Research On The Accuracy Model Of 3D Mechanical Assembly System And Its Application In Gearbox

Assembly accuracy is an important guarantee for the performance of mechanical products,which runs through all aspects of structural design,assembly design and process design.Based on the analysis and research of error modeling methods,error accumulation and transfer mechanism and tolerance optimization methods of assembly systems at home and abroad,based on the geometric physical properties of geometric error formation and transmission,the error modeling method of the geometrical features of the parts under rigid body conditions and small deformation conditions was analyzed.Based on this,the tolerance decoupling model is further proposed,which establishes a bridge between product performance analysis and error analysis;assembly accuracy prediction and product performance and tolerance optimization can be realized in the product design stage.The main research work is as follows:(1)Three-dimensional tolerance analysis and assembly accuracy calculationAiming at the shortcomings of the coordinate system in the traditional tolerance analysis model,a new coordinate system with error tracking function along the dimension chain is established,and a three-dimensional tolerance analysis model of recursive form is formed.Based on the differential transformation principle of rigid body kinematics,a linear general assembly accuracy model of ‘nominal pose + error parameter' is established,and the explicit expression of small displacement torsor is realized.(2)Analysis of assembly precision of small deformation of flexible bodyFor the assembly system with small deformation,the accuracy model of integrated error and deformation based on tolerance analysis and mechanical analysis is proposed.Mechanical analysis of the assembly system with ideal geometric state was performed and the deformation of each tolerance feature(Tolerance Feature,TF,the same below)was obtained;the TF was discretized along the dimension chain,and based on the principle of quadratic differential transformation,the error and deformation at each node coordinate system were accurately integrated.A linearized comprehensive error analysis model was formed.(3)Analysis of factors affecting the decoupling and deviation of tolerance characteristicsTaking a wide range of shaft-hole fit as the research object,the attitude decoupling model and the limit error convex hull model based on the axis tolerance feature of the area coordinate system are proposed.Through the vertices of the convex hull,the limit error of the target feature in multiple degrees of freedom can be obtained intuitively and conveniently;an analytical model is established between the tolerances of the convex hull and the dimensional chain,which can directly trace the limit error.The theoretical basis for the analysis of mechanical product performance under various error conditions from the geometry angle was found.(4)Analysis of meshing characteristics and sensitivity of gearbox based on assembly accuracyAssembly accuracy is one of the most important factors affecting the meshing characteristics of the gearbox.The accuracy model of gear assembly system considering factors such as box tolerance,bearing clearance and gear shaft deformation and Tooth Contact Analysis(TCA,the same below)model considering assembly error were established.The influence of the above error source on the assembly error of the gear system and the meshing characteristics of the helical gear was studied.The global sensitivity analysis was also carried out,which laid the foundation for the design tolerance of the gearbox,the selection of the clearance and the control of the assembly error.(5)Tolerance interval optimization based on product performanceBased on the interval attribute of tolerance,a general model of tolerance interval optimization based on product performance is proposed and applied to the tolerance optimization based on the meshing characteristics of gearbox gears.Taking the product of the tolerance variation coefficient as the objective function and the RPDI level of the gear contact trajectory deviation as the constraint function,the uncertainty nonlinear optimization problem of the tolerance interval is transformed into the deterministic optimization problem;the tolerance interval optimization solution model based on the genetic algorithm is constructed.By optimizing the tolerance and clearance value,the assembly error of the gear system can be controlled to effectively adjust the contact trajectory and improve the meshing characteristics of the gear.