Sliding-Mode Tracking Control of Surface Vessels

A sliding-mode control law is presented and experimentally implemented for trajectory tracking of underactuated autonomous surface vessels. The control law is developed by introducing a first-order sliding surface in terms of surge tracking errors and a second-order surface in terms of lateral motion tracking errors. The resulting sliding-mode control law guarantees position tracking while the rotational motion remains bounded. The experimental vessel is a small boat with two propellers in an indoor pool. The position and orientation of the boat are measured using a camera that detects two infrared diodes attached near the front and back ends of the boat. A computer with a capture card processes the camera image to determine the position, calculates the control forces and their corresponding input voltages, and sends the control signals to wireless receivers on the vessel using a wireless transmitter. Several experiments are performed where the vessel accurately follows straight-line and circular trajectories.