With the emergence of MEMS and LIGA technology piezoceramics can be integrated to create tiny solid state devices. The precision motion that piezoelectric materials can provide is complimented by the tolerances that can be achieved through MEMS and LIGA micromachining. The integration of these two technologies is ideal for microactuation. A LIGA based devices has been developed that is capable of amplifying small motions from a piezoelectric element into an output stroke angle large enough to produce flight. Micro flight is a difficult aerodynamic problem. With small wing areas conventional lift requires velocities that are difficult to achieve. However it is possible to induce lift using drag in the same manner as some birds and insects. Flapping is a highly efficient way to produce flight. For sustained low energy flight both insects and birds use a complex elastodynamic system that only requires them to excite it at its natural frequency. The actuation device presented is based on the same flight principle of insects and birds, a resonating elastodynamic system excited at its natural frequency or at a lower harmonic. This allows for long distance flights that require little energy. Piezoceramics posses a high energy level and force output that can excite the device and induce a flapping motion. The dynamics of the system rely on the LIGA flexure mechanism, the piezoelectric element, as well as the aerodynamic interaction of the wing and the air which is a complex nonlinear problem.

An ice detection system consisting of a resonant piezoelectric sensing-element and microprocessor control has been developed to automatically and distinctly sense ice and water films up to 0.5 mm thick. Accretion of ice and/or water on the sensor surface modifies the effective mass and/or stiffness of the vibrating transducer; these variations are sensed by measuring the changes in transducer resonant frequency. In case of ice films, resonant frequency of the transducer increases steadily from 14 kHz for a 0.06 mm-thick layer to 28 kHz when the ice film is 0.45 mm thick. In contrast, the transducer resonant frequency decreases slightly from 10 kHz for a 0.06 mm-thick layer of water to 9.5 kHz for a 0.45 mm-thick film. Repeatability experiments revealed test-to-test variations of 3.8% and 0.7% for ice and water films, respectively. A portable, low-power, microprocessor-controlled electronic circuit has been designed and implemented to automate the resonant frequency measurement and determine the thickness of ice/water present on the transducer surface.

Active control of fixed wing aircraft using piezoelectric materials has the potential to improve its aeroelastic response while reducing weight penalties. However, the design of active aircraft wings is a complex optimization problem requiring the use of formal optimization techniques. In this paper, a hybrid optimization procedure is applied to the design of an airplane wing, represented by a flat composite plate, with piezoelectric actuation to improve the aeroelastic response. Design objectives include reduced static displacements, improved passenger comfort during gust and increased damping. Constraints are imposed on the electric power consumption and ply stresses. Design variables include composite stacking sequence, actuator/sensor locations and controller gain. Numerical results indicate significant improvements in the design objectives and physically meaningful optimal designs.

This paper outlines the design, fabrication and testing techniques used for a new class of active wings. In support of recent efforts to shrink high authority, high speed aircraft flight controls for Micro Aerial Vehicles (MAVs), a new wing design was conceived. Quasi-vortex lattice methods were used to determine roll control power of unswept wings with (1) conventional ailerons, (2) active twist, and (3) a new method which employs root twist only. It was shown that linear wing twist provides 3.9 times more roll control than conventional ailerons. Root twist manipulations are shown to provide 1.6 times more control than twist. A comparison of control authority per unit actuator weight also shows that root actuators are more than 20% lighter than the other two systems. To drive the new root pitch actuator, a directionally attached piezoelectric (DAP) torque-late actuator was built. A laminated plate theory analysis of the 4' span, 3' chord DAP torque-plate showed good correlation between theory and experiment. The DAP torque plate was integrated into a 30' span, 4' chord graphite-epoxy wing. Structural testing showed wing pitch deflections up to +/- 1.5 degree(s) at rates in excess of 70 Hz. Wind tunnel tests were conducted between 1 and 20 ft/s (typical MAV flight speeds) and showed rolling moment coefficients up to +/- 0.026 (equivalent to +/- 8.4 degree(s) of aileron deflection), indicating that the new wing is well suited to flight control of micro-sized aircraft.

We carried out tests and analysis of flutter and vibration control of rectangular aluminum plate wing. The dimensions of the plate wing (420.0 X 140.0 X 1.0 mmt) were determined based on the wind tunnel size and blowing air velocity. The plate wing was driven by eight piezoceramic actuators bonded on the surfaces at the wing root part. Acceleration sensor was located at the wing tip and the signal was sent to digital signal processor through filters and control signal was sent to power amplifier. Amplified signal drove the piezoceramic actuator and suppressed vibration of the plate wing. System consist of structure, piezoceramic actuator and unsteady aerodynamic force was modeled into the standard form of modern control theory. Piezoceramic actuator's force was modeled using analogy of thermal analysis. Unsteady aerodynamic force in case of flutter control was calculated by DLM (frequency domain), then transformed to Roger's approximation for the purpose of time domain analysis. Full order control law consist of optimum regulator and Kalman's filter was reduced to low order law for practical use. First, we carried out the test for vibration control. In this case, structural damping ratio of the system increased remarkably in both case of gain control and reduced LQG control. Using gain control, that of the system increased up to 0.3. Second, we carried out the wind tunnel test of flutter control. Flutter speed at test increased about 2.9 m/s (10.8%, in calculation 12.2%) using reduced LQG controller.

Miniature, lightweight, low-cost actuators that consume low- power can be used to develop unmatched robotic devices to make an impact on many technology areas. Electroactive polymers (EAP) actuators offer the potential to produce such devices and they induce relatively large bending and longitudinal actuation strains. This reported study is concentrating on the development of effective EAPs and the resultant enabling mechanisms employing their unique characteristics. Several EAP driven mechanisms, which emulate human hand, were developed including a gripper, manipulator arm and surface wiper. The manipulator arm was made of a composite rod with a lifting actuator consisting of a scrolled rope that is activated longitudinally by an electrostatic field. A gripper was made to serve as an end effector and it consisted of multiple bending EAP fingers for grabbing and holding such objects as rocks. An EAP surface wiper was developed to operate like a human finger and to demonstrate the potential to remove dust from optical and IR windows as well as solar cells. These EAP driven devices are taking advantage of the large actuation displacement of these materials for applications that have limited requirement for actuation force capability.

In this paper we present an Output Feedback Sliding Mode Control (OFSMC) architecture for a slewing flexible 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 analytical development, numerical simulation and preliminary experimental results. The OFSMC 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. Numerical simulation studies were performed to compare the benefits of using active rather than passive structures. A nonlinear optimization algorithm was used to determine optimal gains for the OFSMC to produce a rest-to-rest, residual vibration-free, 90 degree(s) near-minimum time maneuver. Several case studies are reviewed that involve optimization of controller gains to minimize a cost function composed of tracking error and residual tip deflection errors. Preliminary experimental studies were performed for both passive and active operational modes. Only empirical controller gains were used. Both numerical and experimental results show a reduction in residual vibration for the active structure case.

Accurately maintaining the position of a communications antenna under environmental loadings, such as that due to wind, can affect the performance of the antenna. This paper describes work that examines the feasibility of using actively controlled guy wires to maintain the position of an antenna tower under wind loading. This study examines the position control of a laboratory scale model antenna under variable wind loading conditions. Two independent active guy wires and passive guy wires control the antenna position. The active guy wires use geared-down stepper motors as actuators. Feedback signals are provided with fiber optic and foil strain gages. The performance of various control algorithms is assessed. The possibility of scaling up the system for use on full-scale systems is discussed.

Advances in conducting polymer composite materials are raising the prospects of realizing large area dynamically controllable microwave smart surfaces. Candidate structures for these are proposed and their characteristics are analyzed, with due regard to the problems of system integration. The discussion is complemented by modelled and measured performance data.

The increasing demand for global communications and limitations on RF communication bandwidth has driven several corporations to baseline optical intersatellite communication links in their constellations. The use of laser communications over a long distance dictates the need for accurate pointing and jitter suppression in order to maintain signal. Vibrations on a satellite cause excessive line-of-sight jitter for optical performance. The solution to these vibration sources is a systems problem involving optical control of coarse and fine steering, vibration isolation of the optical payload, or reduction of the spacecraft disturbances. This paper explains the basics of tracking control of a laser communication package and details the systems trades for vibration isolation. Simulation results based on a vibration isolation and precision pointing of a hypothetical commercial LEO to LEO 4 Gbit/sec laser cross-link system are presented.

