Line-of-sight Guidance Law Research Articles

A Balanced Path-Following Approach to Course Change and Original Course Convergence for Autonomous Vessels

This paper proposes a novel path-following method for autonomous ships that optimizes overall performance by balancing course changes and convergence to the original route. The proposed method extends the line-of-sight (LOS) guidance law by dynamically adjusting key parameters based on the ship’s cross-track error (XTE) and the distance of new course considering maneuvering characteristics. By incorporating these maneuvering characteristics, the method enables more precise adjustments during course changes, improving overall path-following performance. Simulation results showed that the proposed method outperformed three existing methods, including the traditional LOS guidance law, by minimizing overshoot and maintaining reasonable XTE during larger course changes. It achieved the lowest mean absolute cross-track error (MAE) while also significantly reducing the total time required to follow the path, highlighting its superior accuracy and efficiency in path following. These outcomes highlight the method’s potential to enhance significantly the path-following capabilities of autonomous vessels, contributing to greater efficiency and accuracy in pre-determined route navigation.

Unmanned Surface Vessel–Unmanned Aerial Vehicle Cooperative Path Following Based on a Predictive Line of Sight Guidance Law

This paper explores the cooperative control of unmanned surface vessels (USVs) and unmanned aerial vehicles (UAVs) in maritime rescue and coastal surveillance. The USV-UAV system faces challenges of disturbances and substantial inertia-induced overshooting during path following. A novel position prediction line of sight (LOS) guidance law is proposed to address these issues for USV path following control. Radial basis function-based neural networks (RBF-NNs) are used to estimate disturbances, and a high-order differentiator is used to design a velocity observer for unknown USV velocity. The UAV control system employs proportional–derivative (PD) control with feedforward compensation for quadrotor control design and utilizes a finite-time converging third-order differentiator to differentiate non-continuous functions. The simulation results demonstrate strong robustness in the proposed USV-UAV cooperative control algorithm. It achieves path following control in the presence of wind and wave disturbances and exhibits minimal overshoot.

Target tracking based on the extended line of sight guidance law and information fusion

The extended line of sight (LOS) guidance law is designed to track toward a target in a three-dimensional space, and this method presents a family of guidance laws resulting in a rich behaviour for different parameters. First, polar kinematics models for the pursuer and target are established by taking the observer as a reference point. Second, the extended LOS guidance law was deduced through polar kinematics models. Third, information fusion weighted by matrices was applied to target tracking, providing a good estimate for extended LOS guidance. This combination can enrich the application range of guidance laws and information fusion. Finally, the simulations were implemented in MATLAB. The simulation results confirm the availability of this guidance law.

An Improved ELOS Guidance Law for Path Following of Underactuated Unmanned Surface Vehicles.

In this paper, targeting the problem that it is difficult to deal with the time-varying sideslip angle of an underactuated unmanned surface vehicle (USV), a line-of-sight (LOS) guidance law based on an improved extended state observer (ESO) is proposed. A reduced-order ESO is introduced into the identification of the sideslip angle caused by the environmental disturbance, which ensures a fast and accurate estimation of the sideslip angle. This enables the USV to follow the reference path with high precision, despite external disturbances from wind, waves, and currents. These unknown disturbances are modeled as drift, which the modified ESO-based LOS guidance law compensates for using the ESO. In the guidance subsystem incorporating the reduced-order state observer, the observer estimation and track errors are proved uniformly ultimately bounded. Simulation and experimental results are presented to validate the effectiveness of the proposed method. The simulation and comparison results demonstrate that the proposed ELOS guidance can help a USV track different types of paths quickly and smoothly. Additionally, the experimental results confirm the feasibility of the method.

