Formation Control Of Mobile Robots Research Articles

Decentralized Circular Formation Control of Nonholonomic Mobile Robots Under a Directed Sensor Graph

This paper investigates the circular formation control problem of multiple unicycle-type mobile robots under a directed sensor graph. The topology of the sensor graph among all robots is described by a directed graph containing a spanning tree, and the node denoting the center is only required to be globally reachable in the sensor graph. A dynamic control law is developed such that the multi-robot systems with speed constraint are able to globally converge to a circular formation prescribed by a stationary center, a radius, and a spacing configuration. Remarkably, the proposed control law does not rely on any communication, and only requires each robot to use local measurements with respect to its neighbors based on its local coordinate frame, which makes it feasible to implement this control law in a decentralized manner. The global asymptotic stability of the closed-loop multi-robot systems is established by small gain theorem of which the small-gain condition is guaranteed by a low gain parameter in the designed observer.

Formation Control of Non-Holonomic Mobile Robots: Predictive Data-Driven Fuzzy Compensator

A key research topic in the field of robotics is the formation control of a group of robots in trajectory tracking problems. Using organized robots has many advantages over using them individually, such as efficient use of resources, increased reliability due to cooperation, and better resistance against defects. To achieve this, a controller is proposed that steers the leader robot and subsequent follower robots asymptotically to a reference trajectory. The basic controller is feedback linearization. To ensure stability against perturbations, a compensator based on type-3 fuzzy logic systems (T3-FLSs) and a data-driven control strategy is designed. The approach involves employing a finite number of open-loop data and using the model-based predictive controller (MPC) approach to acquire sufficient criteria for stability. An infinite-horizon function is minimized online, which allows the data-based control policy to be considered the optimal control method. The gains of the constrained data-based control signal are computed at each time step to enhance accuracy. Applying the data-based state feedback controller to the system yields positive and stable state trajectories with appropriate transient responses. The suggested data-driven compensator is guaranteed to handle constraints. A practical example is simulated to evaluate the proposed strategy.

Cooperative Control of Multirobot Systems Subject to Control Gain Uncertainty

This article addresses the problem of cooperative control of double-integrator type multirobot systems. Different from some conventional results with the control gain explicitly known, the control gain in this article is subject to uncertainty. Three different collective behaviors are explored, i.e., leaderless consensus, leader-following consensus, and formation control. For leaderless consensus, a sliding variable is constructed, based on which a novel continuous controller is designed such that the sliding surface is reached in finite-time and thus the state agreement of all agents is realized. For leader-following consensus, two different cases are investigated, i.e., the leader with constant velocity and with time-varying velocity. In both cases, sliding-mode based controllers are developed and corresponding stability conditions are established to ensure that the leader state is tracked by all followers. Finally, the theoretical results are applied to achieve formation control of nonholonomic mobile robots and corresponding experimental studies are conducted to demonstrate the effectiveness of the proposed controllers.

Velocity‐free formation control for omnidirectional mobile robots with input saturation

AbstractThis paper presents a command‐filter‐based formation control scheme for the leader‐follower omnidirectional mobile robots (OMRs) subject to the absence of the velocity measurements, input saturation and unknown bounded disturbances. First, an adaptive velocity observer is designed based on a novel state transformation of the OMR dynamics. Then, a finite‐time command filtering strategy is proposed, where the Levant filter is used to estimate the time derivative of the virtual control law, and an error compensator with finite time convergence is constructed to eliminate the filtering error correspondingly. Moreover, the anti‐saturation module and adaptive law are designed to attenuate the influence caused by input saturation and external disturbances. The proposed control scheme can ensure that all signals of the closed‐loop system including the formation error are uniformly bounded, and the effectiveness is verified by the simulations results.

