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随着直接数字控制(DNC)技术和计算机技术的飞速发展，数字式计算机的尺寸和价格的大幅度的降低，数字式计算机的计算能力的大大提高，大量传统的以硬件线路为基础的加工控制单元被以数字计算机为基础的数字控制单元所替代。最初在20世纪70年代使用了小型计算机。后来，随着计算机的进一步小型化，早期的小型计算机逐渐被现在的微型计算机所取代。
Computer numerical control is an NC system using dedicated microcomputer as the machine control unit. Because a digital computer is used in both CNC and DNC, it is appropriate to distinguish between the two types of system. There are three principal differences:
计算机数控(CNC)使用专用的微型计算机作为加工控制单元。因为数字计算机都用于计算机数控(CNC)和直接数控(DNC)，所以应该注意两者之间的区别，可以从3个方面来加以区分。
1) DNC computers distribute instructional data to, and collect data from, a large number of machines. CNC computers control only one machine, or a small number of machines.
(1) DNC计算机是将指令数据发送到许多机床去或从许多机床中收集数据，而CNC计算机每次只控制一台或几台机床。
(2) DNC computers occupy a location that is typically remote from the machines
under their control. CNC computer are located very near their machine tools.
(2) DNC计算机一般位于距机床一定距离的位置，而CNC计算机一般都位于距机床较近的位置。
(3) DNC software is developed not only to control individual pieces of production equipment, but also to serve as part of a management information system in the manufacturing sector of the firm. CNC software is developed to augment the capabilities of a particular machine Tool.
(3) DNC计算机开发的软件不仅可以用于控制单件生产，而且可以用于一个企业制造部门的管理信息系统，而CNC计算机开发的软件一般只用于某个特殊加工的工具。
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NC and CNC
数控技术
The History of NC and CNC Development
数字控制与计算机数字控制的发展历史
Numerical 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 the late 1940s by John Parsons of Traverse 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.
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根洲特拉华城的约翰·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 machine tool that would be able to speed up production methods. Parsons commissioned the Massachusetts Institute of Technology (M.I.T.) to develop 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 not until the late 1970s that computer-based NC became widely used. NC matured as an automation technology when inexpensive and powerful microprocessors replaced hard-wire logic-making computer-based NC systems.
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 Numerical 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 program by tape and so on, the 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 as tape-controlled machines. They were able to control a single operation entered 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，因此数控系统被称为纸带控制机床。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。
Today's 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, 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。
The Applications of NC/CNC
数字控制与计算机数字控制的应用
Since its introduction, NC technology has found many applications, including lathes and turning Centers, milling machines and machining centers , punches , electrical discharg machines(EDM) Flame cutters,grinders,and inspection equipment. the most complex CNC machine tools are the turning center,shown in Fig.4-1(Amodern turning center with a ten-station turret that accepts quick-chang tools.Each tool can be positioned in Seconds with the press of a button).And the machine center shown in Fig.4-2(Vertical machining center,the tool magazine is on the machine.the control panel on the right can be swiveled by the operator)and Fig.4-3(horizontal machining center,equipped with an automatic tool changer .tool magazines can store 200 ctting tools.
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，图4—1所示一个具有十转位的刀架能进行快速换刀的现代车削中心，立式加工中心如图4—2所示(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。如图4—3所示(配有自动换刀系统。刀具库储备有200把切削工具)。
When preparing a progam for a particular operation ,the prommer 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 operator loads the programme into the machine and presses a button to start the cutting crycle .the CNC machine moves automatically from one maching operation to another , changing the cutting tols and applying the coolent.in a surprisingly short time ,the workpiece is
Machined according to the highest quality stangards. But that is not all.no 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 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，切削循环就开始。
Numerical control (NC) is a form of programmable automation in which the processing equipment is controlled by means of numbers, letters, and other symbols. The numbers, letters, and symbols are coded in an appropriate format to define a program of instructions for a particular workpart or job. The instructions are provided by either of the two binary coded decimal systems: the Electronic Industries Association (EIA) code, or the American Standard Code for Information Interchange (ASCII). ASCII-coded machine control units will not accept . EIA coded instructions and vice versa. Increasingly, however, control units are being made to accept instructions in either code. 121Automation operation by NC is readily adaptable to the
operation of all metalworking machines. Lathes, milling machines, drill presses, boring machines, grinding machines, turret punches, flame or wire-cutting and welding machines, and even pipe benders are available with numerical controls.
