Improved RRT*-A*-based Three-Dimensional Path Planning Algorithm for the Robotic Dolphin

The dolphins are fairly well endowed with high turn maneuverability in vertical and horizontal planes. This paper proposes a modified path planning algorithm fusions of rapidly-exploring random tree (RRT) and graph-based methods for a developed robotic dolphin. Considering simultaneously the both minimum yaw radius and minimum pitch radius constraints, a method of calculating a three-dimensional (3D) Dubins curve from two 2D Dubins curves by interpolation is proposed. The 3D Dubins curves and the length of the curves are utilized as the paths and costs of path planning to satisfy the motion constraints of the robotic dolphin. Furthermore, in order to meet the speed and optimization of planned path, a variant RRT algorithm combined with A* algorithm is employed to generate feasible path for the robotic dolphin. The path cost and calculation time of this method is lower. Finally, a tendon-driven continuum robotic dolphin is presented to provide the simulation platform for verifying the effectiveness of the proposed methods.