Two concepts for Smart Vortex Generators have been designed, constructed and tested. The first is based upon the use of Shape Memory Alloy, whereas the second makes use of a pneumatic actuator. Experimental wind tunnel tests were undertaken using Fluorine Flow Visualisation in order to investigate their performance. It was demonstrated that both concepts enabled full control of the vortex generator angle for all speeds up to 35 ms^-1.

Drag reduction for aerial and underwater vehicles has a range of positive ramifications: reduced fuel consumption, larger operational range, greater endurance and higher achievable speeds. Recent Direct Numerical Simulation (DNS) studies have shown that the application of a transversely acting, traveling waveform like force, that is confined to the viscous sublayer of the flow, can result in significant reduction in turbulent drag. Since the action of this force wave is confined to a very small region of fluid right next to the surface, it is postulated that the application of a traveling surface wave, which is also confined to these dimensions, would in effect result in the necessary traveling force wave. In this work, a generalized actuation principle for generating a traveling wave on the surface of a skin is proposed and analyzed. The flow control technique pursued is “micro” in the sense that only micro-scale wave amplitudes (order of 30 m) and energy inputs are expected to produce significant benefits. Hence, a MEMS based approach to the design of the active skin is considered, that utilizes actuation by active materials such as Shape Memory Alloys (SMA)s and piezoelectric actuators. Specifically, a MEMS based design that incorporates thin film SMA actuators is developed and the process flow methodology required for its microfabrication is discussed. For preliminary testing and validation of the DNS results, a mechanically actuated prototype skin, the operation of which has been refined through several iterations, has been manufactured using a rapid prototyping machine.

The twist actuation of piezocomposite actuators embedded in a composite wing is numerically investigated. Parametric analysis of the actuation authority is conducted for wing cross sections with double and triple cells, considering different distributions of anisotropic piezocomposite actuators. The variational asymptotic beam cross-sectional (VABS) analysis is used to compute the airfoil stiffness, actuation force and mass properties. As a result, the regions with the highest specific actuation are determined and a cost-effective way of adding active material to the cross section is proposed. Results indicate that 50% of the maximum mass penalty associated with the addition of active plies is responsible for generating approximately 80% of the maximum available induced twist.

In recent years there was a need for developing efficient NDE techniques for large area inspection. Conventional ultrasonic inspection techniques such as C-scan and B-scan are very time consuming because the transducer needs to be scanned over each point of structure under the test. Ultrasonically, Lamb wave is considered to be a candidate for large area inspection based on its capability of propagating long distances and its media-thickness dependent propagation properties. Unfortunately, Lamb wave inspection is complicated by the existence of at least two modes at any given frequency. The received signal generally contains more than one mode, and the proportions of the different modes present is modified by the mode conversion at defects. The modes are also highly dispersive in nature. As a result the peak detection and hence the flaw detection with these ultrasonic signals becomes highly complicated and the interpretation of the signals becomes very difficult and also leads to signal-to-noise problems. Consequently, a new kind of signal analysis is required to interpret the results of inspection and to determine if there is a defect or not. In order to extract the information on defects from the Lamb wave signal received by an ultrasonic transducer in such noisy environments, we use a method of analysis based on wavelet transforms. The detection of ultrasonic pulses using wavelet transforms is described and the robustness of this method is verified with testing on samples of adhesively bonded composite patch repair of cracked aluminum panels with simulated flaws.

The cure monitoring system with piezoelectric ceramics is constructed. An embedded type piezoelectric ceramics sensor with flat lead wires is developed. And the piezoelectric ceramics is embedded into composite laminate. A dummy piezoelectric ceramics is set in the autoclave oven. The impedance of the piezoelectric ceramics which is embedded in the composite laminate and that of the dummy piezoelectric ceramics are measured by a LCR meter. The piezoelectric ceramics have strong temperature dependency. The temperature dependency of the impedance of piezoelectric ceramics is corrected by the information from the dummy piezoelectric ceramics. A dielectric sensor is also embedded in the composite laminate as a reference sensor for the degree of cure. The change in calculated cure index shows good correspondence with change in the log ion viscosity which is measured by the dielectric cure monitoring sensor.

This paper discusses a new signal-processing tool involving the use of empirical mode decomposition and its application to health monitoring of structures. Empirical mode decomposition is a time series analysis method that extracts a custom set of basis sets to describe the vibratory response of a system. In conjunction with the Hilbert Transform, the empirical mode decomposition method provides some unique information about the nature of the vibratory response. In this paper, the Hilbert phase for discrete onedimensional structural elements is compared to the phase obtained from the use of dereverberated wave mechanics. Simulation results indicate that the Hilbert phase is proportional to mass and stiffness properties between two successive degrees of freedom. Hence, the Hilbert phase can be used to infer, locate and possibly quantify the amount of damage in a structure.

A new mechanical multifunctional dual-stiffness sensor for in-situ real-time stiffness and energy density measurements was developed at the University of Maryland. This sensor is composed of 2 sub-sensors - a stiff and compliant subsensor. The sensor has the ability to predict the elastic field of a given host structure based on the strain state of the two sub-sensors integrated into the structure. This study showed the possibility of using the sensor to deduce the local instantaneous host stiffness and the strain energy density. Because the sensors can be embedded in a structure that is subjected to a complex stress state, Eshelbys equivalent inclusion method was used to derive the elastic properties of the host. An analytical derivation and a sensitivity analysis is given in a paper by Majeed and Dasgupta. Majeed and Dasgupta showed how the stiffness sensor is used to estimate the hosts stiffness. The present study evaluates the use of a dual stiffness sensor using piezoelectric sub-sensors to diagnose damage and to determine the remaining life of structures. The objective of this research is to develop an in-situ health monitoring active sensor for a real structure under its actual lifecycle loading condition. The detection of the onset of any damage, the subsequent monitoring of its growth and the help in predicting the remaining life of the structure constitute the important goals of the system. A numerical verification using finite element analysis (FEA) is presented and the results indicate that the sensor can be used for diagnostics of structures. A distributed array of sensors is used to determine the location of damage. Experimental results are presented for uniaxial experimental tests under monotonic quasistatic loading conditions and indicate that the concept can easily be implemented.

This paper describes cure and health monitoring of glass fiber reinforced plastics (GFRP) textile composites both during a resin transfer molding (RTM) process and in loading tests. Carbon fiber reinforced plastics (CFRP) textile composites also were used for a comparative study. Fiber Bragg grating (FBG) fiber optic sensors were embedded in FRP to monitor internal strain. From the results of cure monitoring, it was found that the embedded FBG sensors were useful to know when cured resin constrained fibers. It also appeared that specimens were subjected to friction stress resulted from difference of coefficient of thermal expansion between FRP and a stainless steel mold in cooling process of RTM molding. After the molding, tensile and fatigue tests were conducted. The results of tensile tests showed that output of the embedded FBG sensors agreed well that of surface-bonded strain gauges despite deterioration of reflected spectra form the sensors. From the results of fatigue tests, the FBG sensors showed good status until 100,000 cycles when specimens had no damage. From these results, it can be concluded that embedded FBG sensors have good capability of monitoring internal strain in textile FRP both during RTM process and in service.

