Presence Of Communication Time Delay Research Articles

Hierarchical Cooperative Control of Connected Vehicles: From Heterogeneous Parameters to Heterogeneous Structures

As one of the typical applications of connected vehicles (CVs), the vehicle platoon control technique has been proven to have the advantages of reducing emissions, improving traffic throughout and driving safety. In this paper, a unified hierarchical framework is designed for cooperative control of CVs with both heterogeneous model parameters and structures. By separating neighboring information interaction from local dynamics control, the proposed framework is designed to contain an upper-level observing layer and a lower-level tracking control layer, which helps address the heterogeneity in vehicle parameters and structures. Within the proposed framework, an observer is designed for following vehicles to observe the leading vehicle's states using neighboring communication, while a tracking controller is designed to track the observed leading vehicle using local feedback control. Closed-loop stability in the absence and presence of communication time delay is analyzed, and the observer is further extended to a finite time convergent one to address string stability under general communication topology. Numerical simulation and field experiment verify the effectiveness of the proposed method.

Robust finite-time consensus subject to unknown communication time delays based on delay-dependent criteria

In this paper, robust finite-time consensus of a group of nonlinear multi-agent systems in the presence of communication time delays is considered. In particular, appropriate delay-dependent strategies which are less conservative are suggested. Sufficient conditions for finite-time consensus in the presence of deterministic and stochastic disturbances are presented. The communication delays don’t need to be time invariant, uniform, symmetric, or even known. The only required condition is that all delays satisfy a known upper bound. The consensus algorithm is appropriate for agents with partial access to neighbor agents’ signals. The Lyapunov–Razumikhin theorem for finite-time convergence is used to prove the results. Simulation results on a group of mobile robot manipulators as the agents of the system are presented.

Finite time consensus of nonlinear multi-agent systems in the presence of communication time delays

In this paper, the finite-time leader-follower consensus of nonlinear Lagrangian multi-agent systems in the presence of communication time delays and dynamic parameter uncertainties is considered. In this regard, three different cases are studied. In the first case, all follower agents are considered informed, i.e., they receive the leader signals. The second case reads a situation where some followers are informed and the others are uninformed, and there is a directed spanning tree topology. In the third case, a new adaptive algorithm in the presence of dynamic parameter uncertainties is proposed. In all these cases, the finite-time consensus of the position and velocity signals is shown. All proofs are derived using the Lyapunov technique without the need to LMIs formulation, a common framework for the stability analysis of delay systems, which is often hard to get feasibility conditions of their solution. At last, in the line of verification of the theoretical results, simulation results on a group of ten identical planar 2-DOF manipulators as the agents of the system are presented.

A composite state convergence scheme for bilateral teleoperation systems

State convergence is a novel control algorithm for bilateral teleoperation of robotic systems. First, it models the teleoperation system on state space and considers all the possible interactions between the master and slave systems. Second, it presents an elegant design procedure which requires a set of equations to be solved in order to compute the control gains of the bilateral loop. These design conditions are obtained by turning the master-slave error into an autonomous system and imposing the desired dynamic behavior of the teleoperation system. Resultantly, the convergence of master and slave states is achieved in a well-defined manner. The present study aims at achieving a similar convergence behavior offered by state convergence controller while reducing the number of variables sent across the communication channel. The proposal suggests transmitting composite master and slave variables instead of full master and slave states while keeping the operator&#x02BC force channel intact. We show that, with these composite and force variables, it is indeed possible to achieve the convergence of states in a desired way by strictly following the method of state convergence. The proposal leads to a reduced complexity state convergence algorithm which is termed as composite state convergence controller. In order to validate the proposed scheme in the absence and presence of communication time delays, MATLAB simulations and semi-real time experiments are performed on a single degree-of-freedom teleoperation system.

