A stereo electronic nose for a mobile inspection robot

Automatic sensing of gas distributions could be very useful for a number of industrial applications. However, while individual gas sensors can be relatively cheap, they can only cover a small area. To cover larger scale environments such as warehouses and factories with a fixed installation of sensors, an arbitrarily large number of sensors would be required, resulting in very high set-up costs. As an alternative solution, the design of an electronic nose is presented (the “Mark III Mobile Nose”) that can be used on mobile robots. One possible application of this mobile nose would be an “electronic watchman” that can detect, localise and identify odours caused by leaking solvents, hazardous gases, fires, etc. However, before such an application can be realized, there are a number of practical problems that must be addressed. For example, the metal oxide sensors used in this research are subject to a long response time and an even longer recovery time. Also, the spread of gases in typical indoor environments tends to be dominated by turbulence rather than diffusion, resulting in very noisy and unpredictable sensor signals. These effects could be lessened by temporal averaging in a static sensor system, but must be minimised by some other method if a mobile system is to cover the environment at reasonable speed. A mobile nose was developed to solve these problems on a K-team Koala robot (Fig. 1(a)) according to the following design decisions. First, it was decided to use metal oxide sensors with a direct measurement of resistance to obtain the required sensor values, in order to minimize costs. Second, due to the non-directional nature of odour measurements, a stereo nose architecture with two tubes or “nostrils” was used (Fig. 1(b)) to measure the spatial gradient of the gas concentration. This is the simplest architecture that can be used to measure the instantaneous gradient of the odour without requiring path integration, as with a single sensor. Third, to reduce the latency of the sensors, suction fans were mounted inside the tubes. Our experiments showed that this design significantly reduced the recovery time of the sensors. Fourth, our experiments also showed that a further increase in performance could be obtained by separating the two tubes with a “septum” or dividing wall to reduce interference between the opposing airflows. 2 Setup of the Mark III Mobile Nose