Proceedings Volume 5049

Smart Structures and Materials 2003: Modeling, Signal Processing, and Control

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Proceedings Volume 5049

Smart Structures and Materials 2003: Modeling, Signal Processing, and Control

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Volume Details

Date Published: 1 August 2003
Contents: 17 Sessions, 70 Papers, 0 Presentations
Conference: Smart Structures and Materials 2003
Volume Number: 5049

Table of Contents

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Table of Contents

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  • Ferromagnetic Materials
  • Shape Memory Alloys I
  • Shape Memory Alloys II
  • Optimization
  • Nonlinear Models
  • Nondestructive Evaluation
  • Structural Models I
  • Structural Control I
  • Structural Control II
  • Adaptive Structures
  • Structural Models II
  • Optimization of Active Structures
  • Optimization
  • Sensors
  • System Identification
  • Control Applications
  • Applications
  • Poster Session
  • Shape Memory Alloys II
  • Poster Session
  • Adaptive Structures
Ferromagnetic Materials
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Analytical and experimental issues in Ni-Mn-Ga transducers
Ferromagnetic shape memory martensites in the Ni-Mn-Ga system have been demonstrated to achieve a number of the criteria required for next generation actuators including the production of large theoretical strains up to 6%. The large strain originates in the rotation of twin variants and associated twin boundary motion which occurs in response to magnetic fields. The magnetic activation holds promise in actuator design because it can lead to higher bandwidths than those achieved through pure martensite-austenite phase transformation, as is the case with thermally-activated shape memory alloys. In this paper, we report on experimental measurements collected from a cylindrical Ni49.0Mn30.0Ga21.0sample alloy, driven as cast by a collinear magnetic field-stress pair. Despite the lack of a known restoring force and the fact that no "training" procedures are applied, quasi-static strains as large as 4300 micro-strain are shown. Furthermore, dynamic results in the DC-20kHz range are presented which would suggest the presence of a Delta-E effect similar to that seen in Terfenol-D but exhibiting an opposite dependence of stiffness with DC field. The potential implications of the results for the design and control of dynamic structures based on Ni-Mn-Ga are very significant.
Shape Memory Alloys I
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A free energy model for thin-film shape memory alloys
Jordan E. Massad, Ralph C. Smith, Gregory Paul Carman
Thin-film shape memory alloys (SMAs) have become excellent candidates for microactuator fabrication in MEMS. We develop a material model based on free energy principles combined with stochastic homogenization techniqies. In the first step of the development, we construct free energies and develop phase fraction and thermal evolution laws for homogeneous, single-crystal SMAs. Second, we extend the single-crystal model to accomodate material inhomogeneities and polycrystalline compounds. The combined model predicts rate-dependent, uniaxial SMA deformations due to applied stress and temperature. Moreover, the model admits a low-order formulation that is suitable for subsequent control design. We illustrate aspects of the model through comparison with thin-film NiTi superelastic hysteresis data.
Thermal stabilization of shape memory alloy wires
Petr Kloucek, Daniel R. Reynolds, Thomas I. Seidman
We show that fast, localized heating and cooling of a Shape Memory material can provide a very effective means of damping vibrational energy. We model the thermally induced pseudo-elastic behavior of a NiTi Shape Memory wire using the variant of Landau-Devonshire potential. We assume that the wire consists of martensitic NiTi single crystal. Dynamically, we model the material response using conservation of momentum and a nonlinear heat equation. We use a frame invariant version of the Fourier heat flux which incorporates dependence on the atomic lattice through the stretch. In the settings used in this paper, the computational experiments confirm that circa 80% of the vibrational energy can be eliminated at the moment of the onset of the thermally induced phase transition.
Micromechanical model of polycrystalline shape memory alloys based on Reuss assumption
Tadashige Ikeda, Florin Andrei Nae, Yuji Matsuzaki
To understand the complicated thermodynamical behaviors of shape memory alloys (SMA) and to optimally design structures with SMA components, a simple yet micromechanical model of SMA was proposed based on Reuss assumption, namely, an assumption of uniform stress state in every grain. Since interaction between grains doesn't exist in Reuss assumption, we considered a specific distribution for phase interaction energy and also hardening due to the grain interaction. Choosing adequate distributions for both grain orientation and phase interaction energy, the model could describe the round shape around yielding stresses and the inner loops on a stress-strain hysteresis relationship and the temperature differences between transformation start and finish. They were in quantitative agreement with available experimental data for wires. Moreover, a heat balance equation was combined with the constitutive equation to take into account the effect of temperature change of the material. This combined model could capture quantitatively a temperature variation of about 20K in one cycle due to self heating and cooling as well as the effect of strain rate on stress-strain hysteresis loops. Finally, by reducing this proposed model to a model for unidirectional loading we showed that the proposed model became our previously developed macromechanical 1D model. Thus we could bridge the gap between a grain-based micromechanical model and a specimen-based macromechanical 1D model.
Shape Memory Alloys II
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Position control of SMA actuators with internal electrical resistance feedback
Ning Ma, Gangbing Song, Ho Jun Lee
This paper presents the development of a position control system for a shape memory alloy (SMA) wire actuator using the electrical resistance feedback. It is commonly known that an SMA actuator is highly nonlinear and a position sensor is often required to achieve a stable and accurate positioning. And this position sensor often contributes a large portion of the system cost. To eliminate the position sensor in an SMA actuator system, a novel control theme is proposed by utilizing the actuator’s electrical resistance feedback. With an SMA wire test setup, the relationship between the electrical resistance and the displacement is experimentally investigated. However, this relationship is highly nonlinear, and a neural network is employed to model this relationship and predicts the position of the actuator using only its electrical resistance information. To enable feedback control of the SMA wire actuator using only its electrical resistance, a Proportional-Integral-derivative (PID) controller is used. Feedback control experiments are performed and the results demonstrate that the proposed position control system achieves a good control performance without using a position sensor.
Intelligent control of a micromanipulator actuated with shape memory alloy tendons
Jason Michael Stevens, Gregory D. Buckner
During the past 20 years, tremendous advancements have been made in the fields of minimally invasive surgery (MIS) and minimally invasive robotic assisted (MIRA) surgery. The technologies associated with these advancements have their own drawbacks, however. The surgical robots used in MIRA procedures are large, costly, and do not offer the miniaturized articulation necessary to facilitate additional advancements. This research tests the hypothesis that miniature actuation can overcome some of the limitations of current robotic systems by demonstrating accurate, repeatable control of a small end-effector. A simple two link manipulator is designed and fabricated, using antagonistic shape memory alloy (SMA) tendons as actuators, to simulate motions of a surgical end-effector. Artificial neural networks (ANNs) are used in conjunction with real-time visual feedback to "learn" the inverse system dynamics and control the manipulator endpoint trajectory. Experimental results are presented for indirect, on-line learning and control. Manipulator tip trajectories are shown to be accurate and repeatable to within 0.5 mm. These results confirm that SMAs can be effective actuators for miniature surgical robotic systems, and that intelligent control can be used to accurately control the trajectory of these systems.
Finite element simulation of adaptive aerospace structures with SMA actuators
Jason Frautschi, Stefan Seelecke
The particular demands of aerospace engineering have spawned many of the developments in the field of adaptive structures. Shape memory alloys are particularly attractive as actuators in these types of structures due to their large strains, high specific work output and potential for structural integration. However, the requisite extensive physical testing has slowed development of potential applications and highlighted the need for a simulation tool for feasibility studies. In this paper we present an implementation of an extended version of the Müller-Achenbach SMA model into a commercial finite element code suitable for such studies. Interaction between the SMA model and the solution algorithm for the global FE equations is thoroughly investigated with respect to the effect of tolerances and time step size on convergence, computational cost and accuracy. Finally, a simulation of a SMA-actuated flexible trailing edge of an aircraft wing modeled with beam elements is presented.
Optimization
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Modeling and optimal control of microscale SMA actuators
Olaf Heintze, Stefan Seelecke, Christof Bueskens
The paper presents an optimal control approach to shape memory alloy (SMA) actuators. Like other active materials, e.g., piezoceramics or magnetostrictive materials, SMAs exhibit a highly non-linear and hysteretic behavior. In certain applications, in particular those with high driving frequencies like MEMS (Micro-Electro-Mechanical Systems) applications, this is known to lead to a breakdown of standard control algorithms. The optimal control approach overcomes this problem by including a model for the hysteretic behavior, and allows criteria like maximal speed and minimal energy consumption to be taken into account. To illustrate the potential benefits of the method, the performance is compared to that of a standard PI control.