The goal of this research is to reduce the likelihood of failure and the cost of maintenance of critical bolted joints. To reduce the self-loosening mode of failure, the concept of a self-sensing and self-healing bolted joint has been developed. This concept combines piezoelectric-based health-monitoring techniques with shape memory alloy (SMA) actuators to restore tension in a loose bolt. Many practical issues need to be addressed before the self-healing bolted joint can become a reality. One of the primary issues is the actuation of the SMA washer. The relatively large mass of the SMA washer and low resistance because of its short length make resistive heating particularly difficult. In addition, the large mass of the members connected by the joint can often act as a heat sink for what heat is generated. Therefore, a series of models was developed to assess the viability of resistive heating and provide an estimate for the power requirements for effective actuation. Modeling and experimental testing have shown that the use of external heater can be used to actuate SMA actuator with conventional power sources. By making the SMA washer substantially easier to actuate, this method provides a convenient alternative to the resistive heating, which requires very large currents needed for heating, and make the adaptive joints more accessible to real-field applications. This paper summarizes considerations needed to design SMA actuators, experimental setup and procedures, and several implementation issues and can be used as a guideline of future investigation.

We investigated a thermal nondestructive evaluation (NDE) technique based on thermography that uses optical fiber thermal sensors to detect damage within a laminated graphite epoxy composite specimen. Composite samples manufactured for testing had fiber optic sensors embedded between layers and thermocouples attached to the exterior. A simulated impact system was used to induce damage of varying degrees into the samples and the damage was confirmed with C-span. The experimental procedures in addition to the test data obtained are presented. The results confirm that the fiber optic thermal sensors can not only detect the presence of damage, but can measure the severity of damage as well.

A new improved nonlinear transient generalized layerwise theory for modeling embedded discrete and continuous sensor(s) outputs in laminated composite plates with acoustic emission from cracks and embedded delaminations is developed. The computational modeling involves development of a finite element scheme using an improved layerwise laminate theory for a composite laminate plate with embedded discrete and continuous sensors and embedded discrete delaminations. The simulated cases studied included cantilever plates with embedded sensors and embedded delamination under low frequency vibration and square plates with discrete embedded sensors and continuous embedded sensor architecture and embedded discrete delaminations under high frequency acoustic emission. The effect on sensor outputs due to scattering of the acoustic emission due to the presence of delamination is also investigated. It is expected that this analytical model would be a useful tool for numerical simulation of composite laminated structures with embedded delaminations and embedded sensor architecture, particularly since experimental investigation could often be prohibitive to simulate different conditions.

The capability of embedded piezoelectric wafer active sensors (PWAS) to perform in-situ nondestructive evaluation (NDE) is explored. Theoretical developments and laboratory tests are used to prove that PWAS transducers can satisfactorily perform Lamb wave transmission and reception, pulse-echo, pitch-catch, and phased array functions of conventional ultrasonics thus opening the road for embedded ultrasonics. Subsequently, crack detection in an aircraft panel with the pulse-echo method is illustrated. For large area scanning, a PWAS phased array is used to create the embedded ultrasonics structural radar (EUSR). For quality assurance, PWAS self-tests with the electromechanical impedance method are discussed.

This paper describes the development of biomimetic structure systems with LIPCA (LIghtweight Piezo-Composite Actuator) and battery supported power control unit. To apply LIPCA as a biomimetic actuator for the control surface of small unmanned air vehicle, a battery supported power control unit was developed, which is composed of a lithium polymer, one step-up converter, four power switching high voltage transistors, on Schmitt triggered comparator, and control logics. A simple RC circuit is used to sample the voltage applied to the LIPCA. H-switch was applied which is composed of the four high voltage transistors to control the voltage or charge and its polarity applied to the LIPCA. From experiments, it was observed that the developed biomimetic adaptronic systems could be constructed with relatively compact and light units and could produce enough displacement and force to be used as a control surface for the elevator and the rudder of a small unmanned vehicle.

This paper represents a "work-in-progress" status report on shape determination and sensing methods for deforming structures utilizing embedded sensors. This work is part of a larger effort in morphing aircraft structures at the Air Force Research Laboratory. The two critical issues involved in the present work are the determination of the number and placement of embedded sensors, and algorithms for transforming the sensor data into displacements to define the shape of the structure. These issues are addressed in the context of a laboratory experiment, which demonstrate many of the challenges inherent in the problem.

Biomimetic wing sections actuated by piezoceramics actuator LIPCA have been designed and their actuation displacements estimated by using the thermal analogy and MSC/NASTRAN based on the linear elasticity. The wing sections are fabricated as the design and tested for evaluation. Measured actuation displacements were larger than the estimated values mainly due to the material non-linearity of the PZT wafer. The biomimetic wing sections can be used for control surfaces of small scale UAVs.

An approach for vibration delocalization of nearly periodic structures using piezoelectric networks with active coupling enhancement is presented. Piezoelectric networks are synthesized to reduce the localization effect by absorbing the vibratory mechanical energy into the electric circuits and distributing it through an additional strong electrical wave channel. The effectiveness of electro-mechanical coupling of the system is increased through the use of active actions via a negative capacitance circuit. It is demonstrated that the delocalization effect of the piezoelectric networks can be greatly enhanced by using the proposed treatment.

This study focuses on the effectiveness of the piezoelectric patches either surface-mounted or embedded for different composite laminate thicknesses. Primarily, two finite element models (FEMs) are considered for this study. The first FEM considers beams with varying thicknesses and non-collocated surface-mounted piezoelectric patches as sensor and actuator. Typical results are shown for four and eight layers graphite/epoxy composite laminates. The second FEM deals with embedded non-collocated piezoelectric patches as sensor and actuator for beams with varying thicknesses. For the embedded case one extra layer is needed to cover the piezoelectric patch and one extra cut-out layer to fill the area around the piezoelectric patch. Therefore, a composite beam for the embedded case in comparison to the surface-mounted case has always four extra constraint layers. Typical results, for these two cases, are compared for the beams with the same number of inner layers (i.e. four and eight). A surface-mounted ACX piezoelectric patch acts as a shaker in both FEMs. Numerical and experimental results from modal and harmonic analyses were compared and excellent comparisons were achieved. Cross-examination between these two FEMs determined the following. 1) The effectiveness of piezoelectric patches acting as an actuator with respect to the laminate thicknesses and the actuator distance from the beam neutral axis for both cases. 2) The influence of the constraint layers on the performance of the embedded piezoelectric patches.

This paper summarizes the experimental work carried out to develop a prototype smart panel with sixteen decentralized vibration control units for the reduction of sound radiation. The system studied consists of a thin aluminum panel of dimensions l_x × l_y = 414 × 314 mm and thickness 1 mm with an embedded array of 4 × 4 square piezoceramic actuators. The sensing system equally consists of an array of 4 × 4 accelerometers that are arranged in such a way as to match the centre positions of the sixteen piezoceramic patches. Each of the sixteen sensor actuator pairs is set to implement decentralized velocity feedback control. In this paper the design of the sixteen modular sensor-controller-actuator systems is discussed in detail. The open loop sensor- actuator measured frequency response function is first analysed and contrasted with that derived from simulations, in a frequency range up to 50 kHz. This analysis is mainly focussed on the higher frequency effects due to the size of the piezoelectric actuator and generated by the dynamics of the accelerometer sensor. The stability of one or all sixteen control units are assessed experimentally using the Nyquist criterion. The reduction of sound radiation and panel vibration is then assessed with reference to a primary force excitation acting on the panel.

