The Research On The Offsetting For 2D-compound Curves

The offsetting technology of 2D-compound curve is a basic problem in CAD/CAM,and has been widely studied in tool path generation for pocket machining.Currently,the most widely used offsetting method for closed 2D-compound curve is pair-wise offsetting method,the disadvantage of this type of methods is that they can not deal with closed 2D-compound curves with islands very well,and the efficiency is expected to be improved.So it is urgent and meaningful to find ways to improve the efficiency and applicability for the current offsetting methods.After a deep research into Choi&Park pair-wise offsetting method,this thesis aims at finding an effective offsetting approach which can deal with closed 2D-compound curves with islands.A new offsetting approach for closed 2D-compound curves with islands is proposed,in which the outloop and islands are treated as independent objects. Firstly,local interfering ranges of the outloop and islands are detected and deleted respectively to obtain the raw valid curve;Secondly,interfering concave vertices are detected and global interfering pairs are determined by applying a gridding approach;Thirdly,all global interfering ranges are detected by invoking a modified Choi&Park pair-wise interfering detection procedure,and global interfering ranges belonging to outloop and islands are deleted respectively;Lastly,the final valid offset curve is obtained by offsetting the remained parts of the raw valid curve.The proposed offsetting approach for closed 2D-compound curves with islands has the following characteristics:First,the outloop and islands are treated as independent objects,realizing the objective of dealing with closed 2D-compound curves with islands,therefore the applicability of offsetting method is improved;Second,a gridding approach is proposed and is applied in the detection of global interfering ranges,the offsetting of global interfering ranges and the dispersion of arcs in the raw offset curve are avoided,reducing the amount of calculation,thus the efficiency of offsetting method is improved.At Last,the proposed offsetting approach for closed 2D-compound curves with islands has been realized with Visual C++6.0 and has been tested with various examples,the results show that the proposed offsetting approach is effective and robust.