Control Of Large Flexible Structures Research Articles

A semi-active shunted piezoelectric tuned-mass-damper for multi-modal vibration control of large flexible structures

A semi-active electromechanical Tuned Mass Damper (SATMD), which consists of a combined spring-piezoelectric device connected to an external resistive-inductive electric circuit is presented, aiming to provide robust multi-modal vibration suppression capabilities in large flexible structures. The combined spring-piezoelectric device provides the stiffness for the resonant mass, and also electromechanical energy conversion and coupling. A reduced-ordered mode superposition structural dynamics model coupled with the SATMD device and the RL shunt electric circuit is formulated, to simulate the response of the integrated structural system. The broadband vibration reduction capabilities of the proposed SATMD are numerically and experimentally evaluated and quantified on a down-scaled simplified airframe model. Very good correlation between numerical and measured results is obtained. The results illustrate that a SATMD configuration with an auxiliary mass equal to 1% of the structural mass and combined resistive-inductive impedance, yields substantial simultaneous vibration suppression over the range of 3 low-frequency structural modes, and can be easily retuned to accommodate in-flight changes in structural and loading parameters.

Consensus Vibration Control for Large Flexible Structures of Spacecraft With Modified Positive Position Feedback Control

In this brief, consensus modified positive position feedback (CMPPF) is proposed to depress the vibration of large flexible structure in the spacecraft. CMPPF is formulated by decentralizing and distributing the modified positive position feedback (MPPF) to a network of control agents. Variables are appropriately selected and the consensus algorithm is employed to make the multiagents consensus with each other. CMPPF convergence conditions are derived and the control parameters are optimized. Amplitude-frequency response analysis and simulations demonstrate that CMPPF suppresses vibrations faster and more evidently than MPPF. Results also indicate how consensus between agents is realized and how agents’ disagreement is eliminated. Effects of different consensus variables and different communication topologies are studied. Meanwhile, results for different types of agents’ failure are presented. CMPPF is robust to topology and agents’ failure and achieves satisfactory performances.

Hybrid frequency domain control for large flexible structures

A hybrid finite frequency controller is proposed for the vibration suppression of a large flexible structure mounted with collocated sensors and actuators. The controller has passive characteristics at low frequencies and small gain characteristics at high frequencies. Compared with a strictly positive real controller based on the standard Kalman–Yakubovich–Popov lemma, the hybrid finite frequency controller has less energy consumption but can obtain approximately identical performance. Furthermore, when the plant passivity is violated at high frequencies by noncollocation of sensors and actuators, the strictly positive real controller based on the Kalman–Yakubovich–Popov lemma is no longer able to attenuate the vibration of the large flexible structures, while the hybrid finite frequency controller is effective in suppressing the vibration and avoiding spillover instability. Simulation results are presented to validate the effectiveness of the hybrid finite frequency controller.

Parallel Feedforward and Simple Adaptive Control of Flexible Structures: First-Order Pole Instead of Collocated Velocity Sensors?

Stable control of large flexible structures has long been a challenge. Even though other research showed that direct velocity control and then position-and-velocity control are feasible, they require perfect or almost perfect collocation of velocity sensors and actuators. A very simple parallel feedforward device, which uses basic stabilizability properties of systems in order to allow implementation of strict positive real configurations, is tested here and is shown to eliminate the need for velocity feedback and collocation.

Wave based optimization of distributed vibration absorbers

The concept of distributed vibration absorbers or DVAs has been investigated in recent years as a method of vibration control and sound radiation control for large flexible structures. These devices are comprised of a distributed compliant layer with a distributed mass layer. When such a device is placed onto a structure it forms a sandwich panel configuration with a very soft core. With this configuration the main effect of the DVA is to create forces normal to the surface of the structure and can be used at low frequencies to either add damping, where constrain layer damper treatments are not very effective, or to pin the structure over a narrow frequency bandwidth (i.e., large input impedance/vibration absorber approach). This paper analyses the behavior of these devices using a wave based approach and finds an optimal damping level for the control of broadband disturbances in panels. The optimal design is calculated by solving the differential equations for waves propagating in coupled plates. It is shown that the optimal damping calculated using the infinite case acts as a good ‘‘rule of thumb’’ for designing DVAs to control the vibration of finite panels. This is bourn out in both numerical simulations and experiments.

