Diann Brei

Piezoelectric Actuation: State of the Art

Significant advances in smart material actuators have taken place in the past decade. The holy grail of actuator research is an architecture that can generate high displacement and force throughout a broad frequency range while not consuming a significant amount of electrical power. The large appeal of using smart material actuators stems from their high mechanical energy density. However, all smart material actuators generally have at least one shortcoming involving either mechanical stroke, force, or frequency capability. Whenever speed is a consideration, piezoelectric actuation is the most commonly employed. The purpose of this paper is to review the most current trends in piezoelectric actuation architectures. The paper does not present the theoretical details of each actuator, but instead strives to highlight the novel concepts used in each design to overcome the stroke limitation of the material.

BENCH-TOP CHARACTERIZATION OF AN ACTIVE ROTOR BLADE FLAP SYSTEM INCORPORATING C-BLOCK ACTUATORS

This paper presents the bench-top testing of a piezoceramic C-block driven active flap system designed to suppress the vibrations of a helicopter rotor blade. The C-block actuators are curved benders designed to generate a larger force output than a straight bender, while providing deflections large enough to eliminate the need for external leveraging systems necessary with stack driven systems. The actuators power a balanced active flap designed to minimize the effect of air speed and rotor speed on flap deflection. Quasi-static experimentation at 1 Hz produced maximum angular flap deflections of 8.4° peak-to-peak. Dynamic tests were conducted over a 40 Hz frequency range demonstrating the ability to generate significant flap deflections both before and after the first natural frequency. Over the 40 Hz range, the flap deflections never dropped below 8° pp, with a first natural frequency of 27 Hz. The flap deflection reached a maximum value of 13.6° pp at 40 Hz. If the applied voltage is increased to the maximum allowable level, it is predicted that flap deflections as large as 20° pp can be achieved.

WIND TUNNEL TESTING OF A HIGH AUTHORITY AIRSPEED INSENSITIVE ROTOR BLADE FLAP

A viable active rotor blade flap system for vibration control needs to address the actuator authority, the sensitivity of flap pitch deflections to changes in angle of attack, aerodynamic moments generated by flap deflections themselves and inertial moments due to blade plunge motions. This paper presents the experimental wind tunnel results of a new active rotor blade flap system that has the potential to overcome these problems. This active rotor blade flap system is insensitive to airspeed, angle of attack changes and plunge motions because of a novel high authority actuation system, C-blocks, and the utilization of a mass and aerodynamically balanced flap. C-block actuators are curved piezoelectric benders which can provide over twice the force of comparable straight benders without requiring the use of external leveraging systems necessary with piezoelectric stacks. The initial wind tunnel results proved that the use of C-block actuators and a mass and aerodynamically balanced flap can generate flap deflections in excess of 17” pealc-topeak that are independent of airspeed. Additionally, it was proven that the C-block driven flap is capable of creating pitch changes of the entire rotor blade section demonstrating potential for full flight control.

Proof-of-concept investigation of active velcro for smart attachment mechanisms

Abstract : This report provides a summary of the motivation, methodology and research results for two different projects supported under this effort. In Electrically integrated active compliant transmission (ACT) Actuation Technologies two different actuation approaches were developed, modeled, fabricated and experimentally validated: 1) a d31-approach based on the Recurve architecture that generates higher forces and 2) a d33-approach based upon a compliant mechanism that provides more amplified strain. A first-generation power amplifier was designed that efficiently swaps energy allowing low voltage batteries to produce high voltage drive signals. Both piezoceramic actuation systems were integrated into the INertially STAbilized Rifle (INSTAR) to eliminate aiming errors by stabilizing the barrel assembly providing a significant advancement in small arms. In the second project, Proof-of-Concept Investigation of Active Velcro Autonomous Docking of Micro- and Nano-Satellites, a new connection methodology, Smart Attachment Mechanism (SAM) technology, was invented, modeled and experimentally characterized that possesses the ability to actively connect two surfaces (engagement, retention, release) and effect relative planar motion between them (translation, rotation). This work laid the necessary foundation for further development of this unique paradigm which is useful for any unstable environment (space, fluidic, moving, vibration, etc) where active connection and motion is simultaneously required.

Deflection-Voltage Model and Experimental Results for Polymeric Piezoelectric C-Block Actuators

This note presented a simple steady state theoretical deflection voltage model for a generic individual C-block. This model was derived by solveing the equations of equilibrium and boundary conditions obtained from Hamiltons principle

Tile-based rigidization surface parametric design study

Inflatable technologies have proven useful in consumer goods as well as in more recent applications including civil structures, aerospace, medical, and robotics. However, inflatable technologies are typically lacking in their ability to provide rigid structural support. Particle jamming improves upon this by providing structures which are normally flexible and moldable but become rigid when air is removed. Because these are based on an airtight bladder filled with loose particles, they always occupy the full volume of its rigid state, even when not rigidized. More recent developments in layer jamming have created thin, compact rigidizing surfaces replacing the loose volume of particles with thinly layered surface materials. Work in this area has been applied to several specific applications with positive results but have not generally provided the broader understanding of the rigidization performance as a function of design parameters required for directly adapting layer rigidization technology to other applications. This paper presents a parametric design study of a new layer jamming vacuum rigidization architecture: tile-based vacuum rigidization. This form of rigidization is based on layers of tiles contained within a thin vacuum bladder which can be bent, rolled, or otherwise compactly stowed, but when deployed flat, can be vacuumed and form a large, flat, rigid plate capable of supporting large forces both localized and distributed over the surface. The general architecture and operation detailing rigidization and compliance mechanisms is introduced. To quantitatively characterize the rigidization behavior, prototypes rigidization surfaces are fabricated and an experimental technique is developed based on a 3-point bending test. Performance evaluation metrics are developed to describe the stiffness, load-bearing capacity, and internal slippage of tested prototypes. A set of experimental parametric studies are performed to better understand the impact of variations in geometric design parameters, operating parameters, and architectural variations on the performance evaluation metrics. The results of this study bring insight into the rigidization behavior of this architecture, and provide design guidelines and expose tradeoffs to form the basis for the design of tile-based rigidization surfaces for a wide range of applications.

Force-Deflection Behavior of a Smart Attachment Mechanism

Active Velcro is a unique form of distributed actuation that generates relative planar motion between two surfaces while maintaining a positive connection. The key distinguishing feature of this active surface is its ability to engage and retain the guest surface. This paper focuses on understanding the mechanism behind this ability. An analytical model that captures the quasi-static force-deflection behavior of this complex mechanism under general loading conditions is derived, while specific models for engagement and retention are presented. The validity of the models was experimentally verified under three common operating scenarios: free deflection, surface positioning and guest surface engagement/retention. The impact of manufacturing effects, friction and plastic deformation are examined. Significant improvement over MEMs based active surfaces is demonstrated.