Controlling a gas/odor plume-tracking robot based on transient responses of gas sensors

Gas sensors provide the artificial sense of smell for a mobile robot to track an airborne gas/odor plume and to locate its source. However, a slow response of gas sensors has been the major factor limiting the development of plume-tracking robots. This paper describes a new control algorithm that overcomes the limitation. The basic idea is to detect the onset of a gas sensor response and start recovery by monitoring the relative change in each sensor output. Fast plume tracking is accomplished by making the robot take appropriate actions immediately when the sensor outputs start changing from one state to another. The detection of output change also leads to reliable plume detection and comparison of multiple sensor outputs since it is less affected by drift or sensitivity mismatch than the previous algorithm based on the absolute levels of sensor outputs. Experimental results have shown that the robot can track down a gas source within the distance of 2 m in 30 s even though semiconductor gas sensors with a long recovery time (> 60 s) are used.