Global Tracking Error Research Articles

Distributed Intelligent Adaptive Controller for Disturbance Rejection in Multiagent Systems

A cooperative task consisting of multiple agents has the advantages of reducing cost, enhancing configurability, and increasing robustness in a large set of mission applications. A distributed strategy, applied using intelligence and adaptability characteristics, can provide the extended potential to achieve high levels of mission protection, especially under disturbances that might lead to operation degradation. This paper describes the design and development of a novel bioinspired distributed adaptive control architecture designed to increase the resilience of multiagent systems. The architecture is formulated using nonlinear bounded functions that characterize the immune system responses of living organisms. Numerical simulations are performed to evaluate the capabilities of this architecture to solve a consensus problem under bounded disturbances. Stability analysis is presented using the Lyapunov direct method to estimate the radius of convergence of the global tracking error under a time-varying disturbance. The proposed distributed controller successfully ensures that consensus is achieved among all agents while simultaneously mitigating the effect of disturbances.

Tracking control on homogeneous spaces: the Equivariant Regulator (EqR)

Accurate tracking of planned trajectories in the presence of perturbations is an important problem in control and robotics. Symmetry is a fundamental mathematical feature of many dynamical systems and exploiting this property offers the potential of improved tracking performance. In this paper, we investigate the tracking problem for input-affine systems on homogeneous spaces: manifolds which admit symmetries with transitive group actions. We show that there is natural manner to lift any desired trajectory of such a system to a lifted trajectory on the symmetry group. This construction allows us to define a global tracking error and apply LQR design to obtain an approximately optimal control in a single coordinate chart. The resulting control is then applied to the original plant and shown to yield excellent tracking performance. We term the resulting design methodology the Equivariant Regulator (EqR). We provide an example input-affine system posed on a homogeneous space, derive the trajectory linearisation in error coordinates and demonstrate the effectiveness of EqR compared to standard approaches in simulation.

Potential and sky coverage for off-axis fringe tracking in optical long baseline interferometry

ABSTRACT The spectacular results provided by the second-generationVLTI instruments GRAVITY and MATISSE on active galactic nuclei (AGN) trigger and justify a strong increase in the sensitivity limit of optical interferometers. A key component of such an upgrade is off-axis fringe tracking. To evaluate its potential and limitations, we describe and analyse its error budget including fringe sensing precision and temporal, angular and chromatic perturbations of the piston. The global tracking error is computed using standard seeing parameters for different sites, seeing conditions and telescope sizes for the current GRAVITY Fringe Tracker (GFT) and a new concept of Hierarchical Fringe Tracker. Then, it is combined with a large catalogue of guide star candidates from Gaia to produce sky coverage maps that give the probability to find a usable off-axis guide star in any part of the observable sky. These maps can be used to set the specifications of the system, check its sensitivity to seeing conditions, and evaluate the feasibility of science programs. We check the availability of guide stars and the tracking accuracy for a large set of 15 799 Quasars to confirm the feasibility of a large program on Broad Line Regions in the K band with the GFT and show how it can be extended to the L, M, and N bands. Another set of 331 well-characterized nearby AGNs shows the high potential of MATISSE for imaging and characterization of the dust torus in the N band under off-axis tracking on both Unit Telescopes and Auxiliary Telescopes.

Indirect Neural Adaptive Control for Wheeled Mobile Robot

For a precise trajectory tracking of a wheeled mobile robot, accurate control of the position along a reference trajectory is essential. Therefore, this paper proposes an indirect neural adaptive controller for a nonholonomic mobile robot based on its dynamical model. This controller takes into account the approximation error. The use of the Lyapunov stability theorem and dynamical neural networks is indeed for deriving respectively stable learning laws for control and identification of a complex nonlinear dynamics system. The global tracking error is incorporated to adjust the neural weight learning laws to ensure the robustness of the system against approximation inaccuracy. Hence, the designed intelligent controller guarantees the convergence of both tracking and identification errors to zero. Simulation results illustrate the ability of the intelligent controller to assure the asymptotic stability of the closed-loop nonlinear uncertain system.

Cooperative tracking control for general linear multiagent systems with directed intermittent communications: An artificial delay approach

SummaryThis paper investigates the consensus tracking problem for general linear multiagent systems on directed graph containing a spanning tree. For the considered linear systems, the consensus tracking aim cannot be achieved by using only memoryless static relative output feedbacks. Of particular interest is that both current and delayed relative output information of agents are required to achieve consensus. For the case of continuous communication among agents, an artificial delay output feedback control method is proposed. By utilizing the Taylor representation for the delayed signal with the remainder in the integral form, a delay‐dependent sufficient condition is presented to guarantee the exponential convergence of the global tracking error systems. For the intermittent case, the consensus tracking performance can still be guaranteed based on a multiple graph‐dependent Lyapunov functionals method. It is theoretically revealed that the time delay plays a key role in the exponential convergence of the closed‐loop systems, and the definite relationships among the time delay, network structure, communication rate, and consensus convergence rate are also provided. The effectiveness of the proposed control scheme is confirmed by numerical simulations.

