机械专业英语11.pptx

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,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,1/36,2,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,2/36,3,Paragraph 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一系列编码指令对机床操作控制，该程序主要由字母和数字符号组成。,3/36,4,Paragraph,2:,We can,see,from this 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 form of programmable automation.,从定义中我们能够看到：这一系列事情能够预先计划也能够预报。换句话说，一系列任何想要做事情都能够经过编写适当指令来实现，也能够经过修改编码指令来修正。,4/36,5,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 using,punched cards,.,数控基本概念并不新鲜，时间能够追溯到工业革命早期,约瑟夫,捷克尔德开发出一个经过穿孔卡片控制织布机方法。,5/36,6,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 fact,this old invention can be considered simple,crude forms of mechanical NC.,然而当他为自己创造申请专利时，因为女王认为它会造成工人失业,(,与今天机器人很相同,),而被否定。实际上，这些古老创造是简单、机械式数控雏形。,6/36,7,Paragraph 4:,A modern version of NC emerged in 1947 at the,Parsons Engineering Company of Traverse City,(,帕森斯特拉弗斯城工程企业,),Michigan,as a result of the need of,John C.,Parsons,(the owner of the company)to manufacture,helicopter rotor blades,fast enough to meet(,准期完成,)his contracts.,当代数控,1947,年出现在密歇根州帕森斯特拉弗斯城工程企业，当初企业主人约翰,帕森斯依据协议要求尽快生产飞机螺旋桨叶片。,7/36,8,Later,Parsons Engineering was awarded a study contract by the,U.S.Air Force Material Command,to,speed up,production and,develop,continuous-path machining,with the,subcontractor,being the,Massachusetts Institute of,Technology(,MIT,麻省理工学院,).,以后帕森斯工程企业得到了与美国空军装备司令部签署研究协议，来提升生产率和开发连续轨迹加工，以后二次转包给麻省理工学院。,8/36,9,The whole task was,afterward,given to MIT,and the machine they developed was successfully demonstrated 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,年数控机床生产与销售量很小。,9/36,10,This type of machine tool later gained widespread industrial application because of the need for consistency of,dimensions and tighter tolerances.,因为（零件）尺寸一致靠近公差需要，这种机床以后被广泛应用于工业生产。,10/36,11,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-axis and the X-axis(i.e.the X and the Y coordinates,respectively).,11/36,12,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 the location of that point.,12/36,13,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.,13/36,14,In the second quadrant,all values of X are negative,and all values of Y are positive,contrary to signs in the fourth quadrant,where it is the other way around.,14/36,15,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 coordinate of a point is positive when it is above the X axis and negative when the point is located below that axis.,15/36,16,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.,Paragraph 6,16/36,17,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控制系统,点对点、直线切削、轮廓切削。,17/36,18,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 precision patterns of holes(,孔系,).,点位系统惯用于数控钻床来加工精密布置孔。,Paragraph 8,18/36,19,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.,19/36,20,The spindle(or machine table)movement from one hole location to the next must be done as fast as possible to bring to a minimum the nonproductive time(,非生产时间,)spent in movement.,Accordingly,speeds of more than 2500 mm/min are quite common.,20/36,21,Paragraph 9,Straight-cut system,直线切削系统,.,The 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).,21/36,22,Again,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).,22/36,23,Nevertheless,motions along lines,coinciding,with or parallel to either the X or the Y-axis can be accurately controlled.,23/36,24,Paragraph 10,Contouring system,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,speeds.,24/36,25,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 same time is called linear interpolation.,25/36,26,A control system of the contouring type can also produce curves to very close tolerances.,Therefore,it is sometimes referred to as the continuous-path system.,Paragraph 11,26/36,27,The method of employing linear interpolation to produce curves involves breaking down 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).,27/36,28,Each and every line segment must,therefore,be programmed in order for the path to conform to the desired curve.,We can obviously see that the larger the number of segments taken,the smaller each of the segment lines becomes and the smoother the machined curve becomes.,28/36,29,Paragraph 12,The advantages of NC machine tools are felt not only on the factory floor but also in many other departments of the business corporation.,Following are some of those advantages,which can be used as justification for employing NC machine tools:,29/36,30,The 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 same program is employed to produce a number of parts,they have exactly identical dimensions.,数控机床结构与设计及机床利用数字控制事实，确保了它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，它们有完全相同尺寸。,30/36,31,Complex-shaped components can be produced automatically,with closer tolerances and very high degrees of reliability.,This,indeed,provides the designer with great degree of flexibility and freedom when preparing designs.,31/36,32,High dimensional accuracy and repeatability enable the manufacture of parts that require long series of operation.,Such parts are difficult to produce by conventional methods,since the,accumulated error,results in completely unacceptable results.,32/36,33,Since NC machine tools can automatically perform any desired task(within their capability)after being programmed and without the need for a human operator to stand beside the machine all the time,they can be employed to carry out operations in hostile environments.,33/36,34,Examples involve machining of some,polymeric materials,where,poisonous gases,evolve as,a result of the machining operation.,34/36,35,NC systems transfer a substantial portion of planning for the processing operation from the shop floor to the offices,where a specialist prepares the NC part program in a comfortable environment.,Consequently(,所以,),production can be directly monitored and controlled by the management.,35/36,36,课后作业：,1,、复习本课单词，预习下一课单词,36/36,