Asymmetric Time-varying Delays Research Articles

Distributed secondary frequency control scheme with A-symmetric time varying communication delays and switching topology

A distributed control of a Microgrid (MG) depends on the communication network for the exchange of information among the Distributed Generators (DGs). Most of the control schemes consider ideal communication among the DGs; however, in practical systems, delays are inherited in a system that can affect the dynamic performance and even destabilize an MG. Therefore, in this research work, delay independent distributed secondary frequency control for MGs is presented. Sufficient delay independent conditions for robust stability of the buffer-free Distributed Averaging Integral (DAI) control scheme is proposed while considering A-symmetric time varying communication delays and switching network topology. Moreover, in this work, slow as well as fast varying delays are analyzed using Lyapunov Krasovskii and Lyapunov Razumikhin's approach. Furthermore, a Lyapunov function based adaptive control approach is employed that updates the constant gain parameters to compensate for the uncertain or varying parameters. Finally, the efficacy of the controller is demonstrated through simulation studies that validate its performance in different scenarios.

An Adaptive Proportional Plus Damping Control for Teleoperation Systems with Asymmetric Time-Varying Communication Delays

Communication delay is an important factor affecting the stability and performance of telerobotic systems. In this paper, a new adaptive proportional damping controller is proposed to improve the stability and performance of the system in the presence of the cases such as asymmetric communication delay, unknown gravity torque, friction torque, and other disturbance torques. The proposed proportional damping control method combines the RBF neural network and adaptive control strategy to compensate for the unknown torque. The stability and robustness of the system are enhanced by adding error-damping items, operator force, and environmental force items. The Lyapunov–Krasovskii functional is employed to analyze and prove the exponential stability and signal boundedness of the closed-loop system. The simulation results verify the correctness of the proposed method, and the comparison with the results of other control methods shows the effectiveness of the designed control strategy.

Adaptive control for position and force tracking of uncertain teleoperation with actuators saturation and asymmetric varying time delays

Abstract This paper presents a new bounded force feedback control law to improve transparency in nonlinear bilateral teleoperation systems in the presence of three problems in practical applications of teleoperation systems such as input saturation, asymmetric time varying communication delays with no restriction on their rates of variation and parametric uncertainties, simultaneously. The proposed controller is a nonlinear-proportional plus nonlinear damping (nP + nD) controller with the addition of a nonlinear adaptive term and nonlinear function of the environment force on the slave side and nonlinear function of the human force and force error on the master side. Using a novel Lyapunov–Krasovskii functional, the asymptotic stability and position and force tracking performance of the teleoperation system are established under specific conditions on the controller parameters, actuator saturation characteristics and maximum allowable time delay. The validity of the theoretical results is corroborated by the simulation results.

Adaptive neural network control for flexible telerobotic systems with communication constraints

This paper investigates the synchronous control problem for a class of flexible telerobotic systems subject to system uncertainties and communication constraints. In view of the asymmetric time-varying communication delays, an adaptive time-delay estimator is designed to reduce the impacts of delays on the system. Moreover, by combining the neural networks and parameter adaptive method, the uncertainties of system dynamics are estimated and compensated. Based on these efforts, a new adaptive compensation control protocol is proposed. Additionally, input quantization in network control induced chattering phenomenon and unknown parameters is also dealt with by the adaptive compensation method. A useful characteristic of this paper is that the “complexity explosion” problem caused by the backstepping technique is circumvented effectively. Finally, sufficient conditions are derived for the synchronous control of the master-slave flexible telerobotic system under Lyapunov stability theory. A numerical example of flexible-joint robotic system is provided to illustrate the effectiveness of the proposed control schemes.

