Group Of Nonholonomic Mobile Robots Research Articles

Trajectory Planning for Autonomous Formation of Wheeled Mobile Robots via Modified Artificial Potential Field and Improved PSO Algorithm

This paper addresses two substantial aspects in the field of robotics: trajectory planning and trajectory tracking for multi-robot systems. The collective movement of the multi-wheeled mobile robots is based on a formation control with a leader–follower strategy. To ensure safe navigation toward the destination within a workspace containing multiple obstacles, we skillfully combine the Modified Artificial Potential Field (MAPF) method and the Improved Particle Swarm Optimization (IPSO) algorithm for a group of nonholonomic mobile robots. A global planner based on IPSO algorithm is assigned to the leader robot, to find the optimal collision-free path. Compared to recent nature-inspired methodologies, the improvement suggested enhance the search capabilities of the algorithm, resulting in a 2% reduction in path length and a 29% decrease in computation time. Simultaneously, the follower robot has the ability to employ either a formation policy or a local planner using MAPF. The proposed modifications address the primary limitations of the conventional method, notably the susceptibility to local minima and the challenge of reaching goals near obstacles. Furthermore, this local planner is adept at evading both static and dynamic obstacles. Extensive real hardware experiments are conducted within multiple scenarios using the mobile robot Qbot-2e to corroborate the obtained simulation results and validate the effectiveness of the proposed approaches both in tracking the desired trajectories, finding the optimal feasible collision-free path and avoiding static and dynamic obstacles for multi-robot systems.

Distributed Adaptive Resilient Formation Control of Uncertain Nonholonomic Mobile Robots Under Deception Attacks

This paper investigates the formation control problem for a group of nonholonomic mobile robots (NMRs) with unknown parameters and deception attacks. The information transmitted among different robots is represented by a directed graph and only a subset of the robots can obtain the full information of the desired trajectory directly. For those robots which cannot access to the reference trajectory directly, distributed estimators are designed to estimate the unknown trajectory information by using only locally available information. Besides, the sensor-to-controller transmitting channels and the communication among connected robots are suffering from deception attacks. Adaptive laws and compensation terms are designed to handle the issue of attack-induced uncertainties. Then, a novel distributed resilient formation control scheme is designed, based on which a sufficient condition is developed to guarantee that the formation errors converge to a compact set and all the closed-loop signals are bounded. Experimental results are given to validate the theoretical studies.

Fixed-time trajectory tracking control for multiple nonholonomic mobile robots

This paper investigates the fixed-time trajectory tracking control for a group of nonholonomic mobile robots, where the desired trajectory is generated by a virtual leader, the leader’s information is available to only a subset of the followers, and the followers are assumed to have only local interaction. According to fixed-time control theory and adding a power integrator technique, distributed fixed-time tracking controllers are developed for each robot such that all states of each robot can reach the desired value in a fixed time. Moreover, the settling time is independent of the system initial conditions and only determined by the controller parameters. Simulation results illustrate and verify the effectiveness of the proposed schemes.

Observer-based multivariable fixed-time formation control of mobile robots

This paper proposes a multivariable fixed-time leader-follower formation control method for a group of nonholonomic mobile robots, which has the ability to estimate multiple uncertainties. Firstly, based on the state space model of the leader-follower formation, a multivariable fixed-time formation kinematics controller is designed. Secondly, to overcome uncertainties existing in the nonholonomic mobile robot system, such as load change, friction, external disturbance, a multivariable fixed-time torque controller based on the fixed-time disturbance observer at the dynamic level is designed. The designed torque controller is cascaded with the formation controller and finally realizes accurate estimation of the uncertain part of the system, the follower tracking of reference velocity and the desired formation of the leader and the follower in a fixed-time. The fixed-time upper bound is completely determined by the controller parameters, which is independent of the initial state of the system. The multivariable fixed-time control theory and the Lyapunov method are adopted to ensure the system stability. Finally, the effectiveness of the proposed algorithm is verified by the experimental simulation.

Adaptive estimator‐based formation maneuvering control of nonholonomic mobile robots

SummaryIn this paper, the formation maneuvering control problem for a group of nonholonomic mobile robots with the objective of having a desired formation shape described by distances between pairs of robots and an overall maneuvering velocity is studied. The desired maneuvering velocity, which can be constant or time‐varying, is only known to a set of agents. A control scheme consisting of an adaptive estimator and a modified gradient control law is proposed to solve this problem. The adaptive estimator is designed to estimate the desired maneuvering velocity in either constant or time‐varying situation. Utilizing the estimated velocity, a modified gradient control law is designed based on the nonholonomic kinematic model so that the objective is achieved. Local asymptotic convergence of the overall system is guaranteed by choosing appropriate control parameters. The effectiveness of the proposed control scheme is demonstrated through simulation results.

