Dynamic Analysis And Experimental Research Of Transmission Joint In Spacecraft With Multi-contact State Fusion

The high-precision and high-reliability transmission mechanism is the fundamental hardware guarantee for supporting spacecraft such as lunar rover,Mars rover,space manipulator and asteroid probe to complete space missions.The dynamic performance of the transmission joint is the key to ensuring the accuracy of the transmission system.At special working conditions such as space microgravity,low speed,light load and solid lubrication,there is a strong coupling between different scales and types of clearances in the transmission joint on the geometric constraints,kinematic relations and force characteristics,causes the kinematic pair to be in a variety of contact states,which has a significant effect on the dynamics of the system.However,the influence mechanism of the change of the contact state in the joint caused by multi-clearance coupling on the dynamic performance of the system is unclear,and it is difficult to accurately describe and predict it.Therefore,carry out the research on the dynamics of the spacecraft transmission joint with the multi-contact state fusion,describe the dynamic behavior of the transmission mechanism under the change of the contact state of the kinematic pair,and reveal its influence mechanism,which has important theoretical guidance and practical engineering significance for the optimization design,failure prediction,and on-orbit maintenance of the spacecraft transmission mechanism.In response to the above problems,this paper takes planetary gear transmission joints as the research object,combining theoretical modeling,simulation analysis and experimental verification to carry out related research,mainly including the following:1.Aiming at the problem of modeling the contact force of typical kinematic pairs in multi-contact state,by studying the assumptions and theories of different contact models,the applicable scope and limitations of the existing contact models are analyzed.The switching conditions of different contact states are established by using the half-contact width parameter,a method for discriminating the transition of contact states is proposed,and the relationship between different contact force models is given.Through the fusion of the existing non-coordinated contact model and the conformal contact model,a contact model fusion method under multiple contact states is proposed,and based on the existing contact force model,a multi-contact state fusion contact model is established.In the aspect of planetary gear transmission joint modeling,the potential energy method is used to deduce the comprehensive meshing stiffness of gears considering multi-gap coupling,and a typical gear pair meshing model with multi-contact state fusion is established.Considering the factors such as various clearances,time-varying mesh stiffness,contact damping and tooth profile error in planetary gear joints,a dynamic model of planetary gear transmission joints with multi-contact state fusion is proposed.The change of comprehensive meshing stiffness of gear teeth caused by tooth tip chipping fault is described,and a nonlinear dynamic model of planetary gear transmission joint with fault characteristics is established.By introducing time scale and displacement scale,a system of differential equations with dimensionless parameters is established.2.For the analysis of the bearing contact characteristics in the planetary gear transmission joint,based on the model of planetary gear transmission joint with multi-contact state fusion established in this paper,the influence law of contact parameters and working condition parameters on the change degree of the contact state of the drive joint is characterized by defining the contact transition rate.The extreme values of the parameters of contact stiffness,load and rotational speed in the design of planetary gear transmission joints are given.The simulation results show that the dynamic parameters of the planetary gear drive joints have small fluctuations in the range of the medium contact stiffness of 1×10~5 N/mm～1×10~6 N/mm and the output speed of 6°/s,respectively.The transition frequency of the contact state is small,and it is easy to be in a single contact state,which is beneficial to the stability of the transmission joint.Under the light load range of 10 kg～100 kg,the collision excitation of each component in the joint and the bearing at the clearanc is more complicated and the collision is severe,which leads to the contact state of each component and the bearing prone to contact state transition,which is not dynamic in terms of dynamic characteristics.The number of regular mutations increases.The contact parameters and working condition value ranges given by the simulation can provide data support for the design optimization and life extension of the planetary gear transmission joint of the spacecraft.3.Aiming at the analysis of the meshing characteristics in the planetary gear transmission joint,the effects of different contact stiffness,load and rotation speed on the meshing characteristics of the internal gears in the joints with the multi-contact state fusion are discussed.The results show that the meshing of each gear in the planetary gear joint is relatively continuous and stable within the range of medium meshing stiffness5×10~5 N/mm～7.5×10~5 N/mm,and the transition rate of the contact state is small;The impact of the collision force coupling effect is small,and the joint operation stability is high;in the range of the output speed of the transmission joint from 6°/s to 9°/s,increasing the speed is beneficial to increase the anti-interference of the planetary gear transmission joint.On this basis,the influence of excitation frequency and clearanc size on the nonlinear dynamics of planetary gear transmission joints with healthy and faulty characteristics is compared and analyzed,and the excitation frequency range that causes joint chaos and bifurcation is given.The clearanc will cause the joint to enter chaotic motion earlier.The range of meshing parameters and working condition parameters given in this paper can provide data basis for the stable operation,fault identification and monitoring of the planetary gear transmission joint of the spacecraft.4.In terms of experimental research on planetary gear transmission joints,the experimental device of internal meshing gear pair and the experimental platform of planetary gear transmission joint with adjustable clearance have been developed respectively.Through spectrum analysis,the vibration characteristics of internal meshing gear pairs at different rotation speed and clearance combinations are studied.Then the vibration characteristics of the planetary gear transmission joint at different clearance combinations is analyzed.It also compared and analyzed the model of planetary gear transmission joint with multi-contact state fusion proposed in this paper and other clearance models.The results show that the calculation results of the model proposed in this paper are more consistent with the experimental results,and have better accuracy and effectiveness than other clearance models.