Formation Control Strategy Research Articles

Cloud-based predictive formation control of networked multi-agent system and its application to air bearing spacecraft simulators

This paper studies a class of networked multi-agent systems with communication delays. A centralized cloud predictive control protocol is proposed to realize formation control of multiple agents and especially the predictive method is introduced to actively compensate for the delays in the network. The analysis of closed-loop networked multi-agent systems provides the necessary and sufficient condition of stability and consensus. Finally, the proposed cloud-based predictive formation control scheme is verified by its application to 3-degree-of-freedom air-bearing spacecraft simulators platform. The results show that the scheme can effectively compensate for the delays in the forward channel and the feedback channel and can be applied to the networked multi-agent systems well.

Distributed Adaptive Fuzzy Formation Control of Uncertain Multiple Unmanned Aerial Vehicles With Actuator Faults and Switching Topologies

This article investigates a distributed fuzzy adaptive formation control for quadrotor multiple unmanned aerial vehicles (UAVs) under unmodeled dynamics and switching topologies. The UAVs dynamics model is described by the Newton–Euler formula, and the actuator faults are considered in the system model in the form of multiplicative factors and additive factors. Due to the underactuated characteristics of the UAVs, two objective attitude commands are generated by designing a virtual control signal, which are transmitted to the attitude subsystem, and then the position controller is solved. By constructing a distributed communication mechanism between UAVs, an adaptive formation control strategy is proposed, which can enable UAVs to update their position and speed online according to their neighbor information, and then achieve the required formation. In addition, a fuzzy adaptive sliding mode controller is designed to ensure that the tracking errors of UAVs converge to the neighborhood of the origin. Finally, the simulation results verify the effectiveness of the proposed control strategy.

Distributed formation control of multi-vehicle system based on hybrid relative measurements

Formation control has been studied extensively along with the potential applications of multi-vehicle system in various areas. In this paper, a distributed control scheme based on the relative bearing and distance measurements is proposed. The main difference from the existing works lies in that the proposed control scheme can realize unambiguous formation tracking while considering the task-specification and environment constraints under practical bearing and distance sensing conditions. First, the uniqueness of the formation based on relative bearings and distances is investigated and the sufficient condition is provided. Further, the distributed formation controllers that are able to dynamically track the formation with both leaderless and leader-follower setups are designed under practical sensing conditions. In the end, to validate the effectiveness and practicability of the proposed distributed hybrid measurements based formation control scheme, both simulations based on synthetic scenarios and experiments with quadrotors equipping cameras and Ultra-Wide Band (UWB) transmitters are carried out. The simulation and experiment results show that the proposed controllers are able to track the desired formation pattern based on the bearing and distance measurements.

Adaptive platoon finite-time control for marine surface vehicles with connectivity preservation and collision avoidance

This paper addresses finite-time platoon formation control scheme for vessel train problem subject to modeling uncertainties and external disturbances. The line-of-sight range and angle constraints are proposed to satisfy the collision avoidance and connectivity maintenance. Barrier Lyapunov function is introduced in the kinematic design such that each vehicle follows its leader within the required distance. To compensate for the uncertain model dynamics, the adaptive scheme is incorporated into the decentralized design to estimate nonlinear functions. Furthermore, a disturbance observer is developed to handle time-varying external disturbances. All closed-loop states are guaranteed bounded by Lyapunov theory, and the errors can be regulated to the small neighborhood around zero in finite time. Finally, simulation results are presented to illustrate the effectiveness of the proposed approach with a group of marine surface vessels.

Nonlinear Extended State Observer-Based Distributed Formation Control of Multiple Vessels with Finite-Time Prescribed Performance

In the presence of unmeasurable velocities and system uncertainties, the distributed formation control problem is investigated in this paper for multiple vessels. A robust formation controller is proposed by incorporating an extended state observer (ESO) and finite-time prescribed performance function (FTPPF). Firstly, a nonlinear ESO is designed to estimate the unmeasurable velocities and system uncertainties. Subsequently, a novel FTPPF is designed to improve the dynamic performance of multi-vessel formation systems, where the upper bound of the convergence time and the constraint bounds can be set in advance based on the actual circumstances. Then, the proposed ESO and FTPPF are applied to the distributed formation controller design for multiple vessels. The proposed formation control scheme can maintain the multiple vessels in an expected formation with high tracking accuracy, a faster convergence speed, and smaller fluctuations. Finally, the performance of the proposed control method is verified by theory analysis and simulations.

