A Drift-Free Navigation System for a Mobile Robot Operating on Unstructured Terrain

The orientation and the angular rates of the body of a robotic vehicle are required for the guidance and control of the vehicle. In the current robotic systems these quantities are obtained by the use of inertial sensing systems. Inertial sensing systems involve drift errors which can be significant even after the vehicle has traversed only short distances on the terrain. A different approach is suggested here which guarantees accurate, drift-free sensing of the angular position and rates of the vehicle body. A camera system consisting of two cameras in fixed relationship to one another is made to continuously track two stationary objects (stars or the sun). The camera system is mounted on the vehicle body through an actuated three-degree-of-freedom joint. The angular positions and rates of these joints can be used to evaluate the angular positions and rates of the vehicle body. An estimate of the absolute position of the vehicle on the terrain can also be obtained from this sensing system. This can serve as the primary system for estimating the position of a vehicle on a planet, or as an inexpensive alternative/backup to a more accurate Global Positioning System (GPS) for estimating the position of a vehicle on earth.