Research On Dynamics And Experiment Of Gear Mechanism Of Spacecraft With Multiple Clearances Coupled

With the development of aerospace engineering and high precision mechanical engineering, there are more and more requirements for mechanism kinematic accuracy, operational stability, reliability and service life. Thus, researchers have come to pay more attention to the influence of clearance in mechanism on the nonlinear dynamic characteristics of the system, especially for mechanism with complex multiple clearances. In microgravity space environment, the influence of the clearence on kinematic accuracy and stability is particularlly evident. The gear is one of the most popular driving mechanisms in spacecraft and there exist the coulping effects between radial clearance and backlash on the dynamic characteristics of gear-rotor system. This paper is dedicated to dynamic modeling, analysis and experimental investigations on the coupling problem in gear mechanism to lay the foundation of the optimization and reliability analysis of multiple clearance mechanism.For multiple clearances mechanism, the dynamic modeling starts with a single pair of gears, and then extended progressively to the planetary gear and the two-axis driving mechanism of satellite antenna. A new method for dynamic modeling of gear-rotor system considering the coupling of multiple clearances is proposed, making the coupling model withmultiple clearences, describing the bearing radial clearance with a two state model and characterizing the dynamic changes of the backlash in circular tooth by the radial clearance function. Furthermore, the dynamic model of gear-rotor system is provided, which contains the radial clearance, the tooth side clearance and variable meshing stiffness. Besides, the dynamic models of planetary gear transmission system with clearance and the two-axis satellite antenna driving mechanism are established, laying the foundation of theoratical research and engineering application of multiple clearances mechanism.In the aspect of experimental study of multiple clearances mechanism, the test bench of gear-rotor system with multiple clearances has been established, and the radical clearence and bakclash in circular tooth are simultaneously considered for the first time, the values are adjustable. With the measurement of vibration performance, the correctness of multiple clearances model can be verified by comparative analysis between the theoretical values and the experimental data for different velocities and clearances. Meanwhile, both of the It provides new ideas of experimental study of multiple clearances mechanism.For the analysis of dynamic characteristics, the differences between models of multiple clearances with and without coupling have been analyzed. Factors, including the velocity and clearence size, are also analyzed step further. The results show that with the influence of coupling of multiple clearances, the revolving speed andclearance size have an obviously effect on the dynamic characteristic of the gear- rotor system. With the increase of revolving speed, the radial runout weakens gradually, while the impact on tooth surface increases. However, the increase of radial clearances leads to the increment of the radial and angle error of the system which reduces the system stability. With the increase of the initial backlash angle error of gear, angle error of gear and amplitude of gear meshing force both increase, and the gear of reverse rotation is more intense. Through the analysis of the spectrum, rotation speed and clearance dimension that may lead to system resonance are found, which provides guidance for improving the operation stability and reliability of the gear system.The results of dynamics characteristics study of planetary gear with multiple clearances indicate that the effects of multiple clearances not only lead to movement deviation of system, increase of the dynamic meshing force and the abrasion between planetary gear and inner ring gear tooth surface, but also give rise to coupled vibrations between the internal components between the system structure. Additionally, there exist obvious influences that rotational speed, clearance size and inertia load to dynamics characteristics. In case of high speed rotation, the larger radial bearing force and engaging force fluctuate wildly. Influences of system dynamics characteristics caused by the clearances size between planet carrier and planetary gear are the most obvious. Bearing radial contact force between planet carrier and planetary gear increases obviously in the condition of larger clearances. Larger load is conducive to stability of the system. Rotation speeds and size of clearances leading to resonance can be found through spectrum analysis. So the location of resonance should be avoided in designing and use process.According to the influence of coulping effects on the movement accuracy and stabilities of the two-axis driving mechanism of satellite antenna, it is apparent that a lower speed should be selected for pitch axis rotating in the process of single shaft rotation. However the rotational speed can be improved appropriately for azimuth axis. But in double shaft rotation, the movement precision and stability of the system reach the best when the speed is 0.98°/s. The larger joint force in azimuth rotation is easy to cause abrasion and fatigue. The clearance size of the azimuth and pitch axes that may lead to resonance phenomenon are found through spectrum analysis. In order to make a proper selection of clearance size, the analysis data in this paper can be referred to in designing the two-axis driving mechanism.