Photoelectric position detector with offset phase grating scales

Details Photoelectric position detector with offset phase grating scales Photoelectric position detector with offset phase grating scales

1992-04-10

1993-05-25

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

25023116, H01J 314

Patent

active

052142809

ABSTRACT:
In a photoelectric position detector a scanning movement of a scanning phase grating relative to a scale member which is provided with a reflective phase grating is detected, light emitted by at least one light source is diffracted by the scanning grating and as it is reflected by the scale member and then again by the scanning grating to form an interference pattern and only groups belonging to said interference pattern and being of a predetermined diffraction order are detected by respective photodetectors and are converted by them to phase-displaced photodetector signals, which are cyclically changed as the scanning grating is moved relative to the scale member. The scale member is provided with two juxtaposed phase grating scales, which are offset from each other by 1/8 of their grating constant, the scanning grating is associated with both scales, and two photodetectors are associated with each scale and adapted to detect the interference of the light beams diffracted toward said photodetectors and in response to said detection to generate photodetector signals having a phase displacement particularly of 180.degree., wherein each of said photodetector signals and the corresponding photodetector signal derived from the other scale are displaced 90.degree. in phase owing to the offset of the scales.

REFERENCES:
patent: 5068530 (1991-11-01), Ieki et al.
patent: 5120132 (1992-06-01), Spies et al.

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