Three Dimensional Assembly Retrieval Method Based On Spatial Connection Skeleton

With the development of computer aided design(CAD)technology in the field of mechanical design,a large number of CAD models have been developed in recent decades.These models contain a great deal of experience and knowledge from designers,and have important reference value.In the process of digital product design,it is important to obtain and effectively utilize the model with reference value for improving design efficiency and optimizing product design.However,as the product model base continues to expand the scale,increase the difficulty of finding a suitable model How to accurately represent existing model information and design requirements and obtain the required design resources has become a major difficulty for designers in the process of design reuse.Product model retrieval is an effective solution to obtain related products,through the retrieval of existing product model and constantly explore the related products in order to obtain design knowledge and experience Products in the field of mechanical design model is mostly based on the assembly form,assembly as the combination parts of the shape information includes not only the parts,also has the coordination relationship and spatial structural relations between parts of the information.Therefore,it has higher design reuse value for assembly medical record.This paper from the assembly space connection and shape information point of view,to construct the assembly of generalized shape descriptor,realize the assembly of global / local similarity calculation,multi-scale support assembly retrieval The main contents of this paper are as follows:1)A generalized shape descriptor based on space connected skeleton is proposed.Firstly,the assembly space expression of parts information of spatial structure in spatial connected skeleton;and then define the concept of generalized shape distance in framework based on the generalized shape function,finally construct the assembly descriptor.The descriptor expresses the spatial relation and shape information of the assembly in a unified way to support the analysis of the similarity of the assembly.2)A method based on Optimal Subsequence Bijection(OSB)matching for assembly similarity analysis is proposed.Based on the generalized assembly shape descriptor,construct parts generalized shape sequence as the comparison unit;then calculate the matching coefficient of generalized shape sequence based on optimal subsequence algorithm of different assembly;finally,according to the matching coefficient optimization calculated by similarity evaluation of two assembly.The method according to the comprehensive connection and shape information of generalized shape descriptors,in part as a comparison object to complete analysis of similar overall assembly,to provide the theoretical basis for the assembly design reuse in the overall retrieval.3)A local structure similarity analysis method based on Ullmann subgraph isomorphism matching is proposed.According to the assembly descriptor construct the generic distance attribute adjacency graph(G-AAG)of assembly;and then used for GAAG pruning optimization algorithm of Ullmann to analyse the relationship between the subgraph isomorphism in G-AAG of assembly and target structure;finally,isomorphic subgraph similarity comparison method is used to calculate the similarity between assembly and target structure.The method provides a theoretical basis for the retrieval of local structure of assembly,and supports the local structural scale retrieval in structural reuse as the object for design reuse.4)The paper takes the common assembly in the mechanical field as object,and verifies the validity of the similarity analysis method proposed above.