Direction Measurable Ultrasonic Sensing Systems for Mobile Robots

Abstract

It is becoming reality that robots act in our living life environment in recent years. Not only in special environment as like factory but also in our daily living office buildings, robots are working without disturbing us. It is important for robot to know environment around itself, in order to move around us safely especially at such conditions. Ultrasonic sensor is one of the most popular external sensor among various external sensors for mobile robots. A pulse-echo method which transmit a pulse and measure distance using time-of-flight is often used for mobile robot ultrasonic sensor. However, it is difficult to measure accurate bearing angle because of its wide beam width. On the other hand, the reflecting objects in indoor environment can be considered as specular in regard to an ultrasonic wave length in the air. When ultrasound reflect specularly, an area corresponding to a leading edge of an echo is assumed as a point. Consequently, if it is possible to improve bearing measurement accuracy, the ultrasonic sensor can measure the reflecting point. The reflecting point shows special feature of the environment, for example position of corner or bearing angle of wall, which are quantitative information. It is very useful for environment recognition of mobile robots to detect those reflecting points which show such information accurately. In a word, it is really important to develop accurate direction measurable ultrasonic sensor for mobile robots. Moreover, simplicity and real-time operation are also important to use it for moving mobile robots. Purpose of this research is the development of highly efficient ultrasonic sensors for indoor mobile robots environment recognition. Especially, it emphasized to improve a weak point of ultrasonic sensor, bad bearing accuracy, without injuring merit, fast measurement speed. For this purpose, fast and accurate reflecting points measurement method are proposed, and their usefulness are confirmed by actual proofs on mobile robots in this research. Two fast and accurate reflecting point measurable methods are concretely investigated and studied: Fast and accurate bearing measurement by a single transducer using frequency directional dependency. Fast and accurate reflecting points measurement of all around the robot based on sonar-ring by using multiple transducers and time-of-flight difference. These methods were implemented on real mobile robots, and investigation of fundamental efficiency are done to confirm its usefulness. In applications of mobile robots motion, wall-following and environment map generation, it gets excellent results that mobile robot can earn good environment information using those direction measurable ultrasonic sensors.