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机电一体化专业英语Unit.ppt

发布:2017-06-17约字共34页下载文档
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Part I Technical and Practical Reading Passage A Basics of Computer Numerical Control What is CNC? CNC stands for Computer Numerical Control and has been around since the early 1970s. Prior to this, it was called NC, for Numerical Control. While people in most walks of life have never heard of this term, CNC has touched almost every form of manufacturing process in one way or another. How CNC works CNC machines are programmed by a CNC programmer, who uses a machining print to determine X, Y, and Z, coordinates for each cutting tool inside the CNC to move to. This causes, the part that is load to be cut, drilled, tapped, bored, counter bored, chamfered, etc. Everything that an operator would be required to do with conventional machine tools is programmable with CNC machines. Once the machine is setup and running, a CNC machine is quite simple to keep running. In fact CNC operators tend to get quite bored during lengthy production runs because there is so little to do. With some CNC machines, even the work-piece loading process has been automated Motion Control All CNC machine types share this commonality: They all have two or more programmable directions of motion called axes. An axis of motion can be linear (along a straight line) or rotary (along a circular path). One of the first specifications that implies a CNC machines complexity is how many axes it has. Generally speaking, the more axes, the more complex the machine. In the beginning stepper motors, which rotate in increments, or steps, were the standard in motion control technology. Positional accuracy defines the precision with which a system can control the actual placement of the X, Y, and Z axes. Three-axis systems are the norm today, although some machines control five to seven axes of motion Programmable Accessories A CNC machine wouldnt be very helpful if all it could only move the work-piece in two or more axes. Almost all CNC machines are programmable in several othe
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