A small oscillatory motor is developed using ionic polymer materials as both the actuator and sensor for feedback control. The motor consists of a small metal ring with multiple ionic polymer actuators as drive elements. The actuation signal produces in-phase motion of the cantilevers. A separate cantilever is attached as an AC displacement or velocity sensor for the motor rotation. A laser vibrometer is utilized to measure the actual rotational displacement of the motor. Experiments are performed to demonstrate the ability of feedback to control the waveform of the motor output. The open-loop bandwidth of the motor is approximately 15 Hz with four cantilevers mounted in the motor. DC actuation of the motor is not possible with the ionic polymer sensor due to the lack of a DC displacement signal from the ionic polymer sensor. Open-loop and closed-loop experiments on the motor illustrate some of the advantages and disadvantages of ionic polymer materials. The advantages are low-voltage operation and the relative simplicity of the feedback control algorithms. Although DC actuation is not possible, waveform control is possible using a highly-resonant bandpass filter as the feedback compensator. Experimental results demonstrate that bandpass compensation enables waveform control in the 3 to 5 Hz frequency range when using four cantilever actuators. The disadvantage of ionic polymer materials are that hydration is required to maximize actuation and that distortion in the sensing output reduces the effectiveness of feedback control. The conclusion of the study is that ionic polymer materials are a viable candidate for low weight motion control although hydration and output distortion limit the motor performance.

It is one of effective ways to increase the running speed of railway vehicles to make the railways more competitive with air transport while providing better safety. However, the high speed of the train would cause significant car body vibrations, which induce the following problems: the ride stability, the ride quality, and the cost of track maintenance. Thus various kinds of railway vehicle suspensions, which can be categorized as passive, active, and semi-active types, have been designed to cushion riders from vibrations. In this paper, it is aimed to investigate semi-active suspension systems using magnetorheological (MR) fluid dampers for improving the ride quality of railway vehicles. A full-scale railway vehicle model with seventeen degrees of freedom is proposed to cope with lateral, yaw and roll motions of the car body, trucks and wheelsets. The governing equations of the railway vehicle integrated with MR fluid dampers in the secondary suspension are developed and the LQG control law using the acceleration feedback is adopted, in which the state variables are estimated from the measurable accelerations with the Kalman estimator. The performance of the semi-active suspension system exploiting MR fluid dampers is compared with those of the active suspension system with linear and unconstraint actuators and the passive suspension system with springs and oil dampers. The results show that the semi-active suspension system with MR fluid dampers possesses a good ride quality improvement ability.

This paper presents a new adaptation technique for R-L shunted piezoelectric patches (PZT) bonded on mechanical structures for single mode vibration suppression. For the implementation of the adaptive R-L shunt circuit, a new variable inductor circuit controlled by transistors is developed. Additionally, a new modeling method for shunted PZTs based on equivalent transformer and gyrator circuits is presented. This leads to a comprehensive model that simplifies the search for optimal shunt circuits. Furthermore, it allows simulating the system consisting of the structure, the PZT patch and a complex transistor or other non-linear shunts on standard electronic simulators like PSpice or Saber. Damping performance of R-L shunted piezoelectric devices is very sensitive to environmental factors changing the circuit’s resonance frequency corresponding to the damped vibration mode. This requires fast adaptive tuning of the R-L shunted circuit, which is implemented using a new adaptation technique. The tuning direction of this adaptation law is obtained by detecting the phase shift between the velocity of the mechanical structure and the current in the shunt circuit. As the exact value of the phase for this technique is not required, one can reduce the adaptation problem to multiplication and integration of current and velocity. The performance of the presented new adaptive R-L shunt is compared with the common adaptation law based on minimizing the RMS value of the strain and then experimentally verified. The adaptive R-L shunt, which minimizes the phase-shift, can tune to the optimal parameters within seconds, but it needs an additional velocity sensor. In contrast, the R-L shunt minimizing the RMS value works without extra sensors, but needs some minutes to tune optimally. The new adaptive R-L shunt circuit can be implemented in small analog electronic chips that allows integrating it in smart materials.

The active suppression of elastic buckling instability has the potential to significantly increase the effective strength of thin-wall structures. Despite all the interest in smart structures, the active suppression of buckling has received comparatively little attention. This paper addresses the effects of embedded actuation on the compression buckling strength of laminated composite plates through analysis and simulation. Numerical models are formulated that include the influence of essential features such as sensor uncertainty and noise, actuator saturation and control architecture on the buckling process. Silicon-based strain sensors and diffuse laser distance sensors are both considered for use in the detection of incipient buckling behavior due to their increased sensitivity. Actuation is provided by paired distributions of piezo-electric material incorporated into both sides of the laminate. Optimal controllers are designed to command the structure to deform in ways that interfere with the development of buckling mode shapes. Commercial software packages are used to solve the resulting non-linear equations, and some of the tradeoffs are enumerated. Overall, the results show that active buckling control can considerably enhance resistance to instability under compressive loads. These buckling load predictions demonstrate the viability of optimal control and piezo-electric actuation for implementing active buckling control. Due to the importance of early detection, the relative effectiveness of active buckling control is shown to be strongly dependent on the performance of the sensing scheme, as well as on the characteristics of the structure.

A hybrid mount featuring elastic rubber and piezoelectric material is proposed and applied to the vibration control of a beam structure subjected to high frequency excitations. A mechanical model of the proposed hybrid mount is derived, and then the frequency-dependent dynamic stiffness of rubber and the voltage-dependent stroke of piezoactuator are verified experimentally. After formulating a mathematical model of the beam structure associated with the hybrid mount and the passive rubber mounts, a robust sliding mode controller is designed to attenuate vibration of the beam structure. The controller is experimentally realized and control responses such as accelerations of the beam structure and force transmission through the hybrid mount and rubber mounts are presented in frequency domain.

In this paper, the electromechanical displacements of curved actuators such as THUNDER are calculated by finite element method to design the optimal configuration of curved actuators. To predict the pre-stress in the device due to the mismatch in coefficients of thermal expansion, the adhesive as well as metal and PZT ceramic is also numerically modeled by using hexahedral solid elements. Because the modeling of these thin layers causes the numbers of degree of freedom to increase, large-scale structural analyses are performed in a cluster system in this study. The curved shape and pre-stress in the actuator are obtained by the cured curvature analysis. The displacement under the piezoelectric force by an applied voltage is also calculated to compare the performance of curved actuator. The thickness of metal and adhesive, the number of metal layer are chosen as design factors.

