Measurement apparatus
AssigneeNational Research Development Corporation
InventorRobert Martin Pettigrew
Life of this patent
Estimating the term…
Abstract
In an apparatus for measuring relative displacement between first and second members, a grating fixed relative to the first member is illuminated by means defining a spatially periodic optical object fixed relative to the second member. Light transmitted or reflected by the grating is detected by a system including means defining a spatially periodic light-receiving array fixed relative to the second member so as to interact with a shadow image formed by the grating, the output of the detection system thus varying cyclically upon relative movement between the first and second members.
Claims23
An apparatus for measuring displacement of a first member relative to a second member in a manner corresponding to motion with one degree of freedom in a given plane, said apparatus comprising:
- a substantially planar grating mounted in a fixed position relative to said first member so as to extend substantially parallel to said given plane, said grating having lines which are spatially periodic in the sense of said motion, the spatial periodicity of said grating in said sense being denoted by f.sub.1 ;
- means for illuminating said grating with light, said illuminating means comprising means mounted in a fixed position relative to said second member and defining a substantially planar optical object which extends substantially parallel to said given plane spaced from said grating and is spatially periodic in said sense, said spatial periodicity of said object in said sense being denoted by f.sub.2 and being at least approximately equal to one half f.sub.1 for causing said grating to form a substantially planar image of said object extending substantially parallel to said given plane at a distance from said grating substantially equal to the distance of said object from said grating, said image being spatially periodic in said sense with a periodicity f.sub.3 in said sense substantially equal to the said object periodicity f.sub.2 and moving in said manner relative to said second member when relative movement in said manner occurs between said first and second members;
- and
- photodetector means responsive to light, said photodetector means comprising means mounted in a fixed position relative to said second member and defining a substantially planar light-receiving array which lies at least approximately in the plane of said image and which is spatially periodic in said sense with a periodicity in said sense at least approximately equal to f.sub.3 for producing at least one signal which varies cyclically by virtue of interaction between said image and light-receiving array when said relative movement occurs between said first and second members.
An apparatus for measuring displacement of a first member relative to a second member in a manner corresponding to motion with one degree of freedom in a given plane, said apparatus comprising:
- a substantially planar reflecting grating mounted in a fixed position relative to said first member so as to extend substantially parallel to said given plane;
- substantially planar transmissive grating means mounted in a fixed position relative to said second member so as to extend substantially parallel to said given plane;
- said reflecting grating and said transmissive grating means being spaced apart and being spatially periodic in the sense of said motion with the periodicity of said reflecting grating being at least approximately equal to twice that of said transmissive grating means;
- means for illuminating said transmissive grating means with light on the side of said transmissive grating means remote from said reflecting grating for causing said reflecting grating to form an image of an optical object defined by said transmissive grating means, said image being disposed at least approximately in the plane of said transmissive grating means;
- and
- photodetector means responsive to light by means of which said image is formed, said photodetector means comprising at least one photodetector disposed to receive light which has been transmitted through said transmissive grating means, then reflected by said reflecting grating, and finally retransmitted through said transmissive grating means.
Dependencies are inferred from the claim text.