Vision based station keeping and docking for floating vehicles

This paper describes a method for station keeping and docking of floating vehicles. We consider the case of a lighter-than-air blimp and that of an underwater robot. Due to the motion disturbances in the environment (currents), these tasks are important to keep the vehicle stabilized relative to an external reference frame. The main difficulties to achieve station keeping and docking are related to the non-holonomic constraints of the floating vehicles moving in 3D, having a limited number of controllable degrees of freedom. The relative position of the vehicle with respect to a docking station is tracked using vision. A planar surface is chosen as a reference plane which allows visual tracking of an environmental region, based on planar projective transformations. An image-based control law is proposed together with a dynamic model for the vehicles. Experiments both with a blimp and an underwater vehicle are described and discussed.