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Lecture Hall ICM - Internationales Congress Center München SPIE Optical Metrology > Optical Measurement Systems for Industrial Inspection XI > Interferometry I
09:40-10:00 h | ICM - Internationales Congress Center München ICM Room 14c
Subjects: Optical Measurement Systems / Optical Metrology
The optical interferometry is one of non-contact dimensional measurement techniques with ultra-high precision. Fundamentally, it provides optical path difference instead of geometrical path difference. In the case of thickness measurements of glass panels, physical thickness can be extracted from the optical thickness when the refractive index of the glass panel is precisely given. Otherwise, precision of the optical interferometer cannot be maintained owing to error of refractive index. To overcome this problem, several studies based on optical interferometry for simultaneously measuring physical thickness and refractive index have been proposed and realized. For in-line inspections, two practical requirements of (1) real-time measurement and (2) vibration insensitivity are necessary. Especially, vibration problem becomes serious due to increase of dimensions of thin glass panels. When delivering the large glass panels, the large vibration is inevitable. The proposed measurement system satisfies the two requirements: one is real-time measurement being realized by spectral-domain interferometric principle, and another is the vibration insensitivity being achieved by transmission-configuration. In this paper, the transmission type spectral-domain interferometer for determining physical thickness and group refractive index of the large glass panel is introduced, which can be even operated under vibration condition. For in-line inspection, large tilt angles of the glass panels are created by swing motion when delivering the large glass panels with high-speed. Even if the proposed method gives physical thickness values successfully under severe vibration condition, the measurement error caused by the vibration effect should be investigated and analyzed to correct the measured thickness values. For that, the theoretical analysis of the error was performed by mathematical modeling. Also, the error of the physical thickness was experimentally analyzed at various tilting angles of the large glass panel. According to Guide to the Expression of Uncertainty in Measurement, the uncertainty was evaluated based on the results of these investigations.