Vibration Transmissibility And Active Control Of A Grid Structure

Micro-vibration in satellites is a primary factor that affects the perfor-mance of remote sensing of high-resolution satellites, such as the pointingprecision and imaging quality. The space environment is special andcomplicate, and the micro-vibration is of tininess and distributed on a broadfrequency band, making it much difficult to analyze and control. Moreover,the space environment has special and strict requirements on the complexity,reliability and stability of vibration control systems. Therefore, consideringthe particularity of space environment, it is necessary to investigate anddevelop new vibration isolation systems. This thesis presents a vibrationtransmission control method by using a plane grid structure integrated withactive elements to meet the requirement of space environment and tosuppress the broadband and narrowband disturbances simultaneously. Thismethod combines the advantages of the passive vibration isolation of thelightweight grid structure and the efficient active control method. Thecoupled vibration of the system, which is formed by the vibration source, thegrid structure and the supporting boundary, is modeled and its vibrationtransmission characteristics are analyzed. The adaptive active control isadopted to further improve the isolation performance of the grid structure.Through theoretical analysis and experimental verification, this thesis revealsthe vibration transmission mechanism of the grid structure, which provides a theoretical basis and reference for the design of the grid structure in vibrationisolation. The investigations are summarized as follows.In Chapter1, the background of this investigation is introduced and thevibration isolation techniques as well as modeling methods for coupledsystems are reviewed.In Chapter2, basic vibration theories of the string, beam and rigid bodyare investigated at first. A synthesized model of the grid structure isestablished with the substructure mobility approach. The vertical vibrationequation of the system is obtained and then validated with the finite elementmethod. Considering the unidirectional coupling between the string and theboundary, a complete vibration description of the boundary is achieved bydecomposing the dynamic tension force in the string to the vertical andhorizontal directions. In terms of the synthesized model, the force trans-mission characteristics are analyzed. The results show that the grid structureplatform is effective in vibration isolation. The vibration transmissibility istunable by adjusting the initial tension force in the prestressed strings.In Chapter3, the structure and working principles of an electromagneticactuator are presented. The finite element model of the actuator is establishedand the magnetic field of the actuator is analyzed. Based on the magneticfield distribution and the electromagnetic force generated by the coil, thestructure of the actuator is optimized, which improves the magnetic field andincreases the actuation force.In Chapter4, an active control method of the grid structure isinvestigated. The adaptive filtering algorithm–LMS, is applied to thevibration control of the grid structure. The vibration of the grid structure andits boundary is suppressed through applying control forces on the rigid platform. The results show that this method is effective in decreasing thevibration of grid structure, and control effects are greatly influenced by theparameters of the string, such as the initial tension.In Chapter5, vibration isolation characteristics and active controlstrategies of the grid structure platform are investigated through experimentaltests. Two motivational techniques are adopted, in which the frequencyresponse characteristics from the grid structure to the boundary and the forceattenuation properties from the upper platform to the boundary, are obtained.The experimental results show that the grid structure platform has excellenteffect on vibration isolation in a wide frequency band, and it has good forceattenuation characteristics above the mount frequency of the rigid platform.In addition, the active control experiment of the grid structure platform showsthat the adaptive control algorithm can effectively suppress the vibration ofthe supporting boundary.In Chapter6, conclusions are summarized, the contribution of this thesisis pointed out, and some problems for further study are suggested as well.