A Novel Delay-Dependent Finite-Time Control of Telerobotics System With Asymmetric Time-Varying Delays

Finite-time stability (FTS) is desirable in teleoperation control as it provides fast transient, high-precision, and better disturbance rejection properties. In most cases, a stringent condition on communication time delays or an additional time-delay estimation method is necessary to guarantee finite-time synchronization with the existing finite-time control schemes for the teleoperation system. This article proposes the first result of global finite-time synchronization control algorithm for the teleoperation system without any approximation function. Specifically, a novel proportional plus damping (P + d) like control algorithm is designed by employing a continuous nonsmooth function on the position synchronization errors and the velocity signals, dexterously. Furthermore, global FTS is proved with the Lyapunov stability theory based on linear-matrix-inequality (LMI) and geometric homogeneous techniques. The delay-dependent FTS criteria are also derived, which can be used to compute the allowable maximal transmission delay with the given control parameters. Finally, simulation results demonstrate the effectiveness of the proposed approach, and experiments on a teleoperated pair of three-degree-of-freedom (DOF) PHANToM robots are also presented to show the superior performances of the control strategy.

Adaptive-observer-based robust control for a time-delayed teleoperation system with scaled four-channel architecture

AbstractThis article presents an innovative adaptive-observer-based scaled four-channel (4-CH) control approach applying damping injection for nonlinear teleoperation systems, which unify the study of robotic dynamic uncertainties, operator/environment force acquirements and asymmetric time-varying delays in the same framework. First, a scaled 4-CH scheme with damping injection is developed to handle time-varying delay while guaranteeing the passivity of communication channels. Then, the improved extended active observer (IEAOB) is deployed to derive the operator/environment force while addressing the issues of measurement noise and model uncertainties. Furthermore, the system stability is analyzed by choosing Lyapunov functional. Finally, the proposed method is validated through simulation.

Finite-Time Synchronization Control for Bilateral Teleoperation Systems With Asymmetric Time-Varying Delay and Input Dead Zone

In this article, the synchronization control problem of bilateral teleoperation systems with time-varying delays and input dead zones is addressed. A novel radial basis function network (RBFN)-based adaptive finite-time synchronization control scheme is proposed, where system uncertainties, asymmetric time-varying delays, and dead-zone phenomena are considered simultaneously. Specifically, an RBFN is designed to approximate system uncertainties and unknown nonlinearities. The approximation error as well as the time-associated uncertainty and the nonlinear margin of the dead zone is compensated by an adaptive compensator. Using a Lyapunov-Krasovskii function and the finite-time stability criteria, the system is proved to be semiglobally practically finite-time stable. The theoretical analysis is given to prove the stability of the closed-loop system. The tracking performance of the designed controller is demonstrated by comparative simulation studies and experiment results.

Composite Adaptive Guaranteed Performances Synchronization Control for Bilateral Teleoperation System With Asymmetrical Time-Varying Delays.

This article studies the guaranteed performance synchronization control problem for networked bilateral teleoperation systems with system uncertainties. The communication channel connecting the master and the slave is subject to asymmetrical varying time delays with unknown upper bounds. The first result on prescribed performance synchronization control for the bilateral teleoperation system under such a weak assumption on the communication time delays is provided. Moreover, a novel composite adaptive control algorithm is proposed under a much weaker interval-excitation (IE) condition. More specifically, parameter adaptive estimation accuracy and speed are quantificationally ensured by employing a composite technique. Therefore, both steady-state performance and transient-state performance are achieved for the position synchronization and parameter estimation with the proposed control strategy. The Lyapunov function and the multidimensional small-gain framework are utilized to derive system stability criteria. It demonstrates that the allowable maximal derivatives of the transmission delays can be easily computed with the given parameters of the control algorithm and the nonlinear performance functions. Finally, both simulation and experimental results are provided to demonstrate the feasibility and superiority of the proposed composite adaptive strategy.

