Active vibration control of large space structures: Modelling and experimental testing of offset piezoelectric stack actuators

To meet demanding mission objectives, most current satellites for Earth and Universe observation are equipped with large flexible appendages. However, due to the coupling between spacecraft rigid and elastic dynamics, unwanted elastic vibrations of such flexible elements may compromise the achievement of pointing and stability requirements. Therefore, control solutions aiming at avoiding instabilities and, at worst, the failure of the mission, are currently needed. In this scenario, growing interest has been recently devoted to Active Vibration Control (AVC) strategies relying on the use of smart materials. Among them, piezoelectric patches are the most studied and tested devices for both actuating and sensing purposes. This paper aims to contribute to this line of research by investigating a different type of actuator, namely an Offset Piezoelectric Stack Actuator (OPSA), to assess its performance in damping out elastic vibrations of large space structures. Moreover, special attention is devoted to compare OPSA performance with standard patch actuators behaviour. In order to develop the AVC system, an equivalent electro-mechanical coupled Finite Element (FE) formulation is implemented, integrating both sensors and piezo-stack elements on the passive hosting structure. The final structural model including both electrical inputs/outputs, as well as modified mass and stiffness due to the additional piezo devices, is then obtained. A parametric analysis is carried out to optimize the maximum control action exerted by the OPSA device. Finally, the OPSA numerical model is experimentally validated by mounting it on a cantilever plate, representative of a scaled solar panel. Experimental data are used not only to verify the device expected functioning, but also to tune the parameters in the OPSA FE model, which can be finally integrated in a planar satellite dynamics simulator to evaluate the AVC system efficiency when performing attitude manoeuvres.