Formation Control Of Multi-robot Systems Research Articles

Distributed Formation Control of Multi-Robot Systems with Path Navigation via Complex Laplacian.

This paper focuses on the formation control of multi-robot systems with leader-follower network structure in directed topology to guide a system composed of multiple mobile robot agents to achieve global path navigation with a desired formation. A distributed linear formation control strategy based on the complex Laplacian matrix is employed, which enables the robot agents to converge into a similar formation of the desired formation, and the size and orientation of the formation are determined by the positions of two leaders. Additionally, in order to ensure that all robot agents in the formation move at a common velocity, the distributed control approach also includes a velocity consensus component. Based on the realization of similar formation control of a multi-robot system, the path navigation algorithm is combined with it to realize the global navigation of the system as a whole. Furthermore, a controller enabling the scalability of the formation size is introduced to enhance the overall maneuverability of the system in specific scenarios like narrow corridors. The simulation results demonstrate the feasibility of the proposed approach.

Minimally Persistent Graph Generation and Formation Control for Multi-Robot Systems under Sensing Constraints

This paper presents a minimally persistent graph generation and formation control strategy for multi-robot systems with sensing constraints. Specifically, each robot has a limited field of view (FOV) and range sensing capability. To tackle this problem, one needs to construct an appropriate interaction topology, namely assign neighbors to each robot such that all their sensing constraints are satisfied. In addition, as a stringent yet reasonable guarantee for the visual constraints, it is also required that the prescribed neighbors always stay within its visual field during the formation evolution. To this end, given a set of feasible initial positions, we first present a depth-first-search (DFS)-based algorithm to generate a minimally persistent graph, which encodes the sensing constraints via its directed edges. Then, based on the resultant graph, by invoking the gradient-based control technique and control barrier function (CBF), we propose a class of distributed formation control laws, rendering not only the convergence to the desired formation but also the satisfaction of sensing constraints. Simulation and experimental results are presented to verify the effectiveness of the proposed approach.

Bipartite consensus-based formation control of high-order multi-robot systems with time-varying delays

This paper considers a multi-robot formation control scheme for high-order bipartite consensus under time-varying delays. First, a third-order bipartite consensus protocol under time-varying delays is presented, and then a high-order bipartite consensus protocol is extended from it. Then, necessary and sufficient conditions for third-order and high-order multi-agent systems without time-delays are given to attain bipartite consensus following the protocols. Communication time-delays are added to the protocols, and the theory of Lyapunov asymptotic stability is used to obtain sufficient conditions for the multi-agent systems with communication delays to ultimately attain a bipartite consensus. Furthermore, the given protocol is employed for the formation control of multi-robot systems, and a formation control scheme for multi-robot systems with time-varying delays is proposed. Finally, a few simulations are implemented to demonstrate the rationality and availability of the method.

Three controllers via 2nd-order sliding mode for leader-following formation control of multi-robot systems

The multi-robot formation has always been an attractive field for cooperative control of robots. This paper uses the improved second-order sliding mode method to control the leader-following formation system. The traditional second-order sliding mode control is not perfect because the disturbances and uncertainties of the system may cause the compensation control to overestimate. The adaptive gain super-twisting sliding mode control suppresses the output oscillation and speeds up the system response by improving the gain function and adding a differential link. However, this method is generally applied to single-input single-output systems. This paper attempts to apply this method to a multi-input-multi-output leader-following formation system and improve its switching function and compensation control part. We use the estimators, i.e., the extreme learning machine and the nonlinear disturbance observer. These estimators can observe disturbance changes to replace the adaptive gain function to realise disturbance estimation and compensation control. Then combine the extreme learning machine and the nonlinear disturbance observer with the super-twisting sliding mode control to produce two new sliding mode methods. We use the Lyapunov method to prove the system stability as well. Finally, we illustrate the feasibility of the three control methods.

Three controllers via 2nd-order sliding mode for leader-following formation control of multi-robot systems

Three controllers via 2nd-order sliding mode for leader-following formation control of multi-robot systems

Multi-robot formation control: a comparison between model-based and learning-based methods

Formation control of multi-robot systems has been extensively studied by model-based methods, where analytic control inputs are constructed based on the kinematics and/or dynamics model and the communication graphs of the multi-robot system. Recently, driven by remarkable advances of robotic learning techniques, emerging studies on learning-based methods for formation control have been developed for adaptive and intelligent control of multi-robot systems. This paper aims to provide a brief overview of our recent development of learning-based formation control, and compare it with a model-based method for a case study of three-robot formation control. Fundamental principles, experimental results and technical challenges are presented, comparing the two different methodologies.

