机械专业英语董建国第22章ppt课件

1、Unit 22TEXT READING MATERIAL Unit 22Unit 22TEXTFundamentals of Numerical Control Controlling a machine tool by means of a prepared program is known as numerical control, or NC. NC equipment has been defined the Electronic Industries Association (EIA) as“A system in which actions are controlled by th

2、e direct insertion of numerical data at some point. The system must automatically interpret at least some portion of this data. Unit 22 In a typical NC system the numerical data which is required for producing a part is maintained on a punched tape and is called the part program. The part program is

3、 arranged in the form of blocks of information, where each block contains the numerical data required to produce one segment of the work-piece. The punched tape is moved forward by one block each time the cutting of a segment is completed. The block contains, in coded form, all the information neede

4、d for processing a segment of the work-piece: the segment length, its cutting speed, feed, etc. Unit 22Dimensional information (length, width, and radii of circles) and the contour form (linear, circular, or other) are taken from an engineering drawing. Dimensions are given separately for each axis

5、of motion (x, y, etc.). Cutting speed, feed-rate, and auxiliary function (coolant on and off, spindle direction, clamp, gear changes, etc.) are programmed according to surface finish and tolerance requirements.Unit 22 Preparing the part program for a NC machine tool requires a part programmer. The p

6、art programmer must possess knowledge and experiences in mechanical engineering. Part Programmers must be familiar with the function of NC machine tools and machining process and have to decide on the optimal sequence of operations.Unit 22 In NC machine tools, each axis of motion is equipped with a

7、separate driving device which replaces the hand-wheel of the conventional machine. The driving device may be a DC motor, a hydraulic actuator, or a stepping motor. The type selected is determined mainly by the power requirements of the machine. Unit 22 The NC machine tool system contains the machine

8、 control unit (MCU) and the machine tool itself. The MCU has to read and decode the part program, to provide the decoded instructions to the control loops of the machine axes of motion, and to control the machine tool operation.Unit 22 The MCU consists of two main units: the data processing unit (DP

9、U) and the control loops unit (CLU). The function of the DPU is to decode the information received from the tape, process it and provide data to the CLU. Such data contains the new required position of each axis, its direction of motion and velocity, and auxiliary control signals to relays. On the o

10、ther hand, the CLU provides a signal announcing that the previous segment is completed and that the DPU can read a new block of the part program. The CLU operates the drives attached of the machine lead-screws and receives feedback signals on the actual position and velocity of each one of the axes.

11、 Each lead-screw is equipped with a separate driving device and a separate feedback device, but the latter exists only in a closed-loop system.Unit 22 In CNC systems, the DPU functions are always performed by the control program contained in the CNC computer. The major part of the CLU, however, is a

12、lways implemented in the most sophisticated CNC systems.Unit 22LEARN TO SPEAKMr. Zhou:Good morning, Miss Yang.Miss Yang: Hi, Mr. Zhou.Mr. Zhou: What are you doing now?Miss Yang: I am turning a work-piece.Mr. Zhou: Is this lathe different from that lathe?Miss Yang:Yes. It is.Mr. Zhou: Where are the d

13、istinctions about them?Miss Yang:This is an NC lathe, and the other is a conventional lathe.Mr. Zhou: What is NC?Miss Yang:NC refers to numerical control, and controlling a machine tool by means of a prepared program.Unit 22Mr. Zhou: What does the NC machine tool system contain?Miss Yang:It contains

14、 the machine control unit and the machine tool itself.Mr. Zhou: Do you like to machine a work-piece on NC machine tools or conventional machine tools.Miss Yang:I would prefer to use NC machine tools very much.Mr. Zhou: Why do you think that?Miss Yang:Because it has some advantages such as increased

15、productivity, reduced the noise, improved operators safety and product quality, and so on.Mr. Zhou: It sounds quite well.Miss Yang:You will like it in the future, too.Mr. Zhou: I think so. Thanks a lot.Miss Yang:You are welcome.Unit 22NEW WORDS AND PHRASESinterpret In5t:prIt v. 解释阐明解释阐明coolant 5ku:l