Stable Nonlinear Trilateral Impedance Control for Dual-User Haptic Teleoperation Systems With Communication Delays

A new nonlinear adaptive impedance-based trilateral controller is proposed to ensure the absolute stability of multi-degrees-of-freedom (DOFs) dual-user haptic teleoperation systems subjected to communication delays. Using this strategy, reference impedance models are realized for the trilateral teleoperation system represented by a three-port network to facilitate cooperation of two human operators in order to perform a remote physical task. For this purpose, an impedance model defines the desired haptic interaction between the two human operators, while another impedance model specifies the desired behavior of the slave robot in terms of tracking the mater robots' trajectories during interaction with the remote environment. It is shown that different performance goals such as position synchronization and force reflection can be achieved via different adjustments to the impedance parameters. The sufficient conditions for the trilateral haptic system's absolute stability are investigated in terms of the impedance models' parameters. Accordingly, guidelines for modification of the impedance parameters are obtained to guarantee the absolute stability of the trilateral haptic system in the presence of communication time delays. A trilateral nonlinear version of the model reference adaptive impedance control (MRAIC) scheme is developed for implementing the proposed reference impedance models on the masters and the slave. The convergence of robots' trajectories to desired responses and the robustness against modeling uncertainties are ensured using the proposed controller as proven by the Lyapunov stability theorem. The proposed impedance-based control strategy is evaluated experimentally by employing a nonlinear multi-DOFs teleoperated trilateral haptic system with and without communication delays.

Asynchronous Periodic Edge-Event Triggered Control for Double-Integrator Networks With Communication Time Delays.

This paper focuses on the average consensus of double-integrator networked systems based on the asynchronous periodic edge-event triggered control. The asynchronous property lies in the edge event-detecting procedure. For different edges, their event detections are performed at different times and the corresponding events occur independently of each other. When an event is activated, the two adjacent agents connected by the corresponding link sample their relative state information and update their controllers. The application of incidence matrix facilitates the transformation of control objects from the agent-based to the edge-based. Practically, due to the constraints of network bandwidth and communication distance, agents usually cannot receive the instantaneous information of some others, which has an impact on the system performance. Hence, it is necessary to investigate the presence of communication time delays. For double-integrator multiagent systems with and without communication time delays, the average state consensus can be asynchronously achieved by designing appropriate parameters under the proposed event-detecting rules. The presented results specify the relationship among the maximum allowable time delays, interaction topologies, and event-detecting periods. Furthermore, the proposed protocols have the advantages of reduced communication costs and controller-updating costs. Simulation examples are given to illustrate the proposed theoretical results.

A novel architecture for cooperative remote rehabilitation system

In this paper, the problem of trilateral interaction between therapist, patient, and virtual environment is considered. Herein, a new architecture for robotic rehabilitation is investigated based on the robots together with patient and therapist, cooperating with each other to accomplish the therapy in the virtual reality, in which the rehabilitation system is divided into three subsystems: patient, therapist, and virtual environment. Each subsystem is controlled locally, ensuring that it is input-to-state stable (ISS). Besides, the associated interconnections are shown to be stable in the presence of communication time delays. First, the patient is capable of generating movements until losing his strength, i.e. interacting with the robot without help of the therapist. Afterwards, the therapist assists the patient to follow up the process, i.e. the patient is active in the former condition while becomes passive in the latter. Therefore, the controllers should be able to deal with not only active but also passive robots. Also, impedance reflection, adaptive projection method, and impedance control are utilized. Finally, simulation and experimental results are extracted in evaluation.

A Fully Distributed Power Dispatch Method for Fast Frequency Recovery and Minimal Generation Cost in Autonomous Microgrids

This paper describes a fully distributed power dispatch method that can achieve fast frequency recovery and minimal generation cost for autonomous microgrids. The method is comprised of two stages. In the first stage, a subgradient-based consensus algorithm is used to recover frequency. The equal increment rate criteria is incorporated into this algorithm to achieve a minimal regulating cost, obtained by economically distributing power among distributed energy resources. Control signals updated with latest local measurements are executed in each iteration step to speed up the frequency recovery procedure. In the second stage, an average consensus algorithm is applied to resolve frequency oscillations caused by measurement errors. Numerical tests are described to demonstrate the validity of the proposed method and its applicability in the presence of communication time delay is discussed.

