机械专业英语ppt课件

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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.
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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.
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).
上一课回顾
单词复习： 1. surface roughness 2. gage 3. Dictate决定；对…有决定性影响 4. Ground down 5. Tool and cutter grinders 6. Pitch diameter 7. Bore
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Lesson 11 Numerical Control 数控
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。
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As with any engineering application, NC programming is based on the Cartesian coordinate system(笛卡儿坐标系).
点位系统常用于数控钻床来加工精密布置的孔。
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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.
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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.
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This type of machine tool later gained widespread industrial application because of the need for consistency of dimensions and tighter tolerances.
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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.
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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.
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。
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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).
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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.
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。
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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).
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。
In fact, 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。
重点词汇：
1. coded instructions 2. Patent n.专利 3. factory floor 工厂车间
4. Massachusetts Institute of Technology MIT麻省理工学院
5. Cartesian coordinate system
6. Counterclockwise
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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).
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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).
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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 the need of John C.
பைடு நூலகம்
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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.