数控技术外文翻译

黄石理工学院 毕业设计（论文）外文文献翻译数控技术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、字符和符号等北边麻城按一定格式定义的指令程序，用于特定的加工或工作。这种指令可采用两种二进制编码的数字系统中的任意一种进行定义，这两种二进制编码的数字系统分别为电工协会代码和美国标准信息交换代码。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，电火花或线切割机床以及焊接机床，甚至弯管机也可采用数控加工技术。数控技术的基本组成一个数控系统主要由以下3个部分组成：(1)程序指令(2)加工控制单元(3)制造装备 程序指令由一条一条的详细指令组成，制造装备按要求执行这些指令。最常用的指令形式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主轴速度选择，道具选择及其他的一些功能。 加工控制单元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。 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。数控技术的类型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。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个程序控制点，通常像钻床这样的加工功能，每个点都可以通过NC程序中的指令进行控制。点对点数控系统适用于钻孔，沉孔加工、沉孔镗孔、铰孔和攻螺纹等。其他冲孔机床、电焊机和装配机床等也都采用点对点数控系统。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盒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可称为插补，逐渐出现了几个不同的方法。有多种插补方法用于处理在轮廓线数控系统中生产光滑的轮廓线时遇到的各种问题，几种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，在数控程序中对类型不同，直径不同的刀具以及在加工过程中的不同刀具磨损量给于不同的补偿。数控系统的编程一个数控系统（NC）的程序包括是数控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。数控程序包括一系列的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、夹具开关等。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）。直接数字控制和计算机数字控制数控技术在批量生产和小批量生产中，不管是在技术上还是在商业上都取得了显著的成就。目前，已经有两种数控技术系统得到了发展，分别是：（1） 直接数字控制(DNC)（2） 计算机数字控制(CNC) 直接数字控制可以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，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道具上。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年代一台商业使用的DNC系统可以控制多达256个机床刀具）。直接数字控制计算机按要求给每个进行加工的刀具提供加工指令，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。随着直接数字控制技术和计算机技术的飞速发展，数字计算机尺寸和价格的大幅度降低，数字计算机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替代。计算机数控使用专用的微型计算机作为加工控制单元。数字计算机都用于计算机数控和直接数控，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计算机开发的软件不仅可以用于控制产品的单件生产，而且还可以用于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。Numerical ControlNumerical control (NC) is a form of programmable automation in which the processing equipment is controlled by means of number, letters, and other symbols. The numbers, letters, and symbols are coded in an appropriate format to define a program of instructions for a particular work part or job. The instructions are provided by either of the two binary coded decimal systems: the Electronic Industries Associations (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. Automation 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. Basic Components of NCA numerical control system consists of the following three basic components:(1) Program instructions.(2) Machine control unit.(3) Processing equipment.The program instructions are the detailed step by step commands that direct the processing equipment. In its most common form, the commands refer to positions of a machine tool spindle with respect to the worktable on which the part is fixed. More advanced instructions include selection of spindle speeds, cutting tools, and other functions.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.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 processing equipment consists of the workable and spindle as well as the motors and controls needed to drive them.Types of NCThere are two basic types of numerical control systems: point to point and contouring. Point to point control system, also called positioning, are 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 system are suitable for hole machining operations such as drilling, countersinking, counterboring, reaming, boring and tapping. Hole punching machines, spotwelding machines, and assembly machines also use point to point systems.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, welding machinery, and machining centers. Movement along the path, or interpolation, occurs 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 program.Programming for NC 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.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, tolls and so on. Travel instructions pertain to the type of instruction and slow or rapid movements of the toll 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).DNC and CNCThe development of numerical control was significant achievement in batch and job shop manufacturing, from both a technological and commercial viewpoint. There have been two enhancements and extensions of NC technology, include:(1) Direct numerical control.(2) Computer numerical control.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. 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.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 conventional NC have been replaced by control units based on the digital computer. Initially, minicomputers were utilized in the early 1970s. As further miniaturization occurred in computers, minicomputers were replaced by todays microcomputers. 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:(1) DNC computers distribute instructional data to, and collect data form, a large number of machines. CNC computers control only one machine, or a small number of machines.(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.(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. 8