Formation control of nonholonomic wheeled mobile robots via fuzzy fractional-order integral sliding mode control

Formation control of nonholonomic wheeled mobile robots via fuzzy fractional-order integral sliding mode control

Formation Control of Multiple Mobile Robots Based on Iterative Learning Distributed Model Predictive Control

Formation Control of Multiple Mobile Robots Based on Iterative Learning Distributed Model Predictive Control

Event-Triggered Finite-Time Formation Control for Networked Nonholonomic Mobile Robots Under Denial-of-Service Attacks

This paper studies the finite-time formation control problem for networked nonholonomic mobile robots (NMRs) under denial-of-service (DoS) attacks. The communication signals are transmitted among topology-connected NMRs by threatened networks, which might be disconnected or recovered at any time due to DoS attacks. Under DoS attacks, the received discontinuous date packets resulting from the directed graph might make the formation error escape to an unknown boundary. In addition, it is demonstrated that the frequency of DoS attacks directly affects the convergence time of controllers. A novel distributed observer is developed for each follower to narrow the unknown boundary, in which a projection operation is used to restrain the estimation of state with a known bounded set. An event-triggered mechanism is developed for each follower to identify the intermittent DoS attacks by verifying the time stamps of the received data packets. To reduce the effects of the attacker on the closed-loop system, a finite-time formation controller is proposed to guarantee formation convergence to the desired position in every duration of DoS attack-shut, preventing formation error accumulation. The Lyapunov tools are utilized to derive the conditions for guaranteeing the finite-time formation convergence under DoS attacks subject to a certain frequency. It is proved that the state estimation errors and formation errors can be regulated to the neighborhoods of origin in every duration of DoS attacks shut. The DoS attack and distributed DoS attack examples are provided to illustrate the correctness and performance of the proposed method for networked NMRs through numerical simulation comparisons.

Formation Control of Wheeled Mobile Robots With Multiple Virtual Leaders Under Communication Failures

To alleviate the threat of communication failures, a formation control system (FCS) with multiple virtual leaders and semi-Markov switching topologies is proposed in this article. A time-varying formation tracking protocol with an error compensation term is introduced to mitigate the effects among the real leader and the virtual leaders. Sufficient and necessary conditions are derived based on the Routh–Hurwitz criterion. Then, a semi-Markov chain with communication delay is presented to characterize the topology switching process in different communication failure scenarios. The FCS is constructed with a varying gain controller, and its tracking performance is analyzed with the Lyapunov–Krasovskii functional. Finally, substantial experiments with Quanser Qbot2 mobile formation demonstrate the effectiveness of position and velocity tracking for FCS.

Formation Control of Wheeled Mobile Robots in Chained Form Using Potential Functions

In recent years, using autonomous mobile robots in a multi agent and intelligent environment, designing the formation control is of particular importance. In this paper, after a preliminary introduction of chained systems and potential functions that have been applied in the design of the formation control. Using the goal and collision avoidance potential functions, the formation control of a group of systems whose equations of motion are in the form of chained systems is designed. Considering the conditions of the problem, the multiple agents whose dynamical systems are in the equation of a chained systems, has a limited control design in such a way that different agents are at the start of movement in different status and do not collide along the path of motion and ultimately reach the intended destination by using goal and collision avoidance potential functions. In the following, with the help of the proposed model, the control path is designed for a group of wheeled robots and its control and linear velocity and angular velocities are obtained. Then, simulation of eight wheeled mobile robots with chained dynamics, each of them at the initial are on a unit circle environment, is carried out to the desired goals where the octahedron is a regular octagon. The results obtained from the simulation that the robots reach their desired goals without collision with the other robots indicate the accuracy and efficiency of the suggested method in the design of the formation control for a group of robots in chained form, including wheeled mobile robots.

Formation Control of Multiple Mobile Robots Based on Fuzzy Adaptive Sliding Mode Control

In order to solve the problems of slow convergence and chattering in formation control of multiple mobile robots, and to optimize the dynamic characteristics of formation system, a hybrid adaptive controller is proposed by analyzing the characteristics of different sliding mode reaching laws, which can accelerate the convergence speed and effectively suppress the chattering of the system. Firstly, the saturation function is introduced into the double power reaching law to form the saturation double power reaching law; Secondly, the hyperbolic tangent reaching law is used to improve the stability of the system when it approaches the sliding surface; Finally, fuzzy logic rules are used to adjust the coefficients of saturated double-power reaching law to optimize the overall dynamic parameters. Simulation results show that the designed controller can improve the convergence speed of the system, effectively suppress the chattering, and realize the fast and stable following of the follower robot to the pilot robot, which verifies the correctness and availability of the proposed controller.