Adaptive Dynamic Model-Based Path Following Controller Design for an Unmanned Surface Vessel

Abstract The effective design of a path following controller for Unmanned Surface Vessels (USVs) under uncertain influences induced by various factors such as environmental disturbances is a challenging task. In this study, we propose to ful?lling this task through taking benefits from an online parameter identi?cation technique, the discrete-time sliding mode control (DSMC) method, and the improved line of sight (LOS) algorithm. The Particle Swarm Optimization algorithm (PSO) was adopted to provide initial settings for the straightforward online identification method, i.e., the Forgetting Factor Recursive Least Square method (FFRLS). In order to handle the time-varying sideslip angle of a ship that exists in reality due to environmental disturbances, a multi-model course control scheme is proposed to improve the control performance. For this control scheme, a flexible selection mechanism in-between a heading angle or a course angle tracking controller based on the DSMC method is designed. A solution to ?xing the tracking deviation problem of the LOS guidance law is investigated for which the gradient descent method is introduced. A series of experiments are carried out at sea with a USV called Orca to verify and validate the proposed hybrid path following approach. The results showed that tracking errors mainly induced by environmental disturbances existed but the maximum magnitude among them was small enough and remaining within the acceptable range especially from the marine engineering point of view. These results, to a high degree, validated the robustness and precision of the proposed controller.

Path following control for large inland ships in a restricted waterway using the nonlinear terminal sliding mode method

In order to solve the problem of path following for large ships travelling in restricted waterways, an adaptive Line-Of-Sight (LOS) guidance with the Nonlinear Terminal Sliding Mode (NTSM) algorithm is proposed in this paper. Compared to classical Sliding Mode Controller (SMC) and Adaptive Sliding Mode Controller (ASMC), the proposed system enables large ships to track the desired path much faster, meanwhile, the course stability can also be achieved with the controller saturation and environmental disturbance. To solve the problems of high nonlinearity and uncertainty of ship motion in restricted waters, the mathematical model with Extended state observer (ESO) is proposed to linearize problem. A drift angle observer is established to observe the drift angle during the vessel's navigation, and the LOS guidance law is used to achieve accurate tracking of the desired trajectory. The simulation results show that the inland ships under the control of the proposed scheme can accurately track the desired trajectory in a restricted waterway. The proposed algorithm has good robustness under the effect of environmental disturbances.

Improved indirect adaptive line-of-sight guidance law for path following of under-actuated AUV subject to big ocean currents

This paper presents a novel indirect adaptive disturbance observer (IADO)-based line-of-sight (LOS) guidance law for path following of under-actuated AUV in the presence of time-varying big ocean currents. The influences of ocean currents on AUV are expressed in the kinematic model. An indirect adaptive disturbance observer is designed and utilized to estimate and compensate for the ocean currents-induced uncertainties when following a curved path. In addition, an adaptive look-ahead distance is proposed for better following the curved path with sharp turnings. Then, an improved LOS guidance law is designed to follow the desired path accurately by introducing an auxiliary variable to the conventional LOS and utilizing the indirect adaptive disturbance observer to estimate the ocean current-induced disturbances in the kinematic model. Furthermore, the closed-loop cascade IADO-LOS guidance system, composed of a tracking error subsystem and estimation error system, is proven to be globally uniformly asymptotically stable according to the Lyapunov stability theory. The proposed guidance law is intended for maneuvering AUVs in the horizontal plane to follow a predefined curved path with sharp turning under time-varying big ocean currents. Extensive simulation studies demonstrate that the proposed approach has good tracking accuracy, low chattering, and anti-jamming ability.

Advances in Line-of-Sight Guidance for Path Following of Autonomous Marine Vehicles: An Overview

Autonomous marine vehicles (AMVs), including autonomous surface and underwater vehicles, are versatile means to explore, exploit, monitor, and protect marine resources and environments. Motion control is a fundamental enabling technique for state-of-the-art AMV development. Especially, guidance is a critical component in AMV motion control. In recent years, line-of-sight (LOS) guidance, as an efficient guidance method, has attracted tremendous interest from both theoretical and practical perspectives. In this paper, an overview of recent advances in LOS guidance for AMV path following is provided. First, a control objective for the path following of an AMV with a kinematic model is specified. Next, major LOS guidance laws for path following are reviewed in detail. Then, LOS guidance laws applicable to coordinated path following of multiple AMVs are elaborated. Finally, six challenging issues for future research are addressed.

