Doctor of Philosophy
School of Information Technology and Computer Science
Stanley, Benjamin D, A comparison of binaural ultrasonic sensing systems, Ph.D., School of Information Technology and Computer Science, University of Wollongong, 2003. http://ro.uow.edu/theses/152
Autonomous robotic systems have been under development for a number of years. This development is being driven partly by the need to explore the processes and logic that humans use in accomplishing repetitive tasks and partly by the need to provide probes and vehicles in environments that present threats to humans. It is this need to send robots into harsh environments which has provided the impetus for this thesis to explore the use of binaural ultrasonic sensors for robotic agents thereby enabling them to take the place of living agents. In all, five sensor systems were built and investigated. Two systems were based upon matched filters with Barker codes. The first used quadrature demodulation while the second used unsynchronised demodulation. The remaining three systems used continuous tone frequency modulated signals. The first was implemented with a discrete Fourier transform spectral estimator, the second with a Yule-Walker spectral estimator and the third using a least squares modified Yule-Walker spectral estimator. The construction, implementation and testing of these five sonar systems reveals that there is no clear preferred system despite the significantly different methodologies adopted to determine the basic time of flight and received power information. The more classical matched filter systems have superior distance of flight precision compared to the newer continuous tone frequency modulated class. However it is clearly demonstrated that the continuous tone frequency modulated class is able to insonify a larger area and operate with a better signal to noise ratio. Once calibrated, this class of sonar is able to at least equal the performance of the matched filter class. The thesis focuses on the rigorous determination of the range and bearing tuple from both the theoretical or model viewpoint and the experimental viewpoint. A rigorous theoretical development of both the inter-aural distance difference and the inter-aural power difference methods of computing bearing and the resolution of the correspondence problem are included. Experimental work was undertaken to validate the models and to provide data on which comparative study may be based. The conventional metric quantities were acquired with a large level of redundancy thereby allowing the determination of strong statistics associated with accuracy, precision and resolution. This thesis shows that, while there are performance differences between the systems, the se-lection of the best system is application dependent. In this work the aim is to equip a robotic agent with a sensory system enabling it to function in the place of a living agent, especially in a harsh or dangerous environment. For this purpose the system suggested by this thesis is a continuous tone frequency modulated sonar system with a least squares modified Yule-Walker spectral estimator.
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