Unit 3 Fundamentals of CNC.ppt

Unit 3 Fundamentals of CNC Index 3.1 Text 3.2 Practice 3.3 Grammar and Translation 3.4 Supplementary Reading 3.5 课文参考译文 3.1 Text Focus of the unit 1. Introduction 2. Motion control-the heart of CNC Focus of the unit Motion control is the heart of CNC. All CNC controls allow axis motion to be commanded by utilizing some form of coordinate system. The CNC control must be told the location of the program zero point. Besides the absolute mode of programming, there is another way of specifying end points for axis motion. [CNC的核心是轴运动的控制，为此，必须建立坐标系，指定编程零点，指定编程方式。] 1. Introduction Here are but a few of the most important benefits offered by CNC equipment. Improved automation. The operator intervention related to producing workpieces can be reduced or eliminated. Consistent and accurate workpieces. Flexibility. Running a different workpiece is almost as easy as loading a different program. 2. Motion control - the heart of CNC The most basic function of any CNC machine is automatic, precise, and consistent motion control. All forms of CNC equipment have two or more directions of motion, called axes. The two most common axis types are linear (driven along a straight path) and rotary (driven along a circular path). CNC machines allow motions to be commanded through programmed commands. The motion type (rapid, linear, and circular), the axes to move, the amount of motion and the motion rate (feedrate) are programmable with almost all CNC machine tools. A CNC command tells the drive motor to rotate a precise number of times. The rotation of the drive motor in turn rotates the ball screw. And the ball screw drives the linear axis (slide). A feedback device (linear scale) on the slide allows the control to confirm that the commanded number of rotations has taken place. How axis motion is commanded - understanding coordinate systems All CNC controls allow axis motion to be commanded utilizing some form of coordinate system, (rectangular coordinate system