Adaptive control of a composite cantilever beam with piezoelectric damping-modal actuators/sensors

Modeling and vibration control of a smart beam is investigated using piezoelectric damping-modal actuators/sensors. Theoretical formulations based on damping-modal actuator/sensors and numerical solutions are presented for the analysis of laminated composite beam with integrated sensors and actuators. Emphasis in this study is also given to the fiber orientation and the effect of actuator location on the control system. An instantaneous optimal close loop control algorithm coupling the direct and inverse piezoelectric effect is presented and used as an adaptive shape control of the dynamic response of the integrated laminated structure. An illustrative example, vibration control of large flexible structures is performed. A good correspondence has been obtained in all the examined results.

On the use of system modes to model multibody flexible structures

This study has the purpose of bringing to light flexibility modelling issues in connection with multibody dynamic simulation. Towards this end, an examination is made of fundamental concerns that arise when one seeks to formulate equations of motion for simulation of dynamics and control of large flexible structures. Quantitative criteria are provided regarding modal discretization and model reduction techniques. In particular, the thermo-structural modelling and interaction effects on the system modal spectrum are investigated using system modes. This approach allows a more accurate modelling of the thermal–structural interaction in large flexible space structures.

γ-PASSIVE SYSTEM AND ITS APPLICATION TO THE CONTROL OF LSS

In this paper a concept of γ-passivity is introduced from the view-point of energy dissipation. In linear systems, a γ-passive system has an interesting phase property. The phase property of γ-passive systems leads to a phase stability theorem which is a generalization of the passivity theorem. Using the idea of the phase stability, control of large flexible structures is considered. A practical criterion for robust stability concerning unmodeled dynamics is obtained.

Decentralized control of large flexible structures by joint decoupling

A decentralized control design method is presented for large complex flexible structures by using the idea of joint decoupling. The derivation is based on a coupled substructure state-space model, which is obtained from enforcing conditions of interface compatibility and equilibrium to the substructure state-space models. It is shown that by restricting the control law to be localized state feedback and by setting the joint actuator input commands to decouple joint 'degrees of freedom' (dof) from interior dof, the global structure control design problem can be decomposed into several substructure control design problems. The substructure control gains and substructure observers are designed based on modified substructure state-space models. The controllers produced by the proposed method can operate successfully at the individual substructure level as well as at the global structure level. Therefore, not only control design but also control implementation is decentralized. Stability and performance requirement of the closed-loop system can be achieved by using any existing state feedback control design method. A two-component mass-spring damper system and a three-truss structure are used as examples to demonstrate the proposed method.

Experimental study of robustness in adaptive control for large flexible structures

An experimental study is performed to investigate the robustness of model reference adaptive control for the large flexible structures control application. The main nonidealities of concern are unmodeled dynamics, input saturation, and time-delay effects (here, actuator and sensor dynamics are lumped into the last item for convenience). This study focuses on the robustness with respect to input saturation and time-delay effects, since robustness to unmodeled dynamics is inherent to the basic algorithm and has been demonstrated experimentally elsewhere. N experimental study is performed to investigate the robustness of model reference adaptive control for the large flexible structures control application. Although adaptive control methods are robust to parametric uncertainty by design, other types of nonidealities are known to lead to degradation and even instability of the closed-loop adaptive system. The main nonidealities of concern in the flexible structures control application are unmodeled dynamics, input saturation, and time-delay effects (here, actuator and sensor dynamics are lumped into the last item for convenience). Because of the use of the command generator tracker (CGT) approach, the adaptive algorithm considered here achieves tracking objectives that are in theory robust to unmodeled dynamics.1'2 This theoretical robustness to unmodeled dynamics has also been verified experimentally in Refs. 3 and 4 and will not be an issue in the present study. In contrast, there are presently no assurances as to the stability of the adaptive system to input saturation and time-delay effects. These latter issues will be the focus of the present study. It is shown experimentally in this paper that the basic adaptive algorithm is robust to input saturation, whereas timedelay effects can cause significant degradation and even instability. It is also shown experimentally that stability in the presence of time delay can be recovered by using a technique advocated by Bar-Kana5 of placing a small feedforward on the plant (or equivalently for the regulation problem, of placing a small feedback on the compensator). This stabilizes the closedloop system and recovers a certain degree of performance in the process. As a side benefit, the input torque requirements are also reduced. Certain theoretical results are included in this paper to support the experimental effort. In particular, it is shown that for structures with collocated actuators and sensors, there always exists a bounded feedforward gain that guarantees L2 stability of the closed-loop adaptive system in the presence of a pure time delay.

Dual Active and Passive Control of Large Flexible Structures

A unified passive damping design algorithm, using active control design techniques and least squares method, is developed to improve the stability and performance of closed-loop controlled structures. To achieve the stringent requirements of large flexible structures (LFS), dual active/passive control using interacting substructure decentralized control and unified passive damping design method is introduced. Physical coordinates are used in modeling; since no modal data is used, no modal errors are involved in the modeling process. Examples are presented to illustrate the design procedures and their effectiveness.

