This paper proposes a displacement measuring technique for detailed noncontact mapping of the interior geometry of pipings. The technique, which is based on the optical triangulation measurement, employs a laser-beam scanner to measure displacement in all radial directions. In order to achieve high precision measurement with this technique, three algorithms that calculate the displacement from sensor output are introduced and experimentally compared. The results clarify two problems : (1) the characteristic curves obtained using the technique are non-linear, (2) the curves differ slightly with respect to measuring direction. An algorithm that calculates the measured displacement by using a characteristic curve in the corresponding direction enables high accuracy measurement. The measurement accuracy of the experimental system is evaluated to be ± 0.2 mm in the range of 33-42 mm radius. A pipe interior geometry mapping system utilizing this technique with computer-managed data-taking and graphic display is also described. Its effectiveness is shown by the experimental results.

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