数字控制与计算机数字控制.docx

1、数字控制与计算机数字控制NC AND CNC数字控制与计算机数字控制1.1 The History of NC and CNC DevelopmentNumerical control (NC) is any machining process in which the operations are executed automatically in sequences as specified by the program that contains the information for the tool movements.The NC concept was proposed in t

2、he late 1940s by John Parsons of Traverrse City,Michigan.Parsons recommended a method of automatic machine control that would guide a milling cutter to produce a “thru-axis curve”in order to generate smooth profiles on work pieces.1.1数字控制与计算机数字控制的发展历史数字控制是按照含有机床（刀具）运动信息程序所指定的顺序自动执行操作的加工过程。数控这一概念是由密歇

3、根洲特拉华诚的约翰 帕森于20世纪四十年代后期提出的。为了在工件上加工光滑的轮廓，帕森提出了一种自动的机床控制方式，它能够引导铣床刀具加工出一种“过轴曲线”。In 1949,The U.S. Air Force awarded Parsons a contract to develop a new type of machinetool that would be able to speed up production methods.Parsons commissioned the Massachusetts Institute of Technology (M.I.T) to develo

4、p a practical implementation of his concept.Scientists and engineers at M.I.T. built a control system for a two-axis milling machine that used a perforated paper tape as the input media. In a short period of time,all major machine tool manufacturers were producing some machines with NC, but it was n

5、ot until the late 1970s that computer-based NC systems. 360毕业设计网 1949年，美国空军与帕森签署了合同，要求开发一种能够提高生产率的新型机床。帕森委托麻省理工学院（MIT）来开发一种新概念机床，麻省理工学院的科学家和工程师研制出了一种用穿孔纸带作为输入媒介的二轴联动铣床控制系统。在较短的时间内，当时所有主要的机床生产商都生产了一些数控机床，但直到20世纪七十年代后期，基于计算机的数字控制才被得到广泛的使用。只有价格低廉且功能强大的微处理芯片代替了计算机数控系统中的硬连线逻辑发生器后，NC才真正成为一门自动化技术。When Nume

6、rical Control is performed under computer supervision, it is called Computer Numerical Control (CNC). Computers are the control units of CNC machines, they are built in or linked to the machines via communications channels. When a programmer input some information in the programby tape and so on, th

7、e computer calculates all necessary data to get the job done.当数控机床在计算机监控下工作时，它就被称为计算机数控机床（CNC）。计算机是CNC机床的控制单元，它们内嵌于数控机床或者通过通讯渠道与数控机床联接，当程序员编程时，通过纸带或磁盘将一些信息输入，计算机将对一些必要的数据进行计算的完成工作。On the first Numerically controlled (NC) machines were controlled by tape,and because of that, the NC systems were known

8、 as tape-controlled machines.They were able to control a single operationentered into the machine by punched or magnetic tape. There was no possibility of editing the program on the machine. To change the program ,a new tape had to be made.由于第一台数控机床的数据是由纸带控制的，因此数控系统被成为纸带控制机床。它们只能控制由输入到机床内的纸带或磁带所规定的单

9、一操作，输入到机床内的程序是不能被编辑的，要改变程序必须重做新纸带。Todays systems have computers to control data;they are called Computer Numerically controlled (CNC) machines. For both NC and CNC systems, work principles are the same. Only the way in which the execution is controlled is different. Normally, new systems are faster,

10、 more powerful, and more versatile.当今的系统都由计算机来控制数据，因而称之为计算机数控机床（简称CNC机床）。NC和CNC系统两者的工作原理一样，仅仅控制执行的方式不同。新型 的数控系统通常速度更快，功率更大，功能更齐全。2.2The Applications of NC/CNC Since its indroduction, NC technology has found many applications, including lathes and turning centers, milling machines and machining cente

11、rs, punches, electrical discharge machines (EDM), flame cutters,grinders, and testing and inspection equipment. The most complex CNC machine tools are the turning center, (A modem turning center with a ten-station turret thar accepts quick-change tools.Each tool can be positioned in Seconds with the

