Development of an Ultrasonic Localization System

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Supervisor:
Kiss Domokos
Department of Automation and Applied Informatics

The objective of my thesis is a complete hardware and software design of an active trilateration based ultrasonic positioning system, which is applicable under the regulations of the Eurobot robotics contest. This new localization system is an improvement of a previously developed sonar system consisting two fixed ultrasonic receivers and a transmitter fitted on the moving robot. The future system has to fulfil the requirement of being able to handle up to four transmitters with the same measurement rate as the previous sonar. Moreover, the precision should be increased by using the maximum allowed number of three fixed receiver modules. Finally, the capability of being integrated with an alternative camera based positioning system is also to be considered during the design.

A radio communication link enables the data transmission and synchronization among the sonar beacons. There is a dedicated master receiver which is responsible for the timing of the measurements. The measurements of the positions for different robots are performed in a time-multiplexed way. The receiver beacons determine their distance from the current sonar transmitter by measuring the propagation time of the sonar package. From these three measured receiver to transmitter distances and the given receiver-to-receiver distances, three trilaterations can be done resulting three possible positions. Hence the position error for each of the trilaterations is location dependent, the final coordinates of the robots are resulted from a weighted average of these three positions. Using this method the precision of the localization system has been increased compared to the performance of the sonar with two receiver modules.

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