Modern Robotics: Mechanics, Planning, and Control [Bookshelf

This book offers a comprehensive contemporary approach to the modeling and control of robotic mechanisms. It presents results on stability analysis and control design of networked teleoperation systems. The text overviews commonly encountered nonlinear teleoperation systems, including the stability analysis of teleoperation systems with asymmetric time-varying delays and interval time delays. This book also presents several high-performance control schemes for teleoperation systems with and without velocity measurements and for systems with nonlinear inputs. The results presented here should be of interest to researchers and students in robotic control theory, nonlinear control theory, and networked control system theory. It is not just another undergraduate textbook on robotics. It offers a comprehensive contemporary approach to the modeling and control of robotic mechanisms. Methods and algorithms for modeling; motion planning; and control of serial, parallel, and mobile robots are introduced along with a thorough (yet accessible) treatment of the geometry of motion. It is the pedagogical strength of this book that concepts from Lie group theory (which form the building blocks of modern kinematics) are presented in a way that will appeal to undergraduate students as well as to researchers and roboticists in general. The reader is given the necessary tools to model the kinematics and dynamics of a robot, plan its motion, and control it. These are the features that distinguish this book from other excellent references in the area of advanced modeling and control of robotic systems.

A simple algebraic criterion for stability of Bilateral Teleoperation Systems under time-varying delays

Abstract Stability analysis of Bilateral Teleoperation Systems (BTSs) is addressed, considering a control architecture subject to asymmetric time-varying delays in the communication links between the locally operated and remote robots. The manipulators are modeled as nonlinear second-order vibrating systems in generalized coordinates and are controlled by the delayed position-error feedback. The Lyapunov-Krasovskii (LK) theory is used to obtain a simple algebraic stability test. By means of this result, it is possible to compute the controller gains, given that the maximum delays in communication are known. Alternatively, if gains are known in advance, it is possible to determine the maximum delays at which the system will remain stable. Numerical experiments show that the proposed test is less conservative or provide the same results than comparable methods available in the literature. Finally, to close the paper, real-world trials illustrate the effectiveness of our result.

Stability analysis of nonlinear telerobotic systems with time-varying communication channel delays using general integral inequalities

Existing controller synthesis schemes for teleoperation of nonlinear master-slave systems with time-varying communication channel are subject to conservative stability criteria. This paper presents a new stability criteria for bilateral tele-operation systems with proportional-derivative, position-position and position-force control architectures, considering both passive/non-passive human operator. The communication channel pertains unknown asymmetric time-varying delays with given lower and upper-bounds. Using the Lyapunov Krasovskii approach, the stability analysis of the dynamic system is examined and the stability conditions are derived in the form of Linear Matrix Inequalities (LMIs). Advanced techniques have been employed to find less conservative integral inequalities in the process of stability analysis of the closed-loop teleoperator. Illustrative numerical examples and simulation results emphasize the effectiveness of the proposed stability criteria in enlarging the stability bounds and providing efficient control performances.

Finite-time consensus for nonlinear multi-agent systems with time-varying delay: An auxiliary system approach

This paper investigates the finite-time consensus problem of uncertain nonlinear multi-agent systems with asymmetric time-varying delays and directed communication topology. An auxiliary system is firstly designed to deal with the continuous or discontinuous time-varying communication delays. Based on the finite-time input-to-output framework, a novel consensus scheme relying on local delayed information exchange is proposed. Moreover, by utilizing an auxiliary integrated regressor matrix and vector method, the system uncertainties can be accurately estimated. Then the consensus of multi-agent systems can be achieved within finite time by selecting the control gains simply. Finally, numerical simulations are provided to demonstrate the effectiveness of the proposed control algorithms.

Energy-Optimized Consensus Formation Control for the Time-Delayed Bilateral Teleoperation System of UAVs

This paper proposes an energy-optimized consensus formation scheme for the time-delayed bilateral teleoperation system of multiple unmanned aerial vehicles (UAVs) in the obstructed environment. To deal with the asymmetric time-varying delays in aerial teleoperation, the local damping is independently distributed on both sides to enforce consensus formation and force tracking of the master haptic device and the slave UAVs. The stability of the time-delayed aerial teleoperation system is analyzed by the Lyapunov function. In addition, a flux-conserved force field is incorporated into the aerial teleoperation system to guarantee a collision-free consensus formation in the obstructed environment. Moreover, to reduce the communication complexity and energy dissipation of the formation, a top-down strategy of 3D optimal persistent graph is first proposed to optimize the formation topology. Under the optimized topology with environmental constraints, communication complexity and energy dissipation can be minimized while the rigid formation can be maintained and transformed persistently in the obstructed environment. Finally, the human-in-the-loop simulations are performed to validate the effectiveness of the proposed scheme.

