The results of preliminary tests on an active helicopter rotor blade are presented. The blade, a Mach-scaled model of a CH-47D helicopter blade, has a discrete piezoelectric actuator embedded within the spar that controls a trailing edge flap via a pushrod. Ultimately, the blade will be tested on a helicopter rotor hover stand at MIT. In this paper, we describe the tests performed prior to hover testing. First, the actuator was tested on the bench to determine its control authority and frequency response. Second, the actuator was tested on a shake table to simulate the out-of-plane accelerations that would be encountered in a full-scale helicopter in forward flight. Third, the actuator was embedded in the model blade, and its response to low-frequency sinusoidal actuation was obtained and compared to the bench test results. Finally, the frequency response of the actuator in the blade was determined using swept sine excitation. All test results indicate that the actuator should produce the desired level of control authority in the model-scale rotor.

A methodology to develop piezostack-based actuator for trailing edge flap on a full-scale helicopter rotor blade is presented. By a systematic down-selection approach through the experimental validation on piezostack characteristics, one among numerous candidates was chosen for current study, which has higher stiffness as well as good strain/block force capability. The prototype actuator was designed and fabricated using two pieces of selected piezostack incorporated with a double-lever amplification mechanism that extends a level-fulcrum amplification concept. To validate the feasibility of the designed actuator, the prototype actuator was tested in vacuum chamber that simulates the centrifugal force environment. It was shown that the actuator operated with no major degradation in performance up to 600g of centrifugal loading. The present actuator has a capability of oscillating the trailing edge flap to the required deflection/frequency to actively control rotor vibration in the rotating environment. Then, a further design refinement was considered to reduce the drawbacks, which finally results in an improved actuator with peak actuation force of 80 lbs at 38 mils stroke.

The results of this feasibility study suggest that active blade twist technology is a viable means to reduce blade- vortex interaction (BVI) noise in rotorcraft systems. A linearized unsteady aerodynamics analysis was formulated and successfully validated with computation fluid dynamics analysis. A simple control scheme with three control points was found to be effective for active BVI noise reduction. Based on current-day actuation technology where 1 to 2 degrees of twist per blade activation span is expected, measurable noise reductions of 2 to 4 dB were predicted for the relatively strong, close vortex interactions. For weaker vortex interactions, reductions of 7 to 10 dB were predicted. The required twist actuation per blade span for complete unsteady loading cancellation, however, may be infeasible because of the large stroke and high frequency activation requirements.

This paper presents the design and preliminary test results of a piezoelectric stack (piezostack) driven leading-edge flap actuator. The actuator uses six commercially available piezostacks with a curved contact tip for force and stroke profile tailoring. Force requirements were calculated using a quasi-steady aerodynamic model. Stroke amplification is achieved through a single lever. Initial results show that the current prototype is not ready to achieve the desired stroke output, but potential problems are identified and action is being take to rectify these problems.

The aeroelastic scaling problem is revisited and it is shown that classical aeroelastic scaling relations, developed for flutter, need to be extended when dealing with modern aeroelastic applications, involving controls and adaptive materials based actuation. For such problems a novel two pronged approach is presented that produces refined aeroelastic scaling laws by a judicious combination of the classical approach with more sophisticated computer simulations. It is also shown that the rotary-wing equivalent to fixed-wing aeroelastic scaling, based on typical cross-section concepts, is the offset hinged spring restrained blade model. Scaling laws for the rotary-wing aeroelastic and aeroservoelastic problem are obtained. These scaling requirements imply that scale model tests, conducted on small models intended to demonstrate active control of vibration using adaptive materials based actuation, use very flexible models that often disregard aeroelastic scaling. Thus, the extension of these results to the full scale configuration is difficult.

Analytical and numerical investigations into active control of longitudinal and flexural waves transmitted through a cylindrical strut are presented in this article. Following along the lines of our previous work, a mechanics based model for a cylindrical strut fitted with magnetostrictive actuators is developed. For harmonic disturbances, a linear dynamic formulation, which describes the motion of the actuator, is integrated with the formulation describing wave transmission through the strut. The resulting system is studied in the frequency domain, and numerical simulations are used to examine the open-loop system. For disturbances transmitted over the frequency range of 10 Hz to 6 kHz, comparisons are made between the system based on piezoelectric actuators and the system based on magnetostrictive actuators. A closed-loop control scheme based on the developed model is proposed for controlling longitudinal vibrations.

Research is currently underway on the development of smart aircraft panels for the reduction of interior cabin noise. This research seeks to adapt previous Active Structural Acoustic Control (ASAC) research on flat plates with attached piezoelectric actuators to the curved panels that compose the exterior skin of an aircraft. In order to predict accurately the closed loop performance of ASAC systems for interior cabin noise reduction, efforts are being made to consider complicating factors in the dynamics of aircraft panels. As part of this research, a state-space model of a curved piezostructure was developed and used to investigate the effects of curvature on panel dynamics. Panel curvature was shown to increase control system bandwidth and to affect transducer coupling. In the present work, the effects of internal pressure loading on the dynamics of a curved piezostructure are investigated through the extension of the previously developed state-space model. The internal pressure model is verified based upon previous work. Pressure loading is shown to increase panel stiffness, thus increasing the natural frequencies of the panel. Further, pressure loading is shown to affect certain modes more than others, resulting in modal reordering. The increased natural frequencies and the model reordering significantly affect control system bandwidth and raise further issues in control design.

A numerical simulation for evaluating methods of predicting and controlling the response of an elastic wing in an airstream is discussed. The technique employed interactively and simultaneously solves for the response in the time domain by considering the air, wing, and controller as elements of a single dynamical system. The method is very modular, allowing independent modifications to the aerodynamic, structural, or control subsystems and it is not restricted to periodic motions or simple geometries. To illustrate the technique, a High Altitude, Long Endurance aircraft wing is used. The wing is modeled structurally as a linear Euler-Bernoulli beam that includes dynamic coupling between the bending and torsional oscillations. It is discretized via finite elements. The general, nonlinear, unsteady vortex lattice method, which is capable of simulating arbitrary subsonic maneuvers of the wing and accounts for the history of the motion, is employed to model the aerodynamics and feedback control via a distributed actuator is used for flutter and gust-load alleviation. The aerodynamic and structural grids do not have to be coincident. A controller that responds to induced loads and bending moments on the wing via a distributed actuator (e.g., piezoelectrics) by simultaneously decreasing the angle of attack is proposed.

Active aeroelastic wing concepts, sometimes also called active flexible wing concepts, have been investigated for several years to improve aircraft performance and stability. Two aspects are addressed in these studies: static aeroelastic effects like control surface effectiveness and the redistribution of aerodynamic forces for load reduction or drag minimization, and dynamic aspects like enhancement of flutter stability or reduction of aerodynamically induced vibrations of the structure.

In this paper, aeroelastic performance of smart composite wing in the presence of delaminations is investigated. A control system is designed to enhance the dynamic stability of the delaminated composite wing. The refined higher order theory for analyzing an adaptive composite plate in the presence of delaminations is used. The theory accurately captures the transverse shear deformation through the thickness, which is important in anisotropic composites, particularly in the presence of discrete actuators and sensors and delaminations. The effects of delamination on the aeroelastic characteristics of composite plates are investigated. An active control system is designed to redistribute the loads and to minimize the effect of delamination. The pole placement technique is applied to design the closed loop system by utilizing piezoelectric actuators. Due to delamination, the significant changes in the natural frequencies of the lower modes are observed. And this causes the reduction on the flutter speed of the delaminated plate model. The aeroelastic control results show that controller makes the delaminated plate model behave like a normal plate. The controller also reduces a significant amount of RMS values of the gust response due to gust.

This paper discusses research and development efforts directed at producing a passive, smart bolt for infrastructure applications. The smart bolts are fabricated from high-strength TRIP (Transformation Induced Plasticity) Steels. TRIP steels gradually transform from a non-magnetic, austenitic parent phase to a ferromagnetic, martensitic product phase. The stress-assisted (elastic range) and strain-induced (plastic range) phase transitions that inherently occur in the material provide a magnetic signature by which the damage state of the bolt can be determined. The irreversible nature of the phase transformations means that the bolt can passively retain peak strain (i.e., peak damage information) for later interrogation. Several different smart bolt design concepts were considered and evaluated. Design modeling and smart bolt optimization were achieved with the aid of a series of Pro/Engineer solid model renderings and a Pro/Mechanica finite element model analysis. The smart bolt was developed for high-tension fastener applications in the USAF C-130 Hercules cargo aircraft. Alloy design efforts, testing, and evaluation data are presented and discussed. Full-scale, smart aircraft bolt manufacturing is discussed and field application scheduling/evaluation plans are outlined. Extension of the smart bolt technology for construction industry applications is discussed.