Adaptive Leader–Follower Formation Control of Nonholonomic Mobile Robots With Prescribed Transient and Steady-State Performance

In this article, we study the formation tracking control problem for a group of nonholonomic mobile robots under communication constraints. We use a simple leader–follower formation tracking control strategy, in which only the leading robot of the robotic group obtains the given trajectory's information, and each robot only receives information from its immediate leader. Thus, the communication graph forms a static and simple directed spanning tree. We assume that the information exchange among the robots is limited by some given communication radius. Under the limited communication range, the leader–follower distance and bearing angle constraints are considered in the formation control design. To provide the given specifications on the transient and steady-state performances of formation tracking errors, the boundaries of the predefined constraints are enforced by designer-specified performance requirements, which are functions of time. Consequently, we incorporate the barrier Lyapunov function into formation control design to mathematically prove that the formation tracking errors evolve always within the predefined regions and converge asymptotically to zero. The proposed formation control strategy can also guarantee the connectivity maintenance and collision avoidance between the leader and the follower. Simulation results show the performance of the proposed formation tracking control.

Vision-Based Flexible Leader–Follower Formation Tracking of Multiple Nonholonomic Mobile Robots in Unknown Obstacle Environments

This brief investigates the flexible leader–follower formation tracking problem for a group of nonholonomic mobile robots, while most of the formation control related work in the literature focuses on the rigid formation. The flexible formation discussed in this brief is defined in curvilinear coordinates in terms of longitudinal separations between robots along the reference trajectory and lateral deviations with respect to this trajectory. Unlike the previous studies on flexible formation control, this brief is under a more challenging assumption that the global position and orientation measurements are not available. To obtain the relative pose relationships amongst robots, a stereo camera is mounted on each follower. In consideration of the fact that visual observations are noise-corrupted and intermittently available, a particle filter-based relative pose estimation approach is employed to estimate the position and orientation of the leader in the local reference frame of the follower using the polluted and discontinuous information. Also, to form a flexible formation, the leader historical trajectory is reconstructed with respect to the current local frame attached on the follower, based on which a reference point is generated. In addition, this brief considers the situation where robots operate in unknown obstacle environments. To ensure robot safety in such environments, a multiobjective control law is proposed to balance reference tracking and collision avoidance in different situations. Simulation and real-robot experiment have been performed to demonstrate the efficacy of the proposed method.

Distributed Estimation and Control for Leader-Following Formations of Nonholonomic Mobile Robots

The problem of the leader-following formation control of nonholonomic mobile robots is addressed in this paper. A distributed formation control strategy using explicitly the coordination errors among robots is proposed without assuming that each follower robot knows the full state of the leader. First, a distributed estimation law is proposed for each follower robot to estimate the states, including the position, orientation, and linear velocity of the leader. The distributed formation control law is then designed based on the estimated states of the leader, and the neighborhood formation tracking error. Under some mild assumptions on the interaction graph among the leader and the follower robots, and the velocity of the leader, asymptotic convergence of formation tracking errors to zero can be achieved. Finally, some numerical simulations and experiments on a group of nonholonomic mobile robots are presented to demonstrate the effectiveness of the proposed strategy. Note to Practitioners —The motivation of this paper is to investigate a practical control strategy for the leader-following formation of multiple autonomous mobile robots subjected to nonholonomic constraints. In most of the existing leader-following formation control schemes for nonholonomic mobile robots, having access to the full state of the leader is a requirement. However, due to limitations in communication bandwidth and range, it is reasonable to assume that the information of the leader is available only to a subset of followers. Hence, this paper suggests a new distributed leader-following formation control strategy based on the distributed estimation of the leader’s states. Moreover, the coordination error between a pair of interacting robots is explicitly used in the control design to weaken the dependence on the estimated state of the leader, and enhance the decentralized nature of the proposed control scheme. The stability and convergence of the system are analyzed mathematically and the experiment using unicycles provides promising results. In ongoing research, we are addressing the issues of collision avoidance and communication delays to provide more realistic setup for the industrial applications of multivehicle systems.

