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1、<p>  Integrated Computer Aided Manufacturing</p><p>  1.INTRODUCTION</p><p>  Today’s industry competes in a truly international marketplace. Efficient transportation networks have created

2、 a “world market” in which we participate on a daily basis. For any industrial country to compete in this market, it must have companies that provide economic high-quality products to their customers in a timely manner.

3、The importance of integrating product design and process design to achieve a design for production system cannot be overemphasized. However, even once a design is finaliz</p><p>  Most U.S.-based manufacturi

4、ng companies look toward CAD/CAM and CIM to provide this flexibility in their manufacturing system . Today ,the use of computers in manufacturing is common . Manufacturing system are being designed that not only process

5、parts automatically ,but also move the parts from machine to machine and sequence the ordering of operations in the system.( Figure 1) contains a plot of the economic regions of manufacturing. It should be noted that man

6、ual handcrafted goods will always</p><p>  Figure 1 Volume versus variety regions for economic manufacturing</p><p>  2.FLEXIBLE MANUFACTURING SYSTEMS</p><p>  A flexible manufac

7、turing system, or FMS as they are more commonly known, is a reprogram-able manufacturing system capable of producing a variety of products automatically. Since Henry Ford first introduced and modernized the transfer line

8、, we have been able to perform a variety of manufacturing operations automatically. However, altering these systems to accommodate even minor changes in the product has been quite taxing. Whole machines might have to be

9、introduced to the system while other machi</p><p>  Job shop type systems were capable of producing a variety of product ,but at a high cost.</p><p>  Transfer lines could produce large volumes

10、of a product at a reasonable cost, but were limited to the production of one ,two, or very few different parts.</p><p>  The advent of numerical control (NC) and robotics has provided us with reprogramming c

11、apabilities at the machine level with minimum setup time. NC machines and robots provide the basic physical building blocks for re-programmable manufacturing systems.</p><p>  2.1.FMS Equipment</p>&l

12、t;p>  2.1.1Machines </p><p>  In order to meet the requirements of the definition of an FMS, the basic processing in the system must be automated. Because automation must be programmable in order to acco

13、mmodate a variety of product-processing requirements, easily alterable as well as versatile machines must perform the basic processing.</p><p>  For this reason, CNC turning centers, CNC machining centers, a

14、nd robotic workstations comprise the majority of equipment in these systems. These machines are not only capable of being easily reprogrammed, but are also capable of accommodating a variety of tooling via a tool changer

15、 and tool-storage system. It is not unusual for a CNC machining center to contain to 12 or more tools (right-hand turning tools, left-hand turning tools ,boring bars, drills ,and so on ) . The automatic tool changer an&l

16、t;/p><p>  Parts must also be moved between processing stations automatically. Several different types of material-handling systems are employed to move these parts from station to station. The selection of the

17、 type of material-handling system is a function of several system features. The material-handling system, first, must be able to accommodate the load and bulk of the part and perhaps the part fixture. Large, heavy parts

18、require large , powerful handling systems such as roller conveyors guided vehicle</p><p>  2.1.2 Tooling and fixtures.</p><p>  Versatility is the key to most FMSs, and as such the tooling used

19、in the system must be capable of supporting a variety of products or parts. The use of special forming tools in an FMS is not typical in practice. The contours obtained by using forming tools can usually be obtained thro

20、ugh a contour-control NC system and a standard mill. The standard mill then can be used for a variety of parts rather than to produce a single special contour. An economic of the cost and benefits of any special to</p

21、><p>  One of the commonly neglected aspects of an FMS is the fixturing used. Because fixtures are part of the tooling of the system, one could argue that they should also be standard for the system. Work on cr

22、eating “flexible fixtures” that could be used to support a variety of components has only recently begun. See Chapter 5.One unique aspect of many FMSs is that the part is also moved about the system in the fixture (or pa

23、llet fixture). Fixtures are made to the same dimensions so that the material-</p><p>  3.COMPUTER CONTROL OF FLEXIBLE MANUFACTURING SYSTEMS</p><p>  3.1 FMS Architecture</p><p>  A

24、n FMS is a complex network of equipment and processes that must be controlled via a computer or network of computers. In order to make the task of controlling an FMS more tractable, the system is usually divided into a t

25、ask-based hierarchy. One of the standard hierarchies that have evolved is the National Institute of Standards and Technology(NIST) factory-control hierarchy. (NIST was formerly the National Bureau of standards. NBS.) Th

26、is hierarchy consists of five levels and is illustrated in </p><p>  The cell is the unit in the hierarchy where interaction between machines becomes part of the system. The cell controller provides the int

27、erface between the machines and material-handling system. As such ,the cell controller is responsible for sequencing and scheduling parts through the system. At the shop level integration of multiple cells occurs as well

28、 as the planning and management of inventory. The </p><p><b>  Fig2</b></p><p>  Figure 3 The relationship between the data-administration (DAS) in the NIST architecture :(1)the topo