Nonlinear Models
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A unified model for hysteresis in ferroic materials
Ralph C. Smith, Stefan Seelecke, Marcelo J. Dapino, et al.
This paper provides a unified modeling framework for ferroelectric, ferromagnetic and ferroelastic materials operating in hysteretic and nonlinear regimes. Whereas the physical mechanisms which produce hysteresis and constitutive nonlinearities in these materials differ at the microscopic level, shared energy relations can be derived at the lattice, or mesoscopic, scale. This yields a class of models which are appropriate for homogeneous, single crystal compounds. Stochastic homogenization techniques are then employed to construct macroscopic models suitable for nonhomogeneous, polycrystalline compounds with variable effective fields or stresses. This unified methodology for quantifying hysteresis and constitutive nonlinearities for a broad class of ferroic compounds facilitates both material characterization and subsequent model-based control design. Attributes of the models are illustrated through comparison with piezoceramic, magnetostrictive and thin film SMA data.
A dynamic hysteresis model for Thunder transducers
This paper summarizes a nonlinear technique for quantifying the displacements generated in THUNDER actuators in response to applied voltages for a variety of boundary conditions and exogenous loads. A PDE model is constructed using Newtonian principles to quantify the displacements in the actuator due to field inputs to the piezoceramic patch. A free energy based hysteretic stress-strain relation is employed to model the electromechanical coupling in the PZT. A finite element method and Crank-Nicholson scheme are developed to discretize the model; properties of the model are illustrated through comparison with experimental data.
Preisach modeling of hysteresis and tracking control of a Thunder actuator system
Xiaoqin Zhou, Jinqiang Zhao, Gangbing Song, et al.
This paper presents the classical Preisach modeling of the hysteresis and tracking control of a Thunder actuator system. The numerical expressions of the classical Preisach model were presented in details for different input variations. It was found that the saturation output values in these numerical expressions could be cancelled out. A series of tests were conducted to study the hysteresis properties of the Thunder actuator system. The classical Preisach model was then applied to simulate the static hysteresis behavior of the system. Higher-order hysteresis reversal curves predicted by the classical Preisach model were verified experimentally. The good agreement found between the measured and predicted curves showed that the classical Preisach model is an effective mean for modeling the hysteresis of the Thunder actuator system. Subsequently, the inverse classical Preisach model was established and applied to the real time microposition tracking control of the Thunder actuator system. Real time tracking control was achieved by combining a lead-lag feedback controller and the inverse model. On a moving range of 0-0.1mm, the tracking error with hysteresis compensation was less than 2.5%, compared to an error of up to 10% without hysteresis compensation. Experimental results showed that control accuracy with hysteresis compensation is greatly improved compared to that without hysteresis compensation.
Nonlinear performance analysis of LIPCA actuator by using an assumed strain shell element
Sang Ki Lee, Hoon Cheol Park, Ki Hoon Park, et al.
In the present work, the existing formulation of nine-node shell element based on Hellinger-Reissner principle is expanded for electro-mechanically coupled field analysis. The electro-mechanical coupling effect of the piezoelectric material is introduced to the formulation through the constitutive relation. Based on the formulation, a linear finite element code is constructed and it is validated by several numerical tests. By using the code, linear analysis of LIPCA(LIghtweight Piezoelectric Composite Actuator) is performed to calculate actuation displacement and stress. Moreover, to improve simulation result more accurately, an experimental piezo-strain function of PZT(3203HD, CTS) wafer that is embedded in LIPCA is obtained from measured data and the function is implemented into the code by adopting incremental method. And then, the actuation displacement of LIPCA is recalculated and the result is compared with the measured data.
Nondestructive Evaluation
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Health monitoring and diagnostics of ground combat vehicles
Elena N. Bankowski, Christopher Miles, Michael S. Saboe, et al.
The proposed technology is the Dependable Automated Reconfigurable Software (DARTS). The DARTS health and situation control continually tests the processing elements with Probe/Agent technology. Algorithms within the Health & Situation Control assess the health of the processors based on a criticality scoring system that considers mission requirements. Probes launched by the DARTS Controller query processing elements. The probed data is sent to a gauge that has a variable sensitivity or gain. Statistical Usage models and criticality scoring control the sensitivity of the gauge. In response to the gauge, the replicating process launches agents that can insert anomalous events for diagnoistic pruposes. In this context, a probe is a subset of an agent having only the abilty to query without affecting framework, I/O protocol or Quality of Service. Each weapon system fitted with a DARTS Controller will control self-repair and reconfiguration of on-board processors utilizing a statistical based intelligent scoring system. It considers criticality of the function in the current battlefield situation. DARTS is a software system that enhances the performance of a weapon system by providing on-the-fly reconfiguration to accomodate the loss or malfunction of processing elements or to optimize onboard performance capability.
Lamb wave interaction with structural defects: modeling and simulations
Lamb waves have shown to have a great potential for Structural Health Monitoring. The method uses acousto-ultrasonic waves propagating in plate-like structures. Structural damage can be identified by an amplitude change and/or mode conversion. However, previous studies show that the voltage amplitude from low-profile piezoceramic sensors can change due to temperature effects or additional vibration excitation. Also, pure Lamb wave modes may generate a variety of other modes by interacting with defects and/or by crossing different boundaries. Therefore simulation studies of wave propagation in structures is important for damage detection analysis. An application of the Local Interaction Simulation Approach (LISA) for Lamb wave interaction with defects is presented in this paper. The simulation results are validated using the experimental analysis. The method shows the potential for complex modeling of acousto-ultrasonic waves in damage detection applications.
Dynamic similarity approach for more robust structural health monitoring in nonlinear, nonstationary, and stochastic systems
Madhura Nataraju, Timothy J. Johnson, Douglas E. Adams
Environmental and operational variability due to changes in the excitation or any other variable can mimic or altogether obscure evidence of structural defects in measured data leading to false positive/negative diagnoses of damage and conservative/tolerant predictions of remaining useful life in structural health monitoring system. Diagnostic and prognostic errors like these in many types of commercial and defense-related applications must be eliminated if health monitoring is to be widely implemented in these applications. A theoretical framework of "dynamic similiarity" in which two sets of mathematical operators are utilized in one system/data model to distinguish damage from nonlinear, time-varying and stochastic events in the measured data is discussed in this paper. Because structural damage initiation, evolution and accumulation are nonlinear processes, the challenge here is to distinguish damage from nonlinear, time-varying and stochastic events in the measured data is discussed in this paper. Because structural damage initiation, evolution and accumulation are nonlinear processes, the challenge here is to distinguish abnormal from normal nonlinear dynamics, which are accentuated by physically or statistically non-stationary events in the operating environment. After discussing several examples of structural diagnosis and prognosis involving dynamic similarity, a simplifeid numerical finite element model of a helicopter blade with time-varying flexural stiffness on a nonlinear aerodynamic elastic foundation that is subjected to a stochastic base excitation is utilized to introduce and examine the effects of dynamic similarity on health monitoring systems. It is shown that environmental variability can be distinguished from structural damage using a physics-based model in conjunction with the dynamic similarity operators to develop more robust damage detection algorithms, which may prove to be more accurate and precise when operating conditions fluctuate.
Structural Models I
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Analysis of hybrid PMN/Terfenol broadband transducers in mechanical series configuration
This paper presents recent advances in the design and characterization of hybrid transducers incorporating magnetostrictive and electrostrictive elements. In order to analyze and validate the properties inherent to hybrid concepts, a transducer was designed and constructed through a mechanical series arrangement of a PMN-PT stack and a Terfenol-D rod. This configuration provides a double resonant frequency response that can be tuned for a variety of applications. The primary objective of this study lies in the determination of the design criteria for achieving maximum transducer bandwidth on the 1 - 6 kHz range. To this end, a linear system model was developed utilizing concepts from vibrations, electroacoustic theory, and linearized constitutive relationships for each class of smart material for low to moderate drive levels. This model provides a means of completely describing the system response and the interactions between electrical and mechanical domains for this hybrid transducer. Experimental data collected from the test device indicate that the measured modes of vibration and resonance peaks agree with the theoretical results, and that the desired bandwidth has been achieved.
Piezoelectic actuation of thin shells with support excitation
Manfred Nader, Michael Krommer, Hans-Georg von Garssen, et al.