The paper presents a linear, lumped-parameter, one-degree- of-freedom model that describes the first mode dynamic response of a piezoelectrically-actuated cantilevered beam. The original system consists of two identical, symmetrically disposed piezoelectric patch actuators bonded to a uniform beam with a tip mass. Specifically, the first mode of the system is described by an equivalent mass-spring-damper system where the equivalent mass, stiffness, damping, and force are functions of the parameters defining the piezoelectrically-actuated system. Experimental data is used to verify model damping and displacement. The model is then utilized to demonstrate that the dynamic response of the system depends upon four independent non-dimensional geometric variables. Numerical simulations are performed to graphically demonstrate this dependence and to indicate an optimal configuration for achieving a maximum deflection at the beam's free end during resonant excitation.

In this paper we present a hybrid adaptive control for rigid body slewing and constant amplitude feedback control for residual vibration suppression for a slewing active structure. This system consists of (1) a single-axis servo DC motor and encoder for rigid motion slewing and (2) a graphite/epoxy composite smart link with embedded strain sensors/actuators for active vibration suppression. The results of this study include the theoretical development and preliminary experimental results. The hybrid control algorithm uses the output sensor data from the encoder and strain sensor along with filters to derive velocity information to compute the control for the motor and strain actuators. Near-minimum time maneuvers based on an equivalent rigid structure are used to slew the flexible active structure. The tip mass was varied so that the robustness of the control system could be evaluated. Experimental slewing studies were performed to compare the benefits of using active rather than passive structures. The experimental results show a reduction in residual vibration and settling time for the active structure case.

NASA exploration missions to Mars, initiated by the Mars Pathfinder mission in July 1997, will continue over the next decade. The missions require challenging innovations in robot design and improvements in autonomy to meet ambitious objectives under tight budget and time constraints. The authors are developing design tools, component technologies and capabilities to address these needs for manipulation with robots for planetary exploration. The specific developments are: (1) a software analysis tool to reduce robot design iteration cycles and optimize on design solutions, (2) new piezoelectric ultrasonic motors for light-weight and high torque actuation in planetary environments, (3) use of advanced materials and structures for strong and light-weight robot arms and (4) intelligent camera-image coordinated autonomous control of robot arms for instrument placement and sample acquisition from a rover vehicle.

The output force-strain relationship typical of the performance of Terfenol-D transducers under varied operating conditions is examined to study transducer blocked force characteristics. The design and construction of a transducer for testing under controlled thermal, magnetic and mechanical load conditions are described. Results of compression tests at various applied magnetic fields and two initial mechanical stress states are used to generate load lines and the blocked force characteristics of the transducer. Comparisons of the transducer's force and strain output are made with published data. This test data is also used to examine the variability in Young's Modulus with applied magnetic field, strain and stress.

This paper reports the initial control experiments performed on a small magnetostrictive wire clamp assembly. Linear, lumped parameter, dynamic models are formulated based on magnetostrictive constitutive relations. Reduced order models are utilized to understand the expected performance in terms of the system parameters (e.g., the magnetoelastic parameters). It is shown that proportional flux rate (phi) feedback is fairly ineffective if used alone. Experimental results of proportional current feedback control are given. The models reported are useful for control analysis and actuator/sensor design.

Passive barriers to transmission of sound waves at frequencies below 500 Hz require large masses. Active noise cancellation systems, on the other hand, are complicated and expensive. We are developing a method for noise control, using an array of panels of magnetostrictive Metglas, which combines the low mass and flexibility of active noise control with the relatively low cost and simplicity of passive noise control. The method is based on the well known fact that an acoustic panel with a reaction mass, resonant at the frequency of the sound wave, will completely reflect that wave, simulating an infinite mass. By wrapping a coil around each Metglas panel, and terminating the coil in an impedance, the stiffness of the Metglas, and hence the resonant frequency of the panel, can be controlled by varying the terminal impedance. By choosing a terminal impedance which is itself frequency dependent, the panel can be made to resonate, and hence to have effective infinite mass, at all frequencies (over some fairly large range) simultaneously. This generally requires negative impedance, which can be produced by a simple circuit with an amplifier and feedback loop. In effect, the Metglas acts like both microphone and speaker in an active noise control system. Preliminary experimental results will be presented.

Active control architectures for broadband acoustic radiation reduction are compared both analytically and experimentally on a representative structure to quantify the capabilities and limitations of the proposed control methodologies. Specifically, three broad categories of control are compared: classical feedback (rate feedback), optimal feedback (Linear Quadratic Gaussian), and adaptive feedforward control (x-filtered Least Mean Square). A simple radiation model of the light fluid, structural-acoustic behavior of the composite panel is utilized to design the compensators and predict closed-loop performance. For each type of control, a single input, single output design is implemented on a composite panel with embedded active fiber composite piezoelectric actuators. Both the vibration and acoustic performance is recorded for each experiment under equivalent conditions to facilitate a generalizable comparison. Experimental results lead to generalized conclusions pertaining to the application of active structural-based control to improve the acoustic performance of complex structures.

The use of white-light interferometric multimode fiber-optic strain sensors is experimentally assessed within a new strategy involving discrete strain sensing for the active control of the radiated sound power. Each strain sensor uses a Fabry-Perot sensing interferometer and a Fizeau cross- correlation interferometer so that the output signal is directly related to the absolute measured strain. Two approaches are used to relate the radiated sound power to the structural strain. The first approach is based on the reconstruction of the transverse structural displacement field from the structural strain field using a finite differences scheme, and a wavenumber transformation of the structural displacement to obtain the radiated sound field; the second approach is based on an exact expression directly relating the radiated sound field to the wavenumber transform of the structural strain. In both approaches, the wavenumber transform is performed over the supersonic (radiating) components of the structural information. Both approaches for using the strain information are implemented into a multi-channel filtered-X LMS algorithm to perform the active control of the sound power radiated from the beam. Experimental results obtained using four strain sensors and both control approaches show that fiber-optic strain sensors and PVDF strain sensors provide similar and good control performance.

Electro-active polymer actuators (EAPA) have been a topic of research interest in the recent decades due to their ability to produce large strains under the influence of relatively low electric fields as compared to commercially available actuators. This paper investigates the feasibility of EAPA for active and passive cabin noise control. The passive damping characteristics of EAPA were determined, by measuring the transmission loss of four samples of various thickness and composition in an anechoic chamber in the 200 - 2000 Hz frequency range. This was then compared to that of Plexiglas and silicone rubber sheets of comparable thickness. The transmission loss of EAPA and Plexiglas were observed to be about the same. The transmission loss of EAPA was greater than that of silicone rubber, of the same thickness. The experimental and theoretical results computed using the mass law agree well. EAPA produces a strain of 0.006 for an applied field of 1 V/m. The ability of EAPA to potentially provide active as well as passive damping in the low to intermediate frequency range, along with being light- weight, pliable and transparent, makes it attractive for noise control applications as active/passive windows or wall papers.

The capabilities of a system developed on the basis of ANN are preliminarily evaluated, in suppressing the vibration field related to a general structural element; to this introductory aim, a numerical FE-model of a flat plate, part of an acoustic box for technology demonstration of architectures for sound radiation reduction, is referred to. The aluminum panel is excited by a 2-tonal point force, with the main peak at 50 Hz. The force may vary in frequency and amplitude (+/- 2% and +/- 10%, respectively). The time delay, between the two components of the signal is considered time-varying. A control system referring to 4 piezoelectric ceramic actuators and 8 accelerometers is used to minimize the vibration field; the placement of the different devices is defined by means of a proper tool based on Genetic Algorithms, and able to consider both the investigated frequencies; time delay (or phase shift), is not take into account in this process. An arbitrary signal, simulating the corresponding reference for the vibration suppression system, is transmitted to an ANN-based observer, aimed at identifying all the characteristic values, namely the amplitudes, the frequencies and the time shift. A classic feed-forward type minimization algorithm, ANN-based, is implemented. The identified solution is validated by means of a FE simulation, developed in the time domain, where the disturbance force is acting with the true values of the component sinusoidal forces (amplitude and frequencies), shifted by the correct value of the imposed phase. To have a first estimate of the capability of the proposed architecture in following the signal variations, a new signal is given to the ANN identifier, and the whole process is repeated.

Health monitoring passenger experiments will be flown on board of X-38 re-entry demonstrator as precursor to reusable launch vehicles such as the Crew Rescue Vehicle. Environmental load impacts and load critical conditions of the Thermal Protection System will be monitored with advanced in-flight and on-ground sensor instrumentation, the structural and functional integrity assessed, and potential consequences regarding the probability of hazardous failure or reduced life time evaluated. Intelligent health monitoring systems can streamline operational and maintenance costs while at the same time satisfying the high safety and reliability requirements. This imposes more stringent requirements on a network of sensors based on innovative technologies such as fiber optics, acoustic emissions, etc. The current development activities within the frame of the national technology program X-38/TETRA, the specific sensor features and the diagnostic expert system for data analyses will be highlighted and discussed in this paper.

A variety of structure integrated damage monitoring systems is based on non destructive testing (NDT) techniques which require sensing only. Damage information can only be given through external stimuli such as loads or vibrations being generated from the structure. Independence is achieved through an actuation system built into the structure, that allows to generate stress waves at any time. This principle is used with ultrasonic or lamb wave techniques and allows NDT to become an integral part a material when piezoelectric elements are adapted or integrated into it. Monitoring of the structure can thus happen on a `push-button' basis. In addition a lot of effort is devoted to sensor signal processing. Sensor signals may be understandable for components of simple geometric shape and isotropic material. With increasing complexity in geometry, anisotropy or damage configuration, signal processing becomes more ambitious, being a challenge for techniques such as neural networks, genetic algorithms, wavelet analysis or fuzzy logic. This paper explains some background logic of an actuator/sensor- based monitoring technique built into the structure. Different techniques for identifying an optimum number of sensors as well as handling complex signals is discussed. Verification of the technique is done for tests performed on a center-cracked panel.