29、logies of the Integrated Manufacturing Data Administration System(IMDAS) data-administration system;(2)the net work data-communication network; (3)the hierarchical system of data-driven control: data preparation is impli

30、ed in (4) the facility level of control facility level is the place in the hierarchy where the master production schedule is constructed and manufacturing resource planning is con</p><p>  3.2 FMS Scheduling

31、 and control</p><p>  Flexible manufacturing systems, like other manufacturing system can differ significantly complexity . This complexity is not only determined by the number of machines and the number of

32、parts resident in the system, but also by the complexity of parts and control requirements of the specific equipment . Some FMSs require only a simple programmable controller to regulate the flow of parts though the syst

33、em, whereas others require sophisticated computer control systems. In the following sections , </p><p>  The most simple FMS consists of a processing machine, a load/unload area, and a material handler (a on

34、e-machine system is the most simple FMS that can be constructed ). Operation of this system consists of loading the part(s) that move down a conveyor the machine. Once the part is loaded onto the machine , the robot is r

35、etracted to a “safe position” and the machining begins.</p><p>  Although this is a very simple system, it illustrates several interesting design and control decisions that must be considered. If only a sing

36、le part is to be processed in the system, a minimum number of switches and sensors necessary for the system. One requirement of the system is that the parts on the conveyor all have to be oriented in the same way. This i

37、s required so that the robot can pick up the part and deliver it to the NC machine in the same orientation every time. A proximity switch </p><p><b>  计算机辅助制造</b></p><p><b>  1

38、.绪论</b></p><p>  当今的工业的竞争已经是真正意义上的国际市场竞争。 高效的运输网络建立了一个我们每天都要参与的 “世界市场”。 对于任何工业化国家要参与这个市场竞争,就必须采用一种适时的方式为其客户提供经济、优质的产品。将产品设计和过程设计进行集成的重要性,在产品系统被怎么强调都不为过。但是, 即使一种设计最终被落实, 制造业者一定愿意通过允许最后的工程设计变化,而没有通过影响装运进

39、度表,或者改变产品质量来适应他们的用户。</p><p>  大多数美国的生产公司基于趋向计算机辅助设计(CAD)/计算机辅助制(CAM)和CIM为他们的制造系统提供灵活性。今天,计算机用于制造已经很平常。现在不仅为零件生产设计制造系统,而且为零件从一台机器运送到另一台机器的命令顺序设计了制造系统,如图(1),它还包含一个经济区域的制造经济计划在美国和其他国家,手工产品总是还有一些市场的,此外真正的工业产品对于特

40、殊的“one-of-a-kind”技术项目还是需要的。“one-of-a-kind”通过大量的货物来表明、各种各样的工业需要各种各样的加工方法。 有些系统将看起来像我们的祖父母曾经工作过的工厂,而其它则呈现出一种未来派的情景。在后文中,我们将展开讨论柔性制造系统。</p><p><b>  图(1)</b></p><p><b>  2.柔性制造系统&l

41、t;/b></p><p>  柔性制造系统(FMS)像人们通常知道的那样的,能使用一个可编程的制造系统自动地生产各种各样的产品。 自从亨利·福特率先提出并且使流水生产线实现现代化,我们就已经能自动执行多种生产的生产。 不过,改变这些系统甚至只作较小的变动,这些产品的生产都会变得相当繁重。 当其他机器或者零部件要经过修理或者废弃,以适应这种萧萧的变化,整个机器才可能被引进到系统。 在今天的竞争性市

42、场里,能适应客户的各种变化是很必要的。传统的制造系统以特征可划分为以下两种: 1.加工车间类型系统能生产多种产品,但是费用高。 2.流水线能以合理费用生产能大量产品, 但是仅局限于几种不同零件的生产。 数控(NC)和机器人技术的时代已经来临,这为我们提供了在最小准备时间里,使机器的程序重新调定。NC机床和机器人是重新可编程序的制造系统的基本物理组成部分。</p><p>  2.1.柔性制造系统的

43、设备</p><p><b>  2.1.1机床</b></p><p>  为了满足柔性制造系统定义的要求,该系统的基本工艺应实现自动化。因为自动化必须是可编程的,以适应不同的产品要求,而易于改变,以及通用机床必须执行这些工艺。计算机数控(CNC)车削中心、计算机数控(CNC)加工中心、及机器人工作站构成了这些设备。这些机器不仅仅是易于重新编程,同时也适应置于刀具存

44、储系统及刀具更换器中的不同刀具。通常CNC加工中心备有60多把或更多刀具(铣刀、钻头、镗刀等)。对于CNC车削中心,备有12把或更多的刀具(右车刀、左车刀、镗杆、钻头等)。书动机床的自动换刀器及刀库使它们对材料的工艺装备作出自然的选择。</p><p>  零件必须在加工站点之间自动化的移动,采用了数种不同的物料输送系统,把这些零件从一个站点输送到另一个站点。物料输送系统的选择是数种系统特征函数。首先,物料输送系

