Ali Reza Mehrabian

A novel technique for optimal placement of piezoelectric actuators on smart structures

The problem of positioning of actuators and sensors on smart materials has been a point of interest in recent years. This is due to the fact that in many practical applications there are limitations in space, weight, etc. of the smart structures, which make the problem of positioning more complex. In addition, it is required that the actuators/sensors have the best possible performance. The development of smart structures technology in recent years has provided numerous opportunities for vibration control applications. The use of piezoelectric ceramics or polymers has shown great promise in the development of this technology. The employment of piezoelectric material as actuators in vibration control is beneficial because these actuators only excite the elastic modes of the structures without exciting the rigid-body modes. This is important since very often only elastic motions of the structures are needed to be controlled. The purpose of this paper is to introduce a novel approach developed for optimizing the location of piezoelectric actuators for vibration suppression of flexible structures. A flexible fin with bonded piezoelectric actuators is considered in this study. The frequency response function (FRF) of the system is then recorded and maximization of the FRF peaks is considered as the objective function of the optimization algorithm to find the optimal placement of the piezoelectric actuators on the smart fin. Three multi-layer perceptron neural networks are employed to perform surface fitting to the discrete data generated by the finite element method (FEM). Invasive weed optimization (IWO), a novel numerical stochastic optimization algorithm, is then employed to maximize the weighted summation of FRF peaks. Results indicate an accurate surface fitting for the FRF peak data and an optimal placement of the piezoelectric actuators for vibration suppression is achieved.

Cooperative tracking control of Euler-Lagrange systems with switching communication network topologies

Formation control of multiple agents has been studied extensively in the past few years. In most of these studies the structure of the communication network was considered to be fixed. However, in some applications this assumption may not hold, specially when the communication among the agents depends on their relative distance or attitude. In this paper, the problem of formation control of multiple Euler-Lagrange (EL) systems under switching network topologies is considered. Our proposed distributed control algorithm guarantees state synchronization and trajectory tracking under arbitrary switching among a family of connected communication topologies. Our proposed control algorithm is extended to cooperative state regulation of multiple EL systems. Simulation results show the effectiveness of our developed control algorithms.

Constrained distributed cooperative synchronization and reconfigurable control of heterogeneous networked Euler-Lagrange multi-agent systems

The main objective of this paper is to design distributed cooperative synchronization and reconfigurable control strategies for a network of heterogeneous multi-agent Euler-Lagrange (EL) systems by taking into account constraints on the control inputs and actuator saturation faults. First, bounded distributed cooperative synchronization (or consensus seeking) controllers are developed by using full state feedback. It is shown that boundedness of the control effort is guaranteed independent of the initial conditions. Second distributed output feedback (i.e. without using full state feedback) controllers are developed for cooperative synchronization. The third objective is to design reconfigurable distributed controllers in presence of actuator saturation faults. Finally, our last objective is to develop a switching-based distributed control reconfiguration strategy that is utilized in case of an actuator fault or an actuator saturation constraint to accomplish cooperative control of networked EL multi-agent systems. Towards the above end, we introduce two classes of distributed controllers that can be used to maintain the overall control objectives of the networked EL multi-agent systems in both the absence and in the presence of actuator faults and actuator constraints. We introduce a procedure that can be employed to switch between the two distributed constrained controllers. In presence of actuator faults and actuator saturations, a switching mechanism is proposed to yield a reconfigurable controller for the networked EL multi-agent system for ensuring and maintaining the overall mission objectives and requirements.

Distributed and cooperative quaternion-based attitude synchronization and tracking control for a network of heterogeneous spacecraft formation flying mission

Abstract Distributed control strategies for the attitude synchronization and set-point tracking control of multiple heterogeneous spacecraft (SC) in a formation flying mission are proposed in this work. The first scheme requires feedback and exchange of angular velocity measurements among the SC in the formation. However, the second scheme does not require measurement and exchange of angular velocities (or their estimates) among the SC in the formation. We have employed unit-quaternion, which is a singularity free attitude representation, to describe the SC attitude so that large attitude maneuvers can be executed. We have also developed two constrained control schemes for attitude synchronization and set-point tracking control for (i) a single SC with and without angular velocity feedback, and (ii) SC formation flying with and without angular velocity feedback. A number of simulation case studies are provided to demonstrate the advantages and benefits of our proposed algorithms as compared to the available results in the literature.