Internal Model Control-Based Observer for the Sideslip Angle of an Unmanned Surface Vehicle

Since the sideslip angle is often ignored or simplified in the process of path following of unmanned surface vehicle by using the line-of-sight (LOS) guidance law because of its fast change and the difficulty of measurement, an observer was proposed by internal model control (IMC) to quickly estimate the sideslip angle in the LOS guidance law. First, a prediction model was established for the tracking error, and a state space model for prediction errors was constructed as an internal model. With the introduction of the auxiliary variables, a new augmented system was set up for a state space model of the prediction errors. Then, the sideslip angle observer was designed by the theory of state feedback with the feature of the control law of a proportional-integral type. Theoretically, the stability of the system was proved based on the Lyapunov criteria. A simulation and experiment verified the effectiveness of the proposed sideslip angle observer in improving the path-following accuracy. The results show that the IMC-based observer introduces a proportional term of tracking error that is not considered by other observers, which is easier to implement and adjust, and has a faster response speed and a smaller steady-state error for the sideslip angle. In addition, the assumption of a small sideslip angle is not introduced in the design process, so the proposed observer provides an accurate estimation method for a large sideslip angle.

Prescribed Performance Line-of-Sight Guidance Law for Underactuated AUVs: Theory and Preliminary Test Results

This paper presents a prescribed performance guidance line-of-sight (LOS) law derived from the traditional LOS algorithm for underactuated AUVs. At the initial stage, the proposed guidance law can be regarded as a proportional LOS guidance law. Then, by the merit of LOS algorithm, the cross-track error will exponentially converges to zero. Subsequently, once the error converges to a threshold so that the performance inequalities is satisfied, the guidance law smoothly switches to a prescribed performance guidance law, which ensures that the cross-track error is confined to the predefined constraints. The asymptotic stability of closed-loop system is established via Lyapunov theory. Moreover, preliminary experimental tests in model basin and lake are carried out to validate the effective of proposed guidance law.

Line-of-sight-based global finite-time stable path following control of unmanned surface vehicles with actuator saturation

This paper focuses on the path following problem of unmanned surface vehicles (USVs) with unknown velocities, model uncertainties, and actuator saturation. To steer a USV rapidly and accurately follow the desired parameterized path, a line-of-sight (LOS)-based finite-time path following scheme is constructed in which the finite-time technique can ensure the fast error convergence, such that some intelligent operations, including patrolling, fuel supplying, and formation control, can be promptly performed. First, USV kinematic and kinetic models are established, and finite-time observers are subsequently employed to identify the unmeasured USV velocities and model uncertainties. Then, an LOS guidance law is designed to achieve the finite-time convergence of the position errors. In addition, an optimized look-ahead distance is developed using a fuzzy algorithm. Meanwhile, the control subsystem is designed at the kinetic level by combining the backstepping sliding mode method and a novel auxiliary dynamic system, where the auxiliary system is applied to address actuator saturation. Subsequently, theoretical analysis is conducted to verify that the entire system is uniformly global finite-time stable (UGFTS). Finally, the simulation studies confirms the availability of the developed method.

Control of Unmanned Surface Vehicle Along the Desired Trajectory Using Improved Line of Sight and Estimated Sideslip Angle

Abstract In order to improve the accuracy and robustness of path following control for an Unmanned Surface Vehicle (USV) suffering from unknown and complex disturbances, a variable speed curve path following a control method based on an extended state observer was proposed. Firstly, the effect of the environmental disturbances on the USV is equivalent to an unknown and time-varying sideslip angle, and the sideslip angle is estimated by using the extended state observer (ESO) and compensated in the Line of Sight (LOS) guidance law. Secondly, based on the traditional LOS guidance law, the design of the surge velocity guidance law is added to enable the USV to self-adjust the surge velocity according to the curvature of the curve path, thus further improving the tracking accuracy. Finally, the heading and speed controller of the USV is designed by using a sliding mode control to track the desired heading and speed accurately, and then the path following control of the USV’s curve path is realised. Simulation results verify the effectiveness of the proposed method.

