Research And Implementation Of 3D Dimension Completeness Testing Technology Based On MBD

MBD(Model Based Definition)realizes the full three-dimensional digital expression of product design,and the labeling information(such as dimensions)was annotated on the three-dimensional geometric model of product.The integrated expression brings two difficulties to the design of dimension scheme:(1)It is difficult to design the three-dimensional dimension completely;(2)It is time-consuming to examine the results of dimension scheme manually.It is very important to realize the automatic testing of dimension scheme in 3D model.Therefore,this thesis studies the 3D dimensions completeness testing technology,which can automatically check the missing dimensions and the redundant dimensions of the part model.Firstly,according to the geometric information of MBD model,the characteristics of common dimensions and TTRS(Technologically and Topologically Related Surfaces)theory,the dimension completeness testing is transformed into the fixed states determination of the relevant geometric elements,and a constraint model of these elements is established to record the constraint state.A dimension constraint information model is established to express the constraint information,and constraint propagation rules are built to solve the dimension constraints and topological constraints,according to the propagation of geometric constraint.Secondly,the analytical algorithm of geometric constraints is summarized based on propagation rules.In order to solve the under-constraint problems caused by missing dimensions,a method of computing weighted value is adopted,the constraint is added actively by specifying the datum or pointing out the missing dimension.And a method is summarized to discriminate redundant dimensions based on constrainted states of elements.On the basis of the above,the whole algorithm of 3D dimensions completeness inspection is proposed.Finally,by applying the secondary development for UG NX8.5 based on Visual Studio 2010 platform,a dimensions completeness testing function is realized,and its validity and applicability is verified by different examples.