<title>Selected problems of optical metrology in industry</title>

Abstract

Abstract The benefit ofoptical metrologyfor testing tires is obvious. The testingprinciple has proven a highdegree ofreliabilily with respect to recognizing defects. The defect is indicated as a bright or dark areain a gra'alue-image ofthe tested area. The grayvalue-image is substituted withfalse colors (green/red).In order to display a tire defect e.g as a red spot an absolute threshold has to be defined. When leavingthe laboratory environment and entering the production control some unexpected problems occurregarding this absolute threshold. Typicalproblems include the differentiation ofreinforced and defectareas, the recognition ofmalfunctions, compensation ofCartesian shearing vs. radial deformation andtaking the individual deformation ofeach single tire into consideration. Some solutions ofthe designatedproblems are discussed. Keywords: Optical Metrology, Shearography, Non-Destructive Testing, Tire Testing 1. Introduction It is a long way from the experiment to the application in industry. In optical metrology the transfer ofexperimental results to practical applications shows inherent problems /1/. The invention of the laserdecisively propelled the progress in optical engineering and related industrial applications /2/, /3/.Optical metrology in industrial application already obtained serious attention in 1983 at the congressmeeting Industrial Applications of Laser Technology (Geneva) /4/, /5/, /6/, /7/. Mainly the researchlaboratories in these days were looking for practical applications. Many applications were found,although restricted to the R&D-areas in industry. Optical metrology in those days was suffering fromhigh costs, poor reliability and high demands on the qualification ofthe operating personnel.Speckle and shearing methods gained more and more importance /8/. Together with the technological