A novel control architecture for physiological tremor compensation in teleoperated systems

Telesurgery delivers surgical care to a 'remote' patient by means of robotic manipulators. When accurate positioning of the surgeon's tool is required, as in microsurgery, physiological tremor causes unwanted imprecision during a surgical operation. Accurate estimation/compensation of physiological tremor in teleoperation systems has been shown to improve performance during telesurgery. A new control architecture is proposed for estimation and compensation of physiological tremor in the presence of communication time delays. This control architecture guarantees stability with satisfactory transparency. In addition, the proposed method can be used for applications that require modifications in transmitted signals through communication channels. Stability of the bilateral tremor-compensated teleoperation is preserved by extending the bilateral teleoperation to the equivalent trilateral Dual-master/Single-slave teleoperation. The bandlimited multiple Fourier linear combiner (BMFLC) algorithm is employed for real-time estimation of the operator's physiological tremor. Two kinds of stability analysis are employed. In the model-base controller, Llewellyn's Criterion is used to analyze the teleoperation absolute stability. In the second method, a nonmodel-based controller is proposed and the stability of the time-delayed teleoperated system is proved by employing a Lyapunov function. Experimental results are presented to validate the effectiveness of the new control architecture. The tremorous motion is measured by accelerometer to be compensated in real time. In addition, a Needle-Insertion setup is proposed as a slave robot for the application of brachytherapy, in which the needle penetrates in the desired position. The slave performs the desired task in two classes of environments (free motion of the slave and in the soft tissue). Experiments show that the proposed control architecture effectively compensates the user's tremorous motion and the slave follows only the master's voluntary motion in a stable manner.

Synchronization of networked Lagrangian systems with input constraints

AbstractThis paper addresses the synchronization problem of systems modeled by Euler-Lagrange equations and subject to input saturations. First, a new control design strategy, based on virtual systems, is proposed. This approach allows to generate control inputs that are a priori bounded in the presence of communication time-delays, regardless of the information flow topology between systems in the network. Second, we remove the requirement of the generalized velocities, leading to a velocity-free synchronization scheme with a priori bounded inputs. The effectiveness of the proposed control schemes is demonstrated through simulation examples on a network of four robot manipulator arms.

Dynamic behavior of discrete-time multiagent systems with general communication structures

In this paper, we discuss the dynamic behavior of networks of dynamic agents with general communication topologies. We first analyze the basic case: systems with communication topologies that have spanning trees, i.e., the systems that solve consensus problems. We establish an algebraic condition to characterize each agent's contributions to the final state. And we also study the influence of time-delays on each agent's contributions. Then, we investigate the general case: systems with weakly connected topologies. By using matrix theory, we prove that the states of internal agents will converge to a convex combination of boundary agents in the absence or presence of communication time-delays, and we also show that the coefficients of the convex combination are independent of time-delays even if the delays are time-varying. These results have broad applications in other areas, e.g., study of swarm behavior, formation control of vehicles, etc.

H∞-Based impedance control of teleoperation systems with time delay

Impedance control is used to adjust the dynamic relationship between the position of a manipulator and the applied forces when it interacts with the environment. In bilateral teleoperation systems, communication time delay may destabilize the closed-loop system and certainly degrade the operator’s intuition and performance. In this paper, a new scheme for impedance control of bilateral teleoperation systems in the presence of communication time delay is proposed. Local controller for master manipulator is firstly designed in order to get a specified master impedance. Then, a global controller is designed based on H∞ framework such that the global system, including communication time delay, is stable and the desired impedance characteristic of the slave manipulator is achieved asymptotically.