Effect of lighting conditions in the study of surface roughness by machine vision - an experimental design approach

In the evaluation of surface roughness by machine vision technique, the scattered light pattern reflected from the machined surface is generally captured and optical surface finish parameters from the images are correlated with the actual roughness. Capturing of the image at appropriate conditions is required for the good correlation of the optical parameters with the roughness. Lighting conditions is a major factor that influences the image pattern and hence the optical parameters. In this work the lighting conditions like grazing angle, the light to specimen distance, the orientation of the striations on the surface to the light are varied and its influence on the optical surface finish parameter are studied. A plan of experiments based on the techniques of Taguchi was designed and executed for conducting the trials and to obtain valid conclusions. The analysis of variance and the signal to noise ratio of robust design are employed to investigate the influence of different lighting conditions on the optical surface finish parameter. The results of both the approaches confirm that grazing angle is the most influencing factor affecting the image parameter.