Analysis And Experiment Of Isolators For Micro-Vibration Active Control Based On Stewart Platform

Micro-vibration in satellites is a primary factor that affects the performance of high-resolution satellites,such as precision and imaging quality.The analysis and control of the micro-vibration is very difficult because it is very tiny and the the space environment is special and complicate.Also,the space environment has a special and strict requirements on the complexity,reliability,stability of the vibration control system.There are many solutions for this problem,including all kinds of active and passive isolators both in China and abroad.This thesis presents a isolator for micro-vibration active control based on the Stewart platform.The kinematic and dynamic modelling of Stewart platform with a cubic architecture is derived to reveal the characters of the platform.This thesis use OMAP-L138 DSP as the controller of the system.An Fx-LMS method is adopted to suppress the foundation vibration.The experiment is carried out to verify the effect of the Stewart platform.The investigations are summarized as follows.In Chapter 1,the backgroud of significance of the investigation,as well as the main content in this thesis is introduced.Reviews on micro-vibrotion isolation technology for spacecraft are presented,especially the isolation based on Stewart platform.In Chapter 2,The cubic configuration of Stewart platform is presented for uniformity of stiffness and control capability in all directions,simplifying mechanical design,etc.The kinematic and dynamic modelling of Stewart platform with a cubic architecture is derived to obtain the Jacobian matrix relating the extension of the piezo actuator to the 6 degree of the top plate and reveal the characteristics of vibration transmissibility.The theory of substructure synthesis based on the frequency response function is presented in order to reveal the dynamic characters.With piezoelectric stack as an active element,the cubic configuration of Stewart platform is proposed.In Chapter 3,the active control method of the Stewart platform is pesented.The adaptive filtering algorithm Fx-LMS,is applied to the active control of the platform.The theory of LMS and Fx-LMS is revealed in detail.Including the smallest root mean square theory,normalization of modified LMS algorithm,Fx-LMS,the principle of system identification.Based on the dynamic modelling of Stewart,Simulations on the Stewart under the tonal and random disturbance are conducted with Fx-LMS using Matlab.The results shows that the effect is very good.In Chapter 4,considering of the limit enviroment in spacecraft,this thesis choose OMAP-L138 DSP core as the controller of the active control system.The characters of the OMAP-L138 DSP is presented.The configuration of core modules is revealed.The adaptive filtering algorithm Fx-LMS is programed.The simulation and test of A/D,D/A,system identification,active control part is presented.The result shows that DSP is excellent for active control interference.In Chapter 5,The tests are carried out to verify the effectiveness of the Stewart platform.The equipment of the test is introduced.In order to test the active micro-vibration isolation performance of the Stewart,the background vibration is tested in the first step due to its possible significant influence on the results.In addition,experiments are conducted to verify the actuation consistency of each actuator over 20-120 Hz and refine the theoretical Jacobian matrix.In the end,tests are carried out to prove the active control performance of Stewart under tonal disturbances.The results show that from 20 Hz to 100 Hz,on the Z drection,the Stewart platform is able to achieve 24 dB attenua-tions under the tonal disturbance.It achieves 6.98 dB under random disturbance from 20Hz~60Hz.For the X rotation direction,he Stewart platform is able to achieve 14 dB attenua-tions under the tonal disturbance from 15Hz~80Hz.In Chapter 6,the whole work of this thesis is summarized.Then it discusses the deficiencies of the thesis and what needs further study,etc.