The use of Doppler in Sonar-based mobile robot navigation: inspirations from biology

So-called CF-FM bats are highly mobile creatures who emit long calls in which much of the energy is concentrated in a single frequency. These bats face sensor interpretation problems very similar to those of mobile robots provided with ultrasonic sensors, while navigating in cluttered environments. This paper presents biologically-inspired engineering on the use of narrowband Sonar in mobile robotics. It replicates, using robotics as a modelling medium, methods CF-FM bats use to exploit Doppler-shifts-a rich source of information not used by commercial robotic ultrasonic range sensors-in different tasks. The experimental platform for the work is RoBat, a 6 DOF biomimetic sonarhead mounted on a commercial 3 DOF mobile platform. The platform is provided with signal processing capabilities inspired by the bat's auditory system. The CF-FM bat modifies-increasing or decreasing-the carrier frequency of its own calls, compensating the Doppler-shift produced when the bat, the reflector or both are moving. This echolocating behaviour, called Doppler-shift compensation, is successfully implemented in RoBat. Inspired by this behaviour, a convoy navigation controller following a set of simple Doppler-dependent rules is successfully devised. The performance of the controller is satisfactory despite low Doppler-shift resolution caused by the lower velocity of the robot when compared to real bats. Finally, Muller's hypothesis on the use of acoustic flow by CF-FM bats for obstacle avoidance is also implemented in RoBat, resulting in a crude estimation of the target's passing distance at small bearing angles, which improves as the angle increases, nevertheless sufficing for avoiding the two reflectors of the experiment. (C) 2003 Elsevier Inc. All rights reserved.