Research On Inverse Problem Of Parameterization Of 3D Assembly Model Of Body-in-White Fixture

The development cycle of traditional BIW(Body-in-White)fixture is no longer able to meet market demand with the acceleration of the development cycle of automotive research.In order to improve the efficiency and quality of BIW fixture design,this thesis takes the CAD model data of automotive welding fixtures as the research object,aiming to explore a new approach to establish parameterized 3D assembly models of BIW fixtures.Therefore,the concept of inverse problem of parameterization of 3D assembly models of BIW fixtures is proposed.The inverse problem of parameterization of 3D assembly model of BIW fixture refers to the case knowledge learning and knowledge acquisition from the 3D assembly model design case,which can extract the kinematics model from the 3D assembly model,automatically identify the types of BIW fixtures,and then identify the main design parameters of the typical 3D assembly model of BIW fixture.Thereby the parameterized assembly model of BIW fixture is constructed,summarizing and organizing the obtained design parameters according to the types of fixtures,and applying the design parameters that meet the design requirements to the parameterized template model of BIW fixtures.The main contents are as follows:The research of obtaining geometric information from the 3D assembly model of BIW fixtures,includes that the neutral files in STEP format converted from different CAD systems are used to identify and extract geometric information using the algorithm based on STEP standards.Not only can it improve the efficiency of information acquisition,but also it can also fully preserve the topology information of the 3D assembly model.The research of extracting the main design parameters of the 3D assembly model of BIW fixtures,includes that the main design parameters that need to be determined when designing different types of BIW fixtures is systematically studied.The main design parameters of fixture are extracted by automatic identification of fixture type through algorithm,and combining with fixture kinematics model and fixture clamping point position.The research of establishing parameterized 3D assembly models for automotive welding fixtures,includes that NX/WAVE technology is applied to establish parameterized template models for different types of fixtures.After clarifying the design requirements of the new task,reasonable values of design parameters are determined through algorithms.And then the design parameters are imported into the parameterized template model to achieve the establishment of parameterized 3D assembly models.The design time of 3D model is saved and the design accuracy is improved.A prototype design system for BIW fixtures is developed using C language on the MS Visual Studio development platform,running on NX software.The design system can determine design requirements from the fixture specification and process documents(master control position and master control section),input them into the system for retrieval and matching.As result,the automatic establishment of parameterized 3D assembly model is achieved.The inverse problem of parameterization of 3D assembly model of BIW fixture is a comprehensive application combining case model retrieval,model type identification,kinematics model extraction and parametric model construction.The correctness of solving algorithm for the inverse problem of parameterization of 3D assembly model is verified through the prototype design system.The system takes the design task of BIW fixtures as input and can output preliminary design of simple fixture units.The whole work proves the feasibility and accuracy of this study,which is a new theoretical attempt and practice for product design parameter modeling methods and design reuse.