Stable Station Keeping of Autonomous Sailing Robots via the Switched Systems Approach for Ocean Observation.

Ocean observation is an emerging field, and sailing robots have several promising features (e.g., long-range sailing, environmental friendliness, energy-saving and low-noise) to perform tasks. In this paper, we define an ocean observation mission in a restricted target area as a station keeping problem. Inspired by an orientation-restricted Dubins path method, the robot keeps sailing and collecting data in a smooth reciprocation, where the trajectories consist of sailing against wind segments and turning downwind parts divided by a goal area and an acceptable area. The upwind sailing segments are of interest for data acquisition. However, the system stability can not be guaranteed during the whole reciprocation especially for sailing outside the goal area. Hereby, we refer to a switched systems approach and propose a desired heading generation scheme to realize safe and stable control in both areas. The stability for subsystems is proved with Lyapunov-like functions. The stable station keeping scheme is verified in both simulation and real experiments. Finally, we completed continuous and effective observation within 50 minutes in the goal area with a radius of 50 meters by a catamaran robot named OceanVoy460.