The present contribution is concerned with a thin shell, which is excited to elastic vibrations by an imposed motion of a supporting boundary. Piezoelectric actuation is used to generate an additional actuation of the shell. As a practical application of dynamic shape control, we consider the suppression of flexural and extensional elastic vibrations, such that the shell performs a rigid body motion only. The idea of this procedure is to eliminate the disturbing acoustic noise caused by elastic deformations. We first point out that a suppression of the elastic vibrations can be achieved provided the distributed piezoelectric actuation coincides with a statically admissible (quasi-static) membrane force and bending moment distribution due to a fictitious inertial body force loading of the shell. For practical applications we assume the exciting support motion to be either translational or rotational, and to be given in advance. As an example of practical relevance, noise radiation of the support-excited shell-type funnel of a magnetic resonance tomograph is considered. Due to the complex geometry of this thin shell made of plastics, numerical methods are used in order to treat the shape control problem. The statically admissible membrane forces and bending moments due to the fictitious body force loading are computed by means of the Finite-Element-Code ANSYS. A distributed piezoelectric actuation coinciding with these forces and moments is derived and is approximated by a sparse distribution of piezoelectric patches. It is numerically demonstrated that this sparse distribution is able to suppress the elastic vibrations caused by the support excitation of the funnel.
Modeling of a piezoelectric beam on a semi-infinite elastic strip
Balajee Ananthasayanam, Eric M. Austin
We have developed a detailed model for a piezoelectric patch bonded perfectly to a semi-infinite substrate. There are well-established techniques for representing the effects of piezoelectric actuation on a flexible substrate by equivalent moments, but the accuracy of moments rely on classical beam behavior in both the actuation and substrate layers. The goal of the work presented here is to present a model capable of predicting both the actuation and sensing ability of a smart material on a general substrate. The piezoelectric layer is modeled by classical beam theory, but no kinematic assumptions other than plane strain are imposed on the substrate. Equilibrium is enforced between the piezoelectric patch and the surface tractions over the interface region, and standard Euler-Bernoulli beam theory is then used to form integral equations in terms of the displacement gradients at the interface with the substrate. Green's functions are then derived for a semi-infinite substrate using techniques from contact mechanics. There is no loss of generality in choosing a semi-infinite substrate since the effects of actuation by a patch disappear quickly outside the contact region. Preliminary results that both validate the current model and support the equivalent-moment action models for certain substrates are presented.
Optimal damping in multilayer sandwich beams
We describe some possible models for a multilayer sandwich beam consisting of alternating stiff and compliant beam layers. The stiff layers are modeled under Euler-Bernoulli assumptions while the compliant layers essentially only carry the shear. We include viscous damping in the compliant layers and consider the optimization problem of choosing the damping parameteres for each layer so that the maximal asymptotic damping angle in the system eigenvalues is obtained. The solution is obtained analytically as a closed-form function of the various material parameters.
Structural Control I
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Experimental implementation of an optimal actuator switching policy algorithm in flexible structures
An experimental implementation of an actuator switching scheme in a flexible structure that employs multiple piezoceramic actuators is reported in this manuscript and whose results support theoretical predictions and agree with numerical findings. The proposed supervisory control scheme attempts to improve controller performance of a system subject to spatiotemporally varying disturbances. The intelligent controller achieves its tasks by switching to different actuating devices at different time intervals. Specifically, the flexible structure under study is assumed to have multiple piezoceramic actuators available with only one being active over a time interval of fixed length while the remaining ones are kept dormant. By monitoring the state of the system, the supervisory controller engages the actuator that lies "spatially" closer to the region (epicenter) of a spatially varying disturbances within the spatial domain. This actuator switching scheme mimics the case of a moving actuator capable of residing in predetermined positions within the spatial domain of the flexible structure. Numerical studies for a flexible beam are presented in conjunction to the experimental ones to support the analytical findings of this work.
Robust control of a magnetostrictive actuator
Applications utilizing smart materials are rapidly increasing and include high speed milling and hybrid motor design. Such application utilize magnetostrictive transducers operating in hysteretic and nonlinear regimes. To achieve the high performance capabilities of these transducers, models and control laws must accommodate the nonlinear dynamics in a manner which is robust and facilitates real-time implementation. To this end, the models and control algorithms must utilize known physics to the highest degree possible, be low order, and be sufficiently robust to operate under realistic conditions. In this paper we consider the robust control of a smart structure with disturbances due to inherent hysteresis and sensor noise. We dmeonstrate the techniques on a magnetostrictive transducers but they are sufficiently general to be utilized on several commonly used smart materials. The performance of the control strategies are illustrated through numerical examples.
Velocity feedback control with time delay using piezoelectrics
John W. Roos, John C. Bruch Jr., James M. Sloss, et al.
An elastic beam is sandwiched between two thin layers of mono-axially oriented piezoelectric material which act as a distributed vibration control. One layer acts as a distributed sensor while the other behaves as an actuator. A velocity feedback control with time delay is implemented in which the distributed sensor signal which is proportional to the time derivative of the strains is amplified and applied to the actuator after a time delay. Because of the nature of the problem the control action enters as a boundary control. The control effectiveness, changes in natural frequency and damping ratios, is analyzed for the case of a cantilever beam. Comparisons are also made with the uncontrolled case and the zero-delay system.
Relaxed zero spillover controller for active structural acoustic control systems
In designing a controller, one way to avoid an energy spillover is to use what is called the zero spillover scheme. However, practical limitations may make such a controller impossible to realize, and one will need to implement a relaxed version of this controller called a relaxed zero spillover controller (RZSC). Here, analytical and experimental investigations into a RZSC scheme are presented. This controller has been used for active structural acoustic control (ASAC) of sound transmission into an enclosure. Noise is transmitted through the flexible boundary of the enclosure, and piezoceramic patches, mounted on the flexible boundary, are used as actuators. Polyvinylidene fluoride sensors are used on the flexible boundary and condenser microphone sensors are used inside and outside the enclosure. The stability of the chosen RZSC scheme for a single input, single output system and the extension to multiple input, multiple output systems are discussed along with other issues.
Adaptive internal model control for simultaneous precision positioning and vibration suppression of smart structures
This paper focuses on adaptive internal model control of smart structures with simultaneous precision positioning and vibration suppression functions. First, the structure, manufacturing, and test of an Active Composite Panel (ACP) with surface-mounted piezoelectric ceramic patches are introduced. Based on the discussion of the 2-DOF internal model control scheme, an adaptive internal model control scheme is then presented, in which the controller is constructed in form of a finite impulse filter, and the filtred-x LMS algorithm is employed to adapt the coefficients of the filter. Finally, the adaptive internal model control scheme is experimentally verified on the ACP, and compared with the adaptive feedforward control scheme, showing that it can produce more accuracy and faster response process. The satisfactory performance confirms that the adaptive internal model control schem is reliable and efficient.
Structural Control II
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Optimal control of piezoceramic actuators
Jinghua Zhong, Stefan Seelecke, Ralph C. Smith, et al.
This paper presents the first results of an optimal control approach to piezoceramic actuators. A one-dimensional free energy model for piezoceramics recently proposed by Smith and Seelecke is briefly reviewed first. It is capable of predicting the hysteretic behavior along with the frequency-dependence present in these materials. The model is implemented into an optimal control package, and two exemplary cases are simulated to illustrate these features and the potential of the method.
Experiments in adaptive optical jitter control
Mark A. McEver, Daniel G. Cole, Robert L. Clark
Optical jitter, the centroid-shifting of a light image, concerns engineers and scientists working with lasers and electro-optical systems. Even micron-level relative motion between individual optical components such as mirrors and lenses causes optical jitter, resulting in pointing inaccuracy, blurred high-resolution images, and poor nanotechnology quality. Typical jitter control technology uses fast-steering mirrors to correct for structural and acoustic disturbances in the beam train. Unknown or time-varying disturbance characteristics necessitate a controller that can adapt its parameters in realtime. The application of one such adaptive feedback controller algorithm has been proposed by the authors. The algorithm uses a technique known as Q-parameterization to structure the controller as a function of plant coprime factors and a free parameter, Q. An inherent property of this structure is the formation of a disturbance estimate based on subtraction of the controller influence from the feedback signal. The free parameter, Q, filters this estimate to form a portion of the control signal. If the controller influence on the feedback signal is estimated from accurately modeled plant dynamics, the disturbance estimate contains no feedback information allowing Q to be designed in an open-loop fashion. A gradient descent Least Mean Squares (LMS) algorithm updates the coefficients of the filter Q in realtime to minimize the frequency-weighted RMS jitter. Experiments on an optical jitter control testbed with Q set to a 200-tap digital finite impulse response (FIR) filter resulted in jitter reductions of 35% - 50%, without requiring prior knowledge of the disturbance spectrum.
