Adaptive LOS Guidance for Under-Actuated Marine Vessels
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Solution Overview
Problem
Current guidance systems for marine surface vessels, particularly under-actuated ones, face challenges in effectively controlling trajectory and addressing cross-track errors and drift, as they often rely on linear radius variations which are inadequate for larger errors and do not account for drift detection.
Innovation Solution
A computer-implemented method and system that uses an exponential function to determine the line-of-sight circle radius and includes a drift detection algorithm to continuously monitor and correct cross-track errors, providing a desired heading angle to the vessel's controller, ensuring accurate trajectory following and drift compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a constant radius LOS guidance system is used, then the system is simple to implement, but it becomes inapplicable when the cross-track error exceeds the radius
Solution Approach 1:
The patent applies the dynamics principle by transitioning from a static constant radius LOS guidance system to a dynamic variable radius LOS guidance system. The radius is made time-varying and adaptive, allowing it to change based on the vessel's current state and cross-track error magnitude. This enables the guidance system to handle both small and large cross-track errors effectively while maintaining simplicity in the underlying methodology.
2Adaptability or versatility
If a linearly varying radius LOS guidance system is used, then the system can cope with any cross-track error, but it lacks drift detection and correction capabilities
Solution Approach 1:
The patent implements feedback by introducing a drift detection mechanism that continuously monitors the vessel's trajectory and cross-track error over time. When drift is detected (persistent parallel motion away from the desired trajectory), the system provides feedback to adjust the LOS radius and guidance commands, enabling automatic drift correction while maintaining the linear radius variation capability for handling various cross-track error magnitudes.
3Adaptability or versatility
If the LOS radius is increased to handle large cross-track errors, then the guidance coverage is improved, but the convergence speed to the desired path decreases
Solution Approach 1:
The patent resolves this contradiction by making the LOS radius dynamic rather than static. The radius adapts its magnitude based on the current cross-track error and drift conditions, allowing it to be large when needed for coverage and adjust appropriately to maintain optimal convergence speed. This dynamic adjustment eliminates the need to choose between coverage range and convergence performance.
4Speed
If the LOS radius is decreased to improve convergence speed, then the vessel converges faster to the path, but the system becomes inapplicable for larger cross-track errors
Solution Approach 1:
The patent applies dynamics by allowing the LOS radius to vary adaptively based on real-time conditions. When cross-track errors are small, the radius decreases to enable fast convergence. When cross-track errors become large or drift is detected, the radius increases to maintain applicability and guidance coverage. This dynamic behavior allows the system to optimize convergence speed while remaining applicable across all error magnitudes.
Data Source
AI summary
A computer implemented method for guiding an under-actuated marine surface vessel in tracking a desired trajectory comprises expressing a predetermined vessel trajectory as a set of straight line segments, determining a desired current line segment, and determining the vessel's current position. A cross-track error and the derivative of the cross-track error are then determined. Next, a radius R of the line-of-sight (LOS) circle using a newly introduced exponential function is determined. Intersection points M and N between the LOS circle and the current desired line segment are determined. A desired heading angle is determined as the angle between the line of sight and a predetermined fixed reference line. A drift detection algorithm is built into the proposed guidance scheme to detect situations whereby the ship moves parallel to its desired trajectory for an extended period of time without being able to correct for the cross track error.