This paper explains how piezoelectric devices can be used to control vibrations in a snowboard. Furthermore the details of the approach, testing, design and analysis of a piezoelectric damper applied to a production snowboard are described here. The approach consisted of determining the principal modes of vibration of a snowboard during its operation (on-slope). This information was used to develop a finite element model of the structure. The finite element model was used to find the areas of higher strain energy where a piezoelectric device could be applied and be effective in reducing undesired vibrations. Several prototype piezoelectric dampers were built, applied to snowboards and tested on snow. The proper amount of damping was selected by the test riders, so that a configuration could be selected for production of the 1998 K2 Electra snowboard. The piezoelectric damper selected reduced the snowboard vibration by 75% at the mode to which it was tuned, allowing for a smoother ride and a more precise control of the snowboard in any kind of snow condition.

An adaptive filtering technique is developed for the control of structures with lightly damped modes. The technique is based on a feedback control strategy that uses tuned second- order filters to add damping to structural resonances. A single-mode system is analyzed to determine the effect of the filter parameters on the closed-loop structural damping. The analysis demonstrates that the closed-loop damping is linearly related to the filter damping for gain margins greater than two and that the closed-loop damping is highly sensitive to changes in the filter frequency. The sensitivity of the closed-damping to errors in the filter frequency motivates the use of a phase-lock loop to identify the structural frequency during transient vibration. The feedback compensator is implemented on a digitally- programmable analog filter whose parameters are set by a microcontroller. The adaptive algorithm is demonstrated on a flexible composite beam with a variable tip mass. Adding or subtracting mass to the tip of the beam varies the first structural mode from 24 Hz to 11 Hz. Control experiments demonstrate that the closed-loop damping is reduced from 21% to 4% critical when the filter parameters are not adapted to the structural frequency. In contrast, the adaptive filter is able to maintain between 14% and 21% critical damping in the structural mode as the frequency varies from 24 Hz to 11 Hz.

Acoustic source used for Active Noise Control at low frequency (80 - 250 Hz) is designed and developed by using a piezoelectric ceramic actuator and a flextensional panel diaphragm. In order to reach the vibration magnitude and radiation area needed for high and flat sound pressure level in the low frequency range. Pseudo-Shear Universal (PSU) actuator has been used as the driving part which is a new type of multilayer piezoelectric actuator originated from MRL offering the advantages of large displacement and high blocking force; on the other hand, Carbon Fiber Reinforced Composite has been used as the diaphragm material which provides a more rigid structure than conventional loudspeaker paper. A prototype device was fabricated which has the following characterizations: 40 layers PSU actuator with a compact dimension: 38 mm X 50 mm X 23.6 mm. Two of them are needed for a device. Diaphragm area is 126 mm X 152 mm. At quasistatic condition (5 Hz) and at the 0.84 kV/cm electric field, 344 micrometers displacement could be achieved at the apex of the diaphragm resulted from the flextensional amplifying mechanism with an amplification factor more than 11. The sound passive level in the frequency range 100 - 250 Hz shows better flat behavior than the acoustic sources studied earlier such as Double Amplifier and PANEL air transducers which exhibit a significant reduction of sound pressure level in the low frequency range. By a slight modification, it is likely to make this device in a total thickness of 10 - 15 mm range. High and stable sound pressure level as well as thin flat structure make it much more competitive in the whole area of applications for low frequency active noise control.

A test structure has been designed to validate active control strategies aimed at reducing the vibration level on a platform connected to a noisy base structure by six stiff bars. The six bars are equipped with piezoelectric translators and force sensors. These sensor/actuator pairs-- three on each bar--are located off the bar neutral axis so that longitudinal and flexural actuation is possible. Typical excitations are due to inertial wheels, cryogenic coolers and other disturbances and can be of sinusoidal or broadband nature. Performance specification is a 40 dB reduction over the 20 - 200 Hz frequency range. Simple feedforward controllers (based on the LMS algorithm) demonstrate a potential rejection performance of more than 40 dB for a sinusoidal disturbance, validating the sensor/actuator concept. Feedback control design has to account for the very rich dynamics of the truss in the frequency band 0 - 3000 Hz, calling for robust control approaches. This design has been carried out on a simplified model of the structure, and real time implementations have been successfully achieved. A rejection of broadband disturbances of about 15 to 20 dB was demonstrated, on the 20 - 200 Hz frequency range. Simultaneous feedforward and feedback controller is possible and allows the rejection of hybrid primary disturbances.

In commercial applications it is important to be able to either cancel noise, such as in the cabin of a combine, or to generate audible noise, such as in the case of an alarm. Piezoelectrics have demonstrated promise for active noise control and sound generation applications. In this investigation, the dynamic and acoustic capabilities of polymer piezoelectric semi-circular transducers were studied for such applications. The dynamic response of semi-circular piezoelectric transducers was determined numerically using the general purpose finite element code ABAQUS, then verified analytically and experimentally. The acoustic response was modeled using the commercial code COMET/Acoustics with the dynamic velocity response calculated by ABAQUS as initial boundary conditions. Experimental studies were performed on fixed-fixed polymeric piezoelectric curved transducers. The sensitivity of the sound generation capabilities of the transducer was investigated with respect to variations in radius, thickness and width parameters to demonstrate the potential of these devices for noise cancellation and audible sound applications.

We discuss a vibration measurement and control system developed to investigate the complex dynamics of boring-bar chatter. A fundamental question is how best to integrate the sensors and actuators for effective control. Is it sufficient to control only motions normal to the machined surface? We consider a smart structure that consists of two actuator/sensor pairs oriented orthogonally to control the motions of a boring tool in directions normal and tangential to the machined surface. Actuation is achieved with Terfenol-D struts that sting the tool near its base. We develop a control strategy by considering a single-degree- of-freedom chatter model for tool motions normal to the machined surface, showing that enhanced structural damping is an effective chatter control. We adapt a second-order feedback compensation scheme from the literature and point out the special design considerations engendered by the use of Terfenol-D actuation. We consider chatter signatures obtained using the system with and without feedback control and show that the system is very effective at chatter suppression. Because we may control each of the dominant structural modes independently, we examine the validity of a single-mode approximation by considering chatter signatures obtained with only tangential control active. We find that so-called mode coupling effects persist; hence, we expand our modeling efforts to include a coupling due to the cutting forces. We see that a variety of chatter modes exist, depending on the operating parameter, and that, to achieve the most robust performance from the controlled system, it is advisable to have control of both directions.

In this paper we introduce a new approach to utilize the inherent sensor effect of a magnetostrictive actuator by evaluating the inductivity of the exciting coil. The external mechanical load on the transducer has an influence on the relative permeability of the magnetostrictive material, which causes a change in the inductivity of the coil. To determine this inductivity two different methods are proposed: integration of the transducer current to receive the magnetic flux and estimation of the electrical network parameters. These methods are both based upon a measurement of the voltage and current at the transducer and thus they are sensitive against errors or offsets. An extension of the well-known parameter identification methods can compensate for these errors leading to an unambiguous relation between the inductivity of the transducer coil and the external force. This knowledge can be used to implement a new form of a smart actuator utilizing the inherent sensor effect while actuating. The algorithms developed for magnetostrictive actuators can be directly transferred to piezoelectric and electrostrictive transducers. As application a magnetostrictive linear motor is proposed, which determines its external mechanical load without additional sensor.

Complete models of highly-magnetostrictive Terfenol-D transducers must be able to characterize the magnetostriction upon knowledge of the impressed electrical energy. Fundamental characterization laws are not available at present, because the existing modeling techniques fail to simultaneously span all operating regimes: electric, magnetic, mechanical, and thermal, across the whole performance space of these transducers. This paper attempts to capture the essential aspects of these regimes and their interactions, i.e. those that the transducer designer is likely to encounter during design, analysis and modeling of magnetostrictive devices. The issues discussed here are the magnetization and stress states, thermal effects, magnetomechanical hysteresis, AC losses, system nonlinearities, and transducer dynamics. In addition, some of the more relevant modeling techniques that address these issues are presented and analyzed.

We consider the modeling of strains generated by magnetostrictive materials in response to applied magnetic fields. The active or external component of the strain is due to the rotation of magnetic moments within the material to align with the applied field. This is characterized through consideration of the Jiles-Atherton mean field theory for ferromagnetic hysteresis in combination with a quadratic moment rotation model for magnetostriction. The second component of the strain reflects the passive or internal dynamics of the rod as it vibrates. This is modeled through force balancing which yields a wave equation with magnetostrictive inputs. The validity of a combined transducer model is illustrated through comparison with experimental data.

