1、机械工程英语第二版第二部分翻译Unit 1Introduction 前言The central and essential ingredient of GAD/CAMis the digital computer.1Its inherent speed and storage capacity have made it possible to achieve the advances in image processing, real-time process control, and a multitude of other important functions that are simp
2、ly too complex and time-consuming to perform manually. To understand CAD/CAM it is important to be familiar with the concepts and technology of the digital computerCAD/CAM 的重要组成部分是数字计算机，它固有的速度以及存储能力似的它能够在图像处理，实时过程控制以及很多因太复杂太费时而人工无法完成的其他重要功能方面获得进步，要想懂得 CAD/CAM，熟悉数字电脑的概念和技术是很重要的.The modern digital com
3、puter is an electronic machine that can perform mathematical and logical calculations and data processing functions in accordance with a predetermined program of instructions. The computer itself is referred to as hardware, whereas the various programs are referred to as software.现在数字计算机是一部能够根据预定的程序
4、来完成数字和逻辑运算以及数据处理功能的电子设备，计算机本身称为硬件，而各种各样的程序称为软件There are three basic hardware components of a general-purpose digital computer;一般用途的数字计算机由三种基本硬件组成.Central processing unit (CPU) 微处理器.Memory 存储器.Input/output ( I/0 )section 输入/输出设备The relationship of these three components is illustrated in Fig. 1.1. Th
5、e central processing unit is often considered to consist of two subsections; a control unit and an arithmetic-logic unit (ALU). 这三个组成部分的关系如图 1.1 所示，中央处理器通常被认为包含两部分:一个控制器和一个运算器.The control unit coordinates the operations of all the other components. 控制器控制所有其他组成部分的运输。It controls the input and output o
6、f information between the computer and the outside world through the I/O section, synchronizes the transference of signals between the various sections of the computer, and commands the other sections in the performance of their functions.它通过输入/输出端口控制电脑与外围设备之间信息的输入与输出、控制电脑各部分间信号的传输，同时也控制其他部分完成各自的功能。
7、 The arithmetic-logic unit carries out the arithmetic and logic manipulations of data. 运算器完成数据的算术和逻辑运算。 It adds, subtracts, multiplies, divides, and compares numbers according to programmed instructions. The memory of the computer is the storage unit. 它根据编制的程序完成数的加、减、乘、除和比较。存储器完成电脑的记忆功能。The data sto
8、red in this section are arranged in the form of words which can be conveniently transferred to the ALU or I/0 section for processing.数据被转译成便于向运算器和输入/输出设备传输以进行处理的字节形式存储在该部分中 Finally, the input/output provides the means for the computer to communicate with the external world. This communication is acc
9、omplished through peripheral equipment such as readers, printers, and process interface devices. 最后，输入/输出设备提供电脑和外部世界的交流手段，这种交流通过像阅读机、打印机和出口设备等外围设备完成。 The computer may also be connected to external storage units (e. g，tapes, disks, etc) through the UO section of the computer 电脑也可以通过输入 /输出设备与外围存储设备（比如
10、磁带、磁盘）链接。.The software consists of the programs and instructions stored in memory and in external storage units. It is the software that assigns the various functions which the user desires the system to accomplish to the computer. 软件由程序和存储在内存与外存中的指令组成。软件将使用者所要求系统完成的各项功能分配给计算机。The usefulness of the
11、computer lies in its ability to execute the instructions quickly and accurately. 电脑的有用性在于它快速准确地执行程序的能力。 Because the contents of the computer s memory can be easily changed, and therefore different programs can be placed into memory, the digital computer can be used for a wide variety of applications
