Robust Control of Flexible Structures Using Multiple Shape Memory Alloy Actuators

Abstract

The design and implementation of control strategies for large, flexible smart structures presents challenging problems. To demonstrate the capabilities of shape-memory-alloy actuators, we have designed and fabricated a three-mass test article with multiple shape-memory-alloy (NiTiNOL) actuators. The force and moment actuators were implemented on the structure to examine the effects of control structure interaction and to increase actuation force. These SMA actuators exhibit nonlinear effects due to deadband and saturation. The first step in the modeling process was the experimental determination of the transfer function matrix derived from frequency response data. A minimal state space representation was determined based on this transfer function matrix. Finally in order to reduce the order of the controller, a reduced order state space model was derived from the minimal state space representation. The simplified analytical models are compared with models developed by structural identification techniques based on vibration test data.From the reduced order model, a controller was designed to dampen vibrations in the test bed. To minimize the effects of uncertainties on the closed-loop system performance of smart structures, a LQGLTR control . methodology has been utilized. An initial standard LQGLTR controller was designed; however, this controller could not achieve the desired performance robustness due to saturation effects. Therefore, a modified LQGLTR design methodology was implemented to accommodate for the limited control force provided by the actuators. The closed-loop system response of the multiple input-multiple output (MIMO) test article with robustness verification has been experimentally obtained and presented in the paper. The modified LQGLTR controller demonstrated performance and stability robustness to both sensor noise and parameter variations.- IntroductionIn recent years there has been considerable interest in the design and implementation of active controllers for smart structures. The application of both piezo-electric and shape memory alloy materials as actuators and sensors in the active control of structures has been extensively reported in the literature. We have utilized the shape memory alloy (SMA), Ni'IiNOL, in the design and implementation of multivariable robust controllers. In addition to the design of multivariable robust controllers, this research examines the effects of control-structure interaction using SMA actuators on a flexible structures. To implement and evaluate the performance of various controllers, we have designed and fabricated a three-mass test article equipped with strain gauge sensors, force and moment SMA actuators, and signal processing circuits. The force and moment SMA actuators allow the application of increased control force and the investigation of control-structure interaction, In order to design active controllers for flexible structures, a mathematical representation of the system is needed. This system contains inherent nonlinearities resulting from bot...

Development Of An Interactive Shape Memory Alloy Demonstration For Smart Materials Curricula

“…In recent years innovative implementations of SMA include: bio-medical devices, including artificial organs, 5,6,8 vibration control of structures, 7 and actuation of dynamic systems. 11 In the future, there will be a growing need and demand for technologies utilizing the unique characteristics of SMA.…”