Decentralized controller design for smart structural systems
In this paper, we show how to design decentralized controllers for smart structural systems to achieve multiple objectives associated with performances defined by H∞ or H2 norm, robust stability for model uncertainty, and limited actuator authority. The decentralized controller is designed in a sequential procedure for each control loop by solving synthesis conditions represented in terms of linear matrix inequalities (LMIs). The simultaneous design of decentralized controller, formulated as a non-convex minimization problem, is also discussed. The proposed design method was experimentally tested on a three-mass structure with three control loops.
Dynamic shape control of small vibrations superposed on large static deformations of thin plates
Michael Krommer, Uwe Pichler, Hans Irschik
Control of continuous structures requires suitably distributed actuation and sensing. In the present contribution, we consider thin composite plates with piezoelastic layers under the action of a given set of imposed forces. Our goal is to suppress the force induced plate vibrations by means of distributed (shaped) piezoelectric actuation. This problem is referred to as the "Shape Control Problem". The present contribution investigates the dynamic shape control problem in the special but practically important case of small vibrations superposed on large deformations of a quasi-static intermediate state. Moderately large deformations are taken into account by means of the kinematic approximation of von Karman. Linearization of the non-linear electromechanical field equations, with respect to the static intermediate state, results in a set of linear partial differential equations for the superposed vibrations. These equations are cast into convolution integral formulations for both the transient piezoelectric actuation and the transient external forces. Comparing the kernels of the convolution integrals, a distributed piezoelectric actuation is found, which exactly eliminates the forced vibrations. The distribution (shape) of the actuation coincides with the distribution of the statically admissible stress due to the transient external forces.
Simulations of decentralized vibration control with a networked embedded system
Tao Tao, Kenneth D. Frampton, Akos Ledeczi
The results of simulations to demonstrate decentralized vibration control with a netowkred embedded system are presented in this work. Conventional vibration control designs rest on centrality, and the central processor deals with information of the entire system. When large-scale systems are considered, decentralized vibration control system provides an alternative design. The simulated system in this work is a simply supported beam that is collocated with 50 localized processor nodes which can communicate with each other. Each node will calculate and supply the control force to control the beam vibration according to the shared sensor information among the nodes and an optimal direct velocity feedback algorithm. The simulation results demonstrate that decentralized vibration control can achieve a global control objective, making it suitable for large-scale systems. The effects of network communication delay and feedback architecture on control performance are demonstrated.
Comparison of controller design approaches from a vibration suppression point of view
Tamara Nestorovic Trajkov, Heinz Koeppe, Ulrich Gabbert
The paper is aimed at presenting, in the sense of analyzing and comparison, some aspects of modeling, simulation and control of piezoelectric flexible smart structures from the vibration suppression point of view. Taking into account the necessity of a good model development for the purpose of the structure simulation and model-based control design, two approaches are considered: finite element (FEM) method based methodology and system identification approach. The finite element analysis includes modal analysis of the structures with piezoelectric active elements (actuators and sensors) together with the active elements dynamics. Resulting dynamic model of the structure is represented in the form of equations of motion, which after appropriate transformations and modal reduction lead to a state-space model convenient for the controller design. As an alternative, the subspace based system identification is proposed, which in case of the real structure availability, provides a model of the structure from the input-output measured data. Controller design for the purpose of vibration suppression is model based. Optimal LQ tracking and direct model reference adaptive control laws are considered. Uncontrolled and controlled behavior of structures is investigated and the comparison of the proposed control laws and their efficiency verification is performed through the examples.
Adaptive Structures
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Synthesis of shape morphing compliant mechanisms using a load path representation method
Kerr-Jia Lu, Sridhar Kota
The performance of many mechanical systems is directly related to the geometric shapes of their components, such as aircraft wings and antenna reflectors. While the shapes of these components are mostly fixed, incorporating shape morphing into these systems can increase the flexibility and enhance the performance. A synthesis approach for shape morphing compliant mechanism is presented in this paper, using a load path generation method to efficiently exclude the invalid topologies (disconnected structures) from the Genetic Algorithm (GA) solution space. The synthesis approach is illustrated through a flexible antenna reflector design and a morphing aircraft trailing edge. The results demonstrate the capability of the load path generation method to create various designs with less design variables. The results also show that the use of compliant mechanisms can indeed provide a viable alternative for shape morphing applications. Methods to improve convergence such as employing a local search within or following the GA are also discussed.
Structural Models II
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Modeling of electromechanical coupling problem using the finite element formulation
Véronique Rochus, Daniel Rixen, Jean-Claude Golinval
A modeling procedure is proposed to handle the strong electro-mechanical coupling appearing in micro-electro-mechanical systems (MEMS). The finite element method is used to discretize simultaneously the electrostatic and mechanical fields. The formulation is consistently derived from variational principles based on the electro-mechanical free energy. In classical weakly coupled formulations staggered iteration is used between the electro-static and the mechanical domain. Therefore, in those approaches, linear stiffness is evaluated by finite differences and equilibrium is reached typically by relaxation techniques. The strong coupling formulation presented here allows to derive exact tangent matrices of the electro-mechanical system. Thus it allows to compute non-linear equilibrium positions using Newton-Raphson type of iterations combined with adaptive meshing in case of large displacements. Furthermore, the tangent matrix obtained in the method exposed in this paper greatly simplifies the computation of vibration modes and frequencies of the coupled system around equilibrium configurations. The non-linear variation of frequencies with respect to voltage and stiffness can then be investigated until pull-in appears. In order to illustrate the effectiveness of the proposed formulation numerical results are shown first for the reference problem of a simple flexible capacitor, then for the model of a micro-bridge.
Dynamic modeling and control of rectangular plate with piezoceramic sensors and actuators
Moon K. Kwak, Seok Heo, Myeong-Il Lee
This paper is concerned with the modeling of the rectangular plate bonded with rectangular piezoceramic sensors and actuators, which can have an arbitrary angle with respect to the plate axis. The equations of motion were derived by the Rayleigh-Ritz method. The cantilever plate with piezoceramic sensors and actuators was built to verify the theoretical development. The theoretical frequency response curve based on the equations of motion was then compared to the experimental frequency response curve. The sensor and actuator characteristics were also studied both theoretically and experimentally. The sensor characteristic is defined as the ratio of the tip displacement to the voltage output and the actuator characteristic is defined as the ratio of the applied voltage to the tip displacement. The final objective of the research is to optimize the sensor and actuator locations as well as orientation to maximize the control performance. The control performance will follow.
Analysis and modeling of a two-axis thin film piezoelectric actuator
Xuesheng Chen, Colin H.J. Fox, Stewart McWilliam
This paper concerns a beam-like two-axis piezoelectric actuator, suitable either for MEMS implementation using piezoelectric films deposited on a single surface of a substrate or for larger scale implementations using bulk piezoelectric actuator plates. An analysis of the mechanics of actuator is presented that quantifies the actuation effect in two perpendicular directions, depending on the pahsing of the actuation voltages applied. The analysis, based on consideration of the stress and strain transfer between the active and passive parts of the structure, extends previously published work on single-axis actuators and leads to the development of simple analytical formulae that are useful for design purposes. Comparison of analytical predictions with Finite Element simulations gives confidence in the validity of the analytical model.
Optimization of Active Structures
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Optimization and vibration suppression of adaptive composite panels using genetic algorithm and disturbance observer technique
In this paper, a model of the adaptive composite panel surfaces with piezoelectric patches is built using the Rayleigh-Ritz method based on the laminate theory. The interia and stiffness of the actuators are considered in the developed model. An optimal actuator location has been proved to be desirable since the piezoelectric actuators often have limitations of delivering large power oiutputs. Due to its effectiveness in seraching optimal design parameters and obtaining globally optimal solutions, the genetic algorithm has been applied to find optimal locations of piezoelectric actuators for the vibration control of a smart composite beam. In addition, the effects of population size, the crossover probability, and the mutation probability on the convergence of the genetic algorithm are investigated. Meanwhile, linear quadric regulator (LQR) and disturbance observer (DOB) are employed for the vibration suppression of the optimized adaptive composite beam (ACB). The experimental results show the robustness of the DOB, which can successfully suppress the vibrations of the cantilevered ACB according to the optimization results in an uncertain system.
Robust design and control of piezoelectric laminate beams using a simultaneous optimization method
Wei Chen, Markus Buehler, Gordon G. Parker, et al.