This paper investigates the issue of inducing large displacements in piezoelectric ceramics for actuator applications through the management of domain walls. Domain wall management involves the control of domain wall evolution with external stresses or electric fields to obtain specific domain structures. Control of these domains is achieved through the use of interdigitated electrodes capable of producing an electric field in either the x or y direction or a combination of the two thereof. Strain up to 4000 (mu) (epsilon) can be obtained using this methodology. One of the major drawbacks of incorporating domain wall motion to obtain large displacements is material fatigue and degradation. Material degradation is shown to be the result of large mechanical stresses in the material that arises from dissimilar domains during polarization switching. This paper will investigate the combined influence of different electric field strengths, temperature, and mechanical loads on the fatigue of the piezoelectric ceramic, PbZr_0.53Ti_0.47O₃ (PZT-5H). Results show that the degree of degradation during polarization switching is dependent upon the magnitude and frequency of the applied electric field. However, cycling the material at high temperatures or under mechanical loads decrease the rate of fatigue degradation. Parametric studies show that higher temperatures and higher preloads will extend the fatigue life of piezoelectric ceramics to well over 10 million switching cycles.

A vibroacoustic modeling methodology for the simulation of noise transmission into an aircraft cabin previously developed by the authors is extended to include the effect of segmented piezoelectric actuation. The structural model of the aircraft fuselage is based on a stiffened shell theory developed by Egle and Sewall. The strain and kinetic energies of the shell, stringers and frames, and the strain energy for the extensional motion of the floor beams are used in a Rayleigh-Ritz analysis to obtain the structural model. The forcing term due to the acoustic pressure disturbance of the propellers is determined by using virtual work considerations. The passive and active effects of the segmented piezoelectric actuators are incorporated in the model by including their energies in the variational approach. The development of the acoustic model of the cabin reduces to a 2D analysis due to the presence of parallel fore and aft bulkheads. The coupled vibroacoustic model, which includes terms that represent the inherent fluid- structure interaction, is developed from the structural and acoustic modal models. The control performance of the piezoelectric actuators is evaluated by considering the minimization of the sum of the squares of the interior sound field or structural response at a number of finite locations as the control objective. The acoustic and structural responses to one actuator and sensor arrangement are evaluated and discussed.

During launch, spacecraft experience severe acoustic and vibration loads. Acoustic loads are primarily transmitted through the shroud or payload fairing of the launch vehicle. In recent years, there has been a trend towards using lighter weight and extremely stiff structures such as sandwich construction and grid-stiffened composites in the manufacturing of payload fairings. While substantial weight savings can be achieved using these materials, the problem of acoustic transmission is exacerbated. For this reason, the Air Force Research Laboratory has been actively engaged in vibroacoustic research aimed at reducing the acoustic and vibration levels seen by payloads during launch. This paper presents experimental results for the simultaneous structural and acoustic cavity mode control of a sub-scale composite isogrid payload fairing structure. In this experiment, actuation is performed through the use of both an internal speaker as well as piezoceramic strain actuators located on the outer skin of the composite structure. Sensing is accomplished using a microphone as well as a piezoelectric strain sensor. The control approach presented in this paper is a decentralized frequency domain approach which makes use of a series of independent control loops. One loop uses the microphone and speaker, while additional loops use the piezoelectric sensors and actuators. The control algorithm consists of independent second-order Positive Position Feedback (PPF) controllers tuned to reduce the magnitude of each cavity mode. A PPF filter in conjunction with an extremely sharp bandpass filter is used on the structural mode of limit spillover. This approach leads to a substantial reduction in the acoustic transmission in the range of 0 - 800 Hz. Transmission coincident with the primary cavity modes of the system are reduced in magnitude by 26 and 9 dB respectively while the structural model that is responsible for the majority of transmission is reduced by approximately 7 dB.

The present work is a continuation of our previous efforts, in which active control of deterministic bandlimited and tonal disturbances in an enclosure with a flexible boundary has been addressed. Multiple tones in the bandwidth of 40 Hz to 1000 Hz are transmitted into the enclosure and local noise control is attempted by using a multi-input, multi- output, digital feedforward control scheme. The specific focus of the current work is on actuator grouping, and this issue is explored through numerical and experimental investigations. It is demonstrated that actuator grouping can be beneficial for controlling enclosed sound fields dominated by widely separated tones.

The field of active noise control is currently very popular due to the fact that it has many practical applications. Some of these applications include decreasing cabin noise in aircraft and automobiles, reducing noise in rocket payload bays, and minimizing machinery noise in factories. Many researchers have developed active control algorithms for vibrating plates radiating sound into free space or enclosures. Most of the controllers employed have been adaptive like the Filtered-x LMS techniques. Very little previous work has been focused on feedback control techniques. In an earlier paper we have described techniques for controlling sound transmission through rectangular plates radiating into a closed cavity. Robust controllers, based on Linear Quadratic Gaussian with Loop Transfer Recovery (LQG/LTR) methods were designed and implemented on simple test articles. In comparison with LMS algorithm, this robust controller did not perform well. The time delay present in the structural system was not considered in the LQG/LTR design method. Hence, a poor performance was the result. In this paper, we have designed and implemented a modified LQG/LTR controller with time delay on an acoustic chamber test article. This controller estimates the previous states from the present output and predicts states for feedback purposes. The time delay of the structure is compensated in the configuration of the estimator of the controller. We have obtained the simulation and experimental results with the modified controller. The performance of the modified LQG/LTR controller is much better than the LMS controller. The performance of the LMS and LQG/LTR controllers is investigated with respect to change in noise frequency and plant parameter variations. The experimental results are included in this paper.

This paper presents an analytic model and validation tests of Froude and Mach scaled rotors featuring piezoelectric bender actuated trailing-edge flaps for active vibration suppression. A finite element structural formulation in conjunction with time domain unsteady aerodynamics is used to develop the rotor blade and bender-flap coupled response in hover. The analysis accounts for the aerodynamic, centrifugal, inertial and frictional loads acting on the coupled bender-flap-rotor system in hover. To investigate the feasibility of piezo-bender actuation and validate the analytic model, a 6 foot diameter, two-bladed Froude scaled rotor with piezo-bender actuation is tested on the hover stand. Flap deflections of +/- 4 to +/- 8 degrees, for 1 to 5 /rev bender excitation were achieved at the Froude scaled operating speed of 900 RPM. The trailing-edge flap activation resulted in a 10% variation in the rotor thrust levels at 6 degrees collective pitch. The analytic model shows good correlation with experimental flap deflections and oscillatory hubloads for different rotor speeds and collective settings. Based on the analytic model, two Mach scaled rotor blades with piezo-bender actuation are designed and fabricated. To achieve the desired flap performance at Mach scale, an 8-layered, tapered bender is fabricated. The bender performance is further improved by selectively applying large electric fields in the direction of polarization for individual piezoceramic elements. A radial bearing is incorporated to reduce frictional loads at the blade-flap interface. Preliminary testing of the Mach scaled blades at 900 RPM in a vacuum chamber revealed negligible degradation in flap performance because of centrifugal and frictional loading. The analysis predicts that flap deflections of +/- 5 to +/- 10 degrees for 1 to 4 /rev bender excitation can be achieved at the Mach scaled operating speed of 2100 RPM. Future work will involve hover and wind tunnel testing at Mach scaled operating speeds.

An active blade designed for the control of rotor vibrations and noise has been developed. Active fiber composites have been integrated within the composite rotorblade spar to induced shear stresses. These shear stresses result in a distributed twisting moment along the blade. The design of an active blade model based on a 1/6th Mach-scale Chinook CH-47D is reviewed. The design goals included +/- 2 degree(s) of blade tip twist with a maximum of 20% added blade mass. Details of the requirements for the active fiber composites subjected to 160 kt, 3g maneuver loads and the experimentally determined actuator capabilities are reviewed. The testing of a half-span active blade test article is described. Twist actuation performance is compared with model predictions. Preliminary results from bench testing and full Mach-scale hover testing of the integral blade are presented.

A design is presented of a 1/6 Mach scaled CH-47D rotor blade incorporating a X-Frame discrete actuator for control of a trailing edge servo-flap. The second generation design of the X-Frame actuator is described focusing on the design changes made from the actuator prototype. The function of the components that restrain the actuator to the rotor blade and connect it to the servo-flap are described. The major challenge in placing a discrete actuator into a rotor blade is in allowing the required functionality in the aggressive acceleration environment of the blade. In particular, a new centrifugal flexure is used to restrain the actuator in the spanwise direction and special fittings are incorporated into the blades to allow the required actuator degrees of freedom while reacting the out of plane vibrational accelerations of the blade. Concentric steel rods are used to transfer actuator motion to the servo-flap and to eliminate the compliant blade fairing from the actuation load path. A slotted flap design was used to reduce the required hinge moments. The aerodynamic implications of using such a flap design are described. Furthermore, retention of the flap and the pre-stress of the actuator were accomplished by a steel wire centered on the flap rotational axis. The design of this part and its influence on choosing an optimum flap length is discussed. The manufacture of the composite rotor blades is described. The diversion of composite unidirectional plies to allow access to the actuator bay within the blade spar is described.

