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Executive Summary

Laser profiling is an emerging concept. Some lasers do not demonstrate the capability to account for the profiler's position and orientation relative to the pipe being inspected. This paper demonstrates how this problem can cause current laser profiling techniques to generate inaccurate pipe profiles, while remaining precise. Laser profiling of sewer pipes is a non-contact inspection method used to determine the pipe-wall profile. This method utilizes a machine vision technique known as optical triangulation. There are three commercialized laser profilers on the market. Colmatec's 3D laser profiler projects a laser line onto the interior surface of the pipe and then captures video with a CCTV camera. The ClearLine Profiler utilizes a carbon fiber and aluminum rod which supports a laser cantilevered out in front of a CCTV camera. The OMC Profiler utilizes a laser triangulation probe to take radial measurements inside a pipe. This paper presents two situations in which a robot undergoing an inspection veered off of the pipe axis either in the horizontal plane (meander) or in the vertical plane (due to a bump or offset joint). Both of these cases were shown to produce erroneous modality and were quantified in an analytical study complete with equations and graphical interpretation.

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