Research On Active Control Methods And Optimization Design Of Micro-vibration Isolation Device On Satellite Based On Stewart Platform

Satellites must deal with varies kinds of disturbances on orbit, which possess thecharacteristics of small amplitude, a wide frequency band, sensitivity and difficultto measure. In order to provide an ultra-quiet environment for the payloads insatellite and ensure them to work normally, Stewart platform that served as amulti-DOF active vibration isolation manipulator could be utilized to control themicro-vibration of satellites.In this thesis, a complete dynamic model of a6-SPS Stewart platform with thebase excitation has been formulated via Newton-Euler method in detail. Therotational effects of each leg can be omitted by analyzing the numerical results. As aresult, the dimension of the6-SPS Stewart platform can be reduced to six. Based onthis fact, a dynamic model that contains base excitation has been derived via Kane’sequation for the first time, which is of simple formula, definite physical meaningand high accuracy. The geometrical nonlinearities appeared in the model are allomitted due to the small amplitude of micro-vibration. Depending on the linear andpiecewise linear assumptions of the spring embedded in each strut, linear and threeorder nonlinear dynamic models have been formulated consequently. The validity ofthe model is verified by Adams.A dynamic model of the platform that considers uncertainties of location of masscenter, stiffness and viscous damper has been formulated for the first time. Tworobust controllers have been designed in detail through H∞and μ-synthesis tohandle the linearized model and linear uncertain model. As for the nonlinear modelwith parameter uncertainties, a modified robust nonlinear controller has beenproposed by this study. The system that contains the controller is theoreticallyproved to be ultimately unitary boundedness. The efficiency of the three controllershas been testified in frequency and time domain. Consequently, the tworequirements of the micro-vibration control have been achieved. All these workshave laid a sound foundation for the controller design of multi-DOF active vibrationisolator.To satisfy the need for micro-vibration and manufacture, a general and concisecondition that ensures the static decoupling is drawn based on the fundamentalconfiguration. The equations of all the six natural frequencies of the decouplingplatform have been derived. When the height of the mass center of the payloadequals zero, dynamic decoupling and translation isotropy can be achieved. Once theheight is not zero, the optimization of the dynamic isotropy is conducted by Genetic Algorithm and Differential Evolution Algorithm to search for the appropriateparameters. That the results of the two algorithms are nearly the same indicates thecredibility of the results. The complete dynamic isotropy cannot be achieved, buttranslation isotropy and combined isotropy can be achieved according to theoptimization results.Some constructive conclusions about design, dynamic and control of the activemicro-vibration control manipulator on satellite have been drawn in the finalsection.