Proceedings of the I998 IEEE International Conference on Robotics zyxwvutsrqpo & Automation Leuven. Belgium - May 1998 Wall Following Using Angle Informat ion Measured by a zyxwv Single Ultrasonic Transducer Teruko YATA* Lindsay KLEEMAN** Shin’ichi YUTA* *Intelligent Robot Laboratory University of Tsukuba Tsukuba 305-8573 Japan Abstract zyxwvut Conventional wall following with an ultrasonic sen- sor uses only range data to the nearest reflecting point. However, the bearing angle information to the wall is more useful for a wall following motion. I n this paper, we propose a simple wall following algorithm, where the robot moves perpendicular to the direction to the nearest reflecting point. Also, in conventional ultrasonic pulse-echo sensing, an accurate target bearing measurement is often re- garded as dificult due to the wide directivity of ultra- sonic transducers. However, by assuming that the zyxwvuts u1- trasonic echo returns from a single direction, the bear- ing angle can be measured. A new sensing method is also proposed to determine accurately the bearing angle to the reflecting point by a single ultrasonic transducer. This paper also presents experimental results from mobile robot wail following experiments using only bearing information measured by a single ultrasonic transducer. These experiments illustrate the efjective- ness of proposed method. 1 Introduction For a mobile robot, wall following is a useful mo- tion in structured environments and can be employed for obstacle avoidance. In many mobile robots, ultra- sonic range sensors are used for wall following. With these robots, the range from robot to wall is commonly measured by an ultrasonic sensor and used for motion control. However, from the point of view of vehicle motion control, the direction angle to the wall is more useful and suitable information to realize wall follow- ing. In this paper, we propose a new strategy for wall following by a robot, ie. “move in a perpendicular direction to the nearest point of an object”. **Dept. ECSEng Monash University Clayton Vic. 3168 Australia To realize the above mentioned motion, the angle information to the nearest wall is required. Conven- tional ultrasonic sensors cannot measure accurately the direction of reflecting point. However ultrasonic sensing is naturally suitable for detecting this angle in- formation. This paper therefore also proposes a simple bearing angle measurement method for use in a mobile robot wall following motion. The method exploits the frequency dependency of the echo signal on the echo arrival direction. Experimental results from real mobile robot wall following using the proposed method are presented to illustrate the effectiveness of this new approach. zy 2 2.1 Wall following with angle informa- tion measured by an ultrasonic sen- sor Wall following 2.1.1 Previous work Wall following is a popular and useful technique for mobile robot navigation in structured or known envi- ronments. Mobile robot path planning or navigation often assumes that robots have the ability to perform wall following. For example, [1] gives a path plan- ning method that depends on wall following. Many research approaches on sensor-based path planning of mobile robots in the unknown and complicated envi- ronment [4] [16] [19], assumed that robots are able to follow a wall in a given environment. However in prac- tice on a real robot, wall following using real sensor data is not always straightforward to implement. Research has been reported on mobile robot wall following navigation using real ultrasonic sensors where the ultrasonic sensors have been used for mea- suring range information. Because of the uncertainty zy 0-7803-4300-~-5/98 $10.00 zyxwvu 0 1998 IEEE 1590