Active Control Of Flexible Structures Research Articles

Compensated positive position feedback for active control of piezoelectric structures

This article presents a compensated positive position feedback strategy for active control of flexible structures with piezoelectric actuators. In the proposed compensated positive position feedback method, a negative feedback compensator is involved to remedy the deficiency of traditional positive position feedback and to introduce roll-off characteristic at low frequencies. Thus, compensated positive position feedback controllers can be developed with minimal influences on lower order modes and cause no steady-state error to the controlled system. For demonstration purpose, the design processes and the effectiveness of the compensated positive position feedback method are illustrated by active control of a cable net structure with integrated piezoelectric stacked actuators. The numerical simulations demonstrate that compared to the conventional positive position feedback method, the proposed compensated positive position feedback approach overcomes the fundamental defects of frequency shift and spillover into lower order modes and achieves the goal of step-tracking with zero steady-state error. These comparative results confirm the efficacy and superiority of the proposed compensated positive position feedback methodology in active control of flexible structures.

Pole-Placement for Collocated Control of Flexible Structures

Pole assignment is one of the central problems in most control systems designs. In relation to low-authority active flexible structural systems where robustness is difficult to achieve primarily due to many closely-spaced low-frequency lightly damped modes, pole-placement techniques are commonly used to design constant gain collocated controllers that will ensure that the transient phenomenon of the structure dies down sufficiently fast. In this paper, the active control of flexible structures is presented for collocated control design using a modified pole-placement approach that reduces the control efforts significantly. The effectiveness of employing the proposed approach is demonstrated using tensegrity structures.

Fuzzy Active Control of Flexible Structures by Using Electromagnetic Actuators

Numerical and experimental investigations are carried out to assess the possibility of controlling a flexible beam by using an electromagnetic actuator (EMA). The advantage of EMAs is that they do not require contact with the structure so they can be applied to light and small mechanisms. Nevertheless, their open-loop instability and nonlinear dynamic behavior relating to excitation frequency can limit their fields of application. The EMA is designed and dimensioned as a function of the structure to be controlled. The effect of the EMA is considered a restoring force; consequently, the structure is still linear, which enables the calculation of the modal matrices of the structure. Moreover, an inverse model of the EMA is proposed to implement a linear action block for the frequency range used. The gap distance is estimated by using a modal approximation of the displacements resulting from the measurements. The control strategy is a fuzzy controller with displacements and velocities as inputs. Fuzzy contro...

Active Robust Fault Estimation on a Composite Beam with Integrated Piezoceramics

The problem addressed here is the application of model-based fault detection algorithm to active control of flexible structures. The modeling of mechanical structures with the finite element (FE) method leads to high order models which must be reduced. This step introduces important uncertainties which make necessary the use of robust fault detection and diagnosis (RFDD) algorithms. Here, we propose to apply a RFDD method using the H2 and H∞ polynomial estimation to estimate the input fault signal. To illustrate the efficiency of this method, it is applied to a composite beam with piezoelectric patches as sensors and actuators.

Adaptive active control of flexible structures subjected to rigid body displacements

When flexible structures are subjected to rigid body displacements, their dynamic behavior presents a coupling between rigid body displacements and flexible modes. Moreover, if these structures are articulated, their inertia characteristics can vary considerably through time and cause this dynamic behavior to become highly nonlinear. The paper presents the principle of a new adaptive controller MIMO. making it possible to render nearly constant the dynamic behavior of multi-articulated flexible structures in spite of changes in the geometry of their masses. The principle of this controller is based on the operation in parallel of a number of finite Gaussian quadratic linear controllers calculated before simulations, for the operating points crossed during the motion. The global multivariable command generated by the adaptive controller is the sum of the commands generated by the linear controllers, weighted by functions of rigid body displacements to allow the smoothing of the control actions on the structure. Adaptive control is first applied to a rigid bi-articulated structure, then to mono-articulated and bi-articulated flexible structures equipped with piezoelectric sensors and piezoelectric and electromechanical actuators. After temporal optimization, the results of the proposed adaptive control are compared with those of a linear controller. This is done by using two methods, chosen according to whether the structures are stressed by disturbances or by tracking. In the case of regulation, the performances of this controller highlight on the one hand, the near-constant dynamic behavior of the controlled structure by eliminating instabilities, in spite of the considerable changes of kinetics and, on the other hand, clearly improved performances when compared to a fixed linear controller. In the case of a set point tracking, performances in terms of rapidity are also appreciably improved compared to those of a linear controller, while guaranteeing stability, significant damping and absolute precision without residual strains when the commands are performed.