While good marksmanship is key to the effectiveness of the infantry mission, all soldiers experience a decrease in accuracy due to combat stress that generates detrimental physiological effects. INSTAR is a tactical rifle designed to address these effects by decoupling unwanted shooter-induced disturbances from the barrel via an active suspension system. The critical design driver for this active suspension was the "complete" actuation system (actuation, driving electronics and power supply). This paper presents an overview to the INSTAR architectural design along with the challenging actuation requirements. The architectural development and experimental performance characterization of the selected Recurve piezoceramic actuation system is discussed in detail along with the specialized driving electronics needed for power conservation. Range-of-motion experiments were conducted on a full-scale, 1 DOF INSTAR prototype, demonstrating the necessary actuation system control authority for a successful active suspension.

Recent developments in ultrasonic motor design have demonstrated that small size tube-shaped motors could be fabricated at low cost. Motors with diameters between 15 and 2.5mm have been fabricated and tested. The performance evaluation of these motors is still in progress, but have already shown promising results: the smallest ones exhibit no-load speeds in the range of 70rad/s and blocked torques close to 0.9mN•m. In this paper, we review the operating principle of these devices and several implementation examples. Then, we show how the finite element method (ATILA) can be used, in combination with genetic optimization procedures, to design tube-shaped motors in various dimensions and for different performance objectives. Several design examples are presented and discussed.

This study investigates biodynamic response mitigation to three different excitations of sinusoidal and random vibrations and shock load using a magnetorheological (MR) seat suspension. In doing so, an MR seat suspension model for military vehicles, with a detailed lumped parameter model of the human body, was developed. The lumped parameter model of the human body consists of four parts: pelvis, upper torso, viscera and head. From the model, the governing equation of motion of the MR seat suspension considering the human body was derived. Based on this equation, a semi-active nonlinear optimal control algorithm appropriate for the MR seat suspension was developed. The simulated control performance of the MR seat suspension was evaluated under three different excitations of sinusoidal and random vibration and tremendous shock load due to a mine explosion. In addition, the mitigation of injuries to humans due to such shock load was also evaluated and compared with the passive seat suspension using a passive hydraulic damper.

In this research a broadband passive vibration control technique using a semi-active circuit is presented. A digitally tunable RL shunt circuit and a semi-active mode identifier are developed using 8-bit CMOS microcontrollers to control multiple vibratory modes in a mechanical system. In order to increase the adaptability of the controller, the effects of additional capacitors in the circuit are investigated. The governing equations for the coupled electro-mechanical system are introduced using Hamilton’s Principle and finite element analysis. The system is verified experimentally using and the simulation and experimental results are provided in multiple formats.

Although many researches of strain measurement using fiber Bragg grating (FBG) sensors were conducted, there were few applications of FBG sensors to spacecraft in operation. It is very significant to develop an onboard system for the real-time strain measurement during the flight operation. In the present research, the real-time strain measurement of a composite liquid hydrogen (LH₂) tank, which consisted of CFRP and aluminum liner, was attempted. Adhesive property of the FBG sensors was investigated first of all. As a result, UV coated FBG sensors and polyurethane adhesive were adopted. Then, reflection spectra from FBG sensors were measured through the tensile test at liquid helium (LHe) temperature. Since the center wavelength shifted in proportion to the applied strain, the FBG sensor was suitable as a precise strain sensor even at LHe temperature. Next, the development of an onboard FBG demodulator was discussed. This onboard demodulator was designed for weight saving to be mounted on a reusable rocket vehicle test (RVT) operated by the Institute of Space and Astronautical Science (ISAS). FBG sensors were bonded on the surface of the composite LH₂ tank for the RVT. Then, strain measurement using the onboard demodulator was conducted through the cryogenic pressure test of the tank and compared with the result measured using the optical spectrum analyzer (OSA).

We propose a damage detection method based on frequency responses measured by FBG sensors during vibration tests. When random noise vibrates a laminated composite panel and a stiffener fastened with bolts, the peak gain of the resonance frequencies can be obtained. We calculated the correlation coefficient of the normalized gain for the frequency responses, and then predicted the location of a missing bolt. This method will make possible to predict the location of damage with a limited number of FBG sensors while a structure is vibrating even if the excitation point changes.

The research in this study develops an analysis technique for mechanized solid-state actuators. The methodology's strength stems from the fact that it can be applied to a single solid-state actuator or an actuator that is coupled to a compliant mechanism (mechanized). The technique couples the actuator to any compliant mechanism and it takes into account interactions between the mechanized actuator and its load. Thus the methodology can be applied to a myriad of loaded systems. The analysis technique is rooted in thermodynamics and thus can be expanded to a wide range of systems (piezoelectric, electrohydraulic, electrostrictive, magnetostrictive, etc.). The methodology uses energy transfer as a medium to develop analytical relationships between input parameters and output parameters. Results of the technique are consistent with existing energy-based techniques and experimental data.

The morphology and the free strain performances of three different piezoelectric ceramic fibers used for the manufacture of active fiber composites (AFCs) have been investigated. The morphology of the fibers has a direct influence on the manufacture of the AFCs. Fibers with non-uniform diameters are more difficult to contact with the interdigitated electrodes and can be the cause of irreparable damages in AFCs. An indirect method requiring the use of a simple analytical model is proposed to evaluate the free strain of active fiber composites. This indirect method presents a relatively good agreement with direct free strain measurements performed with strain gages glued on both sides of an AFC. The results show a systematic difference of ca. 20 % between the indirect and the direct methods. However, the indirect method did not permit to see differences of piezoelectric performance between the types of fibers.

In the use of piezoelectric actuators, it is a clear choice to use stack (or d₃₃ mode) architectures when very high force is required or benders (or d₃₁ mode) architectures when very high displacements are needed. However, the choice isn't as clear for applications that need simultaneously a moderate force and displacement. This paper presents one such application, INSTAR that is posed with this dilemma. INSTAR is a novel rifle system that has an inertially stabilized barrel via an active suspension based on piezoelectric actuation. While the frequency required for this application was low (~10Hz), the displacement (± 200 to 400 microns) and the force (22-45 N) are moderate. Two very different actuation approaches were developed, modeled, fabricated and experimentally validated within the INSTAR demonstration platform: 1) a d₃₁ approach based on the Recurve architecture with focus on generating higher forces than is common for d₃₁ actuators and 2) a d₃₃ approach based upon a compliant mechanism designed using topology optimization with focus on providing more amplified strain than is common for d₃₃ actuators. Both approaches were successful in meeting the INSTAR requirements, but each had its on advantages and disadvantages.