数控技术是一种利用程序实现自动控制的技术，加工制造设备采用数控技术后能由数字、字符和符号等进行控制。这些数字、字符和符号等被编码成按一定格式定义的指令程序用于一个特定的加工或工件，这些指令可以采用两种二进制编码的数字系统中的任意一种进行定义，这两种二进制编码数字系统分别为电工协会代码(EIA)和美国标准信息交换代码(ASCII)。一般来说，ASCII编码的机床控制系统不能接受EIA编码的指令，反之亦然。当然，这样的问题已经逐渐得到解决。数控加工制造目前已经广泛地应用于几乎所有的金属加工机床：车床，铣床，钻床，镗床，磨床，回转冲床，电火化，线切割和焊接机床，甚至弯管机也采用数控加工技术。
Basic Components of NC
数控技术的基本组成
A numerical control system consists of the following three basic components:
一个数控系统主要由以下3个部分组成：
(1) Program instructions
(1)程序指令
(2) Machine control unit
(2)加工控制单元
(3) Processing equipment
(3)制造装备
The program instructions are the detailed step by step commands that direct the processing equipment. [31In its most common form, the commands refer to positions of a machine tool spindle with respect to the worktable on which the part is fixtured. More advanced instructions include selection of spindle speeds, cutting tools, and other functions.
程序指令是由一条一条的详细指令所组成，制造装备按要求执行这些指令。最常用的指令有：可以按要求使机床刀具主轴位于工作台上的具体位置，工作台是用于固定加工零件的，许多更高级的指令还包括用于主轴速度的选择、刀具速度的选择及其他一些功能。
The machine control unit (MCU) consists of the electronics and control hardware that reads and interprets the program of instructions and convert it into mechanical actions of the machine tool or other processing equipment.
加工控制单元(MCU)包括一些用于阅读和解释程序指令并将其转换为机床刀具或其他制造装备的机械动作的电子和控制硬件。
The processing equipment is the component that performs metal process. In the most common example of numerical control, it is used to perform machining operations. The process-ing equipment consists of the worktable and spindle as well as the motors and controls needed to drive them.
制造装备是一种进行金属加工的数控技术装备，在常用的数控技术领域中，制造装备用于进行机械制造。制造装备包括工作台、主轴、电机及控制驱动单元。
Types of NC
数控技术的类型
There are two basic types of numerical control systems: point to point and contouring.
数控技术系统主要有两种类型：点对点数控系统和轮廓线数控系统。
Point to point control system, also called positioning, is simpler than contouring control system. Its primary purpose is to move a tool or workpiece from one programmed point to another. Usually the machine function, such as a drilling operation, is also activated at each point by command from the NC program. Point to point systems are suitable for hole machining operations such as drilling, countersinking, couterbofing, reaming, boring and tapping. Hole punching machines, spotwelding machines, and assembly machines also use point to point NC systems.
点对点数控系统也称为位置数控系统，比轮廓线数控系统简单，其主要的原理是移动刀具或工件从一个程序控制点到另一一个控制点，通常像钻床这样的加工功能，每个点帮司以通过NC程序中的指令进行控制。点对点数控系统适用于像钻孔、沉孔加工、沉孔镗孔、铰孔和攻丝等。其他冲孔机床、点焊机和装配机床等也都采用点对点数控系统。
Contouring system, also known as the continuous path system, positioning and cutting operations are both along controlled paths but at different velocities. Because the tool cuts as it travels along a prescribed path, accurate control and synchronization of velocities and movements are important. The contouring system is used on lathes, milling machines, grinders,incrementally, by one of several basic methods. There are a number of interpolation schemes that have been developed to deal with the various problems that are encountered in generating a smooth continuous path with a contouring type NC system. They include linear interpolation,circular interpolation, helical interpolation, parabolic interpolation and cubic interpolation. In all interpolations, the path controlled is that of the center of rotation of the tool. Compensation for different tools, different diameter tools, or tools wear during machining, can be made in the NC .