An investigation was conducted to develop a real-time identification technique for the prediction of location and force history of low-velocity impacts on composite panels with beam stiffeners. Both analysis and experiments were conducted during the investigation. The technique used measurements from built-in piezoceramic sensors to reconstruct the force history using the smoother-filter algorithm. Impact location was determined by minimizing the difference between modeled response and actual response. A computer code was developed from a model for composite plates that allowed for the variation of structural properties (mass and stiffness) due to the presence of the stiffeners. The model was generalized so that it could potentially be used for any panel that has discontinuous material properties. Extensive experiments were conducted to verify the model and the computer code for impacts both in the bay and on the stiffener. The identification technique, as implemented on a personal computer, demonstrated real- time capability, and good agreement was found between predicted and actual force history and location. Parametric studies on the effects of sensor placement and impact mass on impact prediction were conducted.

The objective of this paper is to determine the strength reduction due to the embedment of a piezoelectric ceramic transducer in a composite. The composite was made from carbon/epoxy prepreg with a cross-ply lay-up. The transducer was embedded in the mid-plane of the composite material. The specimens were tested in tensile and compressive static loading. It was found that the embedded piezoelectric ceramic element with its interconnectors did not reduce the strength of the composite. In tensile and compressive static tests, the final failure did not coincide with the embedded piezoelectric ceramic transducer location in the composite.

In this paper, the use of state feedback control to enhance the sensitivity of modal frequencies to local damage is introduced. The method is intended for smart structures, which embody self-actuation and self-sensing capabilities. A simple example introduces the principle of sensitivity enhancing control for a single degree-of-freedom structure. Then, the method is applied to a finite element model of a cantilevered beam to demonstrate the magnitude of sensitivity enhancement achievable for modest, local damage. Methods of implementing state estimate feedback using point measurements of strain along the beam are described, and initial experiments demonstrating sensitivity enhancement for the cantilevered beam are reported. Results show that enhancement in sensitivity of modal frequencies of vibration to damage can be achieved using a single piezoceramic actuator and multiple piezoelectric strain sensors along the beam. The same sensor-actuator configuration can be used for vibration suppression or other control tasks, providing `dual use' smart structure sensors and actuators.

Flexbeams in hingeless rotors have non-uniform geometries to form virtual hinges for the lead-lag and flap motions of blades. For bearingless rotors, the flexbeams also contain a virtual hinge for the pitch of the blades. Commonly, flexbeams are damaged through high cyclic and vibratory loadings. Damage in the form of delamination for composite beams degrade performance and can potentially cause catastrophic failure. This paper develops an analytical model of tapered rotorcraft flexbeams. In a beam of uniform cross section, the transverse dynamics of a beam can be characterized by four wavetypes. By tracking the progression of the waves along the beam and back again, the wavetypes can be used to model the response. A more practical application of these wavetypes is to use them in a manner similar to shape functions for finite element analysis. The concept of a spectral element methodology is introduced for a uniform beam and then extended for an element with linearly varying width and thickness. A model of the delamination region is then incorporated into the spectral element methodology. Using this model for the dynamics of tapered beams, analytical results are then compared with experimental data for undamaged and damaged cases.

This work presents a practical and quantitative technique for assessment of the location and characterization of damages by longitudinal wave propagation measuring method. It is shown that the damage location can be simply determined by taking the difference of the time response between the healthy condition and the damaged condition, and the damage state would be quantified by the power consumption metric defined in frequency domain. The accuracy and the efficiency were validated by the experiment results on a simple aluminum beam. Further, the technique using piezoelectric materials as actuator and sensor separately and simultaneously is also demonstrated in order to reduce the numbers of the PZT patches embedded in the structures and the cost for wiring.

Health monitoring of structural joints is a major concern of the engineering community. Among joining techniques, spot- welding play a major role. Spot welding is the traditional method of assembly for steel-based automotive structures, while spot-welding of aluminum is being considered for future vehicular structures. Though spot welding of steel is well researched and understood, the spot-welding of aluminum still poses a considerable challenge. The durability and health monitoring of aluminum spot-welded joint is of major importance. The present paper addresses the use of electro- mechanical method and piezoelectric active sensors for health monitoring spot-welded structural joints.

Health monitoring methods using active sensors (e.g. piezoelectric transducers) and wavelet transforms are being developed in the Department of Mechanical Engineering at the University of South Carolina. In these methods, wave propagation signals are collected using arrays of piezoelectric transducers placed on or embedded in a structure. The collected signals are analyzed using appropriate wavelet transforms. The final interpretation of the sensor signals is based on signal patterns uncovered by the wavelet transforms in correlation with elastic-wave propagation theory. A number of specimens have been instrumented and tested, which include simple steel beams and actual composite aircraft panels. Impact tests simulating low velocity impact by foreign-object have been conducted and will be used to illustrate the wavelet-based methods.

In this paper an experimental analysis of Lamb waves interaction with riveted aluminum plates representative of aircraft splice joints submitted to fatigue tests is given. In this joint evaluation technique Lamb waves are excited and received outside the joint area using piezoelectric transducers bonded onto the plates. Detected damages are cracks in joint resulting from fatigue loading. These cracks lead to waveform transformations. This phenomenon is studied in this paper by considering the first derivative of the envelope of the time domain signal. The position of the first derivative curve maximum during cyclical loading gives information about crack development. It suggests, that monitoring the change in the delay of this maximum may provide a means of sizing the defects. By using X-rays, it was possible to measure the size of the cracks and compare it with delay evolution. Results are obtained for two types of fatigue sequences. It is experimentally shown that the relative delay measured is very sensitive to crack development. With the continued progress in the field of damage assessment techniques such as methods relying on Lamb waves, the safety of such structures can be ensured.

This paper presents work in progress concerning the development of a controller for active vibration control of a compliant structure using a magnetostrictive actuator. The paper describes the approach used to develop a model of the plant that includes both the actuator and cantilever beam considered for controller design. The active vibration control capabilities of a magnetostrictive actuator attached to a damped structure are considered. A linear model is assumed and adaptive filtering is used to identify actuator parameters. In addition, a Galerkin method is used to discretize the weak model of the compliant beam, which includes the influence of the attached magnetostrictive actuator. Special attention is paid to the interaction of the actuator and beam during the system identification efforts. An estimation of the model parameters is made through minimization of the beam's free end acceleration cost function. Finally, discussion of the initial observer and controller design effort is included.

In this work an approach to Structural Damage Analysis based on the utilization of actuators made by magnetostrictive materials is presented. New developed magnetostrictive actuators used to vibrate very stiff structures and able to acquire Frequency Response Functions (FRFs) in many points using piezoelectric sensors are the constitutive components of this approach. The numerical elaboration of the FRFs permits to analyze correlation between damaged and integer structures. In this way it is possible to create one or more Damage Indices in order to identify, localize and quantify different kinds of damages simulated on the structure. In particular it has been possible to perform many analyses during experimental tests in many frequency ranges and for different kind of damages. These experiences have led to a Damage Index whose values: (1) show a dependence with the distance between the damage and the sensor by which FRFs have been acquired, (2) increase reducing the distance between the sensor position and the damage location, (3) become higher if the damage extension increases. Furthermore, aim of this paper is to demonstrate and discuss the suitability of magnetostrictive devices for the development of an integrated system devoted to the health monitoring of the structures.

The growing interest in giant magnetostrictive materials for generation of strains in smart structure systems motivates the development of increasingly accurate performance prediction and optimization tools. We propose a model for the strains generated by magnetostrictive materials in response to applied magnetic fields. The direct or magnetostrictive effect is modeled by considering active and passive components of the strain. The active or external component, associated with the alignment of magnetic moments with the external magnetic field, is modeled with a ferromagnetic hysteresis model in combination with a quartic magnetostriction law. The passive or internal component, associated with the elastic response of the transducer materials as they vibrate, is modeled through force balancing which yields a wave equation with magnetostrictive inputs. The effect of stress on the magnetization of the magnetostrictive core, or the magnetomechanical effect, is implemented by considering a `law of approach' to the anhysteretic magnetization caused by stress. This provides a representation of the bi-directional coupling between the magnetic and elastic states. It is demonstrated that the model accurately characterizes the magnetic hysteresis and the strains output by a prototyping transducer.

In this paper novel Micro-Electro-Mechanical-Systems for magnetic field sensing are presented. These devices have been realized by using a micromachining approach which is fully compatible with standard CMOS technology. Several different structures have been developed and tested. Analytical system models have been defined in order to allow effective numerical simulation of the electro-mechanical system behavior. Both static and resonant working modes have been studied for different sensor architectures. Experimental results are reported regarding the metrological characterization of the devices. Particular attention has been also devoted to the effects of interfering inputs on the sensor output.

