An acoustic position estimation prototype system for underground mining safety

The surroundings of underground mining machines represent a hazardous zone for miners due to bad visibility conditions for the engine driver. Within the EU-funded project FEATureFACE, we have developed a prototype system for the estimation of the miners' positions around a machine employing time-of-flight measurements based on audible sound signals. We aimed at 2D-localization within a range of 10 m, and at the determination of a miner's distance within a range of 50 m. Our system consists of a base station located at the machine's side that comprises a set of six loudspeakers, and mobile tags that are worn by the miners. Individual sound signals are emitted by the loudspeakers and received at a mobile tag via a microphone that is mounted on the miner's hard hat. Our system not only provides continuous estimates of the miners' positions, but also yields estimates of the velocity and direction of their movement. We have evaluated the performance of our system in a parking-garage and in a training-mine. With regard to the stationary localization, our results show that our system provides an accuracy down to below 25 cm and a precision lower than 2 cm.