Hybrid Collision Avoidance for ASVs Compliant With COLREGs Rules 8 and 13-17

Bjørn-Olav H Eriksen; Glenn Bitar; Morten Breivik; Anastasios M Lekkas

doi:10.3389/frobt.2020.00011

Hybrid Collision Avoidance for ASVs Compliant With COLREGs Rules 8 and 13-17

Front Robot AI. 2020 Feb 11:7:11. doi: 10.3389/frobt.2020.00011. eCollection 2020.

Authors

Bjørn-Olav H Eriksen¹, Glenn Bitar¹, Morten Breivik¹, Anastasios M Lekkas¹

Affiliation

¹ Department of Engineering Cybernetics, Centre for Autonomous Marine Operations and Systems, Norwegian University of Science and Technology, Trondheim, Norway.

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.

Keywords: COLREGs; COLREGs compliant; autonomous surface vehicle (ASV); energy-optimized control; hybrid collision avoidance; model predictive control (MPC).