Modified Line-of-Sight Guidance Law With Adaptive Neural Network Control of Underactuated Marine Vehicles With State and Input Constraints

This article presents a modified line-of-sight (LOS) guidance law and an adaptive neural network (NN) controller for underactuated marine vehicles in the presence of uncertainties and constraints. Unlike conventional LOS guidance, the proposed guidance law counteracts the drift caused by external disturbances to maintain zero cross-track error. Furthermore, an adaptive NN controller is designed using the barrier Lyapunov function (BLF) to deal with the system constraints and disturbances affecting unknown vehicle dynamics. The stability analysis of the adaptive controller guarantees the uniform ultimate boundedness of the closed-loop system. The proposed control strategy is verified in the simulation and experimental environment in the presence of external disturbances. Both simulation and experimental results confirm that the proposed modified LOS guidance law and adaptive NN controller guarantees asymptotic convergence to the desired path and maintains zero cross-track error despite environmental disturbances.

An improved integral light-of-sight guidance law for path following of unmanned surface vehicles

This paper proposes a path following control system for Unmanned Surface Vehicles (USVs) based on an improved integral Line-Of-Sight (LOS) guidance law. Unlike the conventional LOS guidance law, the look-ahead distance is designed as a function of the USV’s cruising speed and the cross tracking error to adapt to the different cruising speeds of USVs. Meanwhile, a reduced-order state observer is developed for online estimation of the time-varying sideslip angle caused by external disturbances such as wind, wave and current. Then, a heading controller is further designed using the dynamic surface control technique to track the desired heading angle. The guidance system and the reduced-order state observer subsystem are proved to be uniformly asymptotically stable and input-to-state stable respectively. The simulation results show that the path following control system designed in this paper can track the desired curved and straight line paths quickly and smoothly at different cruising speeds.

Path Following Based on Waypoints and Real-Time Obstacle Avoidance Control of an Autonomous Underwater Vehicle.

This paper studies three-dimensional (3D) straight line path following and obstacle avoidance control for an underactuated autonomous underwater vehicle (AUV) without lateral and vertical driving forces. Firstly, the expected angular velocities are designed by using two different methods in the kinematic controller. The first one is a traditional method based on Line-of-sight (LOS) guidance law, and the second one is an improved method based on model predictive control (MPC). At the same time, a penalty item is designed by using the obstacle information detected by onboard sensors, which can realize the real-time obstacle avoidance of the unknown obstacle. Then, in order to overcome the uncertainty of the dynamics model and the saturation of actual control input, the dynamic controller is designed by using sliding mode control (SMC) technology. Finally, in the simulation experiment, the performance of the improved control method is verified by comparison with two traditional control methods based on LOS guidance law. Since the constraint of an AUV’s angular velocities are considered in MPC, simulation results show that the improved control method uses MPC, and SMC not only improves the tracking quality of the AUV when switching paths near the waypoints and realizes real-time obstacle avoidance but also effectively reduces the mean square error (MSE) and saturation rate of the rudder angle. Therefore, this control method is more conducive to the system stability and saves energy.

Intelligent Path-following Control of Unmanned Surface Vehicles Based on Improved Line-of-sight Guidance

For the way point-based path following control of under-actuated unmanned surface vehicle (USV), a new adaptive compensation line-of-sight (LOS) guidance law and speed solver are proposed, and the fuzzy heading control and integral S-plane speed control are designed. The path following control scheme is based on the separation control, and a speed control is added to improve the overall control structure. For adaptive compensation LOS guidance law, confirm the optimal circle radius of the adaptive LOS method first, and then the angle compensation of heading deviation of navigation is conducted for the LOS angle solved by adaptive LOS method, which is used to guide the USV to approach the desired path with the optimal improved LOS angle. Considering the rapidness of path following, a speed solver is designed according to the distance between the two path points, which can calculate the optimal desired speed of the USV in real time. The experimental results testify the effectiveness and superiority of the proposed guidance strategy, the speed solver and the control strategies.

