US4079252A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Photoelectric grating displacement measuring apparatus
Assignee: Ferranti International PLC
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Filing: 1976-08-20
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Granted: 1978-03-14
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Expires: 1996-08-20
Abstract
Abstract A measuring system includes a scale grating carried on one of two relatively movable bodies and an index grating carried on the other. The scale grating is illuminated directly in such a way that light passing from it to the index grating is at least partially diffuse. Detector means are provided to respond to the resulting spatially periodic distribution of illumination.
Inventors
- 👤 David George Brake
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 18:14
CPC Classifications
G; G01; G01D; G01D5/00; G01D5/26; G01D5/32; G01D5/34; G01D5/36; G01D5/38
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
190 words
Apparatus for measuring or detecting the motion of a first member relative to a second member, which includes a scale grating of period p 1 attached to one of the two members and extending in a direction parallel to the direction in which relative motion is to be detected with the grating lines at an angle α with an optical axis, an index grating of period p 2 carried by the other of the two gratings with the grating lines at an angle β to the optical axis, the distance along the optical axis between the two gratings being a, means for illuminating the scale grating directly with radiation such that radiation passing from a scale grating to the index grating is at least partially diffuse, and detector means located at a distance b along the optical axis from the index grating and operable to detect the resulting spatially periodic fringe pattern of period p 3 , the components of the apparatus being arranged so as to satisfy the following two relationships ##EQU3## where n 1 and n 2 are small integers which do not have a common integral divisor.
Claim 2
Dependent Claim
190 words
Apparatus for measuring or detecting the motion of a first member relative to a second member, which includes a scale grating of period p 1 attached to one of the two members and extending in a direction parallel to the direction in which relative motion is to be detected with the grating lines at an angle α with an optical axis, an index grating of period p 2 carried by the other of the two gratings with the grating lines at an angle β to the optical axis, the distance along the optical axis between the two gratings being a, means for illuminating the scale grating directly with radiation such that radiation passing from a scale grating to the index grating is at least partially diffuse, and detector means located at a distance b along the optical axis from the index grating and operable to detect the resulting spatially periodic fringe pattern of period p 3 , the components of the apparatus being arranged so as to satisfy the following two relationships ##EQU3## where n 1 and n 2 are small integers which do not have a common integral divisor.
Claim 3
Dependent Claim
15 words
Apparatus as claimed in claim 1 in which the scale grating is a reflecting grating.
Claim 4
Dependent Claim
24 words
Apparatus as claimed in claim 1 in which the means for illuminating the scale grating is carried on the said other relatively movable member.
Claim 5
Dependent Claim
25 words
Apparatus as claimed in claim 1, in which the detector means includes a third grating of different pitch to the spatially periodic distribution of radiation.
Claim 6
Dependent Claim
40 words
Apparatus as claimed in claim 1 in which the detector means includes a third grating of the same pitch p 3 as the period of the fringe pattern and being skew with respect to the said periodic distribution of radiation.
Claim 7
Dependent Claim
91 words
Apparatus as claimed in claim 1 which includes an optical of focal length f located at a distance b 2 along the optical axis from the index grating and at a distance b 3 along with the optical axis from the detector means, and to focus the spatially periodic fringe pattern onto the detector means, the value of b 3 being given by the expression ##EQU4## and the period p 4 of the fringe pattern now being given by ##EQU5## where b and p 3 are as defined in claim 1.
Claim 8
Dependent Claim
14 words
Apparatus as claimed in claim 6 in which the optical element is a lens.
Claim 9
Dependent Claim
13 words
Apparatus as claimed in claim 1 in which the gratings are linear gratings.
Claim 10
Dependent Claim
37 words
Apparatus as claimed in claim 1 in which the detector means includes four radiation-sensitive devices arranged to respond to different parts of the spatially periodic distribution of radiation derived from the same area of the scale grating.
Claim 11
Dependent Claim
32 words
Apparatus as claimed in claim 1 which includes means for enclosing the major part of the space between the scale grating and the index grating to prevent contamination of the index grating.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1981-03-13 | 1981-09-12 | 1982-03-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1985-03-13 | 1985-09-12 | 1986-03-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1989-03-13 | 1989-09-12 | 1990-03-14 | $7700.00 | Window Closed / Lapsed |