This paper is concerned with the optimal tuning of digitally programmable analog controllers on the ACTEX-1 smart structures flight experiment. The programmable controllers for each channel include a third order Strain Rate Feedback (SRF) controller, a fifth order SRF controller, a second order Positive Position Feedback (PPF) controller, and a fourth order PPF controller. Optimal manual tuning of several control parameters can be a difficult task even though the closed-loop control characteristics of each controller are well known. Hence, the automatic tuning of individual control parameters using Genetic Algorithms is proposed in this paper. The optimal control parameters of each control law are obtained by imposing a constraint on the closed-loop frequency response functions using the ACTEX mathematical model. The tuned control parameters are then uploaded to the ACTEX electronic control electronics and experiments on the active vibration control are carried out in space. The experimental results on ACTEX will be presented.

Launch loads, both mechanical and acoustic, are the prime driver of spacecraft structural design. Passive approaches for acoustic attenuation are limited in their low frequency effectiveness by constraints on total fairing mass and payload volume constraints. Active control offers an attractive approach for low frequency acoustic noise attenuation inside the payload fairing. Smart materials such as piezoceramics can be exploited as actuators for structural-acoustic control. In one active approach, structural actuators are attached to the walls of the fairing and measurements from structural sensors and/or acoustic sensors are fed back to the actuators to reduce the transmission of acoustic energy into the inside of the payload fairing. In this paper, structural-acoustic modeling and test results for a full scale composite launch vehicle payload fairing are presented. These analytical and experimental results fall into three categories: structural modal analysis, acoustic modal analysis, and coupled structural-acoustic transmission analysis. The purpose of these analysis and experimental efforts is to provide data and validated models that will be used for active acoustic control of the payload fairing. In the second part of the paper, this closed-loop acoustic transmission reduction is implemented and measured on a full-scale composite payload fairing.

Experimental results are presented for active vibration control of the Air Force Research Laboratory's UltraLITE Precision Deployable Optical Structure (PDOS), a ground based model of a sparse array, large aperture, deployable optical space telescope. The primary vibration suppression technique employs spatio-temporal filtering, in which a small number of sensors are used to produce modal coordinates for the structural modes to be controlled. The spatio-temporal filtering technique is well suited for the control of complex, real-world structures because it requires little model information, automatically adapts to sensor and actuator failures, is computationally efficient, and can be easily configured to account for time-varying system dynamics. While controller development for PDOS continues, the results obtained thus far indicate the need for an integrated optical/structural control system.

This study seeks to validate a predictive damper analysis, based on an idealized Bingham plastic shear flow mechanism, which incorporates leakage effects in an electrorheological (ER) damper. The ER bypass damper operates by a piston head pushing ER fluid out of a hydraulic cylinder and through an ER fluid bypass. The pressure to force ER fluid through the bypass produces the majority of the device's damping. The ER bypass is composed of an annulus formed from two concentric aluminum tubes. The application of a voltage potential between the aluminum tubes creates an electric field in the annulus that increases the yield stress of the ER fluid. The yield stress modifies the velocity profile of the fluid in the annulus and augments the damping coefficient of the device. The ER fluid damper contains a controlled amount of leakage around the piston head. The leakage allows ER fluid to flow from one side of the piston head to the opposite side without passing through the ER bypass. In this analysis, the leakage damping coefficient with incorporated leakage effects, predict the amount of energy dissipated for a complete cycle of the piston rod. Measured force verses displacement cycles for multiple frequencies and electric fields validate the ability of the non-dimensional groups and the leakage damping coefficient to predict the damping levels for an ER bypass damper with leakage.

This paper presents position control of cylinder system using electro-rheological (ER) valve actuators. Following the identification of field-dependent Bingham characteristics of an ER fluid, a single d.o.f. (degree of freedom) double-rod cylinder system is constructed by adopting bridge-circuit-controlled ER valve actuators. The governing equation of the motion is derived following by the design of a neural network feedback controller. The controller is then experimentally realized to achieve the position tracking control of the system. The single d.o.f. cylinder is extended to a 3 d.o.f. to provide more practical feasibility. The dynamic model of the 3 d.o.f. closed-loop cylinder system is established and a sliding mode controller is formulated by taking into account for parameter uncertainties. The controller is then implemented and position tracking control responses are presented.

A high speed traversing/positioning mechanism using two electro-rheological clutches is described. The traversing mechanism can be used to wind filaments onto bobbins. The traverse speed is 5 m/s, the required turn round period is 10 to 20 milli-seconds, the traverse length is 250 mm, the turn around position must be controllable and repeatable within +/- 1 mm and the traverse requires to be controlled to shape the resulting bobbin ends. These combined criteria of high speed and controllability makes the use of electro- rheological fluids a potentially viable solution. A dynamic simulation is available to predict the performance of the mechanism, however, a number of the electro-rheological fluid properties required by this simulation are temperature dependent. The methodology for predicting the thermal equilibrium temperature of the electro-rheological fluid within the high speed traversing mechanism is presented. Heat generation within the electro-rheological fluid, due to the fundamental operating mechanics of the mechanism, shearing of the electro-rheological fluid and the electrical excitation, are combined with the heat transfer from the mechanism to enable the operating temperature of the fluid to be determined. This operating temperature enables the temperature dependent fluid properties to be used in simulating the dynamic performance of the mechanism.

Our primary objective is to correlate damping predictions from a quasi-steady Bingham plastic damper analysis with experimentally measured steady state damping levels for a magnetorheological (MR) fluid damper. We seek to characterize damper properties of yield force and post-yield damping, and relate the damper parameters to effective MR fluid properties of dynamic yield stress and plastic viscosity. This characterization is done as a function of applied field and frequency. The damper was mounted in a mechanical scotch-yoke type damper dynamometer. The damper shaft was displaced sinusoidally with 1 inch of stroke and the resulting steady state force was measured as a function of applied current and frequency. The resulting force vs. displacement and force vs. velocity data is used to characterize the damper. The nonlinear hysteretic biviscous model is used to identify four physical parameters of the MR damper from the force vs. velocity diagram due to sinusoidal input displacements: pre-yield damping, post-yield damping, yield force, and zero-force velocity intercept. The post- yield damping and the yield force are used to calculate effective MR fluid properties of plastic viscosity and dynamics yield stress, respectively, from the damper data. Using the effective dynamic yield stress and the effective plastic viscosity, the Bingham plastic model is used to predict the damping, and these predictions are correlated with measurements from the force vs. displacement hysteresis cycle. The damping coefficient is the ratio of the damping with the field ON, to the Newtonian damping associated with the plastic viscosity. The resulting damping coefficient vs. nondimensional plug thickness diagram successfully predicts the damping behavior of the MR damper.

Magneto-rheological (MR) fluids are rapidly rising in prominence as a means of producing controllable damping devices for vibration control. MR fluids can be used in various modes of operation in order to provide damping forces. One of the least exploited of these modes is commonly known as squeeze-flow, where large, controllable forces can be generated over relatively small displacement ranges. In this paper the authors describe a recently constructed test facility in which an MR squeeze-flow device is incorporated as the damping element in a vibration isolator.

This paper investigates the behavior of piezoelectric elements as strain sensors. Strain is measured in terms of the charge generated by the element as a result of the direct piezoelectric effect. Strains from piezoceramic and piezofilm sensors are compared with strains from a conventional foil strain gage and the advantages of each type of sensor are discussed, along with their limitations. The sensors are surface bonded and are calibrated by means of a dynamic beam bending setup over a frequency range of 5 - 500 Hz. Correction factors to account for transverse strain and shear lag effects due to the bond layer are analytically derived and validated experimentally. Additionally, design of signal conditioning electronics to collect the signals from the piezoelectric sensors is addressed. The superior performance of piezoelectric sensors compared to conventional strain gages in terms of sensitivity and signal to noise ratio is demonstrated.

The purpose of this research is to address the issue of nonlinearities in APPN (Active-Passive Hybrid Piezoelectric Networks) based systems. Experimental effort is carried out to quantify the high order nonlinearity and hysteresis in piezoelectric actuation. Based on the sliding mode control theory, a robust controller is developed to compensate for the nonlinearities and uncertainties in the integrated system. The effectiveness of the proposed scheme is demonstrated by a numerical example.

A NASTRAN non-linear finite element model has been developed for predicting the dome heights of THUNDER (Thin Layer Unimorph Ferroelectric Driver) piezoelectric actuators. To analytically validate the finite element model, a comparison was made with a non-linear plate solution using Von Karmen's approximation. A 500 volt input was used to examine the actuator deformation. The NASTRAN finite element model was also compared with experimental results. Four groups of specimens were fabricated and tested. Four different input voltages, which included 120, 160, 200, and 240 Vp-p with a 0 volts offset, were used for this comparison.