With the advancement of actuator engineering, adaptive optic technology has grown considerably over the past couple of decades. Recently, there has been attention in lightweight adaptive optics where piezoelectric sheet actuators are directly attached on the back of optical mirrors to achieve a high precision surface shape with minimum addition weight[C. Kuo, R. Bruno, '90, '92; C. Liu and N. Hagood, '93; R. Kapania, P. Mohan, et al, 1998]. Philen and Wang [2001] investigated the shape control performance of a large flexible circular plate structure having directly attached thin strip piezoelectric sheet actuators placed in the plate's radial and circumferential directions. It was discovered that the performance of the system could be further improved if the piezoelectric actuator was decoupled in direction, meaning that the circumferential (radial) action of the radial (circumferential) actuators is eliminated while the radial (circumferential) action is maintained. To realize the decoupling effect, the performance of an active stiffener concept for high-precision shape and vibration control has been studied [Philen and Wang, 2002]. The active stiffener configuration consists of an insert (stiffener) placed between the host structure and the piezoelectric sheet actuator, which could produce the required decoupling effect. Similar to the active stiffener, the Active Fiber Composite (AFC) possesses a unique orthotropic actuation and has many advantages over the commonly used piezoceramic sheet actuator, thus providing a potential actuation scheme for the control of optical surfaces. In this paper, analytical investigations into several piezoelectric-type actuation methods for shape and vibration control of plate structures are presented. For the study, a performance comparison of the Active Fiber Composite (AFC), the Active Stiffener (AS), and the Direct Attached (DA) actuators for shape and vibration control of a circular plate structure is carried out. The shape control results demonstrate that the AS and the AFC perform much better (more reduction of surface error) than the DA actuator due to the reduced authority in the decoupled direction, and the AS outperforms the AFC for the majority of the deformation modes investigated. While the AFC is able to achieve a greater reduction in the surface error when correcting for certain deformation modes, the required voltages for the AFC are much higher than the AS and DA for all the deformation modes investigated. Due to the reduction of the authority in the decoupled directions, the vibration control results show that the AS and the AFC both have less spillover of the controller's energy into the higher uncontrolled vibration modes than the DA. Similar to the shape control analysis, the AFCs perform comparably to the AS when controlling vibration, but at the cost of much higher voltages.

This paper is concerned with the fatigue characteristics of LIPCA (LIghtweight Piezo-Composite Actuator) device systems, composed of a piezoelectric ceramic layer and fiber reinforced light composite layers, where the PZT ceramic layer is typically sandwiched by a top fiber layer with a low CTE (coefficient of thermal expansion) and base layers with a high CTE. The advantages of the LIPCA design include the use of lightweight fiber reinforced plastic layers without compromising the generation of a high force and large displacement, and design flexibility in selecting the fiber direction and size of the prepreg layers. In addition, a LIPCA device can be manufactured without adhesive layers since epoxy resin plays role of bonding material. To investigate the degradation of the actuation performance of LIPCAs due to repeated fatigue loading, repeated loading tests up to several million cycles were performed and the actuation displacement for a given excitation voltage measured during the test. The fatigue characteristics were measured using an actuator test system consisting of an actuator-supporting jig, high-voltage actuating power supplier, and non-contact laser measuring system and evaluated.

This work presents manufacturing and testing of active composite panels (ACPs) with embedded piezoelectric sensors and actuators. The composite material employed here is a plain weave carbon epoxy prepreg fabric with about 0.33 mm ply thickness. The piezoelectric patches employed here are Continuum Control Corporation, CCC, (recently Continuum Photonics, Inc) active fiber composite patches with 0.33 mm thickness, i.e. close to the composite ply thickness. Composite cut-out layers are used to fill the space around the embedded piezoelectric patches to minimize the problems associated with ply drops in composites. The piezoelectric patches were embedded inside the composite laminate. High-temperature wires were soldered to the piezoelectric leads, insulated from the carbon substructure by high-temperature materials, and were taken out of the composite laminates employing a molded-in hole technique that reduces the stress concentration as opposed to a drilled hole, and thereby enhancing the performance of the composite structure. The laminated ACP’s were co-cured inside an autoclave employing the cure cycle recommended by the composite material supplier. The curie temperature of the embedded piezoelectric patches should be well above the curing temperature of the composite materials as was the case here. The manufactured ACP beams and plates were trimmed and then tested for their functionality. Vibration suppression as well as simultaneous vibration suppression and precision positioning tests, using PID control as well as Hybrid Adaptive Control techniques were successfully conducted on the manufactured ACP beams and their functionality were demonstrated. Recommendations on the use of this embedding technique for ACPs are provided.

Piezoelectric materials are well known as actuators and sensors for smart structures. In the past many designs with different shapes and electrodes have been developed. For distributed actuation usually thin piezoceramic plates or fibers are used. Especially for the actuation of fibers very complex electrode structures are necessary. In this paper a new and very simple concept for the manufacturing of smart composite materials is presented. The new design is based on piezoceramic tubes with inner diameters of 200-400 μm and outside diameters of 300-800 μm. The length of the tubes is 150mm and they are provided with inner and outer electrodes to work in the lateral d₃₁ direction. The core of the tube consists of a load carrying and electrically conductive fiber material (e.g CFRP) that is also used to contact the inner electrode. Since the piezoelectric material itself insulates the inner and outer electrode no additional insulation material is necessary. Usual insulation materials like Polyimide are relatively soft (3GPa) what reduces the strain transfer from the piezoceramic to the surrounding material. The design of the smart composite has been optimized using a finite element micro-mechanic model. First samples have been build and tested and show good performance.

A method for designing practical displacement amplification mechanisms for piezoelectric stack actuators was developed. The amplification mechanisms and the piezoelectric stack actuators were modeled using plane-strain finite elements. Optimal sizing and topology optimization were performed simultaneously to maximize the first natural frequency while satisfying free stroke and stress constraints. Optimal sizing variables were selected to control the kinematic behavior of the mechanism while a restricted variable thickness sheet topology optimization method was used to remove unnecessary material from stiff regions of the structure. Calculation of sensitivities was very efficient for the topology optimization variables but required the major portion of computational time for the optimal sizing variables. The method was applied to beam-type lever amplification mechanisms and two devices that included pre-stressing of the piezoelectric ceramics and pure translation of the output point were optimized, manufactured and tested. The results demonstrate that the method presented can be used to design amplified piezoelectric actuators that can be manufactured without interpretation by the designer.

Recent study is to the performance of variable dampers for reducing earthquake response of buildings or wind induced sway. The variable damper using magnetorheological fluid (MR damper) changes its damping force by changing the magnetic field acting on the MR fluid according to an electric current. MR dampers have a simple mechanism and don’t need a large amount of energy. Semi-active control using such a variable damper stabilizes building responses in an earthquake better than the conventional passive control. Basic characteristics of the MR damper have been clarified. This time, authors proposed control algorithm of base-isolated structure, which carried out semi-active control by optimal regulator theory. This control algorithm reduces response displacement and response acceleration for the purpose of, and aims at enhancements, such as safety and amenity. This paper presents a comprehensive study on the performance of the MR damper to base-isolated structure. It's describes shaking table tests on a three-story large-scale test frame with base-isolated structure. The test results verify the controlling system and the control effect as a semi-active device of the MR damper.

The vibration mitigation performance of different feedback controlled damping devices for cable vibration mitigation is investigated. A model-based designed LQG controller estimates the vibration state based on a validated linear cable model. The main nonlinearity of the connected system damping device - cable is compensated by its inverse function. The simulated damping devices are actuator and controllable damper without any actuator/damper dynamics. It is assumed that further constraints such as minimum or maximum force limitations do not exist. The theoretical study compares the potential of vibration mitigation using a feedback controlled actuator and a feedback controlled damper. The comparative study is simulated for two positions of the damping device. One is near the anchorage, which is the only possible position on a real cable-stayed bridge. The other position is characterized by the largest cable displacement within the frequency range of the first four modes. In order to guarantee a fair comparison, the optimal controller parameters are determined for the active controlled actuator and semi-active controlled damper for both positions. The simulation results demonstrate, first, that active controlled actuators can hardly mitigate vibrations more effectively than semi-active controlled dampers because vibration energy must be dissipated. Second, the position of the damping device shows a negligible influence on the mitigation performance because smaller displacements and therefore smaller velocities near the anchorage are compensated by larger actuator/damper forces.

