机械类专业英语教学课件作者韩林烨关雄飞Unit9课件.pptVIP

Unit 9 A Brief History of CAD/CAM CAD is a product of the computer era. It originated from early computer graphic systems to the development of interactive computer graphics. A CRT display and light pen input were used interact with the system. This coincidentally happened at about the same time that NC and APT (automatically Programmed Tool) first appeared. Later, X-Y plotters were used as the standard hard-copy output device for computer graphics. An interesting note is that an X-Y plotter has the same basic structure as a NC drilling machine except that a pen is substituted for the tool on NC spindle. In the beginning, CAD systems were no more than graphics editor with some built-in design symbols. The geometry available to the user was limited to lines, circular arcs, and the combination of the two. The development of free-form curves and surfaces, such as Coon’s patch, Bezier’s patch, and B-spline, enables a CAD system to be used for sophisticated curves and surfaces design. Three-dimensional CAD system allows a designer to move into the third dimension. Because a three-dimensional model contains enough information for NC cutter-path programming, the linkage between CAD and NC can be developed. So called turnkey CAD/CAM systems were developed based on this concept and became popular in the 1970s and 1980s. The 1970s marked the beginning of a era in CAD-——the invention of three-dimensional solid modeling. Solid models contain complete information; therefore, not only can they be used to produce engineering drawing, but engineering analysis can be performed on the same model as well. Later, many commercial systems and research systems were developed Quite a few of these systems were based on the PADL and BUILD systems. Although they were powerful in representation, many deficiencies still exist. It was not until the mid-1980s that solid models made their way into the design environment. Today, their use is as common as drafting and wire-frame model applicat