Objective Route planning is the foundation of the safe and efficient navigation of ships. Due to insufficient consideration of the requirements for autonomous navigation unmanned ships, the current route planning method has two problems: (1) Own to the insufficient consideration for the motion constraints of ships in the planning route, the unmanned ship tends to produce the track deviation near the turning position and is likely to cross the navigation obstruction area while sailing autonomously. (2) The planned route is difficult to guide the unmanned ship to sail autonomously through the specified place flexibly with the course and speed for a specific task. Therefore, we propose a route planning method for autonomous navigation of the unmanned ship with a maximum navigable window sequence that constrains Bezier curves.

Methods First, the navigation obstruction areas are calculated on the basis of electronic navigation charts, the maximum navigable window sequence that does not intersect with the navigation obstruction area is extracted along the pre-generated route, and the navigable constraint space is constructed. Then, the potential of the Bezier curve for the calculation of related motion parameters in the constraint envelope area of control points is excavated, and the route planning is transformed into a problem for the control point of Bezier curves through convex optimization under the double constraints of space and motion parameters. Finally, the method is compared with the existing methods through simulation and real ship experiments.

Results The experimental results show that: (1) This method could effectively reduce the oscillation of track tracing of the unmanned ship at the turning position and significantly improve the tracking control accuracy of the unmanned ship. The maximum horizontal and vertical errors and variances of the track tracing of the route generated by the method are significantly less than those of the improved binary tree method of the route. (2) The actual speed and course are basically consistent with the set speed and direction, which shows that this method could guide the unmanned ship to sail autonomously through the specified place at the speed for a specific task.

Conclusions (1) The method could restrain the ship's motion to plan the route, so as to improve the accuracy of the unmanned ship effectively in executing the planned route. (2) The method could guide the unmanned ship to navigate autonomously through the specified place with the motion parameters such as heading and speed required by the specific task, so as to achieve the purpose of flexible mobility.