Research On Identification Model And Non-destructive Modification Methodology For Design Defects Of Two Modular Spatial Docking Mechanisms

Space rendezvous and docking is an indispensable operation during the long-term on-orbit operation of spacecraft,it is a basic technology that need be mastered in manned spaceflight activities.Space docking mechanism is a system that can realize the on-orbit mechanical connection of spacecraft,establish the connection between spacecrafts,and ensure the safe separation of spacecrafts.Due to the advantages of long service life,low cost and high precision,modular space docking mechanisms(MSDM)are applied in various fields,such as on-orbit assembly services and satellite recovery and capture.Compared with traditional docking mechanisms,MSDM can perform operations such as on-orbit assembly,on-orbit replacement,function expansion and upgrade in complex working environment.It can not only provide supplies for target spacecraft,the payload space of the spacecraft can break through the limitations of the existing launch conditions,but also reduce the cost,improve the efficiency and prolong the service life.Since the MSDM were proposed,MSDM with various configurations have been designed and manufactured,the expected functions have been realized.However,MSDM have not been widely used in the aerospace field,MSDM are still at a great disadvantage compared with the traditional docking mechanisms.Although the docking accuracy and other working performances of MSDM have surpassed that of traditional docking mechanisms,the survivability and reliability of MSDM are far inferior to the traditional docking mechanism in the complex space environment.The reason for above phenomenon is that in the design stage of MSDM,it often focuses on the research of one of the performance,while other potential design defects are ignored,many designs are proposed based on idealized models,lack of a large number of design verification,there are great differences between idealized models and actual products.Systematic researches on the identification model and modification method for design defects of MSDM have very important theoretical significance and practical value for improving the design rationality,use safety and operational reliability.The identification model and modification method of profile curve design defects,geometric characteristics design defects,kinematics accuracy design defects,assembly design defects and transmission reliability design defects of MSDM are studied deeply and systematically in this dissertation,the main contents and innovations of this dissertation are summarized as follows:(1)Based on the semi-space elastic contact theory,two kinds of complete elliptic integrals are introduced,an improved contact model with closed-loop elliptic contact surface characteristics is constructed.By analyzing the contact area with closed-loop ellipse characteristics,the dynamic relationship of the docking contact position is obtained.The instantaneous kinematic relationship corresponding to the dynamic contact force is extracted,the geometric relationship between the docking joint and the docking cone surface is obtained.Minimization the dynamic contact stress between the docking joint and the docking cone surface is chosen as the optimization objective,a minimal contact stress modification method based on the genetic algorithm for profile curve design defect of the docking joint is proposed,the profile curve design defect of the docking joint is modified,the optimal profile curve of the docking joint and the optimal contact point on the docking cone surface are also obtained.(2)Considering the roughness of the docking contact surface and other factors,based on the elastoplastic fractal theory,an ellipsoid elasto-plastic contact model is established,the spherical contact coefficientξ_bis defined by introducing fractal parameters,the dynamic contact characteristics between the docking joint and the docking cone surface are analyzed by using the spherical diameter density distribution function and the elastic-plastic contact mechanics model.Minimization the dynamic contact stress between the docking joint and the docking cone surface is chosen as the optimization objective,the geometric parameter(radius of curvature)at the contact point is selected as design variable,the modification model of the profile curve of the beam-spring-cone docking mechanism is established.Genetic algorithm is used to obtain the geometric parameters of the profile that minimize the contact stress between the docking joint and the docking cone surface,namely,the optimal size of the docking joint and the optimal docking position on the docking cone surface.The elastoplastic characteristics of the three-dimensional topography of the docking contact surface are analyzed,complex relationships between the profile curve,the contact load and the fractal parameters(fractal dimension,friction coefficient,material parameters and roughness amplitude)are studied.