This paper presents ultra precision positioning system consisting of electrorheological(ER) clutch and piezoelectric actuators using dual servo control mechanism. ER clutch and ball screw are adopted for a coarse positioning stage, and magnification device driven by multi-stack piezoelectric actuator is manufactured for a fine positioning stage. After deriving the dynamic modeling for coarse motion stage, a sliding mode controller is designed to achieve robust control performance. In addition, conventional PID controller incorporated with the hysteresis nonlinearity of the piezoelectric actuator is designed to construct a feed-back with feed-forward control scheme for precise and fast positioning of the fine motion stage. Step regulating control performance of the proposed dual servo system is evaluated via experimental works to verify the effectiveness of the proposed position control system.

There is much current interest in the development of smart fluid clutches for use in the design of high-speed machinery. This interest stems from the flexibility, controllability and fast response of such fluids. In this paper the authors outline the modifications to an Electro-rheological clutch mechanism for a robotics application. The clutch mechanism consists of twin ER clutches that are driven in opposite directions. By controlling the electric field applied to each clutch it is possible to cause a toothed belt to move in a desired manner in each direction. This belt motion can then be used to control the motion of a robot arm via a gear train. To improve the positional performance an ER brake is added to the robot arm mechanism. The extension to the dynamic model for the ER clutch mechanism to incorporate the robot arm and ER brake is outlined and is validated experimentally. The displacement response of the robot arm is then examined as a trend study using different motor driving speeds and load inertias. The positional accuracy of the robot arm and its repeatability is then demonstrated over a significant number of reciprocating tests.

Magnetorheological (MR) fluids can be used in a variety of smart semi-active systems. The MR damper shows an especially great potential to mitigate environmentally induced vibration and shocks. Another aspect of MR fluids is the construction of MR valve networks in conjunction with a hydraulic pump resulting in a fully active actuator. Conventional hydraulic pumps, however, are bulky, contain many moving parts, and do not scale favorably with decreasing size motivating development of high energy density piezohydraulic pumps. These devices are simple, have few moving parts and can be easily miniaturized to provide a compact, high energy density pressure source. The present study describes a prototype MR-piezo hybrid actuator that combines the piezopump and MR valve actuator concepts, resulting in a self-contained hydraulic actuation device without active electro-mechanical valves. Durability and miniaturization of the hybrid device are major advantages due to its low part count and few moving parts. An additional advantage is the ability to use the MR valve network in the acuator to achieve controllable damping. The design, construction and testing of a prototype MR-piezo hybrid actuator is described. The performance and efficiency of the device is derived using ideal, biviscous and Bingham-plastic representations of MR fluid behavior, and is evaluated with experimental measurements. This will provide a design tool to develop an actuator for a specific application. The prototype actuator achieved an output velocity of 5.34mm/sec against a mass load of 5.15kg with a piezopump weighing 300gm.

The search for existing or past life in the Universe is one of the most important objectives of NASA's mission. In support of this objective, ultrasonic based mechanisms are currently being developed at JPL to allow probing and sampling of rocks and to use the mechanisms as a sensor platform for in-situ astrobiological analysis. The technology is based on the novel Ultrasonic/Sonic Driller/Corer (USDC), which requires low axial force, thereby overcoming one of the major limitations of planetary sampling using conventional drills in low gravity environments. The USDC was demonstrated to 1) drill ice and various rocks including granite, diorite, basalt and limestone, 2) not require bit sharpening, and 3) operate at high and low temperatures. The capabilities that are being investigated include probing the ground to select sampling sites, collecting various forms of samples, and hosting sensors for measuring various properties. A series of modifications of the USDC basic configuration were implemented leading to an ultrasonic abrasion tool (URAT), Ultrasonic Gopher for deep drilling, and the Lab-on-a-drill.

This paper describes a new electromagnetic device for vibration control of a light-weighted deployable/retractable structure which consists of many small units connected with mechanical hinges. A typical example of such a structure is a solar cell paddle of an artificial satellite which is composed of many thin flexible blankets connected in series. Vibration and shape control of the paddle is not easy, because control force and energy do not transmit well between the blankets which are discretely connected by hinges with each other. The new device consists of a permanent magnet glued along an edge of a blanket and an electric current-conducting coil glued along an adjoining edge of another adjacent blanket. Conduction of the electric current in a magnetic field from the magnet generates an electromagnetic force on the coil. By changing the current in the coil, therefore, we may control the vibration and shape of the blankets. To confirm the effectiveness of the new device, constructing a simple paddle model consisting eight hinge- panels, we have carried out a model experiment of vibration and shape control of the paddle. In addition, a numerical simulation of vibration control of the hinge structure is performed to compare with measured data.

Gossamer or inflatable structures have been a subject of renewed interest for space applications because of their lightweight, on-orbit deployability, and minimal stowage volume. For these structures to be effective, their vibration must be controlled while maintaining the low weight and the foldability criteria. Piezoelectric materials have become strong candidates for actuator and sensor applications in the active vibration control of such structures due to their lightweight, conformability to the host structure, and distributed nature. In this study, vibration suppression of an inflated toroidal structure using piezoelectric actuators and sensors has been attempted. First, following the Sanders' shell theory, the governing equations of motion of a shell under pressure in the presence of piezoelectric patches have been presented, and the actuator/sensor equations are obtained. A sliding mode controller and a sliding mode observer are designed to suppress the vibration of the inflated toroidal structure using Macro-Fiber Composite (MFC) actuators and Polyvinylidene Fluoride (PVDF) sensors. The numerical simulations show that the piezoelectric actuators and sensors are suitable for vibration suppression of an inflatable structure. The robustness properties of the controller and observer against the parameter uncertainty and disturbances are also studied.

An approach for achieving a several order of magnitude reduction of vibration in space telescopes is described. The building blocks encompass: active damping in the payload, passive and active vibration isolation in the payload mount, and active steering of the entire payload using feedback from optical sensors to the actuators in the isolator. The layers of control sequentially mitigate vibrations emanating from the disturbance source. This strategy is especially applicable to large space-based optical systems, such as deployable telescopes. A dynamically scaled test bed has been developed to demonstrate this. The test bed incorporates a full-telescope isolator based on passive isolation technology demonstrated on the Chandra X-ray Observatory. A PZT force sensor and a voice coil actuator have been incorporated to provide additional active isolation at low to mid frequencies. The active isolation is implemented in a stable manner using independent modal space control (IMSC). Residual vibrations in the telescope secondary mirror supports are damped using PZT actuator/sensor patches and local analog feedback. Finally, signals from line-of-sight sensors in the two tilt directions are fed to the tilt states in the IMSC controller to effect payload pointing control.

