High-resolution dimensional measurement apparatus using optical scale with different grating pitches

Hiroo Fujita

doi:10.1117/12.445539

23 October 2001 High-resolution dimensional measurement apparatus using optical scale with different grating pitches

Hiroo Fujita

Proceedings Volume 4398, Optical Measurement Systems for Industrial Inspection II: Application in Industrial Design; (2001) https://doi.org/10.1117/12.445539
Event: Lasers in Metrology and Art Conservation, 2001, Munich, Germany

Abstract

This paper discuses an apparatus used in industrial inspection for optically detecting dimensions. In particular, the configuration of optical unit with compact in size and simpler in construction, and signal processing unit with resolution to be better than 0.1 micrometers are described. The key devices of the new optical unit are optical scale and light source. The optical scale consists of one moving and two stationary gratings. Both of these gratings have different pitch lengths. For example, the pitch of the moving and stationary gratings are 50 micrometers and 10 micrometers , respectively. These pitches are set to odd integer multiples. The optical scale, directly irradiated by a divergent light emitted from a laser diode, generates two sinusoidal signals with a 10 micrometers period. By using the divergent light, the need for a collimating lens is eliminated. This reduces the overall size of the optical unit. The signal processing unit operates on the two signals for detecting the signal phase at the stop position of the moving grating. The basis of this phase detection is a simpler linear operation. By using the linear operation, high resolution detection of the signal phase is accomplished by segmenting an interval of one cycle period of the signal into more than 300 parts.

Citation Download Citation

Hiroo Fujita "High-resolution dimensional measurement apparatus using optical scale with different grating pitches", Proc. SPIE 4398, Optical Measurement Systems for Industrial Inspection II: Application in Industrial Design, (23 October 2001); https://doi.org/10.1117/12.445539

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KEYWORDS

Signal detection

Signal processing

Diffraction gratings

Collimation

Optical testing

Semiconductor lasers

Light sources

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