System identification and controller design of a self-sensing piezoelectric cantilever structure

This paper addresses system identification and vibration control of a cantilever fabricated from piezoelectric materials (PZT), and shows how system identification and state estimation can be used to achieve self-maintenance of a self-sensing system. Currently, self-sensing systems that have concurrent actuation and sensing can be made by using a bridge circuit. However, hardware tuning is still needed due to the unstable nature of an imbalanced bridge circuit. This problem becomes serious in the space environment where human beings may not be available to perform the maintenance. A method of achieving self-sensing without a bridge circuit is proposed in this paper. Analysis of the system dynamics indicates that the subsystem corresponding to the bridge circuit for a self-sensing cantilever with PZT can be described as a direct transmission component in the state space expression of the system. This means that the problem of balancing the bridge circuit is equivalent to the system identification and state estimation problem. By performing a simple experiment, a model of the system was identified using the 4SID (SubSpace State Space IDentification method). Observer theory can be used to estimate state vectors which include information about the mechanical dynamics. Thus, system stability depends on the estimated value of the state vectors. The system can be stabilized using a state feedback controller such as a LQ controller. The proposed method was verified with experimental results, demonstrating that smart structures can achieve self-maintenance.