Modeling and characterization of a piezoceramic inertial actuator

Abstract

An inertial actuator (also known as a proof mass actuator) applies forces to a structure by reacting them against an mass. This approach to actuation may provide some practical benefits in the active control of vibration and structure-borne noise: system reliability may be improved by removing the actuator from a structural load path; effective discrete point-force actuation permits ready attachment to curved surfaces, and an inherent passive vibration absorber effect can reduce power requirements. This paper describes a class of recently developed inertial actuators that is based on mechanical amplification of displacements of an active piezoceramic element. Important actuator characteristics include resonant frequencies, clamped force, and the drive voltage to output force frequency response function. The paper addresses one particular approach to motion amplification. the dual unimorph, in detail. A model of actuator dynamic behavior is developed using an assumed modes method, treating the piezoelectrically-induced stresses as external forces. Predicted actuator characteristics agree well with experimental data obtained for a prototype actuator. The validated actuator dynamic model provides a tool for design improvement. Introduction Active control technology has potential applications to many noise and vibration problems, including aircraft cabin interior noise, spacecraft vibration suppression, and automobile, industrial machinery and home appliances [I-51. Practical deployment of this technology requires, among other things, the development of light, efficient, reliable. cost-effective actuators. Moving coil electrodynamic devices are inherently capable of large displacements and have been widely used as the basis for inertial actuators [6-81. Initial research by the authors had indicated the potential for piezoceramic inertial actuators to provide higher power density, better linearity and decreased power consumption, especially for moderately high frequency (100 to 10,000 Hz) applications [9]. The purpose of the research described herein was to explore the potential performance of piezoceramic inertial actuators in more detail. Both analytical and experimental aspects were addressed. Piezoceramic Inertial Actuator Conceuts Piezoelectric materials have found wide use in inertial sensor (e.g., accelerometer) applications because of high electromechanical transduction properties. These properties also make such materials excellent candidates for use in actuators. The need for rapid, highforce linear response effectively limits the materials Associate Professor of Aerospace Engineering, choice to piezoceramics [lo]. Senior Member AIAA Senior Engineer, Member AIAA Graduate Student, Student Member AIAA Professor of Mechanical Engineering An inertial actuator can be thought of as applying forces to a structure that are reacted by accelerating a supported mass. Even though piezoceramic materials . Copyright O 1995 by PCB Piezotronics. Inc. Published by are capable of providing high forces. there has been the American Institute of Aeronautics and Astronautics, little prior development of inertial actuators using them. Inc. with permission. largely because of the small strains (displacements) 3 4 4 0 American Institute of Aeronautics and Astronautics developed and high inherent stiffness. Both of these factors limit the practical performance achievable using direct piezoelectric acceleration of a given mass in the frequency range of interest. The development and use of mechanical amplification methods is essential to the practical success of piezoceramic inertial actuation. Several approaches to mechanical amplification [c.f., 1 1-15] were explored in this research. Figure 1 shows schematically three of the general concepts considered. For purposes of discussion, these may be considered to be either planar or axisymmetric.