠程控制的“完整”DNC通信協(xié)議是需要的。
該機床的大部分廠商已經(jīng)開發(fā)的專有通信協(xié)議的事實正使包括多廠商設備FMS的開發(fā)和整合復雜化。而且，多廠商設備的物理集成是不同的；例如，在托盤裝載/卸載機械的差異市來自不同廠商的機器刀具的使用變復雜。因此，實施一個柔性制造系統(tǒng)唯一可行的辦法是從主要機床制造商之一購買交鑰匙系統(tǒng)。這些系統(tǒng)是可靠和行之有效的制度，并應不令人滿意的，單一供應商的責任將有助于故障的補救。
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