Appeal No. 96-2953
Application 08/258,565
Representative independent claims 1 is reproduced
as follows:
1. An apparatus for measuring a displacement of a
moving body comprising:
a light source for providing a coherent collimated
beam of wavelength 8 and diameter "D";
a fixed diffraction plate and a movable diffraction
plate each comprising a grating of pitch "p", said grating
having main diffraction components of orders +1, said fixed
and movable diffraction plates being arranged in parallel to
each other with a distance "g" between them, said plates being
provided in an optical path of the collimated beam so as to be
perpendicular to an optical axis of the collimated beam so
that the collimated beam is diffracted by the gratings in the
fixed and movable diffraction plates successively; and
an optical detector for detecting an amount of a
light substantially caused by interference of diffraction
components of orders +1, said diffraction components being
generated by the successive diffraction by the first and
second diffraction plates, said optical detector comprising a
condenser lens and a photosensor, said condenser lens having
an entrance pupil size which is within D - 2g8/p, wherein said
condenser lens condenses the light transmitted through said
fixed and movable diffraction plates, and said photosensor
detecting light condensed by said condenser lens;
whereby a displacement of the movable diffraction
plate can be detected from the detected amount of light.
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