12、.因为电脑存储的内容你能够很容易被改变，并且不同的程序都能够被存入，所以数字电脑能够用于多种应用。Regardless of the application, the computer executes the program through its ability to manipulate data and numbers in their most elementary form. 不考虑这些应用，电脑能自动执行程序并以最基本的形式完成数字和数据的运算。 The data and numbers are represented in the computer by electrical
13、signals which can take one of two alternative states.数据和数字在电脑中以两种形式的电信号的一种表示。This form of representation is called the binary system. 这种表示形式叫做二进制计数法。The more familiar decimal number system and a whole host of soft-ware languages can utilize the binary system to permit communication between computers
14、 and human beings.更多与之类似的十进制计数法以及很多软件语言利用二进制计数法在电脑和人之间实现交流。Central Processing Unit (CPU) 中央处理器The central processing unit (CPU) regulates the operation of all system components and performs the arithmetic and logical operations on the data. 中央处理器控制所有系统组成的操作并进行数据的算术和逻辑运算。To accomplish these functions
15、, the CPU consists of two operating units:为了完成这些功能，中央处理器包含两个结构单元：.Control unitArithmetic-logic unit (ALU) 控制器、运算器The control unit coordinates the various operations specified by the program instructions. 控制器控制由程序制定的各种操作。These operations include receiving data which enter the computer and deciding ho
16、w and when the data should be processed. The control unit directs the operation of the arithmetic-logic unit.这些操作包括接收输入电脑的数据和决定数据的处理形式以及处理时间，控制器控制运算器的操作。 It sends data to the ALU and tells the ALU what functions to perform on the data and where to store the results. 它将数据发送给运算器并告知运算器数据所要求的处理操作和结果的存储位
17、置。The capability of the control unit to accomplish these operations is provided by a set of instructions called an executive program which is stored in memory.控制器完成这些操作的能力是由一组存储在存储器中被称作执行程序的指令程序提供的。The arithmetic-logic unit performs operations such as addition, subtractions, and comparisons. These o
18、perations are carried out on data in binary form. 运算器完成像加、减和比较的功能。这些功能以二进制形式对数据进行处理。 The logic section can also be used to alter the sequence in which instructions are executed when certain conditions are indicated and to perform other functions, such as editing and masking data for arithmetic opera
19、tions. 当指出某些条件时逻辑器能够改变程序执行的顺序，也能够完成其他功能，例如为运算操作编辑和屏蔽数据。Both the control unit and the arithmetic-logic unit perform their functions by utilizing registers. 控制器和运算器都是通过寄存器来完成它们的功能。Computer registers are small memory devices that can receive，hold, and transfer data. Each register consists of binary cel
20、ls to hold bits of data.计算机的寄存器是能够接收、保存和传送数据的小存储设备。每个寄存器都由能够保存二进制数的二进制单元组成。 The number of bits in the register establishes the word length with which the computer is capable of handling. The number of bits per word can be as few as 4 ( early microcomputers ) or as many as 64 ( large scientific compu
21、ters ).Computer Programming Languages 存储器的位数代表了电脑能够处理的字长，每个字所占位数最少到 4 个（早期微型计算机）最多到 64 个（大型科学计算机）The binary number system could be used to represent any decimal number, alphabetic letter, or other common symbol. 二进制数能够用来表示十进制数、字母，或者其他一般符号。 Data and instructions are communicated to the computer in th
22、e form of binary words. In executing a program. the computer interprets the configuration of bits as an instruction to perform electronic operations such as add，subtract, load into memory，and so forth. 数据和程序都以二进制码得形式输入计算机，在执行某一程序时，计算机通过翻译构成指令的字来执行像加、减、保存等电子操作。The sequence of these binary-coded instr
23、uctions defines the set of calculations and data manipulations by which the computer executes the program. 这些二进制编码的顺序限定了计算机执行程序的运算组和数据运算The binary-coded instructions that computers can understand are called machine language. Unfortunately，binary-coded instructions and data are very difficult for hum
