Control Of Pneumatic Isolator And Octo-Actuator Vibration Isolation Platform

During the launch stage, the launch vehicle (LV) provides the most severe dynamic loads that a satellite ever suffers in its whole mission life. Using a six degree of freedom (DOF) vibration isolation platform as the attachment fitting of the LV to the satellite is an effective way to attenuate the vibration transmission, thus improve the dynamic environment of the satellite. In this dissertation, to ensure the reliability and enhance the carrying capability, a six-DOF vibration isolation platform with eight pneumatic actuators is employed to realize the whole satellite vibration isolation (WSVI). The decoupling control problem of the octo-actuator vibration isolation platform (OVIP) is systemically studied.Firstly, the dynamic model of an integrated active and passive pneumatic isolator is established. Performances of the isolator using both the feedback control, where the feedback signals include the payload's acceleration, the relative displacement and the chamber's pressure, and the feedforward control with the base's acceleration are theoretically investigated and experimentally validated. Then the adaptive filter algorithm is employed to control the isolator. An adaptive transversal filter and an adaptive comb filter using the filtered-X LMS algorithm are respectively implemented on the isolator, and major factors that influence the vibration suppression effect are discussed. Experimental results show that the two kinds of filters have the same performance for sinusoidal excitement, while, for multiple-harmonic excitement, the adaptive comb filter has better performance. Low-frequency disturbances of the payload can also be suppressed by using a bias weight in the filter.The dynamic model of a general six-DOF platform with several parallel actuators is established with the Newton-Euler method. Based on this model, the dynamic behavior of the platform is investigated. Analysis result shows that if all actuators are identical in structure, the coupling properties of the platform's feedback channels depend on the configuration of the platform and the arrangement of the payload. Dynamics of the actuator have no influence on the coupling properties. Then several configurations of the six-DOF platform are designed. For a vibration isolation platform with one of these configurations, if the payload satisfies some conditions, the feedback channels of the platform will possess a decoupling feature, so its decoupling control is relatively easy to implement. By comparing these configurations, a symmetric octo-actuator configuration is selected for the WSVI platform studied in this dissertation. The relationship between the stiffness matrix and the configuration parameters of the OVIP is also studied, and a guide line for the stiffness design of the platform is proposed.Following the selection of the platform's configuration, the decoupling control method of the OVIP is systemically studied. Dynamic analysis indicates that when the payload's center of mass is at the extension line of the platform's central axis and the payload's mass matrix is diagonal, the dynamic equation of the platform can be decomposed into two independent single-input single-output channels and two independent two-input two-output subsystems. A decoupling control algorithm, which can further decouple the second-order subsystems, is developed. When the payload is arbitrarily placed, the six input and output channels of the platform are coupled with one another. In this case, the algorithm can also be generalized to realize the decoupling of the platform's feedback channels. Base on the decoupling algorithm, a proportional controller and an adaptive filter controller are respectively designed and verified by numerical simulation.Effects of other factors, such as the payload's flexibility, the actuator's mass and moment of inertia as well as the distributed mass of the mechanical spring, on the performance of the platform are also studied. The flexibility of a satellite will reinforce the coupling among different channels, but the main channels of the platform are still dominant, thus the decoupling control method can also fairly well restrain the vibration of the platform. The dynamic model of the OVIP considering mass and moment of inertia of the actuator is developed. Analyses show that if all actuators have the same structure, its mass and moment of inertia have no effect on the coupling properties of the platform, nevertheless, due to the actuator's moment of inertia, the high-frequency transmissibility of the platform is slightly amplified. As a result of the distributed mass of the mechanical spring, some high-frequency resonances appear on the vibration transmissibility curves of the platform.Finally, experiments are carried out to verify the performance of the OVIP. The decoupling proportional controller and the decoupling adaptive filter controller are separately implemented on the platform. Experimental results show that in the low-frequency range, the two kinds of controllers can both effectively attenuate the vibration of the platform, while, in the high-frequency range, the platform displays the passive performance. Therefore, with the integrated active and passive pneumatic isolator as the actuator, the OVIP can realize the six-DOF integrated active and passive vibration isolation.