On Earth orbit, astronomical observation is in very good condition that is free from any absorptions or disturbances by the Earth's atmosphere. Therefore, some large space telescopes and large space radio telescopes are planned. Diameter of payload bay of launch vehicle might be restriction for the size of such telescopes. That is the reason why structures larger than the payload bay have to be deployed or assembled onboard. Onboard assembling structure is better in surface accuracy and rigidity than deployable structure. We present a constitution of on-board assembling telescope reflector structure and its connecting mechanisms suitable for robot tasks. For assembling of such large structure, space robot has to move around on the structure. Power/signal lines, its connectors and grapple fixtures are needed on the structure for providing power/signal and foot restraints to the mobile robot arm. Compliant motions of robot are needed for constrained motion tasks such as grasping, attaching and mobile inchworm motion of onboard structure assembling. A new control method, active limp control of the robot arm joints, has high response and high stability because of their sensor/actuator collocation. So they are adequate to space robots for onboard assembling tasks. Constitutions of on-board assembling structure, a scenario of its assembling and control methods of the space robot are described in this paper. Characteristics of the new control methods and its suitability for onboard assembling tasks were confirmed by testing with using a prototype joint mechanism and its control system. The testing results and evaluation are also described in this paper.

In this paper, a theoretical study is presented to compare the performance of a non-symmetric (i.e., different damping force characteristics in rebound and compression), fail-safe, magneto rheological fluid (MRF) damper with an Original Equipment Manufacturer (OEM) damper for off-highway, high mobility multi-purpose wheeled vehicle (HMMWV) using a quarter car model. In addition, an experimental set up for a full-scale two degree-of-freedom quarter car model suspension system of a HMMWV is constructed. Simple harmonic displacement input is used as the road profile. Sky-hook algorithm is utilized to control the MRF damper. Displacement and acceleration transmissibility to the sprung mass are determined to compare performances of controlled MRF and passive OEM dampers. The experimental results for OEM damper are also compared with theoretical predictions.

This study focuses on investigation of the time response of a controllable limited slip differential (LSD) clutch consisting of an on-off close-loop control system and a magneto-rheological fluid (MRF). The control law of the controller is based on velocity feedback where the main goal is to keep the relative velocity of the input and output shafts of the clutch less than a predetermined threshold value. The response time of the control system (including the DAQ system and the computer) and the MRF LSD clutch is examined both theoretically and experimentally. System identification experiments are performed to determine the parameters such as bearing friction coefficients, dry and viscous clutch torque coefficients. These coefficients are used in theoretical response time analysis of the MRF LSD clutch using MATLAB Simulink. It is demonstrated that, the simple on-off closed-loop control system is feasible for this clutch application. The response time reduces by increasing solenoid current and increasing velocity. The theoretical model predictions are in good agreement with the experimental results.

Many efforts to understand the response of magnetorheological (MR) fluid dampers have been undertaken in the past several years. Such components are of great interest for use in automotive suspension and safety systems, as well as in aerospace and civil applications. Physically sensible models that contain realistic descriptions of fluid flow would be of great utility in optimizing the performance of these dampers. While simple models based on the familiar Bingham plastic MR fluid constitutive relation capture many of the key features of the steady-state damper response, including the existence of a magnetic-field-dependent 'yield force' and the reduction of the damping coefficient at high velocities, such models do not describe the more complex velocity dependence and dynamic response of the force observed in real dampers. Unfortunately, experimental data on viscometric flows of MR fluids at the high shear rates encountered in MR dampers are scarce. Moreover, a number of sophisticated damper models are available, but many use mathematical constructs that are not easily understood in terms of physical phenomena. Motivated by these challenges, we have measured the response of two automotive MR shock absorbers and developed a lumped-parameter model to describe their dynamic response. Using the parameters provided by this model, we have also compared the measured damper response with that predicted by simple models of magnetic flux and fluid flow in these components.

Experiments and analyses have confirmed the feasibility of an innovative, new class of very simple, reliable, low mass, low packaging volume, and low-cost self-deployable structures for space and commercial applications. The material technology called "cold hibernated elastic memory" (CHEM) utilizes shape memory polymers in open cellular (foam) structures. The CHEM foams are self-deployable and are using the foam's elastic recovery plus their shape memory to erect structures. These structures are under development by the NASA's Jet Propulsion Laboratory (JPL) and Mitsubishi Heavy Industries (MHI). Currently, the CHEM structure concept is well formulated, with clear space and commercial applications. The CHEM structures are described here and their major advantages are identified over other expandable/deployable structures. Previous experimental results were very encouraging and indicated that the CHEM foam technology can perform robustly in the Earth environment as well as in space. Some potential space applications were studied under various programs at JPL with promising results. Although the space community will be the major beneficiary, a lot of potential commercial applications are also foreseen for the "Earth environment" and described in this paper as well.

Shape Memory Alloys (SMA) are a unique type of material characterized by two properties that ordinary metals do not exhibit: Shape Memory Effect (SME) and pseudoelasticity. SMAs can be actuated mechanically and/or thermally, and these properties have already been exploited in a wide variety of engineering applications. The appearance of SMAs in space applications, however, is more recent. This paper presents the motivations leading to interest for SMAs in space applications, as well as an overview of their use from tested mechanisms to ones still in development. As will be shown, many SMA space applications are single use and thermally activated. Although heating is never a problem, cooling SMA actuators in a reasonable amount of time still has to be achieved. A thermoelectric cooling system that allows for thermal control will be presented. This active cooling can allow better thermal actuation of SMA mechanisms using the two way SME. The last section of the paper describes their suitability for passive vibration isolation during launch, with a simple design using SMA hollow tubes at the interface between the payload and the spacecraft.

Shape memory alloys (SMAs) are often used in smart materials and structures as the active components. Their ability to provide a high force and large displacement has been useful in many applications, including devices for damage control, active structural acoustic control, dynamic tuning, and shape control. The paper presents a macroscopic mathematical model which captures the thermomechanical behaviors and the two-way shape memory effect (TWSME) of SMAs, and SMA applications as an actuator to control the shape of a circular composite cylinder where a thin SMA layer actuator is bonded inside the cylinder is investigated numerically. The circular composite cylinder with the thin SMA layer was designed and analyzed to determine the feasibility of such a system for the removal of stiffeners from externally pressurized stiffened composite structures. SMAs start to transform from the martensitic into the austenitic state upon actuation through resistive heating, simultaneously recover the prestrain, and thus cause the composite cylinder to expand in the radial direction. The externally pressurized composite cylinder with the SMA actuators was analyzed using the 3-D finite element method.

In-situ sampling and analysis are important capabilities to allow meeting the major objectives of future NASA's planetary exploration missions. The development of an ultrasonic device that can serve as a probe, sampler and sensors platform for in-situ analysis is currently underway at JPL. The device is based on the novel Ultrasonic/Sonic Driller/Corer (USDC) technology, which was co-developed by the Non-Destructive Evaluation and Advanced Actuator laboratory (NDEAA, http://ndeaa.jpl.nasa.gov/), JPL, and Cybersonics. This sampling technology requires low axial force, thereby overcoming one of the major limitations of planetary sampling in low gravity using conventional drills. This device allows the design of an effective tool that is compact, low mass and uses low power. To assure effective use of power for drilling/coring rocks in-situ probing is needed to allow selecting rocks with the highest probability of containing information (biological markers, water, etc.). While the major function of the USDC is sampling, drilling and coring, it also has great potential to serve as a probing device. The USDC imparts elastic waves into the sampled medium offering a sounding method for geophysical analysis similar to the techniques used by the oil industry. Also, the characteristic of the piezoelectric actuator, which drives the USDC, is affected by the medium to which it is coupled. Using a variety of device configurations, a series of experiments were conducted to measure the elastic wave velocity, scattering, impedance and the shift in resonance frequency. Various rocks are being tested to determine their characteristics. Preliminary results are encouraging. Currently, investigation is conducted to find methods of minimizing the effect of surface roughness, geometry and sample dimensions on the data.

