Abstract
The measurement of the inner surface profile of a straight pipe by using multi-wavelength digital holography has been proposed. To illuminate the inner wall of the straight pipe, a cone-shaped mirror(CSM) is inserted in the pipe and the reflected light from the mirror becomes the object wave and is recorded as phase shifted hologram. When the center of the CSM deviates and/or inclines from the pipe axis, the asymmetric distribution of optical path length around the mirror center is superimposed to the net profile of the pipe inner surface and that causes a crucial error for the inspection. To correct the error, we have proposed the correction method in which both the deviation and the inclination the CSM was taken into account. In this paper, we propose the new automatic error correction method in which the evaluation of the mirror center in the reconstructed image has been improved. We have also performed the experimental verification for the proposed method by using a ring gauge with an inner diameter of 13.97 mm.
