Advanced Correction Method for Surface Profile Caused by the Inclination of Cone-Shaped Mirror in Digital Holographic Pipe Inspection System and its Experimental Verification

Abstract

The measurement of the inner surface profile of a straight pipe by using multi-wavelength digital holography has been conducted. To illuminate the pipe inner surface, a cone-shaped mirror is inserted in the pipe and the reflected light from the mirror becomes object wave and is recorded as hologram. When the center of the cone-shaped mirror deviates and/or inclines from the pipe axis, a crucial error occurs by superimposing asymmetric optical paths on the experimental profile. To correct the error, we have proposed the correction method in which both the deviation and the inclination of mirror was taken into account. In this paper, we propose the automatic error correction method in which the estimation of center in the reconstructed image has been improved. We have also performed experimental verification of the correction method using a ring gauge with the inner diameter of 13.97 mm.