24、an programmers to read or write. 这些计算机所能识别的二进制编码叫做机器语言。不幸的是，对编码人员来说由二进制编码所形成的指令和数据是很难读写的。 Also, different machines use different machine languages. 同时，不同的机器使用不同的机器语言。 To facilitate the task of computer programming, higher-level languages are available which can be learned with relative ease by human
25、 beings. In all there are three levels of computer programming languages;为了便于计算机编程，对人来说相对容易学习的高级语言出现了。计算机程序语言总共有三种：.Machine language.Assembly language.Procedure-oriented ( high-level) languages 机器语言、汇编语言、高级语言Computer Process Interfacing计算机处理技术To be useful, the computer must be capable of communicati
26、ng with its environment. 计算机要想有用必须能和它自己的环境进行交流。 In a data processing system, this communication is accomplished by various input/output devices such as card readers，printers，and CRT consoles. 在数据处理系统中，这种交流是通过输入/输出设备例如读卡器、打印机、CRT 控制板等完成的。 In computer-aided manufacturing, the environment of the comput
27、er includes not only these devices but also includes one or more manufacturing processes. 在计算机辅助制造中，计算机的环境不仅包括这些设备而且包括一种或多种制造工艺。Functioning as a process control system，the computer must be capable of sensing the important process variables from the operation and providing the necessary responses to
28、maintain effective control over the process. 。作为过程控制系统，计算机必须能够感应来自操作的重要的处理变量并提供必需的回应以维持有效地处理控制。 In the following sections we examine some of the important components of a computer process control system. 下面的部分我们检查计算机过程控制系统的一些重要部分制造过程数据。(1) Manufacturing process data. 制造过程数据。The data that must be com
29、municated between the manufacturing process and the computer. 制造过程数据是必须在制造过程和计算机间进行交流的。These data can be classified into three categories:这些数据可以分成 3 类：.Continuous analog signals 连续模拟信号.Discrete binary data 离散的二进制数据.Pulse data 脉冲数据( 2 ) System interpretation of process data. The three categories of m
30、anufacturing process data must be capable of interacting with the computer. 制造过程数据的这三种类型必须能和计算机进行交流。 For monitoring the process，input data must be entered into the computer. 。对于监控过程而言，输入的数据必须输入计算机。 For controlling the process，output data must be generated by the computer and converted into signals u
31、nderstandable by the manufacturing process. 对于控制过程而言， 输出数据必须由计算机产生并转换成制造过程能理解的信号。 There are six categories of computer-process interface representing the inputs and outputs for the three types of process data. These categories are: 有六种计算机过程接口代表了过程数据三种类型的输入和输出。他们是：.Analog to digital A/D.Contact input
32、 触点输入.Pulse counters 脉冲计数器.Digital to analog D/A.Contact output 触点输出.Pulse generators 触点输出Computer Network Structures 计算机网络结构Network introduction 网络介绍The term “ computer network “ refers to the actual physical connections between computers in different areas. 计算机网络这个术语是指计算机和不同的区域之间的物理连接。 Since its f
33、irst appearance in 1964，computer networks have developed through many technology phases such as Multi-computer System，Local Area Network(LAN)，Metropolitan Area Network(MAN )，Wide Area Network(WAN)and Network Computing. 自 1964 年第一次出现以来，计算机网络已经发展经历了许多技术阶段例如，多机系统、局域网、城域网、广域网和以太网。 Now its appearance has
34、 become one of the most significant engineering achievements ever in human history. 现在它的出现已成为在人类历史上最有重要意义的工程成果之一。 It can be used for many purposes such as intercommunication，digital online service and information share. 有很多用途例如，互相联络、数字在线服务和信息共享。 Computer network can be used in almost every case. 计算机