In this study, the problem of controlling flexural waves transmitted through a cylindrical strut is addressed. This cylindrical strut is representative of a helicopter gearbox strut, which is attached at one end to the gearbox and at the other end to the fuselage. The primary disturbance is assumed to be transmitted from the end attached to the gearbox. Secondary forces are generated by a set of carefully positioned piezoelectric actuators, and feedforward and feedback schemes are used to determine the appropriate current inputs into these actuators. In one case, the control inputs to the actuators are chosen based on a performance function that includes the power supplied by the actuators to the strut. The abilities of the considered active control schemes to effectively attenuate the flexural displacements at the fuselage attachment end are examined and discussed. Future considerations for this work are also presented.

This paper provides a quantitative assessment of the performance of interdigital electrode (IDE) actuators and dampers constructed using ACX QuickPack^TM piezoelectric packaging technology. The details of the concept, device design, experimental plan and results, and analysis of the IDE devices are presented. Electromechanical coupling coefficients calculated using two different methods indicated values of 0.45 to 0.71 were achieved for IDE devices, as compared to 0.29 to 0.35 for conventional d₃₁ devices. Experimental results are provided that compare the damping and actuation performance of conventional d₃₁ devices with the performance of IDE devices. Resistively shunted IDE damper devices achieved greater than a factor of two in improvement in added damping over conventional PZT dampers. In addition, the high field generative strain of IDE actuators was shown to be 70% greater than that produced by a d₃₁ actuator.

Shape memory alloys (SMAs) have shown promise as high-force, high displacement actuators. Critical issues such as path- dependence, predictability and sensitivity to testing conditions, however, need to be addressed in order to design controllable actuators using SMAs. This paper presents research aimed at addressing some of design issues involving application of SMAs, particularly at actuators. Quasistatic experiments at constant stress, strain and temperature are consolidated on a critical stress-temperature diagram to delineate the regions of stability of the various phases of the material. The critical points from these quasistatic tests are found to be in excellent agreement with each other, and correlate relatively well with the constitutive models for SMA thermomechanical behavior. It is also observed that the state of the material is not unique at points along the transformation, and is dependent on the history of the material before the start of the test, individual test involved, the method of loading, and loading rates. Significant variation of the state of the material with different rates and conditions of loading are shown to further illustrate this point. This behavior is likely to be decisive in determining the dynamic behavior of the material, and underscores the need for approaches incorporating these issues for design of repeatable actuators.

The primary focus of this work is to develop a new analytical approach for thermal modeling of Nickel Titanium (NiTi) shape memory alloy membranes undergoing both phase transformation and large deflections. This paper describes a thermal model of a NiTi plate or thin film, including all the modes of heat loss and latent heat dissipation during the phase transformation. This model is used to predict the NiTi temperature during cooling. The results are compared with experiments conducted on a NiTi plate and thin film (3 micrometers thick), and very good agreement is found. The thermal model is also used to predict the temperature response of a bubble actuator proposed for use in a forced flow environment. Using a 3 mm diameter, 3 micrometers thickness bubble under forced airflow conditions it is possible to achieve a frequency response faster than 300 Hz. Additional calculations were made to verify the structural stability of the actuator system. Predictions indicated that for specific geometries a pressure of at least 35 kPa can be supported by the NiTi membrane. Deflections of a bubble actuator are shown to be on the order of 10% of its diameter while the strain remains below 4%.

The passive-adaptive approach to vibration control shows promise in its ability to combine the robust stability and low-complexity of passive tuned absorbers with the adaptability of active control schemes. Previous tunable vibration absorbers have been complex and bulky. Shape memory alloys (SMA) with their variable material properties, offer an alternative adaptive mechanism. Heating an SMA causes a change in the elastic modulus of the material by a factor as high as three. Incorporating SMA in parallel with traditional spring materials creates an absorber with a variable spring stiffness and a corresponding variable tuning frequency. Using on-off actuation of the SMA, discrete frequencies of tuning are obtained through the use of multiple SMA elements.

We present here our progress towards the development of a type of biomimetic active hydrofoil that utilizes Shape Memory Alloy (SMA) actuator technology. The actuation is presently applied to the control of hydrodynamic forces and moments, including thrust generation, on a 2D hydrofoil. The SMA actuation elements are two sets of thin wires (0.015' to 0.027') on either side of an elastomer element that provides the main structural support. Controlled heating and cooling of the two wire sets generates bi-directional bending of the elastomer, which in turn deflects (for quasi-static control) or oscillates (for thrust generation) the trailing edge of the hydrofoil. The aquatic environment of the hydrofoil lends itself to cooling schemes that utilize the excellent heat transfer properties of water. The SMA actuator was able to deflect the trailing edge by +/- 5 degree(s) at rates as high as 2 Hz. FEM modeling of hydrofoil response to thermoelectric heating has been carried out using a thermomechanical constitutive model for SMAs. FEM predictions are compared with experimental measurements.

In this report a new wire feeding system for fine wire bonding machines and its development is presented. The system is driven by a piezoelectric actuator, which replaces the electromagnetic actuators used in present bonding machines. To minimize the time used to develop the piezoelectric system, several models of the system have been derived and simulations have been made, to optimize the systems performance. After the wire feeding system has been manufactured, experiments have been made to validate the results conceived from the simulations. The performance improvement to the currently used feeding system is discussed.

The aerospace industry has seen a considerably growth in composite usage over the past ten years, especially with the development of cost effective manufacturing techniques such as Resin Transfer Molding and Resin Infusion under Flexible Tooling. The relatively high cost of raw material and conservative processing schedules has limited their growth further in non-aerospace technologies. In-situ process monitoring has been explored for some time as a means to improving the cost efficiency of manufacturing with dielectric spectroscopy and optical fiber sensors being the two primary techniques developed to date. A new emerging technique is discussed here making use of piezoelectric wafers with the ability to sense not only aspects of resin flow but also to detect the change in properties of the resin as it cures. Experimental investigations to date have shown a correlation between mechanical impedance measurements and the mechanical properties of cured epoxy systems with potential for full process monitoring.

In smart and adaptive structures very often piezoceramic elements are used as sensors or actuators. If these elements are used as actuators, an optimized bonding is necessary for a good efficiency of the overall system. In experiments it was observed, that the quality of the bonding depends on several factors. Therefore, a systematic investigation of the problem is given in the present paper both theoretically and experimentally. The main focus of the paper is to elaborate a simple measurement both of the bonding thickness and of the overall coupling efficiency between the piezoceramic element and the elastic structure. In the paper it is shown that by measuring the electric impedance at different frequency bands it can easily be seen if a bonding is good or bad. The experimental results are compared with theoretical models. One of the main results is that the thickness of the bonding layer should be small, because the loss of the electric field in the ceramic due to the additional capacity between actuator and structure is most important if a nonconductive adhesive is used.

The ongoing research and development of cost effective technology for remotely queried sensors for health and usage monitoring of composite structures has lead to the application of electrically conductive thermoplastic adhesive films. This paper intends to provide an in depth overview of a newly developed technology for the design and manufacturing of smart structures by introducing the application of electrically conductive thermoplastic adhesive films. The current technology is discussed and compared with this newly developed technology. It is shown that the structural aspects of this new technology are advantageous to smart structures' concept as a whole. Fabrication and manufacturing techniques for this new technology is discussed including the suitability of the process for automation. Specifically, standard tensile testing of the manufactured composite coupons with embedded thermoplastic conductive adhesive films has been performed and compared to the test results from copper embedded coupons. The effect of embedded thermoplastic stripes on stiffness as well as strength of the parent laminated- structure is evaluated and discussed. Further, fatigue testing has been done at various ultimate failure strength percentiles to determine some degree of the fatigue life of the composite and the embedded conductive and insulting films. The conductive thermoplastic films are found to be structurally superior to copper when embedded in a composite structure but the electrical conductivity is not as good as copper or other metallic conductors.

Efficient miniature actuators that are compact and consume low power are needed to drive space and planetary mechanisms in future NASA missions. Ultrasonic rotary motors have the potential to meet this NASA need and they are developed as actuators for miniature telerobotic applications. These motors have emerged in commercial products but they need to be adapted for operation at the harsh space environments that include cryogenic temperatures and vacuum and also require effective analytical tools for the design of efficient motors. A finite element analytical model was developed to examine the excitation of flexural plate wave traveling in a piezoelectrically actuated rotary motor. The model uses 3D finite element and equivalent circuit models that are applied to predict the excitation frequency and modal response of the stator. This model incorporates the details of the stator including the teeth, piezoelectric ceramic, geometry, bonding layer, etc. The theoretical predictions were corroborated experimentally for the stator. In parallel, efforts have been made to determine the thermal and vacuum performance of these motors. Experiments have shown that the motor can sustain at least 230 temperature cycles from 0 degree(s)C to -90 degree(s)C at 7 Torr pressure significant performance change. Also, in an earlier study the motor lasted over 334 hours at -150 degree(s)C and vacuum. To explore telerobotic applications for USMs a robotic arm was constructed with such motors.

The development of a linear transducer type piezoelectric motor is shown. This design utilizes the Inchworm principle and features a cylindrical device operating inside a metal tube. The motor is capable of developing high translational forces with macro and micro positioning capabilities. It consists of two cylindrical clamping elements separated by a central driver element which are physically connected but capable of independent operation through three multi-layer actuator stacks connected to a three channel controller. Inchworm type movement is possible through sequential activation of the three elements which allows linear motion along the tube.

