Approaches to Gas Source Tracingand Declaration by Pure Chemo-Tropotaxis

This paper addresses the problem of localising a static gas source in an uncontrolled indoor environment by a mobile robot. In contrast to previous works, especially the condition of an environment that is not artificially ventilated to produce a strong unidirectional airflow is considered. Here, the propagation of the analyte molecules is dominated by turbulence and convection flow rather than diffusion, thus creating a patchy distribution of spatially distributed eddies. Positive and negative tropotaxis, based on the spatial concentration gradient measured by a pair of electrochemical gas sensor arrays, were investigated. Both strategies were implemented utilising a direct sensor-motor coupling (a Braitenberg vehicle) and were shown to be useful to accomplish the gas source localisation task. As a possible solution to the problem of gas source declaration (the task of determining with certainty that the gas source has been found), an indirect localisation strategy based on exploration and concentration peak avoidance is suggested. Here, a gas source is located by exploiting the fact that local concentration maxima occur more frequently near the gas source compared to distant regions.