Leader-follower System Research Articles

Adaptive fault-tolerant consensus for a class of leader-following systems using neural network learning strategy

In this paper, the leader-following consensus problem of a class of nonlinearly multi-dimensional multi-agent systems with actuator faults is addressed by developing a novel neural network learning strategy. In order to achieve the desirable consensus results, a neural network learning algorithm composed of adaptive technique is proposed to on-line approximate the unknown nonlinear functions and estimate the unknown bounds of actuator faults. Then, on the basis of the approximations and estimations, a robust adaptive distributed fault-tolerant consensus control scheme is investigated so that the bounded results of all signals of the resulting closed-loop leader-following system can be achieved by using Lyapunov stability theorem. Finally, efficiency of the proposed adaptive neural network learning strategy-based consensus control strategies is demonstrated by a coupled nonlinear forced pendulums system.

Rescue Project Management with Scenario using a Human Centric Leader Follower System

Rescue Project Management with Scenario using a Human Centric Leader Follower System

Distributed Power Sharing Control of The Grid-connected AC Microgrid

This paper considers a power sharing problem of a grid-connected AC microgrid which consists of multiple dispatchable distributed generators. The microgrid is modeled by a multiagent system and the power sharing problem is formulated as a tracking issue of leader-follower system. Simulations are presented to demonstrate the effectiveness of the proposed control scheme.

Hitchhiking Based Symbiotic Multi-Robot Navigation in Sensor Networks

Robot navigation is a complex process that involves real-time localization, obstacle avoidance, map update, control, and path planning. Thus, it is also a computationally expensive process, especially in multi-robot systems. This paper presents a cooperative multi-robot navigation scheme in which a robot can ‘hitchhike’ another robot, i.e., two robots going to the same (or close) destination navigate together in a leader–follower system assisted by visual servoing. Although such cooperative navigation has many benefits compared to traditional approaches with separate navigation, there are many constraints to implementing such a system. A sensor network removes those constraints by enabling multiple robots to communicate with each other to exchange meaningful information such as their respective positions, goal and destination locations, and drastically improves the efficiency of symbiotic multi-robot navigation through hitchhiking. We show that the proposed system enables efficient navigation of multi-robots without loss of information in a sensor network. Efficiency improvements in terms of reduced waiting time of the hitchhiker, not missing potential drivers, best driver-profile match, and velocity tuning are discussed. Novel algorithms for partial hitchhiking, and multi-driver hitchhiking are proposed. A novel case of hitchhiking based simultaneous multi-robot teleoperation by a single operation is also proposed. All the proposed algorithms are verified by experiments in both simulation and real environment.

Consensus disturbance rejection with channel uncertainties in directed leader-following network system

This paper investigates the consensus disturbance rejection with channel uncertainties problem under directed network systems based on distributed disturbance observer method. The channel uncertainty item is modeled as the unitary transfer function perturbed by norm-bounded parameter. Laplacian matrix is divided into a nonsingular M-matrix to handle the directionality in networked system. Based on the uncertain relative information, a distributed disturbance protocol has been designed to guarantee the states of the agents converge to a consensus trajectory among all the subsystems. The channel uncertainties are added into the traditional disturbance observer-based rejection, and the distributed disturbance protocol is designed based on the relative state information obtained from the neighboring subsystems. According to linear matrix inequalities, sufficient condition for the results is derived. The effectiveness of the proposed protocol is finally verified by performing simulations.

Problem A of 9th China trajectory optimization competition: Results found at NUAA

This paper is intended to introduce a method and results of the NUAA team for problem A of the 9th China Trajectory Optimization Competition (CTOC-9). The cluster analysis, leader-follower system and repeat-groundtrack orbit are employed to obtain the solution with excellent performance index. The optimized process is performed in two parts. The first part is to search the monitoring sequence of GEO satellite beams. These beams have been grouped based on their monitoring features before searching, which is the critical factor that makes us in a dominant position. The simplified gains calculation model, which is built based on the leader-follower cluster system, is used to estimate monitoring gains. The second part is the configuration optimization of the monitoring cluster, which is transformed into the trajectory design of the followers because the leader's trajectory has been fixed. Based on the proposed formation configuration strategy, the trajectories of followers are solved by the genetic algorithm. The final result shows that it takes only 20.428 days to complete the mission, which ranks the first place in this competition.