A linear inchworm motor was developed for applications in adaptive, conformable structures for flow control. The device is compact (82 X 57 X 13 mm), and capable of unlimited displacement and high force actuation (150 N). The static holding force is 350 N. Four piezoceramic stack elements (two for clamping and two for extension) are integrated into the actuator, which is cut from a single block of titanium alloy. Actuation is in the form of a steel shaft pushed through a precision tolerance hole in the device. Unlimited displacements are achieved by repetitively advancing and clamping the steel shaft. Although each step is only on the order of 10 microns, a step rate of 100 Hz results in a speed of 1 mm/s. Since the input voltage can readily control the step size, positioning on the sub-micron level is possible.

The paper presents an inchworm robotic insect that is capable of motion over smooth terrain. The structure is lightly-damped and consists of a unimorph piezoelectric actuator (THUNDER) that acts as both structural member and source of motion and two custom-designed limbs that are attached to the body by means of adjustable clamps. The limbs can either roll or drag on the ground when an appropriate resonance is excited. The approach is called elastodynamic locomotion. A cycle of this `falling-ahead' unidirectional motion is composed of two segments: a shorter one when the front leg is rolling on the ground surface and transports the structure ahead while the rear leg drags on the ground, and a longer one, when the legs interchange their functions. The mathematical model assumes the legs are compliant. The geometry of deformation was utilized to find a configuration that is capable of maximizing the horizontal displacement of the robot. An actual inchworm design produced a motion that confirmed the theoretical predictions. A lumped-parameter dynamic model was formulated that allowed evaluation of the ground reaction forces and the velocity of the robot by using data of the geometric model and solving the inverse dynamics problem.

This paper explores the effectiveness of piezoelectric stack actuators for active control of 2D structures. The experimental results of active vibration reduction of an aluminum plate are presented. Piezoelectric patches are commonly used as a component of smart structures, because they can be either attached to or imbedded directly into the structure. The efficiency of piezo patches for vibration control strongly depends on the frequency and the location of the actuators. Mode shapes and strain distributions help to optimize the location of this actuator type. If the wavelength of the modes is decreased to the size of the actuator's finite length, some modes will always be uncontrollable, even if the actuator is optimally located. This limitation is not valid for point force actuators. Therefore the use of four piezoelectric stack actuators, which simultaneously support a plate structure at each corner and generate the control forces, is investigated in this paper. Because of many unknown parameters, the dynamic model of the test structure is obtained by an identification process instead of Finite Element Modeling. Control outputs are computed on the basis of a modal state observer considering 20 modes in connection with a linear quadratic optimal controller. The developed active vibration control achieves excellent results for the reduction at the resonance frequencies.

In this paper, a numerical simulation is presented that shows active and passive vibration confinement of a pinned- pinned beam. The beam is divided into three regions: an isolated, a transition, and a localized region. Two dynamic vibration absorbers are used in conjunction with two pairs of piezoelectric transducers with a feedback law to reduce the displacement amplitudes in the isolated region and to confine the vibrations to the localized region. The development of an eigenvector shaping technique is also shown. This technique shapes the eigenvectors of the uncontrolled beam to confine vibrations to the localized region. Finally, the numerical results of a randomly forced and a harmonically forced controlled pinned-pinned beam are presented. These results show that the combination of active and passive vibration confinement reduces the total power required for active vibration confinement and demonstrate that piezoelectric transducers are viable actuators for vibration confinement applications.

This article reports on the continued development of an embedded distributed piezoelectric actuator design concept for adaptive structures. The design is motivated by the fact that distributed actuators, as opposed to discrete actuators, will have a major impact on the implementation of modal control of flexible structures. The system under investigation is composed of layers of bimorph piezoelectric actuators, each activating a different mode in the structure. The article encompasses the discussion of theory for a multi-layered structure made of distributed actuators, computer aided modeling and simulations, experimental modal analysis, and correlation analysis. It is shown that the proposed arrangement of actuators removes the limitations associated with actuators' spillover and has the capability of activating desired modes. Furthermore, it is demonstrated that the experimental results for the mode shapes correlated well with those of the computer simulations.

Fatigue behavior of graphite/epoxy laminate, having [0/+/- 45/90]_s lay-up and embedded with piezoelectric (lead zirconate-titanate, PZT) actuator, was investigated under combined mechanical and electrical cycling loading condition. The PZT was inserted into a cutout area in the two middle 90-degrees plies. Experiments involved cycling of specimens at various maximum stress levels along with the excitation of the embedded actuator from -10 V to -100 V or 10 V to 100 V, which resulted in either in-phase or out-of-phase electrically induced strain relative to the applied mechanical loading or strain. In general, PZT performed better in the out-of phase than in the in-phase electromechanical fatigue condition. The fatigue life of the embedded PZT was more than one million cycles, for the applied maximum stress levels well above its design limit in the out-of-phase electromechanical and in only mechanical fatigue conditions. The PZT failed before one million cycles during the in-phase test at the applied maximum stress equal to its design limit. Above this stress level, a sharp drop-off occurred in the fatigue life during the in-phase electromechanical cycling condition.

Standard assumptions about the efficiency of active systems working against a load neglect the electro-mechanical coupling inherent in these systems. This paper contains a derivation for finding the actuation efficiency and work output in electro-mechanically coupled systems working against a load. This general derivation is for fully coupled, non-linear systems working against a generalized load. Three example cases are then shown to demonstrate several key aspects of the general derivation. The first example case is a 1D, linear discrete actuator working against a 1D, linear spring load. This example shows the effects of electro-mechanical coupling on the actuation efficiency. The second example case is of a piezoelectric bender first presented by Lesieutre and Davis in their derivation of the device coupling coefficient. The bender example demonstrates the differences between the device coupling coefficient and actuation efficiency as well as the use of the generalized derivation in mechanically complex problems. The final example presented is a 1D, linear discrete actuator working against a 1D, non-linear load in order to demonstrate the possibility of increasing the work output of a system through the use of non-linear loading functions. Finally, a custom built testing facility measures the work output and actuation efficiency of a discrete actuator working against both linear and non-linear loads. The testing facility was designed for load application with programmable impedances and closed loop testing at frequencies up to 1 kHz. The tests performed on a discrete actuator closely match the expected work outputs and efficiencies predicted by the theory.

A simple impedance based analysis is presented for resonant shunt circuits. The formulation is compatible with arrangement of shunt electronics and is used to clarify previously published resonance condition and to examine power. Since our resonance condition is contrary to previously published results, experimental verification is also presented. The experiments consist of both a series and parallel second mode absorber on a simple beam. Parallel and series shunts are compared.

The effect of bidirectional power flow on the power distribution system of an aircraft is addressed in this paper. The active vibration control problem of the tail surface of an aircraft using piezoelectric actuators is chosen to motivate the study presented. A simple dynamic model of the tail surface is developed. A current controlled switched-mode power amplifier is used to drive the actuators. The integration of the `amplifier-actuator' into the power distribution system of the aircraft is studied in detail. The effect of circulating energy between the actuators and the DC bus on the voltage on the bus is explained. Solutions to avoid instability and undesirable distortion in the DC bus voltage are proposed.

In space and automotive applications, the use of piezoelectric actuators is limited because of the high voltages the actuators usually require (over one thousand volts) and the low displacement levels they can achieve (about ten micrometers). We designed a series of Amplified Piezoelectric Actuators (APAs) that overcome these two drawbacks. These APAs operate with an input voltage less than 200 V because they employ a multilayer technology, and they offer displacement levels ten times greater than Direct Piezoelectric Actuators (DPAs), their direct-actuation counterparts.

Several sports are based upon a tool (club, bat, stick) striking an object (ball, puck) across a field of play. Anytime two structures collide, vibration is created by the impact of the two. The impact of the objects excites the structural modes of the tool, creating a vibration that can be felt by the player, especially if the hit is not at a `sweet spot'. Vibration adversely affects both feel and performance. This paper explains how piezoelectric dampers were developed to reduce vibration and improve the feel of ball-impact sporting goods such as golf clubs. The paper describes how the dynamic characteristics of a golf club were calculated, at first in the free-free condition, and then during its operation conditions (the swing of the club, and the impact with the ball). The dynamic characteristics were used to develop a damper that addressed a specific, or multiple, modes of interest. The damper development and testing are detailed in this paper. Both objective laboratory tests and subjective player tests were performed to evaluate the effectiveness of the piezoelectric dampers. The results of the tests, along with published medical data on the sensitivity of the human body, were used to draw a correlation between human feel and vibration reduction.

Recent advances in robotics, tele-robotics, smart material actuators, and mechatronics raise new possibilities for innovative developments in millimeter-scale robotics capable of manipulating objects only fractions of a millimeter in size. These advances can have a wide range of applications in the biomedical community. A potential application of this technology is in minimally invasive surgery (MIS). The focus of this paper is the development of a single degree of freedom prototype to demonstrate the viability of smart materials, force feedback and compliant mechanisms for minimally invasive surgery. The prototype is a compliant gripper that is 7-mm by 17-mm, made from a single piece of titanium that is designed to function as a needle driver for small scale suturing. A custom designed piezoelectric `inchworm' actuator drives the gripper. The integrated system is computer controlled providing a user interface device capable of force feedback. The design methodology described draws from recent advances in three emerging fields in engineering: design of innovative tools for MIS, design of compliant mechanisms, and design of smart materials and actuators. The focus of this paper is on the design of a millimeter-scale inchworm actuator for use with a compliant end effector in MIS.

