Space structures are expected to be larger for high performance. Additionally, they are required to be lightweight for reducing transportation cost using rockets and space shuttles, and therefore lightweight composite materials have been used because of their high ratio of strength-to-weight. These large and lightweight structures tend to be highly flexible, and then external forces caused by thermal impulse and attitude control can induce the structural vibration easily. Furthermore, the damping ratio is very low in space environment that is highly vacuum and low gravity. Therefore, this vibration may cause the degradation of structural performance and the failure of equipments. For this reason, many studies about the vibration control using sensors and actuators have been carried out.
Piezoelectric materials, such as PZT and PVDF, have received much attention as sensors and actuators. Piezoelectric materials produce an electric field when deformed and they undergo deformation when subjected to an electric field. In addition, piezoelectric materials with very good manufacturability, lightweight, and an efficient conversion between electrical and mechanical energy, can be easily attached on or imbedded into structures. For these reasons, piezoelectric materials are very suitable for vibration control. In vibration measurement and control of structures modeled by a multi-degree-of-freedom system, it is effective to use modal coordinates by decomposing a complex vibration problem into some independent vibration modes. The sensor system that can measure each vibration mode is called as 'modal sensors,' and the actuator system that can control each vibration mode is called as 'modal actuators.' These sensor and actuator systems allow an independent modal space control. Many works have used PVDF sensors for constructing modal sensors. But it is difficult to apply PVDF modal sensors to large and complex structures, since these sensors need large areas to construct the modal sensors. On the contrary, distributed point sensors such as accelerometers, which are placed to optimal locations, can be used for constructing modal sensors. Point sensors need quite smaller areas, and are suitable for applying them to large and complex structures.
In this paper, modal sensors and modal actuators are developed by distributed piezoelectric patches that are placed to optimal locations, and vibration control of CFRP laminated plates is realized. As a result of numerical simulations and experiments, it is shown that modal sensors developed by distributed piezoelectric sensors are effective for vibration control.
edited by Naoki HAGIWARA