Networked mobile robot leader-follower trajectory tracking control with delays

We consider the leader-follower trajectory tracking control problem for networked mobile robots. The leader and follower communicate with each via communication network and the network-induced delays are considered. Firstly, an uncertain system model is presented to describe the leader-follower trajectory tracking control system with delays, where the dynamics induced by the uncertain part of the delay is described by the model uncertainties. Secondly, an extended state observer (ESO) is designed to estimate the uncertainty of the trajectory tracking control system, and then the uncertainties induced by the delays are compensated by the ESO using dynamic linearisation compensation. In this way, the effects of the network induced delays are removed and the linear active disturbance rejection control (LADRC) method is thus implemented to achieve the objective of high performance trajectory tracking control. Finally, an illustrative example is presented to show the effectiveness and superiority of the proposed method.

Stability of cooperative unmanned aerial vehicles based on relative measurements

This paper describes a guidance method which is applicable in the leader–follower formation control. By considering limitations on communication among the aircraft, using airborne seekers for relative states measurement is proposed, and accordingly a kinematic model for the leader–follower system is developed. A main contribution of this work is analysis of the formation keeping in various flight scenarios when a cascade loop-based guidance strategy is used. In the proposed control structure, to regulate the relative ranges and the relative angles toward the desired values, two separate control channels are designed and to overcome the leader maneuvers, two proper acceleration estimators are employed. The effectiveness of the proposed guidance strategy is evaluated via simulation examples.

The Strategy of Management Тraining in the Construction Engineering

The operating efficiency of leaders in the construction industry is largely determined by the level of formation of managerial skills. Along with this, it is stated that the process of formation and development of managerial skills for leaders in the construction engineering is attended by a number of difficulties and frequently doesn’t make it past the threshold. This paper formulates a new approach in the formation of managerial skills of leaders in the construction engineering. The cross-sectoral assessment of managerial skills featuring the heads of the construction engineering and other industries, such as energy, metallurgy, showed low-performing managerial skills for the heads of the construction industry. The reasons of the formation of low-performing managerial skills in this article are referred to as peculiar features of organizational behavior in the construction engineering, in particular an imminent regression in the leader-follower system. Based on the results of the research conducted, the similarity of issues in regard to managerial skills in these areas is inherent in key differences in the formulation of priorities of corporate competencies.

Inglés

Robot operating system (ROS) provides algorithms and services to control different kind of robots. ROS is a useful tool in many issues in the field of autonomous robots, especially in applications as mapping, localization and autonomous navigation in an indoor environment. Autonomous navigation in a dynamic environment is not only challenging, but also uncovers many indoor environmental factors which affect the navigation process. The presented work describes how a ROS-Based control system is used with a Pioneer 3-DX robot for a human leader and robot follower system. The approach for this work is develop a modular system to reach a human follower using PIONEER 3-DX and Carmine Prime sense Sensor supported by threads for each processing steps through ROS packages, these stages are divided in: coordinate human acquisition, robot´s pose estimation, angular and linear speed control and obstacles security module.

Leader-follower consensus and synchronization in numerosity-constrained networks with dynamic leadership.

In this work, we study leader-follower consensus and synchronization protocols over a stochastically switching network. The agents representing the followers can communicate with any other agent, whereas the agents serving as leaders are restricted to interact only with the other leaders. The model incorporates the phenomenon of numerosity, which limits the perceptual capacity of the agents while allowing for shuffling with whom each individual interacts at each time step. We derive closed form expressions for necessary and sufficient conditions for consensus, the rate of convergence to consensus, and conditions for stochastic synchronization in terms of the asymptotic convergence factor. We provide simulation results to validate the theoretical findings and to illustrate the dependence of this factor on system parameters. The closed form results enable us to study the factors affecting the feasibility of consensus. We show that agents' traits can be chosen for an engineered system to maximize the convergence speed and that protocol speed is enhanced as the proportion of the leaders increases in certain cases. These results may find application in the design and control of an engineered leader-follower system, where consensus or synchronization at the fastest possible rate is desired.

Vision-Based Leader Vehicle Trajectory Tracking for Multiple Agricultural Vehicles.