Relative Docking and Formation Control via Range and Odometry Measurements

This article studies the problem of distance-based relative docking of a single robot and formation control of multirobot systems. In particular, an integrated localization and navigation scheme is proposed for a robot to navigate itself to a desired relative position with respect to a fixed landmark at an unknown position, where only range and odometry measurements are used. By carefully embedding historical measurements into equilibrium conditions, we design an integrated estimation-control scheme to achieve the relative docking asymptotically. It is rigorously proved that the robot will converge to the desired docking position asymptotically provided that control gains are chosen to satisfy certain conditions. This scheme is further extended to multirobot systems to consider an integrated relative localization and formation control problem. Unlike widely used spatial cooperation in the existing literature, we propose to exploit both spatial and temporal cooperations for achieving formation control. It is proved that multirobot formation can be achieved with zero error for directed acyclic graphs. Several simulation examples are provided to validate our theoretical results.

Neural network-based region reaching formation control for multi-robot systems in obstacle environment

This study is concerned with the region reaching formation control problem with collision and obstacle avoidance for multi-robot systems in the presence of model uncertainties and external disturbances. A novel neural network based robust control scheme combining with the adaptive compensator and the adaptive control gain is proposed to achieve the region reaching formation control with collision and obstacle avoidance. It is shown that under the proposed control method, all the robots can always reach into the objective region, maintain their formation, and guarantee collision and obstacle avoidance. Illustrative examples are presented to show the effectiveness of the proposed control scheme.

Fixed-Time Formation Control of Multirobot Systems: Design and Experiments

Time delays exist in network-connected systems. Especially for vision-based multirobot systems, time delays are diverse and complicated due to the communication network, camera latency, image processing, etc. At the same time, many tasks, such as searching and rescue, have timing requirement. This paper focuses on fixed-time formation control of multirobot systems subject to delay constraints. First, predictor-based state transformation is employed for each robot to deal with the input delay, and the uncertain terms remained in the transformed systems are carefully considered. Then, a couple of nonlinear fixed-time formation protocols are proposed for the multirobot systems with respectively undirected and directed topology, and the corresponding settling time is derived by using the Lyapunov functions. In particular, the upper-bound estimation of the formation settling time is explicitly given irrelevant to the initial conditions. Finally, the protocols are validated through a numerical simulation example and then implemented on an E-puck robots platform. Both simulation and experimental results demonstrate the effectiveness of the proposed formation protocols.

Adaptive Distributed Fault-tolerant Formation Control for Multi-robot Systems under Partial Loss of Actuator Effectiveness

This paper presents an adaptive distributed fault-tolerant formation control for multi-robot systems. Both the kinematics and dynamics of differential wheeled mobile robots are considered. In particular, the problem caused by actuator faults is investigated. Based on dynamic surface control techniques, adaptive formation controllers can be obtained under a directed communication network. The closed-loop stability is guaranteed by using Lyapunov stability analysis such that all followers can exponentially converge to a leader-follower formation pattern. Simulation and experimental results illustrate that the desired formation pattern can be preserved for a group of wheeled robots subject to unknown uncertainties and actuator faults.

An Overview of Recent Advances in Event-Triggered Consensus of Multiagent Systems.

Event-triggered consensus of multiagent systems (MASs) has attracted tremendous attention from both theoretical and practical perspectives due to the fact that it enables all agents eventually to reach an agreement upon a common quantity of interest while significantly alleviating utilization of communication and computation resources. This paper aims to provide an overview of recent advances in event-triggered consensus of MASs. First, a basic framework of multiagent event-triggered operational mechanisms is established. Second, representative results and methodologies reported in the literature are reviewed and some in-depth analysis is made on several event-triggered schemes, including event-based sampling schemes, model-based event-triggered schemes, sampled-data-based event-triggered schemes, and self-triggered sampling schemes. Third, two examples are outlined to show applicability of event-triggered consensus in power sharing of microgrids and formation control of multirobot systems, respectively. Finally, some challenging issues on event-triggered consensus are proposed for future research.

Formation control for multi-robot systems with collision avoidance

ABSTRACTIn this paper, distributed formation is studied for a team of mobile robots including leaders and followers. Followers are able to sense the relative displacements to neighbouring followers and all of the leaders, and the leaders can be sensed by the followers. Based on such assumption of sensing, distributed formation control scheme is designed, under which both followers team and leaders team are fully independent. The followers and leaders have exchangeable roles within their own group. The leaders can have an arbitrary formation, and around the leaders, the followers need to reach a regular polygon formation with a suitable orientation. Distributed control laws and localised collision avoidance algorithms are designed for each follower, and they use only local displacements. Speed and acceleration sensors are avoided. As the leaders and the followers are independent and exchangeable, both robot teams are scalable and robust against member failures and system delays.

Interval fuzzy sliding-mode formation controller design

This paper focuses on the design of a formation controller for multi-robot dynamic systems using interval fuzzy sliding-mode algorithm. The objective of formation control is to have all robots simultaneously achieve the tracking task with the desired pattern. An interval fuzzy sliding-mode formation controller is proposed to deal with the formation control of multi-robot systems in which the system uncertainties and measured noise are considered. To reduce the computational complexity of a type-reducer, the end points of a type-reduced centroid are approximated by the outputs of two standard fuzzy sliding mechanisms in the proposed interval fuzzy sliding controller. Simulation results are indicated to show the effectiveness of the proposed interval fuzzy sliding-mode consensus controller.