In this paper, robust control of piezoelectric laminate beams by simultaneously optimizing the smart material distribution and the closed-loop control system is implemented. Through topological optimization of smart material, using a homogenization approach and a linear quadratic regulator (LQR), a new type of sensor with the ability to increase the stability margin is obtained. The method is applied to a pinned-pinned beam where two cost functions are considered, both focus on increasing the stability margin of the closed-loop system. The first one is based on the observability gramian and the second one on the control weighting parameter of the LQR cost function. Both cost functions yield optimal sensor distributions that improve the closed-loop performance as compared to uniform density distributions. Although not explicitly considered in the cost function design, the sensor distribution based on the LQR control weighting parameter was consistently smoother than those based on the observability gramian. This is an important practical consideration for sensor fabrication.
Optimization of location and tuning of a state-switched absorber for controlling beam vibration
This paper considers the optimization of the performance of a state-switched absorber (SSA) in controlling the vibration of a continuous beam. A state-switched absorber has the capability to instantaneously change its stiffness, which allows the absorber to 'retune' to a new natural frequency instantaneously. Between each 'retuning', or switch event, the SSA is essentially a passive device, tuned to the resonance frequency of its current state. With proper switching logic, the SSA shows improved performance in vibration control as compared to classical passive devices when the excitation contains more than one frequency component. The SSA considered here is capable of switching between only two discrete stiffnesses. A direct search algorithm is employed for optimization of the absorber's location along the beam as well as the two tuning frequencies needed to achieve the best performance of the state-switched absorber. Several two-frequency component point excitations are considered at a few locations along the beam and over a range of frequencies. The optimized performance of the state-switched absorber is compared to the optimized performance of a classical tuned vibration absorber (TVA) for each forcing case.
Design of a piezoelectric actuator using topology optimization
Joachim Drenckhan, Arnold Lumsdaine
This study investigates the optimal topology for a piezoelectric actuator mounted on a cantilever beam under a concentrated static load at the tip. The project consists of two major parts: implementation of the control law into the commercial finite element code ABAQUS and studies in topology optimization. The first part gives a derivation and explanation of the implementation of static feedback control. The result is compared with a derived analytical solution. The second part examines the results of topology optimizations with different geometries and constraints. Thus, this study develops fundamental understanding of advantageous shapes for optimal performing piezoelectric actuators.
Optimization
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Energy optimization of driving amplifiers for smart actuators
Huiyu Zhu, Chunping Song, Douglas K. Lindner, et al.
A high-efficiency driving amplifier with small profile for smart actuators is essential for portable actuator devices. In this paper, a detailed optimized design of half-bridge switching circuit to drive smart actuators is described. The mathematical optimization procedure is applied to the traditional circuit design to make the circuit smaller and more efficient. The objecitve function presented in this paper is to minimize the total weight of the circuit, including heat sink, inductor and bus capacitor. The calculation of the power dissipation of MOSFET is adopted as a critical step to get the suitable heat sink. The optimization results are presented to demonstrate the effectiveness of this method.
Path planning for the deployment of tensegrity structures
Tensegrity structures consist of tendons (in tension) and bars (in compression). Tendons are strong, light, and foldable, so tensegrity structures have the potential to be light but strong and deployable. Pulleys, NiTi wire, or other actuators to selectively tighten some strings on a tensegrity structure can be used to control its shape. This article describes the problem of asymmetric reconfiguration of tensegrity structures and poses one method of finding the open loop control law for tendon lengths to accomplish the desired geometric reconfiguration. In addition, a practical hardware experiment displays the readiness and feasibility of the method to accomplish shape control of the structure.
Control/structure optimization approach for minimum-time reconfiguration of tensegrity systems
For a new class of tendon-driven robotic systems that is generalized to include tensegrity structures, this paper focuses on a method to jointly optimize the control law and the structural complexity for a given point-to-point maneuvering task. By fixing external geometry, the number of identical stages within the domain is varied until a minimal mass design is achieved. For the deployment phase, a new method is introduced which determines the tendon force inputs from a set of admissible, non-saturating inputs, that will reconfigure each kinematically invertible unit along its own path in minimum time. The approach utilizes the existence conditions and solution of a linear algebra problem that describe how the set of admissible tendon forces is mapped onto the set of path-dependent torques. Since this mapping is not one-to-one, free parameters in the control law always exist. An infinity-norm minimization with respect to these free parameters is responsible for saturation avoidance. In addition to the required time to deploy, the expended control energy during the post-movement phase is also minimized with respect to the total number of stages. Conditions under which these independent minimizations yield the same robot illustrate the importance of considering control/structure interaction within this new robotics paradigm.
Design, modeling, and optimization of compliant tensegrity fabrics for the reduction of turbulent skin friction
In this project, we have designed a new type of flexible surface, which we call a tensegrity fabric, and simulated the interaction of this flexible surface with a near-wall turbulent flow. The fabric is constructed by weaving together both members in tension (tendons) and members in compression (bars) to form a plate-class tensegrity structure, then covering this discrete flexible structure with a continuous flexible membrane. We have modeled the flow/structure interaction by coupling a spectral Direct Numerical Simulation (DNS) code resolving the (continuous) turbulent flow system and an efficient structural dynamics code which simulates direclty the motion of the (discrete) extensive, small-scale, and interconnected tensegrity structure. The structural dynamics code used was developed by Prof. Robert Skelton's lab at UC San Diego. An immersed boundary method is used to capture the effect of the moving boundary in the DNS, and a simple tessellation strategy is used to lump the distributed fluid forces (skin friction and pressure) acting on the membrane onto the nearby nodes of the tensegrity structure. Our ultimate goal is to use this new simulation tool to optimize the design of the tensegrity structure (specifically, the orientation, stiffness, mass, and damping of each of the individual tendons and bars in the unit cell upon which the tensegrity structure is based). Our objective in this optimization is to tune the compliance properties of the fabric in such a way as to reduce the skin-friction drag induced at teh flow/structure interface by weakening the vortices near the wall in the overlying turbulent flow.
A classifier design method based on the invariance properties of the Bhattacharyya distance functional
The Bhattacharyya distance functional invariance classifier design method (BDFICDM) reaches an excellent tradeoff between the accuracy performance of nearly 100% and the time performance as much as there is available computational resources for parallelism. A serial implementation of the method is applied to an image composed of two synthetic and two Bradatz textures preserving its characteristics of being highly suitable to a parallel implementation. This implementation characterizes the pattern by composing independent cells of magnitudes evaluated through the interaction of spatially distributed elementary piece of information (EPI) using the Bhatacharyya distance similarity measure. The localized representation, EPI is composed of shifted frames sampled by a sequential process over a direction in order to preserve the pattern topological information. The representational extension of the functional pattern representation is its reduction focusing only on those EPI best candidates for generating invariance locations and using the graph structures for their representation. The BDF sample is classified within a Bayesian approach by comparing it to only those reduced pattern states of invariance, decreasing abruptly the number of needed interactions and comparisons. The procedure comprises the multiple frame, resolution, hypothesis and class approaches and the image representation used as input in the training and classification processes at the frame decomposition instance, is reduced through the use of the KL transform.
Multiflexible micromanipulator design by using topology optimization
Emilio Carlos Nelli Silva, Shinji Nishiwaki
In the MEMS scale the presence of joints and pins must be avoided due to manufacturing constraints. This makes difficult to design micromechanisms with many degrees of freedom to perform complex movements, such as micromanipulators or micro-robots. However, these microdevices can have a wide range of application such as cell manipulation, microsurgery, nanotechnology equipment,etc. Therefore, in this work, a method for designing multiflexible micromanipulators is proposed by using topology optimization technique based on the homogenization design method. Micromanipulators considered in this work consist of a multiflexible structure actuated by two or more piezoceramics. A multi-flexible structure must generate different output displacements and forces in different specified points of the domain and directions, for different excited piezoceramics. It acts as a mechanical transform by amplifying and changing the direction of the piezoceramics output displacements. The multiflexible structure design is obtained by distributing flexibility and stiffness in the design domain, which can be achieved through topology optimization. Essentially, the topology optimization method consists of finding the optimal material distribution in a perforated design domain with infinite microscale voids. The material in each point can vary from void to full material, also assuming intermediate materials. The optimization problem is posed as the design of a flexible structure that maximizes different output displacements (or grabbing forces) in different specified directions and points of the domain, for different excited piezoceramics. Different types of micromanipulators can be obtained for a desired application depending on the multiflexible structure design connected to the piezoceramics. A linear behavior of piezoceramics is considered. To illustrate the method, the design of some micromanipulators are presented.
