Vibration control of flexible structures using smart materials

Abstract

<p>This work presents the analytic and experimental development of active vibration control of large flexible space structures (LFSS) using smart materials. Two basic configurations were studied: flexible manipulators, and truss structures, which encompass most of the flexible structures in space applications. The dynamics of LFSS are characterized by their high order and the significant presence of lightly damped, closely spaced low frequency modes. In space applications, space structures are required to perform precision trajectory tracking and attitude regulation, tasks that introduce disturbance torques and forces that may excite vibrational modes in the flexible parts of the structures, degrading their performance. To solve this problem, the use of piezoelectric materials coupled to structural members, to form smart structural members, is proposed for the implementation of active control techniques. For the flexible manipulator, the use of shaped piezoelectric sensors is presented. Piezoelectric sensors can be shaped to provide state feedback, which can be used as part of a control law to compensate vibrations induced by flexible degrees of freedom. A robust H∞ state feedback control law is obtained. The control law is implemented using the shaped sensor to stabilize the flexible manipulator. Simulation and experimental results in a single link flexible manipulator confirm the effectiveness of the proposed approach. The design of a truss structure and the control for active damping of vibration is presented, taking advantage of the use of piezoelectric actuators and sensors. Three control techniques are tested: negative velocity feedback, LQG and H∞ control. Simulations and experiments are performed on the closed loop to assess the relative merits of each control technique. Results show that the controllers increase the damping of the structure noticeably. The robust H∞ controller provides the better performance of the control techniques presented, even in the presence of higher order modes and parametric uncertainties not accounted for in the control design process.</p>