AUTHOR=Eriksen Bjørn-Olav H. , Bitar Glenn , Breivik Morten , Lekkas Anastasios M. TITLE=Hybrid Collision Avoidance for ASVs Compliant With COLREGs Rules 8 and 13–17 JOURNAL=Frontiers in Robotics and AI VOLUME=7 YEAR=2020 URL=https://www.frontiersin.org/journals/robotics-and-ai/articles/10.3389/frobt.2020.00011 DOI=10.3389/frobt.2020.00011 ISSN=2296-9144 ABSTRACT=

This paper presents a three-layered hybrid collision avoidance (COLAV) system for autonomous surface vehicles, compliant with rules 8 and 13–17 of the International Regulations for Preventing Collisions at Sea (COLREGs). The COLAV system consists of a high-level planner producing an energy-optimized trajectory, a model-predictive-control-based mid-level COLAV algorithm considering moving obstacles and the COLREGs, and the branching-course model predictive control algorithm for short-term COLAV handling emergency situations in accordance with the COLREGs. Previously developed algorithms by the authors are used for the high-level planner and short-term COLAV, while we in this paper further develop the mid-level algorithm to make it comply with COLREGs rules 13–17. This includes developing a state machine for classifying obstacle vessels using a combination of the geometrical situation, the distance and time to the closest point of approach (CPA) and a new CPA-like measure. The performance of the hybrid COLAV system is tested through numerical simulations for three scenarios representing a range of different challenges, including multi-obstacle situations with multiple simultaneously active COLREGs rules, and also obstacles ignoring the COLREGs. The COLAV system avoids collision in all the scenarios, and follows the energy-optimized trajectory when the obstacles do not interfere with it.