Sensors
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Modeling of the residual stresses acting on a low-birefringence fiber Bragg grating sensor embedded in an epoxy matrix
Laurent Humbert, John Botsis, Federico Bosia
An optical fiber Bragg grating (FBG) embedded in an epoxy matrix is indubitably subjected to non-negligible residual stresses arising from the cure, especially for a strong fiber-matrix interface. The spectral response of the FBG sensor is clearly influenced by the presence of the residual non-homogeneous strain field along the grating and results in a distortion (chirp) of the reflected spectrum. Direct applications for distributed strain sensing, without tracking the residual field into account, can lead to inaccurate results. In the present work the reflected spectrum of a single FBG sensor embedded in an epoxy specimen at the end of the post-curing process is recorded and characterized using an analytical model which accounts for a distributed residual strain profile along the axial direction of the fiber. In addition an equivalent thermo-elastic problem for the matrix material is considered in finite elemetns simulations of the actual specimen. Both approaches show good agreement for the axial field, with some differences in the radial direction, presumably due to the simplifications introduced by the shear lag simplifications in the adopted analytical model. A level of about 20 MPa of compressive residual stresses is found in the vicinity of the fiber matrix interface.
Self-organizing wireless sensor networks for structural health monitoring
A smart sensor node has been developed which has (a) the ability to sense strain of the structure under observation, (b) process this raw sensor data in cooperation with its neighbors and (c) transmit the information to the end user. This network is designed to be self organizing in the sense of establishing and maintaining the inter node connectivity without the need for human intervention. For the envisioned application of structural health monitoring, wireless communication is the most practical solution for node interconnectivity not only because they eliminate interconnecting cables but also for their ability to establish communication links even in inaccessible regions. But wireless nework brings with it a number of issues such as interference, fault tolerant self organizing, multi-hop communication, energy effieiciency, routing and finally reliable operation in spite of massive complexity of the sysetm. This paper addresses the issue of fault tolerant self organiing in wireless sensor networks. We propose a new architecture called the Redundant Tree Network (RTN). RTN is a hierarchical network which exploits redundant links between nodes to provide reliability.
System Identification
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System identification and control of ionic polymer metal composite
Nikhil Bhat, Won-jong Kim
In this paper, we present the development of an empirical force model and the feedback control of the force produced by Ionic Polymer Metal Composite (IPMC). IPMC shows great potential as a low-mass, high-displacement actuator. The high-precision force generation capability of IPMC at low force level makes it ideal for the microdevice applications such as microgrippers. Thus, modeling of the force generated by IPMC is of critical importance along with its control. Force models previously developed are based on the electrochemical and electromechanical phenomena. Most of these models consisted of partial differential equations representing each phenomenon, so it is difficult to develop a force controller on the basis of these models. This paper presents a force model developed for an IPMC strip by system identification and the feedback control of the force produced by the IPMC strip. After the implementation of the controller, the settling time is reduced to 1.5 s from 10 s in open loop, and the overshoot is reduced to 30% from 125% in open loop. The crossover frequency is 1.3 Hz limited by the structural resonance of the polymer strip.
Neural network application in damage identification using multiscale sensing data
Damage identification is an important component for accurate lifetime predictions of any structure. In the case of a composite structure, however, damage can occur at several material scales: it can vary from micro damage, like fiber debonding or micro-cracking, to global damage such as buckling or delamination. These different material scales make damage identification difficult with a single type of sensing device. A single embedded optical fiber, causing little perturbation to the surrounding host structure, can multiplex hundreds of sensors, and furthermore, sensors measuring at different length scales. For example, short Bragg gratings can measure strain at given locations; long Bragg gratings can measure strain gradients; interferometric techniques can measure integrated strain along a given fiber length. The use of multi-scale measurements has been shown by the authors to improve the precision of damage identification. Still the treatment and fusion of these data is a non-trivial problem. This work presents a back propagation Neural Network algorithm used to fuse simulated multi-scale sensor data in order to identify damage. An analytical model of an isotropic plate subjected to a known load and specific forms of damage is used to train the network. The input data are: localized strain, localized strain gradient, and integrated strain measurement along a regularly spaced sensor network. This method is tested against a randomly generated set of damages. The combined use of multi-scale measurements and Neural Network analysis shows a great potential in damage identification for composite structures.
High-resolution evaluation algorithms for SAW-identification tags
Andreas Stelzer, Markus Pichler, Stefan Schuster, et al.
The use of surface acoustic wave (SAW) devices is a widely adopted method for implementing unique identification tags that operate completely passively and can be interrogated wirelessly. Interrogation can be done in the time- or frequency-domain, where in the latter case bandwidth is a restraining factor. Conventional signal evaluation is based on the fast Fourier transformation (FFT), which suffers from resolution limitations. Modern model-based frequency estimators have been investigated for SAW ID-tag identification. A state-space algorithm is applied to measured data and compared to FFT evaluation results.
Nonlinear system identification of base-excited structures using an intelligent parameter varying (IPV) modeling approach
Soheil Saadat, Gregory D. Buckner, Tadatoshi Furukawa, et al.
Health monitoring and damage detection strategies for base-excited structures typically rely on accurate models of the system dynamics. Restoring forces in these structures can exhibit highly non-linear characteristics, thus accurate non-linear system identification is critical. Parametric system identification approaches are commonly used, but require a priori knowledge of restoring force characteristics. Non-parametric approaches do not require this a priori information, but they typically lack direct associations between the model and the system dynamics, providing limited utility for health monitoring and damage detection. In this paper a novel system identification approach, the Intelligent Parameter Varying (IPV) method, is used to identify constitutive non-linearities in structures subject to seismic excitations. IPV overcomes the limitations of traditional parametric and non-parametric approaches, while preserving the unique benefits of each. It uses embedded radial basis function networks to estimate the constitutive characteristics of inelastic and hysteretic restoring forces in a multi-degree-of-freedom structure. Simulation results are compared to those of a traditional parametric approach, the prediction error method. These results demonstrate the effectiveness of IPV in identifying highly nonlinear restoring forces, without a priori information, while preserving a direct association with the structural dynamics.
Control Applications
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Disturbance-observer-based active control of engine-induced vibrations in automotive vehicles
Christian Bohn, Aitor Cortabarria, Volker Härtel, et al.
An approach for active noise and vibration control for systems subject to periodic disturbances with time-varying fundamental frequency is presented. The motivation is active compensation of engine-induced noise in automobiles, where the fundamental frequency (engine firing frequency) goes from 7 Hz (idle, 800 rpm) to 50 Hz (6000 rpm) and the frequency (engine speed) is available. In this new approach, an observer for an input disturbance is designed based on a disturbance model containing all frequencies to be cancelled. The disturbance-model part of the observer is time-varying since the current frequency is measured and fed into this part. Based on this frequency measurement, an observer gain is selected from a set of pre-computed gains. The approach is non-adaptive, and the frequency is a scheduling variable. Theoretical issues of the algorithm (observer design) are discussed and real-time results obtained with an active control system in a vehicle are presented. These results show a major reduction of the interior sound pressure level in the vehicle.
Fuzzy logic control algorithms for MagneShock semiactive vehicle shock absorbers: design and experimental evaluations
Michael J. Craft, Gregory D. Buckner, Richard D. Anderson
Automotive ride quality and handling performance remain challenging design tradeoffs for modern, passive automobile suspension systems. Despite extensive published research outlining the benefits of active vehicle suspensions in addressing this tradeoff, the cost and complexity of these systems frequently prohibit commercial adoption. Semi-active suspensions can provide performance benefits over passive suspensions without the cost and complexity associated with fully active systems. This paper outlines the development and experimental evaluation of a fuzzy logic control algorithm for a commercial semi-active suspension component, Carrera's MagneShockTM shock absorber. The MagneShockTM utilizes an electromagnet to change the viscosity of magnetorheological (MR) fluid, which changes the damping characteristics of the shock. Damping for each shock is controlled by manipulating the coil current using real-time algorithms. The performance capabilities of fuzzy logic control (FLC) algorithms are demonstrated through experimental evaluations on a passenger vehicle. Results show reductions of 25% or more in sprung mass absorbed power (U.S. Army 6 Watt Absorbed Power Criterion) as compared to typical passive shock absorbers over urban terrains in both simulation and experimentation. Average sprung-mass RMS accelerations were also reduced by as much as 9%, but usually with an increase in total suspension travel over the passive systems. Additionally, a negligible decrease in RMS tire normal force was documented through computer simulations. And although the FLC absorbed power was comparable to that of the fixed-current MagneShockTM the FLC revealed reduced average RMS sprung-mass accelerations over the fixed-current MagneShocks by 2-9%. Possible means for improvement of this system include reducing the suspension spring stiffness and increasing the dynamic damping range of the MagneShockTM.