轮廓线数控系统也称为轮廓线路径数控系统，定位和切割操作都是以不同的速度沿着控制的路径进行的。由于刀具沿路径进行切削，因此刀具的运动和速度的精确控制和同步性能是非常重要的。轮廓线数控系统经常应用于车床、铣床、磨床、焊接机床和加工中心中。刀具沿着路径的运动，或称为插补逐渐出现了几个不同的方法。有许多类型的插补方法用于处理轮廓线数控系统中生成光滑的轮廓线时遇到的各种问题。几种比较常用的方法有线性插补，圆形插补，螺旋形插补、抛物线插补和立方插补等，在所有的插补方法中，路径控制是以刀具的旋转中心为标准，对于不同类型、不同直径的刀具，加工过程中的不同刀具磨削量在数控程序中获得不同的补偿。
Programming for NC
数控系统的编程
A program for numerical control consists of a sequence of directions that causes an NC machine to carry out a certain operation, machining being the most commonly used process. Programming for NC may be done by an internal programming department, on the shop floor, or purchased from an outside source. Also, programming may be done manually or with computer assistance.
一个数控系统(NC)的程序包括使数控(NC)机床进行操作和加工的一系列指令。数控程序可以由数控机床内部的程序库开发生成，也可以从外面采购获得。另外，程序可以通过手工编写，也可以进行计算机辅助编程。
The program contains instructions and commands. Geometric instructions pertain to relative movements between the tool and the workpiece. Processing instructions pertain to spindle speeds, feeds, tools, and so on. Travel instructions pertain to the type of interpolation and slow or rapid movements of the tool or worktable. Switching commands pertain to on/off position for coolant supplies, spindle rotation, direction of spindle rotation, tool changes, workpiece feeding, clamping, and so on. The first NC programming language was developed by MIT developmental work on NC programming systems in the late 1950s and called APT(Automatically Programmed Tools).
数控程序包括一系列指令系统和命令系统。几何类指令用于定义刀具和工件之间的相对位置和运动：加工类指令用于定义主轴转速、进给、刀具转速等：传送类指令用于定义刀具或工作台的运动速度和插补的类型等；开关类指令用于冷却液供给、主轴旋转、主轴旋转方向选择、换刀、工件进给、夹具等的开关。第一个用于数控编程的数控编程语言是20世纪50年代由麻省理工学院数控编程系统开发小组专家开发的，并被命名为自动编程工具(APT)。
DNC and CNC
直接数字控制(DNC)和计算机数字控制(CNC)
The development of numerical control was a significant achievement in batch and job shop manufacturing, from both a technological and a commercial viewpoint. There have been two enhancements and extensions of NC technology, including:
数控技术的发展在批量生产和车间生产加工中，不管是在技术上还是在商业上都获得了巨大的成功。目前，已经有两种数控技术系统得到了发展，分别是：
(1) Direct numerical control
(1)直接数字控制(DNC)。
(2) Computer numerical control
(2)计算机数字控制(CNC)。
Direct numerical control can be defined as a manufacturing system in which a number of machines are controlled by a computer through direct connection and in real time. The tape reader is omitted in DNC, thus relieving the system of its least reliable component. Instead of using the tape reader, the part program is transmitted to the machine tool directly from the computer memory. In principle, one computer can be used to control more than 100 separate machines. (One commercial DNC system during the 1970s boasted a control capability of up to 256 machine tools.) The DNC computer is designed to provide instructions to each machine tool on demand. When the machine needs control commands, they are communicated to it immediately.
直接数字控制(DNC)可以被定义为这样一个生产制造系统，该制造系统有许多台加工机床，而相互之间由一台计算机采用直接连接，进行实时控制。这样，在传统的数字控制技术中采用的磁带阅读器在直接数字控制中被取消，从而保证了系统的可靠性。不使用磁带阅读器，被加工的零件程序就从计算机的存储器中直接传送到进行加工的刀具上。从原理上讲，一台计算机可以控制多达100台加工机床，(在20世纪70年代一个商业使用的DNC系统宣称可以控制多达256个机床刀具)。直接数字控制计算机用于按要求提供加工指令给每个进行加工的刀具上，当机床需要控制指令时，计算机就可以马上将指令传送到机床上。
Since the introduction of DNC, there have been dramatic advances in computer
technology. The physical size and cost of a digital computer has been significantly reduced at the same time that its computational capabilities have been substantially increased. In numerical control, the result of these advances has been that the large hard-wired MCUs of conventionalNC have been replaced by control units based on the digital computer. Initially, minicomputers