(3)The profile curve of cam curve groove mechanism is fitted by using the surface family envelope theory,based on the fitted initial profile curve,the conjugate contact relationship between the follower and the cam curve groove is analyzed,the geometric characteristics(pressure angle and principal curvature)model of the cam curve groove mechanism is established.Based on the geometric characteristics model,two independent identification criterias for the geometric characteristics design defects(curvature interference and unreasonable pressure angle)are proposed.According to the identification criterias,the mapping relationship between geometric characteristic space and defect type space is obtained,the correctness of the above geometric characteristic model and identification algorithm are validated by finite element simulation.A modification model of the geometric characteristics design defects of the cam curve groove mechanism is established based on smoothing algorithm,the profile pitch curve at the corner of the cam curve groove is smoothed,the geometric characteristics design defects of the cam curve groove mechanism,such as curvature interference,are modified.(4)Based on the linear contact theory,the meshing transmission model of the hyperbolic cam transmission mechanism is established,the meshing contact temperature field model between the follower and the curved groove is established based on Blok flash temperature theory,the friction and wear characteristic models of the hyperbolic cam transmission mechanism are obtained.The roller and roller pin in the follower are considered as research object,the meshing contact temperature field of the roller and roller pin in the curved groove is obtained by numerical simulation.Based on the meshing contact temperature field,the friction and wear characteristics of the hyperbolic cam mechanism under the initial assembly condition are studied.The minimum wear rate between the roller pin and the curve groove is chosen as the objective function,the assembly relationship parameters between the follower and the curved groove are selected as design variables,the optimal assembly relationship that can ensure the transmission stability and the service life of the cam mechanism is obtained by genetic algorithm,the assembly relationship design defect between the roller,the roller pin and the curved groove is modified.(5)Based on the geometric characteristics of the cam curve groove mechanism,the kinematic characteristic equation is established.Based on the kinematic model of cam curve groove mechanism,the kinematic accuracy mapping relationship of the cam curve groove mechanism and the motion error model of each output parameter are obtained.According to the design index of the cam curve groove,the identification criterion of kinematic accuracy design defect for cam curve groove mechanism is proposed.Considering the characteristic factors,such as roller movement,cam curve groove shape and follower size,the defect characteristic model is established.Through the sensitivity analysis,the design parameters that have great influence on kinematic accuracy are obtained.According to the basic geometric constraints between these design parameters,the motion output errors of the cam curve groove mechanism are obtained.Genetic algorithm is used to search the optimal solution in the evolution graph of design parameter solution,de-characterization modification of kinematic accuracy design defect for the low impact docking mechanisms is implemented.(6)Based on the line contact deformation model,the meshing dynamic contact model of the gear/rack with large transmission ratio is established.The meshing temperature field model of the gear/rack in the transmission process is established by Blok flash temperature theory,thin film lubrication model,heat dissipation and heat conduction analysis method.The width of the broken line is determined by introducing the stress permeability coefficient,a neovel broken line section model is established based on the broken line width of the tooth surface and the strength characteristics of the dangerous section of the gear tooh are analyzed.According to the dynamic stress data series of the tooth root,the transmission reliability model and reliability degradation probability model of the gear/rack mechanism with large transmission ratio are obtained by combining the maximum entropy method with the similarity method.According to the reliability design index of gear transmission mechanism,the identification criterion of the transmission reliability design defect of gear/rack with large transmission ratio is established.The minimum reliability degradation probability is chosen as the objective function,the structural parameters of the gear and the rack are selected as design variables,the modification model for transmission reliability design defect of the gear/rack mechanism with large transmission ratio is established.The optimal structural parameters are obtained by genetic algorithm,Non-destructive modification of the transmission reliability design defect of the gear/rack mechanism with large transmission ratio is implemented.Identification model and non-destructive modification methodology for design defects of two MSDMs are studied deeply and systematically in this dissertation,research results in this dissertation improve the design rationality,use safety and operation reliability of MSDMs,the design cost of MSDM is reduced,design automation technology proficiency of MSDM is improved,design quality and design efficiency of MSDMs are also ensured.Above research works provide feasible theory,effective method and useful technology support for engineering application of MSDMs.