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

  • Authors:

  • Jose M. Carmena;John C. T. Hallam

  • Affiliations:

  • Department of Neurobiology, Duke University Medical Center, 327 Bryan Research Building, Box 3209, Durham, NC;Maersk Institute, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark

  • Venue:
  • Information Sciences—Informatics and Computer Science: An International Journal - Special issue: Bio-inspired systems (BIS)
  • Year:
  • 2004

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Abstract

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 Dopplershifts--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, Müller'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.