EP0132978A2
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Displacement measuring apparatus and method
Assignee: Dr Johannes Heidenhain GmbH
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Filing: 1984-07-10
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Granted: —
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Expires: 2004-07-10
Abstract
Abstract @ Apparatus for measuring displacement comprises a member, such as a reading head, which carries a stepped index diffraction grating (14) and is movable with respect to a reflective scale grating (16). The head also carries a source (10) and lens for directing light on to the index grating and thence on to the scale grating for reflection to the index grating, with the resultant Moire bands detected by a photodetector (18) on the reading head. In order to determine the phase separation or offset, and to avoid high sensitivity thereof to the spacing between the gratings, the index grating (14) has a square-stepped profile resulting in graded, increasing thickness. Alternatively, a conventional index grating may be employed in conjunction with a stepped profile optical element interposed between the two gratings.
Inventors
- 👤 Robert Martin Pettigrew
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-27 07:29
CPC Classifications
G; G01; G01B; G01B11/00; G01D; G01D5/00; G01D5/26; G01D5/32; G01D5/34; G01D5/36; G01D5/38
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
151 words
Displacement measuring apparatus for measuring relative displacement between two members, comprising an index grating mounted on one member, a reflective scale grating mounted on the other member, a light source for illuminating the index grating and then the scale grating with light so that an image of the scale grating interacts with the index grating to form an interference image, and a plurality of detectors for detecting the interference image and deriving corresponding output signals representative of relative movement between the two members, characterised in that said output signals differ in phase in consequence of the optical path length of the light from the index grating (14) to the scale grating (16) being different from the optical path length of the light from the scale grating to the index grating by virtue of the light passing through different thicknesses of a material having a refractive index different from the ambient medium.
Claim 2
Dependent Claim
151 words
Displacement measuring apparatus for measuring relative displacement between two members, comprising an index grating mounted on one member, a reflective scale grating mounted on the other member, a light source for illuminating the index grating and then the scale grating with light so that an image of the scale grating interacts with the index grating to form an interference image, and a plurality of detectors for detecting the interference image and deriving corresponding output signals representative of relative movement between the two members, characterised in that said output signals differ in phase in consequence of the optical path length of the light from the index grating (14) to the scale grating (16) being different from the optical path length of the light from the scale grating to the index grating by virtue of the light passing through different thicknesses of a material having a refractive index different from the ambient medium.
Claim 3
Dependent Claim
15 words
Apparatus according to claim 1, wherein the index grating (14) is of non-uniform increasing thickness.
Claim 4
Dependent Claim
22 words
Apparatus according to claim 2, wherein the index grating (14) has a stepped profile on the side facing the scale grating (16).
Claim 5
Dependent Claim
29 words
Apparatus according to claim 1, having an optical element of non-uniform increasing thickness interposed between the index grating and the scale grating, said optical element having a stepped profile.
Claim 6
Dependent Claim
25 words
Apparatus according to claim 3 or claim 4, wherein the step height (bz) is predetermined to impart a selected phase separation to the output signals.
Claim 7
Dependent Claim
19 words
Apparatus according to claim 5, wherein the step sheight (Az) is predetermined to impart a phase separation of 120°.
Claim 8
Dependent Claim
25 words
Apparatus according to any of claims 3 to 6, wherein the stepped profile is formed by square, uniformly spaced steps (w) of uniform height (Az).
Claim 9
Dependent Claim
19 words
Apparatus according to any of claims 1 to 7, wherein the scale grating (16) has a rectangular profile groove.
Claim 10
Independent Claim
141 words
A method of measuring relative displacement between two members respectively carrying an index grating and a reflective scale grating, comprising the steps of illuminating the index grating and the scale grating with light whereby an image of the scale grating interacts with the index grating to form an interference image, detecting the interference image and deriving corresponding output signals representative of relative movement between the two members, characterised by the step of imparting phase separation or phase offset to the output signals by arranging the optical path lengths of the light from the index grating (14) to the scale grating (16) to be different from the optical path length of the light from the scale grating to the index grating by virtue of the light passing through different thicknesses of a material having a refractive index different from the ambient medium.
Claim 11
Independent Claim
141 words
A method of measuring relative displacement between two members respectively carrying an index grating and a reflective scale grating, comprising the steps of illuminating the index grating and the scale grating with light whereby an image of the scale grating interacts with the index grating to form an interference image, detecting the interference image and deriving corresponding output signals representative of relative movement between the two members, characterised by the step of imparting phase separation or phase offset to the output signals by arranging the optical path lengths of the light from the index grating (14) to the scale grating (16) to be different from the optical path length of the light from the scale grating to the index grating by virtue of the light passing through different thicknesses of a material having a refractive index different from the ambient medium.
Claim 12
Dependent Claim
30 words
A method as claimed in claim 9, according to which the index grating is formed with a stepped shape formed by right angle steps of uniform height at uniform spacing.
References Cited (Backward Citations)
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