Rationality Verification Method Of Datum System Of Geometric Tolerance Based On Ontology

The datum system plays an important role in the assembly and measurement of the actual parts.In the existing computer-aided tolerance design,3D tolerance dimensioning depends on the correct establishment of the datum system.However,at present,the information of datum system is manually designated by designers on the basis of experience,and it is inevitable that the selection of the datum system and the design intention are in contradiction with the design intention.In order to reduce the uncertainty datum selection in tolerance design,it is urgent to verify the rationality of geometric tolerance datum system.This paper draws on the latest achievements of artificial intelligence,and the rationality verification of datum system geometric tolerance is studied by combining computer ontology technology with mathematics calculation method.The main research contents are as follows:A freedom representation model of geometric tolerances is proposed.Based on the theory of degree-of-freedom analysis,the constraint requirements of degrees of freedom for geometric elements under different tolerance indexes are studied,and the principle of establishing local spatial coordinate system is given for the uncertainty of geometric feature types.In this paper,the expression of degrees of freedom for different geometric elements in local spatial coordinate system is established.The rationality verification algorithm of the datum system is established.Based on the existing criterion of datum sequence and the principle of establishing datum system,the validity,redundancy and completeness discrimination of datum are studied based on the existing mathematical methods and the combination of degree of freedom analysis and boolean algebra.The algorithm of verifying the rationality of the datum system and the corresponding expression are constructed.The rationality ontology and reasoning rules of datum system are constructed.In order to improve the reasoning efficiency of tolerance information,the corresponding hierarchical tolerance information model is established,which can be used to represent the tolerance information used in the rationality verification of datum system.The rationality ontology of datum system is constructed by using the established model,which represents the structure and relationship of product geometry information.In the ontology,the reasoning rules based on the rationality verification algorithm of the datum system are defined to describe the knowledge and experience in the verification process.The prototype system is developed to verify the rationality of the datum system.On the basis of the above-mentioned research results,aiming at the engineering example in ASME,the rationality verification algorithm of datum system is transformed into rule base by taking the geometric tolerance information as input.And combined with the visual interface,a software prototype is developed to verify the rationality of the datum system.