| In the launching process of a spacecraft, the dynamic environment is very complex. The spacecraft carries many kinds of precision payloads which require a stable environment to prevent them from being damaged in the launching process. If the spacecraft and launch vehicle are directly connected with large stiffness, it will cause the environmental loads transmitting directly from the connection surface of the rocket to the spacecraft which is a very fatal factor to the spacecraft. So isolation systems between the launch vehicle and the spacecraft have been investigated and widely used in the past decades to isolating the shock and noise transmitting directly to the spacecraft in the process of launching with the purpose of improving the dynamic environment provided to the spacecraft and increasing the safety of the spacecraft during the launch stage. Based upon the research and the design of the electromagnetic actuator, this paper carries out relevant study on typical mechanism including single axis, 6-DOF Stewart platform and large flexible spacecraft, respectivley. The main research contents and results involve the following aspects:Firstly, the priciples, design and implementation of electromagnetic actuator is proposed and discussed as the basis of the whole thesis. The electromagnetic field theory involved in the design of the linear voice coil actuator is introduced. The principles in designing of the actuator are proposed and the design programms are given out. Theoretical calculation and FEM simulation analysis of electromagnetic design for structural optimization and performance analysis are carried out.Secondly, the theory, characteristics and linear state space control methods of single axis vibration isolation system is studied. Two kinds of mathematical model of active vibration isolation are given, and stability criterion is introduced. LQR optimal control method and the control system implementation are studied. The vibration isolation effect under different control parameters are compared by numerical simulations. The PID controller for current loop is proposed to solve the problems of back electromotive force. The active controller of two DOF vibration isolation system is studied by numerical simulation.Thirdly, the Stewart platform with active damping is designed to isolate the vibration from transferring to the payloads in 6 degree-of-freedom. The kinematics and dynamics equations of Stewart platform with spherical joints at both the base and top of each leg are established with Newton-Euler Method in task space and joint space. H?Control Theory is introduced,the uncertainty of the practical mechanism is analysed and the selection of weighting function is given. Robust controller with H?Control Theory is devised considering the system uncertainty, and the effect on vibration isolation of active control is compared with passive method.Fourthly, a new active and passive integrated whole-spacecraft vibration isolator is designed. The structural design is proposed and the change of the inherent characteristics of the whole structure with and without the vibration isolation system are compared. The modal space method for multi DOF system is introduced, the transformation between modal force and actual force is obtained and the steps of independent modal control method is given. System parameters were identified through Eigensystem Realization Algorithm(ERA) method and balanced order reduction method was used for model dimension reduction. H?robust controller is devised and numerical simulations are carried out.Finally, the experimental study for the early designed vibration isolation platforms based on electromagnetic actuator are carried out. Sweeping frequency test and fixed frequency test were taken to verify the single axis vibration isolation system and the 6 DOF Stewart platform. The effectiveness and feasibility of electromagnetic actuator used for vibration isolation for rigid spacecraft are verified. |
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