An intelligent active range sensor for mobile robot guidance

Abstract

The mechatronic design of an eye-safe laser rangefinder, based on the lateral-effect photodiode (LEP) and synchronised scanning, is described. The sensor acquires two-dimensional range data, which has been found sufficient to guide the local manoeuvres of a mobile robot in most environments. An analysis of LEP operation shows that image position measurement repeatability, normalised with respect to the detector half length, is equal to the signal current to noise current ratio. This result suggests a method for estimating the noise density of the measurement process and, along with a geometric model of the ranging process, allows accurate estimation of the variance of individual range measurements, making the sensor particularly amenable to statistically based range feature detection, tracking, and data fusion algorithms. The sensor is active, in the sense that it can change the orientation of its field of view, in order to track useful and stable range features. Range data acquisition, range feature extraction, and control of the active head behaviour are all implemented on a local network of six transputers. This parallel structure is described and it is shown how the sensor constitutes an intelligent agent in a balanced sensor suite for the guidance of close range mobile robot manoeuvres.