Research on Multi-Robot Formation Control Based on MATD3 Algorithm

This paper investigates the problem of multi-robot formation control strategies in environments with obstacles based on deep reinforcement learning methods. To solve the problem of value function overestimation in the deep deterministic policy gradient (DDPG) algorithm, this paper proposes an improved multi-agent twin delayed deep deterministic policy gradient (MATD3) algorithm under the CTDE framework combined with the twin delayed deep deterministic policy gradient (TD3) algorithm, which adopts a prioritized experience replay strategy to improve the learning efficiency. For the problem of difficult obstacle avoidance for a robot formation, a hybrid reward mechanism is designed to use different formation maintenance strategies in obstacle areas and obstacle-free areas to achieve the control goal of obstacle avoidance by reasonably changing the formation. The simulation experiments verified the effectiveness of the multi-robot formation control strategy designed in this paper, and comparative simulations verified that the algorithm has a faster convergence speed and more stable performance.

Event-based formation control for multiple unmanned aerial vehicles under directed topology

This paper focuses on the problem of formation control for multiple unmanned aerial vehicles (UAV) subject to cyber attacks by a novel event-triggered communication scheme. An average method is introduced to design the triggering condition of this communication scheme, by which the amount of wrong triggering events caused by the sudden change of system states is greatly decreased, thereby saving a great deal of network bandwidth and reducing network congestion. Considering cyber attacks, a new event-based formation control strategy is developed for multi-UAV systems under directed topology by utilizing a control compensation approach. Sufficient conditions for the multi-UAV system to achieve the desired formation are acquired. Finally, a simulation example is undertaken to demonstrate the effectiveness of the theoretical results.

Fast fixed-time nonsingular terminal sliding-mode formation control for autonomous underwater vehicles based on a disturbance observer

In this paper, a novel disturbance observer-based fixed-time formation control method is proposed for autonomous underwater vehicles with actuator faults, model uncertainties and unknown disturbances. Firstly, a fast fixed-time stable system is improved, which has a faster convergence rate than existing stable system. Then, the leader-follower formation control strategy is combined with the path planning strategy based on the artificial potential field to obtain a collision-free formation configuration. Besides, a fast fixed-time disturbance observer is designed to compensate for unknown composite disturbances, which enhances the robustness of the system. Further, based on the disturbance estimation information and the improved nonsingular fast fixed-time terminal sliding-mode surface, a robust fast fixed-time formation control method is presented, which achieves the desired formation configuration. Finally, simulation and comparison results show the effectiveness of the proposed control strategy.

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.

New insight into formation mechanism, source and control strategy of severe O3 pollution: The case from photochemical simulation in the Wuhan Metropolitan Area, Central China

The Wuhan Metropolitan Area, located in Central China, has experienced severe O3 pollution in recent years; thus urging to diagnose formation regime and propose reasonable control strategies. Multi-source data of air pollutants and meteorological factors in 4 cities during August 2019 when severe regional O3 pollution occurred were obtained; then, in-situ O3 formation mechanism, the O3-precursors sensitivity, the sources and control strategies of O3 were evaluated based on the combination of the 0-D photochemical observation-based model and the positive matrix factorization model through the analysis of local ozone budget, the relative incremental reactivity, an empirical kinetic model approach and source apportionment. The results indicated the P(O3) (net O3 production rate) was 25 ppbv h−1 in Ezhou and 11–13 ppbv h−1 in other 3 cities. The dominated photochemical production of O3 was NO + HO2 reaction (62–71%), whereas the main pathway to destroy O3 during daytime was NO2 + OH (>70%) and nocturnal loss of O3 with alkenes even reached up to 39–46%. Generally, O3 formation was sensitive to AVOC (Anthropogenic Volatile Organic Compounds), in which reactive aromatics, OVOCs (Oxygenated VOCs), and alkenes (xylenes, ethylene, isoprene, methyl vinyl ketone, hexanal, toluene and methacrolein, specifically) as well as abundant i-pentane should be targeted to alleviate O3 pollution. The highly reactive VOCs sources for O3 formation in this region were vehicular exhaust (28–41%), industrial emissions (20–29% except Ezhou), and solvent use (17–29% except Huangshi). Co-reduction of O3 precursors in aforementioned reactive emissions according to optimal ratios of AVOC to NO2, i.e., 5:1 (Wuhan and Huanggang), 4:1 (Ezhou), and 6:1 (Huangshi), could achieve local O3 effective mitigation. Surprisingly, P(O3) could reduce by 38% and 48% under 40% AVOC cut accompanied by NO2 in more contaminated cities (Wuhan and Ezhou). Overall, our study provides new insight to future collaborative O3 alleviation strategies formulation in Central China, which quantified O3 formation at different precursors levels in different cities suffering from regional O3 pollution, concluded best precursors control ratios and confirmed validity of O3 mitigation through precursors-oriented emission reduction in vital sources.