This paper presents the development of an actuator for a trailing edge flap on a full-scale helicopter rotor blade using a high performance piezoelectric stack device. The actuator was designed and constructed using two identical piezostacks that were selected among commercially available actuators through a systematic testing. To calculate the aerodynamic requirement of the flap actuator, an analytical model was formulated using quasi-steady aerodynamics. A new amplification device utilizing double-lever mechanism was designed and fabricated. An amplification factor of 19.4 and the constant response covering up to 8/rev were obtained experimentally under non-rotating condition. It was shown that the present flap actuator is capable of achieving the required flap deflection to actively control rotor vibration.

This paper examines, analytically and experimentally, a shape memory alloy (SMA) wire actuator to be used for in- flight tracking of helicopter rotor blades. The recovery characteristics of SMA's are utilized to detect a trailing edge trim tab. Conceptually, the tab is deflected using SMA wires with initial pre-strains, and any differential recovery displacement due to a thermal field is transformed into an angular motion of the tab. A 1D thermo-mechanical constitutive model is used to predict the constrained recovery characteristics of SMA's and predicted results are validated with measured values. Good correlation between measured and predicted values is obtained.

Vibration and noise are two long-standing problems that have limited the expansion of military and commercial applications of rotorcraft. The source of these interrelated phenomena is the main rotor, which operates in an unsteady and complex aerodynamic environment. The trailing edge flap concept for smart blade control has been investigated by several researchers for possible use in noise and vibration reduction, and shows promise. The flaps are actuated using piezo-stack, bimorph or magnetostrictive actuators. It is however still unclear if there is a single actuation mechanism that addresses both noise and vibration reduction, while still having enough control authority available to act as an extra control effector in its own right. The uncertainty about the actuation mechanism, about the precise amount of flap deflection available, and about the accuracy of current constitutive models of the actuators lead to significant difficulties in analyzing the potential of the concept for helicopter applications. In this study we propose and execute an innovative approach to the above problem that consists of modeling the smart actuation mechanism using a simple low order linear model that matches test data (with an associated variation or uncertainty). We use this model in association with a helicopter flight dynamic model for carrying out an optimization of flap sizing and placement for minimum fixed frame vibration. Finally, we use the model to carry out an analysis of the effectiveness of the flap in reducing inter-axis coupling, and as a redundant control effector in case of primary actuator failure.

Magnetorheological fluid dampers are attractive candidates for augmentation of lag mode damping in helicopter rotors, where additional damping is required to avert instabilities only during specific flight conditions. Magnetorheological (MR) fluids change properties dramatically with application of a magnetic field. This active damping component presents an advantage over passive elastomeric and fluid-elastomeric dampers. An extensive comparative study of fluid-elastomeric and MR dampers is presented. The study was conducted with four (a pair each) 1/6th Froude scale dampers. The MR dampers were tested with the magnetic field turned off (OFF condition) and with the magnetic field turned on (ON condition). The dampers were rested individually and in pairs, under different preloads, and under single and dual frequency excitation conditions. The fluid-elastomeric and MR (OFF) damper behavior was linear, while the MR (ON) behavior was nonlinear with the stiffness and damping varying with the displacement amplitude. Under dual frequency conditions, the MR dampers (ON condition) showed a significant degradation in damping and stiffness as the dual frequency excitation was increased. The MR (OFF) dampers showed no change in properties. The fluid-elastomeric dampers showed a mild degradation in stiffness and damping under dual frequency excitation conditions. The MR (ON) damper hysteresis was modeled using a nonlinear viscoelastic plastic model. The model captures the nonlinear behavior accurately. Using the single frequency parameters, the dual frequency hysteresis behavior was predicted, and it correlates well with experimental data.

Electrorheological (ER) fluids are not yet exploited within the aerospace industry, however, there are systems on an aircraft which would benefit from the use of this type of smart material and its associated technologies. The use of ER fluid within landing gear (LG) systems can be envisaged, for example the control of the passive damping characteristics of a landing gear oleo. This could be beneficial to the airframers by reducing LG weight, to the landing gear systems providers by reducing costs and over design, as well as for the operators by increasing passenger comfort and confidence. The use of ER fluid within an oleo would, however, result in a non-linear damper the characteristics of which would be dependent upon the design, the mode of deformation of the charged fluid and the control strategy. A design strategy is proposed for the use of ER fluid within a LG oleo and the controller design aspects considered.

This paper explores the feasibility of using Magnetorheological (MR) fluid-based dampers for lag damping augmentation in helicopters. A MR damper model is integrated with a rotor aeromechanical model. Two different control schemes are presented--namely the On-Off scheme and the Feedback Linearization scheme. In the On-Off scheme, two criteria are used to obtain equivalent linear damping for the nonlinear MR damper as a function of the size of perturbation and the applied field. The Feedback Linearization scheme uses a feedback controller to linearize the force output of the MR damper. The two control schemes are compared for lag transient response in ground resonance and their ability to reduce damper load in forward flight. It is shown that a MR damper of a size comparable to an elastomeric damper can provide sufficient damping for ground resonance stabilization and can significantly reduce periodic damper loads with a judicious choice of operation scheme.

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 milli-seconds, the traverse length is 250 mm and the turn round position must be controllable and repeatable within +/- 1 mm. These combined criteria of high speed and controllability makes the use of electro-rheological fluids an attractive proposition. Simulations produced using a dynamic model are compared with experimental results and these validate the simulation techniques. The effect on the performance of various fundamental electro-rheological fluid characteristics, namely electro-rheological shear stress, electron-hydraulic time delays and zero volts viscosity are considered together with the design of the mechanism. This illustrates the need for optimization of such mechanisms to meet the varied and difficult design requirements found in high speed controllable devices. Some practical difficulties in achieving a reliable mechanism are also discussed.

Electrically-structured (ES) fluids offer a potentially elegant means of introducing greater flexibility into a range of industrial machines and structures, and are especially suited to controllable vibration damping. The authors have developed a technique for characterizing ES fluids, leading to a mathematical model and practical device design procedure, the principles of which are verified by testing with an industrial scale, long-stroke electro- rheological damper, suited to the needs of a rail vehicle lateral suspension. In this paper, the model is applied to predict the effect on the test damper steady state performance, and performance envelope, of the principle variables of operating temperature, mechanical displacement amplitude and frequency, and control field excitation, which influence the controllability and control requirements of the damper, and to show that the test damper should achieve the desired range of control.

Energy dissipation devices have been accepted as a promising alternative to dissipate the energy that earthquakes induce in structures; therefore, reducing displacement demands. A large number of new or retrofitted buildings are equipped with fluid dampers or other energy dissipation devices which are expected to suppress earthquake induced shaking. They can be incorporated in the isolation system of a building2 or within the skeleton of a structure7. When structures are built near a potential fault, the expected displacement demands in the structure are large and there is a tendency to equip structures with supplement damping -in most cases of nearly viscous type2. On the other hand, near source ground motions usually contain one or more distinct and coherent pulses; and it is known that for pulse motions the efficiency of viscous damping in reducing displacement demands is limited when the system is highly damped14 In a recent paper, the senior author showed that plastic damping is more efficient than viscous damping in reducing the response of a SDOF structure when subjected to pulse motion represented by cycloidal fronts with duration close to the natural period of the structure. Recent developments on controllable fluid dampers showed that both electrorheological (ER) and magnetrorheological (MR) dampers are capable of delivering the desirable plastic or viscoplastic behavior. In this paper an analytical study on the response of a 2 DOF isolated structure equipped with controllable fluid damper subjected to a variety of near source earthquakes is presented in order to understand the difference between viscous and friction damping, and to investigate possible advantages of controllable fluid dampers. The isolated structure is considered to be supported either on elastomenc bearings or sliding bearings.

