数控生产设备--中英文翻译.doc

南通职业大学毕业设计九、外文翻译NUMERICAL CONTROL OF PRODUCTION EQUIPMENTSNumerical 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. When the job changes, the program of instructions is changed. The capability to change the program is what makes NC suitable for low-and medium-volume production. It is much easier to write new programs than to make major alterations of the processing equipment.BASIC COMPONENTS OF NCA numerical control system consists of the following three basic components:Program of instructionsMachine control unitProcessing equipmentThe general relationship among the three components is illustrated in Fig.2.1. The program is fed into the control unit, which directs the processing equipment accordingly.The program of instructions is 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 fixtured. More advanced instructions include selection of spindle speeds, cutting tool, and other function. The most common medium in use over the last several decades has been 1-in. -wide punched tape. Because of the widespread use of the punched tape, NC is sometimes called “tape control”. However, this is a misnomer in modern usage of numerical control. Coming into use more recently have been magnetic tape cassettes and floppy diskettes.The machine control unit (MCU) consists of the electronics and control hardware that read and interpret the program of instruction and convert it into mechanical actions of the machine tool or other processing equipment.The processing equipment is the third basic component of an NC system. It is the component that performs useful work. In the most common example of numerical control, one that performs machining operations, the processing equipment consists of the worktable and spindle as well as the motors and controls needed to drive them.TYPES OF CONTROL SYSTEMSThere are two basic types of control systems in numerical control: point-to-point and contouring. In the point-to-point system, also called positioning, each axis of the machine is driven separately by leadscrews and, depending on the type of operation, at different velocities. The machine moves initially at maximum velocity in order to reduce nonproductive time but decelerates as the tool reaches its numerically defined position. Thus in an potation such as drilling or punching, the positioning and cutting take place sequentially. After the hole is drilled or punched, the tool retracts, moves rapidly to another position, and repeats the operation. The path followed from one position to another is important in only one respect: The time required should be minimized for efficiency. Point-to-point systems are used mainly in drilling, punching, and straight milling operations.In the 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. In all interpolations, the path controlled is that of the center of rotation of the tool. Compensation for different tools, different diameter tools, or tool wear during machining, can be made in the NC program.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 interpolationCircular interpolationHelical interpolationParabolic interpolationCubic interpolationEach of these interpolation procedures permits the programmer (or operator) to generate machine instructions for linear or curvilinear paths, using a relatively few input parameters. The interpolation module in the MCU performs the calculations and directs the tool along the path.Linear interpolation is the most basic and is used when a straight-line path is to be generated in continuous-path NC. Two-axis and three-axis linear interpolation routines are sometimes distinguished in practice, but conceptually they are the same. The program is required to specify the beginning point and end point of the straight line, and the feed rate that is to be followed along the straight line. The interpolator computes the feed rates for each of the two (or three) axes in order to achieve the specified feed rate.Linear interpolation for creating a circular path would be quite inappropriate because the programmer would be required to specify the line segments and their respective end points that are to be used to approximate the circle. Circular interpolation schemes have been developed that permit the programming of a path consisting of a circular arc by specifying the following parameters of the arc: the coordinates of its end points, the coordinates of its center, its radius, and the direction of the cutter along the arc. The tool path that is created consists of a series of straight-line segments, but the segments are calculated by the interpolation module rather than the programmer. The cutter is directed to move along each line segment one by one in order to generate the smooth circular path. A limitation of circular interpolation is that the plane in which the circular arc exists must be a plane defined by two axes of the NC system.Helical interpolation combines the circular interpolation scheme for two axes described above with linear movement of a third axis. This permits the definition of a helical path in three-dimensional space.Parabolic and cubic interpolation routines are used to provide approximations of free-form curves using higher-order equations. They generally require considerable computational power and are not as common as linear and circular interpolation. Their applications are concentrated in the automobile industry for fabricating dies for car body panels styled with free-form designs that cannot accurately and conveniently be approximated by combining linear and circular interpolations.PROGRAMMING FOR NCA 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, 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.