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1、,机电技术专业英语,2,Lesson Seventeen,Text,Computer numerical control is a complete departure from the conventional machine tool operation where an operator or machinist studies an engineering drawing or print and guides a cutting spindle based on the print information. The successful operation of a conventi
2、onal machine tool depends in large part on the skill of the operator or machinist developed over many years of practice. With CNC, the drawings are studied and the information about the workpiece or part is converted to a series of appropriate code numbers by the part programmer, the code numbers re
3、present every movement, path, or action the machine tool must take to properly machine the workpiece on a machine tool is known as a part program.,CNC Versus Conventional Machining,Lesson Seventeen,The movements and functions of the machine tool have now become the programmers responsibility , while
4、 the role of the operator is drastically changed, thus the basic functioning of the machine does not rest with the person who is standing by monitoring the operation, but with the one who developed the part program in a coded form which guides and directs the workpiece machining. Machine tools canno
5、t read numbers, however, the coded instructions are read by a program reader which is part of the overall Machine Control Unit often called the MCU. The function of the MCU is to act upon the coded instructions to convert them into movement and operation of the machine tool. Normally the control uni
6、t output signals are converted by electronic, hydraulic or mechanical servomechanisms. It is important to know that CNC is not a mechanical brain and cannot think, evaluate, judge, discern, or show any real adaptability.,Lesson Seventeen,Sometimes a choice of alternatives or limits can be set up in
7、the program so that incorrect or faulty instructions will not be followed by overriding the programmed instructions; however, all of these conditions with their possible choice of alternatives have to be included in the program.,Lesson Seventeen,New Words and Expressions,Lesson Seventeen,Lesson Seve
8、nteen,参考译文,计算机数控机床完全脱离了传统的加工机床模式。利用传统机床加工首先需要操作者或机械师研究工程图样或印刷图样，并且要引导切削轴按照图样信息进行加工。传统机床加工的成功操作很大程度上依赖于操作者或机械师多年生产实践的经验。而对数控机床来说，零件图设计好以后，由程序员将零件图转化成一系列相应的程序代码。这些数字代码代表的每一个动作都必须与图样上描述的零件相适应。所有的连续代码都是在加工机床上生产零件所必需的，我们称其为零件加工程序。 现在，机床的运动与运行已经成为程序员的责任，而操作者的作用彻底地改变了。因此，机床的基本功能的发挥不再取决于站在机床前监视操作的工人而是取决于研究编
9、写零件加工程序的程序员，这些加工程序员指导机床加工零件。机床不能读取数字信息，加工代码指令是由程序读卡器读取的，它是机床控制单元的一部分。机床控制单元的功能就是依照代码指令，将代码转化成机床的运动和加工操作。通常控制单元的输出信息是通过电信号、液压信号或机械伺服机构改变过的。,数控机床与传统机床的比较,Lesson Seventeen,数控机床不是人的大脑，它不能思考，不能计算，不能判断，不能辨别，也没有适应性，了解这一点是很重要的。 有时候，在程序中设置一种选择或一种限制， 使错误的或不完善的指令不会被程序执行；但是，所有选择的可能性都必须包含在程序中。,谢谢观赏,,Thank You !,
