Whole field measurement of surface roughness using laser speckle

Abstract

The importance of accurate measurements of the surface roughness of products can never be over-emphasised, for instance, the design and manufacture of moulds and dies is never complete without their surface roughness being specified and measured. The surface finish of products, normally expressed in terms of roughness, is also frequently an acceptance criterion in the metal-forming industry. There have also been attempts to correlate roughness with the behaviour and service life of products. Current techniques for surface roughness measurements can be classified into two broad categories: those using a measuring stylus which requires direct contact with the test object and those using non-contacting laser techniques. In these techniques, a common drawback is the small area where the roughness can be measured at any one time. In this paper, a whole field method of recording surface roughness using laser speckle for subsequent measurement and analysis is presented. The method enables direct measurement of the local roughness at any point on the test surface as well as the average roughness of the entire surface. It is found that roughness in the range of approximately 0.4 μm to 50 μm can be measured using this method. © 1993.