| Three dimensional printing stacks materials to complete forming by different methods based on discrete and stacking principle. With this technique, people can print complex parts which are difficult to be manufactured by traditional processing. But also as a result of accumulation layer-by-layer, a layer of material must be supported by its lower material. Therefore, overhangs require a disposable support structure to be printed. The design of support structure is a key technique in three dimensional printing technology, according to the characteristics of three dimensional printing, some studies about efficient support structure are proposed. The contents of this paper are as follows:(1) Due to the large volume and materials’ cost of straight and oblique vertical support structure, a projected support structure is proposed. First, the critical angle of printing materials is obtained through experiments, then supporting regions are got by merging common edge triangles. Finally we obtain support lines by sweeping and generate vertical support planes based on the support lines.(2) For large volume of straight and oblique vertical support structure, support lines remained after removing projected support structure, an automatic generation algorithm is proposed based on critical angle constraint. Firstly, the algorithm detects areas that required support. Secondly, support points are obtained by adaptive sampling based on the area. Then, the algorithm constructs node structures and combines all nodes information in a tree. Through critical angle constraint, the nodes in branching support structures are calculated. Finally, the resulting structure is obtained by the sweep surface after possion reconstruction.(3) For branching structure sometimes is unreliable, a bridge support structure based on enumeration and score is proposed. The first step of our approach is to determine a set of points that require support by slicing the model without any support. Then possible bridges are enumerated by sweeping a vertical plane along a fixed direction in the XY-plane. We connect the bridges and model with pillars. Finally we use a simple Boolean operation to transformed the bridges and pillars into a whole.The approaches based on VS2008 and Open GL software platform in this paper, and the test results are satisfactory. |