The aim of this study was to design a navigation system composed of a human-controlled leader vehicle and a follower vehicle. The follower vehicle automatically tracks the leader vehicle. With such a system, a human driver can control two vehicles efficiently in agricultural operations. The tracking system was developed for the leader and the follower vehicle, and control of the follower was performed using a camera vision system. A stable and accurate monocular vision-based sensing system was designed, consisting of a camera and rectangular markers. Noise in the data acquisition was reduced by using the least-squares method. A feedback control algorithm was used to allow the follower vehicle to track the trajectory of the leader vehicle. A proportional–integral–derivative (PID) controller was introduced to maintain the required distance between the leader and the follower vehicle. Field experiments were conducted to evaluate the sensing and tracking performances of the leader-follower system while the leader vehicle was driven at an average speed of 0.3 m/s. In the case of linear trajectory tracking, the RMS errors were 6.5 cm, 8.9 cm and 16.4 cm for straight, turning and zigzag paths, respectively. Again, for parallel trajectory tracking, the root mean square (RMS) errors were found to be 7.1 cm, 14.6 cm and 14.0 cm for straight, turning and zigzag paths, respectively. The navigation performances indicated that the autonomous follower vehicle was able to follow the leader vehicle, and the tracking accuracy was found to be satisfactory. Therefore, the developed leader-follower system can be implemented for the harvesting of grains, using a combine as the leader and an unloader as the autonomous follower vehicle.

Leader–follower system using two robot tractors to improve work efficiency

Two robot tractors were used in a leader–follower system for agricultural field work. Each of the robots is fully independent and can conduct field work alone. They can also work together to form a certain spatial arrangement during the operation. During the headland turn, to make the best use of headland, the two robots coordinate to turn to next path and do not keep the spatial arrangement. Each robot is simplified as a rectangular zone, and the two robots cooperate and coordinate to turn to the next path without collision. This system is designed for practical application, and the system gains the ability to tolerate most of the disturbances in a real field. Fault tolerant methods in accordance with agricultural work are illustrated to solve the common disturbances from the GPS and the IMU. Field experiments were conducted to determine the effectiveness of the system. The results of the experiments showed that the two robot tractors can work safely together to complete the field work. The average lateral error of the navigation system of the robots was less than 0.04m, and the efficiency of the leader–follower system was improved by 95.1% compared with that of a conventional single robot.

Leader selection for fast consensus in networks

This paper considers a leader-follower system with the aim to select an optimal leader so as to drive the remaining nodes to reach the desired consensus with the fastest convergence speed. An index called consensus centrality (CC) is proposed to quantify how fast a leader could guide the network to achieve the desired consensus. The experiment results explored the big similarities between the distributions of CC and degree in the network, which suggest that the suboptimal leader selected by the maximum degree can approximately approach the optimal leader in heterogeneous networks. Combining the degree-based k-shell decomposition with consensus centrality, a leader selection algorithm is proposed to reduce the computational complexity in large-scale networks. Finally, the convergence time of an equivalent discrete-time model is given to illustrate the properties of the suboptimal solutions.

Distributed Switching Control to Achieve Almost Sure Safety for Leader-Follower Vehicular Networked Systems

Leader-follower formation control is a widely used distributed control strategy that requires systems to exchange their information over a wireless radio communication network to attain and maintain formations. These wireless networks are often subject to deep fades, where a severe drop in the quality of the communication link occurs. Such deep fades inevitably inject a great deal of stochastic uncertainties into the system, which significantly impact the system's performance and stability, and cause unexpected safety problems in applications like smart transportation systems. Assuming an exponentially bursty channel that varies as a function of the vehicular states, this paper proposes a distributed switching control scheme under which the local controller is reconfigured in response to the changes of channel state, to assure almost sure safety for a chain of leader-follower system. Here almost sure safety means that the likelihood of vehicular states entering a safe region asymptotically goes to one as time goes to infinity. Sufficient conditions are provided for each local vehicle to decide which controller is placed in the feedback loop to assure almost sure safety in the presence of deep fades. Simulation results of a chain of leader-follower formation are used to illustrate the findings.