Switching formation control of multi-lane autonomous vehicle platoons robust to relative position measurement noises

This paper studies formation control of multi-lane platoons of vehicles, endowed with local positioning capabilities, under the influence of noises and inconsistencies of inter-vehicle relative position measurements. We propose a distributed two-level control framework that consists of a high-level relative position based distributed formation control scheme and low-level individual dynamic controllers of the platoon vehicles. The proposed formation control scheme utilizes deadzone based switching for robustness against sensor noises and adaptive longitudinal controllers for enabling the platoon of heterogeneous vehicles to track the desired platoon velocity.

Formation Control for Leader–Follower Wheeled Mobile Robots Based on Embedded Control Technique

The formation control problem for leader–follower wheeled mobile robots (WMRs) is investigated in this article. A formation control strategy is proposed based on the embedded control technique. Different from the conventional design philosophy of designing the formation controller based on the formation tracking errors directly, the proposed strategy decomposes the formation control task into two subtasks. One is the virtual signal generator (i.e., virtual follower) design, and the other is the trajectory tracking controller design. The virtual signal generator is devised to act as a virtual follower such that it “achieves” the desired formation control goal, whose output is taken as the reference trajectory for the follower. To solve the subtask of trajectory tracking controller design, an unconstrained controller and a constrained controller with saturated velocities are designed, respectively. A rigorous stability analysis of the closed-loop system is given under these two kinds of controllers. Comparative simulations and experiments among the unconstrained controller with higher gains/lower gains and the constrained controller are given to illustrate the feasibility and effectiveness of the proposed formation control strategy.

Robust multiplexed piecewise affine MPC-based decentralized control of multi-satellite formations using aerodynamic forces

Aerodynamic forces are well suited to be exploited for Low Earth Orbit satellite formation control. However, some critical gaps still exist in control schemes suitable for multi-satellite formation applications, especially when facing atmospheric environmental uncertainties. This paper proposes a scalable and flexible decentralized control scheme for the multi-satellite formation using only aerodynamic forces. This scheme adopts a strategy of updating the control inputs alternatively and is applicable to various formation configurations with different architectures without increasing the computational complexity and communication pressure of each satellite. Aerodynamic forces are changed by reorienting the satellite, and the linear formation control model with pointing angles as inputs is obtained by the PWA (piecewise affine) approximation method. A decentralized control scheme is proposed in which each satellite only has to communicate with its neighboring satellites and update its own inputs. This control scheme allows various generalizations of formation architectures, such as one that includes local chief satellites. To deal with model uncertainties, an improved MPC algorithm named Robust PWA-MMPC is developed using the constraint tightening approach, and then its feasibility and stability issues are analyzed. Hard-in-the-loop simulations are carried out for formation maintenance and reconfiguration, in which aerodynamic force uncertainties are considered.

State-Transformation-Based Recursive Design Strategy for Leader-Follower Safety Formation Control of Uncertain Multiple Quadrotors

State-Transformation-Based Recursive Design Strategy for Leader-Follower Safety Formation Control of Uncertain Multiple Quadrotors

Formation mechanism and control strategy of M-shaped and W-shaped profile defects in hot rolling of aluminum plate

Good profile is one of the important control objectives in hot rolling of aluminum plate. However, M-shaped profile defect often appears for wide aluminum plate and W-shaped profile defect often appears for narrow aluminum plate. In order to reveal the formation mechanism of the two typical profile defects, the evaluation indexes of the M-shaped profile defect and W-shaped profile defect are proposed, and the roll-plate coupling deformation model and the roll thermal expansion model are established. The effects of rolling force, bending force and work roll thermal expansion on the profile are analyzed using these models. The results show that the rolling force and bending force has little effect on M-shaped profile defect, and the main reason for this problem is the uneven thermal expansion of work roll. Meanwhile, the W-shaped profile defect is produced under the combined action of the roll thermal expansion and large roll deflection, and the roll thermal expansion is the necessary condition for the formation of W-shaped profile defect. The greater the thermal crown of the roll, the smaller the rolling force and the greater the bending force, the more obvious the W-shaped profile defect. Based on the above conclusions, industrial tests were carried out. By increasing the cooling flow in the middle of the roll, the frequency of M-shaped profile defect decreases from 29.4% to 9.0%. Meanwhile, by increasing the positive shifting of CVC rolls, reducing the bending force, and decreasing the cooling flow of work roll at the edge of the plate, the frequency of W-shaped profile defect decreases from 42.1% to 14.1%. The profiles of the hot rolled aluminum plates are effectively improved by the developed control strategies.

