Experiments of a robust controller for active vibration reduction of space structures with linear and patch PZT devices

The interaction between spacecraft structural dynamics and its rigid-body control system is a well-known issue in the space field. Indeed, this phenomenon often leads to the worsening of pointing performance, to unwanted large flexible deformations and even to instabilities or failures. Active Vibration Control (AVC) is a strategy adopted to reduce elastic vibrations in flexible structures, thus mitigating, in case of space systems, the coupling with the attitude dynamics. To this purpose, different actuators can be used, ranging from proof-mass to shape memory alloys, to piezoelectric (PZT) devices. In this research, Offset Piezoelectric Stack Actuators (OPSA) are paired to PZT patch sensors to suppress the elastic vibrations of a space system. In detail, a robust control architecture is implemented to guarantee the desired closed-loop performance, while coping with the presence of several parametric uncertainties of the flexible structure: modal shapes and frequencies, damping factors, sensors and actuators dynamics, structural modeling approximations. In particular, the controller is designed to shape the system desired closed-loop behaviour while accounting for actuating capability limits, input disturbances and sensor noise. To address system uncertainties with an efficient approach and carry out the robust synthesis/analysis, the uncertain state space model is put into a Linear Fractional Transformation (LFT) framework. The efficiency of the proposed AVC framework is verified numerically, by means of a structured singular value analysis performed on a finite element model of the controlled system, and then experimentally validated. To this purpose, a cantilevered panel actuated via an OPSA is equipped with a PZT patch to sense elastic deformations and close the control loop. The testbed is also provided with an external contactless metrology system, i.e. a motion capture VICON device, used as benchmark for piezo embedded measurements. Finally, the performance of the proposed AVC based on robust control technique will be evaluated and compared with a classical but well established vibration controller (PPF compensator). Further steps paving the way for a coupled attitude/elastic MIMO control will be then suggested.