Optical method and sensor for measuring displacements

Claim 2

An optical method of measuring displacement of an object characterised in that it comprises: directing light within each of at least two discrete wavelength bands onto a detector along a path including a first member (51) having light transmissive or reflective properties which vary spatially in the same manner for light in each said wavelength band in at least one direction transverse to said path and a second member (9) having a light transmissive or reflective properties which vary spatially in a different manner for light within each said wavelength band in at least one direction transverse to said path, said first'(51) and second members (9) being arranged so that displacement of the object (3) causes said first and second members to be displaced relative to one another in a direction transverse to said path; utilising the output of said detector to measure the quantity of light transmitted within each of said wavelength bands along said light path; and determining the change in the ratio of said quantities resulting from displacement of the object (3).

Claim 3

A sensor for use in an optical method of measuring displacement of an object characterised in that it comprises; a light guide (5); a concave light reflective element (9) positioned such that one end (7) of said light guide (5) is directed towards said reflective element (9) from a position substantially at the centre of curvature of said reflective element (9); a light transmissive member (51) interposed between said one end of said light guide and said reflective element, one of said member and said reflective element having transmissive or reflective properties as appropriate which for light within each of at least two different wavelength bands varies spatially in at least one direction transverse to the optical axis of said reflective element (9) in a different manner for light in each said wavelength band, and the other of said member and said reflective element having light transmissive or reflective properties, as appropriate, which vary spatially in said one direction in the same manner for light in each said wavelength band, said member (51) and said reflective element (9) being supported so as to allow them to be displaced relative to each other in said one direction with displacement of said object (3).

Claim 4

A sensor for use in an optical method of measuring displacement of an object characterised in that it comprises; a light guide (5); a concave light reflective element (9) positioned such that one end (7) of said light guide (5) is directed towards said reflective element (9) from a position substantially at the centre of curvature of said reflective element (9); a light transmissive member (51) interposed between said one end of said light guide and said reflective element, one of said member and said reflective element having transmissive or reflective properties as appropriate which for light within each of at least two different wavelength bands varies spatially in at least one direction transverse to the optical axis of said reflective element (9) in a different manner for light in each said wavelength band, and the other of said member and said reflective element having light transmissive or reflective properties, as appropriate, which vary spatially in said one direction in the same manner for light in each said wavelength band, said member (51) and said reflective element (9) being supported so as to allow them to be displaced relative to each other in said one direction with displacement of said object (3).

Claim 5

A sensor according to Claim 2 in which said reflective element (9) is supported in a fixed position relative to said one end of said light guide, and said member is adapted for displacement with said object.

Claim 6

A sensor according to Claim. 2 or Claim 3 wherein said member (51) and reflective element (9) are arranged for relative rotary displacement with displacement of said object (3).

Claim 7

A sensor according to Claim 4 wherein said member (51) is mounted for rotation on the end of a shaft (3) extending through a central aperture in the reflective element (9) from the side of said reflective element (9) remote from said light guide (5).

Claim 8

A sensor according to Claim 4 or 5 wherein said one of said member (51) and said reflective element (9) has two areas (1, 2) each of which transmits or reflects light only within a respective one of said two discrete wavelength bands and the other of said member (51) and said reflective element (9) transmits or reflects light only in an area having a shape substantially the same as one of said two areas (12) of said one of said member (51) and said reflective element (9).

Claim 9

A sensor according to any one of Claims 2 to 6 in which said one of said member (51) and said reflective element (9) is said reflective element (9), and said member (51) consists of an element which partially obstructs the light path between said one end (7) of said light guide (5) and said reflective element (9).

Claim 10

A sensor according to Claim 7 when dependent on Claim 5 wherein said member (51) is a shutter comprising at least one arm of light opaque material extending radially from the part of the member lying on the optical axis of said reflective element (9).

Claim 11

A sensor according to Claim 9 wherein said shutter (51) has four radial arms so as to be in the form of a Maltese Cross.