Proposed Formation Scheme Research Articles

Robust adaptive formation tracking of autonomous surface vehicles with guaranteed performance and actuator faults

This paper investigates a performance-guaranteed formation tracking problem of autonomous surface vehicles (ASVs) under uncertain environments. Especially, model uncertainties, external disturbances and actuator faults exist simultaneously. Based on graph theory and adaptive techniques, a novel two-layer robust adaptive fault-tolerant formation scheme is developed. In kinematic layer, a transformation is made to get a performance unconstrained problem and an adaptive control strategy is incorporated to stabilize transformed errors. In kinetic layer, two types of robust adaptive fault-tolerant formation controllers, i.e. the fault-based one and the fault-unknown one, are designed for different fault scenarios. These controllers share the same structure of single-parameter updating laws to adjust adaptive parameters. It is shown that: 1) using the proposed formation scheme with either designed fault-tolerant controller, desired formation configurations of ASVs are achieved if the interaction topology is connected and control parameters satisfy given conditions; 2) prescribed formation tracking performance can be ensured and all error signals are guaranteed to be uniformly ultimately bounded; 3) a trade-off between two designed controllers exists, that is although the assumption for fault-unknown controller is weaker, larger control parameters are required to behave like fault-based one. Simulations and comparisons are provided to illustrate the effectiveness of theoretical results.

Bearing-Based Adaptive Neural Formation Scaling Control for Autonomous Surface Vehicles With Uncertainties and Input Saturation.

When a group of autonomous surface vehicles (ASVs) sail from a wide waterway to a narrow waterway, one difficulty is to keep relative formation with collision avoidance. Scaling the formation sizes with formation shapes invariant is a promising way. This article investigates such a formation scaling control problem of ASVs with uncertainties and input saturation. A novel bearing-based adaptive neural formation scaling control scheme for ASVs is developed. The main idea of this formation scheme is as follows. Choose a small number of leader ASVs based on bearing rigidity theory and program their trajectories according to the kinematics of formation scaling maneuver. Steer remaining ASVs to follow leader ASVs via adaptive neural techniques and the formation sizes can be scaled only by leaders without redesigning control inputs of followers. To deal with the uncertainties of ASVs, weights updating of neural networks is simplified into one-parameter estimation in each control channel. Auxiliary systems are introduced for each ASV to reduce the effect of limited actuator capability. It is shown that desired formation scaling maneuver of ASVs can be achieved with the proposed formation scheme if the augmented formation is infinitesimally bearing rigid. Formation errors are guaranteed to be uniformly ultimately bounded. The main advantage of our scheme over existing results is that directional, computational, and actuator constraints are satisfied simultaneously in the formation scaling control of ASVs. Simulations and comparisons are provided to illustrate the effectiveness of theoretical results.

Finite-time circular formation around a moving target with multiple underactuated ODIN vehicles

In this paper, we present a framework for achieving circular formation of a two-dimensional moving target using a team of underactuated Omni-Directional Intelligent Navigator (ODIN) vehicles. The main goal is to ensure uniform circumnavigation of the moving target with prescribed radius, velocity and inter-vehicle spacing. In the formation, part of vehicle group is capable of obtaining information from the moving target. Distributed adaptive control laws are developed for the group of vehicles by merging the techniques of command filter and backstepping control. A robust controller is designed to compensate for the effect of non-smooth actuator saturation. With the proposed control, the convergence to a circular formation performance can be ensured in a finite time. Finally, numerical simulations are presented to show the effectiveness of the proposed formation scheme.

3D Formation Control of Multiple Torpedo-type Underactuated AUVs

This paper considers the formation problem for a group of torpedo-type AUVs (autonomous underwater vehicles). For each vehicle, there are only three control inputs available for the vehicle’s 6-DOF motion in the water. So this is a typical underactuated system. For these underactuated multi-agent system, we propose a sort of virtual structure based formation scheme. Virtual structure is a graph with each node taken as virtual leader for each specific agent vehicle. And for the vehicle’s motion control, a sort of path following scheme is used to force the vehicle to follow the virtual leader’s trajectory. Proposed formation scheme can guarantee the exponential following in the spherical coordinate frame, and some of simulation studies are carried out to demonstrated this kind of following performance.

