Sewer Pipe Measurement Robot Using Parallel Laser Sheets

Abstract

Sewer pipes over 380 000 kilometers in total are existed under the ground in Japan. However, worn pipes have been increased and a number of subsidences of a ground caused by the collapse were occurred. Recently, the inspection of the pipe is executed by the moving cart with CCD camera. Currently human inspector judges the condition of the pipe by the images recorded by the CCD camera. It should be noted that the judgment by the human causes the individual variation since it depends on the person's sense. Quantitative measurement is required. In this paper, the 3D quantitative measurement system for a sewer pipe is introduced. Two parallel laser sheets are projected from the inside of the pipe and the two circular laser streaks appeared on the inside surface of the pipe are recorded by the CCD. The measurement of the cross-section is established by analyzing the recorded streaks. Amount of displacement between two circular streaks are used to detect the tilt of the system against the axis of the pipe. The pipe is reconstructed by stacking of the cross-sections on considering the moved distance and the tilt of the robot. The automatic calibration using a liquid crystal display is also introduced in this paper. The calibration method reduces the lens distortion of a wide-angle lens and a high accurate measurement is established. Experimental result shows the feasibility of the system.