Hyperbolic-Tangent LOS Guidance-Based Finite-Time Path Following of Underactuated Marine Vehicles

In this article, a novel hyperbolic-tangent line-of-sight (LOS) guidance-based finite-time path following (HLOS-FPF) framework is created to render an underactuated marine vehicle (UMV) rapidly and accurately follow the desired path, in the presence of complex unknowns including internal dynamics, external disturbances, and arbitrary sideslip. By defining a virtually desired sideslip angle of which the tangent-nonlinearity is exactly identified by a finite-time sideslip observer, the hyperbolic-tangent LOS (HLOS) guidance laws collaboratively governing heading, surge, and virtual ship velocity are devised in a finite-time manner such that cross-track error sensitively excites heading guidance. With the aid of nonsmooth auxiliary dynamics, guidance errors are finely dominated with finite-time convergence. Finite-time heading and surge controllers are further synthesized by integral and nonsingular terminal sliding-mode techniques, and ensure that HLOS guidance signals can be exactly tracked, whereby complex unknowns are exactly compensated by finite-time unknown observer. Eventually, nonsmooth analysis together with Lyapunov approach guarantees that the entire HLOS-FPF scheme is globally finite-time stable and contributes to exact path-following under heading-surge collaborative guidance. Simulation results and comprehensive comparisons with typical methods demonstrate remarkable superiority of the innovative HLOS-FPF scheme.

Design and Analysis of a Robust UAV Flight Guidance and Control System Based on a Modified Nonlinear Dynamic Inversion

The work presented in this paper focuses on the design of a robust nonlinear flight control system for a small fixed-wing UAV against uncertainties and external disturbances. Toward this objective, an integrated UAV waypoints guidance scheme based on Carrot Chasing guidance law (CC) in comparison with the pure pursuit and line of sight-based path following (PLOS) guidance law is analyzed. For path following based on CC, a Virtual Track Point (VTP) is introduced on the path to let the UAV chase the path. For PLOS, the pure pursuit guidance law directs the UAV to the next waypoint, while the LOS guidance law steers the vehicle toward the line of sight (LOS). Nonlinear Dynamic Inversion (NLDI) awards the flight control system researchers a straight forward method of deriving control laws for nonlinear systems. The control inputs are used to eliminate unwanted terms in the equations of motion using negative feedback of these terms. The two-time scale assumption is adopted here to separate the fast dynamics—three angular rates of aircraft—from the slow dynamics—the angle of attack, sideslip, and bank angles. However, precise dynamic models may not be available, therefore a modification of NLDI is presented to compensate the model uncertainties. Simulation results show that the modified NLDI flight control system is robust against wind disturbances and model mismatch. PLOS path-following technique more accurately follows the desired path than CC and also requires the least control effort.

Curved Path Following for Unmanned Surface Vehicles With Heading Amendment

This article presents two interrelated problems-along tracking and cross tracking-in guidance design for curved path following for unmanned surface vehicles. Since these two types of directional tracking are interactively constrained in most research work, an iteration mechanism is first put forward to optimize the path parameter in each closed loop such that along tracking will not affect cross tracking in the subsequent time period. An extended line-of-sight (ELOS) guidance principle is then proposed by varying the look-ahead distance with the cross-track error such that sideslip in cross tracking can be promptly compensated through vehicle heading amendment. Both simulation and experimental results verify the effectiveness of the proposed methods, which perform better than the conventional line-of-sight (LOS) and integral LOS (ILOS) guidance laws.

Path following of the autonomous airship with compensation of unknown wind and modeling uncertainties

The motion control of the airship has been an attractive topic in recent years. This paper investigates the problem of the path following of the autonomous airship. Due to the characteristics of the large volume, slow speed, and low-maneuverability, the airship is sensitive to the wind. Based on the design idea of the line-of-sight (LOS) guidance law, a parameter-observer-based LOS (POBLOS) guidance law is proposed. The unknown and time-varying influence from the wind is estimated by the parameter observer and then compensated in the design of the guidance loop. In order to overcome the disturbances of the modeling uncertainties and drift forces induced by the wind, the method of the command filtered backstepping control (CFBC) combined with the disturbance observer is employed in the control loop. The disturbance observer is constructed based on the formulation of the nonlinear disturbance observer (NDO) and improved by adding the status estimation error feedback, which results in a more robust performance when modeling uncertainties and time-varying disturbances exist. The stability analysis shows that the path following error is ultimately bounded. The results of the simulation indicate that the path following system has a good performance and is robust against the influence of the wind and modeling uncertainties.