Navigating vehicles through an unstructured environment with sonar

A procedure to navigate a vehicle from a source to a destination through an unstructured environment using only a sonar sensor is described. The environment considered is a two-dimensional floor plan, consisting of line segments of arbitrary size that is extended into the third dimension. To ensure that a sonar-guided vehicle does not collide with an obstacle, it is necessary to consider an obstacle that produce the weakest echoes and determine the conditions under which these obstacles can be detected. In this environment, the smallest echo is produced by the line that defines the boundary between the two planes, or the edge; and distant edges become invisible. This physical principle then becomes the basis for the navigation strategy, indicating the necessary scanning pattern and maximum step size that guarantee that no collision will occur. The approach is illustrated with results produced by a vehicular robot equipped with a Polaroid sensor. A representative floor plan and the automatically determined path are shown; a blind alley was included to observe the behavior of the algorithm