ACTIVE VIBRATION ANALYSIS AND CONTROL OF MEMBRANE REFLECTOR

Abstract

Current space-based imaging platforms are significantly constrained in both size and weight by the launch vehicle. Increased payload size and weight results in increased cost and a decrease in launch responsiveness. Use of a membrane antenna on remote sensing satellites is now possible because of new materials and manufacturing technologies. This would allow space organizations to cut cost and weight by a non-negligible factor. All possible failure modes must be fully analyzed before these are sent to space. Wrinkling is a common phenomenon found in a variety of membrane structures due to lack of bending and compression stiffness. In most practical situations, wrinkling is undesirable because it will seriously undermine the performance and the reliability of membrane structures. For example, the occurrence of wrinkles could lead to a curved reflecting surface in membrane reflectors, or non-uniform heating in solar sails. A better understanding of the effects of wrinkles on the structural performance and stability of these structures is essential and desirable. Thus, a method to measure the wrinkling out-of-plane deformation is introduced, and the stress distributing in membrane wrinkled area is analyzed. Also, a dynamic analytical model of rectangular shear wrinkled membrane is proposed and the membrane vibration mode shapes are thus obtained. Results indicate that the stress in wrinkled area is not uniform, i.e. it is larger in wrinkling wave peaks along wrinkles. Vibration modes of wrinkled membrane are strongly correlated with the wrinkling configurations. Results show that vibration frequency increases with the vibration of wave peaks. The membrane antenna also exhibits undesirable vibrations that can be caused by internally-induced excitations by electronic components on-board. The undesirable vibration degrades the performance of the reflector. This work aims at modeling and active vibration control of a square membrane augmented with smart actuators. To evaluate the stability and controllability properties equation of motion is used to obtain the mass, stiffness and damping matrices in second order form which are further used for obtaining state and control matrices of the first order model. An optimal PID controller is then used in a closed loop for active vibration control of the membrane augmented with bimorph actuators