| A large number of 3D CAD models have been accumulated in the long-term design activities with CAD technology.How to excavate the value of the existing CAD model and reuse them has become realistic demand.In this paper,the retrieval technology of 3D assembly model is researched by using the constraint and fit information among parts.According to the mapping between the assembly constraints and the kinematic relations among the parts in the assembly,the assembly is expressed as adjacency graph of kinematic relations.Then the paper uses improved VF2 algorithm to search the maximum common subgraph between two kinematics relations adjacency graphs.and obtains corresponding relations of the parts in the similar substructures of two assembly.The number of parts pairs in the similar substructure is considered as the topological similarity between two assemblies.Points sample is carried out on the surface of all parts of the assembly,and the distance between any two points on the surface of same parts is calculated to generate the histogram of part shape distribution.The histogram distance of shape distribution of all parts with corresponding relationship is calculated and summed,which is normalized as part shape dissimilarity.The coordinates of the center points of the parts bounding box in the assembly coordinate system are gotten and normalized,and the distances of the center points between all corresponding parts are calculated and summed as the dissimilarity of the assembly parts spatial distribution.Finally,the dissimilarity of assembly constraint is calculated according to different assembly constraint.Considering the topological structure similarity of the assembly,the shape of the parts dissimilarity in the assembly,the spatial distribution dissimilarity of the parts in the assembly and the assembly constraints dissimilarity,the retrieval of the assembly model is realized.In order to realize retrieval based on assembly interface,part models in assembly are expressed as attribute adjacency graphs in this paper.The type of face is assigned to node,the angle between faces is assigned to real edge between nodes,and redundant edge is added to record the distance and angle between faces that meet certain conditions.Then DFS algorithm is used to solve the subgraph isomorphism problem to query the assembly which has assembly relation with the selected assembly interface,and a series of pruning algorithms are used to improve the efficiency of the algorithm.Experiments show that the proposed algorithms has high accuracy and can meet the needs of assembly model retrieval in many applications. |