In the literature distributed arrays of piezeoelectric patches are employed to actively control structural vibrations. In the present work in order to damp beam vibrations a completely passive electric controller is proposed, exploiting distributed piezoelectric transduction. The optimization of the distributed electric controller is performed analyzing the free wave propagation in the composite smart beam. The proposed controller allows for an optimal attenuation of wave propagation over any frequency range. A prototype of the proposed novel smart structure (Piezo-ElectroMechanical beam) is designed, allowing for appreciating its technical feasibility and effectiveness.

A new vibration control system, named 'block-by-block' distributed cluster control system, is presented with a CFRP board with stiffeners. Distributed cluster control system which had been applied for flat simple board is a control system includes 'cluster sensing' which classified numberless vibration modes into some limited number of clusters by using a group of sensors, and 'cluster actuation' which can actuate only specific cluster. It means, this system controls only target clusters. When the system is applied to complex structure such as this CFRP board with stiffeners, it is not possible to applied directly since the forms of vibration modes are not as simple as the one of flat board but there exist three blocks; 2 side blocks and one center block between two stiffeners. In this paper, after a rough explanation of distributed cluster control system, the idea of 'block-by-block' control is explained and verified experimentally with FEM analysis using some kinds of sensors and actuator.

When using a Gough-Stewart Platform (GSP) for a vibration isolation or precision motion task, the geometry of that GSP is often chosen on an ad hoc basis. This can result in a number of problems: singularities or poor conditioning; inability to produce desired motions or forces; high dynamic coupling between axes; poor fault tolerance. This paper will show that the class of orthogonal GSPs has a number of useful properties. Denoting the mapping from Cartesian payload velocities to strut velocities as a 6x6 matrix M, orthogonal GSPs are those where either the rows or columns of M are orthogonal. In other words, either MM^T or M^TM are diagonal matrices. This paper will derive the properties of orthogonal GSPs wherein MM^T is diagonal. In particular, it will first discuss the possible geometries that yield orthogonal GSPs. This will make it clear when these geometries are appropriate for a desired application. By re-arranging the rows and columns of M, a block diagonal form is found. Based on this block diagonal form, methods of designing Stewart platforms meeting desired position and force specifications are derived.

Aerospace structures such as antennas and solar panels often consist of truss elements which are connected by bolted joints. Friction damping in these bolted joint connections structures has been identified as a major source of damping. It has been proposed that an improvement in vibration reduction could be obtained by controlling the normal contact force using integrated piezoelectric elements in order to maximize the energy dissipated at the interface between the connected parts. This paper presents analytical and experimental results in order to demonstrate the interest of implementing semi-active vibration reduction by dissipating energy through dry friction contact surfaces. This work fits within the scope of a research project aiming at the development of a semi-active compact piezoelectric friction device which can be bonded to any light structure. In this device, a moving component will rub on two friction surfaces and the normal force on friction surfaces will be controlled so that the distance between moving component and friction surfaces is neither too small (to avoid shock and stiction that cancel the slip between two surfaces and then friction effect) or too large (lose of contact surface). This device will then be positioned on the structure in order to allow the maximum energy dissipation by friction to reduce the vibrations of the structure. Such semi-active device will ensure stability of the control approach and will avoid the spillover effect found with the active approach in addition to reduce energy consumption cost. In this paper, an analytical and experimental study is carried out on two beams assembled by a joint bolted to show the influence of the normal gripping force (tightening torque in this case), directly related to the friction force, on the damping of the modes.

A new topology for a prestressed tensegrity plate, the unstable-unit tensegrity plate (UUTP), is introduced, together with a detailed algorithm for its design. The plate is a truss made of strings (flexible elements) and bars (rigid elements), which are loaded in tension and compression, respectively, where bars do not touch each other. Given the outline dimensions of the desired plate, and the number of bars along the plate's width and length, the algorithm solves for the nodes' positions and the prestress forces that make a plate in equilibrium. This is done by solving a non-linear matrix equation via Newton's method. This equation reflects static equilibrium conditions. We've designed several such plates, proving the feasibility of the proposed topology and the effectiveness of its design algorithm. Two such plates are characterized in detail, both statically and dynamically (via simulation). The proposed algorithm may be extended to solve for other tensegrity structures having different topologies and/or different shapes. The UUTP may be used as a building block of many types of structures, both uncontrolled and controlled, either large-scale or miniature-scale.

In a continuing effort to examine the effectiveness of Lamb wave methods for the health monitoring of composite structures, this paper presents the conclusions of an analytical and experimental study optimizing piezoelectric patches to detect damage within composite laminates. Previous research has demonstrated the ability of Lamb waves to provided useful information about the presence of damage in simple narrow coupons, and they have yielded the possibility of estimating severity and location of damage as well. During the course of this NRO funded research program, several types of piezoelectric materials in various configurations were analyzed in order to produce the highest force actuator and best resolution sensor at the lowest power level. Consideration was also placed towards directionality of wave propagation, and durability, reliability and reproducibility of the sensing patch itself. Experiments were then carried out on narrow coupon laminates to qualify and tune these actuating/sensing patches. New algorithms were used to filter and decompose the resulting signals to more efficiently detect the presence of damage for automated use, and gather information relating to the damage type, severity and location. SHM technologies will enable condition-based maintenance for efficient structural design, will reduced overall life-cycle costs, and eliminate scheduled inspections.

Modern design briefs increasingly stipulate the need to reduce the weight of high technology structures due to the large costs involved in transport. As a result, these light structures are prone to unwanted vibrations. The uncertain surrounding environment necessitates the assumption of no fixed base to operate sensing/actuation devices with reference to. These conditions have made piezoceramic devices ideal candidates to operate as distributed actuators to apply vibration control to smart structures. The limited actuation of these devices, however, makes it essential to consider the problems associated with actuator saturation on the resulting controllers. This paper compares Pole-placement and Generalised Minimum Variance controllers for application to a vibrating cantilever beam. Certain desired closed-loop pole-positions are found to lead to limit cycling behaviour with the Pole-placement controller in both experiment and simulation. Subsequent application of saturation compensation is shown to return stability to the closed-loop system. Due to the control signal penalising property of the Generalised Minimum Variance controller this method is shown not to require compensation. Utilising the Nelder-Mead simplex algorithm, efficient controllers have been obtained for both controller types. Experimental results have shown that the controllers are able to suppress both the free and forced disturbances of the experimental system in the presence of control signal saturation and plant model mismatch. The results show that a developed reduced order model results in a controller performance that is comparable to that using a larger order Auto Regressive with eXogenous inputs model.