Research On Technologies Of Offset And Sweep Based On Discrete Data

Offset and sweep are common technique of CAD/CAM. Offset often used in computing NC milling path, moving path planning of robotics and so on. Sweep applied to solid modeling, collision detection, NC machining simulation and verification. In general, sweep also contains extrude and loft. As quickly and efficient modeling methods, offset and sweep play an important role in CAD modeling software for rapid prototyping. Combing the actual situation of discrete modeling in RP, we research sweeping method and applied the self-intersection handling method to the self-intersection in swept surface, the main contents of this paper are as follows:(1) Because of the discrete characteristic of RP data, we use coordinate transformation and projection to construct sweep surface, and the accumulation of chord length parameterization approach is used to resample the trajectory curve. We discussed the methods of extrude and loft, and used B-spline to fitting the profile curves of loft surface. Finally, this paper discuss the factors that influence the precision of sweep surface by contrast model.(2) Curve offsetting methods in R2, self-intersection detecting and handling approach were researched due to the connection between offset and sweep. This paper proposed an outline extracting algorithm to remove self-intersection in offset curve, and applied it to the processing of self-intersection in sweep surface which based on 2D sketch.(3) Covering method for the opening in surface was proposed in this paper, so that the model data can be loaded into RP device.Based on the above analysis, we used VS 2008 as software platform, finished the feature development of sweep, extrude and loft based on discrete data, and applied them in the system for 3D printing. They achieved good results.