Research On Ultrasonic Motors With High Energy Conversion Efficiency For Spacecraft

With the continuous development of space technology,China's space exploration program has made great progress.China's lunar exploration project(CLEP)has successfully completed the in-situ detection and inspection of the lunar surface.The upcoming program for deep space exploration needs to accomplish sampling the extraterrestrial objects and safe returning.It also puts forward higher performance requirements on the ultrasonic motor(USM)system since it is the functional component for precision drive of the spacecraft.The USM mainly relies on the piezoelectric conversion and the friction transmission between the stator and the rotor to output torques and drive loads.The factors affecting the energy conversion efficiency and the output performance of USMs include friction materials,interface contact states,piezoelectric materials,control methods and input parameters,e.g.excitation frequency,voltage amplitude and phase difference.The maximum efficiency of polytetrafluoroethylene-based(PTFE)traveling wave rotary ultrasonic motor-60(TRUM-60)is about 30%,which is insufficient to meet the needs of the future spacecraft's design requirements for functional component for precision drive.In this thesis,the energy conversion efficiency and output performance of the USMs are improved with respect to both the new friction materials and the textured contact interfaces.The pre-loads and input parameters of the new TURM-60 are optimized and the environmental tolerance are verified.The working mechanisms of the USMs,the preparations for friction materials,the design and processing of surface textures,the construction of test systems,the optimization of parameters and the verification of working capability in vacuum and high/low temperature environments are studied systematically.1.Based on the motion mechanism of USMs,the influence of friction material characteristics on its output performance is studied.A new type of polyimide(PI)friction material has been developed.The elastic modulus and friction coefficient of PI are improved by adjusting the proportion of the matrix material and the functional components.The anisotropy,wear resistance and thermal stability of PI are improved by carbon fiber reinforcement,solid lubricant and nanoparticle modification.Based on the elliptical motion of stator particle,the contact state between the stator and rotor contact interface is analyzed.The mechanical model of high frequency vibration friction interface is established.The relationship between the amplitude of the stator particle and the friction coefficient is revealed.The influence of the input parameters of ultrasonic vibration on the interface tribological characteristics is analyzed.The performance test system for the USM is built,and the output performances test method which is well suited to TRUM-60 is proposed.The control of the driving system with multi-input parameters as well as the synchronous acquisition and processing of output performance are realized.The influence of PI-based friction material characteristics on the performance of USM is obtained.2.The surface texturing technology is introduced into the manufacture of friction contact interface of the USMs.Surface textures of different characteristic parameters is constructed on the stator and rotor respectively.The influence of the textured interface on the friction characteristics and the output performance of USMs is studied.The energy conversion efficiency and output performance of the USMs are improved.When the stator and the textured PI friction material were used as tribo-pairs,the optimum area density of the circular surface texture was obtained to be 7.06%.The influence of surface texture on the performance of the USMs is analyzed by using the theory of dynamic transmission between the stator and rotor.The textured rotors effectively improve the energy conversion efficiency and output performance of the USMs,and the maximum efficiency can be further increased to 58.61%.However,textured stators reduce the energy conversion efficiency and output performance of the USMs.3.An optimization scheme of pre-load and input parameters for the new USMs is proposed.Considering the requirements of energy conversion efficiency and output performance for the TRUM-60,the optimal ranges of the pre-load,excitation frequency,voltage amplitude and phase difference are obtained.Based on the influence and mechanism of input parameters on the amplitude of the stator particle,the effects of the excitation frequency,input voltage amplitude and phase difference on the performance of the USMs are studied,which provides experimental basis for the multi-parameter control of the USMs.4.Based on the requirements of USMs in vacuum and high/low temperature environments,the PI-based contact interface and the performances of the TRUM-60 are studied under environments.The effects of vacuum(10^-6 Pa)and high/low temperature(-60?120?C)environments on the interface friction characteristics and the performances of the USMs are studied.The environmental tolerance of the new PI-based TRUM-60 is verified.By optimizing the friction material and input parameters,the output performance of the USM in vacuum and high temperature environment is further improved.