16、Ent n. 冷却液冷却液optimal 5BptIm(E)l adj. 最正确的，最正确的，最理想的最理想的decode di:5kEJd v. 解码，译码解码，译码implemented 5ImplImEnt v. 实行，实行，执行执行sophisticated sE5fIstIkeItId adj. 复复杂的杂的Unit 22numerical control (NC) 数字控制the Electronic Industries Association (EIA) (美国)电子工业协会auxiliary function 辅助功能surface finish 外表粗糙度D.C. moto

17、r 直流电机stepping motor 步进电机machine control unit (MCU) 机床控制单元data processing unit(DPU) 数据处置单元computer numerical control (CNC) 计算机数字控制Unit 22NOTES 1NC equipment has been defined as “A system in which actions are controlled by the direct insertion of numerical data at some point. The system must automati

18、cally interpret at least some portion of this data. 数控设备被定义为：数控设备被定义为：“采用在某些点直接插采用在某些点直接插入数据来控制操作的系统，此系统至少要能入数据来控制操作的系统，此系统至少要能自动解读部分数据。自动解读部分数据。 这个句子中，这个句子中，A system 是是as的宾语。的宾语。A system后是由后是由which引导的定语从句，修饰引导的定语从句，修饰system。Unit 22 2Part programmers must be familiar with the function of NC machine

19、tools and machining process and have to decide on the optimal sequence of operations. 零件编程人员要熟习数控机床的功能及加工工艺，并决议最正确的加工顺序。 句中，the optimal sequence of operations意思是最正确的加工顺序。Unit 22 3In NC machine tools, each axis of motion is equipped with a separate driving device which replaces the hand-wheel of the

20、conventional machine. 在数控机床中，每个轴向的运动都要有单独的驱动安装替代普通机床中的手轮来驱动。 句中，which引导的定语从句修饰device。Unit 22 4Each lead-screw is equipped with a separated driving device and a separate feedback device, but the latter exists only in a close-loop system. 每个丝杠都有一个单独的驱动安装和反响安装，不过反响安装只出如今闭环系统中。 Unit 22EXERCISES 1put the

21、 following into Chinese and recite them: (1) 1) NC: Numerical Control 2) CNC: Compute Numerical Control 3) MCU: Machine Control Unit 4) CPU: Center Process Unit 5) DPU: Data Processing Unit 6) CLU: Control Loops UnitUnit 22(2)1) dimensional information2) auxiliary function3) NC machine tools4) The o

22、ptimal sequence of operations5) a DC motor 6) a stepping motor Unit 22 2Fill in the blanks with proper words: machines controlled by means of prepared programs are called machines. In NC system, the part program is maintained on a or punched card. Each block of program contains some information in f

23、orm. After one block is carried out, the punched tape is moved , so another block of information is read to the machine. The part program is often prepared by a part , who have to decide on the sequence of . Programming may be done or with the aid of computer, which is usually called (CAP).Unit 22 3

24、Translate the following passage into Chinese: 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 instr

25、uctions for a particular workpart or job. When the job changes, the program of instruction is changed. The capability to change the program is what makes NC suitable for low- and medium-volume production. Unit 22READING MATERIAL Numerical Control of Machining Process Numerical control of machine too

26、ls by computers has made great advances in recent years. Generally,automatic tools are efficient and accurate when large quantities of parts of the same shape are required,but changing from one automatic cycle to another is a long and expensive process and would only be carried out for a long run.Bu

27、t there are many examples when only a few parts are required and it is in such work that the computer-controlled machine is valuable.Unit 22 There are two types of computers-digital and analogue. A digital computer works with numbers given in digital form,a digit being one of a certain set of symbol

28、s used to show numbers.It is the digital computer which is used in electronic data processing.The analogue computer is based on an analogy of quantity.It deals with physical quantities and not numbers.Unit 22 In a digital control system information from a drawing is put on a disc which is put into a

29、 computer which computers from the information to the continuous motion of the cutting tool. The output is put on a disc which is put into the machine-tool control unit when required. One computer services a number of machines. Disc can be stored and used any number of times in future cases,simply by replaying them if the same parts are wanted again.For best resu