This paper presents a robust feedback control performance of a full-car suspension system featuring electro-rheological (ER) dampers for a passenger vehicle. The field-dependent yield stress of an ER fluid is obtained using a couette type electroviscometer, and a cylindrical ER damper is designed and manufactured by incorporating the yield stress of the ER fluid. A full-car suspension system installed with four independent ER dampers is then constructed and its governing equation of motion which includes vertical, pitch and roll motions is derived. A sliding mode controller which has inherent robustness against parameter uncertainties is then formulated by taking account of mass uncertainty. Control characteristics for vibration suppression of the ER suspension system are evaluated under various road conditions through the hardware-in-the-loop simulation for the demonstration of its practical feasibility.

This work utilizes a previously developed phenomenological model of an electrorheological fluid to predict the response of the material in the presence of an electric field. The model consists of discrete elements, namely, enhanced non- linear Bingham type damping. Newtonian damping and an inertial term, to account for momentum effects. The model is incorporated into a non-linear least squares algorithm to assess the parametric coefficients required to successfully simulate response. For the evaluation of the algorithm experimental data from rheometer tests is utilized.

A health monitoring system for composite material structures combining good compatibility of each embedded sensor and small number of needed sensors could be an active system based on Lamb waves propagation and using for both generation and detection only optical fibers. The present work deals with laser generation of ultrasounds inside the composite material, thanks to embedded optical fibers driving the laser pulse. Emphasis is given to: (1) the energy deposition in the vicinity of the optical fiber tip and the existence of an energy threshold for safe and repetitive use of the delivery system, (2) the relative configuration of the embedded fiber optic and reinforcement fibers, (3) the displacement field generated. Results obtained with pure resin and carbon-epoxy samples are presented.

A new modular multisensor measuring system for data fusion is proposed in this paper. The measuring system is based on the paradigm of Cellular Neural Networks. Some novel theoretical results for the system analysis together with a suitable methodology for the design of the multisensor fusion procedure are introduced. An analog implementation of the measuring system proposed for this modular multisensor fusion system is reported with applications in the field of smart structures and systems. Experimental results are also reported in order to show the suitability of the proposed approach.

Polymer based piezoelectric composite materials can be readily integrated within laminated composite structures to provide sensing and actuating capabilities. In this study composite films of ferroelectric ceramic/polymer materials have been developed and characterized as in-situ multi purpose sensing elements for the nondestructive monitoring of fiber reinforced composites. In this paper the response of embedded composite films to simulated acoustic emission signals will be presented and discussed. Results show the ability of the composite sensors to detect signals from acoustic emission sources over a wide bandwidth.

The problem of detecting impacts in composite panels before and after damage is addressed in this paper. The data is taken from a simple impact experiment in which piezoceramic sensors are used to collect the impulse strain response. The data are subsequently analyzed using neural networks to predict the impact location and energy on the basis of features extracted by various pre-processing algorithms. One of the main aims of the paper is to establish if the impact location and quantification results are affected by damage to the structure.

Currently, the Air Force's fleet of aircraft, and helicopters in particular, are aging. These aircraft are nearing the end of their design life, but are being required to continue service well into the next century. In an attempt to help extend the life of these aircraft, the area of health monitoring has received considerable interest. In the case of the MH-53J PAVE LOW, this health monitoring has taken the form of vibration monitoring. The initial effort at health monitoring has consisted of placing accelerometers on the bearing support brackets for the tail rotor drive shaft. The results of this monitoring have provided information that allows the maintainers to replace the bearings only when the bearing is showing signs of wear rather than at a given interval. Additionally, the data has been used to make near real time evaluations of the airworthiness of the aircraft. The result has been a decrease of 50% in the number of missions canceled due to vibration related issues. The Air Force is looking at expanding the present vibration monitoring system to the entire fleet of MH-53J aircraft. In conjunction with this expansion, this paper looks at evaluating a transducer specifically designed for monitoring bearings. A comparison between accelerometer responses and the bearing transducer response is made.

From August 28 to September 18, 1997, Honeywell's Rotor Acoustic Monitoring System was successfully flight-tested at Patuxent River Naval Base. This flight-test was the culmination of an ambitious, 40-month, proof-of-concept effort to demonstrate the feasibility of detecting crack propagation in helicopter rotor components. During the three weeks of flight-testing, the system was operated on 12 flights plus one ground test and accumulated more than 16 hours of flight data recorder data and about 25 Gbyte of digital data from eight on-rotor acoustic sensors. The flight-test showed that rotor head acoustic monitoring could be uniquely valuable not only for rotor crack and fault detection but also for monitoring the general health of the entire rotor assembly. This paper presents preliminary results from that flight-test.

The appearance of delaminations caused by excessive vibratory and fatigue loads in composite rotorcraft flexbeams can lead to degradation in flapwise and lagwise performance of the rotor blade. In addition, delaminations in composite rotorcraft flexbeams under cyclic loading can result in rapid fatigue failure of these elements leading to catastrophic results. A novel detection strategy is evaluated which attempts to use the scattering of structural waves generated from piezoelectric actuators to locate damage in the form of a delamination. Previous approaches to damage detection have focused on using the modal response of the structure. The approach reported in this work relies primarily on more accurate local continuum mechanics descriptions of the structural dynamics. The method developed here exploits the wave propagation solution of uncoupled equations of motion for thin composite flexbeams under rotation. Local models of structural damage in the form of chordwise interply delaminations are developed by accounting for how waves scatter at structural discontinuities. The scattering matrix, which characterizes how incoming and outgoing waves scatter at a structural defect, is used as a performance metric to quantify damage. Finally, experimental validation of the structural damage modeling and damage identification strategy were carried out on [0/90]s graphite epoxy (Gr/Ep) beams in vacuum under rotation. Chordwise midplane delaminations in the form of a teflon layer were inserted into several test specimen to simulate local structural damage in a rotorcraft flexbeam.

The emerging electro-mechanical impedance technology has high potential for in-situ health monitoring and NDE of structural systems and complex machinery. At first, the fundamental principles of the electro-mechanical impedance method are briefly reviewed and ways for practical implementation are highlighted. The equations of piezo- electric material response are given, and the coupled electro-mechanical impedance of a piezo-electric wafer transducer as affixed to the monitored structure is discussed. Due to the high frequency operation of this NDE method, wave propagation phenomena are identified as the primary coupling method between the structural substrate and the piezo-electric wafer transducer. Attention is then focused on several recent advancements that have extended the electro-mechanical impedance method into new areas of applications and/or have developed its underlying principles. US Army Construction Engineering Research Laboratory used the electro-mechanical impedance method to monitor damage development in composite overlaid civil infrastructure specimens under full-scale static testing. A simplified E/M impedance measuring technique was employed at the Polytechnic University of Madrid, Spain, to detect damage in GFRP composite specimens. The development of miniaturized `bare-bones' impedance analyzer equipment that could be easily packaged into transponder-size dimensions is being studied at the University of South Carolina. US Army Research Laboratory developed novel piezo-composite film transducers for embedment into composite structures. Disbond gauges for monitoring the structural joints of adhesively bonded rotor blades have been studies in the Mechanical Engineering Department at the University of South Carolina. These recent developments accentuate the importance and benefits of using the electro-mechanical impedance method for on-line health monitoring and damage detection in a variety of applications. Further investigation of the electro-mechanical impedance method is warranted. A further examination of the complex interaction between wave propagation, drive-point impedance, structural damage and electro-mechanical impedance of the piezo-electric wafer transducer is needed. Once these aspects are better understood, the E/M impedance method has the potential to become a widely used NDE technique with large applicability in diverse engineering fields (aerospace, automotive, infrastructure and biomedical implants).

The main advantages of piezoelectrical actuators are their high resolution in motion and their excellent dynamic behavior. Especially the very short response times of solid state actuators presents new opportunities in developing high dynamical systems with unsurpassable characteristics. New concepts of piezoelectrically driven microoptical devices, e.g. optical fiber switches, intensity modulators and choppers, can be developed. Very compact systems with parallel motion and high accuracy can be realized by the integration of piezoelectrical actuators into special mechanical frames with solid state hinges. Due to the combination of piezoelectrical actuators and mechanical lever transmission systems decisive advantages compared with other actuation concepts can be obtained. Appropriate displacements can be reached with comparatively small sized and thus low capacitance actuators. Low capacitance actuators enable the use of efficient electrical amplifiers for high dynamics. The behavior of the mechanical system is equivalent to a spring-mass-oscillator with a high quality factor. Because of their high stiffness the resonance frequencies of piezoelectrical actuators are quite high, but parasitic oscillations can appear if the element is driven with unsteady electrical functions e.g. square- or triangle- functions. Unwanted oscillations can deteriorate the general characteristics of dynamic actuators or in worst cases they can cause mechanical break down. New hybrid piezoelectrical actuator systems for dynamical applications are presented. General aspects of improving the dynamics of piezoelectrical systems and different methods for adequate passive damping will be discussed in this paper.

