Using acoustic cats eyes to improve mobile robot navigation

The processes of navigation and guidance of a mobile robot depend on inferences made from sensor measurements. These inferences become computationally more feasible, more reliable, and more accurate as the reliability and accuracy of the sensor measurements improve. Acoustic rangers offer the prospect of a simple means of determining range and direction, but cannot in general be relied upon to measure the `true´ range. To overcome this problem we attached acoustic cats eyes (The acoustical analog of optical retroreflectors found on highways.) to the smooth vertical surfaces in our laboratory. A standard Polaroid sonar ranger was rotated through one complete circle while range measurements were taken at regular intervals. This experiment was repeated without these devices. The range readings were then superimposed onto an architect´s plan view of the area. The range scans taken with the Acoustic Cats Eyes show a significantly higher degree of correspondence to the plan view than do the range scans taken without them. We show that by identifying step changes in the range data and step changes in the derivative (the curvature) with respect to direction a decision space is created from which the presence and location of corners, walls and doorways may be inferred