12、 press of a button). And the machining center shown in (Vertical machining center, the tool magazine is on the left of the machine. The control panel on the right can be swiveled by the operator) and(Horizontal machining center, equipped with an automatic tool changer.Tool magazines can store 200 cu

13、tting tools).2.2数字控制与计算机数字控制的应用数控技术自创立以来就得到了广泛的应用，包括车床和车削中心、铣床和加工中心、冲床、电火花（EDM）加工机床、线切割机床、磨床以及测试检测装置等。最复杂的计算机数控机床是车削中心，一个具有十转位的刀架能进行快速换刀的现代车削中心，立式加工中心（刀具库在机床的左边。右边的控制面板可由操作者通过转臂转动），以及卧式加工中心，通过按下按钮每把刀可在数秒钟内定位。（配有自动换刀系统。刀具库储备有200把切削工具）。 When preparing a program for a particular operation, the programm

14、er must select all cutting data using recommendations for conventional machining. This includes proper selection of cutting speeds, feedrate, tools and tool geometry,and so on. When the programmer has chosen all of the necessary information properly, the operater loads the program into the machine a

15、nd presses a button to start the cutting cycle.The CNC machinemoves automatically from one machining operation to another, changing the cutting tools and applying the coolant. In a surprisingly short time, the workpiece is machined according to the highest quality standards. But that is not all. No

16、matter how big the work series is ,all of the parts will be almost identical in size and surface finishing. At this time of advanced technology, with its high demands for surface finishing and tolerances of components in, for example, aerospace, nuclear, and medical equipment manufacturing, only CNC

17、 machines provide successful results.当为某项操作编程时，程序员必须选择传统的加工切削数据推荐值。这些切削数据包括切削速度、进给率、刀具和刀具几何形状等。当程序员正确选择所有必要信息后，操作人员将程序载入机床并按下按钮，切削循环开始。通过变换切削刀具及使用冷却液，计算机数控机床可以自动从一个加工工序转向另一个加工工序。在极短时间内，工件依据最佳质量标准被加工出来。但是那并不是全部，无论工件批量有多大，所有零部件在尺寸和表面精度上几乎是一致的。在当今先进技术时代，随着对零件表面精度和公差要求的提高，例如，航空业、核工业及医疗器械设备的制造，只有计算机数控机床才

18、能胜任。2.3 The Advantages and Disadvantages of CNC MachinesCNC machines have many advantages over conventional machines, some of them are:(1) There is a possibility of performing multiple operations on the same machine in one setup.(2) Because of the possibility of simultaneous multi-axis tool movement

19、,special profile tools are not necessary to cut unusual part shaps.(3) The scrap rate is significantly reduced because of the precision of the CNC machine and lesser operator impact.(4) It is easy to incorporate part design changes when CAD/CAM systems are used.(5) It is easier to perform quality as

20、surance by a spot-check instead of checking all parts.(6) Productionis significantly increased.2.3计算机数控机床的优缺点1、计算机数控机床和传统机床相比具有很多优点，它们是：（1）在同一机床上，一次装夹可完成多个操作。（2）由于机床可以实现多轴联动，切削非常规的零件形状时，可以不必使用成形刀具。（3）由于计算机数控机床的精度高，受操作者影响小，废品率明显降低。（4）采用CAD/CAM系统后，对零配件装配设计的修改就变得很容易。（5）通过抽检代替全检，质量更容易保证。（6）生产率显著提高。2、CNC

21、 machines also have some disadvantages:(1) They are quite expensive.(2) They have to be programmed, set up, operated, and maintained by highly skilled personnel.2、计算机数控机床也有一些缺点：（1）价格昂贵。（2）必须由高级技术人员来编程、安装、操作与维护。Obviously,CNC machines have more advantages than disadvantages. The companies that adopt C

22、NC technology increase their competitive edge. As always with new technology, the cost per CNC unit is being cut further and more companies can afford CNC equipment, which enables them to answer the incresingly strong requirements for production speed and quality that competitive markets demand. In