Introducing an interaction energy in the free energy function, the first two of the present authors proposed a 1D pseudoelastic model of shape memory alloys. The model has been demonstrated to represent qualitatively well some complicated experimental data on stress-strain-temperature relationships. To study the effect of large hysteresis due to pseudoelasticity of the alloys on their vibrational behavior, we carry out numerical simulations of vibration of a simple mass-spring system connected with a prestrained shape memory alloy wire whose constitutive equation is expressed by the present authors' pseudoelastic model.

A dynamics model of an electrostrictive ceramic actuator is integrated with a linear mechanical system. Electrostrictive ceramics have a non-linear displacement response to applied field, which creates harmonic distortion of actuator's output. Traditionally, nonlinear dynamics problems are solved in the time-domain, then Fast Fourier Transforms are used to convert the solution into the more convenient frequency-domain. In this paper, a new approach is introduced separates the nonlinear, actuator from the linear structure. The structure can be represented as an impedance that constrains the actuator, and the actuator problem is solved in the frequency domain directly. The approach significantly simplifies the nonlinear problem. The actuator-mechanical system model is used to predict actuator output and distortion as a function of signal frequency. DC voltage bias is treated as a model parameter than must be tuned to optimized output while minimizing distortion. Power requirements and energy transfer to the attached structure are also examined. The problem of a flextensional underwater sonar transducer with an electrostrictive driver is examined as an example case.

For active vibration control of buildings in Japan, new system alterative to current active mass dampers are required. Smart structures are candidates for the alternative systems. In order to investigate the possibility, a smart structure was tested for active vibration control of frame structures, in which bending moment of the columns was controlled by magnetostrictive actuators integrated into the columns. The actuators were installed in stages in the bottom part of the column of a H- section. The stages had a different section for effective integration of the actuators into the column, while they had the same bending stiffnesses of the column in the two lateral directions. Excitation tests were carried out for a 3-story building model of a 3.4 m height and a 1600 kg total mass by using a shaking table. In the building model, each column had 2 stages in it's bottom part in the first story, and 4 actuators were installed in each stage of one column. Thus 32 actuators in total were used. The magnetostrictive actuator developed for the building model consisted of a magnetostrictive rod of a 40 mm length and a 20 mm diameter surrounded by a driving coil. The controllers for the building model were designed by the model-matching method and the H^(infinity ) control theory to control the 1st-, 2nd-, and 3rd-mode responses, and both controllers were designed so that the system had a 15% damping ratio in all modes. Through the tests, it was shown that the smart structure could effectively reduce the responses of the building model, and the two control strategies had almost the same performance.

In this work, analytical investigations into active control of longitudinal and flexural vibrations transmitted through a cylindrical strut are conducted. A mechanics based model for a strut fitted with a piezoelectric actuator is developed. For harmonic disturbances, a linear dynamic formulation describing the motion of the actuator is integrated with the formulation describing wave transmission through the strut, and the resulting system is studied in the frequency domain. Open-loop studies are conducted with the aid of numerical simulations, and the potential of active control schemes to attenuate the transmitted vibrations over the frequency range of 10 Hz to 6000 Hz is examined. The relevance of the current work to control of helicopter cabin interior noise is also discussed.

In this paper, the design and implementation of smart actuators for active vibration control of mechanical systems are considered. A smart actuator is composed of one or several layers of piezo-electric materials which work both as sensors and actuators. Such a system also includes micro- electronic or power electronic amplifiers, depending on the power requirements and applications, as well as digital signal processing systems for digital control implementation. In addition, PWM type micro/power amplifiers are used for control implementation. Such amplifiers utilize electronic switching components that allow for miniaturization, thermal efficiency, cost reduction, and precision controls that are robust to disturbances and modeling errors. An adaptive control strategy is then developed for vibration damping and motion control of cantilever beams using the proposed smart self-sensing actuators.

Tuned liquid damper (TLD) is a device which absorbs energy of structural vibration through sloshing of fluid when sloshing frequency is tuned to the structural frequency. TLD is widely used to control wind-induced vibrations in civil structures. Its performance is shown to degrade either when there exists error in tuning between sloshing and structural frequencies, or when the structure is subject to non- stationary excitation. To improve the performance of TLD, active TLD which consists of magnetic fluid activated by electromagnets is proposed. At the first part of the paper, characteristics of sloshing motion of magnetic fluid subject to dynamic magnetic field is studied experimentally. Because sloshing is nonlinear phenomenon, standard linear control theory is not applicable in construction of control laws directly. Hence, a rule-based control law which effectively controls the sloshing motion and base shear force is constructed based on a rule-based control law of active dynamic vibration absorbers. At the last part of the paper, the performance of the proposed active TLD is verified experimentally using a two-story building model. Active TLD is found to give higher reduction of vibration and to be less sensitive to the error of tuning.

This paper investigates the behavior of piezoceramic actuators under different types of excitation and mechanical loading. The research focuses on the application of these actuators to the development of smart rotor systems. The free strain response of the actuators under DC excitation is investigated experimentally along with the associated drift of the strain over time. Effect of tensile stress on the DC response is investigated. Strain response to an AC excitation is also investigated for a free actuator and for a pair of actuators surface bonded to a host structure. The phase lag of the strain response and non-linear hysteretic effects have been observed and the power consumption has been validated by the impedance method. Additionally, depoling of the actuators is discussed, along with the feasibility of recovering performance by repoling in the event of accidental depoling.

A new class of bimorph actuators, called C-block actuators for their curved shape, have recently been proposed to provide improved performance characteristics over conventional straight bimorph actuators. Existing mathematical models of these actuators are based on classical curved beam theory which neglects transverse shear effects. An improved mathematical model for C-block actuators of arbitrary thickness is developed. The first order shear deformation based theory model accounts for through-the-thickness transverse shear stresses in thick piezoelectric C-block actuators. The results obtained from the first order shear deformation theory are validated with results from finite element analysis, available experimental data and an exact elasticity solution. The developed theory is used to predict the performance of multilayered C-block actuators of various configurations to demonstrate the importance of shear effects.

C-blocks are novel piezoelectric actuators that allow for a variety of different architectural configurations that will directly address application requirements without external leveraging. A very useful architecture is a series in which C-blocks are connected end-to-end. Serial architectures increase the deflection of the actuation system without impacting the force output. This paper presents the derivation of an theoretical model that accurately predicts the quasi-static force-deflection behavior of a generic C- block serial actuator configuration. This model is verified with five experimental case studies. In these case studies, the effects of changes in geometry, material, and configuration parameters were investigated using a variety of prototypes fabricated from polymeric and piezoceramic materials.

We discuss vibration control of a cantilevered plate with multiple sensors and actuators. An architecture is chosen to minimize the number of control and sensing wires required. A custom VLSI chip, integrated with the sensor/actuator elements, controls the local behavior of the plate. All the actuators are addressed in parallel; local decode logic selects which actuator is stimulated. Downloaded binary data controls the applied voltage and modulation frequency for each actuator, and High Voltage MOSFETs are used to activate them. The sensors, which are independent adjacent piezoelectric ceramic elements, can be accessed in a random or sequential manner. An A/D card and GPIB interconnected test equipment allow a PC to read the sensors' outputs and dictate the actuation procedure. A visual programming environment is used to integrate the sensors, controller and actuators. Based on the constitutive relations for the piezoelectric material, simple models for the sensors and actuators are derived. A two level hierarchical robust controller is derived for motion control and for damping of vibrations.

In choosing positions for sensors and actuators for structural control, the first step is usually to develop a model that describes the motion of the structure in response to an excitation. The next step depends on the type of sensors and actuators used. If displacement or acceleration sensors and shakers are used, the model serves as a guide to find locations on the structure where displacement is large for a given disturbance. If in-plane strain-based smart sensors and actuators are used, the model is used to identify locations with large in-plane strain. If the structure is relatively complex, there is a good chance that the initial model will not predict motion that agrees completely with the measured motion of the structure. This initial model is then typically adjusted so that the behavior it predicts agrees with a measured modal analysis of the structure. This process can be extremely time consuming, and while the reconciled modes often agree well with a modal analysis, there can be large errors with respect to in-plane strain. Prediction of in-plane is necessary for accurate location of smart sensors and actuators like piezoceramics. In this paper an experimental method is introduced which uses in-plane sensors to find good smart sensor and actuator locations to control acoustic excitation of a complex structure. Experimental results are also presented which demonstrate the proposed technique.

