Research On The 6-Dof Fault Tolerant Control Of The Vibration Isolation Platform With Eight Actuators

Launching stage is the most severe dynamic environment that satellites will ever experience during their whole missions. Whole Satellite Vibration Isolation technique, proven to be the trend, is to install an isolator between the rocket and the satellite to attenuate the vibration load transmitting to the satellite, for the purpose of enhancing satellites'reliability and reducing the structural weight of the satellites. Integrated active-passive vibration isolation adopts advantages from both active and passive vibration isolation, which is realized by adding active control elements in parallel with the passive ones. The active part can suppress the resonant peaks and improve the isolation ability as well as stiffness in the low frequency range. On the other hand, in the higher frequency range, passive vibration isolation is still employed. In this way, the capacity of isolating vibrations in the whole frequency range is achieved and the energy consumption remains reasonable.The structure of eight parallel actuators is able to realize six-degree-of-freedom vibration isolation, which also guarantees high reliability. Compared with typical Stewart platforms with only six actuators, the symmetrical arrangement insignificantly increases the complexity of the platform dynamics. Each actuator is capable of providing passive and active vibration isolation by integrating pneumatic cylinder, spring and damper in parallel and is connected to the mobile platform and the base through spherical joints.This thesis investigates the active control system of the pneumatic octo-strut vibration isolation platform. Coupling among the input-output channels of the platform is complicated which makes it hard to implement control algorithm. Thus, the thesis focuses on the decoupling techniques of the'healthy'system and the system with actuator failures.Based upon the complete dynamic model of the platform, some insignificant factors are ignored to obtain a simplified model suitable for control system design. Then through input-output transformations, the decoupling among feedback channels of the platform is achieved and single-input-single-output control algorithm for each channel can be designed individually. Moreover, the application of fault diagnosis based on state observer to the platform is also analyzed; combined with above mentioned control algorithm, the platform is able to provide six-degree-of-freedom vibration isolation in presence of one-or-two actuator failure. Finally, the transmissibility of the'healthy'system and the system with actuator failures is measured experimentally and the result shows the validity of the vibration control algorithm.