Object tracking with enhanced data association using a 3D range sensor for an unmanned ground vehicle

This paper describes a novel object tracking method which combines a conventional global nearest-neighbor (GNN) method with an enhanced data association approach using 3D data features for an unmanned ground vehicle. If an object crosses in front of an observation system which has a measurement sensor equipped on a vehicle, a conventional distance-based object tracking mechanism encounters a data association problem owing to high uncertainties and a leak of information: correspondence between observations and tracks. To overcome these correspondence problems, we use the object’s 3D information such as statistical and geometrical information. In this paper, we describe a clustering and segmentation processes in conjunction with a distance-based nearest-neighbor approach, RBNN-2, and applied GNN with enhanced data association using both a kinematic and geometric models derived from 3D range data. To evaluate our method using a 3D LADAR sensor, a Velodyne HDL-32e, installed on the vehicle, we conducted an experiment involving two crossing humans and a ground vehicle to identify different human trajectories for a leader-following system.

Adaptive tracking control of leader–follower systems with unknown dynamics and partial measurements

In this paper, a decentralized adaptive tracking control is developed for a second-order leader–follower system with unknown dynamics and relative position measurements. Linearly parameterized models are used to describe the unknown dynamics of a self-active leader and all followers. A new distributed system is obtained by using the relative position and velocity measurements as the state variables. By only using the relative position measurements, a dynamic output–feedback tracking control together with decentralized adaptive laws is designed for each follower. At the same time, the stability of the tracking error system and the parameter convergence are analyzed with the help of a common Lyapunov function method. Some simulation results are presented to validate the proposed adaptive tracking control.

Trophallaxis network control approach to formation flight of multiple unmanned aerial vehicles

A novel network control method based on trophallaxis mechanism is applied to the formation flight problem for multiple unmanned aerial vehicles (UAVs). Firstly, the multiple UAVs formation flight system based on trophallaxis network control is given. Then, the model of leader-follower formation flight with a virtual leader based on trophallaxis network control is presented, and the influence of time delays on the network performance is analyzed. A particle swarm optimization (PSO)-based formation controller is proposed for solving the leader-follower formation flight system. The proposed method is applied to five UAVs for achieving a ‘V’ formation, and a series of experimental results show its feasibility and validity. The proposed control algorithm is also a promising control strategy for formation flight of multiple unmanned underwater vehicles (UUVs), unmanned ground vehicles (UGVs), missiles and satellites.

Optimal interconnection design for leader–follower coordination with noise

In this study, we address a leader–follower coordination problem with noise in a multi-agent system. In order to minimise the mean-square deviation of the individual state of followers from the state of the leader, we develop a strategy to select a subset of followers to connect with the leader. We adopt the method of convex optimisation to solve both constant edge weight and different edge weight case. Furthermore, we propose optimised algorithms to find the fastest convergence speed. We also study optimisation problems for leader–follower system with a dynamic leader, and also provide a sufficient condition for the convergence of the expected value of the total mean-square deviation. Examples and applications of the developed methodology are also discussed.

The effects of allowance of deferred herbage and concentrate supplementation when offered to ewe lambs, and system of allocation when offered to ewes in late gestation, on animal performance

AbstractThe effects of allowance of extended (deferred) grazed herbage (AEGH) and herbage allocation management (HAM) were studied in ewe lambs (248) and late‐gestation ewes (152), respectively, on commercial farms in south‐east Ireland in 2005–06. In Experiment 1, which consisted of four treatments, the effects of AEGH (0·75, 1·25 and 1·75 kg DM per head daily) and concentrate supplementation (0·5 kg per head daily with the 0·75 kg DM herbage allowance) on lamb performance during the extended grazing (16 December to 3 March) and subsequent grazing (4 March to 11 August) seasons were evaluated. Increasing AEGH increased herbage intake linearly (P < 0·001) and live weight (P < 0·001) at the end of extended grazing and the subsequent grazing season. In Experiment 2, single‐ and twin‐bearing ewes were allocated to either a conventional (single‐ and twin‐bearing ewes grazed separately) or leader–follower system (twin‐ and single‐bearing ewes, as leaders and followers respectively) of HAM from 30 January to 24 March. The same quantities of herbage were offered daily for each system. System of HAM affected ewe condition score at lambing but did not alter (P > 0·05) subsequent lamb birth or weaning weights. It is concluded that increasing AEGH to ewe lambs increased liveweight gain during extended grazing and resulted in heavier animals in mid August of the subsequent grazing season. For ewe lambs each 1 kg concentrate DM had the same feed value as 2·4 kg DM AEGH. Use of a leader–follower system for ewes in late pregnancy did not alter lamb birth weight or subsequent performance.