World modeling and position estimation for a mobile robot using ultrasonic ranging

The author describes a system for dynamically maintaining a description of the limits to free space for a mobile robot using a belt of ultrasonic range sensors. A model is presented for the uncertainty inherent in such sensors, and the projection of range measurements into external Cartesian coordinates is described. Line segments are then expressed by a set of parameters represented by an estimate and a precision. A process is presented for extracting line segments from adjacent collinear range measurements, and a fast algorithm is presented for matching these line segments to a model of the limits to free space of the robot. A side effect of matching observations to a local model is a correction to the estimated position of the robot at the time that the observation was made. A Kalman filter update equation is developed to permit the correspondence of a line segment to the model to be applied as a correction to estimated position. Examples of segment extraction, position correction and modeling are presented using real ultrasonic data