A hybrid piezohydraulic pump is under development for smart structures applications. Structural control applications often require large force be delivered over a large displacement. Piezoelectric actuators produce a large force over a small displacement. This can be repeated many times per second. Step and repeat piezoelectric devices, such as inchworm motors, increase the power output of the actuators and have the potential to produce large forces and large displacements simultaneously. The piezohydraulic pump makes use of the step and repeat capability. The pump utilizes a piezoelectric stack actuator to drive a piston in a cylinder. The forward stroke pressurizes the hydraulic fluid in the cylinder and forces it out through a check valve. The reverse stroke draws fluid into the cylinder through a second check valve. The prototype pump has produced a working pressure of 6.9 MPa (1000 psi) and a flow rate of 45 ccm.

NASA's Next Generation Space Telescope (NGST) has a large deployable, fragmented optical surface (>= 8 m in diameter) that requires autonomous correction of deployment misalignments and thermal effects. Its high and stringent resolution requirement imposes a great deal of challenge for optical correction. The threshold value for optical correction is dictated by (lambda) /20 (30 nm for NGST optics). Control of an adaptive optics array consisting of a large number of optical elements and smart material actuators is so complex that power distribution for activation and control of actuators must be done by other than hard-wired circuitry. The concept of microwave-driven smart actuators is envisioned as the best option to alleviate the complexity associated with hard-wiring. A microwave-driven actuator was studied to realize such a concept for future applications. Piezoelectric material was used as an actuator that shows dimensional change with high electric field. The actuators were coupled with microwave rectenna and tested to correlate the coupling effect of electromagnetic wave. In experiments, a 3 X 3 rectenna patch array generated more than 50 volts which is a threshold voltage for 30-nm displacement of a single piezoelectric material. Overall, the test results indicate that the microwave-driven actuator concept can be adopted for NGST applications.

Recently the design of curved thunder actuators (deflections from 1 mm - 15 mm) has been a topic of study for many researchers. The work in this study deals with the development of a general technique based on shell theory. The technique can be applied to a broad array of actuators to include: Rainbows, Thunders, C-Blocks and others. The formulation begins with the equations for a general shell theory. Next the equations are reduced to the forms of equations for the particular actuators in a manner that they can be applied to a myriad of curved composite actuators. The technique is then experimentally verified on a Thunder actuator system. Next, the system is controlled using both classical and intelligent control techniques. In addition hardware and circuitry issues are explored.

In this paper, we first formulate the equations of the electrical network. This network is composed of resistors, current sources, voltage sources and voltage to voltage amplifiers. It has an arbitrary shape. It is connected to piezoelectrical patches which are distributed transducers on the elastic thin shell. A 2D Reisner-Mindlin model of piezoelectrical thin shell is obtained under coupled to electronic network. A second model is derived under co- localization assumption. The two models are written under the form of a global variational formulation. Sufficient conditions on the network are stated in order to insure existence and uniqueness of the solution of the coupling. They are based on a graph interpretation of abstract conditions stated in the framework of functional analysis. Finally, numerical simulations of the Reisner-Mindlin shell in vibrations are presented for a particular choice of electric circuit. This last is designed in order to act as a stabilizer of the shell vibrations.

This paper considers analysis and simulation of the dynamics and control of the elastic vibrations of a shallow spherical shell. Active control is carried out using piezoceramic materials (PZT, i.e. Lead Zirconate Titanate) as actuators. By using Galerkin's method and modal discretization, a mathematical model of the dynamics of the spherical shell is developed. The generalized forces produced by the actuators are determined considering the interaction between the shell structure and the PZT actuators via the principle of virtual work. Feedback control is carried out using two methods namely, LQR and Velocity Feedback methods. The effects of unmodeled modes and physical parameter uncertainty on the control performance of the system are investigated.

Piezoelectric materials can be used for structural actuation and sensing. Compensation schemes for local control using such actuators and sensors are investigated. It is found that increasing the rolloff of the dereverberated transfer function by shaping the actuator and sensor improves control design. However, experimental data shows little rolloff; this is attributed to unmodeled dynamics.

Haptic rendering is the process of computing and generating forces in response to user interaction with virtual objects. The interaction modality of haptic feedback gains more and more of importance for simulation tasks in virtual environments. However there are only very few portable haptic interfaces, with which the user can experience in a natural way the sensation of force feedback. The scope of this paper is to present a new portable haptic interface using shape memory alloy wires as actuators. Shape memory alloys, and especially the nickel-titanium compositions, offer a number of engineering properties available in no other material. The ability to respond with significant force and motion to small changes in ambient temperature and the capability to convert heat energy into mechanical work provide the designer with a new array of possibilities. Beside some application specific characterization of the actuator material with respect to energy consumption and dynamic behavior for loading, the mechanical layout of the interface is discussed in detail. To realize a light and compact design of the interface, a flexure hinge is considered as an essential part of interface.

The functionality of modern products is increased by the distinct interaction of mechanics, electronics, control engineering and computer science. Simultaneously the life cycles of such smart and often called mechatronic systems are becoming shorter. Thus it becomes more difficult to minimize development time and cost. The development process can be improved significantly by using interdisciplinary development methods and tools. However, all existing design strategies of the participating disciplines are ineligible. Either the strategies are domain specific or they are insufficient for the development of mechatronic systems. In addition, software tools, involved persons and organization structures are often not regarded. This paper suggests a new strategy for the development of mechatronic systems that tempts to meet five major challenges: simultaneous engineering, integration of shape and function, virtual prototyping, experimental validation and computer aided engineering. It considers the development process from the product idea to the first functioning prototype and combines functional and geometrical modeling techniques. The strategy bases on established strategies and our experiences in the development of wire bonding machines, which are used in semiconductor manufacturing. The development of an exemplary subsystem is resumed.

To assist in the development of vibration isolation systems, we have developed an actuator which seeks to improve performance using only internal position measurements. As such, the actuator can act as a variable-stiffness member and can improve vibrational performance of the structure. In addition to providing good isolation itself, such as actuator also has the potential to enhance the performance of systems based on more sophisticated controllers.

In this paper, the design and implementation of smart actuators for active vibration control of mechanical systems are considered. The proposed smart actuator is composed of one or several layers of piezoelectric materials that works both as a sensor and an actuator, in vibration control applications. An adaptive technique is developed for estimating the unknown equivalent capacitance of the piezoelectric material, which would be used for separating the effect of actuation from the measured (sensed) signal due to the strain in the material. This algorithm can be implemented in real time on a digital signal processor (DSP), allowing for the development of a DSP-based adaptive self-sensing actuator. This self-sensing actuator is then used in the vibration control of flexible structures. The vibration control system includes a power electronic amplifier, a data acquisition system, and a DSP for digital control implementation. A simple PID control strategy is employed for vibration reduction and motion control of cantilever beams using the proposed self-sensing actuators. Simulations and preliminary experiments show good results.

A smart structures system based on the fiber optic sensors and ER fluids actuators have been developed to used active vibration control in this paper. There are many advantages of this optical sensor such as high accurate, simple construction and low cost. A method of sensing vibration using the detection of changes in the spatial distribution of energy in the output of a multi-mode optic fiber has been demonstrated. A multi-mode optical fiber whose diameter is 200/230 micrometers is used in the present experiment. A multi- mode optical fiber vibration sensor based on the detection of the spatial speckle has been made. The experimental test have been finished. It has been found that this fiber optic sensor has higher sensitivity and better dynamic and static properties. At the meantime, the electrorheological (ER) fluids have been used as actuator to vibration control because of it's fast strong reversible change of the rheological properties under external electric field. A smart composite beam embedded ER fluids and fiber optic vibration sensor have been made in this paper. Finally, the experiment of structural vibration active control of smart structure incorporating the ER fluids and fiber optic vibration sensor have been finished.

In this study, distributed piezoelectric sensor/actuator systems for the vibration control of the composite plate are designed. A new 2D modal transducer theory is developed based on the finite element modeling of the integrated structure. This theory enables one to determine spatial gain distribution required for the realization of specific modal transducer, without restrictions on the geometry and boundary conditions of the structure. As the practical means for the implementation of optimal gain distribution obtained, two design methods for the distributed modal transducers are developed. First, using multi-layered PVDF film, modal transducers are designed by optimizing electrode patterns, lamination angles, and relative poling directions of each PVDF layer. Second, modal transducers are designed by dividing whole spatial area of a single PVDF film into several electrode segments and optimizing gain-weight on each electrode segment. These two design methods correspond to the approximation of a continuous function using discrete values. For the experimental demonstration, sensors/actuator systems for the control of first and second vibration modes of cantilever composite plate are designed using the proposed methods. Sensors are designed to minimize the observation spillover and actuators are designed based on the criterion of minimizing the system energy in the control modes. The real-time vibration control of integrated smart structures is successfully achieved.

