Apparatus for detecting relative movement

Details Apparatus for detecting relative movement Apparatus for detecting relative movement

1995-02-01

1996-09-24

Warden, Jill

Electricity: motive power systems

Braking

Automatic and/or with time-delay means

250237G, 25023116, G01B 902

Patent

active

055596002

ABSTRACT:
The apparatus disclosed herein employs a grating or scale which concentrates light at a preselected wavelength into the positive and negative first orders while minimizing the zeroth order. The scale is illuminated with monochromatic light of the selected wavelength and a poly-phase periodic detector has its sensing plane spaced from the scale a distance less than ##EQU1## 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 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 is greater than ##EQU2## so that the detector response does not include substantial components from diffraction orders higher than the first.

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