机械专业英语11优秀课件

1、1n单词复习：nsurface roughnessngagenDictate决定；对有决定性影响 nGround downnTool and cutter grindersnPitch diameter 1.Bore上一课回顾2Lesson 11 Numerical Control 数控数控重点词汇：ncoded instructionsnPatent n.专利nfactory floor 工厂车间工厂车间nMassachusetts Institute of Technology MIT麻省理工学院nCartesian coordinate systemnCounterclockwise 3

2、Paragraph 1nNumerical control (NC) can be defined as the control of operation of machine tools by a series of coded instructions called the program, which consists mainly of alphanumeric characters (numbers and letters数字和字母).n数字控制是指称为程序的一系列编码指令对机床操作的控制，该程序主要由字母和数字符号组成。4Paragraph 2:nWe can see from t

3、his definition that the sequence of events is both preplanned and predicable. nIn other words, any desired sequence of events can be obtained by coding the appropriate instructions and can also be changed by changing those coded instructions(编码指令).n Therefore, NC systems are considered to be the typ

4、ical form of programmable automation.n从定义中我们可以看到：这一系列的事情可以预先计划也可以预报。换句话说，一系列任何想要做的事情都可以通过编写适当的指令来实现，也可以通过修改编码指令来修正。5Paragraph 3:nThe basic concept of NC is not new at all and dates back to the early years of the Industrial Revolution, when Joseph Jacquard developed a method to control textile looms

5、by using punched cards. n数控的基本概念并不新鲜，时间可以追溯到工业革命早期约瑟夫捷克尔德开发出一种通过穿孔卡片控制织布机的方法。6nBut when he applied for a patent for his invention, he was denied that right by the Queen of England, because she believed that it would have put poor workers out of work (notice the similarity with robots nowadays). nIn

6、fact, this old invention can be considered simple, crude forms of mechanical NC. n然而当他为自己的发明申请专利时，由于女王认为它会造成工人失业(与今天的机器人很相似)而被否定。事实上，这些古老的发明是简单的、机械式数控的雏形。7Paragraph 4:nA modern version of NC emerged in 1947 at the Parsons Engineering Company of Traverse City(帕森斯特拉弗斯城的工程公司), Michigan, as a result of

7、the need of John C. Parsons (the owner of the company) to manufacture helicopter rotor blades fast enough to meet(如期完成) his contracts. n现代数控1947年出现在密歇根州的帕森斯特拉弗斯城的工程公司，当时公司主人约翰帕森斯根据合同要求尽快生产飞机螺旋桨叶片。8nLater, Parsons Engineering was awarded a study contract by the U.S. Air Force Material Command to spee

8、d up production and develop continuous-path machining, with the subcontractor being the Massachusetts Institute of Technology(MIT麻省理工学院). n后来帕森斯工程公司得到了与美国空军装备司令部签订的研究合同，来提高生产率和开发连续轨迹加工，后来二次转包给麻省理工学院。9nThe whole task was afterward given to MIT, and the machine they developed was successfully demonstr

9、ated in 1952.nBetween the years of 1953 and 1960, the rate(速度) of building and selling NC machines in the United States was very slow.n 整个任务给了MIT，机器成功开发是在1952年。在美国1953-1960年数控机床的生产与销售量很小。10nThis type of machine tool later gained widespread industrial application because of the need for consistency o

10、f dimensions and tighter tolerances.n由于（零件）尺寸一致接近公差的需要，这种机床后来被广泛应用于工业生产。11Paragraph 5nAs with any engineering application, NC programming is based on the Cartesian coordinate system(笛卡儿坐标系).n According to that coordinate system, any point within a plane can be defined with its distances from the Y-a

11、xis and the X-axis (i.e. the X and the Y coordinates, respectively). 12nAlso, the point of intersection(相交) of these two perpendicular axes is called the origin, or zero point. nThe coordinates of a point can both be positive, both be negative, or one be negative and the other positive, depending up

12、on the location of that point. 13nIn fact, those two perpendicular intersecting axes divide the plane into four quadrants, which are numbered counterclockwise. nAll values of X and Y are positive in the first quadrant and negative in the third quadrant. 14nIn the second quadrant, all values of X are