35、网络几乎可用于任何事。 The utilization of computer network in mechanical engineering includes many scientific subjects such as Network Manufacturing, Virtual Manufacturing, Flexible Manufacturing System and Agile Manufacturing. 计算机网络在机械工程上的使用包括许多科学项目例如，网络制造、虚拟制造、柔性制造系统和敏捷制造。Unit2 Numerical Control of Productio
36、n EquipmentNumerical 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 o
37、r 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. （1）数控是程序控制的自动化，在数字控制系统中，设备通过数字
38、，字母和符号来编码，以一种合适的格式为每一个特定的零件或工件定义一个程序指令集。当工件变化时，程序也变化，改变程序的能力也就是适合中小批量生产。写一个新程序比改变大量生产设备要容易的多。Basic Components of NCA numerical control system consists of the following three basic components:.program of instructions.Machine control unit.Processing equipment基本结构：数控系统由下面三部分组成：1.控制程序；2.机器控制单元；3.加工设备。Th
39、e 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.三部分的基本关系，由图2.1 所示。程序输入到控制单元由送入的程序来引导加工设备控制。The program of instructions is the detailed step-by-step commands that direct the proces
40、sing equipment. In its most common form, the commands refer to positions of machine tool spindle with respect to the worktable on which the part is fixture. More advanced instructions include selection of spindle speeds, cutting tools, and other functions. The program is coded on a suitable medium f
41、or submission to the machine control unit. The most common medium in sue over the last several decades has been 1-in.-wide punched tape. Because of the widespread sue of the punched tape, NC is sometimes called “tape control”. However, this is a misnomer in modern usage of numerical control. Coming
42、into use more recently have been magnetic tape cassettes and floppy diskettes.指导程序是一步步详细的指导加工设备的指令。通常指令把主轴上刀具相对于安装工具的工作台定位。更多先进的说明包括主轴的转速，加工工具的选择及其功能。程序刻在合适的介质中，提交到机器控制单元中，在过去几十年中，最常用的介质是一英寸宽的打孔纸带。由于打孔纸带的广泛使用，NC 有时也叫纸带控制，然而这是现代数控使用的误称。现在进入使用更多的是磁带和软盘。The machine control unit (MCU) consists of the el
43、ectronics 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.机器控制单元（MUC）由电子和控制硬件组成，机器控制单元可以读出和执行指令程序，可以自动改变加工工具和其他加工设备。The processing equipment is the third basic component of an NC system.
44、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.执行单元是数控系统的第三基础部分，执行原件是有效执行工作的原件，最常见的数控例子其中的一个
45、加工操作，加工设备由工作台和主轴组成，就像用电动机来驱动一样。加工设备由控制单元来驱动控制系统的类型。Types of Control Systems控制系统的类型There 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,
46、depending on the type of operation, at different velocities.数控有2种基本类型，点对点式和轮廓式控制，点对点式控制也称定位控制，每个轴都是通过丝杠单独驱动，根据加工类型不同，加工速度也不一样。The machine moves initially at maximum velocity in order to reduce nonproductive time but decelerates as the tool reaches its numerically defined position. 机器开始以最大速度运行来减少非加工时
47、间，但当他达到数据定义的位置时，机器开始减速。Thus in an operation such as drilling or punching, the positioning and cutting take place sequentially.因此在一个操作中，如钻或冲孔操作先定位再加工。After the hole is drilled of punched, the tool retracts, moves rapidly to another position, and repeats the operation. 在钻或冲孔之后，迅速收起工具移动到另一个位置重复此操作。The
48、path followed from one position to another is important in only one aspect: The time required should be minimized for efficiency.从一个位置移到另一个位置是非常重要的，要遵循一个原则，从效率上考虑只要时间最短即可。Point-to point systems are used mainly in drilling, punching, and straight milling operations.点对点系统主要用于钻，冲孔，直铣操作中。In the contouri
49、ng 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.轮廓式也就是连续路径式系统，定位和切削同时按不同速度来控制，由于刀具在指定路线运动同时切削，因此速度和运动的同步控制是非常重要的。The contouring system is used on lathes, milling machines, grinders, welding machinery, and machining centers.轮廓式系统常用于车床铣床磨床焊接设备和加工中心。Movement along the path, or interpolation, occurs incrementally, by one of several basic methods. I