P-like controllers with collision avoidance for passive bilateral teleoperation of a UAV

PurposeThis paper aims to tele-operate the movement of an unmanned aerial vehicle (UAV) in the obstructed environment with asymmetric time-varying delays. A simple passive proportional velocity errors plus damping injection (P-like) controller is proposed to deal with the asymmetric time-varying delays in the aerial teleoperation system.Design/methodology/approachThis paper presents both theoretical and real-time experimental results of the bilateral teleoperation system of a UAV for collision avoidance over the wireless network. First, a position-velocity workspace mapping is used to solve the master-slave kinematic/dynamic dissimilarity. Second, a P-like controller is proposed to ensure the stability of the time-delayed bilateral teleoperation system with asymmetric time-varying delays. The stability is analyzed by the Lyapunov–Krasovskii function and the delay-dependent stability criteria are obtained under linear-matrix-inequalities conditions. Third, a vision-based localization is presented to calibrate the UAV’s pose and provide the relative distance for obstacle avoidance with a high accuracy. Finally, the performance of the teleoperation scheme is evaluated by both human-in-the-loop simulations and real-time experiments where a single UAV flies through the obstructed environment.FindingsExperimental results demonstrate that the teleoperation system can maintain passivity and collision avoidance can be achieved with a high accuracy for asymmetric time-varying delays. Moreover, the operator could tele-sense the force reflection to improve the maneuverability in the aerial teleoperation.Originality/valueA real-time bilateral teleoperation system of a UAV for collision avoidance is performed in the laboratory. A force and visual interface is designed to provide force and visual feedback of the slave environment to the operator.

Finite-Time Control of Teleoperation Systems With Input Saturation and Varying Time Delays

This paper develops a finite-time control approach for nonlinear teleoperation systems, which is capable of unifying the study of model uncertainties, actuator saturation, and asymmetric time-varying delays in the same framework. First, a novel anti-windup compensator is designed to analyze the effect of actuator saturation. To achieve the finite-time tracking, a nonsmooth generalized switched filter is also investigated. By introducing the anti-windup compensator and the generalized switched filter into the adaptive fuzzy control torque design, a novel finite-time controller is developed. By using the multiple Lypaunov–Krasovskii functionals method, the resulting closed-loop system is state-independent input-to-output practical stable (SIIOpS) and based on this, it is proved to be finite-time SIIOpS. It is shown that the asymptotic convergence of the adaptive estimation errors and the finite-time convergence of the position tracking errors are obtained, whether the robots contact with the human operator/environment or not. Finally, the effectiveness is demonstrated by the simulation results.

A Novel Switching-Based Control Framework for Improved Task Performance in Teleoperation System With Asymmetric Time-Varying Delays.

This paper addresses the adaptive control for task-space teleoperation systems with constrained predefined synchronization error, where a novel switched control framework is investigated. Based on multiple Lyapunov-Krasovskii functionals method, the stability of the resulting closed-loop system is established in the sense of state-independent input-to-output stability. Compared with previous work, the developed method can simultaneously handle the unknown kinematics/dynamics, asymmetric varying time delays, and prescribed performance control in a unified framework. It is shown that the developed controller can guarantee the prescribed transient-state and steady-state synchronization performances between the master and slave robots, which is demonstrated by the simulation study.

Multilateral Telecoordinated Control of Multiple Robots With Uncertain Kinematics.

