Research On Feature-Based Automatic Dimensioning For 3D Part Models

At present,product design is in an important transition phase,which from the traditional two-dimensional processing to completely rely on three-dimensional processing.The 3D model has become the main carrier of part information expression.Model Based Definition designing method using integrated three-dimensional solid model to completly express product information and has been more and more widely used in the field of aerospace.As an important aspect of the model's digital definition of intelligence,three-dimensioning or three-dimensioning PMI means adding the model design,manufacturing and other information to the model.Three-dimensioning avoids the model frequently switching between 2D and 3D in the process of information transmission and improves the efficiency of information transmission.For this background,this paper studies automatic dimensioning for 3D part models.At present,domestic and foreign research on automatic dimensioning for 3D part models mainly has two methods: one based on the entity geometry model and the other based on the CSG tree.The shortcomings of the former is that there is a lot of redundancy,and the latter problem is that the feature basic body is destroyed,and the dimensioning facing the difficulty of rebuilding the basic body.In view of this situation,this paper presents a method for automatic dimensioning for 3D part models based on the geometric shape residual surface of shape feature.This method uses shape features as the labeling unit,and the dimensioning of the model is transformed to the dimensioning of the feature plane from both the shaping and the positioning dimensions aspects.On the one hand the problem of labeling redundancy is avoided,on the other hand the difficulty of rebuilding the basic body is avoided.At the same time,the efficiency of labeling is improved due to decentralized dimensioning.The topological relations between features and faces are analyzed,then the features are divided into isolated features and associated features.And different automatic dimensioning algorithms are given for different types of features.According to the characteristics of shape features,combined with TTRS theory,the model will be automatically dimensioned from both the shaping and the positioning dimensions aspects.Finally,according to the technical route of this article,based on UG platform,the prototype system of automatic dimensioning for 3d part models is developed.