Active control of flexible structures using a fuzzylogic algorithm

This study deals with the development and applicationof an active control law for the vibration suppression ofbeam-like flexible structures experiencing transientdisturbances. Collocated pairs of sensors/actuators provideactive control of the structure. A design methodology for the closed-loop control algorithm based on fuzzy logic is proposed.First, the behavior of the open-loop system is observed. Then,the number and locations of collocated actuator/sensor pairsare selected. The proposed control law, which is based on theprinciples of passivity, commands the actuator to emulate thebehavior of a dynamic vibration absorber. The absorber is tuned to a targeted frequency, whereas the damping coefficient of thedashpot is varied in a closed loop using a fuzzy logic basedalgorithm. This approach not only ensures inherent stabilityassociated with passive absorbers, but also circumvents thephenomenon of modal spillover. The developed controller isapplied to the AFWAL/FIB 10 bar truss. Simulated results using MATLAB© show that the closed-loop system exhibitsfairly quick settling times and desirable performance, as wellas robustness characteristics. To demonstrate the robustness ofthe control system to changes in the temporal dynamics of theflexible structure, the transient response to a considerably perturbed plant is simulated. The modal frequencies of the 10 bar truss were raised as well as lowered substantially, therebysignificantly perturbing the natural frequencies of vibration.For these cases, too, the developed control law providesadequate settling times and rates of vibrational energydissipation.

A self-organizing fuzzy logic controller for the active control of flexible structures using piezoelectric actuators

Abstract This paper proposes an on-line self-organizing fuzzy logic controller (FLC) design applied to the control of vibrations in flexible structures containing distributed piezoelectric actuator patches. In this methodology, the fuzzy rules are generated using the history of input/output (I/O) pairs without using any plant model. The generated rules are stored in the fuzzy rule space and updated on-line by a self-organizing procedure. The validity of the proposed fuzzy logic control has been demonstrated experimentally in a steel cantilever test beam and a set of experimental tests are made in the system to verify the efficiency of the on-line self-organizing fuzzy controller.

Numerical methods for the control of flexible structures extended abstract of briffaut's thesis

AbstractThis paper is an extended abstract of the thesis of J.‐S. Briffaut. It treats the active control of flexible structures. In the first part the design of open‐loop control laws for beams is considered. In the second the implementation of Komornik's full state feed‐back law. In the third and fourth numerical results for the control of frames made of beams under bending and traction‐compression.

Piezoelectric actuators and sensors location for active control of flexible structures

A method for optimal positioning of piezoelectric actuators and sensors on a flexible structure is presented. First, a two-dimensional (2-D) model of a piezoelectric actuator bonded to a plate is obtained. Then, a Ritz formulation is used to find a state model of the system in view of its control. To define an optimal positioning strategy, an energy based approach is developed. This leads quite naturally to the study of controllability and observability properties of the overall dynamical model. A new criterion based on energy assessment is proposed to locate actuators and sensors.

Substructural neural network controller

A substructure-based neural network is proposed for the active control of flexible structures. A flexible structure is divided into substructures. Subsequently, subcontrollers are designed for these substructures using the linear quadratic regulator (LQR) control method. These subcontrollers are assembled to obtain the central feedback controller for the whole structure. A radial basis function neural network is trained to emulate the behavior of this central controller designed from substructure levels. The training is based only on the outputs of sensors collocated with the actuators. Therefore, two distinct advantages of the proposed neural network controller are noted as its training being based on substructural LQR controller and collocated sensor data. The performance of the neural network controller is compared favorably with the complete structural LQR controller for various input forces acting on a large flexible structure.

Actuators and Sensors Positioning for Active Vibration Control in Flexible Systems

Energetic criteria for optimal positioning of actuators and sensors in view of active control of flexible structure are defined. The structure is modeled as a finite dimension linear dynamical system and it is shown that controllability and observability gramian matrices lead to a criterion for optimal location of actuators and sensors. Numerical results are given in the case of a clamped beam and a clamped plate. An experimental study on a beam shows the efficiency of the positioning approach.

Optimization of Piezoactuator Configuration in Control of Flexible Structures

In order to find the optimum dimensions and locations of piezoactuators in the active control systems, a novel procedure for simultaneous dimension and location optimization of piezoactuators for active control of flexible structures is introduced. Three optimization criteria are investigated and compared which leads to an optimal configuration of the actuators particularly relevant when the weight and geometry limitations are important. In the first criterion we seek a configuration of the piezoactuator which maximizes the overall damping ratio of the closed loop system. Minimization of the overall real part of eigenvalues of the controlled system is the second criterion. For the third criterion, we seek the minimum LQR cost function over possible dimensions and locations. The optimization indicates that the best configuration of piezoactuators in active control systems is the shortest and widest.

Experimental study on active vibration control of a flexible cantilever using an artificial neural-network state predictor

Active control of flexible structures is crucial for the successful operation of large aerospace structures. One of the predominant difficulties in the active control of flexible structures is that such structures have a number of vibratory modes within or beyond the bandwidth of the controller. In the active control of flexible structures, spillover can occur because only a few vibratory modes are dealt with by the control. Although modal-space-based optimal control is known to avoid spillover, it requires a large number of sensors and actuators. In this study the modified independent modal space control (MIMSC) algorithm proposed by Baz et al is adopted to minimize the number of actuators. An artificial neural network is also proposed to identify the system characteristics and to reduce the number of sensors. Experiments are performed for the active vibration control of a flexible aluminum cantilever beam employing a piezoactuator. It is experimentally found that active control with the proposed artificial neural-network state predictor is able to suppress vibration successfully without spillover.