Formation control with obstacle avoidance of second-order multi-agent systems under directed communication topology

This paper addresses the obstacle avoidance problem of formation control for the multi-agent systems modeled by double integrator dynamics under a directed interconnection topology. The control task is finished by a leader-follower formation scheme combined with an artificial potential field (APF) method. The leader-follower scheme is carried out by taking the desired trajectory with the desired velocity as virtual leader, while the APF method is carried out by dealing with the obstacles as the high potential points. When the obstacle avoidance tasks are finished, the artificial potential forces degrade the formation performance, so their undesired effects are treated as disturbances, which is analyzed by the robust ${{H}_{\infty~}}$ performance. Based on Lyapunov stability theory, it is proved that the proposed formation approach can realize the control objective. The result is also extended to the switching multi-agent formation. The effectiveness of the proposed formation scheme is further confirmed by simulation studies.

Adaptive formation control in absence of leader's velocity information

In the leader-following approach, it has been commonly assumed that the leader robot's velocity information may be either measured or telecommunicated. However, in some circumstances, it is difficult to satisfy it because the follower robots may not have the sensor or the communication device to obtain accurate enough leader robot's velocity. Therefore this study proposes an adaptive formation control approach for multiple mobile robots in the absence of the velocity information of the leader robot. The proposed control system only requires a knowledge of the leader–follower relative distance and the bearing angle. The smooth projection algorithm is employed to estimate time-invariant or time-varying velocities of the leader robot. Using Lyapunov stability theory, it is shown that the formation errors are uniformly ultimately bounded and converge to an adjustable neighbourhood of the origin. Simulation and experiment results are provided to demonstrate the performance and stability of the proposed formation scheme.

작동기수가 부족한 자율무인잠수정 그룹의 편대제어기법

This paper presents an asymptotic formation control scheme for a group of underactuated autonomous underwater vehicles (AUVs) where only three control inputs - surge force, yaw moment and pitch moment are available for each vehicle's six degree of freedom (DOF) underwater motion. Usually, the dynamics agents applied in most of the formation algorithms presented so far have been modeled as particle systems, which is a simple double-integrator system. Therefore, these algorithms cannot be directly applicable to the practical systems, especially to the underwater vehicles whose dynamics are highly nonlinear. Moreover, the vehicles considered in this paper are underactuated. The formation control is derived using general potential function method, and the corresponding potential function consists of two parts: interactions between vehicles and virtual-leader following. Proposed formation scheme guarantees asymptotic local stability of closed-loop system. Numerical simulations are carried out to illustrate the effectiveness of proposed formation scheme.

The role of magnetic reconnection and differential rotation in spheromak formation

The physical processes involved in the formation of a spheromak are studied. Using one-fluid axisymmetric resistive magnetohydrodynamic equations together with a temperature equation, investigations of the essential physics aspects of the formation specifically for the new Maryland Spheromak (MS) [J. Antoniades, C. Chin-Fatt, A. DeSilva, G. Goldenbaum, R. Hess, and R. Shaw, in Proceedings of the Sixth U. S. Symposium on Compact Torus Research, Princeton, 1984 (Princeton Plasma Physics Laboratory, Princeton, NJ, 1985), p. 65] have been performed. These studies elucidate the role of differential rotation in accelerating the penetration of toroidal field Bφ and in forcing I≡ rBφ to be a flux function. Another important aspect of the formation is the magnetic reconnection that occurs at the X point between the two reversal coils. A strong toroidal current is generated by the reconnection, and the X point is converted into an O point that finally becomes the magnetic axis of the spheromak. In this latter phase of reconnection, the plasma is heated very strongly. Studies have also been done on the effect of the difference in phase and time scales for the reversal and Iz banks for the purpose of optimization. The effect of radiation from carbon and oxygen is examined and found to have very little effect on the proposed formation scheme. The results are also relatively insensitive to changes in the anomalous electron thermal conduction models used.