Direct position plus velocity feedback control of large flexible space structures

The authors demonstrate the feasibility of shape and position control of large flexible structures with collocated sensors and actuators using direct position-plus-velocity feedback. This result is important for large space structures where the number of modes is very large and eventually unknown. When the number of inputs equals the number of outputs, the stabilizing feedback gain stands for any positive definite matrix, including diagonal matrices. This result may explain the success of decentralized adaptive controllers when a reasonable number of sensors is used to satisfy the observability assumption.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Control of Large Flexible Structures Using Pole Placement Technique

The paper considers two methods for active control of large flexible structures using pole assignment for the purpose of stabilizing the neglected dynamics of the unmodeled higher modes of vibration. The first one based on pole placement in a vertical strip has the merit of minimizing control forces and infusing damping in a wide range of modal frequencies. The second approach based on using linear state feedback regulator with Kalman filter observer also uses pole placement in a prescribed region through a quite natural and easy design of the regulator and observer. Both methods have been applied for active stabilization of a flexible feed-support structure for a large parabolic antenna.

Practical Implementation Issues for Active Control of Large Flexible Structures

Most active control strategies, whether designed in the discrete or continuous domain, will most likely be implemented using a digital control system. Therefore, it is important to study the effects of digital implementation on the desired control law. In this work, the effect of quantization due to the finite wordlength of microprocessors, analog-to-digital, and digital-to-analog converters, on the desired control law is investigated. Additionally, the practical effect of actuator dynamics on the stability and performance of the control law is addressed. Finally, an active control experiment is reported on which takes into account and demonstrates some of these practical considerations.

Integrated control of large flexible structures

A procedure for the design of algebraic feedback that aims to improve the stability of flexible structures is presented. This algebraic controller design can be integrated into the design of a reduced-order dynamic controller. The algebraic feedback design is developed and improved from earlier works. An application to the solar optical telescope (SOT) model is shown.

Application of Adaptive Observers to the Control of Flexible Spacecraft

A difficulty in the control of large flexible structures arises from model uncertainty of a deterministic nature. The modern state-space theory of quadratic regulators yields a robust feedback design, that is one that is relatively insensitive to uncertainty. However, the state estimator (i.e. asymptotic observer) limits the overall robustness of the controller. State estimation may be enhanced by using Kreisselmeier's (1982) continuous-time adaptive observer, modified to adapt on a small number of physically meaningful parameters. The above techniques are applied to the stationkeeping-mode attitude control of a possible growth version of OLYMPUS having much larger solar arrays. No special test signal is used to force the convergence of the parameter identification loop. The controllers are evaluated in the presence of noise, thruster nonlinearity and unmodelled dynamics. The use of the adaptive observer is found to enhance the robustness of the controller, whilst maintaining the pointing within specification. The method shows promise for more general flexible space structures.

Lumped Parameter Dynamic Models for Large Space Structures with Flexible and Rigid Parts

The active control of large flexible structures has become a major topic in many fields of activity such as the stabilization of artificial satellites with extended solar panels or antennas, the design of lighter and saffer aircraft, the construction of antiseismic structures and buildings.As it is well known, the parameters of these kinds of systems are intrinsecally distributed, i.e. the mathematical models must use partial differential equations (the derivatives being made with respect to time and space). Unfortunately, in order to design active controls the models of the systems must employ ordinary differential equations, that is, should have lumped (and not distributed) parameters.The aim of this paper is to show a procedure in order to obtain lumped parameter models for systems described by sets of ordinary and partial differential equations, that is for systems having both rigid and flexible parts.The proposed procedure relies on an “ad hoc” application of the well known method of solution of partial differential equations using Fourier series expansions, that is the method which underlies most of the studies on the dynamics of structures.

Enhanced modal control of flexible structures via innovations feedthrough

Abstract Active control of large flexible structures in space requires the control of a very large dimensional system with one of substantially lower dimension. Modern modal control (MMC) has been developed previously to deal with this active structure problem ; however, control and observation spillover (as well as modelling error) can seriously degrade the controller performance by causing pole-shifts from the desired closed-loop locations. In this paper, the original MMC is enhanced by the addition of an innovations feedthrough term to the control law and a residual mode aggregation term to the state estimator. Under conditions presented the enhanced MMC can eliminate the observation spillover from critical residual modes ; hence, the spillover-induced pole shifting in these modes can be mitigated without changing the design of the original MMC. As shown, the trade-off is that the number of residual modes that can bo so enhanced is directly related to the number of available sensors