The online generalized predicitive control combined with a fast transversal filter
Suk-Min Moon, Robert L. Clark, Daniel G. Cole
The concept of generalized predictive control (GPC) design is extended by combining it with the recursive least squares (RLS) system identification algorithm. In this paper, GPC is combined with the classical RLS system identification algorithm, and with the fast transversal filter (FTF), a modified version of the classical RLS algorithm. The classical RLS algorithm is a straightforward approach for identifying a model from input and output data, and one of the advantages of the classical RLS algorithm is that a model is obtained without time-consuming processes like matrix inversion. The FTF is also an RLS algorithm, but it exploits the shifting property of serialized data and thereby results in a substantial reduction in computational complexity. The advantages of both combined algorithms are no prior system model is required, since the process of system identification is performed recursively from real-time system input and output data, and the controller is updated adaptively in the presence of a changing operating environment.
Design and control issues on a hybrid linear motor working on self-moving cell concept
Jaehwan Kim, Byungwoo Kang, Janghwan Lim
This paper presents the development of a hybrid linear motor that operates based on self-moving cell concept. The working principle is far different from the conventional linear inchworm motor. The new linear motor has three cells and each cell is constructed with one piezo-stack actuator and a shell structure. A cell train is constructed by connecting there cells and the train is fitted into a guideway with interference. By activating each cell in succession, the train moves along the guideway. Keys to realization of this goal are the design and control of moving cell, and these issues are addressed. One of the merits of this motor is that it can move by macro motion and micro motion. In macro motion, the cell train can move fast by activating each cell in succession. In micro motion, in contract, the first cell can move in nano scale by adjusting the activating voltage for the cell. The moving performance of the motor is demonstrated. As results the maximum speed of 70μm/s with the resolution of 20nm were achieved. Since this linear motor uses piezo-stack actuator with unified clamping cell, it can produce fast speed, high resolution and large push force.
Applications
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Maximum modal damping of cable space vibration control with viscous damper in cable-stayed bridge
Bing Nan Sun, Shuid Sheng Chen, Wen Juan Lou
Taking the bending stiffness, cable static sag and cable inclinded angle into consideration, the equations of space vibration of the cable-damper system are formulted in this paper. Applying the variable separation strategy and center difference method, the partial differential equations are discrete in space and a set of complex eigenvalue equations are sovled by state space method. Then both the maximum modal damping ratio and the optimal damper parameters are obtained. Some typical stay cables are investigated for both the in-plane and out-plane vibration modes with different cable parameters and damper parameters. The results show the damping ratio for the first in-plane vibration modes with different cable parameters and damper parameters. The resutls show the dampingn ratio for the first in-plane mode is significantly affected by the cable static sag only, but those for the other modes are affected slightly, and cable static sag do not affect the optimal damper parameter for all modes. However the bending stiffness will changes both the maximum modal damping ratios and the optimal damper parameters. Some valuable suggestions are proposed for the optimal damper design.
Dynamic shape control of conformal antennas
Michael Krommer, Vasundara V. Varadan
The present paper is concerned with dynamic shape control of conformal antennas on vehicles that may undergo deformations large enough to interfere with antenna performance. If the antenna is conformal to a vehicle or structure is will deform with the vehicle/structure. The objective of this paper is to develop a methodology and simulation technique to control the shape and contour of the antena and to keep it as close to the non-defomed state as possible. Dynamic shape contorl of such surfaces and structures is important to preserve integrity of the electromagnetic performance of the antenna. An exact elimination of the deformation of the whole structure therefore is not required. Our goal is to design the actuator with the purpose of controlling the dynamic deformation of the structure only in the region of the conformal antenna. As an example we consider a plate type structure with the conformal antenna situated in an arbitrary region. Given an external disturbance to the plate, we seek a distributed piezoelectric actuation, which is capable of controlling the motion of the region of the conformal antenna. The goal can be to either eliminate displacements in the region or keep it constant over the region. Our solution of this problem is based on integral formulations for both, the motion imposed by the external distrubance and the motion imposed by the distributed piezoelectric actuation. Comparing the kernels of the integral formation results in a simple solution of the problem: if the distributed piezoelectric actuation conicides with the statically admissible stress due to the external disturbance, the antenna is kep as close to the non-defomed states as possible.
Transient behavior of an ultrasonic wobbling-disk motor
Stefanie Gutschmidt, Peter Hagedorn
Stationary behavior of a wobbling-disk ultrasonic motor has already been studied in a previous publication with the help of a simple mathematical model. The model is able to capture basic motor features both quantitatively and qualitatively. The mathematical model presented in this paper describes the transient behavior of an ultrasonic wobbling-disk motor. Bending stator vibrations are generated in the ultrasonic motor with the help of a piezoceramic element. Two phase-shifted bending modes cause the upper plate of the stator to undergo a wobbling motion. The rotor is pressed against the stator and driven by frictional forces at the contact point. Both, stator and rotor are modeled as rigid and are elastically supported. The kinematics is described taking into account all geometric nonlinearities. In modeling the transient motion, special attention is given to differentiating between slip and stick contact conditions. Further improvements will include modeling the piezoceramic excitation in more detail. It is presently described by a rotating torque, generating the wobbling motion of the stator.
Signal processing and damage detection in a frame structure excited by chaotic input force
This paper discusses the development of a general time-frequency data analysis method, the Empirical Mode Decomposition (EMD) and Hilbert Spectrum, and its application to structural health monitoring. The focus of this work is on feature extraction from structural response time series data. This is done by tracking unique characteristics of the adaptive decomposition components and developing a damage index based on previously introduced fundamental relationships connecting the instantaneous phase of a measured time series to the structural mass and stiffness parameters. Damage detection applications are investigated for a laboratory experiment of a simple frame (a model of a multi-story building) where damage is incurred by removing bolts at various locations. The frame is excited by a low dimensional deterministic chaos input as well as by broadband random signal. The time series output of the frame response is then analyzed with the EMD method. The time-frequency features and instantaneous phase relationships are extracted and examined for changes which may occur due to damage. These results are compared to results from other newly developed detection algorithms based on geometric properties of a chaotic attractor. Our results illustrate that the EMD and instantaneous phase detection approach, based on time-frequency analysis along with simple physics-based models, can be used to determine the presence and location of structural damage and permits the development of a reliable damage detection methodology.
The optimal selection of mother wavelet shape for the best time-frequency localization of the continuous wavelet transform
Jin-Chul Hong, Yoon Young Kim
The continuous wavelet transform (CWT) has been utilized as an effective and powerful time-frequency analysis tool for identifying the rapidly-varying characteristics of some dispersive wave signals. Particularly, in the applications of continuous Gabor wavelet transform, its effectiveness is strongly influenced by the shape of the applied Gabor wavelet so the determination of an optimal shape tracing well the time-frequency evolution of a given signal. Since the characteristics of signals are rarely known in advance, the determination of the optimal shape is usually difficult. The main objective of this work is to propose a method to determine the signal-dependent optimal shape of the Gabor wavelet for the best time-frequency localization. To find the optimal Gabor wavelet shape, the notion of the Shannon entropy which measures the extent of signal energy concentration in the time-frequency plane, is employed. To verify the validity of the present approach, a set of elastic bending wave signals generated by an impact in a solid cylinder are analyzed.
Novel computational structure for real-time wavelet analysis
V. P. Devassia, M. G. Mini, Tessamma Thomas
The advent of high-speed signal processors combined with real-time complex algorithms has resulted in truly elegant industrial systems and controllers. Wavelet Transform (WT) is one among the smart signal processing tools, which has already excelled over the conventional ones. In this paper we present an efficient implementation structure for real-time computation of the Discrete Wavelet Transform (DWT) and its Inverse (IDWT). The wavelet and scaling function coefficients at each level are computed by successive convolutions and the computation of transform coefficients at all levels is performed in parallel. Adopting the principle of polyphase splitting, the input sequence and filter coefficients at each level ’j’ are divided into 2j subsequences, incorporating additional parallelism within levels. Expressions for the computational complexity are derived and a comparison of complexity against the popular filter-bank tree structure is made, for variations of signal length, order of wavelet and the number of levels. The Parallel Multiple Subsequence (PMS) structure suggested here, involves much less computation than state-of-the-art algorithms up to 6 levels of processing for Haar wavelet and 3 levels for others, for any data length. For higher decomposition levels and for real-time applications, the proposed algorithm is made superior by optimal selection of processing frame size.