This paper addresses the telecoordinated control of multiple robots in the simultaneous presence of asymmetric time-varying delays, nonpassive external forces, and uncertain kinematics/dynamics. To achieve the control objective, a neuroadaptive controller with utilizing prescribed performance control and switching control technique is developed, where the basic idea is to employ the concept of motion synchronization in each pair of master-slave robots and among all slave robots. By using the multiple Lyapunov-Krasovskii functionals method, the state-independent input-to-output practical stability of the closed-loop system is established. Compared with the previous approaches, the new design is straightforward and easier to implement and is applicable to a wider area. Simulation results on three pairs of three degrees-of-freedom robots confirm the theoretical findings.

Fixed-time Coordination Control for Bilateral Telerobotics System with Asymmetric Time-varying Delays

Fixed-time coordination in dynamical systems means system trajectories converge to the desired trajectories in determined time which is independent of the system initial states. In this paper, a novel fixed-time coordination control approach for nonlinear telerobotics system with asymmetric time-varying delays is proposed to provide faster convergence rate and higher convergence precision. The neural networks (NNs) and the parameter adaptive method are combined to approximate the uncertain model of the teleoperator, the upper bound of the NNs estimation errors and the external disturbances. Then the corresponding adaptive NNs fixed-time controller is designed without using the derivatives of the time-varying delays. Dynamic surface control (DSC) is employed to avoid the singularity. Moreover, considering the nonpassive human operator and remote environment insert forces, the stability criterion for the closed-loop system is also developed. Then by choosing proper Lyapunov functions, the master-slave coordination errors converging into a deterministic domain in fixed-time with the new controller is proved in the presence of the exogenous forces from human operator and remote environment. Furthermore, the exact convergence time is presented only with the designed parameters. Some comparisons are conducted in simulation to show the superior performance of the proposed control approach. Finally, experimental results are also given to demonstrate the effectiveness of the new control method.

Adaptive Control for Teleoperation System With Varying Time Delays and Input Saturation Constraints

This paper addresses the adaptive control of teleoperation system with actuator saturation. To unify the study of actuator saturation, passive/nonpassive external forces, asymmetric time-varying delays, and unknown dynamics in the same framework, a novel switched control scheme is developed, where a special switched filter is investigated. In the saturation scenario, the designed controller consists of a generalized controller and a nonlinear saturation function. By placing the nonlinear saturation function on the outside of the generalized controller, and further jointing with the design of switched filter, the designed generalized controller needs not consider the actuator saturation. Specifically, it is designed to be in the form of proportional plus damping injection plus switched filter. Then, the complete closed-loop system is modeled as a special switched system. It is finally established to be state-independent input-to-output stable, where the ultimate boundedness of the tracking error is ensured for any bounded exogenous forces, which is demonstrated by the experimental studies.

Adaptive Control of Semi-Autonomous Teleoperation System With Asymmetric Time-Varying Delays and Input Uncertainties.

This paper addresses the adaptive task-space bilateral teleoperation for heterogeneous master and slave robots to guarantee stability and tracking performance, where a novel semi-autonomous teleoperation framework is developed to ensure the safety and enhance the efficiency of the robot in remote site. The basic idea is to stabilize the tracking error in task space while enhancing the efficiency of complex teleoperation by using redundant slave robot with subtask control. To unify the study of the asymmetric time-varying delays, passive/nonpassive exogenous forces, dynamic parameter uncertainties and dead-zone input in the same framework, a novel switching technique-based adaptive control scheme is investigated, where a special switched error filter is developed. By replacing the derivatives of position errors with their filtered outputs in the coordinate torque design, and employing the multiple Lyapunov-Krasovskii functionals method, the complete closed-loop master (slave) system is proven to be state-independent input-to-output stable. It is shown that both the position tracking errors in task space and the adaptive parameter estimation errors remain bounded for any bounded exogenous forces. Moreover, by using the redundancy of the slave robot, the proposed teleoperation framework can autonomously achieve additional subtasks in the remote environment. Finally, the obtained results are demonstrated by the simulation.