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1、1,单词复习： surface roughness gage Dictate决定；对有决定性影响 Ground down Tool and cutter grinders Pitch diameter Bore,上一课回顾,2,Lesson 11 Numerical Control 数控,重点词汇： coded instructions Patent n.专利 factory floor 工厂车间 Massachusetts Institute of Technology MIT麻省理工学院 Cartesian coordinate system Counterclockwise,3,Para
2、graph 1,Numerical 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). 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。,4,Paragraph 2:,We can see from thi
3、s definition that the sequence of events is both preplanned and predicable. In 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). Therefore, NC systems are considered to be the typical
4、 form of programmable automation. 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。,5,Paragraph 3:,The 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 by
5、 using punched cards. 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。,6,But 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). In fac
6、t, this old invention can be considered simple, crude forms of mechanical NC. 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。,7,Paragraph 4:,A 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 th
7、e 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. 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。,8,Later, Parsons Engineering was awarded a study contract by the U.S. Air Force Material Command to speed
8、up production and develop continuous-path machining, with the subcontractor being the Massachusetts Institute of Technology(MIT麻省理工学院). 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。,9,The whole task was afterward given to MIT, and the machine they developed was successfully demonstrat
9、ed in 1952. Between the years of 1953 and 1960, the rate(速度) of building and selling NC machines in the United States was very slow. 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。,10,This type of machine tool later gained widespread industrial application because of the need for consistency of
10、dimensions and tighter tolerances. 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。,11,Paragraph 5,As with any engineering application, NC programming is based on the Cartesian coordinate system(笛卡儿坐标系). According to that coordinate system, any point within a plane can be defined with its distances from the Y-ax
11、is and the X-axis (i.e. the X and the Y coordinates, respectively).,12,Also, the point of intersection(相交) of these two perpendicular axes is called the origin, or zero point. The coordinates of a point can both be positive, both be negative, or one be negative and the other positive, depending upon
12、 the location of that point.,13,In fact, those two perpendicular intersecting axes divide the plane into four quadrants, which are numbered counterclockwise. All values of X and Y are positive in the first quadrant and negative in the third quadrant.,14,In the second quadrant, all values of X are ne
13、gative, and all values of Y are positive, contrary to signs in the fourth quadrant, where it is the other way around.,15,In 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 Y c
14、oordinate of a point is positive when it is above the X axis and negative when the point is located below that axis.,16,The 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 axes.,
15、Paragraph 6,17,Paragraph 7,There are three basic types of control systems for NC machine tools, point-to-point, straight cut, and contouring. 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。,18,Point-to-Point system点位系统. The point-to-point system is usually used in NC drilling machines that are employed in drilling p
16、recision patterns of holes(孔系). 点位系统常用于数控钻床来加工精密布置的孔。,Paragraph 8,19,The 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. As soon as the desired hole is drilled, the system moves the spindle to the next programmed location to drill another hole, and so on.,20,The spindle (or machine table) movement from one hole location to the next must be done as fast as possible to bring to a min