Integral formulas for non-self-adjoint distributed dynamic systems

Integral formulas for analytical prediction of the dynamic response of a class of non-self-adjo int distributed systems are studied. Combined non-self-adjoint effects of damping, gyroscopic, and circulatory forces are examined. The response of the distributed system subject to arbitrary external, boundary, and initial disturbances is obtained in a closed-form Green's function integral. The Green's function is expanded in an eigenfunction series, without assuming completeness of system eigenfunctions. In addition, a generalized reciprocal theorem is derived. ISTRIBUTED dynamic systems whose parameters are dependent on the spatial domain are common in many branches of science and technology. The mathematical description of these systems usually leads to boundary-init ial value problems associated with partial differential equations. The development of modern technologies, including optimal design and active control of flexible structures, requires accurate prediction of the dynamic response of distributed systems. This work investigates integral formulas for analytical prediction of the dynamic response of a class of linear distributed systems that have combined non-self-adjoint effects of damping, gyroscopic, and circulatory forces, and are under arbitrary external, boundary, and initial disturbances. Mainly, three issues are addressed: 1) Green's function formulation for transient response prediction, 2) modal expansion of system Green's function, and 3) a generalized reciprocal principle. These issues are important to structural dynamics and structural control and lay a foundation for the development of analytical and numerical solution methods. The concept of Green's functions is by no means new. It was first introduced by G. Green as early as 1828 and since has been applied to various problems in mathematical physics. Several excellent monographs on the subject have been published.14 Instead of its many advantages, the Green's function method has been for formal and

Active control of flexible structures by use of segmented piezoelectric elements

Active control of flexible structures by use of segmented piezoelectric elements

Optimal sensor location in active control of flexible structures

This paper presents a new algorithm for the optimal distribution of concentrated sensors to measure displacements or strains in flexible structures; this procedure is applicable in quasistatic shape control (e.g., parabolic mirrors). The proposed approach is based on the analysis of the properties of a linear matrix equation describing the modal strain decomposition, where observable as well as interfering modes are taken into account

Active Control of Flexible Structures Subject to Distributed and Seismic Disturbances

The purpose of this paper is to present a method of active control for suppressing the vibration of a mechanically flexible cantilever beam which is subject to a distributed random disturbance and also a seismic input at the clamped end. First, the mathematical model of the flexible structure is established by a stochastic partial differential equation which describes the Euler-Bernoulli type distributed parameter system with internal viscous damping and subject to the seismic and distributed random inputs. Second, the distributed parameter model, which is considered as an infinite-dimensional system, is reduced to a finite-dimensional one by using the modal expansion, and split into the controlled part and the uncontrolled (residual) one. The principal approach is to regard the observation spillover due to uncontrolled part as a colored observation noise and construct an estimator, and then we construct the optimal control system. Finally, simulation studies are presented by using a real earthquake accelerogram data.

Survey of experiments and experimental facilities for control of flexible structures

This paper presents a survey of ground experiments primarily conducted in the United States and U.S. facilities dedicated to the study of active control of flexible structures. The facilities are briefly described in terms of capability, configuration, size, and instruments. Topics on the experiments include vibration suppression, slewing control, and system identification. The experiments are listed in tables containing the experiment's name, the responsible organization, a brief description of the test article configuration, and the actuator/sensor devices used in the experiment. Selected experiments will be further discussed to help illustrate the control problems. Some of the test facilities dedicated to ground testing of large space structures are discussed in more detail, to give the reader a better appreciation of ground-testin g work. Several research issues are mentioned, including real-time computer systems, test article suspension, and new actuator/sensor technology development.

地震外乱および不規則外乱を受ける柔軟構造物のアクティブ制御

地震外乱および不規則外乱を受ける柔軟構造物のアクティブ制御

A first-order Lyapunov robustness method for linear systems with uncertain parameters

A method for stability-robustness analysis based on a quadratic Lyapunov function that varies linearly with uncertainty parameters is derived. Linear time-invariant systems with structured uncertainties are discussed. The Lyapunov function is optimized numerically to maximize the robustness region in parameter space. Numerical results are given for four examples in which the first-order method is compared to previous Lyapunov methods for robustness analysis. While the zero-order method is slightly better than the first-order method for one example, the first-order method is clearly superior in the other three, more realistic, examples. The first-order method is especially superior for applications to active control of flexible structures, where robustness with respect to unmodeled coupling between modeled modes are important issues. For such applications, the first-order method is much better at detecting the increased robustness associated with increased separation between frequencies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>