Formation control of nonholonomic mobile robots with inaccurate global positions and velocities

AbstractIn this article, leader‐following formation control is investigated for nonholonomic mobile robots with inaccurate measurements of global positions and velocities. In many existing results, the leader robot's velocities are assumed to be precisely measured and transmitted to follower robots, and unmodeled parts of the kinematic model caused by inaccurate global position are often ignored. First, an error‐based extended state observer (EBESO) for each robot is designed to counteract influence of the inaccurate global positions and velocities in real time. Then, an EBESO‐based formation controller without the leader robot's velocities is proposed to guarantee the accurate formation tracking performances. Furthermore, both convergence of the EBESO and stability analysis of the closed‐loop error system are provided, respectively. The superiority of the proposed method is verified and illustrated by experiments.

Formation Control of Mobile Robots Based on Pin Control of Complex Networks

Robot formation control has several advantages that make it interesting for research. Multiple works have been published in the literature using different control approaches. This work presents the control of different groups of robots to achieve a desired formation based on pinning control of complex networks and coordinate translation. The implemented control law comprises complex network bounding, proportional, and collision avoidance terms. The tests for this proposal were performed via simulation and experimental tests, considering different networks of differential robots. The selected robots are Turtlebot3® Waffle Pi robots. The Turtlebot3® Waffle Pi is a differential mobile robot with the Robot Operating System (ROS). It has a light detection and ranging (LiDAR) sensor used to compute the collision avoidance control law term. Tests show favorable results on different formations testing on various groups of robots, each composed of a different number of robots. From this work, implementation on other devices can be derived, as well as trajectory tracking once in formation, among other applications.

Kernel-based multiagent reinforcement learning for near-optimal formation control of mobile robots

Kernel-based multiagent reinforcement learning for near-optimal formation control of mobile robots

Path-Guided Finite-Time Formation Control of Nonholonomic Mobile Robots Based on an Extended State Observer

In this paper, we study the finite-time formation control problem of uncertain nonholonomic mobile robots following a parameterized path. A path-guided formation control scheme based on an extended state observer is proposed. To compensate for unmeasured velocities and disturbances simultaneously, a third-order fast finite-time extended state observer (FFTESO) is proposed. Then, a distributed formation control solution is developed to achieve the kinematic and dynamic system coordination control of the nonholonomic mobile robots. For the kinematic system control, a path-parameter-updating law is developed for a virtual leader, and the desired linear velocity and heading angle are developed for the mobile robots. For the kinetic control, an anti-disturbance control protocol is designed based on the estimated signals. The salient features of the proposed algorithms lie in that the estimations of disturbances and unmeasured velocities are achieved against the system’s nonholonomic constraints, and the path following the control and cooperative control is synthesized together for path-guided formation, which reduces the complexity of the controller design. Finally, simulation studies are conducted to demonstrate the effectiveness of the proposed algorithm.

Formation Control and Tracking of Mobile Robots using Distributed Estimators and A Biologically Inspired Approach.

This paper investigates the formation control problem for multiple nonholonomic wheeled mobile robots using distributed estimators and a biologically inspired approach. The formation pattern of the system adopts leader–follower structure and the communication topology among the multi-robot system is modelled by an undirected graph. In our proposed methodology, first, we develop an adaptive trajectory tracking control for the leader robot to follow the desired trajectory. Second, a distributed estimator is designed for each follower mobile robot, which uses its own information to estimate the leader's states, such as position, orientation, and linear velocity. Then, distributed formation tracking control laws are designed based on the distributed estimator. Furthermore, a bioinspired controller is developed to address the impractical velocity jump problem. The closed-loop system stability is analysed with the Lyapunov stability theory showing that tracking errors are asymptotically converge to zero. Finally, simulation results are provided to demonstrate the effectiveness of the proposed methods.