State Synchronization of Networked Euler-Lagrange Systems with Switching Communication Topologies Subject to Actuator Faults

Abstract Reconfigurable control of networked heterogeneous Euler-Lagrange (EL) systems subject to actuator faults is considered in this paper. It is assumed that the communication network is time-varying (switching). We first introduce a distributed control strategy for state synchronization of multiple EL systems. This controller is denoted as the “nominal” controller. To guarantee state synchronization of the switching communication network topologies we require existence of a non-vanishing dwell-time between any two sequential switches. Next, we consider two types of actuator faults namely (1) an additive actuator fault, and (2) a loss of effectiveness actuator fault. By employing the nominal control algorithm developed for state synchronization, we introduce two other control algorithms for state synchronization in presence of the faults. Simulation results illustrate and demonstrate the effectiveness of our proposed control algorithms.

Coordinated Attitude Control of Spacecraft Formation without Angular Velocity Feedback: A Decentralized Approach ∗

In this paper, motivated by recent developments of velocity-free spacecraft (SC) attitude control techniques and behavioral-based SC formation control a decentralized control algorithm for attitude coordination of SC formation without angular velocity feedback is presented. Asymptotic stability of the SC formation is guaranteed by using Lyapunov analysis and LaSalle’s theorem. The advantage of our proposed algorithm is that it requires limited information exchange among the SC in the formation (only attitude information exchange is necessary). Additionally, the proposed algorithm can be extremely useful when angular velocity information of the SC in the formation in not available due to sensor failures or communication constraints. Unlike other popular methods in the robotics area which tend to assume simple dynamics such as linear systems and single or double integrator dynamic models, in this paper, the full nonlinear attitude dynamics of the SC is considered to track fast time-varying reference trajectories.

The Concept of Stratified Sampling of Execution Traces

Execution traces can be overwhelmingly large. To reduce their size, sampling techniques, especially the ones based on random sampling, have been extensively used. Random sampling, however, may result in samples that are not representative of the original trace. We propose a trace sampling framework based on stratified sampling that not only reduces the size of a trace but also results in a sample that is representative of the original trace by ensuring that the desired characteristics of an execution are distributed similarly in both the sampled and the original trace.

Velocity synchronization of networked Euler-Lagrange systems with switching network topologies subject to actuator faults

In this paper, we first introduce a distributed control strategy for velocity synchronization (or velocity consensus seeking) of multiple heterogeneous Euler-Lagrange (EL) systems with switching communication network topologies. This controller is denoted as the “nominal” controller. To guarantee velocity synchronization for switching communication network topologies we require existence of non-vanishing dwell-time between any two sequential switches. Next, we consider two types of actuator faults namely (1) additive actuator fault, and (2) loss of effectiveness actuator fault. By employing the nominal control algorithm developed for velocity synchronization, we introduce two control algorithms for velocity synchronization in presence of the two types of faults. Simulation results illustrate and demonstrate the effectiveness of our proposed control algorithms.

Reconfigurable control of networked nonlinear Euler-Lagrange systems subject to fault diagnostic imperfections

The main objective of this paper is to design a distributed reconfigurable controller for networked nonlinear Euler-Lagrange (EL) systems in presence of actuator faults and imperfections in the fault detection and identification (FDI) algorithm. Specifically, we propose an adaptive distributed control algorithm which has the capability of estimating the faults (both intermittent and permanent). We incorporate the information provided from the FDI algorithm (which is assumed to be running in parallel with the controller) in the design of the adaptive controller. We consider three main types of imperfections in the FDI algorithm, namely, (1) fault detection imperfection, that is when fault is not detected by the FDI algorithm, (2) fault isolation imperfection, that is when the fault is detected in the wrong channel or in the wrong agent, and (3) fault identification imperfection, that is when the fault estimation is not exact. We show that our proposed distributed reconfigurable controller can maintain the closed-loop networked EL systems stability under these scenarios and can improve the performance of the closed-loop system in the third scenario. Simulation results for the attitude control of a network of spacecraft demonstrate the effectiveness and capabilities of our proposed distributed reconfigurable control algorithm.

Distributed Formation Recovery Control of Heterogeneous Multiagent Euler–Lagrange Systems Subject to Network Switching and Diagnostic Imperfections

This brief is concerned with the design of distributed formation recovery control laws for nonlinear heterogeneous multiagent Euler-Lagrange (EL) systems that are simultaneously subject to: 1) diagnostic information imperfections and unreliabilities; 2) parametric uncertainties and external disturbances; and 3) random switching of communication network topologies. The proposed recovery control techniques ensure both state synchronization and set-point tracking of a team of multiagent systems, while the agents have access only to local information. Our results are obtained for both fixed and switching communication network topologies. Distributed control recovery solutions for a general class of nonlinear multiagent EL systems have not been investigated earlier in the literature under the above simultaneous three realistic scenarios. The simulation results for the attitude control of a network of eight spacecraft tasked in a formation flying mission subject to communication topology switching demonstrate the effectiveness and capabilities of our proposed distributed recovery control strategies.