Marine Vessel Position Control for Low-Oscillation Auto-Docking
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Solution Overview
Problem
Existing marine vessel control systems face challenges in precisely maneuvering vessels near target locations, particularly in maintaining position and orientation, especially when within close proximity to objects, due to limitations in sensor accuracy and control algorithms that can cause oscillation or failure to accurately align with setpoints.
Innovation Solution
A control system that utilizes a marine propulsion system with independently steerable propulsion devices, a control module communicating with GPS, IMU, and proximity/vision-based sensors to determine required movements and control thrust vectors, allowing for precise translation and rotation by managing components of movement one or two degrees of freedom at a time once within a predetermined range of the target location.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional control algorithms are used to maneuver the vessel near the target location, then the control system is simple, but the vessel experiences oscillation and fails to accurately align with the setpoint
Solution Approach 1:
The control algorithm segments the six degrees of freedom into two groups: three translational degrees (surge, sway, heave) and three rotational degrees (roll, pitch, yaw). This segmentation allows the controller to manage each degree of freedom independently, reducing oscillation and improving positioning accuracy without requiring an overly complex integrated control system.
Solution Approach 2:
The control system dynamically adjusts the thrust vectors of the propulsion devices based on real-time vessel position and orientation data. By continuously modifying the control parameters (thrust magnitude and direction) in response to vessel state changes, the system achieves precise alignment with the setpoint while adapting to varying operational conditions.
2Adaptability or versatility
If the vessel uses full six-degree-of-freedom movement control, then the positioning capability is comprehensive, but the control complexity increases and oscillation occurs
Solution Approach 1:
The control system segments the six degrees of freedom into translational and rotational components, managing them through separate control loops. This segmentation maintains comprehensive positioning capability while reducing overall control complexity by breaking down the complex six-DOF problem into more manageable sub-problems.
Solution Approach 2:
The control algorithm applies partial action by controlling only the necessary degrees of freedom at any given time based on the vessel's operational context. Rather than simultaneously controlling all six degrees of freedom with equal complexity, the system selectively activates control for specific DOFs as needed, reducing overall system complexity while maintaining versatility.
3Productivity
If the vessel approaches the target location quickly, then the docking time is reduced, but the alignment accuracy and safety decrease
Solution Approach 1:
The control system dynamically adjusts the thrust vector magnitudes based on the vessel's distance from the target location. At greater distances, higher thrust values enable faster approach, while near the setpoint, the controller automatically reduces thrust to ensure precise alignment and prevent oscillation, thereby maintaining both speed and accuracy throughout the docking sequence.
Solution Approach 2:
The control algorithm implements periodic adjustment of thrust vectors, alternating between aggressive positioning maneuvers when far from the target and fine-tuning adjustments when near the setpoint. This periodic modulation of control intensity allows the vessel to maintain high average docking speed while ensuring high precision during the critical final alignment phase.
Data Source
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AI summary
A marine vessel is powered by a marine propulsion system and movable with respect to first, second, and third axes that are perpendicular to one another and define at least six degrees of freedom of potential vessel movement. A method for controlling a position of the marine vessel near a target location includes measuring a present location of the marine vessel, and based on the vessel's present location, determining if the marine vessel is within a predetermined range of the target location. The method includes determining marine vessel movements that are required to translate the marine vessel from the present location to the target location. In response to the marine vessel being within the predetermined range of the target location, the method includes automatically controlling the propulsion system to produce components of the required marine vessel movements one degree of freedom at a time during a given iteration of control.