Differentially-Driven Robots Moving in Formation—Leader–Follower Approach

The paper is devoted to the leader–follower approach for multiple mobile robots control and its experimental verification. The formation control of mobile robots is motivated by the concept of virtual leader tracking, which is enhanced by the collision avoidance between the robots proposed in our previous work. The effectiveness of this approach was verified through realisation of experiments with use of MTracker mobile robots. The OptiTrack vision system was used for robots localization. Software part with control algorithms and communication was prepared with use of the Robot Operating System.

Low-Complexity Leader-Following Formation Control of Mobile Robots Using Only FOV-Constrained Visual Feedback

This article aims to solve the problem of formation control of mobile robots based on image and provide a low-cost as well as ease-of-implementation solution for mobile robots relying merely on a monocular camera under field-of-view (FOV) constraints. A low-complexity image-based visual servo controller is proposed, which can achieve the desired relative position on the image plane and solve the FOV constraints without the feature depth and leader’s velocities information. To facilitate the control design, a state transformation is first performed to decouple the visual motion kinematics. Then, an error transformation is introduced to handle the FOV constraints, and performance specifications are incorporated in the error transformation to achieve the predefined control performance. Finally, a simple static controller is derived using only information from images, and the stability of the uncertain system with unknown control direction/coefficients under the given performance control condition is analyzed. The effectiveness and performance of the proposed visual servoing controller can be illustrated using both simulations and experiments.

Distributed leader-following formation control for multiple nonholonomic mobile robots via bioinspired neurodynamic approach

This paper investigates the distributed leader-following formation control problem for multiple nonholonomic wheeled mobile robots via a bioinspired neurodynamic approach. To do this, first, we develop a distributed estimator for each follower robot which uses its own information and the information of its neighboring robots to estimate the leader’s states. Second, a formation tracking control law is proposed for each follower robot based on the estimated states of the leader using the backstepping technique. Then, a bioinspired neurodynamics-based backstepping controller is designed to solve the impractical velocity jumps problem. Furthermore, Lyapunov function-based approach is utilized to derive sufficient conditions which guarantee asymptotic stability of the multiple mobile robot system. Finally, simulation results are presented to illustrate the effectiveness of the proposed controllers.

Privacy-preserving dynamic average consensus via state decomposition: Case study on multi-robot formation control

Dynamic average consensus is a decentralized control/estimation framework where a group of agents cooperatively track the average of local time-varying reference signals. In this paper, we develop a novel state decomposition-based privacy preservation scheme to protect the privacy of agents when sharing information with neighboring agents. Specifically, we first show that an external eavesdropper can successfully wiretap the reference signals of all agents in a conventional dynamic average consensus algorithm. To protect privacy against the eavesdropper, a state decomposition scheme is developed where the original state of each agent is decomposed into two sub-states: one succeeds the role of the original state in inter-node interactions, while the other sub-state only communicates with the first one and is invisible to other neighboring agents. Rigorous analyses are performed to show that (1) the proposed privacy scheme preserves the convergence of the average consensus; and (2) the privacy of the agents is protected such that an eavesdropper cannot discover the private reference signals with guaranteed accuracy. The developed privacy-preserving dynamic average consensus framework is then applied to the formation control of multiple non-holonomic mobile robots, in which the efficacy of the scheme is demonstrated. Numerical simulation is provided to illustrate the effectiveness of the proposed approach.

Formation control of multiple wheeled mobile robots based on model predictive control

AbstractThis paper considers the problem of formation control for a team of nonholonomic wheeled mobile robots considering obstacle avoidance. A new control algorithm based on the model predictive control (MPC) and the nonlinear dynamics of the system is presented here. The control algorithm is applied to the nonlinear system using two different controllers including linear MPC and nonlinear MPC. The virtual structure formation approach and artificial potential field method are employed to determine the reference trajectories of the robots and to solve the problem of obstacle avoidance. A control algorithm consisting of two parts is proposed to track the trajectories and maintain the team’s formation. Two advantages of using MPC techniques are the ability to consider control and state constraints which are of high importance in practical applications. The main contribution of this paper is the design of two robust control systems to disturbance with respect to actuator saturation limits. Simulation results demonstrate the effectiveness and robustness of the proposed control algorithm in trajectory tracking and formation maintenance in the presence of disturbance and actuator limits.