Apparatus for optically measuring the distance between two grating-like structures and the size of periodic pattern elements forming one of the grating-like structures.

摘要

The distance between first and second grating-like structures such as a shadow mask (11) and a faceplate (12) of a color picture tube or the size of pattern elements of the second grating-like structure such as black stripes (13) formed on the inner surface of the faceplate (12) is optically measured. The shadow mask (11) has a periodic pattern of apertures or slots and the faceplate (12) has a periodic pattern of the black stripes (13). An optical system (15 to 19) located between a light source (14) and an assembly of the first and second grating-like structures (11, 12) applies parallel rays of light to the assembly and is arranged to vary an incident angle of the parallel rays to the assembly. A photodetector (24) detects the quantity of light passed through the assembly to produce an electric signal whose amplitude periodically varies with variation in the incident angle of the parallel rays to the assembly. A signal processing unit (30) evaluates the distance between the first and second grating-like structures (11, 12) or the size of pattern elements (13) forming the second grating-like structure (12) on the basis of the electric signal from the photodetector (24).