Some selected problems of optical metrology in industry

The benefit of optical metrology for testing tires is obvious. The testing principle has proven a high degree of reliability with respect to recognizing defects. The defect is indicated as a bright or dark area in a grayvalue-image of the tested area. The grayvalue-image is substituted with false colors (green/red). In order to display a tire defect e.g. as a red spot an absolute threshold has to be defined. When leaving the laboratory environment and entering the production control some unexpected problems occur regarding this absolute threshold. Typical problems include the differentiation of reinforced and defect areas, the recognition of malfunctions, compensation of Cartesian shearing vs. radial deformation and taking the individual deformation of each single tire into consideration. Some solutions of the designated problems are discussed.