Research On Symmetry Detection For Product CAD Model

Symmetry of product CAD model can not only provide semantic information in the creative design process to facilitate the restructuring and matching parts,but also simplify the calculation and improve the accuracy in engineering analysis.Therefore,it is of great significance to identify the symmetry of product CAD model.In this dissertation,two kinds of symmetry identification methods are studied for IGES format model and feature model.In the study of the symmetry recognition of IGES format model,this dissertation firstly calculates loops property of the model and identifies the matching loops.And then the axes and planes of symmetry are constructed according to the matching loops.Finally,this dissertation merge the planes and the axes of symmetry and calculate the cumulative number,the cumulative loop area,perimeter of each element which called cumulative weight.The planes of symmetry of the larger weight which are compared with the value of the rotation axes are intersected to get the principle axis.In the research of the identification of the feature model,this dissertation traverses the feature design tree of the part model and identifies the features contained in it.In order to improve the efficiency of symmetric merging,the feature sets are sorted firstly,and then the symmetry merging rules for feature sets are used,so as to realize the self identification to obtain the parts of symmetry,which contains the rotation axis of symmetry and the reflection plane of symmetry.In the study of the symmetry detection of the feature assembly model,this dissertation traverses the feature design tree of the assembly model to identifies and classifies the parts included.And then the part sets are sorted according to their number,and those sets which contained fewer parts are merged symmetry.According to the center of mass of the part and the data of the bounding box,the rotation,reflection and translational symmetry of the parts are identified in the inner of sets.Then the global symmetry of an assembly model could be derived after the symmetry merging inside and among the part sets.The inside symmetry merging task use the rules of symmetry elements merging.And the outside symmetry merging task relies on part sets voting.The dissertation uses the C++ language and the SolidWorks function library to realize the program and generate the plug-in.The plug-in to identify the symmetry of feature part model can recognize and classify the features,sort the feature sets and merge symmetry for feature sets.And the plug-in to identify the symmetry of feature assembly model can recognize and classify the parts,sort the part sets and analyze symmetry.And the plug-in to identify the symmetry of IGES format model can calculate the loops property,identify the matching loops,construct the plane and the axis of symmetry,merge symmetry of the elements,extract the principle axis of the model.The experimental results show that the proposed method can quickly and accurately identify intra-part symmetry,the inter-part symmetry and the global symmetry of the feature assembly model,and detect the reflection plane,the rotation axis of symmetry and the principle axis of the IGES format model.