DIRECTIONAL DECOUPLING OF PIEZOELECTRIC SHEET ACTUATORS FOR HIGH-PRECISION SHAPE AND VIBRATION CONTROL OF PLATE STRUCTURES

Open Access
- Author:
- Philen, Michael Keith
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 20, 2006
- Committee Members:
- Kon Well Wang, Committee Chair/Co-Chair
Christopher Rahn, Committee Member
Panagiotis Michaleris, Committee Member
George A Lesieutre, Committee Member - Keywords:
- adaptive mirror
shape control
vibration control
smart materials
directional decopuling
piezoceramics
plate - Abstract:
- The purpose of this thesis is to investigate directional decoupling of piezoceramic-based actuators for high precision shape and vibration control of twodimensional plate structures. Significant research exists concerning shape control of two-dimensional adaptive optical structures with attached piezoelectric ceramic sheet actuators. Researchers have investigated the optimal placement, size, and electrode pattern of the piezoceramic actuators to maximize the system performance. In many situations, the performance could be further improved with tailoring of the actuator configuration. For example, it was found that to avoid creating short wavelength deformation (higher order deformation modes) in two-dimensional structures, the ideal actuator would be one that is directionally decoupled, i.e., only actuates in one direction when controlling certain static deformation modes of interests. In applications where high precision is a requirement, a directional decoupled actuator can improve the shape control performance by decreasing the actuation authority to the higher order undesired deformations while maintaining sufficient authority for the controlled modes. In addition to shape control, vibration control of large flexible space structures is continually challenging to engineers due to the large number of actuators and sensors, and the large number of vibration modes within the operational bandwidth. For these structures, due to the small amount of damping available, spillover effects need to be addressed when active controls are utilized. In this thesis, two directional decoupling methods are proposed for high-precision shape and vibration control, namely the Active Stiffener (AS) and the MacroFiber Composite (MFC). The objectives of the investigation are to analyze the two configurations, understand their characteristics, provide insights for better design and control, and experimentally validate the theoretical findings. iv The Active Stiffener is a new stiffener-piezoceramic actuator pair concept that consists of a passive insert (stiffener) placed between the host structure and the active piezoelectric actuator. The basic premise is that the insert (stiffener) will reduce the transmitted moment to the host structure in the direction desired for decoupling while allowing an adequate moment to transmit in the actuation direction. In this study, a local analysis of the AS actuator is first developed to gain a proficient understanding of the actuator and determine parameters that can best achieve the decoupling actions. Using finite element analysis techniques, investigations of a single AS attached to rigid and flexible host structures are presented. The effects of various material and system parameters on the applied bending moments (active authority in both directions) to the host structure are illustrated. It is shown that, with proper design, the AS can significantly reduce the active authority in a selected direction while maintaining sufficient authority in the orthogonal direction. To demonstrate the effectiveness of the new AS configuration for shape and vibration control, analytical and experimental efforts are carried out to examine the performance of the AS actuators in controlling 2-dimensional plate structures. Analysis is performed on two large flexible circular plate structures, one having the Direct Attached (DA) actuators and the other utilizing the AS actuators. For shape control, more reductions in surface error can be achieved with the AS compared to equivalent systems having DA actuators. The DA actuators generate more localized deformation than the AS in the structure due to the coupled planar actuation of the DA actuator. The analysis results performed for each deformation shape demonstrate that a stiffener height greater than zero maximizes the shape control performance, i.e. the DA actuator is never the ideal actuator. The experimental results verify the analytical predictions and clearly demonstrate the performance improvement of the AS concept over the DA actuator. For vibration control, analytical and experimental efforts are carried out to examine the ability of the Active Stiffener actuators for reducing controller spillover through the stiffeners’ decoupling properties. It is shown that significant reductions in v controller spillover can be achieved in systems using the Active Stiffener actuators when compared to systems having Direct Attached actuators, thus resulting in improved vibration control performance. Vibration analysis results confirm the shape control results where a stiffener height greater than zero is always the ideal actuator. The experimental results verify the analytical predictions where the AS has an increased stability margin due to the reduced controller spillover effect. Similar to the Active Stiffener, the MacroFiber Composite (MFC) actuator possesses several advantages over the planar monolithic piezoceramic actuator, such as increased toughness, flexibility, higher longitudinal strains, and higher specific work output. Also, the anisotropy of the actuator can be modified or changed by the selection of the parameters at the material, lamina, and laminate levels of fabrication. Many applications have been explored using the composite actuators; however, they have not been specifically studied and utilized for their directional decoupling characteristics. Analytical and experimental efforts are performed to examine the feasibility of using the MFC’s for high precision shape and vibration control. The analytical and experimental results demonstrate that the MFC’s can dramatically reduce the surface error and controller spillover for shape and vibration control. When compared to equivalent systems having DA and AS actuators, the MFC performs better than the DA for all modes and is comparable in performance to the AS. While the MFC treatment requires much larger voltages than the AS treatment, it’s power requirement is lower. Using a 3- D composites model of the actuator based upon the Uniform Fields Model, it is observed that the system performance can be maximized or the voltage requirements can be reduced through tailoring the fiber volume fraction. The research achievements of this thesis are summarized in the final chapter. Recommendations are made for improving upon the work presented here, and some possible future research directions on related topics are also presented.