13、 negative, and all values of Y are positive, contrary to signs in the fourth quadrant, where it is the other way around. 15nIn other words, when a point falls to the right of the Y axis, its X coordinate is positive, but when it is to the left of that axis, its X coordinate is negative, whereas the

14、Y coordinate of a point is positive when it is above the X axis and negative when the point is located below that axis. 16nThe Cartesian coordinate system can be extended to describe a point in space by adding a third dimension along the Z axis, which is perpendicular to the plane of the X and Y axe

15、s.Paragraph 617Paragraph 7nThere are three basic types of control systems for NC machine tools, point-to-point, straight cut, and contouring.n数控机床有三种基本类型的控制系统点对点、直线切削、轮廓切削。18nPoint-to-Point system点位系统点位系统. nThe point-to-point system is usually used in NC drilling machines that are employed in drilli

16、ng precision patterns of holes(孔系). n点位系统常用于数控钻床来加工精密布置的孔。Paragraph 819nThe function of the NC system is, therefore, to move the spindle (or machine table) to the exact location, as given by a tape command, so that a hole can be drilled. nAs soon as the desired hole is drilled, the system moves the

17、spindle to the next programmed location to drill another hole, and so on. 20nThe spindle (or machine table) movement from one hole location to the next must be done as fast as possible to bring to a minimum the nonproductive time(非生产时间) spent in movement. nAccordingly, speeds of more than 2500 mm/mi

18、n are quite common. 21Paragraph 9nStraight-cut system直线切削系统直线切削系统. nThe straight-cut system is quite similar to the previous system, except that the feed rate of the spindle along each machine axis is controlled so as to(为了) be suitable for machining (e. g., a milling operation on a vertical mill).

19、22nAgain, the spindle cannot be controlled such that it moves along a line inclined to the X- and Y-axes of the machine, since the motion along each axis is independent from that along the other axis, because it is controlled by a separate NC circuit (or subsystem). 23nNevertheless, motions along li

20、nes coinciding with or parallel to either the X or the Y-axis can be accurately controlled. 24Paragraph 10nContouring system轮廓系统轮廓系统. In order to make angular cuts on the work piece, the two driving servo motors (one for the X-axis motion and the other for the Y-axis motion) have to run at unequal s

21、peeds. 25 In fact, the rate of travel along the Y direction by that along the X direction must be equal to tan, where is the angle that the angular cut makes with the X direction. The capability of a control system to regulate the rate of spindle (or table) travel along two axes of motion at the sam

22、e time is called linear interpolation.26nA control system of the contouring type can also produce curves to very close tolerances. nTherefore, it is sometimes referred to as the continuous-path system. Paragraph 1127nThe method of employing linear interpolation to produce curves involves breaking do

23、wn curve or an arc into a large number of straight lines in such a manner(于是，如此) that the end of each line is the beginning of the next one (tip-to-tail fashion). 28nEach and every line segment must, therefore, be programmed in order for the path to conform to the desired curve. nWe can obviously se

24、e that the larger the number of segments taken, the smaller each of the segment lines becomes and the smoother the machined curve becomes. 29Paragraph 12nThe advantages of NC machine tools are felt not only on the factory floor but also in many other departments of the business corporation. nFollowi

25、ng are some of those advantages, which can be used as justification for employing NC machine tools: 30The design and construction of NC machine tools, together with the fact that these machines are controlled by numerical values, ensure positioning accuracy and repeatability. In other words, if the

26、same program is employed to produce a number of parts, they have exactly identical dimensions. 数控机床的结构与设计及机床利用数字控制的事实，保证了它的定位精度和重复加工能力。换句话说，同一程序加工同一批零件，它们有完全相同的尺寸。31n Complex-shaped components can be produced automatically, with closer tolerances and very high degrees of reliability.n This, indeed, provides the designer with great degree of flexibility and freedom when preparing designs. 32 High dimensional accuracy and repeatability enable the manufacture of parts that requir