Vector Field Based Formation Control of Multi-Robot System

Abstract Multi-robot system as formation can perform better than a single robot in many situations like collective movement of objects, search and rescue operations etc. In this paper a vector field framework is used for achieving path planning for a single robot, and a nonlinear controller is designed for tracking this path. The tracking controller is later extended for achieving formation control of multi-robot system. Asymptotic stability of the controller for any reference path is ensured by using Lyapunov theory. The robots may encounter obstacles in their path during tracking or may collide with each other during the switching of formation patterns. Obstacle avoidance and collision avoidance have been achieved by modified vector field. If the terrain is constrained then it needs to switch from one formation to another according to the terrain requirements. Thus the capability of switching of formation or reconfiguration is an important aspect in the control of multiple mobile robots. If one of the member robots is lost, then the other robots continue with the remaining formation structure and thus ensures robustness against loss of team member. From the extensive simulations using Matlab environment it is seen that any formation of mobile robots is achieved in addition to reconfiguration and obstacle avoidance. The formation control algorithm has been experimentally demonstrated by a series of experiments conducted using LEGO NXT Mindstorm robot kit.

Robust fault-tolerant cooperative control of multi-agent systems: A constructive design method

This paper investigates the distributed cooperative controller design problem for multi-agent systems in the presence of actuator faults. Both the partial loss of actuator effectiveness and the actuator bias faults are considered. A constructive design method is presented to achieve the synchronization and/or tracking control of multi-agent systems. The control protocol for each agent consists of three modules: the actuator fault detection module, the nominal control module, and the auxiliary control module. The auxiliary control module is activated as soon as the actuator faults are detected. The control protocols are locally distributed in the sense that the control modules designed for each agent only require the information of itself and its neighbors. The loss of symmetry in the digraph Laplacian matrix is also considered. The analysis is suitable for the multi-agent systems with a general directed communication graph. The proposed fault-tolerant control schemes are applied in the formation control of multi-robot systems. Numerical simulation results are presented to show the effectiveness of the proposed control methods.

Decentralized time-varying formation control for multi-robot systems

In this paper, a distributed controller–observer schema for tracking control of the centroid and of the relative formation of a multi-robot system with first-order dynamics is presented. Each robot of the team uses a distributed observer to estimate the overall system state and a motion control strategy for tracking control of time-varying centroid and formation. Proof of the overall convergence of the controller–observer schema for different kinds of connection topologies, as well as for the cases of unsaturated and saturated control inputs is presented. In particular, the solution is proven to work in the case of strongly connected non-switching topologies and in the case of balanced strongly connected switching topologies. In order to complete the work, the approach is validated by experimental tests with a team of five wheeled mobile robots.

Flexible Morphogenesis based Formation Control for Multi-Robot Systems

Inspired by how biological cells communicate with each other at a cell-to-cell level; morphogenesis emerged to be an effective way for local communication between homogenous robots in multi-robot systems. In this paper, we present the first steps towards a scalable morphogenesis style formation control technique, which address the drawbacks associated with current morphogenesis type formation control techniques, including their inability to distribute robots evenly across target shapes. A series of experiments, which demonstrate that the proposed technique enables groups of non-holonomic ground moving robots to generate formations in less than 9 seconds with three robots and less than 22 seconds with five robots, is also presented. These experiments furthermore reveal that the proposed technique enables groups of robots to generate formations without significantly increasing the total travel distance when faced with obstacles. This work is an important contribution to multi-robot control theory as history has shown that the success of groups often depends on efficient and robust formation control.

Flexible Morphogenesis based Formation Control for Multi-Robot Systems

Flexible Morphogenesis based Formation Control for Multi-Robot Systems

Decentralized Discrete-Time Formation Control for Multirobot Systems

Inspired from the collective behavior of biological entities for the group motion coordination, this paper analyzes the formation control of mobile robots in discrete time where each robot can sense only the position of certain team members and the group behavior is achieved through the local interactions of robots. The main contribution is an original formal proof about the global convergence to the formation pattern represented by an arbitrary Formation Graph using attractive potential functions. The analysis is addressed for the case of omnidirectional robots with numerical simulations.

Formation control of robotic swarm using bounded artificial forces.

Formation control of multirobot systems has drawn significant attention in the recent years. This paper presents a potential field control algorithm, navigating a swarm of robots into a predefined 2D shape while avoiding intermember collisions. The algorithm applies in both stationary and moving targets formation. We define the bounded artificial forces in the form of exponential functions, so that the behavior of the swarm drove by the forces can be adjusted via selecting proper control parameters. The theoretical analysis of the swarm behavior proves the stability and convergence properties of the algorithm. We further make certain modifications upon the forces to improve the robustness of the swarm behavior in the presence of realistic implementation considerations. The considerations include obstacle avoidance, local minima, and deformation of the shape. Finally, detailed simulation results validate the efficiency of the proposed algorithm, and the direction of possible futrue work is discussed in the conclusions.