Poster Session
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Optimization of CMOS APS pixel
Victor A. Shilin, Pavel A. Skrylev, Alexander L. Stempkovsky
Nowadays CMOS active pixel sensor (APS) cameras are widely used in video applications. APS consists of photodiode and some control transistors. During integration time photogenerated signal charges are collected by the photodiode. The main problem for CMOS active pixel sensors (APS) design is its fill factor and photosensitivity improvement. The fill factor is the aim function of optimization in CMOS pixel design. The constraints, which are imposed on the function, are: reset and read-out times delays, signal-to noise ratio, values of horizontal and vertical modulation transfer function (MTF), pixel sizes, and project rules. Analytical models are used in order to describe APS features. 2D numerical models for process, potential, and charge distributions simulation have been used for calibration of analytical model coefficients. Small changing of the process parameters has allowed getting required charge capacity and antiblooming possibility for the photodiode. Integrated signal charge has reduced effective depth of photodiode potential well. Using pixel layout the geometrical model has been developed. The model takes into consideration sizes and layouts of the pixel components: photodiode, transistors, buses, and also project rule. The possible CMOS APS design method that allows maximization of fill factor and photosensitivity has been presented. Using developed CMOS APS models we have solved this problem as mathematical optimization task. As example, we have considered APS with 4 control transistors.
How much more rain?
Smart Dust particles, are small smart materials used for generating weather maps. We investigate question of the optimal number of Smart Dust particles necessary for generating precise, computationally feasible and cost effective 3-D weather maps. We also give an optimal matching algorithm for the generalized scenario, when there are N Smart Dust particles and M ground receivers.
Adaptive backstepping control of a class of hysteretic systems
Fayçal Ikhouane, Victor Mañosa, José Rodellar
A backstepping-based adaptive control is designed for a class of one degree of freedom hysteretic system. The true hysteretic behavior does not need to be known for the controller design. A polynomial description is assumed with uncertain coefficients and an uncertain residual function. These uncertainties are bounded and lump the discrepancies between the adopted description and the real hysteretic behavior. The adaptive controller is able to handle these uncertainties and make the closed loop globally uniformly ultimately bounded when the system is subject to an unknown excitation from which a bound is known. The efficiency of the approach is tested by numerical simulations on a hysteretic system under a seismic excitation. This system is mathematically described by the differential Bouc-Wen model, which is widely used in structural dynamics.
Design of genetic-algorithm-based multimode controller
Moo Sun Kim, Myung Seok Yun, Woo Il Lee
In this study, the Genetic Algorithm (GA) was used to search the 4 modes filter frequencies to be applied to the multiple Positive Position Feedback (PPF) controller. The PPF technique, which makes use of generalized displacement measurements to maximize damping in a specific mode effectively and accomplish vibration suppression was employed as control scheme. However it is necessary to tune the filter frequency of the controller to the structural resonance prior to compensator design. Another disadvantage in the multi mode PPF control is that the lower mode natural frequency is shifted to the low-ward as the effect of the higher mode control by PPF controller. To minimize the effect of frequency shift and search the optimal filter frequencies for the multiple modes PPF controller, the GA was applied. The generally used fitness function of the GA in low modes PPF control, the square sum of sensor voltage output hardly distinguishes the definite difference in higher modes. Instead of it, in this study, the GA with the fitness function as the power spectrum information was performed. As a result of GA algorithm with this fitness function, the optimal filter frequencies of higher modes were found successfully.
Damage detection in a sandwich composite beam using wavelet transforms
Tariq A. Dawood, R. Ajit Shenoi, Sandor M. Veres, et al.
There is a growing interest in developing non-destructive damage detection methods for damage assessment of composite structures, especially in the aerospace and marine industries. Although damage detection of composite laminates has been widely investigated, little work has been carried out on sandwich composite configurations. A technique using the Lipschitz exponent, which is estimated by wavelet transforms, as a damage sensitive signal feature is outlined here to identify damage in sandwich composites. It is based on the fact that damage causes singularities to appear in the structure’s dynamic response which can be identified, and its severity estimated, using the Lipschitz exponent. In order to demonstrate this technique, damage in cantilevered fibre reinforced plastic (FRP) sandwich beams is investigated both numerically and experimentally.
Online detection method for transient waves applied to continuous health monitoring of carbon-fiber-reinforced polymer composites with embedded optical fibers
Jean-Michel Papy, Sabine Van Huffel, Laurent Rippert, et al.
It has been proven that the embedment of optical fibers into a composite material could offer an alternative to robust piezoelectric transducers used for Acoustic Emission (AE) monitoring. In this configuration optical fibers are used as intensity-modulated sensors. A set of propagating elastic waves is generated whenever damage occurs in the composite material. These waves locally modify the optical and geometrical properties of the optical fiber and hence can be detected by them as a transient signal that modulates the light intensity. In this paper a method for detecting the transients by on-line signal processing is presented. It is then applied to optical signals resulting from tensile tests performed on CFRP composites material with embedded optical fibers. By means of the Short-Time Fourier Transform (STFT), the level of the noise added to the signal is estimated by filtering the time trajectories. This filter is continuously adapted according to the principle of minimization of the mean squared error. Finally the detection is achieved by a constant false alarm rate power-law detector. This technique is fast and doesn't take into account neither the statistical distribution of the noise nor the frequency content of the transients as long as the frequency component distribution can be approximated by an exponential law. The detected transient features can be correlated with the AE results but an off-line analysis and classification is still needed.
A first example in economic simulation design
The economic simulation design problem is that given performance requirements, design the simulation of a linear system and distribute precision among the instruments such that the computational cost is minimized without violating the simulation accuracy. In this paper, we consider the simulation of a large-scale linear system in digital devices with fixed-point arithmetic and finite wordlength. Given the output variance upperbound, we focus on finding an optimal realization and the allocation of wordlength among A/D converter, computer and sensors. This problem is in general not convex because of the scaling constraint. By exploring the special structure of this joint optimization problem and under reasonable assumptions, we simplify this problem and find the optimal coordinate transformation and the wordlength allocation scheme simultaneously by solving LMIs (linear matrix inequalities). Numerical results are given which compare this new realization with the balanced realization and random realizations.
Shape Memory Alloys II
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Thermodynamics of a 1D shape memory alloy: modeling, experiments, and application
John A. Shaw, Bi-chiau Chang, Mark A. Iadicola, et al.
A thermomechanical model for a shape memory alloy (SMA) wire under uniaxial loading is implemented in a finite element framework, and its results are compared with new experimental data. The constitutive model is a one-dimensional continuum model of an SMA element, including two internal field variables, strain gradient effects, possible unstable mechanical behavior, and the relevant thermomechanical couplings resulting from latent heat effects. The model is calibrated to recent experiments of typical commercially available polycrystalline NiTi wire. The shape memory effect and pseudoelastic behaviors are demonstrated numerically as a function of applied loading rate and environmental parameters, and the results are found to be quite similar to experimental data. The model is then used to simulate a simple SMA actuator device, and the model proves to be a useful tool to assess the performance.
Poster Session
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Computer simulation of optimal sensor locations in loading identification
Dong-Sheng Li, Hong-Nan Li, Xing Lin Guo
A method is presented for the selection of a set of sensor locations from a larger candidate sent for the purpose of structural loading identification. The method ranks the candidate sensor locations according to their effectiveness for identifying the given known loadings. Measurement locations that yield abnormal jumps in identification results or increase the condition number of the frequency response function are removed. The final sensor configuration tends to minimize the error of the loading identification results and the condition number of the frequency response function. The initial candidate set is selected based on the modal kinetic energy distribution that gives a measure of the dynamic contribution of each physical degree freedom to each of the target mode shapes of interest. In addition, excitation location is considered when selecting appropriate response measurement locations. This method was successfully applied to the optimal sensor location selection and loading identification of a uniform cantilever beam in experiment. It is shown that computer simulation is a good way to select the optimal sensor location for loading identification.
Adaptive Structures
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On the identification of Preisach measures
Matthew E. Shirley, Ram Venkataraman
The phenomenon of hysteresis is commonly encountered in the study of magnetic materials. The Preisach operator and its variants have been successfully used in the modeling of a physical system with hysteresis. In an application, one has to determine a density function for the Preisach operator using the input-output behavior of the system at hand. In this paper, we describe a method for numerically determining an approximation of the density function when there is not enough experimental data to uniquely solve for the density function. We also present numerical results where we estimate an approximate density function from data published in the literature for a magnetostrictive actuator and an electro-active polymer.