We consider the problem of suppressing the vibrations of a structure that is subjected to a principal parametric excitation. The vibration amplitudes resulting from such resonance cannot be fully controlled by conventional techniques, such as the addition of linear damping through velocity feedback or by the implementation of conventional mass absorbers. However, it has been shown that the growth of the response is limited by nonlinearities. In this work, we capitalize on this fact and devise a simple nonlinear feedback law to suppress the vibrations of a cantilever beam when subjected to a parametric resonance. We model the dynamics of the first mode of the beam with a second-order nonlinear ordinary-different equation. The model accounts for viscous damping, air drag, and inertia and geometric nonlinearities. We propose a control law based on cubic position and velocity feedback. We use the method of multiple scales to derive two first-order ordinary- differential equations that govern the time variation of the amplitude and phase of the response. We conduct a stability study and analyze the effect of the control gains on the response of the system. The results show that cubic velocity feedback leads to effective vibration suppression and bifurcation control.

Successful active vibration control using piezoceramic (PZT) elements is usually based on a full understanding of the system. When a large number of sensors and actuators are used, mechanical coupling between the piezo-elements and the host structures may be strong. The control of such systems requires simulation models capable of taking the full coupling into account. This paper presents such a model on the basis of a rectangular plate with symmetrically integrated piezo-elements. Experimental validations have been systematically performed and showed that the established model is applicable to plates exhibiting relatively complex modal behavior. Using this model, actuators of different shapes (rectangular, circular, oval, etc.) and optimal control of the plate structure using PZT actuators and sensors are investigated. This work allows one to have a better understanding of active control of vibration with PZT and provides information about the importance of shape, size and number of sensors and actuators for active control applications.

Static shape control of adaptive structures is currently an important and active research area in the smart structures field. Numerous actuation schemes using smart materials have been proposed and developed for shape control of structures. While the results of the smart material based technology is promising, it is also, however, showing more serious limitations such as scalability of laboratory-scale prototype models into real-scale models. In addition, the smart material based approach for shape control requires a multitude of actuators distributed throughout the host structure, the hence, complicates the control system. This paper introduces a novel alternative design concept for shape control of flexible adaptive structures using a single actuator which need not necessarily be smart material based. The novelty in this concept is that it employs distributed compliance in design--through compliant mechanisms, a class of mechanisms that transmit motion through inherent flexibility--rather than distributed actuation to accomplish the shape changes. The paper outlines a method for synthesis of such compliant mechanisms. The concept, and the synthesis method are illustrated through an example where a specified shape change in the leading edge of an airfoil structure is accomplished. The new concept has a great potential to not only eliminate the scalability problem, but also reduce the control complexity, the weight, and cost of the entire system as well.

This study describes the development of a novel opto- mechanical actuator suitable for integration in all-optical smart systems. Its action relies on the out-of-plane thermo- mechanical deflection of a thin optical-acrylic membrane due to the absorption of radiation from a laser source. The response of the actuator can be adapted to suit different applications by coating the surfaces of the element with either fully or partially absorbing or reflective coatings. The transient and steady state opto-thermo-mechanical behavior of different element configurations has been modelled analytically and using finite element analysis. In simple actuator configurations, the dynamic response of the element can be represented by that of a linear first order system. These modelling and simulation procedures have been verified with experimental data and have been used to optimize different actuator designs. One of these opto- mechanical actuators has been employed as an active optical element in the realization of a novel all-optical interferometric device employing active drift compensation.

Smart material patches are currently an impractical choice in applications requiring fine spatial resolution or control of complex areas. The static nature of electrodes, the conventional choice for control signal application to many smart materials, makes them unsuitable in these instances. To address this issue the use of electron guns as charge sources for smart material control is investigated in this paper. In the electron gun control method the need for separate electrodes and wire leads is eliminated by depositing the control charges directly on the surface of the piezoelectric material. Since piezoelectric materials are dielectrics the charges remain where deposited by the electron gun. The spatial resolution of this control method is as small as the spot size of the electron beam, which in a focused beam can be as small as tens of microns. Large areas can be covered by a single electron gun simply by scanning the beam using deflection plates. Some practical aspects of electron gun control are presented in this paper. A description of an experimental test bed assembled to evaluate electron gun control of PZT-5H is presented, as are results and conceptual models of the system behavior.

A magnetostrictive water pump using Terfenol-D has been designed and built, achieving a flow rate of 15 ml/sec at 5 psi, using 41 watts. This is a higher flow rate and lower pressure than previous magnetostrictive pumps. The pump is 6' long and 3.6' in diameter. A model of pump performance has been developed, including valve inertia which limits the drive frequency, and trapped air in the chamber, which can reduce the flow rate and make the pump noisy. Methods have been developed to eliminate trapped air. The pump uses a hydraulic stroke amplifier, which turned out much stiffer axially than it was designed to be. This has adversely affected pump performance, because of finite Terfenol compliance and finite housing compliance. With a stroke amplifier of optimal stiffness, and with better quality Terfenol, the pump should be able to achieve a flow rate of 30 ml/sec at 5 psi, consuming 25 to 35 watts. Although the power is more than would be needed by a piezoelectric pump of the same performance, a Terfenol-D actuator offers important advantages, including low voltage and no known fatigue mechanism. Furthermore, much of the modeling would be relevant to a piezoelectric pump as well.

Piezomotors are an increasingly competitive alternative to electromagnetic stepper motors, especially in applications where large bandwidths and/or precise positioning control are desired. Piezomotors use a combination of electromechanical and frictional forces and, compared to conventional electromagnetic motors, have the advantages that no power supply is required to maintain the motor in position and no lubrication is necessary in the device. The operating principle of these motors relies on the use of an ultrasonic vibration, which is created via the piezoelectric effect (at resonance in most cases), in order to generate vibration forces at the `stator/rotor' contact interface. A mechanical preload is also applied at this contact interface and is responsible for the motor's holding force at rest. To meet the specifications of an aerospace application, we developed a new design of Linear PiezoMotors (LPMs). The first prototype we built shows very promising results, and makes the LPM a serious candidate to replace conventional stepper motors. The LPM features the following characteristics: a standing force of 100 N, a blocked force of 37 N, a maximum actuation speed of 23 mm/s, a maximum run of 10 mm, a mass of 500 g, an electrical power of 2.2 W, and a position accuracy superior to 1 micrometers . To our knowledge, the driving force delivered by the LPM has never before been achieved in resonant devices. This paper describes the physical operating principles of the LPM, as well as the modeling tools and experimental techniques we used for its development. Several implementation schemes are also presented and show the wide range of possible applications offered by the linear piezomotor.

A linear inchworm motor was developed for structural shape control applications. One motivation for this development was the desire for higher speed alternatives to shape memory alloy based devices. Features of the subject device include compactness (60 X 40 X 20 mm), large displacement range (approximately 1 cm), and large holding force capability (approximately 200 N). There are three active piezoelectric elements within the inchworm: two `clamps' and one `pusher'. Large displacements are achieved by repetitively advancing and clamping the pushing element. Although each pusher step is small, on the order of 10 microns, if the step rate is high enough, substantial speeds may be obtained (approximately 1 cm/s). In the past, inchworm devices have been used primarily for precision positioning. The development of a robust clamping mechanism is essential to the attainment of high force capability, and considerable design effort focused on improving this mechanism. To guide the design, a lumped parameter model of the inchworm was developed. This model included the dynamics of the moving shaft and the frictional clamping devices, and used a variable friction coefficient. It enables the simulation of the time response of the actuator under typical loading conditions. The effects of the step drive frequency, the pre-load applied on the clamps, and the phase shifts of the clamp signals to the main pusher signal were investigated. Using this tool, the frequency bandwidth, the optimal pre-load and phase shifts which result in maximum speed were explored. Measured rates of motion agreed well with predictions, but the measured dynamic force was lower than expected.

The development and frequency response of a novel proof-of- concept prototype Mesoscale Actuator Device (MAD) is described in this paper. The MAD is similar to piezoelectric driven inchworm motors with the exception that mechanically interlocking microridges replace the traditional frictional clamping mechanisms. The interlocked microridges, microfabricated from single crystal silicon, are shown to support macroscopic loads. Tests conducted on the current design demonstrate that the interlocked microridges support 16 MPa in shear or that two sets of 3 X 5 mm locked chips support a 50 kgf. Operation of three generations of prototype MAD device containing microridges are accomplished at relatively large frequencies using an open loop control signal. Synchronizing the locking and unlocking of the microridges with the elongating and contracting actuator requires a dedicated waveform in the voltage signal supplied and permitted large operational frequencies. First generation operates at 0.6 Hz and demonstrated 1000s microridges can be engaged without problem, second generation moves like an inchworm up to 32 Hz, and the third generation including an external force was successfully operated from 0.2 Hz to 500 Hz corresponding to speeds from 2 micrometers /s to 5 mm/s. The upper limit (500 Hz) was imposed by software limitations and not related to physical limitations of the current device.

