Unit 4 CAD and Applications.pptVIP

Unit 4 CAD and Applications 粤节割玲废锚默帚地扎藐述隅伍颂翟范梳恬动教瓢姆晕赂工绕滑松烫厕板Unit 4 CAD and ApplicationsUnit 4 CAD and Applications * Unit 4 CAD and Applications Before we present the basics of CAD, it is appropriate to give a brief history. CAD is a product of the computer era. It originated from early computer graphic systems to the development of interactive computer graphics. Such two systems include the Sage Project at the Massachusetts Institute of Technology (MIT) and Sketchpad. The Sage Project was aimed at developing CRT displays and operating systems. Sketchpad was developed under the Sage Project. A CRT display and light pen input were used to interact with the system. This coincidentally happened at about the same time that NC and APT (Automatically Programmed Tool) first appeared[1]. 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[2]. 靳约潞谆梨龋肝擂液忌公侦赵缀点赤嘛姓节安壶闰瞎源抱褥阶梅矮诀烩躲Unit 4 CAD and ApplicationsUnit 4 CAD and Applications * Unit 4 CAD and Applications 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 Coons patch, Beziers patch, and B-spline, enables a CAD system to be used for sophisticated curves and surface design. Three-dimensional CAD systems allow 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. 束颇署椒涵督莽班砷骇臣津阶频邯诱析格艘挪兔糯莱矽赤谎俩让倾豹猾桩Unit 4 CAD and ApplicationsUnit 4 CAD and Applications * Unit 4 CAD and Ap