Research On The Retrieval Method Of CAD Assembly Model In Standard Format

The wide application of CAD systems makes enterprises accumulate a large number of CAD product models.CAD model retrieval technology can promote model reuse and accelerate product design in enterprises.Product models are often saved in different formats and exchanged in standard format among different CAD systems.This paper studies a retrieval method for CAD assembly models in standard format which can be used to retrieve CAD assembly models in both standard format and various commercial formats.The assembly retrieval method based on the part model parameter vector is studied.Some parameters are directly extracted from the part model,and the part model parameter vector is constructed by normalizing these parameters.The parameter vectors corresponding to all parts in the assembly are combined to form a vector set as the assembly model descriptor.The Earth Mover's Distance and Modified Hausdorff distance algorithm are used to perform many-to-many matching and calculate the dissimilarity between assembly models respectively.The retrieval experiment proves that the retrieval method based on the part model parameter vector is effective and fast.The assembly information recognition for the CAD assembly model in standard format is studied.The clearance-based assembly relationships are identified by the geometric information at the bottom of the model and the redundant assembly relationships are filtered.The contact-based assembly relationships are identified by the API of Solid Works interference checking,and twenty kinds of assembly relationships are coded.Considering that gears are widely used in mechanical transmission,the method using the shape characteristics of gears to identify gears is studied,and further gear pairs can be identified.The degree of freedom information is derived from five common types of surfaces,the degrees of freedom between parts are reduced,and the final degrees of freedom of translation and rotation are obtained.The kinematic pair between parts is obtained through the mapping relationship between the degree of freedom and kinematic pair.Seven kinds of kinematic pairs are coded.Experiments show that assembly information and gear pair identification can be effectively performed.Combining parts model parameters and assembly information for assembly model retrieval is carried out.The attribute graph which is used as the descriptor of the assembly model is constructed by using the part model parameter vector and assembly information.MCSPLIT algorithm is used to solve the maximum common subgraph between the two attribute graph,and the similarity between assemblies is measured form multiple levels:kinematic pair,assembly relationship and shape.The studied method supports kinematic pair graph and specific models as input for retrieval.Experiments show that this method is fast and effective.