(1) Manual Programming Manual part programming consists of first calculating dimensional relationships of the tool, workpiece, and work table, based on the engineering drawings of the part, and manufacturing operations to be performed and their sequence. A program sheet is then prepared, which consists of the necessary information to carry out the operation, such as cutting tools, spindle speeds, feeds, depth of cut, cutting fluids, power, and tool or workpiece ally a paper tape is first prepared for trying out and debugging the program. Depending on how often it is to be used, the tape may be made of more durable Mylar.Manual programming can be done by someone knowledgeable about the particular process and able to understand, read, and change part programs. Because they are familiar with machine tools and process capabilities, skilled machinists can do manual programming with some training in programming. However, the work is tedious, time consuming, and uneconomical-and is used mostly in simple point-to-point applications.(2) Computer-Aided Programming Computer-aided part programming involves special symbolic programming languages that determine the coordinate points of corners, edges, and surfaces of the part. Programming language is the means of communicating with the computer and involves the use of symbolic characters. The programmer describes the component to be processed in this language, and the computer converts it to commands for the NC machine. Several languages having various features and applications are commercially available. The first language that used English-like statements was developed in the late 1950s and is called APT (for Automatically Programmed Tools). This language, in its various expanded forms, is still the most widely used for both point-to-point and continuous-path programming.Computer-aided part programming has the following significant advantages over manual methods: Use of relatively easy to use symbolic languageReduced programming time. Programming is capable of accommodating a large amount of data concerning machine characteristics and process variables, such as power, speeds, feed, tool shape, compensation for tool shape changes, tool wear, deflections, and coolant use. Reduced possibility of human error, which can occur in manual programming Capability of simple changeover of machining sequence or from machine to machine. Lower cost because less time is required for programming.Selection of a particular NC programming language depends on the following factors:a) Level of expertise of the personnel in the manufacturing facility.b) Complexity of the part.c) Type of equipment and computers available.d) Time and costs involved in programming.Because numerical control involves the insertion of data concerning workpiece materials and processing parameters, programming must be done by operators or programmers who are knowledgeable about the relevant aspects of the manufacturing processes being used. Before production begins, programs should be verified, either by viewing a simulation of the process on a CRT screen or by making the part from an inexpensive material, such as aluminum, wood, or plastic, rather than the material specified for the finished part数控生产设备数字控制是用数字、字母和其他控制字符进行编程，来实现机械设备自动化的一种形式。号码，字母和符号是为特定的工作环境或工作而设定的一种适当的内编码。根据程序指示的改变，机械的加工也随之改变方式。更易改写程序的优越性使NC系统更适合加工微小体积的产品。与更换生产设备相比，通过编辑新的程序来实现产品的加工要容易得多。NC的基本零部件一个数控系统包括以下3个基本零部件： （1）指示程序 （2）机器控制单元 （3）机床三者的关系如下图。指示程序机器控制单元机 床机床根据输入计算机的程序来执行相应的动作。详细的指示程序直接控制机床一步一步的执行命令。在通常情况下，刀具参考点的指令与工作台的机床原点位置有关。更先进的指令系统包括机床进给速度的选择，切削工具和其他功能。在过去几十年里最常用的信息载体是1英寸宽的穿孔纸带。因为穿孔纸带的广泛使用，NC系统有时也叫“带子控制”，不过，这是现代用法过程中对数字控制的误称。近年来，卡型盒式磁带和软磁盘开始广泛使用。机器控制单元（MCU）由读取并理解程序说明，进而将程序转变成机床或另外生产设备可执行的机械动作所需的硬件和电子元件组成。机床是NC系统中的第3个基本零部件。它是有用的执行部件，在数字控制的最普通的例子里，进行机器加工操作就是其中之一，机床由工作台、主轴和控制主轴所必须的驱动电机组成。控制系统的类型在数字控制过程中有两类基本的控制系统：点位控制和轮廓控制。点位控制也被称作为位置控制，通过电机以不同的速度分别驱动机器的各轴，这取决于操作的方式。为了减少空操作的时间，机器在最初是以最大速度移动，但在刀具到达设定的位置时，要降低速度，这样，在进行过程中，如钻孔或打洞的操作是在准确的位置进行持续切削。在钻孔或打洞后，刀具退回并迅速移动到另一个位置进行重复操作。从一点大另一点的路径是一个重要的方面：为提高效率，要求移动时间降到最小。点位控制系统主要用于钻孔、打洞及直线磨削等方面。在轮廓控制，也就是所谓的连续路径运行系统中，位置的确定和切削操作同时沿着设定的路径以不同的速度运行。因为当刀具沿着规定的路径切削进给时，准确控制速度和运动的同步性是相当重要的，连续切削控制用于车床、铣床、磨床、焊接机器和机械加工中心。沿路径运动或位置插补是几种基本的方法之一。在整个插补过程中，路径控制以刀具的转动为中心。对于不同的刀具补偿，不同的刀具，及在机器加工过程中刀具的磨损，都能通过NC程序进行调节。有许多插补程序被开发用于处理连续切削控制系统中形成光滑、连续的轨迹所遇到的各种各样的问题，他们包括： 直线插补 圆弧插补 螺旋线插补 抛物线插补这些插补程序是程序员（或操作员）用来生成直线或曲线路径的机器指令，以相对减少输入饿参数。在MCU方面的插补模式进行计算并按指定的路径执行。直线插补是最基本的方法，在NC系统中生成连续轨迹时经常用到。在实践中，两轴和三轴直线插补有时有所区别，但他们的原理是相同的。程序被要求指定直线的起点和终点，及沿着直线跟随的进给量，为了取得被指定的进给量，插补器为两轴（或三轴）中的每个轴计算插补量。因为程序员要求指定的直线部分和将用来接近圆的各自的终点有差别，用直线插补生成圆弧轨迹不适合。圆弧插补程序被开发用于圆弧插补，通过指定组成圆弧轨迹的下列参数：终点、中心、半径。刀具沿着圆弧的指示坐标进给，被生成的刀具轨迹由一系列直线部分组