DEVELOPMENT OF AUTONOMOUS COLLISION AVOIDANCE MODULE FOR SHIP SIMULATOR BASED ON ARTIFICIAL POTENTIAL FIELD METHOD

Abstract

Along with the advancement of the sensing, communication and control technology, autopilots have been developed for various types of vehicles. To achieve autonomous piloting of marine vessels, the obstacle avoidance is a safety issue to be investigated. The obstacle avoidance functions must follow the Convention on the International Regulations for Preventing Collisions at Sea (COLREGs) which is addressed by International Maritime Organization (IMO) to avoid marine accidents. This study provides an efficient way to avoid obstacles by combining the artificial potential field method (APF) and closest point of approach method (CPA). Obstacle avoidance could be achieved by implementing this method and modifying system parameters according to the size and performance of vessels, size of obstacles and the distance between vessels and obstacles. A safest sailing direction could also be provided by utilizing artificial potential field, distance at the closest point of approach (DCPA) and time to closest point of approach (TCPA), which are derived from two vessel’s velocity and orientation. Results are then applied into two vessel models with length respectively of 5 m and 13 m for performance simulations. The algorithm includes two modes, the static avoidance mode and the dynamic avoidance mode. A repulsion force is generated in the potential field if an obstacle exists within the detection range, while a target point generates attraction force. The synthesis of potential field forces is employed to assist in modifying guidance point for a vessel to avoid obstacles. To avoid the local mini-mum, dynamic avoidance mode combines parallel correction navigation method additionally, and also considers the related distance between vessel and obstacle by offsetting the guidance points. Hence, the collision avoidance is compliant with COLREGs. The feasibility of this research is verified by implementing vessel’s motion characteristics into a ship simulator, which involves simulations of the wind, wave and current influences. The result shows that the vessel is able to avoid dynamic obstacles in sea state 3. Since both environmental interference and vessel dynamics are considered, the result of this research could be applied into navigation system of different vessels by modifying their vessel sizes and performance parameters.