45、统的选择必须适应零件(或许是零件的夹具)的负荷及批量。大型的、重型的零件需要大型的、强力的输送系统,如滚子输送、导向小车、轨道驱动车辆系统。构成的机床数量及机床布置也提供了另一种设计上的考虑。如果用单一的物料输送机来运送零件到系统内的所有机床,则运输机的工作覆盖面至少必须是和整个系统一样大。通常一台机器人定位于一两台机床或一个装卸站。一台输送机或自动导向车可以扩大到数英里的工厂区域。物料输送也可以以即时的方式将零件从一台机床输送到另一台

46、机床。如果系统内的机床耗费大量的时间在等待输送零件的到来,则其生产率是不会高地。如果有许多种零件包括在系统内,而且这些零件要经常输送到机床上,物料系统要能够支持这些活动。通常由采用极快的输送装置或靠平行地使用几种装置来实现。例如:用一台机器人支持一台机床,而不是用一台机器人运送零件到系统内的所有机床。</p><p>  2.1.2刀具及夹具</p><p>  用途多样性是柔性制造系统的

47、关键,由此,在系统中使用的刀具必须能够支持多种零件及产品的生产。在柔性制造系统中,使用专用的或成型刀具并不典型。使用成型刀具得到轮廓,通常可以通过轮廓书空系统或标准的铣刀得到。标准的铣刀可以用于各种不同的零件而不是只能加工单一的轮廓。使用任何专用刀具其利润和成本的经济分析都是必须的,以确定最佳的刀具组合。然而,因书空机床仅有有限数量的刀具可供存取,极少数的刀具应当包括在内。</p><p>  柔性制造系统通常容

48、易忽视的一个方面是所使用的夹具。因为夹具是系统中工具的一部分。人们会争议这样一个事实,对系统中的夹具也应标准化。工件装在创制出的“柔性夹具”中,这种仅在几年前才开始使用的夹具可以支持多种零件。许多柔性制造系统的独特方面是零件装在夹具(或随行夹具)中而在系统中运动,夹具做成相同的尺寸,这样物料输送系统可以专门化去输送单一的几何形体,零件精确的定位在夹具上,同时随同夹具从一个站点运动大另一个站点。这种类型的夹具,通常称为随行夹具。现在所应用

49、的许多随行夹具都加工出标准的T型槽,同时使用标准的夹具组件创建出适应于切削加工的零件的定位及夹紧的条件。</p><p>  3.柔性制造系统的计算机控制</p><p><b>  3.1 FMS构架</b></p><p>  FMS是一个必须被通过一台计算机或者计算机网络控制的设备和过程的复杂的网络。 为了使控制FMS的任务更易处理,系统

50、通常被分成一个个基于任务的阶层。 已经逐步成的标准之一的是国家标准与技术局(NIST)工厂控制阶层。 (NIST以前叫国家标准局, NBS.) 这个阶层由5 步组成, 在图(2)表示了系统由物质机器加工设备,图(3)系统的最低的组成部分。 工作站设备恰好处于过程水平面存在并且起着预防综合和设备接口的作用。 例如棘瓜固定设备和编程要素也是工作站的一部分。 工作站通常提供人力机器接口和机器零件接口。 而脱机程序适合NC那种易于AML给机器人

51、工作的工作站水平。 小屋是在在机器之间的相互作用阶层的单位,并成为系统的一部分。 小屋控制器提供了那些机器和物质处理系统之间的接口。 照此,小屋控制器负责系统的排序和调度部分。车间水平的集成和多房间重现生成了存货清单的计划和管理。 </p><p><b>  图(2)</b></p><p><b>  图(3)</b>&l

52、t;/p><p>  3.2 FMS安排和控制 柔性制造系统,像其他制造系统一样,能区别出零件之间较大的复杂性。 这复杂性不仅包括系统中机器的数量和确定的数量, 而且包括那些复杂性的部分和控制要求的那些具体设备。一些FMS只要求有一个简单的可编程控制器就行了,而其它的还要求有复杂的计算机控制系统。在以后的章节里,还要提出一些FMS及其控制的例子。 最简单的FMS由一台处理器、装载/卸载区域和原料

53、处理机(一个最简单的FMS可以只由一台机器构成)。 这系统的操作包括了往下的一个传输装置。一旦零件被装到机器上,机器人缩回到一个“安全的位置”,然后机器开始加工。 </p><p>  虽然这是一个非常简单的系统,但是它例举了几种有趣的设计和必须考虑的控制部件。如果在系统中,只有一个部分在运作,那么系统就只需要最小数量的开关和传感器。系统所需要的是,所有传输带上的零件使用同样的方法定位。这还需要使机器人每一次都用

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