Apparatus for detecting relative movement

Details Apparatus for detecting relative movement Apparatus for detecting relative movement

G - Physics

01

B

G01B 9/02 (2006.01) G01D 5/38 (2006.01)

Patent

CA 2118110

The apparatus disclosed herein employs a grating or scale (13) which concentrates light at a preselected wavelength into the positive (33) and negative (35) first orders while minimizing the zeroth order (31). The scale (13) is illuminated with monoch- romatic light of the selected wavelength and a poly-phase periodic detector (25) has its sensing plane spaced from the scale a dis- tance less than W: 2 tan .THETA. where .THETA. = arcain [.lambda.: P], where W is the width of the illuminated region of the scale. The period of the poly-phase detector is equal to P/2 so that each detector element (51) or phase responds principally to interference between the positive and negative first orders without requiring magnification or redirection of the diffracted light. Preferably, the distance of the sensing plane from the scale (13) is greater than W: 2 tan .PSI. where .PSI. = arcsin [3.lambda.: P], so that the detector response does not include substantial components from diffraction orders higher than the first.

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