Fault-Tolerant Consensus Tracking Control for Linear Multiagent Systems Under Switching Directed Network

In this paper, for linear leader-follower networks with multiple heterogeneous actuator faults, including partial loss of effectiveness fault and actuator bias fault, a cooperative fault-tolerant control (CFTC) approach is developed. Assume that the interaction network topology among all nodes is a switching directed graph. To address the difficulty of designing the distributed compensation control laws under the time-varying asymmetrical network structure, a novel distributed-reference-observer-based fault-tolerant tracking control approach is established, under which the global tracking errors are proved to be asymptotically convergent in the presence of actuator failures. First, by constructing a group of distributed reference observers based on neighborhood state information, all followers can estimate the leader's state trajectories directly. Second, a decentralized adaptive fault-tolerant tracking controller via local estimation is designed to achieve the global synchronization. Furthermore, the reliable coordination problem under switching directed topology with intermittent communications is solved by utilizing the presented CFTC approach. Finally, the effectiveness of the proposed coordination control protocol is illustrated by its applications to a networked aircraft system.

Closed-Loop Control of the Centre of Pressure in Post-Stroke Patients With Balance Impairments.

When a lightly touched surface is moved according to a closed-loop control law, it has been shown in young adults that the centre of pressure (CoP) can be displaced in a controllable way without the conscious cooperation of participants. In this closed-loop paradigm, the surface velocity was continuously adjusted according to the CoP position. Since the closed-loop control of the CoP does not require the participant's voluntary cooperation, it could be of interest for the development of innovative biofeedback devices in balance rehabilitation. Before anticipating the implementation of this closed-loop control paradigm with patients, it is necessary to establish its effects on people suffering from balance impairments. The aim of this paper was to assess the effects of this CoP closed-loop control in post-stroke (PS) patients and aged-matched healthy controls. Efficacy of the closed-loop control for driving the patients' CoP was assessed using the saturation time and two scores computing the error between the predefined and the current CoP trajectories. 68% and 83% of the trials were considered as successful in patients and controls, respectively. The global tracking error of the closed-loop score was similar between the two groups. However, when examining the real CoP displacement from the starting position to the desired one, PS patients responded to the closed-loop control to a lesser extent than controls. These results, obtained in the same conditions for healthy and PS individuals could be improved by tuning the closed-loop parameters according to individual characteristics. This paper paves the road towards the development of involuntary/automatic biofeedback techniques in more ecological conditions.

Adaptive Reliable Coordination Control for Linear Agent Networks With Intermittent Communication Constraints

This paper studies the adaptive reliable coordination control problem for a class of multiagent systems under time-varying topology in the presence of intermittent communication constraints and actuator faults. The underlying communication network is assumed to switch among finite undirected connected graphs. A new fault-tolerant consensus tracking control scheme is presented by utilizing the distributed adaptive technique. In contrast to the existing results on the cooperative tracking control problem against intermittent communications, no assumption on zero input of the leader is made in the discussions. By introducing the estimates to account for the unknown faulty efficiency factors and the bounds of the leader's control input signal, the local controller parameters are updated in individual nodes. Also, a novel topology-allocation-dependent average dwell time approach is proposed to deal with network switching jumps effectively. By combining multiple Lyapunov functions method and algebraic graph theory, it is shown that the global tracking errors are uniformly ultimately bounded even in the cases of intermittent communication constraints and actuator failures. Finally, the simulation study demonstrates the effectiveness of the proposed reliable coordination control strategy.

Cooperative tracking control for linear multi-agent systems with external disturbances under a directed graph

ABSTRACTThis paper studiesthe cooperative tracking control problem for multi-agent systems with unknown external disturbances under a directed graph. The leader's input is nonzero and unavailable to the followers. Based on the relative output measurements of neighbouring agents, a novel observer-based cooperative tracking protocol is presented, where the a group of intermediate estimators are constructed to estimate the tracking errors and the combined signal of the disturbances and the leader's input simultaneously, then decentralised tracking protocols are designed based on the obtained estimates. The states of the global tracking error system are proved to be uniformly ultimately bounded. A numerical example of aircraft illustrates the effectiveness of the cooperative tracking protocol.

Adaptive robust consensus tracking for nonlinear second‐order multi‐agent systems with heterogeneous uncertainties

SummaryThis paper addresses the consensus tracking problem for a class of heterogeneous nonlinear second‐order multi‐agent systems with parametric uncertainties, unmodeled dynamics, and bounded external disturbances. By linearly parameterizing the control input of the leader, two distributed adaptive robust consensus tracking control protocols with dynamic and fixed coupling gains are constructed based on the relative information from neighboring agents. The global tracking errors are shown to be guaranteed to exponentially converge to a ball with a constant radius at a prescribed rate of convergence under external disturbances. Finally, a numerical example is provided to verify the theoretical results. Copyright © 2017 John Wiley & Sons, Ltd.

Evaluation of Heliostat Field Global Tracking Error Distributions by Monte Carlo Simulations

Several error sources can contribute to the global tracking error of heliostats. These sources can be, for instance, angular offset in the reference position of the tracking mechanisms, imperfect leveling of the heliostat pedestal, lack of perpendicularity between the tracking axes, lack of precise clock synchronization. All these possible errors are characterized by angles that have very specific numerical values for each heliostat in a central receiver installation. However, they are intrinsically random in nature, and the errors in different heliostats are independent from each other. In principle, the overall drift behavior of the heliostats can be characterized by a statistical distribution of tracking errors. This global distribution characterizes the angular deviation of the heliostat normal and is used in ray tracing simulations of heliostat fields. It is usually assumed to be Gaussian, although some authors argue in favor of other types of distributions. In the present work, the dependence of the global tracking error distribution on the above mentioned primary error sources is investigated by means of Monte Carlo simulations. Random values are assumed for the different error parameters, and the resulting global tracking error distributions are evaluated for different times of the year for a heliostat field.