23、the futhure the broader use of CNC machines will be one of the best ways to enhance automation in manufacturing.显然，计算机数控机床利大于弊。已经采用计算机数控机床的企业正在提高他们的竞争力。随着新技术的采用。每台计算机数控单元的价格正在进一步降低，更多的公司能够买得起计算机数控装备，使其能够满足竞争市场对产品生产速度和质量日益增强的需求。将来计算机数控机床的广泛使用成为制造业提高自动化程度的最佳选择之一。2.4The Construction of CNC Machines2.4计

24、算机数控机床的结构 CNC machine tools are complex assemblies. However, in general, any CNC machine tool consists of the following units:CNC结构较为复杂。一般来说，任何CNC机床都包含以下几个单元组成： Computers 计算机Control systerms控制系统Drive motors驱动电机 Tool changers换刀机构 According to the construction of CNC machine tools, CNC machines work i

25、n the following manner根据CNC机床的结构，CNC机床以下列方式工作：(1) The CNC machine language, which is programming language of binary notation used on computuers, not on CNC machines.（1）CNC机床语言是一种用在计算机上的二进制符号编程语言，而不是用在CNC机床上。(2) When the operator starts the execution cycle the computer translates binary codes into el

26、ectronic pulses which are automatically seent to the machines power units. The control units compare the number of pulses sent and received.（2）当操作者开始执行循环时，计算机将二进制代码翻译成电脉冲，并自动的送给机床的控制单元。控制单元将发出的脉冲数与接受的脉冲数加以比较。(3) When the motors receiveeach pulse, they automatically transform the pulses into rotation

27、s that drive the spindle and lead screw, causing the spindle rotation and slide or table movement. The part on the milling machine table or the tool in the lathe turret is driven to the position specified by the program.（3）电动机每接收一个脉冲，就自动的将脉冲信号转换成旋转信号从而驱动主轴和丝杠，带动主轴旋转和拖板或工作台的移动。铣床工作台上的零件或车床转塔刀架上的刀具被驱动

28、到程序指定的位置。 1)、 Computers The computer reacts on. As with all computers, the CNC machine computer works on a binary principle using only two characters 1 and 0 for information processing precise time impulses form the circuit. There are two states,a steta with voltage, 1,and a state without voltage, 0

29、 Series of ones and zeros are the only states that the computer distinguishes a called machine language, it is the only language the computer understands. When creating the program, the programmer does not care about the machine language. He or she simply uses a list of codes and keys in the meaning

30、ful information. Special built-in software compiles the program into machine language and the machine moves the tool by its servomotors. However, the programmability of the machine is dependent on whether there is a computer in the machines control.If there is a minicomputer programming,say a radius

31、(which is a rather simple task), the computer will calculate all the pointson the tool path. On the machine without a minicomputer, this may prove to be a tedious task, since the programmer must calculate all the pointe of intersection on the tool path. Modern CNC machines use 32-bit processors in t

32、heir computuers that allow fast and accurate processing of information.1)、计算机 如所有其它计算机，CNC机床的计算机也是根据二进制原理，只有两个字符1和0作为电路的时间脉冲信息，有两个状态，高电平为1，低电平为0，1和0的序列是计算机区别于所谓的机器语言的唯一状态，也是计算机理解的唯一语言。编程时程序员不必关心机器语言，只需简单的应用一系列代码和符号来表达有用的信息。机器内的特殊软件将程序翻译为机器语言，由伺服电动机带动刀具工作。然而，机床程序的可用性是依速于机床控制系统中是否有计算机，如果用一个微型计算机进行程序设计，例如，半径（一个相当简单的任务），计算机将计算刀具路径上所有的点坐标值，如果机床上没有微型计算机，这个计算将是一个繁琐的工作，因为程序员必须计算刀具路径上的所有交点位置。现代CNC机床的计算机使用32位处理器可以实现信息的快速准确处理。 2)、Control Systems There are two types of control systems on NC/CNC machines:open loop and closed loop. The type of control l