Aggressive Formation Tracking for Multiple Quadrotors Without Velocity Measurements Over Directed Topologies

This paper addresses the aggressive formation tracking problem of quadrotors without velocity measurements over directed interaction topologies. A distributed formation control scheme is proposed for a multiple quadrotors system, which includes an outer-loop position controller to achieve the desired formation and an inner-loop attitude controller to regulate the attitudes. First, a second-order auxiliary system is designed to overcome the unmeasurable linear velocity. Next, the posotion controller is presented using only the position information under the directed topologies. Then, the geometric attitude controller is developed to carry out aggressive rotation maneuvers. Furthermore, an auxiliary system based on Lie algebra is proposed to eliminate the unreliable angular velocity feedback caused by disturbances and bias perturbations. Using Lyapunov stability theory on a cascaded system, it is rigorously proven that the proposed formation controller is asymptotically stable. Finally, the applicability and performance of the proposed control scheme are demonstrated by the numerical simulations.

Formation Control for Connected and Autonomous Vehicles Based on Distributed Consensus Embedded With Risk Potential Field

Cooperative control for multiple vehicles is a promising technology with the capability to improve traffic efficiency and fuel savings. Given its potential for both commercial and military applications, multiple unmanned vehicle formation has attracted considerable attention recently. In this paper, the use of formation control for connected and autonomous vehicles was explored and a novel distributed formation control approach was proposed. To begin, the evolution mechanism of multi-lane formation was investigated and a formation transition model based on a finite state machine was constructed. A bi-level formation control scheme was then proposed; this framework’s upper and lower levels were used to perform trajectory planning and MPC-based control, respectively. A novel trajectory planning approach was constructed by combining the distributed consensus algorithm and the potential field method. Moreover, additional acceleration constraints were imposed on the trajectory planning algorithm. Finally, three scenarios were designed to validate the proposed formation control algorithm using Webots. The results illustrate that a formation deployed with the proposed formation control algorithm can handle abnormal situations and realize consensus within 12s.

Adaptive Formation Control for Multiple Quadrotors with Nonlinear Uncertainties Using Lipschitz Neural Network

This paper proposes a new distributed formation control scheme for multiple quadrotors with uncertainties, which is more practical for real implementation. The proposed design takes into account the inherent nonlinear and coupled dynamics of quadrotor and incorporates the Lipschitz model uncertainty. The multi-quadrotor formation control system is divided into the high-level distributed formation controller for position control, and the low-level attitude controller for desired acceleration tracking. To improve the performance of the low-level system, we employ the Lipschitz neural network (LipNet) adaptation. LipNet adaptation learns the model uncertainty and provides a significant improvement in acceleration tracking by modifying the reference signal of the low-level system. Consequently, the performance of the whole system is enhanced. We provide a stability analysis of the proposed design and validate the performance by some simulation examples.

Predefined-Time Leader-Following Formation Control of Nonlinear Multiagent Systems under Switching Topologies

The paper proposes a predefined-time leader-following formation control scheme for nonlinear multi-agent systems with external perturbations under switching topologies. Unlike previous work on predefined-time containment control, we aim to create an isosceles triangle shaped formation instead of being covered by a generic convex hull by having followers follow the leader's trajectories. To ensure convergence along the sliding surface within a predefined-time, we present a nonlinear sliding surface. A terminal sliding mode controller is then used to obtain the desired formation within a predefined-time. The convergence time is independent of both initial values and control parameters. Using, common Lyapunov function, predefined-time stability of closed-loop system is investigated. Simulation examples demonstrate that the developed control protocol is feasible and robust.

Free Will Arbitrary Time Consensus-Based Distributed Spacecraft Formation Control

A distributed formation control scheme is proposed for achieving a desired formation of multiple spacecraft in orbit around the Earth within a free will arbitrary settling time, over an undirected communication network. Using the Clohessy-Wiltshire equations as relative position dynamics model for the spacecraft in a circular reference orbit around the Earth, the proposed control strategy is able to achieve the desired formation of the spacecraft using only relative position measurements. Simulations are presented to demonstrate the effectiveness of the proposed strategy.