網格縮減對逆向工程與快速原型間產品模型設計之研究

Mesh Reduction for Product Model Design in Reverse Engineering and Rapid Prototyping Process

逆向工程設計與快速原型技術，近年來已廣泛應用於產品開發與造形設計，一般在逆向工程為求得產品模型尺寸精確，對工件輪廓點群量取資料量均相當大，而造成由點群資料匯入快速原型機前，所轉出的標準STL三角網格檔，也相對的龐大，進而影響模型於快速原型機中成型速度。本研究即針對逆向工程與快速原型機所支援的STL三角網格檔進行縮減之研究，在不影響模型尺寸精度條件下，藉由搜尋整個STL參考網格與其包圍網格方式，依個數比例或差值比例法建立一套權重值法則來判斷執行刪減；網格經過縮減後，將可減少部分非必要的網格，達成STL三角網格的數量縮減與形狀平滑化的目標，而有利於縮短快速原型成型的時間，或在進行網路化產品設計與製造時，縮短檔案傳輸的時間。 本文以自行發展的STL三角網格縮減程式，完成網格STL檔縮減，並以兩組不同的實例，說明網格縮減對不同產品模型的探討，以驗證經由本研究所得的網格縮減結果與產品原型相較，在產品精度要求範圍下，網格可適當縮減，而達到令人滿意的程度。本研究在逆向工程與快速原型產品開發上，具有相當的應用價值，並可提供產、學界相關領域應用的參考。

Reverse engineering design and rapid prototyping technology are widely used in today's product development and shape design. For higher dimensional accuracy in model construction, the point data must be scanned in a large amount for the reverse engineering process. This will cause the standard imported STL file to the rapid prototyping machine relatively large and complicated. This paper presents how to simplify the STL mesh in the reverse engineering and rapid prototyping process. First, the whole STL triangles are searched for finding all the reference triangular meshes and surrounding meshes in advanced. Secondly, either by percentage amount method or by deviation value method as the weighting factor can be set for reducing the surrounding meshes. After reducing the STL mesh file, some redundant mesh can be deleted and a smoother shape can be achieved. The main profits for this research are reducing the time for rapid prototyping machine forming and the time for STL file transferring for web design and manufacturing. By using the self developed STL triangular mesh reduction program in Visual Basic, STL file can be reduced according to the desired ratio. Two examples are introduced to examine the process of STL file reduction for the reverse engineering and rapid prototyping process. A good result can be reached after the mesh reduction. The results can be used both in industry and research field for reverse engineering and rapid prototyping.