| This project is concerned with the in-field autonomous operation of unmanned marine vehicles in accordance with convention for safe and proper collision avoidance as prescribed by the Coast Guard Collision Regulations (COLREGS). These rules are written to train and guide safe human operation of marine vehicles and are heavily dependent on human common sense in determining rule applicability as well as rule execution, especially when multiple rules apply simultaneously. To capture the flexibility exploited by humans, this work applies a novel method of multi-objective optimization, interval programming, in a behavior-based control framework for representing the navigation rules, as well as task behaviors, in a way that achieves simultaneous optimal satisfaction. We validate this approach using multiple autonomous surface craft. |
| Although the COLREGS is a document suitable for guiding human behavior, it is not suitable for direct input into a vehicle control system. In practice, there are often multiple rules simultaneously in effect, and to varying degrees. This is particularly true in congested waters. In many situations there are also multiple distinct vehicle maneuvers that would satisfy a given rule. Humans are fairly good at dealing with conflicting rules and capitalizing on flexibility within rules, but these situations present the harder challenges for autonomous vehicle control. To address this problem, we have used a novel method of multi-objective optimization, interval programming (IvP), \cite{ben04b}, within a behavior-based architecture for capturing COLREGS rules. Each rule corresponds to a behavior that produces an objective function over the vehicle's decision, i.e., actuator, space. The objective functions capture the behavior prescribed by the COLREGS rule (in the peak areas of the function), but also capture its flexibility (in the non-peak areas). Each iteration of the vehicle control loop then involves the creation and solution of a multi-objective optimization problem, where each module contributes one function. This approach is suitable for building additional mission modules, on top of a COLREGS foundation where the mission modules also produce additional functions alongside the COLREGS modules. |
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Video of Rule 14 (Head-on collision avoidance) between two autonomous kayaks. July 7th on the Charles River in Boston | |
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Replay of vehicle data executing Rule 14 head-on collision avoidance. Data from July 7th vehicle log files. | |
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Replay of vehicle data executing Rule 15,16 crossing collision avoidance. Data from November 5th vehicle log files. | |