The authors have developed an active microvibration control system using voice coil linear motors, air and piezoelectric actuators. This system is designed to reduce microvibration of the six degrees of freedom associated with rigid body modes of the vibration isolation table by giving feedback of the absolute displacement and absolute velocity of the table. To improve vibration isolation performance, a feed- forward control force is added to the sway components in each dimension. This system can also control bending modes of the table in the frequency range up to 200 Hz by applying a new proposed Virtual Tuned-Mass Damper theory, which is a type of the pole assignment method. In pole assignment problems, the semi-optimal pole is chosen by a Genetic Algorithm. As the result, the microvibration of the floor at around 0.5 cm/s² and small earthquake at around 8 cm/s² were reduced to about 1/100 in acceleration waveforms at the vibration isolation table. In comparison with the floor, the vibrations of the isolation table were decreased over the entire frequency range. This system showed good vibration control performance when an impact excitation was applied to the table directly. Vibrations were damped even within a time scale of around 0.1 sec. The resonance amplitudes around the bending modes of the table were reduced from 1/5 to 1/15 by the Virtual Tuned-Mass Damper method.

The structural responses of beams and tubes is investigated in theory and experiment in order to locate and assess damage in the form of fatigue cracks. Crack length measurements are performed in transversely vibrating beams by determining the resonant frequency, which is stabilized through a phase locked loop. Cracks are initiated and propagate from the notch of the structure which is vibrating at resonance. The frequency in relation to the crack length is modeled including the nonlinearity effect due to closing of the crack. Fatigue tests were also carried out with piezoelectrically excited microstructures.

Telescopes are pointed to their targets on the sky by the movement of their optical system (reflectors, mirrors) in two or three axes. The achievable pointing accuracy is depending on the quality of the elasto-mechanical system, which is supporting the optics, and the drive system, which is actuating the axes movements, and limited in existing telescopes by the number of sensors and actuators in the axes. With the classical arrangements only the rigid body regime of the structural system can be controlled. Effects in the quasi-static regime and in the flexible body regime of structural deformations are out of influence of the position sensors and drives of the axes and must be handled by other means. With now available smart structure concepts it is possible to overcome these restrictions and to enhance the pointing accuracy of the telescopes by rather inexpensive additional means. In the paper a smart system approach is described, which is based on a modal observer concept. The observer uses the eigenmodes of the structural system to predict the deformation behavior based on the measurements of modal sensors. Results of the achievable improvements are demonstrated by two telescope projects, in which the modal observer enhancement will be realized.

We have developed a control strategy based entirely on the relative position of the armature and body. Additionally, we have developed an actuator which has the necessary features to take advantage of this approach. This strategy provides a modular approach to vibration isolation because it acts independently of the dynamics of any attached structures. While the system is unable to match the peak performance of adaptive multiple-input multiple-output controllers, it provides significant broadband isolation with a simple, local controller. Further, this control can be implemented within the actuator, providing more sophisticated controllers with an actuator that has less force transmission than conventional devices. This offers the potential of additional gains in isolation performance. We present the analytical model of such an actuator and control algorithm, and investigate practical limits on the general problem of position-based control for vibration isolation of structures. Within these limits, we propose a method for controlling an actual system which provides good broadband isolation with a simple control architecture. Finally, we prove the approach by demonstrating it experimentally.

We are studying structures in CFRP with bonded piezoelectric sensors and actuators, able to monitor and compensate the vibrations affecting the performance of these systems. In this paper a detailed description of the simulation model is presented and the results compared with the experimental measurements. The transient response of a plate structure under vibrations with and without feedback control are shown.

This paper reports on practical tradeoffs and design considerations associated with the use of active control to dynamically stabilize structural members against linear buckling. The relationship between active control and other limitations on structural stability, such as yield strength, is examined for the case of axially loaded columns. Graphical constructs compare active control of buckling to various passive alternatives, such as changing the cross- section of a member to increase the moment of inertia, and hence the buckling load. These constructs serve to delineate the design space, showing for which geometrical regimes active control of buckling is a viable option. This delineation of the design space suggests where to look (and where not to look) to find potential applications of active buckling control. This research exposes an open question in our understanding of the effects of material yield strength on systems undergoing active stabilization. This result highlights the need to revisit certain classic experiments that form the basis for our understanding of the delineation between elastic and plastic failure modes to address the active stabilization regime.

The resonance modes and the displacement sensitivity of a dual-stage, piezoelectric micro-actuator/suspension for high track density magnetic recording systems were investigated by finite element method. Theoretical dynamic and electrostatic analyses were performed to investigate the resonance frequency of in-plane bending mode and the displacement sensitivity of the piezoelectric actuator with different shapes. Based upon the analyses of piezoelectric actuators, the optimization of piezoelectric suspension was conducted to achieve a high resonance frequency of sway mode and large displacement sensitivity. The finite element simulation results on a planar piezoelectric suspension agree quite well with the experimental measurements using a Laser Doppler Vibrometer. The optimized piezoelectric suspension demonstrates better performances than those of the planar piezoelectric suspension.

The response of five commercial piezoelectric stack actuators under electrical, mechanical, and combined electro-mechanical loading was investigated in this study. The focus was to understand the behavior of piezoelectric materials under the combined electro-mechanical loading scenario, and to determine fundamental properties important for design of actuator systems that incorporate these materials. Parameters that were evaluated include strain output, permittivity, mechanical stiffness, energy density, and coupling coefficients as a function of mechanical preload and electric field values representative of in- service conditions. Stiffness measurements indicate strong dependence on applied electric field and mechanical preload, as well as the number of mechanical cycles. For certain actuators, stiffness values change by as much as 100% depending on the operating conditions. The voltage induced strain output of some of these samples which include both PZT and PLZT compositions exceeds 2,000 microstrain for certain operating conditions (under the constant preload). Initially, the strain output is enhanced with an increase in mechanical preload and the maximum strain values are obtained when the stacks are preloaded between 4 - 6 ksi. High values of output energy density can be achieved for this operating region. Applying a higher preload has the advance effect on the stacks response since mechanical loading impedes domain wall motion reducing the overall strain output. A similar effect is observed under the combined out-of-phase electro-mechanical loading, and we have found that the highest energy density is obtained if the mechanical loading amplitude does not exceed +/- 2.5 ksi.

Circular samples of Polyvinylidene Fluoride (PVDF) have been designed, fabricated, and tested to determine the feasibility of using this material as the active element of an inexpensive, multifunctional, co-located sensor array that can simultaneously measure strain and acoustic pressure. The custom electrode etching capability of PVDF, along with its ability to produce a linear response signal without the need of an external power source, makes this material very attractive. Custom etching allows many mechanical strain and acoustic sensors to be easily developed on the same film. This sensor system can then be used in structural noise and vibration control applications as well as damage detection applications. Feasibility tests were conducted in an anechoic chamber facility located at the University of Maryland. Sensor specimens of 28 micrometers and 52 micrometers thickness were tested using a loudspeaker and a calibrated condenser microphone. An analytical model describing the PVDF's plate response under acoustic loading was derived and illustrates the trend of the experimental data. Exact agreement between the analytical and experimental data is complicated because of the unknown cavity stiffness. This preliminary work suggests that a more refined model is required.

We investigate how the Space Interferometer Mission (SIM) will be able to meet its instrument astrometric pointing requirements. The most demanding SIM pointing requirement is to independently point each interferometer arm to better than 0.07 micro-radian RMS residual jitter using a 0.01 Hz bandwidth optical sensor. The predominant contributors to the pointing error are the spinning spacecraft reaction wheel assemblies which emit disturbances from 2 Hz to 1 kHz. An estimate of the residual pointing error is presented for this most challenging vibration attenuation problem which is with isolated reaction wheels with no optical compensation. Central to this estimate is the Micro-Precision Interferometer testbed which is a softly suspended hardware model of a future space-borne optical interferometer and is dimensionally representative of SIM. The prediction of the on-orbit pointing error is determined in part by measuring broadband disturbance transfer functions from the testbed's isolated reaction wheel location to the camera output, where the pointing must be stabilized. Off-line, the procedure combines the measured testbed transfer functions with an empirical model of the reaction wheel disturbance to determine jitter over the entire range of wheel speeds. Results suggest that the most demanding SIM pointing requirement is currently violated by a factor of ten.

Piezoelectric actuator technology has now reached a level where macro-positioning applications in the context of smart structures can be considered. One application with high payoffs is vibration reduction, noise reduction, and performance improvements in helicopters. Integration of piezoelectric actuators in the rotor blade is attractive, since it attacks the problem at the source. The present paper covers the development of a piezoelectric actuator for trailing edge flap control on a 34-foot diameter helicopter main rotor. The design of an actuator using bi-axial stack columns, and its bench, shake, and spin testing are described. A series of enhancements lead to an improved version that, together with use of latest stack technology, meets the requirements. Next steps in this DARPA sponsored program are development of the actuator and full scale rotor system for wind tunnel testing in the NASA Ames 40 X 80 foot wind tunnel and flight testing on the MD Explorer.