Even Børhaug

Straight Line Path Following for Formations of Underactuated Marine Surface Vessels

The problem of formation control and path following for underactuated 3-degrees-of-freedom (3-DOF) marine surface vessels is considered. The proposed decentralized controller makes the vessels asymptotically constitute a desired formation that follows a given straight line path with a given forward speed profile. The controller consists of a cross-track control law, based on line-of-sight guidance, and a nonlinear synchronization control law. The closed-loop dynamics of both the cross-track errors and the synchronization errors are analyzed in detail using nonlinear cascaded systems theory and the overall cascaded system is shown to be both uniformly globally asymptotically stable and uniformly globally exponentially stable under mild assumptions. The proposed control strategy is validated in experiments in both calm water and in waves using a scale model vessel.

Integral LOS control for path following of underactuated marine surface vessels in the presence of constant ocean currents

In this paper, we consider the development of a control strategy for path following of underactuated marine surface vessels in the presence of ocean currents. The proposed control strategy is based on a modified Line-of-Sight (LOS) guidance law with integral action and a pair of adaptive feedback controllers. Traditional LOS guidance has several nice properties and is widely used in practice for path following of marine vehicles. However, it has the drawback of being susceptible to environmental disturbances. In this work, we propose a modified LOS guidance law with integral action for counteracting environmental disturbances. Paired with a set of adaptive feedback controllers, we show that this approach guarantees global asymptotic path following of straight-line paths in the presence constant and irrotational ocean currents.

Cross-track control for underactuated autonomous vehicles

This paper considers 3-dimensional cross-track control for a class of underactuated autonomous vehicles. A control strategy is presented that guarantees global k-exponential stability of the cross-track error to straight line trajectories in three dimensional space. The results are based on a Line-of-Sight guidance algorithm and stability results are proven using nonlinear cascaded systems theory. Globally k-exponentially stabilizing controllers are synthesized using the technique of sliding mode with eigenvalue decomposition, and the performance of the proposed control strategyis evaluated bya case studywith an AUV.

Path following of underactuated autonomous underwater vehicles in the presence of ocean currents

A control strategy allowing underactuated underwater vehicles to accomplish 3D straight line path following tasks in the presence of ocean currents is developed. The ocean current is considered constant, irrotational and acting in any direction of the inertial frame. The control technique is based on a modified three-dimensional Line-of-Sight (LOS) guidance law with two integrators and three feedback controllers. The integral effect is introduced to successfully counteract the drifting caused by the unknown current. The integration laws are chosen to reduce the risk of wind-up effects. Furthermore, due to the irrotational nature of the ocean current, it is seen that the vehicle dynamics can be defined in terms of relative velocities only. This significantly simplifies the control system compared to approaches based on absolute velocities, and as a result no adaption laws are required. Uniform global asymptotic stability and uniform local exponential stability for the closed loop system are proven and explicit bounds on the guidance law parameters are given.

Straight line path following for formations of underactuated underwater vehicles

In this paper we consider the problem of straight line path following for formations of underactuated underwater vehicles. The proposed decentralized controller makes the vehicles exponentially constitute a desired formation that follows a given straight line path with a given forward speed profile. This work builds on previous work for 2D motion of 3DOF underactuated surface vessels and extends the ideas of [2] to 3D motion of 5DOF underactuated underwater vehicles. Motivated by [2], simplifying assumptions from previous works on this subject are avoided and a complete stability analysis is provided. Graph theory is used to model the inter-vehicle communication, and the proposed coordination controller respects the topological constraints of the communication network.

Straight line path following for formations of underactuated surface vessels under influence of constant ocean currents

The problem of path following and formation control for underactuated 3-degrees-of-freedom surface vessels in the presence of unknown ocean currents is considered. The proposed controllers make the vessels asymptotically constitute a desired formation that follows a given straight-line path with a desired speed profile. This control goal is achieved in the presence of currents of unknown direction and magnitude. The proposed controller consists of an adaptive yaw controller, which makes every vessel converge to its desired path, and a surge controller, which guarantees formation assembly along the path with the desired forward speed. The results are illustrated by simulations.

Cross-track formation control of underactuated surface vessels

The problem of cross-track formation control for underactuated 3-degrees-of-freedom (3-DOF) surface vessels is considered. The proposed decentralized controllers make the vessels asymptotically constitute a desired formation that follows a given straight-line path with a given forward speed profile. The proposed controllers consist of two blocks. The first block, which is based on a line of sight (LOS) guidance law, makes every vessel asymptotically follow straight line paths corresponding to the desired formation motion. The second block manipulates the forward speed of every vessel in such a way that they asymptotically converge to the desired formation and move with a desired forward speed profile. The results are illustrated with simulations

Integral LOS guidance for horizontal path following of underactuated autonomous underwater vehicles in the presence of vertical ocean currents

A control strategy allowing underactuated underwater vehicles to perform horizontal path following tasks in the presence of vertical irrotational ocean currents is developed. It is based on a modified three-dimensional Line-of-Sight (LOS) guidance law with integral action and three adaptive feedback controllers. The traditional LOS guidance technique is often used in the marine field for path following purposes. It is however highly susceptible to environmental disturbances such as unknown currents. The integral effect is hence successfully introduced to counteract the current and the chosen integration law is defined to reduce the risk of wind-up effects. Furthermore, a simple translation of the equations of motion is used to simplify the underactuated design problem. The closed loop stability is addressed and path following of horizontal straight-line paths is proved. Finally, simulation results are presented.

Cross-Track Formation Control of Underactuated Autonomous Underwater Vehicles

The problem of 3D cross-track control for underactuated 5-degrees-of-freedom (5-DOF) autonomous underwater vehicles (AUV) is considered. The proposed decentralized controllers make the AUVs asymptotically constitute a desired formation that follows a given straight-line path with a given forward speed profile. The proposed controllers consist of two blocks. The first block, which is based on a Line of Sight guidance law, makes every AUV asymptotically follow straight line paths corresponding to the desired formation motion. The second block manipulates the forward speed of every AUV in such a way that they asymptotically converge to the desired formation and move with a desired forward speed profile. The results are illustrated with simulations.

Adaptive way-point tracking control for underactuated autonomous vehicles

This paper presents a control strategy for global k-exponential way-point tracking control of a class of underactuated mechanical systems with movement in six degrees of freedom. We use a cascaded approach and find sufficient conditions for global k-exponential convergence to the desired way-point. A backstepping-based method for synthesizing controllers that satisfy the developed dynamical constraints is presented, and it is shown how adaption can be included to counteract environmental disturbances in all six degrees of freedom while guaranteeing global asymptotic way-point tracking. A case study presenting simulation results for the method applied to a model of the HUGIN AUV is presented.