Cooperative Control of Multiple Nonholonomic Robots for Escorting and Patrolling Mission Based on Vector Field

This paper investigates the cooperative control problem of multiple nonholonomic robots for an escorting and patrolling mission with respect to a target with a time-varying velocity. The goal of the multi-robot system is to orbit a moving target in a common circle with a prescribed radius and circular velocity, while maintaining even spacing along the perimeter of the circle. This paper proposes a distributed control strategy based on the vector field that does not require each robot to know the full state of the target. A distributed estimation law is developed to enable each robot to estimate the position of the target, and a tracking differentiator is used to estimate the velocity of the target. Based on these estimates of the target, the distributed control law is designed to ensure the asymptotic convergence of the multi-robot system to achieve the desired motion. Under some mild assumptions about the interaction graph among the target and the robots, and the velocity of the target, explicit stability and convergence analyses are presented using Lyapunov tools. Simulation results from test cases of a group of nonholonomic mobile robots verify the effectiveness of the proposed distributed control algorithms.

Distributed finite-time trajectory tracking control for multiple nonholonomic mobile robots with uncertainties and external disturbances

ABSTRACTThis paper investigates the distributed finite-time trajectory tracking control for a group of nonholonomic mobile robots with time-varying unknown parameters and external disturbances. At first, the tracking error system is derived for each mobile robot with the aid of a global invertible transformation, which consists of two subsystems, one is a first-order subsystem and another is a second-order subsystem. Then, the two subsystems are studied respectively, and finite-time disturbance observers are proposed for each robot to estimate the external disturbances. Meanwhile, distributed finite-time tracking controllers are developed for each mobile robot such that all states of each robot can reach the desired value in finite time, where the desired reference value is assumed to be the trajectory of a virtual leader whose information is available to only a subset of the followers, and the followers are assumed to have only local interaction. The effectiveness of the theoretical results is finally illustrated by numerical simulations.

Decentralised consensus-based formation tracking of multiple differential drive robots

ABSTRACTThis article investigates the control problem for formation tracking of multiple nonholonomic robots under distributed manner which means each robot only needs local information exchange. A class of general state and input transform is introduced to convert the formation-tracking issue of multi-robot systems into the consensus-like problem with time-varying reference. The distributed observer-based protocol with nonlinear dynamics is developed for each robot to achieve the consensus tracking of the new system, which namely means a group of nonholonomic mobile robots can form the desired formation configuration with its centroid moving along the predefined reference trajectory. The finite-time stability of observer and control law is analysed rigorously by using the Lyapunov direct method, algebraic graph theory and matrix analysis. Numerical examples are finally provided to illustrate the effectiveness of the theory results proposed in this paper.

Distributed consensus-based formation control for nonholonomic wheeled mobile robots using adaptive neural network

This paper investigates the distributed formation control problem for multiple nonholonomic wheeled mobile robots. A variable transformation is first proposed to convert the formation control problem into a state consensus problem. Then, when the dynamics of the mobile robots are considered, the distributed kinematic controllers and neural network torque controllers are derived for each robot such that a group of nonholonomic mobile robots asymptotically converge to a desired geometric pattern along the specified reference trajectory. The specified reference trajectory is assumed to be the trajectory of a virtual leader whose information is available to only a subset of the followers. Also the followers are assumed to have only local interaction. Moreover, the neural network torque controllers proposed in this work can tackle the dynamics of robots with unmodeled bounded disturbances and unstructured unmodeled dynamics. Some sufficient conditions are derived for accomplish the asymptotically stability of the systems based on algebraic graph theory, matrix theory, and Lyapunov control approach. Finally, simulation examples illustrate the effectiveness of the proposed controllers.

Adaptive distributed formation control for multiple nonholonomic wheeled mobile robots

This paper investigates the adaptive distributed formation control problem for multiple nonholonomic wheeled mobile robots. First, the formation control problem is converted into a state consensus problem by the aid of a variable transformation. Then, distributed kinematic controllers and adaptive dynamic controllers are developed for each robot such that a group of nonholonomic mobile robots asymptotically converge to a desired geometric pattern with its centroid moving along the specified reference trajectory. The specified reference trajectory is assumed to be the trajectory of a virtual leader whose information is available to only a subset of the followers. Also the followers are assumed to have only local interaction. Some sufficient conditions are derived for accomplishing the asymptotically stability of the systems based on algebraic graph theory, matrix theory, and Lyapunov control approach. Finally, simulation examples illustrate the effectiveness of the proposed controllers.

Formation Control of Nonholonomic Vehicles Under Time Delayed Communications

This document considers the formation control problem for a group of non-holonomic mobile robots under time delayed communications. The agents are assumed to be working under a directed and fixed communication topology. A recently developed formation control technique, based on a consensus protocol for linear systems is revisited. The stability analysis of this control technique, in the domain of the time delays, is performed using the CTCR paradigm under the SDS domain approach. This analysis leads to an exact declaration of the stability boundaries in the domain of the delays. This linear control law is adapted to the nonlinear dynamics of the non-holonomic carts by means of feedback linearization. Simulation results show the applicability of this method to the class of agents considered here.

