The System Of Electronic Speckle Correlation And The Measurement Of Surface Roughness

The measurement of laser speckle is a method with many advantages, such as, non-contact, high precision and whole field, etc, and it has been especially applied to surface measurement in a large amount. The advance in manufacturing automation has created the need to develop on-line measurement of surface roughness. The laser speckle correlation method is an ideal on-line measurement of surface roughness without contacting and damaging to the specimen surface.This paper describes the cause of laser speckle, analyzes the first-order and second-order statistic property of the speckle field. In addition, several familiar laser speckle measure methods are given which include reference beam speckle interferometric method, dual-beam symmetrical illumination speckle interferometric method, electronic speckle interference subtraction technology and laser speckle digital correlation technology. The focus is the theoretical analysis to the measurement of surface roughness by laser speckle correlation technique. On the basis of the theoretical analysis, a system of surface roughness measurement by electronic angular speckle correlation in the far-field plane is designed and assembled, and the error analysis of this system is carried out.The specimen surface is illuminated by a coherent polarization laser beam, the first speckle pattern is recorded through CCD camera, then the second one is recorded with a little changed incident angle of the laser beam. The speckle patterns are put into the computer by using a image grab card, and then after surface roughness of the specimen surface is obtained after the data processing,. In order to increase the precision of the rotating angle, a light probe is designed in experimental arrangement. The method of automatically researching the maximum degree of correlation compensates the error of CCD displacement and increased the precision and the reliability of this system..The experiment results show a good agreement with the known roughness values of a standard specimen. The rationality and the applicability of this system are proved experimentally. It also makes us to be sure of the theory of surface roughness measurement by laser speckle correlation.