Development of Inspection Technique for Metal Cylinder Surfaces Using Reflected Light Observation

Abstract

The purpose of this study is to develop an in-line inspection technique for detecting fine defects on the surface of metal cylinders. The magic-mirror method, which involves a wide field of view and exhibits high sensitivity, was employed, and a prototype inspection system was developed. This system operates as follows: a sheet beam with a width of 350 mm is irradiated onto the surface of the sample, and the reflected light illuminated onto a cylindrical screen is captured through a line sensor camera; the screen can be rotated to reduce speckle noise. When the cylindrical screen was rotated with a peripheral velocity of 883 mm/s, the speckle contrast decreased by 36% compared to the case when the screen was non-rotating. To evaluate the detection sensitivity, the surface of a metal rod with a diameter of 22 mm and length of 340 mm was inspected. Experimental results show that the system is able to detect concave defects with a diameter of 35 µm and depth of 3.9 µm as well as hairline defects with a width of 75 µm and depth of 1 µm as light and dark patterns on the inspection image.