Leader-follower-based formation control of nonholonomic mobile robots with mismatched uncertainties via integral sliding mode

This article focuses on the control of a group of nonholonomic mobile robots. A leader-follower coordinated control scheme is developed to achieve formation maneuvers of such a multi-robot system. The scheme adopts the methodology of integral sliding mode control to form up and maintain the robots in predefined trajectories. The dynamic equations of the scheme are subject to mismatched uncertainties. The mismatched uncertainties challenge formation stabilization because they cannot be suppressed by the invariance of integral sliding mode control. In light of Lyapunov’s direct method, a sufficient condition is drawn to guarantee the reachability condition of integral sliding mode control in the presence of the mismatched uncertainties. To verify the feasibility and effectiveness of the proposed strategy, simulation results are illustrated by an uncertain multi-robot system composed of three nonholonomic mobile robots.

Trajectory Tracking, Pose Regulation and Adaptive Formation Control of a Group of Nonholonomic Mobile Robots

In this paper the formation and trajectory tracking control problem for multi-agent systems is presented. Initially, a control strategy for a group of holonomic robots is proposed. The proposed control is extended to the nonholonomic case. The control scheme is based on potential functions which make possible the design of decentralized formation control scheme while avoiding agents collisions. The trajectory tracking is achieved defining leaders which attract the formation to a desired trajectory. Furthermore, if at least two leaders are defined, the formation orientation tends to a desired pose (for the planar case). Assuming that the communication graph is always connected, a stability analysis using Lyapunov theory ensures the minimization of the potential function and the trajectory tracking. The control strategies are verified by simulation.

Distributed consensus-based formation control for multiple nonholonomic mobile robots with a specified reference trajectory

In this paper, the distributed formation control problem for multiple nonholonomic mobile robots using consensus-based approach is considered. A transformation is given to convert the formation control problem for multiple nonholonomic mobile robots into a state consensus problem. Distributed control laws are developed for achieving the formation control objectives: a group of nonholonomic mobile robots at least exponentially converge to a desired geometric pattern with its centroid moving along the specified reference trajectory. Rigorous proofs are provided by using graph, matrix , and Lyapunov theories. Simulations are also given to verify the effectiveness of the theoretical results.

Comparative Study of Three Different Path Tracking Controls in Mobile Robots

paper presents a comparative study of three different path tracking control laws for the formation of a group of nonholonomic mobile robots. By introducing a unified error of the formation and trajectory tracking using; the dynamic feedback linearization control (1), dynamic-static feedback linearization control (2) and nonlinear time-invariant control (3) are compared. The simulations results show that the dynamic-static feedback linearization technique presents a stable tracking with smoother behaviour and avoiding discontinuities for tracking trajectory of the robot leader. Finally, this method was implemented experimentally in three different paths formatting a simple triangle with three mobile robots in a leader-follower type motion. Moreover, the analysis in this paper reveals some important issues raising that the following control on this system can be extended to underactuated AUVs in future work.

Finite‐time formation control of multiple nonholonomic mobile robots

SUMMARYThis paper considers finite‐time formation control problem for a group of nonholonomic mobile robots. The desired formation trajectory is represented by a virtual dynamic leader whose states are available to only a subset of the followers and the followers have only local interaction. First of all, a continuous distributed finite‐time observer is proposed for each follower to estimate the leader's states in a finite time. Then, a continuous distributed cooperative finite‐time tracking control law is designed for each mobile robot. Rigorous proof shows that the group of mobile robots converge to the desired geometric formation pattern in finite time. At the same time, all the robots can track the desired formation trajectory in finite time. Simulation example illustrates the effectiveness of our method. Copyright © 2012 John Wiley & Sons, Ltd.

Behavior Based Multi Robot Formations with Active Obstacle Avoidance Based on Switching Control Strategy

This paper considers the problem of formation control and obstacle avoidance for a group of non-holonomic mobile robots in a leader referenced model based on reactive switching control strategy. Three important issues related to the multi robot formation namely distributed formation control framework, dynamic role switching algorithm and real time implementations are investigated. The switching control strategy combines together formation planning, navigation and active obstacle avoidance in a layered control framework composed of functional behaviors based on the relative motion states of the robots employed in the group. Dynamic role switching mechanism incorporated in this work to tackles the problem of obstacle avoidance in the follower path. The proposed approach is validated through laboratory experiments using commercially available robot research platforms and the results obtained are discussed.