SatCon is developing linear and rotary motors that rely on the peristaltic motion of a Terfenol-D element along a tight-fitting channel. Magnetostrictive inchworm motors offer extended or unlimited travel, as well as those attributes normally associated with magnetostrictive actuators: high force and torque densities, quick response, and fine resolution motion. Unlike Kiesewetter's cylindrical design, the Terfenol-D element is a rectangular slab placed between two tight-fitting plates that are spring-loaded to maintain proper contact in spite of wear. Also, the excitation coils do not enclose the Terfenol-D element, allowing extension of the concept to rotary motors. A model for inchworm performance has been developed, based on observations of a prototype linear inchworm motor. Speed is approximately the product of peak magnetostrictive strain and phase velocity of the magnetic field, but is reduced by the finite element of the contact zone between the Terfenol- D and the plates. As a result, speed drops with load, since magnetostrictive strain is reduced and the contact zone grows longer with increasing applied load. The speed was limited by the skin effect present in the Terfenol-D element. A second prototype employs composite Terfenol-D with its high resistivity, in order to permit operation at higher speeds. SatCon is also developing a rotary motor and making improvements to the design of linear motors.

This study deals with a micromotor based on the use of magnetostrictive thin films. This motor belongs to the category of the Standing Wave Ultrasonic Motors. The active part of the motor is the rotor, which is a 100 micrometers thick ring vibrating in a flexural mode. Teeth (300 micrometers high) are placed on special positions of the rotor and produce an oblique motion which can induce the relative motion of any object in contact with them. The magnetic excitation field is radial and uses the transverse coupling of the 4 micrometers thick magnetostrictive film. The film, deposited by sputtering on the ring, consists of layers of different rare-earth/iron alloys and was developed during a European Brite-Euram project. The finite element technique was used in order to design a prototype of the motor and to optimize the active rotor and the energizer coil. The prototype we built delivered a speed of 30 turns per minute with a torque of 2 (mu) N.m (without prestress applied on the rotor). Our experimental results show that the performance of this motor could easily be increased by a factor of 5. The main advantage of this motor is the fact that it is remotely powered and controlled. The excitation coil, which provides both power and control, can be placed away from the active rotor. Moreover, the rotor is completely wireless and is not connected to its support or to any other part. It is interesting to note that it would not be possible to build this type of motor using piezoelectric technology. Medical applications of magnetostrictive micromotors could be found for internal microdistributors of medication (the coil staying outside the body). Other applications include remote control micropositioning, micropositioning of optical components, and for the actuation of systems such as valves, electrical switches, and relays.

Efficient miniature actuators that are compact and consume low power are needed to drive telerobotic devices and space 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. The technology that has emerged in commercial products requires rigorous analytical tools for effective design of such motors. A finite element analytical model was developed to examine the excitation of flexural plate wave traveling in a rotary piezoelectrically actuated motor. The model uses annular finite elements that are applied to predict the excitation frequency and modal response of an annular stator. This model is being developed to enable the design of efficient ultrasonic motors (USMs) and it incorporates the details of the stator which include the teeth, piezoelectric crystals, stator geometry, etc. The theoretical predictions were corroborated experimentally for the stator. Parallel to this effect, USMs are made and incorporated into a robotic arm and their capability to operate at the environment of Mars is being studied. Motors with two different actuators layout were tested at cryovac conditions and were shown to operate down to -150 degree(s)C and 16-mTorr when the activation starts at ambient conditions.

Electromechanical modeling of a structure is used to position piezoelectric elements and to devise readout networks for their use as self-sensing transducers. The positioning is aimed to act selectively on given vibration modes and is carried on by means of simple spatial filtering techniques. The piezoelectric readout network is implemented using active components to avoid the coupling between mechanical and electrical states usually found with passive circuits. The proposed layout is well suited for both the testing and the active control of smart structures.

A resin pocket surrounding an optical fiber in a laminated structure will produce residual stresses in the optical fiber due to the mismatch of the coefficients of thermal expansion (CTE) between the laminate, resin, and optical fiber. This paper describes an analytical tool that generates a solid 3D finite element model (FEM) of a plate- like fiber optic smart structure for any ply stacking sequence, any optical fiber embedding location through-the- thickness of the laminate, and any optical fiber orientation. Classical laminate plate theory and a linear elastic model are employed to estimate the resin pocket geometry along a user specified optical fiber path. The unknowns of the system are evaluated using the method of minimum potential energy, which is comprised of the bending strain energy of the reinforcing fibers, the compressive strain energy of the laminate, and the work performed on the system. Using the geometry of the optical fiber, the lamina, and the resin pocket, a solid 3D FEM is generated in the neighborhood of the optical fiber along the user defined optical fiber path. The FEM will be used to evaluate the strain field in the optical fiber due to the CTE mismatch in the system.

This paper presents dynamic modeling and shape control of a smart plate filled with an electrorheological (ER) fluid. Firstly, a dynamic model incorporated with complex shear modulus of the ER fluid itself is developed to estimate field-dependent modal parameters of the plate structure via finite element approach. Following a construction of a four partitioned ER fluid-based plate, an extensive modal test is experimentally conducted to identify modal parameters with respect to both the magnitude and the area of the applied electric fields to the ER fluid domain. In order to validate the effectiveness of the proposed smart plate, globally and locally controlled mode shapes and natural frequencies are investigated. Both the experimental and analytical results indicate that the ER fluid imbedded in the distributed- parameter system of plate-like structures has a great authority in tuning structural shapes and elastodynamic properties.

The design of systems based on smart structure technologies for active shape and vibration control and high precision positioning requires a good knowledge of the behavior of the active materials (electrostrictive and piezoelectric ceramics and polymers, magnetostrictive and shape memory alloys...) and of commercially available actuators. Extensive theoretical studies have been made on the behavior of active materials during the past decades but there are only a few developments on experimental comparisons between different kinds of commercially available actuators. The purpose of this study is to find out the pertinent parameters for the design of such systems, to set up a common static test procedure for all types of actuators and to define comparison criteria in terms of output force and displacement, mechanical and electrical energy, mass and dimensions. After having define the pertinent parameters of the characterization and having described the resulting testing procedure, test results are presented for different types of actuators based on piezoceramics and magnetostrictive alloys. The performances of each actuator are compared through both the test results and the announced characteristics: to perform this comparison absolute and relative criteria are chosen considering aeronautical and space applications.

Active Constrained Layer Damping (ACLD) treatment has been used successfully for controlling the vibration of various flexible structures. It provides an effective means for augmenting the simplicity and reliability of passive damping with the low weight and high efficiency of active controls to attain high damping characteristics over broad frequency bands. In this paper, optimal placement strategies of ACLD patches are devised using the modal strain energy (MSE) method. These strategies aim at minimizing the total weight of the damping treatments while satisfying constraints imposed on the modal damping ratios. A finite element model is developed to determine the modal strain energies of plates treated with ACLD treatment. The treatment is then applied to the elements that have highest MSE in order to target specific modes of vibrations. Numerical examples are presented to demonstrate the utility of the devised optimization technique as an effective tool for selecting the optimal locations of the ACLD treatment to achieve desired damping characteristics over a broad frequency band.

This paper presents an experimental study of the effects of varied magnetic bias, AC magnetic field amplitude and frequency on the characteristics of hysteresis loops produced in a magnetostrictive transducer. The study uses a magnetostrictive transducer designed at Iowa State University that utilizes an 11.5 cm (4.54 in) long by 1.27 cm (0.5 in) diameter cylindrical Terfenol-D rod. This transducer allows controlled variation of the following operating conditions: mechanical prestress, magnitude and frequency of AC magnetic field, and magnetic bias. By performing extensive experimental tests, material property trends can be developed for use in the optimization of transducer design parameters for different applications. For the results presented, the magnetic bias, the AC magnetic field amplitude, and the frequency of excitation were independently varied while temperature, mass load and prestress were kept constant. The minor hysteresis loops of the strain versus applied magnetic field, flux density versus applied magnetic field, and magnetization versus applied magnetic field are presented and compared. Material property trends identified from the minor loops are presented for the axial strain coefficient, permeability, susceptibility, and energy losses.