| The vehicle-borne radar actuating system was assembled by many parts.The accumulation of assembly characteristic errors directly affect the position and attitude accuracy of the vehicle-borne radar antenna surface,thus affecting the performance of the radar.Traditional tolerance analysis and design was based on two-dimensional dimensional chain,which is difficult to effectively express the coupling relationship between tolerances and the posture requirements of the mechanism end parts.By describing the change of assembly features in three-dimensional space,the tolerance coupling relationship which cannot be expressed by two-dimensional dimension chains can be introduced into the mechanism assembly error transfer model,so that the analysis results of assembly error were more intuitive and accurate.In this dissertation,the lifting mechanism of vehicle-borne radar was taken as the research object.Aiming at the analysis and optimization of assembly accuracy,the error transfer law of its assembly characteristics was studied based on three-dimensional tolerance.The main contents of this dissertation could be summarized as follows:(1)The requirement of assembly accuracy was analyzed combined with the structural characteristics of the vehicle-borne radar lifting mechanism.Small displacement torsors method was used to describe the error variation of geometric element.According to tolerance coupling situations of common geometric elements,the corresponding error variation inequality were established.Assembly relation of vehicle-borne radar lifting mechanism was described by modified assembly oriented graph.Joint surface was divided into parallel connection and series connection and the solving method of the actual error transfer properties of parallel joint surfaces was proposed.The assembly error transfer model of the vehicle-borne radar lifting mechanism was established by the homogeneous transformation matrix.(2)The definition and related concepts of assembly accuracy reliability were studied based on the reliability theory of mechanical precision.The Monte Carlo method is adopted to calculate the reliability.According to the accuracy requirements of vehicle-borne radar lifting mechanism,the tolerance optimization of the parts was implemented,with assembly accuracy reliability,processing capacity,and assemblability of parallel joint surfaces as constraint conditions and lowest cost as the goal.The optimization model was solved using genetic algorithm where fitness function was established combining reliability with total cost.The VisVSA software was used to verify the optimization model substituting the optimized tolerance scheme.The assembly error accumulation process of the vehicle-borne radar lifting mechanism was studied to obtain the key assembly process,and the assembly parameter adjustment method was proposed.(3)The function of assembly precision analysis system of vehicle-borne radar lifting mechanism was designed.The software and hardware development environment of the system was introduced,and the technical structure and function module of the system were established.The function modules were developed based on the method of assembly error model and tolerance optimization.The applicability of the analysis system was verified through assembly analysis of the vehicle-borne radar lifting mechanism.In this dissertation,in light of the structural characteristics of vehicle-borne radar lifting mechanism,assembly error model was established and the assembly accuracy were quantitatively evaluated by assembly accuracy reliability.The tolerance of parts were optimized and the assembly accuracy analysis system was developed to improve assembly accuracy at the design stage.The theoretical research and technological development work in this dissertation can provide effective methods and tools for assembly accuracy analysis and optimization of similar mechanical products. |
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