Research On Methods Of Design Feature Boundary Segmentation For STEP Solid Models

The feature-based modeling method can express the design intent of products better,and can modify and redesign the model more conveniently,which is a mainstream modeling method in current commercial CAD software.As each CAD system has its own data format,different software systems can only exchange low-level geometric information.As a result,the feature information and design intent of the product model are lost.The exchanged model is difficult to be edited and redesigned,which is often called as the “freezed model”.Design feature recognition is a process of identifying design features from the solid boundary model of mechanical parts.Design feature boundary segmentation is the basis of design feature reconstruction and has important research value.In this paper,the representation of the solid model,the STEP standard and the feature-based design are studied in depth.The design rules of the fillet feature and the modeling process of feature modeling are analyzed deeply.In view of the model with fillet features,this paper proposes a method of segmenting design feature boundaries using Boolean segmentation loops.This method extracts the geometric information from STEP neutral files at first,and constructs the STEP solid boundary model using the extracted geometric information.Based on the reconstructed boundary representation,the geometrical shape of the fillet surface is identified,and the design intent of the general fillet features is captured.Furthermore,the fillet features and their modeling order are identified.A directed graph is used to describe the relationship between blend features,and a linear sequence of blend features is obtained by topologically sorting the directed graph.Finally,the feature vertex adjacent graph of the model is constructed,and a method of searching the Boolean segmentation loop node tree is used to identify and construct the Boolean segmentation loop.The face adjacency attribute graph of the model is constructed and decomposed into multiple connected subgraphs using the Boolean segmentation loop to obtain the design feature boundaries.The algorithm proposed in this paper has been implemented in Visual Studio C++ 2008 and JhSolid platform.JhSolid is a 3D modeling software with OpenGL as the display engine.Examples are given to verify the validity and feasibility of the algorithm.This research lays the foundation for subsequent design feature reconstruction.